Polarizing plates and optical display devices including polarizing plates

Abstract

This invention provides a polarizing plate and an optical display device including the polarizing plate. The polarizing plate includes: a polarizer; and a first retardation layer and a second retardation layer, which are sequentially stacked on the lower surface of the polarizer. The first retardation layer has an in-plane retardation (Re) of 200 nm to 250 nm at a wavelength of 550 nm; the second retardation layer has an in-plane retardation (Re) of 80 nm to 140 nm at a wavelength of 550 nm; and the polarizing plate has a total transmittance difference of 2% or greater between its total transmittance at a wavelength of 450 nm and its total transmittance at a wavelength of 420 nm.

Description

[0001] Cross-references to related applications

[0002] This application claims the benefit of Korean Patent Application No. 10-2021-0072430, filed on June 3, 2021, with the Korean Intellectual Property Office, the entire disclosure of which is incorporated herein by reference. Technical Field

[0003] This invention relates to a polarizing plate and an optical display device comprising the polarizing plate. Background Technology

[0004] Organic light-emitting diode (OLED) displays can suffer from reduced visibility and contrast due to the reflection of external light. To address this issue, a polarizing plate containing a polarizer and a retardation film can be used. The polarizing plate achieves anti-reflection functionality by preventing the leakage of reflected external light.

[0005] Organic light-emitting diode (OLED) displays need to exhibit good reflective visibility relative to external light on the lateral side in non-operating states, while maintaining good screen quality in operating states. Lateral reflective visibility can be achieved by reducing lateral reflectivity. However, reduced lateral reflective visibility can lead to degraded black level visibility due to poor forward visibility.

[0006] To improve black visibility on the front side, controlling the color value of the polarizing plate can be considered. However, there are limitations to improving black visibility on the front side solely by controlling the color value of the polarizing plate.

[0007] The background technology of this invention is disclosed in Korean Patent Publication No. 10-2013-0103595, etc. Summary of the Invention

[0008] One objective of this invention is to provide a polarizing plate that improves black visibility, i.e., makes the screen of a display device appear black. Another objective of this invention is to provide a polarizing plate that provides low reflectivity on both the front and lateral sides.

[0009] One aspect of the present invention is directed to a polarizing plate.

[0010] 1. A polarizing plate comprises: a polarizer; and a first retardation layer and a second retardation layer, sequentially stacked on the lower surface of the polarizer, wherein: the first retardation layer has an in-plane retardation (Re) of 200 nm to 250 nm at a wavelength of 550 nm; the second retardation layer has an in-plane retardation (Re) of 80 nm to 140 nm at a wavelength of 550 nm; and the polarizing plate has a total transmittance difference of 2% or greater between the total transmittance at a wavelength of 450 nm and the total transmittance at a wavelength of 420 nm.

[0011] 2. In 1, the polarizing plate may have a total transmittance of 30% or more at a wavelength of 450 nm and a total transmittance of 40% or less at a wavelength of 420 nm.

[0012] 3. In 1 to 2, the polarizing plate may have a total transmittance of 2% or less at a wavelength of 380 nm.

[0013] 4. In 1 to 3, the first retardation layer may have an out-of-plane retardation of 95 to 200 nanometers and a biaxiality of 1 to 1.5 at a wavelength of 550 nanometers.

[0014] 5. In 1 to 4, the second retardation layer can have an out-of-plane retardation of -250 nm to -50 nm and a biaxiality of -2 to -0.1 at a wavelength of 550 nm.

[0015] 6. In 1 to 5, the first retardation layer may comprise a resin having positive (+) birefringence, and the second retardation layer may comprise a resin having negative (-) birefringence.

[0016] 7. In 1 to 6, each of the first retardation layer and the second retardation layer may be a non-liquid crystal layer.

[0017] 8. In 1 to 7, the second delayed layer may comprise at least one selected from cellulose ester polymers and polystyrene polymers.

[0018] 9. In 1 to 8, the laminate of the first and second retardation layers may have a total transmittance of 90% or greater at wavelengths of 420 nm to 450 nm.

[0019] 10. In 1 to 9, the polarizer can have a total transmittance of 40% to 45% at wavelengths from 380 nm to 780 nm.

[0020] 11. In 1 to 10, the polarizer may contain 1% to 5% by weight of potassium iodide.

[0021] 12. In 1 to 11, the absolute value of the tilt angle of the slow axis of the first retardation layer relative to the transmission axis of the polarizer can be in the range of 50° to 80°, and the absolute value of the tilt angle of the slow axis of the second retardation layer relative to the transmission axis of the polarizer can be in the range of 0° to 10°.

[0022] 13. In 1 to 12, the polarizing plate may further contain a light absorber.

[0023] 14. In 13, the light absorber may have a maximum absorption wavelength of 330 nm to 380 nm.

[0024] 15. In 1 to 14, the polarizing plate may further include a protective film formed on the upper surface of the polarizer.

[0025] Another aspect of the present invention relates to an optical display device.

[0026] Optical display devices may include a polarizing plate according to the present invention. Attached Figure Description

[0027] Figure 1 This is a cross-sectional view of a polarizing plate according to an embodiment of the present invention.

[0028] Figure 2 This is a cross-sectional view of a polarizing plate according to another embodiment of the present invention.

[0029] Figure 3 This is a diagram showing the reflected color values ​​a* and b*.

[0030] Figure 4 This is the evaluation result of Example 1.

[0031] Figure 5 This is the evaluation result of Comparative Example 3.

[0032] Explanation of icon numbers

[0033] 110: Polarizing film;

[0034] 120: First Delay Layer;

[0035] 130: Second Delay Layer;

[0036] 140: Protective film;

[0037] 150: Adhesive layer;

[0038] a*: Reflected color value;

[0039] b*: Reflected color value. Detailed Implementation

[0040] In the following description, embodiments of the invention will be described in detail with reference to the accompanying drawings. The following embodiments will be described in detail with reference to the accompanying drawings to provide those skilled in the art with a thorough understanding of the invention. In the drawings, components irrelevant to the description are omitted for clarity of description, and similar components will be indicated by similar reference numerals throughout the specification. Although the length, thickness, or width of various components may be enlarged for understanding the drawings, the invention is not limited thereto.

[0041] In this document, spatial relative terms such as “upper” and “lower” are defined with reference to the accompanying drawings. Therefore, it will be understood that the term “upper surface” is used interchangeably with the term “lower surface”.

[0042] In this paper, "in-plane delay Re", "out-of-plane delay Rth", and "biaxiality NZ" are represented by equations A, B, and C, respectively:

[0043] Re = (nx - ny)xd, --- (A)

[0044] Rth=((nx+ny) / 2-nz)xd,---(B)

[0045] NZ=(nx-nz) / (nx-ny), ---(C)

[0046] Where nx, ny, and nz are the refractive indices of the optical device along the slow axis, fast axis, and thickness direction, respectively, at the measurement wavelength, and d is the thickness of the optical device (unit: nanometers (nm)). In equations A to C, the measurement wavelength can be 450 nm, 550 nm, or 650 nm.

[0047] In this paper, "short wavelength dispersion" refers to Re(450) / Re(550), and "long wavelength dispersion" refers to Re(650) / Re(550). Re(450), Re(550), and Re(650) refer to the in-plane retardation (Re) of a single retardation layer or a laminate of retardation layers at wavelengths of approximately 450 nm, 550 nm, and 650 nm, respectively.

[0048] As used in this article, to indicate angles, "+" means counterclockwise around the reference point, and "-" means clockwise around the reference point.

[0049] In this article, the term "(meth)propenyl" refers to propenyl and / or methpropenyl.

[0050] As used in this article, in order to express a specific range of values, the expression "X to Y" means "greater than or equal to X and less than or equal to Y (X ≤ and ≤ Y)".

[0051] In this paper, the "total transmittance (Ts)" can be measured by emitting light from the second retardation layer of the polarizer to the polarizer of the polarizer.

[0052] In this article, the visual sensitivity of reflection (black visibility), the reflected color value "a*", and the reflected color value "b*" refer to the a* and b* values ​​in the CIE coordinate system, respectively. The reflected color values ​​a* and b* can be obtained from the CIE coordinate system, where the x-axis indicating the a* value is orthogonal to the y-axis indicating the b* value. The a* value becomes redder as its absolute value increases in the positive direction and greener as its absolute value increases in the negative direction, while the b* value becomes yellower as its absolute value increases in the positive direction and bluer as its absolute value increases in the negative direction. The reflected color values ​​"a*" and "b*" can be measured using a reflected color value measurement device (e.g., DMS803, NI) by transmitting light from the OLED panel to a polarizer attached to the OLED panel. Black visibility is the appearance of black on the screen of a display device.

[0053] Polarizing plates typically suffer from reduced black visibility on the front side when the visual sensitivity to reflections on the lateral side decreases. The inventors of this invention have developed a polarizing plate that achieves low reflectivity on both the front and lateral sides, while improving not only the visual sensitivity to reflections on the lateral side but also the black visibility on the front side.

[0054] The polarizing plate according to the invention comprises a first retardation layer and a second retardation layer, each having an in-plane retardation within a specific range described below, and improves black visibility by controlling the difference between the total transmittance at a wavelength of 450 nm and the total transmittance at a wavelength of 420 nm.

[0055] In one embodiment, when evaluating front-side black visibility based on reflected color values ​​a* and b*, the polarizer may have color values ​​a* and b* that satisfy the following relationship: 0 ≤ |a*| + |b*| ≤ 2.5. Within this range, the polarizer improves front-side black visibility. Preferably, the polarizer has reflected color values ​​a* and b* ranging from -2.5 to 2.5. The measurements of reflected color values ​​a* and b* can be performed using the methods described in the examples described below. The relationship 0 ≤ |a*| + |b*| ≤ 2.5 is set as an evaluation reference indicating the improvement in front-side black visibility when the polarizer is actually mounted on a module used in an optical display device. Figure 3 The reflected color values ​​a* (corresponding to the x-axis) and b* (corresponding to the y-axis) are shown. Preferably, the polarizing plate has reflected color values ​​a* and b* that satisfy |a*|+|b*| in the range of 0 to 1.5. Specifically, as... Figure 4 As shown, the polarizing plate according to the invention exhibits a significant improvement in black visibility by satisfying the relationship 0≤|a*|+|b*|≤2.5 not only on the front side but also at all azimuth angles.

[0056] Even without a patterned layer on the lower surface of the polarizer, the polarizer can improve the black visibility on its front side by ensuring lower reflectivity on its front side.

[0057] When applied to optical display devices, the polarizing plate may have a forward reflectance of 1.0% or less, preferably 0.5% or less, and a lateral reflectance of 2.0% or less, preferably 1.5% or less. Within this range, the polarizing plate can improve the screen quality on both the front and lateral sides.

[0058] In this article, we assume that the front side is indicated by 0°, and the "lateral" side, that is, each of the right and left sides, refers to a direction in the range of 45° to 75°, specifically in the direction of 60°.

[0059] The inventors of this invention have developed a polarizing plate comprising: a polarizer; and a first retardation layer and a second retardation layer, sequentially stacked on the lower surface of the polarizer, wherein the total transmittance difference (Ts(450)-Ts(420)) between the total transmittance Ts(450) at a wavelength of 450 nm and the total transmittance Ts(420) at a wavelength of 420 nm is controlled within 2% or greater than 2%. Within this range, the polarizing plate can improve screen quality by improving black visibility.

[0060] Specifically, the total transmittance difference can be 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, 9%, 9.5%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19% or 20%, preferably 3.5% to 20%, more preferably 3.5% to 16%.

[0061] In one embodiment, the polarizing plate may have a total transmittance of 30% or greater at a wavelength of 450 nm, specifically 30%, 31%, 32%, 33%, 34%, 35%, 36%, 37%, 38%, 39%, 40%, 41%, 42%, 43%, 44%, or 45%, for example, 30% to 45% or 40% to 45%, and a total transmittance of 40% or less at a wavelength of 420 nm, specifically 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, etc. 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, 30.5%, 31%, 31.5%, 32%, 32.5%, 33%, 33.5%, 34%, 34.5%, 35%, 35.5%, 36%, 36.5%, 37%, 37.5%, 38%, 38.5%, 39%, 39.5%, or 40%, preferably 35% to 40%. Within this range, the polarizing plate can easily fix the total transmittance difference within the above range.

[0062] The first retardation layer can have an in-plane retardation Re of 200 to 250 nanometers at a wavelength of 550 nanometers, and the second retardation layer can have an in-plane retardation of 80 to 140 nanometers at a wavelength of 550 nanometers. Within this range, the polarizer can reduce the reflectivity on its front and lateral sides and darken the reflected color to improve screen quality.

[0063] Preferably, each of the first retardation layer and the second retardation layer is a non-liquid crystal layer. The polarizing plate according to the invention comprises a first retardation layer and a second retardation layer, which are formed as non-liquid crystal layers on the lower surface of the polarizer and each has a specific in-plane retardation within the aforementioned range and a specific total transmittance difference within the aforementioned range, thereby improving black visibility.

[0064] The polarizing plate may have a total transmittance of 2% or less at a wavelength of 380 nm. Within this range, compared to a polarizing plate comprising a first retardation layer and a second retardation layer and having a total transmittance difference of 2% or greater, the polarizing plate can further improve black visibility. Specifically, the polarizing plate may have the following total transmittance at a wavelength of 380 nm: 0.01%, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, or 2%, preferably from 0.01% to 2%, more preferably from 0.2% to 1%.

[0065] Next, refer to Figure 1 A polarizing plate according to an embodiment of the present invention is described.

[0066] refer to Figure 1 The polarizing plate includes: a polarizer 110; a protective film 140 stacked on the upper surface of the polarizer 110; and a first retardation layer 120 and a second retardation layer 130 stacked sequentially on the lower surface of the polarizer 110 in the order stated.

[0067] First Delay Layer

[0068] The first retardation layer 120 has an in-plane retardation (Re) of 200 nm to 250 nm at a wavelength of 550 nm. Within this range, the polarizer can help improve screen quality by reducing reflectivity on both its front and lateral sides while improving black visibility on the front side. Specifically, the first retardation layer 120 may have the following in-plane retardations at a wavelength of 550 nm: 200 nm, 201 nm, 202 nm, 203 nm, 204 nm, 205 nm, 206 nm, 207 nm, 208 nm, 209 nm, 210 nm, 211 nm, 212 nm, 213 nm, 214 nm, 215 nm, 216 nm, 217 nm, 218 nm, 219 nm, 220 nm, 221 nm, 222 nm. The wavelengths are 223 nm, 224 nm, 225 nm, 226 nm, 227 nm, 228 nm, 229 nm, 230 nm, 231 nm, 232 nm, 233 nm, 234 nm, 235 nm, 236 nm, 237 nm, 238 nm, 239 nm, 240 nm, 241 nm, 242 nm, 243 nm, 244 nm, 245 nm, 246 nm, 247 nm, 248 nm, 249 nm, or 250 nm. Preferably, the first retardation layer 120 has an in-plane retardation of 200 nm to 240 nm at a wavelength of 550 nm, more preferably an in-plane retardation of 220 nm to 240 nm.

[0069] The first retardation layer 120 exhibits positive wavelength dispersion, for example, short-wavelength dispersion of 0.8 to 1.1, specifically 0.8, 0.85, 0.9, 0.95, 1.0, 1.05, or 1.1, and long-wavelength dispersion of 0.96 to 1, specifically 0.96, 0.97, 0.98, 0.99, 0.995, or 1. Within this range, the polarizer can reduce forward and lateral reflectivity during use. Preferably, the first retardation layer 120 has short-wavelength dispersion of 1 to 1.1, more specifically greater than 1 to 1.1, and long-wavelength dispersion of 0.98 to 1, 0.99 to 1, more specifically 0.995 to less than 1.

[0070] In one embodiment, the first retardation layer 120 may have an in-plane retardation of 180 nm to 280 nm at a wavelength of 450 nm, specifically 180 nm, 190 nm, 200 nm, 210 nm, 220 nm, 230 nm, 240 nm, 250 nm, 250 nm, 260 nm, 270 nm, or 280 nm, preferably 185 nm to 260 nm, more preferably 190 nm to 250 nm, and may have an in-plane retardation of 175 nm to 270 nm at a wavelength of 650 nm, specifically 175 nm, 180 nm, 190 nm, 200 nm, 210 nm, 220 nm, 230 nm, 240 nm, 250 nm, 260 nm, or 270 nm, preferably 180 nm to 255 nm, more preferably 185 nm to 240 nm. Within this range, the first retardation layer can easily achieve short-wavelength dispersion and long-wavelength dispersion within the aforementioned ranges.

[0071] The first retardation layer 120 can have a positive (+) out-of-plane retardation at a wavelength of 550 nm, for example, an out-of-plane retardation of 95 nm to 200 nm, specifically 95 nm, 100 nm, 105 nm, 110 nm, 115 nm, 120 nm, 125 nm, 130 nm, 135 nm, 140 nm, 145 nm, 150 nm, 155 nm, 160 nm, 165 nm, 170 nm, 175 nm, 180 nm, 185 nm, 190 nm, 195 nm, or 200 nm, preferably 105 nm to 180 nm, 120 nm to 160 nm, or 120 nm to 150 nm at a wavelength of 550 nm. Within this range, the polarizer can improve the lateral reflectivity.

[0072] The first retardation layer 120 may have a positive (+) biaxiality at a wavelength of 550 nm, for example, a biaxiality of 1 to 1.5, specifically 1, 1.05, 1.1, 1.15, 1.2, 1.25, 1.3, 1.35, 1.4, 1.45, or 1.5, preferably 1.1 to 1.3 at a wavelength of 550 nm. Within this range, the polarizer can improve the lateral reflectivity.

[0073] The first delay layer 120 may be a non-liquid crystal layer and may include a film formed of an optically transparent resin. "Non-liquid crystal layer" may mean: a layer not formed of at least one selected from liquid crystal monomers, liquid crystal oligomers and liquid crystal polymers, or a layer formed of a material that is not converted into liquid crystal monomers, liquid crystal oligomers or liquid crystal polymers by light irradiation.

[0074] The first retardation layer 120 may comprise a resin having positive (+) birefringence. Here, "positive (+) birefringence" means that a transparent film having birefringence properties imparted by stretching exhibits an increase in refractive index in the stretching direction.

[0075] For example, the first retardation layer 120 may be formed from at least one resin selected from the following: cellulose resins, including triacetyl cellulose (TAC); polyester resins, including polyethylene terephthalate (PET), polybutylene terephthalate, polyethylene naphthalate, polybutylene naphthalate, etc.; cyclic polyolefin (COP) resins; polycarbonate resins; polyethersulfone resins; polysulfone resins; polyamide resins; polyimide resins; polyolefin resins; polyarylate resins; polyvinyl alcohol resins; polyvinyl chloride resins; and polyvinylidene chloride resins. Preferably, to ensure short-wavelength and long-wavelength dispersion within the above range, the first retardation layer 120 may comprise a cyclic polyolefin film. In a polarizing plate, the cyclic polyolefin film can provide an effect of improving forward reflectivity.

[0076] The first retardation layer 120 may have a thickness of 10 micrometers to 60 micrometers, specifically 20 micrometers to 50 micrometers. Within this range, the first retardation layer 120 can be used in a polarizing plate.

[0077] The first delay layer 120 can be formed by stretching a non-stretched film made of optically transparent resin and can be stacked on a polarizer to manufacture a polarizing plate by a roll-to-roll process, thereby improving processability.

[0078] In one embodiment, the first delay layer 120 is formed of an obliquely stretched film stretched at a predetermined angle relative to the film's processing direction in an unstretched state, and a slow axis inclined relative to the film's processing direction is ensured. The obliquely stretched film method can be performed by typical methods known to those skilled in the art.

[0079] For the first retardation layer formed by the obliquely stretched film, the slow axis of the first retardation layer can be tilted at a predetermined angle relative to the transmission axis of the polarizer, thereby the polarizer can reduce the forward reflectivity and lateral reflectivity while improving the ellipticity of the lateral side, and can have color values ​​a* and b* that satisfy the relationship 0≤|a*|+|b*|≤2.5 to improve the black visibility on the front side.

[0080] The absolute value of the tilt angle α1 of the slow axis of the first retardation layer 120 relative to the transmission axis of the polarizer 110 is in the range of 50° to 80°, specifically 50°, 51°, 52°, 53°, 54°, 55°, 56°, 57°, 58°, 59°, 60°, 61°, 62°, 63°, 64°, 65°, 66°, 67°, 68°, 69°, 70°, 71°, 72°, 73°, 74°, 75°, 76°, 77°, 78°, 79°, or 80°. Within this range, the angle defined between the slow axis of the first retardation layer and the slow axis of the second retardation layer can be within a specific range, thereby reducing the reflectivity on both the front and lateral sides of the polarizer. Preferably, the absolute value of angle α1 is in the range of 52° to 75°, more preferably in the range of 54° to 73°.

[0081] although Figure 1 Although not shown, the first retardation layer 120 can be bonded to the polarizer 110 via a first bonding layer. The first bonding layer can be formed, for example, by a water-based adhesive and / or a photocurable adhesive. Preferably, the first bonding layer is formed by a photocurable adhesive, whereby the bonding between the protective film and the polarizer and the bonding between the polarizer and the first retardation layer can be achieved in a single step by light irradiation, thereby improving the processability of the polarizer.

[0082] Second Delay Layer

[0083] The second retardation layer 130 has an in-plane retardation of 80 nm to 140 nm at a wavelength of 550 nm. Within this range, the second retardation layer can help improve screen quality by reducing the reflectivity on both the front and lateral sides. Specifically, the second retardation layer 130 can have the following in-plane retardations at a wavelength of 550 nm: 80 nm, 81 nm, 82 nm, 83 nm, 84 nm, 85 nm, 86 nm, 87 nm, 88 nm, 89 nm, 90 nm, 91 nm, 92 nm, 93 nm, 94 nm, 95 nm, 96 nm, 97 nm, 98 nm, 99 nm, 100 nm, 101 nm, 102 nm, 103 nm, 104 nm, 105 nm, 106 nm, 107 nm, 108 nm, 1 The wavelengths are 0.9 nm, 110 nm, 111 nm, 112 nm, 113 nm, 114 nm, 115 nm, 116 nm, 117 nm, 118 nm, 119 nm, 120 nm, 121 nm, 122 nm, 123 nm, 124 nm, 125 nm, 126 nm, 127 nm, 128 nm, 129 nm, 130 nm, 131 nm, 132 nm, 133 nm, 134 nm, 135 nm, 136 nm, 137 nm, 138 nm, 139 nm, or 140 nm. Preferably, the second retardation layer 130 has an in-plane retardation of 90 nm to 130 nm or 100 nm to 120 nm at a wavelength of 550 nm.

[0084] The second retardation layer 130 is formed on the lower surface of the first retardation layer 120. By stacking the polarizer 110, the second retardation layer 130 and the first retardation layer 120 in the order stated, the polarizer cannot effectively achieve the effects of the present invention, and more precisely, it cannot satisfy 0≤|a*|+|b*|≤2.5.

[0085] The second retardation layer 130 exhibits positive wavelength dispersion and may have a short-wavelength dispersion of 1 to 1.15, specifically 1, 1.11, 1.12, 1.13, 1.14, or 1.15, and a long-wavelength dispersion of 0.94 to 1, specifically 0.94, 0.95, 0.96, 0.97, 0.98, 0.99, or 1. Within this range, the difference in wavelength dispersion between the first and second retardation layers can be reduced to improve the ellipticity at each wavelength, thereby improving reflectivity. Preferably, the second retardation layer has a short-wavelength dispersion of 1 to 1.12 and a long-wavelength dispersion of 0.94 to 0.99.

[0086] In one embodiment, the second retardation layer 130 may have an in-plane retardation of 80 nm to 160 nm at a wavelength of 450 nm, specifically 80 nm, 90 nm, 100 nm, 110 nm, 120 nm, 130 nm, 140 nm, 150 nm, or 160 nm, preferably 85 nm to 135 nm, more preferably 90 nm to 125 nm, and may have an in-plane retardation of 80 nm to 140 nm at a wavelength of 650 nm, specifically 80 nm, 90 nm, 100 nm, 110 nm, 120 nm, 130 nm, or 140 nm, preferably 80 nm to 125 nm. Within this range, the second retardation layer can easily achieve both short-wavelength and long-wavelength dispersion.

[0087] The second retardation layer 130 can have a negative (-) out-of-plane retardation at a wavelength of 550 nm, for example, an out-of-plane retardation from -250 nm to -50 nm, specifically -250 nm, -245 nm, -240 nm, -235 nm, -230 nm, -225 nm, -220 nm, -215 nm, -210 nm, -205 nm, -200 nm, -195 nm, -190 nm, -185 nm, -180 nm, -175 nm, -170 nm, -165 nm, etc. The wavelengths are -160 nm, -155 nm, -150 nm, -145 nm, -140 nm, -135 nm, -130 nm, -125 nm, -120 nm, -115 nm, -110 nm, -105 nm, -100 nm, -95 nm, -90 nm, -85 nm, -80 nm, -75 nm, -70 nm, -65 nm, -60 nm, -55 nm, or -50 nm, preferably -150 nm to -60 nm at a wavelength of 550 nm. Within this range, the polarizer can improve the lateral reflectivity by improving the circular polarization relative to the lateral side.

[0088] The second retardation layer 130 may have a negative (-) biaxiality at a wavelength of 550 nm, for example, a biaxiality of -2 to -0.1, specifically -2, -1.9, -1.8, -1.7, -1.6, -1.5, -1.4, -1.3, -1.2, -1.1, -1.0, -0.9, -0.8, -0.7, -0.6, -0.5, -0.4, -0.3, -0.2, or -0.1, preferably -1.5 to -0.1, and more preferably -0.5 to -0.1 at a wavelength of 550 nm. Within this range, the polarizer can improve the lateral reflectivity by improving the circular polarization on the lateral side.

[0089] The second retardation layer 130 may have a refractive index of 1.4 to 1.6, preferably 1.5 to 1.6. Within this range, the polarizer can achieve improved transparency compared to the first retardation layer by controlling the refractive index.

[0090] The second retardation layer 130 is formed from the composition for the second retardation layer described below. Here, the second retardation layer can be formed such that the slow axis of the second retardation layer can be tilted relative to the transmission axis of the polarizer at an angle within a predetermined range by controlling the coating direction and / or coating method, thereby improving the ellipticity of the polarizer on the lateral side while reducing the forward reflectivity and lateral reflectivity, and achieving color values ​​a* and b* that satisfy the relationship 0≤|a*|+|b*|≤2.5 to improve the black visibility on the front side.

[0091] The absolute value of the tilt angle α2 of the slow axis of the second retardation layer 130 relative to the transmission axis of the polarizer 110 is in the range of 0° to 10°, specifically 0°, 0.5°, 1°, 1.5°, 2°, 2.5°, 3°, 3.5°, 4°, 4.5°, 5°, 5.5°, 6°, 6.5°, 7°, 7.5°, 8°, 8.5°, 9°, 9.5°, or 10°. Within this range, the angle defined between the slow axes of the first and second retardation layers can be within a specific range, thereby reducing the forward and lateral reflectivity of the polarizer. Preferably, the absolute value of angle α2 is in the range of 5° to 10°.

[0092] In one embodiment, angle α1 can be in the range of +50° to +80°, and angle α2 can be in the range of 0° to +10°. In another embodiment, angle α1 can be in the range of -80° to -50°, and angle α2 can be in the range of -10° to 0°.

[0093] In one embodiment, the angle defined between the slow axis of the first retardation layer 120 and the slow axis of the second retardation layer 130 can be in the range of 50° to 70°, specifically 50°, 51°, 52°, 53°, 54°, 55°, 56°, 57°, 58°, 59°, 60°, 61°, 62°, 63°, 64°, 65°, 66°, 67°, 68°, 69°, or 70°, preferably 57° to 70°, and more preferably 57° to 67°. Within this range, the polarizer can have a higher circular polarization on the front side.

[0094] The second retardation layer 130 may have a thickness of about 1 micrometer to about 10 micrometers, preferably about 2 micrometers to about 8 micrometers. Within this range, the second retardation layer can effectively exhibit good out-of-plane retardation (Rth) over its entire width, and achieve a reduction in the thickness of the polarizer.

[0095] In order to ensure the aforementioned in-plane retardation at a wavelength of 550 nm, the second retardation layer 130 may comprise a coating formed from the composition for the second retardation layer described below as a non-liquid crystal layer.

[0096] The second retardation layer 130 may comprise a resin having negative (-) birefringence. Here, "negative (-) birefringence" means that a transparent film having birefringence properties imparted by stretching exhibits an increase in refractive index in a direction perpendicular to the stretching direction.

[0097] The composition for the second delay layer will be described below.

[0098] The second retardation layer can be a non-liquid crystal layer. For a second retardation layer containing liquid crystal, an alignment film for aligning the liquid crystal at a certain angle must be provided to the polarizing plate, which leads to the generation of foreign matter.

[0099] In one embodiment, the composition for the second delay layer is a non-liquid crystal composition and comprises a cellulose ester polymer and / or a polystyrene polymer.

[0100] Next, cellulose ester polymers will be described.

[0101] In this article, "polymer" means oligomer, polymer, or resin.

[0102] Cellulose ester polymers may comprise ester polymers having units, wherein at least some of the hydroxyl groups [C2 hydroxyl, C3 hydroxyl, or C6 hydroxyl] of the sugar monomers constituting cellulose are unsubstituted or substituted, as represented by Formula 1:

[0103]

[0104] Where n is 1 or an integer greater than 1.

[0105] The substituents used in cellulose ester polymers may include at least one selected from: halogen atoms, nitro groups, alkyl groups (e.g., C1 to C12). 20 Alkyl), alkenyl (e.g., C2 to C3) 20 alkenyl), cycloalkyl (e.g., C3 to C4) 10 cycloalkyl), aryl (e.g., C6 to C6) 20 aryl), heteroaryl (e.g., C3 to C4), 10 Heteroaryl), alkoxy (e.g., C1 to C1), 20 Alkoxy, acyl, and halogen-containing functional groups. Substituents may be the same as or different from each other.

[0106] In this article, the term "acyl" may refer to RC(=O)-* (* is the linkage site, and R is C1 to C2). 20 Alkyl, C3 to C 20 cycloalkyl, C6 to C20 Aryl or C7 to C 20 Aryl groups, as known in the art. The "acyl" group is coupled to the cellulose ring via an ester bond (through an oxygen atom) in cellulose.

[0107] Here, for convenience, "alkyl," "alkenyl," "cycloalkyl," "aryl," "heteroaryl," "alkoxy," and "acyl" refer to non-halogenated compounds. The composition used for the second delay layer may comprise a single cellulose ester polymer or a mixture comprising cellulose ester polymers.

[0108] Here, "halogen" refers to fluorine (F), Cl, Br or I, preferably F.

[0109] A "halogen-containing functional group" is an organic functional group containing at least one halogen atom, and may include aromatic, aliphatic, or alicyclic functional groups. For example, a halogen-containing functional group may refer to C1 to C2 atoms that have been halogenated. 20 Alkyl groups, halogenated C2 to C3 groups 20 Alkenyl, halogenated C2 to C 20 Alkyne group, halogenated C3 to C 10 cycloalkyl, halogenated C1 to C 20 Alkoxy, halogenated acyl, halogenated C6 to C 20 Aryl or halogenated C7 to C 20 Aryl groups, but not limited to them.

[0110] "Halogen-substituted acyl group" can be represented as R'-C(=O)-* (* is the linkage site, R' is the halogen-substituted C1 to C2 group). 20 Alkyl groups, halogenated C3 to C4 groups 20 cycloalkyl, halogenated C6 to C 20 Aryl or halogenated C7 to C 20 Aryl group). "Halogen-substituted acyl group" can be coupled to the cellulose ring via an ester bond (through an oxygen atom) in cellulose.

[0111] Preferably, the composition for the second retardation layer comprises a cellulose ester polymer substituted with acyl, halogen, or halogen-containing functional groups. More preferably, the halogen is fluorine. The halogen may be present in the cellulose ester polymer in an amount from 1% to 10% by weight. Within this range, the composition allows for the easy formation of a second retardation layer having the properties of the present invention and can improve circular polarization (ellipticity).

[0112] For the formation of the second delayed layer, the cellulose ester polymer can be prepared by typical methods known to those skilled in the art or can be obtained from commercially available products. For example, a cellulose ester polymer having an acyl group as a substituent can be prepared by reacting trifluoroacetic acid or trifluoroacetic anhydride with a sugar monomer or polymer of a sugar monomer constituting cellulose represented by Formula 1, by reacting trifluoroacetic acid or trifluoroacetic anhydride with it, followed by further reacting it with an acylating agent (e.g., a carboxylic anhydride or carboxylic acid), or by reacting trifluoroacetic acid or trifluoroacetic anhydride with it and an acylating agent.

[0113] Polystyrene polymers may contain portions represented by Formula 2:

[0114]

[0115] Where R 1 R 2 and R 3 Each of the elements is independently a hydrogen atom, an alkyl group, a substituted alkyl group, or a halogen; R is independently a substituent on the styrene ring; and n is an integer from 0 to 5 indicating the number of substituents on the styrene ring.

[0116] Examples of substituents on the styrene ring may include alkyl, substituted alkyl, halogen atom, hydroxyl, carboxyl, nitro, alkoxy, amino, sulfonate, phosphate, acyl, acyloxy, phenyl, alkoxycarbonyl, and cyano.

[0117] In one embodiment, R 1 R 2 and R 3 At least one of them may be a halogen, preferably fluorine.

[0118] The composition for the second retardation layer may further comprise an aromatic fused-ring additive. The aromatic fused-ring additive is used to adjust wavelength dispersion. Examples of aromatic fused-ring additives include 2-naphthylbenzoate, anthracene, phenanthrene, 2,6-naphthyldicarboxylate, etc. The aromatic fused-ring additive may be present in the composition of the second retardation layer in an amount from 0.1% to 30% by weight, preferably from 1% to 10% by weight. Within this range, the aromatic fused-ring additive can adjust both retardation and wavelength dispersion.

[0119] The composition used for the second delay layer may also contain typical additives known to those skilled in the art. Additives may include pigments and antioxidants, but are not limited thereto.

[0120] although Figure 1 Not shown, but an adhesive or bonding layer is formed on the lower surface of the second delay layer 130 to allow the polarizing plate to be stacked on the device of an optical display device, such as a light-emitting diode panel.

[0121] Laminate of first and second delay layers

[0122] The laminate of the first and second retardation layers can have an in-plane retardation of 120 nm to 200 nm at a wavelength of 550 nm, specifically 120 nm, 125 nm, 130 nm, 135 nm, 140 nm, 145 nm, 150 nm, 155 nm, 160 nm, 165 nm, 170 nm, 175 nm, 180 nm, 185 nm, 190 nm, 195 nm, or 200 nm, preferably 140 nm to 180 nm. Within this range, the polarizer can reduce reflectivity while improving circular polarization.

[0123] The laminate containing the first and second retardation layers has a total transmittance of 90% or more, specifically 90% to 100%, at wavelengths from 420 nm to 450 nm, or more specifically at wavelengths of 420 nm, 430 nm, 440 nm, or 450 nm. Within this range, the laminate can be applied to polarizing plates.

[0124] A laminate of the first and second retardation layers can be formed by coating a composition of the second retardation layer onto the first retardation layer and then obliquely stretching it relative to the MD of the first retardation layer. Specifically, the laminate of the first and second retardation layers can be formed by coating a composition of the second retardation layer onto the first retardation layer, or onto a non-stretched or obliquely stretched film of the first retardation layer, in a non-stretched or obliquely stretched state to form a coating for the second retardation layer, and then obliquely stretching it relative to the MD of the first retardation layer or the film for the first retardation layer, either on the MD or in an oblique direction. Preferably, the retardation difference between the first and second retardation layers in the polarizer according to the invention is achieved by obliquely stretching the first retardation layer or the film for the first retardation layer in an oblique direction relative to the MD of the first retardation layer or the film for the first retardation layer.

[0125] polarizer

[0126] Polarizer 110 is used to convert natural light or polarized light into polarized light by linear polarization in a certain direction, and can be produced from a polymer film that substantially contains polyvinyl alcohol resin. Specifically, polarizer 110 can be produced by dyeing the polymer film with iodine or dichroic dyes, followed by stretching the film on a polymer film (MD). More specifically, polarizer 110 can be produced by expansion, dyeing, stretching, and crosslinking.

[0127] The polarizer 110 may have a total transmittance of 40% or greater, for example, 40% to 45%, and a polarization of 99% or greater, for example, 99% to 100%. Within this range, the polarizer can improve the anti-reflective properties of the polarizing plate by combining it with a first retardation layer and a second retardation layer.

[0128] The polarizer 110 can have a thickness of 2 micrometers to 30 micrometers, specifically 4 micrometers to 25 micrometers. Within this range, the polarizer can be used in polarizing plates.

[0129] In one embodiment, the polarizer may have a total transmittance of about 40% to about 45%, specifically about 41% to about 45%, in the wavelength range of 380 nm to 780 nm. Within this range, the polarizer can readily achieve the total transmittance difference according to the invention.

[0130] In one embodiment, the polarizer may contain 1% to 5% by weight of potassium iodide (KI), specifically 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, or 5%, preferably 1% to 3% by weight. Within this range, the polarizer can readily achieve the total transmittance difference according to the invention.

[0131] Next, the method for manufacturing polarizers will be described in detail.

[0132] First, a process for manufacturing dyed and stretched polyvinyl alcohol films by dyeing and stretching with iodine and / or dichroic dyes will be described.

[0133] A dyed and stretched polyvinyl alcohol (PVA) film can be manufactured by dyeing the PVA film and then stretching the dyed film. In the method of manufacturing polarizing films, the order of dyeing and stretching is not particularly restricted. That is, the PVA film can be dyed and then stretched, stretched and then dyed, or dyed and stretched simultaneously.

[0134] The polyvinyl alcohol (PVA) film can comprise any typical PVA film commonly used in the manufacture of typical polarizers. Specifically, the PVA film can be a film formed from polyvinyl alcohol or its derivatives. The PVA film or its derivatives can have a degree of polymerization of 1,000 to 5,000 and a degree of saponification of 80 mol% to 100 mol%. The PVA film can have a thickness of 1 micrometer to 30 micrometers, specifically 3 micrometers to 30 micrometers. Within these ranges, PVA films can be used to manufacture thin polarizers.

[0135] Polyvinyl alcohol (PVA) films can be washed with water and swelled before dyeing and stretching. Washing the PVA film with water removes foreign matter from its surface. Swelling of the PVA film promotes dyeing or stretching. Here, as those skilled in the art know, the swelling of the PVA film can be performed by immersing it in an expansion bath filled with an aqueous solution. The temperature and swelling time of the expansion bath are not particularly limited. The expansion bath may further contain boric acid, inorganic acids, surfactants, etc., and its contents can be appropriately adjusted.

[0136] Polyvinyl alcohol (PVA) films can be dyed by immersing them in a dyeing bath containing iodine and / or a dichroic dye. In the dyeing process, the PVA film may be immersed in a dyeing solution. Here, the dyeing solution may be an aqueous solution containing iodine and / or a dichroic dye. Specifically, it is provided in the form of an iodine-based dye. The iodine-based dye may comprise at least one selected from: potassium iodide, hydrogen iodide, lithium iodide, sodium iodide, zinc iodide, aluminum iodide, lead iodide, and copper iodide.

[0137] The staining solution may be an aqueous solution containing 1% to 5% by weight of iodine and / or a dichroic dye. Within this range, the polarizer may have a polarization degree within the range specified herein, and thus may be used in optical displays.

[0138] In one embodiment, the staining solution may be an aqueous solution containing 1% to 5% potassium iodide. Within this range, the polarizer can have a polarization within the range specified herein while ensuring the concentration of potassium iodide in the polarizer, thereby facilitating the achievement of the effects of the invention.

[0139] The temperature of the dyeing bath can be in the range of 20°C to 45°C, and the polyvinyl alcohol film can be immersed in the dyeing bath for 10 seconds to 300 seconds. Within these ranges, the polarizer can have the polarization within the range specified herein while ensuring the concentration of potassium iodide in the polarizer, thereby promoting the achievement of the effects of the present invention.

[0140] Dyed polyvinyl alcohol (PVA) films are stretched in a stretching bath to acquire polarizing properties due to the orientation of iodine and / or dichroic dyes. Specifically, the stretching of dyed PVA films can be performed using either a dry stretching method or a wet stretching method. Dry stretching methods may include inter-roll stretching, compression stretching, heated roll stretching, etc., while wet stretching methods may involve stretching the dyed PVA film in a wet stretching bath containing water at 35°C to 65°C. The wet stretching bath may also contain boric acid to enhance stretching efficiency.

[0141] In one embodiment, the wet stretching bath may be filled with an aqueous solution containing 0% to 5% by weight, specifically 1% to 5% by weight, of potassium iodide and 0% to 5% by weight, specifically 1% to 5% by weight, of boric acid. Within these ranges, the polarizer can have a polarization degree within the range specified herein while ensuring the concentration of potassium iodide in the polarizer, thereby facilitating the achievement of the effects of the invention.

[0142] The polyvinyl alcohol (PVA) film can be stretched to a predetermined elongation. Specifically, the PVA film can be stretched to 5 to 7 times its original length, and more specifically, 5.5 to 6.5 times its original length. Within this elongation range, tearing or wrinkling of the PVA film during stretching can be prevented, and polarizers with high polarization and high transmittance can be achieved. Here, the PVA film can be uniaxially stretched in a single stage. Alternatively, stretching can be performed in multiple stages, such as two or three stages, thereby enabling the manufacture of thin polarizers without breakage.

[0143] Although the polyvinyl alcohol film was stretched after dyeing in the above embodiments, it should be understood that the invention is not limited thereto, and dyeing and stretching can be performed in the same bath.

[0144] Colored polyvinyl alcohol (PVA) films can be cross-linked in a cross-linking bath before or after stretching. Through cross-linking, PVA films can be more strongly colored with iodine and / or dichroic dyes. Boric acid can be used as a cross-linking agent. Phosphoric acid compounds, potassium iodide, etc., can be further included in the cross-linking bath to enhance cross-linking efficiency.

[0145] In one embodiment, the crosslinking bath may be filled with an aqueous solution containing optionally 5% by weight or less than 5% by weight, specifically 1% by weight to 5% by weight of boric acid. Within these ranges, the polarizer can have a polarization within the range specified herein while ensuring the concentration of potassium iodide in the polarizer, thereby facilitating the achievement of the effects of the invention. In one embodiment, the crosslinking bath may have a temperature of 20°C to 45°C.

[0146] Dyed and stretched polyvinyl alcohol (PVA) films can undergo color correction in a color correction bath. In the color correction process, the dyed and stretched PVA film is immersed in a color correction bath filled with a color correction solution containing potassium iodide. In this way, the color value of the polarizer can be reduced, and iodine anions (I-) can be removed from the polarizer. - This improves the durability of the polarizer. The temperature of the color correction bath can range from 20°C to 45°C, and the polyvinyl alcohol film can be immersed in the color correction bath for 10 seconds to 300 seconds.

[0147] In one embodiment, the color correction bath may be filled with an aqueous solution of optionally 5% or less than 5% by weight, specifically 1% to 5% by weight, potassium iodide and 5% or less than 5% by weight, specifically 1% to 5% by weight, boric acid. Within these ranges, the polarizer can have a polarization degree within the range specified herein while ensuring the concentration of potassium iodide in the polarizer, thereby facilitating the achievement of the effects of the invention.

[0148] In polarizing films, during the manufacturing process, the concentration of potassium iodide can be adjusted by changing the concentrations of boric acid and potassium iodide in each of the dyeing bath, wet stretching bath, and color correction bath.

[0149] Protective film

[0150] A protective film 140 is formed on the upper surface of the polarizer 110 to protect the polarizer from damage while improving its mechanical strength.

[0151] The protective film 140 is used to protect the polarizer from external environmental influences and can be an optically transparent film formed from at least one resin selected from the following: cellulose resin, including triacetyl cellulose (TAC); polyester resin, including polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate (PEN), polybutylene naphthalate, etc.; cyclic polyolefin resin; polycarbonate resin; polyethersulfone resin; polysulfone resin; polyamide resin; polyimide resin; polyolefin resin; polyaryl ester resin; polyvinyl alcohol resin; polyvinyl chloride resin; and polyvinylidene chloride resin. Specifically, the protective film can be a TAC film or a PET film.

[0152] The protective film 140 can have a thickness of 5 micrometers to 70 micrometers, specifically 15 micrometers to 45 micrometers. Within this range, the protective film can be used in polarizing plates.

[0153] although Figure 1 Not shown, but functional coatings may be further formed on the upper surface of the protective film 140 to provide additional functionality to the polarizer. For example, the functional coatings may include a hard coating, an anti-fingerprint layer, and an anti-reflective layer. These functional coatings may be stacked individually or in combination.

[0154] although Figure 1 Although not shown, the protective film 140 can be bonded to the polarizer 110 via a second bonding layer. The second bonding layer can be formed from at least one selected from water-based adhesives and photocurable adhesives. Preferably, the second bonding layer is formed from a photocurable adhesive, whereby the bonding between the protective film and the polarizer and the bonding between the polarizer and the first retardation layer can be achieved in a single step by light irradiation, thereby improving the processability of the polarizer.

[0155] The second bonding layer can have a thickness of 0.1 micrometers to 10 micrometers, specifically 0.5 micrometers to 5 micrometers. Within this range, the second bonding layer can be used in polarizing plates.

[0156] Next, we will refer to Figure 2 A polarizing plate according to another embodiment of the present invention is described.

[0157] refer to Figure 2The polarizing plate may include: a polarizer 110; a protective film 140 formed on the upper surface of the polarizer 110; and a first retardation layer 120, a second retardation layer 130, and an adhesive layer 150, which are sequentially formed on the lower surface of the polarizer 110. Except for the adhesive layer 150, the polarizer and... Figure 1 The polarizing plates are largely the same.

[0158] The adhesive layer 150 is used to adhesively attach the polarizing plate to the panel of the optical display device. Additionally, the adhesive layer 150 may contain a light absorber, thereby allowing the polarizing plate to have a total transmittance of 2% or less at a wavelength of 380 nm. Within this range, compared to a polarizing plate containing a first retardation layer and a second retardation layer and having a total transmittance difference of 2% or greater, the polarizing plate can further improve black visibility. Preferably, the polarizing plate has a total transmittance of 0.01% to 2%, more preferably 0.2% to 1%, at a wavelength of 380 nm.

[0159] The light absorber may comprise a UV absorber having a maximum absorption wavelength of 330 nm to 380 nm, specifically 330 nm, 335 nm, 340 nm, 345 nm, 350 nm, 355 nm, 360 nm, 365 nm, 370 nm, 375 nm, or 380 nm, preferably 340 nm to 360 nm. Within this range, the polarizer can readily achieve a total transmittance of 2% or less at a wavelength of 380 nm. Herein, "maximum absorption wavelength" means the wavelength at which the absorbance reaches its maximum value when measured in a light absorber solution diluted to a density of 10 mg / L in chloroform.

[0160] The light absorber may include at least one selected from the following: indole-based light absorbers, phenylbenzotriazole-based light absorbers, and triazine-based light absorbers containing hydroxyphenyltriazine light absorbers.

[0161] The light absorber may be present in the adhesive layer in an amount from 0.1 wt% to 6 wt%, specifically 0.1 wt%, 0.5 wt%, 1 wt%, 1.5 wt%, 2 wt%, 2.5 wt%, 3 wt%, 3.5 wt%, 4 wt%, 4.5 wt%, 5 wt%, 5.5 wt%, or 6 wt%, preferably 1 wt% to 5 wt%. Within this range of light absorber amounts, the polarizing plate can easily achieve the aforementioned total transmittance without the light absorber leaching out from the adhesive layer.

[0162] The adhesive layer 150 may be formed from a composition comprising a typical adhesive resin with adhesive properties and a light absorber. The adhesive resin may include (meth)acrylate resin, urethane resin, silicone resin, epoxy resin, etc.

[0163] The adhesive layer 150 can have a thickness of 5 micrometers to 70 micrometers, specifically 15 micrometers to 45 micrometers. Within this range, the adhesive layer can be used in polarizing plates.

[0164] Figure 2 The diagram illustrates a polarizing plate in which a light absorber is contained in an adhesive layer. However, it should be understood that the light absorber may be contained in at least one of the following: a protective film, a polarizer, a first retardation layer, a second retardation layer, and a bonding layer, as long as the light absorber does not affect the effectiveness of the invention.

[0165] Next, a polarizing plate according to another embodiment of the present invention will be described.

[0166] In the polarizing plate according to this embodiment, the protective film, polarizer, first retardation layer, and second retardation layer can be stacked sequentially, and an undercoat layer can be further formed on the lower surface of the first retardation layer. The undercoat layer is formed directly on the first and second retardation layers. The undercoat layer formed directly on the lower surface of the first retardation layer allows the second retardation layer to exhibit high adhesion to the first retardation layer and prevents the first retardation layer from being blocked in the roll-to-roll process, thereby promoting the formation of a laminate of the first and second retardation layers. Specifically, when the first retardation layer is a blockable cyclic polyolefin film, making it difficult to form the second retardation layer thereon by the roll-to-roll process, the undercoat layer formed on the first retardation layer can improve the processability during the formation of the second retardation layer.

[0167] Next, the base coat will be described in detail.

[0168] In one embodiment, the undercoat may contain particles. Adjusting the particle size in the undercoat during the formation of the laminate of the first and second retardation layers can improve the adhesion and processability of the second retardation layer to the first retardation layer. In one embodiment, the average particle size (D50) of the particles is smaller than the thickness of the undercoat and can vary, for example, from 1 nanometer to 500 nanometers, preferably from 100 nanometers to 300 nanometers. Within this range, the undercoat prevents the first retardation layer from being blocked and improves the adhesion of the second retardation layer to the first retardation layer. The particles may have a spherical or non-spherical shape, but are not limited thereto. Preferably, the particles have a spherical shape. The particles may contain silicon oxide (e.g., silica) and / or titanium oxide (e.g., TiO2), but are not limited thereto.

[0169] The particles may be present in the base coating in an amount of 10% to 50% by weight, specifically 10% to 30% by weight. Within this range, the base coating prevents the first retardation layer from being blocked when it is wound onto the roller and improves the adhesion between the first and second retardation layers.

[0170] A base coat can be formed by coating a composition comprising particles and a curable resin, followed by curing. The curable resin may include, but is not limited to, thermosetting resins and / or photocurable resins. For example, the curable resin may include, but is not limited to, modified or unmodified olefin resins of acrylic resins, ethylene resins, and acrylic resins.

[0171] The base coating can have a thickness of 100 nanometers to 500 nanometers, specifically 150 nanometers to 300 nanometers, which is greater than the average particle size. Within this range, the base coating can prevent obstruction by the first retardation layer, improve the adhesion of the second retardation layer, and allow for a reduction in the thickness of the polarizer.

[0172] In another embodiment, a base coat can be formed by applying a composition containing a curable resin without particles and then curing it.

[0173] In another embodiment, the polarizing plate may further include a third delay layer.

[0174] Next, a polarizing plate according to yet another embodiment of the present invention will be described.

[0175] According to this embodiment, the polarizing plate includes a protective film, a polarizer, a third retardation layer, a first retardation layer, and a second retardation layer. Except for the third retardation layer, which is additionally formed between the polarizer and the first retardation layer, the polarizing plate according to this embodiment... Figure 1 The polarizing plates shown are largely the same.

[0176] In the case of a third retardation layer formed between the polarizer and the first retardation layer, the polarizer can achieve an additional improvement in lateral reflectivity.

[0177] The third retardation layer may include a positive C retardation layer, which satisfies the relationship: nz>nx≒ny (nx, ny, and nz are the refractive indices of the third retardation layer at a wavelength of 550 nm in the slow direction, fast direction, and thickness direction, respectively).

[0178] In one embodiment, the third retardation layer may have an out-of-plane retardation (Rth) of -300 nm to 0 nm, for example, -200 nm to -30 nm, at a wavelength of 550 nm. The third retardation layer may also have an in-plane retardation (Re) of 0 nm to 10 nm, for example, 0 nm to 5 nm, at a wavelength of 550 nm. Within this range, the polarizer can achieve reduced reflectivity on the front side.

[0179] In one embodiment, the third retardation layer may be a liquid crystal layer. The liquid crystal layer may be formed from well-known typical materials to achieve the aforementioned out-of-plane retardation (Rth).

[0180] In another embodiment, the third delay layer may be formed from the composition described above for the second delay layer.

[0181] The optical display device according to the present invention may include a polarizing plate according to embodiments of the present invention. For example, the optical display device may include an organic light-emitting diode (OLED) display and a liquid crystal display.

[0182] In one embodiment, the OLED display device may include: an OLED panel comprising a flexible substrate; and a polarizing plate according to the invention stacked on the OLED panel.

[0183] In another embodiment, the OLED display device may include: an OLED panel comprising a non-flexible substrate; and a polarizing plate according to the invention stacked on the OLED panel.

[0184] The invention will now be described in more detail with reference to examples. However, it should be noted that these examples are provided for illustrative purposes only and should not be construed as limiting the invention in any way.

[0185] Example 1

[0186] Fabrication of a laminate with a first retardation layer and a second retardation layer

[0187] The second delayed layer is formed by depositing a composition [a non-liquid composition containing a cellulose ester polymer (containing trifluoroacetyl groups)] onto the lower surface of a cyclic polyolefin (COP) membrane (ZD membrane, Zeon Co., Ltd.) stretched at an angle of 45° relative to the MD. The cellulose ester polymer is prepared by adding trifluoroacetic acid and trifluoroacetic anhydride to unsubstituted cellulose, followed by reaction and polymerization.

[0188] After drying the coating, the laminate of the coating and the COP film is stretched to 1.5 times the elongation relative to the MD of the COP film at 135°C, thereby preparing a laminate with a first retardation layer (positive wavelength dispersion, thickness: 45 μm) and a second retardation layer (positive wavelength dispersion, thickness: 3 μm) having the specifications listed in Table 1.

[0189] Manufacturing polarizers

[0190] A polyvinyl alcohol film (PS#60, pre-stretched thickness: 60 micrometers, Kuraray Co., Ltd., Japan) washed with water was subjected to expansion in an expansion bath containing water at 30°C.

[0191] Subsequently, the polyvinyl alcohol film was placed in a dyeing bath filled with an aqueous solution containing 3% by weight of potassium iodide at 30°C for 200 seconds. Next, the polyvinyl alcohol film was passed through a wet crosslinking bath filled with an aqueous solution containing 2.5% by weight of boric acid at 30°C. Then, in a wet stretching bath filled with an aqueous solution containing 2.5% by weight of boric acid and 3% by weight of potassium iodide at 50°C, the polyvinyl alcohol film was stretched to a total elongation of 6 times its initial length.

[0192] Next, the polyvinyl alcohol film was immersed in a color correction bath containing 1% boric acid and 5% potassium iodide at 25°C for 100 seconds, followed by washing and drying, thus preparing a polarizer (thickness: 12 micrometers).

[0193] Manufacturing polarizing plates

[0194] As a protective layer, a TAC film (thickness: 27 micrometers, Konica Minolta Co., Ltd.) is bonded to the upper surface of the polarizer, and a laminate of the first and second retardation layers is attached to the lower surface of the polarizer via an adhesive layer, thereby manufacturing a polarizing plate comprising a protective film, a polarizer, a first retardation layer, a second retardation layer, and an adhesive film stacked in the order stated. The adhesive film is an acrylic adhesive film containing a UV absorber with a maximum absorption wavelength of 360 nanometers (a UV absorber based on hydroxyphenyl-triazine, Tinuvin 477, BASF).

[0195] Examples 2 to 5

[0196] The polarizing plate was manufactured in the same manner as in Example 1, except that the concentration of potassium iodide in the polarizer and / or the in-plane retardation of each of the first and second retardation layers were changed as listed in Table 1.

[0197] Example 6

[0198] The polarizing plate was manufactured in the same manner as in Example 1, except that the adhesive film did not contain UV absorbers.

[0199] Comparative Examples 1 to 3

[0200] The polarizing plate was manufactured in the same manner as in Example 1, except that the concentration of potassium iodide in the polarizer and / or the in-plane retardation of each of the first and second retardation layers were changed as listed in Table 1.

[0201] The retardation values ​​Re, Rth, and NZ of each of the first and second retardation layers were measured at a wavelength of 550 nm using an AxoScan polarimeter (AxoMetricCo.,Ltd.).

[0202] The following properties were evaluated for polarizing plates manufactured in example and comparative examples. The results are shown in Table 1 and... Figure 4 and Figure 5 middle.

[0203] (1) Potassium iodide content in the polarizer (unit: wt%): The potassium iodide content in each of the polarizers manufactured in the examples and comparative examples was measured by iodine titration. Specifically, 1 gram of polarizer and 50 grams of deionized water were placed in a beaker and heated at 80°C to completely dissolve the polarizer, and an aqueous solution of AgNO3 with a concentration of 0.1 equivalence was added for titration to obtain the potassium iodide content in the polarizer.

[0204] (2) Total transmittance of polarizer (unit: %): For each of the polarizers manufactured in the examples and comparative examples, the total transmittance of the polarizer was measured at wavelengths from 380 nm to 780 nm using a spectrophotometer (V730, JASCO Corporation).

[0205] (3) Total transmittance of polarizing plate (unit: %): The total transmittance of each of the polarizing plates manufactured in the examples and comparative examples was measured using a spectrophotometer (V730, Nippon Spectrophotometer Co., Ltd.) at wavelengths of 450 nm, 420 nm and 380 nm.

[0206] (4) Black Visibility Color Values ​​a* and b*: Modules of the optical display device were manufactured by attaching each of the polarizing plates produced in the examples and comparative examples to the upper surface of the organic light-emitting diode (OLED) panel. The modules for the optical display device were irradiated with light in a direction from the polarizing plate to the front side (0.05°) using a spectrophotometer (DMS803, Instrument Systems Inc.), and the black visibility color values ​​a* and b* at the front side (0°) were measured according to CIE 1976a*b* standards, based on the reflected and leaked light from the polarizing plate and OLED panel of each of the examples and comparative examples. Additionally, the black visibility color values ​​a* and b* were measured at different angles. The results are shown in… Figure 4 and Figure 5 middle.

[0207] Table 1

[0208]

[0209] *Angle 1: The angle between the slow axis of the first retardation layer and the transmission axis of the polarizer.

[0210] *Angle 2: The angle between the slow axis of the second retardation layer and the transmission axis of the polarizer.

[0211] Total transmittance difference of polarizing plates: Total transmittance of polarizing plates at 450 nm - Total transmittance of polarizing plates at 420 nm

[0212] As shown in Table 1, the polarizing plate according to the present invention exhibits a value of 0 to 2.5 when |a*| + |b*| is measured on its front side, thereby demonstrating a significant improvement in black visibility and lower reflectivity on both the front and lateral sides. Therefore, although not shown in Table 1, the polarizing plate according to the present invention can improve screen quality by improving black visibility. Thus, the present invention provides a polarizing plate capable of improving black visibility. Furthermore, the present invention provides a polarizing plate with lower reflectivity on both the front and lateral sides.

[0213] Conversely, although the total transmittance difference was satisfied, the polarizers of Comparative Examples 1 and 2 failed to satisfy the in-plane retardation of the first retardation layer, and although the in-plane retardation of each of the first and second retardation layers was satisfied, the polarizer of Comparative Example 3 failed to satisfy the total transmittance difference. All polarizers from Comparative Examples 1 to 3 had a |a*|+|b*| greater than 2.5 and showed no significant improvement in black visibility.

[0214] In addition, such as Figure 4 As shown, the polarizing plate according to the invention has color values ​​a* and b* within a square area from -2 to 2, and thus is expected to have good screen quality. Conversely, as Figure 5 As shown, the polarizer of Comparative Example 3 has color values ​​a* and b* outside the square area from -2 to 2, and is therefore expected to have poor screen quality.

[0215] Although some embodiments have been described herein, it should be understood that various modifications, alterations, changes, and equivalent embodiments can be made by those skilled in the art without departing from the spirit and scope of the invention.

Claims

1. A polarizing plate, comprising: Polarizing film; as well as A first retardation layer and a second retardation layer are sequentially stacked on the lower surface of the polarizer, wherein: The first delay layer has an in-plane delay of 200 to 250 nanometers at a wavelength of 550 nanometers; The second retardation layer has an in-plane retardation of 80 nm to 140 nm at a wavelength of 550 nm; and The polarizing plate has a total transmittance difference of 2% to 20% between the total transmittance at a wavelength of 450 nm and the total transmittance at a wavelength of 420 nm. The polarizing plate has a total transmittance of 30% or more at a wavelength of 450 nm and a total transmittance of 35% to 40% at a wavelength of 420 nm.

2. The polarizing plate according to claim 1, wherein the polarizing plate has a total transmittance of 2% or less at a wavelength of 380 nm.

3. The polarizing plate according to claim 1, wherein the first retardation layer has an out-of-plane retardation of 95 nm to 200 nm and a biaxiality of 1 to 1.5 at a wavelength of 550 nm.

4. The polarizing plate according to claim 1, wherein the second retardation layer has an out-of-plane retardation of -250 nm to -50 nm and a biaxiality of -2 to -0.1 at a wavelength of 550 nm.

5. The polarizing plate according to claim 1, wherein the first retardation layer comprises a resin having positive birefringence, and the second retardation layer comprises a resin having negative birefringence.

6. The polarizing plate according to claim 1, wherein each of the first retardation layer and the second retardation layer is a non-liquid crystal layer.

7. The polarizing plate according to claim 1, wherein the second retardation layer comprises at least one selected from cellulose ester polymers and polystyrene polymers.

8. The polarizing plate according to claim 1, wherein the laminate of the first retardation layer and the second retardation layer has a total transmittance of 90% or greater than 90% at wavelengths from 420 nm to 450 nm.

9. The polarizing plate according to claim 1, wherein the polarizer has a total transmittance of 40% to 45% at wavelengths from 380 nm to 780 nm.

10. The polarizing plate according to claim 1, wherein the polarizing plate contains 1% to 5% by weight of potassium iodide.

11. The polarizing plate according to claim 1, wherein the absolute value of the tilt angle of the slow axis of the first retardation layer relative to the transmission axis of the polarizer is in the range of 50° to 80°, and the absolute value of the tilt angle of the slow axis of the second retardation layer relative to the transmission axis of the polarizer is in the range of 0° to 10°.

12. The polarizing plate according to claim 1, wherein the polarizing plate further comprises a light absorber.

13. The polarizing plate according to claim 12, wherein the light absorber has a maximum absorption wavelength of 330 nm to 380 nm.

14. The polarizing plate according to claim 1, further comprising a protective film formed on the upper surface of the polarizing plate.

15. An optical display device comprising the polarizing plate according to any one of claims 1 to 14.

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