Polarizing plates for foldable displays

Abstract

[Problem] To provide a polarization plate for a folding display for which there is no risk of distortions arising in an image displayed on the folding section after having been bent repeatedly. [Solution] The polarization plate for a folding display has a polarizer protection film comprising a polyester film layered on at least one surface of a polarizer. The polyester film satisfies the following conditions: (1) the refractive index in the bending direction is 1.590 to 1.620, (2) the refractive index in the direction of the folding portion is 1.670 to 1.700, (3) the refractive index in the thickness direction is 1.520 or lower, and (4) the density is 1.380 g / cm3 or greater. (Herein, the bending direction is a direction that is orthogonal to the folding portion when folding the polyester film.)

Description

[Technical Field]

[0001] The present invention relates to a polarizing plate for a folding display, a circularly polarizing plate for a folding display, a method for manufacturing a circularly polarizing plate for a folding display, and a folding display. [Background technology]

[0002] As mobile devices become thinner and lighter, smartphones and other mobile devices are becoming more and more popular. While mobile devices are required to have a variety of functions, they also need to be convenient. For this reason, the most popular mobile devices must be able to be operated with one hand for simple operations and have a small screen size of around 6 inches, as they are designed to be stored in a pocket or similar.

[0003] On the other hand, tablet devices with screen sizes of 7 to 10 inches are highly functional and are intended for not only video content and music, but also business use, drawing, reading, etc. However, they cannot be operated with one hand, are less portable, and have issues with convenience.

[0004] To achieve these goals, a method has been proposed of connecting multiple displays to make them more compact (see Patent Document 1), but this method has not become widespread because the bezel remains, resulting in a truncated image and reduced visibility.

[0005] In recent years, mobile devices incorporating flexible and foldable displays have been proposed, allowing users to conveniently carry around large-screen mobile devices without image interruption.

[0006] In LCD displays, linear polarizers are installed on both sides of the liquid crystal cell, while in EL displays and the like, circular polarizers are installed on the viewing side of the cell to prevent reflections. However, when creating a full-screen display with a folding section, it is necessary to use a polarizer that is flexible and has a sufficient degree of polarization. However, in foldable displays, the area corresponding to the folding section is repeatedly folded, which causes the polarizer in that area to deform over time, posing problems such as distorting the image displayed on the display. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Laid-Open No. 2010-228391 Summary of the Invention [Problem to be solved by the invention]

[0008] The present invention aims to provide a polarizing plate and a circular polarizing plate for a foldable display that are free from the risk of image distortion at the folded portion after repeated folding, a method for manufacturing a circular polarizing plate, and a foldable display. [Means for solving the problem]

[0009] That is, the present invention comprises the following: 1. A polarizing plate for a folding display, in which a polarizer protective film made of a polyester film is laminated on at least one surface of a polarizer, wherein the polyester film satisfies the following conditions: (1) Refractive index in the bending direction is 1.590 to 1.620 (2) The refractive index in the direction of the folding part is 1.670 to 1.700 (3) Refractive index in the thickness direction is 1.520 or less (4) Density is 1.380 g / cm 3 End (Here, the bending direction refers to the direction perpendicular to the fold when folding the polyester film.) 2. A circular polarizing plate for a folding display, comprising the polarizing plate for a folding display according to 1 above, and a retardation layer on at least one surface thereof. 3. The circular polarizing plate for a folding display according to 2 above, wherein there is no free-standing film other than the polyester film, or there is only one free-standing film other than the polyester film. 4. The polarizing plate for a folding display according to claim 1, wherein the polarizer has a thickness of 12 μm or less. 5. The circular polarizing plate for a folding display according to the above item 2 or 3, wherein the polarizer has a thickness of 12 μm or less. 6. The polarizing plate for a folding display according to item 1 or 4 above, wherein the polarizer comprises a polymerizable liquid crystal compound and a dichroic dye. 7. The circular polarizing plate for a folding display according to any one of claims 2, 3, and 5, wherein the polarizer comprises a polymerizable liquid crystal compound and a dichroic dye. 8. A foldable display comprising the polarizing plate for a foldable display according to claim 1, 4, or 6. 9. A foldable display comprising the circular polarizer for a foldable display according to 2, 3, 5 or 7 above, wherein the retardation layer comprises a liquid crystal compound. 10. The following steps: (A) preparing a polyester film having the following characteristics: (1) Refractive index in the bending direction is 1.590 to 1.620 (2) The refractive index in the direction of the folding part is 1.670 to 1.700 (3) Refractive index in the thickness direction is 1.520 or less (4) Density is 1.380 g / cm 3 End (Here, the bending direction refers to the direction perpendicular to the fold when folding the polyester film.) (B) providing a polarizer on the polyester film by either method (a) or (b); (a) A method of transferring a polarizer provided on a releasable supporting substrate to a substrate film; (b) A method in which a polarizing film composition comprising a polymerizable liquid crystal compound and a dichroic dye is applied to a substrate film and then aligned to form a polarizer; and (C) laminating a retardation layer on the polarizer; The method for producing a circular polarizing plate for a folding display, comprising: 11. The following steps: (A) preparing a polyester film having the following characteristics: (1) Refractive index in the bending direction is 1.590 to 1.620 (2) The refractive index in the direction of the folding part is 1.670 to 1.700 (3) Refractive index in the thickness direction is 1.520 or less (4) Density is 1.380 g / cm 3 End (Here, the bending direction refers to the direction perpendicular to the fold when folding the polyester film.) (B) laminating a polarizer on the polyester film; and (C) providing a retardation layer on the polarizer by either method (c) or (d); (c) A method of transferring a retardation layer provided on a releasable supporting substrate onto a polarizer; (d) A method of coating a retardation layer composition comprising a liquid crystal compound on a polarizer and orienting the composition to form a retardation layer; The method for producing a circular polarizing plate for a folding display, comprising: 12. (C) The step of laminating a retardation layer on the polarizer (c) A method of transferring a retardation layer provided on a releasable supporting substrate onto a polarizer, or (d) A method of coating a retardation layer composition comprising a liquid crystal compound on a polarizer and orienting the composition to form a retardation layer; 11. The method for producing a circularly polarizing plate for a folding display according to claim 10, wherein the circularly polarizing plate is any one of the following: [Effects of the Invention]

[0010] The polarizing plate and circularly polarizing plate of the present invention are unlikely to leave crease marks even when folded repeatedly, and there is no risk of image distortion at the folded portions, making them suitable for use in foldable displays. Furthermore, the foldable display of the present invention can display images without distortion at the folded portions. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 2 is a schematic diagram showing the bending radius when the foldable display of the present invention is folded. [Figure 2] FIG. 2 is a schematic diagram showing the bending direction of a polyester film used in the polarizing plate for a foldable display of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0012] (display) The term "display" as used herein refers to display devices in general, and examples of the display include LCDs, organic EL displays, inorganic EL displays, LEDs, and FEDs. LCDs, organic EL displays, and inorganic EL displays that have a bendable structure are preferred. Organic EL displays and inorganic EL displays that can reduce the number of layers are particularly preferred, and organic EL displays that have a wide color gamut are even more preferred.

[0013] (foldable display) A foldable display is a single continuous display that can be folded in half or otherwise when carried. Folding reduces the size by half, improving portability. The bending radius of a foldable display is preferably 5 mm or less, and more preferably 3 mm or less. A bending radius of 5 mm or less allows for a thinner display when folded. A smaller bending radius is preferable, but the smaller the bending radius, the more likely it is that creases will form. A bending radius of 0.1 mm or more is preferable, but it can also be 0.5 mm or more, or even 1 mm or more. Even a bending radius of 1 mm can achieve a practically thin display when carried. The bending radius when folded is measured at the location indicated by the symbol 11 in the schematic diagram of Figure 1 and refers to the radius of the inside of the folded portion when folded. The surface protection film, described below, may be located on either the outside or inside of the folded portion of the foldable display. Furthermore, the foldable display may be tri-folded or quadruple-folded, or may be a rollable type, all of which are considered to fall within the scope of the foldable display of the present invention.

[0014] A. Polarizing plate Foldable displays use polarizing plates. Liquid crystal displays have polarizing plates on both sides of the liquid crystal cell, while electroluminescent displays often use circular polarizing plates to prevent reflections from the internal structure. A typical polarizing plate preferably has a laminated structure of a polarizer and a polarizer protective film for protecting the polarizer.

[0015] 1.Polarizer protection film First, the polarizer protective film of the polarizing plate will be described. In the present invention, the polarizer protective film is preferably a film made of polyester. Hereinafter, when describing the polarizer protective film alone, the polarizer protective film may be simply referred to as a polyester film.

[0016] The polyester film may be a single-layer film made of one or more types of polyester resin, or when two or more types of polyester are used, it may be a multilayer film or an ultra-multilayer laminate film with a repeating structure.

[0017] Examples of polyester resins used in polyester films include polyester films made of polyethylene terephthalate, polybutylene terephthalate, polyethylene-2,6-naphthalate, or copolymers containing these resin components as main components. Among these, stretched polyethylene terephthalate films are particularly preferred in terms of mechanical properties, heat resistance, transparency, cost, etc.

[0018] When a polyester copolymer is used for the polyester film, examples of the dicarboxylic acid component of the polyester include aliphatic dicarboxylic acids such as adipic acid and sebacic acid; aromatic dicarboxylic acids such as terephthalic acid, isophthalic acid, phthalic acid, and 2,6-naphthalenedicarboxylic acid; and polyfunctional carboxylic acids such as trimellitic acid and pyromellitic acid. Examples of the glycol component include fatty acid glycols such as ethylene glycol, diethylene glycol, 1,4-butanediol, propylene glycol, and neopentyl glycol; aromatic glycols such as p-xylene glycol; alicyclic glycols such as 1,4-cyclohexanedimethanol; and polyethylene glycols having an average molecular weight of 150 to 20,000. The mass ratio of the copolymerization components in the copolymer is preferably less than 20% by mass. A mass ratio of less than 20% by mass is preferred because film strength, transparency, and heat resistance are maintained.

[0019] In addition, in the production of polyester films, the intrinsic viscosity of at least one type of resin pellets is preferably in the range of 0.50 to 1.0 dL / g. When the intrinsic viscosity is 0.50 dL / g or higher, the impact resistance of the resulting film is improved, and disconnection of the internal circuitry of a display due to external impact is less likely to occur, which is preferable. On the other hand, when the intrinsic viscosity is 1.00 dL / g or lower, the increase in filtration pressure of the molten fluid is prevented from becoming too large, which facilitates stable film production operations, which is preferable.

[0020] The thickness of the polyester film is preferably 10 to 80 μm, and more preferably 25 to 75 μm. A thickness of 10 μm or more provides excellent handling properties and improved impact resistance, while a thickness of 80 μm or less is advantageous for weight reduction and also provides excellent flexibility, processability, and handling properties.

[0021] The haze of the polyester film is preferably 3% or less, more preferably 2% or less, and most preferably 1% or less. A haze of 3% or less can improve the visibility of images. The lower the haze limit, the better, but from the standpoint of stable production, a haze of 0.1% or more is preferred, and 0.3% or more is also acceptable.

[0022] As mentioned above, in order to reduce haze, it is better if the film surface does not have too much unevenness. However, in order to provide a certain degree of slipperiness from the viewpoint of ease of handling, unevenness can be formed by blending particles into the surface polyester resin layer or by coating a coating layer containing particles during film formation.

[0023] The method of blending particles into the polyester resin layer can be a known method. For example, they can be added at any stage of polyester production, but preferably they can be added as a slurry dispersed in ethylene glycol or the like at the stage of esterification, or after the completion of the transesterification reaction and before the start of the polycondensation reaction, to proceed with the polycondensation reaction. Alternatively, they can be added by a method of blending a slurry of particles dispersed in ethylene glycol or water with polyester raw materials using a vented kneading extruder, or a method of blending dried particles with polyester raw materials using a kneading extruder.

[0024] Among these, a method in which aggregate inorganic particles are homogeneously dispersed in a monomer liquid that will become a part of the polyester raw material, and then the filtered product is added to the remainder of the polyester raw material before, during, or after the esterification reaction is preferred. This method facilitates homogeneous dispersion of the particles and high-precision filtration of the slurry, since the monomer liquid has a low viscosity. Furthermore, when the monomer liquid is added to the remainder of the raw material, the particles are well dispersible and new aggregates are unlikely to form. From this perspective, it is particularly preferred to add the monomer liquid to the remainder of the raw material at a low temperature before the esterification reaction.

[0025] Furthermore, the number of protrusions on the film surface can be further reduced by a method (masterbatch method) in which a polyester containing particles is prepared in advance and then the pellets are kneaded and extruded with pellets containing no particles.

[0026] The polyester film may contain various additives, such as antistatic agents, UV absorbers, and stabilizers, as long as the total light transmittance remains within a preferred range.

[0027] The total light transmittance of the polyester film is preferably 85% or more, and more preferably 87% or more. A transmittance of 85% or more ensures sufficient visibility. The higher the total light transmittance of the polyester film, the better, but from the viewpoint of stable production, a total light transmittance of 99% or less is preferable, and 97% or less is also acceptable.

[0028] The maximum heat shrinkage of the polyester film after heat treatment at 150°C for 30 minutes is preferably 6% or less, and more preferably 5% or less. A heat shrinkage of 6% or less can suppress flatness defects such as curling and undulation during lamination processing. The lower the heat shrinkage, the better, but a value of -1% or more is preferable, and 0% or more is more preferable. A negative value here means expansion after heating, and a value of -1% or more is preferable as there is no risk of flatness defects.

[0029] Next, a method for producing a biaxially stretched polyester film will be described in detail using an example in which polyethylene terephthalate (hereinafter sometimes referred to as PET) pellets are used as the raw material for the polyester film, but the method is not limited to this. Furthermore, the number of layers, such as a single layer or a multilayer structure, is not limited.

[0030] After mixing and drying PET pellets in a predetermined ratio, the mixture is fed into a known melt lamination extruder, extruded through a slit die into a sheet, and cooled and solidified on a casting roll to form an unstretched film. While a single extruder is sufficient for a single-layer film, multilayer films can be produced using two or more extruders and two or more manifolds or merging blocks (e.g., merging blocks with rectangular merging sections) to laminate the multiple film layers that make up the outermost layers, extrude a two or more layer sheet from the die, and cool it on a casting roll to form an unstretched film.

[0031] In this case, it is preferable to perform high-precision filtration to remove foreign matter contained in the resin at any location where the molten resin is maintained at about 280°C during melt extrusion. The filter material used for high-precision filtration of the molten resin is not particularly limited, but a stainless steel sintered filter material is preferred because it has excellent performance in removing aggregates mainly composed of Si, Ti, Sb, Ge, and Cu and high-melting-point organic matter.

[0032] Furthermore, the filtration particle size (initial filtration efficiency 95%) of the filter material is preferably 20 μm or less, particularly preferably 15 μm or less. If the filtration particle size (initial filtration efficiency 95%) of the filter material exceeds 20 μm, foreign matter of 20 μm or more in size cannot be sufficiently removed. Although high-precision filtration of molten resin using a filter material with a filtration particle size (initial filtration efficiency 95%) of 20 μm or less may reduce productivity, it is preferable to obtain a film with fewer protrusions due to coarse particles.

[0033] (Refractive index in bending direction) In the present invention, the refractive index of the polyester film in at least one of the longitudinal direction (machine flow direction) and width direction is preferably 1.590 to 1.620, more preferably 1.591 to 1.600. Furthermore, when used as a polarizing plate, the refractive index of the polyester film, which serves as a polarizer protective film, in the bending direction is preferably 1.590 to 1.620, more preferably 1.591 to 1.600. Here, the bending direction refers to the direction perpendicular to the folding portion (reference numeral 21) expected in the use of a folding display, as indicated by reference numeral 22 on the polyester film (reference numeral 2) in FIG. 2 . A refractive index of 1.590 to 1.620 in at least one of the longitudinal direction and width direction is preferably 1.590 to 1.620, since deformation during repeated folding is minimal, and there is no risk of degrading the image quality of the folding display. The refractive index is more preferably 1.591 to 1.600. Of course, the bending direction is preferably the bending direction. If the refractive index is 1.590 or more, there is no risk of cracks occurring in the folded direction after the bending test described below, and of course no breakage occurs, so the visibility of the display can be maintained at a good level. The refractive index of the polyester film can be effectively adjusted by adjusting the stretching ratio and stretching temperature. A relaxation step in the stretching direction and multi-stage stretching may also be used to adjust the refractive index. When multi-stage stretching is performed, it is preferable to set the stretching ratios in the second and subsequent stages higher than the stretching ratio in the first stage.

[0034] By controlling the refractive index in at least one of the longitudinal direction (machine flow direction) and width direction of the polyester film within the above range, and more preferably by controlling the refractive index in the bending direction within the above range, fatigue due to compressive stress applied to the inside of the fold when folded can be reduced. Fatigue due to compressive stress is thought to occur mainly in crystalline parts, and the fewer crystals there are in the bending direction, the less fatigue there is. Therefore, it is thought that lowering the refractive index reduces the amount of oriented crystals in the bending direction, thereby suppressing compressive fatigue.

[0035] Furthermore, the creep phenomenon caused by tensile stress applied to the outside of the fold when folded can be suppressed by reducing the refractive index. Fatigue due to tensile stress is thought to occur mainly in the amorphous portion, and repeated stress causes molecular chains to align, resulting in deformation. It can be assumed that the fewer molecular chains aligned in the bending direction, the less deformation due to alignment. Furthermore, since fatigue due to tension can be suppressed with fewer amorphous portions, a higher degree of crystallinity, i.e., a higher density, is preferable.

[0036] In the present invention, the stretching ratio of the unstretched polyester sheet in at least one of the longitudinal direction (machine flow direction) and the transverse direction is preferably 1.2 to 2.0 times, more preferably 1.7 to 2.0 times. The stretching direction is preferably the bending direction. A stretching ratio of 1.2 times or more is preferred because it prevents deformation during post-processing, such as hard coating, while a stretching ratio of 2.0 times or less is preferred because it prevents thickness unevenness in the film. The stretching temperature is preferably 75 to 120°C, more preferably 75 to 105°C. Heating methods during stretching can be conventionally known, such as hot air heating, roll heating, and infrared heating. Setting the stretching temperature to 75 to 120°C can prevent significant thickness unevenness due to stretching at the above stretching ratio. Furthermore, by stretching at a temperature as low as possible within a range that does not cause significant thickness unevenness, the refractive index in the thickness direction can be reduced.

[0037] (Refractive index in the direction of the fold) The refractive index of the polyester film in a direction perpendicular to the direction in which the refractive index is 1.590 to 1.620 is preferably 1.670 to 1.700. That is, the refractive index in the direction perpendicular to the bending direction (the direction of the folded portion) is preferably 1.670 to 1.700. By adjusting the refractive index to 1.670 to 1.700, deformation when folded in the bending direction can be reduced. By adjusting the refractive index to 1.700 or less, cracks and breakage in the direction of the folded portion can be suppressed. By adjusting the refractive index to 1.670 or more, flexibility in the bending direction can be improved. 1.680 to 1.695 is more preferable. Methods for adjusting the refractive index in the direction perpendicular to the bending direction include the stretching ratio, stretching preheating temperature, stretching temperature, multi-stage stretching, and film relaxation. The stretching ratio is preferably 4.0 to 6.0 times, more preferably 4.4 to 6.0 times. Furthermore, the stretching preheating temperature in the direction perpendicular to the bending direction is preferably 70 to 110°C. When multistage stretching is performed in the direction perpendicular to the bending direction, it is preferable to use a higher stretch ratio in the second and subsequent stages than in the first stage. The film may be relaxed by 1 to 10% in either the machine direction (longitudinal direction) or the perpendicular direction (width direction).

[0038] (Refractive index in the thickness direction) The refractive index in the thickness direction is preferably 1.520 or less. By setting the refractive index to 1.520 or less, in-plane orientation can be strengthened, and deformation during folding can be reduced. The refractive index is more preferably 1.515 or less, even more preferably 1.510 or less, particularly preferably 1.505 or less, and most preferably 1.500 or less. A low refractive index in the thickness direction is preferable, but from the viewpoint of stable production, it is preferably 1.3 or more, and may even be 1.4 or more. A refractive index of 1.410 or more is particularly preferable. It can be said that the above range can be achieved by increasing the stretch ratio in both the bending direction and the folding direction. However, in order to control the refractive index in the thickness direction after controlling the refractive index in the bending direction and width direction within the preferred range, it is preferable to set the conditions while checking the balance of the conditions for each process in the film formation process.

[0039] Methods for controlling the refractive index in the thickness direction within the above range include the preheating temperature, stretching temperature, and stretching ratio in the bending direction, and the preheating temperature, stretching temperature, multi-stage stretching, high-ratio stretching, or heat setting temperatures in the folding direction. The preheating temperature for stretching in the bending direction is preferably 70°C to 110°C. The stretching temperature in the bending direction is preferably 75°C to 120°C. The stretching ratio in the bending direction is preferably 1.2 to 2.0 times, more preferably 1.7 to 2.0 times. By lowering the stretching temperature and stretching at a low stretching ratio, the refractive index in the thickness direction can be effectively reduced while maintaining the flexibility in the bending direction. The preheating temperature for stretching in the folding direction is also preferably 75°C to 110°C. The stretching temperature is preferably 75°C to 120°C. The stretching ratio in the folding direction is preferably 4.0 to 6.0 times, more preferably 4.4 to 6.0 times. The refractive index in the thickness direction can be effectively reduced while maintaining or reducing the refractive index in the bending direction. Multistage stretching may be used as a method for high-ratio stretching. In this case, it is preferable to set the stretching ratio in the second stage higher than that in the first stage, as this allows for effective control of the refractive index. A method in which stretching is performed again after the crystallization step may also be used. Accelerated stretching, in which the stretching speed is increased from the initial stage to the latter stage of stretching, may also be used. The heat setting temperature is preferably 180 to 240° C. By performing heat setting, oriented crystallization in the stretching direction progresses, and the refractive index in the thickness direction can be reduced. The reason why lowering the refractive index in the thickness direction improves the hardness of the film surface is not entirely clear, but it is thought that aromatic groups such as benzene rings in the molecular chain are oriented in the plane direction, which has the effect of suppressing deformation due to stress applied in the thickness direction.

[0040] (Regarding polyester film density) The density of polyester film is 1.380 g / cm 3 It is preferable that the density is 1.383 g / cm or more. 3 More preferably, it is 1.380 g / cm or more. 3 The higher the density, the better. Although it depends somewhat on the presence or absence of particles in the film, the film density is 1.40 g / cm 3By setting the heat setting temperature during film formation to 180 to 240°C, crystallization can be promoted and the density can be effectively increased.

[0041] The bending direction of the polyester film is preferably aligned with the longitudinal direction (machine flow direction). This facilitates biaxial stretching to reduce the refractive index in the bending direction and improve flexibility. That is, a polyester film is preferably obtained by stretching an unstretched polyester sheet in the longitudinal direction at a stretching ratio of 1.2 to 2.0, more preferably 1.7 to 2.0. Furthermore, a preferred embodiment is to stretch the polyester sheet in the width direction at a stretching ratio of 4.0 to 6.0, more preferably 4.4 to 6.0.

[0042] In the present invention, the polyester film (1) Refractive index in the bending direction is 1.590 to 1.620 (2) The refractive index in the direction of the folding part is 1.670 to 1.700 (3) Refractive index in the thickness direction is 1.520 or less (4) Density is 1.380 g / cm 3 End Although it is particularly preferable to simultaneously achieve the above four properties, even within the above-mentioned preferred manufacturing conditions, if the combination of conditions is not optimal within each preferred manufacturing condition range, such as a stretch ratio in the bending direction of 1.4 or less, a stretch ratio in the folded direction of less than 4.4, and a heat setting temperature of 220° C. or less, it may not necessarily be possible to simultaneously achieve the above four properties. In this case, the above four properties can be simultaneously achieved by fine-tuning any of the conditions or by combining them, such as increasing the stretch ratio in the bending direction to 1.7 or more, increasing the stretch ratio in the folded direction to 4.4 or more, increasing the heat setting temperature to about 230° C., or lowering the stretching temperature in the bending direction and / or the folded direction.

[0043] Although any film-forming method such as stretching, relaxation, heat setting, or surface treatment may be used to adjust film-forming properties, film strength, thermal dimensional stability, and appearance defects, controlling the refractive index and density of the film within the above-mentioned preferred ranges is a particularly preferred embodiment of the present invention. By controlling the refractive index and density within the preferred ranges, a polyester film suitable for foldable displays can be provided.

[0044] Specifically, for example, PET pellets are thoroughly vacuum-dried, fed into an extruder, melt-extruded into a sheet at approximately 280°C, and cooled to solidify, forming an unstretched PET sheet. The resulting unstretched sheet is stretched 1.2 to 2.0 times, more preferably 1.7 to 2.0 times, in the longitudinal direction using rolls heated to 75 to 120°C to obtain a uniaxially oriented PET film. The film is then gripped at its edges with clips and introduced into a hot air zone heated to 75 to 120°C, where it is dried and then stretched 4.0 to 6.0 times, more preferably 4.4 to 6.0 times, in the transverse direction. Subsequently, the film is introduced into a heat treatment zone at 180 to 240°C, where it is heat-treated for 1 to 60 seconds. During this heat treatment process, if necessary, a relaxation treatment of 0 to 10% may be performed in the transverse or longitudinal direction.

[0045] The intrinsic viscosity of the polyester film is preferably in the range of 0.50 to 1.0 dL / g. When the intrinsic viscosity is 0.50 dL / g or more, not only the film formability is stabilized but also the impact resistance is improved, making it less likely to crack due to external impact, which is preferable. On the other hand, when the intrinsic viscosity is 1.00 dL / g or less, the increase in filtration pressure of the molten fluid is not too large, and film production is stable, which is preferable.

[0046] (Easy adhesion layer) The polyester film may be provided with an easy-adhesion layer (easy-adhesion layer P1) in order to improve adhesion to a polarizing film or an alignment layer, which will be described later. Examples of resins used in the adhesion layer include polyester resins, polyurethane resins, polyester polyurethane resins, polycarbonate resins, polycarbonate polyurethane resins, and acrylic resins. Of these, polyester resins, polyester polyurethane resins, polycarbonate polyurethane resins, and acrylic resins are preferred. The adhesion layer is preferably crosslinked. Examples of crosslinking agents include isocyanate compounds, melamine compounds, epoxy resins, and oxazoline compounds. Adding a resin similar to the resin used in the alignment layer or polarizing film, such as polyvinyl alcohol, polyamide, polyimide, or polyamideimide, is also a useful means for improving adhesion.

[0047] The adhesive layer can be provided by applying a water-based coating containing the resin and, if necessary, a crosslinking agent, particles, etc. to the polyester film and drying the coating. Examples of the particles include those used for the substrate. The easy-adhesion layer can be provided offline on the stretched substrate film, or can be provided in-line during the film-forming process. The easy-adhesion layer is preferably provided in-line during the film-forming process. When the easy-adhesion layer is provided in-line, it may be provided either before longitudinal stretching or transverse stretching. In particular, it is preferable to provide the easy-adhesion layer in-line by applying the water-based coating material immediately before transverse stretching, preheating and heating with a tenter, and drying and crosslinking during the heat treatment process. Note that, when in-line coating is performed immediately before longitudinal stretching with rolls, it is preferable to apply the water-based coating material, dry it in a vertical dryer, and then introduce it into the stretching rolls. The coating amount of the water-based coating material is 0.01 to 1.0 g / m 2 is preferable, and 0.03 to 0.5 g / m 2 is more preferred.

[0048] (Functional layer) It is also a preferred embodiment that a functional layer such as a hard coat layer, an anti-reflection layer, a low-reflection layer, an anti-glare layer, or an anti-static layer is provided on the side of the polyester film opposite to the surface on which the polarizing film is laminated. The thickness of these functional layers can be set appropriately, and is preferably 0.1 to 50 μm, more preferably 0.5 to 20 μm, and even more preferably 1 to 10 μm. A plurality of these layers may be provided.

[0049] When a functional layer is provided, an easy-adhesion layer (easy-adhesion layer P2) may be provided between the substrate film and the functional layer. The easy-adhesion layer P2 is preferably made of the resins, crosslinking agents, etc. listed above for the easy-adhesion layer P1. The easy-adhesion layer P1 and the easy-adhesion layer P2 may have the same composition or different compositions. The adhesive layer P2 is also preferably provided in-line. The adhesive layer P1 and the adhesive layer P2 can be formed by sequentially coating and drying. It is also a preferred embodiment to simultaneously coat the adhesive layer P1 and the adhesive layer P2 on both sides of the polyester film.

[0050] In the following description, the polarizer protective film and polyester film include not only those films that do not have an easy-adhesion layer but also those films that have an easy-adhesion layer. Similarly, those films that have a functional layer are also included in the polarizer protective film and polyester film.

[0051] 2. Polarizer The polarizer (polarizing film) of the polarizing plate used in the present invention may be provided directly on a polarizer protective film, or may be provided on an alignment layer provided on the polarizer protective film. In the present invention, the alignment film and the polarizing film may be collectively referred to as a polarizer. In addition, when a polarizing film is provided on a polarizer protective film without providing an alignment film, the polarizing film may be referred to as a polarizer.

[0052] (polarizing film) A polarizing film has the function of passing polarized light in only one direction. Examples of polarizing films that can be used without particular limitation include stretched films of polyvinyl alcohol (PVA) or the like blended with iodine or a dichroic dye, dichroic dye films or coated films of polymerizable liquid crystal compounds blended with a dichroic dye, stretched polyene films, wire grids, etc. Among these, a polarizing film in which iodine is adsorbed to PVA and a polarizing film in which a dichroic dye is blended with a polymerizable liquid crystal compound are preferred examples.

[0053] First, we will explain the polarizing film in which iodine is adsorbed onto PVA. A polarizing film in which iodine is adsorbed into PVA can generally be obtained by immersing an unstretched PVA film in a bath containing iodine and then uniaxially stretching the film, or by immersing a uniaxially stretched film in a bath containing iodine and then crosslinking the film in a boric acid bath.

[0054] The thickness of the polarizing film is preferably 1 to 30 μm, more preferably 1.5 to 20 μm, and even more preferably 2 to 15 μm. If the thickness of the polarizing film is less than 1 μm, it may not exhibit sufficient polarization properties and may be too thin and difficult to handle. If the thickness of the polarizing film is more than 30 μm, it will not meet the goal of a thin film to ensure flexibility.

[0055] When laminating a polarizing film in which iodine is adsorbed to PVA and a polarizer protective film, it is preferable to bond the polarizer protective film to the polarizing film. Any adhesive that has been conventionally used for bonding can be used without limitation. Among these, PVA-based aqueous adhesives and ultraviolet-curable adhesives are preferred, and ultraviolet-curable adhesives are more preferred.

[0056] In this way, the polarizing film in which iodine is adsorbed into PVA can be laminated with a polarizer protective film using the film as a polarizer alone. Alternatively, a polarizer laminated on a releasable support substrate (a releasable support substrate-laminated polarizer) obtained by coating PVA on a releasable support substrate and stretching it in that state can be used to laminate the polarizing film to the polarizer protective film by a method of transferring the polarizing film to the polarizer protective film. Similar to the above-mentioned lamination method, this transfer lamination method is also preferred as a method for laminating a polarizer and a polarizer protective film. In this transfer method, the thickness of the polarizer is preferably 12 μm or less, more preferably 10 μm or less, even more preferably 8 μm or less, and particularly preferably 6 μm or less. Even such a very thin polarizer is easy to handle due to the releasable support substrate, and the polarizer can be easily laminated to a polarizer protective film. Using such a thin polarizer further ensures flexibility during repeated use. The technique of laminating a polarizer and a polarizer protective film is known, and reference can be made to, for example, JP-A Nos. 2001-350021 and 2009-93074.

[0057] A method for laminating a polarizer and a polarizer protective film by transfer is specifically described below. First, PVA is applied to a releasable support substrate made of a thermoplastic resin that is unstretched or uniaxially stretched perpendicular to the longitudinal direction, and the resulting laminate of the releasable support substrate made of a thermoplastic resin and PVA is stretched in the longitudinal direction by 2 to 20 times, preferably 3 to 15 times. The stretching temperature is preferably 80 to 180°C, more preferably 100 to 160°C. Subsequently, the stretched laminate is immersed in a bath containing a dichroic dye to adsorb the dichroic dye. Examples of dichroic dyes include iodine and organic dyes. When iodine is used as the dichroic dye, it is preferable to use an aqueous solution containing iodine and potassium iodide as a dye bath. Subsequently, the laminate is immersed in an aqueous solution of boric acid for treatment, washed with water, and then dried. Note that, prior to adsorption of the dichroic dye, a pre-stretching of 1.5 to 3 times may be performed. The above method is merely an example, and the dichroic dye may be adsorbed before stretching, or the film may be treated with boric acid before adsorption of the dichroic dye. Stretching may also be performed in a bath containing the dichroic dye or in a bath of an aqueous boric acid solution. These steps may also be combined in multiple stages.

[0058] Examples of releasable support substrates (release films) made of thermoplastic resin include polyester films such as polyethylene terephthalate, polyolefin films such as polypropylene and polyethylene, polyamide films, polyurethane films, etc. The release force of the releasable support substrates (release films) made of thermoplastic resin can be adjusted by subjecting them to corona treatment or by providing them with a release coating, an easy-adhesion coating, or the like.

[0059] The polarizer surface of a releasable support substrate-laminated polarizer is attached to a polarizer protective film using a pressure-sensitive adhesive or adhesive, and then the releasable support substrate is peeled off to obtain a laminate of a polarizer protective film and a polarizer. The thickness of commonly used pressure-sensitive adhesives is 5 to 50 μm, while that of adhesives is 1 to 10 μm. To achieve a thinner film, it is preferable to use an adhesive, and it is more preferable to use an ultraviolet-curable adhesive. The use of a pressure-sensitive adhesive is also preferable from the viewpoint of process efficiency, since no special equipment is required.

[0060] Next, a polarizing film in which a dichroic dye is blended with a polymerizable liquid crystal compound will be described.

[0061] A dichroic dye is a dye that has different absorbance in the direction of the long axis of the molecule and in the direction of the short axis.

[0062] The dichroic dye preferably has an absorption maximum wavelength (λMAX) in the range of 300 to 700 nm. Examples of such dichroic dyes include organic dichroic dyes such as acridine dyes, oxazine dyes, cyanine dyes, naphthalene dyes, azo dyes, and anthraquinone dyes. Of these, azo dyes are preferred. Examples of azo dyes include monoazo dyes, bisazo dyes, trisazo dyes, tetrakisazo dyes, and stilbene azo dyes. Of these, bisazo dyes and trisazo dyes are preferred. The dichroic dyes may be used alone or in combination. To adjust the color tone (to achieve achromatic color), it is preferred to combine two or more types, and more preferably three or more types. It is particularly preferred to combine three or more types of azo compounds.

[0063] Preferred azo compounds include dyes described in JP-A Nos. 2007-126628, 2010-168570, 2013-101328, and 2013-210624.

[0064] The dichroic dye is also preferably a dichroic dye polymer introduced into the side chain of a polymer such as acrylic. Examples of such dichroic dye polymers include the polymers described in JP-A-2016-4055 and polymers obtained by polymerizing the compounds of [Chemical Formula 6] to [Chemical Formula 12] described in JP-A-2014-206682.

[0065] From the viewpoint of achieving good orientation of the dichroic dye, the content of the dichroic dye in the polarizing film is preferably 0.1 to 30% by mass, more preferably 0.5 to 20% by mass, even more preferably 1.0 to 15% by mass, and particularly preferably 2.0 to 10% by mass.

[0066] The polarizing film preferably contains a polymerizable liquid crystal compound in order to improve film strength, polarization degree, film uniformity, etc. The polymerizable liquid crystal compound also includes a polymerized film. The polymerizable liquid crystal compound is a compound that has a polymerizable group and exhibits liquid crystallinity. The polymerizable group refers to a group that participates in a polymerization reaction, and is preferably a photopolymerizable group. Here, the photopolymerizable group refers to a group that can undergo polymerization with an active radical, acid, or the like generated from a photopolymerization initiator, as described below. Examples of the polymerizable group include a vinyl group, a vinyloxy group, a 1-chlorovinyl group, an isopropenyl group, a 4-vinylphenyl group, an acryloyloxy group, a methacryloyloxy group, an oxiranyl group, and an oxetanyl group. Among these, an acryloyloxy group, a methacryloyloxy group, a vinyloxy group, an oxiranyl group, and an oxetanyl group are preferred, with an acryloyloxy group being more preferred. The compound exhibiting liquid crystallinity may be a thermotropic liquid crystal or a lyotropic liquid crystal, and may be a nematic liquid crystal or a smectic liquid crystal in the thermotropic liquid crystal.

[0067] The polymerizable liquid crystal compound is preferably a smectic liquid crystal compound, and more preferably a high-order smectic liquid crystal compound, in that it can provide higher polarization properties. When the liquid crystal phase formed by the polymerizable liquid crystal compound is a high-order smectic phase, a polarizing film with a higher degree of orientational order can be produced.

[0068] Specific examples of preferred polymerizable liquid crystal compounds include those described in, for example, JP-A Nos. 2002-308832, 2007-16207, 2015-163596, JP-T No. 2007-510946, JP-A No. 2013-114131, WO2005 / 045485, Lub et al. Recl. Trav. Chim. Pays-Bas, 115, 321-328 (1996), and the like.

[0069] The content of the polymerizable liquid crystal compound in the polarizing film is determined so as to increase the orientation of the polymerizable liquid crystal compound. From this viewpoint, the content of the polarizing film is preferably from 70 to 99.5% by mass, more preferably from 75 to 99% by mass, still more preferably from 80 to 97% by mass, and particularly preferably from 83 to 95% by mass.

[0070] A polarizing film containing a polymerizable liquid crystal compound and a dichroic dye can be provided by coating a composition for a polarizing film. The composition for polarizing film may contain, in addition to the polymerizable liquid crystal compound and the dichroic dye, a solvent, a polymerization initiator, a sensitizer, a polymerization inhibitor, a leveling agent, a polymerizable non-liquid crystal compound, a crosslinking agent, and the like.

[0071] The solvent can be any solvent that dissolves the polymerizable liquid crystal compound. Specific examples of the solvent include water; alcohol-based solvents such as methanol, ethanol, isopropyl alcohol, ethylene glycol, propylene glycol, and cellosolve; ester-based solvents such as ethyl acetate, butyl acetate, and γ-butyrolactone; ketone-based solvents such as acetone, methyl ethyl ketone, cyclopentanone, and cyclohexanone; aromatic hydrocarbon solvents such as toluene and xylene; and ether-based solvents such as tetrahydrofuran and dimethoxyethane. These solvents may be used alone or in combination.

[0072] The polymerization initiator can be used without limitation as long as it can polymerize the polymerizable liquid crystal compound. As the polymerization initiator, a photopolymerization initiator that generates active radicals by light is preferred. Examples of the polymerization initiator include benzoin compounds, benzophenone compounds, alkylphenone compounds, acylphosphine oxide compounds, triazine compounds, iodonium salts, and sulfonium salts.

[0073] The sensitizer is preferably a photosensitizer, and examples of the photosensitizer include xanthone compounds, anthracene compounds, phenothiazine, and rubrene.

[0074] Examples of the polymerization inhibitor include hydroquinones, catechols, and thiophenols. The leveling agent may include various known surfactants.

[0075] The polymerizable non-liquid crystal compound is preferably one that copolymerizes with the polymerizable liquid crystal compound. For example, when the polymerizable liquid crystal compound has a (meth)acryloyloxy group, the polymerizable non-liquid crystal compound may be (meth)acrylates. The (meth)acrylates may be monofunctional or polyfunctional. The use of polyfunctional (meth)acrylates can improve the strength of the polarizing film. When a polymerizable non-liquid crystal compound is used, its content in the polarizing film is preferably 1 to 15% by mass, more preferably 2 to 10% by mass, and even more preferably 3 to 7% by mass. If the content of the polymerizable non-liquid crystal compound exceeds 15% by mass, the polarization degree may decrease.

[0076] Examples of the crosslinking agent include a compound capable of reacting with a functional group of the polymerizable liquid crystal compound and the polymerizable non-liquid crystal compound, etc. Specific examples of the crosslinking agent include an isocyanate compound, melamine, an epoxy resin, and an oxazoline compound.

[0077] The composition for a polarizing film is applied directly onto a polarizer protective film or onto an alignment layer, and then dried as necessary and heated to cure, thereby providing a polarizing film.

[0078] As the coating method, known methods such as gravure coating, die coating, bar coating, and applicator coating, and printing methods such as flexography can be used.

[0079] The coated polarizer protective film is dried in a hot air dryer, an infrared dryer, or the like, preferably at 30 to 170° C., more preferably 50 to 150° C., and even more preferably 70 to 130° C. The drying time is preferably 0.5 to 30 minutes, more preferably 1 to 20 minutes, and even more preferably 2 to 10 minutes.

[0080] Heating can be performed to more firmly align the dichroic dye and the polymerizable liquid crystal compound in the polarizing film. The heating temperature is preferably within a temperature range in which the polymerizable liquid crystal compound forms a liquid crystal phase.

[0081] Since the composition for polarizing film contains a polymerizable liquid crystal compound, it is preferably cured. Curing methods include heating and light irradiation, with light irradiation being preferred. Curing can fix the dichroic dye in an aligned state. Curing is preferably carried out in a state where a liquid crystal phase has been formed in the polymerizable liquid crystal compound, and the composition may be cured by light irradiation at a temperature at which the liquid crystal phase is exhibited. Examples of light for irradiation include visible light, ultraviolet light, laser light, etc. Ultraviolet light is preferred because it is easy to handle.

[0082] The irradiation intensity varies depending on the type or amount of the polymerization initiator or resin (monomer), and is, for example, 100 to 10,000 mJ / cm at 365 nm. 2 is preferred, and 200 to 5000 mJ / cm 2 is more preferred.

[0083] A polarizing film is produced by applying a composition for a polarizing film onto an alignment layer, which is provided as needed, so that the dye is aligned along the alignment direction of the alignment layer, resulting in a polarized light transmission axis in a predetermined direction. When the composition for a polarizing film is directly applied to a substrate without providing an alignment layer, the polarizing film can also be aligned by curing the composition for a polarizing film by irradiating it with polarized light. In this case, the polarized light is irradiated in a direction oblique to the longitudinal direction of the polarizer protective film. It is preferable to further align the dichroic dye firmly along the alignment direction of the polymer liquid crystal by subsequent heat treatment.

[0084] The thickness of the polarizing film is usually 0.1 to 5 μm, preferably 0.3 to 3 μm, and more preferably 0.5 to 2 μm.

[0085] When laminating a polarizing film containing a polymerizable liquid crystal compound and a dichroic dye with a polarizer protective film, not only a method of directly providing a polarizing film on a substrate film and laminating the film, but also a method of providing a polarizing film on another release film in accordance with the above-mentioned method and transferring the film to the polarizer protective film is preferred.Preferred examples of the release film include the release support substrates used in the release support substrate-laminated polarizer laminated with the above-mentioned release support substrate, and particularly preferred examples of the release film include polyester film and polypropylene film.The release film can be subjected to corona treatment or provided with a release coating, an easy-adhesion coating, or the like to adjust the peel strength.

[0086] The method for transferring the polarizing film to the polarizer protective film is the same as the method for the releasable supporting substrate-laminated polarizer laminated with the releasable supporting substrate described above.

[0087] (Alignment layer) As described above, the polarizer used in the present invention may be a polarizing film alone, or may be a combination of a polarizing film and an alignment layer. The alignment layer controls the alignment direction of the polarizing film, and by providing an alignment layer, a polarizer with a higher degree of polarization can be obtained. The alignment layer may be any layer that can orient the polarizing film in a desired state. Methods for imparting an alignment state to the alignment layer include, for example, rubbing the surface, oblique deposition of an inorganic compound, and formation of a layer having microgrooves. Furthermore, a method in which the molecules are oriented by irradiation with polarized light to form a photo-alignment layer that exhibits an alignment function is also preferred. Two examples of the rubbed alignment layer and the photo-alignment layer will be described below.

[0088] (Rubbing treatment alignment layer) As the polymer material used for the alignment layer formed by rubbing treatment, polyvinyl alcohol and its derivatives, polyimide and its derivatives, acrylic resin, polysiloxane derivatives, etc. are preferably used.

[0089] First, a coating solution for a rubbed alignment layer containing the above-mentioned polymer material is applied onto a polarizer protective film, followed by heat drying or the like to obtain an alignment layer before rubbing. The coating solution for the alignment layer may contain a crosslinking agent. Examples of crosslinking agents include compounds containing multiple isocyanate groups, epoxy groups, oxazoline groups, vinyl groups, acrylic groups, carbodiimide groups, alkoxysilyl groups, etc.; amide resins such as melamine compounds; and phenolic resins.

[0090] The solvent for the coating solution for the rubbed alignment layer can be any solvent that dissolves the polymer material. Specific examples of the solvent include water; alcohol-based solvents such as methanol, ethanol, isopropyl alcohol, ethylene glycol, propylene glycol, and cellosolve; ester-based solvents such as ethyl acetate, butyl acetate, and γ-butyrolactone; ketone-based solvents such as acetone, methyl ethyl ketone, cyclopentanone, and cyclohexanone; aromatic hydrocarbon solvents such as toluene and xylene; and ether-based solvents such as tetrahydrofuran and dimethoxyethane. These solvents may be used alone or in combination.

[0091] The concentration of the coating solution for the rubbing treatment alignment layer can be adjusted appropriately depending on the type of polymer, the thickness of the alignment layer to be produced, etc., and is preferably 0.2 to 20 mass % in terms of solid content concentration, more preferably 0.3 to 10 mass %. As the application method, known methods such as gravure coating, die coating, bar coating, and applicator methods, and printing methods such as flexography methods can be used. The heat drying temperature varies depending on the polarizer protective film, but in the case of PET, it is preferably in the range of 30 to 170°C, more preferably in the range of 50 to 150°C, and even more preferably in the range of 70 to 130°C. If the drying temperature is too low, a long drying time will be required, which may result in poor productivity. If the drying temperature is too high, it will affect the orientation state of the polarizer protective film, causing problems such as failure to achieve the designed optical function and poor flatness. The heat drying time is usually 0.5 to 30 minutes, preferably 1 to 20 minutes, and more preferably 2 to 10 minutes.

[0092] The thickness of the rubbed alignment layer is preferably 0.01 to 10 μm, more preferably 0.05 to 5 μm, and even more preferably 0.1 to 1 μm.

[0093] Rubbing treatment can generally be carried out by rubbing the surface of the polymer layer with paper or cloth in a certain direction. Generally, the surface of the alignment film is rubbed using a rubbing roller made of raised fabric of fibers such as nylon, polyester, or acrylic. In order to provide a polarizing film having a transmission axis in a predetermined direction oblique to the longitudinal direction of the long polarizer protective film, the rubbing direction of the alignment layer must also be set at an angle corresponding to the direction of the transmission axis. The angle can be adjusted by adjusting the angle between the rubbing roller and the polarizer protective film, the conveying speed of the polarizer protective film, the rotation speed of the roller, etc.

[0094] It is also possible to directly rub the polarizer protective film to provide the surface of the polarizer protective film with an alignment layer function, and this case is also within the technical scope of the present invention.

[0095] (photo alignment layer) The photo-alignment layer is an alignment film formed by applying a coating liquid containing a polymer or monomer having a photoreactive group and a solvent to a substrate film and then irradiating the coating with polarized light, preferably polarized ultraviolet light, to impart alignment control. The photoreactive group is a group that exhibits liquid crystal alignment ability upon light irradiation. Specifically, it induces a photoreaction that is the origin of liquid crystal alignment ability, such as molecular orientation induction or isomerization, dimerization, photocrosslinking, or photodecomposition, upon light irradiation. Among such photoreactive groups, those that undergo dimerization or photocrosslinking are preferred because they provide excellent alignment and maintain the smectic liquid crystal state of the polarizing film. As photoreactive groups capable of undergoing such reactions, unsaturated bonds, particularly double bonds, are preferred, and groups having at least one bond selected from the group consisting of C=C, C=N, N=N, and C=O bonds are particularly preferred.

[0096] Examples of photoreactive groups having a C=C bond include vinyl groups, polyene groups, stilbene groups, stilbazole groups, stilbazolium groups, chalcone groups, and cinnamoyl groups. Examples of photoreactive groups having a C=N bond include groups having structures such as aromatic Schiff bases and aromatic hydrazones. Examples of photoreactive groups having an N=N bond include those having azobenzene groups, azonaphthalene groups, aromatic heterocyclic azo groups, bisazo groups, formazan groups, and azoxybenzenes as basic structures. Examples of photoreactive groups having a C=O bond include benzophenone groups, coumarin groups, anthraquinone groups, and maleimide groups. These groups may have substituents such as alkyl groups, alkoxy groups, aryl groups, allyloxy groups, cyano groups, alkoxycarbonyl groups, hydroxyl groups, sulfonic acid groups, and halogenated alkyl groups. Among these, photoreactive groups capable of undergoing photodimerization are preferred, and cinnamoyl and chalcone groups are preferred because they require a relatively small amount of polarized light irradiation for photoalignment and are likely to produce a photoalignment layer with excellent thermal stability or stability over time. Furthermore, polymers having photoreactive groups are particularly preferred that have cinnamoyl groups such that the terminals of the polymer side chains have cinnamic acid structures. Examples of main chain structures include polyimide, polyamide, (meth)acrylic, and polyester.

[0097] Specific examples of the alignment layer include those disclosed in JP-A-2006-285197, JP-A-2007-76839, JP-A-2007-138138, JP-A-2007-94071, JP-A-2007-121721, JP-A-2007-140465, JP-A-2007-156439, JP-A-2007-133184, and JP-A-2009- Examples of such alignment layers include those described in JP-A Nos. 109831, 2002-229039, 2002-265541, 2002-317013, JP-T Nos. 2003-520878, 2004-529220, 2013-33248, 2015-7702, and 2015-129210.

[0098] The solvent for the coating liquid for forming the photo-alignment layer can be any solvent that dissolves the polymer and monomer having a photoreactive group. Specific examples of the solvent include those listed for the rubbed alignment layer. If necessary, a photopolymerization initiator, a polymerization inhibitor, various stabilizers, etc. can also be added to the coating liquid for forming the photo-alignment layer. Furthermore, polymers other than the polymer and monomer having a photoreactive group, and monomers copolymerizable with the monomer having a photoreactive group but not having a photoreactive group, etc. may also be added to the coating liquid for forming the photo-alignment layer.

[0099] The concentration, coating method, drying conditions, etc. of the coating solution for forming the photo-alignment layer can be exemplified by those mentioned for the rubbed alignment layer. The preferred thickness of the photo-alignment layer is also the same as that of the rubbed alignment layer.

[0100] By irradiating the thus obtained pre-orientation photo-alignment layer with polarized light at a predetermined angle to the longitudinal direction of the polarizer protective film, a photo-alignment layer can be obtained in which the direction of the alignment control force is oblique to the longitudinal direction of the long polarizer protective film.

[0101] Polarized light may be irradiated directly onto the photo-alignment layer before alignment, or may be transmitted through a polarizer protective film.

[0102] The wavelength of the polarized light is preferably in a wavelength range in which the photoreactive group of the polymer or monomer having the photoreactive group can absorb light energy, specifically, ultraviolet light in the wavelength range of 250 to 400 nm. Examples of polarized light sources include xenon lamps, high-pressure mercury lamps, ultra-high-pressure mercury lamps, metal halide lamps, and ultraviolet lasers such as KrF and ArF, with high-pressure mercury lamps, ultra-high-pressure mercury lamps, and metal halide lamps being preferred.

[0103] Polarized light can be obtained, for example, by passing light from the light source through a polarizer. The direction of polarization can be adjusted by adjusting the polarization angle of the polarizer. Examples of polarizers include polarizing filters; polarizing prisms such as Glan-Thompson and Glan-Taylor; and wire grid polarizers. The polarized light is preferably substantially parallel light.

[0104] By adjusting the angle of the polarized light to be irradiated, the direction of the alignment regulating force of the photo-alignment layer can be adjusted as desired.

[0105] The irradiation intensity varies depending on the type or amount of the polymerization initiator or resin (monomer), and is, for example, 10 to 10,000 mJ / cm at 365 nm. 2 is preferred, and 20 to 5000 mJ / cm 2 is more preferred.

[0106] (Angle between the transmission axis of the polarizer and the slow axis of the polarizer protective film) The angle between the transmission axis of the polarizer and the slow axis of the polarizer protective film is not particularly limited. For the purpose of preventing blackout or coloration when viewing an image through polarized sunglasses, the angle is preferably in the range of 30 to 60 degrees, more preferably 35 to 55 degrees. To reduce slight rainbow spots and the like when viewing an image from a shallow oblique angle with the naked eye, the angle is preferably 10 degrees or less, more preferably 7 degrees or less, or 80 to 100 degrees, or even 83 to 97 degrees. These angles can be adjusted by the bonding angle between the polarizer protective film and the polarizer, the stretching direction of the oblique stretching of the polarizer protective film, or the angle of alignment control of the alignment layer.

[0107] 3. Retardation layer In the present invention, it is also a preferred embodiment that a retardation layer is laminated on the polarizing plate. Although the retardation layer is preferably laminated on one side of a polarizing plate having polarizer protective films on both sides of a polarizer, it is more preferable that a polarizer protective film is laminated on one side of a polarizer and a retardation layer is provided on the other side of the polarizer. By adopting such a configuration to reduce the thickness, high flexibility can be achieved and creases when folded can be prevented.

[0108] If the foldable display is a liquid crystal display, the retardation layer can be any retardation layer commonly used in liquid crystal displays, such as a positive or negative A plate, a positive or negative C plate, or a tilted alignment of discotic liquid crystal compounds, depending on the type of liquid crystal cell.

[0109] When the foldable display is an organic EL display or the like, the retardation layer is preferably a quarter-wave layer in order to serve as a circular polarizer for anti-reflection. Hereinafter, the retardation layer will be described by taking a circular polarizing plate in which the retardation layer is a quarter wavelength layer as a representative example.

[0110] In a circular polarizing plate, a retardation layer is present on the side of the polarizer opposite to the polarizer protective film surface. It is preferable that there is no free-standing film or only one free-standing film between the polarizer and the retardation layer (here, the term "between the polarizer and the retardation layer" includes the retardation layer itself). Here, the free-standing film refers to a film that exists independently in the process. The "retardation layer" referred to here is a layer that functions as a circular polarizer, and specifically refers to a quarter-wave layer, a half-wave layer, a C-plate, or the like. The absence of a self-supporting film between the polarizer and the retardation layer means that a retardation layer that is not a self-supporting film is directly laminated on the polarizer. Here, "directly" means that there is no layer between the polarizer and the retardation layer and between the retardation layers, or if there is a layer, it is only an adhesive layer or a pressure-sensitive adhesive layer. The presence of one free-standing film between the polarizer and the retardation layer means that only one of the polarizer protective film and all of the retardation layers is a free-standing film.

[0111] The quarter-wave layer can be obtained by laminating a retardation film (freestanding film) having a coated quarter-wave layer (described later) separately prepared on an oriented film (freestanding film) such as polycarbonate or cycloolefin, or on such a film or a triacetyl cellulose (TAC) film. However, from the viewpoint of thinning, it is preferable to provide the coated quarter-wave layer directly on the polarizer. A coated quarter-wave layer is a quarter-wave layer formed by coating, and does not exist as an independent layer. Methods for providing a quarter-wave layer include coating a retardation compound on a polarizer, and providing a quarter-wave layer on a separate, releasable substrate and then transferring the layer onto the polarizer. The quarter-wave layer is preferably a layer made of a liquid crystal compound. Examples of liquid crystal compounds include rod-shaped liquid crystal compounds, polymeric liquid crystal compounds, and liquid crystal compounds having reactive functional groups. A method for coating a retardation compound on a polarizer is preferably to perform a rubbing treatment on the polarizer, or to provide an alignment layer as described above on the polarizer to provide alignment control, and then coat the liquid crystal compound on the polarizer.

[0112] In the method of separately providing a coated quarter-wave layer on a releasable substrate and then transferring this onto a polarizer, it is preferable to perform a rubbing treatment on the releasable substrate, or to provide an alignment layer as described above on the releasable substrate to give it alignment control power, and then coat the liquid crystal compound (quarter-wave layer). As a transfer method, a method in which a birefringent resin is applied to a substrate having releasability and then stretched together with the substrate to form a quarter wavelength layer is also preferred.

[0113] The transferable quarter-wave layer thus obtained is attached to a polarizer using an adhesive or pressure-sensitive adhesive, and then the releasable substrate is peeled off. To achieve a thinner film, it is preferable to use an adhesive, particularly a UV-curable adhesive, for attachment. It is also preferable to use a pressure-sensitive adhesive, as this process does not require special equipment. A preferred method is to provide a coated quarter-wave layer separately on a releasable substrate and transfer this onto the polarizer, since the polarizer is less susceptible to the coating solvent of the quarter-wave layer.

[0114] The front retardation of the quarter wavelength layer is preferably 100 to 180 nm, more preferably 120 to 150 nm.

[0115] These methods and retardation layers can be learned from, for example, JP-A Nos. 2008-149577, 2002-303722, WO2006 / 100830, and 2015-64418.

[0116] Furthermore, a quarter-wave layer alone may not provide a quarter-wavelength across a wide wavelength range of visible light, resulting in coloration. In such cases, a half-wave layer may be provided. In this case, it is preferable to provide a half-wave layer between the polarizer and the quarter-wave layer.

[0117] The preferred materials, configurations, manufacturing methods, lamination methods, etc. of the half-wave layer are the same as those of the quarter-wave layer described above. The front retardation of the half-wave layer is preferably 200 to 360 nm, more preferably 240 to 300 nm.

[0118] When only a quarter wavelength layer is used as the retardation layer, the angle between the alignment axis (slow axis) of the quarter wavelength layer and the transmission axis of the polarizer is preferably 35 to 55 degrees, more preferably 40 to 50 degrees, and even more preferably 42 to 48 degrees.

[0119] When a quarter-wave layer and a half-wave layer are used in combination as a retardation layer, the angle (θ) between the alignment axis (slow axis) of the half-wave layer and the transmission axis of the polarizer is preferably 5 to 20 degrees, more preferably 7 to 17 degrees. The angle between the alignment axis (slow axis) of the half-wave layer and the alignment axis (slow axis) of the quarter-wave layer is preferably in the range of 2θ+45 degrees±10 degrees, more preferably 2θ+45 degrees±5 degrees, and even more preferably 2θ+45 degrees±3 degrees.

[0120] When an oriented film is laminated, these angles can be adjusted by the lamination angle, the stretching direction of the oriented film, etc. In the case of coated quarter-wave and half-wave layers, the thickness can be controlled by the rubbing angle, the irradiation angle of the polarizer outer rays, and the like. In the method of providing a coating type quarter-wave layer on a substrate and transferring this onto a polarizer, it is preferable to control the rubbing angle or the irradiation angle of the polarizer external light so that a predetermined angle is obtained when the layers are laminated by roll-to-roll. Furthermore, when an oriented film is used, or when a birefringent resin is applied to a polarizer protective film and stretched together with the substrate, it is preferable to stretch the film in an oblique direction so that a predetermined angle is obtained when the films are laminated together by roll-to-roll bonding.

[0121] Furthermore, it is also a preferred embodiment to provide a C-plate layer on the quarter-wave layer to reduce changes in color when viewed obliquely. A positive or negative C-plate layer is used as the C-plate layer, depending on the characteristics of the quarter-wave layer or half-wave layer. The C-plate layer is preferably a liquid crystal compound layer. The C-plate layer may be provided by directly applying a coating liquid to form the C-plate layer on the quarter-wave layer, or by transferring a separately prepared C-plate layer onto the quarter-wave layer.

[0122] As a lamination method, various methods can be adopted, for example, the following methods. A method in which a half-wave layer is formed on a polarizer by transfer, and then a quarter-wave layer is formed on top of that by transfer. A method in which a quarter-wave layer and a half-wave layer are placed in that order on a release film, and then transferred onto a polarizer. A method in which a half-wave layer is applied to the polarizer by coating, and a quarter-wave layer is applied by transfer. A method in which a film-like half-wave layer is prepared, a quarter-wave layer is formed on top of it by coating or transfer, and then this is laminated onto the polarizer.

[0123] Furthermore, various methods can be used for laminating a C plate, such as a method of providing a C plate layer on a quarter-wave layer provided on a polarizer by coating or transferring, or a method of laminating a C plate layer in advance on a quarter-wave layer to be transferred or bonded. In the present invention, it is preferable that the layers between the polarizer and the quarter-wave layer (including the quarter-wave layer), and if a C-plate layer is present, all layers between the polarizer and the C-plate layer (including the C-plate layer) are coated layers. This means that there is no free-standing film on the side of the polarizer opposite the polarizer protective film. Specifically, only any combination of an adhesive layer, a pressure-sensitive adhesive layer, a protective coating layer, an alignment layer, and a coated retardation layer is present on the side of the polarizer opposite the polarizer protective film. This configuration allows the circular polarizing plate to be made thinner.

[0124] Specific preferred examples of lamination between the polarizer and the quarter wavelength layer include: Polarizer / adhesive layer / 1 / 4 wavelength layer, Polarizer / protective coating layer / adhesive layer / 1 / 4 wavelength layer, Polarizer / 1 / 2 wavelength layer / adhesive layer / 1 / 4 wavelength layer, Polarizer / adhesive layer / 1 / 2 wavelength layer / adhesive layer / 1 / 4 wavelength layer, Polarizer / protective coating layer / 1 / 2 wavelength layer / adhesive layer / 1 / 4 wavelength layer, Examples include polarizer / protective coating layer / adhesive layer / ½ wavelength layer / adhesive layer / ¼ wavelength layer. The pressure sensitive adhesive layer may be an adhesive layer. The quarter wave layer and the half wave layer may include an alignment layer on either side thereof.

[0125] For the adhesive layer, adhesives such as rubber-based, acrylic-based, urethane-based, olefin-based, and silicone-based adhesives can be used without limitation. Among these, acrylic adhesives are preferred. The adhesive can be applied to the object, for example, the polarizer surface of a polarizing plate. A preferred method is to peel off the release film on one side of a substrate-less optical transparent adhesive (release film / adhesive layer / release film), and then attach it to the polarizer surface to provide an adhesive layer. As the adhesive, ultraviolet Hardening type, urethane type and epoxy type are preferably used. The adhesive layer or pressure-sensitive adhesive layer is used to attach a polarizer, a protective coating layer, a coated retardation layer, or an image display cell.

[0126] In the above example, a retardation layer (quarter-wave layer or half-wave layer) is provided on a laminate of a polarizer protective film and a polarizer, and then the laminate is attached to the object. However, a retardation layer (quarter-wave layer or half-wave layer) may be provided on the object in advance, and then the laminate of a polarizer protective film and a polarizer may be attached to the object. The same applies when a C-plate layer is provided.

[0127] When the retardation layer is a layer made of a liquid crystal compound, a protective coating layer may be provided on the side of the retardation layer opposite to the polarizer. Also, a protective film (self-supporting film) may be provided, but it is preferable not to use a protective film in order to reduce the thickness.

[0128] The thickness of the circularly polarizing plate thus obtained is preferably 130 μm or less, more preferably 100 μm or less, even more preferably 90 μm or less, and particularly preferably 85 μm or less.

[0129] The circular polarizing plate is preferably attached to the touch panel, organic EL cell, or the like with an adhesive or pressure sensitive adhesive.

[0130] B. Display cells The foldable display of the present invention includes the polarizing plate described above on the viewing side of the display cell. As the image display cell, any foldable display cell such as a liquid crystal cell, an organic electroluminescence (EL) cell, or an inorganic EL cell can be used without any particular restrictions. Among these, an organic EL cell is preferred because it is thin and has excellent flexibility. The image display cell and the polarizing plate are preferably bonded together with an adhesive. As a folding display, it is preferably used as either an image display device that can be folded into a V-shape, Z-shape, W-shape, double door shape, etc. when carried (folding image display device), or a display that can be wound up into a roll (roll-up display).

[0131] When a folding display has a display unit on the inner surface of the fold, the bending radius of the circular polarizer in the folded state becomes small. In such an image display device, by arranging the main orientation direction of the substrate film perpendicular to the folding direction (the direction of the folding operation), it is possible to effectively reduce the occurrence of folding marks due to repeated folding operations. In the perpendicular direction, the angle between the main orientation direction of the polarizer protective film and the folding direction is preferably 75 to 105 degrees, more preferably 80 to 100 degrees, and even more preferably 83 to 97 degrees.

[0132] The foldable display of the present invention can be a foldable display with a bending radius of 5 mm or less, further 4 mm or less, particularly 3 mm or less.

[0133] C. Other materials The foldable display of the present invention may have other components in addition to the image display cell and the polarizing plate (circular polarizing plate). Examples of other components include a touch panel, a surface protective film, and a back surface protective film. Furthermore, in the case of a liquid crystal display device, it is preferable that the display device has a backlight. These components are preferably bonded together using an adhesive or pressure-sensitive adhesive.

[0134] It is also a preferred embodiment to use the polyester film used as the polarizer protective film of the present invention as a base film for these members. In particular, it is a preferred embodiment to use the polarizing plate of the present invention as a polarizing plate in a foldable display, and to use the polyester film used as the polarizer protective film of the present invention as at least one or both of a surface protective film and a back surface protective film. In this case, the surface protective film may be either a surface protective film incorporated in the foldable display, called a window, or a surface protective film replaceable by the user, called an after, or both.

[0135] When the polyester film is used as a base film for the above-mentioned members, it is also preferable that the longitudinal direction of the polyester film be the bending direction.

[0136] In the case of a member such as a touch panel that is provided between an image display cell and a polarizing plate, it is preferable to use a film with low birefringence as the substrate film so as not to change the circular polarization characteristics. Specifically, a polyimide film, a polyamide film, a polyamideimide film, a polycarbonate film, an acrylic film, a triacetyl cellulose film, a cycloolefin polymer film, a polyphenylene sulfide film, a polymethylpentene film, or the like, with an in-plane retardation of 100 nm or less, preferably 50 nm or less, and particularly preferably 30 nm or less, is preferably used. [Example]

[0137] Next, the present invention will be described with reference to examples and comparative examples. First, the evaluation methods of the characteristic values ​​used in the present invention will be described below.

[0138] (1) Intrinsic viscosity The film or polyester resin was crushed and dried, then dissolved in a 60 / 40 (mass ratio) phenol / tetrachloroethane mixed solvent. After centrifuging the solution to remove inorganic particles, an Ubbelohde viscometer was used to measure the flow time of a 0.4 (g / dL) solution at 30°C and the flow time of the solvent alone. The intrinsic viscosity was calculated from the ratio of these times using the Huggins equation, assuming a Huggins constant of 0.38.

[0139] (2) Bending resistance of polyester film sample (bending radius 1.5 mm) A polyester film sample measuring 20 mm in width and 110 mm in machine direction was prepared. Using a no-load U-shaped stretch tester (Yuasa System Co., Ltd., DLDMLH-FS), the sample was bent 200,000 times at a rate of 1 bend / second with a bend radius of 1.5 mm. The sample was fixed at 10 mm positions on both long sides, and the bending area was 20 mm x 90 mm. Figure 1 is a schematic diagram showing the bend radius when a foldable display is folded. Considering the case where a polyester film is disposed on the inner surface of the folded display, the bending test was performed as a model, with the bending radius set to 1.5 mm at the point indicated by reference numeral 11 in Figure 1. After the bending process, the sample was placed on a flat surface with the bent inner side facing down and visually observed. ○: No cracks or deformations were observed in the sample. ×: The sample has cracks or creases, and when placed horizontally, the maximum lift is 5 mm or more.

[0140] (3) Bending resistance of polyester film sample (bending radius 0.5 mm) Using the same method as in the bending test described above, the display was bent 200,000 times at a bending radius of 0.5 mm and a rate of 1 bend per second. Figure 1 is a schematic diagram showing the bending radius when the foldable display is folded. Taking into account the case where a polyester film is disposed on the inner surface of the folded display, the bending test was performed as a model, with the bending radius set to 0.5 mm at the location indicated by reference numeral 11 in Figure 1 . The film surface outside the bent portion was observed at 700x magnification using a digital microscope (HIROX RH8800) to check for the presence or absence of wrinkles (cracks). In addition to the visual observation of bending resistance with a bending radius of 1.5 mm described above, this test was performed with a bending radius reduced to 0.5 mm to evaluate the display under conditions similar to those in actual use, where a hard coat layer or other components are laminated or attached. This test, separate from the visual observation with a bending radius of 1.5 mm, was also performed to detect minute defects that are difficult to detect visually, such as those prone to breakage or cracking. ○: No defects on the film surface on the outer side of the bend. ×: The film broke or wrinkles (cracks) were observed on the film surface on the outer side of the bend.

[0141] (4) Bending resistance of circular polarizer (bending radius 3 mm) A circularly polarizing plate sample measuring 50 mm x 100 mm was prepared and placed in a no-load U-shaped stretch tester ( Using a Yuasa System Co., Ltd. DLDMLH-FS, the bending radius was set to 3 mm. The sample was bent 100,000 times at a speed of 1 time / second. The bending part is 50mm x 80mm, and the inside of the bending part is the base film side. The slow axis of the substrate film was set perpendicular to the bending direction. The tube was placed on a flat surface with the inner side of the bend facing downwards and subjected to a visual inspection. It was also observed using a digital microscope. The evaluation criteria were as follows: ◯: No deformation or breakage of the sample was observed, and no wrinkles (cracks) were observed. ×: The sample was deformed or had wrinkles (cracks).

[0142] (5) Refractive index In accordance with JIS K 7142:2008 "Method for measuring refractive index of plastics (Method A)", the refractive index in the longitudinal direction, width direction, and thickness direction was determined using an Abbe refractometer (manufactured by Atago Co., Ltd., NAR-4T, measurement wavelength 589 nm).

[0143] (6) Total light transmittance, haze The measurement was carried out using a haze meter (NDH5000, manufactured by Nippon Denshoku Industries Co., Ltd.).

[0144] (7) Density The density was measured according to the method (density gradient tube method) in accordance with JIS K 7112:1999 (unit: g / cm 3 ).

[0145] (8) Maximum heat shrinkage rate The sample film was cut to a size of 10 mm lengthwise and 250 mm widthwise, and marks were made at 200 mm intervals along the long side in the direction to be measured. The distance A between the marks was measured under a constant tension of 5 g. The sample film was then left in an oven at 150°C for 30 minutes without load, and then removed from the oven and cooled to room temperature. The distance B between the marks was then measured under a constant tension of 5 g, and the thermal shrinkage (%) was calculated using the following formula. The thermal shrinkage was measured at three equal positions across the width of the sample film, and the average value of the three points was taken as the thermal shrinkage (%). Heat shrinkage rate (%) = [(AB) x 100] / A The sample film is cut so that the length and width of the sample film are different in both the bending direction and the folding direction, and measurements are taken. The data in the direction where the measurement value is larger is the maximum heat shrinkage rate (%).

[0146] <Production of Easy-Adhesion Layer Component> (Polymerization of polyester resin) A stainless steel autoclave equipped with a stirrer, thermometer, and partial reflux condenser was charged with 194.2 parts by weight of dimethyl terephthalate, 184.5 parts by weight of dimethyl isophthalate, 14.8 parts by weight of dimethyl-5-sodium sulfoisophthalate, 233.5 parts by weight of diethylene glycol, 136.6 parts by weight of ethylene glycol, and 0.2 parts by weight of tetra-n-butyl titanate, and the transesterification reaction was carried out at a temperature of 160 to 220°C for 4 hours. The mixture was then heated to 255°C, and the reaction system was gradually reduced in pressure. The reaction was then carried out under a reduced pressure of 30 Pa for 1 hour and 30 minutes to obtain a copolymerized polyester resin. The resulting copolymerized polyester resin was pale yellow and transparent. The reduced viscosity of the copolymerized polyester resin was measured and found to be 0.70 dL / g. The reduced viscosity was measured at 30°C using 25 mL of a mixed solvent of phenol (60% by mass) and 1,1,2,2-tetrachloroethane (40% by mass) per 0.1 g of resin. The glass transition temperature measured by DSC was 40°C.

[0147] (Preparation of Polyester Water Dispersion) A reactor equipped with a stirrer, thermometer, and reflux device was charged with 30 parts by mass of polyester resin and 15 parts by mass of ethylene glycol n-butyl ether, and the resin was dissolved by stirring while heating at 110°C. After the resin was completely dissolved, 55 parts by mass of water was gradually added to the polyester solution while stirring. After the addition was completed, the mixture was cooled to room temperature while stirring, yielding a milky white polyester water dispersion with a solids content of 30% by mass.

[0148] (Preparation of aqueous polyvinyl alcohol solution) 90 parts by mass of water was placed in a vessel equipped with a stirrer and a thermometer, and 10 parts by mass of polyvinyl alcohol resin (manufactured by Kuraray, polymerization degree 500 and saponification degree 74%) was gradually added while stirring. After the addition was completed, the mixture was heated to 95°C while stirring to dissolve the resin. After the resin was dissolved, the mixture was cooled to room temperature while stirring to obtain an aqueous polyvinyl alcohol solution with a solids content of 10% by mass.

[0149] (Polymerization of Blocked Polyisocyanate Crosslinking Agent Used in Adhesion Layer P1) A flask equipped with a stirrer, thermometer, and reflux condenser was charged with 100 parts by mass of a polyisocyanate compound having an isocyanurate structure (Duranate TPA, manufactured by Asahi Kasei Chemicals Corporation), 55 parts by mass of propylene glycol monomethyl ether acetate, and 30 parts by mass of polyethylene glycol monomethyl ether (average molecular weight 750), and the mixture was maintained at 70°C for 4 hours under a nitrogen atmosphere. The temperature of the reaction solution was then lowered to 50°C, and 47 parts by mass of methyl ethyl ketoxime was added dropwise. The infrared spectrum of the reaction solution was measured to confirm that the absorption of the isocyanate group had disappeared, yielding an aqueous dispersion of blocked polyisocyanate with a solids content of 75% by mass.

[0150] (Preparation of Coating Solution for Adhesion Layer P1) The following raw materials were mixed to prepare a coating solution. Water 40.61% by mass Isopropanol 30.00% by mass Polyester water dispersion 11.67% by mass Polyvinyl alcohol aqueous solution 15.00% by mass Blocked isocyanate crosslinking agent 0.67% by mass Particles (silica sol with an average particle size of 100 nm, solid content of 40% by mass) 1.25% by mass Catalyst (organotin compound, solid concentration 14% by mass) 0.3% by mass Surfactant (silicone-based, solid content 10% by mass) 0.5% by mass

[0151] (Polymerization of urethane resin used in easy-adhesion layer P2) A urethane resin containing an aliphatic polycarbonate polyol as a constituent component was prepared as follows. 43.75 parts by mass of 4,4-diphenylmethane diisocyanate, 12.85 parts by mass of dimethylol butanoic acid, 153.41 parts by mass of polyhexamethylene carbonate diol with a number-average molecular weight of 2000, 0.03 parts by mass of dibutyltin dilaurate, and 84.00 parts by mass of acetone as a solvent were added to a four-neck flask equipped with a stirrer, Dimroth condenser, nitrogen inlet tube, silica gel drying tube, and thermometer. The mixture was stirred at 75°C for 3 hours under a nitrogen atmosphere, and it was confirmed that the reaction solution had reached the required amine equivalent. Next, the temperature of the reaction solution was lowered to 40°C, and 8.77 parts by mass of triethylamine was added to obtain a polyurethane prepolymer solution. Next, 450 g of water was added to a reaction vessel equipped with a homodisperser capable of high-speed stirring, the temperature was adjusted to 25°C, and the water was stirred for 2000 min. -1 While stirring and mixing at 40°C, the polyurethane prepolymer solution was added and dispersed. Then, acetone and a portion of the water were removed from the mixed solution under reduced pressure to prepare a water-soluble polyurethane resin with a solids content of 35%. The glass transition temperature of the resulting polyurethane resin, which contained an aliphatic polycarbonate polyol as a constituent component, was -30°C.

[0152] (Polymerization of oxazoline-based crosslinking agent used in adhesive layer P2) A flask equipped with a thermometer, nitrogen gas inlet tube, reflux condenser, dropping funnel, and stirrer was charged with a mixture of 58 parts by mass of ion-exchanged water and 58 parts by mass of isopropanol as an aqueous medium, and 4 parts by mass of a polymerization initiator (2,2'-azobis(2-amidinopropane) dihydrochloride). A mixture of 16 parts by mass of 2-isopropenyl-2-oxazoline as a polymerizable unsaturated monomer having an oxazoline group, 32 parts by mass of methoxypolyethylene glycol acrylate (average number of moles of ethylene glycol added: 9 moles, Shin-Nakamura Chemical Co., Ltd.), and 32 parts by mass of methyl methacrylate was charged to the dropping funnel and added dropwise over 1 hour at 70°C under a nitrogen atmosphere. After the dropwise addition, the reaction solution was stirred for 9 hours and then cooled to obtain a water-soluble resin having an oxazoline group with a solids concentration of 40% by mass.

[0153] (2) Preparation of Coating Solution for Adhesion Layer P2 The following raw materials were mixed to prepare a coating solution for forming a coating layer with excellent adhesion to the functional layer. Successful. Water 55.62% by mass Isopropanol 30.00% by mass Polyurethane resin 11.29% by mass Oxazoline crosslinker aqueous solution 2.26% by mass Particles (silica sol with an average particle size of 40 nm, solid content concentration of 40% by mass) 0.71% by mass Particles (silica sol with an average particle size of 450 nm, solid content concentration of 40% by mass) 0.07% by mass Surfactant (silicone-based, solid content 100% by mass) 0.05% by mass

[0154] (Preparation of polyethylene terephthalate pellets) A continuous esterification reactor consisting of a three-stage complete mixing vessel equipped with an agitator, a partial condenser, a raw material inlet, and a product outlet was used as the esterification reactor. TPA was supplied at a rate of 2 ton / hr, EG at 2 moles per mole of TPA, and antimony trioxide in an amount such that the Sb atom concentration in the produced PET was 160 ppm. These slurries were continuously supplied to the first esterification reactor of the esterification reactor and reacted at normal pressure for an average residence time of 4 hours at 255°C. Next, the reaction product in the first esterification reactor was continuously removed from the system and fed to a second esterification reactor, and EG distilled off from the first esterification reactor was fed into the second esterification reactor in an amount of 8% by mass relative to the produced polymer (produced PET). Further, an EG solution containing magnesium acetate in an amount to give 65 ppm of Mg atoms relative to the produced PET and an EG solution containing TMPA in an amount to give 20 ppm of P atoms relative to the produced PET were added, and the reaction was carried out at atmospheric pressure for an average residence time of 1.5 hours at 260°C. Next, the reaction product in the second esterification reactor was continuously removed from the system and fed to a third esterification reactor, and further, an EG solution containing TMPA in an amount to give 20 ppm of P atoms relative to the produced PET was added, and the reaction was carried out at atmospheric pressure for an average residence time of 0.5 hours at 260°C. The esterification reaction product produced in the third esterification reactor was continuously supplied to a three-stage continuous polycondensation reactor to carry out polycondensation, and then filtered through a stainless steel sintered filter medium (nominal filtration accuracy: 90% cutoff of 5 μm particles) to obtain polyethylene terephthalate pellets with an intrinsic viscosity of 0.62 dl / g.

[0155] (PET film 1) Polyethylene terephthalate pellets were fed into an extruder and melted at 285 ° C. The polymer was filtered through a stainless steel sintered filter medium (nominal filtration accuracy 10 μm particle 95% cut), extruded into a sheet form from a die, and then contacted with a casting drum at a surface temperature of 30 ° C. using an electrostatic casting method, cooled and solidified, to produce an unstretched film. This unstretched film was uniformly heated to 75 ° C. using a heated roll, heated to 85 ° C. using a non-contact heater, and roll stretched 1.4 times (longitudinal stretching). The above-mentioned easy-adhesion layer forming coating liquid P1 was applied to one side of the obtained uniaxially stretched film, and P2 was applied to the other side by roll coating, and then dried at 80 ° C. for 20 seconds. The final coating amount after drying (after biaxial stretching) was 0.06 g / m 2 The film was then introduced into a tenter, preheated to 105°C, transversely stretched 4.0 times at 95°C, heat-set at 230°C for 5 seconds with the width fixed, and then relaxed by 4% in the width direction at 180°C to obtain a polyethylene terephthalate film (PET film 1) with a thickness of 50 μm. The evaluation results are shown in Table 1.

[0156] (PET film 2-3) PET films 2 and 3 were obtained in the same manner as PET film 1, except that the longitudinal stretching ratio was changed to that shown in Table 1.

[0157] (PET film 4) PET film 4 was obtained in the same manner as PET film 1, except that the draw ratio in the width direction was changed to 4.4 times and the heat setting temperature was changed to 220°C.

[0158] (PET film 5-6) PET films 5 and 6 were obtained in the same manner as PET film 4, except that the stretching ratio in the longitudinal direction was changed as shown in Table 1.

[0159] (PET film 7) PET film 7 was obtained in the same manner as PET film 1, except that the draw ratio in the width direction was changed to 5.5 times and the heat setting temperature was changed to 190°C.

[0160] (PET film 8-9) PET films 8 to 9 were obtained in the same manner as PET film 7, except that the stretching ratio in the longitudinal direction was changed as shown in Table 1.

[0161] (PET film 10) PET film 10 was obtained in the same manner as PET film 5, except that in the manufacturing process of PET film 5, after stretching in the longitudinal direction, a 10% relaxation heat treatment was carried out at 100°C.

[0162] (PET film 11) PET film 11 was obtained in the same manner as PET film 5, except that in the manufacturing process of PET film 5, the clips were released at 200°C after heat setting and relaxation heat treatment was performed in the longitudinal and width directions. The tenter speed and take-up roll speed were adjusted so that the relaxation rate in the longitudinal direction was 3%. The relaxation in the width direction was left in a free state.

[0163] (PET film 12) PET film 12 was obtained in the same manner as PET film 1, except that the temperature during longitudinal stretching was changed to 75°C and the heat setting temperature was changed to 220°C.

[0164] (PET film 13) PET film 13 was obtained in the same manner as PET film 1, except that the temperature during longitudinal stretching was changed to 75°C, the stretching ratio was changed to 1.2 times, and then the stretching ratio was changed to 5.0 times in the width direction.

[0165] (PET film 14) PET film 14 was obtained in the same manner as PET film 3, except that the longitudinal stretching of PET film 3 was performed in two stages, with the first stage stretching ratio being 1.2 times and the second stage stretching ratio being 1.67 times. The total longitudinal stretching ratio was approximately 2.0 times.

[0166] (PET film 15) PET film 15 was obtained in the same manner as PET film 5, except that the preheating temperature during widthwise stretching was changed to 95°C and the heat setting temperature was changed to 190°C.

[0167] (PET film 16) PET film 16 was obtained in the same manner as PET film 2, except that the widthwise stretching of PET film 2 was performed in two stages, with the first stage stretching ratio being 1.5 times and the second stage stretching ratio being 4.0 times, and the heat setting temperature being changed to 190°C. The total widthwise stretching ratio was 6.0 times.

[0168] (PET film 17-18) PET films 17 and 18 were obtained in the same manner as PET film 2, except that the thickness was changed as shown in Table 1.

[0169] (PET film 19) PET film 19 was obtained in the same manner as PET film 1, except that the relaxation heat treatment in the width direction was not carried out in the production process of PET film 1.

[0170] (PET film 20) An unstretched film was prepared in the same manner as in PET film 1, and then the unstretched film was preheated at 75°C in a tenter and stretched laterally at 85°C to 1.4 times its original size. The above-mentioned coating solution for forming an easy-adhesion layer was applied to both sides of the obtained uniaxially stretched film by roll coating, and then dried at 80°C for 20 seconds. The final coating amount after drying (after biaxial stretching) was 0.06 g / m 2 The film was uniformly heated to 105°C using a heated roll, then heated to 95°C using a non-contact heater, and roll-stretched (longitudinal stretching) at 4.0 times its original size. The film was then heat-set at 230°C for 5 seconds with the width fixed, to obtain a PET film 20 with a thickness of 50 μm.

[0171] (PET film 21) An ET film 21 was obtained in the same manner as the PET film 7, except that the film was not stretched in the longitudinal direction but was stretched only in the width direction, i.e., transversely uniaxially stretched.

[0172] (PET film 22) PET film 22 was obtained in the same manner as PET film 1, except that the heat setting temperature was changed to 220° C. and the thickness was changed to 75 μm.

[0173] (PET film 23) PET film 23 was obtained in the same manner as PET film 4, except that the heat setting temperature was changed to 100°C.

[0174] The properties of each film are shown in Table 1. [Table 1]

[0175] (Polarizer stack) The following two methods were used to provide a polarizer on the polyester film (polarizer protective film). (A) A method in which a rubbed alignment layer is provided on a polyester film, and a polarizing film comprising a liquid crystal compound and a dichroic dye is provided thereon (polarizer lamination method A). (B) A method in which a polarizing film made of PVA / iodine is provided on a thermoplastic substrate and then transferred onto a polyester film (polarizer lamination method B). Each method is described in detail below.

[0176] Polarizer lamination method A (Formation of rubbing alignment layer) A coating material for a rubbed alignment layer having the following composition was applied to the adhesive layer P1 surface of the polyester film using a bar coater and dried at 120°C for 3 minutes to form a film with a thickness of 200 nm. The surface of the resulting film was then treated with a rubbing roll wrapped with a nylon napped cloth to obtain a polyester film laminated with a rubbed alignment layer. The rubbing direction was parallel or perpendicular to the slow axis of the polyester film.

[0177] Rubbed alignment layer coating Fully saponified polyvinyl alcohol, molecular weight 800, 2 parts by weight Ion-exchanged water 100 parts by mass

[0178] (Synthesis of polymerizable liquid crystal compounds) The following compound (A) and the following compound (B) were synthesized with reference to the description in paragraph

[0134] of JP-A No. 2007-510946 and Lub et al., Recl. Trav. Chim. Pays-Bas, 115, 321-328 (1996).

[0179] [ka]

[0180] [ka]

[0181] The following dye (C) was synthesized with reference to Example 1 of JP-A-63-301850.

[0182] [ka]

[0183] A dye (IV) represented by the following formula (4) was synthesized with reference to Example 2 of JP-B-5-49710.

[0184] [ka]

[0185] The following dye (e) was synthesized with reference to the method for producing the compound of formula (1) described in Japanese Patent Publication No. 63-1357.

[0186] [ka]

[0187] (Formation of polarizing film) A coating material for a polarizing film consisting of 75 parts by mass of compound (A), 25 parts by mass of compound (B), 2.5 parts by mass of dye (C), 2.5 parts by mass of dye (D), 2.5 parts by mass of dye (E), 6 parts by mass of IRGACURE® 369E (manufactured by BASF), and 250 parts by mass of orthoxylene was applied to a substrate film having a rubbed alignment layer laminated thereon using a bar coater, and dried at 110°C for 3 minutes to form a film with a thickness of 2 μm. Subsequently, UV light was irradiated to form a polarizer on the substrate film.

[0188] Polarizer lamination method B (Manufacturing of substrate-laminated polarizer) An unstretched film having a thickness of 100 μm was prepared using polyethylene terephthalate pellets (a) as a thermoplastic resin substrate, and an aqueous solution of polyvinyl alcohol with a polymerization degree of 2400 and a saponification degree of 99.9 mol% was applied to one side of the unstretched film and dried to form a PVA layer. The resulting laminate was stretched twice in the longitudinal direction between rolls with different peripheral speeds at 120°C and then wound up. Next, the resulting laminate was treated with a 4% aqueous boric acid solution for 30 seconds, then immersed in a mixed aqueous solution of iodine (0.2%) and potassium iodide (1%) for 60 seconds to dye it, and subsequently treated with a mixed aqueous solution of potassium iodide (3%) and boric acid (3%) for 30 seconds. This laminate was then uniaxially stretched in the longitudinal direction in a mixed aqueous solution of boric acid (4%) and potassium iodide (5%) at 72°C. The stretched laminate was subsequently washed with a 4% aqueous solution of potassium iodide, the aqueous solution was removed with an air knife, and then it was dried in an oven at 80°C. Both ends were slit and wound up to obtain a substrate-laminated polarizer 30 cm wide and 1000 m long. The total stretching ratio was 6.5 times, and the polarizer thickness was 5 μm. The thickness was measured by embedding the substrate-laminated polarizer in epoxy resin, cutting out slices, and observing them under an optical microscope.

[0189] (Lamination of polarizing layers) After a UV-curable acrylic adhesive was applied to a polyester film, the polarizer surface of a substrate-laminated polarizer cut to a required length was attached to the polyester film, and UV light was irradiated from the substrate-laminated polarizer side to laminate the substrate-laminated polarizer onto the polyester film. Thereafter, the thermoplastic resin substrate was peeled off, and a polarizer was provided on the polyester film.

[0190] (Lamination of retardation layers) The following two methods were used to provide a retardation layer on a polarizer. (C) A method in which a quarter-wave layer and a half-wave layer are provided on a release film and then transferred onto a polarizer (method C of laminating a retardation layer) (D) A method in which a 1 / 2 wavelength layer is provided on a 1 / 4 wavelength layer by coating, and the 1 / 2 wavelength layer surface is attached to a polarizer (method D of laminating a retardation layer). Each method is described in detail below.

[0191] Retardation layer lamination method C A 50 μm thick biaxially stretched polyethylene terephthalate (PET) film was rubbed, and the rubbed surface was coated with a retardation layer-forming solution having the following composition by bar coating. The coated film was dried, oriented, and then cured by UV irradiation to form a quarter-wave layer. Solution for forming retardation layer LC242 (BASF) 75 parts by mass 20 parts by mass of the following compound

[0192] [ka]

[0193] Trimethylolpropane triacrylate 5 parts by mass Irgacure 379 3 parts by weight Surfactant 0.1 parts by mass Methyl ethyl ketone 250 parts by mass

[0194] Furthermore, a 2% by mass aqueous solution of polyvinyl alcohol (fully saponified polyvinyl alcohol 1000, surfactant 0.2%) was applied onto the quarter-wave layer and dried to obtain a polyvinyl alcohol film with a thickness of approximately 100 nm. Next, the surface of the polyvinyl alcohol film was subjected to a rubbing treatment. A solution for forming a retardation layer was applied onto the rubbed surface of the PVA by the bar coating method, dried, and subjected to an alignment treatment. After that, the solution was cured by irradiating with ultraviolet light to form a half-wave layer. The phase difference was adjusted by the film thickness, and the angle between the rubbing direction when the quarter-wave layer was applied and the rubbing direction when the half-wave layer was applied was set to 60 degrees. The light-release liner of the optical transparent adhesive sheet was peeled off, and the adhesive surface was bonded to the half-wave layer surface. The heavy-release liner of the optical transparent adhesive sheet was then peeled off, and the sheet was bonded to the polarizer attached to the polarizer protection film. The biaxially stretched PET film was then peeled off. The sheets were bonded so that the rubbing direction of the half-wave layer was 15 degrees to the absorption axis of the polarizer, and the rubbing direction of the quarter-wave layer was 75 degrees to the absorption axis of the polarizer.

[0195] Retardation layer lamination method D A quarter-wave film with a slow axis along its length was unwound from a roll and cut to the required length. The surface was then rubbed. A solution for forming a retardation layer was applied to the rubbed surface using a bar coating method, dried, and aligned. The solution was then cured by UV irradiation to form a half-wave layer. The light-release liner of the optically transparent adhesive sheet was peeled off, and the adhesive surface was bonded to the half-wave layer. The heavy-release liner of the optically transparent adhesive sheet was then peeled off, and the sheet was then bonded to the polarizer attached to the polarizer protective film. The quarter-wave film (20 μm thick) was produced by extruding a propylene-ethylene random copolymer (ethylene content 5%) into a sheet and stretching it lengthwise with a roll. The lamination was performed so that the rubbing direction of the half-wave layer and the slow axis direction of the quarter-wave layer were at 15° and 75°, respectively, with respect to the absorption axis of the polarizer.

[0196] The thickness of the retardation layer obtained by the above coating was 1.2 μm for the ¼ wavelength layer and 2.3 μm for the ½ wavelength layer, and the thickness of the adhesive layer was 3 μm.

[0197] Examples 1 to 26, Comparative Examples 1 to 3 A circularly polarizing plate was prepared by providing a polarizer and a retardation layer on a PET film shown in Table 2 by the method shown in Table 2, and the bending resistance was evaluated.

[0198] [Table 2] [Industrial Applicability]

[0199] The polarizing plate and circular polarizing plate for foldable displays of the present invention are unlikely to leave creases even when folded repeatedly, and there is no risk of image distortion at the folded portions, making them suitable for use in foldable displays. Furthermore, the foldable displays of the present invention can display images without distortion at the folded portions. [Explanation of symbols]

[0200] 1: Foldable display 11: Bending radius 2: Polyester film for polarizer protection film included in polarizer plates of folding displays 21: Folding section 22: Bending direction (direction perpendicular to the folding part)

Claims

1. A foldable organic EL display comprising a polarizing plate for a foldable organic EL display, in which a polarizer protective film made of a polyester film is laminated on at least one surface of a polarizer, wherein the polyester film satisfies the following condition: (1) Refractive index in the bending direction is 1.591 to 1.600 (2) The refractive index in the direction of the folded portion is 1.670 to 1.700 (3) A refractive index in the thickness direction of 1.520 or less (4) Density is 1.380 g / cm ３ End (5) The polyester film is a biaxially oriented polyethylene terephthalate film. (Here, the bending direction refers to the direction perpendicular to the fold when folding the polyester film.)

2. A foldable organic EL display having a retardation layer on at least one surface of the polarizing plate for a foldable organic EL display according to claim 1.

3. 3. The foldable organic EL display according to claim 2, wherein there is no or only one free-standing film other than the polyester film.

4. 2. The foldable organic electroluminescent display according to claim 1, wherein the polarizer has a thickness of 12 μm or less.

5. 4. The foldable organic electroluminescent display according to claim 2, wherein the polarizer has a thickness of 12 μm or less.

6. 5. The foldable organic electroluminescent display according to claim 1, wherein the polarizer comprises a polymerizable liquid crystal compound and a dichroic dye.

7. 6. The foldable organic electroluminescent display according to claim 2, wherein the polarizer comprises a polymerizable liquid crystal compound and a dichroic dye.

8. A foldable organic EL display as described in claim 2, 3, 5, or 7, wherein the retardation layer contains a liquid crystal compound.

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