Polarizing plate and optical display device

Abstract

Provided are a polarizing plate and an optical display device including the polarizing plate. The polarizing plate includes a polarizer and a retardation layer on one surface of the polarizer. The polarizing plate has an orthogonal transmittance of 1% or less at a wavelength of 600 nm, and the retardation layer includes a cholesterol liquid crystal layer in which an angle formed by a slow axis of the cholesterol liquid crystal layer at a wavelength of 450 nm with respect to a slow axis of the cholesterol liquid crystal layer at a wavelength of 550 nm is less than or equal to 5 DEG. And an angle formed by a slow axis of the cholesterol liquid crystal layer at a wavelength of 650 nm with respect to a slow axis of the cholesterol liquid crystal layer at a wavelength of 550 nm is less than or equal to 5 DEG.

Description

[0001] CITATION OF RELATED APPLICATIONS

[0002] This application claims priority to and the benefit of Korean Patent Application No. 10-2024-0122473, filed on September 9, 2024, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference. TECHNICAL FIELD

[0003] One or more embodiments of the present disclosure relate to a polarizing plate and an optical display apparatus. BACKGROUND

[0004] A light emitting diode display including an organic light emitting diode can include a polarizing plate to improve optical characteristics. The polarizing plate includes a polarizing sheet and a retardation layer disposed on one surface of the polarizing sheet.

[0005] In some cases, the retardation layer can consist of a single layer. In some cases, the retardation layer can be a stack of a negative dispersion retardation layer and a positive C retardation layer to improve reflection colors. When the polarizing plate including the stack is applied to an optical display apparatus, a screen of the optical display apparatus can exhibit red and blue colors depending on a panel type of the optical display apparatus and an arrangement of pixels in the optical display apparatus. Accordingly, it is desirable to prevent the screen of the optical display apparatus from exhibiting red and blue colors. SUMMARY

[0006] One or more aspects of some embodiments of the present disclosure relate to a polarizing plate that, when applied to an optical display apparatus, allows a screen to exhibit green color while preventing blue and red colors to be visible on its side as reflection colors, and can reduce a difference in reflection colors between left and right sides. Other aspects will be partially set forth in the following description, and partially will be apparent to those of ordinary skill in the art from the description, or can be learned by practice of the embodiments of the present disclosure provided.

[0007] According to one or more embodiments of the present disclosure, a polarizing plate is provided.

[0008] The polarizing plate includes a polarizing sheet and a retardation layer stacked on a surface (e.g., one surface) of the polarizing sheet, wherein the polarizing plate has a cross-transmittance of 1% or less at a wavelength of 600 nm, the retardation layer includes a cholesteric liquid crystal layer, an angle formed by a slow axis of the cholesteric liquid crystal layer at a wavelength of 450 nm with respect to a slow axis of the cholesteric liquid crystal layer at a wavelength of 550 nm is less than or equal to 5°, and an angle formed by a slow axis of the cholesteric liquid crystal layer at a wavelength of 650 nm with respect to the slow axis of the cholesteric liquid crystal layer at the wavelength of 550 nm is less than or equal to 5°.

[0009] According to one or more embodiments of the present disclosure, an optical display apparatus is provided.

[0010] An optical display device includes a polarizing plate according to one or more embodiments of the present disclosure.

[0011] Some embodiments of the present disclosure provide a polarizing plate that, when applied to an optical display device, allows a screen to present green color while preventing blue and red colors as reflected colors visible on its side, and can reduce a difference in reflected colors between left and right sides. BRIEF DESCRIPTION OF DRAWINGS

[0012] The accompanying drawings are included to provide a further understanding of the present disclosure, and are incorporated in and constitute a part of this disclosure. The drawings illustrate embodiments of the present disclosure and, together with the description, serve to explain principles of the present disclosure. The above and other aspects, features, and advantages of the present disclosure will become more apparent from the following detailed description, taken in conjunction with the accompanying drawings, in which:

[0013] Figure 1 is a cross-sectional view of a polarizing plate according to one or more embodiments of the present disclosure.

[0014] Figure 2 is a cross-sectional view of a polarizing plate according to one or more embodiments of the present disclosure.

[0015] Figure 3 is a cross-sectional view of a polarizing plate according to one or more embodiments of the present disclosure.

[0016] Figure 4 shows an exemplary cholesteric orientation liquid crystal layer according to one or more embodiments of the present disclosure.

[0017] Figure 5 is a graph showing evaluation results of reflected color values a* and b* in a polarizing plate applying a stack including a typical negative dispersion retardation layer and a positive C layer, in which ■ is a color coordinate of reflected color values a* and b* at a side (8°), ▲ is a color coordinate of reflected color values a* and b* at a side (30°), ● is a color coordinate of reflected color values a* and b* at a side (45°), and ★ is a color coordinate of reflected color values a* and b* at a side (60°).

[0018] Figure 6 is a graph showing evaluation results of reflected color values a* and b* in a polarizing plate applying a stack including a typical negative dispersion retardation layer and a positive C layer, in which ■ is a color coordinate of reflected color values a* and b* at a side (8°), ▲ is a color coordinate of reflected color values a* and b* at a side (30°), ● is a color coordinate of reflected color values a* and b* at a side (45°), and ★ is a color coordinate of reflected color values a* and b* at a side (60°). DETAILED DESCRIPTION

[0019] Hereinafter, some exemplary embodiments of the present disclosure will be described with reference to the accompanying drawings. It is to be understood that the present disclosure can be embodied in many ways and is not limited to the following embodiments. It is also to be understood that the following embodiments are provided in order to fully disclose and enable those skilled in the art to fully understand the present disclosure. In the drawings, the width or thickness of each element can be exaggerated or reduced, only for the purpose of convenience and clarity. Throughout the present disclosure, the same reference numbers denote the same components, and the repeated description thereof can not be repeated for the sake of brevity.

[0020] Herein, spatial relative terms, such as "upper" and "lower", are defined with reference to the drawings. Accordingly, it will be understood that the term "upper surface" is used interchangeably with the term "lower surface", and when an element, such as a layer or a film, is referred to as being disposed "on" another element, it can be directly disposed on the other element, or one or more intervening elements can be present therebetween. Conversely, when an element is referred to as being "directly" disposed "on" another element, no intervening element is present therebetween.

[0021] The terms used herein are only for the purpose of describing exemplary embodiments and are not intended to limit the present disclosure. 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.

[0022] Herein, the "in-plane retardation (Re)" of a cholesteric liquid crystal layer is measured by S in x M = S out The Mueller matrix is calculated to measure, and the slow axis and Re are obtained by matrix calculation, where,

[0023] S in : Stokes vector of an incident light beam, M: Mueller matrix, S out : Stokes vector of a reflected light beam.

[0024] In one or more embodiments of the present disclosure, the measurement wavelength of the in-plane retardation can be a wavelength of 450 nm, 550 nm, or 650 nm.

[0025] Herein, the axis in which the refractive index of an optical element in the in-plane direction achieves the maximum level will be defined as the slow axis, and the axis in which the refractive index of the optical element in the in-plane direction achieves the minimum level will be defined as the fast axis.

[0026] As used herein, "(meth)acrylic acid" means acrylic acid and / or methacrylic acid.

[0027] 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)".

[0028] Typically, an anti-reflective polarizer may include a polarizer and a stack of a negative dispersion retardation layer and a positive C layer stacked on the surface of the polarizer (e.g., one). When the anti-reflective polarizer is applied to an optical display device, the negative dispersion retardation layer cannot achieve complete absorption of blue and red light, resulting in the screen appearing blue and / or red when viewed from the side.

[0029] Figure 6 This is a graph showing the evaluation results of the reflectance values ​​a* and b* in a polarizer using a stack of typical negative dispersion retardation layers and positive C layers.

[0030] refer to Figure 6 It can be seen that, based on the azimuth angles of 8°, 30°, 45° and 60°, the reflected color values ​​a* and b* are concentrated in blue and red.

[0031] Typically, the above phenomenon is not easily observed on large-area optical display devices. However, it can be easily observed on small-area optical display devices such as laptops or tablets.

[0032] However, when applied to optical display devices, the polarizing plate according to one or more embodiments of this disclosure can prevent the screen from displaying blue and red depending on the azimuth angle by allowing the screen to display green. Therefore, when applied to optical display devices, the polarizing plate can prevent reflected colors from varying according to the field of view by allowing the entire screen to display green without displaying blue and red.

[0033] In this respect, when a polarizing plate according to one or more embodiments is applied to an optical display device, the optical display device has a reflectance color value a* of -2.5 to 2 and a reflectance color value b* of -2 to 3 over the entire field of view (e.g., at a side incident angle of 8°), and has a reflectance color value a* of 0 or less and a reflectance color value b* of 0 or greater at a side incident angle of 60°.

[0034] The polarizing plate includes a cholesteric liquid crystal layer as a delay layer disposed between the polarizer and the panel (e.g., screen) of the optical display device, wherein the angle formed by the slow axis of the cholesteric liquid crystal layer at a wavelength of 450 nm relative to the slow axis of the cholesteric liquid crystal layer at a wavelength of 550 nm, the angle formed by the slow axis of the cholesteric liquid crystal layer at a wavelength of 650 nm relative to the slow axis of the cholesteric liquid crystal layer at a wavelength of 550 nm, and the orthogonal transmittance of the polarizing plate at a wavelength of 600 nm are adjusted.

[0035] According to one or more embodiments, the polarizing plate may include a polarizer and a retardation layer stacked on the surface of the polarizer (e.g., one), wherein the polarizing plate has an orthogonal transmittance of 1% or less at a wavelength of 600 nm, and the retardation layer includes a cholesteric liquid crystal layer, wherein the angle formed by the slow axis of the cholesteric liquid crystal layer at a wavelength of 450 nm relative to the slow axis of the cholesteric liquid crystal layer at a wavelength of 550 nm is less than or equal to 5°, and the angle formed by the slow axis of the cholesteric liquid crystal layer at a wavelength of 650 nm relative to the slow axis of the cholesteric liquid crystal layer at a wavelength of 550 nm is less than or equal to 5°.

[0036] Light transmittance of polarizing plate

[0037] The polarizing plate has an orthogonal transmittance (Tc) of 1% or less at a wavelength of 600 nm. By making the orthogonal transmittance at a wavelength of 600 nm 1% or less at some wavelengths, the polarizing plate can increase the green light absorption when external light enters it, thereby preventing the reflected color value from turning blue and red, while allowing the reflected color value to turn green across the entire screen.

[0038] In one or more embodiments, the polarizing plate may have an orthogonal transmittance of 0 to 1%, 0 to 0.5%, 0.1% to 0.5%, or 0.3% to 0.5% at a wavelength of 600 nm.

[0039] The cross-transmittance at a wavelength of 600 nm can be determined not only by the cholesteric liquid crystal layer, but also by the protective layer, bonding layer, etc., that may be included in the polarizer, and can be mainly achieved by adjusting the cross-transmittance of the polarizer at a wavelength of 600 nm. The method for adjusting the cross-transmittance of the polarizer at a wavelength of 600 nm will be described in more detail below.

[0040] The polarizing plate can have a single-unit light transmittance (Ts) of 40% to 47%, for example 42% to 46%, at a wavelength of 550 nm. Within this range, the effects of the polarizing plate described above can be easily achieved.

[0041] The polarizing plate can have a single-unit light transmittance of 3% or less, for example, 0 to 3%, at a wavelength of 380 nm. Within this range, it can prevent external light from damaging the light-emitting diode. A single-unit light transmittance of 3% or less at a wavelength of 380 nm can be achieved by adding a UV absorber to at least one of the polarizer, cholesteric liquid crystal layer, or protective layer in the polarizing plate.

[0042] Cholesterol liquid crystal layer

[0043] The inventors of this disclosure acknowledge that while a polarizing plate with 1% or less of crossed light transmittance at a wavelength of 600 nm can make the entire screen appear green by increasing green light absorption, there are limitations in achieving this effect. A cholesteric liquid crystal layer can increase green light absorption, thereby making the reflected color value green across the entire screen, with no difference in reflected color value between the left and right sides.

[0044] For example, the angle formed by the slow axis of the cholesterol liquid crystal layer at a wavelength of 450 nm relative to the slow axis of the cholesterol liquid crystal layer at a wavelength of 550 nm (hereinafter referred to as "angle A") is less than or equal to 5°, and the angle formed by the slow axis of the cholesterol liquid crystal layer at a wavelength of 650 nm relative to the slow axis of the cholesterol liquid crystal layer at a wavelength of 550 nm (hereinafter referred to as "angle B") is less than or equal to 5°.

[0045] In this paper, since angle A is the absolute value of the angle formed by the slow axis of the cholesteric liquid crystal layer at a wavelength of 450 nm relative to the slow axis of the cholesteric liquid crystal layer at a wavelength of 550 nm, angle A can be in the range of 0° to 5°.

[0046] In this paper, since angle B is the absolute value of the angle formed by the slow axis of the cholesteric liquid crystal layer at a wavelength of 650 nm relative to the slow axis of the cholesteric liquid crystal layer at a wavelength of 550 nm, angle B can be in the range of 0° to 5°.

[0047] When both angles A and B are less than or equal to 5°, the absorption of green light can be increased, thus making the reflected color value green across the entire screen, with no difference in reflected color value between the left and right sides.

[0048] If (for example, when) angle A is less than or equal to 5° and angle B is greater than 5°, there may be a problem that the lateral reflectivity may be increased and the reflected color on the side may be biased towards reddish / bluish.

[0049] If (for example, when) angle B is less than or equal to 5° and angle A is greater than 5°, there may be a problem that the lateral reflectivity may be increased and the reflected color on the side may be biased towards a slightly reddish / slightly blue tint.

[0050] In one or more embodiments, angle A can be in the range of 0° to 5°, for example, greater than 0° and less than or equal to 5°, 0° to 4.5°, and 2° to 4.5°. In one or more embodiments, angle B can be in the range of 0° to 5°, for example, greater than 0° and less than or equal to 5°, 0° to 3°, and 0° to 1°. Within these ranges, polarizing plates can be easily manufactured.

[0051] In one or more embodiments, at least one of angle A or angle B may be greater than 0°.

[0052] The slow axis of the cholesterol liquid crystal layer can be measured using the AxoScan measurement device at a wavelength of 450 nm, its slow axis at a wavelength of 550 nm, and its slow axis at a wavelength of 650 nm.

[0053] Angles A and B can be achieved by controlling the content (e.g., amount) of the chiral reagent used in the process of preparing the cholesterol liquid crystal layer. The process will be described in more detail below.

[0054] The cholesteric liquid crystal layer can have a slow axis at a wavelength of 450 nm, a slow axis at a wavelength of 550 nm, and a slow axis at a wavelength of 650 nm, which are different from each other. That is, the angle formed by the slow axis at wavelengths of 450 nm, 550 nm, and 650 nm relative to the light absorption axis (i.e., absorption axis) of the polarizer can be different.

[0055] In one or more embodiments, the cholesterol liquid crystal layer can satisfy Relation 1. Therefore, the polarizing plate can reduce lateral reflectivity and allow the reflected color to be green.

[0056] Relationship 1

[0057] A450>A550≥A650

[0058] Here, A450 is the absolute value of the angle formed by the slow axis of the cholesteric liquid crystal layer relative to the absorption axis of the polarizer at a wavelength of 450 nm.

[0059] A550 is the absolute value of the angle formed by the slow axis of the cholesteric liquid crystal layer relative to the absorption axis of the polarizer at a wavelength of 550 nm.

[0060] A650 is the absolute value of the angle formed by the slow axis of the cholesteric liquid crystal layer relative to the absorption axis of the polarizer at a wavelength of 650 nm.

[0061] In one or more embodiments, the cholesterol liquid crystal layer can satisfy relation 1-1:

[0062] Relationship 1-1

[0063] A450 > A550 > A650

[0064] Among them, A450, A550 and A650 are the same as those defined in relation 1.

[0065] In relation 1, A450 can be in the range of 45° to 50°, for example, 46° to 49°, or 47° to 49°; A550 can be in the range of 44° to 47°, for example, 44° to 46°, or 45° to 46°; and A650 can be in the range of 43° to 46°, for example, 44° to 46°, or 45° to 46°. Within these ranges, angles A and B can be easily realized.

[0066] In one or more embodiments, the cholesterol liquid crystal layer can satisfy relation 2. Therefore, the polarizing plate can reduce lateral reflectivity and allow the reflected color to be green.

[0067] Relationship 2

[0068] B450 <B550<B650

[0069] Wherein, B450 is the in-plane retardation of the cholesteric liquid crystal layer at a wavelength of 450 nm.

[0070] B550 is an in-plane retardation of a cholesteric liquid crystal layer at a wavelength of 550 nm, and

[0071] B650 is the in-plane retardation of a cholesterol liquid crystal layer at a wavelength of 650 nm.

[0072] In relation 2, B450 can be in the range of 100nm to 150nm, for example, 100nm to 140nm, or 100nm to 130nm; B550 can be in the range of 110nm to 160nm, for example, 110nm to 150nm, or 120nm to 140nm; and B650 can be in the range of 120nm to 170nm, for example, 120nm to 160nm, or 130nm to 160nm. Within these ranges, cholesteric liquid crystal layers can be easily manufactured.

[0073] Cholesterol liquid crystal layers can have a thickness of 10 μm or less, for example, a thickness greater than 0 μm and less than or equal to 10 μm.

[0074] The cholesterol liquid crystal layer may include cholesterol liquid crystal (CLC) regions with a cholesterol (cholesterol phase) orientation. The CLC region may be a liquid crystal region having a helical structure in which liquid crystal molecules are layered and oriented, and the directors of the liquid crystal molecules are twisted along a helical axis.

[0075] Figure 4 An exemplary cholesterol-oriented liquid crystal layer according to one or more embodiments is shown.

[0076] refer to Figure 4 CLC regions contain liquid crystal molecules (Figure 4 In the n) layering orientation and the direction vector of the liquid crystal molecules along the helical axis ( Figure 4 The H) twisted helical structure. The director of the liquid crystal molecules completes a 360-degree rotation within the CLC region structure by a distance ( Figure 4 The term P in this context is called "pitch". In this paper, the term "CLC region" can refer to the area where the director of a CLC molecule completes a 360-degree rotation. The director of a liquid crystal molecule can refer to the slow axis direction. For example, the director of a liquid crystal molecule can represent the normal direction of the disk in a disk-shaped liquid crystal or the long axis direction of the rod-shaped body in a rod-shaped liquid crystal.

[0077] Cholesterol liquid crystal layers can be obtained by maintaining a cholesterol liquid crystal phase. Preferably, the structure for maintaining the cholesterol liquid crystal phase is one in which the orientation of the liquid crystal compound constituting the cholesterol liquid crystal phase is supported. For example, the polymerizable liquid crystal compound is oriented to the cholesterol liquid crystal phase, and then polymerized and cured by UV light radiation, heat, etc., to form a non-liquid layer, simultaneously becoming a structure in which the orientation of the cholesterol liquid crystal molecules is not changed by external loads or forces. Alternatively, the structure for maintaining the cholesterol liquid crystal phase can be any structure in which the optical properties of the cholesterol liquid crystal phase are maintained and the liquid crystal compound does not need to exhibit liquid crystallinity. For example, in one or more embodiments, the polymerizable liquid crystal compound can be polymerized through a curing reaction to lose its liquid crystallinity.

[0078] Materials with cholesterol liquid crystal structures may include liquid crystal compositions containing liquid crystal compounds. In one or more embodiments, the liquid crystal compound includes a polymerizable liquid crystal compound.

[0079] In one or more embodiments, the liquid crystal composition containing the polymerizable liquid crystal compound further comprises a surfactant, a chiral agent, and a polymerization initiator.

[0080] The polymerizable liquid crystal compound can be a rod-shaped or disc-shaped liquid crystal compound. Non-limiting examples of polymerizable groups included in the polymerizable liquid crystal compound may include acryloyl, methacryl, epoxy, vinyl, etc. By curing the polymerizable liquid crystal compound, the orientation of the liquid crystal compound can be ensured. Liquid crystal compounds having polymerizable groups can be monomers or relatively low molecular weight liquid crystal compounds with a degree of polymerization of less than 100.

[0081] The disc-shaped liquid crystal compound can be, for example, a compound having a triphenylene structure. On the other hand, since disc-shaped liquid crystal compounds having a 3-substituted benzene structure have a larger Δn (birefringence) and can broaden the selective reflection wavelength range compared to disc-shaped liquid crystal compounds having a triphenylene structure, a disc-shaped liquid crystal compound having a triphenylene structure can be appropriately selected as needed.

[0082] Rod-shaped liquid crystal compounds may include methylimine, azooxides, cyanophenyl esters, benzoates, cyclohexanecarboxylic acid phenyl esters, cyanophenylcyclohexane, cyano-substituted phenylpyrimidines, alkoxy-substituted phenylpyrimidines, phenyl dioxanes, and / or alkenylcyclohexylbenzonitrile.

[0083] The chiral agent may include at least one of a levorotatory chiral agent or a dextrorotatory chiral agent. In one or more embodiments, the chiral agent is a levorotatory chiral agent.

[0084] The chiral agent may be present in an amount of 1 to 4 parts by weight, for example 3 to 4 parts by weight, relative to 100 parts by weight of the polymerizable liquid crystal compound. Within this range, the chiral agent can readily realize a cholesterol liquid crystal layer.

[0085] The angles A and B of the cholesterol liquid crystal layer can be controlled according to the content (e.g., amount) of the chiral reagent.

[0086] Delay layer

[0087] In one or more embodiments, the delay layer may consist of only a cholesterol liquid crystal layer.

[0088] In one or more embodiments, the delay layer may include a cholesterol liquid crystal layer and a protective layer on at least one surface of the cholesterol liquid crystal layer.

[0089] The protective layer may be substantially the same as described below.

[0090] polarizer

[0091] Polarizers are used to reduce reflected color and reflectivity across the entire field of view by linearly polarizing external light or light incident from a delayed stack.

[0092] The polarizer can have a polarization degree of 99% or greater. By simultaneously satisfying this polarization degree and single-unit light transmittance (Ts), the polarizer can significantly reduce reflectivity when stacked on a delay stack. "Single-unit light transmittance" refers to the single-unit light transmittance (Ts) measured in the visible spectrum, for example, at wavelengths from 400 nm to 700 nm, and can be measured by typical methods known to those skilled in the art. Polarization degree can be measured by any method known to those skilled in the art. For example, the polarizer can have a polarization degree of 99% to 99.9999%.

[0093] The polarizer can have an orthogonal transmittance of 1% or less at a wavelength of 600 nm. Within this range, the polarizer can easily achieve the orthogonal transmittance at a wavelength of 600 nm described above.

[0094] The polarizer can have a thickness of 5 μm to 40 μm. Within this range, the polarizer can be used in a polarizing plate.

[0095] The light absorption axis of a polarizer can correspond to the stretching direction, such as the machine orientation (MD) of the polarizer when it is made from a polyvinyl alcohol film.

[0096] In one or more embodiments, the polarizer may include a polyvinyl alcohol polarizer manufactured by uniaxially stretching a polyvinyl alcohol film. In one or more embodiments, the polarizer may be manufactured by dyeing, stretching, crosslinking, and color correcting a polyvinyl alcohol film.

[0097] To manufacture a polarizing plate with an orthogonal transmittance of 1% or less at a wavelength of 600nm, the polarizer can be manufactured by the following method.

[0098] The polyvinyl alcohol film can be any typical polyvinyl alcohol film known to those skilled in the art.

[0099] In one or more embodiments, the polyvinyl alcohol film contains hydrophilic and hydrophobic functional groups. The hydrophobic functional group is present in the polyvinyl alcohol film along with the hydrophilic functional group, and the hydrophilic functional group is a hydroxyl (OH) group.

[0100] Hydrophobic functional groups may be present in at least one of the main chain or side chains of the polyvinyl alcohol resin constituting the polyvinyl alcohol film. Herein, the main chain refers to the portion constituting the main backbone of the polyvinyl alcohol resin, and the side chain refers to a backbone or chain connected to the main chain. In one or more embodiments, the hydrophobic functional groups are present in the main chain of the polyvinyl alcohol resin.

[0101] Polyvinyl alcohol resins having hydrophilic and hydrophobic functional groups incorporated therein can be prepared by polymerizing one or more vinyl ester monomers (such as vinyl acetate, vinyl formate, vinyl propionate, vinyl butyrate, vinyl pentanoate, isopropylene acetate, etc.) with a monomer providing a hydrophobic functional group. In one or more embodiments, the vinyl ester monomer includes vinyl acetate. The monomer providing the hydrophobic functional group may include monomers providing a hydrocarbon repeating unit, including ethylene, propylene, etc.

[0102] The polyvinyl alcohol film may have a thickness of 50 μm or less, for example, from 10 μm to 50 μm. Within this range, the polyvinyl alcohol film does not undergo melting and breakage during the stretching process.

[0103] The dyeing process involves treating a polyvinyl alcohol (PVA) film in a dyeing bath containing a dichroic material. In the dyeing process, the PVA film is immersed in the dyeing bath containing the dichroic material. The dyeing bath containing the dichroic material comprises an aqueous solution containing both the dichroic material and a boron compound (e.g., boric acid). Because the dyeing bath contains both the dichroic material and the boron compound, the dyed PVA film can be prevented from breaking when stretched under the stretching conditions described below.

[0104] Dichroic materials may include iodine selected from at least one of the following: potassium iodide, hydrogen iodide, lithium iodide, sodium iodide, zinc iodide, aluminum iodide, lead iodide, and cuprous iodide. The dichroic material may be present in the staining bath (e.g., in the staining solution) at an amount of 0.5 mol / ml to 10 mol / ml, for example, 0.5 mol / ml to 5 mol / ml. Within this range, uniform staining can be achieved.

[0105] Boron compounds can help prevent polyvinyl alcohol (PVA) films from melting and breaking during stretching. Even when stretched at high temperatures and with a high draw ratio, boron compounds can help prevent PVA films from melting and breaking during subsequent stretching processes.

[0106] The boron compound may include at least one of boric acid or borax. The boron compound may be present in the dyeing bath (e.g., in a dyeing solution) in an amount of 0.1 wt% to 5 wt%, for example 0.3 wt% to 3 wt%. Within this range, the polyvinyl alcohol film does not undergo melting and breakage during the stretching process and can achieve high reliability.

[0107] The dyeing solution can have a temperature of 20°C to 50°C, for example, 25°C to 50°C. The dyeing process is carried out by immersing the polyvinyl alcohol film in the dyeing bath for 30 seconds to 120 seconds, for example, 40 seconds to 80 seconds.

[0108] The stretching process includes uniaxially stretching dyed polyvinyl alcohol films at a temperature of 57°C or higher, for example, at a stretch ratio of 5.7 times or greater, for example, 5.7 times to 7 times, at a temperature of 57°C or higher, for example, at a stretch ratio of 57°C to 65°C.

[0109] The stretching process is performed by wet stretching or dry stretching. In one or more embodiments, the stretching process includes wet stretching to apply a boron compound during the stretching process. Wet stretching involves uniaxial stretching of a polyvinyl alcohol film in an aqueous solution containing a boron compound along the machine direction.

[0110] The boron compound may include at least one of boric acid or borax. The boron compound may be present in the stretching bath (e.g., in the stretching solution) in an amount of 0.5 wt% to 10 wt%, for example 1 wt% to 5 wt%. Within this range, the polyvinyl alcohol film does not undergo melting and breakage during the stretching process and can achieve high reliability.

[0111] A crosslinking process is performed to enhance the adsorption of dichroic materials onto the stretched polyvinyl alcohol film. The crosslinking solution used in the crosslinking process includes boron compounds. Boron compounds can help enhance the adsorption of the dichroic materials described above, while improving the reliability of the polarizer even when it is subjected to thermal shock conditions.

[0112] The boron compound may include at least one of boric acid or borax. The boron compound may be present in the crosslinking bath (e.g., in the crosslinking solution) in an amount of 0.5 wt% to 10 wt%, for example, 1 wt% to 5 wt%. Within this range, the adsorption of dichroic materials to the polyvinyl alcohol film is enhanced, and high reliability of the polyvinyl alcohol film can be achieved. The crosslinking solution may have a temperature of 20°C to 55°C, for example, 25°C to 55°C. The crosslinking process is performed by immersing the polyvinyl alcohol film in the crosslinking bath for 30 sec to 120 sec, for example, 40 sec to 80 sec.

[0113] Color correction processes improve the durability of polyvinyl alcohol (PVA) films. The color correction bath may contain 10 wt% or less, for example, 1 wt% to 5 wt%, or 3 wt% to 5 wt% potassium iodide. The color correction solution may have a temperature of 20°C to 50°C, for example, 25°C to 50°C. The color correction process can be performed by immersing the PVA film in the color correction bath for 5 to 30 seconds, for example, 5 to 20 seconds.

[0114] The drying process can be performed after the color correction process by treating the polyvinyl alcohol film at a temperature of 30°C to 80°C, for example, 40°C to 80°C, for 2 minutes or less, for example, 1 minute to 2 minutes. The drying process can be performed by hot air drying, but is not limited to this.

[0115] In one or more embodiments, a polarizer with an orthogonal transmittance of 1% or less at a wavelength of 600 nm can be achieved by adjusting the conditions of the stretching process (e.g., stretching ratio, stretching temperature, etc.). In one or more embodiments, a polarizer with an orthogonal transmittance of 1% or less at a wavelength of 600 nm can be achieved by adjusting the conditions of the color correction process and the drying process.

[0116] In one or more embodiments, the polyvinyl alcohol film may be further subjected to at least one of a cleaning process or a swelling process before the dyeing process.

[0117] In the cleaning process, the polyvinyl alcohol film is washed with water to remove foreign matter.

[0118] In the swelling process, a polyvinyl alcohol film is immersed in a swelling bath within a predetermined temperature range to aid in dyeing and stretching with dichroic materials. The swelling process can be carried out for 30 to 50 seconds at temperatures ranging from 15°C to 35°C, for example, from 20°C to 30°C.

[0119] In one or more embodiments, the polarizing plate may further include at least one lower protective layer on the lower surface of the polarizer. In one or more embodiments, the polarizing plate may further include at least one upper protective layer on the upper surface of the polarizer.

[0120] protective layer

[0121] A protective layer may be stacked on the upper and / or lower surface of the polarizer to protect it. The protective layer protects the polarizer to improve its reliability and mechanical strength. If, for example, the mechanical properties of the polarizer can be ensured without a protective layer, then no protective layer may be provided. The protective layer may be stacked in one or more layers on the upper and / or lower surface of the polarizer.

[0122] The protective layer may include at least one of an optically transparent protective film or a protective coating. The protective film (i.e., the optically transparent protective film) may include a film formed from one or more of the following: cellulose ester resins, including triacetyl cellulose (TAC); cyclic polyolefin resins, including amorphous cyclic olefin polymers (COP); polycarbonate resins; polyester resins, including polyethylene terephthalate (PET); polyethersulfone resins; polysulfone resins; polyamide resins; polyimide resins; acyclic polyolefin resins; poly(meth)acrylate resins, including poly(methyl methacrylate); polyvinyl alcohol resins; polyvinyl chloride resins; and polyvinylidene chloride resins, but not limited thereto.

[0123] The protective coating can be formed from a photocurable resin composition comprising a photocurable compound and a polymerization initiator. The photocurable compound may include at least one selected from the group consisting of cationic polymerizable curable compounds, free radical polymerizable curable compounds, polyurethane resins, and silicone resins.

[0124] The protective layer can be formed of a non-retarded film or can have an in-plane retardation within a predetermined range. For example, the protective layer can have an in-plane retardation of less than 5,000 nm, 5,000 nm or greater, 120 nm to 160 nm, or 5 nm to 0 nm at a wavelength of 550 nm. Within this range, the polarizer can be protected without affecting the performance of the retarded stack.

[0125] The protective layer can have a thickness of 10 μm or less, or 5 μm to 300 μm, or 5 μm or less, or 5 μm to 200 μm. Within this range, the protective layer can be used in polarizing plates.

[0126] In one or more embodiments, the polarizing plate may further include a functional coating formed on at least one surface of the protective layer. The functional coating may include, but is not limited to, at least one selected from: a hard coating, an anti-fingerprint layer, an anti-reflective layer, an anti-glare layer, a low-reflection layer, and an ultra-low-reflection layer.

[0127] In one or more embodiments, the protective layer has low moisture permeability to further improve the durability of the polarizer after placement under high temperature / high humidity conditions. For example, in one or more embodiments, the protective layer may have a moisture permeability of 1 g / m³. 2 • Days or more, for example 1g / m 2 · up to 100g / m 2 • Moisture permeability. Within this range, polarizing plates exhibit excellent durability and can be easily manufactured with protective layers.

[0128] In one or more embodiments, at least one of the protective layer, adhesive layer, or bonding layer may be further disposed between the polarizer and the cholesteric liquid crystal layer and / or on the lower surface of the delay stack.

[0129] Figures 1 to 3 These are cross-sectional views of a polarizing plate according to an embodiment of the present invention.

[0130] A polarizing plate according to one or more embodiments may include a polarizer 100, an upper protective layer 200 stacked on the upper surface of the polarizer 100, and a retardation layer 300A stacked on the lower surface of the polarizer 100, wherein the retardation layer 300A may include a cholesteric liquid crystal layer 310.

[0131] A polarizing plate according to one or more embodiments may include a polarizer 100, an upper protective layer 200 stacked on the upper surface of the polarizer 100, and a retardation layer 300B stacked on the lower surface of the polarizer 100, wherein the retardation layer 300B may include a cholesteric liquid crystal layer 310 and a lower protective layer 320.

[0132] A polarizing plate according to one or more embodiments may include a polarizer 100, an upper protective layer 200 stacked on the upper surface of the polarizer 100, and a retardation layer 300C stacked on the lower surface of the polarizer 100, wherein the retardation layer 300C may include a lower protective layer 320 and a cholesteric liquid crystal layer 310.

[0133] Optical display devices

[0134] An optical display device according to one or more embodiments of the present disclosure includes a polarizing plate according to one or more embodiments of the present disclosure.

[0135] Optical display devices may include light-emitting diode (LED) displays. The LEDs may include at least one selected from organic LEDs, inorganic LEDs, and organic / inorganic LEDs.

[0136] The present disclosure will now be described in more detail with reference to some embodiments. However, it should be noted that these embodiments are provided for illustrative purposes only and should not be construed as limiting the present disclosure in any way.

[0137] Example 1

[0138] (1) Manufacturing polarizers

[0139] A polyvinyl alcohol film (VF-TS#4500, thickness: 45μm, Kuraray Co., Ltd.) that was washed with water at 25°C was swollen with water in a swelling bath at 50°C.

[0140] After swelling treatment, the membrane was immersed in a staining bath containing an aqueous solution of 1 mol / ml potassium iodide and 1 wt% boric acid for 65 seconds at 50°C. After staining treatment, the membrane was stretched at a stretch ratio of 5.7 times in a wet stretching bath containing an aqueous solution of 3 wt% boric acid at 60°C. After stretching treatment, the membrane was crosslinked at 55°C for 65 seconds in a crosslinking bath containing an aqueous solution of 3 wt% boric acid.

[0141] After crosslinking treatment, the film was subjected to color correction treatment for 10 seconds at 50°C in a color correction bath containing a color correction solution (an aqueous solution containing 4.5 wt% potassium iodide). After color correction treatment, the film was washed with water and dried with hot air at 80°C for 1 minute to prepare a polarizer (thickness: 17 μm).

[0142] (2) Manufacturing polarizing plates

[0143] A triacetylcellulose film with an anti-glare layer on one surface was prepared as the upper protective layer of a polarizing plate.

[0144] A membrane having a cholesterol liquid crystal layer formed on one surface of a triacetylcellulose membrane was prepared. The cholesterol liquid crystal layer comprised a rod-shaped liquid crystal compound and a levorotatory chiral agent. The levorotatory chiral agent was present in an amount of 3 parts by weight relative to 100 parts by weight of the rod-shaped liquid crystal compound.

[0145] The upper protective layer is bonded to the upper surface of the polarizer using an adhesive.

[0146] A polarizing plate is prepared by bonding a film having a cholesterol liquid crystal layer on one surface of a triacetylcellulose film to the lower surface of the polarizer.

[0147] Here, the film is bonded to the polarizer, thereby setting the angle of the slow axis of the cholesteric liquid crystal layer in the in-plane direction relative to the light absorption axis of the polarizer at a wavelength of 550 nm as listed in Table 1. In this way, the angles of the slow axis of the cholesteric liquid crystal layer relative to the light absorption axis of the polarizer at wavelengths of 450 nm and 650 nm can be provided as listed in Table 1.

[0148] Example 2

[0149] The polarizing plate was manufactured in essentially the same manner as in Example 1, except that angles A and B were changed by altering the content (e.g., amount) of the chiral reagent to 3.2 parts by weight relative to 100 parts by weight of the rod-shaped liquid crystal compound.

[0150] Example 3

[0151] The polarizing plate was manufactured in essentially the same manner as in Example 1, except that angles A and B were changed by altering the content (e.g., amount) of the chiral reagent to 3.3 parts by weight relative to 100 parts by weight of the rod-shaped liquid crystal compound.

[0152] Comparative Example 1

[0153] The polarizing plate was manufactured in essentially the same manner as in Example 1, except that the angles A and B were changed by altering the content (e.g., amount) of the chiral reagent to 6 parts by weight relative to 100 parts by weight of the rod-shaped liquid crystal compound.

[0154] Comparative Example 2

[0155] The polarizing plate was manufactured in essentially the same manner as in Example 1, except that angles A and B were changed by altering the content (e.g., amount) of the chiral reagent to 0.1 parts by weight relative to 100 parts by weight of the rod-shaped liquid crystal compound.

[0156] Comparative Example 3

[0157] (1) Manufacturing polarizers

[0158] A polyvinyl alcohol film (VF-TS#4500, thickness: 45μm, Kuraray Co., Ltd.) that was washed with water at 25°C was swollen with water in a swelling bath at 50°C.

[0159] After swelling treatment, the membrane was immersed in a staining bath containing an aqueous solution of 1 mol / ml potassium iodide and 1 wt% boric acid for 65 seconds at 50°C. After staining treatment, the membrane was stretched at a stretch ratio of 5.7 times in a wet stretching bath containing an aqueous solution of 3 wt% boric acid at 60°C. After stretching treatment, the membrane was crosslinked at 55°C for 65 seconds in a crosslinking bath containing an aqueous solution of 3 wt% boric acid.

[0160] After crosslinking treatment, the film was subjected to color correction treatment for 10 seconds at 50°C in a color correction bath containing a color correction solution (an aqueous solution containing 2.8 wt% potassium iodide). After color correction treatment, the film was washed with water and dried with hot air at 80°C for 1 minute to prepare a polarizer (thickness: 17 μm).

[0161] (2) Manufacturing polarizing plates

[0162] The polarizing plate was manufactured in essentially the same manner as in Example 1, except that angles A and B were changed by altering the content of the chiral reagent to 3.3 parts by weight relative to 100 parts by weight of the rod-shaped liquid crystal compound. The polarizing plate was then prepared using the prepared polarizing film in essentially the same manner as in Example 1.

[0163] Reference Example 1

[0164] The polarizer was manufactured in essentially the same manner as in Example 1.

[0165] A triacetylcellulose membrane (haze 15%, Toppan Co., Ltd.) with an anti-glare layer on one surface was prepared as the upper protective layer of the polarizing plate.

[0166] The upper protective layer is bonded to one surface of the polarizer. The polarizing plate is manufactured by sequentially stacking a negative dispersion retardation layer (positive A layer, liquid crystal layer) and a positive C layer (liquid crystal layer) on the other surface of the polarizer.

[0167] The following characteristics of each of the polarizing plates in the embodiments and comparative examples were evaluated, and the evaluation results are shown in Table 1. Figure 5 and Figure 6 middle.

[0168] (1) Orthogonal transmittance of polarizing plate: Each of the polarizing plates in the examples and comparative examples is placed in the light transmittance measuring device V-7100, and the orthogonal light transmittance at a wavelength of 600nm is obtained by transmitting light from the upper protective layer side to the polarizing plate in the normal direction in the in-plane direction of the polarizing plate.

[0169] (2) Reflection color values ​​a* and b*: The reflection color values ​​a* and b* on the sides (8°, 30°, 45° and 60°) were obtained using a DMS-803 (Minolta Co., Ltd.) goniometer.

[0170] Table 1

[0171]

[0172] *Slow axis angle: The angle between the slow axis of the cholesterol liquid crystal layer and the light absorption axis of the polarizer at the corresponding wavelength.

[0173] *In-plane retardation: In-plane retardation of cholesterol liquid crystal layers.

[0174] As shown in Table 1, when applied to an optical display device, each of the polarizing plates in the embodiments can minimize the difference in reflected color according to the field of view by allowing the screen to display green while preventing blue and red as reflected colors from being visible on its sides.

[0175] Conversely, the polarizing plate in the comparative example has no significant effect compared to the polarizing plate in the embodiment.

[0176] Figure 5 This is a graph showing the evaluation results of the reflectance color values ​​a* and b* in the polarizer of Application Example 1. (Reference) Figure 5 As can be seen, the overall reflected color value turns green.

[0177] Figure 6 This is a graph showing the evaluation results of the reflectance color values ​​a* and b* in the polarizer used in the reference example. (Reference) Figure 6 As can be seen, the reflected color values ​​change to blue and red across the entire screen.

[0178] In this disclosure, the terms "comprising," "including," or "having" will be understood to indicate the presence of the stated features, numbers, steps, operations, elements, and / or components, but do not exclude the presence or addition of one or more other features, numbers, steps, operations, elements, components, and / or groups thereof. Furthermore, the terms "comprising," "including," "having," or other similar terms include or support the terms "consisting of" and "substantially consisting of," which indicate the presence of the stated features, numbers, steps, operations, elements, and / or components, while other features, numbers, steps, operations, elements, components, and / or groups thereof are absent or substantially absent. Additionally, when describing embodiments of this disclosure, the use of "may" means "one or more embodiments of this disclosure."

[0179] In this disclosure, when placed before a list of elements, expressions such as “at least one of,” “one of,” and “selected from” modify the entire list of elements rather than individual elements of the list. For example, “at least one of a, b, or c,” “selected from at least one of a, b, and c,” “selected from at least one of a to c,” etc., can mean only a, only b, only c, both a and b (e.g., simultaneously), both a and c (e.g., simultaneously), both b and c (e.g., simultaneously), all of a, b, and c, or variations thereof. Furthermore, unless otherwise specifically indicated to the contrary, when “A and / or B,” “A or B,” or “A / B” is mentioned throughout the disclosure, it means A, B, or A and B.

[0180] It should be understood that even if the terms “about,” “approximately,” or “substantially” are not explicitly referenced in a given element (e.g., a claim element), the scope of such an element is intended to include non-substantial variations or variations that are understood by a person skilled in the art. For example, the numerical values ​​and ranges provided herein are intended to include tolerances and measurement uncertainties that would be recognized by a person skilled in the art, and elements (e.g., claim elements) should be considered to cover these equivalents.

[0181] Any numerical range listed herein is intended to include all subranges of the same numerical precision contained within the listed range. For example, the range “1.0 to 10.0” is intended to include all subranges between (and including) the listed minimum value of 1.0 and the listed maximum value of 10.0, i.e., a minimum value equal to or greater than 1.0 and a maximum value equal to or less than 10.0, such as 2.4 to 7.6. Any maximum numerical limit listed herein is intended to include all smaller numerical limits falling within it, and any minimum numerical limit listed in this disclosure is intended to include all larger numerical limits falling within it. Therefore, the applicant reserves the right to modify this disclosure (including the claims) to expressly list any subranges falling within the range expressly listed herein.

[0182] The foregoing description is a illustrative account of some embodiments of this disclosure and should not be construed as limiting it. Although some embodiments have been described, those skilled in the art will readily understand that various modifications to the embodiments are possible without departing from the spirit and scope of this disclosure. It will be understood that, unless otherwise described, the description of features or aspects within each embodiment should generally be considered applicable to similar features or aspects in other embodiments. Therefore, as will be apparent to those skilled in the art, unless specifically indicated otherwise, features, characteristics, and / or elements described in connection with specific embodiments may be used alone or in combination with features, characteristics, and / or elements described in connection with other embodiments. Therefore, it should be understood that the foregoing description is a illustrative account of several exemplary embodiments and should not be construed as limiting to the specific embodiments disclosed herein, and various modifications to the disclosed embodiments and other exemplary embodiments are intended to be included within the spirit and scope of this disclosure as defined by the appended claims and their equivalents.

Claims

1. A polarizing plate comprising: a polarizing sheet, and a retardation layer on a surface of the polarizing sheet; wherein the polarizing plate has a positive cross transmission of 1% or less at a wavelength of 600 nm, the retardation layer includes a cholesteric liquid crystal layer, an angle A formed by a slow axis of the cholesteric liquid crystal layer at a wavelength of 450 nm with respect to a slow axis of the cholesteric liquid crystal layer at a wavelength of 550 nm is less than or equal to 5°, and an angle B formed by a slow axis of the cholesteric liquid crystal layer at a wavelength of 650 nm with respect to the slow axis of the cholesteric liquid crystal layer at the wavelength of 550 nm is less than or equal to 5°.

2. The polarizing plate according to claim 1, wherein the polarizing plate has a monomer light transmission of 40% to 47% at a wavelength of 550 nm.

3. The polarizing plate according to claim 1, wherein the polarizing plate has a monomer light transmission of 3% or less at a wavelength of 380 nm. 4.The polarizing plate according to claim 1, wherein the angle A formed by the slow axis of the cholesteric liquid crystal layer at the wavelength of 450 nm with respect to the slow axis of the cholesteric liquid crystal layer at the wavelength of 550 nm is in a range of 0° to 5°, and the angle B formed by the slow axis of the cholesteric liquid crystal layer at the wavelength of 650 nm with respect to the slow axis of the cholesteric liquid crystal layer at the wavelength of 550 nm is in a range of 0° to 5°.

5. The polarizing plate according to claim 1, wherein at least one of the angle A or the angle B is greater than 0°.

6. The polarizing plate according to claim 1, wherein the cholesteric liquid crystal layer satisfies a relationship 1: relationship 1 A450 > A550 ≥ A650, wherein A450 is an absolute value of an angle formed by a slow axis of the cholesteric liquid crystal layer with respect to an absorption axis of the polarizing sheet at a wavelength of 450 nm, A550 is an absolute value of an angle formed by the slow axis of the cholesteric liquid crystal layer with respect to the absorption axis of the polarizing sheet at a wavelength of 550 nm, and A650 is an absolute value of an angle formed by the slow axis of the cholesteric liquid crystal layer with respect to the absorption axis of the polarizing sheet at a wavelength of 650 nm.

7. The polarizing plate according to claim 6, wherein in the relationship 1, A450 is in a range of 45° to 50°, A550 is in a range of 44° to 47°, and A650 is in a range of 43° to 46°.

8. The polarizing plate according to claim 1, wherein the cholesteric liquid crystal layer satisfies a relationship 2: relationship 2 B450 < B550 < B650, wherein B450 is an in-plane retardation of the cholesteric liquid crystal layer at a wavelength of 450 nm, B550 is an in-plane retardation of the cholesteric liquid crystal layer at a wavelength of 550 nm, and B650 is an in-plane retardation of the cholesteric liquid crystal layer at a wavelength of 650 nm.

9. The polarizing plate according to claim 8, wherein in the relationship 2, B450 is in a range of 100 nm to 150 nm, B550 is in a range of 110 nm to 160 nm, and B650 is in a range of 120 nm to 170 nm.

10. The polarizing plate according to claim 1, wherein the cholesteric liquid crystal layer has a thickness of 10 µm or less.

11. The polarizing plate according to claim 1, wherein the cholesteric liquid crystal layer includes a polymerizable liquid crystal compound and a left-handed chiral agent.

12. The polarizing plate according to claim 11, wherein an amount of the left-handed chiral agent is 1 part by weight to 4 parts by weight based on 100 parts by weight of the polymerizable liquid crystal compound.

13. The polarizing plate according to claim 11, wherein the polymerizable liquid crystal compound includes at least one of a rod-like liquid crystal compound or a discotic liquid crystal compound.

14. The polarizing plate according to claim 1, wherein The retardation layer includes only the cholesteric liquid crystal layer.

15. The polarizing plate according to claim 1, wherein The retardation layer includes the cholesteric liquid crystal layer and a protective layer on at least one surface of the cholesteric liquid crystal layer.

16. An optical display device comprising the polarizing plate according to any one of claims 1 to 15.

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