KR102280078B1 - Liquid crystal display device - Google Patents

Abstract

The liquid crystal display of the present invention improves the contrast ratio in the diagonal direction in the dark state by applying the positive C plate and the positive A plate having inverse dispersion characteristics, color shift and color is characterized by improving

Description

Liquid crystal display device {LIQUID CRYSTAL DISPLAY DEVICE}

The present invention relates to a liquid crystal display device, and more particularly, to a liquid crystal display device including an optical compensation film for improving a contrast ratio in a diagonal direction.

Among lightweight thin-film flat panel displays, liquid crystal displays (LCDs) are devices that express images using the optical anisotropy of liquid crystals, and have excellent resolution, color display, and image quality, and are actively applied to laptops and desktop monitors. .

A liquid crystal display is largely composed of a color filter substrate, an array substrate, and a liquid crystal layer formed between the color filter substrate and the array substrate.

At this time, the color filter substrate distinguishes between the color filter and the sub-color filter composed of a plurality of sub-color filters that implement colors of red (R), green (G), and blue (B), It consists of a black matrix that blocks light passing through the liquid crystal layer, and a transparent common electrode that applies a voltage to the liquid crystal layer.

The array substrate includes a plurality of gate lines and data lines that are arranged vertically and horizontally to define a plurality of pixel regions, a thin film transistor (TFT), which is a switching element formed in an intersection region of the gate line and the data line, and a pixel formed in the pixel region. made up of electrodes.

The color filter substrate and the array substrate configured as described above are bonded to face each other by a sealant formed outside the image display area to constitute a liquid crystal panel.

In this case, the color filter substrate and the array substrate are bonded through a bonding key formed on the color filter substrate or the array substrate.

The liquid crystal display device described above represents a twisted nematic (TN) type liquid crystal display device in which liquid crystal molecules of a nematic phase are driven in a direction perpendicular to a substrate. The TN type liquid crystal display has a disadvantage in that the viewing angle is as narrow as 90 degrees. This is due to the refractive anisotropy of the liquid crystal molecules, and the liquid crystal molecules aligned horizontally with the substrate are aligned in a direction substantially perpendicular to the substrate when a voltage is applied to the liquid crystal panel.

Accordingly, an in-plane switching (IPS) type liquid crystal display device has been developed in which the viewing angle is improved to 170 degrees or more by driving the liquid crystal molecules in a horizontal direction with respect to the substrate. Hereinafter, an in-plane switching type liquid crystal display will be described in detail with reference to the drawings.

1 is a plan view illustrating a part of an array substrate of a general in-plane switching type liquid crystal display device as an example.

In an actual liquid crystal display device, MxN pixels exist by crossing N gate lines and M data lines. However, one pixel is shown in the drawing for simplicity of explanation.

And, FIG. 2 is a view schematically showing a cross-section taken along line I-I' of the array substrate shown in FIG. 1 . At this time, FIG. 2 shows a color filter substrate bonded to the array substrate shown in FIG. 1 together.

1 and 2 , a gate line 16 and a data line 17 that are arranged vertically and horizontally to define a pixel area are formed on the transparent array substrate 10 . In addition, a thin film transistor T, which is a switching device, is formed at the intersection of the gate line 16 and the data line 17 .

At this time, the thin film transistor T has a gate electrode 21 connected to the gate line 16 , a source electrode 22 connected to the data line 17 , and a drain connected to the pixel electrode 18 through the pixel electrode line 181 . composed of electrodes 23 . In addition, the thin film transistor is connected to the source electrode 22 and the source electrode 22 by the gate voltage supplied to the first insulating film 15a and the gate electrode 21 for insulation between the gate electrode 21 and the source/drain electrodes 22 and 23 . An active pattern 24 for forming a conductive channel between the drain electrodes 23 is included.

For reference, reference numeral 25 denotes an ohmic-contact layer that makes ohmic contact between the source/drain region of the active pattern 24 and the source/drain electrodes 22 and 23 .

At this time, in the pixel region, the common line 81 and the storage electrode 18s are arranged in a direction parallel to the gate line 16 . In addition, in the pixel region, a plurality of common electrodes 8 and pixel electrodes 18 for switching liquid crystal molecules (not shown) by generating a transverse electric field 90 are parallel to the data line 17 . are arranged as

In this case, the storage electrode 18s overlaps a portion of the common line 81 under the first insulating layer 15a interposed therebetween to form a storage capacitor Cst.

In addition, on the transparent color filter substrate 5, the thin film transistor T, the gate line 16, and the data line 17 to prevent light from leaking through the black matrix 6 and red, green and blue colors are implemented. A color filter 7 for

Alignment films (not shown) for determining the initial alignment direction of liquid crystal molecules are respectively formed on opposite surfaces of the array substrate 10 and the color filter substrate 5 configured as described above. Polarizing plates (not shown) are disposed on the outer surfaces of the array substrate 10 and the color filter substrate 5 so that light transmission axes are perpendicular to each other.

In a typical in-plane switching type liquid crystal display device, the common electrode 8 and the pixel electrode 18 are disposed on the same array substrate 10 to generate a transverse electric field, and liquid crystal molecules are transversely parallel to the array substrate 10 . Since it is arranged in parallel with the electric field 90, it has the advantage of improving the viewing angle.

However, this in-plane switching type liquid crystal display device has a disadvantage in that light leakage occurs in a diagonal direction when displaying a black state, resulting in a low contrast ratio.

3A and 3B are diagrams illustrating, as an example, luminance and viewing angle characteristics in a dark state in a general in-plane switching type liquid crystal display.

In this case, FIG. 3A is a diagram showing a simulation result of a luminance viewing angle characteristic in a dark state, and FIG. 3B is a diagram illustrating a measurement result of a luminance viewing angle characteristic in a dark state.

3a and 3b illustrate the luminance and viewing angle characteristics in the dark state when a 0-RT (TAC (Tri-acetyl cellulose) film with Rth close to 0 nm) is applied between the polyvinyl alcohol (PVA) layer and the liquid crystal layer of the polarizing plate. is showing

In addition, the lower polarizing plate and the upper polarizing plate are arranged so that light absorption axes are perpendicular to each other, and the optical axis of the liquid crystal layer is parallel to the light absorption axis of the lower polarizing plate.

3A and 3B , in the dark state, large light leakage occurs at 45 degrees, 135 degrees, 225 degrees, and 315 degrees corresponding to the diagonal directions of the liquid crystal panel to increase the luminance, and accordingly, the contrast of the liquid crystal display device It can be seen that the contrast ratio is lowered.

However, this disadvantage is due to the polarizing plate generally used rather than due to the in-plane switching type liquid crystal display itself. That is, as in the in-plane switching type liquid crystal display device, the transverse electric field mode can determine the initial alignment state so as not to be affected by the liquid crystal in all directions. In this case, the light leakage is entirely attributable to the polarizer.

4A is a view schematically showing light transmission axes of upper and lower polarizing plates that are orthogonal to each other when viewed from the front.

And, FIG. 4B is a view schematically showing the light transmission axes of the upper and lower polarizers orthogonal to each other when viewed from a diagonal direction.

At this time, the solid line shown in FIGS. 4A and 4B indicates, for example, the direction of the light absorption axis of the upper polarizing plate, and the dotted line indicates the direction of the light absorption axis of the lower polarizing plate.

Referring to FIGS. 4A and 4B , even if the optical absorption axes of the polarizing plates are orthogonal to each other, the orthogonality of the two polarizing plates is broken depending on the direction of the viewing angle.

That is, when the liquid crystal panel is viewed from the front as shown in FIG. 4A , the light absorption axes of the upper and lower polarizers form 90 degrees to realize a dark state.

However, when the liquid crystal panel is viewed from a diagonal direction as shown in FIG. 4B , the light absorption axes of the upper and lower polarizers become more than 90 degrees, and the orthogonality of the two polarizers is broken, so that light leakage occurs.

As described above, in the liquid crystal display of the in-plane switching method, a transverse electric field is applied to the liquid crystal layer, and the phase retardation change of the liquid crystal according to the voltage is small, and the optical axes of the upper and lower polarizers maintain a vertical state in the vertical and horizontal directions. Therefore, the viewing angle is excellent. However, light leakage occurs in the diagonal direction in which the vertical state of the optical axis of the upper and lower polarizers is broken, resulting in deterioration of image quality.

In addition, even when a film-type viewing angle compensation film is applied to improve this, due to the wavelength dispersion of the compensation film, the level of compensation for light leakage in the diagonal direction varies for each wavelength, and thus a color is displayed at the diagonal viewing angle.

That is, the viewing angle compensation film composed of a biaxial film cannot completely block light leakage for all wavelengths due to dispersion according to wavelength, and it reduces light leakage through a compensation design for green (550nm) light, which has a large effect on luminance. make it In this case, as light of short wavelength (blue) and long wavelength (red) is partially transmitted, long and short wavelength light leakage occurs at the viewing angle, and thus the light is colored.

An object of the present invention is to solve the above problem, and it is an object of the present invention to provide a liquid crystal display device that prevents light leakage in a diagonal direction in a dark state.

Another object of the present invention is to provide a liquid crystal display having improved color shift and color.

In addition, other objects and features of the present invention will be described in the following description of the invention and claims.

In order to achieve the above object, a liquid crystal display device according to an exemplary embodiment of the present invention provides a liquid crystal panel including an array substrate and a color filter substrate, a first liquid crystal panel disposed on an outer surface of the array substrate, and including a first polarizing element. A polarizing plate and a second polarizing plate disposed on the outer surface of the color filter substrate and including a first optical compensation film, a second optical compensation film, and a second polarizing element may be included.

In this case, the first optical compensation film may be composed of a positive C plate, the second optical compensation film may be composed of a positive A plate, and at least one of the first optical compensation film and the second optical compensation film may be composed of a reverse dispersion film. have.

The absorption axis of the first polarizing element and the absorption axis of the second polarizing element may be perpendicular to each other, and the optical axis of the liquid crystal layer may be parallel to the absorption axis of the first polarizing element.

The first and second optical compensation films may be positioned between the color filter substrate and the second polarizing element, and the second optical compensation film may be positioned between the first optical compensation film and the second polarizing element.

The first optical compensation film may be composed of a positively dispersed film, and the second optical compensation film may be composed of an inversely dispersed film.

At this time, the first optical compensation film has a value of -105 nm to -125 nm as a retardation value (Rth) in the thickness direction, and the second optical compensation film has a value of 135 nm to 160 nm as a retardation value (Re) in the plane direction. can have

In this case, the second optical compensation film may have dispersion characteristics of 0.84±0.03, 1.0, and 1.07±0.03 ratios in the order of blue (450 nm), green (550 nm), and red (650 nm).

The first optical compensation film and the second optical compensation film may be composed of a reverse dispersion film.

At this time, the first optical compensation film has a value of -105 nm to -125 nm as a retardation value (Rth) in the thickness direction, and the second optical compensation film has a value of 142 nm to 162 nm as a retardation value (Re) in the plane direction. can have

In this case, the first and second optical compensation films may have dispersion characteristics of 0.84±0.03, 1.0, and 1.07±0.03 ratios in the order of blue (450 nm), green (550 nm), and red (650 nm).

As described above, in the liquid crystal display according to an embodiment of the present invention, by applying the positive C plate and the positive A plate as an optical compensation film, the luminance in the diagonal direction is reduced in the dark state, thereby improving the contrast ratio. .

In addition, the liquid crystal display according to an embodiment of the present invention can reduce color shift and improve color by applying the positive C plate and the positive A plate as an optical compensation film having reverse dispersion characteristics. Accordingly, an effect of improving image quality is provided.

1 is a plan view illustrating a portion of an array substrate of a general in-plane switching type liquid crystal display device as an example.
FIG. 2 is a view schematically showing a cross-section taken along line I-I' of the array substrate shown in FIG. 1;
3A and 3B are diagrams illustrating, as an example, luminance and viewing angle characteristics in a dark state in a general in-plane switching type liquid crystal display.
4A is a view schematically showing light transmission axes of upper and lower polarizing plates orthogonal to each other when viewed from the front;
4B is a view schematically showing light transmission axes of upper and lower polarizers orthogonal to each other when viewed from a diagonal direction;
5 is a view exemplarily showing a structure of a liquid crystal display device according to a first embodiment of the present invention.
6 is an exploded view showing the structure of the liquid crystal display according to the first embodiment of the present invention.
7 is a graph showing wavelength dispersion characteristics.
8A and 8B are views for explaining a positive C plate and a positive A plate used as an optical compensation film in the liquid crystal display according to the first embodiment of the present invention;
9A and 9B are diagrams showing arbitrary elliptically polarized light and a Poancare vector corresponding thereto in a Cartesian coordinate system.
10 is a view showing a polarization state of light passing through each optical element using a pointy sphere when viewed from the front;
11A and 11B are views showing the polarization state of light passing through each optical element when viewed from a diagonal direction using a pointy sphere;
12 is a view showing the polarization state of light passing through each optical element in a liquid crystal display including an optical compensation film composed of a positive biaxial film and a negative biaxial film using a pointy sphere;
13 is a view exemplarily showing the structure of a liquid crystal display device according to a second embodiment of the present invention.
14A and 14B are views showing the polarization state of light passing through each optical element using a pointy sphere when viewed from a diagonal direction;
15 is a graph showing, for example, luminance characteristics according to a phase delay value of each optical compensation film when viewed from a maximum luminance viewing angle.
16 is a graph showing, as an example, color shift characteristics according to a phase delay value of each optical compensation film when viewed from a maximum luminance viewing angle.
17 is a graph showing, as an example, luminance characteristics according to a phase delay value of each optical compensation film when viewed from a diagonal direction;
18 is a graph showing, as an example, color shift characteristics according to a phase delay value of each optical compensation film when viewed from a diagonal direction;
19 is a view showing, as an example, luminance and viewing angle characteristics in a dark state in a liquid crystal display including an optical compensation film made of a positive biaxial film and a negative biaxial film;
20A to 20I are views illustrating, as an example, luminance and viewing angle characteristics in a dark state according to a phase delay value of each optical compensation film in a liquid crystal display according to a second embodiment of the present invention;
21 is a view showing, as an example, color characteristics at a viewing angle in a diagonal direction in a liquid crystal display including an optical compensation film made of a positive biaxial film and a negative biaxial film;
22A to 22I are views illustrating color characteristics at a viewing angle in a diagonal direction according to a phase delay value of each optical compensation film in a liquid crystal display according to a second exemplary embodiment of the present invention.
23 is a graph showing, as an example, color shift according to the phase delay value of each optical compensation film.

Hereinafter, a preferred embodiment of a liquid crystal display according to the present invention will be described in detail with reference to the accompanying drawings so that a person skilled in the art can easily implement the present invention.

Advantages and features of the present invention and methods of achieving them will become apparent with reference to the embodiments described below in detail in conjunction with the accompanying drawings. However, the present invention is not limited to the embodiments disclosed below, but will be implemented in various different forms, and only these embodiments allow the disclosure of the present invention to be complete, and common knowledge in the art to which the present invention pertains It is provided to fully inform those who have the scope of the invention, and the present invention is only defined by the scope of the claims. Like reference numerals refer to like elements throughout. The sizes and relative sizes of layers and regions in the drawings may be exaggerated for clarity of description.

Reference to an element or layer to another element or “on” or “on” includes not only directly on the other element or layer, but also with other layers or other elements interposed therebetween. do. On the other hand, reference to an element "directly on" or "directly on" indicates that there are no intervening elements or layers.

The spatially relative terms "below, beneath", "lower", "above", "upper", etc. are one element or component as shown in the drawings. and can be used to easily describe the correlation with other devices or components. Spatially relative terms should be understood as terms including different orientations of the device during use or operation in addition to the orientation shown in the drawings. For example, if an element shown in the figures is turned over, an element described as "beneath" or "beneath" another element may be placed "above" the other element. Accordingly, the exemplary term “below” may include both directions below and above.

The terminology used herein is for the purpose of describing the embodiments, and thus is not intended to limit the present invention. As used herein, the singular also includes the plural unless specifically stated otherwise in the phrase. As used herein, “comprise” and/or “comprising” refers to the presence of one or more other components, steps, operations and/or elements mentioned. or addition is not excluded.

5 is a view exemplarily showing the structure of a liquid crystal display device according to a first embodiment of the present invention.

6 is an exploded view showing the structure of the liquid crystal display according to the first embodiment of the present invention. At this time, FIG. 6 shows, as an example, the polarization state in each configuration in the liquid crystal display according to the first embodiment of the present invention.

7 is a graph showing wavelength dispersion characteristics.

Hereinafter, an in-plane switching (IPS) type liquid crystal display device is exemplified as the liquid crystal display device, but the present invention is not limited thereto.

5 and 6 , the liquid crystal display 100 of the in-plane switching method according to the first embodiment of the present invention is positioned below the liquid crystal panel 110 and the liquid crystal panel 110 for outputting an image. It may be configured to include a first polarizing plate 105 and a second polarizing plate 115 positioned on the liquid crystal panel 110 .

Here, the upper and lower portions of the liquid crystal panel 110 are not limited to specific positions, and the first polarizing plate 105 is positioned on the liquid crystal panel 110 and the second polarizing plate 115 is positioned on the lower portion of the liquid crystal panel 110 . This may be located

In this case, the first polarizing plate 105 includes a first support 102 and a second support 104 , and a first polarizer 103 positioned between the first support 102 and the second support 104 . In addition, the second polarizing plate 115 includes the third support 112 and the first and second optical compensation films 120 and 130 and the third support 112 and the first and second optical compensation films 120 and 130 . and a second polarizing element 113 positioned therebetween.

The first polarizer 103 and the second polarizer 113 may be made of polyvinyl alcohol (PVA).

The first support 102 and the third support 112 may be formed of a protection film without retardation, for example, of tri-acetyl cellulose (TAC). . In addition, the second support 104 may be made of a protective film without a phase delay to protect the first polarizer 103, for example, 0-RT (Rth means a modified TAC close to 0 nm, , also referred to as 0-TAC) or COP (Cyclo-Olefin-Polymer).

The first polarizing element 103 and the second polarizing element 113 refer to films that can be converted from natural light or polarized light into arbitrary polarized light. At this time, the first polarization element 103 and the second polarization element 113 have a function of passing one of the polarization components when the incident light is divided into two orthogonal polarization components and the other polarization component. Those having at least one function selected from the function of absorbing, reflecting, and scattering may be used.

The optical film used for the first polarizing element 103 and the second polarizing element 113 is not particularly limited, but for example, a polymer film containing iodine or a PVA-based resin containing a dichroic dye as a main component. and an O-type polarizing element in which a liquid crystal composition containing a stretched film, a dichroic substance and a liquid crystal compound is oriented in a predetermined direction, and an E-type polarizing element in which a lyotropic liquid crystal is oriented in a predetermined direction, and the like.

The absorption axis of the first polarizer 103 is disposed to be substantially perpendicular to the absorption axis of the second polarizer 113 . At this time, the optical axis of the liquid crystal layer, that is, the rubbing direction of the liquid crystal panel 110 is parallel to the light absorption axis of the first polarizer 103 . In addition, the rubbing direction of the liquid crystal panel 110 and the optical axis of the second optical compensation film 130 on the liquid crystal panel 110 are parallel to each other.

On the other hand, when the first polarizing plate 105 is positioned above the liquid crystal panel 110 and the second polarizing plate 115 is positioned under the liquid crystal panel 110 as described above, the optical axis of the liquid crystal layer is the second polarizing element 113 . ) is parallel to the light absorption axis.

Next, although not shown in detail, the liquid crystal panel 110 may be largely composed of an array substrate, a color filter substrate, and a liquid crystal layer formed between the array substrate and the color filter substrate.

The liquid crystal layer may include nematic liquid crystals homogeneously oriented in the absence of an electric field, and this liquid crystal layer may exhibit a refractive index distribution of nx > ny = nz (provided that the in-plane refractive index is nx and ny, and the refractive index in the thickness direction is nz). At this time, in the present specification, ny = nz includes not only the case where ny and nz are completely the same, but also the case where ny and nz are substantially the same.

As a driving mode using the liquid crystal layer exhibiting such a refractive index distribution, for example, an in-plane switching method or a fringe field switching (FFS) method may be used.

In this case, the in-plane switching method uses a voltage-controlled birefringence (ECB) effect to drive a homogeneously oriented nematic liquid crystal in the absence of an electric field through a lateral electric field by a pixel electrode and a common electrode. way to do it.

In addition, the fringe field switching method is driven in the same way as the in-plane switching method. The transverse electric field of the fringe field switching method is called a fringe field. , can be formed by setting the gap between the lower substrates to be narrower.

In this case, the pixel electrode and the common electrode may have a straight shape, but may also have a zigzag shape. Alternatively, one of the pixel electrode and the common electrode may have a linear shape and the other may have a zigzag shape. Alternatively, one of the pixel electrode and the common electrode may have a straight or zigzag shape, and the other may have a rectangular shape. That is, the present invention is not limited to the shape of the pixel electrode and the common electrode.

In addition, the pixel electrode and the common electrode may be formed of a transparent conductive material, but at least one of the pixel electrode and the common electrode may be formed of an opaque conductive material, for example, copper (Cu) or a copper alloy (Cu alloy). It is also possible That is, the present invention is not limited to the material for forming the pixel electrode and the common electrode.

Here, in the case of the present invention, the liquid crystal display 100 of the in-plane switching method is described as an example, but as described above, the present invention is not limited thereto. The present invention can also be applied to the liquid crystal display device 100 of the FFS method, the Super-IPS method, and the reverse TN IPS method.

At this time, the color filter substrate distinguishes between the color filter and the sub-color filter composed of a plurality of sub-color filters that implement colors of red (R), green (G), and blue (B), It consists of a black matrix that blocks light passing through the liquid crystal layer.

An overcoat layer made of a predetermined organic material may be formed on the color filter substrate on which the color filter and the black matrix are formed to prevent the dye from flowing out and to planarize the surface of the color filter. Alternatively, a color filter and an overcoat layer may be formed on the color filter substrate, and a black matrix may be formed.

Also, the color filter and the black matrix can be formed in a zigzag shape. That is, the present invention is not limited to the shape of the color filter and the black matrix.

In addition, the array substrate is arranged vertically and horizontally and is formed in a plurality of gate lines and data lines defining a plurality of pixel regions, a thin film transistor which is a switching device formed in an intersection region of the gate line and the data line, and a pixel region to generate a transverse electric field. It consists of a pixel electrode and a common electrode.

The array substrate and the color filter substrate are bonded to face each other by a sealant formed outside the image display area to constitute the liquid crystal panel 110 . In this case, an alignment layer for alignment of the liquid crystal layer is formed on the inner surfaces of the array substrate and the color filter substrate.

As described above, the first polarizing plate 105 and the second polarizing plate 115 are respectively attached to the lower and upper portions of the liquid crystal panel 110 configured as described above.

In this case, in the liquid crystal display 100 according to the first embodiment of the present invention, the first optical compensation film 120 and the second optical compensation film 130 are disposed between the second polarizing element 113 and the liquid crystal panel 110 . It is characterized in that it is located.

That is, in the present invention, the first optical compensation film 120 and the second optical compensation film 130 are disposed between the second polarizing element 113 and the liquid crystal panel 110 in order to improve the viewing angle characteristic in the diagonal direction. In this case, the first optical compensation film 120 is configured as a positive C plate (+C plate), and the second optical compensation film 130 is configured as a positive A plate (+A plate).

Accordingly, it is possible to improve the contrast ratio in the diagonal direction in the dark state.

In particular, the first embodiment of the present invention is characterized in that color and wavelength dispersion can be improved by limiting the dispersion of red and blue light by applying the reverse dispersion film to the positive C plate and the positive A plate.

That is, the liquid crystal display 100 according to the first embodiment of the present invention including a positive C plate and a positive A plate having reverse dispersion characteristics such that Δn (450 nm) < Δn (550 nm) < Δn (650 nm) In comparison with a liquid crystal display including a biaxial film optical compensation film, path differences are collected for each wavelength of red, green, and blue. Accordingly, it can be seen that the color shift at the diagonal viewing angle is reduced.

For reference, referring to FIG. 7 for the characteristics of the reverse dispersion film, it can be seen that the phase delay value decreases as the wavelength decreases as opposed to the normal dispersion, and the change in the phase delay value for each wavelength is smaller than that of the normal dispersion.

Hereinafter, the positive C plate and the positive A plate used as the retardation film as the optical compensation film will be described in detail with reference to the drawings.

8A and 8B are diagrams for explaining a positive C plate and a positive A plate used as an optical compensation film in the liquid crystal display according to the first embodiment of the present invention. That is, FIGS. 8A and 8B are diagrams for explaining refractive indices of the positive C plate and the positive A plate, respectively.

The retardation film is divided into uniaxial and biaxial according to the number of optical axes, and is divided into positive and negative according to the difference between the refractive index in the optical axis direction and the refractive index in other directions. For example, if there is one optical axis, it is classified as uniaxial, if there are two, it is classified as biaxial. If the refractive index in the optical axis direction is larger than the refractive index in the other directions, it is positive. When the refractive index in the optical axis direction is smaller than the refractive index in the other directions. classified as negative.

Such a retardation film may be expressed as a refractive index in each direction in the xyz coordinate system. For example, when the retardation film exists in the xy plane, the x-axis and the y-axis refer to the plane direction of the retardation film, and the refractive indices of nx, ny, and nz along the x-axis, y-axis, and z-axis, respectively. ) has

In this case, Re (or Rin) means a phase delay (or in-plane phase difference) value in the plane direction, and Rth means a phase delay (or phase difference in thickness direction) value in the thickness direction. In addition, Nz denotes an index indicating the degree of biaxiality of the biaxial retardation film, and is expressed in Equation 1 below.

In this case, d represents the thickness of the film.

When nx = ny < nz, it is called a positive C plate, and the retardation value Rth in the thickness direction can be defined using the difference between the in-plane refractive index and the refractive index in the thickness direction and the thickness of the film.

The C plate has the same refractive index in the x-axis direction (nx) and the refractive index in the y-axis direction (ny), and the refractive index in the z-axis direction (nz) is the refractive index in the x-axis direction (nx) and the refractive index in the y-axis direction (ny). ) and different from If the refractive index in the x-axis direction (nx) and the refractive index in the y-axis direction (ny) are smaller than the refractive index in the z-axis direction (nz), it is a positive C plate, and the refractive index in the x-axis direction (nx) and the refractive index in the y-axis direction (ny) ) is larger than the refractive index (nz) in the z-axis direction, it is a negative C plate.

When nx > ny = nz, it is referred to as a positive A plate, and the in-plane retardation value Rin can be defined using the thickness of the film and the difference of two refractive indices placed on the plane.

That is, the A plate has the same refractive index (ny) in the y-axis direction and the refractive index (nz) in the z-axis direction, and the refractive index (nx) in the x-axis direction is the refractive index in the y-axis direction (ny) and the refractive index in the z-axis direction. It is characterized by being different from (nz). If the refractive index in the x-axis direction (nx) is greater than the refractive index in the y-axis direction (ny) and the refractive index in the z-axis direction (nz), it is a positive A plate, and the refractive index in the x-axis direction (nx) is the refractive index in the y-axis direction (ny) and if it is smaller than the refractive index nz in the z-axis direction, it is a negative A plate.

The positive A plate is a film in which the retardation value Rth in the thickness direction is almost 0, and the in-plane retardation value Rin has a positive value.

The positive C plate and the positive A plate mainly consist of Cyclo-Olefin-Polymer (COP) film or polycarbonate film, UV curable horizontal or horizontally oriented liquid crystal film, polystyrene resin, and polyethyleneterephthalate (polyethyleneterephthalate). ) can be used.

At this time, in the first embodiment of the present invention, a positive C plate having Rth = -105 nm to -125 nm (Nz → ∞) is used, and a positive A plate having Rin = 142 nm to 162 nm (Nz = 1±0.05) is used. characterized. In this case, the phase delay value is obtained through simulation, and may be slightly changed according to various process conditions of the components constituting the actual liquid crystal panel and the first and second polarizing plates.

Here, the phase delay values of all films applied to the present invention may have a predetermined error due to process variations or external influences.

In addition, in the first embodiment of the present invention, the positive C plate and the positive A plate having reverse dispersion characteristics are used as optical compensation films to improve color and wavelength dispersion.

At this time, the dispersion characteristics of the positive C plate may have a ratio of 0.84±0.03, 1.0, and 1.07±0.03 in the order of blue (450 nm), green (550 nm), and red (650 nm).

In addition, the dispersion characteristics of the positive A plate may have a ratio of 0.84±0.03, 1.0, and 1.07±0.03 in the order of blue (450 nm), green (550 nm), and red (650 nm).

The positive C plate and the positive A plate according to the first embodiment of the present invention having such optical conditions compensate for the breakage of the orthogonality of the first and second polarizers in the diagonal direction, thereby reducing light leakage in the diagonal direction. This is explained in detail using the Poincare sphere expression.

To geometrically interpret the optical properties of a transparent medium such as liquid crystal, we use the Poancare sphere representation of the polarization state.

First, the Jones vector can represent only complete polarization, and a Stokes parameter defined as in Equation 2 below is used to express more general partial polarization.

는 시간평균을 나타내며, 이 네 변수 사이에는

의 부등식이 성립하는데, 등식은 완전편광에서만 적용된다.At this time,

represents the time average, and between these four variables is

The inequality of is established, which applies only to perfect polarization.

In the case of fully polarized light, the relationship of Equation 3 below is established between the normalized variables s ₁ , s ₂ and s _{3 obtained by dividing S 1} , S _{2 ,} and S ₃ by the brightness S _{0 of the light.}

This is the equation of a sphere with a radius of 1 in three-dimensional space, _{and a sphere consisting of points with (s 1} , s ₂ , s ₃ ) as Cartesian coordinates means a pointy sphere.

At this time, in the Poancare sphere, all points on the equator correspond to linear polarization, the north pole corresponds to the right-hand circular polarization, and the south pole corresponds to the left-hand circular polarization. All points in the northern hemisphere correspond to right-handed elliptically polarized light, and all points in the southern hemisphere correspond to left-handed elliptically polarized light.

9A and 9B are diagrams illustrating arbitrary elliptically polarized light and a Poancare vector corresponding thereto in a Cartesian coordinate system.

이다. 이 점이 북반구에 있으면 전기장 벡터의 회전방향이 시계방향이고 남반구에 있으면 반시계방향이다. 뽀앙카레 구 위의 대척점들은 서로 직교하는 편광 상태를 나타낸다.9A and 9B , the latitude angle of the Poancare vector P corresponding to the elliptically polarized light having an azimuth angle of the major axis of the polarization ellipse is Ψ and an elliptic angle x is 2x, the azimuth angle is 2Ψ, and the Cartesian coordinate is

to be. If this point is in the Northern Hemisphere, the direction of rotation of the electric field vector is clockwise, and if it is in the Southern Hemisphere, it is counterclockwise. Antipodes on the Poancare sphere represent polarization states that are orthogonal to each other.

In addition, a unitary matrix describing the change in polarization state when light passes through a transparent medium can be interpreted as a rotational transformation on the Poancare sphere.

10 is a view showing the polarization state of light passing through each optical element using a pointy sphere when viewed from the front.

11A and 11B are diagrams showing the polarization state of light passing through each optical element when viewed from a diagonal direction using a pointy sphere.

In this case, FIG. 11B is a diagram illustrating two-dimensionally a mechanism in which an optical path is compensated using the pointy sphere shown in FIG. 11A. That is, FIG. 11B corresponds to a view viewed from the front of the point of care shown in FIG. 11A . Although the two-dimensional representation of Fig. 11B uses arrows in the figure to represent the movement before and after each change in the polarization state, it is pointed out by rotation at a specific angle around a specific axis determined corresponding to each optical characteristic. It can be expressed on a sphere.

In this case, as described above, the Poancare sphere expresses all the polarization states of light on a sphere, and if the optical axis and the phase delay value of the optical element are known, the polarization state can be easily predicted using the Poancare sphere.

In such a Poancare sphere, all points on the equator indicate linearly polarized light, the north pole S ₃ indicates right-handed circularly polarized light, and the south pole -S ₃ indicates left-handed circular polarization. In addition, the northern hemisphere of the remaining region shows right-handed elliptically polarized light, and the southern hemisphere shows left-handed elliptically polarized light.

At this time, referring to FIG. 10, points A and A' indicate the absorption axis of the lower polarizing plate and the transmission axis of the upper polarizing plate when the liquid crystal display is viewed from the front, and points B and B' are the transmission axes of the lower polarizing plate and The absorption axis of the upper polarizing plate is shown. The polarization states of the upper polarizing plate and the lower polarizing plate are symmetrical with respect to the center (O) of the Poancare sphere and are perpendicular to each other, thereby indicating an excellent dark state. That is, as described above, the antipodes (A, B') on the Poancare sphere represent polarization states orthogonal to each other.

However, referring to FIGS. 11A and 11B, when the liquid crystal display device is viewed from a diagonal direction, the transmission axis (A') of the upper polarizing plate and the transmission axis (B) of the lower polarizing plate move a predetermined distance toward the _{S 2 axis,} The absorption axis (B') of the upper polarizing plate and the absorption axis (A) of the lower polarizing plate are moved by a predetermined distance toward the _{-S 2 axis.} In this case, since the point A and the point B' are not symmetric with respect to the center O, the polarization states of the upper polarizing plate and the lower polarizing plate are not perpendicular to each other.

Therefore, by using the optical compensation film according to the first embodiment of the present invention, the optical axis of the light reaching the upper polarizing plate is made to coincide with the absorption axis of the upper polarizing plate. Here, the polarization state of the incident light passing through the lower polarizing plate corresponds to the point B, and the polarization state of the light absorbed and blocked by the absorption axis of the upper polarizing plate corresponds to the B' point.

That is, after the incident light passes through the lower polarizing plate with the absorption axis direction at the point A on the point A, it is linearly polarized and located at the point B. Then, the linearly polarized light passes through a homogeneous liquid crystal layer. Since the alignment direction of the liquid crystal layer is orthogonal to the polarization direction of the linearly polarized light, there is no phase change in the linearly polarized light in the liquid crystal layer. Accordingly, the light passing through the liquid crystal layer maintains the same linear polarization state and has a polarization state corresponding to point B.

However, in reality, light of all wavelengths passing through the liquid crystal layer is not accurately located at point B as dispersion is made for each wavelength, and although not shown, it is dispersed near point B for each wavelength of red, green, and blue.

As described above, in the liquid crystal display of the in-plane switching method, the light leakage generated off the axis in the diagonal direction is caused by the mismatch between the points B and B'. Therefore, the optical compensation film according to the first embodiment of the present invention is used to cause a change in the polarization state of the incident light from the point B to the point B', including the change in the polarization state of the liquid crystal layer.

Accordingly, when the liquid crystal display of the in-plane switching method according to the first embodiment of the present invention is viewed from a diagonal direction, the polarization state of light passing through each optical element is as follows.

First, it moves from point B to point C by the positive C plate (+C), which is the first optical compensation film, and moves from point C to point B' by the positive A plate (+A), which is the second optical compensation film. do. Therefore, the polarization state (point B') of the light reaching the upper polarizing plate coincides with the absorption axis of the upper polarizing plate, and the light is blocked thereby, indicating an excellent dark state.

Specifically, when unpolarized light from the backlight is incident on the first polarizing plate, it is linearly polarized. Most of the light is absorbed by the absorption axis A of the first polarizing plate, and the polarization state of the light passing through the first polarizing plate is located at the B point. That is, as described above, the transmission axis of the first polarizing plate is located at point B. In this case, the absorption axis of the second polarizing plate is located at the point B' and is spaced apart from the transmission axis of the first polarizing plate by a predetermined distance.

When the red, green and blue light linearly polarized by the first polarizing plate passes through the positive C plate (+C) according to the first embodiment of the present invention, the optical axis of the positive C plate (+C) (ie, the thickness of the film) The polarization state moves from point B to point C by rotating counterclockwise around the direction S _{1 axis).}

That is, the linearly polarized light is rotated counterclockwise by 2π times the effective phase delay value of the positive C plate (+C) divided by 450 nm, 550 nm and 650 nm for each wavelength with respect to the _{S 1 axis and is elliptically polarized at point C.} change to light

At this time, when the phase delay value (Rth) of the positive C plate (+C) has a value of -105 nm to -125 nm, the rotation angle of the polarization state is about 68.7° to 81.9° with respect to the green light. And, considering the dispersion characteristics of the above-described positive C plate (+C), the rotation angle of the polarization state becomes about 70.56° to 84° in blue light, and about 62.2° to 74.1° in red light.

The elliptically polarized red, green and blue light meets the second optical compensation film, the positive A plate (+A).

When the red, green, and blue light elliptically polarized by the positive C plate (+C) passes through the positive A plate (+A) according to the first embodiment of the present invention, the optical axis of the A plate (+A) is centered rotates counterclockwise, and the polarization state moves from point C to point B'.

That is, the elliptically polarized light rotates counterclockwise by 2π times the effective phase delay value of the positive A plate (+A) divided by 450 nm, 550 nm and 650 nm for each wavelength with respect to the _{S 2 axis and rotates counterclockwise to point B' (i.e.} , all wavelengths of light move closer to point B') and change to linearly polarized light.

At this time, when the phase delay value Rin of the positive A plate (+A) has a value of 142 nm to 162 nm, the rotation angle of the polarization state is about 92.9° to 106° with respect to the green light. And, considering the dispersion characteristics of the positive A plate (+A) described above, the rotation angle of the polarization state is about 95.4° to 108.9° in blue light, and about 84.2° to 96° in red light.

In this case, since the point B' represents the absorption axis of the upper polarizing plate, most of the incident light is absorbed by the upper polarizing plate, indicating an excellent dark state.

As described above, in the first embodiment of the present invention, the polarization state is controlled by sequentially using the positive C plate (+C) and the positive A plate (+A) to prevent light leakage in the diagonal direction to prevent a decrease in the contrast ratio. can do.

In addition, in the first embodiment of the present invention, by using the positive C plate (+C) and the positive A plate (+A) having reverse dispersion characteristics as the optical compensation film, color and wavelength dispersion can be improved.

12 is a view showing the polarization state of light passing through each optical element in a liquid crystal display including an optical compensation film made of a positive biaxial film and a negative biaxial film; It is a diagram showing using .

As described above, light has a different phase delay value for each wavelength, and referring to FIG. 12 , the phase delay value is large in light of a short wavelength (ie, blue (450 nm)) due to the wavelength dispersion characteristic, and thus the blue light It can be seen that the path travels the most.

As a result, a phenomenon of bluish color occurred at the diagonal viewing angle.

That is, light leakage is reduced through a compensation design for green (550 nm) light, which has a large influence on luminance. In this case, as light of short wavelength (blue) and long wavelength (red) is partially transmitted, long and short wavelength light leakage occurs at the viewing angle, and thus the light is colored.

However, as in the present invention, while applying the positive C plate (+C) and the positive A plate (+A) as an optical compensation film, a reverse dispersion film is applied to compensate for the phase delay value for each wavelength, thereby improving color and wavelength dispersion. can be improved

Meanwhile, in the present invention, the reverse dispersion film may be applied to only one of the positive C plate (+C) and the positive A plate (+A).

Hereinafter, a second embodiment of the present invention in which a reverse dispersion film is applied to the positive A plate (+A) and a positive dispersion film is applied to the positive C plate (+C) will be described in detail with reference to the drawings.

13 is a view exemplarily showing the structure of a liquid crystal display device according to a second embodiment of the present invention.

Referring to FIG. 13 , the liquid crystal display 200 of the in-plane switching method according to the second embodiment of the present invention includes a liquid crystal panel 210 that outputs an image and a first liquid crystal panel 210 positioned below the liquid crystal panel 210 . The polarizing plate 205 and the second polarizing plate 215 positioned on the liquid crystal panel 210 may be included.

As described above, the upper and lower portions of the liquid crystal panel 210 are not limited to specific positions, and the first polarizing plate 205 is positioned on the liquid crystal panel 210 and the second polarizing plate 205 is positioned on the lower portion of the liquid crystal panel 210 ( 215) may be located.

In this case, the first polarizing plate 205 includes a first support 202 and a second support 204 , and a first polarizer 203 positioned between the first support 202 and the second support 204 . In addition, the second polarizing plate 215 includes a third support 212 and first and second optical compensation films 220 and 230 , and a third support 212 and first and second optical compensation films 220 and 230 . and a second polarizer 213 positioned therebetween.

The first polarizer 203 and the second polarizer 213 may be made of polyvinyl alcohol (PVA).

The first support 202 and the third support 212 may be made of a general protection film without retardation, for example, may be made of tri-acetyl cellulose (TAC). have. In addition, the second support 204 may be formed of a general protective film without phase delay to protect the first polarizer 203 , and may be formed of, for example, 0-RT or COP (Cyclo-Olefin-Polymer). can

The absorption axis of the first polarizer 203 is disposed to be substantially perpendicular to the absorption axis of the second polarizer 213 . At this time, the optical axis of the liquid crystal layer, that is, the rubbing direction of the liquid crystal panel 210 is parallel to the light absorption axis of the first polarizer 203 . In addition, the rubbing direction of the liquid crystal panel 210 and the optical axis of the second optical compensation film 230 on the liquid crystal panel 210 are parallel to each other.

On the other hand, when the first polarizing plate 205 is positioned above the liquid crystal panel 210 and the second polarizing plate 215 is positioned under the liquid crystal panel 210 as described above, the optical axis of the liquid crystal layer is the second polarizing element 213 . ) is parallel to the light absorption axis.

Next, although not shown in detail, the liquid crystal panel 210 may largely include an array substrate, a color filter substrate, and a liquid crystal layer formed between the array substrate and the color filter substrate.

The liquid crystal layer may include nematic liquid crystals homogeneously oriented in the absence of an electric field, and this liquid crystal layer may exhibit a refractive index distribution of nx > ny = nz (provided that the in-plane refractive index is nx and ny, and the refractive index in the thickness direction is nz).

Here, in the case of the present invention, the in-plane switching type liquid crystal display 200 is described as an example, but as described above, the present invention is not limited thereto. The present invention can also be applied to the liquid crystal display 200 of the FFS method, the Super-IPS method, and the reverse TN IPS method.

As described above, the array substrate and the color filter substrate are bonded to face each other by a sealant formed outside the image display area to constitute the liquid crystal panel 210 . In this case, an alignment layer for alignment of the liquid crystal layer is formed on the inner surfaces of the array substrate and the color filter substrate.

As described above, the first polarizing plate 205 and the second polarizing plate 215 are respectively attached to the lower and upper portions of the liquid crystal panel 210 configured as described above.

In this case, the liquid crystal display 200 according to the second embodiment of the present invention is sequentially arranged between the second polarizer 213 and the liquid crystal panel 210 in the same manner as in the first embodiment of the present invention. The compensation film 220 and the second optical compensation film 230 are positioned.

That is, in the case of the present invention, the first optical compensation film 220 and the second optical compensation film 230 are disposed between the second polarizer 213 and the liquid crystal panel 210 in order to improve the viewing angle characteristics in the diagonal direction. do. In this case, the first optical compensation film 220 is configured as a positive C plate (+C plate), and the second optical compensation film 230 is configured as a positive A plate (+A plate).

Accordingly, it is possible to improve the contrast ratio in the diagonal direction in the dark state.

In particular, the second embodiment of the present invention is characterized in that the reverse dispersion film is applied only to the positive A plate.

That is, a positive C plate having a positive dispersion characteristic of Δn (450 nm) > Δn (550 nm) > Δn (650 nm) and a reverse dispersion characteristic of Δn (450 nm) < Δn (550 nm) < Δn (650 nm) The liquid crystal display 200 according to the second embodiment of the present invention including a positive A plate having will be gathered Accordingly, it can be seen that the color shift at the diagonal viewing angle is reduced.

The positive C plate and the positive A plate mainly consist of Cyclo-Olefin-Polymer (COP) film or polycarbonate film, UV curable horizontal or horizontally oriented liquid crystal film, polystyrene resin, and polyethyleneterephthalate (polyethyleneterephthalate). ) can be used.

At this time, in the second embodiment of the present invention, a positive C plate having Rth = -105nm ~ -125nm (Nz → ∞) is used, and Rin = 135nm ~ 160nm (preferably Rin = 147m ~ 157nm) (Nz = 1± 0.05), which is characterized by using a positive A plate.

Here, the phase delay values of all films applied to the present invention may have a predetermined error due to process variations or external influences.

In addition, in the second embodiment of the present invention, a positive A plate having reverse dispersion characteristics is used as an optical compensation film to improve color and wavelength dispersion.

At this time, the dispersion characteristics of the positive A plate may have a ratio of 0.84±0.03, 1.0, and 1.07±0.03 in the order of blue (450 nm), green (550 nm), and red (650 nm).

The positive C plate and the positive A plate according to the second embodiment of the present invention having such optical conditions may reduce light leakage in the diagonal direction by compensating for broken orthogonality of the first and second polarizing plates in the diagonal direction. This will be described in detail using the aforementioned Poincare sphere expression.

14A and 14B are diagrams showing the polarization state of light passing through each optical element when viewed from a diagonal direction using a pointy sphere.

At this time, FIG. 14B is a diagram illustrating two-dimensionally a mechanism in which an optical path is compensated using the pointy sphere shown in FIG. 14A. That is, FIG. 14B corresponds to a view viewed from the front of the point of care shown in FIG. 14A. Although the two-dimensional representation of Fig. 14B uses arrows in the figure to represent the movement before and after each change in the polarization state, it is pointed out by rotation at a specific angle around a specific axis determined corresponding to each optical characteristic. It can be expressed on a sphere.

14A and 14B, when the liquid crystal display is viewed from the diagonal direction as described above, the transmission axis A' of the upper polarizing plate and the transmission axis B of the lower polarizing plate move a predetermined distance toward the _{S 2 axis.} and the absorption axis (B') of the upper polarizing plate and the absorption axis (A) of the lower polarizing plate are moved by a predetermined distance toward the _{-S 2 axis.} In this case, since the point A and the point B' are not symmetric with respect to the center O, the polarization states of the upper polarizing plate and the lower polarizing plate are not perpendicular to each other.

Therefore, by using the optical compensation film according to the second embodiment of the present invention, the optical axis of the light reaching the upper polarizing plate is made to coincide with the absorption axis of the upper polarizing plate. Here, the polarization state of the incident light passing through the lower polarizing plate corresponds to the point B, and the polarization state of the light absorbed and blocked by the absorption axis of the upper polarizing plate corresponds to the B' point.

That is, after the incident light passes through the lower polarizing plate with the absorption axis direction at the point A on the point A, it is linearly polarized and located at the point B. Then, the linearly polarized light passes through a homogeneous liquid crystal layer. Since the alignment direction of the liquid crystal layer is orthogonal to the polarization direction of the linearly polarized light, there is no phase change in the linearly polarized light in the liquid crystal layer. Accordingly, the light passing through the liquid crystal layer maintains the same linear polarization state and has a polarization state corresponding to point B.

However, in reality, light of all wavelengths passing through the liquid crystal layer is not accurately located at point B as dispersion is made for each wavelength, and although not shown, it is dispersed near point B for each wavelength of red, green, and blue.

As such, in the liquid crystal display of the in-plane switching type, the off-axis light leakage in the diagonal direction is caused by the mismatch between the points B and B'. Therefore, the optical compensation film according to the second embodiment of the present invention is used to cause a change in the polarization state of the incident light from the point B to the point B', including the change in the polarization state of the liquid crystal layer.

Accordingly, when the liquid crystal display of the in-plane switching method according to the second embodiment of the present invention is viewed from a diagonal direction, the polarization state of light passing through each optical element is as follows.

First, it moves from point B to point C by the positive C plate (+C), which is the first optical compensation film, and moves from point C to point B' by the positive A plate (+A), which is the second optical compensation film. do. Therefore, the polarization state (point B') of the light reaching the upper polarizing plate coincides with the absorption axis of the upper polarizing plate, and the light is blocked thereby, indicating an excellent dark state.

Specifically, when unpolarized light from the backlight is incident on the first polarizing plate, it is linearly polarized. Most of the light is absorbed by the absorption axis A of the first polarizing plate, and the polarization state of the light passing through the first polarizing plate is located at the B point. That is, as described above, the transmission axis of the first polarizing plate is located at point B. In this case, the absorption axis of the second polarizing plate is located at the point B' and is spaced apart from the transmission axis of the first polarizing plate by a predetermined distance.

When the red, green, and blue light linearly polarized by the first polarizing plate passes through the positive C plate (+C) according to the second embodiment of the present invention, counterclockwise around the optical axis of the positive C plate (+C). , and the polarization state moves from point B to near point C.

That is, the linearly polarized light rotates counterclockwise by 2π times the effective phase delay value of the positive C plate (+C) divided by 450 nm, 550 nm, and 650 nm for each wavelength based on the _{S 1 axis and is elliptically polarized near the point C.} change to light

At this time, when the phase delay value (Rth) of the positive C plate (+C) has a value of -105 nm to -125 nm, the rotation angle of the polarization state is about 68.7° to 81.9° with respect to the green light. And, since the positive C plate (+C) has a positive dispersion characteristic, the rotation angle of the polarization state is about 84° to 100° in blue light, and about 58.2° to 69.2° in red light.

The elliptically polarized red, green and blue light meets the second optical compensation film, the positive A plate (+A).

When the red, green, and blue light elliptically polarized by the positive C plate (+C) passes through the positive A plate (+A) according to the second embodiment of the present invention, the optical axis of the A plate (+A) is centered rotates counterclockwise, and the polarization state moves from near point C to near point B'.

That is, the elliptically polarized light rotates counterclockwise by 2π times the effective phase delay value of the positive A plate (+A) divided by 450 nm, 550 nm and 650 nm for each wavelength based on the _{S 2 axis,} change to linearly polarized light.

At this time, when the phase delay value (Rin) of the positive A plate (+A) has a value of 135 nm to 160 nm, the rotation angle of the polarization state is about 88.4° to 104.8° with respect to the green light. And, considering the dispersion characteristics of the positive A plate (+A) described above, the rotation angle of the polarization state is about 90.7° to 107.5° in blue light, and about 80° to 94.9° in red light.

Alternatively, when the phase delay value Rin of the positive A plate (+A) has a value of 147 nm to 157 nm, the rotation angle of the polarization state is about 96.2° to 102.8° with respect to the green light. And, the rotation angle of the polarization state is about 98.8° to 105.5° in blue light, and about 87.1° to 93° in red light.

In this case, since the point B' represents the absorption axis of the upper polarizing plate, most of the incident light is absorbed by the upper polarizing plate, indicating an excellent dark state.

As described above, in the second embodiment of the present invention, the polarization state is adjusted by sequentially using the positive C plate (+C) and the positive A plate (+A) in the same manner as in the first embodiment of the present invention described above in the diagonal direction. It is possible to prevent the deterioration of the contrast ratio by preventing light leakage from the

In addition, in the second embodiment of the present invention, a positive C plate (+C) having a positive dispersion characteristic and a positive A plate (+A) having an inverse dispersion characteristic are used as the optical compensation film, thereby improving color and wavelength dispersion. can do.

In this case, the optimal phase delay values at which the luminance and color shift in the dark state are improved can be seen as 115 nm and 152 nm for the positive C plate (+C) and the positive A plate (+A), respectively. At this time, it can be seen that the luminance is reduced by about 30% and the color shift is reduced by about 70% compared to the liquid crystal display including the optical compensation film of the comparative example shown in FIG. 12 .

15 is a graph showing, as an example, luminance characteristics according to a phase delay value of each optical compensation film when viewed from a maximum luminance viewing angle.

And, FIG. 16 is a graph showing, as an example, color shift characteristics according to the phase delay value of each optical compensation film when viewed from the maximum luminance viewing angle.

At this time, in the graphs of FIGS. 15 and 16 , the horizontal axis indicates the phase delay value in the thickness direction of the positive C plate, and the vertical axis indicates the phase delay value in the plane direction of the positive A plate.

In addition, the graphs of FIGS. 15 and 16 show the change in luminance and color shift in % compared to the liquid crystal display device including the optical compensation film made of the positive biaxial film and the negative biaxial film shown in FIG. 12 . . A minus (-) of % means a decrease in luminance and color shift compared to the comparative example, and a plus (+) signifies an increase in luminance and color shift compared to the comparative example.

In the graphs of FIGS. 15 and 16 , the indicated points indicate points at which the phase delay values in the thickness direction of the positive C plate and the phase delay values in the plane direction of the positive A plate are 108 nm and 147 nm.

15, it can be seen that the luminance of the dark state decreases as the phase delay value in the thickness direction of the positive C plate approaches the 108 nm point, and decreases as the phase delay value in the plane direction of the positive A plate approaches 147 nm. have.

Accordingly, it can be seen that the luminance in the dark state is maximally reduced at the points where the phase delay value in the thickness direction of the positive C plate and the phase delay value in the plane direction of the positive A plate are 108 nm and 147 nm.

Referring to FIG. 16 , it can be seen that the color shift decreases as the phase delay value in the thickness direction of the positive C plate increases, and decreases as the phase delay value in the plane direction of the positive A plate approaches 147 nm.

17 is a graph showing, as an example, luminance characteristics according to a phase delay value of each optical compensation film when viewed from a diagonal direction.

18 is a graph showing, as an example, color shift characteristics according to the phase delay value of each optical compensation film when viewed from a diagonal direction.

In this case, FIGS. 17 and 18 exemplify a case in which φ and θ are viewed from a diagonal direction of 45 degrees and 60 degrees, respectively.

In addition, in the graphs of FIGS. 17 and 18 , the horizontal axis indicates the phase delay value in the thickness direction of the positive C plate, and the vertical axis indicates the phase delay value in the plane direction of the positive A plate.

The graphs of FIGS. 17 and 18 show changes in luminance and color shift in % compared to the liquid crystal display including the optical compensation film shown in FIG. 12 .

In the graphs of FIGS. 17 and 18 , the indicated points indicate points at which the phase delay values in the thickness direction of the positive C plate and the phase delay values in the plane direction of the positive A plate are 111 nm and 148 nm.

Referring to FIG. 17, it can be seen that the luminance in the dark state decreases as the phase delay value in the thickness direction of the positive C plate approaches 111 nm, and decreases as the phase delay value in the plane direction of the positive A plate approaches 148 nm. have.

Accordingly, it can be seen that the luminance in the dark state is maximally decreased at the points where the phase delay value in the thickness direction of the positive C plate and the phase delay value in the plane direction of the positive A plate are 111 nm and 148 nm.

Referring to FIG. 18 , it can be seen that the color shift decreases as the phase delay value in the thickness direction of the positive C plate increases, and decreases as the phase delay value in the plane direction of the positive A plate approaches 148 nm.

FIG. 19 is a view showing, as an example, luminance and viewing angle characteristics in a dark state in a liquid crystal display (Comparative Example) including an optical compensation film made of a positive biaxial film and a negative biaxial film.

20A to 20I are diagrams illustrating, as an example, the luminance and viewing angle characteristics in the dark state according to the phase delay value of each optical compensation film in the liquid crystal display according to the second embodiment of the present invention.

At this time, FIGS. 20A, 20B and 20C show the dark state in the case where the positive C plate has a phase delay value in the thickness direction of 90 nm, and the positive A plate has a phase delay value in the plane direction of 137 nm, 147 nm and 157 nm, respectively. It shows the luminance viewing angle characteristics.

20D, 20E, and 20F show the luminance viewing angles in the dark state when the positive C plate has a phase delay value of 105 nm in the thickness direction and the positive A plate has 137 nm, 147 nm, and 157 nm phase delay values, respectively. shows the characteristics.

20G, 20H, and 20I show the luminance viewing angles in the dark state when the positive C plate has a phase delay value of 115 nm in the thickness direction and the positive A plate has 137 nm, 147 nm, and 157 nm phase delay values, respectively. shows the characteristics.

In this case, FIGS. 19 and 20A to 20I exemplify the luminance viewing angle characteristics in the dark state when φ and θ are viewed from a diagonal direction of 45 degrees and 60 degrees, respectively.

20A to 20I, it can be seen that the luminance in the dark state is reduced in all cases except for the case where the positive C plate has a phase delay value in the thickness direction of 90 nm and the positive A plate has a phase delay value in the plane direction of 137 nm. can

That is, when the phase delay value in the thickness direction of the positive C plate is 90 nm and the phase delay value in the plane direction of the positive A plate is 137 nm, the luminance in the dark state increases by about 4%.

On the other hand, when the phase delay value in the thickness direction of the positive C plate is 90 nm and the phase delay value in the plane direction of the positive A plate is 147 nm and 157 nm, the luminance in the dark state is decreased by 4% and 9%, respectively.

When the phase delay value in the thickness direction of the positive C plate is 105 nm and the phase delay value in the plane direction of the positive A plate is 137 nm, 147 nm and 157 nm, the luminance in the dark state is reduced by 25%, 41%, and 29%, respectively. .

When the phase delay value in the thickness direction of the positive C plate is 115 nm and the phase delay value in the plane direction of the positive A plate is 137 nm, 147 nm and 157 nm, the luminance in the dark state is reduced by 20%, 46%, and 25%, respectively. .

21 is a view illustrating color characteristics at a viewing angle in a diagonal direction in a liquid crystal display (Comparative Example) including an optical compensation film made of a positive biaxial film and a negative biaxial film.

22A to 22I are diagrams illustrating color characteristics at a viewing angle in a diagonal direction according to a phase delay value of each optical compensation film in the liquid crystal display according to the second embodiment of the present invention.

23 is a graph showing a color shift according to a phase delay value of each optical compensation film, that is, a color coordinate change (u'v') as an example.

For reference, there is a very big difference between displaying the main properties of color in a two-dimensional plane and displaying them in a three-dimensional space. Also, even the most basic RGB color space displayed in the same three-dimensional space has a different shape depending on how the concept is defined.

And, even in the same two-dimensional planar space, the shape of the space changes depending on how the color properties are defined.

In the case of the CIE xy color space, which has been used since 1931, there is a significant difference between the visual color difference and the numerical color difference, so research was continued to compensate for this. In 1960, the CIE uv color space was adopted as a new standard. And, through additional research, the CIE u'v' color space was adopted as a standard in 1976. This CIE u'v' is the degree to which u' = u and v' = 3/2v in CIE uv, and only the ratio is changed.

22A to 22I , in the case of the second embodiment of the present invention, it can be seen that the maximum viewing angle luminance value and color shift are improved compared to the comparative example.

In addition, referring to FIG. 23 , when the phase delay value in the thickness direction of the positive C plate is 90 nm and the phase delay value in the plane direction of the positive A plate is 147 nm, and the positive C plate has a phase delay value in the thickness direction of 105 nm and positive It can be seen that the color shift was reduced in all cases except for the case where the phase delay value in the plane direction of the A plate was 147 nm.

That is, when the phase delay value in the thickness direction of the positive C plate is 90 nm and the phase delay value in the plane direction of the positive A plate is 147 nm, the color shift is increased by about 21%.

In addition, when the phase delay value in the thickness direction of the positive C plate is 105 nm and the phase delay value in the plane direction of the positive A plate is 147 nm, the color shift increases by about 1%.

On the other hand, when the phase delay value in the thickness direction of the positive C plate is 90 nm and the phase delay value in the plane direction of the positive A plate is 137 nm and 157 nm, the color shift is reduced by 7% and 28%, respectively.

When the thickness direction of the positive C plate has a phase delay value of 105 nm and the positive A plate has 137 nm and 157 nm phase delay values, the color shift is reduced by 34% and 68%, respectively.

When the phase delay value in the thickness direction of the positive C plate is 115 nm and the phase delay value in the plane direction of the positive A plate is 137 nm, 147 nm and 157 nm, the color shift is reduced by 35%, 41%, and 80%, respectively.

Although many matters are specifically described in the above description, these should be construed as examples of preferred embodiments rather than limiting the scope of the invention. Therefore, the invention should not be defined by the described embodiments, but should be defined by the claims and equivalents to the claims.

100,200: liquid crystal display device 103,203, 113,213: polarizing element
105,205, 115,215: polarizing plate 110,210: liquid crystal panel
120,220: first optical compensation film 130,230: second optical compensation film

Claims (10)

a liquid crystal panel comprising an array substrate and a color filter substrate and a liquid crystal layer interposed between the array substrate and the color filter substrate;
a first polarizing plate positioned on an outer surface of the array substrate and including a first polarizing element; and
a second polarizing plate positioned on the outer surface of the color filter substrate and including a first optical compensation film, a second optical compensation film, and a second polarizing element;
The first optical compensation film is made of a positive C plate having a positive dispersion characteristic,
The second optical compensation film is a liquid crystal display device comprising a positive A plate having an inverse dispersion characteristic. The liquid crystal display of claim 1 , wherein an absorption axis of the first polarizing element and an absorption axis of the second polarizing element are perpendicular to each other. The liquid crystal display of claim 2 , wherein an optical axis of the liquid crystal layer is parallel to an absorption axis of the first polarizing element. The method of claim 1, wherein the first and second optical compensation films are positioned between the color filter substrate and the second polarizing element, and the second optical compensation film comprises the first optical compensation film and the second polarizing element. A liquid crystal display located between the delete According to claim 1, wherein the first optical compensation film has a phase retardation value (Rth) in the thickness direction of -105nm ~ -125nm value, the second optical compensation film has a phase retardation value (Re) in the plane direction A liquid crystal display having a value of 135 nm to 160 nm. The liquid crystal display of claim 6 , wherein the second optical compensation film has dispersion characteristics of 0.84±0.03, 1.0, and 1.07±0.03 in the order of blue (450 nm), green (550 nm), and red (650 nm). delete delete delete

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