CN113625384A

CN113625384A - Polarizing plate and optical display device including the same

Info

Publication number: CN113625384A
Application number: CN202110489918.7A
Authority: CN
Inventors: 具埈谟; 李相钦; 金奉春; 柳政勋; 申光浩; 李承俊; 李昇勋
Original assignee: Samsung SDI Co Ltd
Current assignee: Samsung SDI Co Ltd
Priority date: 2020-05-06
Filing date: 2021-05-06
Publication date: 2021-11-09
Anticipated expiration: 2041-05-06
Also published as: CN113625384B; KR20210135888A

Abstract

The present invention relates to a polarizing plate and an optical display device including the same. The polarizing plate includes 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 180nm to 240nm at a wavelength of 550 nm; the second retardation layer has an in-plane retardation (Re) of 70nm to 120nm at a wavelength of 550 nm; the polarizing plate further includes a layer containing a light absorbing agent; and the slow axis of the first retardation layer is inclined at an absolute value of an angle (α 1) of 60 ° to 80 ° with respect to the transmission axis of the polarizer, and the slow axis of the second retardation layer is inclined at an absolute value of an angle (α 2) of 0 ° to 10 ° with respect to the transmission axis of the polarizer.

Description

Polarizing plate and optical display device including the same

Citations to related applications

This application claims the benefit of korean patent application No. 10-2020-0054124, filed in the korean intellectual property office on 6/5/2020, the entire disclosure of which is incorporated herein by reference.

Technical Field

The present invention relates to a polarizing plate and an optical display device including the same.

Background

The organic light emitting diode display may suffer from deterioration in visibility and contrast due to reflection of external light. To solve such a problem, a polarizing plate including a polarizer and a retardation film may be used. The polarizing plate may realize an anti-reflection function by preventing reflected external light from leaking.

The organic light emitting diode display is required to exhibit good screen quality in an operating state while exhibiting good reflection visibility against external light of a lateral side in a non-operating state. The visibility of the reflection at the side face can be obtained by reducing the side face reflectance. However, the reduction in the reflective visibility of the side face may cause deterioration in the black visibility due to poor frontal visibility.

In order to improve black visibility of the front surface, it may be considered to control the color value of the polarizing plate. However, there is a limit to improve the black visibility of the front surface only by controlling the color value of the polarizer.

The background art of the present invention is disclosed in korean patent laid-open publication No. 10-2013-0103595 and the like.

Disclosure of Invention

An object of the present invention is to provide a polarizing plate (polarizing plate) which improves black visibility of the front surface.

It is another object of the present invention to provide a polarizing plate having low reflectivity on both front and side surfaces.

It is still another object of the present invention to provide a polarizing plate having a circular polarization degree (ellipticity) of 62% or more at a side surface.

One aspect of the present invention relates to a polarizing plate.

1. The polarizing plate includes 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 180nm to 240nm at a wavelength of 550 nm; the second retardation layer has an in-plane retardation (Re) of 70nm to 120nm at a wavelength of 550 nm; the polarizing plate further includes a layer containing a light absorbing agent; and the slow axis of the first retardation layer is inclined at an absolute value of an angle (α 1) of 60 ° to 80 ° with respect to the transmission axis of the polarizer, and the slow axis of the second retardation layer is inclined at an absolute value of an angle (α 2) of 0 ° to 10 ° with respect to the transmission axis of the polarizer.

2. In 1, the layer containing a light absorber may include a light absorber having a maximum absorption wavelength of 380nm to 420 nm.

3. In 2, the light absorber may be present in the layer containing the light absorber in an amount of 0.1 to 6 wt%.

4. In 2, the light absorber may include at least one selected from the group consisting of indole, phenylbenzotriazole, and triazine light absorbers.

5. In 1 to 4, each of the first and second retardation layers may exhibit positive wavelength dispersion.

6. In 1 to 5, the laminate (laminate) of the first and second retardation layers may have an in-plane retardation (Re) of 120nm to 200nm at a wavelength of 550 nm.

7. In 1 to 6, the first retardation layer may have a positive out-of-plane retardation (Rth) at a wavelength of 550nm, and the second retardation layer may have a negative out-of-plane retardation (Rth) at a wavelength of 550 nm.

8. In 1 to 7, the first retardation layer may have a positive biaxial degree (NZ) at a wavelength of 550nm, and the second retardation layer may have a negative biaxial degree at a wavelength of 550 nm.

9. In 1 to 8, an angle defined between the slow axis of the first retardation layer and the slow axis of the second retardation layer may be in a range of 50 ° to 70 °.

10. In 1 to 9, the angle α 1 may be in the range of +60 ° to +80 ° and the angle α 2 may be in the range of 0 ° to +10 °, or the angle α 1 may be in the range of-80 ° to-60 ° and the angle α 2 may be in the range of-10 ° to 0 °.

11. In 1 to 10, a layer including a light absorbing agent may be formed on a lower surface of the second retardation layer, between the first retardation layer and the second retardation layer, between the polarizer and the first retardation layer, and/or on an upper surface of the polarizer.

12. In 1 to 11, the second retardation layer may include at least one selected from a cellulose ester polymer and a polystyrene polymer.

13. In 1 to 12, the polarizing plate may further include a protective film formed on an upper surface of the polarizer.

14. In 1 to 13, the polarizer may further include a positive C layer. .

Another aspect of the invention relates to an optical display device.

An optical display device may comprise a polarizer according to the present invention.

The invention provides a polarizing plate which improves black visibility of a front surface.

The present invention provides a polarizing plate having low reflectance at both front and side surfaces.

The present invention provides a polarizing plate having a circular polarization degree (ellipticity) of 62% or more at a side surface.

Drawings

Fig. 1 is a cross-sectional view of a polarizing plate according to one embodiment of the present invention.

Fig. 2 is a diagram showing an arrangement relationship among a transmission axis of a polarizer, a slow axis of a first retardation layer, and a slow axis of a second retardation layer in a polarizing plate of an embodiment of the present invention.

Fig. 3 is a cross-sectional view of a polarizer according to another embodiment of the present invention.

Fig. 4 is a graph showing color values a and b.

Detailed Description

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

Spatially relative terms, such as "upper" and "lower," are defined herein with reference to the drawings. Thus, it will be understood that the term "upper surface" may be used interchangeably with the term "lower surface".

Herein, "in-plane retardation Re", "out-of-plane retardation Rth", and "biaxial degree NZ" are expressed by equations A, B and C, respectively:

[ equation A ]

Re＝(nx-ny)×d

[ equation B ]

Rth＝((nx+ny)/2-nz)×d

[ equation C ]

NZ＝(nx-nz)/(nx-ny)。

Where nx, ny, and nz are refractive indices in a slow axis direction, a fast axis direction, and a thickness direction of the corresponding optical device at the measurement wavelength, respectively, and d is a thickness (unit: nm) of the optical device. In equations a to C, the measurement wavelength may be 450nm, 550nm, or 650 nm.

Herein, "short wavelength dispersion" refers to Re (450)/Re (550), and "long wavelength dispersion" refers to Re (650)/Re (550), where Re (450), Re (550), and Re (650) refer to in-plane retardation (Re) of a single retardation layer or a laminate of retardation layers at wavelengths of about 450nm, 550nm, and 650nm, respectively.

As used herein to denote angle, "+" denotes a counterclockwise direction about the reference point, and "-" denotes a clockwise direction about the reference point.

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

As used herein to refer to particular numerical ranges, the expression "X to Y" means "greater than or equal to X and less than or equal to Y (X ≦ and ≦ Y)".

The polarizing plate generally deteriorates black visibility of the front surface due to a reduction in visual sensitivity of reflection from the side surface. The inventors of the present invention have developed a polarizing plate capable of realizing low reflectance at the front and side surfaces while improving not only the lateral-side reflex visual acuity but also the black visibility of the front surface. Herein, it is assumed that the front face is represented by 0 °, and the "side" face, i.e., each of the right and left sides, refers to a direction in the range of 45 ° to 75 °, particularly in the direction of 60 °.

In one embodiment, the polarizer may have color values a and b satisfying the following relationship: when the black visibility of the front is evaluated by the color values a and b, 0 ≦ a | + | b ≦ 2.5. Within this range, the polarizing plate can improve black visibility of the front surface. Preferably, the polarizer has a color value a of-2.5 to 2.5 and a color value b of-2.5 to 2.5. The determination of a and b can be carried out by the methods described in the examples. The relationship is as follows: 0 ≦ a ≦ b ≦ 2.5 is set as an evaluation reference, indicating that the polarizing plate improves black visibility of the front side when actually mounted on the module of the optical display device. Fig. 4 shows color values a (corresponding to the x-axis) and color values b (corresponding to the y-axis). The polarizing plate according to the present invention may have color values a and b satisfying | a | + | b |, within a range of 0 to 2.5. For example, polarizer color values a and b satisfying | a | + | b |, of 0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2.0, 2.1, 2.2, 2.3, 2.4, or 2.5 are satisfied.

For example, the polarizer may have a color value a of-2.5, -2.4, -2.3, -2.2, -2.1, -2.0, -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, -0.1, 0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2.0, 2.1, 2.2, 2.3, 2.4, or 2.5.

For example, the polarizer may have a color value b of-2.5, -2.4, -2.3, -2.2, -2.1, -2.0, -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, -0.1, 0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2.0, 2.1, 2.2, 2.3, 2.4, or 2.5.

In one embodiment, the polarizer may have a front side reflectance of 1.0% or less, preferably 0.5% or less, and a side reflectance of 2.0% or less, preferably 1.5% or less, when applied to an optical display device. Within this range, the polarizing plate can improve the front and side screen quality.

For example, when applied to an optical display device, the polarizing plate may have a front-side reflectance of 0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, or 1.0%, and a side-side reflectance of 0, 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 2.0%.

In one embodiment, the polarizer has a minimum lateral ellipticity (degree of circular polarization) of 62% or more, for example, 62% to 80%, when applied to an optical display device. Within this range, the polarizer can improve the screen quality (minimize the color variation at the 60 ° side and at the 0 ° to 360 ° azimuth angle). For example, the minimum side ellipticity of the polarizing plate is 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, or 80%.

According to the present invention, the polarizing plate includes 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 180nm to 240nm at a wavelength of 550 nm; the second retardation layer has an in-plane retardation (Re) of 70nm to 120nm at a wavelength of 550 nm; the polarizing plate further includes a layer containing a light absorbing agent; and the slow axis of the first retardation layer is tilted at an absolute value of an angle of 60 ° to 80 ° with respect to the transmission axis of the polarizer, and the slow axis of the second retardation layer is tilted at an absolute value of an angle of 0 ° to 10 ° with respect to the transmission axis of the polarizer.

Next, a polarizing plate according to an embodiment of the present invention will be described with reference to fig. 1.

Referring to fig. 1, the polarizing plate includes a polarizer 110; a protective film 150 laminated on the upper surface of the polarizer 110; and a first retardation layer 120, a second retardation layer 130, and a layer 140 containing a light absorbing agent, which are sequentially laminated in the above-described order on the lower surface of the polarizer 110.

First retardation layer

The first retardation layer 120 has an in-plane retardation (Re) of 180nm to 240nm at a wavelength of 550 nm. In a typical polarizing plate, 1/2 in-plane retardation layer and 1/4 in-plane retardation layer are sequentially stacked on the lower surface of the polarizer to reduce the front and side reflectivities. In the polarizing plate according to the present invention, the first retardation layer has an in-plane retardation of 180nm to 240nm at a wavelength of 550nm, which is significantly different from 1/2 phase difference of 260nm to 280 nm. By this structure, in combination with the second retardation layer having the above-described in-plane retardation at a wavelength of 550nm and the layer containing a light absorbing agent, the first retardation layer can significantly reduce front and side reflectances while ensuring an ellipticity (degree of circular polarization) of 62% or more, and color values a and b satisfying the following relationships: and | a | + | b | is more than or equal to 0 and less than or equal to 2.5.

Preferably, the first retardation layer 120 has an in-plane retardation (Re) of 180nm to 240nm at a wavelength of 550 nm. For example, the first retardation layer 120 may have an in-plane retardation (Re) of 180nm, 181nm, 182nm, 183nm, 184nm, 185nm, 186nm, 187nm, 188nm, 189nm, 190nm, 191nm, 192nm, 193nm, 194nm, 195nm, 196nm, 197nm, 198nm, 199nm, 200nm, 201nm, 202nm, 203nm, 204nm, 205nm, 206nm, 207nm, 208nm, 209nm, 210nm, 211nm, 212nm, 213nm, 214nm, 215nm, 216nm, 217nm, 218nm, 219nm, 220nm, 221nm, 222nm, 223nm, 224nm, 225nm, 226nm, 227nm, 228nm, 229nm, 230nm, 231nm, 232nm, 233nm, 234nm, 235nm, 236nm, 237nm, 238nm, 239nm, or 240nm at a wavelength of 550 nm.

The first retardation layer 120 exhibits positive wavelength dispersion and may have short wavelength dispersion of 1 to 1.1 and long wavelength dispersion of 0.96 to 1. Within this range, the polarizing plate can reduce the front and side reflectances in use while increasing the ellipticity. Preferably, the first retardation layer has a short wavelength dispersion of 1.03 to 1, and a long wavelength dispersion of 0.98 to 1, 0.99 to 1, or 0.995 to 1.

In one embodiment, the first retardation layer 120 may have an in-plane retardation (Re) of 180nm to 280nm, preferably 185nm to 260nm, more preferably 190nm to 250nm at a wavelength of 450nm, and an in-plane retardation (Re) of 175nm to 270nm, preferably 180nm to 255nm, more preferably 185nm to 240nm at a wavelength of 650 nm. In this range, the first retardation layer can easily achieve short-wavelength dispersion and long-wavelength dispersion.

The first retardation layer 120 may have a positive out-of-plane retardation (Rth) at a wavelength of 550nm, for example, an out-of-plane retardation (Rth) of 95nm to 200nm, preferably 105nm to 180 nm. Within this range, the polarizer can improve the side reflectance.

The first retardation layer 120 may have a positive biaxiality at a wavelength of 550nm, for example, a biaxiality of 1 to 1.3, preferably 1.1 to 1.3. Within this range, the polarizer can improve the side reflectance. For example, the first retardation layer 120 may have a positive biaxiality of 1, 1.01, 1.02, 1.03, 1.04, 1.05, 1.06, 1.07, 1.08, 1.09, 1.1, 1.11, 1.12, 1.13, 1.14, 1.15, 1.16, 1.17, 1.18, 1.19, 1.2, 1.21, 1.22, 1.23, 1.24, 1.25, 1.26, 1.27, 1.28, 1.29, or 1.3.

The first retardation layer 120 may be a non-liquid crystal layer, and may include a film formed of an optically transparent resin. The "non-liquid crystal layer" may refer to a layer not formed of at least one selected from a liquid crystal monomer, a liquid crystal oligomer, and a liquid crystal polymer, or a layer formed of a material that is not converted into a liquid crystal monomer, a liquid crystal oligomer, or a liquid crystal polymer by light irradiation.

For example, the first retardation layer 120 may be formed of at least one resin selected from cellulose resins including triacetyl cellulose (TAC) and the like, polyester resins including polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate (PEN), polybutylene naphthalate and the like, 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, in order to secure the short wavelength dispersion and the long wavelength dispersion, the first retardation layer 120 may include a cyclic polyolefin film. In the polarizing plate, the cyclic polyolefin film may provide an effect of improving front-side reflectance.

The first retardation layer 120 may have a thickness of 10 μm to 60 μm, specifically 20 μm to 50 μm. Within this range, the first retardation layer 120 may be used in a polarizer.

The first retardation layer 120 may be formed by stretching a non-stretched film formed of an optically transparent resin, or may be stacked on a polarizer by a roll-to-roll process to manufacture a polarizer, thereby improving processability.

In one embodiment, the first retardation layer 120 is formed of an obliquely stretched film that is stretched in an oblique direction at a predetermined angle with respect to the machine direction of the film in a non-stretched state, and a slow axis that is oblique with respect to the machine direction of the film can be secured. The process of obliquely stretching the film may be performed by typical methods known to those skilled in the art.

For the first retardation layer formed of the obliquely stretched film, the slow axis of the first retardation layer may be inclined at a predetermined angle with respect to the transmission axis of the polarizer, so that the polarizing plate may reduce front and side reflectances while improving ellipticity at the side, and may have color values a and b satisfying the following relationships: and | a | + | b | ≦ 2.5 to improve the black visibility of the front side.

Referring to fig. 2, the slow axis 120a of the first retardation layer 120 is inclined at an absolute value of an angle α 1 of 60 ° to 80 ° with respect to the transmission axis 110a of the polarizer 110. In this range, an angle defined between the slow axis of the first retardation layer and the slow axis of the second retardation layer may be within a preset range, so that the polarizer may reduce front and side reflectivities. Preferably, the absolute value of the angle α 1 is in the range of 62 ° to 75 °, more preferably in the range of 64 ° to 73 °. For example, the absolute value of the angle α 1 may be 60 °, 61 °, 62 °, 63 °, 64 °, 65 °, 66 °, 67 °, 68 °, 69 °, 70 °, 71 °, 72 °, 73 °, 74 °, 75 °, 76 °, 77 °, 78 °, 79 °, or 80 °.

Although not shown in fig. 1, the first retardation layer 120 may be bonded to the polarizer 110 via a first adhesive layer. The first adhesive layer may be formed of, for example, a water-based adhesive and/or a photocurable adhesive. Preferably, the first adhesive layer is formed of a light-curable adhesive, whereby the adhesion between the protective film and the polarizer and the adhesion between the polarizer and the first retardation layer can be achieved by one light irradiation, thereby improving the workability of the polarizing plate.

A second retardation layer

The second retardation layer 130 has an in-plane retardation (Re) of 70nm to 120nm at a wavelength of 550 nm. In a typical polarizer, in order to reduce front and side reflectivities, 1/2 in-plane retardation layers and 1/4 in-plane retardation layers are stacked in this order on the lower surface of the polarizer. In the polarizing plate according to the present invention, the second retardation layer has an in-plane retardation of 70nm to 120nm at a wavelength of 550nm, which is significantly different from 1/4 phase difference of 130nm to 150 nm. By this structure, in combination with the first retardation layer and the light absorber-containing layer, the second retardation layer can significantly reduce front and side reflectances, particularly at the side of 60 °, and color values a and b satisfying the following relationships while ensuring an ellipticity (circular polarization degree) of the side of 62% or more: and | a | + | b | is more than or equal to 0 and less than or equal to 2.5.

Preferably, the second retardation layer 130 may have an in-plane retardation (Re) of 85nm to 115nm, specifically 90nm to 110nm, at a wavelength of 550 nm. For example, the second retardation layer 130 may have an in-plane retardation (Re) of 70nm, 71nm, 72nm, 73nm, 74nm, 75nm, 76nm, 77nm, 78nm, 79nm, 80nm, 81nm, 82nm, 83nm, 84nm, 85nm, 86nm, 87nm, 88nm, 89nm, 90nm, 91nm, 92nm, 93nm, 94nm, 95nm, 96nm, 97nm, 98nm, 99nm, 100nm, 101nm, 102nm, 103nm, 104nm, 105nm, 106nm, 107nm, 108nm, 109nm, 110nm, 111nm, 112nm, 113nm, 114nm, 115nm, 116nm, 117nm, 118nm, 119nm, or 120nm at a wavelength of 550 nm.

The second retardation layer 130 is formed on the lower surface of the first retardation layer 120. In a laminate in which the polarizer 110, the second retardation layer 130 and the first retardation layer 120 are sequentially laminated in the above-described order, the polarizing plate according to the present invention cannot effectively achieve the effects of the present invention, and particularly cannot satisfy 0 ≦ a ≦ b ≦ 2.5.

The second retardation layer 130 exhibits positive wavelength dispersion and may have short wavelength dispersion of 1 to 1.15 and long wavelength dispersion of 0.94 to 1. Within this range, the difference in wavelength dispersion between the first retardation layer and the second retardation layer can be reduced to increase the ellipticity at each wavelength, thereby increasing the reflectance. Preferably, the second retardation layer has a short wavelength dispersion of 1 to 1.06, and a long wavelength dispersion of 0.97 to 1.

For example, the second retardation layer 130 may have a short wavelength dispersion of 1, 1.01, 1.02, 1.03, 1.04, 1.05, 1.06, 1.07, 1.08, 1.09, 1.1, 1.11, 1.12, 1.13, 1.14, or 1.15, and a long wavelength dispersion of 0.94, 0.95, 0.96, 0.97, 0.98, 0.99, or 1.

In one embodiment, the second retardation layer 130 may have an in-plane retardation (Re) of 80nm to 120nm, preferably 85nm to 115nm, more preferably 90nm to 110nm at a wavelength of 450nm, and an in-plane retardation (Re) of 80nm to 110nm, preferably 85nm to 105nm at a wavelength of 650 nm. In this range, the second retardation layer can easily achieve short-wavelength dispersion and long-wavelength dispersion.

The second retardation layer 130 may have a negative out-of-plane retardation (Rth) at a wavelength of 550nm, for example, of-250 nm to-50 nm, preferably-150 nm to-60 nm. Within this range, the polarizing plate can improve the side reflectance by improving the degree of circular polarization with respect to the side.

The second retardation layer 130 may have a negative biaxiality of, for example, -2 to-0.1, preferably-1.5 to-0.1, more preferably-0.5 to-0.1, at a wavelength of 550 nm. Within this range, the polarizer can improve the side reflectance. Within this range, the polarizing plate can improve the side reflectance by improving the degree of circular polarization at the side.

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 transparency of the polarizer may be improved by controlling the refractive index as compared to the first retardation layer.

The second retardation layer 130 is formed of a composition for the second retardation layer described below. Here, the second retardation layer may be formed such that a slow axis of the second retardation layer may be inclined at an angle within a predetermined range with respect to a transmission axis of the polarizer by controlling a coating direction and/or a coating method, so that the polarizing plate may reduce front and side reflectances while improving an ellipticity of the side, and color values a and b satisfying the following relationships may be realized: and | a | + | b | ≦ 2.5 to improve the black visibility of the front side.

Referring to fig. 2, the slow axis 130a of the second retardation layer 130 is inclined at an absolute value of an angle α 2 of 0 ° to 10 ° with respect to the transmission axis 110a of the polarizer 110. In this range, an angle defined between the slow axis of the first retardation layer 120 and the slow axis of the second retardation layer may be within a preset range, so that the polarizer may reduce front and side reflectivities. Preferably, the absolute value of the angle α 2 is in the range of 6 ° to 8 °. For example, the absolute value of the angle α 2 may be 0 °, 1 °, 2 °, 3 °, 4 °, 5 °,6 °, 7 °, 8 °, 9 °, or 10 °.

In one embodiment, the angle α 1 may be in the range of +60 ° to +80 °, and the angle α 2 may be in the range of 0 ° to +10 °. In another embodiment, angle α 1 may be in the range of-80 ° to-60 °, and angle α 2 may be in the range of-10 ° to 0 °.

For example, the angle α 1 may be +60 °, +61 °, +62 °, +63 °, +64 °, +65 °, +66 °, +67 °, +68 °, +69 °, +70 °, +71 °, +72 °, +73 °, +74 °, +75 °, +76 °, +77 °, +78 °, +79 ° or +80 °, and the angle α 2 may be 0 °, +1 °, +2 °, +3 °, +4 °, +5 °, +6 °, +7 °, +8 °, +9 ° or +10 °.

For example, the angle α 1 may be-80 °, -79 °, -78 °, -77 °, -76 °, -75 °, -74 °, -73 °, -72 °, -71 °, -70 °, -69 °, -68 °, -67 °, -66 °, -65 °, -64 °, -63 °, -62 °, -61 °, or-60 °, and the angle α 2 may be-10 °, -9 °, -8 °, -7 °, -6 °, -5 °, -4 °, -3 °, -2 °, -1 °, or 0 °.

In one embodiment, referring to fig. 2, the angle defined between the slow axis 120a of the first retarder 120 and the slow axis 130a of the second retarder 130 may be in the range of 50 ° to 70 °, preferably 57 ° to 70 °, more preferably 57 ° to 67 °. Within this range, the polarizing plate can have a high degree of circular polarization. For example, the angle defined between the slow axis 120a of the first retarder layer 120 and the slow axis 130a of the second retarder layer 130 may be 50 °, 51 °, 52 °, 53 °, 54 °, 55 °, 56 °, 57 °, 58 °, 59 °, 60 °, 61 °, 62 °, 63 °, 64 °, 65 °, 66 °, 67 °, 68 °, 69 °, or 70 °.

The second retardation layer 130 may have a thickness of 1 μm to 10 μm, preferably 2 μm to 8 μm. Within this range, the second retardation layer can effectively exhibit good out-of-plane retardation (Rth) over the entire width thereof, and the thickness of the polarizing plate can be reduced.

In order to ensure the above in-plane retardation at a wavelength of 550nm, the second retardation layer 130 may include a coating layer formed of a composition for the second retardation layer described below as a non-liquid crystal layer.

Hereinafter, the composition for the second retardation layer will be described.

The second retardation layer may be a non-liquid crystal layer. For the second retardation layer including liquid crystal, an alignment film for aligning the liquid crystal at an angle must be provided to the polarizing plate, thereby causing generation of impurities.

In one embodiment, the composition for the second retardation layer is a non-liquid crystal composition and includes at least one selected from a cellulose ester polymer and a polystyrene polymer.

Next, the cellulose ester polymer will be described.

Herein, "polymer" refers to an oligomer, polymer or resin.

The cellulose ester polymer may include an ester polymer having an acyl unit in which at least some of the hydroxyl groups [ C ] of the sugar monomer constituting the cellulose₂Hydroxy, C₃Hydroxy or C₆Hydroxy radical]Is unsubstituted or substituted, as shown in formula 1:

[ formula 1]

Wherein n is an integer of 1 or more.

The substituent of the cellulose ester polymer or the acyl unit may include one or more substituents selected from halogen atoms, nitro groups, alkyl groups (e.g., C)₁To C₂₀Alkyl groups), alkenyl groups (examples)E.g. C₂To C₂₀Alkenyl), cycloalkyl (e.g. C)₃To C₁₀Cycloalkyl), aryl (e.g. C)₆To C₂₀Aryl), heteroaryl (e.g., C)₃To C₁₀Aryl), alkoxy (e.g. C)₁To C₂₀Alkoxy), acyl, and halogen-containing functional groups. The substituents may be the same as or different from each other.

Herein, the term "acyl" may denote R-C (═ O) - (, as the linking site, R being C₁To C₂₀Alkyl radical, C₃To C₂₀Cycloalkyl radical, C₆To C₂₀Aryl or C₇To C₂₀Arylalkyl) as is well known in the art. An "acyl group" is coupled to the cellulose ring via an ester bond (via an oxygen atom) in the cellulose.

Herein, for convenience, "alkyl", "alkenyl", "cycloalkyl", "aryl", "heteroaryl", "alkoxy" and "acyl" refer to non-halogen based compounds. The composition for the second retardation layer may comprise only the cellulose ester polymer or a mixture comprising the cellulose ester polymer.

Here, "halogen" means fluorine (F), Cl, Br or I, preferably F.

A "halogen-containing functional group" is an organic functional group that contains at least one halogen atom, and may include aromatic, aliphatic, or cycloaliphatic functional groups. For example, a halogen-containing functional group may refer to halogen-substituted C₁To C₂₀Alkyl, halogen substituted C₂To C₂₀Alkenyl, halogen substituted C₂To C₂₀Alkynyl, halogen substituted C₃To C₁₀Cycloalkyl, halogen substituted C₁To C₂₀Alkoxy, halogen-substituted acyl, halogen-substituted C₆To C₂₀Aryl or halogen substituted C₇To C₂₀Arylalkyl, but is not limited thereto.

The "halogen-substituted acyl" may be R ' -C (═ O) - (' is the linking site, R ' is halogen-substituted C₁To C₂₀Alkyl, halogen substituted C₃To C₂₀CycloalkanesAlkyl, halogen substituted C₆To C₂₀Aryl or halogen substituted C₇To C₂₀Arylalkyl). "halogen-substituted acyl" can be coupled to the cellulose ring via an ester bond (via an oxygen atom) in the cellulose.

Preferably, the composition for the second retardation layer may include a cellulose ester polymer substituted with an acyl group, a halogen or a halogen-containing functional group. More preferably, the halogen may be fluorine. The halogen can be present in the cellulose ester polymer in an amount of 1 wt% to 10 wt%. Within this range, the composition makes it easy to form the second retardation layer having the properties of the present invention, and the degree of circular polarization (ellipticity) can be improved. For example, the halogen can be present in the cellulose ester polymer in an amount of 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10 wt%.

To form the second retardation layer, the cellulose ester polymer may be prepared by typical methods known to those skilled in the art, or may be obtained from commercially available products. For example, the cellulose ester polymer having an acyl group as a substituent may be prepared by reacting trifluoroacetic acid or trifluoroacetic anhydride with a sugar monomer or a polymer of sugar monomers constituting the cellulose represented by formula 1, by reacting trifluoroacetic acid or trifluoroacetic anhydride therewith, and then additionally reacting an acylating agent (for example, carboxylic anhydride or carboxylic acid) therewith, or by reacting both trifluoroacetic acid or trifluoroacetic anhydride and the acylating agent therewith.

The polystyrene polymer may include a moiety represented by formula 2:

[ formula 2]

Wherein R is¹、R²And R³Each independently is a hydrogen atom, an alkyl group, a substituted alkyl group or a halogen; rs are each independently a substituent on the styrene ring; and n is an integer of 0 to 5 representing the number of substituents on the styrene ring.

Examples of the substituent R on the styrene ring may include an alkyl group, a substituted alkyl group, a halogen atom, a hydroxyl group, a carboxyl group, a nitro group, an alkoxy group, an amino group, a sulfonate group, a phosphate group, an acyl group, an acyloxy group, a phenyl group, an alkoxycarbonyl group, and a cyano group.

In one embodiment, R¹、R²And R³Is halogen, preferably fluorine.

The composition for the second retardation layer may further comprise an additive containing aromatic fused rings. Additives containing aromatic fused rings are used to adjust chromatic dispersion. Examples of the aromatic fused ring-containing additive may include 2-naphthyl benzoate, anthracene, phenanthrene, 2, 6-naphthalenedicarboxylic diester, and the like. The additive containing aromatic fused rings may be present in the composition for the second retardation layer in an amount of 0.1 to 30 wt%, preferably 1 to 10 wt%. Within this range, the additive containing aromatic condensed rings can adjust retardation and wavelength dispersion. For example, the aromatic fused ring-containing additive may be present in the composition for the second retardation layer in an amount of 0.1 wt%, 0.2 wt%, 0.3 wt%, 0.4 wt%, 0.5 wt%, 0.6 wt%, 0.7 wt%, 0.8 wt%, 0.9 wt%, 1 wt%, 2 wt%, 3 wt%, 4 wt%, 5 wt%, 6 wt%, 7 wt%, 8 wt%, 9 wt%, 10 wt%, 11 wt%, 12 wt%, 13 wt%, 14 wt%, 15 wt%, 16 wt%, 17 wt%, 18 wt%, 19 wt%, 20 wt%, 21 wt%, 22 wt%, 23 wt%, 24 wt%, 25 wt%, 26 wt%, 27 wt%, 28 wt%, 29 wt%, or 30 wt%.

The composition for the second retardation layer may further comprise typical additives known to those skilled in the art. The additives may include pigments and antioxidants, but are not limited thereto.

Although not shown in fig. 2, an adhesive layer or an adhesive layer is formed on the lower surface of the second retardation layer 130 so that the polarizing plate is stacked on a device of the optical display apparatus, for example, a light emitting diode panel.

Laminate of a first retardation layer and a second retardation layer

The laminate of the first and second retardation layers may have an in-plane retardation (Re) of 120nm to 200nm, preferably 140nm to 180nm, at a wavelength of 550 nm. Within this range, the polarizing plate can reduce the reflectance while increasing the degree of circular polarization. For example, a laminate of the first and second retarder layers may have an in-plane retardation (Re) of 120nm, 125nm, 130nm, 135nm, 140nm, 145nm, 150nm, 155nm, 160nm, 165nm, 170nm, 175nm, 180nm, 185nm, 190nm, 195nm, or 200nm at a wavelength of 550 nm.

The laminate of the first retardation layer and the second retardation layer may be formed by coating the composition for the second retardation layer on the first retardation layer and then performing oblique stretching with reference to the MD of the first retardation layer. Specifically, the laminate of the first retardation layer and the second retardation layer may be formed by coating the composition for the second retardation layer on the first retardation layer or on the non-stretched or obliquely stretched film for the first retardation layer in a non-stretched or obliquely stretched state, and then obliquely stretching in the MD direction or oblique direction with respect to the MD of the first retardation layer or the film for the first retardation layer. Preferably, the first retardation layer and the second retardation layer realize a retardation difference between the first retardation layer and the second retardation layer in the polarizing plate according to the present invention by oblique stretching in an oblique direction with respect to the MD of the first retardation layer or the film for the first retardation layer.

Polarizer

The polarizer 110 serves to convert natural light or polarized light into polarized light by linear polarization in a specific direction, and may be made of a polymer film substantially containing a polyvinyl alcohol resin. Specifically, the polarizer 130 may be prepared by dyeing a polymer film with iodine or a dichroic dye, and then stretching the film in MD. Specifically, the polarizer may be produced by swelling, dyeing, stretching, and crosslinking.

The polarizer 110 may have a total light transmittance of 40% or more, e.g., 40% to 47%, and a degree of polarization of 99% or more, e.g., 99% to 100%. Within this range, the polarizer may improve the anti-reflection property of the polarizing plate by being combined with the first retardation layer and the second retardation layer.

The polarizer 110 may have a thickness of 2 μm to 30 μm, specifically 4 μm to 25 μm. In this range, a polarizer may be used in the polarizing plate.

ComprisesIs provided withLayer of light absorber

The layer containing a light absorber contains a light absorber having a maximum absorption wavelength of 380nm to 420 nm. When the first retardation layer and the second retardation layer are laminated in the polarizing plate according to the present invention, the light absorber can help improve black visibility of the front surface. Herein, the "maximum absorption wavelength" refers to a wavelength at which the absorbance reaches a maximum value when measured in a light absorber solution diluted to a concentration of 10mg/L in chloroform. Preferably, the layer containing the light absorber may have a maximum absorption wavelength of 380nm to 400nm, more preferably 390nm to 400 nm. For example, the layer containing the light absorber may have a maximum absorption wavelength of 380nm, 385nm, 390nm, 395nm, 400nm, 405nm, 410nm, 415nm, or 420 nm.

In one embodiment, the layer containing a light absorber may have a light transmittance of 10% or less, for example, 5% or less, at a wavelength of 380 to 420 nm. In this range, the polarizing plate can improve the visual sensitivity of the front reflection. For example, the layer containing a light absorber can have a light transmittance of 0%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, or 10%.

The light absorbing agent may be selected from any light absorbing agents as long as the light absorbing agent can achieve the above-mentioned maximum absorption wavelength. In particular, the light absorber may include at least one selected from the group consisting of indole, phenylbenzotriazole, and triazine light absorbers. In the polarizing plate according to the present invention, these light absorbers can improve black visibility of the front surface.

The light absorber can be present in the layer containing the light absorber in an amount of 0.1 wt% to 6 wt%, for example 0.3 wt% to 5 wt%. Within this range, the light absorber can improve the front black visibility and reliability without bleeding out or affecting the retardation values of the first retardation layer and the second retardation layer. For example, the light absorber can be present in an amount of 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 2%, 3%, 4%, 5%, or 6% by weight.

The layer containing a light absorbing agent may be an adhesive layer or a non-adhesive layer depending on the kind of base resin forming the layer containing a light absorbing agent. In one embodiment, the layer containing a light absorbing agent may be an adhesive layer through which the polarizing plate according to the present invention may be attached to a panel or the like.

The layer containing the light absorber may have a thickness of 1 μm to 20 μm, specifically 5 μm to 1.5 μm. In this range, a layer containing a light absorbing agent may be used in the polarizing plate.

Fig. 1 shows a polarizing plate in which a layer 140 containing a light absorber is formed on the lower surface of a second retardation layer 130. Alternatively, the layer 140 containing the light absorbing agent may be formed between the first retardation layer 120 and the second retardation layer 130, between the polarizer 110 and the first retardation layer 120, and/or between the protective film 150 and the polarizer 110.

Protective film

A protective film 150 is formed on the upper surface of the polarizer 110 to protect the polarizer from the external environment while improving the mechanical strength of the polarizer.

The protective film 150 serves to protect the polarizer from the external environment, and may be an optically transparent film formed of, for example, at least one resin selected from cellulose resins including triacetyl cellulose (TAC) and the like, polyester resins including polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate (PEN), polybutylene naphthalate and the like, 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. Specifically, the protective film may be a TAC film or a PET film.

The protective film 150 may have a thickness of 5 μm to 70 μm, specifically 15 μm to 45 μm. Within this range, a protective film may be used in the polarizing plate.

Although not shown in fig. 1, a functional coating layer may be further formed on the upper surface of the protective film 150 to provide an additional function to the polarizer. For example, the functional coating may include a hard coat layer, an anti-fingerprint layer, and an anti-reflective layer. These functional coatings may be stacked individually or in combinations thereof.

Although not shown in fig. 1, the protective film 150 may be bonded to the polarizer 110 via a second adhesive layer. The second adhesive layer may be formed of at least one selected from a water-based adhesive and a photocurable adhesive. Preferably, the second adhesive layer is formed of a light-curable adhesive, whereby the adhesion between the protective film and the polarizer and the adhesion between the polarizer and the first retardation layer can be achieved by one light irradiation, thereby improving the workability of the polarizing plate.

The second adhesive layer may have a thickness of 0.1 μm to 10 μm, specifically 0.5 μm to 5 μm. Within this range, the second adhesive layer may be used in the polarizing plate.

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

In the polarizing plate according to the present embodiment, a protective film, a polarizer, a first retardation layer, a second retardation layer, and a layer containing a light absorbing agent may be sequentially stacked in this order, and a primer layer may be further formed on the lower surface of the first retardation layer. The primer layer is formed directly on the first retardation layer and the second retardation layer. The primer layer directly formed on the lower surface of the first retardation layer allows the second retardation layer to exhibit high adhesion to the first retardation layer and can prevent the first retardation layer from being blocked in a roll-to-roll process, thereby facilitating the formation of a laminate of the first and second retardation layers. In particular, when the first retardation layer is a cyclic polyolefin film that can be blocked, making it difficult to form the second retardation layer thereon by a roll-to-roll process, the workability of forming the primer layer on the first retardation layer at the time of forming the second retardation layer may be improved.

Now, the primer layer will be described in detail.

In one embodiment, the primer layer may comprise particles. Adjusting the size of the particles in the primer layer may improve the adhesion of the second retardation layer to the first retardation layer and the processability in forming a laminate of the first and second retardation layers. In one embodiment, the average particle diameter (D50) of the particles is less than the thickness of the primer layer, and may be betweenFor example in the range of 1nm to 500nm, preferably 100nm to 300 nm. Within this range, the primer layer may prevent the first retardation layer from being blocked and may improve 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 comprise a material selected from the group consisting of silica (e.g., silica) and titania (e.g., TiO)₂) But is not limited thereto.

The particles can be present in the primer layer in an amount of 10 wt% to 50 wt%, specifically 10 wt% to 30 wt%. Within this range, the primer layer may prevent the first retardation layer from being blocked when the first retardation layer is wound onto a roll, and may improve adhesion between the first retardation layer and the second retardation layer. For example, the particles can be present in the primer layer in an amount of 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, or 50 weight percent.

The primer layer may be formed by coating a composition including particles and a curable resin, and then curing. The curable resin may include at least one selected from a thermosetting resin and a photocurable resin, but is not limited thereto. For example, the curable resin may include modified or unmodified olefin resins such as acrylic, ethylene, and propylene resins, but is not limited thereto.

The primer layer may have a thickness of 100nm to 500nm, specifically 150nm to 300nm, which is greater than the average particle diameter of the particles. Within this range, the primer layer may prevent blocking of the first retardation layer, may increase adhesion of the second retardation layer, and may reduce the thickness of the polarizing plate.

In another embodiment, the primer layer may be formed by coating a composition comprising a particle-free curable resin, followed by curing.

In further embodiments, the polarizer may further include a third retardation layer.

Next, a polarizing plate according to a further embodiment of the present invention will be described with reference to fig. 3.

Referring to fig. 3, the polarizing plate includes a protective film 140, a polarizer 110, a third retardation layer 160, a first retardation layer 120, and a second retardation layer 130. The polarizing plate according to this embodiment is substantially the same as the polarizing plate shown in fig. 1, except that a third retardation layer 160 is additionally formed between the polarizer 110 and the first retardation layer 120.

By the structure in which the third retardation layer 160 is additionally formed between the polarizer 110 and the first retardation layer 120, the reflectance of the polarizer at the side surface can be further improved.

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

In one embodiment, the third retardation layer may have an out-of-plane retardation (Rth) of-300 nm to 0nm, for example, -200nm to-30 nm, at a wavelength of 550 nm. The third retardation layer may have an in-plane retardation (Re) of 0nm to 10nm, for example 0nm to 5nm, at a wavelength of 550 nm. In this range, the polarizing plate can achieve a reduction in reflectance of the front surface.

In one embodiment, the third retardation layer 160 may be a liquid crystal layer. The liquid crystal layer may be formed of a known typical material realizing the above-described out-of-plane retardation (Rth).

In another embodiment, the third retarder layer 160 may be formed of the composition for the second retarder layer described above.

The optical display device according to the present invention may include the polarizing plate according to an embodiment of the present invention. For example, the optical display device may include an Organic Light Emitting Diode (OLED) display and a liquid crystal display.

In one embodiment, an OLED display device may include: an OLED panel including a flexible substrate; and a polarizer according to the present invention stacked on the OLED panel.

In another embodiment, an OLED display device may include: an OLED panel including a non-flexible substrate; and a polarizer according to the present invention stacked on the OLED panel.

Next, the present invention will be described in more detail with reference to examples. It should be understood, however, that these examples are provided for illustrative purposes only and should not be construed as limiting the invention in any way.

Example 1

A polyvinyl alcohol film (PS #60, pre-stretched thickness: 60 μm, Kuraray co., ltd., Japan) was stretched to 6 times its original length in an iodine aqueous solution at 55 deg.c, thereby preparing a polarizer 12 μm thick having a transmittance of 43%.

The coating layer for the second retardation layer was formed by depositing a composition for the second retardation layer [ an amorphous composition comprising a cellulose ester polymer (comprising trifluoroacetyl group) ] on the lower surface of a cyclic polyolefin (COP) film (ZD film, Zeon co., Ltd.) stretched at an angle of 45 ° with respect to the MD. Cellulose ester polymers are prepared by adding trifluoroacetic acid and trifluoroacetic anhydride to unsubstituted cellulose, followed by reaction and polymerization.

After drying the coating, the laminate of the coating and COP film was stretched to an elongation of 1.5 times at 135 ℃ with respect to the MD of the COP film, thereby producing a laminate having a first retardation layer (positive wavelength dispersion) and a second retardation layer (positive wavelength dispersion) of the specifications listed in table 1.

A TAC film (thickness: 27 μm, Konica Minolta co., Ltd.) was adhered to the upper surface of the polarizer via an adhesive layer by depositing an adhesive for a polarizing plate on the upper surface of the polarizer as a protective layer, and a laminate of a first retardation layer and a second retardation layer was attached to the lower surface of the polarizer by depositing an adhesive for a polarizing plate on the lower surface of the polarizer, and then irradiated with UV light in a direction from the lower surface of the second retardation layer to the protective film.

A composition containing a light absorber (maximum absorption wavelength: 391nm, indole-based light absorber, Bonasorb UA3912, Orient chemical co., Ltd.) and an isocyanate curing agent (Coronate L) was prepared with respect to 100 parts by weight of a (meth) acrylic adhesive resin. The composition was deposited on the lower surface of the second retardation layer at a predetermined thickness and then cured to form a layer (thickness: 10 μm) containing a light absorber, thereby forming a polarizing plate. As shown in Table 1, in the layer containing the light absorber, the content (unit: wt%) of the light absorber was adjusted.

Examples 2 to 4

A polarizing plate was manufactured in the same manner as in example 1, except that the retardation of each of the first and second retardation layers and the content of the light absorbing agent in the layer containing the light absorbing agent were changed as listed in table 1.

Example 5

A polarizing plate comprising a TAC film, a polarizer, a third retardation layer, a first retardation layer and a second retardation layer stacked in this order was manufactured in the same manner as in example 1, except that a positive C layer (read 550 nm: 0.3nm, rth 550 nm: -35nm) was additionally formed as the third retardation layer on the upper surface of the first retardation layer.

Comparative example 1

A polarizing plate was manufactured in the same manner as in example 1, except that a composition comprising 100 parts by weight of a (meth) acrylic adhesive resin and 9 parts by weight of an isocyanate curing agent (Coronate L) was used instead of the layer containing a light absorbing agent to form an adhesive layer.

Comparative examples 2 to 8

A polarizing plate was manufactured in the same manner as in example 1, except that the in-plane retardation of each of the first and second retardation layers and/or the angle of the slow axis of each of the first and second retardation layers with respect to the transmission axis of the polarizer was changed as listed in table 1.

The retardation values Re, Rth and NZ of each of the first and second retardation layers were measured at a wavelength of 550nm using an Axoscan polarimeter (AxoMetric co., Ltd.).

Each of the polarizing plates manufactured in examples and comparative examples was evaluated for the following properties. The results are shown in Table 1.

(1) Reflectance (unit:%): the reflectance was measured using an goniometer (DMS 803, Instrument Systems Inc. (Konica Minolta Group), Japan). After the measurement of the whiteboard supplied to the goniometer, the brightness and contrast are measured using the angle scanning function. Each of the polarizing plates manufactured in examples and comparative examples was adhered to a panel (glass substrate) by a pressure-sensitive adhesive, and then front and side reflectances were measured. Here, θ was measured at intervals of 5 °, and the reflectance was determined by obtaining spectral transmittance/reflectance (SCE) values of incident light from the front face (0 °) and the side face (60 °).

(2) Black visibility color values a and b: a module for an optical display apparatus was manufactured by attaching each polarizer manufactured in examples and comparative examples to the upper surface of an organic light emitting diode panel via a layer containing a light absorber. The module for an optical display device was irradiated with light in a direction from the polarizer to the front surface (0.05 °) using a spectrophotometer DMS 803(Instrument Systems), and light was reflected and leaked from the polarizer of each of the examples and comparative examples, and black visibility color values a and b of the front surface of the organic light emitting diode panel were measured according to the CIE 1976a b standard.

(3) Ellipticity (%): the ellipticity was measured by passing the optical side (60 °) through a polarizer using an Axoscan polarimeter. The ellipticity was then measured by passing light through the polarizer at the side (60 °) while rotating the polarimeter 360 degrees. The minimum value of the circular polarization degree at the side face (60 °) is shown in table 1.

TABLE 1

Angle 1: angle of slow axis of first retardation layer with respect to transmission axis of polarizer

Angle 2: angle of slow axis of second retardation layer with respect to transmission axis of polarizer

As shown in table 1, the polarizing plate according to the present invention has low reflectance at both front and side surfaces, satisfies the relationship between color values a and b to improve black visibility of the front surface, and satisfies an ellipticity of 62% or more.

In contrast, the polarizing plate of comparative example 1, which did not include the layer containing the light absorbing agent, did not improve the visibility of black at the front surface because the relationship between the color values a and b could not be satisfied, and the polarizing plates of comparative examples 2 to 8, which did not satisfy the conditions of the first retardation layer and the second retardation layer according to the present invention, had higher reflectance than the polarizing plate according to the present invention despite the presence of the layer containing the light absorbing agent, and did not improve the visibility of black at the front surface because the relationship between the color values a and b could not be satisfied.

Although a few embodiments have been described herein, it will be appreciated that various modifications, alterations, changes, and equivalents may be made by those skilled in the art without departing from the spirit and scope of the invention.

Claims

1. 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 first retardation layer has an in-plane retardation of 180nm to 240nm at a wavelength of 550 nm;

the second retardation layer has an in-plane retardation of 70nm to 120nm at a wavelength of 550 nm;

the polarizing plate further includes a layer containing a light absorbing agent; and is

The slow axis of the first retardation layer is inclined at an absolute value of an angle α 1 of 60 ° to 80 ° with respect to the transmission axis of the polarizer, and the slow axis of the second retardation layer is inclined at an absolute value of an angle α 2 of 0 ° to 10 ° with respect to the transmission axis of the polarizer.

2. The polarizing plate according to claim 1, wherein the layer containing a light absorber comprises a light absorber having a maximum absorption wavelength of 380nm to 420 nm.

3. The polarizing plate according to claim 2, wherein the light absorber is present in the layer containing the light absorber in an amount of 0.1 to 6 wt%.

4. The polarizing plate according to claim 2, wherein the light absorber comprises at least one selected from the group consisting of indole, phenylbenzotriazole and triazine light absorbers.

5. The polarizing plate according to claim 1, wherein the first retardation layer and the second retardation layer each exhibit positive wavelength dispersion.

6. The polarizing plate according to claim 1, wherein a laminate of the first retardation layer and the second retardation layer has an in-plane retardation of 120nm to 200nm at a wavelength of 550 nm.

7. The polarizer of claim 1, wherein the first retarder layer has a positive out-of-plane retardation at a wavelength of 550nm and the second retarder layer has a negative out-of-plane retardation at a wavelength of 550 nm.

8. The polarizing plate according to claim 1, wherein the first retardation layer has a positive biaxial degree at a wavelength of 550nm, and the second retardation layer has a negative biaxial degree at a wavelength of 550 nm.

9. The polarizing plate according to claim 1, wherein an angle defined between the slow axis of the first retardation layer and the slow axis of the second retardation layer is in a range of 50 ° to 70 °.

10. The polarizing plate according to claim 1, wherein the angle α 1 is in a range of +60 ° to +80 ° and the angle α 2 is in a range of 0 ° to +10 °, or the angle α 1 is in a range of-80 ° to-60 ° and the angle α 2 is in a range of-10 ° to 0 °.

11. The polarizing plate according to claim 1, wherein the layer containing a light absorber is formed on a lower surface of the second retardation layer, between the first retardation layer and the second retardation layer, and/or between the polarizer and the first retardation layer.

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

13. The polarizing plate according to claim 1, further comprising: a protective layer formed on an upper surface of the polarizer.

14. The polarizing plate according to claim 1, further comprising: and a positive C layer.

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