Polarizing plate and optical display apparatus

Abstract

This invention discloses a polarizing plate and an optical display device. The polarizing plate includes: a polarizer; and an optical functional layer formed on a surface of the polarizer, wherein the optical functional layer includes a matrix and needle-like particles embedded in the matrix, the needle-like particles being aligned in the in-plane direction of the optical functional layer with an average orientation angle of -10° to +10°, and the anisotropic diffusion rate of the optical functional layer is 1.5 to 2.5.

Description

[Technical Field]

[0001] [Cross-reference to related applications] This application claims priority to Korean Patent Application No. 10-2024-0050697, filed on April 16, 2024, with the Korean Intellectual Property Office, the entire disclosure of which is incorporated herein by reference for all purposes.

[0002] This disclosure relates to a polarizing plate and an optical display device. [Previous Technology]

[0003] The liquid crystal display has a structure in which a viewing-side polarizing plate, a liquid crystal panel, and a light source-side polarizing plate are stacked in sequence.

[0004] While liquid crystal displays (LCDs) offer numerous advantages, they suffer from side visibility and low brightness. To address these issues, a method has been proposed that involves providing a visibility enhancement layer to the viewing-side polarizer. This layer comprises two resin layers with different refractive indices and a pattern at their interface. However, this enhancement layer requires an additional patterning process, leading to reduced yield and increased material costs. Therefore, a polarizer that improves visibility without requiring such a enhancement layer is needed.

[0005] The background technology disclosed herein is published in Korean Patent Publication No. 2018-0047569, etc. [Summary of the Invention]

[0006] The purpose of this disclosure is to provide a polarizing plate that provides enhanced visibility, front brightness and side contrast even without a pattern, embodiment, visibility enhancement pattern or visibility enhancement layer having such a pattern.

[0007] Corresponding to one embodiment of this disclosure, the polarizing plate includes: a polarizer; and an optical functional layer stacked on one surface of the polarizer, wherein the optical functional layer includes a matrix and anisotropic particles embedded in the matrix and the matrix includes needle-like particles, at least some of the needle-like particles are aligned along the in-plane direction of the optical functional layer, the needle-like particles are aligned with an average orientation angle of -10° to +10°, and the optical functional layer has an anisotropic diffusivity of 1.5 to 2.5.

[0008] According to another aspect of the present disclosure, an optical display device includes a polarizing plate according to the present disclosure.

[0009] Embodiments of this disclosure provide a polarizing plate that, even without a pattern, can provide enhanced visibility, front brightness, and side contrast; for example, a visibility-enhancing pattern or a visibility-enhancing layer having such a pattern is provided. [Simplified Explanation of Figure Equations]

[0010] Figure 1 is a conceptual diagram of needle-like particles. Figure 2 is a conceptual diagram of the optical functional layer in a polarizing plate. Figure 3 is a schematic diagram showing the tilt angle distribution of the long axis direction of the needle-like particles relative to the reference plane, assuming the light absorption axis of the polarizer is tilted by 90° relative to the reference plane. Figure 4 is a conceptual diagram showing anisotropic diffusion rate. Figures 5 to 8 are cross-sectional views of the polarizing plate according to an embodiment. Figure 9 is a schematic diagram showing a method for measuring anisotropic diffusion rate.

Implementation Method

[0011] In the following, examples of the present disclosure will be described in detail with reference to the accompanying drawings, but it should be noted that the examples are not limited thereto.

[0012] The following detailed description is provided to help the reader fully understand the methods, apparatus, and / or systems described herein. However, after understanding this disclosure, various modifications, refinements, and equivalent equations of the methods, apparatus, and / or systems described herein will become apparent. For example, the order of operations described herein is merely an example and is not limited to the order described herein, but can be changed, as will become apparent after understanding this disclosure, except for operations that must be performed in a specific order. Furthermore, for clarity and brevity, descriptions of features known in this art may be omitted.

[0013] The features described herein may be implemented in different forms and should not be construed as limited to the examples described herein. Rather, the examples described herein are merely illustrative of some of the many possible ways to implement the methods, apparatus and / or systems described herein, which will become apparent upon understanding this disclosure.

[0014] Throughout this specification, when an element such as a layer, region, or substrate is described as being "located" "on," "connected to," or "coupled to" another element, the element may be directly "located" "on," directly "connected to," or directly "coupled to" the other element, or there may be one or more other elements in between. In contrast, when an element is described as being "directly located" "on," "directly connected to," or "directly coupled to" another element, there may be no other elements in between.

[0015] As used in the text, “and / or” includes any one of the related listed items and any combination of any two or more items; similarly, “at least one of” includes any one of the related listed items and any combination of any two or more items.

[0016] Although terms such as "first," "second," and "third" may be used herein to describe various components, parts, areas, layers, or sections, these components, parts, areas, layers, or sections are not limited by these terms. Rather, these terms are used only to distinguish individual components, parts, areas, layers, or sections. Therefore, without departing from the teaching of the examples, the first component, first part, first area, first layer, or first section mentioned in the examples described herein may also be referred to as the second component, second part, second area, second layer, or second section.

[0017] For ease of explanation, spatially relative terms such as "above," "upper," "lower," "below," and similar terms may be used herein to describe the relationship between one element and another shown in the figures. These spatially relative terms are intended to encompass different orientations of the device during use or operation, other than those illustrated in the figures. For example, if the device in the figures is flipped, an element described as being "above" or "upper" relative to another element will be "below" or "below" relative to that other element. Therefore, the term "above" encompasses both upper and lower orientations depending on the spatial orientation of the device. The device may also be oriented in other ways (rotated 90° or in other orientations), and the spatially relative terms used herein should be interpreted accordingly.

[0018] The terminology used herein is for illustrative purposes only and is not intended to limit this disclosure. Unless the context clearly indicates otherwise, the articles "a" and "the" are intended to include complex equations as well. The terms "comprises," "includes," and "has" indicate the presence of stated features, numbers, operations, components, elements, and / or combinations thereof, but do not preclude the presence or addition of one or more other features, numbers, operations, components, elements, and / or combinations thereof.

[0019] Due to manufacturing techniques and / or tolerances, the shape shown in the graphical equation may vary. Therefore, the examples described herein are not limited to the specific shapes shown in the graphical equation, but include shape variations that occur during manufacturing.

[0020] In this document, it should be noted that the use of the term "may" (for example, what an instance may include or implement) means that there is at least one instance that includes or implements such a feature, but not all instances are limited to this.

[0021] Here, "in-plane delay Re" refers to the value measured at a wavelength of 550 nm, expressed by equation A:

[0022] Re is (nx–ny)×d,----(A)

[0023] Where nx and ny are the refractive indices of the protective layer measured along the slow axis and fast axis at a wavelength of 550 nm, respectively, and d is the thickness of the protective layer (unit: nm).

[0024] In this article, "(meth)acrylate" refers to acrylate and / or methacrylic acid.

[0025] In this document, "refractive index" may refer to the value measured at wavelengths from 380 nm to 780 nm, specifically at 550 nm.

[0026] Here, "light transmittance" has the characteristics of total light transmittance, parallel light transmittance and diffuse transmittance measured at wavelengths from 400 nm to 700 nm, and can refer to the value measured in the visible spectrum at a wavelength of 550 nm.

[0027] As used herein, in order to indicate 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] In one embodiment, the polarizing plate provides a visibility enhancement effect even without a patterned visibility enhancement layer or a resin layer with a pattern at the interface. The polarizing plate increases the relative brightness of the front side and improves the contrast of the sides.

[0029] A polarizing plate according to one embodiment includes: a polarizer; and an optical functional layer stack on a surface of the polarizer, wherein the optical functional layer includes a matrix and anisotropic particles embedded in the matrix and including needle-like particles, at least some of the needle-like particles being aligned in the in-plane orientation of the optical functional layer, the needle-like particles being aligned with an average orientation angle of -10° to +10°, and the optical functional layer having an anisotropic diffusivity of 1.5 to 2.5.

[0030] In one embodiment, the optical functional layer may be a contrast enhancement layer or a visibility enhancement layer.

[0031] Hereinafter, anisotropic particles will be referred to as needle-like particles. It should be understood that anisotropic particles can also be realized by other types of anisotropic particles. Preferably, the anisotropic particles are needle-like particles.

[0032] In one embodiment, the upper and / or lower surfaces of the optical functional layer may be flat.

[0033] The needle-like particle has a short axis and a long axis.

[0034] Refer to Figure 1 for an explanation of the needle-like particles in the short axis and long axis directions. Figure 1 is a conceptual diagram of needle-like particles.

[0035] Referring to Figure 1, unlike spherical particles, needle-shaped particles can have a long major axis L and a short minor axis S that is shorter than the major axis.

[0036] According to one embodiment, the long axis of the needle-like particle can correspond to its longitudinal direction, while the short axis of the needle-like particle can correspond to its side direction.

[0037] Next, the alignment of the needle-like particles in the optical functional layer will be explained. Figure 2 is a conceptual diagram of the optical functional layer in the polarizer.

[0038] Referring to FIG2, the needle-like particles 1 can be aligned in one direction within the optical functional layer 10. According to this embodiment, the needle-like particles can be aligned along their long axis. The needle-like particles 1 can be aligned in one direction within the matrix 2 of the optical functional layer 10.

[0039] The needle-like particles can be aligned with an average orientation angle of -10° to +10°.

[0040] Here, "orientation angle" refers to the angle between the light absorption axis of the polarizer and the long axis of the needle-like particle when the light absorption axis of the polarizer is 0°. Spherical particles, especially isotropic particles, have a spherical shape and no short axis or long axis. Therefore, spherical particles have no orientation angle.

[0041] When the average alignment angle is in the range of -10° to +10°, the light emitted from the polarizer will be guided in different directions after passing through the needle-like particles, which is beneficial to improving the contrast and brightness of the front and sides. The light absorption axis of the polarizer can correspond to the machine direction (MD) of the polarizer.

[0042] The average alignment angle is described with reference to Figure 3. Figure 3 is a schematic diagram showing the tilt angle distribution of the long axis direction of the needle-like particles relative to the reference plane, assuming the light absorption axis of the polarizer is tilted by 90° relative to the reference plane. Referring to Figure 3, it can be seen that the average alignment angle is in the range of -10° to +10°.

[0043] The value obtained by subtracting 90° from the average tilt angle (average tilt angle - 90°) is the average orientation angle. For example, if the average tilt angle is 80°, the average orientation angle is -10°; if the average tilt angle is 100°, the average orientation angle is 10°. The orientation angle can be determined by the following method.

[0044] The average orientation angle of the needle-like particles can be in the range of -5.0° to +5.0°, preferably in the range of -4.0° to 4.0°, and more preferably in the range of -2.5° to 2.5°. Within this range, the needle-like particles can further enhance the effect of this disclosure.

[0045] In one embodiment, the needle-like particles may have an orientation angle standard deviation of less than 20°. Within this range, the needle-like particles can easily improve frontal brightness and side contrast. The orientation angle of the needle-like particles can have a standard deviation of 0° to 8.5°, preferably 5° to 8.5°, more preferably 5° to 8°. Within this range, the needle-like particles can further enhance the effects of this disclosure.

[0046] The standard deviation of the orientation angle can be measured by any typical method known to those skilled in the art.

[0047] In one embodiment, the optical functional layer includes needle-like particles such that at least 90% (for example, 95% to 100%) of the needle-like particles are aligned with an alignment angle of -10° to 10°. Within this range, the polarizer can ensure uniform contrast and improve visibility. Here, "%" refers to the weight ratio of the needle-like particles with an alignment angle of -10° to 10° to the total weight of the needle-like particles contained in the optical functional layer.

[0048] The optical functional layer may have an anisotropic diffusion rate of 1.5 to 2.5 and an average alignment angle of -10° to 10°, thereby further improving the relative brightness of the front side and the contrast of the side side.

[0049] Next, the anisotropic diffusion rate will be explained. Figure 4 is a conceptual diagram showing the anisotropic diffusion rate.

[0050] Anisotropic diffusivity is a value representing the degree of diffusion of light incident from a polarizer or similar source onto a needle-like particle. Anisotropic diffusivity can be calculated using Equation 1.

[0051] The anisotropic diffusion rate is (Xt / Xi) / (Yt / Yi),---(1)

[0052] where Xt is the light diffusivity measured in the short axis direction of the needle-like particles in the matrix embedded with the needle-like particles.

[0053] Yt is the light diffusivity measured along the long axis of the needle-like particles in the matrix embedded with the needle-like particles.

[0054] Xi is the light diffusivity measured in the matrix without embedded needle-like particles along the same direction as Xt, and.

[0055] Yi is the light diffusivity measured in the same direction as Yt in a matrix without embedded needle-like particles.

[0056] In Figure 4, (a) represents the light diffusivity Xi and the light diffusivity Yi, and (b) represents the optical diffusivity Xt and Yt.

[0057] As shown in Figure (a), it can be seen that the light diffusivity Xi and light diffusivity Yi of the matrix without embedded needle-like particles and the matrix with embedded needle-like particles in Figure (b) are basically the same in the short axis and long axis directions. In (a), the white mark indicates the degree to which light diffuses through the matrix from the point source when incident from the point source, while the black mark indicates the area through which the light does not pass.

[0058] As shown in (b), the light diffusivity Xt and light diffusivity Yt of the matrix with embedded needle-like particles were measured in the short-axis and long-axis directions of the needle-like particles, respectively. In (b), the white markings indicate the degree to which light incident from a point source is scattered from the position of the point source when light passes through the matrix in the light diffusivity measurement, and the black markings indicate the areas where light does not pass through. Referring to (b), it can be seen that the degree of diffusivity of the needle-like particles in the short-axis direction is different from that in the long-axis direction; more light diffuses in the short-axis direction than in the long-axis direction.

[0059] The matrix without embedded needle-like particles is basically the same as the matrix with embedded needle-like particles, excluding the needle-like particle manifestation.

[0060] The anisotropic diffusion rate is set in the range of 1.5 to 2.5 to evaluate whether the optical functional layer, including the needle-like particles, can improve the visibility and contrast of the front and sides. Assuming that the optical functional layer allows incident light to diffuse along the short axis of the needle-like particles, the anisotropic diffusion rate is set in the range of 1.5 to 2.5 for this purpose.

[0061] If the anisotropic diffusion rate of the optical functional layer is less than 1.5, the optical functional layer will not greatly improve the contrast between the front and the side. The polarizer cannot improve the contrast between the front and the side by adding an optical functional layer, and the improvement in the relative brightness of the front is negligible.

[0062] If the anisotropic diffusion rate of the optical functional layer is greater than 2.5, the relative brightness of the front side of the polarizer will be too low to be applied to an optical display device.

[0063] For example, the optical functional layer may have an anisotropic diffusion rate of 1.5 to 2.3, for example, the anisotropic diffusion rate may be 1.5 to 2.1.

[0064] The anisotropic diffusion rate is a value measured for the optical functional layer, preferably in a matrix with embedded needle-like particles. The alignment direction of the needle-like particles can be distinguished as the long axis direction and the short axis direction.

[0065] An anisotropic diffusion rate of 1.5 to 2.5 can be easily achieved by satisfying all of the following conditions (i) to (iv) of the optical functional layer.

[0066] (i) The average aspect ratio of the needle-like particles is 5 to 50.

[0067] (ii) The refractive index of the needle-like particles along their short axis - the refractive index of the matrix is ​​0.15 to 0.3.

[0068] (iii) The content of needle-like particles in the optical functional layer is 1 wt% to 10 wt%.

[0069] and (iv) the ratio of the average surface area of ​​the needle-like particles in the short axis direction to the average surface area of ​​the needle-like particles in the long axis direction is 0.2 to 900.

[0070] The anisotropic diffusion rate of 1.5 to 2.5 is set through a matrix containing needle-like particles and the needle-like particles satisfying the above-mentioned average orientation angle and standard deviation of orientation angle, in order to improve the relative brightness of the front and the contrast of the side.

[0071] By satisfying conditions (i) to (iv), an anisotropic diffusion rate of 1.5 to 2.5 can be achieved.

[0072] For (i), the average aspect ratio of the needle-like particles can refer to the average aspect ratio, which is calculated by the ratio of the maximum length of the needle-like particles in the long axis direction to the minimum cross-sectional diameter of the needle-like particles in the short axis direction. With an average aspect ratio of 5 to 50, the optical functional layer can easily achieve an anisotropic diffusion rate in the range of 1.5 to 2.5. Furthermore, with an average aspect ratio of 5 to 50, the optical functional layer can provide a light diffusion effect in the short axis direction of the needle-like particles.

[0073] For example, the average aspect ratio of the needle-like particles may be 5 to 40, or 10 to 35.

[0074] According to one embodiment, the minimum cross-sectional diameter of the needle-like particles in the short axis direction can be from 0.5 μm to 4.0 μm. For example, the minimum cross-sectional diameter of the needle-like particles in the short axis direction can be from 1.0 μm to 3.0 μm, preferably from 1.0 μm to 2.0 μm. Within this range, the needle-like particles can provide a lateral light diffusion effect through an increase in aspect ratio. Here, the cross-sectional diameter can refer to the cross-sectional diameter of the needle-like particles, which can be the largest diameter among the diameters measured in the cross-section of the needle-like particles.

[0075] In one embodiment, the needle-like particles may have a circular cross-section, an elliptical cross-section, etc.

[0076] According to one embodiment, the maximum length of the needle-like particles in their long axis direction can be from 10 μm to 45 μm, for example, from 10 μm to 40 μm, and specifically for 15, from μm to 40 μm. Within this range, the needle-like particles can be easily aligned to help improve the contrast and brightness of the sides.

[0077] For (ii), the difference between the refractive index of the needle-like particles in the short axis direction and the refractive index of the matrix (the refractive index of the needle-like particles in the short axis direction - the refractive index of the matrix) ranges from 0.15 to 0.3.

[0078] When the difference between the refractive index of the needle-like particles in the short axis direction and the refractive index of the matrix is ​​in the range of 0.15 to 0.3, the optical functional layer can easily achieve anisotropic diffusivity in the range of 1.5 to 2.5. For example, the difference in refractive index may be in the range of 0.15 to 0.25.

[0079] According to this disclosure, the refractive index of the needle-like particles along their short axis and the refractive index of the matrix are considered. If the difference between the refractive index of the needle-like particles along their long axis and the refractive index of the matrix is ​​considered instead of the refractive index of the needle-like particles along their short axis, then as the refractive index difference increases, there may be a problem of increased light diffusion along the long axis.

[0080] In one embodiment, the needle-like particles may have a refractive index of 1.65 to 2.8 in their short axis direction. Within this range, the optical functional layer can easily achieve an anisotropic diffusion rate in the range of 1.5 to 2.5.

[0081] For example, the needle-like particles may have a refractive index of 1.65 to 2.0 in the direction of their short axis, for example, the needle-like particles may have a refractive index of 1.65 to 1.9 or 1.65 to 1.7 in the direction of their short axis.

[0082] The refractive index of needle-like particles along their short axis can refer to the average refractive index of needle-like particles in the matrix along their short axis.

[0083] The refractive index of the needle-like particles in the short axis direction can be achieved by adjusting the material and / or composition of the needle-like particles, or by surface modification of the needle-like particles.

[0084] According to one embodiment, the needle-like particles can be modified with at least one of a silane compound, a surfactant, and an oil selected from the group consisting of: preferably, the needle-like particles are surface modified with a silane compound containing a (meth)acryloxy group or a (meth)acrylate group.

[0085] Silicon compounds containing (meth)acryloyloxy or (meth)acrylate groups may include 3-(meth)acryloyloxypropylmethyldimethoxysilane, 3-(meth)acryloyloxypropyltrimethoxysilane, 3-(meth)acryloyloxypropylmethyldiethoxysilane, and 3-(meth)acryloyloxypropyltrimethoxysilane. The silane is selected from at least one of the following: ne), 3-(meth)acryloyloxypropyltriethoxysilane, 3-(meth)acryloyloxypropyltrimethoxysilane, and preferably at least one of 3-(meth)acryloyloxypropyltrimethoxysilane.

[0086] Such modification can be carried out by mixing needle-like particles or a mixture of needle-like particles with a solution containing a modifying compound, followed by a modification reaction. In one embodiment, the refractive index of the needle-like particles in their minor axis direction can be controlled by adjusting the content of the modifying compound in the solution relative to the needle-like particles or the mixture of needle-like particles, and the content of the modifying compound in the solution during the modification of the needle-like particles. For example, the solution containing the modifying compound may include 50 wt% to 80 wt% of the modifying compound, for example, the solution containing the modifying compound may include 50 wt% to 60 wt% of the modifying compound. The solution may include, but is not limited to, methyl ethyl ketone as a solvent. The solution containing the modifying compound may be 50 parts by weight to 200 parts by weight relative to 100 parts by weight of needle-like particles or a mixture of 100 parts by weight, for example, the solution containing the modifying compound may be 80 parts by weight to 150 parts by weight.

[0087] According to one embodiment, needle-like particles can undergo surface modification through the hydrolysis and condensation of surface hydroxyl groups.

[0088] Prior to surface modification, the refractive index of the needle-like particles can be from 1.5 to 2.2, preferably from 1.6 to 1.8, and more preferably from 1.65 to 1.7. Within this range, the needle-like particles can have an appropriate refractive index relative to the resin layer (or matrix) described below to help improve contrast and visibility.

[0089] Needle-shaped particles may include organic particles, inorganic particles, organic-inorganic particles, etc. For example, needle-shaped particles may include at least one of the following metal oxides: such as titanium oxide (for example, TiO2), zirconium oxide (for example, ZrO2), zinc oxide (for example, ZnO), etc.; inorganic particles, such as calcium carbonate (for example, CaCO3), boehmite, aluminum borate (for example, AlBO3), calcium silicate (for example, CaSiO3, wollastonite), magnesium sulfate (MgSO4), magnesium sulfate hydrate (for example, MgSO4∙7H2O), potassium titanate (for example, K2Ti8O17), glass, etc.; and organic particles, such as synthetic resins. Preferably, the needle-like particles are formed of calcium carbonate to facilitate the realization of the effects disclosed herein and their preparation.

[0090] According to one embodiment, the refractive index of the needle-like particles in the direction of their short axis can be greater than the refractive index of the needle-like particles in the direction of their long axis.

[0091] The needle-like particles may have a refractive index of 1.50 to 1.55 in the direction of their long axis. Within this range, the needle-like particles can ensure that the light diffusion in the direction of their short axis is better than that in the direction of their long axis, and the optical functional layer can easily achieve anisotropic diffusion in the range of 1.5 to 2.5.

[0092] The refractive index of the needle-like particles along their long axis can be the average refractive index of the needle-like particles contained in the matrix along their long axis.

[0093] The refractive index of the matrix can be from 1.45 to 1.54, for example, from 1.47 to 1.53. Within this range, condition (ii) can be easily achieved.

[0094] The matrix may be a cured product of a composition including at least one of thermosetting resin or photocurable resin.

[0095] In one embodiment, the thermosetting resin and the photochemical radiation-curing resin may each have a weight average molecular weight of 500,000 g / mol or more, for example, from 500,000 g / mol to 2,000,000 g / mol.

[0096] Thermosetting resin refers to a resin that is cured by drying and / or heat treatment, and may include, for example, resins having thermosetting reactive groups, such as (meth)acrylate groups, epoxy groups, urethane groups, urethane (meth)acrylate groups, etc. For example, thermosetting resin may include (meth)acrylic resin, etc. The matrix formed from the composition containing the thermosetting resin may serve as an adhesive layer, but is not limited thereto.

[0097] Photochemical radiation-curable resin refers to a resin that is cured by ultraviolet light or the like. For example, the resin may include a resin having photocurable reactive groups. For example, photocurable reactive groups may include vinyl groups, (meth)acrylate groups, etc., and the photochemical radiation-curable resin may have one or more photocurable reactive groups. For example, the photochemical radiation-curable resin may be selected from any resin that can achieve the effects disclosed herein, such as (meth)acrylate resin, urethane (meth)acrylate resin, epoxy (meth)acrylate resin, silicone (meth)acrylate resin, etc.

[0098] The composition may further include an initiator capable of curing at least one of a thermosetting resin or a photocurable resin. For example, the initiator may include a thermal initiator and / or a photoinitiator. Thermal initiators may include azo initiators, peroxide initiators, etc. Photoinitiators may include photoradical initiators, such as phosphorescent photoinitiators, phosphine oxide photoinitiators, ketone photoinitiators, cyclohexyl ketone photoinitiators, etc.

[0099] The composition may further include at least one of a thermosetting crosslinking agent or a photocurable crosslinking agent. The thermosetting crosslinking agent may include isocyanate crosslinking agents, epoxy crosslinking agents, amine crosslinking agents, etc. The photocurable crosslinking agent may include a multifunctional photocurable monomer having at least two photocurable reactive groups.

[0100] This composition may include typical additives known to those skilled in the art, for example, surface modifiers, antistatic agents, dispersants, dyes, pigments, etc.

[0101] The refractive index of the matrix can be achieved by adjusting the type and / or content of the monomers constituting the thermosetting resin or the photocurable resin.

[0102] In one embodiment, the matrix may be a cured product of a copolymer comprising a monomer mixture of alkyl-containing (meth)acrylic acid monomers and hydroxyl-containing (meth)acrylic acid monomers and a curing agent. The cured product may be a thermosetting product or a photocurable product.

[0103] Alkyl-containing (meth)acrylate monomers may include (meth)acrylates having unsubstituted straight or branched C1 to C10 alkyl groups. For example, (meth)acrylates may include, but are not limited to, methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, n-butyl (meth)acrylate, t-butyl (meth)acrylate, iso-butyl (meth)acrylate, pentyl (meth)acrylate, hexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, heptyl (meth)acrylate, octyl (meth)acrylate, iso-octyl (meth)acrylate, nonyl (meth)acrylate, and decyl (meth)acrylate. These can be used individually or as a mixture of their forms.

[0104] Hydroxyl-containing (meth)acrylate monomers may include (meth)acrylates containing at least one hydroxyl group. For example, hydroxyl-containing (meth)acrylates may include (meth)acrylates containing an alkyl group, said alkyl group being a C2 to C10 alkyl group having at least one hydroxyl group. Specifically, hydroxyl-containing (meth)acrylates may include at least one of 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, and 6-hydroxyhexyl (meth)acrylate. Preferably, the hydroxyl-containing (meth)acrylate includes at least one of 4-hydroxybutyl (meth)acrylate, 2-hydroxyethyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, and 3-hydroxypropyl (meth)acrylate.

[0105] In the monomer mixture, the content of the alkyl-containing (meth)acrylic acid monomer may be from 50 wt% to 95 wt%, for example, 55 wt% to 95 wt%, 60 wt% to 95 wt%, or 70 wt% to 95 wt%. In the monomer mixture, the content of the hydroxyl-containing (meth)acrylic acid monomer may be from 5 wt% to 50 wt%, for example, the content of the hydroxyl-containing (meth)acrylic acid monomer may be from 5 wt% to 40 wt%, or 5 wt% to 30 wt%.

[0106] For example, the monomer mixture may contain 10 wt% to 80 wt% of n-butyl (meth)acrylate, 10 wt% to 60 wt% of meth (meth)acrylate, and 5 wt% to 30 wt% of 4-hydroxybutyl (meth)acrylate. Within this range, the monomer mixture can readily form a matrix that promotes the orientation of anisotropic particles.

[0107] The monomer mixture may also include (meth)acrylic acid monomers having aromatic groups. (Meth)acrylic acid monomers having aromatic groups can be used to increase the refractive index of the matrix.

[0108] A (meth)acrylic acid monomer having an aromatic group may include one or more (meth)acrylic acid monomers having substituted or unsubstituted aromatic groups. For example, a (meth)acrylic acid monomer having an aromatic group may include, but is not limited to, the compound shown in Equation 1.

[0109] CH2 is C(R1)-C(O)-O-R2-Ar,

[0110] wherein R1 is hydrogen or methyl, and R2 is a substituted or unsubstituted C1 to C20 or alkylene or substituted or unsubstituted C1 to C20 epoxy group.

[0111] and Ar are substituted or unsubstituted C6 to C20 monovalent aromatic hydrocarbon groups.

[0112] For example, the aromatic (meth)acrylate monomer may include at least one of phenoxybenzyl (meth)acrylate, phenyl phenoxyethyl (meth)acrylate, 2-hydroxy-3-phenoxypropyl (meth)acrylate, ethoxylated phenyl phenoxy (meth)acrylate, benzyl (meth)acrylate, and biphenylmethyl (meth)acrylate.

[0113] In the monomer mixture, the content of the aromatic (meth)acrylic acid monomer can be from 10 wt% to 45 wt%, for example, the content of the aromatic (meth)acrylic acid monomer can be from 20 wt% to 45 wt%. Within this range, the monomer mixture can easily form a matrix with a high refractive index without impairing other properties of the matrix.

[0114] For example, the monomer mixture may contain 25 wt% to 55 wt% of n-butyl (meth)acrylate, 10 wt% to 40 wt% of 2-ethylhexyl (meth)acrylate, 5 wt% to 40 wt% of 4-hydroxybutyl (meth)acrylate, and 20 wt% to 45 wt% of biphenylmethyl (meth)acrylate. Within this range, the monomer mixture can readily form a matrix with a high refractive index while promoting the orientation of anisotropic particles.

[0115] The curing agent is used for thermosetting copolymers and may include any typical curing agent known to those skilled in the art. For example, the curing agent may include at least one of isocyanate curing agents, epoxy curing agents, aziridine curing agents, and amine curing agents. These curing agents may be selected from any suitable type known to those skilled in the art.

[0116] The content of the curing agent may be from 0.1 parts by weight to 10 parts by weight, or from 1 part by weight to 5 parts by weight, relative to 100 parts by weight of the copolymer. Within this range, the curing agent can fully cure the copolymer.

[0117] For (iii), the content of needle-like particles in the optical functional layer is 1 wt% to 10 wt%. Within this range, the optical functional layer can easily achieve anisotropic diffusion. For example, the content of needle-like particles can be 3 wt% to 8 wt%. Within this range, the optical functional layer can easily achieve anisotropic diffusion in the range of 1.5 to 2.5, while improving the contrast of the sides.

[0118] For (iv), the needle-like particles have an average surface area ratio of 0.2 to 900 (the ratio of the average surface area of ​​the needle-like particles in the short axis direction to the average surface area in the long axis direction). The average surface area ratio can be used as a standard to judge the degree of diffusion of light incident from the polarizer onto the needle-like particles in the short and long axis directions of the needle-like particles. Within this range, the anisotropic diffusion rate described above can be easily achieved in the optical functional layer. For example, the needle-like particles may have an average surface area ratio of 0.5 to 150, 5 to 100, or 5 to 100.

[0119] The surface area ratio can be achieved by adjusting the average surface area of ​​the needle-like particles in the short axis and long axis directions.

[0120] According to one embodiment, the needle-like particles may have an average surface area of ​​5 μm2 to 180 μm2 in the direction of their short axis. For example, the needle-like particles may have an average surface area of ​​10 μm2 to 120 μm2 or 15 μm2 to 80 μm2 in the direction of their short axis.

[0121] According to one embodiment, the needle-like particles may have an average surface area of ​​0.2 μm2 to 15 μm2 in the direction of their long axis, for example, the needle-like particles may have an average surface area of ​​0.5 μm2 to 8 μm2, or 0.5 μm2 to 4 μm2 in the direction of their long axis.

[0122] The optical functional layer can be formed by applying a composition for the optical functional layer to an adhesive and then curing the composition. Here, the average alignment angle and the standard deviation of the alignment angle can be achieved by adjusting the viscosity of the optical functional layer composition. The average alignment angle and the standard deviation of the alignment angle can also be achieved by adjusting the pressure of composition deposition, etc.

[0123] Optical functional layer, for example, the matrix thickness can be 5 μm to 50 μm, preferably 10 μm to 40 μm, more preferably 10 μm to 30 μm.

[0124] Next, the polarizing plate will be explained.

[0125] A polarizing plate includes a polarizer and an optical functional layer.

[0126] The light transmittance of a polarizing plate can be 95% or higher. For example, the light transmittance of a polarizing film can be 96% to 100%. Within this range, the polarizing plate can be used as a viewing-side polarizing plate.

[0127] The optical functional layer is stacked on the light exit surface of the polarizer. The light exit surface refers to the surface on which light from inside the backlight unit reaches the polarizer and exits.

[0128] The optical functional layer can be an adhesive layer, which can be directly stacked on the protective layer or polarizer as described below, without the need for an intermediate layer adhesive.

[0129] An optical functional layer can be formed by depositing a composition of the optical functional layer onto an adhesive and then curing the composition.

[0130] The polarizing plate may also include at least one polarizer, a protective layer (including a delay layer), an adhesive layer and / or an adhesive layer, a functional film (including a functional coating), etc.

[0131] (i) Polarizer

[0132] A polarizer is a linear light-absorbing polarizer that provides polarization by transmitting a portion of incident light in one direction while absorbing a portion of incident light perpendicular to that direction.

[0133] A polarizer can be a polarizer made by dyeing and stretching a polyvinyl alcohol (PVA) film, or a polyene polarizer made by dehydrating a polyvinyl alcohol film.

[0134] The polarizer can have a thickness of less than 50 μm, for example, the polarizer can have a thickness of 5 μm to 30 μm. Within this range, the film will not melt or break when stretched.

[0135] (ii) Protective layer

[0136] The protective layer serves to protect the polarizer or increase the mechanical strength of the polarizing plate. The protective layer can act as an adhesive, and the optical functional layer can be adhered to it.

[0137] The protective layer can be set at any position on the polarizing plate, one or more.

[0138] The protective layer may include a transparent base. The refractive index of the transparent base may be higher or lower than that of the optical functional layer. Preferably, the transparent base has a higher refractive index than the optical functional layer. This feature helps to improve contrast and brightness.

[0139] The transparent substrate may include an optically transparent resin film, comprising: a light incident angle surface; and a light exit surface opposite to the light incident surface. The transparent substrate may be a single-layer resin film. However, this disclosure is not limited thereto. The transparent substrate may also be a stack of multiple resin films. The resin may include at least one of the following: cellulose resins, including triacetylcellulose (TAC), cyclic polyolefin resins, including amorphous cyclic olefin polymers (COP), polycarbonate resins, polyester resins, including polyethylene terephthalate (PET), polyether sulfone resins, polysulfone resins, polyamide resins, polyimide resins, noncyclic polyolefin resins, poly(methacrylate) resins, including poly(methyl methacrylate), polyvinyl alcohol resins, polyvinyl chloride resins, and polyvinylidene chloride resins, but not limited thereto. Preferably, the transparent substrate includes a polyester resin, such as polyethylene terephthalate (PET), to ensure further improvement in contrast and brightness.

[0140] The haze of the transparent substrate can be less than 30%, specifically, the haze of the transparent substrate can be from 2% to 30%, and the light transmittance is more than 90%, specifically, the light transmittance is from 95% to 100%. Within the above range of haze and light transmittance, the transparent substrate can be used for polarizing plates.

[0141] The transparent substrate can have a thickness of 5 μm to 200 μm, for example, the transparent substrate can have a thickness of 30 μm to 120 μm. Within this range, the transparent substrate can be used for polarizing plates.

[0142] The protective layer may also include a functional layer on at least one surface of the transparent substrate. The functional layer may include a primer layer, an anti-glare layer, an anti-reflective layer, a low refractive index layer, a high refractive index layer, a hard coating layer, an anti-fingerprint layer, etc.

[0143] The protective layer may be an isotropic film with substantially zero retardation. However, this disclosure is not limited thereto, and the protective layer may have an in-plane retardation within a predetermined range to provide additional functionality when combined with a polarizing plate.

[0144] In one embodiment, the protective layer may have an in-plane delay of more than 3000 nm at a wavelength of 550 nm. Within this range, the protective layer may be combined with an optical functional layer to help improve contrast and / or brightness. The protective layer may have an in-plane delay of more than 4000 nm, specifically, an in-plane delay of more than 8000 nm, more specifically, an in-plane delay of more than 10000 nm, more specifically, an in-plane delay greater than 10000 nm, more specifically, an in-plane delay of 10100 nm to 30000 nm, more specifically, an in-plane delay of 10100 nm to 15000 nm.

[0145] In another embodiment, the protective layer may have an in-plane delay of less than 3,000 nm at a wavelength of 550 nm. For example, the protective layer may have an in-plane delay of 0 nm to 1,000 nm or 10 nm to 500 nm at a wavelength of 550 nm.

[0146] The protective layer may be the first protective layer, the second protective layer or the third protective layer as described below.

[0147] (iii) Adhesive layer and / or bonding layer

[0148] The adhesive layer and / or bonding layer can be used to bond or bond polarizers, optical functional layers, protective layers and functional films to each other.

[0149] The adhesive layer may be an adhesive layer formed from typical compositions known to those skilled in the art. For example, the adhesive layer may be a (meth)acrylate adhesive layer, an epoxy resin adhesive layer, a silicone adhesive layer, a urethane adhesive layer, an epoxy resin (meth)acrylate adhesive layer, or a urethane (meth)acrylate adhesive layer. For example, the adhesive layer may be a pressure-sensitive adhesive (PSA) layer.

[0150] The adhesive layer may be formed from typical compositions known to those skilled in the art. For example, the adhesive layer may be formed from water-based adhesives, UV-curable adhesives, etc.

[0151] (iv) Functional membrane

[0152] The functional film can be selectively used in polarizing plates to provide additional functions to the polarizing plates.

[0153] For example, the functional film or functional coating can be an anti-glare film, an anti-reflection film, an ultra-low reflectivity film, a low refractive index film, a high refractive index film, or an anti-fingerprint film.

[0154] Figures 5 to 8 are cross-sectional views of the polarizing plate according to the embodiment.

[0155] A polarizing plate according to one embodiment may include a polarizer 30; and an optical functional layer 10 and a first protective layer 20 stacked on the light exit surface of the polarizer 30.

[0156] According to another embodiment, the polarizing plate may include a polarizer 30; an optical functional layer 10, a first protective layer 20 and a functional coating 40 are sequentially stacked on the light exit surface of the polarizer 30.

[0157] According to a further embodiment, the polarizing plate may include a polarizer 30; an optical functional layer 10, a first protective layer 20 and a functional coating 40 are sequentially stacked on the light exit surface of the polarizer 30.

[0158] According to another embodiment, the polarizing plate may include a polarizer 30; a second protective layer 50, an optical functional layer 10, a first protective layer 20 and a functional coating 40 are sequentially stacked on the light exit surface of the polarizer 30.

[0159] According to another embodiment, the polarizing plate may include an optical functional layer 10, a first protective layer 20 and a functional coating layer 40 sequentially stacked on the light exit surface of the polarizer 30; and a third protective layer 70 formed on the light incident surface of the polarizer 30. The second protective layer 50 may also be disposed between the polarizer 30 and the optical functional layer 10.

[0160] The layers of the polarizing plate can be stacked and connected as needed via adhesive layers or bonding layers.

[0161] According to another aspect of the present disclosure, an optical display device includes a polarizing plate according to the present disclosure.

[0162] In one embodiment, the optical display device may include a polarizing plate that, according to the present disclosure, corresponds to a viewing-side polarizing plate on the liquid crystal panel. Here, "viewing-side polarizing plate" refers to a polarizing plate disposed on the side of the liquid crystal panel facing the screen, that is, on the side of the liquid crystal panel facing away from the light source.

[0163] In one embodiment, the liquid crystal display device may include a light-concentrating backlight unit, a light source-side polarizing plate, a liquid crystal panel, and a viewing-side polarizing plate stacked sequentially, wherein the viewing-side polarizing plate may include the polarizing plate according to the present disclosure. Here, "light source-side polarizing plate" refers to a polarizing plate disposed on the side of the liquid crystal panel facing the light source. The liquid crystal panel may employ vertical alignment (VA) mode, IPS mode, patterned vertical alignment (PVA) mode, or super-patterned vertical alignment (S-PVA) mode, but is not limited thereto.

[0164] The optical display device may be a foldable or flexible optical display device or a non-foldable or non-flexible optical display device.

[0165] Next, some embodiments will be described in more detail. However, it should be noted that these embodiments are for illustration only and should not be construed as limiting the present disclosure in any way.

[0166] Example 1

[0167] (1) At room temperature, 100 parts by weight of CaCO3 mixture particles (Whiscal A, CaCO3: needle-shaped anisotropic microparticles, length: 10 μm to 30 μm, cross-sectional diameter: 0.5 μm to 2.0 μm, refractive index: 1.68, Maruo Calcium Co., Ltd) were added to a methyl ethyl ketone solution containing 3-methacryloxypropyltrimethoxysilane (KBM503) and then dried in an oven at 90 °C to remove the solvent, thereby preparing needle-shaped particles of CaCO3 mixture modified with 3-methacryloxypropyltrimethoxysilane. Here, 100 parts by weight of a methyl ethyl ketone solution containing 3-methylpropoxypropyltrimethoxysilane is added to 100 parts by weight of a mixture of CaCO3 particles, and 3-methylpropoxypropyltrimethoxysilane (KBM503) is present in the methyl ethyl ketone solution in an amount of 50 parts by weight.

[0168] (2) Under a nitrogen atmosphere, in a 1-liter (L) reactor equipped with a cooling device for temperature control, the monomer mixture and solvent were added in a 1:1 ratio to make the solid content 50 wt%. Ethyl acetate was used as the solvent. The monomer mixture was prepared by mixing 60 parts by weight of n-butyl acrylate, 30 parts by weight of methyl acrylate and 30 parts by weight of 4-hydroxybutyl acrylate. Nitrogen was introduced into the reactor for 1 hour to remove oxygen from the monomer mixture, and the internal temperature of the reactor was maintained at 70°C. After the monomer mixture was stirred evenly, 0.05 parts by weight of azobisisobutyronitrile (AIBN) was added to the reactor as an initiator and reacted with the monomer mixture for 12 hours to prepare a solution containing an acrylic resin with a weight average molecular weight of 700,000 g / mol. Ethyl acetate was added to the solution to make the solid content of the solution 25 wt%.

[0169] (3) Add 7 parts by weight of surface-modified CaCO3 particles and 2 parts by weight of hexamethylene diisocyanate curing agent (CK-164, NCI) to 100 parts by weight of prepared acrylic resin to prepare an optical functional layer composition.

[0170] (4)Stretch the polyvinyl alcohol film to 3 times its initial length along the machine direction (MD) at 60°C, dye the film with iodine, and then stretch the dyed film to 2.5 times along the machine direction in a boric acid aqueous solution at 40°C to obtain a polarizer (thickness: 13μm, light transmittance: 44%).

[0171] (5) A polarizing film is formed by passing a polyethylene terephthalate (PET) film (TA053, Toyobo Co., Ltd.) and a cyclic olefin polymer (COP) film through an adhesive onto the upper and lower surfaces of the prepared polarizer.

[0172] (6)The components of the prepared optical functional layer are coated on the lower surface of the surface-treated polyethylene terephthalate (PET) film (DSG-17(Z)PET80, DNP) with a coating rod to form a thickness of 20 μm. After drying, it is heat-cured at 80°C for 2 minutes and placed at room temperature for 1 day to form an optical functional layer (thickness 25 μm). The optical functional layer is attached to the polarizing film prepared in (5) to prepare a polarizing plate.

[0173] The refractive index of the matrix in the optical functional layer is 1.47. The refractive index of the surface-modified CaCO3 particles is 1.68 in the short axis direction and 1.53 in the long axis direction, and the content in the optical functional layer is about 6.4 wt%.

[0174] The surface-modified CaCO3 particles had an average surface area of ​​1.77 μm² along the long axis and an average surface area of ​​33.75 μm² along the short axis, with a ratio of 19.1 between the average surface areas along the long and short axes. The average surface area was measured in both directions using a scanning electron microscope (SEM).

[0175] Example 2

[0176] The preparation method of the optical functional layer and the polarizing plate is the same as in Example 1, except that the monomer mixture is made by mixing 40 parts by weight of n-butyl acrylate, 20 parts by weight of 2-ethylhexyl acrylate, 10 parts by weight of 4-hydroxybutyl acrylate and 30 parts by weight of biphenyl methyl acrylate.

[0177] The refractive index of the matrix in the optical functional layer is 1.51. The refractive index of the surface-modified CaCO3 particles is 1.68, and the refractive index along the long axis is 1.53.

[0178] Example 3

[0179] The preparation method of the optical functional layer and the polarizing plate is the same as in Example 1, except that a mixture of CaCO3 particles (Whiscal A, CaCO3: needle-shaped anisotropic particles, length: 10 μm to 30 μm, cross-sectional diameter: 0.5 μm to 2.0 μm, refractive index 1.68, Maruo Calcium Co., Ltd.) with a length of 15 μm to 25 μm is used. The average aspect ratio of the anisotropic particles in the optical functional layer is 20 ± 5, showing better uniformity than in Example 1.

[0180] Comparative Example 1

[0181] The preparation method of the optical functional layer and the polarizing plate is the same as in Example 1, except that the composition of the optical functional layer is made by adding 3 parts by weight of potassium titanate particles (TISMPN, refractive index: 2.68, diameter: 0.5 μm, length: 10 μm to 20 μm, Otsuka Chemical Co., Ltd.) as needle-like particles and 2 parts by weight of hexamethylene diisocyanate curing agent to 100 parts by weight of acrylic resin prepared in Example 1. The matrix in the optical functional layer has a refractive index of 1.47. The potassium titanate particles have a refractive index of 2.68 in their short axis direction.

[0182] Comparative Example 2

[0183] The preparation method of the optical functional layer and the polarizing plate is the same as in Example 1, except that the composition of the optical functional layer is achieved by adding 7 parts by weight of cubic calcium carbonate particles (MX-14, CaCO3: cubic anisotropic microparticles, length: 1 μm to 3.0 μm, cross-sectional diameter: 0.5 μm to 2.0 μm, refractive index: 1.68, Maruo Calcium Co., Ltd.) as needle-like particles and 2 parts by weight of hexamethylene diisocyanate curing agent (CK-164, NCI) to 100 parts by weight of acrylic resin prepared in Example 1. The matrix in the optical functional layer has a refractive index of 1.47. The calcium carbonate particles have a refractive index of 1.68 in their short axis direction.

[0184] Comparative Example 3

[0185] The preparation method of the optical functional layer and the polarizing plate is the same as in Example 1, except that the monomer mixture is prepared by mixing 70 parts by weight of biphenylmethyl acrylate, 15 parts by weight of phenoxy benzyl acrylate, and 15 parts by weight of 4-hydroxybutyl acrylate. The matrix in the optical functional layer has a refractive index of 1.6. The surface-modified CaCO3 particles have a refractive index of 1.68 and a refractive index of 1.53 along the long axis.

[0186] Comparative Example 4

[0187] The polarizing plate was prepared in the same manner as in Example 2, except that the particle content was changed to 12 parts by weight relative to 100 parts by weight of acrylic resin. The content of surface-modified CaCO3 in the optical functional layer was approximately 10.5 wt%.

[0188] Comparative Example 5

[0189] The polarizing plate is prepared in the same way as in Example 2, except that a solvent is added to the composition to obtain an optical functional layer, and the orientation angle of the anisotropic particles is changed by changing the viscosity of the composition.

[0190] Reference Embodiment

[0191] The polarizing plate is prepared in the same way as in Example 1, except that the polyethylene terephthalate (PET) film (DSG-17(Z)PET80, DNP) and the cyclic olefin polymer (COP) film are bonded to the upper and lower surfaces of the polarizer through an adhesive (excluding the optical functional layer).

[0192] The performance of the prepared polarizing plate was evaluated as follows, and the results are shown in Table 1.

[0193] Refractive index of the particle in the short axis and long axis directions.

[0194] The refractive indices of the particle in the short axis and long axis directions are calculated as average values.

[0195] The average aspect ratio of the particle.

[0196] The average aspect ratio is calculated by averaging the aspect ratios of the particles.

[0197] The ratio of the average surface area of ​​particles along the short axis to the average surface area of ​​particles along the long axis.

[0198] The average surface area of ​​particles along the major axis and minor axis is measured by scanning electron microscopy, and the ratio of the average surface area of ​​particles along the minor axis to the average surface area of ​​particles along the major axis is calculated.

[0199] The mean orientation angle (unit: °) and standard deviation of the orientation angle (unit: °) of anisotropic particles.

[0200] Surface images of each optical functional layer prepared in the examples and comparative examples were obtained and stored using an optical microscope (Olympus MX61L, magnification (x500, 10x50)). The average orientation angle and the standard deviation of the orientation angle were calculated by adjusting the surface height of each optical functional layer and by operating the FIJI program (method: Fourier component N bis: 90°, Histogram start: 0°, Histogram end: 180° input).

[0201] Anisotropic diffusion rate of optical functional layers.

[0202] The anisotropic diffusion rate of needle-like particles along the long axis and the anisotropic diffusion rate of the optical functional layer along the short axis were measured. Specifically, the anisotropic diffusion rate was measured using a diffuser (manufactured by D-World Co., Ltd.).

[0203] Figure 9 is a conceptual diagram for measuring anisotropic diffusion rate. Referring to Figure 9, a sample stage 200 and an area camera 300 are sequentially arranged above a light-emitting diode point light source 100. An optical functional layer 210 is provided on the sample stage 200, allowing light emitted from the point light source 100 to pass through and diffuse within the optical functional layer 210. The diffusion area can be measured using the area camera 300. The area camera 300 is equipped with a 50 mm diameter lens and a resolution of 5 megapixels.

[0204] Relative brightness (unit: %) and relative contrast (unit: %).

[0205] A liquid crystal display (LCD) comprising a single-sided incident LED light source is manufactured by assembling a light-emitting diode (LED) light source, a light guide plate, and a viewing angle measurement model. The LCD (excluding the structure of the LCD module in the embodiments and comparative embodiments, having the same structure as a Samsung TV (55-inch, model KQ55QNA90AFXKR)) includes a single-sided incident LED light source, a light guide plate, and a viewing angle measurement module. In a spherical coordinate system (EZCONTRASTX88RC (EZXL-176R-F422A4, ELDIM), the contrast ratio is measured at the front (0°, 0°) and side (0°, 60°) positions. The contrast ratio is calculated as the ratio of brightness in white light mode to brightness in dark mode. Relative brightness and relative contrast ratio are calculated based on the brightness and contrast ratio measured in the reference example. Picture quality can be improved when the relative brightness reaches 85% or more and the relative contrast ratio reaches 130% or more.

[0206] [Table 1] Example Comparative Examples Reference Implementation Examples 1 2 3 1 2 3 4 5 Particle content (relative to resin) 7 7 7 3 7 7 12 7 - matrix refractive index 1.47 1.51 1.47 1.47 1.47 1.6 1.51 1.51 - particle Refractive index along the minor axis 1.68 1.68 1.68 2.68 1.68 1.68 ​1.68 1.68 - Refractive index along the major axis 1.53 1.53 1.53 2.32 1.53 1.53 1.53 1.53 - Average aspect ratio 20±15 20±15 20±5 20±15 1.5±0.4 20±15 20±15 20±15 - Surface area along the major axis 1.77 1.77 1.77 0.20 0.79 1.77 1.77 1.77 - Surface area along the minor axis 33.75 33.75 33.75 7.5 1.5 33.75 33.75 33.75 - The ratio of the average surface area along the minor axis to the average surface area along the major axis 19.1 19.1 19.1 38.2 1.9 19.1 19.1 19.1 - Refractive index difference (minor axis) 0.21 0.17 0.21 1.21 0.21 0.08 0.17 0.17 - Orientation angle of anisotropic particles -5 to 5 -5 to 5 -5 to 5 -5 to 5 -90 to 90 -5 to 5 -5 to 5 15 - Standard deviation of alignment angle 7.3 6.6 5.8 6.9 29.91 7.5 7.8 14.5 - Anisotropic diffusion rate 2.05 1.5 2 1.45 1.01 1.03 3 1.5 - front brightness 748 774.4 756.8 506 681.8 862.4 660 774.4 880 Relative brightness 85 88 86 58 77 98 75 88 100 side Contrast 515.2 493.12 522.56 382.2 303 379.04 559.36 441.6 368 Relative contrast 140 134 142 141 83 103 152 120 100

[0207] As shown in Table 1, the polarizing plate disclosed herein can ensure uniform visibility and screen quality between the front and sides by improving side brightness and contrast even without a pattern.

[0208] Those skilled in the art will understand that various modifications, alterations, changes and equivalent embodiments can be made without departing from the spirit and scope of the present invention.

Claims

1. A polarizing plate, comprising: polarizer; An optical functional layer is formed on one surface of the polarizer, wherein the optical functional layer comprises a matrix and needle-like particles embedded in the matrix, at least some of the needle-like particles are aligned in the in-plane direction of the optical functional layer, the needle-like particles are aligned in the in-plane direction of the optical functional layer with an average orientation angle of -10° to +10°, and the optical functional layer has an anisotropic diffusion rate of 1.5 to 2.5, and the optical functional layer satisfies conditions (i) to (iv): (i) the average aspect ratio of the needle-like particles is 5 to 50; (ii) the refractive index of the needle-like particles in their short axis direction is 0.15 to 0.3 compared to the refractive index of the matrix; (iii) the content of the needle-like particles in the optical functional layer is 1 wt% to 10 wt%; and (iv) the ratio of the average surface area of ​​the needle-like particles in the short axis direction to the average surface area in the long axis direction is 0.2 to 900.

2. The polarizing plate as claimed in claim 1, wherein the needle-like particles have a refractive index of 1.65 to 2.8 in the short axis direction and a refractive index of 1.50 to 1.55 in the long axis direction.

3. The polarizing plate as claimed in claim 1, wherein the needle-like particles are surface-treated with a silane compound having (meth)acryloxy or (meth)acrylate groups.

4. The polarizing plate as claimed in claim 1, wherein the substrate has a refractive index of 1.45 to 1.

54.

5. The polarizing plate as claimed in claim 1, wherein the needle-like particles comprise at least one selected from titanium dioxide, zirconium oxide, zinc oxide, calcium carbonate, gibbsite, aluminum borate, calcium silicate, magnesium sulfate, magnesium sulfate hydrate, potassium titanate, glass particles, and synthetic resin particles.

6. The polarizing plate as claimed in claim 1, wherein the standard deviation of the orientation angle of the needle-like particles is less than 20°.

7. The polarizing plate as claimed in claim 1, wherein the optical functional layer includes a visibility enhancement layer.

8. The polarizing plate as described in claim 1, further comprising a protective layer.

9. An optical display device comprising a polarizing plate as described in any one of claims 1 to 8.

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