KR102249166B1 - In plane switching mode liquid crystal display device having optical compensation film - Google Patents

Abstract

The present invention includes an optical compensation film in which the contrast ratio in the diagonal direction is improved in a dark state by applying a positive biaxial film and a negative biaxial film. It relates to an in-plane switching (IPS) type liquid crystal display device.
The liquid crystal display of the in-plane switching method including the optical compensation film of the present invention compensates for the path of light by applying an in-cell retarder of the positive A plate. It is characterized by improving light leakage.
In addition, the liquid crystal display of the in-plane switching method including the optical compensation film of the present invention limits the dispersion of blue light by applying an inverse dispersion film to the negative biaxial film, so that the in-cell-retarder structure is bluish ( bluish) to improve color.

Description

In-plane switching type liquid crystal display device including optical compensation film {IN PLANE SWITCHING MODE LIQUID CRYSTAL DISPLAY DEVICE HAVING OPTICAL COMPENSATION FILM}

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

Recently, as interest in information display has increased and the demand to use portable information media has increased, it has become a lightweight thin-film flat panel display (FPD) that replaces the existing display device, Cathode Ray Tube (CRT). Research and commercialization of Korea are being focused. In particular, among these flat panel display devices, a liquid crystal display (LCD) is a device that expresses an image by using the optical anisotropy of liquid crystal, and has excellent resolution, color display, and image quality, so it is actively applied to laptops and desktop monitors. have.

A liquid crystal display device is largely composed of a color filter substrate as a first substrate, an array substrate as a second 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 a color filter composed of a plurality of sub-color filters implementing colors of red (R), green (G), and blue (B) and a sub-color filter. 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 is arranged vertically and horizontally to define a plurality of pixel regions, a plurality of gate lines and data lines, a thin film transistor (TFT), which is a switching element formed in an intersection region between the gate line and the data line, and pixels formed on the pixel region. It consists of electrodes.

The color filter substrate and the array substrate configured as described above are bonded to each other by a sealant formed on the outer edge of the image display area to form a liquid crystal panel, and the bonding of the color filter substrate and the array substrate is performed on the color filter substrate or the array substrate. It is done through a bonding key.

At this time, the above-described liquid crystal display device represents a twisted nematic (TN) liquid crystal display device that drives nematic liquid crystal molecules in a direction perpendicular to the substrate, and the TN liquid crystal display device has a viewing angle of 90 It has the disadvantage of being narrow enough to be too narrow. This is due to the refractive index anisotropy of the liquid crystal molecules, and this is because liquid crystal molecules aligned horizontally with the substrate are aligned in a substantially vertical direction with the substrate when a voltage is applied to the liquid crystal panel.

Accordingly, there is an in-plane switching (IPS) liquid crystal display device in which the viewing angle is improved to 170 degrees or more by driving liquid crystal molecules in a horizontal direction with respect to the substrate. The liquid crystal display device of will be described in detail.

1 is a plan view schematically showing a part of an array substrate of a general in-plane switching type liquid crystal display. For simplicity, one pixel is shown in the drawing.

In addition, FIG. 2 is a view showing a cross section of the array substrate shown in FIG. 1 along the line I-I', and shows a color filter substrate bonded to correspond to the array substrate shown in FIG. 1.

1 and 2, a gate line 16 and a data line 17 are formed on a transparent array substrate 10 and arranged vertically and horizontally to define a pixel region, and a gate line 16 and a data line ( A thin film transistor T, which is a switching element, is formed in the cross region of 17).

In this case, the thin film transistor T is a drain connected to the pixel electrode 18 through the gate electrode 21 connected to the gate line 16, the source electrode 22 connected to the data line 17, and the pixel electrode line 18l. It consists of an electrode 23. In addition, the thin film transistor is connected to the source electrode 22 by the gate voltage supplied to the gate electrode 21 and the first insulating film 15a for insulation between the gate electrode 21 and the source/drain electrodes 22 and 23. It includes an active pattern 24 forming a conductive channel between the drain electrodes 23.

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

At this time, in the pixel region, the common line 8l and the storage electrode 18s are arranged in a direction parallel to the gate line 16, and a lateral electric field 90 is generated in the pixel region to generate liquid crystal molecules (not shown). A plurality of switching common electrodes 8 and pixel electrodes 18 are arranged in a direction parallel to the data line 17.

At this time, the storage electrode 18s overlaps with a part of the common line 8l below the first insulating layer 15a to form a storage capacitor Cst.

In addition, on the transparent color filter substrate 5, a black matrix 6 that prevents light from leaking to the thin film transistor T, the gate line 16, and the data line 17, and red, green, and blue colors are implemented. The color filter 7 for this is formed.

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

In a general in-plane switching type liquid crystal display, the common electrode 8 and the pixel electrode 18 are disposed on the same array substrate 10 to generate a transverse electric field, and the liquid crystal molecules are 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, such an in-plane switching type liquid crystal display has a problem in that light leaks in diagonal directions when displaying a black state, resulting in a low contrast ratio.

3A is a diagram showing a simulation result of a luminance viewing angle characteristic in a dark state in a general in-plane switching type liquid crystal display device, and FIG. 3B is a diagram showing a measurement result of a luminance viewing angle characteristic in a dark state.

At this time, FIGS. 3A and 3B illustrate the luminance viewing angle characteristics in a dark state when a 0-RT (Tri-acetyl cellulose (TAC) film with Rth close to 0 nm) is applied between the PVA (polyvinyl acetate) layer and the liquid crystal layer of the polarizing plate. An example is shown.

Further, the lower polarizing plate and the upper polarizing plate are arranged so that their light absorption axes are orthogonal 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, when in a dark state, a large light leakage occurs at 45 degrees, 135 degrees, 225 degrees, and 315 degrees corresponding to the diagonal direction of the liquid crystal panel, thereby increasing the brightness. It can be seen that the contrast ratio decreases.

However, this problem is not a problem of an in-plane switching type liquid crystal display device itself, but a problem due to a generally used polarizing plate. That is, in general, diagonal light leakage is more effective by the polarizing plate than by the liquid crystal layer, and the transverse electric field mode, like the in-plane switching type liquid crystal display, determines the initial alignment state so that it is not affected by the liquid crystal in all directions. In this case, the light leakage is entirely due to the polarizer.

4A is a view schematically showing the light transmission axes of the upper and lower polarizing plates that are orthogonal when viewed from the front, and FIG. 4B is a schematic view of the light transmission axes of the upper and lower polarizing plates that are orthogonal when viewed from a diagonal direction. It is a drawing shown as.

Referring to FIGS. 4A and 4B, this is because a phenomenon in which the orthogonality of the two polarizing plates is broken according to the viewing angle direction occurs even if the polarizing plates have light absorption axes that are orthogonal to each other. In this case, the solid lines shown in FIGS. 4A and 4B indicate, 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.

As shown in FIG. 4A, when the liquid crystal panel is viewed from the front, the light absorption axis of the upper and lower polarizing plates is 90 degrees, thereby implementing a dark state. However, as shown in FIG. 4B, the liquid crystal panel is placed in a diagonal direction. When looking, the light absorption axis of the upper and lower polarizing plates is 90 degrees or more, and the orthogonality of the two polarizing plates is broken, causing light leakage.

In this way, the in-plane switching type liquid crystal display is a method in which a transverse electric field is applied to the liquid crystal layer, so that the change in phase retardation of the liquid crystal according to the voltage is small, and the optical axes of the upper and lower polarizing plates are maintained in a vertical state in the vertical and horizontal directions. Therefore, the viewing angle is excellent, but light leakage occurs in a diagonal direction in which the vertical state of the optical axes of the upper and lower polarizing plates is broken, resulting in deterioration of image quality.

Meanwhile, even when viewed from the front, light leakage occurs due to external stress applied to the liquid crystal panel. This is because the glass substrate has refractive index anisotropy due to interference between the apparatus and the liquid crystal panel and stress applied to the glass substrate during the array and color filter process.

Ideally, anisotropic glass has refractive index anisotropy as a phase delay value (Re = β×t×F) is generated in proportion to the stress (F) in the manufacturing process. In this case, β and t represent the photoelastic coefficient and thickness of the glass, respectively.

An object of the present invention is to solve the above-described problem, and to provide an in-plane switching type liquid crystal display device including an optical compensation film that prevents light leakage in front and diagonal directions in a dark state.

Another object of the present invention is to provide an in-plane switching type liquid crystal display device including a compensation film for improving bluish color in an in cell retarder structure.

In addition, other objects and features of the present invention will be described in the configuration and claims of the invention to be described later.

In order to achieve the above object, an in-plane switching liquid crystal display device including an optical compensation film according to an embodiment of the present invention is a liquid crystal panel composed of an array substrate and a color filter substrate, and is located on the outer surface of the array substrate. It may include a first polarizing plate, a second polarizing plate positioned on the outer surface of the color filter substrate, and an in-cell-retarder formed on the inner surface of the color filter substrate.

In this case, the liquid crystal panel may include an array substrate and a color filter substrate, and a liquid crystal layer formed between the array substrate and the color filter substrate.

The first polarizing plate is positioned on the outer surface of the array substrate, and may include a first polarizing element.

The second polarizing plate is positioned on the outer surface of the color filter substrate, and may include first and second optical compensation films and a second polarizing element.

In this case, the first optical compensation film may be formed of a positive biaxial film, and the second optical compensation film may be formed of a negative biaxial film.

In this case, the first optical compensation film may have a positive dispersion characteristic, and the second optical compensation film may have a reverse dispersion characteristic.

The absorption axis of the first polarizing element and the absorption axis of the second polarizing element may be perpendicular to each other.

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.

In this case, the second optical compensation film may be formed of a negative biaxial film having a biaxiality (Nz) of 1.375.

In addition, the second optical compensation film may have a phase delay value (Re) of 110±10 nm in a plane direction, and a phase delay value Rth of 80±5 nm in a thickness direction.

The in-cell-retarder may be made of a positive A plate type RM (Reactive Mesogen) having a phase delay value of 156±20 nm.

As described above, the liquid crystal display of the in-plane switching method including the optical compensation film according to an embodiment of the present invention applies a positive biaxial film and a negative biaxial film as an optical compensation film in a diagonal direction in a dark state. The luminance of is reduced by more than 90%, providing the effect of improving the contrast ratio.

In addition, the liquid crystal display of the in-plane switching method including the optical compensation film according to an embodiment of the present invention is generated by external stress by compensating the path of light by applying the in-cell-retarder of the positive A plate. It is possible to reduce the light leakage in the front direction by more than 73%.

In addition, the in-plane switching type liquid crystal display device including the optical compensation film according to an embodiment of the present invention applies an inverse dispersion film to a negative biaxial film to limit the dispersion of blue light, thereby limiting the dispersion of blue light. It is possible to improve the bluish color of the structure. Accordingly, it provides an effect of improving the quality of image quality.

1 is a plan view illustrating a part of an array substrate of a general in-plane switching type liquid crystal display device, for example.
FIG. 2 is a schematic cross-sectional view of the array substrate shown in FIG. 1 taken along line II′.
3A is a view showing a simulation result of a luminance viewing angle characteristic in a dark state in a general in-plane switching type liquid crystal display device.
3B is a view showing measurement results of luminance viewing angle characteristics in a dark state in a general in-plane switching type liquid crystal display device.
4A is a view schematically showing light transmission axes of upper and lower polarizing plates that are orthogonal when viewed from the front.
4B is a diagram schematically showing light transmission axes of upper and lower polarizing plates that are orthogonal when viewed from a diagonal direction.
5 is a cross-sectional view illustrating an in-plane switching type liquid crystal display device including an optical compensation film according to a first embodiment of the present invention.
6 is a liquid crystal panel to which an in-cell retarder is applied in the in-plane switching type liquid crystal display device including the optical compensation film according to the first embodiment of the present invention shown in FIG. Cross-sectional view schematically showing the structure of the
7A and 7B are views for explaining a positive biaxial film and a negative biaxial film used as an optical compensation film in the in-plane switching type liquid crystal display device according to the first embodiment of the present invention.
8A and 8B are diagrams showing an arbitrary elliptical polarization in a Cartesian coordinate system and a Poangcare vector corresponding thereto.
9 is a view showing a state of polarization of light passing through each optical element using a Poangcare sphere when viewed from the front.
10A and 10B are views showing a polarization state of light passing through each optical element by using a Poangcare sphere when viewed from a diagonal direction.
11 is a view showing a state in which light leakage occurs due to external stress using a Poangcare sphere.
12A and 12B are views for explaining a state in which light leakage is improved by applying the in-cell-retarder according to the first embodiment of the present invention, using a Poangcare sphere.
13A and 13B are views showing a polarization state of light passing through each optical device by dividing each wavelength when viewed from a diagonal direction.
14A and 14B are diagrams showing measurement results of luminance viewing angle characteristics in a dark state.
15 is a cross-sectional view illustrating an in-plane switching type liquid crystal display device including an optical compensation film according to a second embodiment of the present invention.
16 is a graph showing wavelength dispersion characteristics.
17A and 17B are views for explaining a state in which the color feel is improved by applying the reverse dispersion film according to the second embodiment of the present invention, using a Poangcare sphere.
18 is a view showing a measurement result of a luminance viewing angle characteristic in a dark state in an in-plane switching liquid crystal display device including an optical compensation film according to a second exemplary embodiment of the present invention.
19A, 19B, and 19C are diagrams showing simulation results of light leakage according to a phase delay value of an inverse dispersion film when viewed from a diagonal direction.

Hereinafter, with reference to the accompanying drawings, a preferred embodiment of an in-plane switching type liquid crystal display device including an optical compensation film according to the present invention can be easily implemented by those of ordinary skill in the art. It will be described in detail so that.

Advantages and features of the present invention, and a method of achieving them will become apparent with reference to the embodiments described below in detail together with the accompanying drawings. However, the present invention is not limited to the embodiments disclosed below, but will be implemented in a variety of different forms, only the present embodiments are intended to complete the disclosure of the present invention, and common knowledge in the technical field to which the present invention pertains. It is provided to completely inform the scope of the invention to those who have, and the invention is only defined by the scope of the claims. The same reference numerals refer to the same elements throughout the specification. In the drawings, the sizes and relative sizes of layers and regions may be exaggerated for clarity of description.

When an element or layer is another element or referred to as “on” or “on”, it includes not only directly above the other element or layer, but also a case in which another layer or other element is interposed in the middle. do. On the other hand, when a device is referred to as "directly on" or "directly on", it indicates that no other device or layer is interposed therebetween.

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

The terms used in the present specification are for describing exemplary embodiments, and therefore, are not intended to limit the present invention. In this specification, the singular form also includes the plural form unless specifically stated in the phrase. As used in the specification, "comprise" and/or "comprising" refers to the presence of one or more other components, steps, actions and/or elements in which the recited component, step, operation and/or element Or does not preclude additions.

5 is a cross-sectional view illustrating an in-plane switching type liquid crystal display including an optical compensation film according to a first embodiment of the present invention.

In addition, FIG. 6 is an in-plane switching liquid crystal display device including an optical compensation film according to the first embodiment of the present invention shown in FIG. 5 in which an in-cell retarder is applied. It is a cross-sectional view schematically showing the structure of a liquid crystal panel.

5 and 6, the in-plane switching type liquid crystal display device 100 according to the first embodiment of the present invention is located under the liquid crystal panel 110 and the liquid crystal panel 110 for outputting an image. It consists of a first polarizing plate 105 and a second polarizing plate 115 positioned above the liquid crystal panel 110. Here, the upper and lower portions of the liquid crystal panel 110 are not limited to a specific position. Accordingly, 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. ) May be located.

In this case, the liquid crystal panel 110 is largely composed of a color filter substrate 111 and an array substrate 101, and a liquid crystal layer (not shown) formed between the color filter substrate 111 and the array substrate 101.

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

As a driving mode using a 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 mentioned.

At this time, the in-plane switching method uses a voltage-controlled birefringence (ECB) effect, and uses a horizontal electric field formed by forming a nematic liquid crystal homogeneously oriented in the absence of an electric field as a pixel electrode and a common electrode. It is a driving method.

In addition, the fringe field switching method is driven in the same manner as the in-plane switching method. The lateral electric field of the fringe field switching method is referred to as a fringe field, and the fringe field is made of a transparent conductive material. , It can be formed by setting it to be narrower than the interval between the lower substrates.

Here, in the case of the first embodiment of the present invention, an in-plane switching type liquid crystal display is described as an example, but the present invention is not limited thereto, and the present invention is also applied to a fringe-field switching type liquid crystal display. I can.

In addition, although the shape of the pixel electrode and the common electrode is not shown in the drawing, in FIG. 1, the pixel electrode and the common electrode have a straight shape, but the pixel electrode and the common electrode have a zig-zag shape. It is possible. 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 linear or zigzag shape, and the other may have a rectangular shape. That is, in the present invention, the shape of the pixel electrode and the common electrode is not limited.

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 a metal such as copper (Cu) or a copper alloy. Do. That is, in the present invention, the material for forming the pixel electrode and the common electrode is not limited.

The color filter substrate 111 includes a color filter 107 and a sub-color filter composed of a plurality of sub-color filters implementing colors of red (R), green (G), and blue (B). It consists of a black matrix 106 that divides the space and blocks light that passes through the liquid crystal layer.

On the color filter substrate 111 on which the color filter 107 and the black matrix 106 are formed, the overcoat layer 108 made of a predetermined organic material to prevent the leakage of the dye and to planarize the surface of the color filter 107 Can be formed.

In addition, the rough filter 107 and the black matrix 106 can also have a zigzag shape. That is, the present invention is not limited to the shape of the color filter and the black matrix.

Further, although not shown for convenience, the array substrate 101 is arranged vertically and horizontally to define a plurality of pixel regions, a plurality of gate lines and data lines, a thin film transistor, which is a switching element formed in a cross region between the gate line and the data line, and A pixel electrode and a common electrode are formed on the pixel region to generate a lateral electric field.

The color filter substrate 111 and the array substrate 101 configured as described above are bonded to face each other by the sealant 140 formed on the outer edge of the image display area to form the liquid crystal panel 110. At this time, the color filter substrate 111 and the array substrate 101 Alignment layers 109 and 119 for aligning the liquid crystal layer are formed on the inner surface of the array substrate 101.

At this time, in the liquid crystal panel 110 according to the first embodiment of the present invention, in order to improve light leakage from the front side, an in-cell-retarder 152 made of a positive A plate is disposed between the color filter substrate 111 and the liquid crystal layer. It is characterized in that it is formed in. The drawing shows an example in which the in-cell-retarder 152 is formed on the lowermost layer of the color filter substrate 111, but the present invention is not limited thereto.

The in-cell-retarder 152 may be formed of a positive A plate type RM (Reactive Mesogen) having a phase delay value of about 156±20 nm on a predetermined alignment layer 151.

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

The first polarizing plate 105 includes a first support 102 and a second support 104 and a first polarizing element 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. It includes a second polarizing element 113 positioned therebetween.

At this time, in the in-plane switching type liquid crystal display device 100 according to the first embodiment of the present invention, the first optical compensation film 120 and the second optical compensation film 130 are sequentially formed on the liquid crystal panel 110. It is characterized in that it is located.

The first polarizing element 103 and the second polarizing element 113 may be made of polyvinyl alcohol (PVA), and the first support 102 and the third support 112 have a retardation. It may be made of a general protective film (protection film) without, for example, may be made of tri-acetyl cellulose (TAC). In addition, the second support 104 may be made of a general protective film without a phase delay to protect the PVA layer, for example, 0-RT (means a modified TAC whose Rth approaches 0 nm, 0-TAC Also referred to as) or COP (Cyclo-olefin-Polymer).

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

In addition, 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. A oriented film, an O-type polarizing element in which a liquid crystal composition containing a dichroic material and a liquid crystal compound are oriented in a predetermined direction, and an E-type polarizing element in which a lyotropic liquid crystal is oriented in a predetermined direction.

The first polarizing element 103 is disposed so that the absorption axis thereof is substantially perpendicular to the absorption axis of the opposite second polarizing element 113, and the optical axis of the liquid crystal axis absorbs light of the first polarizing element 103. It is parallel to the axis. On the other hand, as described above, when the first polarizing plate 105 is positioned above the liquid crystal panel 110 and the second polarizing plate 115 is positioned below the liquid crystal panel 110, the optical axis of the liquid crystal axis is the second polarizing element 113 It is in a state parallel to the light absorption axis of.

Here, in the case of the first embodiment of the present invention, in order to improve the viewing angle characteristic in a diagonal direction, the first optical compensation film 120 and the second optical compensation film ( 130), wherein the first optical compensation film 120 is formed of a positive biaxial film, while the second optical compensation film 130 is formed of a negative biaxial film. Characterized in that.

Hereinafter, a retardation film used as the first optical compensation film 120 and the second optical compensation film 130 will be described in detail with reference to the drawings.

7A and 7B are views for explaining a positive biaxial film and a negative biaxial film used as an optical compensation film in the in-plane switching type liquid crystal display device according to the first embodiment of the present invention. That is, FIGS. 7A and 7B are views for explaining refractive indices of a positive biaxial film and a negative biaxial film, 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 in the size of the refractive index in the optical axis direction and the refractive index in the other direction. For example, if there is one optical axis, it is classified as uniaxial, and if there is two, it is classified as biaxial.If the refractive index in the optical axis direction is greater than the refractive index in other directions, positive, if the refractive index in the optical axis direction is less than the refractive index in other directions Classified as negative.

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

At this time, Re (or Rin) means a phase delay (or phase difference) value in the plane direction, and Rth means a phase delay 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.

[Equation 1]

Re = (nx-ny) d

Rth = (nx-nz) d

Nz = Rth / Re

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

The positive biaxial film (or +B plate) is an optical film whose Nz is less than 0, and has an optical axis between nz and ny as it has a relationship of nz> nx> ny.

In addition, the negative biaxial film (or -B plate) is an optical film having an Nz greater than 1.0 and has a relationship of nx> ny> nz, so that the optical axis is located between nz and nx.

At this time, films that can be used as positive and negative biaxial films include uniaxial stretched TAC (Uniaxial stretched TAC), uniaxially stretched PNB (Polynorbonene), biaxially stretched PC (Polycarbonate), and biaxially stretched COP, Biaxial liquid crystal film (Biaxial LC film), and the like.

The first optical compensation film 120 and the second optical compensation film 130 according to the first embodiment of the present invention having such optical conditions have orthogonality of the first and second polarizing plates 105 and 115 in a diagonal direction. By compensating for cracking, it is possible to reduce light leakage in the diagonal direction, which will be described in detail using the Poincare sphere expression.

In order to geometrically analyze the optical properties of a transparent medium such as a liquid crystal, the expression of the point of polarization is used.

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

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

The inequality of is established, which applies only to perfectly polarized light.

In the case of fully polarized light, the relationship of the following equation (3) 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 radius 1 in 3D space, _{and a sphere consisting of points with (s 1} , s ₂ , s ₃ ) as Cartesian coordinates means a Poencaré sphere.

At this time, all points on the equator line in the Poangcare sphere correspond to linearly polarized light, the north pole to the right-handed circular polarization, and the south pole to the left-handed circularly polarized light. And, all points in the northern hemisphere correspond to the right-handed elliptical polarization, and all points in the southern hemisphere correspond to the left-handed elliptical polarization.

8A and 8B are diagrams showing an arbitrary elliptical polarization and a corresponding point of care vector 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.8A and 8B, the latitude angle of the Poangcare vector P corresponding to the elliptical polarization in which the long axis of the polarization ellipse is Ψ and the ellipse angle is χ is 2χ and 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; if it is in the southern hemisphere, it is counterclockwise. The counterpoints on the Poencaré sphere represent polarization states that are orthogonal to each other.

In addition, the Unitary Jones matrix, which describes the change in the polarization state when light passes through a transparent medium, can be interpreted as a rotational transformation on the Poancaré sphere.

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

In addition, FIGS. 10A and 10B are diagrams showing a polarization state of light passing through each optical element using a Poangcare sphere when viewed from a diagonal direction.

In this case, FIG. 10B is a two-dimensional view illustrating a mechanism for compensating an optical path using the Poangcare sphere shown in FIG. 10A. That is, FIG. 10B corresponds to a view looking at the Poangkare sphere shown in FIG. 10A from the front, and although FIG. 10B, which is expressed in two dimensions, shows the movement before and after each change in the polarization state using arrows in the drawing. Even if it is, it can be expressed on the Poencaré sphere by rotation at a specific angle around a specific axis that is determined corresponding to each optical characteristic.

At this time, as described above, the Poangcare sphere is a representation of all polarization states of light on a spherical surface, and if the optical axis and phase delay values of the optical device are known, the polarization state can be easily predicted using the Poancare sphere, so it is used when designing a compensation film .

In this Poencaré sphere, all points on the equator line represent linearly polarized light _{, the point at the north pole S 3} represents the right-hand circular polarization, and the _{point at the south pole -S 3} represents the left hand circular polarization. In addition, the northern hemisphere of the rest area represents the right-handed elliptical polarization, and the southern hemisphere represents the left-handed elliptical polarization.

In this case, as shown in FIG. 9, points A and A'represent 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 of the lower polarizing plate. It represents the axis and the absorption axis of the upper polarizing plate. The polarization states of the upper polarizing plate and the lower polarizing plate are symmetrical with respect to the center (O) of the Poancaré sphere and are perpendicular to each other, thereby indicating an excellent dark state. That is, as described above, the counterpoints A and B'on the Poangcare sphere represent polarization states that are orthogonal to each other.

However, as shown in FIGS. 10A and 10B, when the liquid crystal display 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.} And, the absorption axis (B') of the upper polarizing plate and the absorption axis (A) of the lower polarizing plate move a predetermined distance toward the _{-S 2 axis.} At this time, since the points A and 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 light reaching the upper polarizing plate must be aligned 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 point B'.

That is, after the incident light passes through the lower polarizing plate in which the absorption axis direction is located at point A on the Point A, the point B is linearly polarized and positioned at 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, the linearly polarized light does not have a phase change in the liquid crystal layer. Accordingly, the light passing through the liquid crystal layer maintains the same linearly polarized state and has a polarization state corresponding to point B.

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

Therefore, when the liquid crystal display device 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, first, a positive two-axis film, which is the first optical compensation film. The film PB moves from point B to point C, and moves from point C to point B'by the negative biaxial film NB, the second optical compensation film. Accordingly, the polarization state of the light reaching the upper polarizing plate (point B') coincides with the absorption axis of the upper polarizing plate, and the light is blocked thereby indicating an excellent dark state.

Specifically, when the linearly polarized light passes through the positive biaxial film PB according to the first embodiment of the present invention, the optical axis is located in a predetermined region between nz and ny, the linearly polarized light is a positive biaxial film PB. Light elliptical polarized light at point C by rotating counterclockwise at 2π times of the value dividing the effective phase delay value of the positive biaxial film (PB) by 550nm, the wavelength of green that affects the luminance, based on the optical axis of Will change. The elliptically polarized light meets the second optical compensation film, the negative biaxial film (NB).

The optical axis of the negative biaxial film NB is located in a predetermined region between nz and nx, and the elliptically polarized light is the effective phase delay value of the negative biaxial film NB around the optical axis of the negative biaxial film NB. By rotating counterclockwise by 2π times the value divided by 550nm, it changes into linearly polarized light at point B'. At this time, since the point B'represents the absorption axis of the upper polarizing plate, the incident light is completely absorbed by the upper polarizing plate, thereby exhibiting an excellent dark state.

As described above, in the first embodiment of the present invention, by sequentially using a positive biaxial film and a negative biaxial film to adjust the polarization state, light leakage in a diagonal direction can be prevented and a decrease in contrast ratio can be prevented.

On the other hand, even when viewed from the front as described above, light leakage occurs due to external stress applied to the liquid crystal panel, which is caused by interference between the device and the liquid crystal panel and stress during the array and color filter process. This is because it has anisotropy.

11 is a diagram showing a state in which light leakage occurs due to external stress using a Poangcare sphere.

Referring to FIG. 11, when an in-plane switching liquid crystal display device without an in-cell retarder is viewed from the front, the polarization state of light passing through each optical element First, when passing through the lower glass substrate (ie, the array substrate), the light path moves from B to D. This is because the glass substrate has refractive index anisotropy due to external stress, and the light path moves from B to D by the phase delay value (~ 10 nm) of the glass substrate.

Thereafter, the liquid crystal layer having a phase delay value of 280 to 350 nm moves from point D to point E, and moves from point E to point F again by the upper glass substrate (ie, color filter substrate).

At this time, the liquid crystal layer has a phase delay value of 280 to 350 nm, but since the alignment direction is perpendicular to the polarization direction of the light linearly polarized by the lower polarizing element, the linearly polarized light does not have a phase change in the liquid crystal layer. However, when the glass substrate has refractive index anisotropy, the light linearly polarized by the lower polarizing element is changed into elliptically polarized light by the phase delay value of the glass substrate before it meets the liquid crystal layer. The light passing through is elliptically polarized again by the phase delay value of the liquid crystal layer and moves to point E.

Then, it moves from point F to point G by the positive biaxial film and the negative biaxial film, which are optical compensation films. Accordingly, the polarization state of light reaching the upper polarizing element does not coincide with the absorption axis (point B) of the upper polarizing element, and accordingly, light leakage occurs.

12A and 12B are views for explaining a state in which light leakage is improved by applying the in-cell-retarder according to the first embodiment of the present invention, using a Poangcare sphere.

In this case, FIG. 12B is a two-dimensional view illustrating a mechanism for compensating an optical path using the Poangcare sphere shown in FIG. 12A.

12A and 12B, when an in-plane switching liquid crystal display device in a state in which an in-cell-retarder is applied according to the first embodiment of the present invention is viewed from the front direction, each optical element passes through the liquid crystal display. As for the polarization state of light, the path of light moves from B to D when it first passes through the lower glass substrate (ie, the array substrate).

Thereafter, as described above, the liquid crystal layer having a phase delay value of 280 to 350 nm moves from point D to point E.

Thereafter, according to the phase delay value of the in-cell-retarder according to the first embodiment of the present invention, it moves from point E to point F'(= point D), and by the upper glass substrate (i.e., color filter substrate). Again, it moves from point F'to point G'(= point B).

In this case, the in-cell-retarder may be made of a positive A plate type RM (Reactive Mesogen) having a phase delay value of about 156±20 nm.

The optical axis of the positive A plate is located in a predetermined area of nx, and the light elliptically polarized by the liquid crystal layer is counterclockwise by 2π times the effective phase delay value of the positive A plate divided by 550 nm around the optical axis of the positive A plate. By rotating in the direction, it moves from point E to point F'.

Then, the light moving to the G'point (= point B) is finally moved to the point B while maintaining the polarization state by the positive biaxial film and the negative biaxial film, which are optical compensation films. Therefore, the incident light is completely absorbed by the upper polarizing element, thereby exhibiting an excellent dark state in the front direction.

As described above, according to the present invention, as the path of light twisted by the glass substrate is compensated by the in-cell-retarder, it has the same path of light as when the glass substrate is isotropic. Accordingly, it is possible to improve light leakage in the front direction caused by external stress.

On the other hand, above has been described based on light of green wavelength, which mainly affects luminance, but in the above-described in-cell-retarder structure, compared to the previous (i.e., a structure in which in-cell-retarder is not applied) A phenomenon in which colors appear bluish occurs at the viewing angle, and thus the polarization state of light is divided and examined by wavelength.

13A and 13B are views showing the polarization states of light passing through each optical device by dividing each wavelength when viewed from a diagonal direction.

In this case, FIG. 13A shows the polarization state of light passing through each optical element in two dimensions when the in-cell-retarder is not applied. In addition, FIG. 13B shows a two-dimensional polarization state of light passing through each optical device in the case of applying the in-cell-retarder.

That is, as described above, although FIGS. 13A and 13B expressed in two dimensions are shown as movements before and after each change in the polarization state using arrows in the drawing, It can be expressed on a Poencaré sphere by rotation at a specific angle.

14A and 14B are diagrams showing measurement results of luminance viewing angle characteristics in a dark state when viewed from a diagonal direction. In this case, FIG. 14A shows, for example, a luminance viewing angle characteristic in a dark state when an in-cell-retarder is not applied. In addition, FIG. 14B shows, for example, a luminance viewing angle characteristic in a dark state when an in-cell-retarder is applied.

13A and 13B, as described above, the polarization state of light passing through each optical device (when green is based) is first determined by B by the positive biaxial film PB, which is the first optical compensation film. It moves from point C to point C, and moves from point C to point B'by the negative biaxial film (NB), the second optical compensation film.

Specifically, when the linearly polarized red, green, and blue light passes through the positive biaxial film PB located in a predetermined area between nz and ny, the positive 2 axial film PB is based on the optical axis of the positive biaxial film PB. The effective phase delay value of the axial film PB is rotated counterclockwise by 2π times the value divided by each wavelength of red, green, and blue, thereby respectively changing into elliptical polarized light near the point C. The elliptically polarized red, green, and blue light meets the second optical compensation film, the negative biaxial film NB.

In the negative biaxial film NB, the optical axis is located in a predetermined region between nz and nx, and the elliptically polarized red, green, and blue light is centered on the optical axis of the negative biaxial film NB. The effective phase delay value of) is rotated counterclockwise by 2π times the value divided by the respective wavelengths of red, green, and blue, so that each change into linearly polarized light near the point B'. At this time, the point B'represents the absorption axis of the upper polarizing plate, and when green is used as the reference, the incident light is completely absorbed by the upper polarizing plate, indicating an excellent dark state.

However, light has a different phase delay value for each wavelength, and at this time, the phase delay value is large in the light of a short wavelength (i.e., blue (= 450 nm)) due to the wavelength dispersion characteristic, which causes the path of blue light to move the most. do.

In this case, as shown in FIG. 13B, when the in-cell-retarder is applied, the phase delay value of the liquid crystal panel increases by about 158 nm, and thus, the path of blue light moves more than before. As a result, a bluish phenomenon occurs in a diagonal viewing angle (see Figs. 14A and 14B).

At this time, it can be seen that the largest factor affecting the light movement path is the configuration of a negative biaxial film that moves from point C to point B'with reference to FIGS. 13A and 13B. Therefore, in the present invention, by applying an inverse dispersion film to a negative biaxial film to limit the dispersion of blue light, it is intended to improve the bluish color in the in-cell-retarder structure. It will be described in detail through examples.

15 is a cross-sectional view illustrating an in-plane switching type liquid crystal display device including an optical compensation film according to a second exemplary embodiment of the present invention.

In this case, the second embodiment of the present invention shown in FIG. 15 is substantially the same as the configuration of the first embodiment of the present invention, except for applying the reverse dispersion film to the negative biaxial film. Accordingly, the structure of the liquid crystal panel to which the in-cell-retarder is applied is substantially the same as that of FIG. 6, and a description thereof will be made with reference to FIG. 6.

In addition, FIG. 16 is a graph showing the wavelength dispersion characteristics, and compares the normal dispersion and the inverse dispersion characteristics.

Referring to FIG. 15, 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 located below the liquid crystal panel 210. It consists of a polarizing plate 205 and a second polarizing plate 215 positioned above the liquid crystal panel 210.

In this case, the liquid crystal panel 210 is largely composed of a color filter substrate and an array substrate, and a liquid crystal layer formed between the color filter substrate and the array substrate.

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

As described above, in the case of the second embodiment of the present invention, an in-plane switching type liquid crystal display is described as an example, but the present invention is not limited thereto, and the present invention is a fringe-field switching type liquid crystal display device. It can also be applied to

The color filter substrate is composed of a color filter composed of a plurality of sub-color filters implementing colors of red, green, and blue, and a black matrix that separates the sub-color filters and blocks light passing through the liquid crystal layer.

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

In addition, the array substrate is arranged vertically and horizontally to generate a lateral electric field by being formed on a plurality of gate lines and data lines defining a plurality of pixel areas, a thin film transistor, which is a switching element, and a pixel area that is a switching element formed in an intersection area between the gate line and the data line. It consists of a pixel electrode and a common electrode.

The color filter substrate and the array substrate configured as described above are bonded to each other by a sealant formed on the outer edge of the image display area to form the liquid crystal panel 210, and at this time, an alignment layer for alignment of the liquid crystal layer is formed on the inner surface of the color filter substrate and the array substrate. Is formed.

At this time, the liquid crystal panel 210 according to the second embodiment of the present invention is characterized in that an in-cell-retarder made of a positive A plate is formed between the color filter substrate and the liquid crystal layer to improve light leakage from the front side. It is done.

Such an in-cell-retarder may be formed of a positive A plate type RM (Reactive Mesogen) having a phase delay value of about 156±20 nm on a predetermined alignment layer.

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.

The first polarizing plate 205 includes a first support 202 and a second support 204, and a first polarizing element 203 positioned between the first support 202 and the second support 204. In addition, the second polarizing plate 215 includes the third support 212 and the first and second optical compensation films 220 and 230 ′, and the third support 212 and the first and second optical compensation films 220 and 230. ') and a second polarizing element 213 located between.

In this case, the in-plane switching type liquid crystal display 200 according to the second exemplary embodiment of the present invention includes a first optical compensation film 220 and a second optical compensation film 230 ′ on the liquid crystal panel 210 in turn. It is characterized in that it is located.

The first polarizing element 203 and the second polarizing element 213 may be made of polyvinyl alcohol, and the first support 202 and the third support 212 may be made of a general protective film without phase delay, For example, it may be made of triacetyl cellulose. In addition, the second support 204 may be made of a general protective film without a phase delay in order to protect the PVA layer, for example, 0-RT (Rth means a modified TAC approaching 0 nm, 0-TAC Also referred to as) or COP (Cyclo-olefin-Polymer).

The optical film used for the first polarizing element 203 and the second polarizing element 213 is not particularly limited, but, for example, a stretched film of a polymer film containing as a main component a PVA-based resin containing iodine or a dichroic dye , An O-type polarizing element in which a liquid crystal composition containing a dichroic material and a liquid crystal compound are aligned in a predetermined direction, and an E-type polarizing element in which a lyotropic liquid crystal is aligned in a predetermined direction.

The first polarizing element 203 is disposed so that its absorption axis is substantially perpendicular to the absorption axis of the second polarizing element 213 opposite, and the optical axis of the liquid crystal axis absorbs light of the first polarizing element 203. It is parallel to the axis. On the other hand, as described above, when the first polarizing plate 205 is located above the liquid crystal panel 210 and the second polarizing plate 215 is located below the liquid crystal panel 210, the optical axis of the liquid crystal axis is the second polarizing element 213 It is in a state parallel to the light absorption axis of.

Here, in the case of the second embodiment of the present invention, in order to improve the viewing angle characteristic in a diagonal direction, the first optical compensation film 220 and the second optical compensation film ( 230) is disposed, wherein the first optical compensation film 220 is formed of a positive biaxial film while the second optical compensation film 230' is formed of a negative biaxial film.

In particular, the second optical compensation film 230' according to the second embodiment of the present invention is characterized in that it is formed of a negative biaxial film having an inverse dispersion characteristic.

At this time, the positive biaxial film (or +B plate) is an optical film having Nz less than 0, and has a relationship of nz> nx> ny, so that the optical axis is located between nz and ny.

In addition, the negative biaxial film (or -B plate) is an optical film having an Nz greater than 1.0 and has a relationship of nx> ny> nz, so that the optical axis is located between nz and nx. For example, the negative biaxial film according to the second embodiment of the present invention is characterized in that Nz is about 1.375, Re has a value of 110±10nm, and Rth has a value of 80±5nm.

At this time, Re (or Rin) means a phase delay (or phase difference) value in the plane direction, and Rth means a phase delay value in the thickness direction. In addition, Nz means an index indicating the degree of biaxiality of the biaxial retardation film, and is the same as in Equation 1 above.

Referring to FIG. 16 for the inverse dispersion characteristic, as opposed to the positive dispersion, as the wavelength decreases, the phase delay value decreases, and it can be seen that the change in the phase delay value for each wavelength is less than that of the positive dispersion.

As described above, the biggest factor influencing the light movement path is the configuration of the negative biaxial film. Therefore, in the second embodiment of the present invention, the movement of blue light is prevented by applying an inverse dispersion film to the negative biaxial film. By minimizing it, it is possible to improve the bluish color in the in-cell-retarder structure.

17A and 17B are views for explaining a state in which the color sense is improved by applying the reverse dispersion film according to the second embodiment of the present invention, using a Poangcare sphere.

In this case, FIGS. 17A and 17B are views showing the polarization states of light passing through each optical device by dividing each wavelength when viewed from a diagonal direction.

In particular, FIG. 17B is a two-dimensional view illustrating a mechanism by which the color sense is improved by using the Poangcare sphere shown in FIG. 17A. That is, FIG. 17B corresponds to a view of the Poencaré sphere shown in FIG. 17A from the front, and although FIG. 17B, which is expressed in two dimensions, shows the movement before and after each change in the polarization state using arrows in the drawing. Even if it is, it can be expressed on the Poencaré sphere by rotation at a specific angle around a specific axis that is determined corresponding to each optical characteristic.

In addition, FIG. 18 is a view showing a measurement result of a luminance viewing angle characteristic in a dark state in an in-plane switching liquid crystal display device including an optical compensation film according to a second exemplary embodiment of the present invention.

Referring to FIGS. 17A and 17B, as described above, the polarization state of light passing through each optical device (when green is based) is first determined by B by the positive biaxial film PB, which is the first optical compensation film. It moves from point C to point C, and moves from point C to point B'by the negative biaxial film (NB), the second optical compensation film.

Specifically, when the linearly polarized red, green, and blue light passes through the positive biaxial film PB located in a predetermined area between nz and ny, the positive 2 axial film PB is based on the optical axis of the positive biaxial film PB. The effective phase delay value of the axial film PB is rotated counterclockwise by 2π times the value divided by each wavelength of red, green, and blue, thereby respectively changing into elliptical polarized light near the point C. The elliptically polarized red, green, and blue light meets the second optical compensation film, the negative biaxial film NB.

In the negative biaxial film NB, the optical axis is located in a predetermined region between nz and nx, and the elliptically polarized red, green, and blue light is centered on the optical axis of the negative biaxial film NB. The effective phase delay value of) is rotated counterclockwise by 2π times the value divided by the respective wavelengths of red, green, and blue, so that each change into linearly polarized light near the point B'. At this time, the point B'represents the absorption axis of the upper polarizing plate, and when green is used as the reference, the incident light is completely absorbed by the upper polarizing plate, indicating an excellent dark state.

At this time, in the second embodiment of the present invention, as the negative biaxial film NB has inverse dispersion characteristics, the positive biaxial film PB is characterized by offsetting the normal dispersion characteristics. In other words, light has a different phase delay value for each wavelength, and in this case, the phase delay value is large in light of a short wavelength (i.e., blue (= 450 nm)) due to the wavelength dispersion characteristic (in the case of a positive dispersion characteristic), and thus, the blue light The path of will travel the most. In this case, in the second embodiment of the present invention, as the negative biaxial film NB is used as a film having inverse dispersion characteristics, it is possible to minimize the movement of blue light, which has a lot of movement by the positive biaxial film PB. do.

As a result, it can be seen that the final moving path of the blue light is smaller than before, and as shown in FIG. 18, it can be seen that the bluish color is improved.

19A, 19B, and 19C are diagrams showing simulation results of light leakage according to a phase delay value of an inverse dispersion film when viewed from a diagonal direction.

In this case, FIGS. 19A, 19B, and 19C show simulation results of light leakage when Re of the reverse dispersion film is 100 nm, 110 nm, and 120 nm, respectively (Rth = 80 nm).

Referring to FIG. 19A, when Re of the reverse dispersion film is 100 nm, it can be seen that the maximum transmittance of the diagonal viewing angle in the dark state corresponds to about 0.001376.

Further, referring to FIGS. 19B and 19C, when Re of the reverse dispersion film is 110 nm, the maximum transmittance of the diagonal viewing angle in the dark state is about 0.001301, and when Re of the reverse dispersion film is 100 nm, it is about 0.001330. You can see that it is.

As the Rth of the reverse dispersion film increases, a reddish color is obtained, and it can be seen that the luminance value in the dark state is minimized at 110 nm and 80 nm of Re and Rth, respectively.

Although many items are specifically described in the above description, this should be construed as an example of a preferred embodiment rather than limiting the scope of the invention. Therefore, the invention should not be determined by the described embodiments, but should be determined by the claims and equivalents to the claims.

100,200: liquid crystal display device 101,111: glass substrate
103,203, 113,213: polarizing element 105,205, 115,215: polarizing plate
106: black matrix 107: color filter
109,119,151: alignment layer 110,210: liquid crystal panel
120,220, 130,230': Optical compensation film
152: In-Cell-Retarder

Claims (8)

A liquid crystal panel including an array substrate and a color filter substrate, and a liquid crystal layer formed 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;
A second polarizing plate positioned on an outer surface of the color filter substrate and including first and second optical compensation films and second polarizing elements; And
Including an in-cell-retarder formed between the color filter substrate and the liquid crystal layer,
The first optical compensation film is made of a positive biaxial film having a positive dispersion characteristic, the second optical compensation film is made of a negative biaxial film having an inverse dispersion characteristic,
The in-cell-retarder is an in-plane switching type liquid crystal display including an optical compensation film made of a positive A plate type RM (Reactive Mesogen). The liquid crystal display of claim 1, wherein the absorption axis of the first polarizing element and the absorption axis of the second polarizing element are perpendicular to each other. The liquid crystal display of claim 1, wherein the optical axis of the liquid crystal layer comprises an optical compensation film parallel to the 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. An in-plane switching type liquid crystal display including an optical compensation film positioned therebetween. delete The liquid crystal display of claim 4, wherein the second optical compensation film comprises an optical compensation film made of a negative biaxial film having a biaxiality (Nz) of 1.375. The method of claim 1, wherein the second optical compensation film has a phase delay value (Re) of 110±10 nm in a plane direction, and a phase delay value (Rth) of 80±5 nm in a thickness direction. An in-plane switching type liquid crystal display including an optical compensation film. The in-plane switching method of claim 1, wherein the in-cell-retarder is made of a positive A plate type RM (Reactive Mesogen) having a phase delay value of 156±20 nm. Liquid crystal display.

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