Polarizer protective film, polarizing plate and image display device

Abstract

To provide a polarizer protection film, a polarizing plate and an image display device, capable of accommodating the thinning of an image display device and suppressing deterioration in visibility due to iridescent spots.SOLUTION: A polarizer protection film includes a polyester film, where the slow axis direction of the polyester film is approximately parallel to an MD direction, and the in-plane birefringence ΔNxy of the polyester film is 0.06 or more and 0.20 or less, the polarizer protection film further satisfying the following (A) or (B): (A) the refractive index in the fast axis direction of the polyester film is 1.580 or more and 1.630 or less; and (B) the smaller value out of tear strengths by a right angle tear method in the slow axis direction and the fast axis direction of the polyester film is 250 N / mm or more.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a polarizer protective film, a polarizing plate, and an image display device such as a liquid crystal display device or an organic EL display device. More specifically, the present invention relates to a polarizer protective film, a polarizing plate, and an image display device (such as a liquid crystal display device or an organic EL display device) that have good visibility and are suitable for thinning. [Background technology]

[0002] Polarizing plates used in liquid crystal displays (LCDs) typically consist of a polarizer made of iodine-dyed polyvinyl alcohol (PVA) or similar material sandwiched between two polarizer protective films, typically triacetyl cellulose (TAC) film. In recent years, thinner polarizers have been required to meet the demand for thinner LCDs and cost reductions. However, reducing the thickness of the TAC film used as the protective film to achieve this goal results in insufficient mechanical strength and poor moisture permeability. Furthermore, TAC film is very expensive, and there is a strong demand for cheaper alternative materials.

[0003] Polyester films are more durable than TAC films, but unlike TAC films, they have birefringence, which causes a problem of image quality degradation due to optical distortion when used as a polarizer protective film. Since birefringent polyester films have a certain optical anisotropy (retardation), when used as a polarizer protective film, rainbow-like color spots appear when observed from an oblique direction, resulting in degradation of image quality. Therefore, Patent Document 1 addresses the rainbow-like color spots by controlling the in-plane retardation of the polyester film within a specific range. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] WO2011-162198 Summary of the Invention [Problem to be solved by the invention]

[0005] However, in the market, there is a demand for thinner image display devices such as liquid crystal display devices, and when the thickness of polarizer protective films is reduced, it has been difficult to ensure a retardation sufficient to sufficiently suppress rainbow-like color spots. Furthermore, as the thickness of the film decreases, the mechanical strength required for processing is insufficient, making it difficult to meet the demand for thinner films.

[0006] An object of the present invention in one embodiment is to provide a polarizer protective film, a polarizing plate, and an image display device (such as a liquid crystal display device or an organic EL display) that can accommodate the thinning of image display devices such as liquid crystal display devices and organic EL displays (i.e., that has sufficient mechanical strength) and that suppresses deterioration of visibility due to rainbow-like color spots. [Means for solving the problem]

[0007] Representative aspects of the present invention are as follows. Section A1. A polarizer protective film comprising a polyester film, 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 0.20 or less, The refractive index of the polyester film in the fast axis direction is 1.580 or more and 1.630 or less. Polarizer protection film. Section A2. The polarizer protective film according to item A1, wherein the smaller of the tear strengths of the polyester film in the slow axis direction and the fast axis direction measured by a right-angle tearing method is 250 N / mm or more. Section A3. The polarizer protective film according to item A1 or A2, wherein the polyester film has an NZ coefficient of 1.5 or more and 2.5 or less. Section A4. The polarizer protective film according to any one of items A1 to A3, wherein the retardation of the polyester film is 1500 nm or more and 30000 nm or less. Section A5. The polarizer protective film according to any one of items A1 to A4, wherein the polyester film has a thickness of 25 to 60 μm. Section A6. The polarizer protective film according to any one of items A1 to A5, wherein the angle formed between the slow axis direction and the MD direction of the polyester film is 3 degrees or less. Section A7. The polarizer protective film according to any one of items A1 to A6, wherein the polyester film has an MD modulus of elasticity of 3000 MPa or more. Section A8. A polarizing plate comprising a polarizer protective film according to any one of items A1 to A7 laminated on at least one surface of a polarizer. Section A9. A polarizing plate in which the polarizer protective film according to any one of items A1 to A7 is laminated on one surface of a polarizer, and no film is laminated on the other surface of the polarizer. Section A10. A polarizing plate comprising a polarizer protective film according to any one of items A1 to A7 laminated on one surface of a polarizer, and a quarter-wave plate laminated on the other surface of the polarizer. Section A11. An image display device comprising the polarizing plate according to any one of items A8 to A10. Section A12. A liquid crystal display device comprising the polarizing plate according to item A8 or A9. Section A13. An organic EL display comprising the polarizing plate according to any one of items A8 to A10. Section A14. A QLED display including the polarizing plate according to any one of items A8 to A10.

[0008] Section B1. A polarizer protective film comprising a polyester film, 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 smaller of the tear strengths of the polyester film in the slow axis direction and the fast axis direction measured by a right-angle tear method is 250 N / mm or more; Polarizer protection film. Section B2. Item B1. The polarizer protective film according to Item B1, wherein the polyester film has an NZ coefficient of 1.5 or more and 2.5 or less. Section B3. The polarizer protective film according to item B1 or B2, wherein the retardation of the polyester film is 1500 nm or more and 30,000 nm or less. Section B4. The polarizer protective film according to any one of Items B1 to B3, wherein the polyester film has a thickness of 25 to 60 μm. Section B5. The polarizer protective film according to any one of items B1 to B4, wherein the angle between the slow axis direction and the MD direction of the polyester film is 3 degrees or less. Section B6. The polarizer protective film according to any one of items B1 to B5, wherein the polyester film has an MD modulus of elasticity of 3000 MPa or more. Section B7. A polarizing plate having the polarizer protective film according to any one of items B1 to B6 laminated on at least one surface of a polarizer. Section B8. A polarizing plate in which the polarizer protective film according to any one of items B1 to B6 is laminated on one surface of a polarizer, and no film is laminated on the other surface of the polarizer. Section B9. A polarizing plate comprising a polarizer protective film according to any one of items B1 to B6 laminated on one surface of a polarizer, and a quarter-wave plate laminated on the other surface of the polarizer. Section B10. An image display device comprising the polarizing plate according to any one of items B7 to B9. Section B11. A liquid crystal display device comprising the polarizing plate according to item B7 or B8. Section B12. An organic EL display comprising the polarizing plate according to any one of items B7 to B9. Section B13. A QLED display including the polarizing plate according to any one of items B7 to B9.

[0009] Section C1. A polarizer protective film comprising a polyester film, 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 thickness of the polyester film is 15 to 60 μm. Polarizer protection film. Section C2. Item C1. The polarizer protective film according to item C1, wherein the polyester film has an NZ coefficient of 1.5 or more and 2.5 or less. Section C3. The polarizer protective film according to item C1 or C2, wherein the retardation of the polyester film is 1500 nm or more and 30000 nm or less. Section C4. The polarizer protective film according to any one of items C1 to C3, wherein the angle formed between the slow axis direction and the MD direction of the polyester film is 3 degrees or less. Section C5. The polarizer protective film according to any one of items C1 to C4, wherein the polyester film has an MD modulus of elasticity of 3000 MPa or more. Section C6. A polarizing plate having a polarizer protective film according to any one of items C1 to C5 laminated on at least one surface of a polarizer. Section C7. A polarizing plate in which the polarizer protective film according to any one of items C1 to C5 is laminated on one surface of a polarizer, and no film is laminated on the other surface of the polarizer. Section C8. A polarizing plate comprising a polarizer protective film according to any one of items C1 to C5 laminated on one surface of a polarizer, and a quarter-wave plate laminated on the other surface of the polarizer. Section C9. An image display device comprising the polarizing plate according to any one of items C6 to C8. Section C10. A liquid crystal display device comprising the polarizing plate according to item C6 or C7. Section C11. An organic EL display comprising the polarizing plate according to any one of items C6 to C8. Section C12. A QLED display including the polarizing plate according to any one of items C6 to C8. [Effects of the Invention]

[0010] The polarizer protective film, polarizing plate, and image display device (such as a liquid crystal display device or an organic EL display) of the present invention can ensure good visibility with rainbow-like color spots (hereinafter referred to as rainbow spots) suppressed at any observation angle. Furthermore, the polarizing plate and polarizer protective film of the present invention have mechanical strength suitable for thinning, ensuring good processability. According to the present invention, it is possible to provide a polarizer protective film, polarizing plate, and image display device in which deterioration of visibility due to rainbow-like color spots is significantly suppressed even when the film is thinned. DETAILED DESCRIPTION OF THE INVENTION

[0011] 1.Polarizer protection film In one embodiment, the polarizer protective film of the present invention is a polarizer protective film including a polyester film, wherein 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 0.20 or less, and the refractive index of the polyester film in the fast axis direction is 1.580 or more and 1.630 or less.

[0012] In one embodiment, the polarizer protective film of the present invention is a polarizer protective film including a polyester film, wherein 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, and the smaller of the tear strengths in the slow axis direction and fast axis direction of the polyester film measured by a right-angle tearing method is 250 N / mm or more.

[0013] In one embodiment, the polarizer protective film of the present invention is a polarizer protective film including a polyester film, wherein 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 0.20 or less, and the thickness of the polyester film is 15 to 60 μm. An object of this embodiment is to provide a polarizer protective film in which deterioration of visibility due to rainbow-like color spots is significantly suppressed even when the film is made thin, and to provide a thin polarizing plate and image display device (such as a liquid crystal display device or an organic EL display).

[0014] The slow axis of the polyester film used as the polarizer protective film of the present invention is preferably approximately parallel to the MD direction (the running direction during film formation) from the viewpoint of suppressing rainbow-like color spots. Here, approximately parallel means that the angle between the slow axis direction of the polyester film and the MD direction (the running direction during film formation) is preferably within 10 degrees, more preferably within 7 degrees, even more preferably within 5 degrees, particularly preferably within 3 degrees, and most preferably within 2 degrees.

[0015] The direction of the slow axis can be determined using a molecular orientation meter (MOA-6004 molecular orientation meter manufactured by Oji Scientific Instruments Co., Ltd.).

[0016] In this specification, the MD direction refers to the running direction during film production and is sometimes referred to as the machine direction, and the TD direction refers to the width direction during film production and is sometimes referred to as the transverse direction.

[0017] When image display devices (such as liquid crystal display devices and organic EL displays) are industrially produced using polarizing plates that use polyester films as polarizer protective films, the absorption axis of the polarizer and the slow axis of the polyester film are usually arranged perpendicular to each other. This is due to the following reasons: The polyvinyl alcohol film used as the polarizer is produced by MD uniaxial stretching. Therefore, the polyvinyl alcohol film used as the polarizer is usually a film that is long in the stretching direction and has an absorption axis in the MD direction. On the other hand, the polyester film used as the protective film is usually produced by MD stretching followed by TD stretching, so that the main axis of orientation (slow axis direction) of the polyester film is the TD direction. From the viewpoint of production efficiency, these films are usually laminated together using a roll-to-roll process so that their longitudinal directions are parallel to each other to produce a polarizing plate. In this case, the slow axis of the polyester film and the absorption axis of the polarizer are usually perpendicular to each other.

[0018] On the other hand, in the present invention, the main axis direction (slow axis direction) of the polyester film is preferably the MD direction. Such a polyester film can be obtained by strongly stretching the polyester film in the MD direction. When a polarizing plate is produced by laminating this polyester film and a polarizer produced by MD uniaxial stretching in a roll-to-roll manner so that the longitudinal directions are parallel, the absorption axis of the polarizer and the slow axis of the polyester film are parallel. The present inventors have discovered that lamination in which the absorption axis of the polarizer and the slow axis of the polyester film are parallel provides a better iridescence suppression effect than lamination in which the absorption axis of the polarizer and the slow axis of the polyester film are perpendicular. In order to efficiently produce a polarizing plate with excellent iridescence suppression effect using an industrially advantageous roll-to-roll method, it is preferable to strongly stretch the polyester film in the MD direction and use a polyester film in which the MD direction and the slow axis direction are approximately parallel.

[0019] The in-plane birefringence ΔNxy of the polyester film used in the polarizer protective film of the present invention is preferably 0.06 to 0.2, more preferably 0.07 to 0.19, and even more preferably 0.08 to 0.18. If ΔNxy is less than 0.06, rainbow-like color spots are likely to be observed when observed from an oblique direction. Furthermore, a film with ΔNxy greater than 0.2 will not exhibit rainbow-like color spots, but will approach complete uniaxiality (uniaxial symmetry), resulting in a significant decrease in mechanical strength in the direction parallel to the orientation direction. The in-plane birefringence 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. The refractive index was measured at a wavelength of 589 nm.

[0020] In one embodiment, the refractive index (ny) in the fast axis direction of the polyester film used in the polarizer protective film of the present invention, in which the slow axis direction is approximately parallel to the MD direction, is preferably 1.58 to 1.63, more preferably 1.584 to 1.625, and even more preferably 1.588 to 1.62. If the refractive index (ny) in the fast axis direction is less than 1.58, the film approaches complete uniaxiality (uniaxial symmetry), resulting in a significant decrease in mechanical strength (tear strength) in the direction parallel to the orientation direction. Furthermore, if the refractive index (ny) in the fast axis direction exceeds 1.63, rainbow-like color spots are likely to be observed when observed from an oblique direction.

[0021] The smaller of the tear strengths measured by a right-angle tearing method in the slow axis direction and the fast axis direction of the polyester film used in the polarizer protective film of the present invention is preferably 250 N / mm or more, more preferably 280 N / mm or more, and even more preferably 300 N / mm or more. In films with a high ΔNxy value, the tear strength in the slow axis direction tends to be smaller than that in the fast axis direction. In the past, as the film thickness decreased, the mechanical strength required for processing was insufficient, making it difficult to meet the demand for thinner films. However, this problem can be solved by providing the smaller of the tear strengths measured by a right-angle tearing method in the slow axis direction and the fast axis direction of the film of 250 N / mm or more. If the tear strength is less than 250 N / mm, the film easily tears, resulting in reduced stability during film formation and processing. On the other hand, the higher the tear strength, the greater the stability during film formation and processing, but the higher the biaxiality (biaxial symmetry) and the more likely it is that rainbow-like color spots will occur. Therefore, it is preferable to increase the tear strength to a level that does not cause rainbow-like color spots, and realistically, 500 N / mm or less is preferable. The tear strength is measured according to the right-angle tear method (JIS K-7128-3) to determine the tear strength (N / mm) per film thickness.

[0022] The NZ coefficient of the polyester film used in the polarizer protective film of the present invention is preferably 1.5 or more and 2.5 or less, more preferably 1.6 or more and 2.3 or less, and even more preferably 1.7 or more and 2.1 or less. The smaller the NZ coefficient, the less likely rainbow-like color spots will occur depending on the observation angle. A completely uniaxial (uniaxially symmetric) film has an NZ coefficient of 1.0, but as the film approaches a completely uniaxial (uniaxially symmetric) film, the mechanical strength in the direction parallel to the orientation direction tends to decrease.

[0023] The NZ coefficient can be calculated as follows. The film's main axis (slow axis) direction is determined using a molecular orientation meter (MOA-6004 molecular orientation meter, manufactured by Oji Scientific Instruments Co., Ltd.). The biaxial refractive index (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 calculated using an Abbe refractometer (NAR-4T, manufactured by Atago Co., Ltd., measurement wavelength 589 nm). The NZ coefficient can be calculated by substituting the thus calculated nx, ny, and nz into the formula |nx - nz| / |nx - ny|. The refractive indexes are measured at a wavelength of 589 nm.

[0024] From the viewpoint of further reducing rainbow spots, the polyester film used for the polarizer protective film preferably has a retardation of 1500 nm or more and 30000 nm or less. The lower limit of the retardation is preferably 2500 nm, and the next more preferable lower limit is 3000 nm.

[0025] On the other hand, the upper limit of the retardation is 30,000 nm. Even if a polyester film having a retardation higher than this is used, not only will the effect of further improving visibility not be substantially obtained, but the thickness of the film will also increase considerably, which is undesirable as an industrial material and reduces its handleability. In one embodiment, the upper limit of the retardation is preferably 8,000 nm, more preferably 6,000 nm, even more preferably 5,500 nm, and particularly preferably 5,000 nm.

[0026] The birefringence can be determined by measuring the refractive index in two axial directions, or by using a commercially available automatic birefringence measuring device such as KOBRA-21ADH (Oji Scientific Instruments Co., Ltd.). The wavelength for measuring the refractive index is 589 nm.

[0027] The polyester film used in the polarizer protective film of the present invention preferably has a modulus of elasticity in the MD direction of 3000 MPa or more. In recent years, as LCDs have become thinner, components have also become thinner. In this context, as glass substrates used in liquid crystal panels have become thinner, the problem of warping of liquid crystal panels due to shrinkage of polarizing plates has become more apparent. The shrinkage of polarizing plates is caused by shrinkage of the PVA film polarizer (mainly shrinkage in the absorption axis direction), and it is preferable to control the shrinkage of the polarizer by the rigidity of the protective film. If the modulus of elasticity in the running direction of the protective film is 3000 MPa or more, sufficient control force is exerted against the shrinkage of the polarizer, making it possible to prevent warping of the liquid crystal panel. However, if the modulus is significantly lower than 3000 MPa, warping of the liquid crystal panel may become apparent. The lower limit of the modulus of elasticity in the MD direction is preferably 3500 MPa, more preferably 4000 MPa, and even more preferably 4500 MPa.

[0028] The polyester used in the polarizer protective film of the present invention 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 the in-plane birefringence can be easily controlled by stretching. In particular, polyethylene terephthalate is the most suitable material because it has a large intrinsic birefringence and can relatively easily achieve a large in-plane birefringence.

[0029] Furthermore, in order to suppress deterioration of optically functional dyes such as iodine dyes, the polarizer protective film of the present invention desirably has a light transmittance of 20% or less at a wavelength of 380 nm. The light transmittance at 380 nm is more preferably 15% or less, even more preferably 10% or less, and particularly preferably 5% or less. When the light transmittance is 20% or less, deterioration of the optically functional dye due to ultraviolet rays can be suppressed. Note that the transmittance in the present invention is measured perpendicular to the plane of the film and can be measured using a spectrophotometer (for example, Hitachi U-3500 model).

[0030] In order to achieve a transmittance of 20% or less at a wavelength of 380 nm for the polarizer protective film of the present invention, it is desirable to appropriately adjust the type and concentration of the UV absorber and the film thickness. The UV absorber used in the present invention is a known substance. Examples of UV absorbers include organic and inorganic UV absorbers, with organic UV absorbers being preferred from the viewpoint of transparency. Examples of organic UV absorbers include benzotriazoles, benzophenones, cyclic imino esters, and combinations thereof, but are not particularly limited as long as they satisfy the absorbance range specified in the present invention. However, from the viewpoint of durability, benzotriazoles and cyclic imino esters are particularly preferred. When two or more UV absorbers are used in combination, UV rays of different wavelengths can be simultaneously absorbed, thereby further improving the UV absorption effect.

[0031] Examples of benzophenone-based ultraviolet absorbers, benzotriazole-based ultraviolet absorbers, and acrylonitrile-based ultraviolet absorbers 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'-hydroxy-3'-tert-butyl-5'-methylphenyl)-5-chlorobenzotriazole, and 2-(5-chloro(2H)-benzotriazol-2-yl)-4-methyl-6-(tert-butyl)phenol. 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, but are not limited to these.

[0032] In addition to the UV absorber, it is also a preferred embodiment to incorporate various additives other than the catalyst, provided that the effects of the present invention are not impaired. 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, and the like. To achieve high transparency, it is also preferable for the polyester film to be substantially free of particles. "Substantially free of 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, and particularly preferably below the detection limit.

[0033] In a preferred embodiment, the polarizer protective film of the present invention may be coated on the surface with various hard coats for the purposes of preventing reflection, suppressing glare, and suppressing scratches.

[0034] Furthermore, in the present invention, the polyester film may be subjected to corona treatment, coating treatment, flame treatment, or the like in order to improve adhesion to a polarizer or various hard coat layers.

[0035] In the present invention, in order to improve adhesion to the polarizer, it is preferable that at least one surface of the film of the present invention has an easy-adhesion layer containing at least one of polyester resin, polyurethane resin, and polyacrylic resin as a main component. 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 of the present invention 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.

[0036] The easy-adhesion layer can be obtained by applying a coating liquid to at least one of the film surfaces in any step during the polyester film manufacturing process, followed by drying at 100 to 150° C. The final coating amount of the easy-adhesion layer is 0.05 to 0.2 g / m 2 It is preferable to control the coating amount to 0.05 g / m 2 If the coating amount is significantly less than 0.2 g / m, the adhesiveness to the resulting polarizer may be insufficient. 2When the adhesive layer is provided on both sides of the polyester film, the coating amounts of the adhesive layers on both sides may be the same or different, and each can be independently set within the above range.

[0037] It is preferable to add particles to the adhesion layer to impart slipperiness. It is preferable to use particles with an average particle size of 2 μm or less. If the average particle size of the particles significantly exceeds 2 μm, the particles tend to fall off from the coating layer. 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, as well as 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.

[0038] The coating solution 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, or pipe doctor coating, which can be used alone or in combination.

[0039] The average particle size of the particles is measured as follows: the particles are photographed with a scanning electron microscope (SEM), and the maximum diameters (the distance between the two furthest 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.

[0040] The polyester 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 extruded polyester in the machine direction and the cross direction at a temperature equal to or higher than the glass transition temperature, and then heat-treating the extruded polyester.

[0041] The polyester film of the present invention may be either a uniaxially stretched film or a biaxially stretched film. However, when a biaxially stretched film is used as a polarizer protective film, rainbow-like color spots are not observed when observed from directly above the film surface, but rainbow-like color spots may be observed when observed from an oblique direction, so care must be taken.

[0042] This phenomenon occurs because biaxially stretched films are composed of index ellipsoids with different refractive indices in the machine, width, and thickness directions, and there exists a direction within the film where the retardation is zero (the index ellipsoid appears as a perfect circle) depending on the direction of light transmission. Therefore, when the display screen is observed from a specific oblique direction, a point where the retardation is zero may appear, and rainbow-like color spots appear concentrically around that point. If the angle θ is defined as the angle from directly above the film surface (normal direction) to the point where the rainbow-like color spots are visible, this angle θ increases as the birefringence in the film plane increases, making the rainbow-like color spots less visible. Because the angle θ tends to be smaller in biaxially stretched films, uniaxially stretched films are preferred because they make the rainbow-like color spots less visible.

[0043] However, a completely uniaxial (uniaxially symmetric) film is not preferred because it significantly reduces the mechanical strength in the direction parallel to the orientation direction. In the present invention, it is preferable for the film to have biaxiality (biaxial symmetry) within a range in which rainbow-like color spots do not occur substantially, or within a range in which rainbow-like color spots do not occur within the viewing angle range required for the display screen.

[0044] The polyester film of the present invention may be produced under either sequential or simultaneous biaxial stretching conditions. However, in typical sequential biaxial stretching, longitudinal stretching is performed using rolls, which can easily scratch the film. Therefore, from the viewpoint of preventing scratches during stretching, simultaneous biaxial stretching without using rolls is preferred. Specifically, the longitudinal and transverse stretching temperatures are preferably 80 to 150°C, and particularly preferably 90 to 140°C. The longitudinal stretching ratio is preferably 5.5 to 7.5 times, more preferably 6.0 to 7.0 times, and particularly preferably 6.5 to 7.0 times. The transverse stretching ratio is preferably 1.5 to 3.0 times, and particularly preferably 1.8 to 2.8 times. To control the slow axis direction, ΔNxy, refractive index in the fast axis direction, NZ coefficient, and tear strength within the above ranges, it is preferable to control the longitudinal and transverse stretching ratios. If the difference between the longitudinal and transverse stretching ratios is too small, it becomes difficult to increase ΔNxy, which is not preferable. Also, setting the stretching temperature low is a preferable measure for increasing ΔNxy.

[0045] In order to set the refractive index in the fast axis direction within the above-mentioned range and to increase the tear strength, it is preferable to impart moderate biaxiality under conditions where ΔNxy satisfies the range specified in this application rather than a completely uniaxial film. In the subsequent heat treatment, the treatment temperature is preferably 100 to 250°C, particularly preferably 180 to 245°C.

[0046] As mentioned above, ΔNxy and NZ coefficients can be controlled within specific ranges by appropriately setting the stretching ratio and stretching temperature. For example, the higher the stretching ratio and the lower the stretching temperature, the easier it is to obtain a high ΔNxy. Conversely, the lower the stretching ratio and the higher the stretching temperature, the easier it is to obtain a low ΔNxy. In addition to controlling ΔNxy and NZ coefficients, it is preferable to set the final film-forming conditions taking into account the physical properties required for processing.

[0047] The thickness of the polyester film used as the polarizer protective film of the present invention is not particularly limited, but is preferably in the range of 15 to 200 μm, more preferably 15 to 150 μm. A film with a thickness of less than 15 μm exhibits significant deterioration in mechanical properties, making it more susceptible to tearing and rupture, and its practicality as an industrial material tends to be significantly reduced. The lower limit of the thickness is preferably 25 μm, more preferably 30 μm, and even more preferably 35 μm. On the other hand, if the upper limit of the thickness of the polarizer protective film exceeds 200 μm, the resulting polarizing plate becomes too thick, which is undesirable. From the viewpoint of practicality as a polarizer protective film, the upper limit of the thickness is preferably 150 μm, more preferably 80 μm, even more preferably 60 μm, even more preferably 55 μm, even more preferably 50 μm, and even more preferably 45 μm. In order to control the ΔNxy, NZ coefficient and tear strength within the ranges of the present invention even within the above thickness range, the polyester used as the film substrate is preferably polyethylene terephthalate.

[0048] The method for incorporating the ultraviolet absorber into the polyester film of the present invention can be a combination of known methods. For example, the ultraviolet absorber can be incorporated by a method in which a dried ultraviolet absorber is blended in advance with a polymer raw material using a kneading extruder to prepare a master batch, and then the predetermined master batch and the polymer raw material are mixed during film formation.

[0049] In this case, the concentration of the UV absorber in the masterbatch is preferably 5 to 30% by mass in order to disperse the UV absorber uniformly and to compound it economically. The conditions for preparing the masterbatch are preferably a kneading extruder, with the extrusion temperature being above the melting point of the polyester raw material and below 290°C for 1 to 15 minutes. At temperatures above 290°C, the weight loss of the UV absorber is significant, and the viscosity of the masterbatch also decreases significantly. At extrusion temperatures below 1 minute, it becomes difficult to uniformly mix the UV absorber. At this time, stabilizers, color adjusters, and antistatic agents may be added as needed.

[0050] In addition, in the present invention, it is preferable that the 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 confluence block (e.g., a confluence block with a rectangular confluence), 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. In the present invention, high-precision filtration is preferably performed during melt extrusion to remove foreign matter contained in the raw polyester that causes optical defects. The filtration particle size (initial filtration efficiency 95%) of the filter material used for high-precision filtration of the molten resin is preferably 15 μm or less. If the filtering particle size of the filter material significantly exceeds 15 μm, the removal of foreign matter of 20 μm or larger tends to be insufficient.

[0051] 2. Polarizing plate The polarizing plate has a configuration in which a polarizer protective film is laminated on at least one surface of a polarizer dyed with iodine, such as PVA. The polarizing plate of the present invention preferably uses the polarizer protective film of the present invention having the specific polyester film described above as at least one of the polarizer protective films constituting the polarizing plate. In a preferred embodiment, the polarizer protective film of the present invention having the specific polyester film described above is laminated on one surface of a polarizer, and a polarizer protective film or optical compensation film having no birefringence, such as a TAC film, a norbornene film, or an acrylic film, is laminated on the other surface of the polarizer. In another preferred embodiment, the polarizer protective film of the present invention including the specific polyester film described above is laminated on one surface of a polarizer, and no film is laminated on the other surface of the polarizer (i.e., no independent film is attached to the other surface of the polarizer). In the above-mentioned another preferred embodiment, a coating layer (such as a hard coat layer, an antiglare layer, an antireflection layer, a low-reflection layer, a moisture-resistant layer (which may be made of an organic or inorganic material), or a layer having a combination of these functions) may be provided on the surface of the polarizer opposite to the surface on which the specific polyester film is laminated.

[0052] As described above, from the viewpoint of suppressing iridescence and warping of the liquid crystal panel, the polarizing plate of the present invention is preferably laminated so that the absorption axis of the polarizer and the slow axis of the polyester film are substantially parallel to each other. Here, "substantially parallel" means that a slight misalignment is permitted. The angle formed by the absorption axis of the polarizer and the slow axis of the polyester film is preferably within 10 degrees, more preferably within 7 degrees, even more preferably within 5 degrees, particularly preferably within 3 degrees, and most preferably within 2 degrees.

[0053] 3. Image display device The image display device includes a liquid crystal display device, an organic EL display, a QLED display, and the like, which includes a polarizing plate inside the image display device.

[0054] 4.Liquid crystal display device Generally, a liquid crystal panel is composed of a rear module, a liquid crystal cell, and a front module, in that order from the side facing the backlight light source to the side where an image is displayed (the viewing side). The rear module and the front module are generally composed of a transparent substrate, a transparent conductive film formed on the surface facing the liquid crystal cell, and a polarizing plate disposed on the opposite side. Here, the polarizing plate is disposed on the side facing the backlight light source in the rear module, and on the side where an image is displayed (the viewing side) in the front module.

[0055] A liquid crystal display device comprises at least a backlight source and a liquid crystal cell disposed between two polarizing plates, and may also include other components such as a color filter, a lens film, a diffusion sheet, and an anti-reflection film, as appropriate.

[0056] The arrangement of the polarizer protective film of the present invention having a specific polyester film is not particularly limited. However, in the case of a liquid crystal display device having a polarizing plate arranged on the incident light side (light source side), a liquid crystal cell, and a polarizing plate arranged on the exit light side (viewing side), it is preferable that the polarizer protective film on the incident light side of the polarizing plate arranged on the incident light side and / or the polarizer protective film on the exit light side of the polarizing plate arranged on the exit light side be the polarizer protective film of the present invention having the specific polyester film. A particularly preferred embodiment is one in which the polarizer protective film on the incident light side of the polarizing plate arranged on the incident light side is the specific polyester film. Arranging the polyester film in a position other than the above may change the polarization properties of the liquid crystal cell. Since it is not preferable to use the polarizer protective film of the present invention in a location where polarization properties are required, it is preferable to use it as a protective film for a polarizing plate in such a specific position.

[0057] The backlight may be configured as an edge light type having a light guide plate, a reflector, etc. as constituent members, or as a direct type.

[0058] White light-emitting diodes (white LEDs) are preferably used as backlight sources for LCD devices. In the present invention, a white LED refers to a phosphor-based device that emits white light by combining a light-emitting diode (LED) that emits blue or ultraviolet light using a compound semiconductor with a phosphor. Phosphors include yttrium-aluminum-garnet-based yellow phosphors and terbium-aluminum-garnet-based yellow phosphors. Among these, white light-emitting diodes that combine a blue light-emitting diode using a compound semiconductor with a yttrium-aluminum-garnet-based yellow phosphor have a continuous, broad emission spectrum and excellent luminous efficiency. A continuous emission spectrum here refers to the absence of a wavelength at which the light intensity is zero, at least in the visible light range. Furthermore, the method of the present invention enables the widespread use of low-power white LEDs, thereby achieving energy savings.

[0059] Also preferred as the backlight light source are white light sources having emission spectrum peaks in the wavelength regions of 400 nm or more and less than 495 nm (B region), 495 nm or more and less than 600 nm (G region), and 600 nm or more and less than 780 nm (R region). For example, white light sources using quantum dot technology, phosphor-based white LED light sources using phosphors with emission peaks in the R (red) and G (green) regions by excitation light and blue LEDs, three-wavelength white LED light sources, white LED light sources combined with red lasers, and others, such as those with the composition formula K2SiF6:Mn 4+Examples of such white light sources include white LED light sources that use a blue LED and a fluoride phosphor (also referred to as "KSF"). These white light sources have attracted attention as backlight sources for wide-color-gamut liquid crystal display devices, and all of them have narrower peak half-widths than conventional white light-emitting diode light sources that use a light-emitting element that combines a blue light-emitting diode with an yttrium-aluminum-garnet-based yellow phosphor. When using backlight sources that use these white light sources, compared to backlight sources that use a white light-emitting diode with an emitting element that combines a blue light-emitting diode with an yttrium-aluminum-garnet-based yellow phosphor, there has been a problem in that rainbow spots tend to occur more easily when a polyester film having retardation is used as a polarizer protective film, which is a component of a polarizing plate. However, the polarizer protective film of the present invention can significantly suppress rainbow spots.

[0060] 5. OLED and QLED displays The organic EL element can be appropriately selected from organic EL elements known in the technical field. The use of an organic EL element is preferable in terms of a wide viewing angle, high contrast, and high-speed response. An organic EL element is typically an emitter (organic electroluminescence emitter) having a structure in which an anode as a transparent electrode, an organic light-emitting layer, and a cathode as a metal electrode are laminated in this order on a transparent substrate. When a voltage is applied between the anode and the cathode, an organic EL cell emits light by recombining holes (positive holes) injected from the anode and electrons injected from the cathode in the organic light-emitting layer.

[0061] Any transparent substrate can be used as the transparent substrate. For example, the transparent substrate can be selected from the group consisting of a glass substrate, a ceramic substrate, a semiconductor substrate, a metal substrate, and a plastic substrate. Specific examples of plastic substrates include conventionally used transparent resin films. The transparent substrate may be provided with a surface treatment layer, if necessary. Examples of the surface treatment layer include a moisture-proof layer, a gas barrier layer, a hard coat layer, and an undercoat layer.

[0062] Examples of materials constituting the anode and cathode include metals, metal oxides, alloys, electrically conductive compounds, and mixtures thereof. Specific examples of 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. Specific examples of materials constituting the cathode include magnesium, aluminum, indium, lithium, sodium, cesium, silver, magnesium-silver alloys, magnesium-indium alloys, and lithium-aluminum alloys.

[0063] The thickness of the anode and cathode can be set arbitrarily depending on the materials constituting the anode and cathode. The thickness of the anode can be set appropriately, for example, from 10 nm to 200 nm, preferably from 10 nm to 100 nm. The thickness of the cathode can be set appropriately, for example, from 10 nm to 1000 nm, preferably from 10 nm to 200 nm.

[0064] The organic light-emitting layer is a layer that has the function of providing a site for recombination of holes and electrons when a voltage is applied, thereby emitting light. The organic light-emitting layer contains an organic light-emitting material and may have a single layer structure or a laminated structure of two or more layers. In the case of a laminated structure, each layer may emit light of a different color. The thickness of the organic light-emitting layer is optional and can be set appropriately within the range of, for example, 3 nm to 3 μm.

[0065] The organic light-emitting material used in the organic light-emitting layer can be appropriately selected from any light-emitting material, specifically, olefin-based light-emitting materials such as 4,4'-(2,2-diphenylvinyl)biphenyl; 9,10-di(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-biphenylyl)-9,9'-bisanthracene, 9,10,9',10'-tetraphenylene; The light-emitting material can be appropriately selected from the group consisting of anthracene-based light-emitting materials such as tetraphenyl-2,2'-bianthryl and 1,4-bis(9-phenyl-10-anthracene)benzene; spiro-based light-emitting materials such as 2,7,2',7'-tetrakis(2,2-diphenylvinyl)spirobifluorene; carbazole-based light-emitting materials such as 4,4'-dicarbazolebiphenyl and 1,3-dicarbazolylbenzene; and pyrene-based light-emitting materials such as 1,3,5-tripyreninebenzene.

[0066] The organic EL element may include a sealing member formed to cover the organic EL element, in order to isolate the organic EL element composed of the anode, the organic light-emitting layer, and the cathode on the substrate from the outside air. By providing the sealing member, it is possible to prevent deterioration of the light-emitting characteristics of the organic light-emitting layer due to moisture and oxygen in the outside air.

[0067] The organic EL device may further include any optional components (for example, a hole injection layer, a hole transport layer, an electron injection layer, and / or an electron transport layer) at any appropriate position.

[0068] When an organic EL cell is used as the image display cell, it is preferable to have a polarizing plate on the viewing side. Because the organic light-emitting layer is thin, at approximately 10 nm, external light is reflected by the metal electrode and then emitted back to the viewing side, which can cause the display surface of the organic EL display device to appear mirror-like when viewed from the outside. To block such specular reflection of external light, it is preferable to provide a polarizing plate on the viewing side of the organic EL cell and further provide a quarter-wave plate between the organic EL cell and the polarizing plate. The polarizing plate can be any of the above-described polarizing plates, and it is preferable that a polarizer protective film made of the polyester film of the present invention is laminated on the viewing side of the polarizer. Another preferable embodiment is to laminate a quarter-wave plate on the polarizer instead of the protective film on the organic EL element side of the polarizer. By combining these viewing-side polarizing plates and quarter-wave plates to form a circular polarizing plate, the external light specularly reflected by the metal electrode of the organic EL cell is blocked by the circular polarizing plate, thereby suppressing a decrease in visibility of the image display device. A half-wave plate or the like may be further laminated on the organic EL element side or polarizer side of the quarter-wave plate. Preferably, a half-wave plate or the like is laminated on the organic EL element side of the quarter-wave plate with the optical axes of the plates inclined relative to each other, as disclosed in JP-A-10-68816 and JP-A-2017-97379.

[0069] QLED displays are similar to organic EL displays in that they utilize the ability of quantum dots to emit light when electricity is applied, and are attracting attention as next-generation displays. [Example]

[0070] 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.

[0071] (1) Evaluation of the slow axis direction of the film The slow axis direction of the film was evaluated by measurement using a molecular orientation meter (MOA-6004 molecular orientation meter, manufactured by Oji Scientific Instruments Co., Ltd.).

[0072] (2) ΔNxy and retardation (Re) Retardation is a parameter defined by the product (ΔNxy × d) of the refractive index anisotropy of two orthogonal axes on a 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 using the following method. The slow axis direction of the film was determined using a molecular orientation meter (MOA-6004 molecular orientation meter, manufactured by Oji Scientific Instruments Co., Ltd.), and a 4 cm × 2 cm rectangle was cut out so that the slow axis direction was parallel to the long side of the measurement sample, and used as the measurement sample. For this sample, the refractive indices of two perpendicular axes (refractive index in the slow axis direction: nx, refractive index in the in-plane direction perpendicular to the slow axis direction (i.e., refractive index in the fast axis direction: ny) and the refractive index in the thickness direction (nz) were measured using an Abbe refractometer (Atago Co., Ltd., NAR-4T, measurement wavelength 589 nm), and the absolute value of the difference in the biaxial refractive indices (|nx - ny|) was taken as the refractive index anisotropy (ΔNxy). The film thickness d (nm) was measured using an electric micrometer (Fine Rufu Co., Ltd., Millitron 1245D) and converted to units in nm. The retardation (Re) was calculated from the product (ΔNxy × d) of the refractive index anisotropy (ΔNxy) and the film thickness d (nm).

[0073] (3) NZ coefficient (2) The values of nx, ny, and nz measured by the Abbe refractometer were substituted into |nx-nz| / |nx-ny| to obtain the NZ coefficient.

[0074] (4) Elastic modulus The elastic modulus of the polyester film was evaluated using a Seiko Instruments dynamic viscoelasticity measuring device (DMS6100) in accordance with JIS-K7244 (DMS) after leaving it to stand for 168 hours in an environment of 25°C and 50% RH. The temperature dependence was measured from 25°C to 120°C under the conditions of tensile mode, drive frequency of 1Hz, chuck distance of 5mm, and heating rate of 2°C / min, and the average storage modulus from 30°C to 100°C was taken as the elastic modulus. The measurement was performed in the MD direction.

[0075] (5-1) Iridescence observation (liquid crystal display device) A roll of a polarizer made of iodine and polyvinyl alcohol film, which had been uniaxially stretched in the MD direction, was laminated to a roll of PET film (Polarizer Protective Films 1 to 9, described below) in a roll-to-roll manner so that their MD directions were parallel. A roll of TAC film (manufactured by Fujifilm Corporation, 40 μm thick) was also laminated to the other side of the polarizer in a roll-to-roll manner to create a polarizing plate consisting of PET film / polarizer / TAC film. The resulting polarizing plate was placed on the incident light side and the exit light side of a liquid crystal display device (NICHIA Corporation, NSPW500CS) using a white LED light source consisting of a blue light-emitting diode and an yttrium-aluminum-garnet yellow phosphor. The polyester film of the incident light-side polarizing plate was positioned on the light source side, while the polyester film of the exit light-side polarizing plate was positioned on the viewing side. The polarizing plates of the liquid crystal display device were visually observed from the front and oblique angles, and the presence or absence of iridescence was evaluated as follows:

[0076] ○: No rainbow spots are observed from any direction. △: When observed obliquely, faint rainbow spots can be observed depending on the angle. ×: When observed from an oblique direction, rainbow spots are clearly visible.

[0077] (5-2) Iridescence observation (organic EL display) A roll of a polarizer made of iodine and polyvinyl alcohol film, which had been produced by uniaxial stretching in the MD direction, and a roll of PET film, one of the polarizer protective films 1 to 9 described below, were laminated together in a roll-to-roll manner so that their MD directions were parallel to each other. A roll of a quarter-wave plate was also laminated to the other side of the polarizer in a roll-to-roll manner to produce a polarizing plate consisting of PET film / polarizer / (quarter-wave plate). The circular polarizer (located on the viewing side of the OLED) was removed from a commercially available OLED display (LG C6P 55-inch OLED TV), and the polarizer obtained above was placed inside the OLED display in its place, with the PET film located on the viewing side. The OLED display was visually observed from the front and oblique angles, and the presence or absence of rainbow spots was evaluated as follows:

[0078] ○: No rainbow spots are observed from any direction. △: When observed obliquely, faint rainbow spots can be observed depending on the angle. ×: When observed from an oblique direction, rainbow spots are clearly visible.

[0079] (6) Warpage evaluation of LCD panels A roll of a polarizer made of iodine and a polyvinyl alcohol film uniaxially stretched in the MD direction and a roll of a PET film of a polarizer protective film (described later) were laminated together in a roll-to-roll manner so that their MD directions were parallel to each other. A roll of TAC film (manufactured by Fujifilm Corporation, thickness: 40 μm) was also laminated to the other side of the polarizer in a roll-to-roll manner to produce a polarizing plate consisting of a PET film / polarizer / TAC film. Next, the above-mentioned polarizing plates of the same size were laminated to both sides of a glass plate measuring 125 mm wide, 220 mm long, and 0.4 mm thick using PSA in a crossed-Nicol relationship (the absorption axis of one polarizing plate was parallel to the width direction, and the absorption axis of the other polarizing plate was parallel to the length direction). The upper and lower polarizing plates used had the same shrinkage force. The polarizer protective film of the present invention was laminated so that it was positioned on the outside. Next, the sample was heat-treated for 30 minutes in a gear oven set at 100°C, and then cooled for 10 minutes in an environment set at room temperature of 25°C. After that, the height of the four corners was measured with a tape measure and the maximum value was read. A measurement value of 5 mm or less was considered to be in the good range.

[0080] (7) Tear strength The tear strength (N / mm) per film thickness for each film was measured using a Shimadzu Autograph (AG-X plus) according to the right-angle tearing method (JIS K-7128-3). The tear strength was measured in two directions, parallel and perpendicular to the film's main orientation axis (slow axis) (i.e., the slow axis direction and the fast axis direction), and the smaller value was recorded as the tear strength in Table 1. The main orientation axis (slow axis direction) was measured using a molecular orientation meter (Oji Scientific Instruments, MOA-6004 molecular orientation meter).

[0081] (8) Film forming properties The start time was one hour after the start of film formation, and the number of breaks in one hour from that point was compared, and film formability was evaluated as follows.

[0082] ○: Less than 3 breaks △: Number of breaks is 3 or more but less than 6 ×: Breaks six or more times

[0083] (9) Scratch evaluation method One hour after the start of film formation, the film was inspected using a defect inspection device, and the number of scratches with a maximum height Sz of 0.6 μm or more measured using a laser microscope (OLS4100, manufactured by Olympus Corporation) was judged as follows.

[0084] ○: 3 scratches / m 2 less than △: 3 scratches / m 2 More than 6 pieces / m 2 less than ×: 6 scratches / m 2 End

[0085] (Production Example 1 - Polyester A) The 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. 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 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 atmospheric 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, where a polycondensation reaction was carried out under reduced pressure at 280°C.

[0086] 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 and solidified using cooling water that had been previously filtered (pore diameter: 1 μm or less), and cut into pellets. The intrinsic viscosity of the resulting polyethylene terephthalate resin (A) was 0.62 dl / g, and it contained substantially no inert particles or internally precipitated particles (hereinafter abbreviated as PET (A)).

[0087] (Production Example 2 - Polyester 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 0.62 dL / g) were mixed and the mixture was kneaded using an extruder to obtain polyethylene terephthalate resin (B) containing an ultraviolet absorber (hereinafter abbreviated as PET (B)).

[0088] (Production Example 3 - Preparation of Adhesion-Modifying Coating Liquid) A water-dispersible sulfonate metal salt-containing copolymerized polyester resin was prepared by conventional transesterification and polycondensation reactions. The dicarboxylic acid components (based on the total dicarboxylic acid components) were 46 mol% terephthalic acid, 46 mol% isophthalic acid, and 8 mol% sodium 5-sulfonatoisophthalate. The glycol components (based on the total glycol components) were 50 mol% ethylene glycol and 50 mol% neopentyl glycol. Next, 51.4 parts by weight of water, 38 parts by weight of isopropyl alcohol, 5 parts by weight of n-butyl cellosolve, and 0.06 parts by weight of a nonionic surfactant were mixed and heated with stirring. When the temperature reached 77°C, 5 parts by weight of the water-dispersible sulfonate metal salt-containing copolymerized polyester resin was added. Stirring was continued until the resin clumps disappeared, and the resin aqueous dispersion was cooled to room temperature to obtain a uniform water-dispersible copolymerized polyester resin solution with a solids concentration of 5.0% by weight. 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.

[0089] (Polarizer protective film 1) As raw materials for the intermediate layer of the base film, 90 parts by weight of particle-free PET (A) resin pellets and 10 parts by weight of PET (B) resin pellets containing a UV absorber were dried under reduced pressure (1 Torr) at 135 ° C for 6 hours and then fed into Extruder 2 (for intermediate layer II). PET (A) was dried by conventional methods and fed into Extruder 1 (for outer layers I and III), respectively, and melted at 285 ° C. These two polymers were each filtered through a stainless steel sintered filter medium (nominal filtration accuracy 10 μm particle 95% cut). The two polymers were laminated in a two-type, three-layer merging block, extruded into a sheet from a die, and then wrapped around a casting drum at a surface temperature of 30 ° C using an electrostatic casting method, cooled, and solidified to produce an unstretched film. The output of each extruder was adjusted so that the thickness ratio of layers I, II, and III was 10:80:10.

[0090] 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 became 1 / 2 mm, the coating liquid was dried at 80° C. for 20 seconds.

[0091] The unstretched film with this coating layer formed was introduced into a simultaneous biaxial stretching machine, and while holding the edges of the film with clips, it was introduced into a hot air zone at 125°C and stretched 6.5 times in the running direction and 2.2 times in the width direction. Next, while maintaining the stretched width in the width direction, it was treated at 225°C for 30 seconds to obtain a biaxially oriented PET film with a film thickness of approximately 40 μm. This was wound into a film roll (film roll with a film length in the MD direction of 500 m). The slow axis of the obtained film was within 3° of the running direction. This was designated as Polarizer Protective Film 1.

[0092] (Polarizer protective film 2) A biaxially oriented PET film with a film thickness of approximately 40 μm was obtained in the same manner as Polarizer Protective Film 1, except that the thickness of the unstretched film was changed and it was stretched 6.0 times in the running direction and 2.2 times in the width direction. This was taken up into a roll to form a film roll (film roll with a length in the MD direction of 500 m). The slow axis of the obtained film was within 3° from the running direction. This was designated Polarizer Protective Film 2.

[0093] (Polarizer protective film 3) An unstretched film was prepared in the same manner as Polarizer Protective Film 1. It was heated to 105°C using a sequential biaxial stretching machine with a group of heated rolls and an infrared heater. It was then stretched 6.5 times in the running direction using a group of rolls with different peripheral speeds. It was then introduced into a hot air zone at 125°C and stretched 2.2 times in the width direction. Next, while maintaining the stretched width, it was treated at 225°C for 30 seconds to obtain a biaxially oriented PET film with a film thickness of approximately 40 μm. This was wound into a roll (film roll with a length in the MD direction of 500 m). The slow axis of the resulting film was within 5° from the running direction. This was designated Polarizer Protective Film 3.

[0094] (Polarizer protective film 4) A uniaxially oriented PET film with a film thickness of approximately 40 μm was obtained in the same manner as Polarizer Protective Film 1, except that the thickness of the unstretched film was changed and stretched 1.0 times in the running direction and 4.0 times in the width direction. This was wound into a roll to form a film roll. The slow axis of the obtained film was within 4° from the width direction. This was designated Polarizer Protective Film 4. Because the slow axis of Polarizer Protective Film 4 was in the width direction, faint rainbow-like color spots were observed at certain angles when observed from an oblique direction. Furthermore, the film had low tear strength and easily tore. For example, when Polarizer Protective Film 4 was laminated to a polarizer to produce a polarizing plate using a roll-to-roll process, it cracked more frequently in the width direction than other films.

[0095] (Polarizer protective film 5) The unstretched film was heated to 105°C using a group of heated rolls and an infrared heater, stretched 4.0 times in the running direction using a group of rolls with different peripheral speeds, and then introduced into a hot air zone at 125°C and stretched 1.0 times in the width direction. Next, while maintaining the stretched width, the film was treated at 225°C for 30 seconds to obtain a uniaxially oriented PET film with a thickness of approximately 40 μm. This was wound into a roll. The slow axis of the resulting film was within 8° of the running direction. This film was designated Polarizer Protective Film 5. While no rainbow-like color spots were observed in Polarizer Protective Film 5, it had low tear strength and easily tore.

[0096] (Polarizer protective film 6) A biaxially oriented PET film with a film thickness of approximately 40 μm was obtained in the same manner as Polarizer Protective Film 1, except that the thickness of the unstretched film was changed and it was stretched 4.5 times in the running direction and 2.4 times in the width direction. This was wound into a roll to form a film roll (film roll with a length in the MD direction of 500 m). The slow axis of the obtained film was within 8° from the running direction. Because the obtained film had low ΔNxy, rainbow-like color spots were observed when observed from an oblique direction.

[0097] (Polarizer protection film 7) The unstretched film was heated to 105°C using a sequential biaxial stretching machine with a group of heated rolls and an infrared heater. It was then stretched 2.2 times in the running direction using a group of rolls with different peripheral speeds, and then introduced into a hot air zone at 125°C and stretched 5.5 times in the width direction. Next, while maintaining the stretched width, the film was treated at 225°C for 30 seconds to obtain a biaxially oriented PET film with a thickness of approximately 40 μm. This was then wound into a roll (film roll with a length in the MD direction of 500 m). The slow axis of the resulting film was within 6° of the width direction. Because the slow axis of the resulting film was aligned in the width direction, rainbow-like color spots were observed when observed obliquely.

[0098] (Polarizer protection film 8) A biaxially oriented PET film with a film thickness of approximately 40 μm was obtained in the same manner as Polarizer Protective Film 1, except that the thickness of the unstretched film was changed and it was stretched 6.0 times in the running direction and 1.5 times in the width direction. This was taken up into a roll to form a film roll (film roll with a length in the MD direction of 500 m). The slow axis of the obtained film was within 3° from the running direction. This was designated Polarizer Protective Film 8.

[0099] (Polarizer protection film 9) A biaxially oriented PET film with a film thickness of approximately 40 μm was obtained in the same manner as Polarizer Protective Film 1, except that the thickness of the unstretched film was changed and it was stretched 6.5 times in the running direction and 2.7 times in the width direction. This was taken up into a roll to form a film roll (film roll with a length in the MD direction of 500 m). The slow axis of the obtained film was within 3° from the running direction. This was designated Polarizer Protective Film 9.

[0100] Polarizer Protective Films 1 to 9 were subjected to observation of rainbow spots and measurement of tear strength, etc., and the results are shown in Table 1 below.

[0101] [Table 1]

[0102] As shown in Table 1, when polarizer protective films 1 to 3, 5, 8, and 9 were used for rainbow observation, no rainbow was observed when observed from the front or at an oblique angle. On the other hand, for polarizer protective film 4, thin rainbows were observed in some areas when observed at an oblique angle. Polarizer protective film 5 did not show any rainbows, but had low tear strength and was unstable during film formation. Polarizer protective films 6 and 7 showed clear rainbows when observed at an oblique angle. Furthermore, liquid crystal display devices were produced in the same manner as in the above-mentioned (5-1) rainbow observation section, except that a polarizing plate consisting of a PET film / polarizer in which only a PET film was laminated to the polarizer without a TAC film was used. Rainbow observation was also performed in the same manner. The results were the same as those shown in Table 1. Furthermore, when polarizer protective films 1 to 3, 5, 8, and 9 were used to evaluate the warpage of liquid crystal panels using the method described in (6) above, the measured values were 5 mm or less, which were all good results. [Industrial Applicability]

[0103] By using the polarizer protective film, polarizing plate, and image display device (liquid crystal display device, organic EL display, etc.) of the present invention, it is possible to contribute to thinner and less expensive LCDs without reducing visibility due to rainbow-like color spots, and the industrial applicability is extremely high.

Claims

1. A polarizer protective film comprising a polyester film, the angle between the slow axis direction and the MD direction of the polyester film is within 10 degrees, The in-plane birefringence ΔNxy of the polyester film is 0.06 or more and 0.20 or less, The retardation of the polyester film is 2500 nm or more and 30000 nm or less, Furthermore, a polarizer protective film that satisfies the following (A) and / or (B): (A) the refractive index of the polyester film in the fast axis direction is 1.580 or more and 1.630 or less; (B) The smaller of the tear strengths measured by a right-angle tearing method in the slow axis direction and the fast axis direction of the polyester film is 250 N / mm or more.

2. The polarizer protective film according to claim 1 , wherein the polyester film has an NZ coefficient of 1.5 or more and 2.5 or less.

3. 3. The polarizer protective film according to claim 1, wherein the polyester film has a thickness of 15 to 60 μm.

4. 4. The polarizer protective film according to claim 1, wherein the angle formed between the slow axis direction and the MD direction of the polyester film is 3 degrees or less.

5. 5. The polarizer protective film according to claim 1, wherein the polyester film has an elastic modulus in the machine direction of 3000 MPa or more.

6. A polarizing plate comprising a polarizer protective film according to any one of claims 1 to 5 laminated on at least one surface of a polarizer.

7. A polarizing plate comprising a polarizer protective film according to any one of claims 1 to 5 laminated on one surface of a polarizer, and no film laminated on the other surface of the polarizer.

8. A polarizing plate comprising a polarizer protective film according to any one of claims 1 to 5 laminated on one surface of a polarizer, and a quarter-wave plate laminated on the other surface of the polarizer.

9. An image display device comprising the polarizing plate according to any one of claims 6 to 8.

10. A liquid crystal display device comprising the polarizing plate according to claim 6 or 7.

11. An organic EL display comprising the polarizing plate according to any one of claims 6 to 8.

12. A QLED display comprising the polarizer according to any one of claims 6 to 8.

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