KR20210007465A - Polarizing Plate - Google Patents

Abstract

This application relates to a polarizing plate. One object of the present application is to provide a polarizing plate that can be applied to a display device to secure a high CR (Contrast Ratio) even at an inclination angle, and can secure a uniform color in all directions of an inclination angle. In one example, the polarizing plate of the present application may be applied to a liquid crystal panel in a so-called plane switching mode, and the liquid crystal panel in a plane switching mode may be a liquid crystal panel having a non-contact alignment layer.

Description

Polarizing Plate

This application relates to a polarizing plate.

A liquid crystal display (LCD) may be classified into a twisted nematic (TN) mode, a vertical alignment (VA), and an in-plane switching (IPS) mode. In the TN (Twisted Nematic) mode, although a liquid crystal display having a relatively simple structure, there is a problem in that the viewing angle is limited because the arrangement of liquid crystals is asymmetric according to the viewing angle.

VA (Vertical Alignment) and IPS (In-Plane Switching) modes have been studied to compensate for the shortcomings of the TN mode. In particular, the IPS mode is advantageous for realizing a wide viewing angle.

In general, a liquid crystal display includes a liquid crystal panel, and the liquid crystal panel includes a liquid crystal material 200 between two substrates 101 and 102 oppositely disposed as shown in FIG. 3. As shown in the figure, the edges of the two substrates 101 and 102 are sealed with a so-called sealant 300, and a liquid crystal material is positioned between them. Liquid crystal alignment layers 401 and 402 are present on the surfaces of the substrates 101 and 102 facing the liquid crystal material, and the alignment direction of the liquid crystal alignment layers 401 and 402 is determined according to the mode of the liquid crystal panel. Polarizing plates 501 and 502 are usually attached to both sides of such a liquid crystal panel.

As the liquid crystal alignment layers 401 and 402, a so-called rubbing alignment layer, a layer to which alignment is imparted by a rubbing treatment, is mainly used, and recently, a non-contact alignment layer such as a photo-alignment layer is also applied.

Various optical structures have been proposed to compensate for the conventional so-called In-Plane Switching mode, and most of these optical structures are designed in consideration of the asymmetry of the liquid crystal panel itself.

That is, since the conventional rubbing alignment layer has a large pre-tilt angle of more than a certain level, liquid crystal materials have an asymmetry of more than a certain level. Therefore, most of the conventional optical compensation structures also consider the asymmetry of the liquid crystal panel.

However, recently applied non-contact alignment films (e.g., photo-alignment films) have little or no pretilt, or their angles are very small, so the liquid crystal panel has more symmetrical properties, but a conventional optical compensation structure is appropriate for such a new liquid crystal panel. There is a problem that cannot be applied properly.

This application relates to a polarizing plate. One object of the present application is to provide a polarizing plate that can be applied to a display device to secure a high CR (Contrast Ratio) even at an inclination angle, and can secure a uniform color in all directions of an inclination angle. In one example, the polarizing plate of the present application may be applied to a liquid crystal panel in a so-called plane switching mode, and the liquid crystal panel in a plane switching mode may be a liquid crystal panel having a non-contact alignment layer.

The reference wavelength of optical properties such as retardation, refractive index and/or refractive index anisotropy mentioned in the present specification is approximately 550 nm unless otherwise specified.

In the present specification, the term in-plane retardation is an optical characteristic defined by Equation 1 below, the retardation in the thickness direction is an optical characteristic defined by Equation 2 below, and the Nz coefficient is an optical characteristic determined by Equation 3 below.

[Equation 1]

R _in = d × (n _x -n _y )

[Equation 2]

R _th = d × (n _z -n _y )

[Equation 3]

Nz = (n _x -n _z ) / (n _x -n _y )

In Equations 1 to 3, R _in is the in-plane retardation, R _th is the retardation in the thickness direction, d is the thickness of the layer, n _x is the refractive index in the slow axis direction of the layer, and n _y is the refractive index in the fast axis direction of the layer, n _z is the refractive index in the thickness direction of the layer.

In the above, the term layer is a layer to be measured of an in-plane retardation, a thickness direction retardation, and/or an Nz coefficient, and thus, for example, a layer in the above formulas for obtaining an in-plane retardation, a thickness direction retardation, and an Nz coefficient of the retardation layer. Is the phase difference layer.

In this specification, the terms vertical, horizontal, orthogonal and parallel are vertical, horizontal, orthogonal and parallel in a practical sense, and are within approximately ±10 degrees, within ±9 degrees, within ±8 degrees, and within ±7 degrees, Errors within ±6 degrees, within ±5 degrees, within ±4 degrees, within ±3 degrees, within ±2 degrees, or within ±1 degrees may be included.

The term inclination angle referred to in this specification is defined as follows unless otherwise specified. In Fig. 2, when the plane formed by the x-axis and y-axis is referred to as a reference plane (for example, the reference plane may be a display surface on which an image is displayed in a display device or a surface of a polarizing plate), the z-axis, which is the normal line of the reference plane For this, the angle formed as in FIG. 2 is defined as the inclination angle (the inclination angle at point P in FIG. 2 is Θ). In Fig. 2, when the plane formed by the x-axis and y-axis is referred to as a reference plane (for example, the reference plane may be a display surface on which an image is displayed in a display device or a surface of a polarizing plate), the x-axis of the reference plane is set to 0 degrees. At this time, the angle formed as shown in FIG. 2 with respect to the x-axis is defined as the moving angle (the moving angle at point P in FIG. 2 is Φ).

The polarizing plate of the present application may include at least a polarizing layer and first and second retardation layers present under the polarizing layer. In the above, the polarization layer may be an absorption type or a reflection type polarization layer, and in an example, it may be an absorption type linear polarization layer. Accordingly, the absorption-type polarizing layer may have a transmission axis formed in one direction and an absorption axis formed in a different direction. In general, in the absorption type linear polarization layer, the transmission axis and the absorption axis are formed perpendicular to each other.

In the polarizing plate of the present application, the first and second retardation layers may be positioned on one surface of the polarizing layer, and specifically, may be positioned below the polarizing layer. In this specification, the term “lower” refers to a direction from the polarizing layer toward the first or second retardation layer, and the upper part refers to the opposite direction. In one example, when the polarizing plate of the present application is applied to a liquid crystal display device, the lower portion may coincide with a direction from the polarizing plate toward the display device.

In the present specification, the term polarizing layer refers to a film, sheet, or device having a reflective or absorbing polarizing function. The polarizing layer is a functional device capable of extracting light vibrating in one direction from incident light vibrating in several directions.

In the present application, as the polarizing layer, an absorption type linear polarizing layer may be used. As such a polarizing layer, a poly(vinyl alcohol) (PVA) polarizing layer is typically known, but the type of polarizing layer that can be applied in the present application is not limited to the PVA polarizing layer. For example, as a polarizing layer including a liquid crystal host and a dichroic dye polymerized in a horizontally oriented state, a polarizing layer known as a coating type polarizing layer may also be applied in the present application.

Various polarizing layers as described above are known, and a method of manufacturing or obtaining such a polarizing layer is also well known. In the present application, such known polarizing layers may be applied without any particular limitation.

There is no particular limitation on the thickness of the applied absorption-type polarizing layer, and may have a thickness of a known polarizing layer. Usually, the thickness of the polarizing layer may be in the range of about 0.5 um to 30 um.

First and second retardation layers are present under the polarizing layer of the polarizing plate of the present application. In one example, in the polarizing plate, the first retardation layer is present under the polarizing layer, and the second retardation layer is present under the first retardation layer, so that the polarizing layer 300 and the second retardation layer are present as shown in FIG. 3. The first phase difference layer 100 and the second phase difference layer 200 may be stacked in the above order. Hereinafter, the structure shown in FIG. 3 may be referred to as the first structure of the present application.

In an example, the present application is applied to a display device, particularly an IPS (In-Plane Switching) mode liquid crystal display device having a non-contact alignment layer by designing the optical properties of each phase difference layer as follows with the positional relationship as described above. It is possible to provide a polarizing plate capable of securing a high CR (Contrast Ratio) even at an inclination angle and securing a uniform color in all directions of the inclination angle.

In the first structure, the first retardation layer has a retardation in the thickness direction (based on a wavelength of 550 nm) of approximately 20 to 90 nm. The thickness direction retardation is about 25 nm or more, about 30 nm or more, 35 nm or more, 40 nm or more, 45 nm or more, 50 nm or more, 55 nm or more, 60 nm or more, 65 nm or more, 70 nm or more, or 75 nm or more, or , 85 nm or less, 80 nm or less, 75 nm or less, 70 nm or less, 65 nm or less, 60 nm or less, 55 nm or less, 50 nm or less, 45 nm or less, 40 nm or less, or 35 m or less.

In the first structure of the present application, a second retardation layer is present under the first retardation layer of the polarizing plate. The second retardation layer may be in contact with the first retardation layer, or other elements may exist between the first and second retardation layers.

In the first structure, a retardation layer having an Nz coefficient of 0.4 to 1 according to Equation 3 may be applied as the second retardation layer. The Nz coefficient is, in another example, about 0.45 or more, 0.5 or more, 0.55 or more, 0.6 or more, 0.65 or more, 0.7 or more, or 0.75 or more, about 0.95 or less, 0.9 or less, 0.85 or less, 0.8 or less, 0.75 It may be less than or equal to 0.7, less than or equal to 0.65, less than or equal to 0.6, or less than or equal to 0.55. The Nz coefficient is a measure of the biaxiality of the retardation layer, and the retardation layer having the Nz coefficient in the above-described range reduces light leakage from the polarizing plate at an inclination angle, thereby being combined with the first retardation layer. The purpose of the present application, such as widening the viewing angle, can be effectively achieved.

In the first structure, the second retardation layer has an in-plane retardation based on a wavelength of 550 nm in a range of approximately 150 nm to 200 nm. In other examples, the in-plane retardation is about 151 nm or more, 152 nm or more, 153 nm or more, 154 nm or more, 155 nm or more, 156 nm or more, 157 nm or more, 158 nm or more, 159 nm or more, 160 nm Anomaly, 161 nm or more, 162 nm or more, 163 nm or more, 164 nm or more, 165 nm or more, 166 nm or more, 167 nm or more, 168 nm or more, 169 nm or more, 170 nm Anomaly, 171 nm or more, 172 nm or more, 173 nm or more, 174 nm or more, or 175 nm or more, 195 nm or less, 194 nm or less, 193 nm or less, 192 nm or more, 191 nm or less, 190 nm or less, 189 nm or less, 188 nm or less, 187 nm or less, 186 nm or less, 185 nm or less, 184 nm or less, 183 nm or less, 182 nm or less, 181 It may be about nm or less, about 180 nm or less, about 179 nm or less, about 178 nm or less, about 177 nm or less, about 176 nm or less, or about 175 nm or less.

In the above arrangement of the polarizing plate, the slow axis of the second retardation layer may be parallel to the absorption axis of the polarizing layer. In the above, the term parallelism is substantially parallel and means that the axes form an angle within a range of approximately 170 degrees to 190 degrees. As described above, by making the slow axis of the second phase difference layer and the absorption axis of the polarizing layer parallel to each other, the optical path may be controlled so that the desired effect of the present application can be achieved.

In another example, the angle of the axis is approximately 171 degrees or more, 172 degrees or more, 173 degrees or more, 174 degrees or more, 175 degrees or more, 176 degrees or more, 177 degrees or more, 178 degrees or more, 179 degrees or more, or 180 degrees or more, or 189 It may be less than or equal to 188 degrees, less than 187 degrees, less than 186 degrees, less than 185 degrees, less than 184 degrees, less than 183 degrees, less than 182 degrees, less than 181 degrees, or less than 180 degrees.

In another example, in the polarizing plate, the second phase difference layer is present under the polarizing layer, and the first phase difference layer is present under the second phase difference layer, so that the polarizing layer 300 as shown in FIG. , The second phase difference layer 200 and the first phase difference layer 100 may be stacked in the above order. Hereinafter, the structure of FIG. 4 may be referred to as the second structure of the present application.

In another example, by designing the optical properties of each phase difference layer as follows with the positional relationship as described above, the present application is applied to a display device, particularly a liquid crystal display device of an IPS (In-Plane Switching) mode having a non-contact alignment layer. As a result, it is possible to provide a polarizing plate capable of securing a high CR (Contrast Ratio) even at an inclination angle and securing a uniform color in all directions of an inclination angle.

In the second structure of the present application, a retardation layer having an Nz coefficient in the range of 0.4 to 1 according to Equation 3 is applied as the second retardation layer. In another example, the Nz coefficient is about 0.45 or more, about 0.5 or more, about 0.99 or less, 0.98 or less, 0.97 or less, 0.96 or less, 0.95 or less, 0.94 or less, 0.93 or less, 0.92 or less, It may be 0.91 or less, 0.9 or less, 0.89 or less, 0.88 or less, 0.87 or less, 0.86 or less, 0.85 or less, 0.84 or less, 0.83 or less, 0.82 or less, 0.81 or less, or 0.8 or less. The Nz coefficient is a measure of the biaxiality of the retardation layer, and the retardation layer having the Nz coefficient in the above-described range reduces light leakage from the polarizing plate at an inclination angle, thereby being combined with the first retardation layer. The purpose of the present application, such as widening the viewing angle, can be effectively achieved.

In the second structure, the second retardation layer has an in-plane retardation based on a wavelength of 550 nm in a range of approximately 160 nm to 250 nm. In another example, the in-plane retardation is about 165 nm or more, about 170 nm or more, 176 nm or more, 177 nm or more, 178 nm or more, 179 nm or more, 180 nm or more, 181 nm or more, 182 nm or more , 183 nm or more, 184 nm or more, 185 nm or more, 186 nm or more, 187 nm or more, 188 nm or more, 189 nm or more, 190 nm or more, 191 nm or more, 192 nm or more , 193 nm or more, 194 nm or more, or 195 nm or more, about 245 nm or less, about 240 nm or less, about 235 nm or less, about 230 nm or less, about 225 nm or less, about 220 nm or less, about 215 nm or less , 214 nm or less, 213 nm or less, 212 nm or less, 211 nm or less, 210 nm or less, 209 nm or less, 208 nm or less, 207 nm or less, 206 nm or less, 205 nm or less , 204 nm or less, 203 nm or less, 202 nm or less, 201 nm or less, 200 nm or less, 199 nm or less, 198 nm or less, 197 nm or less, 196 nm or less, or 195 nm or less I can.

In the second structure, the first retardation layer has a retardation in a thickness direction (based on a wavelength of 550 nm) of approximately 40 to 100 nm. In another example, the retardation in the thickness direction is about 45 nm or more, about 50 nm or more, 55 nm or more, 60 nm or more, 65 nm or more, or 70 nm or more, or about 95 nm or less, about 90 nm or less, 85 nm or less, 80 nm or less , 75 nm or less or 70 nm or less.

In the above arrangement of the polarizing plate, the slow axis of the second retardation layer may be perpendicular to the absorption axis of the polarizing layer. In the above, the term vertical is substantially vertical and means that the axes form an angle within a range of approximately 80 degrees to 100 degrees. In the above arrangement, the optical path may be controlled so that the effect of the present application can be achieved by making the slow axis of the second phase difference side and the absorption axis of the polarizing layer perpendicular to each other.

In other examples, the angle of the axis is approximately 81 degrees or more, 82 degrees or more, 83 degrees or more, 84 degrees or more, 85 degrees or more, 86 degrees or more, 87 degrees or more, 88 degrees or more, 89 degrees or more, or 90 degrees or more, 99 degrees. Below, it may be 98 degrees or less, 97 degrees or less, 96 degrees or less, 95 degrees or less, 94 degrees or less, 93 degrees or less, 92 degrees or less, 91 degrees or less, or 90 degrees or less.

The first retardation layer of the first and/or second structure may be a layer that does not substantially have an in-plane retardation layer. The in-plane retardation (based on a 550 nm wavelength) of such a first retardation layer is, for example, approximately 10 nm or less, 9 nm or less, 7 nm or less, 6 nm or less, 5 nm or less, 4 nm or less, 3 nm or less, 2 nm Or less or 1 nm or less, or substantially 0 nm.

In the case of the first retardation layer, substantially no in-plane retardation as described above, and thus the arrangement of its slow axis does not significantly affect the performance of the polarizing plate. However, when there is a slow axis in the first phase difference layer, the arrangement may be vertical or horizontal with the absorption axis of the polarizing layer.

It is effective that the first retardation layer of the first and/or second structure exhibits a wavelength dispersion characteristic designed in a predetermined range while the retardation based on the 550 nm wavelength is within the above-described range. For example, the first phase difference layer may have a dispersion coefficient of 1 or less according to Equation 4 below.

[Equation 4]

Variance coefficient = R _th (450)/R _th (550)

In Equation 4, R _th (450) is the retardation in the thickness direction based on the 450 nm wavelength of the first retardation layer, and R _th (550) is the retardation in the thickness direction based on the 550 nm wavelength of the first retardation layer.

If the first retardation layer exhibits a dispersion characteristic of the retardation in the thickness direction in the above range, it may exhibit an appropriate level of compensation function according to the wavelength in the visible light region through a combination of the retardation value described above and the second retardation layer described later, Accordingly, the brightness and color characteristics desired in the present application can be effectively secured.

In another example, the dispersion coefficient is 0.99 or less, 0.98 or less, 0.97 or less, 0.96 or less, 0.95 or less, 0.94 or less, 0.93 or less, 0.92 or less, 0.91 or less, or 0.90 or less, or 0.1 or more, 0.2 or more, 0.3 or more, 0.4 or more, 0.5 or more, 0.6 or more, 0.7 or more, 0.8 or more, 0.81 or more, 0.82 or more, 0.83 or more, or 0.84 or more, 0.85 or more, about 0.86 or more, about 0.87 or more, about 0.88 or more, about 0.89 or more, or about 0.9 or more.

The second retardation layer of the first and/or second structure may also have dispersion characteristics designed in a predetermined range. The second phase difference layer may have a dispersion coefficient of 1 or less according to Equation 5 below.

[Equation 5]

Variance Coefficient = R _in (450)/R _in (550)

In Equation 5, R _in (450) is the in-plane retardation based on the 450 nm wavelength of the second retardation layer, and R _in (550) is the in-plane retardation based on the 550 nm wavelength of the second retardation layer.

The degree of dispersion of the in-plane retardation is controlled as described above, and the second retardation layer, in which the in-plane retardation and Nz coefficient are controlled, is combined with the first retardation layer at a predetermined position to perform an appropriate compensation function for light in the visible region according to the wavelength. It achieves an effect suitable for the purpose of the present application.

In another example, the dispersion coefficient is 0.99 or less, 0.98 or less, 0.97 or less, 0.96 or less, 0.95 or less, 0.94 or less, 0.93 or less, 0.92 or less, 0.91 or less, or 0.90 or less, or 0.1 or more, 0.2 or more, 0.3 or more, 0.4 or more, It may be 0.5 or more, 0.6 or more, 0.7 or more, 0.8 or more, 0.81 or more, 0.82 or more, 0.83 or more, or 0.84 or more.

The polarizing plate may include other elements above and/or below the polarizing layer and the first and second retardation layers. However, the polarizing plate may include only the first and second retardation layers as retardation layers. That is, the polarizing plate may further include only a so-called isotropic layer except for the polarizing layer and the first and second retardation layers. The isotropic layer referred to in the present specification may be treated as an isotropic layer as long as it has a phase difference that does not damage the optical structure designed for the polarizing plate even if the layer has a certain phase difference as a substantially isotropic layer. In one example, the term isotropic layer referred to in the present application is a layer in which the in-plane retardation and the retardation in the thickness direction are simultaneously 20 nm or less. The phase difference is 19 nm or less, 18 nm or less, 17 nm or less, 16 nm or less, 15 nm or less, 14 nm or less, 13 nm or less, 12 nm or less, 11 nm or less, 10 nm or less, 9 nm or less, It may be 8 nm or less, 7 nm or less, 6 nm or less, 5 nm or less, 4 nm or less, 3 nm or less, 2 nm or less, 1 nm or less, or 0 nm. Thus, on the contrary, a layer in which any one of the in-plane retardation and the thickness direction retardation exceeds 20 nm may be treated as a retardation layer in the present application.

As the first and second retardation layers, various types of retardation layers may be used without limitation, as long as the above-mentioned characteristics are satisfied.

Usually, as the retardation layer, a liquid crystal film or liquid crystal polymer film formed by aligning and polymerizing a polymerizable liquid crystal compound (so-called RM (Reactive Mesogen)), or a stretched polymer film imparting optical anisotropy by stretching such as uniaxial or biaxial stretching. Applied, as long as the above-described characteristics are satisfied, all known retardation layers as described above may be used.

Various polymerizable liquid crystal compounds (so-called RM (Reactive Mesogen)) that can be applied to the production of a liquid crystal film are also known, and a method of manufacturing a liquid crystal film by applying the same is also known. As the polymerizable liquid crystal compound as described above, a so-called polymerizable nematic liquid crystal compound, a polymerizable smectic liquid crystal compound, and the like are known. Although it is effective to apply such a polymerizable liquid crystal compound from the viewpoint of ease of adjustment of the dispersion coefficient, other types of films are applicable as long as the requirements of the present application are satisfied.

As the stretched polymer film, for example, a polyolefin film such as a polyethylene film or a polypropylene film, a cyclic olefin polymer (COP) film such as a polynorbornene film, an acrylic film, a polyvinyl chloride film, and a polyacrylic film. Cellulose ester polymer films such as ronitrile film, polysulfone film, polyacrylate film, polyvinyl alcohol film or triacetyl cellulose (TAC) film, or PET (poly(ethylene terephthalate)) film or PC (polycarbonate) film, etc. Among the monomers forming the polyester film or the polymer, a copolymer film of two or more monomers may be exemplified. In one example, as the polymer film, a cyclic olefin polymer film or an acrylic film may be used. In the above, as the cyclic olefin polymer, a cyclic olefin ring-opening polymer such as norbornene or a hydrogenated product thereof, an addition polymer of a cyclic olefin, a copolymer of another comonomer such as a cyclic olefin and an alpha-olefin, or the polymer or Graft polymers in which the copolymer is modified with an unsaturated carboxylic acid or derivative thereof may be exemplified, but are not limited thereto.

In one example, as the first retardation layer, a so-called vertically aligned liquid crystal film, a liquid crystal layer including a polymerized vertically aligned polymerizable liquid crystal compound, or a film exhibiting desired physical properties among the stretched polymer films may be applied. have.

In one example, as the second phase difference layer, a so-called horizontally aligned liquid crystal film, a liquid crystal layer including a polymerized horizontally aligned polymerizable liquid crystal compound, or a film exhibiting desired physical properties among the stretched polymer films may be applied. have.

There is no particular limitation on the thickness of the first and second retardation layers, and an appropriate type may be selected within a range capable of representing a desired retardation.

The types of the first and second phase difference layers are controlled as described above, and are combined at a predetermined position to provide an appropriate compensation function for light in the visible region according to the wavelength, thereby providing excellent CR (Contrast Ratio), color and visual characteristics even at an inclination angle. A polarizing plate that can be maintained can be provided.

The polarizing plate of the present application may include various additional elements in addition to the above-described elements. As the type of such a layer, other polymer films such as a polarizing layer protective film, an alignment layer, a release layer, a hard coating layer, a low reflection layer, an antireflection layer, an adhesive layer, or an adhesive layer may be exemplified, but is not limited thereto. The specific type of each layer is not particularly limited, and for example, various types used to construct a polarizing plate having an optical function desired in the industry may be used without limitation.

In order to secure proper performance, the polarizing plate of the present application includes the polarizing layer protective film attached to one surface of the polarizing layer, and the first and second retardation layers are directly provided without a protective film on the other surface of the polarizing layer. It can have structures attached in sequence. In addition, a pressure-sensitive adhesive layer or an adhesive layer for attaching the polarizing plate to the display device may be present under the second retardation layer.

The present application also relates to a display device. An exemplary display device may include the polarizing plate.

The specific type of the display device including the polarizing plate is not particularly limited. The device may be, for example, a liquid crystal display device such as a reflective or semi-transmissive liquid crystal display, or an organic light emitting device.

The arrangement form of the polarizing plate in the display device is not particularly limited, and for example, a known form may be employed.

As described above, the polarizing plate is applied to a liquid crystal display device of an IPS (In-Plane Switching) mode among various display devices to enable effective optical compensation. In particular, in a liquid crystal display of the IPS mode to which a non-contact alignment layer (photo-alignment layer, etc.) is applied. It can be applied effectively. In one example, the polarizing plate may be applied as a viewing side polarizing plate of the liquid crystal display. The meaning of the viewing-side polarizing plate is as known, for example, in two polarizing plates applied to a liquid crystal display, a polarizing plate disposed close to the backlight is a rear-side polarizing plate, and another polarizing plate, that is, disposed further away from the backlight among the two polarizing plates. The polarizing plate is a rear-side polarizing plate. In the present application, for example, as the polarizing plate as described above, it can be effectively applied to a liquid crystal display in which the in-plane retardation of the liquid crystal layer at the time of horizontal alignment is in the range of about 100 to 500 nm and about 200 to 450 nm based on the 550 nm wavelength. have.

The configuration of the IPS mode liquid crystal display to which the polarizing plate of the present application is applied is not particularly limited. That is, the polarizing plate may be applied in a known IPS mode liquid crystal display according to a known application method of the polarizing plate, and the applicable IPS liquid crystal display mode includes a so-called O mode or E mode, and is not particularly limited.

Such a liquid crystal display generally includes two substrates disposed opposite to each other; A liquid crystal layer positioned between the two substrates; And a liquid crystal panel in an IPS (planar switching) mode including a liquid crystal alignment layer disposed between the liquid crystal layer and at least one of the two substrates, and a polarizing plate attached to both sides of the liquid crystal panel, The polarizing plate described above can be used as the polarizing plate disposed on at least one surface of the polarizing plate. In this case, the polarizing plate may be, for example, an upper polarizing plate or a viewing side polarizing plate. That is, a liquid crystal display generally includes a liquid crystal panel, a polarizing plate attached to both sides thereof, and a backlight unit (BLU) disposed adjacent to any one of the two polarizing plates. The arranged polarizing plate is generally referred to as a lower polarizing plate, and the other polarizing plate is referred to as an upper polarizing plate, and such an upper polarizing plate becomes a viewer-side polarizing plate.

The polarizing plate of the present application may be applied as a polarizing plate on the viewing side as described above, but the application position is not limited thereto.

In addition, when the polarizing plate of the present application is applied as a viewing-side polarizing plate, a known polarizing plate may be applied as a lower polarizing plate without any particular limitation, but the first and second phase differences between the polarizing layer of the lower polarizing plate and the polarizing layer of the upper polarizing plate It is effective that no other phase difference layer exists except for the layer and the liquid crystal layer of the liquid crystal panel.

Meanwhile, in the above structure, two layers of liquid crystal alignment layers are present on each of the two substrates facing each other. Such a liquid crystal alignment film has a so-called pretilt angle of 1 degree or less, 0.9 degrees or less, 0.8 degrees or less, 0.7 degrees or less, 0.6 degrees or less, 0.5 degrees or less, 0.4 degrees or less, 0.3 degrees or less, 0.2 degrees or less, 0.1 degrees or less, It can be around 0 degrees. A method of checking such a pretilt angle is known, and for example, a crystal rotation method or the like may be applied.

The kind of the liquid crystal alignment layer as described above is not particularly limited, and generally, a non-contact alignment layer such as a photo alignment layer exhibits the aforementioned pretilt angle.

Other configurations of the liquid crystal display, for example, the type of the substrate or liquid crystal material, and the like, are not particularly limited, and a known conventional method may be applied.

The present application, in particular, is applied to a display device such as a relatively symmetric IPS mode LCD, and can provide a polarizing plate capable of maintaining excellent CR (Contrast Ratio), color and luminous characteristics even at an inclination angle.

1 and 2 are diagrams showing exemplary structures of the polarizing plate of the present application.
3 is a diagram for explaining the structure of a liquid crystal panel.
4 is a diagram for describing an inclination angle and a moving angle.
5 to 18 are diagrams showing results of evaluating the performance of the polarizing plate of Examples.

Hereinafter, the present application is specifically described through Examples and Comparative Examples, but the scope of the present application is not limited to the following.

In the following Examples and Comparative Examples, the symbol R _th represents the retardation in the thickness direction of the retardation layer based on the 550 nm wavelength, unless otherwise specified, and R _in is also based on the 550 nm wavelength unless otherwise specified. Represents the in-plane retardation of the retardation layer, and Nz denotes a value obtained according to Equation 3.

Example 1

In a liquid crystal panel, the cell gap is about 3.1 μm, the birefringence (Δn) of the liquid crystal layer for light of 550 nm wavelength is 0.11, the dielectric anisotropy is Δε> 0, and the IPS (In -plane switching) mode liquid crystal panel was applied. The luminance and minimum contrast ratio values at all inclination angles were evaluated for IPS-LCDs manufactured by attaching an upper polarizing plate (viewer side polarizing plate) and a lower polarizing plate to both sides of the liquid crystal panel, respectively. As an upper polarizing plate, a first retardation layer and a second retardation layer are sequentially stacked on one side of a polarizing layer (a conventional PVA (poly(vinyl alcohol)) polarizing layer), and an isotropic triacetyl cellulose (TAC) film (Fuji Corporation , Thickness: 40 μm) was used, and isotropic TAC (Triacetyl cellulose) film (Fuji, thickness: 40 μm) on both sides of the polarizing layer (normal PVA (poly(vinyl alcohol)) polarizing layer) as the lower polarizing plate ) Was used. The upper polarizing plate was attached so that the first and second retardation layers exist between the polarizing layer and the liquid crystal panel. As the first retardation layer, a vertical orientation in which the retardation in the thickness direction (R _th ) for light having a wavelength of 550 nm is 30 nm and a dispersion coefficient (R _th (450)/R _th (550) according to Equation 4) is 0.9. A liquid crystal film was used, and as the second retardation layer, the Nz value according to Equation 3 is about 0.5, the in-plane retardation (R _in ) for the 550 nm wavelength is about 192 nm, and the dispersion coefficient according to Equation 5 is about 0.84. A stretched polymer film was used. For the IPS-LCD manufactured as described above, the maximum luminance and minimum contrast ratio values at all directions and inclination angles were evaluated using TechWiz LCD 1D equipment. The evaluation results are put together in Table 1 and shown in Fig. 5.

Example 2.

As the second retardation layer, the Nz value according to Equation 3 is 0.5, the in-plane retardation (R _in ) for light of 550 nm wavelength is 192 nm, except that a stretched polymer film having a dispersion coefficient of about 0.9 according to Equation 5 is used. Then, in the same manner as in Example 1, an IPS LCD was manufactured and evaluated. The evaluation results are put together in Table 1 and shown in Fig. 6.

Example 3.

As the first retardation layer, R _th is 50 nm, and a vertically aligned liquid crystal film having a dispersion coefficient of 0.9 according to Equation 4 is used, and as the second retardation layer, Nz is 0.6 and R _in is 185 nm, according to Equation 5 In the same manner as in Example 1, except that a stretched polymer film having a dispersion coefficient of 0.84 was used, IPS-LCD was prepared and evaluated. The evaluation results are put together in Table 1 and shown in Fig. 7.

Example 4.

As a second retardation layer, an IPS-LCD was prepared in the same manner as in Example 3, except that a stretched polymer film having an Nz value of 0.6, an R _in of 185 nm, and a dispersion coefficient of 0.9 according to Equation 5 was applied, and evaluated. Proceeded. The evaluation results are put together in Table 1 and shown in [Fig. 8].

Example 5.

As the first retardation layer, a vertically aligned liquid crystal film having R _th of 60 nm and a dispersion coefficient of 0.9 according to Equation 4 is used, and as the second retardation layer, an Nz value is 0.7, R _in is 170 nm, and a dispersion coefficient according to Equation 5 An IPS-LCD was prepared and evaluated in the same manner as in Example 1, except that a 0.84 stretched polymer film was applied. The evaluation results are put together in Table 1 and shown in Fig. 9.

Example 6.

As the first retardation layer, a vertically aligned liquid crystal film having R _th of 80 nm and a dispersion coefficient of 0.9 according to Equation 4 is used, and as the second retardation layer, the Nz value is 0.8 and R _in is 156 nm, and the dispersion coefficient according to Equation 5 An IPS-LCD was prepared and evaluated in the same manner as in Example 1, except that a stretched polymer film of 0.84 was used. The evaluation results are put together in Table 1 and shown in Fig. 10.

Example 7.

For IPS-LCDs manufactured by attaching an upper polarizing plate (viewing side polarizing plate) and a lower polarizing plate to both sides of the same liquid crystal panel as in Example 1, the luminance and minimum contrast ratio values at all inclination angles were evaluated. As an upper polarizing plate, a second retardation layer and a first retardation layer are sequentially stacked on one side of a polarizing layer (usually a PVA (poly(vinyl alcohol)) polarizing layer), and an isotropic triacetyl cellulose (TAC) film (Fuji Corp.) , Thickness: 40 μm) was used, and isotropic TAC (Triacetyl cellulose) film (Fuji, thickness: 40 μm) on both sides of the polarizing layer (normal PVA (poly(vinyl alcohol)) polarizing layer) as the lower polarizing plate ) Was used. The upper polarizing plate was attached so that the second and first retardation layers existed between the polarizing layer and the liquid crystal panel.

As the first retardation layer, a vertically aligned liquid crystal film having R _th of 50 nm and a dispersion coefficient of 0.9 according to Equation 4 was used, and the Nz value of the second retardation layer is 0.5, R _in is 211 nm, and dispersion according to Equation 5 A stretched polymer film having a coefficient of 0.84 was used. The results evaluated in the same manner as in Example 1 are summarized in Table 1 and shown in [Fig. 11].

Example 8.

As a second retardation layer, an IPS-LCD was prepared and evaluated in the same manner as in Example 7, except that a stretched polymer film having an Nz value of 0.5, an R _in of 211 nm, and a dispersion coefficient of 0.9 according to Equation 5 was applied. I did. The evaluation results are put together in Table 1 and shown in [Fig. 12].

Example 9.

As the first retardation layer, a vertically aligned liquid crystal film having R _th of 60 nm and a dispersion coefficient of 0.9 according to Equation 4 is used, and as the second retardation layer, an Nz value is 0.6, R _in is 206 nm, and a dispersion coefficient according to Equation 5 An IPS-LCD was prepared in the same manner as in Example 7 except that a stretched polymer film of 0.84 was applied, and evaluation was conducted. The evaluation results are put together in Table 1 and shown in [Fig. 13].

Example 10.

As the second retardation layer, an IPS-LCD was prepared and evaluated in the same manner as in Example 9, except that a stretched polymer film having an Nz value of 0.6, an R _in of 206 nm, and a dispersion coefficient of 0.9 according to Equation 5 was used. I did. The evaluation results are put together in Table 1 and shown in Fig. 14.

Example 11.

As the first retardation layer, a vertically aligned liquid crystal film having R _th of 80 nm and a dispersion coefficient of 0.9 according to Equation 4 is used, and as the second retardation layer, the Nz value is 0.7, R _in is 185 nm, and dispersion according to Equation 5 An IPS-LCD was prepared and evaluated in the same manner as in Example 7, except that a stretched polymer film having a coefficient of 0.84 was used. The evaluation results are put together in Table 1 and shown in Fig. 15.

Example 12.

As a second retardation layer, an IPS-LCD was prepared and evaluated in the same manner as in Example 11, except that a stretched polymer film having an Nz value of 0.7, an R _in of 185 nm, and a dispersion coefficient of 0.9 according to Equation 5 was applied. I did. The evaluation results are put together in Table 1 and shown in Fig. 16.

Example 13.

As the first retardation layer, a vertically aligned liquid crystal film having R _th of 90 nm and a dispersion coefficient of 0.9 according to Equation 4 was applied, and as the second retardation layer, the Nz value is 0.8 and R _in is 175 nm, and the dispersion coefficient according to Equation 5 An IPS-LCD was prepared in the same manner as in Example 7 except that a stretched polymer film of 0.84 was applied, and evaluation was conducted. The evaluation results are put together in Table 1 and shown in Fig. 17.

Example 14.

As a second retardation layer, an IPS-LCD was prepared and evaluated in the same manner as in Example 13, except that a stretched polymer film having an Nz value of 0.8, an R _in of 175 nm, and a dispersion coefficient of 0.9 according to Equation 5 was applied. I did. The evaluation results are put together in Table 1 and shown in Fig. 18.

The evaluation results when the design values of the first and second retardation films were applied as shown in Table 1 below are shown.

[Table 1]

10: polarizing plate
101: upper polarizing plate, 102: lower polarizing plate
100: polarizing layer
201: first phase difference layer
202: second phase difference layer
301, 302: substrate
400: liquid crystal material
500: sealant
601, 602: liquid crystal alignment layer

Claims (14)

A polarizing layer;
A first retardation layer positioned below the polarizing layer and having a retardation in the thickness direction according to Equation 2 below in a range of 20 to 90 nm based on a wavelength of 550 nm; And
A polarizing plate including a second retardation layer positioned under the first retardation layer, having an Nz coefficient in the range of 0.4 to 1 according to Equation 3 below, and having an in-plane retardation in the range of 150 to 200 nm based on a wavelength of 550 nm :
[Equation 2]
R _th = d × (n _z -n _y )
[Equation 3]
Nz = (n _x -n _z )/(n _x -n _y )
In Equations 1 and 2, R _th is the retardation in the thickness direction, d is the thickness of the retardation layer, n _x is the refractive index in the slow axis direction of the retardation layer, n _y is the refractive index in the fast axis direction of the retardation layer, and n _z is the retardation. It is the refractive index in the thickness direction of the layer. The polarizing plate of claim 1, wherein a slow axis of the second retardation layer and an absorption axis of the polarizing layer are horizontal. A polarizing layer;
A second retardation layer positioned below the polarizing layer, having an Nz coefficient in the range of 0.4 to 1 according to Equation 3 below, and having an in-plane retardation in the range of 160 to 250 nm based on a wavelength of 550 nm; And
A polarizing plate including a first retardation layer positioned under the second retardation layer and having a retardation in the thickness direction according to Equation 2 below in a range of 40 to 100 nm based on a wavelength of 550 nm:
[Equation 2]
R _th = d × (n _z -n _y )
[Equation 3]
Nz = (n _x -n _z )/(n _x -n _y )
In Equations 1 and 2, R _th is the retardation in the thickness direction, d is the thickness of the retardation layer, n _x is the refractive index in the slow axis direction of the retardation layer, n _y is the refractive index in the fast axis direction of the retardation layer, and n _z is the retardation. It is the refractive index in the thickness direction of the layer. The polarizing plate of claim 3, wherein a slow axis of the second phase difference layer and an absorption axis of the polarizing layer are perpendicular to each other. The polarizing plate according to claim 1 or 3, wherein the in-plane retardation of the first retardation layer is 10 nm or less based on a wavelength of 550 nm. The polarizing plate according to claim 1 or 3, wherein the first phase difference layer has a dispersion coefficient of 1 or less according to Equation 4 below:
[Equation 4]
Variance coefficient = R _th (450)/R _th (550)
In Equation 4, R _th (450) is the retardation in the thickness direction based on the 450 nm wavelength of the first retardation layer, and R _th (550) is the retardation in the thickness direction based on the 550 nm wavelength of the first retardation layer. The polarizing plate according to claim 1 or 3, wherein the second phase difference layer has a dispersion coefficient of 1 or less according to Equation 5 below:
[Equation 5]
Variance Coefficient = R _in (450)/R _in (550)
In Equation 5, R _in (450) is the in-plane retardation based on the 450 nm wavelength of the second retardation layer, and R _in (550) is the in-plane retardation based on the 550 nm wavelength of the second retardation layer. The polarizing plate according to claim 1 or 3, wherein the first retardation layer is a liquid crystal layer or a stretched polymer film containing a polymerized vertically aligned polymerizable liquid crystal compound. The polarizing plate according to claim 1 or 3, wherein the second retardation layer is a liquid crystal layer or a stretched polymer film containing a polymerized horizontal alignment polymerizable liquid crystal compound. The polarizing plate according to claim 1 or 3, wherein the retardation layer includes only the first and second retardation layers. A liquid crystal panel in an area switch mode; And the polarizing plate of claim 1 or 3 disposed on at least one surface of the liquid crystal panel. The liquid crystal display device according to claim 11, wherein the pretilt angle of the liquid crystal aligning film is 1 degree or less. A liquid crystal panel in an area switch mode; And the polarizing plate of claim 1 or 3 disposed on the viewer side of the liquid crystal panel. The liquid crystal display device according to claim 13, wherein the pretilt angle of the liquid crystal aligning film is 1 degree or less.

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