Polarizing plate with curved-surface processing and method for manufacturing the same

Abstract

To provide a polarizing plate having excellent optical characteristics and capable of preventing cracks, fractures or yellow discoloration from occurring even with curved-surface processing, and a simple method for manufacturing the same.SOLUTION: A polarizing plate includes a polarizer and a protective layer arranged at least on one side of the polarizer, and has been processed to have a curved surface, with a fracture elongation E per unit thickness of the polarizer is 0.25 (% / μm) or more. A method for manufacturing a polarizing plate includes: preparing a polarizing plate containing a polarizer and a protective layer arranged at least on one side of the polarizer; bonding the polarizing plate onto a mold having a prescribed surface shape; heating the polarizing plate bonded onto the mold to apply curved-surface processing; and applying a humidification treatment to the polarizing plate having received the curved-surface processing, for 40 minutes or more under an environment of 40°C to 65°C and 85%RH to 95%RH.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a curved polarizing plate and a method for producing the same. [Background technology]

[0002] Polarizing plates are widely used in image display devices such as liquid crystal display devices and organic electroluminescence (EL) display devices to realize image display and / or improve the performance of the image display. Depending on the application, polarizing plates may be required to be curved. Curving typically involves molding the polarizing plate into a predetermined shape in a high-temperature environment. However, curved polarizing plates have problems such as deterioration of optical properties and susceptibility to cracking, breakage, and / or yellowing. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 8-136731 Summary of the Invention [Problem to be solved by the invention]

[0004] The present invention has been made to solve the above-mentioned conventional problems, and its main object is to provide a polarizing plate that has excellent optical properties despite being curved and that can suppress the occurrence of cracks, breakage, and yellowing, and a simple method for producing the same. [Means for solving the problem]

[0005] A polarizing plate according to an embodiment of the present invention includes a polarizer and a protective layer disposed on at least one side of the polarizer, and is curved, and the polarizer has a breaking elongation E per unit thickness of 0.25 (% / μm) or more. In one embodiment, the product E×R of the breaking elongation E (% / μm) and the radius of curvature R (mm) of the curved surface processing is not less than 20. In one embodiment, the radius of curvature R is not more than 70 mm. In one embodiment, the polarizing plate is subjected to a humidification treatment after being curved in an environment of 40° C. to 65° C. and 85% RH to 95% RH for 40 minutes or longer. According to another aspect of the present invention, there is provided a method for producing a curved polarizing plate, which includes: preparing a polarizing plate including a polarizer and a protective layer disposed on at least one side of the polarizer; heating the polarizing plate together with a mold having a predetermined curved shape to form a curved surface; and humidifying the curved polarizing plate for 40 minutes or more in an environment of 40°C to 65°C and 85% RH to 95% RH. In one embodiment, the heating temperature in the curved surface processing is 100° C. or higher. [Effects of the Invention]

[0006] According to an embodiment of the present invention, a curved polarizing plate has excellent optical properties and can be prevented from cracking, breaking, and yellowing by setting the breaking elongation per unit thickness of the polarizer to 0.25 (% / μm) or more. A polarizer (and consequently, a polarizing plate) having such a breaking elongation can be achieved by subjecting the curved polarizing plate to a predetermined humidification treatment. [Brief explanation of the drawings]

[0007] [Figure 1] 1 is a schematic perspective view of a polarizing plate according to one embodiment of the present invention. [Figure 2] FIG. 2 is a schematic cross-sectional view of the polarizing plate of FIG. [Figure 3] 3(a) to 3(c) are schematic diagrams illustrating an example of a method for manufacturing a curved polarizing plate according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0008] Representative embodiments of the present invention will be described below with reference to the drawings, but the present invention is not limited to these embodiments. Note that the drawings are schematic for ease of understanding, and the shape, thickness, radius of curvature, etc. may differ from the actual ones and may also differ between drawings.

[0009] A. Polarizing plate A-1. Overall structure of polarizing plate FIG. 1 is a schematic perspective view of a polarizing plate according to one embodiment of the present invention; and FIG. 2 is a schematic cross-sectional view of the polarizing plate of FIG. 1. The polarizing plate 100 in the illustrated example has been curved. In other words, the polarizing plate is a polarizing plate whose properties (typically, optical properties, chemical properties, and mechanical properties) have been temporarily deteriorated due to the curved surface processing (i.e., in a high-temperature environment). According to an embodiment of the present invention, a polarizing plate whose properties have been temporarily deteriorated can be restored by subjecting the polarizing plate to a humidification treatment described below. As a result, the curved polarizing plate maintains its excellent optical properties and is less susceptible to cracking, breakage, and yellowing. The curved surface processing temperature may be, for example, 100°C or higher, or, for example, 120°C or higher, or, for example, 140°C or higher, or, for example, 160°C or higher. The upper limit of the curved surface processing temperature may be, for example, 200°C. The curved surface processing time may be, for example, 15 seconds to 5 minutes.

[0010] Any appropriate shape may be adopted as the curved surface shape depending on the purpose. Specific examples of curved surface shapes include a dome shape and a semi-cylindrical shape as shown in FIG. 1. Examples of such curved polarizing plates include polarizing plates used in curved image display devices. Examples of curved image display devices include virtual reality (VR) goggles and digital signage installed on curved walls or pillars. Note that although the polarizing plate in the illustrated example is convex on the viewing side, the polarizing plate may also be convex on the side opposite to the viewing side depending on the purpose.

[0011] Polarizing plate 100 typically includes a polarizer 10, a protective layer 20 arranged on one side of the polarizer (the viewing side in the illustrated example), and a protective layer 30 arranged on the other side. Depending on the purpose, either protective layer 20 or protective layer 30 may be omitted. In this specification, protective layer 20 may be referred to as the viewing-side protective layer, and protective layer 30 may be referred to as the inner protective layer.

[0012] In an embodiment of the present invention, the breaking elongation E per unit thickness of the polarizer is 0.25 (% / μm) or more, preferably 0.30 (% / μm) or more, more preferably 0.50 (% / μm) or more, even more preferably 0.60 (% / μm) or more, and particularly preferably 0.70 (% / μm) or more. The upper limit of the breaking elongation E may be, for example, 5.0 (% / μm). A breaking elongation E in this range means that a polarizer (and consequently a polarizing plate) that has hardened due to curved surface processing recovers and softens by the humidification treatment described below. As a result, a polarizing plate including a polarizer having such a breaking elongation E has excellent optical properties even after curved surface processing, and the occurrence of cracks, breakage, and yellowing can be suppressed. The breaking elongation E can be obtained by dividing the breaking elongation of a polarizer measured in accordance with JIS K 7161 by the polarizer thickness. More specifically, a test sample of a predetermined shape is prepared from a polarizer (actually a polarizing plate) that has been heated at the same temperature as the curved surface processing and then subjected to a humidification treatment to restore its properties, and the test sample is subjected to a tensile test to measure the breaking strength.

[0013] In one embodiment, the product E×R of the breaking elongation E (% / μm) and the radius of curvature R (mm) of the curved surface is preferably 20 or more, more preferably 25 or more, even more preferably 30 or more, and particularly preferably 35 or more. The product E×R may be, for example, 50 or more, or, for example, 70 or more, or, for example, 80 or more, or, for example, 90 or more. The upper limit of the product E×R may be, for example, 1000. If the product E×R is within this range, even a polarizing plate curved with a small (tight) radius of curvature exhibits excellent optical properties and can suppress the occurrence of cracks, breakage, and yellowing. The radius of curvature R may be, for example, 70 mm or less, or, for example, 60 mm or less, or, for example, 50 mm or less, or, for example, 40 mm or less, or, for example, 30 mm or less. The lower limit of the radius of curvature R may be, for example, 10 mm.

[0014] Polarizing plates are typically subjected to a humidification treatment (essentially a heat / humidification treatment) after being curved. By subjecting a curved polarizing plate to a heat / humidification treatment, the optical properties of the polarizer can be restored and cracks, breakage, and yellowing can be suppressed. Such heat / humidification treatment has an unexpectedly excellent effect. Details are as follows: Heat / humidification treatment is usually performed as a durability test for polarizing plates. Subjecting a normal polarizing plate to a heat / humidification treatment is premised on the assumption that the optical properties of the polarizing plate will deteriorate (the degree of deterioration is used as an indicator of durability). In other words, it is common technical knowledge in the industry that heat / humidification treatment deteriorates the optical properties of polarizing plates. Meanwhile, the present inventors have discovered that a polarizing plate whose properties have been once deteriorated in a high-temperature environment (e.g., due to curved surface processing) can be restored by subjecting the polarizing plate to a heat / humidification treatment. That is, the heating and humidifying treatment in the embodiment of the present invention is based on a technical concept contrary to the common technical knowledge in the art, and the results are unexpectedly excellent. The heating temperature in the heating and humidifying treatment is preferably 40°C to 65°C, more preferably 55°C to 65°C, even more preferably 57°C to 63°C, particularly preferably 58°C to 62°C, and especially preferably about 60°C. If the heating temperature is too high or too low, the properties may not be sufficiently restored. The humidity in the heating and humidifying treatment is preferably 85%RH to 95%RH, more preferably 87%RH to 93%RH, even more preferably 88%RH to 92%RH, and especially preferably about 90%RH. If the humidity is too high or too low, the properties may not be sufficiently restored. The treatment time is preferably 40 minutes or more, more preferably 50 minutes or more, even more preferably 1 hour or more, and especially preferably 2 hours or more. The upper limit of the treatment time may be, for example, 5 hours. If the treatment time is too short, the properties may not be sufficiently restored, whereas if the treatment time is too long, the effect obtained will not change substantially, and therefore an excessively long treatment time may not be effective.

[0015] The polarizer and the protective layer will be specifically described below.

[0016] A-2. Polarizer A polarizer is typically made of a resin film containing a dichroic substance (e.g., iodine, dichroic dye). Any appropriate resin film that can be used as a polarizer can be adopted as the resin film. The resin film is typically a polyvinyl alcohol resin (hereinafter referred to as "PVA resin") film. The resin film may be a single-layer resin film or a laminate of two or more layers.

[0017] Specific examples of polarizers composed of a single-layer resin film include PVA-based resin films that have been subjected to a dyeing treatment with iodine and a stretching treatment (typically, uniaxial stretching). The dyeing with iodine is carried out, for example, by immersing the PVA-based film in an iodine aqueous solution. The stretching ratio in the uniaxial stretching is preferably 3 to 7 times. The stretching may be carried out after the dyeing treatment or while dyeing. Alternatively, the film may be dyed after stretching. If necessary, the PVA-based resin film may be subjected to a swelling treatment, a crosslinking treatment, a washing treatment, a drying treatment, or the like. For example, by immersing the PVA-based resin film in water and washing it before dyeing, it is possible to clean off stains and antiblocking agents on the surface of the PVA-based film and also to swell the PVA-based resin film, thereby preventing uneven dyeing.

[0018] Specific examples of polarizers obtained using laminates include a laminate of a resin substrate and a PVA-based resin layer (PVA-based resin film) laminated on the resin substrate, or a polarizer obtained using a laminate of a resin substrate and a PVA-based resin layer coated on the resin substrate. A polarizer obtained using a laminate of a resin substrate and a PVA-based resin layer coated on the resin substrate can be produced, for example, by applying a PVA-based resin solution to the resin substrate and drying the resin substrate to form a PVA-based resin layer on the resin substrate, thereby obtaining a laminate of the resin substrate and the PVA-based resin layer; and then stretching and dyeing the laminate to convert the PVA-based resin layer into a polarizer. In this embodiment, a polyvinyl alcohol-based resin layer containing a halide and a polyvinyl alcohol-based resin is preferably formed on one side of the resin substrate. The stretching typically involves immersing the laminate in a boric acid aqueous solution and stretching it. Furthermore, the stretching may further include, if necessary, in-air stretching of the laminate at an elevated temperature (e.g., 95°C or higher) before stretching in the boric acid aqueous solution. Additionally, in this embodiment, the laminate is preferably subjected to a drying shrinkage treatment by heating while being transported in the longitudinal direction, thereby shrinking the laminate by 2% or more in the width direction. Typically, the manufacturing method of this embodiment includes subjecting the laminate to an in-air auxiliary stretching treatment, a dyeing treatment, an underwater stretching treatment, and a drying shrinkage treatment, in this order. By introducing the auxiliary stretching, it is possible to increase the crystallinity of the PVA, even when the PVA is coated on a thermoplastic resin, thereby achieving high optical properties. Furthermore, by simultaneously increasing the orientation of the PVA in advance, problems such as a decrease in the orientation or dissolution of the PVA when immersed in water in the subsequent dyeing or stretching steps can be prevented, thereby achieving high optical properties. Furthermore, when the PVA-based resin layer is immersed in a liquid, the disordering of the orientation of the polyvinyl alcohol molecules and the decrease in the orientation can be suppressed compared to when the PVA-based resin layer does not contain a halide. This can improve the optical properties of a polarizer obtained through treatment steps, such as a dyeing treatment and an underwater stretching treatment, in which the laminate is immersed in a liquid. Furthermore, the drying shrinkage treatment causes the laminate to shrink in the width direction, thereby improving the optical properties.The obtained resin substrate / polarizer laminate may be used as is (i.e., the resin substrate may be used as a protective layer for the polarizer), or the resin substrate may be peeled off from the resin substrate / polarizer laminate and any appropriate protective layer depending on the purpose may be laminated on the peeled surface. Details of such a polarizer manufacturing method are described in, for example, JP 2012-73580 A and Japanese Patent No. 6470455 A. The entire disclosures of these publications are incorporated herein by reference.

[0019] The thickness of the polarizer can be any appropriate thickness depending on the purpose. The thickness of the polarizer is, for example, 35 μm or less, preferably 20 μm or less, more preferably 15 μm or less, even more preferably 12 μm or less, particularly preferably 10 μm or less, even more particularly preferably 8 μm or less, particularly preferably 6 μm or less, and most preferably 5 μm or less. The lower limit of the thickness of the polarizer is preferably 2 μm, more preferably 1 μm.

[0020] The initial polarization degree of the polarizer (polarization degree before curved surface processing) is preferably 97.0% or more, more preferably 99.0% or more, and even more preferably 99.9% or more. The initial single transmittance of the polarizer (single transmittance before curved surface processing) is preferably 40.0% to 46.0%, more preferably 41.0% to 43.5%. The polarization degree of the polarizer after curved surface processing is, for example, 0.005% or more smaller than the initial polarization degree (the polarization degree as an optical property is reduced). The polarization degree of the polarizer after humidification treatment (described below) is, for example, 0.005% or more larger than the polarization degree after curved surface processing (the polarization degree as an optical property is restored). In other words, the humidification treatment can restore the polarization degree that has decreased (deteriorated) due to curved surface processing to approximately the initial polarization degree.

[0021] A-3.Protective layer The viewer-side protective layer and the inner protective layer are each formed of any suitable film that can be used as a protective layer for a polarizer. Specific examples of materials that can be the main component of the film include cellulose-based resins such as triacetyl cellulose (TAC), and transparent resins such as polyesters, polyvinyl alcohols, polycarbonates, polyamides, polyimides, polyethersulfones, polysulfones, polystyrenes, polynorbornenes, polyolefins, (meth)acrylics, and acetates. Other examples include thermosetting or ultraviolet-curing resins such as (meth)acrylics, urethanes, (meth)acrylic urethanes, epoxy resins, and silicones. Other examples include glassy polymers such as siloxane polymers. Polymer films described in JP 2001-343529 A (WO 01 / 37007) can also be used. Examples of materials that can be used for this film include a resin composition containing a thermoplastic resin having substituted or unsubstituted imide groups in its side chains and a thermoplastic resin having substituted or unsubstituted phenyl and nitrile groups in its side chains, such as a resin composition containing an alternating copolymer of isobutene and N-methylmaleimide and an acrylonitrile-styrene copolymer.The polymer film can be, for example, an extrusion molded product of the above resin composition.

[0022] The inner protective layer is preferably optically isotropic. In this specification, "optically isotropic" means that the in-plane retardation Re(550) is 0 nm to 10 nm and the thickness direction retardation Rth(550) is -10 nm to +10 nm. Here, "Rth(λ)" is the thickness direction retardation measured at 23°C using light with a wavelength of λ nm. For example, "Rth(550)" is the thickness direction retardation measured at 23°C using light with a wavelength of 550 nm. Rth(λ) can be calculated by the formula: Rth(λ)=(nx-nz)×d, where d (nm) is the thickness of the layer (film). nz is the refractive index in the thickness direction.

[0023] When the polarizing plate is disposed on the viewing side of the image display device, the viewing-side protective layer may be subjected to surface treatment such as hard coating, anti-reflection treatment, anti-sticking treatment, anti-glare treatment, etc. If necessary, the viewing-side protective layer may also be subjected to treatment to improve visibility when viewed through polarized sunglasses (typically, by imparting an (elliptically) circular polarization function or an ultra-high phase difference).

[0024] The protective layer may have any appropriate thickness. The thickness of the protective layer is, for example, 10 μm to 90 μm, preferably 20 μm to 80 μm, more preferably 20 μm to 60 μm, and even more preferably 20 μm to 40 μm. When a surface treatment is applied, the thickness of the protective layer includes the thickness of the surface treatment layer.

[0025] B. Polarizing Plate Manufacturing Method The polarizing plate described in the above item A is typically a polarizing plate whose properties are restored by humidification treatment after curved surface processing. Therefore, embodiments of the present invention also include a manufacturing method for a polarizing plate that includes curved surface processing and humidification treatment. Figures 3(a) to 3(c) are schematic diagrams illustrating an example of a manufacturing method for a curved polarizing plate according to an embodiment of the present invention.

[0026] In the manufacturing method according to the embodiment of the present invention, first, a polarizing plate 100' including a polarizer and a protective layer disposed on at least one side of the polarizer is prepared as shown in Fig. 3(a). At the same time, a mold 200 having a predetermined curved shape (a dome shape in the illustrated example) is also prepared as shown in Fig. 3(a).

[0027] Next, in one embodiment, the polarizing plate 100' is attached to the mold 200 as shown in FIG. 3(b). Attaching the polarizing plate 100' to the mold 200 can be performed in any suitable manner. In the illustrated example, the polarizing plate 100' is attached to the mold 200, for example, via an adhesive. Next, the polarizing plate 100' is heated while attached to the mold 200, and the polarizing plate is curved (formed). In another embodiment (not shown), the polarizing plate 100' is heated in a vacuum state to a curved surface processing temperature while placed on the mold 200, and after the curved surface processing temperature is reached, the system is opened and the polarizing plate is curved (formed) under air pressure (atmospheric pressure). The curved surface processing temperature is as described in Section A above.

[0028] Next, the curved polarizing plate is subjected to a humidifying treatment. The humidifying treatment may be performed while the polarizing plate is still attached to or placed on the mold, or after the polarizing plate is removed from the mold as shown in FIG. 3(c). The conditions for the humidifying treatment are as described in Section A above. In this manner, a curved polarizing plate 100 can be obtained. [Example]

[0029] The present invention will be specifically described below using examples, but the present invention is not limited to these examples. The evaluation items in the examples are as follows. Unless otherwise specified, "parts" and "%" in the examples are by weight.

[0030] (1) Elastic modulus, breaking strength and breaking elongation The polarizing plate before curved processing was heated under the same conditions as the curved processing (100°C for 150 seconds). This was used as a comparative polarizing plate. The comparative polarizing plate was then heated and humidified (65°C, 95% RH, 2 hours) to prepare a polarizing plate corresponding to the example. A 100 mm x 10 mm test sample was prepared by punching out the comparative polarizing plate or the example polarizing plate. The test sample was subjected to a tensile test using an autograph (Shimadzu Corporation). The measurement environment was a temperature of 23°C, a humidity of 50% RH, and a tensile speed of 300 mm / min. The test sample was pulled at this tensile speed until it broke, and the breaking strength (breaking stress) and breaking elongation were determined. The breaking strength was measured automatically using the autograph. The breaking elongation was calculated using the following formula. Measurements were performed independently three times, and the average values ​​were used as the breaking strength and breaking elongation. Breaking elongation (%) = {change in sample length up to breaking point (mm) / initial length (100 mm)} × 100 The elastic modulus was calculated from the following formula within a tensile stress range of 10N to 20N. Elastic modulus = {(20N - 10N) / sample cross-sectional area (mm 2 )} / {ε(20)-ε(10)} Here, ε(20) is the strain per unit length (mm / mm: i.e., an absolute number) when the stress is 20N, and ε(10) is the strain per unit length when the stress is 10N. (2) Single unit transmittance and polarization degree The curved (dome-shaped) polarizing plates obtained in the Examples and Comparative Examples were measured using an ultraviolet-visible spectrophotometer (LPF-200, manufactured by Otsuka Electronics Co., Ltd.) to determine the single transmittance Ts, parallel transmittance Tp, and crossed transmittance Tc, respectively. These Ts, Tp, and Tc are Y values ​​measured using a 2-degree visual field (C light source) according to JIS Z8701 and corrected for visibility. From the obtained Tp and Tc, the degree of polarization P was calculated using the following formula. Polarization degree P(%)={(Tp-Tc) / (Tp+Tc)} 1 / 2 ×100 The measurements were performed as follows: the dome-shaped polarizing plate was divided into nine grid-like sections (each section size: 15 mm x 15 mm), excluding the bottom edge, and measurements were taken for each section, with the average values ​​being used as the single transmittance and polarization degree. The measurements were performed by fixing the dome-shaped polarizing plate in a sample holder and positioning it so that each section could be accurately measured. Note that the Ts and P of the polarizing plate are essentially dominated by the polarizer characteristics. (3) Appearance The appearance of the curved polarizing plates obtained in the Examples and Comparative Examples was visually observed and evaluated according to the following criteria: The polarizing plates of the Comparative Examples were left in a normal environment for 2 hours (the same time as the humidification treatment time for the polarizing plates of the Examples), and then the appearance was visually observed. ○: No cracks, breaks or yellowing were observed △: Either cracks, breaks or yellowing was observed ×: Two or more of cracks, breaks, or yellowing were observed

[0031] Example 1 1. Polarizer Fabrication A long, amorphous isophthalic copolymerized polyethylene terephthalate film (thickness: 100 μm) having a Tg of about 75° C. was used as the thermoplastic resin substrate, and one side of the resin substrate was subjected to a corona treatment. A PVA aqueous solution (coating solution) was prepared by dissolving 100 parts by weight of a PVA-based resin made by mixing polyvinyl alcohol (polymerization degree 4200, saponification degree 99.2 mol%) and acetoacetyl-modified PVA (manufactured by Nippon Synthetic Chemical Industry Co., Ltd., trade name "GOHSEFFIMER") in a 9:1 ratio, to which 13 parts by weight of potassium iodide was added, in water. The above PVA aqueous solution was applied to the corona treated surface of the resin substrate and dried at 60° C. to form a PVA resin layer with a thickness of 13 μm, thereby producing a laminate. The resulting laminate was uniaxially stretched 2.4 times in the machine direction (longitudinal direction) in an oven at 130°C (auxiliary in-air stretching treatment). Next, the laminate was immersed in an insolubilizing bath (a boric acid aqueous solution obtained by mixing 4 parts by weight of boric acid with 100 parts by weight of water) at a liquid temperature of 40°C for 30 seconds (insolubilizing treatment). Next, the film was immersed in a dye bath (an aqueous iodine solution obtained by mixing iodine and potassium iodide in a weight ratio of 1:7 with 100 parts by weight of water) at a liquid temperature of 30°C for 60 seconds while adjusting the concentration so that the single transmittance (Ts) of the finally obtained polarizer would be a predetermined value (dyeing treatment). Next, the sample was immersed in a crosslinking bath (a boric acid aqueous solution obtained by blending 3 parts by weight of potassium iodide and 5 parts by weight of boric acid with 100 parts by weight of water) at a liquid temperature of 40°C for 30 seconds (crosslinking treatment). The laminate was then immersed in a boric acid aqueous solution (boric acid concentration 4 wt %, potassium iodide concentration 5 wt %) at a liquid temperature of 70°C and uniaxially stretched in the longitudinal direction (longitudinal direction) between rolls with different peripheral speeds to a total stretch ratio of 5.5 times (underwater stretching treatment). Thereafter, the laminate was immersed in a cleaning bath (aqueous solution obtained by mixing 3 parts by weight of potassium iodide with 100 parts by weight of water) at a liquid temperature of 20° C. (cleaning treatment). Thereafter, the film was dried in an oven maintained at about 90°C, and brought into contact with a heated roll made of SUS whose surface temperature was maintained at about 75°C (drying shrinkage treatment). In this manner, a polarizer was formed on the resin substrate, and a laminate having a resin substrate / polarizer structure was obtained.

[0032] 2. Preparation of Polarizing Plates An acrylic resin film (40 μm thick) was attached as a viewer-side protective layer to the surface of the polarizer of the laminate obtained above (the surface opposite to the resin substrate) via a UV-curable adhesive. Specifically, the curable adhesive was applied so that the total thickness was approximately 1.0 μm, and the layers were attached using a roller. The adhesive was then cured by irradiating it with UV light from the acrylic resin film side. The resin substrate was then peeled off to obtain a polarizing plate having a configuration of acrylic resin film (viewer-side protective layer) / polarizer.

[0033] 3. Curved surface processing of polarizing plates The resulting polarizing plates were punched into individual sheets and then curved (molded) into dome shapes with radii of curvature of 48 mm, 70 mm, and 105 mm. Specifically, the punched polarizing plates were placed in dome-shaped molds with the respective radii of curvature and heated to 100°C under vacuum. After reaching this temperature, the system was opened and the plates were curved (molded) under air pressure (atmospheric pressure). The actual processing time (pressure time) was 150 seconds. The curved polarizing plates were then placed in a chamber set at 65°C and 95% RH for 2 hours for heating and humidification. In this way, curved polarizing plates were obtained. The resulting polarizing plates were subjected to the evaluations (2) and (3) above. The results are shown in Table 1.

[0034] <Example 2> A 75 μm thick polyvinyl alcohol film (VF-PS7500 manufactured by Kuraray Co., Ltd.) was stretched to a stretching ratio of 2.5 times while immersed in pure water at 30°C for 60 seconds, dyed in an iodine aqueous solution at 30°C (weight ratio: pure water / iodine (I) / potassium iodide (KI) = 100 / 0.01 / 1) for 45 seconds, stretched in a 4 wt% boric acid aqueous solution to a total stretching ratio of 5.8 times, immersed in pure water for 10 seconds, and then dried at 60°C for 3 minutes while maintaining the tension of the film to obtain a polarizer (thickness 28 μm).

[0035] A triacetyl cellulose (TAC) film (thickness 47 μm) was attached to one surface of the obtained polarizer as a viewing-side protective layer, and an acrylic resin film (thickness 30 μm) was attached to the other surface as an inner protective layer to obtain a polarizing plate.

[0036] A curved polarizing plate was obtained in the same manner as in Example 1. The obtained polarizing plate was subjected to the same evaluation as in Example 1. The results are shown in Table 1.

[0037] <Examples 3 and 4> A curved polarizing plate was obtained in the same manner as in Example 1, except that a polarizing plate having the configuration shown in Table 1 was used. The obtained polarizing plate was subjected to the same evaluation as in Example 1. The results are shown in Table 1.

[0038] <Comparative Example 1> A curved polarizing plate was obtained in the same manner as in Example 2, except that the heating and humidifying treatment was not carried out. The obtained polarizing plate was subjected to the same evaluations as in Example 1. The results are shown in Table 1.

[0039] <Comparative Examples 2 and 3> A curved polarizing plate was obtained in the same manner as in Comparative Example 1, except that a polarizing plate having the configuration shown in Table 1 was used. The obtained polarizing plate was subjected to the same evaluations as in Example 1. The results are shown in Table 1.

[0040] [Table 1]

[0041] As is clear from Table 1, according to the examples of the present invention, the properties of the polarizing plate deteriorated by curved surface processing can be restored by heating and humidifying treatment. More specifically, as is clear from comparisons between Example 2 and Comparative Example 1, Example 3 and Comparative Example 2, and Example 4 and Comparative Example 3, the polarizing plates of the examples dramatically recover the single transmittance and polarization degree, as well as the polarizer breaking elongation E, which had deteriorated due to curved surface processing, by heating and humidifying treatment. It can be seen that the polarizing plates of such examples are suppressed from cracking, breaking, and yellowing. [Industrial Applicability]

[0042] The polarizing plate according to the embodiment of the present invention can be suitably used in an image display device having a curved surface (for example, a curved image display device). [Explanation of symbols]

[0043] 10 Polarizer 20 protective layer 30 protective layer 100 Polarizer

Claims

1. A method for manufacturing a polarizing plate having a curved surface, comprising the steps of: providing a polarizing plate including polarizers and a protective layer disposed on at least one side of the polarizers; heating the polarizing plate together with a mold having a predetermined curved shape to form a curved surface; and humidifying the curved polarizing plate for 40 minutes or more in an environment of 40°C to 65°C and 85% RH to 95% RH; Including, The polarizer has a breaking elongation E per unit thickness of 0.25 (% / μm) or more.

2. The manufacturing method according to claim 1 , wherein the heating temperature in the curved surface processing is 100° C. or higher.

Images