Optical film, polarizing plate including same, and liquid crystal display

Abstract

The invention discloses an optical film, a polarizing plate including the optical film, and a liquid crystal display including the polarizing plate. The optical film includes: a protective layer; and a contrast improvement layer, wherein the contrast improvement layer includes a second resin layer and a first resin layer facing the second resin layer stacked in order from the protective layer.

Description

[0001] The present invention is a divisional application of the invention patent application with application number 201811324107.6 filed on November 8, 2018 and invention name “Optical film, polarizing plate including the same and liquid crystal display”. Technical Field

[0002] The invention relates to an optical film, a polarizing plate comprising the optical film and a liquid crystal display comprising the polarizing plate. Background Art

[0003] The liquid crystal display is operated to emit light through the liquid crystal panel after receiving light from the backlight unit. Since the light emitted from the backlight unit is vertically incident on the screen of the liquid crystal display, the screen of the liquid crystal display inevitably has a lower contrast ratio (CR) when viewed in the lateral direction than when viewed in the front direction. Therefore, a contrast improvement optical film for improving the side contrast ratio is being developed.

[0004] The optical film includes a low refractivity layer and a high refractivity layer, and improves the side contrast ratio of the optical display through an optical pattern. The side contrast ratio of the optical display can be improved by an optical film in which flat sections and optical patterns are alternately formed. However, although the optical film can improve the side contrast ratio of the optical display, the optical display generally experiences a degradation in the front contrast ratio due to the optical pattern blocking light emitted from the front side of the optical display, and suffers from an increase in reflectivity due to external light entering the optical pattern during non-operation of the optical display.

[0005] An example of the background art is disclosed in Japanese Unexamined Patent Publication No. 2006-251659. Summary of the invention

[0006] An object of the present invention is to provide an optical film that can improve the front contrast ratio while reducing the reflectivity.

[0007] Another object of the present invention is to provide an optical film that can reduce brightness at a side surface thereof in a black mode.

[0008] Still another object of the present invention is to provide an optical film that allows efficient curing of a composition for a low-refractive layer to minimize separation of a dye from the low-refractive layer, thereby providing a good appearance.

[0009] Still another object of the present invention is to provide a polarizing plate including the optical film for improving the contrast ratio according to the present invention and an optical display including the polarizing plate.

[0010] Another object of the present invention is to provide a liquid crystal display comprising the above optical film.

[0011] According to one aspect of the present invention, an optical film includes: a protective layer; and a contrast improvement layer; wherein the contrast improvement layer includes a second resin layer and a first resin layer facing the second resin layer stacked in sequence from the protective layer, wherein the second resin layer has a lower refractive index (index of refraction) than the first resin layer, and the first resin layer includes a patterned portion, the patterned portion is formed in at least a certain area of ​​the first resin layer facing the second resin layer and includes at least two raised optical patterns and a flat section arranged between the raised optical patterns adjacent to each other, the raised optical pattern has a bottom angle θ of 75° to 90°, the patterned portion satisfies Equation 1, and the second resin layer includes at least one of a metal complex salt dye and an organic black dye.

[0012] <Equation 1>

[0013] 1 <P / W≤10

[0014] (wherein P is the pitch of the patterned portion (unit: μm), and W is the maximum width of the raised optical pattern (unit: μm)).

[0015] In one embodiment, the at least one of the metal complex salt dye and the organic black dye may be present in the second resin layer in an amount of 0.01 wt % to 10 wt %.

[0016] In one embodiment, each of the metal complex salt dye and the organic black dye may have an average particle diameter (D50) of 30 nm or less.

[0017] In one embodiment, the metal complex salt dye may include a black dye containing chromium, nickel, cobalt, or copper.

[0018] In one embodiment, the metal complex salt dye may include a black dye containing chromium.

[0019] In one embodiment, the metal complex salt dye may include an azo dye.

[0020] In one embodiment, the metal complex salt dye may include C6 to C 20 Azo dyes with monocyclic or polycyclic aromatic functional groups.

[0021] In one embodiment, the metal complex salt dye may include chromium and C6 to C 20The azo dye having a monocyclic or polycyclic aromatic functional group may have an average particle diameter (D50) of 30 nm or less, and may be present in the second resin layer in an amount of 0.01 wt % to 10 wt %.

[0022] In one embodiment, the organic black dye may include a mixture of a first dye having a maximum absorption wavelength of 430 nm to 450 nm, a second dye having a maximum absorption wavelength of 510 nm to 530 nm, and a third dye having a maximum absorption wavelength of 590 nm to 610 nm.

[0023] In one embodiment, each of the first dye, the second dye, and the third dye may include an azo-based dye.

[0024] In one embodiment, the first dye may be represented by Formula 1; the second dye may be represented by Formula 2; and the third dye may be represented by Formula 3:

[0025] <Formula 1>

[0026]

[0027] <Formula 2>

[0028]

[0029] <Formula 3>

[0030]

[0031] In one embodiment, the first resin layer may be an adhesive layer.

[0032] In one embodiment, the raised optical pattern may include a trapezoidal optical pattern, a rectangular optical pattern, or a square optical pattern in a cross-sectional view.

[0033] According to another aspect of the present invention, a polarizing plate may include a polarizing film and the optical film according to the present invention disposed on the polarizing film.

[0034] According to still another aspect of the present invention, a liquid crystal display may include the polarizing plate according to the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0036] Figure 2 FIG. 4 is a cross-sectional view of a polarizing plate according to an embodiment of the present invention. DETAILED DESCRIPTION

[0037] Embodiments of the present invention will be described in detail with reference to the accompanying drawings to provide a thorough understanding of the present invention to those skilled in the art. It should be understood that the present invention can be implemented in different ways and is not limited to the following embodiments. In the accompanying drawings, parts that are not related to the description will be omitted for clarity. Throughout the specification, the same components will be marked with the same reference numerals.

[0038] Herein, spatially relative terms such as "upper" and "lower" are defined with reference to the accompanying drawings. Therefore, it should be understood that the term "upper surface" can be used interchangeably with the term "lower surface", and when an element (such as a layer or film) is said to be placed "on" another element, the element can be placed directly on the other element, or there can be intervening elements. On the other hand, when an element is said to be placed "directly" on another element, there are no intervening elements between the element and the other element.

[0039] Herein, the terms "horizontal direction" and "vertical direction" refer to the longitudinal direction and the lateral direction of the rectangular screen of the liquid crystal display, respectively. Herein, "side" refers to a region in a spherical coordinate system represented by (φ, θ) where θ is within the range of 0° to 30° or 0° to 60°, in which the front side is indicated by (0°, 0°) with reference to the horizontal direction, the left end point is indicated by (180°, 90°), and the right end point is indicated by (0°, 90°).

[0040] Herein, the term "top portion" refers to the highest portion in the raised optical pattern.

[0041] Herein, "aspect ratio" refers to the ratio of the maximum height of an optical pattern to its maximum width (maximum height / maximum width).

[0042] Herein, "pitch" means the sum of the maximum width W of an optical pattern and the width L of a flat section.

[0043] Herein, “in-plane retardation (Re)” is a value measured at a wavelength of 550 nm and is represented by Equation A:

[0044] <Formula A>

[0045] Re=(nx-ny)×d

[0046] Wherein nx and ny are the refractive indices on the slow axis and fast axis of the corresponding protective layer or substrate layer at a wavelength of 550 nm, respectively, and d is the thickness of the protective layer or substrate layer (unit: nm).

[0047] Herein, the term "(meth)acrylic acid" refers to acrylic acid and / or methacrylic acid.

[0048] Herein, the term "average particle size (D50)" refers to a particle size of 50 weight % of particles based on a particle size distribution, and may be measured by a typical method well known to those skilled in the art.

[0049] The inventors of the present invention have completed the present invention based on the following discovery: when the second resin layer having a lower refractive index in the optical film including the patterned portion described in detail below contains at least one of a metal complex salt dye and an organic black dye, the optical film can improve the front contrast ratio by the patterned portion without affecting the improvement of the side contrast ratio, can achieve a significant reduction in reflectivity, and can reduce the brightness at the side surface of the optical display in the black mode. When the optical display can reduce the brightness at its side surface in the black mode, the optical display can increase the front relative brightness. In addition, compared with an optical film in which a metal complex salt dye, an organic black dye or an inorganic black pigment is contained in the first resin layer having a higher refractive index, the optical film according to the present invention has a high white brightness, thereby enabling power to be reduced by reducing the brightness of the backlight unit.

[0050] Below, we will refer to Figure 1 An optical film according to an embodiment of the present invention will be described. Figure 1 is a cross-sectional view of an optical film according to one embodiment of the present invention.

[0051] Reference Figure 1 The optical film 10 includes a protective layer 100 and a contrast improvement layer 200 sequentially formed on the optical film 10 .

[0052] Protective layer

[0053] The protective layer 100 may be formed on one surface of the contrast improvement layer 200 to support the contrast improvement layer 200. The protective layer 100 is directly formed on the second resin layer 220 of the contrast improvement layer 200 to reduce the thickness of the optical film 10. As used herein, "directly formed" on another element or between elements means that no adhesive layer, bonding layer, or adhesive / bonding layer is interposed between the protective layer 100 and the contrast improvement layer 200. The contrast improvement layer 200 is formed on the light incident surface of the protective layer 100.

[0054] The protective layer 100 may have a total transmittance of 90% or more, for example, 90% to 100% in the wavelength band of visible light. Within this transmittance range, the protective layer 100 allows incident light to pass through the protective layer 100 without affecting the incident light.

[0055] The protective layer 100 may be a protective film or protective coating including a light incident surface and a light exiting surface opposite to the light incident surface. Preferably, the protective layer is a protective film that ensures good support for the contrast improvement layer.

[0056] When the protective layer is a protective film, the protective layer may be composed of a single layer of optically transparent resin film. Alternatively, the protective layer may have a multilayer structure of optically transparent resin films stacked on top of each other. The protective film can be formed by melting and extruding the resin. The resin can be further stretched as needed. The optically transparent resin may include at least one selected from the following: cellulose esters, including triacetyl cellulose (TAC); cyclic polyolefin resins, including amorphous cyclic olefin polymers (cyclic olefin polymer, COP); polycarbonate resins; polyester resins, including polyethylene terephthalate (PET); polyether sulfone resins; polysulfone resins; polyamide resins; polyimide resins; non-cyclic polyolefin resins; poly(meth)acrylic resins, including poly(methyl methacrylate); polyvinyl alcohol resins; polyvinyl chloride resins; and polyvinylidene chloride resins.

[0057] The protective film may be an unstretched film, a delay film obtained by stretching the resin using a certain method and having a specific delay range, or an isotropic optical film. In one embodiment, the protective film may be an isotropic optical film with Re of 60nm or less, specifically 0nm to 60nm, and more specifically 40nm to 60nm. Within this Re range, the protective film can provide good image quality by compensating for the viewing angle. Herein, the term "isotropic optical film" means a film with substantially the same nx, ny, and nz, and the expression "substantially the same" includes not only the case where nx, ny, and nz are exactly the same, but also the case where there is an acceptable error margin between nx, ny, and nz. In another embodiment, the protective film may be a delay film with Re of 60nm or more than 60nm. For example, the protective film may have Re of 60nm to 500nm or 60nm to 300nm. Alternatively, the protective film may have an Re of 8,000 nm or more, specifically 10,000 nm or more, more specifically more than 10,000 nm, more specifically 10,100 nm to 30,000 nm, more specifically 10,100 nm to 15,000 nm. Within this range, the protective film can prevent the generation of rainbow spots while further diffusing the light diffused by the contrast improvement layer.

[0058] When the protective layer is a protective coating, the protective coating may be formed of an actinic radiation curable resin composition comprising an actinic radiation curable compound and a polymerization initiator. The actinic radiation curable compound may include at least one of a cationically polymerizable curable compound, a free radically polymerizable curable compound, a urethane resin, and a silicone resin. The cationically polymerizable curable compound may be an epoxy compound having at least one epoxy group per molecule or an oxetane compound having at least one oxetane ring per molecule. The epoxy compound may include at least one of a hydrogenated epoxy compound, a chain aliphatic epoxy compound, a cyclic aliphatic epoxy compound, and an aromatic epoxy compound.

[0059] Examples of free radical polymerizable curable compounds may include (meth)acrylate monomers having at least one (meth)acryloyloxy group per molecule and (meth)acrylate oligomers obtained by reacting a compound containing at least two functional groups and having at least two (meth)acryloyloxy groups per molecule. Examples of (meth)acrylate monomers may include monofunctional (meth)acrylate monomers having one (meth)acryloyloxy group per molecule, difunctional (meth)acrylate monomers having two (meth)acryloyloxy groups per molecule, and multifunctional (meth)acrylate monomers having three or more (meth)acryloyloxy groups per molecule. Examples of (meth)acrylate oligomers may include urethane (meth)acrylate oligomers, polyester (meth)acrylate oligomers, and epoxy (meth)acrylate oligomers. A polymerization initiator may cure the actinic radiation curable compound. The polymerization initiator may include at least one of a photocationic initiator and a photosensitizer. The photocationic initiator may include any typical photocationic initiator known in the art.

[0060] The protective layer 100 may have a thickness of 5 μm to 200 μm, specifically 30 μm to 120 μm. In addition, the protective film type protective layer 100 may have a thickness of 30 μm to 100 μm, preferably 50 μm to 90 μm, and the protective coating type protective layer 100 may have a thickness of 1 μm to 50 μm. Within this thickness range, the protective layer 100 can be used for a polarizing plate.

[0061] A surface treatment layer (e.g., a primer layer), a hard coating layer, an anti-fingerprint layer, an anti-reflection layer, an anti-glare layer, a low-reflection layer, and an ultra-low-reflection layer may be further formed on at least one surface of the protective layer 100. The hard coating layer, the anti-fingerprint layer, the anti-reflection layer, etc. may provide additional functions to the protective layer, the polarizing film, etc. The primer layer may improve the adhesion between the protective layer and an adherend (e.g., a contrast improvement layer or a polarizer).

[0062] Contrast Improvement Layer

[0063] The contrast improvement layer 200 includes a first resin layer 210 and a second resin layer 220 facing the first resin layer 210. Preferably, the contrast improvement layer 200 is composed of the first resin layer 210 and the second resin layer 220.

[0064] The first resin layer 210 is formed on the light incident surface of the second resin layer 220 so that light entering the lower surface of the first resin layer 210 can pass through the first resin layer 210 and enter the second resin layer 220. The first resin layer 210 can diffuse the light by allowing the light having entered the lower surface of the first resin layer 210 to be refracted in various directions depending on the incident position of the light and to leave the first resin layer 210.

[0065] The first resin layer 210 is formed directly on the second resin layer 220 , and includes a patterned portion at an interface between the first resin layer 210 and the second resin layer 220 (a lower surface of the second resin layer). Figure 1 The patterned portion is shown to completely contact the second resin layer 220. Alternatively, the patterned portion may contact at least a portion of the second resin layer 220. A non-contact portion between the second resin layer 220 and the first resin layer 210 may be filled with air or a resin containing air or having a predetermined refractive index.

[0066] The patterned portion may be composed of at least two raised optical patterns 221 and a flat section 222 between adjacent optical patterns 221. In the patterned portion, a combination of the raised optical patterns 221 and the flat section 222 is repeatedly formed. The first resin layer 210 is composed of an upper surface 210a and a lower surface 210b. The upper surface 210a of the first resin layer 210 corresponds to the patterned portion located at the interface between the first resin layer 210 and the second resin layer 220.

[0067] The patterned portion satisfies the following equation 1, and the optical pattern 221 has a base angle θ of 75° to 90°. The base angle θ means an angle defined between the inclined surface 223 of the optical pattern 221 and an imaginary line extending from the maximum width W of the optical pattern 221. Here, the inclined surface 223 means an inclined surface directly connected to the flat section 222 of the optical pattern 221. Within this range, the contrast improvement layer can improve the side contrast ratio and the contrast ratio at the same side viewing angle. Specifically, the patterned portion can have a base angle θ of 80° to 90° and a P / W value (ratio of P to W) of 1.2 to 8.

[0068] <Equation 1>

[0069] 1 <P / W≤10,

[0070] Wherein P is the pitch of the patterned portion (unit: μm), and W is the maximum width of the raised optical pattern (unit: μm).

[0071] For example, the optical pattern 221 may have a base angle θ of 75°, 76°, 77°, 78°, 79°, 80°, 81°, 82°, 83°, 84°, 85°, 86°, 87°, 88°, 89°, or 90°.

[0072] For example, the optical pattern 221 may have a P / W of 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10.

[0073] although Figure 1 A structure in which the optical pattern has the same base angle θ at both sides thereof is shown, but the optical pattern may have different base angles θ as needed as long as the base angle θ is within a range of 75° to 90°.

[0074] The optical pattern 221 may be a convex optical pattern including a first surface 224 formed at a top portion of the optical pattern 221 and at least one inclined surface 223 connected to the first surface 224. Figure 1 A trapezoidal optical pattern is shown in which two adjacent inclined surfaces 223 are connected to each other via a first surface 224, but it should be understood that the present invention is not limited thereto. Alternatively, the optical pattern may have a rectangular cross-sectional shape or a square cross-sectional shape.

[0075] The first surface 224 is formed at the top portion of the optical pattern and can improve the viewing angle and brightness by further diffusing the light reaching the second resin layer 220 in the optical display. Therefore, the optical film can improve light diffusion, thereby minimizing the brightness loss. Therefore, the optical film according to this embodiment can minimize the brightness loss by improving light diffusion. The first surface 224 may be a flat surface to facilitate the process of manufacturing the optical film. Alternatively, the first surface 224 may have a fine roughness or a curved surface. In a structure where the first surface 224 is a curved surface, the optical pattern can be implemented by a lenticular lens pattern. Referring to Figure 1 , the optical pattern has a trapezoidal cross-section in which the first surface formed at the top portion is a flat surface and the inclined surface is a flat surface (for example, a truncated prism pattern with a truncated triangular cross-section, i.e., a truncated prism shape or a cut prism shape). Alternatively, the convex optical pattern may have a shape in which the first surface is formed at its top portion and the inclined surface is a curved surface (for example, the contrast improvement layer has a truncated lens-shaped (cut lens-shaped) lens pattern or a truncated microlens (cut microlens) pattern). Preferably, the optical pattern has a square or rectangular cross-section. In addition, the optical pattern may include a pattern having an N-gon cross-sectional shape (N is an integer from 3 to 20), wherein the N-gon cross-sectional shape includes a rectangular cross-sectional shape or a square cross-sectional shape.

[0076] The first surface 224 may be parallel to at least one of the flat section 222 , the lowermost surface of the first resin layer 210 , and the uppermost surface of the second resin layer 220 (ie, the upper surface of the second resin layer). Figure 1 The structure in which the first surface 224 of the optical pattern 221 , the flat section 222 , the lowermost surface of the first resin layer 210 , and the uppermost surface of the second resin layer 220 are parallel to each other is shown.

[0077] The first surface 224 may have a width A of 0.5 μm to 30 μm, specifically, 1 μm to 15 μm. Within this range, the first surface 224 may be used for an optical display, and a contrast ratio may be improved.

[0078] The optical pattern 221 may have an aspect ratio (H1 / W) of 0.1 to 10, specifically 0.1 to 7, more specifically 0.1 to 5, and more specifically 0.1 to 1. Within this range, the optical display may exhibit improved contrast ratio and viewing angle in a lateral direction.

[0079] The optical pattern 221 may have a maximum height H1 of 20 μm or less, specifically 15 μm or less, more specifically 10 μm or less. Within this range, the optical display may exhibit improved contrast ratio, viewing angle, and brightness without suffering from Moire phenomenon, etc.

[0080] The optical pattern 221 may have a maximum width W of 20 μm or less, specifically 15 μm or less, more specifically 10 μm or less. Within this range, the optical display may exhibit improved contrast, viewing angle, and brightness without suffering from a moire phenomenon or the like.

[0081] although Figure 1 The structure in which adjacent optical patterns of the patterned portion have the same base angle, the same first surface width, the maximum height and the maximum width is shown; however, the adjacent optical patterns may have different base angles, different first surface widths, different maximum heights and different maximum widths.

[0082] Upon receiving light from the first resin layer 210 , the flat section 222 emits the light to the second resin layer 220 , thereby improving front brightness.

[0083] The ratio (W / L) of the maximum width W of the optical pattern 221 to the width L of the flat section 222 may be 9 or less, specifically 0.1 to 3, more specifically 0.15 to 2. Within this maximum width range, the optical film can reduce the difference between the front contrast ratio and the side contrast ratio while improving the contrast ratio at the same side viewing angle and the same front viewing angle. In addition, the optical film can prevent the moire phenomenon. The flat section 222 may have a width L of 1 μm to 50 μm, specifically 1 μm to 20 μm. Within this range, the optical film can improve the front brightness.

[0084] The maximum width W of one optical pattern 221 and the flat section 222 adjacent to the optical pattern 221 form a pitch P. The pitch P may be in the range of 1 μm to 50 μm, specifically 1 μm to 40 μm. Within this range, the optical pattern can improve brightness and contrast ratio without causing a moire phenomenon.

[0085] although Figure 1 The structure in which adjacent optical patterns of the patterned portion have the same pitch and the same maximum width is shown, however it should be understood that adjacent optical patterns may have different pitches and different maximum widths.

[0086] The first resin layer 210 may have a refractive index of 1.50 or more, specifically 1.55 to 1.70. Within this range, the optical film may promote light diffusion, may be easily manufactured, and may provide diffusion of polarized light and significant improvement in contrast ratio.

[0087] The first resin layer 210 may be formed of a composition for the first resin layer comprising a curable compound. The composition for the first resin layer may further comprise an initiator. The curable compound and the initiator are the same as the curable compound and the initiator of the composition for the second resin layer described below. The composition for the first resin layer may further comprise an additive added to the composition for the second resin layer.

[0088] The first resin layer 210 may be a non-adhesive layer that does not exhibit adhesion. In this case, the optical film may be stacked on an adherend (e.g., a polarizing film) via an adhesive agent, a bonding agent, or a bonding / bonding agent. In another embodiment, the first resin layer 210 may be an adhesive. In this case, the first resin layer 210 may be formed directly on the protective layer 200. When the first resin layer 210 is self-adhesive, the optical film can be stacked on an adherend (e.g., a polarizing film) without the need for an additional adhesive, a bonding agent, or a bonding / bonding agent, thereby enabling the thickness of the optical film to be reduced.

[0089] although Figure 1 Not clearly shown, however Figure 1The optical pattern is shown as a structure extending in a strip shape. Alternatively, the optical pattern can be formed in a dot shape. Herein, "dot" means that the optical pattern is dispersed. Preferably, the optical pattern extends in a strip shape to expand the viewing angle at the right and left sides.

[0090] The second resin layer 220 has a lower refractive index than the first resin layer 210. Therefore, when light enters the light incident surface of the first resin layer 210, the contrast improvement layer 200 diffuses the light and emits the light, thereby improving the side contrast ratio while minimizing the reduction of the front contrast ratio, reducing the difference between the front contrast ratio and the side contrast ratio, and improving the contrast ratio at the same side viewing angle and the same front viewing angle. The difference in refractive index between the first resin layer 210 and the second resin layer 220 may be 0.05 or more, specifically 0.05 to 3, and more specifically 0.05 to 0.2. Within this range, the optical film can provide a significant effect in terms of diffusion of collected light while improving the contrast ratio.

[0091] The second resin layer 220 may have a refractive index of less than 1.52, specifically, 1.35 to less than 1.50. Within this range, the optical film may have a good effect on light diffusion.

[0092] The second resin layer 220 may be formed of a composition for a second resin layer, the composition including at least one of a metal complex salt dye and an organic black dye; and a curable resin.

[0093] At least one of the metal complex salt dye and the organic black dye may include a black dye dispersion having an average particle size D50 of 30 nm or less, preferably 5 nm to 10 nm. In addition, the average particle size of at least one of the metal complex salt dye and the organic black dye is much smaller than the maximum width of the optical pattern and the width of the flat section. For example, the ratio of the average particle size of at least one of the metal complex salt dye and the organic black dye to each of the maximum width of the optical pattern and the width of the flat section may be in the range of 1:300 to 1:800. Within this average particle size range, the optical film can obtain the advantageous effects of the present invention.

[0094] The second resin layer 220 may improve the front contrast ratio and reduce the reflectivity and the brightness at the side surface of the optical display in the black mode by at least one of the metal complex salt dye and the organic black dye having an average particle diameter within the above range.

[0095] When there is a metal complex salt dye or an organic black dye having an average particle size in the above range between adjacent optical patterns, the metal complex salt dye or the organic black dye does not affect the light emitted from the flat section of the first resin layer, thereby improving the front contrast ratio, and does not affect the light emitted from the side surface of the optical pattern, thereby improving the side contrast ratio via the patterned portion. In addition, by using a metal complex salt dye or an organic black dye, the composition for the second resin layer can improve the front contrast ratio while reducing the reflectivity increased by the number of layers. In addition, the composition for the second resin layer can improve black visibility, which can be reduced by the side light leakage of the liquid crystal display (LCD) panel. When measured on the protective layer of the optical film, the LCD panel can have a reflectivity of 5% or less, preferably 4.9% or less. Within this range, the optical film can reduce the reflectivity of the optical display, thereby improving the appearance.

[0096] In one embodiment, at least one of a metal complex salt dye and an organic black dye may be present in the second resin layer in an amount of 0.01 wt % to 10 wt %, preferably 0.01 wt % to 3 wt %, more preferably 0.01 wt % to 1 wt %, and even more preferably 0.01 wt % to 0.5 wt %. Within this range, the metal complex salt dye or the organic black dye may improve the front contrast ratio, reflectivity, and black visibility, and may be provided to the second resin layer.

[0097] The second resin layer may have a light transmittance of 50% to 92%, preferably 75% to 85%, at a wavelength of 550 nm. Within this range, the second resin layer may improve the side contrast ratio via the patterned portion and improve the front contrast ratio via the metal complex salt dye.

[0098] Next, the metal complex salt dye will be explained in detail.

[0099] The metal complex salt dye can be a black dye containing metal. The metal may include at least one selected from chromium, nickel, cobalt and copper. The metal complex salt dye can be classified into 1:1 metal complex salt dye and 1:2 metal complex salt dye. 1:1 metal complex salt dye refers to a metal complex salt dye in which a metal element is coupled to a dye molecule (ligand), and 1:2 metal complex salt dye refers to a metal complex salt dye in which a metal element is coupled to two dye molecules. The dye molecule may include an azo compound (e.g., a monoazo compound) containing a hydroxyl, carboxyl or amino group. Therefore, the second resin layer can improve the side contrast ratio via the patterned portion, improve the front contrast ratio via the metal complex salt dye, and improve black visibility while reducing reflectivity.

[0100] In one embodiment, the metal complex salt dye is a metal-containing azo dye and may contain C6 to C 20 Preferably, the metal complex dye contains C8 to C 15 Monocyclic or polycyclic aromatic functional groups (e.g., phenyl or naphthyl) are used as monocyclic or polycyclic aromatic functional groups. Therefore, during mixing with the ultraviolet (UV) curable resin contained in the composition for the second resin layer, the metal complex salt dye enables efficient mixing with the UV curable resin, thereby improving the hardness of the second resin layer while preventing the metal complex salt dye from separating from the second resin layer.

[0101] In one embodiment, the metal complex salt dye may be composed of one dye. In another embodiment, the metal complex salt dye may be composed of a mixture of a red metal complex salt dye, a green metal complex salt dye and a blue metal complex salt dye.

[0102] The metal complex salt dye may have a refractive index of 1.6 to 2.2, preferably 1.9 to 2.1. Within this range, the metal complex salt dye does not affect the refractive index when contained in the second resin layer.

[0103] The metal complex salt dye may be a commercially available product and is not limited thereto. For example, the metal complex salt dye may include orisol Black X55 (BASF) and At least one of black X51 (BASF).

[0104] Next, the organic black dye will be explained in detail.

[0105] Organic black dyes are non-metallic black dyes that do not contain metals, and have good properties in terms of dispersibility (minimum dispersion unit: 1nm to 5nm), transparency and brightness. In contrast, inorganic black pigments (such as carbon black) show poor dispersibility (minimum dispersion unit: 50nm to 400nm) and are opaque. The optical film according to the present invention needs to be suitable for a dispersion size of several nanometers for a micro-pattern size, and needs to be a solvent-free film for an embossing process. Therefore, since the optical film according to the present invention needs to have good dispersibility and high transmittance while reducing the brightness in the black mode, an organic black dye is preferred over carbon black as an inorganic black pigment.

[0106] The organic black dye may have a refractive index of about 1.6 to about 2.2, preferably about 1.9 to about 2.1. Within this range, the organic black dye does not affect the refractive index when included in the second resin layer.

[0107] The organic black dye may be a commercially available product and is not limited thereto.

[0108] In one embodiment, the organic black dye is a mixture of dyes of three colors, and can be a mixture of the first dye (orange color dye), the second dye (red color dye) and the third dye (blue color dye). The first dye can have a maximum absorption wavelength of 430nm to 450nm, preferably 440nm, and can include a dye whose absorption wavelength is 360nm to 640nm. The second dye can have a maximum absorption wavelength of 510nm to 530nm, preferably 520nm, and can include a dye whose absorption wavelength is 360nm to 740nm. The third dye can have a maximum absorption wavelength of 590nm to 610nm, preferably 600nm, and can include a dye whose absorption wavelength is 360nm to 740nm. Herein, "maximum absorption wavelength" is a value measured for each dye in 5mg / L (5% by weight) of methyl ethyl ketone as a solvent. Such concentration can be considered to be suitable for measuring transmittance.

[0109] In one embodiment, the organic black dye can be a mixture of 30 wt % to 50 wt %, preferably 40 wt % to 50 wt % of the first dye, 1 wt % to 20 wt %, preferably 1 wt % to 10 wt % of the second dye, and 30 wt % to 50 wt %, preferably 40 wt % to 50 wt % of the third dye. Within these ranges, the organic black dye can exhibit high brightness.

[0110] The first dye (orange dye) is an azo dye, for example, a dye represented by Formula 1 (Synolonyellow Brown K-2RS, Kyung-In Synthetic Co.):

[0111]

[0112] The second dye (red dye) is an azo dye, for example, a dye represented by Formula 2 (Synolon rubine K-GFL, Kyung In Synthetic Co., Ltd.):

[0113]

[0114] The third dye (blue dye) is an azo dye, for example, a dye represented by Formula 3 (Synolon navy blue K-GLS, Kyung In Synthetic Co., Ltd.):

[0115]

[0116] The organic black dye may be a commercially available product and is not limited thereto. For example, the organic black dye may include BS01 (Kyung In Synthetics Co., Ltd.), BS02 (Kyung In Synthetics Co., Ltd.), and the like.

[0117] The curable compound may include at least one of an ultraviolet curable compound and a heat curable compound. Preferably, the curable compound is an ultraviolet curable compound so that the second resin layer can be formed quickly and a good pattern shape can be provided when forming a pattern. The curable compound may include a (meth)acrylic acid monomer, an oligomer thereof, or a resin thereof.

[0118] The curable compound may have a refractive index of less than 1.52, preferably 1.35 to less than 1.50 after curing. Within this range, the curable compound may ensure a desired refractive index of the second resin layer.

[0119] The composition for the second resin layer may also include an initiator. The initiator is used to cure the curable resin and may include at least one of a photoinitiator and a thermal initiator. These initiators may be selected from typical initiators known to those skilled in the art. The photoinitiator may include at least one of a phosphorus initiator, a triazine initiator, an acetophenone initiator, a benzophenone initiator, a thioxanthone initiator, a benzoin initiator, an oxime initiator, and a phenyl ketone initiator. In the second resin layer or in the composition for the second resin layer, based on solid content, there may be an initiator in an amount of 5 wt % or less, for example, 2 wt % to 5 wt %. Within this range, the initiator can fully cure the composition for the second resin layer, and the transmittance of the contrast improvement layer will not be degraded due to residual initiators.

[0120] Due to the coatability of the composition for the second resin layer, the composition may further include typical solvents such as ethanol (EtOH), propylene glycol monomethyl ether acetate (PGME), methyl ethyl ketone (MEK) and methyl isobutylketone (MIBK), but is not limited thereto.

[0121] The composition for the second resin layer may further include typical additives well known to those skilled in the art. The additives may include at least one of a leveling agent, a surface modifier, an antioxidant, a defoaming agent, an ultraviolet absorber, and a light stabilizer.

[0122] The second resin layer 220 may have a maximum thickness of 30 μm or less, for example, 20 μm or less. Within this thickness range of the second resin layer, the optical film may prevent warping such as curling.

[0123] The value obtained by subtracting the maximum height of the optical pattern 221 from the maximum thickness of the second resin layer 220 (maximum thickness of the second resin layer 220 - maximum height of the optical pattern 221) (also referred to as "net thickness") may be 30 μm or less, for example, 20 μm or less or 10 μm or less. Within this range, the optical film may have an effect of minimizing the degradation of the side contrast ratio.

[0124] Like the first resin layer, the second resin layer 220 may be an adhesive layer or a non-adhesive layer.

[0125] The contrast improvement layer 200 may have a thickness of 10 μm to 100 μm, specifically 10 μm to 50 μm, and more specifically 10 μm to 40 μm. Within this thickness range, the contrast improvement layer may be used for an optical display.

[0126] The contrast improvement layer can be formed by a general method known to those skilled in the art. For example, the contrast improvement layer can be formed by coating the composition for the second resin layer on the protective layer, applying an optical pattern and a flat section and curing to form the second resin layer, and then coating the composition for the first resin layer on the second resin layer and curing, but is not limited thereto.

[0127] Next, we will refer to Figure 2 A polarizing plate according to an embodiment of the present invention will be described. Figure 2 FIG. 4 is a cross-sectional view of a polarizing plate according to an embodiment of the present invention.

[0128] Reference Figure 2 The polarizing plate 20 according to the present embodiment includes a polarizing film 300 and a contrast improvement film, and the contrast improvement film may include an optical film according to an embodiment of the present invention. The optical film may be formed on a light emitting surface of the polarizing film 300. The optical film diffuses polarized light having passed through the polarizing film 300, thereby improving the front contrast ratio, the side contrast ratio, the viewing angle, and the black visibility.

[0129] The polarizing film 300 may polarize light received from the liquid crystal panel and transmit the light toward the contrast improvement layer 200. The polarizing film 300 is formed on a light incident surface of the contrast improvement layer 200.

[0130] The polarizing film 300 may include a polarizer. Specifically, the polarizer may include a polyvinyl alcohol polarizer obtained by uniaxially stretching a polyvinyl alcohol film or a polyolefin-based polarizer obtained by dehydrating a polyvinyl alcohol film. The polarizer may have a thickness of 5 μm to 40 μm. Within this range, the polarizing film 300 may be used for an optical display.

[0131] The polarizing film 300 may include a polarizer and a protective layer formed on at least one surface of the polarizer. The protective layer protects the polarizer, thereby improving the reliability and mechanical strength of the polarizing plate. The protective layer may include at least one of an optically transparent protective film and an optically transparent protective coating. The protective layer is the same as described above.

[0132] The polarizing plate can be manufactured by a typical method.

[0133] In one embodiment, the polarizing plate is made by forming an optical film by the above method and then bonding the polarizing film to the other surface of the first resin layer of the optical film. The bonding of the polarizing film can be performed using a typical adhesive (such as a water-based adhesive or a light-curable adhesive).

[0134] In another embodiment, the polarizing plate is made by forming a first resin layer by depositing a composition for a first resin layer on one surface of a polarizing film, applying an optical pattern and flat sections to the first resin layer and curing, then depositing a composition for a second resin layer, placing a protective layer and curing, but is not limited to this.

[0135] According to the present invention, a liquid crystal display may include a polarizing plate according to the present invention. In one embodiment, the liquid crystal display may include a polarizing plate located at the observer side relative to the liquid crystal panel. Herein, the term "polarizing plate located at the observer side" refers to a polarizing plate placed on the screen side of the liquid crystal panel (i.e., on the side of the liquid crystal panel opposite to the light source).

[0136] In one embodiment, a liquid crystal display may include a backlight unit, a first polarizing plate, a liquid crystal panel, and a second polarizing plate stacked in the order of the statements, wherein the second polarizing plate may include a polarizing plate according to the present invention. The liquid crystal panel may adopt a vertical alignment (VA) mode, an in-plane switching (IPS) mode, a patterned vertical alignment (PVA) mode, or a super-patterned vertical alignment (S-PVA) mode, but is not limited thereto. In another embodiment, the liquid crystal display may include a polarizing plate located at the light source side. Herein, the term "polarizing plate located at the light source side" refers to a polarizing plate disposed at the light source side relative to the liquid crystal panel. In yet another embodiment, the polarizing plate located at the observer side relative to the liquid crystal panel and the polarizing plate located at the light source side may include a polarizing plate according to the present invention.

[0137] The present invention provides an optical film which can improve the front contrast ratio while reducing the reflectivity.

[0138] The present invention provides an optical film that can reduce brightness at a side surface of an optical display in a black mode.

[0139] Next, the present invention will be described in more detail with reference to some examples. However, it should be noted that these examples are provided for illustrative purposes only and should not be construed as limiting the present invention in any way.

[0140] Example 1

[0141] 40 parts by weight of methyl ethyl ketone as a diluent and 0.15 parts by weight of Black X55 (average particle size (D50): 10 nm, powder, complex salt of metal chromium: azo compound (1:2), BASF) was mixed and then stirred at 1,000 rpm for 1 hour using a stirrer. Next, 100 parts by weight of an adhesive acrylic copolymer (PL8540, SAIDEN) was added to the mixture and mixed with 40 parts by weight of methyl ethyl ketone as a diluent, and then stirred at 2,000 rpm for 1 hour using a stirrer to prepare a composition for a second resin layer.

[0142] As the resin for the first resin layer (high reflection layer), an ultraviolet curable resin (SSC-5760, SHIN-AT&C Co., Ltd.) was used.

[0143] The resin for the first resin layer was deposited on one surface of a PET film of a three-layer structure of PET / PVA / COP polarizing film (AMN-6143CPS (CO), Samsung SDI) to form a coating layer. Next, a film on which an optical pattern and a flat section were alternately formed was applied to the coating layer to form an optical pattern and a flat section on the coating layer, and then irradiated at 500 mJ / cm 2 The first resin layer including the patterned portion is formed by ultraviolet curing under the condition of 0.1% mol / l. Table 1 shows the specifications of the patterned portion formed on the contrast improvement layer.

[0144] Next, the prepared composition for the second resin layer was deposited on the patterned portion of the first resin layer to form a coating layer. As a protective film, a polyethylene terephthalate (PET) film (TA044, thickness: 80 μm, Toyobo Co., Ltd.) was bonded to one surface of the coating layer and cured in a drying oven at 90° C. for 4 minutes to form a second resin layer, thereby preparing a polarizing plate having an optical film formed thereon.

[0145] Example 2

[0146] In addition to using 0.3 parts by weight of Black X55 is used to replace 0.15 parts by weight An optical film and a polarizing plate were produced in the same manner as in Example 1 except for Black X55.

[0147] Example 3

[0148] In addition to using 0.15 parts by weight of 0.15 parts by weight of black X51 (average particle size (D50): 10 nm, complex salt of metal chromium: azo compound (1:2)) was used instead An optical film and a polarizing plate were produced in the same manner as in Example 1 except for Black X55.

[0149] Example 4

[0150] In addition to using 0.3 parts by weight of Black X51 is used to replace 0.15 parts by weight An optical film and a polarizing plate were produced in the same manner as in Example 1 except for Black X55.

[0151] Example 5

[0152] In addition to using 0.15 parts by weight of BS01 (Kyung In Synthetic Co., Ltd., powder) as an organic black dye in place of 0.15 parts by weight of Except for black X55, an optical film and a polarizing plate were prepared in the same manner as in Example 1. The organic black dye had an average particle size (D50) of 10 nm and was a mixture of three colors of organic dyes prepared by mixing 45 wt % of Xilong Yellow Brown K-2RS (Kyung-In Synthetics Co., Ltd.) for orange color, 10 wt % of Xilong Ruby Red K-GFL (Kyung-In Synthetics Co., Ltd.) for red color, and 45 wt % of Xilong Deep Blue K-GLS (Kyung-In Synthetics Co., Ltd.) for blue color.

[0153] Example 6

[0154] In addition to using 0.3 parts by weight of BS01 (Kyung In Synthetic Co., Ltd., powder) as an organic black dye in place of 0.15 parts by weight of An optical film and a polarizing plate were produced in the same manner as in Example 1 except for Black X55.

[0155] Comparative Example 1

[0156] A polarizing film (AMN-6143CPS (CO), Samsung SDI Co., Ltd.) having a structure of PET / PVA / COP and not including an optical film was used.

[0157] Comparative Example 2

[0158] Except that no An optical film and a polarizing plate were produced in the same manner as in Example 1 except for Black X55.

[0159] Comparative Example 3

[0160] A composition for the second resin layer was prepared by mixing 100 parts by weight of an adhesive acrylic copolymer (PL8540, Seiden Corporation) with 80 parts by weight of methyl ethyl ketone as a diluent solvent, and then stirring at 500 rpm for 30 minutes using a stirrer.

[0161] 100 parts by weight of ultraviolet curable resin (SSC-5760, New Asia T&C Co., Ltd.) and 0.15 parts by weight of Black X55 was mixed and then stirred at 2,000 rpm for 2 hours to prepare a composition for a first resin layer.

[0162] A polarizing plate including the optical film formed above was produced in the same manner as in Example 1 using the composition for a first resin layer and the composition for a second resin layer.

[0163] Comparative Example 4

[0164] In addition to using 0.3 parts by weight of Black X55 is used to replace 0.15 parts by weight An optical film and a polarizing plate were produced in the same manner as in Comparative Example 3 except for Black X55.

[0165] Comparative Example 5

[0166] In addition to using 0.4 parts by weight of carbon black dispersion (CI-M-400) instead of using An optical film and a polarizing plate were produced in the same manner as in Comparative Example 3 except for Black X55.

[0167] Table 1

[0168]

[0169] The following properties were evaluated with respect to the optical films and polarizing plates prepared in Examples and Comparative Examples, and the evaluation results are shown in Tables 2 and 3.

[0170] Panel reflectivity: The optical film bonded to each polarizing plate prepared in the examples and comparative examples was attached to an LCD VN type Superb Ultra High Definition (SUHD) 55" liquid crystal panel (Samsung Electronics Co., Ltd.) via an adhesive having a refractive index of 1.46 to 1.50, and then the reflectivity in a specular component include (SCI) reflection mode (light source: D65 light source) was measured using a spectrophotometer (CM-2600D, Konica Minolta Co., Ltd.) at a wavelength of 320 nm to 800 nm.

[0171] Making a polarizing plate on the light source side

[0172] A polarizer was produced by stretching a polyvinyl alcohol film at 60°C to 3 times its initial length and adsorbing iodine to the stretched film, and then stretching the film at 40°C in a boric acid aqueous solution to 2.5 times the stretched length of the film. As a base layer, a triacetyl cellulose film (thickness: 80 μm) was bonded to both surfaces of the first polarizer using a binder for polarizing plates (Z-200, Nippon Goshei Co., Ltd.), thereby producing a polarizing plate. The produced polarizing plate was used as a polarizing plate located at the light source side.

[0173] Making LCD display modules

[0174] The polarizing plate manufactured at the light source side, the liquid crystal panel (PVA mode) and each polarizing plate manufactured in the examples and comparative examples were assembled in the order described to provide a module of a liquid crystal display. Here, each polarizing plate prepared in the examples and comparative examples was assembled to the module so that the protective layer of the polarizing plate was placed at the outermost side of the module.

[0175] A module of a light emitting diode (LED) light source, a light guide plate, and a liquid crystal display is assembled to provide a liquid crystal display including a single-sided edge-type LED light source (except for each module of the liquid crystal display of the use example and the comparative example, which has the same configuration as a Samsung LED TV (55", model: UN55KS8000F)).

[0176] The luminance in each of the white mode and the black mode was measured at the coordinates (0°, 0°) and each of the coordinates (0°, 30°) and the coordinates (0°, 60°) in a spherical coordinate system using EZCONTRAST X88RC (EZXL-176R-F422A4, ELDIM Co., Ltd.).

[0177] The front contrast ratio is calculated as the ratio of the brightness in the white mode to the brightness in the black mode at the coordinates (0°, 0°) in the spherical coordinate system. The side contrast ratio is calculated as the ratio of the brightness in the white mode to the brightness in the black mode at the coordinates (0°, 30°) and the coordinates (0°, 60°) in the spherical coordinate system.

[0178] The front relative brightness in the white mode was calculated as the ratio of the brightness of each module of the example and the comparative example in the white mode to the brightness of the module of the comparative example 1. The front relative brightness in the black mode was calculated as the ratio of the brightness of each module of the example and the comparative example in the black mode to the brightness of the module of the comparative example 1. The side relative brightness in the black mode was calculated in the same manner.

[0179] Table 2

[0180]

[0181] Table 3

[0182]

[0183] As shown in Table 2, the optical film according to the present invention can reduce the reflectivity while improving the front contrast ratio and the side contrast ratio. In addition, the optical film according to the present invention can improve the front relative brightness and the front contrast ratio by reducing the side relative brightness.

[0184] In contrast, the optical film of Comparative Example 2, in which each of the second resin layer and the first resin layer does not include at least one of the metal complex salt dye and the organic black dye, exhibits high reflectivity and high side relative brightness in the black mode. In addition, each of the optical films of Comparative Examples 3 to 5, in which at least one of the metal complex salt dye and the organic black dye is included in the first resin layer instead of the second resin layer, exhibits high side relative brightness in the black mode and exhibits lower front contrast ratio and side contrast ratio than the optical film of the example.

[0185] It should be understood that various modifications, changes, variations and equivalent embodiments may be made by those skilled in the art without departing from the spirit and scope of the present invention.

Claims

1. An optical film, characterized in that: include: Protective layer; as well as Contrast improvement layer; wherein the contrast improvement layer comprises a second resin layer and a first resin layer stacked in sequence from the protective layer, and the first resin layer faces the second resin layer, wherein the second resin layer has a lower refractive index than the first resin layer, and The first resin layer includes a patterned portion, the patterned portion is formed in at least some areas of the first resin layer facing the second resin layer, and includes at least two raised optical patterns and a flat section disposed between the raised optical patterns adjacent to each other, the raised optical patterns having a base angle θ of 75° to 90°, the patterned portion satisfying Equation 1, <Equation 1> 1 <P / W≤10 Wherein P is the pitch of the patterned portion, and W is the maximum width of the raised optical pattern, The second resin layer comprises at least one of a metal complex salt dye and an organic black dye and an ultraviolet curable resin, The contrast improvement layer is formed on the light incident surface of the protective layer, At least one of the metal complex salt dye and the organic black dye is present in the second resin layer in an amount of 0.15 wt % to 0.3 wt %, The second resin layer has a light transmittance of 75% to 85% at a wavelength of 550 nm, The organic black dye has a minimum dispersion unit of 1 nm to 5 nm, The metal complex salt dye is a metal-containing azo dye.

2. The optical film according to claim 1, characterized in that: Each of the metal complex salt dye and the organic black dye has an average particle diameter of 30 nm or less.

3. The optical film according to claim 1, characterized in that: The metal complex salt dyes include black dyes containing chromium, nickel, cobalt or copper.

4. The optical film according to claim 3, characterized in that: The metal complex salt dye includes a black dye containing chromium.

5. The optical film according to claim 1, characterized in that: The metal complex salt dye includes C6 to C 20 Azo dyes with monocyclic or polycyclic aromatic functional groups.

6. The optical film according to claim 1, characterized in that: The metal complex salt dye includes chromium and C6 to C 20 The azo dye having a monocyclic or polycyclic aromatic functional group has an average particle size of 30 nm or less.

7. The optical film according to claim 1, characterized in that: The organic black dye includes a mixture of a first dye having a maximum absorption wavelength of 430 nm to 450 nm, a second dye having a maximum absorption wavelength of 510 nm to 530 nm, and a third dye having a maximum absorption wavelength of 590 nm to 610 nm.

8. The optical film according to claim 7, characterized in that: Each of the first dye, the second dye, and the third dye includes an azo-based dye.

9. The optical film according to claim 8, characterized in that: The first dye is represented by Formula 1; the second dye is represented by Formula 2; and the third dye is represented by Formula 3: <Formula 1> <Formula 2> <Formula 3> 10. The optical film according to claim 1, characterized in that: The first resin layer is an adhesive layer.

11. The optical film according to claim 1, characterized in that: The raised optical pattern includes a trapezoidal optical pattern, a rectangular optical pattern, or a square optical pattern in a cross-sectional view.

12. A polarizing plate, characterized in that: include: polarizing film; as well as The optical film according to any one of claims 1 to 11, wherein the optical film is formed on a light exit surface of the polarizing film.

13. A liquid crystal display, characterized in that: Comprising the polarizing plate as claimed in claim 12.

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