Polarizing plate and optical display device

Abstract

Provided are a polarizing plate and an optical display device including the same. The polarizing plate includes: a polarizer; and a retardation layer formed on a lower surface of the polarizer, in which the retardation layer is an O-plate type liquid crystal layer having reverse wavelength dispersion, and the retardation layer has a liquid crystal beta angle maximum value of 40 DEG to 60 DEG and a liquid crystal beta angle average value of 20 DEG to 40 DEG.

Description

Technical Field

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

[0002] Due to the reflection of external light, the organic light emitting device display may suffer from a decrease in visibility and contrast. To solve this problem, a polarizing plate including a polarizer and a retardation film may be used to achieve an anti-reflection function by preventing leakage of reflected external light.

[0003] Generally, a polarizing plate for anti-reflection includes a polarizer and a retardation film stacked on one surface of the polarizer. As the retardation film, a stack of a retardation film providing a 1 / 2 phase retardation and a retardation film providing a 1 / 4 phase retardation, or a stack of a 1 / 4 phase retardation film and a positive C plate can be used. However, the retardation film includes at least two retardation films that achieve different phase retardations, and is therefore disadvantageous in terms of processability and economic feasibility.

[0004] On the other hand, with the recent increase in interest in foldable displays, there is also a need for polarizing plates for anti-reflection to have foldable properties. However, since the folding properties of each retardation film must be considered when improving the folding properties of a polarizing plate including two or more retardation films configured to achieve different phase retardations, the polarizing plate including two or more retardation films has limitations in improving the folding properties.

[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, when applied to a light-emitting device display, effectively reduces the reflectivity of both the front and side surfaces by using a single-piece structure of an O-plate type delay layer, while achieving the advantages of a single-piece negative dispersion delay layer or a double-piece negative dispersion delay layer including a negative dispersion delay layer and a positive C-plate.

[0008] Another object of the present invention is to provide a polarizing plate which, when applied to a light-emitting device display, has a smaller thickness than a single-layer negative dispersion delay layer or a double-layer negative dispersion delay layer including a negative dispersion delay layer and a positive C plate, thereby ensuring good folding characteristics by improving film properties.

[0009]

Technical solution

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

[0011] 1. The polarizing plate comprises: a polarizer; and a retardation layer formed on the lower surface of the polarizer, wherein the retardation layer comprises an O-plate type negative dispersion liquid crystal layer and has a maximum liquid crystal β angle of 40° to 60° and an average liquid crystal β angle of 20° to 40°.

[0012] 2. In 1, the retardation layer may be composed of a single layer.

[0013] 3. In 1 to 2, the retardation layer may have a short wavelength dispersion of 0.81 to 0.90 and a long wavelength dispersion of 1.01 to 1.10.

[0014] 4. In 1 to 3, when the surface of the retardation layer adjacent to the polarizer in the thickness direction of the retardation layer is called the top surface and the surface of the retardation layer opposite to the top surface is called the bottom surface, the liquid crystal compound on the top surface may have a larger or smaller liquid crystal β angle than the liquid crystal compound on the bottom surface.

[0015] 5. In 1 to 4, the retardation layer may have a liquid crystal β angle ranging from 5° to 90°.

[0016] 6. In 1 to 5, the retardation layer may have an in-plane retardation (Re) of 120 nm to 160 nm at a wavelength of 550 nm.

[0017] 7. In 1 to 6, the retardation layer may have an out-of-plane retardation (Rth) of 0 nm to 90 nm at a wavelength of 550 nm.

[0018] 8. In 1 to 7, the retardation layer may have a biaxiality (NZ) of 1.0 or less at a wavelength of 550 nm.

[0019] 9. In 1 to 8, the slow axis of the retardation layer may be inclined at an angle of 40° to 50° relative to the light absorption axis of the polarizer.

[0020] 10. In 1 to 9, the polarizing plate may include only a retardation layer as a retardation film on a lower surface of the polarizer.

[0021] 11. In 1 to 10, the retardation layer may include a solidified layer or a cured layer of a composition including a liquid crystal compound containing a mesogen group.

[0022] 12. In 11, the liquid crystal compound may include nematic liquid crystal.

[0023] 13. In 11 to 12, the liquid crystal compound may include a thermotropic liquid crystal compound.

[0024] 14. In 1 to 13, the retardation layer may have a thickness of 3 μm or less.

[0025] 15. In 1 to 14, the polarizing plate may further include a protective layer on an upper surface of the polarizer.

[0026] Another aspect of the present invention relates to an optical display device.

[0027] An optical display device includes the polarizing plate according to the present invention.

[0028]

Beneficial Effects

[0029] The present invention provides a polarizing plate, which, when applied to a light-emitting device display, effectively reduces the reflectivity of both the front and side surfaces by using a single-piece structure of an O-plate type delay layer, while achieving the advantages of a single-piece negative dispersion delay layer or a double-piece negative dispersion delay layer including a negative dispersion delay layer and a positive C-plate.

[0030] The present invention provides a polarizing plate which, when applied to a light-emitting device display, has a smaller thickness than a single-plate negative dispersion retardation layer or a double-plate negative dispersion retardation layer including a negative dispersion retardation layer and a positive C plate, thereby ensuring good folding characteristics by improving film characteristics. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 is a cross-sectional view of a polarizing plate according to one embodiment of the present invention.

[0032] Figure 2 This is a conceptual diagram of the liquid crystal β angle.

[0033] Figure 3 This is a conceptual diagram of the delay layer.

[0034] Figure 4 is a graph showing the measurement results of the in-plane retardation of the retardation layer of Example 1 measured from all angles (0° to 360°) at a wavelength of 550 nm according to viewing angles of 10° and 60°.

[0035] Figure 5 is a graph showing the measurement results of the in-plane retardation of the retardation layer of Example 2 measured from all angles (0° to 360°) at a wavelength of 550 nm according to viewing angles of 10° and 60°.

[0036] Figure 6 is a graph showing the measurement results of the in-plane retardation of the retardation layer of Example 3 measured from all angles (0° to 360°) at a wavelength of 550 nm according to viewing angles of 10° and 60°.

[0037] Figure 7is a graph showing the measurement results of the in-plane retardation of the retardation layer of Example 4 measured from all angles (0° to 360°) at a wavelength of 550 nm according to viewing angles of 10° and 60°.

[0038] Figure 8 is a graph showing the measurement results of the in-plane retardation of the retardation layer of Comparative Example 1 measured from all angles (0° to 360°) at a wavelength of 550 nm according to viewing angles of 10° and 60°.

[0039] Fig. 9 is a graph showing the measurement results of the in-plane retardation of the retardation layer of Comparative Example 2 measured from all angles (0° to 360°) at a wavelength of 550 nm according to viewing angles of 10° and 60°. 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 implemented in various ways and is not limited to the following embodiments.

[0041] The terminology used herein is for the purpose of describing exemplary embodiments and is not intended to be limiting of the 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.

[0042] In the drawings, in order to clearly describe the present invention, components irrelevant to the description are omitted, and the same components will be represented by the same reference numerals throughout the specification. Although the length, thickness or width of various components may be exaggerated for understanding in the drawings, the present invention is not limited thereto.

[0043] Herein, spatially relative terms such as “upper” and “lower” are defined with reference to the accompanying drawings. Therefore, it should be understood that the “upper surface” can be used interchangeably with the “lower surface”.

[0044] In this article, "in-plane retardation (Re)", "out-of-plane retardation (Rth)" and "biaxiality (NZ)" are represented by equations A, B and C, respectively:

[0045] [Equation A]

[0046] Re=(nx-ny)xd

[0047] [Equation B]

[0048] Rth=((nx+ny) / 2-nz)xd

[0049] [Equation C]

[0050] NZ=(nx-nz) / (nx-ny)

[0051] Wherein, nx, ny and nz are the refractive indices of the optical device measured at the measurement wavelength in its slow axis direction, fast axis direction and thickness direction, respectively, and d is its thickness (unit: nm). In equations A to C, the measurement wavelength may be 450nm, 550nm or 650nm.

[0052] Herein, the “slow axis direction” refers to an in-plane direction in which an optical device has a relatively high refractive index, and the “fast axis direction” refers to an in-plane direction in which an optical device has a relatively low refractive index.

[0053] In this document, "short wavelength dispersion" refers to Re(450) / Re(550) and "long wavelength dispersion" refers to Re(650) / Re(550). Re(450), Re(550) and Re(650) refer to the in-plane retardation (Re) values ​​of a single optical device or optical device stack at wavelengths of 450 nm, 550 nm and 650 nm, respectively.

[0054] As used herein, to express a specific numerical range, “X to Y” refers to values ​​greater than or equal to X and less than or equal to Y (X≤ and ≤Y).

[0055] The polarizing plate according to the present invention comprises: a polarizer; and a retardation layer formed on the lower surface of the polarizer, wherein the retardation layer comprises an O-plate type negative dispersion liquid crystal layer and has a maximum liquid crystal β angle of 40° to 60° and an average liquid crystal β angle of 20° to 40°.

[0056] Therefore, the polarizing plate according to the present invention can be used as a polarizing plate for anti-reflection in a light-emitting device display including an organic light-emitting diode (OLED) display, etc. When applied to a light-emitting device display, the polarizing plate can improve the screen quality by reducing the reflectivity of both the front and side surfaces. In addition, the polarizing plate according to the present invention includes a single sheet of an O-plate type liquid crystal layer to improve film properties by a thin thickness, and thus can be used for a foldable display in a wide temperature range including room temperature.

[0057] In the following, reference will be made to Figure 1 , Figure 2 and Figure 3 A polarizing plate according to an embodiment of the present invention is described.

[0058] refer to Figure 1 The polarizing plate may include a polarizer 30 , a protective layer 20 stacked on an upper surface of the polarizer 30 , and a retardation layer 10 stacked on a lower surface of the polarizer 30 .

[0059] Although in Figure 1Although not shown in the figure, an adhesive layer, a bonding layer, etc. may be formed on the lower surface of the retardation layer 10 so that the polarizing plate can be stacked on the panel of the display device.

[0060] The polarizing plate may have a retardation layer 10 as a retardation film on the lower surface of the polarizer 30, and may include an adhesive layer or a bonding layer on which the polarizer 30 and the retardation layer 10 may be stacked. Even with this structure, the polarizing plate can significantly reduce the reflectivity of the front and side surfaces. The polarizing plate according to the present invention includes only an O-plate type negative dispersion liquid crystal layer as the entire retardation layer arranged on the lower surface of the polarizer.

[0061] Herein, “upper surface of the polarizer” refers to a surface of the polarizer through which light emitted by the light-emitting device is emitted and on which external light is first incident.

[0062] Herein, “the lower surface of the polarizer” refers to a surface of the polarizer on which light emitted by the light-emitting device is incident and through which external light first exits from the polarizer.

[0063] Herein, a “light-emitting device” is a concept that may include an organic light-emitting device, an inorganic light-emitting device, or both organic and inorganic light-emitting devices.

[0064] Delay layer

[0065] The delay layer 10 can be stacked on the lower surface of the polarizer to provide an anti-reflection effect together with the polarizer. In addition, the delay layer is composed of a single layer and has a thinner thickness than a typical single-piece negative dispersion delay layer or a double-piece negative dispersion delay layer including a negative dispersion delay layer and a positive C-plate film, thereby providing a polarizing plate with good folding characteristics. Here, "good folding characteristics" refers to using a polarizing plate sample cut into a predetermined size at room temperature and fixed to a measuring device for folding testing (such as a CFT series tester (COVOTEC Co, Ltd.)) so that the sample is bent at its middle part in its longitudinal direction, and even after 100,000 rounds of bending tests, the polarizing plate does not delaminate and does not generate bubbles, wherein each bending test is performed at a rate of 30 cycles / minute, and the sample is folded so that the bent portion of the sample has a radius of curvature of 3mm, and then the sample is unfolded and returned to 180° (1 cycle refers to a single operation of folding and unfolding the sample).

[0066] The retardation layer may have a thickness of 3 μm or less, specifically, greater than 0 μm, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8, 2.9 or 3 μm, for example, greater than 0 μm and less than or equal to 3 μm, for example, 0.5 μm to 3 μm. Within this range, the thin thickness and good folding characteristics of the polarizing plate can be easily ensured for the retardation layer.

[0067] In this aspect, the delay layer includes an O-plate type negative dispersion liquid crystal layer and has a maximum liquid crystal β angle of 40° to 60° and an average liquid crystal β angle of 20° to 40°. With a delay layer having a maximum liquid crystal β angle of 40° to 60° and an average liquid crystal β angle of 20° to 40°, the polarizing plate can achieve a significant reduction in the reflectivity of the front and side surfaces even when the delay layer has a thin thickness. Specifically, in the delay layer, the maximum liquid crystal β angle can be 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59 or 60°, and the average liquid crystal β angle can be 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39 or 40°.

[0068] The delay layer exhibits negative dispersion. Negative dispersion provides a constant phase delay regardless of wavelength, and when applied to a polarizing plate, negative dispersion can easily significantly reduce the reflectivity of the front and side surfaces. As used herein, "negative dispersion" refers to that the short wavelength dispersion is less than the long wavelength dispersion. In one embodiment, the delay layer can have a short wavelength dispersion of 0.81 to 0.90, such as 0.81, 0.82, 0.83, 0.84, 0.85, 0.86, 0.87, 0.88, 0.89 or 0.90, and a long wavelength dispersion of 1.01 to 1.10, such as 1.01, 1.02, 1.03, 1.04, 1.05, 1.06, 1.07, 1.08, 1.09 or 1.10.

[0069] The retardation layer includes an O plate. As known to those skilled in the art, the O plate refers to when the liquid crystal β angle of the liquid crystal compound is oriented in an oblique direction in the thickness direction of the retardation layer, and when one surface of the retardation layer is referred to as the top surface and the other surface facing the one surface is referred to as the bottom surface in the thickness direction of the retardation layer, the top surface is opposite to the bottom surface, and the liquid crystal β angle gradually increases or decreases in the direction from the top surface to the bottom surface, rather than being uniform. Here, the "oblique direction" refers to a direction that is not substantially parallel or perpendicular to a surface of a layer adjacent to the retardation layer (e.g., the lower surface of a polarizer).

[0070] As used herein, "liquid crystal β angle" may have the same meaning as defined by those skilled in the art. For example, "liquid crystal β angle" may be formed in the retardation layer and refers to the tilted orientation angle of the liquid crystal in the thickness direction of the retardation layer, wherein the tilted orientation angle varies from the top surface to the bottom surface. If the tilted orientation angle in the thickness direction is parallel to the top surface or the bottom surface of the retardation layer, the liquid crystal β angle is defined as 0°.

[0071] The liquid crystal β angle may have a positive (+) or negative (-) value, depending on the direction of the maximum refractive index of the liquid crystal compound relative to the direction of one surface orientation of the layer adjacent to the retardation layer. In this article, for convenience, the liquid crystal β angle is described as a positive (+) value. However, the liquid crystal β angle may also be a negative value. For example, a liquid crystal β angle of 60° may also be -60°.

[0072] refer to Figure 2 , the liquid crystal β angle will be described.

[0073] refer to Figure 2 When the direction of the maximum refractive index of the liquid crystal compound is counterclockwise (such as θ1) relative to the angle of one surface of the layer adjacent to the retardation layer, the angle is defined as a positive (+) value. When the direction of the maximum refractive index of the liquid crystal compound is clockwise (such as θ2) relative to the angle of one surface of the layer adjacent to the retardation layer, the angle is defined as a negative (-) value.

[0074] The liquid crystal β angle can be measured by a typical method known to those skilled in the art. For example, a liquid crystal β angle measuring device (such as AxoScan or KOBRA) can be used to measure the liquid crystal β angle. The average and maximum liquid crystal β angles of the retardation layer according to the present invention can be measured using a liquid crystal β angle measuring device.

[0075] refer to Figure 3 For convenience, in the thickness direction of the retardation layer 10 , the surface of the retardation layer adjacent to the polarizing plate 30 is referred to as a top surface 11 , and the surface of the retardation layer opposite to the top surface 11 is referred to as a bottom surface 12 .

[0076] The liquid crystal β angle θ of the liquid crystal compound on the top surface 11 Pmay be larger than the liquid crystal β angle θ of the liquid crystal compound on the bottom surface B Here, the liquid crystal β angle θ of the liquid crystal compound on the top surface 11 is P The liquid crystal β angle of the liquid crystal compound in the retardation layer may be in the range of 5° to 90°, specifically, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47 , 48, 49, 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, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89 or 90°, for example, 5° to 60°, 10° to 60° or 20° to 90°.

[0077] Although not shown in the drawings, when the surface of the retardation layer 10 adjacent to the polarizer 30 in the thickness direction of the retardation layer 10 is referred to as the top surface 11 and the surface opposite to the top surface 11 is referred to as the bottom surface 12, the liquid crystal β angle θ of the liquid crystal compound on the top surface 11 is P is smaller than the liquid crystal β angle θ of the liquid crystal compound on the bottom surface 12 B and the liquid crystal β angle θ of the liquid crystal compound on the bottom surface 12 B The structure equal to the maximum liquid crystal β angle is also within the scope of the present invention. Here, the liquid crystal β angle θ of the liquid crystal compound on the bottom surface 12 is B The retardation layer has a liquid crystal β angle of 5 to 90°, specifically, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 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, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89 or 90°, for example 10° to 60° or 20° to 90°.

[0078] At a wavelength of 550 nm, the retardation layer 10 may have an in-plane retardation of 120 nm to 160 nm, such as 120, 121, 122, 123, 124, 125, 126, 127, 128, 129, 130, 131, 132, 133, 134, 135, 136, 137, 138, 139, 140, 141, 142, 143, 144, 145, 146, 147, 148, 149, 150, 151, 152, 153, 154, 155, 156, 157, 158, 159 or 160 nm, such as 130 nm to 150 nm, such as 130 nm to 145 nm. Within this range, the polarizing plate can effectively achieve an anti-reflection effect.

[0079] At a wavelength of 550 nm, the retardation layer 10 has an out-of-plane retardation of 0 nm to 90 nm, specifically, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 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 7, 48, 49, 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, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89 or 90 nm, for example, greater than 0 nm and less than or equal to 90 nm, 5 nm to 40 nm or 15 nm to 40 nm. Within this range, the polarizing plate can effectively achieve an anti-reflection effect.

[0080] At a wavelength of 550 nm, the retardation layer 10 has a biaxiality of 1.0 or less, specifically, 0.7, 0.71, 0.72, 0.73, 0.74, 0.75, 0.76, 0.77, 0.78, 0.79, 0.8, 0.81, 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 or 1.0, such as 0.7 to 1.0 or 0.8 to 1.0. Within this range, the polarizing plate can effectively achieve an anti-reflection effect.

[0081] The slow axis of the retardation layer 10 can be tilted at an angle of 40° to 50° relative to the light absorption axis of the polarizer, specifically, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49 or 50°, for example, 42° to 48°. Within this range, the retardation layer can improve the effect of the present invention. Here, "slow axis" refers to the axis of the retardation layer in its in-plane direction, wherein the retardation layer has a higher refractive index than other axes.

[0082] The maximum liquid crystal β angle and the average liquid crystal β angle of the retardation layer can be achieved by adjusting the composition of the liquid crystal compound and the composition of the additives when forming the retardation layer.

[0083] The retardation layer is a hardened layer or a solidified layer of a composition containing a liquid crystal compound. The hardened layer refers to a layer formed by solidifying a composition containing a liquid crystal compound in a solution state by cooling, etc. The solidified layer refers to a layer formed by crosslinking a composition containing a liquid crystal compound in a solution state using heat and / or light.

[0084] The retardation layer may be formed of a liquid crystal compound including a calamitous liquid crystal compound, a rod-like liquid crystal compound, etc. For example, the retardation layer may be formed of a nematic liquid crystal compound.

[0085] In one embodiment, the liquid crystal compound may include a thermotropic liquid crystal (temperature transition) compound. A thermotropic liquid crystal compound refers to a liquid crystal compound that allows the orientation of the liquid crystal to be changed by heat, so that the liquid crystal changes to a non-isotropic molten state at its melting point when heated, rather than to an isotropic liquid state. Thermotropic liquid crystal compounds may be advantageous for achieving a retardation layer having a maximum liquid crystal β angle and an average liquid crystal β angle according to the present invention.

[0086] In one embodiment, the retardation layer may be formed of a liquid crystal compound including a mesogen group.

[0087] The liquid crystal original group has an aromatic group and may include, for example, a di(meth)acrylate group, a di(meth)acrylate butanediol group, a butadiene divinyl group, a biphenyl group, a phenyl benzoate group, a phenylcyclohexane group, an azooxyphenyl group, an azomethine group, an azophenyl group, a phenylpyrimidine group, a diphenylethynyl group, a diphenyl benzoate group, a dicyclohexane group, a cyclohexylphenyl group, a tertiary phenyl group, etc., but is not limited thereto. These liquid crystal original groups may further include at least one substituent, such as an alkoxy group, a cyano group, a halogen group, an alkyl group, etc.

[0088] The liquid crystal compound may further include at least one cross-linking functional group. The cross-linking functional group may include a di(meth)acrylate group, a di(meth)acrylate butanediol group, a divinyl butadiene group, a (meth)acryloyl group, an epoxy group, a vinyl ether group, a cinnamoyl group, a cinnamyl group, a coumarin group, a benzophenone group, a group containing a (meth)acryloyl group, etc., but is not limited thereto. The group containing a (meth)acryloyl group may be a (meth)acryloyl furanyl group, a (meth)acryloyl biphenyl group, or a (meth)acryloyl naphthyl group.

[0089] The retardation layer according to the present invention may be implemented by forming the retardation layer by any typical method known to those skilled in the art, for example, by the following method.

[0090] The delay layer can be formed by the following process: subjecting a substrate to an orientation treatment; preparing a coating solution containing a liquid crystal compound and a solvent; applying the coating solution to a surface of the substrate subjected to the orientation treatment to form a laminate; heating the laminate to a liquid crystal temperature range in a state where an interface of the substrate opposite to the surface of the substrate coated with the coating solution contacts air; and cooling the laminate to a temperature lower than the liquid crystal temperature range.

[0091] The alignment treatment may include a vertical alignment treatment, a horizontal alignment treatment or an inclined alignment treatment. The alignment treatment may include a method of adsorbing an alignment agent to the surface of a substrate to form an alignment film, a method of shaping the surface of an alignment film formed on a substrate, or a method of irradiating the surface of an alignment film formed on a substrate with light. For example, the alignment agent may include lecithin, organosilane, octadecylmalonic acid, tetrafluoroethylene, polyimide, stearic acid, carbon, polyethylene oxide, etc., but is not limited thereto. Depending on the type of photochemical reaction of the compound containing a photoreactive functional group used in the photo-alignment film, light irradiation may be performed by any suitable method in the art. The light source for light irradiation may include an ultra-high pressure mercury lamp, a flash lamp, a high pressure mercury lamp, a low pressure mercury lamp, a xenon lamp, a metal halide lamp, etc.

[0092] In one embodiment, the alignment treatment may include forming an alignment film. In one embodiment, the alignment film may be formed by applying a composition for an alignment film to a substrate film, drying the composition, and tilting the composition at 5° to 50°, and then applying an ionizing agent at a wavelength of 200 nm to 400 nm at a temperature of 10 to 100 mJ / cm 2 The composition was cured using linearly polarized UV (LPUV) irradiation at a dosage of 100 Å.

[0093] Any suitable method for preparing a coating solution containing a liquid crystal compound and a solvent may be used. The solvent may include acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, cyclopentanone, 2-pentanone, 2-hexanone, ether, tetrahydrofuran, dioxane, anisole, ethyl acetate, butyl acetate, toluene, xylene, chloroform, methylene chloride, dichloroethane, dimethylformamide, dimethylacetamide, methyl celulose, etc., but is not limited thereto.

[0094] The process of heating the composition to the liquid crystal temperature range may be performed using heat, energy rays (eg, visible light, ultraviolet light, radiation, etc.), or the like.

[0095] although Figure 1 Not shown in the figure, an alignment film for liquid crystal alignment may also be formed on the top surface 11 of the retardation layer 10 adjacent to the polarizing plate 30 , or on the bottom surface 12 of the retardation layer 10 opposite to the top surface 11 .

[0096] Although in Figure 1 Although not shown in the figure, a transparent substrate film may be further stacked between the polarizer 30 and the retardation layer 10 and / or on the lower surface of the retardation layer 10. However, the transparent substrate film may be an optically transparent film (having a light transmittance of 90% or more at a wavelength of 380 nm to 780 nm) having substantially zero retardation (which does not affect the phase retardation characteristics of the retardation layer 10) and, for example, having an in-plane retardation of 10 nm or less, for example, 0 nm to 5 nm, at a wavelength of 550 nm.

[0097] Polarizer

[0098] The polarizer 30 is used to convert natural light or polarized light into linear polarized light by linear polarization in a certain direction, and can be formed of a polymer film mainly composed of a polyvinyl alcohol resin. Specifically, the polarizer 10 can be manufactured by dyeing the polymer film with iodine or a dichroic dye and stretching the dyed film in the machine direction (MD). Specifically, the polarizer 10 can be formed by stretching, dyeing, stretching, and cross-linking.

[0099] The polarizer 30 may have a light transmittance of 40% or more (eg, 40% to 47%) and a polarization degree of 99% or more (eg, 99% to 100%). Within this range, the polarizer may improve anti-reflection performance when combined with the first retardation layer and the second retardation layer.

[0100] The polarizer 30 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.

[0101] The polarizer 30 has a light absorption axis and a light transmission axis in its in-plane direction, wherein the light transmission axis is substantially orthogonal to the light absorption axis. With this structure, the polarizer can absorb a linearly polarized portion of light having a vibration direction parallel to the light absorption axis while transmitting other linearly polarized portions of the light. The light absorption axis of the polarizer may correspond to the machine direction (MD) of the polarizer and the light transmission axis may correspond to the transverse direction (TD) of the polarizer.

[0102] Protective layer

[0103] The protective layer 20 is formed on the upper surface of the polarizer 10 to protect the polarizer from the external environment and increase the mechanical strength of the polarizer.

[0104] The protective layer 20 is used to protect the polarizer 10 from the external environment, and can include an optically transparent film formed by at least one region selected from the following: for example, a cellulose resin including triacetyl cellulose (TAC), a polyester resin including polyethylene terephthalate (PET), polybutylene terephthalate, polyethylene naphthalate, polybutylene naphthalate, etc., a cyclic polyolefin 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.

[0105] The protective layer 20 may have a thickness of 5 μm to 70 μm, specifically 5 μm to 45 μm. Within this range, the protective layer may be used in a polarizing plate.

[0106] although Figure 1 Not shown, a functional coating may be formed on the upper surface of the protective film 20 to provide additional functions to the polarizing plate, and may include, for example, a hard coating, an anti-fingerprint layer, an anti-reflection layer, an anti-glare layer, etc., which may be used alone or as a stack thereof.

[0107] 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 a light emitting device display including various light emitting devices, such as an organic light emitting diode (OLED) display, and the like. [Specific implementation method]

[0109] 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 in any way as limiting the present invention.

[0110] Example 1

[0111] A polarizer having a light transmittance of 45% was prepared by stretching a polyvinyl alcohol film (TS#60, pre-stretched thickness: 20 μm, Japan Kuraray Co., Ltd.) to 6 times its initial thickness in an iodine aqueous solution at 60°C.

[0112] The composition for an alignment film (HSPA-256, Nissan Co., Ltd.) was bar-coated on a triacetyl cellulose (TAC) film and thermally dried at 125° C. for 2 minutes. After thermal drying, the TAC film was tilted 40° on a glass plate and heated at a wavelength of 313 nm and 25 mJ / cm 2 The film was irradiated with linearly polarized UV (LPUV) light at a dose of 100 to form an alignment film. A composition for an O-plate type liquid crystal layer (liquid crystal compound including thermotropic liquid crystal molecules, Merck Co., Ltd.) was spin-coated on the alignment film and then dried to form an O-plate type liquid crystal retardation layer (thickness: 2.7 μm, negative dispersion).

[0113] As a protective film, an HC-TAC film (25FJCHCN-TC, TAC film formed with a hard coating layer, thickness: 32 μm, Toppan Co., Ltd.) was stacked on the upper surface of the polarizer. A polarizing plate was prepared by stacking the prepared retardation layer on the lower surface of the prepared polarizer.

[0114] Examples 2 to 4

[0115] A polarizing plate was prepared in the same manner as in Example 1, except that the composition of the retardation layer was changed as listed in Table 1 by changing the liquid crystal composition forming the retardation layer.

[0116] Comparative Example 1

[0117] A polarizing plate was prepared in the same manner as in Example 1, except that the retardation layer was changed to a monolithic positive A-plate liquid crystal layer (negative dispersion) as shown in Table 1.

[0118] Comparative Example 2

[0119] Polarizing plates were prepared in the same manner as in Example 1 except that the retardation layer was changed to a single-plate positive A-plate liquid crystal layer (negative dispersion) and a double-plate positive A-plate liquid crystal layer (flat dispersion) as shown in Table 1.

[0120] Re and Rth of the retardation layer were measured at a wavelength of 550 nm using AxoScan (Axometry). Wavelength dispersion of the retardation layer was measured using AxoScan (Axometry).

[0121] The polarizing plates of Examples and Comparative Examples were evaluated by the following methods, and the results are shown in Tables 1 and Figure 4 .

[0122] (1) Reflectivity (unit: %): The reflectivity was measured using Instrument Systems DMS 803 (Konica Minolta Group, Japan). In the measurement of the reflectivity, the angle scanning function was used after measuring relative to a white plate provided to Instrument Systems DMS803 (Konica Minolta Group, Japan). Each polarizing plate prepared in the Examples and Comparative Examples was attached to a panel (including a glass substrate) by a pressure-sensitive adhesive, and then the reflectivity of the front and side surfaces was measured. θ was measured in increments of 5°, and the spectral transmittance / reflectivity (SCE) values ​​were taken at 0 degrees (T=0°) on the front and 60 degrees (T=60°) on the side to obtain the average SCE reflectivity at a wavelength of 400 nm to 700 nm.

[0123] (2) Phase retardation characteristics: The phase retardation characteristics were measured using AxoScan (Axometry) on the front and side of the sample facing the retardation layer (O plate, +A plate, or a stack of +A plate and +C plate). Each sample was placed on a measurement plate, θ and azimuth were measured in increments of 10°, and the in-plane retardation value at a wavelength of 550 nm was measured, and then the in-plane retardation values ​​at 10° and 60° were plotted in a circular graph.

[0124] Table 1

[0125]

[0126]

[0127] As shown in Table 1 and Figures 4 to 7 As shown, the polarizing plate according to the present invention has lower reflectivity on both the front and side surfaces. In addition, the polarizing plate according to the present invention has a thickness thinner than a double-plate type negative dispersion retardation layer including a negative dispersion retardation layer and a positive C-plate film.

[0128] Therefore, the polarizing plate according to the present invention is expected to provide good folding characteristics due to improved film characteristics. In addition, the polarizing plate according to the present invention is expected to achieve process simplification and cost reduction by realizing the performance of two layers of positive A plate and positive C plate in a single layer.

[0129] In contrast, the polarizing plate of Comparative Example 1 had a reflectivity of more than 0.4% at the side surface, which was higher than that of the polarizing plate of the example.

[0130] In addition, if Figures 4 to 9As shown, according to θ, the polarizing plate of the embodiment shows better retardation deviation than the positive A plate of Comparative Example 1, and its Phi (azimuth) value gradually becomes a left-right asymmetric shape (from Example 1 to Example 4). Therefore, it can be seen that since the polarizing plate has a more symmetrical Phi (azimuth) value, the polarizing plate has dependence on the liquid crystal β angle and shows better side reflectivity. Because the retardation layer of the polarizing plate of Comparative Example 2 has a thickness of 3μm, it is expected that the polarizing plate of Comparative Example 2 has limitations in providing good folding characteristics.

[0131] It should be understood that various modifications, changes, substitutions, 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: Polarizer; and a retardation layer formed on the lower surface of the polarizer, The retardation layer includes an O-plate type negative dispersion liquid crystal layer and has a maximum liquid crystal β angle of 40° to 60° and an average liquid crystal β angle of 20° to 40°.

2. The polarizing plate according to claim 1, wherein The retardation layer consists of a single layer.

3. The polarizing plate according to claim 1, wherein The retardation layer has a short wavelength dispersion of 0.81 to 0.90 and a long wavelength dispersion of 1.01 to 1.

10.

4. The polarizing plate according to claim 1, wherein When the surface of the retardation layer adjacent to the polarizer in the thickness direction of the retardation layer is called a top surface and the surface of the retardation layer opposite to the top surface is called a bottom surface, the liquid crystal compound on the top surface has a larger or smaller liquid crystal β angle than the liquid crystal compound on the bottom surface.

5. The polarizing plate according to claim 1, wherein The retardation layer has a liquid crystal beta angle in the range of 5° to 90°.

6. The polarizing plate according to claim 1, wherein The retardation layer has an in-plane retardation (Re) of 120 nm to 160 nm at a wavelength of 550 nm.

7. The polarizing plate according to claim 1, wherein The retardation layer has an out-of-plane retardation (Rth) of 0 nm to 90 nm at a wavelength of 550 nm.

8. The polarizing plate according to claim 1, wherein The retardation layer has a biaxiality (NZ) of 1.0 or less at a wavelength of 550 nm.

9. The polarizing plate according to claim 1, wherein: The slow axis of the retardation layer is inclined at an angle of 40° to 50° with respect to the light absorption axis of the polarizer.

10. The polarizing plate according to claim 1, wherein The polarizing plate includes only a retardation layer as a retardation film on a lower surface of the polarizer.

11. The polarizing plate according to claim 1, wherein The retardation layer includes a hardened or cured layer of a composition including a liquid crystal compound containing a mesogen group.

12. The polarizing plate according to claim 11, wherein The liquid crystal compound includes nematic liquid crystal.

13. The polarizing plate according to claim 11, wherein The liquid crystal compound includes a thermotropic liquid crystal compound.

14. The polarizing plate according to claim 1, wherein The retardation layer has a thickness of 3 μm or less. 15 . The polarizing plate according to claim 1 , further comprising a protective layer formed on an upper surface of the polarizer. 16 . An optical display device comprising the polarizing plate according to claim 1 .

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