Polarizing plate and optical display device

Abstract

Provided are a polarizing plate and an optical display device including the same, wherein the polarizing plate includes: a polarizer; and a phase retardation layer stacked on the lower surface of the polarizer, where the phase retardation layer includes a negative C layer, a negative A layer, and a positive A layer stacked on the lower surface of the polarizer in sequence, where the negative C layer has a thickness dependent phase retardation of 20 nm to 60 nm at a wavelength of 550 nm.

Description

Technical Field

[0001] The present invention relates to a polarizing plate and an optical display device. Background Art

[0002] Due to the reflection of external light, an organic light emitting diode display may have problems of deteriorated visibility and contrast. To solve this problem, a polarizing plate is adopted in the organic light emitting diode display. The polarizing plate can achieve an antireflection function by reducing the reflectance of the reflected external light. The polarizing plate generally needs to significantly improve the screen quality by improving the black visibility at the front side.

[0003] The polarizing plate includes a polarizer and an antireflection layer stacked on the lower surface of the polarizer. The antireflection layer may be a sheet-type retardation layer or a two-sheet-type retardation layer. The sheet-type retardation layer generally achieves negative wavelength dispersion characteristics. The two-sheet-type retardation layer generally achieves negative wavelength dispersion characteristics by laminating retardation layers each having positive wavelength dispersion characteristics. Although the two-sheet-type retardation layer may have a larger thickness than the sheet-type retardation layer, the two-sheet-type retardation layer can be formed by stacking retardation layers that are lower in price than the sheet-type retardation layer and exhibit positive wavelength dispersion characteristics, to ensure price competitiveness and improvement in productivity.

[0004] A retardation layer can be formed by the following operations: stretching an unstretched film formed of a composition containing a polymer resin, or coating a liquid crystal composition to a predetermined thickness on an alignment layer and then drying and / or curing. Although the retardation layer composed of two-sheet liquid crystal has a smaller thickness than the retardation layer composed of two-sheet stretched film, when the polarizing plate is placed under high temperature / high humidity conditions, since iodine elutes from the polarizer and diffuses into the panel, the retardation layer composed of two-sheet liquid crystal may cause deterioration of the durability of the panel due to electrode corrosion. Although a method that fundamentally prevents iodine from eluting from the polarizer can be used, this method has limitations in practice.

[0005] The background art of the present invention is disclosed in Korean Patent Publication No. 10-2013-0103595. Summary of the Invention

[0006] Technical Challenges

[0007] An object of the present invention is to provide a polarizing plate having a very low reflectance at the lateral side and achieving good black visibility at the same time.

[0008] Another object of the present invention is to provide a polarizing plate capable of minimizing contamination of the liquid crystal layer and / or the panel caused by elution of iodine from the polarizing plate when placed under high temperature / high humidity conditions for a long period of time.

[0009] Another object of the present invention is to provide a polarizing plate capable of achieving a reduced thickness.

[0010] Means for Solving the Problem

[0011] One embodiment of the present invention relates to a polarizing plate.

[0012] 1. The polarizing plate includes: a polarizer; and a retardation layer stacked on the lower surface of the polarizer, wherein the retardation layer includes a negative C layer, a negative A layer, and a positive A layer stacked in sequence on the lower surface of the polarizer, and the negative C layer has an out-of-plane retardation of 20 nanometers to 60 nanometers at a wavelength of 550 nanometers.

[0013] 2. In 1, the negative C layer may have a front in-plane retardation of 0 nanometers to 10 nanometers at a wavelength of 550 nanometers.

[0014] 3. In 1 to 2, as calculated according to Equation 1, the negative C layer may have a ratio of 0.0005 nanometer / nanometer to 0.003 nanometer / nanometer:

[0015] [Equation 1]

[0016] A / B,

[0017] where A is the out-of-plane retardation (unit: nanometer) of the negative C layer at a wavelength of 550 nanometers, and

[0018] B is the thickness (unit: nanometer) of the negative C layer.

[0019] 4. In 1 to 3, the negative C layer may have a water vapor transmission rate (WVTR) of 400 grams per square meter per day (g / m 2 ·day) or less than 400 grams per square meter per day.

[0020] 5. In 1 to 4, the negative C layer may be a film or a coating containing a polymer exhibiting positive inherent birefringence.

[0021] 6. Among 1 to 5, the negative C layer can be a film or a coating composed of triacetylcellulose (TAC), cyclic olefin polymer (COP), or cyclic olefin copolymer (COC) resin.

[0022] 7. Among 1 to 6, the thickness ratio of the laminate of the negative C layer, the negative A layer, and the positive A layer to the retardation layer can be 95% or greater than 95%.

[0023] 8. Among 1 to 7, the laminate of the negative A layer and the positive A layer can have negative wavelength dispersion characteristics.

[0024] 9. Among 1 to 8, the laminate of the negative A layer and the positive A layer can have a linear retardation of 120 nm to 180 nm at a wavelength of 550 nm.

[0025] 10. Among 1 to 9, the positive A layer can have a lower in-plane retardation on the front side than the negative A layer at a wavelength of 550 nm.

[0026] 11. In 10, the positive A layer can have an in-plane retardation of 100 nm to 140 nm at a wavelength of 550 nm, and the negative A layer can have an in-plane retardation of 200 nm to 280 nm at a wavelength of 550 nm.

[0027] 12. Among 1 to 11, the slow axis of the positive A layer can be inclined at an angle of 55° to 65° with respect to the slow axis of the negative A layer.

[0028] 13. Among 1 to 12, the slow axis of the positive A layer can be inclined at an angle of 70° to 85° with respect to the light transmission axis of the polarizer, and the slow axis of the negative A layer can be inclined at an angle of 10° to 25° with respect to the light transmission axis of the polarizer.

[0029] 14. Among 1 to 13, each of the positive A layer and the negative A layer can be a liquid crystal layer.

[0030] 15. In 14, the positive A layer can be a nematic liquid crystal layer, and the negative A layer can be a discotic liquid crystal layer.

[0031] 16. Among 1 to 15, the polarizing plate can further include a second protective layer stacked on the upper surface of the polarizer.

[0032] Another embodiment of the present invention relates to an optical display device.

[0033] The optical display device includes a polarizing plate according to the present invention.

[0034] Advantages of the Invention

[0035] The present invention provides a polarizing plate having a very low reflectance at a lateral side while achieving good black visibility at the lateral side.

[0036] The present invention provides a polarizing plate capable of minimizing contamination of a liquid crystal layer and / or a panel caused by elution of iodine from the polarizing plate when placed in high temperature / high humidity conditions for a long period of time.

[0037] The present invention provides a polarizing plate capable of achieving a thickness reduction. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 is a cross-sectional view of a polarizing plate according to an embodiment of the present invention.

[0039] Figure 2 is a cross-sectional view of a polarizing plate according to another embodiment of the present invention.

[0040] Figure 3 is a graph showing the variation of the maximum reflectance (Y-axis, unit: %) at a lateral side (60°) with the Rth (X-axis, unit: nm) of a negative C layer. DETAILED DESCRIPTION

[0041] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art can easily implement the present invention. It should be understood that the present invention can be implemented in different ways and is not limited to the following embodiments.

[0042] The terms used herein are for the purpose of describing exemplary embodiments and are not intended to limit the scope of the present invention. In this document, unless the context clearly indicates otherwise, the singular forms "a" and "an" and "the" are also intended to include the plural forms.

[0043] In the drawings, parts not relevant to this description will be omitted for clarity. Throughout the specification, the same components will be denoted by the same reference numerals. Although the lengths, thicknesses, or widths of various components may be exaggerated in the drawings for the purpose of describing the present invention, the present invention is not limited thereto.

[0044] In this document, spatial relative terms such as "upper" and "lower" are defined with reference to the drawings. Therefore, it should be understood that the "upper surface" can be used interchangeably with the "lower surface".

[0045] In this document, "in-plane retardation (Re)", "out-of-plane retardation (Rth)", and "degree of biaxiality (NZ)" are represented by Equation A, Equation B, and Equation C, respectively:

[0046] [Equation A]

[0047] Re = (nx - ny) × d

[0048] [Equation B]

[0049] Rth = ((nx + ny) / 2 - nz) × d,

[0050] [Equation C]

[0051] NZ = (nx - nz) / (nx - ny)

[0052] (where nx, ny, and nz are the refractive indices of the retardation layer in the slow axis direction, fast axis direction, and thickness direction of the retardation layer at the measurement wavelength, respectively, and d represents the thickness of the retardation layer (unit: nanometer)).

[0053] Unless otherwise specified, nx, ny, and nz indicate the refractive indices of the retardation layer in the slow axis direction, fast axis direction, and thickness direction at a wavelength of 550 nanometers, respectively. In this document, the slow axis is defined as the axis that provides the highest refractive index in the in-plane direction, and the fast axis is defined as the axis that provides the lowest refractive index in the in-plane direction. The slow axis may be substantially orthogonal to the fast axis, but is not limited thereto.

[0054] In this document, "reflectivity" refers to the value calculated based on the assumption that the Organic Light Emitting Diode (OLED) bare panel (the OLED panel without a polarizer) has 100% reflectivity, excluding the primary reflectivity at the outermost region.

[0055] In this document, the "Water Vapor Transmission Rate (WVTR)" can be measured by a typical method known to those skilled in the art and refers to the value measured, for example, at 23°C and 99% relative humidity (RH) to 100% RH. The Water Vapor Transmission Rate can be measured using a water vapor transmission rate meter (PERMATRAN-W, model 700), but is not limited thereto. A sample for measuring the water vapor transmission rate can be prepared by cutting, for example, the negative C layer into a size of 10 cm × 10 cm (length × width).

[0056] The present invention provides a polarizing plate capable of achieving a very low reflectance and good black visibility at a lateral side when attached to a panel including an organic light-emitting diode, an inorganic light-emitting diode, or an organic / inorganic light-emitting diode. The present invention provides an antireflection polarizing plate achieving a maximum reflectance of less than 2.5% at a lateral side (e.g., at a lateral viewing angle of 60°).

[0057] The present invention provides a polarizing plate capable of minimizing contamination of a liquid crystal layer and / or a panel caused by elution of iodine from the polarizing plate when placed under high temperature / high humidity conditions for a long period of time. The retardation layer includes a liquid crystal layer having a thinner layer. For a retardation layer including a liquid crystal layer located between a polarizer and a panel, when the polarizing plate is placed under high temperature / high humidity conditions for a long period of time, iodine can be eluted from the polarizer and contaminate the liquid crystal layer and the panel. When iodine contaminates the liquid crystal layer and the panel, the screen quality may deteriorate due to the color of iodine (e.g., purple).

[0058] The present invention improves the durability of the polarizing plate by solving these problems. Here, "elution of iodine" can be evaluated based on a color change indicating the degree of iodine elution, which is determined by observing the periphery of the polarizing plate through a microscope after placing the polarizing plate in a chamber under high temperature and high humidity (60 °C and 90% relative humidity) conditions for 250 hours.

[0059] The present invention provides a polarizing plate including a thin retardation layer to reduce the thickness of the polarizing plate. In one embodiment, the retardation layer of the polarizing plate may have a thickness of 20 micrometers to 100 micrometers (e.g., 20 micrometers, 25 micrometers, 30 micrometers, 35 micrometers, 40 micrometers, 45 micrometers, 50 micrometers, 55 micrometers, 60 micrometers, 65 micrometers, 70 micrometers, 75 micrometers, 80 micrometers, 85 micrometers, 90 micrometers, 95 micrometers, or 100 micrometers), preferably 20 micrometers to 90 micrometers, more preferably 20 micrometers to 80 micrometers. Within this range, the polarizing plate can achieve a thickness reduction.

[0060] The polarizing plate according to the present invention may include: a polarizer; and a retardation layer stacked on the lower surface of the polarizer, wherein the retardation layer includes a negative C layer, a negative A layer, and a positive A layer sequentially stacked on the lower surface of the polarizer, and the negative C layer has an out-of-plane retardation of 20 nanometers to 60 nanometers at a wavelength of 550 nanometers.

[0061] In one embodiment, the retardation layer may be a laminate of the three retardation layers of a negative C layer, a negative A layer, and a positive A layer.

[0062] According to the present invention, a negative A layer and a positive A layer are sequentially stacked on the lower surface of a polarizer as retardation layers, and a negative C layer is further stacked between the polarizer and the negative A layer, wherein the out-of-plane retardation of the negative C layer at a wavelength of 550 nm is adjusted to a specific range of 20 nm to 60 nm, whereby the polarizing plate can easily achieve a maximum reflectance of less than 2.5% at the lateral side.

[0063] For the polarizing plate according to the present invention, wherein the negative C layer is disposed between the positive A layer and the negative A layer or on the lower surface of the positive A layer, it may be difficult to achieve a maximum reflectance of less than 2.5% at the lateral side.

[0064] For the polarizing plate according to the present invention, wherein the negative C layer has an out-of-plane retardation of less than 20 nm at a wavelength of 550 nm, it may be difficult to achieve a maximum reflectance of less than 2.5% at the lateral side and the thickness of the negative C layer becomes too thin, so that when the polarizing plate is placed under high temperature / high humidity conditions for a long period of time, iodine contamination will occur to the polarizing plate and / or the panel. For the polarizing plate according to the present invention, wherein the negative C layer has an out-of-plane retardation of greater than 60 nm at a wavelength of 550 nm, it may be difficult to achieve a maximum reflectance of less than 2.5% at the lateral side and achieve a thickness reduction.

[0065] In one embodiment, the negative C layer may have an out-of-plane retardation of 20 nm, 21 nm, 22 nm, 23 nm, 24 nm, 25 nm, 26 nm, 27 nm, 28 nm, 29 nm, 30 nm, 31 nm, 32 nm, 33 nm, 34 nm, 35 nm, 36 nm, 37 nm, 38 nm, 39 nm, 40 nm, 41 nm, 42 nm, 43 nm, 44 nm, 45 nm, 46 nm, 47 nm, 48 nm, 49 nm, 50 nm, 51 nm, 52 nm, 53 nm, 54 nm, 55 nm, 56 nm, 57 nm, 58 nm, 59 nm or 60 nm, preferably 30 nm to 40 nm at a wavelength of 550 nm.

[0066] Hereinafter, each component of the polarizing plate according to the present invention will be described in detail.

[0067] Polarizer

[0068] A polarizer is used to convert natural light or polarized light into linearly polarized light by linearly polarizing in a specific direction, and can be made of a polymer film mainly composed of a polyvinyl alcohol resin. Specifically, the polarizer can be made by dyeing the polymer film with iodine or a dichroic dye and then stretching the dyed film in its longitudinal direction (machine direction, MD). In one embodiment, the polarizer can be made by swelling, dyeing, stretching, and optional color correction and / or crosslinking.

[0069] The polarizer has a light absorption axis and a light transmission axis in its in-plane direction, where the light absorption axis can correspond to the longitudinal direction (MD) of the polarizer, and the light transmission axis can correspond to the transverse direction (transverse direction, TD) of the polarizer.

[0070] The polarizer can have a total light transmittance of 40% or higher than 40% (e.g., 40% to 46%), and a degree of polarization of 95% or higher than 95% (e.g., 95% to 99.999%). Within this range, the polarizer can be combined with a retardation layer to improve the antireflection efficiency. Here, the "light transmittance" and "degree of polarization" are values measured at wavelengths from 380 nm to 780 nm and correspond to the visibility within the corresponding wavelength range.

[0071] The polarizer can have a thickness of 2 μm to 30 μm, specifically 4 μm to 25 μm. Within this range, the polarizer can be applied to a polarizing plate.

[0072] The polarizer can be directly stacked on the negative C layer without an adhesive layer or a bonding layer, or stacked on the negative C layer via an adhesive layer or a bonding layer.

[0073] Positive A layer and negative A layer

[0074] The stack of the positive A layer and the negative A layer can help achieve a maximum reflectance of less than 2.5% at the lateral side. However, the polarizing plate alone cannot achieve a maximum reflectance of less than 2.5% at the lateral side by the stack of the positive A layer and the negative A layer.

[0075] The stack of the positive A layer and the negative A layer is stacked on the lower surface of the polarizer. The polarizing plate can include a negative A layer and a positive A layer stacked in sequence on the polarizer, thereby easily achieving the effects of the present invention.

[0076] The stack can exhibit negative wavelength dispersion characteristics. Therefore, the polarizing plate can easily achieve a maximum reflectance of less than 2.5% at the lateral side. Here, the negative wavelength dispersion characteristics mean that the stack satisfies the relationship:

[0077] Re(450) < Re(550) and Re(550) < Re(650). Here, Re(450), Re(550), and Re(650)

[0078] are the linear retardation values at wavelengths of 450 nm, 550 nm, and 650 nm for the stacked layers, respectively.

[0079] In one embodiment, the stacked layers may have a Re(450) / Re(550) value less than 1 (e.g., from 0.8 to less than 1). The stacked layers may have a Re(650) / Re(550) value greater than 1 (e.g., greater than 1 to 1.2). Within this range, the polarizing plate can easily achieve negative wavelength dispersion characteristics.

[0080] For example, a stack of a positive A layer and a negative A layer may have a retardation of 110 nm to 170 nm, preferably 120 nm to 160 nm, at a wavelength of 450 nm, a retardation of 120 nm to 180 nm, preferably 130 nm to 170 nm, at a wavelength of 550 nm, and a retardation of 130 nm to 190 nm, preferably 140 nm to 180 nm, at a wavelength of 650 nm. Within this range, the polarizing plate can easily achieve negative wavelength dispersion characteristics.

[0081] Specifically, the retardation of the "stacked layers of retardation layers" is expressed by the linear retardation value calculated from the Mueller Matrix of the stacked layers of retardation layers. Here, the Mueller Matrix of the stacked layers of retardation layers is expressed by Equation D and can be easily measured using a retardation meter (e.g., AxoScan).

[0082] [Equation D]

[0083]

[0084] Here, the "linear retardation (R L )" is expressed by Equation E and is well-known to those skilled in the art. The linear retardation can be easily measured using a retardation meter (e.g., AxoScan).

[0085] [Equation E]

[0086]

[0087] (In Equation E, m 23 , m 32 , m 31 , m 13 , m 11 , m 22 and m 33 are obtained from Equation D.)

[0088] In Equation D and Equation E, the measurement wavelength may be 450 nm, 550 nm, or 650 nm.

[0089] The positive A layer is a retardation layer that satisfies the following refractive index relationship: nx > ny ≒ nz. The positive A layer may have a lower in-plane retardation at a wavelength of 550 nm compared to the negative A layer. Therefore, the polarizing plate can easily achieve the effects of the present invention.

[0090] In one embodiment, the positive A layer may have an in-plane retardation of 100 nm to 140 nm at a wavelength of 550 nm. Within this range, the positive A layer, together with the negative A layer and the negative C layer, enables the polarizing plate to easily achieve a maximum reflectance of less than 2.5% at the lateral side. For example, the positive A layer may have an in-plane retardation of 100 nm, 101 nm, 102 nm, 103 nm, 104 nm, 105 nm, 106 nm, 107 nm, 108 nm, 109 nm, 110 nm, 111 nm, 112 nm, 113 nm, 114 nm, 115 nm, 116 nm, 117 nm, 118 nm, 119 nm, 120 nm, 121 nm, 122 nm, 123 nm, 124 nm, 125 nm, 126 nm, 127 nm, 128 nm, 129 nm, 130 nm, 131 nm, 132 nm, 133 nm, 134 nm, 135 nm, 136 nm, 137 nm, 138 nm, 139 nm, or 140 nm at a wavelength of 550 nm. Preferably, the positive A layer has an in-plane retardation of 110 nm to 130 nm at a wavelength of 550 nm.

[0091] The positive A layer may exhibit positive wavelength dispersion characteristics. Herein, positive wavelength dispersion characteristics mean that the in-plane retardation gradually decreases as the wavelength increases. In one embodiment, the positive A layer may have a Re(450) / Re(550) value greater than 1 (e.g., 1.01 to 1.5), and a Re(650) / Re(550) value less than 1 (e.g., 0.8 to 0.99).

[0092] The positive A layer may have an out-of-plane retardation of 50 nm to 70 nm (e.g., 50 nm, 51 nm, 52 nm, 53 nm, 54 nm, 55 nm, 56 nm, 57 nm, 58 nm, 59 nm, 60 nm, 61 nm, 62 nm, 63 nm, 64 nm, 65 nm, 66 nm, 67 nm, 68 nm, 69 nm, or 70 nm), specifically 55 nm to 65 nm, at a wavelength of 550 nm. Within this range, the effects of the present invention can be easily achieved.

[0093] The positive A layer may have a biaxiality of 0.9 to 1.1 (e.g., 0.9, 0.91, 0.92, 0.93, 0.94, 0.95, 0.96, 0.97, 0.98, 0.99, 1, 1.01, 1.02, 1.03, 1.04, 1.05, 1.06, 1.07, 1.08, 1.09, or 1.1), specifically 0.95 to 1.05, at a wavelength of 550 nm. Within this range, the effects of the present invention can be easily achieved.

[0094] The positive A layer may have a slow axis and a fast axis in its in-plane direction, wherein the slow axis of the positive A layer may be inclined at an angle of 70° to 85° (e.g., 70°, 71°, 72°, 73°, 74°, 75°, 76°, 77°, 78°, 79°, 80°, 81°, 82°, 83°, 84°, or 85°), preferably 75° to 80°, with respect to the optical transmission axis of the polarizer. Within this range, the effects of the present invention can be easily achieved.

[0095] The positive A layer may have a thickness of 1.0 μm to 3.0 μm, specifically 1.0 μm to 2.0 μm. Within this range, the polarizing plate can achieve a reduction in thickness.

[0096] Although the positive A layer may be a non-liquid crystal layer, the positive A layer is preferably a liquid crystal layer to achieve a reduction in the thickness of the polarizing plate. In one embodiment, the positive A layer may be a nematic liquid crystal layer.

[0097] The nematic liquid crystal layer may be formed of a composition that achieves a nematic liquid crystal. The composition may include a polymerizable compound.

[0098] The polymerizable compound may have at least one polymerizable crosslinking group. For example, the polymerizable crosslinking group may include an acrylate group, a methacrylate group, a vinyl group, a vinyloxy group, an epoxy group, an oxetanyl group, a thiol group, a maleimide group, or a derivative thereof. Specifically, the polymerizable crosslinking group may include at least one selected from Formulas R-1 to R-15:

[0099]

[0100] The composition may further include a liquid crystal compound. Although the liquid crystal compound does not have a polymerizable crosslinking group, when the composition is cured, the liquid crystal compound can also impart liquid crystallinity to the composition.

[0101] The composition may further include typical additives for achieving a liquid crystal layer, such as a photoinitiator, a surface modifier, an antioxidant, and similar additives. The composition may include a solvent to facilitate the formation of a liquid crystal layer having a uniform surface.

[0102] The negative A layer is a retardation layer that satisfies the following refractive index relationship: nz ≒ nx > ny.

[0103] The negative A layer can exhibit positive wavelength dispersion characteristics. Here, positive wavelength dispersion characteristics mean that the in-plane retardation decreases as the wavelength increases. In one embodiment, the negative A layer can have a Re(450) / Re(550) value greater than 1 (e.g., 1.01 to 1.5), and a Re(650) / Re(550) value less than 1 (e.g., 0.8 to 0.99).

[0104] In one embodiment, the negative A layer can have a front in-plane retardation of 200 nm to 280 nm at a wavelength of 550 nm. Within this range, the negative A layer, together with the positive A layer and the negative C, enables the polarizer to easily achieve a maximum reflectance of less than 2.5% at the lateral side. In one embodiment, the negative A layer can have a front in-plane retardation of 200 nm, 201 nm, 202 nm, 203 nm, 204 nm, 205 nm, 206 nm, 207 nm, 208 nm, 209 nm, 210 nm, 211 nm, 212 nm, 213 nm, 214 nm, 215 nm, 216 nm, 217 nm, 218 nm, 219 nm, 220 nm, 221 nm, 222 nm, 223 nm, 224 nm, 225 nm, 226 nm, 227 nm, 228 nm, 229 nm, 230 nm, 231 nm, 232 nm, 233 nm, 234 nm, 235 nm, 236 nm, 237 nm, 238 nm, 239 nm, 240 nm, 241 nm, 242 nm, 243 nm, 244 nm, 245 nm, 246 nm, 247 nm, 248 nm, 249 nm, 250 nm, 251 nm, 252 nm, 253 nm, 254 nm, 255 nm, 256 nm, 257 nm, 258 nm, 259 nm, 260 nm, 261 nm, 262 nm, 263 nm, 264 nm, 265 nm, 266 nm, 267 nm, 268 nm, 269 nm, 270 nm, 271 nm, 272 nm, 273 nm, 274 nm, 275 nm, 276 nm, 277 nm, 278 nm, 279 nm or 280 nm. Preferably, the negative A layer has a front in-plane retardation of 220 nm to 280 nm at a wavelength of 550 nm.

[0105] The negative A layer may have an out-of-plane retardation of -140 nm to -100 nm (e.g., -140 nm, -139 nm, -138 nm, -137 nm, -136 nm, -135 nm, -134 nm, -133 nm, -132 nm, -131 nm, -130 nm, -129 nm, -128 nm, -127 nm, -126 nm, -125 nm, -124 nm, -123 nm, -122 nm, -121 nm, -120 nm, -119 nm, -118 nm, -117 nm, -116 nm, -115 nm, -114 nm, -113 nm, -112 nm, -111 nm, -110 nm, -109 nm, -108 nm, -107 nm, -106 nm, -105 nm, -104 nm, -103 nm, -102 nm, -101 nm, or -100 nm), specifically -130 nm to -110 nm, at a wavelength of 550 nm. Within this range, the effects of the present invention can be easily achieved.

[0106] The negative A layer may have a biaxiality of -0.1 to 0.1 (e.g., -0.1, -0.09, -0.08, -0.07, -0.06, -0.05, -0.04, -0.03, -0.02, -0.01, 0, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, or 0.1), specifically -0.05 to 0.05, at a wavelength of 550 nm. Within this range, the effects of the present invention can be easily achieved.

[0107] The negative A layer may have a slow axis and a fast axis in its in-plane direction, where the slow axis of the negative A layer may be inclined at an angle of 10° to 25° (e.g., 10°, 11°, 12°, 13°, 14°, 15°, 16°, 17°, 18°, 19°, 20°, 21°, 22°, 23°, 24°, or 25°), preferably 15° to 20°, with respect to the optical transmission axis of the polarizer. Within this range, the effects of the present invention can be easily achieved.

[0108] The angle defined between the slow axis of the positive A layer and the slow axis of the negative A layer may be in the range of 55° to 65° (e.g., 55°, 56°, 57°, 58°, 59°, 60°, 61°, 62°, 63°, 64°, or 65°), preferably 57° to 63°. Within this range, the effects of the present invention can be easily achieved.

[0109] The negative A layer may have a thickness of 1.0 μm to 5.0 μm, specifically 2.0 μm to 4.0 μm. Within this range, the polarizing plate can achieve a thickness reduction.

[0110] Although the negative A layer may be a non-liquid crystal layer, the negative A layer is preferably a liquid crystal layer to achieve a reduction in the thickness of the polarizing plate. In one embodiment, the negative A layer may be a discotic liquid crystal layer.

[0111] The discotic liquid crystal layer may be formed from a composition that achieves a discotic liquid crystal. The composition may include a polymerizable compound.

[0112] The polymerizable compound may have at least one polymerizable crosslinking group. For example, the polymerizable crosslinking group may be an acrylate group, a methacrylate group, a vinyl group, a vinyloxy group, an epoxy group, an oxetanyl group, a thiol group, a maleimide group, or a derivative thereof. Specifically, the polymerizable crosslinking group may include at least one selected from Formulas R-1 to R-15:

[0113]

[0114] The composition may further include a liquid crystal compound. Although the liquid crystal compound does not have a polymerizable crosslinking group, the liquid crystal compound may impart liquid crystallinity to the composition when the composition is cured.

[0115] The composition may further include typical additives for achieving a liquid crystal layer, such as a photoinitiator, a surface modifier, an antioxidant, and similar additives. The composition may include a solvent to facilitate the formation of a liquid crystal layer having a uniform surface.

[0116] A laminate of the positive A layer and the negative A layer including an interlayer adhesive or binder therebetween may have a thickness of 2.0 micrometers to 13.0 micrometers, preferably 4.0 micrometers to 11.0 micrometers. Within this range, the laminate may achieve a reduction in the thickness of the polarizing plate.

[0117] The laminate of the positive A layer and the negative A layer may be formed by bonding the positive A layer to the negative A layer via an adhesive layer or a bonding layer. As an alternative, the laminate of the positive A layer and the negative A layer may be formed by coating the composition of the positive A layer on one surface of the negative A layer, followed by drying and / or curing. In such a case, the positive A layer may be formed on the negative A layer by direct coating without the need for an adhesive layer or a bonding layer.

[0118] The laminate of the positive A layer and the negative A layer may further include at least one first protective layer. The first protective layer may provide additional functions to the laminate and / or the polarizing plate. For example, the first protective layer supplements the thickness of the laminate to improve the durability and mechanical strength of the laminate. As an alternative, when at least one of the positive A layer and the negative A layer is a liquid crystal layer, the first protective layer may be a base film for forming the liquid crystal layer.

[0119] The first protective layer is an optically transparent film and can be formed from at least one resin selected from, for example, cellulose-based resins including triacetyl cellulose (TAC), polyester-based resins including polyethylene terephthalate (PET), polybutylene terephthalate, polyethylene naphthalate, polybutylene naphthalate (PEN), cycloolefin polymer (COP)-based resins, cycloolefin copolymer (COC)-based resins, polycarbonate-based resins, polyethersulfone-based resins, polysulfone-based resins, polyamide-based resins, polyimide-based resins, polyolefin-based resins, polyarylate-based resins, polyvinyl alcohol-based resins, polyvinyl chloride-based resins, and polyvinylidene chloride-based resins.

[0120] In one embodiment, the first protective layer may have an in-plane retardation of 10 nanometers or less than 10 nanometers (e.g., 0 nanometers to 5 nanometers) at a wavelength of 550 nanometers. Within this range, the first protective layer does not affect the effect of reducing reflectivity at the lateral sides of the laminate.

[0121] For a polarizing plate in which a laminate including only a negative A layer and a positive A layer serves as a retardation layer, it may be difficult to achieve a reflectivity of less than 2.5% at the lateral sides. Specifically, when each of the negative A layer and the positive A layer is a liquid crystal layer, when the polarizing plate is placed under high temperature / high humidity conditions for a long period of time, iodine may elute from the polarizing plate, thus contaminating the liquid crystal layer and the panel. As described below, a negative C layer that exhibits out-of-plane retardation at a wavelength of 550 nanometers is stacked between the laminate of the negative A layer and the positive A layer and the polarizer, so that the polarizing plate can easily achieve a maximum reflectivity of less than 2.5% at the lateral sides, and also prevent contamination of the liquid crystal layer and the panel due to the elution of iodine from the polarizer even when the polarizing plate is placed under high temperature / high humidity conditions for a long period of time.

[0122] Negative C layer

[0123] The negative C layer has an out-of-plane retardation of 20 nanometers to 60 nanometers at a wavelength of 550 nanometers. Within this range, the negative C layer can be sandwiched between the polarizer and the negative A layer so that the polarizing plate can achieve a maximum reflectivity of less than 2.5% at the lateral sides. Preferably, the negative C layer has an out-of-plane retardation of 30 nanometers to 40 nanometers.

[0124] Specifically, as calculated according to Equation E, when the laminate of the positive A layer and the negative A layer has a linear retardation (R L ) of 120 nanometers to 180 nanometers, preferably 130 nanometers to 170 nanometers, at a wavelength of 550 nanometers, the negative C layer having an out-of-plane retardation of 20 nanometers to 60 nanometers at a wavelength of 550 nanometers enables the polarizing plate to easily achieve a maximum reflectivity of less than 2.5% at the lateral sides.

[0125] Figure 3 It is a graph showing that the maximum reflectance (Y-axis, unit: %) at the lateral side (60°) changes with the Rth of the negative C layer (X-axis, unit: nanometer).

[0126] Referring to Figure 3 , it can be confirmed that when the negative C layer has an out-of-plane retardation of 20 to 60 nanometers at a wavelength of 550 nanometers, the polarizing plate can achieve a maximum reflectance of less than 2.5% at the lateral side. On the contrary, it can be confirmed that when the negative C layer has an out-of-plane retardation of less than 20 nanometers or more than 60 nanometers at a wavelength of 550 nanometers, the polarizing plate cannot achieve a maximum reflectance of less than 2.5% at the lateral side. Specifically, compared with the maximum reflectance of the polarizing plate when the negative C layer has an out-of-plane retardation of 10 nanometers at a wavelength of 550 nanometers, when the negative C layer has an out-of-plane retardation of 20 nanometers at a wavelength of 550 nanometers, the maximum reflectance of the polarizing plate at the lateral side is significantly reduced. In addition, compared with the maximum reflectance of the polarizing plate when the negative C layer has an out-of-plane retardation of 70 nanometers, when the negative C layer has an out-of-plane retardation of 60 nanometers at a wavelength of 550 nanometers, the maximum reflectance of the polarizing plate at the lateral side is significantly reduced.

[0127] The negative C layer has a front in-plane retardation of 0 to 10 nanometers (such as 0 nanometer, 1 nanometer, 2 nanometers, 3 nanometers, 4 nanometers, 5 nanometers, 6 nanometers, 7 nanometers, 8 nanometers, 9 nanometers or 10 nanometers), preferably 0 to 5 nanometers at a wavelength of 550 nanometers. Within this range, the effects of the present invention can be easily achieved.

[0128] The negative C layer is a retardation layer that satisfies the following refractive index relationship: nx≒ny>nz.

[0129] In one embodiment, as calculated according to Equation 1, the negative C layer may have a ratio of 0.0005 nm / nm to 0.003 nm / nm. Within this range, the negative C layer enables the polarizing plate to easily achieve a reflectance of less than 2.5% at the lateral sides. For example, as calculated according to Equation 1, the negative C layer may have a ratio of 0.0005 nm / nm, 0.0006 nm / nm, 0.0007 nm / nm, 0.0008 nm / nm, 0.0009 nm / nm, 0.001 nm / nm, 0.0011 nm / nm, 0.0012 nm / nm, 0.0013 nm / nm, 0.0014 nm / nm, 0.0015 nm / nm, 0.0016 nm / nm, 0.0017 nm / nm, 0.0018 nm / nm, 0.0019 nm / nm, 0.002 nm / nm, 0.0021 nm / nm, 0.0021 nm / nm, 0.0022 nm / nm, 0.0023 nm / nm, 0.0024 nm / nm, 0.0025 nm / nm, 0.0026 nm / nm, 0.0027 nm / nm, 0.0028 nm / nm, 0.0029 nm / nm or 0.003 nm / nm. Preferably, as calculated according to Equation 1, the negative C layer has a ratio of 0.001 nm / nm to 0.003 nm / nm, more preferably 0.0015 nm / nm to 0.003 nm / nm. Within this range, the negative C layer enables the polarizing plate to easily achieve a reflectance of less than 2.5% at the lateral sides and can effectively prevent iodine elution when the polarizing plate is placed under high temperature / high humidity conditions for a long period of time.

[0130] [Equation 1]

[0131] A / B,

[0132] where A is the out-of-plane retardation (unit: nm) of the negative C layer at a wavelength of 550 nm, and B is the thickness (unit: nm) of the negative C layer.

[0133] In one embodiment, the negative C layer has a water vapor transmission rate of 400 g / m²·day or less than 400 g / m²·day (e.g., 0 g / m²·day, 10 g / m²·day, 20 g / m²·day, 30 g / m²·day, 40 g / m²·day, 50 g / m²·day, 60 g / m²·day, 70 g / m²·day, 80 g / m²·day, 90 g / m²·day, 100 g / m²·day, 150 g / m²·day, 200 g / m²·day, 250 g / m²·day, 300 g / m²·day, 350 g / m²·day or 400 g / m²·day (e.g., 0 g / m²·day to 400 g / m²·day)), specifically 0 g / m²·day to 300 g / m²·day. Within this range, even when the polarizing plate is placed under high temperature / high humidity conditions for a long period of time, the negative C layer can prevent the contamination of the liquid crystal layer and the panel due to the elution of iodine from the polarizer.

[0134] The negative C layer can have a thickness of 10 μm to 80 μm (e.g., 10 μm, 15 μm, 20 μm, 25 μm, 30 μm, 35 μm, 40 μm, 45 μm, 50 μm, 55 μm, 60 μm, 65 μm, 70 μm, 75 μm or 80 μm), preferably 20 μm to 80 μm, more preferably 20 μm to 40 μm. Within this range, the negative C layer can be used in a polarizing plate.

[0135] The negative C layer can be formed of any material as long as the negative C layer can satisfy the out-of-plane retardation at a wavelength of 550 nm, the ratio of Equation 1, and the above water vapor transmission rate. In one embodiment, the negative C layer can be a non-liquid crystal layer.

[0136] Preferably, the negative C layer is a film or coating containing a polymer exhibiting positive intrinsic birefringence. Here, positive intrinsic birefringence means that the refractive index increases in the longitudinal direction (MD).

[0137] In one embodiment, the negative C layer can be formed of a cellulose resin including triacetyl cellulose (TAC), etc., or a norbornene resin including cycloolefin polymer (COP), cycloolefin copolymer (COC), etc.

[0138] The negative C layer can be directly formed on the polarizer with no adhesive layer or bonding layer between the negative C layer and the polarizer, or can be bonded to the polarizer via an adhesive layer or bonding layer between the negative C layer and the polarizer.

[0139] The negative C layer can be formed by a solution casting method using a composition containing a polymer exhibiting positive intrinsic birefringence. In the solution casting method, the negative C layer can be formed by dissolving a polymer exhibiting positive intrinsic birefringence and an additive in a solvent, and then casting the prepared solution onto a substrate. The negative C layer can be obtained after removing the solvent. Thus, as described above, the negative C layer can easily achieve out-of-plane retardation at a wavelength of 550 nm and the ratio of Equation 1.

[0140] As an alternative, as described above, by changing the degree of polymerization or the degree of substitution of a cellulose resin (e.g., cellulose ester), the negative C layer can easily achieve out-of-plane retardation at a wavelength of 550 nm and the ratio of Equation 1.

[0141] The stack of the negative C layer, the negative A layer, and the positive A layer can have a thickness ratio of 95% or more than 95% (e.g., 95%, 96%, 97%, 98%, 99%, 100%, or 98% to 100% (e.g., 100%)) of the thickness of the retardation layer stacked on the lower surface of the polarizer. Within this range, the polarizing plate can ensure improved processability. Preferably, only the stack of the negative C layer, the negative A layer, and the positive A layer is stacked on the lower surface of the polarizer.

[0142] The stack of the negative C layer, the negative A layer, and the positive A layer can have a thickness ratio of 80% or more than 80% (e.g., 80%, 85%, 90%, 95%, 100%, or 80% to 100%) of the total thickness of the retardation layer and the first protective layer stacked on the lower surface of the polarizer. Within this range, the polarizing plate can ensure improved processability. Preferably, only the stack of the negative C layer, the negative A layer, and the positive A layer is stacked on the lower surface of the polarizer.

[0143] The polarizing plate may further include a second protective layer on the upper surface of the polarizer. The second protective layer can be stacked on the upper surface of the polarizer singly or plurally.

[0144] Second protective layer

[0145] The second protective layer is used to protect the polarizer from the external environment while improving the mechanical strength of the polarizing plate. The second protective layer can include a protective film and / or a protective coating.

[0146] In one embodiment, the second protective layer is an optically transparent film and can be formed of at least one resin selected from, for example, cellulose-based resins including triacetyl cellulose (TAC), polyester-based resins including polyethylene terephthalate (PET), polybutylene terephthalate, polyethylene naphthalate, polybutylene naphthalate (PEN), etc., cycloolefin polymer (COP)-based resins, cycloolefin copolymer (COC)-based resins, polycarbonate-based resins, polyethersulfone-based resins, polysulfone-based resins, polyamide-based resins, polyimide-based resins, polyolefin-based resins, polyarylate-based resins, polyvinyl alcohol-based resins, polyvinyl chloride-based resins, and polyvinylidene chloride-based resins.

[0147] The polarizing plate may further include a functional coating on at least one surface of the second protective layer. For example, the functional coating may include an anti-reflection layer, a low reflectivity layer, a hard coating, an anti-fingerprint layer, an anti-glare layer, a primer layer, and similar layers.

[0148] The second protective layer may have a thickness of 5 to 70 μm, specifically 15 to 45 μm. Within this range, the second protective layer can be used in the polarizing plate.

[0149] Figure 1 and Figure 2 is a cross-sectional view of a polarizing plate according to an embodiment of the present invention.

[0150] Referring to Figure 1 , the polarizing plate may include: a polarizer (30); and a negative C layer (10), a negative A layer (20), and a positive A layer (40), which are stacked in sequence on the lower surface of the polarizer (30). Referring to Figure 2 , the polarizing plate may include: a polarizer (30); a negative C layer (10), a negative A layer (20), and a positive A layer (40), which are stacked in sequence on the lower surface of the polarizer (30); and a second protective layer (50), which is stacked on the upper surface of the polarizer (30).

[0151] The optical display device includes a polarizing plate according to the present invention. The optical display device may include an organic light emitting diode (OLED) display device and a liquid crystal display device.

[0152] In one embodiment, the OLED display device may include an organic light emitting diode panel and a polarizing plate according to the present invention stacked on the organic light emitting diode panel, and the organic light emitting diode panel includes a flexible substrate.

[0153] In another embodiment, the OLED display device may include an organic light emitting diode panel and a polarizing plate according to the present invention stacked on the organic light emitting diode panel, and the organic light emitting diode panel includes a non-flexible substrate.

[0154] Forms of implementing the present invention

[0155] Next, the present invention will be described in more detail with reference to examples. However, it should be understood that these examples are for illustration only and should not be construed as limiting the present invention in any way.

[0156] Example 1

[0157] A polarizing plate having a total light transmittance of 45% was prepared by stretching a polyvinyl alcohol film (PS#60, pre-stretched thickness: 60 μm, Nippon Kuraray Co., Ltd.) in an iodine aqueous solution at 55°C to 6 times the initial thickness of the polyvinyl alcohol film in the longitudinal direction of the polarizing plate.

[0158] A positive A layer (QLAA218, FUJI Co., Ltd.), a negative A layer (QLAB218, FUJI Co., Ltd.), and a negative C layer (SDI Co., Ltd.) were prepared.

[0159] A polarizing plate including a laminate of a TAC film, a polarizer, a negative C layer, a negative A layer, and a positive A layer was prepared by sequentially stacking the negative C layer, the negative A layer, and the positive A layer on the lower surface of the polarizer through an adhesive, and then bonding a TAC film (KC4UX, KONICA Co., Ltd.) to the upper surface of the polarizer.

[0160] The positive A layer exhibits positive wavelength dispersion characteristics and is a nematic liquid crystal layer. In addition, the positive A layer has a front in-plane retardation of 120 nm and an out-of-plane retardation of 60 nm at a wavelength of 550 nm, and a biaxiality of 1; and the slow axis of the positive A layer is inclined at an angle of 77.5° with respect to the light transmission axis of the polarizer.

[0161] The negative A layer exhibits positive wavelength dispersion characteristics and is a discotic liquid crystal layer. In addition, the negative A layer has a front in-plane retardation of 240 nm and an out-of-plane retardation of -120 nm at a wavelength of 550 nm, and a biaxiality of 0; and the slow axis of the negative A layer is inclined at an angle of 17.5° with respect to the light transmission axis of the polarizer.

[0162] The laminate of the positive A layer and the negative A layer exhibits negative wavelength dispersion characteristics and has an in-plane retardation R of 151.5 nm at a wavelength of 550 nm L .

[0163] The negative C layer is a non-liquid crystal layer and is formed of a cycloolefin copolymer (COC) film. According to Equation 1, the negative C layer has a front in-plane retardation of 0 nm and an out-of-plane retardation of 40 nm at a wavelength of 550 nm, a water vapor transmission rate of 35 g / m²·day, and a ratio of 0.002 nm / nm.

[0164] Examples 2 to 4

[0165] A polarizing plate was prepared in the same manner as in Example 1, except that a cycloolefin copolymer (COC) film was used as the negative C layer, and the negative C layer having the specifications listed in Table 1 was prepared by adjusting the drying temperature and / or flow rate and / or thickness during the preparation of the COC film.

[0166] Examples 5 and 6

[0167] A polarizing plate was prepared in the same manner as in Example 1, except that a triacetyl cellulose (TAC) film corresponding to a non-liquid crystal layer was used as the negative C layer, and the negative C layer having the specifications listed in Table 1 was prepared by adjusting the drying temperature and / or flow rate and / or thickness during the preparation of the TAC film.

[0168] Comparative Example 1

[0169] A polarizing plate was prepared in the same manner as in Example 1, except that a TAC film, a polarizing plate, a negative A layer, and a positive A layer were sequentially stacked without stacking the negative C layer.

[0170] Comparative Examples 2 and 4 to 7

[0171] A polarizing plate was prepared in the same manner as in Example 1, except that a cycloolefin copolymer (COC) film was used as the negative C layer, and the negative C layer having the specifications listed in Table 1 was prepared by adjusting the drying temperature and / or flow rate and / or thickness during the preparation of the COC film.

[0172] Comparative Example 3

[0173] A polarizing plate was prepared in the same manner as in Example 1, except that a TAC film, a polarizing plate, a negative C layer, a positive A layer, and a negative A layer were sequentially stacked.

[0174] Re, Rth, and NZ of each of the retardation layers were measured at a wavelength of 550 nm using an Axiscan.

[0175] The following properties of the polarizing plates prepared in the examples and comparative examples were evaluated, and the evaluation results are shown in Table 1.

[0176] (1) Prevention of iodine elution: The polarizing plates prepared in the examples and comparative examples were placed in a chamber under high temperature / high humidity conditions (60 °C and 90% RH) for 250 hours, and the edge portions of the polarizing plates were observed through a microscope to compare the degree of iodine elution. A polarizing plate that was completely discolored to purple due to iodine elution was rated as "poor", a polarizing plate that was slightly discolored to purple was rated as "good", and a polarizing plate that was not discolored was rated as "very good".

[0177] (2) Maximum reflectance at the lateral side (incident angle: 60°): The reflectance of each of the polarizing plates prepared in the examples and comparative examples was measured in all directions except the initial reflection by the simulation program Techwiz1D (Sanai System Co., Ltd., Korea) to calculate the maximum reflectance of each of the polarizing plates in the direction in which the reflectance of the external light entering the polarizing plate becomes maximum.

[0178] [Table 1]

[0179]

[0180] [Table 2]

[0181]

[0182] As shown in Table 1, the polarizing plate according to the present invention achieves a very low reflectance at the lateral side (i.e., a maximum reflectance of less than 2.5%), and good black visibility, and minimizes the contamination of the liquid crystal layer and / or the panel caused by the elution of iodine from the polarizing plate even when placed under high temperature / high humidity conditions for a long period of time.

[0183] In contrast, as shown in Table 2, the polarizing plate of the comparative example suffers from the contamination of the liquid crystal layer and / or the panel due to the elution of iodine from the polarizer and / or cannot provide a very low reflectance at the lateral side (i.e., a maximum reflectance of less than 2.5%) when placed under high temperature / high humidity conditions for a long period of time.

[0184] It should be understood that various modifications, changes, alterations and equivalent embodiments can be made by those skilled in the art without departing from the spirit and scope of the present invention.

Claims

1. A polarizing plate, comprising: Polarizer; and a retardation layer stacked on the lower surface of the polarizer, wherein the retardation layer includes a negative C layer, a negative A layer, and a positive A layer stacked in sequence on the lower surface of the polarizer, and the negative C layer has an out-of-plane retardation of 20 nanometers to 60 nanometers at a wavelength of 550 nanometers.

2. The polarizing plate according to claim 1, wherein the negative C layer has a front in-plane retardation of 0 nanometers to 10 nanometers at a wavelength of 550 nanometers.

3. The polarizing plate according to claim 1, wherein, as calculated according to Equation 1, the negative C layer has a ratio of 0.0005 nanometer / nanometer to 0.003 nanometer / nanometer: A / B, ----(1) (where A is the out-of-plane retardation (unit: nanometer) of the negative C layer at a wavelength of 550 nanometers, and B is the thickness (unit: nanometer) of the negative C layer).

4. The polarizing plate according to claim 1, wherein the negative C layer has a water vapor transmission rate of 400 grams per square meter per day or less than 400 grams per square meter per day.

5. The polarizing plate according to claim 1, wherein the negative C layer is a film or coating containing a polymer exhibiting positive intrinsic birefringence.

6. The polarizing plate according to claim 1, wherein the negative C layer is formed of triacetyl cellulose, cycloolefin polymer, or cycloolefin copolymer resin.

7. The polarizing plate according to claim 1, wherein the stack of the negative C layer, the negative A layer, and the positive A layer has a thickness ratio to the retardation layer of 95% or greater than 95%.

8. The polarizing plate according to claim 1, wherein the stack of the negative A layer and the positive A layer has negative wavelength dispersion characteristics.

9. The polarizing plate according to claim 1, wherein the stack of the negative A layer and the positive A layer has a linear retardation of 120 nanometers to 180 nanometers at a wavelength of 550 nanometers.

10. The polarizing plate according to claim 1, wherein the positive A layer has a lower front in-plane retardation than the negative A layer at a wavelength of 550 nanometers.

11. The polarizing plate according to claim 10, wherein the positive A layer has a front in-plane retardation of 100 nanometers to 140 nanometers at a wavelength of 550 nanometers, and the negative A layer has a front in-plane retardation of 200 nanometers to 280 nanometers at a wavelength of 550 nanometers.

12. The polarizing plate according to claim 1, wherein the slow axis of the positive A layer is inclined at an angle of 55° to 65° with respect to the slow axis of the negative A layer.

13. The polarizing plate according to claim 1, wherein the slow axis of the positive A layer is inclined at an angle of 70° to 85° with respect to the light transmission axis of the polarizer, and the slow axis of the negative A layer is inclined at an angle of 10° to 25° with respect to the light transmission axis of the polarizer.

14. The polarizing plate according to claim 1, wherein each of the positive A layer and the negative A layer is a liquid crystal layer.

15. The polarizing plate according to claim 14, wherein the positive A layer is a nematic liquid crystal layer, and the negative A layer is a discotic liquid crystal layer.

16. The polarizing plate according to claim 1, further comprising: A second protective layer is stacked on the upper surface of the polarizer.

17. An optical display device includes a polarizing plate according to any one of claims 1 to 16.

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