Polarizing plate and liquid crystal display including the same

Abstract

A polarizing plate and a liquid crystal display including the polarizing plate. The polarizing plate includes a polarizing film and a contrast-improving optical film stacked in sequence. The contrast-improving optical film includes a contrast-improving layer, and the contrast-improving layer includes a first resin layer and a second resin layer facing the first resin layer. The second resin layer includes a patterned portion, and the patterned portion has an optical pattern and a plane section arranged between the optical patterns. The second resin layer satisfies equation 1, and the polarizing plate has a contrast ratio gain of 1.00 or more represented by equation 2. Therefore, it is possible to improve the side contrast ratio while minimizing the reduction in the front contrast ratio.

Description

[0001] The present invention is a divisional application of the invention patent application with application number 201810020940.5 filed on January 9, 2018 and invention name “Polarizing plate and liquid crystal display including the polarizing plate”. Technical Field

[0002] Various aspects of the embodiments of the present invention relate to a polarizing plate and a liquid crystal display including the polarizing plate. More specifically, the present invention relates to a polarizing plate for a liquid crystal display (LCD) and a liquid crystal display including the polarizing plate. Background Art

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

[0004] Generally speaking, contrast-improving optical films use optical patterns to improve contrast ratios. For example, the contrast ratio can be improved by an optical film in which plane segments and optical patterns are alternately formed. The optical pattern includes an inclined surface and can improve the contrast ratio by refracting and diffusing light incident on the inclined surface, and the plane segments can diffuse the light and maintain brightness by emitting the light reaching the plane segments. However, although the side contrast ratio can be improved by such an optical pattern, the front contrast ratio is generally reduced. Therefore, there is a need for a polarizing plate that can improve the side contrast ratio while minimizing or reducing the reduction in the front contrast ratio.

[0005] One example of the background art is disclosed in Japanese Patent Laid-Open No. 2006-251659. Summary of the invention

[0006] An aspect of the present invention is to provide a polarizing plate capable of improving a side contrast ratio while minimizing a reduction in a front contrast ratio.

[0007] Another aspect of the present invention is to provide a polarizing plate capable of improving a side viewing angle.

[0008] Another aspect of the present invention is to provide a liquid crystal display including the polarizing plate according to the present invention.

[0009] According to one aspect of the present invention, a polarizing plate includes a polarizing film and a contrast-improving optical film stacked in sequence, wherein the contrast-improving optical film includes a contrast-improving layer, the contrast-improving layer includes a first resin layer and a second resin layer facing the first resin layer, the second resin layer includes a patterned portion, the patterned portion has an optical pattern and a plane section arranged between the optical patterns, and the second resin layer satisfies equation 1:

[0010] <Equation 1>

[0011] 0≤(maximum thickness of the second resin layer-maximum height of the optical pattern) / (maximum height of the optical pattern)≤1, and

[0012] The polarizing plate has a contrast ratio (CR) gain of 1.00 or more represented by Equation 2:

[0013] <Equation 2>

[0014] Contrast ratio gain = side relative contrast ratio × front relative contrast ratio

[0015] Each of the side relative contrast ratio and the front relative contrast ratio is as described in the following detailed description.

[0016] According to another aspect of the present invention, there is provided a liquid crystal display including the polarizing plate according to the present invention.

[0017] The present invention provides a polarizing plate capable of improving a side contrast ratio while minimizing a reduction in a front contrast ratio.

[0018] The invention provides a polarizing plate capable of improving the side viewing angle. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 is a cross-sectional view of a polarizing plate according to an embodiment of the present invention.

[0020] Figure 2 yes Figure 1 Cross-sectional view of a contrast-enhancing optical film for a polarizing plate is shown.

[0021] Figure 3 FIG. 4 is a cross-sectional view of a contrast-improving optical film for a polarizing plate according to another embodiment of the present invention.

[0022] [Explanation of Symbols]

[0023] 10: Polarizing plate

[0024] 100A, 100B: Contrast improvement layer

[0025] 110A, 110B: first resin layer

[0026] 111: Fill pattern

[0027] 120A, 120B: Second resin layer

[0028] 121: Optical Pattern

[0029] 122: Plane section

[0030] 123: Sloped surface

[0031] 124: First Surface

[0032] 200: Protective layer

[0033] 300: Polarizing film

[0034] A: Width of the first surface

[0035] H1: Minimum thickness of the first resin layer

[0036] H2: Maximum height of the optical pattern

[0037] H3: Maximum thickness of the second resin layer - maximum height of the optical pattern

[0038] L: Width of the flat section

[0039] P: Pitch of patterned part

[0040] W: Maximum width of the optical pattern

[0041] θ: base angle DETAILED DESCRIPTION

[0042] 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 without being limited to the following embodiments. In the accompanying drawings, parts that are not related to the description may be omitted for clarity. Throughout the specification, the same components will be indicated by the same reference numerals.

[0043] In this document, 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 (e.g., 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 more than one intervening element. 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.

[0044] In this document, 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. In this document, "front" and "side" refer to the horizontal direction, and the side is represented by (0°, 60°) in a spherical coordinate system represented by (φ, θ), where the front is represented by (0°, 0°), the left end point is represented by (180°, 90°), and the right end point is represented by (0°, 90°).

[0045] As used herein, the term "top" refers to the highest portion of an engraved optical pattern.

[0046] As used herein, "aspect ratio" refers to the ratio of the maximum height of an optical pattern to its maximum width (maximum height / maximum width).

[0047] Herein, "pitch" refers to the distance between adjacent optical patterns, that is, the sum of the maximum width of one optical pattern and the width of one planar section.

[0048] Herein, "in-plane retardation (Re)" is a value measured at a wavelength of 550 nanometers and expressed by Equation A:

[0049] Re=(nx-ny)×d<Equation A>

[0050] In equation A, nx and ny are the refractive indices of the corresponding protective layer or underlying layer on the slow optical axis and the fast optical axis respectively at a wavelength of 550 nanometers, and d is the thickness of the protective layer or underlying layer (unit: nanometer).

[0051] As used herein, the term "(meth)acrylic acid" refers to acrylic acid and / or methacrylic acid.

[0052] Below, we will refer to Figure 1 and Figure 2 A polarizing plate according to an embodiment of the present invention is described. Figure 1 is a cross-sectional view of a polarizing plate according to an embodiment of the present invention. Figure 2 According to one embodiment of the present invention Figure 1 Cross-sectional view of a contrast-enhancing optical film for a polarizing plate is shown.

[0053] Reference Figure 1 , the polarizing plate 10 according to an embodiment of the present invention may include a polarizing film 300 and a contrast-improving optical film, wherein the contrast-improving optical film includes a contrast-improving layer 100A and a protective layer 200. The contrast-improving optical film is formed on a light-exiting surface of the polarizing film 300. The contrast-improving optical film includes a contrast-improving layer 100A satisfying Equation 1.

[0054] Will refer to Figure 2 The contrast-enhancing optical film is further described in detail.

[0055] Contrast Improvement Layer

[0056] The contrast improvement layer 100A includes a first resin layer 110A and a second resin layer 120A facing the first resin layer 110A.

[0057] Second resin layer

[0058] The second resin layer 120A is formed on the first resin layer 110A, specifically, on the light exiting surface of the first resin layer 110A. The second resin layer 120A may increase light diffusion by diffusing light incident from the light exiting surface of the first resin layer 110A.

[0059] The second resin layer 120A includes a patterned portion having one or more optical patterns 121 and a plane section 122 between adjacent optical patterns 121. The optical pattern 121 includes at least one inclined surface 123 inclined with respect to the plane section 122. Figure 2 An example is shown in which the optical pattern 121 is an engraved pattern.

[0060] The second resin layer 120A satisfies Equation 1:

[0061] <Equation 1>

[0062] 0≤(maximum thickness of the second resin layer-maximum height of the optical pattern) / (maximum height of the optical pattern)≤1

[0063] If the second resin layer 120A satisfies Equation 1, when polarized light passing through the first resin layer 110A passes through the second resin layer 120A, the side contrast ratio can be improved by refraction of the polarized light on the optical pattern 121, and the front brightness in the black mode can be reduced by reducing the scattering degree of light in the second resin layer 120A, thereby improving the contrast ratio gain represented by Equation 2. Compared with a polarizing plate without a contrast improvement layer, the contrast ratio gain represented by Equation 2 can determine the improvement effect of visibility in both the front and side directions by reducing the reduction amount of the front contrast ratio and increasing the increase amount of the side contrast ratio.

[0064] Specifically, according to the present invention, the polarizing plate 10 includes a first surface on the top of the optical pattern 121. The expression "(maximum thickness of the second resin layer-maximum height of the optical pattern)" is included in Equation 1, and thus the scattering degree of light that passes through the first resin layer 110A and also exists between the top of the optical pattern 121 and the protective layer can be controlled within a certain range, thereby improving the contrast ratio gain while improving or maintaining the side contrast ratio. Preferably, the value of the expression "(maximum thickness of the second resin layer-maximum height of the optical pattern) / (maximum height of the optical pattern)" is in the range of 0 to 0.75, and more preferably, 0.

[0065] As such, the polarizing plate 10 may have a contrast ratio (CR) gain of about 1.00 or more represented by Equation 2. Within this range, the polarizing plate 10 may reduce a reduction in the front contrast ratio while improving side visibility.

[0066] <Equation 2>

[0067] Contrast ratio gain = side relative contrast ratio × front relative contrast ratio

[0068] wherein the front relative contrast ratio is the ratio of the front contrast ratio of the polarizing plate 10 including the contrast improvement layer to the front contrast ratio of the corresponding polarizing plate not including the contrast improvement layer, and

[0069] The side relative contrast ratio is a ratio of the side contrast ratio of the polarizing plate 10 including the contrast improvement layer to the side contrast ratio of the corresponding polarizing plate not including the contrast improvement layer.

[0070] The contrast ratio gain represented by equation 2 represents the effect of improving visibility by increasing the amount of increase in the side contrast ratio, and when the contrast ratio gain represented by equation 2 is 1.00 or more, the amount of increase in the side contrast ratio may be greater than the amount of decrease in the front contrast ratio. Preferably, the polarizing plate 10 has a contrast ratio gain of 1.00 or more, or 1.05 to about 1.5.

[0071] The value of the expression "(the maximum thickness of the second resin layer 120A (H2+H3)-the maximum height of the optical pattern 121 (H2))" (i.e., H3) may be in the range of 0 micrometers to 5 micrometers. Within this range, the contrast-improving optical film may increase the amount of increase in the side contrast ratio while reducing the amount of decrease in the front contrast ratio. Preferably, the value of the expression "(the maximum thickness of the second resin layer 120A (H2+H3)-the maximum height of the optical pattern 121 (H2))" is 0 micrometers, and in this case, the first surface 124 of the optical pattern 121 contacts the protective layer 200.

[0072] Figure 1 and Figure 2A structure in which the optical patterns 121 have the same height is shown. However, the optical patterns 121 may have different heights or at least one of the adjacent optical patterns 121 may have different heights. In this case, the maximum height H2 of the optical pattern 121 refers to a height calculated by SEM measurement.

[0073] The patterned portion may satisfy Equation 3, and the optical pattern 121 may have a base angle θ of 75° to 90°. The base angle θ refers to an angle formed between the inclined surface 123 of one of the optical patterns 121 and a line extending from the maximum width W of one of the optical patterns 121. Within this range, the contrast-improving optical film may improve relative brightness in the forward direction, improve both the front contrast ratio and the side contrast ratio, reduce the difference between the front contrast ratio and the side contrast ratio, and improve the contrast ratio at the same side viewing angle and the same front viewing angle. Specifically, the optical pattern 121 has a base angle θ of 80° to 90°, preferably 90°, and has a P / W value of 1.2 to 8, preferably 1.2 to 5.

[0074] <Equation 3>

[0075] 1<P / W≤10

[0076] Wherein P is the pitch of the patterned portion (unit: micrometer), and W is the maximum width of the optical pattern 121 (unit: micrometer).

[0077] although Figure 2 A structure in which two base angles of each optical pattern 121 are equal to each other is shown, but the optical patterns 121 may also have different base angles as long as the base angles are within the range of 75° to 90° as described above.

[0078] Each of the optical patterns 121 may be an optical pattern including a first surface 124 formed at a top thereof and at least one inclined surface 123 connected to the first surface 124. Figure 2 A trapezoidal optical pattern in which two adjacent inclined surfaces 123 are connected to each other through the first surface 124 is shown, but the present invention is not limited thereto.

[0079] The first surface 124 is formed at the top of each optical pattern 121 and can improve viewing angle and brightness by further diffusing light reaching the second resin layer 120A in the optical display. Therefore, the contrast-improving optical film can improve light diffusion, thereby minimizing or reducing brightness loss.

[0080] The first surface 124 may be a flat surface to facilitate the process for forming a contrast-improving optical film. Alternatively, the first surface 124 may have a slightly rough or curved surface. In a structure in which the first surface 124 is a curved surface, the optical pattern 121 may be implemented by a lenticular lens pattern.

[0081] The first surface 124 may be parallel to at least one of the planar section 122 , the lowermost surface of the first resin layer 110A, and the uppermost surface of the second resin layer 120A. Figure 2 A structure is shown in which the first surface 124 of the optical pattern 121 , the plane section 122 , the lowermost surface of the first resin layer 110A, and the uppermost surface of the second resin layer 120A are parallel to each other.

[0082] The first surface 124 may have a width A of 0.5 micrometers to 30 micrometers, specifically 2 micrometers to 20 micrometers. Within this range, the first surface 124 may be used for a polarizing plate.

[0083] Figure 2 Each optical pattern 121 is shown to have an engraved pattern including one flat surface and a flat inclined surface formed at the top thereof, and having a trapezoidal cross-sectional shape (e.g., a truncated prism pattern having a truncated triangular cross-sectional shape, i.e., a truncated prism shape or a cut-prism shape). Alternatively, the optical pattern may be an engraved pattern in which the first surface is formed at the top thereof and the inclined surface is a curved surface (e.g., a contrast improvement layer having a truncated lenticular (cut lenticular) lens pattern or a truncated microlens (cut microlens) pattern). Preferably, the optical pattern 121 has a square or rectangular cross-sectional shape.

[0084] The optical pattern 121 may have an aspect ratio (H2 / W) of 0.3 to 3.0, specifically 0.4 to 2.5, more specifically 0.4 to 1.5. Within this range, the optical display may exhibit improved contrast and improved viewing angle in a lateral direction.

[0085] The optical pattern 121 may have a maximum height H2 of 15 μm or less, specifically 10 μm or less, more specifically 5 μm to 7 μm. Within this range, the optical display may exhibit improvements in contrast ratio, viewing angle, and brightness without suffering from a moire phenomenon, etc.

[0086] The optical pattern 121 may have a maximum width W of 80 micrometers or less, specifically 50 micrometers or less, more specifically 5 micrometers to about 20 micrometers or 5 micrometers to 10 micrometers. Within this range, the optical display may show improvements in contrast ratio, viewing angle, and brightness without suffering from a moire phenomenon, etc. Figure 2 A structure in which the optical patterns 121 of the patterned portion have the same maximum width is shown, but the engraved optical patterns 121 may have different maximum widths, or at least one of adjacent engraved optical patterns 121 may have different maximum widths.

[0087] Upon receiving light from the first resin layer 110A, the planar section 122 emits the light to the second resin layer 120A, thereby improving front brightness.

[0088] The ratio (W / L) of the maximum width W of the optical pattern 121 to the width L of the plane segment 122 may be about 9 or less, and specifically, may be in the range of 0.1 to 3, more specifically 0.15 to 2. Within this range, the contrast-improving optical film may improve the relative brightness in the front direction, reduce the difference between the front contrast ratio and the side contrast ratio, and improve the contrast ratio at the same side viewing angle and the same front viewing angle. In addition, the contrast-improving optical film may prevent or substantially prevent the moire phenomenon. The plane segment 122 may have a width L of 1 micrometer to 300 micrometers, specifically 3 micrometers to 50 micrometers. Within this range, the contrast-improving optical film may improve the front brightness.

[0089] A maximum width W of one optical pattern 121 and a plane section 122 directly adjacent to the one optical pattern 121 form a pitch P.

[0090] The pitch P may be in the range of 5 micrometers to 500 micrometers, specifically, 10 micrometers to 50 micrometers. Within this range, the optical pattern 121 may improve brightness and contrast ratio without causing a moire phenomenon. Figure 2 A structure in which adjacent pitches P of patterned portions are the same is shown, but it should be understood that the pitches P may be different from each other or at least one of the adjacent pitches P may be different from the other pitches P.

[0091] The second resin layer 120A may have a maximum thickness (H2+H3) of 20 μm or less, for example, 5 μm to 15 μm. Within this range, the contrast-improving optical film may minimize or reduce a reduction in a side contrast ratio.

[0092] Figure 2 A structure is shown in which each optical pattern 121 is an engraved pattern. Alternatively, the optical pattern may be an embossed pattern.

[0093] although Figure 2It is not clearly shown, but Figure 2 A structure in which the optical pattern 121 extends in a stripe shape is shown. Alternatively, the optical pattern 121 may be formed in a dot shape. The term "dot" means that a combination of a fill pattern and an optical pattern is dispersed.

[0094] The second resin layer 120A has a higher refractive index than the first resin layer 110A. Therefore, when light enters the light incident surface of the first resin layer 110A, the contrast improvement layer 100A diffuses and emits the light, thereby improving relative brightness in the front direction, improving both the front contrast ratio and the side contrast ratio, increasing the side contrast ratio while minimizing or reducing the amount of reduction in 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.

[0095] The absolute value of the difference in refractive index between the second resin layer 120A and the first resin layer 110A (the refractive index of the second resin layer 120A minus the refractive index of the first resin layer 110A) may be in the range of 0.05 to 0.20, specifically 0.06 to 0.15. Within this range, the contrast-improving optical film may provide a large effect of diffusing condensed light while improving the contrast ratio. Specifically, when the difference in refractive index is in the range of 0.06 to 0.12, the contrast-improving optical film may have an excellent effect of diffusing polarized light in an optical display, and thus improve brightness even at the same viewing angle.

[0096] The second resin layer 120A may have a refractive index of 1.50 or more, more specifically 1.50 to 1.70, or 1.50 to 1.62. Within this range, the contrast-improving optical film may have an excellent effect in terms of light diffusion. The second resin layer 120A may include an ultraviolet curable or heat curable composition, including at least one of a (meth) acrylic resin, a polycarbonate resin, a silicone resin, and an epoxy resin, but is not limited thereto.

[0097] First resin layer

[0098] The first resin layer 110A, when receiving light from the optical display through its lower surface, may refract and emit light in various directions according to a light incident position, thereby diffusing the light. The first resin layer 110A at least partially contacts the second resin layer 120A.

[0099] The first resin layer 110A may include a filling pattern 111 that at least partially fills one of the optical patterns 121. When an element is said to "at least partially fill" an optical pattern 121, the element may completely fill the optical pattern 121, or partially fill the optical pattern 121. When the filling pattern 111 partially fills the optical pattern 121, the remaining space of the optical pattern 121 may be filled with air or a resin having a certain refractive index. Specifically, the refractive index of the resin may be less than or equal to the refractive index of the first resin layer 110A and greater than or equal to the refractive index of the second resin layer 120A.

[0100] The first resin layer 110A may be a layer including a filling pattern 111. The first resin layer 110A may have a refractive index less than 1.52, specifically 1.35 or greater than 1.35 and less than 1.50. Within this range, the contrast-improving optical film may have a large light diffusion effect, may be easy to form, and may have a large effect in polarized light diffusion and improving contrast ratio. The first resin layer 110A may be formed of an ultraviolet curable or thermosetting composition including a transparent resin. Specifically, the transparent resin may include at least one of a (meth) acrylic resin, a polycarbonate resin, a silicone resin, and an epoxy resin, but is not limited thereto. The transparent resin may have a light transmittance of 90% or greater after curing.

[0101] The first resin layer 110A may have a minimum thickness H1 of 1 micron or more, for example, 5 microns to 20 microns. Within this range, the first resin layer 110A can be used for a contrast-improving optical film. Specifically, when the first resin layer 110A is self-adhesive and can therefore be directly attached to the polarizing film 300, the first resin layer 110A enables the contrast-improving optical film to be well attached to the polarizing film 300.

[0102] Figure 1 A structure in which the second resin layer 120A has a higher refractive index than the first resin layer 110A is shown. However, the second resin layer 120A may have a lower refractive index than the first resin layer 110A. Here, the second resin layer 120A may have a refractive index less than 1.52, specifically 1.35 or more than 1.35 and less than 1.50, and the first resin layer 110A may have a refractive index of 1.50 or more than 1.50, specifically 1.50 to 1.70 or 1.50 to 1.60. Within this range, the contrast-improving optical film may have an excellent light diffusion effect. Within this range, the contrast-improving optical film may improve the side contrast ratio.

[0103] The contrast improvement layer 100A may have a thickness of 10 to 100 micrometers, specifically 20 to 60 micrometers, and more specifically 20 to 45 micrometers. Within this range, the contrast improvement layer 100A may be used in an optical display.

[0104] The contrast improvement layer 100A may be stacked on the protection layer 200 .

[0105] In one embodiment, the second resin layer 120A may be a non-adhesive layer without adhesiveness. In this case, one or more adhesive layers, bonding layers, or adhesive bonding layers may be formed between the second resin layer 120A and the protective layer 200. In another embodiment, the second resin layer 120A may be self-adhesive. In this case, the second resin layer 120A may be directly formed on or in contact with the protective layer 200. When the second resin layer 120A is self-adhesive, the second resin layer 120A may be formed of at least one of an acrylic resin, an epoxy resin, and a urethane resin.

[0106] Protective layer

[0107] The protection layer 200 may be formed on the contrast improvement layer 100A, support the contrast improvement layer 100A, and emit light having passed through the contrast improvement layer 100A.

[0108] The protective layer 200 may include at least one of an optically transparent protective film and a protective coating.

[0109] When the protective layer 200 is a protective film type, the protective layer 200 may include a protective film formed of an optically transparent resin. The protective film may be formed by melting and extruding the resin. The resin may be further stretched as needed. The optically transparent resin may include at least one selected from the following: cellulose esters, including triacetyl cellulose; cyclic polyolefins, including amorphous cyclic olefin polymers (cyclic olefin polymers, COP); polycarbonates; polyesters, including polyethylene terephthalate (PET); polyether sulfones; polysulfones; polyamides; polyimides; non-cyclic polyolefins; polyacrylates, including poly (methyl methacrylate); polyvinyl alcohol; polyvinyl chloride; and polyvinylidene chloride resins.

[0110] The protective film may be a non-stretched film, a retardation film having a certain retardation range obtained by stretching the resin in a certain method, or an isotropic optical film. In one embodiment, the protective film may have an in-plane retardation Re of 8,000 nanometers or more, specifically 10,000 nanometers or more, more specifically more than 10,000 nanometers, and more specifically 10,100 nanometers to 15,000 nanometers. Within this range, the protective film can prevent or substantially prevent the generation of rainbow spots while further diffusing the light diffused by the contrast improvement layer. In another embodiment, the protective film may be an optically isotropic film having Re of 60 nanometers or less, specifically 0 nanometers to 60 nanometers, and more specifically 40 nanometers to 60 nanometers. Within this range, the protective film can provide good image quality by compensating for the viewing angle. Herein, the term "isotropic optical film" refers to a film having 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.

[0111] although Figure 2It is not shown in the figure, but the protective film may include a base film and a primer layer formed on at least one surface of the base film. The ratio of the refractive index of the primer layer to the refractive index of the base film (i.e., the refractive index of the primer layer / the refractive index of the base film) may be 1.0 or less than 1.0, and specifically, may be between 0.6 and 1.0, more specifically 0.69 to 0.95, more specifically 0.7 to 0.9, and more specifically 0.72 to 0.88. Within this range, the first bottom layer may have an improved transmittance. The base film may have a refractive index of 1.3 to 1.7, specifically 1.4 to 1.6. Within this range, the base film may be used as the first bottom layer, which may make it easy to control the refractive index relative to the primer layer, and may improve the transmittance of the first bottom layer. The base film may include a film formed of a resin as described above. The primer layer may have a refractive index of 1.0 to 1.6, specifically 1.1 to 1.6, and more specifically 1.1 to 1.5. In this scope, the primer layer has a suitable refractive index compared with the base film, thereby improving the transmittance of the bottom layer. The primer layer can have a thickness of about 1 nanometer to 200 nanometers, specifically 60 nanometers to 200 nanometers. In this scope, the primer layer can be used for optical film, can have a suitable refractive index compared with the base film, and therefore improve the transmittance of the bottom layer without embrittlement (embrittlement). The primer layer can be a non-urethane primer layer without carbamate groups. Specifically, the primer layer can be formed by a primer layer composition (for example, polyester, acrylic, etc.) including a resin or a monomer. By controlling the mixing ratio (for example, molar ratio) between these monomers, the primer layer can have a refractive index as described above. The primer layer composition can also include at least one of additives such as ultraviolet light absorbers, antistatic agents, defoamers, surfactants, etc.

[0112] When the protective layer 200 is a protective coating type, the protective layer 200 can provide excellent properties in terms of adhesion with the second resin layer 120A, transparency, mechanical strength, thermal stability, moisture resistance, and durability. In one embodiment, the protective coating can be formed of an actinic radiation-curable resin composition including an actinic radiation-curable compound and a polymerization initiator.

[0113] 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 or an oxetane compound having at least one oxetane ring per molecule. The free radically polymerizable curable compound may be a (meth)acrylic compound having at least one (meth)acryloyloxy group per molecule.

[0114] The epoxy compound may include at least one of a hydrogenated epoxy compound, a chain-type alicyclic epoxy compound, a cycloaliphatic epoxy compound, and an aromatic epoxy compound.

[0115] The free radical polymerizable curable compound can realize a protective coating with excellent hardness, mechanical strength and high durability. Examples of free radical polymerizable curable compounds may include: a (meth) acrylate monomer having at least one (meth) acryloyloxy group per molecule, and a (meth) acrylate oligomer having at least two (meth) acryloyloxy groups per molecule obtained by reacting at least two compounds containing functional groups. Examples of (meth) acrylate monomers may include: a monofunctional (meth) acrylate monomer having one (meth) acryloyloxy group per molecule, a difunctional (meth) acrylate monomer having two (meth) acryloyloxy groups per molecule, and a multifunctional (meth) acrylate monomer 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.

[0116] The polymerization initiator can 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. Specifically, the photocationic initiator may include an onium salt comprising a cation and an anion. Specifically, the cation may include: diaryl iodonium, such as diphenyl iodonium, 4-methoxydiphenyl iodonium, bis(4-methylphenyl)iodonium, bis(4-tert-butylphenyl)iodonium, bis(dodecylphenyl)iodonium, and (4-methylphenyl)[(4-(2-methylpropyl)phenyl)iodonium[(4-methylphenyl)[4-(2-methylpropyl)phenyl]iodonium]; triaryl sulfonium, such as triphenylsulfonium and diphenyl-4-thiophenoxyphenylsulfonium; and bis[4-(diphenylsulfonium)phenyl]sulfide. Specifically, the anion may include hexafluorophosphate (PF6 - ), tetrafluoroborate (BF4 - ), hexafluoroantimonate (SbF6 - ), hexafluoroarsenate (AsF6 - ) and hexachloroantimonate (SbCl6 - ). The photosensitizer may be any typical photosensitizer known in the art. Specifically, the photosensitizer may include at least one selected from thioxanthone photosensitizer, phosphorescent photosensitizer, triazine photosensitizer, acetophenone photosensitizer, benzophenone photosensitizer, benzoin photosensitizer, and oxime photosensitizer.

[0117] The actinic radiation curable resin composition may further include general additives such as silicone leveling agents, ultraviolet absorbers, antistatic agents, and the like.

[0118] The protective layer 200 may have a thickness of 5 to 200 microns, specifically 30 to 120 microns. In addition, the protective film type protective layer 200 may have a thickness of 35 to 100 microns, and the protective coating type protective layer 200 may have a thickness of 5 to 50 microns. Within this range, the protective layer 200 can be used in a light-emitting display.

[0119] A surface treatment layer, such as 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 200. The primer layer may improve the adhesion between the polarizer and the protective layer 200. The hard coating layer, the anti-fingerprint layer, the anti-reflection layer, and the like may provide additional functions to the protective layer 200, the polarizing film 300, and the like.

[0120] The contrast-improving optical film may have a thickness of 30 μm to 120 μm, for example, 40 μm to 110 μm. Within this range, the contrast-improving optical film may ensure processability and exhibit improved surface hardness.

[0121] The contrast-improving optical film may be formed by a general method known to those skilled in the art. For example, the resin for the second resin layer 120A may be applied to the protective layer 200, the optical pattern 121 and the plane section 122 may be applied to the resin, and then cured, thereby forming the second resin layer 120A. Next, the resin for the first resin layer may be applied to the second resin layer while filling the optical pattern 121, and then cured, thereby forming the contrast-improving optical film. However, it should be understood that the present invention is not limited thereto.

[0122] Polarizing film

[0123] The polarizing film 300 may polarize light received from the liquid crystal panel and transmit the light. The polarizing film 300 is formed on a light exiting surface of the contrast improvement layer 100A.

[0124] 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 polyene-based polarizer obtained by dehydrating a polyvinyl alcohol film. The polarizer may have a thickness of 5 micrometers to 40 micrometers. Within this range, the polarizing film 300 can be used in an optical display.

[0125] 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 10. The description of the protective layer 200 is the same or substantially the same as the description of the protective layer included in the contrast improvement optical film. Preferably, the protective layer is a polyester protective film (e.g., a polyethylene terephthalate film) having an Re of 8,000 nm or more, specifically 10,000 nm or more, more specifically more than 10,000 nm, and more specifically 10,100 nm to 15,000 nm.

[0126] The contrast improvement layer 100A may be formed on the polarizing film 300 .

[0127] In one embodiment, the first resin layer 110A may be a non-adhesive layer without adhesiveness. In this case, one or more adhesive layers, bonding layers, or adhesive bonding layers may be formed between the first resin layer 110A and the polarizing film 300. In another embodiment, the first resin layer 110A may be self-adhesive. In this case, the first resin layer 110A may be directly formed on or in contact with the polarizing film 300. When the first resin layer 110A is self-adhesive, the first resin layer 110A may be formed of at least one of an acrylic resin, an epoxy resin, and a urethane resin.

[0128] although Figure 1 Although not shown in the drawings, an adhesive layer may be formed on the lower surface of the polarizing film 300 to attach the polarizing plate 10 to the liquid crystal panel.

[0129] although Figure 1 Although not shown in the figure, one or more protective layers, anti-reflection films, etc. may be further stacked on the light exiting surface of the protective layer 200 via an adhesive layer.

[0130] Below, we will refer to Figure 3 A polarizing plate according to another embodiment of the present invention is described.

[0131] Reference Figure 3 , the polarizing plate includes a contrast improvement layer 100B in which the value of (maximum thickness of the second resin layer-maximum height of the optical pattern) / (maximum height of the optical pattern) is 0. In this way, the polarizing plate can maximize or increase the front contrast ratio. The contrast improvement layer 100B includes a first resin layer 110B and a second resin layer 120B facing the first resin layer 110B.

[0132] 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 on the viewer side relative to the liquid crystal panel. In this document, the term "polarizing plate located on the viewer side" refers to a polarizing plate placed on the screen side of the liquid crystal panel (that is, placed on the side of the liquid crystal panel opposite to the light source).

[0133] In one embodiment, the liquid crystal display may include a backlight unit, a first polarizing plate, a liquid crystal panel, and a second polarizing plate stacked in sequence, 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 IPS mode, a patterned vertical alignment (PVA) mode, or a super-patterned vertical alignment (S-PVA) mode, but is not limited thereto.

[0134] In another embodiment, the liquid crystal display may include a polarizing plate located on the light source side. In this document, the term "polarizing plate located on the light source side" refers to a polarizing plate disposed on the light source side relative to the liquid crystal panel.

[0135] In yet another embodiment, both the polarizing plate located on the viewer side and the polarizing plate located on the light source side relative to the liquid crystal panel may include the polarizing plate according to the present invention.

[0136] 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 interpreted as limiting the present invention in any way.

[0137] Example 1

[0138] An ultraviolet curable resin (SSC-5760, SHIN-A T&C Co., Ltd.) was applied to one surface of a polyethylene terephthalate (PET) film (thickness: 80 μm, Re=8,000 nm at a wavelength of 550 nm, Toyobo Co., Ltd.) used as a protective layer. Then, a film having a patterned portion was applied to the coating to form an engraved pattern and a flat section, and then cured to form a film including the engraved pattern (such as Figure 1 A second resin layer (refractive index: 1.60) having a square cross-sectional shape as shown in Table 1 having patterned portions and plane segments on both sides thereof having the same bottom angle, wherein the film having the patterned portions includes optical patterns having the same bottom angle on both sides thereof and a plane segment formed between the optical patterns.

[0139] An ultraviolet curable resin (SSC-4560, Shinya T&C Co., Ltd.) was applied to the second resin layer while completely filling the engraved pattern, and then the ultraviolet curable resin was cured to form a contrast-improving optical film in which a first resin layer (refractive index: 1.48) with a filling pattern completely filling the engraved pattern was formed. The first resin layer was self-adhesive.

[0140] The polarizer was prepared by stretching a polyvinyl alcohol film to three times its original length at 60° C., adsorbing iodine to the stretched film, and then stretching the film in a boric acid aqueous solution at 40° C. to 2.5 times the stretched length of the film.

[0141] The polarizing plate is prepared by bonding the first resin layer of the contrast-improving optical film to one surface of the polarizer.

[0142] Example 2 and Example 3

[0143] Each polarizing plate was prepared in the same manner as in Example 1, except that a patterned portion including an optical pattern and a planar segment modified as listed in Table 1 was formed.

[0144] Comparative Example 1

[0145] A polarizing plate was prepared in the same manner as in Example 1, except that a patterned portion including an optical pattern and a planar segment modified as listed in Table 1 was formed.

[0146] Reference Example 1

[0147] A polarizing plate was prepared in the same manner as in Example 1, except that the contrast improving layer was not formed.

[0148] The contrast-improving optical film and polarizing plate in each of Examples, Reference Examples, and Comparative Examples were evaluated for the properties listed in Table 1. The results are shown in Table 1.

[0149] The front brightness, relative brightness, front contrast ratio, and side contrast ratio were evaluated using the module for a liquid crystal display manufactured in the following manner.

[0150] Preparation Example 1: Preparation of the first polarizing plate

[0151] The first polarizer was prepared by stretching a polyvinyl alcohol film to three times its original length at 60° C., adsorbing iodine to the stretched film, and then stretching the film to 2.5 times the stretched length of the film in a boric acid aqueous solution at 40° C. A triacetyl cellulose film (thickness: 80 μm) as a base layer was bonded to both sides of the first polarizer using a bonding agent for polarizing plates (Z-200, Nippon Goshei Co., Ltd.), thereby manufacturing the first polarizing plate.

[0152] Preparation Example 2: Making a Module for a Liquid Crystal Display

[0153] The first polarizing plate of Preparation Example 1, the liquid crystal panel (PVA mode), and each polarizing plate prepared in the example, reference example, and comparative example were assembled together in order to manufacture a module of a liquid crystal display. Each polarizing plate prepared in the example, reference example, and comparative example was used as a viewer-side polarizing plate, and an anti-reflection film was placed at the uppermost position on the viewer side.

[0154] Modules of an LED light source, a light guide plate, and a liquid crystal display are assembled together to produce a liquid crystal display including a one-side edge type LED light source (except that each module of the liquid crystal display produced in the use example, reference example, and comparative example has the same configuration as a Samsung LED TV (UN32H5500)).

[0155] The luminance in each of the white mode and the black mode was measured at each of the coordinates (0°, 0°) and the coordinates (0°, 60°) in the spherical coordinate system using EZCONTRAST X88RC (EZXL-176R-F422A4, ELDIM Co., Ltd.). The front contrast ratio was calculated as the ratio of the luminance in the white mode at the coordinates (0°, 0°) to the luminance in the black mode in the spherical coordinate system. The side contrast ratio was calculated as the ratio of the luminance in the white mode at the coordinates (0°, 60°) to the luminance in the black mode in the spherical coordinate system. The front relative contrast ratio was calculated by the expression (front contrast ratio of each module of the example and the comparative example / front contrast ratio of the module of reference example 1). The side relative contrast ratio was calculated by the expression (side contrast ratio of each module of the example and the comparative example / side contrast ratio of the module of reference example 1).

[0156] The angular position at which the measured brightness is 1 / 2 of the front brightness in the white mode is taken as the 1 / 2 viewing angle.

[0157] Table 1

[0158]

[0159] As shown in Table 1, compared with the polarizing plate not including the contrast improvement layer, the polarizing plates of Examples 1 to 3 have good visibility in both the front and side directions by increasing the increase in the side contrast ratio while reducing the decrease in the front contrast ratio. In addition, the polarizing plates of Examples 1 to 3 increase the 1 / 2 viewing angle, and thus can increase the side viewing angle.

[0160] On the other hand, compared with the polarizing plate according to the present invention, the polarizing plate of Comparative Example 1, which does not satisfy Equation 1 despite having a contrast improvement layer, has a larger reduction in front contrast ratio and a smaller increase in side contrast ratio, and therefore has a contrast ratio gain of less than 1.00 represented by Equation 2.

[0161] It should be understood that various modifications, changes, variations and equivalent embodiments may be made by those skilled in the art without departing from the spirit and scope of the present invention.

Claims

1. A polarizing plate, characterized in that: It includes polarizing films and contrast-enhancing optical films stacked in sequence. wherein the contrast-improving optical film comprises a contrast-improving layer, The contrast improvement layer includes a first resin layer and a second resin layer facing the first resin layer, The second resin layer includes a patterned portion having optical patterns and a planar section disposed between the optical patterns, The second resin layer satisfies Equation 1: <Equation 1> 0≤(maximum thickness of the second resin layer-maximum height of the optical pattern) / (maximum height of the optical pattern)≤1 The polarizing plate has a contrast ratio gain of 1.00 or more represented by Equation 2: <Equation 2> Contrast ratio gain = side relative contrast ratio × front relative contrast ratio wherein the front relative contrast ratio is a ratio of the front contrast ratio of the polarizing plate including the contrast improvement layer to the front contrast ratio of the polarizing plate not including the contrast improvement layer, and The side relative contrast ratio is a ratio of the side contrast ratio of the polarizing plate including the contrast improvement layer to the side contrast ratio of the polarizing plate not including the contrast improvement layer, wherein the second resin layer has a maximum thickness of 5 μm to 15 μm, The first resin layer has a minimum thickness of 5 micrometers to 20 micrometers.

2. The polarizing plate according to claim 1, characterized in that The optical pattern has a base angle of 75° to 90°, and the patterned portion satisfies Equation 3, <Equation 3> 1<P / W≤10 Wherein P is the pitch of the patterned portion (in micrometers) and W is the maximum width of each of the optical patterns (in micrometers).

3. The polarizing plate according to claim 1, characterized in that The optical pattern is a trapezoidal optical pattern in which two adjacent inclined surfaces are connected to each other through a first surface.

4. The polarizing plate according to claim 1, characterized in that The optical pattern has an aspect ratio of 0.3 to 3.

0.

5. The polarizing plate according to claim 1, characterized in that A difference in refractive index between the second resin layer and the first resin layer is 0.05 to 0.

20.

6. The polarizing plate according to claim 1, characterized in that The second resin layer has a higher refractive index than the first resin layer.

7. The polarizing plate according to claim 1, characterized in that: The value of the expression in Equation 1 (maximum thickness of the second resin layer-maximum height of the optical pattern) is 5 micrometers or less.

8. The polarizing plate according to claim 1, wherein: The optical pattern has a maximum height of 15 micrometers or less.

9. The polarizing plate according to claim 1, wherein: At least one of the first resin layer and the second resin layer is self-adhesive.

10. The polarizing plate according to claim 1, characterized in that The contrast-enhancing optical film further includes a protective layer.

11. The polarizing plate according to claim 10, characterized in that: The protective layer includes at least one of a protective film and a protective coating.

12. The polarizing plate according to claim 1, characterized in that The contrast-improving optical film is on a light-exiting surface of the polarizing film, and the polarizing plate further includes at least one of a protective layer and an anti-reflection film on the light-exiting surface of the contrast-improving optical film.

13. The polarizing plate according to claim 1, wherein The value of the expression (maximum thickness of the second resin layer-maximum height of the optical pattern) in Equation 1 is 0 micrometers, and the optical pattern has a base angle of 90°.

14. A liquid crystal display, characterized in that: The polarizing plate comprises the polarizing plate as claimed in any one of claims 1 to 13.

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