Polarizing plate and optical display device

Abstract

Provided is a polarizing plate including a polarizer and a retardation layer laminated on a lower surface of the polarizer, wherein the retardation layer has a maximum ratio of 1.1 to 1.8 and a minimum ratio of 0.3 to 0.7 as defined in Formula 1. [Formula 1] Ratio = B / A (in Formula 1, A is the front retardation (unit: nm) of the retardation layer at a wavelength of 550 nm, and B is the tilt retardation (unit: nm) measured by rotating the retardation layer by +60° or -60° around the fast axis of the retardation layer at a wavelength of 550 nm).

Description

[Technical Field]

[0001] The present invention relates to a polarizing plate and an optical display device including the same. [Background technology]

[0002] A polarizer may be used in an organic light emitting diode display device. The polarizer can reduce the reflectance of reflected external light and realize an anti-reflection function. The polarizer may be preferable because it can significantly improve screen quality by improving the black visibility from the front.

[0003] The polarizing plate may include a polarizer and a retardation layer. Generally, the retardation layer may be configured with two retardation layers, a half wave plate (HWP) layer and a quarter wave plate (QWP) layer. Compared to conventional two-layer retardation layers, the use of a single retardation layer may improve processability and significantly reduce reflectance at the front and side surfaces.

[0004] The background art of the present invention is disclosed in Korean Patent Publication No. 10-2013-0103595 and the like. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Korean Patent Publication No. 10-2013-0103595 Summary of the Invention [Problem to be solved by the invention]

[0006] An object of the present invention is to provide a polarizing plate that significantly reduces the reflectance at the front and side surfaces and has a low difference in reflectance between the front and side surfaces, thereby achieving an excellent effect of uniforming the screen image between the front and side surfaces.

[0007] Another object of the present invention is to provide a polarizing plate that includes a single-sheet liquid crystal retardation layer and has the above-mentioned excellent effects.

[0008] A further object of the present invention is to provide a polarizing plate that includes a single O-plate type liquid crystal retardation layer and has excellent effects as described above.

[0009] A further object of the present invention is to provide a polarizing plate which is thin, has a simplified manufacturing process, and is economical. [Means for solving the problem]

[0010] One aspect of the present invention is a polarizing plate.

[0011] 1. A polarizing plate includes a polarizer and a retardation layer laminated on a lower surface of the polarizer, wherein the retardation layer has a maximum ratio of 1.1 to 1.8 in the following formula 1 and a minimum ratio of 0.3 to 0.7 in the following formula 1:

[0012] [Formula 1] Ratio=B / A (In the above formula 1, A is the front retardation (unit: nm) of the retardation layer at a wavelength of 550 nm, B is the tilt retardation (unit: nm) measured by rotating the retardation layer by +60° or −60° around the fast axis of the retardation layer at a wavelength of 550 nm.

[0013] In 2.1, A in the above formula 1 can be 110 nm to 170 nm.

[0014] In 3.1-2, the maximum value of B in the above formula 1 can be 120 nm to 310 nm, and the minimum value can be 20 nm to 120 nm.

[0015] In 4.1-3, when the retardation layer is rotated by +60° or −60° around the fast axis of the retardation layer at a wavelength of 550 nm as the rotation axis, the difference between the maximum and minimum values ​​of the tilt retardation can be 45 nm or more.

[0016] In 5.1-4, the retardation layer may have a tilt retardation of 130 nm to 240 nm when the retardation layer is rotated by +60° or −60° around the slow axis of the retardation layer at a wavelength of 550 nm as the rotation axis.

[0017] In 6.1-5, the retardation layer may have reverse wavelength dispersion.

[0018] In 7.1-6, the retardation layer may have an asymmetrical shape in a graph showing the tilt retardation measured with the fast axis of the retardation layer as the rotation axis, where the X axis represents the rotation angle (°) of a retardation measuring device and the Y axis represents the relative value of the tilt retardation (nm) to the front retardation (nm) (tilt retardation / front retardation).

[0019] In 8.1-7, the retardation layer may have a symmetrical shape in a graph showing the tilt retardation measured with the slow axis of the retardation layer as the rotation axis, in which the X axis represents the rotation angle (°) of a retardation measuring device and the Y axis represents the relative value of the tilt retardation (nm) to the front retardation (nm) (tilt retardation / front retardation).

[0020] In 9.1-8, the slow axis of the retardation layer may form an angle of 40° to 50° when the light transmission axis of the polarizer is 0°.

[0021] In 10.1-9, the retardation layer may include an O-plate type liquid crystal retardation layer.

[0022] In 11.10, when one surface of the O-plate type liquid crystal retardation layer in the thickness direction is a top surface and the other surface opposite to the top surface is a bottom surface, the liquid crystal tilt angle at the top surface may be larger than the liquid crystal tilt angle at the bottom surface.

[0023] In 12.11, the liquid crystal tilt angle on the TOP surface may be 30° to 90°, and the liquid crystal tilt angle on the BOTTOM surface may be 0° to 10°.

[0024] In 13.11-12, the top surface may be disposed closer to the polarizer than the bottom surface.

[0025] In 14.11-13, the absolute value of the difference between the liquid crystal tilt angle at the TOP surface and the liquid crystal tilt angle at the BOTTOM surface may be 30° to 90°.

[0026] In 15.10-14, the O-plate type liquid crystal retardation layer may be a nematic liquid crystal layer.

[0027] In 16.10-15, the retardation layer may consist of only the O-plate type liquid crystal retardation layer.

[0028] In 17.10-16, a first protective layer may be further included on the lower surface of the polarizer.

[0029] In 18.17, the first protective layer may have an in-plane retardation of 10 nm or less at the front surface at a wavelength of 550 nm.

[0030] In 19.1-18, the polarizer may further include at least one of a second protective layer laminated on an upper surface and a third protective layer laminated on a lower surface.

[0031] One aspect of the present invention is an optical display device.

[0032] An optical display device includes the polarizing plate of the present invention. [Effects of the Invention]

[0033] The present invention can provide a polarizing plate that significantly reduces the reflectance at the front and side surfaces and has a low difference in reflectance between the front and side surfaces, thereby providing an excellent effect of uniforming the screen image between the front and side surfaces.

[0034] The present invention can provide a polarizing plate that includes a single-sheet type liquid crystal retardation layer and has excellent effects as described above.

[0035] The present invention can provide a polarizing plate that includes a single O-plate type liquid crystal retardation layer and has excellent effects as described above.

[0036] The present invention can provide a polarizing plate that is thin, has a simplified manufacturing process for the polarizing plate, and is economical. [Brief explanation of the drawings]

[0037] [Figure 1] FIG. 2 is an exploded view of a retardation layer and a polarizer, which is an example of a retardation layer. [Figure 2] FIG. 1 is a conceptual diagram of a liquid crystal tilt angle. [Figure 3] This is a diagram showing the tendency of phase difference depending on the rotation angle when the retardation layer is rotated around the fast axis and the slow axis of the retardation layer. In Fig. 3, the X axis represents the rotation angle (unit: °) of the retardation measurement device, and the Y axis represents the relative value (tilt phase difference / front phase difference) of the tilt phase difference (unit: nm) to the front phase difference (unit: nm). In Fig. 3, the solid line represents the relative value when the fast axis is the rotation axis, and the dashed line represents the relative value when the slow axis is the rotation axis. [Figure 4] FIG. 1 is a cross-sectional view of a polarizing plate according to an embodiment of the present invention. [Figure 5] FIG. 1 is a cross-sectional view of a polarizing plate according to an embodiment of the present invention. [Figure 6] FIG. 1 is a cross-sectional view of a polarizing plate according to an embodiment of the present invention. [Figure 7] FIG. 1 is a cross-sectional view of a polarizing plate according to an embodiment of the present invention. [Figure 8] FIG. 1 is a cross-sectional view of a polarizing plate according to an embodiment of the present invention. [Figure 9] FIG. 1 is a cross-sectional view of a polarizing plate according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0038] The present invention will now be described in detail by way of example with reference to the accompanying drawings, so that those skilled in the art can easily carry out and practice the invention. As the present invention may be embodied in various different forms, it is not limited to the embodiments set forth herein.

[0039] The terms used herein are merely used to describe exemplary embodiments and are not intended to limit the present invention. The singular expressions include the plural expressions unless the context clearly indicates otherwise.

[0040] In the drawings, parts that are not relevant to the description are omitted in order to clearly explain the present invention, and the same names are used for the same or similar components throughout the specification. The length and size of each component in the drawings are for the purpose of explaining the present invention, and the present invention is not limited to the length and size of each component shown in the drawings.

[0041] In this specification, "upper" and "lower" are defined based on the drawings, and "upper" may be changed to "lower" and "lower" may be changed to "upper" depending on the viewing point.

[0042] For the optical elements in this specification, the "front in-plane retardation (Re)" is expressed by the following formula A, the "degree of biaxiality (NZ)" is expressed by the following formula B, and the "thickness direction retardation (Rth)" is expressed by the following formula C.

[0043] [Formula A] Re=(nx-ny)×d [Formula B] NZ=(nx-nz) / (nx-ny) [Formula C] Rth=((nx+ny) / 2-nz)×d (In the above formulas A to C, nx, ny, and nz are the refractive indices of the optical element in the slow axis direction, fast axis direction, and thickness direction, respectively, at the measurement wavelength, and d is the thickness of the retardation layer (unit: nm).)

[0044] The optical element may be a retardation layer, a protective layer, or a laminate thereof. Unless otherwise specified, the retardation, the degree of biaxiality, and the thickness direction retardation refer to values ​​measured by transmitting light in the normal direction to the in-plane direction of the optical element.

[0045] In this specification, the in-plane axis with the highest refractive index is defined as the “slow axis,” and the in-plane axis with the lowest refractive index is defined as the “fast axis.” In one specific example, the slow axis and the fast axis may be substantially perpendicular to each other, but are not limited to this.

[0046] In this specification, when a numerical range is indicated, "X to Y" means X or more and Y or less (X≦and≦Y).

[0047] The polarizing plate of the present invention includes a polarizer and a retardation layer laminated on the lower surface of the polarizer. When the polarizing plate is applied to an optical display device, the retardation layer is disposed between the polarizer and a panel for the optical display device. That is, the retardation layer may be disposed on the light incident surface of the polarizer when viewed with respect to light emitted from a light-emitting element such as an OLED. The optical display device may be a light-emitting element display device such as an OLED.

[0048] The retardation layer has a maximum ratio of 1.1 to 1.8 in the following formula 1, and a minimum ratio of 0.3 to 0.7 in the following formula 1.

[0049] [Formula 1] Ratio=B / A (In the above formula 1, A is the in-plane retardation (unit: nm) of the front surface of the retardation layer at a wavelength of 550 nm, B is the tilt retardation (unit: nm) measured by rotating the retardation layer by +60° or −60° around the fast axis of the retardation layer at a wavelength of 550 nm as the rotation axis.

[0050] The ratio of Equation 1 was devised to determine the conditions that the retardation layer must have so that the reflectance reduction effect at the front and side surfaces is significantly excellent when the polarizer is applied to the optical display device. Therefore, the polarizer of the present invention can be used as an excellent anti-reflection polarizer in light emitting device displays, such as organic light emitting device displays, inorganic light emitting device displays, and organic / inorganic light emitting device displays.

[0051] As will be described below, the ratio of Equation 1 makes it possible to determine whether a significant effect of reducing reflectance can be achieved at the front and side of a polarizer when the retardation layer is a single-layer (single-layer) O-plate type liquid crystal retardation layer. In addition, the ratio of Equation 1 was devised to determine the conditions for realizing the effect of reducing reflectance at the front and side and the effect of minimizing the difference in reflectance between the front and side when the retardation layer has reverse wavelength dispersion.

[0052] The in-plane retardation of the retardation layer at the front side is a single value. On the other hand, the tilted retardation measured by rotating the retardation layer by +60° or -60° around the fast axis of the retardation layer has a maximum value and a minimum value. The ratio in Equation 1 is calculated based on the in-plane retardation value of the retardation layer at the front side and the tilted retardation value of the retardation layer.

[0053] When the maximum value of the ratio in Equation 1 is 1.1 to 1.8 and the minimum value of the ratio in Equation 1 is 0.3 to 0.7, the polarizer has a significantly excellent effect of reducing reflectance at the front and side, and the difference in reflectance measured at the front and side is reduced, so that the screen image between the front and side of the display device may become more uniform. For example, the maximum value may be 1.1, 1.15, 1.2, 1.25, 1.3, 1.35, 1.4, 1.45, 1.5, 1.55, 1.6, 1.65, 1.7, 1.75, 1.8, 1.2 to 1.75, 1.2 to 1.7, or 1.3 to 1.6. For example, the minimum value may be 0.3, 0.35, 0.4, 0.45, 0.5, 0.55, 0.6, 0.65, 0.7, 0.3 to 0.65, 0.35 to 0.65, 0.4 to 0.6.

[0054] The maximum value of the ratio in Formula 1, 1.1 to 1.8, and the minimum value of the ratio in Formula 1, 0.3 to 0.7, can be achieved by adjusting the solvent evaporation rate (e.g., air volume) and / or drying temperature in a coating layer formed from a composition for an O-plate type liquid crystal retardation layer, and / or the amount of UV light irradiation during photo-curing of the coating layer, when preparing a retardation layer, particularly an O-plate type liquid crystal retardation layer, as will be described in detail below.

[0055] Each component of the polarizing plate of the present invention will be described in detail below.

[0056] Polarizer A polarizer can convert incident natural light or polarized light into linearly polarized light in a specific direction. The polarizer may be manufactured from a polymer film mainly composed of a polyvinyl alcohol-based resin. For example, the polarizer may be manufactured by dyeing the polymer film with iodine or a different color dye and stretching it in the MD (machine direction), or by forming a polyene bond through a dehydration reaction using an acid catalyst. In one specific example, the polarizer may be manufactured through a swelling process, a dyeing step, and a stretching step of the polyvinyl alcohol-based film, or alternatively through one or more of a complementary color step and a crosslinking step.

[0057] The polarizer has a light contraction axis and a light transmission axis in the in-plane direction, and the light absorption axis may be in the MD of the polarizer, and the light transmission axis may be in the TD (transverse direction) of the polarizer.

[0058] The polarizer may have a light transmittance of 40% or more, for example, 40% to 47%, and a polarization degree of 95% or more, for example, 95% to 99.9999%. Within these ranges, the polarizer can enhance anti-reflection performance when combined with a retardation layer. The "light transmittance" and "polarization degree" are values ​​measured at wavelengths of 380 nm to 780 nm, reflecting the luminosity in the wavelength range, and may be measured by a conventional method known to those skilled in the art.

[0059] The polarizer may have a thickness of 2 μm to 30 μm, specifically 4 μm to 25 μm, and in this range, the polarizer can be used in a polarizing plate.

[0060] The polarizer may be laminated directly to the retardation layer or protective layer described below without using an adhesive layer or a sticking layer, or may be laminated via an adhesive layer or a sticking layer.

[0061] retardation layer The retardation layer has a maximum ratio of 1.1 to 1.8 and a minimum ratio of 0.3 to 0.7. Within this range, the polarizer can significantly reduce reflectance at the front and side surfaces, and can achieve excellent image uniformity due to the low reflectance difference between the front and side surfaces. In one specific example, the maximum value can be 1.2 to 1.75, 1.2 to 1.7, or 1.3 to 1.6, and the minimum value can be 0.3 to 0.65, 0.35 to 0.65, or 0.4 to 0.6.

[0062] In one embodiment, the retardation layer may have a ratio of Formula 1 of 0.3 to 1.8, for example, 0.3, 0.35, 0.4, 0.45, 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9, 0.95, 1.0, 1.05, 1.1, 1.15, 1.2, 1.25, 1.3, 1.35, 1.4, 1.45, 1.5, 1.55, 1.6, 1.65, 1.7, 1.75, or 1.8.

[0063] A and B in the ratio of Equation 1 will be described in detail. A and B are values ​​measured at a wavelength of 550 nm and may be measured using a retardation measurement device, such as an AXOSCAN. An AXOSCAN is commonly used by those skilled in the art to measure retardation.

[0064] A is the in-plane retardation at the front side measured when the retardation layer is mounted on a retardation measurement device and light is incident in the normal direction to the in-plane direction of the retardation layer.

[0065] B is determined from the retardation value measured after mounting the retardation layer on a retardation measurement device and rotating the retardation layer by +60° or -60° around the fast axis of the retardation layer as the rotation axis. +60° is defined as clockwise around the rotation axis, and -60° is defined as counterclockwise around the rotation axis, or +60° is defined as counterclockwise around the rotation axis, and -60° is defined as clockwise around the rotation axis.

[0066] In one embodiment, A in Formula 1 may be 110 nm to 170 nm, for example, 110 nm, 115 nm, 120 nm, 125 nm, 130 nm, 135 nm, 140 nm, 145 nm, 150 nm, 155 nm, 160 nm, 165 nm, 170 nm, 120 nm to 160 nm, or 130 nm to 150 nm. Within this range, the maximum and minimum ranges of the ratio in Formula 1 of the present invention can be easily reached, and the retardation layer can be easily manufactured.

[0067] In one embodiment, in B of Equation 1, the maximum value is 120 nm to 310 nm, for example, 120 nm, 130 nm, 140 nm, 150 nm, 160 nm, 170 nm, 180 nm, 190 nm, 200 nm, 210 nm, 220 nm, 230 nm, 240 nm, 250 nm, 260 nm, 270 nm, 280 nm, 290 nm, 300 nm, 310 nm, 130 nm to 29 The range of the maximum and minimum values ​​of the ratio of the formula 1 of the present invention can be easily achieved within this range, and the retardation layer can be easily manufactured.

[0068] In one specific example, when the retardation layer is rotated by +60° or −60° around the fast axis of the retardation layer at a wavelength of 550 nm as the rotation axis, the difference between the maximum value and the minimum value of the tilt retardation is 45 nm or more, for example, 45 nm to 250 nm, 45 nm, 50 nm, 55 nm, 60 nm, 65 nm, 70 nm, 75 nm, 80 nm, 85 nm, 90 nm, 95 nm, 100 nm, 105 nm, 110 nm nm, 115 nm, 120 nm, 125 nm, 130 nm, 135 nm, 140 nm, 145 nm, 150 nm, 155 nm, 160 nm, 165 nm, 170 nm, 175 nm, 180 nm, 185 nm, 190 nm, 195 nm, 200 nm, 205 nm, 210 nm, 215 nm, 220 nm, 225 nm, 230 nm, 235 nm, 240 nm, 245 nm, and 250 nm. Within these ranges, the effects of the present invention can be easily realized.

[0069] When the retardation layer is rotated by +60° or -60° with the slow axis of the retardation layer at a wavelength of 550 nm as the rotation axis, the tilt retardation may be 130 nm to 240 nm, for example, 130 nm, 135 nm, 140 nm, 145 nm, 150 nm, 155 nm, 160 nm, 165 nm, 170 nm, 175 nm, 180 nm, 185 nm, 190 nm, 195 nm, 200 nm, 205 nm, 210 nm, 215 nm, 220 nm, 225 nm, 230 nm, 235 nm, 240 nm, 140 nm to 220 nm, or 150 nm to 200 nm. Within this range, the effects of the present invention can be easily realized.

[0070] The retardation layer may have inverse wavelength dispersion. Through this, the polarizing plate can easily provide the effect of reducing the reflectance on the front and side surfaces. The "inverse wavelength dispersion" means that the retardation layer satisfies Re(450) < Re(550) and Re(550) < Re(650). Re(450), Re(550), and Re(650) are the in-plane retardations of the front surface of the retardation layer at wavelengths of 450 nm, 550 nm, and 650 nm, respectively.

[0071] In one specific example, for the retardation layer, Re(450) / Re(550) may be less than 1, for example, 0.82 or more and less than 1, 0.82, 0.83, 0.84, 0.85, 0.86, 0.87, 0.88, 0.89, 0.9, 0.91, 0.92, 0.93, 0.94, 0.95, 0.96, 0.97, 0.98, 0.99. In one specific example, for the retardation layer, Re(650) / Re(550) may be more than 1, for example, more than 1 and 1.18 or less, 1.01, 1.02, 1.03, 1.04, 1.05, 1.06, 1.07, 1.08, 1.09, 1.10, 1.11, 1.12, 1.13, 1.14, 1.15, 1.16, 1.17, 1.18. Within this range, the wavelength dispersion of the retardation layer of the present invention can be easily achieved.

[0072] In one specific example, the retardation layer may have a front in-plane retardation of 90 nm to 170 nm, for example, 100 nm to 160 nm, at a wavelength of 450 nm, and a front in-plane retardation of 110 nm to 200 nm, for example, 120 nm to 190 nm, at a wavelength of 650 nm.

[0073] In one specific example, the retardation layer may be a single-layer retardation layer. Here, the term "single-layer retardation layer" means that the retardation layer is composed of a single layer having the same composition, rather than a combination (or direct bonding) of two or more retardation layers having different front retardations. Thus, even when the polarizing plate of the present invention has only a single-layer retardation layer satisfying the above-mentioned Equation 1 as the retardation layer laminated on the lower surface of the polarizer, for example, between the lower surface of the polarizer and the panel for an optical display device, the polarizing plate of the present invention has an excellent effect of reducing the reflectance at the front and side surfaces and the difference in reflectance between the front and side surfaces, thereby providing a thinner polarizing plate, a simplified manufacturing process for the polarizing plate, and excellent cost-effectiveness.

[0074] In one embodiment, the retardation layer may have a thickness of 1 μm to 10 μm, for example, 2 μm to 8 μm, which can provide a thin polarizing plate.

[0075] The retardation layer may be an O-plate type liquid crystal layer. The present invention provides an O-plate type liquid crystal layer as a retardation layer, and by adjusting the maximum and minimum values ​​of the ratio of the O-plate type liquid crystal layer in Equation 1, it is possible to provide an effect of reducing the reflectance at the front and side surfaces and an effect of reducing the difference in reflectance between the front and side surfaces.

[0076] The O-plate type means that the liquid crystal compound is aligned so that the liquid crystal tilt angle of the liquid crystal compound is inclined in the thickness direction of the retardation layer, and when one surface in the thickness direction of the retardation layer is defined as a TOP surface and the other surface opposite to the TOP surface is defined as a BOTTOM surface, the liquid crystal tilt angle gradually increases or decreases from the TOP surface to the BOTTOM surface. The "inclined direction" means a direction that is not substantially parallel and / or not substantially perpendicular to the TOP surface or BOTTOM surface of the retardation layer.

[0077] FIG. 1 is a cross-sectional view of an O-plate type retardation layer, in which the liquid crystal tilt angle (θ P , θ B ) gradually decreases.

[0078] In one embodiment, the liquid crystal tilt angle at the TOP surface of the retardation layer is larger than that at the BOTTOM surface, and the liquid crystal tilt angle at the TOP surface may be 30° to 90°, for example, 30°, 35°, 40°, 45°, 50°, 55°, 60°, 65°, 70°, 75°, 80°, 85°, 90°, or 40° or more but less than 90°, and the liquid crystal tilt angle at the BOTTOM surface may be 0° to 10°, for example, 0°, 1°, 2°, 3°, 4°, 5°, 6°, 7°, 8°, 9°, 10°, 0° to 5°, or more than 0° but less than 5°.

[0079] In another embodiment, the liquid crystal tilt angle at the TOP surface of the retardation layer is smaller than the liquid crystal tilt angle at the BOTTOM surface, and the liquid crystal tilt angle at the TOP surface is 0° to 10°, for example, 0°, 1°, 2°, 3°, 4°, 5°, 6°, 7°, 8°, 9°, 10°, 0° to 5°, or more than 0° to 5°, and the liquid crystal tilt angle at the BOTTOM surface may be 30° to 90°, for example, 30°, 35°, 40°, 45°, 50°, 55°, 60°, 65°, 70°, 75°, 80°, 85°, 90°, or more than 40° but less than 90°.

[0080] In one embodiment, as shown in Fig. 1, the top surface of the retardation layer may be disposed closer to the polarizer 30 than the bottom surface. The liquid crystal tilt angle at the top surface of the retardation layer may be larger than the liquid crystal tilt angle at the bottom surface. In this case, the effect of the present invention can be more easily realized.

[0081] In one embodiment, the retardation layer may have an absolute value of the difference between the liquid crystal tilt angle at the TOP surface and the liquid crystal tilt angle at the BOTTOM surface of 30° to 90°, for example, 30°, 35°, 40°, 45°, 50°, 55°, 60°, 65°, 70°, 75°, 80°, 85°, 90°, or 40° to 80°. Within this range, the effects of the present invention can be easily realized.

[0082] In this specification, the term "liquid crystal tilt angle" may have substantially the same meaning as that defined by those skilled in the art. For example, the term "liquid crystal tilt angle" may be measured within the retardation layer and refers to the tilted alignment angle of liquid crystal in the thickness direction of the retardation layer, and the tilted alignment angle changes from the top surface to the bottom surface. When the tilted alignment angle is parallel to the top or bottom surface of the retardation layer, the liquid crystal tilt angle is defined as 0°.

[0083] The liquid crystal tilt angle may be expressed as a positive (+) or negative (-) value depending on the direction of the maximum refractive index of the liquid crystal compound relative to the surface of the layer adjacent to the retardation layer. In this specification, the liquid crystal tilt angle is described as a positive (+) value for convenience. However, the liquid crystal tilt angle can also mean a negative (-) value. For example, if the liquid crystal tilt angle is 60°, it may also mean -60°.

[0084] Referring to Figure 2, the liquid crystal tilt angle is defined as the angle between the direction of the maximum refractive index of the liquid crystal compound and one surface of the retardation layer. When the angle between the direction of the maximum refractive index of the liquid crystal compound and one surface of the layer adjacent to the retardation layer is counterclockwise, as in θ1, it is defined as a positive (+) value. On the other hand, when the angle between the direction of the maximum refractive index of the liquid crystal compound and one surface of the layer adjacent to the retardation layer is clockwise, as in θ2, it is defined as a negative (-) value.

[0085] The liquid crystal tilt angle may be measured by a conventional method known to those skilled in the art, for example, by a liquid crystal tilt angle measuring device such as AXOSCAN or KOBRA.

[0086] In one embodiment, the retardation layer may be mounted in a retardation measurement device and then rotated by +60° or −60° around the fast axis of the retardation layer as the rotation axis, resulting in asymmetric tilt retardation. This can easily achieve the above-described effects of the present invention. This will be described with reference to FIG. 3.

[0087] FIG. 3 shows the tendency of the ratio obtained by dividing the inclined retardation value by the front retardation value when the retardation layer of one specific example of the polarizing plate of the present invention is rotated by ±60° around the fast axis and the slow axis of the retardation layer as the rotation axes.

[0088] In Figure 3, the X axis represents the rotation angle (°) of the retardation measurement device, and the Y axis represents the relative value of the tilted retardation (nm) to the front in-plane retardation (nm) (tilted retardation / front retardation). In Figure 3, the solid line represents the relative value when the fast axis is the rotation axis, and the dashed line represents the relative value when the slow axis is the rotation axis. Figure 3 is the result of measuring the retardation layer used in the following examples.

[0089] Referring to FIG. 3, in the graph where the X axis represents the rotation angle (°) of the retardation measurement device and the Y axis represents the relative value of the tilted retardation (nm) to the front in-plane retardation (nm) (tilted retardation / front retardation), it can be seen that the retardation layer has asymmetrical relative values ​​measured with the fast axis as the rotation axis, while the relative values ​​measured with the slow axis as the rotation axis are symmetrical.

[0090] Although not particularly limited, FIG. 3 shows values ​​at a wavelength of 550 nm.

[0091] In one embodiment, the retarder layer may be a liquid crystal layer or a non-liquid crystal layer, for example, to provide the above-mentioned O-plate type liquid crystal retarder layer.

[0092] In one embodiment, the retardation layer may be formed from a composition containing a liquid crystal compound. For example, the retardation layer may be formed from a composition embodying nematic liquid crystal. When the retardation layer is rotated by +60° or -60° around the fast axis as the rotation axis, nematic liquid crystal easily achieves the ratio range of Equation 1 of the present invention by making the tilt retardation asymmetric as shown in Figure 3. However, even when a composition embodying nematic liquid crystal is used, a retardation layer satisfying the ratio of Equation 1 of the present invention can be manufactured only by adjusting the solvent evaporation rate (e.g., air volume) and / or drying temperature in the coating layer formed from the composition, and / or the amount of UV light irradiation during photo-curing of the coating layer.

[0093] In one embodiment, the composition embodying the nematic liquid crystal may include a polymerizable compound.

[0094] The polymerizable compound may have one or more polymerizable crosslinking groups. For example, the polymerizable crosslinking group may be an acrylate group, a methacrylate group, a vinyl group, a vinyloxy group, an epoxy group, an oxetane group, a thiol group, a maleimide group, or a modified form thereof. Specifically, the polymerizable crosslinking group may include one or more of the following chemical formulas R-1 to R-15:

[0095] [ka]

[0096] The composition may further include a liquid crystal compound. The liquid crystal compound does not have one or more polymerizable crosslinking groups, but when included in the composition, the retardation layer can be easily formed.

[0097] The composition may further include additives typically included in the formation of a liquid crystal layer, such as a photoinitiator, a surface modifier, an antioxidant, etc. The composition may include a solvent to facilitate the formation of a liquid crystal layer having a uniform surface.

[0098] The slow axis of the retardation layer, for example, the O-plate type liquid crystal retardation layer, can be 40° to 50°, for example, 40°, 41°, 42°, 43°, 44°, 45°, 46°, 47°, 48°, 49°, 50°, or 43° to 47°, when the light transmission axis of the polarizer is 0°. Within this range, the effects of the present invention can be easily realized.

[0099] A retardation layer, for example, an O-plate type liquid crystal retardation layer, may be formed using a composition containing the above-described liquid crystal compound. In the present invention, the UV light irradiation amount, drying temperature, drying air volume, etc. were adjusted during the preparation of the retardation layer so that the maximum value of the ratio in the above-described formula (1) satisfies 1.1 to 1.8 and the minimum value of the ratio in the formula (1) satisfies 0.3 to 0.7. It was confirmed that the solvent evaporation rate significantly affects the tilt angle at the top plane of the liquid crystal. It was also confirmed that the solvent evaporation rate increases with increasing drying temperature and drying air volume, and the tilt angle of the liquid crystal generally increases. The tilt angle at the bottom plane is related to the anchoring energy and can be adjusted by photoalignment or rubbing conditions. Generally, a higher anchoring energy results in a higher tilt angle at the bottom plane.

[0100] In one embodiment, the retardation layer may be the O-plate type liquid crystal retardation layer alone. This means that the lower surface of the polarizer contains only an O-plate type liquid crystal retardation layer as a retardation layer having a front in-plane retardation of more than 0 nm, for example, more than 10 nm, at a wavelength of 550 nm. In this case, the O-plate type liquid crystal retardation layer may be directly laminated on the polarizer or may be laminated on the lower surface of the polarizer via an adhesive layer or a sticking layer.

[0101] In another embodiment, a first protective layer may be further provided on the lower surface of the polarizer.

[0102] In one embodiment, the polarizing plate may include a first protective layer and an O-plate type liquid crystal retardation layer sequentially stacked on the lower surface of the polarizer.

[0103] In another embodiment, the polarizing plate may include an O-plate type liquid crystal retardation layer and a first protective layer sequentially stacked on the lower surface of the polarizer.

[0104] The first protective layer can provide additional functions to the retardation layer and / or polarizing plate. For example, the first protective layer can enhance the durability and mechanical strength of the retardation layer by complementing the thickness of a thin O-plate type liquid crystal retardation layer. Alternatively, the first protective layer can serve as a substrate film for forming an O-plate type liquid crystal retardation layer. Alternatively, the first protective layer can prevent iodine, which may be eluted from the polarizer after the polarizing plate is left at high temperature and humidity for a long period of time, from contaminating the retardation layer and / or panel.

[0105] The first protective layer is an optically transparent film, and may be a film made of one or more resins selected from the group consisting of cellulose-based resins including triacetyl cellulose (TAC) and the like, polyester-based resins including polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate (PEN), polybutylene naphthalate and the like, cyclic polyolefin-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.

[0106] In one specific example, the first protective layer may have an in-plane retardation at the front surface at a wavelength of 550 nm of 10 nm or less, for example, 0 nm, 1 nm, 2 nm, 3 nm, 4 nm, 5 nm, 6 nm, 7 nm, 8 nm, 9 nm, 10 nm, or 0 nm to 5 nm. In this range, the effect of reducing the reflectance at the front and side surfaces by the O-plate type liquid crystal retardation layer is not affected, and the effect of using the first protective layer can be obtained.

[0107] The first protective layer may have a thickness of 5 μm to 100 μm, for example, 15 μm to 45 μm, and in this range, the first protective layer can be used in a polarizing plate.

[0108] For example, the retardation layer may be formed by coating a composition containing the above-described liquid crystal compound on the first protective layer, followed by drying and curing. In this case, an alignment film may be formed on the coated surface of the first protective layer to align the liquid crystal compound. The alignment film may be formed by a conventional method known to those skilled in the art. For example, the alignment film may be an acrylic alignment film. The resulting laminate of the O-plate type liquid crystal layer and the first protective layer may be attached to a polarizer.

[0109] As another example, the retardation layer may be formed by coating a composition containing the above-described liquid crystal compound on a substrate film, followed by drying and curing. In this case, an alignment film may be formed on the coated surface of the substrate film to align the liquid crystal compound. The alignment film may be formed by a conventional method known to those skilled in the art. For example, the alignment film may be an acrylic alignment film. The manufactured O-plate type liquid crystal layer may be peeled from the substrate film and then attached to a polarizer by transfer.

[0110] An adhesive layer or a bonding layer may be laminated on the lower surface of the retardation layer, thereby allowing the polarizing plate to adhere to the panel.

[0111] The polarizing plate may further include a second protective layer (described below) on the upper surface of the polarizer. One or more second protective layers may be laminated on the upper surface of the polarizer.

[0112] 2nd protective layer The second protective layer may further have the effect of protecting the polarizer from the external environment and increasing the mechanical strength of the polarizing plate. The second protective layer may be one or more of a protective film and a protective coating layer.

[0113] In one specific example, the second protective layer is an optically transparent film, and may be a film made of one or more resins selected from the group consisting of cellulose-based materials including triacetyl cellulose (TAC) and the like, polyester-based materials including polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate (PEN), polybutylene naphthalate and the like, cyclic olefin polymer (COP)-based materials, cyclic olefin copolymer (COC)-based materials, polycarbonate-based materials, polyethersulfone-based materials, polysulfone-based materials, polyamide-based materials, polyimide-based materials, polyolefin-based materials, polyarylate-based materials, polyvinyl alcohol-based materials, polyvinyl chloride-based materials, and polyvinylidene chloride-based materials.

[0114] The second protective layer may have a front retardation of 0 nm or more, for example, 0 nm to 10,000 nm, at a wavelength of 550 nm. Within this range, the effects of the present invention can be easily achieved.

[0115] A functional coating layer may be additionally formed on at least one surface of the second protective layer, such as an anti-reflection layer, a low-reflection layer, a hard coating layer, an anti-fingerprint layer, an anti-glare layer, or a primer layer.

[0116] The second protective layer may have a thickness of 5 μm to 100 μm, for example, 15 μm to 90 μm, and within this range, the second protective layer can be used in a polarizing plate.

[0117] The polarizing plate may further include a third protective layer (described below) on the lower surface of the polarizer. One or more third protective layers may be laminated on the lower surface of the polarizer. In one specific example, the third protective layer may be disposed between the polarizer and the retardation layer, or may be disposed on the lower surface of the retardation layer.

[0118] 3rd protective layer The third protective layer is an optically transparent film, and may be a film made of one or more resins selected from the group consisting of cellulose-based resins including triacetyl cellulose (TAC) and the like, polyester-based resins including polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate (PEN), polybutylene naphthalate and the like, cyclic polyolefin-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.

[0119] In one specific example, the third protective layer may have a front retardation of 10 nm or less, for example, 0 to 5 nm, at a wavelength of 550 nm, which allows the effect of using the third protective layer to be obtained without affecting the effect of reducing the reflectance at the front and side surfaces of the O-plate type liquid crystal retardation layer.

[0120] The third protective layer may have a thickness of 5 μm to 100 μm, for example, 15 μm to 45 μm, and within this range, the third protective layer can be used in a polarizing plate.

[0121] The third protective layer may have the same or different material, retardation, and / or thickness as the first protective layer.

[0122] 4 to 9 are cross-sectional views of a polarizing plate according to an embodiment of the present invention.

[0123] The polarizing plate may include a polarizer 30 , an O-plate type liquid crystal retardation layer 10 laminated on the lower surface of the polarizer 30 , and a second protective layer 20 laminated on the upper surface of the polarizer 30 .

[0124] The polarizing plate may include a polarizer 30, a first protective layer 40 and an O-plate type liquid crystal retardation layer 10 sequentially stacked on the lower surface of the polarizer 30, and a second protective layer 20 stacked on the upper surface of the polarizer 30.

[0125] The polarizing plate may include a polarizer 30, an O-plate type liquid crystal retardation layer 10 and a first protective layer 40 sequentially stacked on the lower surface of the polarizer 30, and a second protective layer 20 stacked on the upper surface of the polarizer 30.

[0126] The polarizing plate may include a polarizer 30, a third protective layer 50 and an O-plate type liquid crystal retardation layer 10 sequentially stacked on the lower surface of the polarizer 30, and a second protective layer 20 stacked on the upper surface of the polarizer 30.

[0127] The polarizing plate may include a polarizer 30, a third protective layer 50 sequentially stacked on the lower surface of the polarizer 30, an O-plate type liquid crystal retardation layer 10, a first protective layer 40, and a second protective layer 20 stacked on the upper surface of the polarizer 30.

[0128] The polarizing plate may include a polarizer 30, a third protective layer 50 sequentially stacked on the lower surface of the polarizer 30, a first protective layer 40, an O-plate type liquid crystal retardation layer 10, and a second protective layer 20 stacked on the upper surface of the polarizer 30.

[0129] Although not shown in FIGS. 4 to 9, the O-plate type liquid crystal retardation layer has one surface as a top surface in the thickness direction and another surface opposite to the top surface as a bottom surface, and when the liquid crystal tilt angle at the top surface is larger than the liquid crystal tilt angle at the bottom surface, the top surface of the O-plate type liquid crystal retardation layer may be disposed closer to the polarizer than the bottom surface, or the bottom surface may be disposed closer to the polarizer than the top surface.

[0130] Although not shown in FIGS. 4 to 9, an optical display panel may be laminated on the lower surface of the polarizer via an adhesive layer or a bonding layer to form an optical display device.

[0131] The optical display device of the present invention includes a polarizer according to an embodiment of the present invention. The optical display device may include a light emitting device display device such as an organic light emitting diode (OLED) display device, and a liquid crystal display device.

[0132] In one embodiment, the organic light emitting device display device may include an organic light emitting device panel including a flexible substrate, and the polarizer of the present invention laminated on the organic light emitting device panel. In another embodiment, the organic light emitting device display device may include an organic light emitting device panel including a non-flexible substrate, and the polarizer of the present invention laminated on the organic light emitting device panel. [Example]

[0133] The present invention will be described in more detail with reference to preferred embodiments thereof below, however, these are merely preferred examples of the present invention and should not be construed as limiting the present invention in any way.

[0134] Example 1 A polyvinyl alcohol film (TS#20, Kuraray, Japan, thickness: 20 μm) was stretched 6 times in an iodine aqueous solution at 55° C. to produce a polarizer with a light transmittance of 45%.

[0135] An acrylic alignment film (HSPA-239, NISSAN Chem.) was formed on one side of the substrate film. A nematic liquid crystal layer composition (RMM-2126, Merck) was applied to a predetermined thickness on the acrylic alignment film, and then cured at a predetermined temperature and airflow to form an O-plate retardation layer. The O-plate retardation layer was peeled off from the substrate film. The O-plate retardation layer was attached to the bottom surface of the prepared polarizer using an adhesive layer, and a TAC film (KC2UAW, KONICA, front retardation at a wavelength of 550 nm: 3 nm) was attached to the top surface of the polarizer using an adhesive layer as a protective layer to produce a polarizing plate consisting of TAC film, adhesive layer, polarizer, adhesive layer, and O-plate liquid crystal retardation layer.

[0136] The O-plate type retardation layer has reverse wavelength dispersion, and the top surface of the O-plate type retardation layer is disposed closer to the polarizer than the bottom surface, and the slow axis forms a 45° angle with the light transmission axis of the polarizer. The detailed structures of the manufactured polarizer and O-plate type liquid crystal retardation layer are shown in Table 1.

[0137] Examples 2 to 4 A polarizing plate was manufactured in the same manner as in Example 1, except that the temperature and air volume during curing of the composition were changed when manufacturing the O-plate type liquid crystal retardation layer in Example 1.

[0138] Comparative Examples 1 to 4 A polarizing plate was manufactured in the same manner as in Example 1, except that the temperature and air volume during curing of the composition were changed when manufacturing the O-plate type liquid crystal retardation layer in Example 1.

[0139] The retardation of each of the retardation layer and the protective layer is a value measured at a wavelength of 550 nm using an AXOSCAN retardation measuring device.

[0140] The polarizing plates of the examples and comparative examples were evaluated for the following physical properties, and the results are shown in Table 1 below.

[0141] (1) Front and tilted retardation 1 of O-plate type liquid crystal retardation layer (unit: nm, @550 nm): For the retardation layers of the examples and comparative examples, light was transmitted in the normal direction to the in-plane direction of the retardation layer using AXOSCAN, and the front in-plane retardation was measured. For the retardation layers of the examples and comparative examples, light was transmitted while rotating the retardation layer by ±60° based on the fast axis of the retardation layer using AXOSCAN, and the tilted retardation 1 was measured.

[0142] (2) Inclined retardation 2 of O-plate type liquid crystal retardation layer (unit: nm, @550 nm): For the retardation layers of the examples and comparative examples, light was transmitted while rotating the retardation layer by ±60° based on the slow axis of the retardation layer using AXOSCAN, and the inclined retardation 2 was measured.

[0143] (3) Reflectance from the front and side: For the polarizers manufactured in the examples and comparative examples, the reflectance of external light incident on the inside, excluding primary reflection, was measured in all directions using the simulation program Techwiz 1D (Sany System, Republic of Korea), and the reflectance value in the direction with the maximum value was calculated.

[0144] [Table 1] *Difference in reflectivity: Side reflectivity - Front reflectivity

[0145] As shown in Table 1, the polarizing plate of the present invention has a single liquid crystal retardation layer, and has a significantly excellent effect of reducing reflectance at the front and side surfaces. Since the difference in reflectance between the front and side surfaces is small, the polarizing plate has an excellent effect of uniforming the screen.

[0146] On the other hand, the polarizing plates of the comparative examples that do not satisfy the maximum and minimum values ​​of the ratio in Equation 1 of the present invention were unable to obtain the effects of the present invention.

[0147] The retardation layer used in the examples was measured for the in-plane retardation and tilt retardation at a wavelength of 550 nm using an AXOSCAN retardation measuring instrument while changing the rotation angle of the retardation measuring instrument. At this time, the fast axis or fast axis of the retardation layer was used as the rotation axis. The relative values ​​(ratios) of the tilt retardation to the front retardation were calculated and shown in Tables 2 to 5 below, and the results are shown in Figure 3.

[0148] [Table 2]

[0149] [Table 3]

[0150] [Table 4]

[0151] [Table 5]

[0152] As shown in FIG. 3, it can be seen that the retardation layer included in the polarizing plate of the present invention is asymmetric depending on the rotation angle when rotated around the fast axis, but is symmetric depending on the rotation angle when rotated around the slow axis.

[0153] Simple modifications or variations of the present invention can be easily implemented by those skilled in the art, and all such modifications and variations can be considered to be included within the scope of the present invention.

Claims

1. A polarizer and a retardation layer laminated on a lower surface of the polarizer, The retardation layer has a maximum ratio of 1.1 to 1.8 and a minimum ratio of 0.3 to 0.7 in the following formula 1: [Formula 1] Ratio = B / A (In the above formula 1, A is the front retardation (unit: nm) of the retardation layer at a wavelength of 550 nm, B is a tilt retardation (unit: nm) measured by rotating the retardation layer by +60° or −60° around the fast axis of the retardation layer at a wavelength of 550 nm as the rotation axis.

2. The polarizer of claim 1 , wherein A in the formula 1 is 110 nm to 170 nm.

3. The polarizing plate of claim 1 , wherein B in the formula 1 has a maximum value of 120 nm to 310 nm and a minimum value of 20 nm to 120 nm.

4. 2. The polarizing plate according to claim 1, wherein when the retardation layer is rotated by +60° or −60° around a fast axis of the retardation layer at a wavelength of 550 nm as a rotation axis, a difference between a maximum value and a minimum value of an inclined retardation is 45 nm or more.

5. 2. The polarizing plate according to claim 1, wherein the retardation layer has a tilt retardation of 130 nm to 240 nm when the retardation layer is rotated by +60° or −60° around a slow axis of the retardation layer at a wavelength of 550 nm as a rotation axis.

6. The polarizing plate according to claim 1 , wherein the retardation layer has reverse wavelength dispersion.

7. 2. The polarizing plate according to claim 1, wherein the retardation layer has an asymmetrical relative value in a graph showing a tilt retardation measured with the fast axis of the retardation layer as a rotation axis, the relative value being a tilt retardation (nm) relative to a front retardation (nm) (tilt retardation / front retardation), where the X axis represents a rotation angle (°) of a retardation measuring instrument and the Y axis represents a relative value being a tilt retardation (nm) relative to a front retardation (nm).

8. 2. The polarizing plate according to claim 1, wherein the retardation layer has a tilt retardation measured with the slow axis of the retardation layer as a rotation axis, the tilt retardation being symmetrical in a graph where the X axis represents the rotation angle (°) of a retardation measuring instrument and the Y axis represents the relative value of the tilt retardation (nm) to the front retardation (nm) (tilt retardation / front retardation).

9. 2. The polarizing plate according to claim 1, wherein the slow axis of said retardation layer forms an angle of 40° to 50° when the light transmission axis of said polarizer is set to 0°.

10. The polarizing plate according to claim 1 , wherein the retardation layer comprises an O-plate type liquid crystal retardation layer.

11. 11. The polarizing plate according to claim 10, wherein when one surface of the O-plate type liquid crystal retardation layer in a thickness direction is a top surface and another surface opposite to the top surface is a bottom surface, a liquid crystal tilt angle at the top surface is larger than a liquid crystal tilt angle at the bottom surface.

12. 12. The polarizer of claim 11, wherein the liquid crystal tilt angle at the top surface is 30 to 90 degrees, and the liquid crystal tilt angle at the bottom surface is 0 to 10 degrees.

13. The polarizing plate according to claim 11 , wherein the top surface is disposed closer to the polarizer than the bottom surface.

14. 12. The polarizing plate of claim 11, wherein an absolute value of a difference between the liquid crystal tilt angle at the top surface and the liquid crystal tilt angle at the bottom surface is 30[deg.] to 90[deg.].

15. The polarizer according to claim 10 , wherein the O-plate type liquid crystal retardation layer is a nematic liquid crystal layer.

16. The polarizing plate according to claim 10 , wherein the retardation layer is composed of only the O-plate type liquid crystal retardation layer.

17. The polarizing plate according to claim 10 , wherein the retardation layer includes the O-plate type liquid crystal retardation layer and a first protective layer.

18. The polarizing plate according to claim 17 , wherein the first protective layer has a front retardation of 10 nm or less at a wavelength of 550 nm.

19. The polarizing plate of claim 1 , further comprising at least one of a second protective layer laminated on an upper surface of the polarizer and a third protective layer laminated on a lower surface of the polarizer.

20. An optical display device comprising the polarizing plate of any one of claims 1 to 19.

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