Polarizing plate and optical display device including same

Abstract

Provided are a polarizing plate and an optical display device including the same, the polarizing plate including: a polarizer; and a first phase difference layer and a second phase difference layer sequentially stacked on a lower surface of the polarizer, in which a slow axis of a stack of the first phase difference layer and the second phase difference layer forms 111 DEG to 113 DEG with respect to a light transmission axis of the polarizer, and a front-side linear phase difference value of the stack measured from the front side at a wavelength of 550 nm is 140 nm to 160 nm, and when the stack is rotated by + / -40 DEG around a slow axis of the stack as a rotation axis at a wavelength of 550 nm, a tilt linear difference value of the stack is 145 nm to 170 nm.

Description

Technical Field

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

[0002] Organic light emitting diode displays suffer from degradation of visibility and contrast due to reflection of external light. To solve this problem, organic light emitting diode displays can use polarizing plates to achieve anti-reflection functions by reducing the reflectivity of external light. Polarizing plates are generally required to significantly improve screen quality by improving black visibility on the front side.

[0003] The polarizing plate includes a polarizer and an anti-reflection layer stacked on the lower surface of the polarizer. The anti-reflection layer can be a single-piece retardation layer or a double-piece retardation layer. The single-piece retardation layer generally realizes negative wavelength dispersion characteristics. The double-piece retardation layer generally realizes negative wavelength dispersion characteristics by laminating retardation layers each having a positive wavelength dispersion characteristic. Although the double-piece retardation layer can have a greater thickness than the single-piece retardation layer, the double-piece retardation layer can be formed by stacking a retardation layer having a lower price than the single-piece retardation layer and showing a positive wavelength dispersion characteristic, thereby ensuring price competitiveness and improving productivity.

[0004] The retardation layer may be formed by stretching an unstretched film formed of a composition containing a polymer resin, or by coating a liquid crystal composition on an alignment layer to a predetermined thickness, followed by drying and / or curing. Although the retardation layer composed of a double-sheet liquid crystal has a smaller thickness than the retardation layer composed of a double-sheet stretched film, when the polarizing plate is placed under high temperature / humidity conditions, the retardation layer composed of a double-sheet liquid crystal may cause degradation of panel durability by electrode corrosion due to iodine eluted from the polarizer and diffused into the panel.

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

[0006] Technical issues

[0007] An object of the present invention is to provide a polarizing plate which does not elute iodine even after being left under high temperature / humidity conditions and shows good durability.

[0008] Another object of the present invention is to provide a polarizing plate having a thin thickness.

[0009] Another object of the present invention is to provide a polarizing plate that provides a good anti-reflection effect by reducing the reflectivity of the front and side surfaces.

[0010] Still another object of the present invention is to provide a polarizing plate having good black visibility.

[0011] Technical Solution

[0012] One aspect of the present invention relates to a polarizing plate.

[0013] 1. The polarizing plate comprises: a polarizer; and a first retardation layer and a second retardation layer stacked in sequence on the lower surface of the polarizer, wherein the slow axis of the stack of the first retardation layer and the second retardation layer is inclined at an angle of 111° to 113° relative to the light transmission axis of the polarizer, and wherein the stack has a front linear retardation of 140nm to 160nm measured on the front side at a wavelength of 550nm, and a tilted linear retardation of 145nm to 170nm measured at a wavelength of 550nm when the stack is rotated ±40° around the slow axis of the stack as a rotation axis.

[0014] 2. In 1, the first retardation layer may have a smaller thickness than the second retardation layer.

[0015] 3. In 1 to 2, the thickness of the first retardation layer may range from 1% to 20% of the thickness of the second retardation layer.

[0016] 4. In 1 to 3, the first retardation layer may be a liquid crystal layer and the second retardation layer may be a non-liquid crystal layer.

[0017] 5. In 4, the liquid crystal layer may be a discotic liquid crystal layer.

[0018] 6. In 1 to 5, the non-liquid crystal layer may include a stretched film formed from a composition comprising at least one resin selected from the group consisting of cellulose resin, polyester resin, cyclic polyolefin (COP) resin, cyclic olefin copolymer (COC) resin, polycarbonate resin, polyether sulfone resin, polysulfone resin, polyamide resin, polyimide resin, polyolefin resin, polyarylate resin, polyvinyl alcohol resin, polyvinyl chloride resin, polyvinylidene chloride resin and acrylic resin.

[0019] 7. In 1 to 6, the first retardation layer may have negative birefringence and the second retardation layer may have positive birefringence.

[0020] 8. In 1 to 7, the second retardation layer may have a higher biaxiality (NZ) than the first retardation layer at a wavelength of 550 nm.

[0021] 9. In 8, the first retardation layer may have a biaxiality of -0.1 to 0.1 at a wavelength of 550 nm, and the second retardation layer may have a biaxiality greater than or equal to 1 and less than 1.3 at a wavelength of 550 nm.

[0022] 10. In 9, the first retardation layer may have a biaxiality of 0 at a wavelength of 550 nm, and the second retardation layer may have a biaxiality greater than or equal to 1 and less than 1.3 at a wavelength of 550 nm.

[0023] 11. In 1 to 10, the first retardation layer may be a negative A plate and the second retardation layer may be a negative B plate.

[0024] 12. In 1 to 11, the first retardation layer may have a front in-plane retardation of 200 nm to 280 nm at a wavelength of 550 nm, and the second retardation layer may have a front in-plane retardation of 100 nm to 150 nm at a wavelength of 550 nm.

[0025] 13. In 1 to 12, the slow axis of the first retardation layer may be inclined at an angle of 10° to 20° relative to the light transmission axis of the polarizer.

[0026] 14. In 1 to 13, the slow axis of the second retardation layer may be inclined at an angle of 70° to 85° relative to the light transmission axis of the polarizer.

[0027] 15. In 1 to 14, a buffer layer may be formed on an upper surface of the second retardation layer.

[0028] Another aspect of the present invention relates to an optical display device.

[0029] An optical display device includes the polarizing plate according to the present invention.

[0030] Beneficial Effects

[0031] The present invention provides a polarizing plate which does not elute iodine even after being left under high temperature / humidity conditions and shows good durability.

[0032] The present invention provides a polarizing plate having a thin thickness.

[0033] The present invention provides a polarizing plate which provides a good anti-reflection effect by reducing the reflectivity of the front and side surfaces.

[0034] The present invention provides a polarizing plate with good black visibility. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 is a cross-sectional view of a polarizing plate according to one embodiment of the present invention.

[0036] Figure 2 The evaluation results of the maximum reflectivity of Example 1 at the side surface (incident angle: 60°) are shown.

[0037] Figure 3The evaluation results of the maximum reflectivity of Comparative Example 1 at the side surface (incident angle: 60°) are shown.

[0038] Figure 4 The evaluation results of the maximum reflectivity of Comparative Example 2 at the side surface (incident angle: 60°) are shown.

[0039] Figure 5 The evaluation results of the maximum reflectivity of Comparative Example 3 at the side surface (incident angle: 60°) are shown. DETAILED DESCRIPTION

[0040] Hereinafter, exemplary 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 embodied in different ways and is not limited to the following embodiments.

[0041] In the accompanying drawings, components irrelevant to the description are omitted in order to clearly describe the present invention, and the same components will be represented by the same reference numerals throughout the specification. Although the length, thickness or width of each component may be exaggerated in the accompanying drawings for understanding the present invention, the present invention is not limited thereto.

[0042] Herein, spatially relative terms such as “upper” and “lower” are defined with reference to the accompanying drawings. Therefore, it should be understood that the term “upper surface” can be used interchangeably with the term “lower surface”.

[0043] The terms used herein are for the purpose of describing exemplary embodiments and are not intended to be limiting of the present invention.As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise.

[0044] Herein, "front-side in-plane retardation (Re)", "biaxiality (NZ)" and "out-of-plane retardation (Rth)" of a single retardation layer are represented by equations A, B and C, respectively.

[0045] [Equation A]

[0046] Re=(nx-ny)xd

[0047] [Equation B]

[0048] NZ=(nx-nz) / (nx-ny)

[0049] [Equation C]

[0050] Rth=((nx+ny) / 2-nz)xd

[0051] (In equations A to C, nx, ny and nz are the refractive indices of a single retardation layer measured at the measurement wavelength in its slow axis direction, fast axis direction and thickness direction, respectively, and d is its thickness (unit: nm)).

[0052] Herein, the "Mueller Matrix of the retardation layer" is represented by the following equation D and can be directly measured without difficulty using a retardation meter (eg, AxoScan).

[0053] [Equation D]

[0054]

[0055] In this paper, “linear delay (R L )" is represented by the following equation E. Linear retardation is well known to those skilled in the art and can be directly measured without difficulty using a retardation meter (e.g., AxoScan).

[0056] [Equation E]

[0057]

[0058]

[0059] (In equation E, m 23 、m 32 、m 31 、m 13 、m 11 、m 22 and m 33 Obtained from equation D).

[0060] In equations A to E, the measurement wavelength may be 450 nm, 550 nm, or 650 nm.

[0061] A stack of two retardation layers with different retardation values ​​and slow axes has different characteristics from a single retardation layer. Therefore, in order to obtain the retardation value of the stack, different concepts of retardation are needed. For this purpose, the concepts of linear retardation, circular retardation and total retardation are introduced.

[0062] A single retardation layer has a total retardation and a linear retardation that are equal to each other, and there is no circular retardation. However, a stack of two retardation layers having different retardation values ​​and different physical properties of the slow axis (e.g., retardation value>0) has a linear retardation different from the total retardation, wherein the linear retardation is not 0. The retardation value can be calculated by converting the retardation layer into a Mueller matrix. This can be easily accomplished using AxoScan (Axometrics, Inc., USA), which is a Mueller matrix-based retardation meter.

[0063] In this article, the "slow axis" is defined as the axis providing the highest refractive index in the in-plane direction, and the "fast axis" is defined as the axis providing the lowest refractive index in the in-plane direction. Because the "slow axis" is usually orthogonal to the "fast axis", if the angle of the "slow axis" is given, the angle of the "fast axis" can also be obtained.

[0064] For a single retardation layer, the measurement and calculation of the "slow axis" is very easy. However, for a stack of two retardation layers with different retardation values ​​and different physical properties of the slow axis (e.g., retardation value>0), the slow axis of the stack is calculated by equation F.

[0065] [Equation F]

[0066]

[0067] (In equation F, a1 and a2 are the values ​​obtained in equation E)

[0068] As used herein, to express a specific numerical range, “X to Y” means “greater than or equal to X and less than or equal to Y (X≤ and ≤Y)”.

[0069] A polarizing plate according to the present invention includes: a polarizer; and a first retardation layer and a second retardation layer sequentially stacked on a lower surface of the polarizer.

[0070] As described below, the first delay layer is a liquid crystal layer, and the second delay layer is a non-liquid crystal layer, preferably a stretched resin film. Therefore, compared with a polarizing plate including a stack of liquid crystal layers as a stack of delay layers, the polarizing plate according to the present invention will not suffer from iodine elution even after being placed under high temperature / humidity conditions, and thus shows good durability. In this article, the edge of the polarizing plate can be observed by microscopy after the polarizing plate is placed in a high temperature / humidity (60°C and 90% relative humidity) room for 250 hours, and the "iodine elution" can be evaluated based on the degree of iodine decolorization.

[0071] The polarizing plate according to the present invention includes a stack of a liquid crystal layer and a non-liquid crystal layer, which is thicker than the stack of the liquid crystal layer. However, by controlling the front retardation measured at a wavelength of 550nm on the front and the tilted linear retardation measured at a wavelength of 550nm when the stack rotates ±40° around the slow axis of the stack as the rotation axis, the stack of the liquid crystal layer and the non-liquid crystal layer reduces the reflectivity of the side while improving black visibility. Therefore, the polarizing plate according to the present invention can be used as a polarizing plate for anti-reflection in a light-emitting diode display including a light-emitting diode.

[0072] “Front linear retardation” refers to a value calculated according to Equation E when light is incident on a stack of a first retardation layer and a second retardation layer in a normal direction to an in-plane direction of the first retardation layer, with the stack fixed and not moved by rotation or the like.

[0073] "Tilted linear retardation" refers to the value calculated according to Equation E when light is incident on the stack of the first retardation layer and the second retardation layer in the normal direction of the in-plane direction of the first retardation layer, and the slow axis of the stack is rotated by +40° and -40° respectively around the slow axis of the stack as the rotation axis.

[0074] The polarizing plate according to the present invention includes a polarizer; and a delay layer stack on the lower surface of the polarizer, the delay layer stack including a first delay layer and a second delay layer, wherein the slow axis of the stack of the first delay layer and the second delay layer is inclined at an angle of 111° to 113° relative to the light transmission axis of the polarizer, and wherein the stack has a front linear delay of 140nm to 160nm measured on the front side at a wavelength of 550nm and a tilted linear delay of 145nm to 170nm measured at a wavelength of 550nm when the stack is rotated ±40° around the slow axis of the stack as a rotation axis.

[0075] In the following, reference will be made to Figure 1 A polarizing plate according to one embodiment of the present invention is described.

[0076] refer to Figure 1 , the polarizing plate includes a polarizer 130 , a protective film 140 stacked on an upper surface of the polarizer 130 , and a retardation layer stack stacked on a lower surface of the polarizer 130 .

[0077] As used herein, “upper surface of a polarizer” refers to a surface on which external light is first incident on the polarizer or a surface on which light emitted from a light emitting device is emitted through the polarizer.

[0078] Herein, "the lower surface of the polarizer" refers to a surface on which light emitted from a light emitting diode is incident on the polarizer or a surface from which external light having entered the polarizer is first emitted.

[0079] In one embodiment, if Figure 1 As shown, the retardation layer stack may refer to a stack of two retardation layers including a first retardation layer 110 and a second retardation layer 120 sequentially stacked from a lower surface of the polarizer 130 .

[0080] In another embodiment, the delay layer stack includes a first delay layer and a second delay layer stacked in sequence from the lower surface of the polarizer, and a base layer may be further stacked between the polarizer and the first delay layer, between the first delay layer and the second delay layer, and / or on the lower surface of the second delay layer. The base layer supporting each of the first delay layer and the second delay layer may be a zero delay film or a delay film having a front in-plane delay of 30 nm or less, specifically 0 nm to 10 nm, at a wavelength of 550 nm.

[0081] The protective film 140 may be an example of a protective layer including a protective coating, etc. If the function of the polarizing plate is not impaired, the protective film 140 may be omitted.

[0082] Although in Figure 1 Although not shown in the drawings, an adhesive layer or a bonding layer may be further stacked on a lower surface of the second retardation layer 120 to adhesively attach the polarizing plate to the optical display panel.

[0083] The first retardation layer 110 and the second retardation layer 120 may be stacked on a lower surface of the polarizer, thereby circularly polarizing linearly polarized light emitted from the polarizer by linear polarization of external light to provide an anti-reflection effect.

[0084] The first retardation layer 110 may be a liquid crystal layer and the second retardation layer 120 may be a non-liquid crystal layer. Compared with a polarizing plate including a stack of liquid crystal layers as the retardation layer, the polarizing plate according to the present invention does not suffer from iodine elution and thus has good durability, and compared with a polarizing plate including a stack of resin films of non-liquid crystal layers as the retardation layer, a thickness reduction can be achieved.

[0085] The liquid crystal layer used for the first retardation layer 110 may include broad discotic liquid crystals. For example, the liquid crystal may include a monomer, an oligomer, or a polymer.

[0086] The liquid crystal layer may include reactive mesogen liquid crystals. For example, the liquid crystal may have at least one reactive cross-linking group. The reactive mesogen liquid crystal may, for example, include at least one selected from the following: a rod-shaped aromatic derivative having at least one reactive cross-linking group; propylene glycol 1-methyl; propylene glycol 2-acetate; and a compound represented by P1-A1-(Z1-A2)n-P2, wherein P1 and P2 each independently include an acrylate group, a methacrylate group, a vinyl group, a vinyloxy group, an epoxy group, or a combination thereof, A1 and A2 each independently include 1,4-phenylene, naphthalene-2,6-diyl, or a combination thereof, Z1 may include a single bond, -COO-, -OCO-, or a combination thereof, and n is 0, 1, or 2, but is not limited thereto.

[0087] The liquid crystal layer may be formed of a composition comprising the above-mentioned reactive mesogen liquid crystal and typical additives commonly used in the art such as photoinitiators, surface modifiers, etc. The composition for the liquid crystal layer may include a solvent to facilitate the preparation of a liquid crystal layer having a uniform surface.

[0088] Preferably, the liquid crystal layer includes a discotic liquid crystal layer. The discotic liquid crystal layer may have a predetermined biaxiality, which may make it easier to reduce the reflectivity of the side surface while improving black visibility in the stack of the first retardation layer and the second retardation layer according to the present invention.

[0089] The first retardation layer 110 has a biaxiality (NZ) in the range 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, preferably -0.05 to 0.05, more preferably 0) at a wavelength of 550 nm. Within this range, the stack of the first retardation layer and the second retardation layer according to the present invention can easily reduce the reflectivity of the side while improving black visibility.

[0090] The first retardation layer 110 may be a positive wavelength dispersion layer and may satisfy the relationship: Re(450)>Re(550)>Re(650) [wherein Re(450), Re(550) and Re(650) are front in-plane retardation values ​​of the first retardation layer at wavelengths of 450 nm, 550 nm and 650 nm, respectively]. With this structure, the stack of the first retardation layer and the second retardation layer shows negative wavelength dispersion, whereby the polarizing plate can improve black visibility and screen quality by significantly reducing the reflectivity of the front and side surfaces.

[0091] The first retardation layer 110 may be a negative A-plate having a refractive index relationship of nx≒nz>ny. Herein, nx, ny and nz represent the refractive index of the first retardation layer in its slow axis direction, fast axis direction and thickness direction at a wavelength of 550 nm, respectively.

[0092] At a wavelength of 550 nm, the first retardation layer 110 has a higher front in-plane retardation than the second retardation layer, and may have a front in-plane retardation in the range of 200 nm to 280 nm (e.g., 200 nm, 210 nm, 220 nm, 230 nm, 240 nm, 250 nm, 260 nm, 270 nm or 280 nm, preferably 220 nm to 260 nm) at a wavelength of 550 nm. Within this range, the polarizing plate can easily improve black visibility and screen quality by significantly reducing the reflectivity of the front and side surfaces.

[0093] The first retardation layer 110 has a slow axis and a fast axis in the in-plane direction. The slow axis of the first retardation layer 110 is tilted at an angle of 10° to 20° (e.g., 10°, 11°, 12°, 13°, 14°, 15°, 16°, 17°, 18°, 19° or 20°, preferably 15° to 19°) relative to the light transmission axis of the polarizer. Within this range, the polarizer can easily improve black visibility and screen quality by significantly reducing the reflectivity of the front and side surfaces.

[0094] The first retardation layer 110 has a much smaller thickness than the second retardation layer 120. This is because the first retardation layer 110 is formed by applying the composition for the liquid crystal layer to a predetermined thickness described below, while the second retardation layer 120 is formed of a resin film. In one embodiment, for example, the thickness of the first retardation layer 110 may be in the range of 1% to 20% of the thickness of the second retardation layer 120, for example, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19% or 20%, preferably 10% to 20%.

[0095] The first retardation layer 110 may have a thickness of 1 μm to 5 μm, preferably 2 μm to 3 μm. Within this range, the first retardation layer may achieve the above retardation value.

[0096] The first retardation layer 110 may be formed by depositing the composition for the liquid crystal layer to a predetermined thickness on the upper surface of the second retardation layer, followed by drying and / or curing. In one embodiment, the first retardation layer 110 may be directly formed on the second retardation layer. As used herein, "directly formed" means that no adhesive layer, bonding layer or tacky layer is formed between the first retardation layer and the second retardation layer.

[0097] The second retardation layer may further include an alignment film for forming the first retardation layer on an upper surface thereof.

[0098] The first retardation layer may have negative birefringence and the second retardation layer may have positive birefringence.

[0099] The second retardation layer 120 is a non-liquid crystal layer. The second retardation layer 120 can be used as a base film or a support for forming the first retardation layer, and at the same time, together with the first retardation layer, provides an anti-reflection effect of the polarizing plate according to the present invention. "Non-liquid crystal" may include a material that is not at least one of a liquid crystal monomer, a liquid crystal oligomer, or a liquid crystal polymer and is not converted into a liquid crystal monomer, a liquid crystal oligomer, or a liquid crystal polymer by light irradiation, heat treatment, etc.

[0100] The second delay layer 120 may include a stretched film formed by a composition comprising at least one resin selected from the following: cellulose resin (including triacetyl cellulose, etc.), polyester resin (including polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polybutylene naphthalate (PEN), etc.), cycloolefin polymer (COP) resin, cycloolefin copolymer (COC) resin, polycarbonate resin, polyether sulfone resin, polysulfone resin, polyamide resin, polyimide resin, polyolefin resin, polyarylate resin, polyvinyl alcohol resin, polyvinyl chloride resin, polyvinylidene chloride resin and acrylic resin. Preferably, the second delay layer includes cyclic polyolefin resin to facilitate the realization of the following wavelength dispersion and delay characteristics. Cyclic polyolefin resin can help to achieve the effect of the present invention.

[0101] The second retardation layer 120 may have a much greater thickness than the first retardation layer 110. In one embodiment, the second retardation layer 120 may have a thickness of 15 to 35 μm, preferably 15 to 25 μm. Within this range, the second retardation layer may achieve the following retardation and may be used as a base film or a support.

[0102] At a wavelength of 550 nm, the second retardation layer 120 may have a higher biaxiality (NZ) than the first retardation layer 110. This relationship may contribute to improving the reflectivity and black visibility of the polarizing plate according to the present invention, and suppressing light leakage.

[0103] In one embodiment, the second delay layer 120 has a biaxiality greater than or equal to 1 and less than 1.3 (for example, 1, 1.01, 1.02, 1.03, 1.04, 1.05, 1.06, 1.07, 1.08, 1.09, 1.1, 1.11, 1.12, 1.13, 1.14, 1.15, 1.16, 1.17, 1.18, 1.19, 1.2, 1.21, 1.22, 1.23, 1.24, 1.25, 1.26, 1.27, 1.28 or 1.29, preferably 1.05 to 1.25, more preferably 1.05 to 1.2, most preferably 1.1 to 1.15) at a wavelength of 550nm. Within this range, the above-mentioned front retardation range and oblique retardation range of the stack of the first retardation layer and the second retardation layer according to the present invention can be easily achieved, and the reflectivity and light leakage of the side can be easily reduced while improving black visibility.

[0104] The second retardation layer 120 can show flat or positive wavelength dispersion and can satisfy the relationship: Re(450)≥Re(550)≥Re(650) [wherein Re(450), Re(550) and Re(650) are the front in-plane retardation values ​​of the second retardation layer at wavelengths of 450nm, 550nm and 650nm, respectively]. With this structure, the stack of the first retardation layer and the second retardation layer shows negative wavelength dispersion, whereby the polarizing plate can improve black visibility and screen quality by significantly reducing the reflectivity of the front and side surfaces.

[0105] The second retardation layer 120 may include a negative B plate having a refractive index relationship of nx>ny>nz. Herein, nx, ny and nz represent the refractive index of the first retardation layer in its slow axis direction, fast axis direction and thickness direction at a wavelength of 550 nm, respectively.

[0106] At a wavelength of 550 nm, the second retardation layer 110 has a lower front in-plane retardation than the first retardation layer, and may have a front in-plane retardation in the range of 100 nm to 150 nm (e.g., 100 nm, 105 nm, 110 nm, 115 nm, 120 nm, 125 nm, 130 nm, 135 nm, 140 nm, 145 nm or 150 nm, preferably 110 nm to 130 nm) at a wavelength of 550 nm. Within this range, the polarizing plate can easily improve black visibility and screen quality by significantly reducing the reflectivity of the front and side surfaces.

[0107] The second retardation layer 120 has a slow axis and a fast axis in the in-plane direction. The slow axis of the second retardation layer 120 is tilted 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°) relative to the light transmission axis of the polarizer. Within this range, the polarizer can easily improve black visibility and screen quality by significantly reducing the reflectivity of the front and side surfaces.

[0108] In one embodiment, the angle between the slow axis of the first retardation layer 110 and the slow axis of the second retardation layer 120 may be in the range of 50° to 80° (e.g., 50°, 51°, 52°, 53°, 54°, 55°, 56°, 57°, 58°, 59°, 60°, 61°, 62°, 63°, 64°, 65°, 66°, 67°, 68°, 69°, 70°, 71°, 72°, 73°, 74°, 75°, 76°, 77°, 78°, 79° or 80°, preferably 55° to 75°). Within this range, the effects of the present invention can be easily achieved.

[0109] The second retardation layer 120 may be prepared by stretching an unstretched film for the second retardation layer by MD uniaxial stretching, TD uniaxial stretching, oblique stretching, or a combination thereof. The stretching may be performed by any typical method known to those skilled in the art.

[0110] The second retardation layer 110 may further include an alignment film for forming the first retardation layer 110 on its upper surface. The alignment film may be formed by any typical alignment film composition known to those skilled in the art. The alignment film may be prepared by depositing the alignment film composition to a predetermined thickness and then physically orienting the alignment film composition by rubbing, or by depositing the alignment film composition to a predetermined thickness and then photo-orienting.

[0111] The stack of the first retardation layer 110 and the second retardation layer 120 may show negative wavelength dispersion. This may contribute to a significant reduction in the reflectivity of the front and side surfaces to improve black visibility while improving screen quality. Negative wavelength dispersion means that the short wavelength dispersion of the stack of the first retardation layer 110 and the second retardation layer 120 has a lower value than the long wavelength dispersion. "Negative wavelength dispersion" means that the stack has the following relationship: the tilted linear retardation at a wavelength of 450nm < the tilted linear retardation at a wavelength of 550nm < the tilted linear retardation at a wavelength of 650nm. However, the linear retardation of the stack on the front surface may have R L (550) <R L (450) <R L (650) value. L (450), R L (550) and R L (650) denotes the front linear retardation values ​​of the stack at wavelengths of 450 nm, 550 nm, and 650 nm, respectively.

[0112] The slow axis of the stack of the first retardation layer 110 and the second retardation layer 120 is tilted at an angle of 111° to 113° relative to the light transmission axis of the polarizer, and the stack of the first retardation layer 110 and the second retardation layer 120 has a front linear retardation of 140nm to 160nm measured at a wavelength of 550nm on the front side, and a tilted linear retardation of 145nm to 170nm measured at a wavelength of 550nm when the stack rotates ±40° around the slow axis of the stack as a rotation axis. By satisfying all the angles within the above ranges, the front linear retardation and the tilted linear retardation, the polarizer can reduce the reflectivity of the front and side surfaces to provide a good anti-reflection effect and good black visibility. If any of the angles within the above ranges, the front linear retardation and the tilted linear retardation are not satisfied, the anti-reflection effect and the effect of improving black visibility of the present invention may be significantly deteriorated.

[0113] In one embodiment, the slow axis of the stack may be tilted at an angle of 111°, 111.5°, 112°, 112.5°, or 113° relative to the light transmission axis of the polarizer.

[0114] In one embodiment, the stack may have a front side linear retardation of 140 nm, 141 nm, 142 nm, 143 nm, 144 nm, 145 nm, 146 nm, 147 nm, 148 nm, 149 nm, 150 nm, 151 nm, 152 nm, 153 nm, 154 nm, 155 nm, 156 nm, 157 nm, 158 nm, 159 nm or 160 nm measured on the front side at a wavelength of 550 nm.

[0115] In one embodiment, the stack may have a tilted linear retardation of 145nm, 146nm, 147nm, 148nm, 149nm, 150nm, 151nm, 152nm, 153nm, 154nm, 155nm, 156nm, 157nm, 158nm, 159nm, 160nm, 161nm, 162nm, 163nm, 164nm, 165nm, 167nm, 168nm, 169nm or 170nm measured at a wavelength of 550nm with the stack rotated ±40° about the slow axis of the stack as the rotation axis.

[0116] For a typical stack of retardation layers, front retardation or in-plane retardation refers to the retardation value measured in the normal direction relative to the in-plane direction of the stack. By adjusting the angle of the slow axis of the stack of the first retardation layer 110 and the second retardation layer 120 according to the present invention as described above, and controlling not only the retardation measured in the normal direction relative to the in-plane direction of the stack, but also the tilt retardation measured when the slow axis of the stack rotates, the present invention improves both the anti-reflection effect and the black visibility effect. In one embodiment, the first retardation layer may include a liquid crystal layer, preferably a discotic liquid crystal layer, and the second retardation layer may include a non-liquid crystal layer, preferably a stretched film or a stretched coating. In one embodiment, the first retardation layer may have a biaxiality (NZ) of -0.1 to 0.1 at a wavelength of 550nm, and the second retardation layer may have a biaxiality (NZ) greater than or equal to 1 and less than 1.3 at a wavelength of 550nm. In one embodiment, the first retardation layer may be a negative A plate and the second retardation layer may be a negative B plate.

[0117] The two linear retardation values ​​of the stack can be achieved by adjusting the front in-plane retardation of each of the first retardation layer and the second retardation layer, the slow axis relationship between the first retardation layer and the second retardation layer, and the like.

[0118] The first retardation layer 110 may be formed by depositing a composition for a first retardation layer (ie, a liquid crystal layer composition) to a predetermined thickness on one surface of the second retardation layer 120 and then drying and / or curing the composition.

[0119] In one embodiment, a liquid crystal layer composition is deposited to a predetermined thickness on one surface of the second retardation layer, and in this process, a buffer layer may be formed on one surface of the second retardation layer by corrosion by a solvent included in the liquid crystal layer composition.

[0120] The polarizer 130 is used to convert natural light or polarized light into linear polarized light by linear polarization in a specific direction, and can be made of a polymer film mainly composed of a polyvinyl alcohol resin. Specifically, the polarizer 110 can be manufactured by dyeing the polymer film with iodine or a dichroic dye and then stretching the dyed film in its machine direction (longitudinal direction, MD). Specifically, the polarizer can be manufactured by swelling, dyeing, stretching and cross-linking.

[0121] The polarizer 130 has a light absorption axis and a light transmission axis in its in-plane direction, wherein the light absorption axis may correspond to a machine direction (MD) of the polarizer and the light transmission axis may correspond to a transverse direction (TD) thereof.

[0122] The polarizer 130 may have a light transmittance of 40% or more, for example, 40% to 46%, and a polarization degree of 95% or more, for example, 95% to 99.999%. Within this range, when combined with the first retardation layer and the second retardation layer, the polarizer may improve anti-reflection performance. In this article, "light transmittance" and "polarization degree" are values ​​corresponding to visibility at a wavelength of 380nm to 780nm.

[0123] The polarizer 130 may have a thickness of 2 μm to 30 μm, specifically 4 μm to 25 μm. Within this range, the polarizer may be used in a polarizing plate.

[0124] Although in Figure 1 Not shown, but the polarizer 130 can be bonded to the stack of the first retardation layer and the second retardation layer via an adhesive layer. The adhesive layer can be formed of at least one of a water-based adhesive or a photocurable adhesive. Preferably, the adhesive layer is formed of a photocurable adhesive to allow bonding between the protective film and the polarizer and bonding between the polarizer and the first retardation layer to be achieved once light irradiation is performed, thereby improving the manufacturing processability of the polarizing plate. The adhesive layer can have a thickness of 0.1 μm to 10 μm, specifically 0.5 μm to 5 μm. Within this range, the adhesive layer can be used in a polarizing plate.

[0125] The protection film 140 is formed on the upper surface of the polarizer 130 and may protect the polarizer from the external environment while improving the mechanical strength of the polarizing plate.

[0126] The protective film 140 is used to protect the polarizer from the external environment, and includes a film formed by, for example, at least one resin selected from the following as an optically transparent film: a cellulose resin including triacetyl cellulose (TAC), a polyester resin including polyethylene terephthalate (PET), polybutylene terephthalate, polyethylene naphthalate, polybutylene naphthalate (PEN), etc., a cyclic polyolefin (COP) resin, a cyclic olefin copolymer (COC) resin, a polycarbonate resin, a polyether sulfone resin, a polysulfone resin, a polyamide resin, a polyimide resin, a polyolefin resin, a polyarylate resin, a polyvinyl alcohol resin, a polyvinyl chloride resin, and a polyvinylidene chloride resin. Specifically, a TAC or PET film can be used as a protective film.

[0127] The protective film 140 may have a thickness of 5 μm to 70 μm, specifically 15 μm to 45 μm. Within this range, the protective film may be used for a polarizing plate.

[0128] Although Figure 1 Although not shown, a functional coating may be formed on the upper surface of the protective film 140 to provide additional functions to the polarizing plate, and may include, for example, a hard coating, a moisture barrier, an anti-reflection layer, an anti-glare layer, etc., which may be used alone or as a stack thereof.

[0129] Although in Figure 1 Although not shown in the drawings, the protective film 140 may be bonded to the polarizer 110 via an adhesive layer. The adhesive layer may be formed of at least one of a water-based adhesive or a photocurable adhesive.

[0130] The adhesive layer may have a thickness of 0.1 μm to 10 μm, specifically 0.1 μm to 5 μm. Within this range, the adhesive layer may be used in the polarizing plate.

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

[0132] In one embodiment, an organic light emitting diode display may include an organic light emitting diode panel including a flexible substrate and a polarizing plate according to the present invention stacked on the organic light emitting diode panel.

[0133] In another embodiment, an organic light emitting diode display may include an organic light emitting diode panel including a non-flexible substrate and a polarizing plate according to the present invention stacked on the organic light emitting diode panel.

[0134] Invention Mode

[0135] Next, the present invention will be described in more detail with reference to some examples. However, it should be noted that these examples are provided for illustration only and should not be construed as limiting the present invention in any way.

[0136] Example 1

[0137] A polarizer having a light transmittance of 45% was prepared by stretching a polyvinyl alcohol film (PS#60, thickness before stretching: 60 μm, Nippon Kuraray Co., Ltd.) in its machine direction to 6 times its original length in an iodine aqueous solution at 55°C.

[0138] The second retardation layer (negative B plate) was formed by preparing an unstretched cyclic polyolefin (COP) film and sequentially performing oblique stretching and MD stretching in MD of the prepared film.

[0139] An orientation film is formed on the upper surface of the prepared second delay layer, and a composition for a discotic liquid crystal layer is deposited on the orientation film, and the composition is then cured to prepare a stack of a first delay layer and a second delay layer, wherein the discotic liquid crystal layer is stacked on the upper surface of the second delay layer as a first delay layer (negative A plate, positive dispersion).

[0140] A polarizing plate is prepared by stacking an HC-TAC film (Toppan, 25FJCHCN-TC, thickness: 32 μm) as a protective film on the upper surface of the prepared polarizer, and then stacking a first retardation layer and a second retardation layer on the lower surface of the polarizer (the first retardation layer and the second retardation layer are stacked on the lower surface of the polarizer in sequence).

[0141] Examples 2 to 4

[0142] A polarizing plate was prepared in the same manner as in Example 1, except that the first retardation layer and the second retardation layer were changed as listed in Table 1 below by changing the stretching ratio, stretching temperature, etc. when forming the second retardation layer and changing the thickness, etc. when forming the first retardation layer.

[0143] Comparative Examples 1 to 3

[0144] A polarizing plate was prepared in the same manner as in Example 1, except that the first retardation layer and the second retardation layer were changed as listed in Table 1 below by changing the stretching ratio, stretching temperature, etc. when forming the second retardation layer and changing the thickness, etc. when forming the first retardation layer.

[0145] Re and NZ of each of the first retardation layer and the second retardation layer were measured at a wavelength of 550 nm using AxoScan.

[0146] The following properties of the polarizing plates prepared in Examples and Comparative Examples were evaluated, and the evaluation results are shown in Tables 1 and Figures 1 to 5 middle.

[0147] (1) Front linear retardation and tilt linear retardation of the stack (unit: nm, @550nm): The front linear retardation and tilt linear retardation of the stack of the first retardation layer and the second retardation layer prepared in each of the embodiments and comparative examples were measured using AxoScan, which is a measuring device based on the Mueller matrix.

[0148] (2) Iodine elution: The polarizing plate prepared in each of Examples and Comparative Examples was placed in a high temperature / humidity (60° C. and 90% relative humidity) chamber for 250 hours, and the edge of the polarizing plate was observed by a microscope to evaluate the degree of iodine decolorization.

[0149] (3) Reflectivity of the side: The reflectivity of each polarizing plate prepared in the embodiment and the comparative example was measured in all directions by the simulation program TechWiz 1D (Sanayi System, South Korea), thereby calculating the reflectivity in the direction where the reflectivity of the external light (excluding the primary reflection) entering the polarizing plate becomes the maximum value. It is desirable that the reflectivity of the polarizing plate is less than 6%, preferably less than 5.6%.

[0150] (4) Black visibility: The polarizing plate prepared in each of Examples and Comparative Examples was attached to an aluminum plate via an adhesive, and then black visibility was evaluated by naked eyes. When blue and / or yellow was not visible and looked completely black, it was evaluated as "good".

[0151] Table 1

[0152]

[0153]

[0154] * In Table 1,

[0155] ① Slow axis angle: The angle of the slow axis of the stack relative to the light transmission axis of the polarizer, which can be obtained according to equations E and F.

[0156] ② Angle 1: The angle of the slow axis of the first retardation layer relative to the light transmission axis of the polarizer.

[0157] ③ Angle 2: The angle of the slow axis of the second retardation layer relative to the light transmission axis of the polarizer.

[0158] As shown in Table 1, the polarizing plate according to the present invention has good durability without iodine elution, has a significant effect of improving side reflectivity and light leakage, and shows good black visibility.

[0159] On the contrary, the polarizing plates of Comparative Examples 1 and 2, which do not satisfy the front linear retardation and the oblique linear retardation within the retardation range according to the present invention at a wavelength of 550 nm, suffer from significant degradation of black visibility. The polarizing plate of Comparative Example 3, which does not satisfy the slow axis angle according to the present invention, has no significant effect on improving side reflectivity and light leakage and black visibility.

[0160] like Figure 2 As shown, the polarizing plate of the embodiment provides good black visibility and low side reflectivity. Figures 3 to 5 As shown, it can be seen that the polarizing plate of the comparative example has strong yellow or red visibility, provides poor black visibility and high reflectivity.

[0161] It should be understood that various modifications, changes, variations and equivalent embodiments may 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 a polarizer and a first retardation layer and a second retardation layer sequentially stacked on a lower surface of the polarizer, wherein the slow axis of the stack of the first retardation layer and the second retardation layer is inclined at an angle of 111° to 113° relative to the light transmission axis of the polarizer, and wherein the stack has a front linear retardation of 140 nm to 160 nm measured on the front side at a wavelength of 550 nm, and a tilted linear retardation of 145 nm to 170 nm measured at a wavelength of 550 nm with the stack rotated ±40° around the slow axis of the stack as a rotation axis. 2 . The polarizing plate according to claim 1 , wherein the first retardation layer has a thickness smaller than that of the second retardation layer. 3 . The polarizing plate according to claim 1 , wherein a thickness of the first retardation layer is in the range of 1% to 20% of a thickness of the second retardation layer. 4 . The polarizing plate according to claim 1 , wherein the first retardation layer is a liquid crystal layer and the second retardation layer is a non-liquid crystal layer. The polarizing plate according to claim 4 , wherein the liquid crystal layer is a discotic liquid crystal layer.

6. The polarizing plate according to claim 4, wherein the non-liquid crystal layer comprises a stretched film formed of a composition comprising at least one resin selected from the group consisting of cellulose resins, polyester resins, cyclic polyolefin (COP) resins, cyclic olefin copolymer (COC) resins, polycarbonate resins, polyether sulfone resins, polysulfone resins, polyamide resins, polyimide resins, polyolefin resins, polyarylate resins, polyvinyl alcohol resins, polyvinyl chloride resins, polyvinylidene chloride resins and acrylic resins. 7 . The polarizing plate according to claim 1 , wherein the first retardation layer has negative birefringence and the second retardation layer has positive birefringence. 8 . The polarizing plate of claim 1 , wherein the second retardation layer has a higher biaxiality (NZ) than the first retardation layer at a wavelength of 550 nm. 9 . The polarizing plate of claim 8 , wherein the first retardation layer has a biaxiality of −0.1 to 0.1 at a wavelength of 550 nm, and the second retardation layer has a biaxiality of greater than or equal to 1 and less than 1.3 at a wavelength of 550 nm. 10 . The polarizing plate of claim 9 , wherein the first retardation layer has a biaxiality of 0 at a wavelength of 550 nm, and the second retardation layer has a biaxiality of greater than or equal to 1 and less than 1.3 at a wavelength of 550 nm. 11 . The polarizing plate according to claim 1 , wherein the first retardation layer is a negative A plate and the second retardation layer is a negative B plate. 12 . The polarizing plate of claim 1 , wherein the first retardation layer has a front in-plane retardation of 200 nm to 280 nm at a wavelength of 550 nm, and the second retardation layer has a front in-plane retardation of 100 nm to 150 nm at a wavelength of 550 nm. 13 . The polarizing plate according to claim 1 , wherein a slow axis of the first retardation layer is inclined at an angle of 10° to 20° with respect to a light transmission axis of the polarizer. 14 . The polarizing plate according to claim 1 , wherein a slow axis of the second retardation layer is inclined at an angle of 70° to 85° with respect to a light transmission axis of the polarizer. 15 . The polarizing plate of claim 1 , wherein a buffer layer is formed on an upper surface of the second retardation layer. 16 . An optical display device comprising the polarizing plate according to claim 1 .

Images