KR101408258B1 - In plane switching mode liquid crystal display device having optical compensation film - Google Patents

Abstract

The transverse electric field type liquid crystal display device including the optical compensation film of the present invention can be manufactured by applying a positive biaxial film and a negative C plate like film to the upper and lower sides in a dark state A liquid crystal display panel including a liquid crystal layer for improving contrast ratio in left and right and diagonal directions and reducing color shift; A first polarizer located at a lower portion of the liquid crystal display panel, the first polarizer comprising a first support and a second support, and a first polarizer disposed between the first and second supports; And a second polarizing element positioned on the liquid crystal display panel and positioned between the third support and the first and second optical compensation films and between the third support and the first and second optical compensation films, Wherein the first optical compensation film is defined as -8.0 <Nz <0, where Nz = Rth / Re, Re = (nx-ny) d and Rth = (nx-nz) nx, ny and nz denote refractive indexes in the x direction, the y direction and the z direction, respectively, and d denotes the thickness of the film), and the second optical compensation film is made of a negative C plate And the first optical compensation film is positioned between the second optical compensation film and the liquid crystal display panel.

 Positive biaxial film, negative C plate-like film, transverse electric field system

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a transverse electric field type liquid crystal display (LCD)

BACKGROUND OF THE INVENTION 1. Field of the Invention [0002] The present invention relates to a transverse electric field type liquid crystal display, and more particularly, to a transverse electric field type liquid crystal display including an optical compensation film for improving the contrast ratio in up, down, left and right and diagonal directions.

Recently, interest in information display has increased, and a demand for using portable information media has increased, and a light-weight flat panel display (FPD) that replaces a cathode ray tube (CRT) And research and commercialization are being carried out. Particularly, among such flat panel display devices, a liquid crystal display (LCD) is an apparatus for displaying an image using the optical anisotropy of a liquid crystal, and is excellent in resolution, color display and picture quality and is actively applied to a notebook or a desktop monitor have.

The liquid crystal display comprises 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 includes a color filter composed of a plurality of sub-color filters implementing colors of red (R), green (G), and blue (B) A black matrix for isolating light passing through the liquid crystal layer, and a transparent common electrode for applying a voltage to the liquid crystal layer.

The array substrate may include a plurality of gate lines and data lines arranged vertically and horizontally to define a plurality of pixel regions, a thin film transistor (TFT) which is a switching element formed in a crossing region between the gate line and the data line, And a pixel electrode formed on the pixel region.

The color filter substrate and the array substrate are adhered to each other so as to face each other with a sealant formed on the outer periphery of the image display area to constitute a liquid crystal display panel, And a joining key formed on the array substrate.

In this case, the above-described liquid crystal display device is a twisted nematic (TN) type liquid crystal display device in which nematic liquid crystal molecules are driven in a direction perpendicular to the substrate. The liquid crystal display device of the above- As shown in Fig. This is because of the refractive anisotropy of the liquid crystal molecules, and liquid crystal molecules aligned horizontally with the substrate are oriented in a direction substantially perpendicular to the substrate when a voltage is applied to the liquid crystal display panel.

(IPS) type liquid crystal display device in which a liquid crystal molecule is driven in a horizontal direction with respect to a substrate to improve a viewing angle to 170 degrees or more. Referring to the drawings, the liquid crystal display device of the lateral electric field system Will be described in detail.

FIG. 1 is a plan view schematically showing a part of an array substrate of a general transverse electric field type liquid crystal display device. In an actual liquid crystal display device, there are MxN pixels where N gate lines and M data lines intersect. However, In the drawing, one pixel is shown.

2 is a cross-sectional view taken along line I-I 'of the array substrate shown in Fig. 1, and shows the array substrate shown in Fig. 1 together with the color filter substrate bonded thereto corresponding to the array substrate .

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

The thin film transistor T is connected to the pixel electrode 18 through a gate electrode 21 connected to the gate line 16, a source electrode 22 connected to the data line 17 and a pixel electrode line 18l. And a drain electrode 23 connected to the drain electrode 23. The thin film transistor includes a first insulating layer 15a for insulating between the gate electrode 21 and the source and drain electrodes 22 and 23 and a first insulating layer 15b for insulating the source and drain electrodes 22 and 23 by a gate voltage supplied to the gate electrode 21. [ And an active pattern 24 that forms a conductive channel between the drain electrode 22 and the drain electrode 23. [

Reference numeral 25 denotes an ohmic contact layer for ohmic contact between the source / drain region of the active pattern 24 and the source / drain electrodes 22 and 23. [

In this case, a common line 81 and a storage electrode 18s are arranged in the pixel region in a direction parallel to the gate line 16, and a transverse electric field 90 is generated in the pixel region, A plurality of common electrodes 8 and pixel electrodes 18 for switching the data lines 17 are arranged in a direction parallel to the data lines 17.

At this time, the storage electrode 18s is overlapped with a part of the common line 81 below the first insulating layer 15a to form a storage capacitor Cst.

The transparent color filter substrate 5 is provided with a black matrix 6 for preventing light from leaking into the thin film transistor T, the gate line 16 and the data line 17 and a red, green and blue color The color filter 7 is formed.

An alignment film (not shown) for determining the initial alignment direction of the liquid crystal molecules is formed on the surface of the array substrate 10 and the color filter substrate 5, 10 and the color filter substrate 5 are arranged with polarizing plates (not shown) so that their light transmission axes are perpendicular to each other.

In the general transverse electric field type liquid crystal display device having the above structure, the common electrode 8 and the pixel electrode 18 are arranged on the same array substrate 10 to generate a transverse electric field, And thus the viewing angle can be improved.

However, such a transverse electric field type liquid crystal display device has a problem that light leakage occurs in the diagonal direction when displaying a black state, resulting in a low contrast ratio.

FIG. 3A is a graph showing a simulation result of a luminance viewing angle characteristic in a dark state in a general transverse electric field type liquid crystal display device, and FIG. 3B is a diagram showing a result of measuring a luminance viewing angle characteristic in a dark state.

3A and 3B are graphs showing the luminance viewing angle characteristics in the dark state when 0-RT (TAC (Tri-acetyl cellulose) film with Rth near 0 nm) is applied between the PVA (polyvinyl acetate) layer and the liquid crystal layer of the polarizing plate For example.

The lower polarizer plate and the upper polarizer plate are arranged such 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 polarizer plate.

As shown in the figure, large light leakage occurs at 45 degrees, 135 degrees, 225 degrees, and 315 degrees corresponding to the diagonal direction of the liquid crystal display panel in the dark state, thereby increasing the brightness, The contrast ratio is lowered. For example, at 45 degrees in the diagonal direction, the luminance is measured to be about 8 nits, and the maximum transmittance of the diagonal viewing angle in the dark state is about 0.001920 when the inclination angle and the isometric angle are 60 and 45, respectively.

However, such a problem is not a problem of the transverse electric field type liquid crystal display device itself but a problem caused by a polarizing plate generally used. That is, in general, the diagonal light leakage is more effective than the effect due to the liquid crystal layer due to the polarizing plate, and since the transverse electric field mode, like the transverse electric field type liquid crystal display device, can determine the initial alignment state so as not to be influenced by the liquid crystal in all directions, In the case of light, the light leakage is caused entirely by the polarizing plate.

This is because even if the light absorption axes of the polarizing plates are orthogonal to each other, the orthogonality of the two polarizing plates is broken along the viewing angle direction as shown in Figs. 4A and 4B. 4A and 4B show, for example, the optical absorption axis direction of the upper polarizer plate, and the dotted line shows the light absorption axis direction of the lower polarizer plate.

As shown in FIG. 4A, when the liquid crystal display panel is viewed from the front, the optical absorption axes of the upper and lower polarizers are 90 degrees to realize the dark state. However, as shown in FIG. 4B, When the panel is viewed, the light absorption axis of the upper and lower polarizers becomes 90 degrees or more, and light leakage occurs because the orthogonality of the two polarizers is broken.

As described above, in the transverse electric field type liquid crystal display device, a retardation change of the liquid crystal depending on the voltage is small in a manner that a transverse electric field is applied to the liquid crystal layer, and the optical axis of the upper and lower polarizers maintains a vertical state in the up, However, in the diagonal direction where the optical axes of the upper and lower polarizers are broken, the light leakage occurs and the image quality deteriorates.

In order to improve the image quality degradation in the diagonal direction, a compensation film should be applied. However, current optical compensation films protecting the PVA layer of the polarizing plate have a limitation in compensation. At this time, since the PVA layer is a polarizing element that affects the polarizing property of the polarizing plate and is vulnerable to moisture, it is generally protected by using a film such as TAC, 0-RT. Can not be compensated for.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a transverse electric field type liquid crystal display device including an optical compensation film for preventing light leakage in a diagonal direction in a dark state.

It is another object of the present invention to provide a transverse electric field type liquid crystal display device including an optical compensation film for reducing color shift.

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 transverse electric field type liquid crystal display device including an optical compensation film of the present invention comprises: a liquid crystal display panel including a liquid crystal layer; A first polarizer located at a lower portion of the liquid crystal display panel, the first polarizer comprising a first support and a second support, and a first polarizer disposed between the first and second supports; And a second polarizing element positioned on the liquid crystal display panel and positioned between the third support and the first and second optical compensation films and between the third support and the first and second optical compensation films, Wherein the first optical compensation film is defined as -8.0 <Nz <0, where Nz = Rth / Re, Re = (nx-ny) d and Rth = (nx-nz) nx, ny and nz denote refractive indexes in the x direction, the y direction and the z direction, respectively, and d denotes the thickness of the film), and the second optical compensation film is made of a negative C plate And the first optical compensation film is positioned between the second optical compensation film and the liquid crystal display panel.

Another transversal liquid crystal display device including the optical compensation film of the present invention includes a liquid crystal display panel including a liquid crystal layer; A first polarizer located at a lower portion of the liquid crystal display panel, the first polarizer comprising a first support and a second support, and a first polarizer disposed between the first and second supports; And a second polarizing element positioned on the liquid crystal display panel and positioned between the third support and the first and second optical compensation films and between the third support and the first and second optical compensation films, Wherein the first optical compensation film comprises a positive biaxial film and the second optical compensation film comprises a negative C plate similar film and the first optical compensation film comprises the second optical compensation film and the liquid crystal display And is positioned between the panels.

As described above, the transverse electric field type liquid crystal display device including the optical compensation film according to the present invention has the effect of reducing the darkness of the dark state by 80% or more and improving the contrast ratio of the diagonal viewing angle by 80% or more.

Further, the transverse electric field type liquid crystal display device including the optical compensation film according to the present invention provides an effect of improving the image quality by improving the color shift according to the viewing angle.

Hereinafter, preferred embodiments of the transverse electric field type liquid crystal display device including the optical compensation film according to the present invention will be described in detail with reference to the accompanying drawings.

5 is a cross-sectional view schematically showing a transverse electric field type liquid crystal display device including an optical compensation film according to a first embodiment of the present invention.

As shown in the figure, a transverse electric field type liquid crystal display (LCD) 100 according to a first embodiment of the present invention includes a liquid crystal display panel 110 for outputting an image and a liquid crystal display panel 1 polarizing plate 105 and a second polarizing plate 115 located above the liquid crystal display panel 110. [ The upper and lower portions of the liquid crystal display panel 110 are not limited to specific positions and thus the first polarizer 105 is positioned above the liquid crystal display panel 110 and the lower portion of the liquid crystal display panel 110 The second polarizing plate 115 may be positioned on the second polarizing plate 115.

Although not shown in detail in the drawing, the liquid crystal display panel 110 mainly comprises 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 liquid crystal layer may include nematic liquid crystals homogeneously oriented in the absence of an electric field, and the liquid crystal layer may exhibit a refractive index distribution of nx> ny = nz The refractive index is nx and ny, and the refractive index in the thickness direction is nz). In this specification, ny = nz includes not only the case where ny and nz are completely equal but also the case where ny and nz are substantially equal.

The driving mode using the liquid crystal layer exhibiting such a refractive index distribution may be, for example, a transverse electric field system or a fringe field switching (FFS) mode.

In the transverse electric field system, a nematic liquid crystal homogeneously aligned in a state in which no electric field is present is driven by a transverse electric field formed by a pixel electrode and a common electrode using an Electrically Controlled Birefringence (ECB) to be.

The FFS mode is driven in the same manner as the transverse electric field system. The transverse electric field in the FFS mode is called a fringe field. The fringe field is a field between the pixel electrode and the common electrode formed of a transparent conductive material, By setting the distance between the first electrode and the second electrode.

Here, in the first embodiment of the present invention, a lateral electric field type liquid crystal display device is described as an example, but the present invention is not limited thereto, and the present invention can also be applied to the FFS mode liquid crystal display device.

The color filter substrate is divided into a color filter composed of a plurality of sub-color filters implementing the colors of red (R), green (G) and blue (B) And a black matrix for blocking light transmitted through the liquid crystal layer.

The array substrate includes a plurality of gate lines and data lines arranged vertically and horizontally to define a plurality of pixel regions, a thin film transistor which is a switching element formed in a crossing region between the gate lines and the data lines, And a common electrode.

The first polarizer 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. The second polarizing plate 115 is disposed between the third support 112 and the first and second optical compensation films 120 and 130 and the first and second optical compensation films 120 and 130, And a second polarizing element 113 positioned between the first polarizing element 113 and the second polarizing element 113.

Here, the first polarizer 103 and the second polarizer 113 may be made of polyvinyl alcohol (PVA), and the first and second support members 102 and 112 may have phase retardation And can be made of, for example, triacetyl cellulose (TAC). The second support 104 may be made of a general protective film having no phase delay. For example, the second support 104 may be made of 0-RT (modified TAC with Rth approaching 0 nm, also referred to as 0-TAC) Or the TAC that is the same as the first and second supports 102 and 112. For reference, the expression that there is no phase delay means that Re is 0, the TAC is a protective film in which Re is 0 and Rth is not 0, and 0-RT is a protective film in which Re is 0 and Rth is close to 0 .

The first polarizing element 103 and the second polarizing element 113 are films that can be converted into natural polarized light or polarized light. The first polarizing element 103 and the second polarizing element 113 have a function of passing one of the polarized light components when the incident light is divided into two polarized light components orthogonal to each other, And a function of absorbing, reflecting, and scattering the component may be used.

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

The first polarizing element 103 is disposed such that its absorption axis is substantially orthogonal to the absorption axis of the second polarizing element 113. The optical axis of the liquid crystal axis is parallel to the absorption axis of the first polarizing element 103, And is in parallel with the light absorption axis of the light source. When the first polarizing plate 105 is positioned above the liquid crystal display panel 110 and the second polarizing plate 115 is positioned below the liquid crystal display panel 110 as described above, Becomes parallel to the light absorption axis of the second polarizing element 113.

Here, in the case of the first embodiment of the present invention, the first optical compensation film 120 and the second optical compensation film 120 are provided between the second polarizing element 113 and the liquid crystal display panel 110 in order to improve the viewing angle characteristics in the diagonal direction. The first optical compensation film 120 is formed of a positive biaxial film having -8.0 < Nz < 0, while the second optical compensation film 130 is formed of a positive biaxial film, And a negative C plate ((-) C plate) film.

Here, the definition of Re, Rth, and Nz used in the present invention is expressed by Equation 1 below.

Re = (nx - ny) d

Rth = (nx - nz) d

Nz = Rth / Re

Here, nx, ny, and nz refer to refractive indexes in the x, y, and z directions, respectively, and d represents the thickness of the film, with reference to FIGS. 6A and 6B. 6A and 6B are diagrams showing the refractive indexes of the positive biaxial film and the negative C plate similar film, respectively.

Therefore, Re means a retardation value in a plane, and Rth means a retardation value in the thickness direction. Further, Nz means an index indicating the degree of biaxiality of the biaxial retardation film.

The positive biaxial film may have a value of about -8.0 to about 0 in the case of the present invention, and Re and Rth may have values of 50 to 180 nm and -400 to 0 nm, respectively, . In addition, the positive biaxial film has a relationship of nz> nx> ny, so that the optical axis is positioned between nz and ny.

At this time, the wavelength dispersion characteristics of the positive biaxial film may have a normal wavelength dispersion, a flat wavelength dispersion, and a reverse wavelength dispersion. The film usable as the positive biaxial film includes a UV curable liquid crystal film using a nematic liquid crystal, a biaxially oriented PC (Polycarbonate), and the like.

In addition, the negative C plate-like film has a Re value of 0 and a Rth value of greater than 0. In the present invention, Re may have a value of 0, and Rth may have a value of 0 to 400 nm or so.

The negative C plate-like film refers to a negative uniaxial optical element whose refractive index distribution satisfies nx = ny > nz, and the negative uniaxial optical element in which the refractive index distribution satisfies nx = ny> Respectively.

The negative C plate-like film used in the first embodiment of the present invention may include a polymer film containing a thermoplastic resin as a main component. The thermoplastic resin may be a polymer film containing an amorphous polymer as a main component, Has an advantage of being excellent in transparency.

Examples of the thermoplastic resin include a polyolefin resin, a cycloolefin resin, a polyvinyl chloride resin, a cellulose resin, a styrene resin, an acrylonitrile-butadiene styrene resin, an acrylonitrile-styrene resin, a polymethacrylic acid General-purpose plastics such as methyl, polyvinyl acetate and polyvinylidene chloride resins; General engineering plastics such as polyamide resins, polyacetal resins, polycarbonate resins, modified polyphenylene ether resins, polybutylene terephthalate resins and polyethylene terephthalate resins; Based resin, polyphenylene sulfide-based resin, polysulfone-based resin, polyethersulfone-based resin, polyetheretherketone-based resin, polyallylate-based resin, liquid crystalline resin, polyamideimide-based resin, polyimide- And super engineering plastics such as an ethylene resin. At this time, the above thermoplastic resins may be used alone or in combination of two or more. The thermoplastic resin may be used by carrying out any suitable polymer denaturation. Examples of the polymer denaturation include denaturation such as copolymerization, crosslinking, molecular terminal, and stereoregularity.

The negative C plate-like film may include a stretched film of a polymer film containing a thermoplastic resin as a main component.

And, the negative C plate-like film may include a retardation film using a liquid crystal composition.

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 are arranged in the order of the first and second polarizing plates 105 and 115 in the diagonal direction The light leakage in the diagonal direction can be reduced by compensating for the cracking of orthogonality, 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 a polarized state is used.

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

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 equation applies only to complete polarization.

In the case of the fully polarized light, the relationship of the following Equation 3 holds between the normalized parameters s ₁ , s ₂ and s ₃ obtained by dividing S ₁ , S ₂ and S ₃ by the light brightness S ₀ .

This is an equation of a sphere with a radius of one in three-dimensional space, and a sphere consisting of points with (s ₁ , s ₂ , s ₃ ) as orthogonal coordinates means a pork curry sphere.

In this case, all the points on the equatorial line in the Poincare sphere correspond to linear polarized light, 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 elliptical polarized light, and all points in the southern hemisphere correspond to left-handed elliptical polarized light.

Figs. 7A and 7B are diagrams showing arbitrary elliptical polarized light in the orthogonal coordinate system and the corresponding percoke vector. Fig.

이다. 이 점이 북반구에 있으면 전기장 벡터의 회전방향이 시계방향이고 남반구에 있으면 반시계방향이다. 뽀앙카레 구 위의 대척점들은 서로 직교하는 편광 상태를 나타낸다.As shown in the figure, the latitude angle of the pornographic vector P corresponding to the elliptical polarized light having the azimuthal angle Ψ of the major axis of the polarization ellipse and the elliptical angle x is 2x, the azimuth angle is 2Ψ, The

to be. If this point is in the northern hemisphere, the direction of rotation of the electric field vector is clockwise and counterclockwise if it is in the southern hemisphere. The opposite points on the Porcine Curve show polarized states perpendicular to each other.

In addition, the Unitary Jones matrix describing the change in polarization state when a light is transmitted through a transparent medium can be interpreted as a rotation transformation on a Porcocare sphere.

FIGS. 8A and 8B are diagrams showing a Poincare sphere representing the polarization state of light passing through each optical element in the transverse electric field type liquid crystal display device according to the first embodiment of the present invention having the structure of FIG. 8A is a perspective view of a liquid crystal display panel viewed from the front, and FIG. 8B is a view showing a perspective view of a liquid crystal display panel in a diagonal direction.

9 is a diagram for two-dimensionally explaining the optical compensation mechanism according to the first embodiment of the present invention using the Porcocare sphere shown in FIG. 8B. 9 is a view showing the Porcocare sphere shown in FIG. 8B from the front, and FIG. 9 represented in two dimensions shows movement in the polarization state before and after the change in polarized state , It can be expressed on a porch curry sphere by rotation to a specific angle around a specific axis determined corresponding to each optical characteristic.

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

As shown in the figure, all points on the equatorial line in this Poincare sphere represent linear polarized light, and the point at the north pole S ₃ represents the right-handed circular polarization and the point at the south pole -S ₃ represents the left-handed circular polarization. In the remaining region, the northern hemisphere represents right-handed elliptical polarized light, and the southern hemisphere represents left-handed elliptical polarized light.

8A, the point A and the point A 'represent the absorption axis of the lower polarizer and the transmission axis of the upper polarizer when the liquid crystal display device is viewed from the front, and the points B and B' The transmission axis and the absorption axis of the upper polarizer plate. The polarization state of the upper polarizer plate and the lower polarizer plate is symmetrical with respect to the center O of the Porcine curry sphere, and they are perpendicular to each other, and thus exhibit an excellent dark state. That is, as described above, the opposite points (A, B ') on the porch curlephere show polarized states orthogonal to each other.

8B, when the liquid crystal display device is viewed from the diagonal direction, the transmission axis A 'of the upper polarizer and the transmission axis B of the lower polarizer plate move a predetermined distance toward the S ₂ axis, The absorption axis B 'of the upper polarizer and the absorption axis A of the lower polarizer are shifted a predetermined distance toward the -S ₂ axis. At this time, since the points A and B 'are not symmetrical with respect to the center O, the polarization states of the upper polarizer and the lower polarizer are not perpendicular to each other. Therefore, the optical compensation film according to the first embodiment of the present invention should be used so that the optical axis of the light reaching the upper polarizer coincides with the absorption axis of the upper polarizer.

Referring to FIGS. 8B and 9, the polarization state of the incident light passing through the lower polarizer corresponds to point B, and the polarization state of the light absorbed by the absorption axis of the upper polarizer is blocked at point B ' .

That is, when the incident light passes through the lower polarizer plate in which the absorption axis direction is located at point A on the porcine curve, it is linearly polarized and positioned at point B. 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 has no phase change in the liquid crystal layer. Therefore, the light passing through the liquid crystal layer maintains the same linear polarization state and has a polarization state corresponding to the B point.

In the transverse electric field type liquid crystal display device as described above, the light leakage deviating from the axis in the diagonal direction is caused by the discrepancy 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 incident light from the B point to the B 'point, including a change in the polarization state of the liquid crystal layer.

Accordingly, when the transverse electric field type liquid crystal display device according to the first embodiment of the present invention is viewed from the diagonal direction, the polarization state of light passing through each optical element is first determined by the positive biaxial film as the first optical compensation film Moves from the point B to the point C, and moves from the point C to the point B 'by the negative C plate-like film which is the second optical compensation film. Accordingly, the polarization state (point B ') of the light reaching the upper polarizer is aligned with the absorption axis of the upper polarizer, and the light is blocked thereby exhibiting an excellent dark state.

That is, when the linearly polarized light passes through the positive biaxial film according to the first embodiment of the present invention in which the optical axis is located in a predetermined region between nz and ny, the polarized state of the linearly polarized light located at the point B becomes positive And is rotated clockwise around the optical axis of the biaxial film. At this time, the linearly polarized light changes into an elliptically polarized light by rotating an effective phase retardation value of the positive biaxial film by 2π times a value obtained by dividing an effective phase retardation value of the positive biaxial film by a wavelength of 550 nm which is a green wavelength affecting luminance, The light then meets a negative C plate similar film, the second optical compensation film.

In the negative C plate-like film, the optical axis is located on the S ₂ axis, which is the thickness direction of the film, and the elliptically polarized light is rotated counterclockwise with respect to the S ₂ axis to change to linearly polarized light at the B 'point do. Since the point B 'represents the absorption axis of the upper polarizer, the incident light is completely absorbed by the upper polarizer, thereby exhibiting a good dark state.

As described above, in the first embodiment of the present invention, by controlling the polarization state using the positive biaxial film and the negative C plate-like film, it is possible to prevent the decrease of the contrast ratio by blocking the light leakage.

On the other hand, in a transverse electric field type liquid crystal display device, a color shift phenomenon occurs depending on a viewing angle due to a dispersion characteristic of a liquid crystal. In the case of the first embodiment of the present invention, The light of all the wavelength ranges is gathered at almost one point at the point B ', so that the color shift can be improved.

FIGS. 10A to 10C are views showing conditions and transmittance characteristics of the optical compensation film used in the transverse electric field type liquid crystal display device according to the first embodiment of the present invention. FIG.

FIGS. 10A to 10C show the values of Rth and Nz of the positive biaxial film along with Re in the order of 50 nm to 180 nm based on Re of the positive biaxial film.

In the negative C plate-like film, Re has a value of 0, and Rth is a value satisfying the compensation condition corresponding to Re and Rth of the positive biaxial film.

As shown in the figure, the maximum transmittance of each of the diagonal viewing angles measured according to the optical conditions of the positive biaxial film and the negative C plate-like film and the magnitude of the transmittance in relation to the reference condition are shown.

3A and 3B, the maximum transmittance of the diagonal viewing angle corresponds to 0.001905. In the case of the first embodiment of the present invention, the maximum transmittance of the diagonal viewing angle is 4.8 to 61.2% Of the total.

Particularly, in the case of the first embodiment of the present invention, when the Re of the positive biaxial film is 120 nm and the Rth is -24 nm (Nz = -0.2) and Re and Rth of the negative C plate-like film correspond to 0 nm and 90 nm The maximum transmittance of the diagonal viewing angle is 0.000092, corresponding to about 4.8% of the reference condition, and the light leakage in the diagonal direction is minimized.

When the Re and Rth of the positive biaxial film having Nz of -8 are 50 nm and -400 nm, respectively, and the Rth of the negative C plate-like film is 330 nm, the maximum transmittance of the diagonal viewing angle is 0.000261, 13.7%. When the Re and Rth of the positive biaxial film having Nz of -0.1 are 90 nm and -9 nm, respectively, and the Rth of the negative C plate-like film is 80 nm, the maximum transmittance of the diagonal viewing angle is 0.000550, which is about 28.9% of the reference condition.

When the Re and Rth of the positive biaxial film having Nz of -0.1 are respectively 110 nm and -11 nm and the Rth of the negative C plate similar film is 90 nm, the maximum transmittance of the diagonal viewing angle is 0.000224, The maximum transmittance of the diagonal viewing angle corresponds to about 11.8%, and the Re and Rth of the positive biaxial film having Nz of -0.1 are 120 nm and -12 nm, respectively, and the Rth of the negative C plate- 0.000122, which is about 6.4% of the reference condition.

In another case where the Re and Rth of the positive biaxial film having Nz of -0.1 are 130 nm and -13 nm respectively and the Rth of the negative C plate similar film is 90 nm, the maximum transmittance of the diagonal viewing angle is 0.000104, , The Re and Rth of the positive biaxial film corresponding to Nz of -0.1 are 140 nm and -14 nm, respectively, and the Rth of the negative C plate-like film is 100 nm, the maximum transmittance of the diagonal viewing angle Is 0.00017, which is about 8.9% of the reference condition.

When the Re and Rth of the positive biaxial film having Nz of -0.1 are respectively 150 nm and -15 nm and the Rth of the negative C plate similar film is 100 nm, the maximum transmittance of the diagonal viewing angle is 0.000235, And the Re and Rth of the positive biaxial film corresponding to Nz of -0.1 are about 160 nm and -16 nm, respectively, and the Rth of the negative C plate-like film is 100 nm, the maximum transmittance of the diagonal viewing angle Is 0.000404, which is about 21.2% of the reference condition.

When the Re and Rth of the positive biaxial film having Nz of -0.1 are 170 nm and -17 nm respectively and the Rth of the negative C plate similar film is 100 nm, the maximum transmittance of the diagonal viewing angle is 0.000618, About 32.4%, and the Re and Rth of the positive biaxial film having Nz of -0.1 are 180 nm and -18 nm, respectively, and the Rth of the negative C plate-like film is 90 nm, the maximum transmittance of the diagonal viewing angle is 0.000864, which is about 45.4% of the reference condition.

11A and 11B show simulation results of viewing angle characteristics in the dark state in the transverse electric field type liquid crystal display device according to the first embodiment of the present invention having such a structure.

11A and 11B are diagrams showing the results of simulating the color shift viewing angle characteristics and the darkness viewing angle characteristics of the dark state in the transverse electric field type liquid crystal display device according to the first embodiment of the present invention.

Here, the lower polarizer plate and the upper polarizer plate are arranged so that the 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 polarizer plate.

11B is a cross-sectional view of a transverse electric field type liquid crystal display (LCD) including an optical compensation film according to the first embodiment of the present invention at an inclination angle of 0 to 80 degrees with respect to all the long axis angles (or azimuth angles) Which is the result of simulating the contrast ratio characteristics.

In Fig. 11B, the center of the circle indicates the case where the inclination angle is 0, and the inclination angle increases as the radius of the circle increases.

As shown in the figure, it can be seen that the viewing angle characteristics of the color shift are improved. In the dark state, when the light leakage is remarkably reduced at 45 degrees, 135 degrees, 225 degrees and 315 degrees corresponding to the diagonal direction of the liquid crystal display panel . As a result, the brightness of the liquid crystal display device is reduced and the contrast ratio is improved in the dark state. For example, it can be seen that the maximum transmittance of the diagonal viewing angle in the dark state is about 0.000358 when the inclination angle and the angular tolerance are (60, 45). This means that the darkness of the dark state is reduced by 80% or more and the contrast ratio of the diagonal viewing angle is increased by 80% or more as compared with the conventional liquid crystal display device shown in FIG. 3B.

12 is a cross-sectional view schematically showing a transverse electric field type liquid crystal display device including an optical compensation film according to a second embodiment of the present invention, except that the TAC is used instead of the negative C plate similar film. The liquid crystal display device is composed of the same components as those of the conventional lateral electric field type liquid crystal display device.

As shown in the figure, the transverse electric field type liquid crystal display device 200 according to the second embodiment of the present invention includes a liquid crystal display panel 210 for outputting images, and a liquid crystal display panel 210 disposed below the liquid crystal display panel 210 1 polarizing plate 205 and a second polarizing plate 215 located above the liquid crystal display panel 210. [

The first polarizer 205 may include a first polarizer 203 disposed between the first and second supports 202 and 204 and a first support 202 and a second support 204. The first polarizer 205 may include a first polarizer 203 disposed between the first and second supports 202 and 204, do. The second polarizing plate 215 is disposed between the third supporting body 212 and the fourth supporting body 212 'and the first optical compensating film 220 and between the third supporting body 212 and the fourth supporting body 212' And a second polarizing element 213 positioned in the second polarizing element 213. Here, the first optical compensation film 220 according to the second embodiment of the present invention is positioned between the fourth support 212 'and the liquid crystal display panel 210.

The first polarizer 203 and the second polarizer 213 may be made of PVA and the first and second supports 212 and 212 may have phase retardation For example, TAC. &Lt; / RTI &gt; The second support body 204 is made of a general protective film having no phase delay and may be made of, for example, 0-RT, or may be formed of the first support body 202, the third support body 212 and the fourth support body 212 &Apos;). &Lt; / RTI &gt;

The first optical compensation film 220 may be formed of a positive biaxial film having -8.0 < Nz < 0.

13 is a cross-sectional view schematically showing a transverse electric field type liquid crystal display device including an optical compensation film according to a third embodiment of the present invention, in which a TAC is additionally inserted between a second polarizing element and a negative C plate- The liquid crystal display device of the present embodiment is the same as the liquid crystal display device of the lateral electric field system of the first embodiment.

As shown in the figure, the transverse electric field type liquid crystal display device 300 according to the third embodiment of the present invention includes a liquid crystal display panel 310 for outputting an image, and a liquid crystal display panel 310 disposed below the liquid crystal display panel 310 1 polarizing plate 305 and a second polarizing plate 315 located above the liquid crystal display panel 310. [

The first polarizer 305 includes a first polarizer 303 and a second polarizer 303 positioned between the first and second supports 302 and 304. The first polarizer 305 includes a first polarizer 303 and a second polarizer 303, do. The second polarizer 315 includes a third support 312 and a fourth support 312 ', first and second optical compensation films 320 and 330, a third support 312 and a fourth support 312' And a second polarizing element 313 located between the second polarizing element 312 '. Here, the first and second optical compensation films 320 and 330 according to the third embodiment of the present invention are positioned between the fourth support body 312 'and the liquid crystal display panel 310.

The first polarizing element 303 and the second polarizing element 313 may be made of PVA and the first supporting body 302 and the third supporting body 312 and the fourth supporting body 312 ' For example, TAC. &Lt; / RTI &gt;

The first optical compensation film 320 may be formed of a positive biaxial film having -8.0 < Nz < 0, and the second optical compensation film 330 may be formed of a negative C plate similar film.

FIG. 14 is a cross-sectional view schematically showing a transverse electric field type liquid crystal display device including an optical compensation film according to a fourth embodiment of the present invention, in which 0-RT is additionally inserted between a second polarizing element and a negative C plate- The liquid crystal display device of the present embodiment has the same constituent elements as those of the liquid crystal display device of the lateral electric field system of the first embodiment.

As shown in the drawing, a transverse electric field type liquid crystal display device 400 according to a fourth embodiment of the present invention includes a liquid crystal display panel 410 for outputting an image, and a liquid crystal display panel 410 disposed below the liquid crystal display panel 410 1 polarizing plate 405 and a second polarizing plate 415 disposed on the upper portion of the liquid crystal display panel 410.

The first polarizer 405 includes a first polarizer 403 positioned between the first and second supports 402 and 404 and a first and a second support 402 and 404, do. The second polarizer 415 includes a third support 412 and a fourth support 414 and first and second optical compensation films 420 and 430 and a third support 412 and a fourth support 412. [ And a second polarizing element 413 disposed between the first polarizing element 413 and the second polarizing element 413. Here, the first and second optical compensation films 420 and 430 according to the fourth embodiment of the present invention are positioned between the fourth support body 414 and the liquid crystal display panel 410.

The first polarizing element 403 and the second polarizing element 413 may be made of PVA and the first and second supporting bodies 402 and 412 may be made of a general protective film having no phase delay , For example TAC. The second support 404 and the fourth support 414 may be formed of a general protective film having no phase delay and may be formed of, for example, 0-RT, 402 and the third support 412. In this case,

The first optical compensation film 420 may be formed of a positive biaxial film having -8.0 < Nz < 0, and the second optical compensation film 430 may be formed of a negative C plate similar film .

FIG. 15 is a cross-sectional view schematically showing a transverse electric field type liquid crystal display device including an optical compensation film according to a fifth embodiment of the present invention, in which TAC is used in place of a negative C plate-like film while the second polarizing element and the TAC Except that another TAC is further inserted between the liquid crystal display device of the first embodiment and the liquid crystal display device of the second embodiment.

As shown in the figure, a transverse electric field type liquid crystal display device 500 according to a fifth embodiment of the present invention includes a liquid crystal display panel 510 for outputting an image and a liquid crystal display panel 1 polarizing plate 505 and a second polarizing plate 515 located on the liquid crystal display panel 510.

The first polarizer 505 includes a first polarizer 503 and a second polarizer 503 disposed between the first and second supports 502 and 504. The first polarizer 505 includes a first support 502 and a second support 504, do. The second polarizing plate 515 is disposed between the third support 512 and the fourth support 512 'and the fifth support 512' ', the first optical compensation film 520 and the third support 512 And a second polarizing element 513 located between the fifth supports 512 &quot;. Here, the first optical compensation film 520 according to the fifth embodiment of the present invention is located between the fourth support 512 'and the liquid crystal display panel 510.

The first polarizing element 503 and the second polarizing element 513 may be made of PVA and the first supporting body 502, the third supporting body 512, the fourth supporting body 512 ' The second support body 504 is made of a general protective film having no phase delay, and may be formed of, for example, 0-RT or the same TAC as the first and second supports 502 and 512 and the fourth and fifth supports 512 'and 512'.

The first optical compensation film 520 may be formed of a positive biaxial film having a refractive index of -8.0 <Nz <0.

16 is a cross-sectional view schematically showing a transverse electric field type liquid crystal display device including an optical compensation film according to a sixth embodiment of the present invention in which TAC is used in place of a negative C plate similar film while a second polarizing element and the TAC Except that 0-RT is additionally inserted between the liquid crystal display device of the first embodiment and the liquid crystal display device of the second embodiment.

As shown in the drawing, the transverse electric field type liquid crystal display 600 according to the sixth embodiment of the present invention includes a liquid crystal display panel 610 for outputting images, and a liquid crystal display panel 610 disposed below the liquid crystal display panel 610 1 polarizing plate 605 and a second polarizing plate 615 located above the liquid crystal display panel 610.

The first polarizer 605 includes a first polarizer 603 and a second polarizer 603 disposed between the first and second supports 602 and 604. The first polarizer 605 includes a first polarizer 602 and a second polarizer 604, do. The second polarizing plate 615 includes a third support 612, a fourth support 612 ', a fifth support 614, a first optical compensation film 620, a third support 612, 5 support 614. The second polarizing element 613 is disposed between the first and second polarizing elements 614 and 614. Here, the first optical compensation film 620 according to the sixth embodiment of the present invention is positioned between the fourth support 612 'and the liquid crystal display panel 610.

The first polarizing element 603 and the second polarizing element 613 may be made of PVA and the first and second supporting bodies 602 and 612 and the fourth supporting body 612 ' For example, TAC. &Lt; / RTI &gt; The second support body 604 and the fifth support body 614 are made of a general protective film having no phase delay and are made of, for example, 0-RT, The second support member 602, the third support member 612, and the fourth support member 612 '.

The first optical compensation film 620 may be formed of a positive biaxial film having -8.0 < Nz < 0.

While a great many are described in the foregoing description, it should be construed as an example of preferred embodiments rather than limiting the scope of the invention. Therefore, the invention should not be construed as limited to the embodiments described, but should be determined by equivalents to the appended claims and the claims.

1 is a plan view schematically showing a part of an array substrate of a general transverse electric field type liquid crystal display device.

2 is an exemplary view showing a cross section taken along line I-I 'of the array substrate shown in FIG. 1;

FIG. 3A is a diagram showing a simulation result of a luminance viewing angle characteristic in a dark state in a general transverse electric field type liquid crystal display; FIG.

FIG. 3B is a diagram showing a result of measurement of a luminance viewing angle characteristic in a dark state in a general transverse electric field type liquid crystal display device. FIG.

4A is an exemplary view schematically showing the light transmission axis of orthogonal upper and lower polarizing plates when viewed from the front;

Fig. 4B is an exemplary diagram schematically showing the light transmission axis of the orthogonal upper and lower polarizing plates when viewed from the diagonal direction; Fig.

5 is a cross-sectional view schematically showing a transverse electric field type liquid crystal display device including an optical compensation film according to a first embodiment of the present invention.

6A and 6B are diagrams for defining Re, Rth and Nz used in the present invention.

Figs. 7A and 7B are diagrams showing arbitrary elliptic polarized light in the orthogonal coordinate system and a corresponding porcine curve vector; Fig.

FIGS. 8A and 8B are diagrams showing a porcine curve showing the polarization state of light passing through each optical element in the transverse electric field type liquid crystal display device according to the first embodiment of the present invention having the structure of FIG.

9 is a view for two-dimensionally explaining the optical compensation mechanism according to the first embodiment of the present invention using the Porcocare sphere shown in Fig. 8; Fig.

FIGS. 10A to 10C are diagrams showing the conditions of the optical compensation films used in the transverse electric field type liquid crystal display device according to the first embodiment of the present invention, and the transmittance characteristics thereof. FIG.

11A and 11B are diagrams showing the results of simulating the color shift viewing angle characteristics and the darkness viewing angle characteristics of the dark state in the transverse electric field type liquid crystal display device according to the first embodiment of the present invention.

12 is a cross-sectional view schematically showing a transverse electric field type liquid crystal display device including an optical compensation film according to a second embodiment of the present invention.

13 is a sectional view schematically showing a transverse electric field type liquid crystal display device including an optical compensation film according to a third embodiment of the present invention.

14 is a cross-sectional view schematically showing a transverse electric field type liquid crystal display device including an optical compensation film according to a fourth embodiment of the present invention.

15 is a sectional view schematically showing a transverse electric field type liquid crystal display device including an optical compensation film according to a fifth embodiment of the present invention.

16 is a cross-sectional view schematically showing a transverse electric field type liquid crystal display device including an optical compensation film according to a sixth embodiment of the present invention.

DESCRIPTION OF REFERENCE NUMERALS

100 to 600: liquid crystal display devices 110 to 610: liquid crystal display panel

102 to 602: first supporting member 103 to 603: first polarizing element

104 to 604: second support 105 to 605: first polarizer

112 to 612: Third support member 113 to 613: Second polarizing element

115 to 615: second polarizing plate 120 to 620: first optical compensation film

130, 330, 430: second optical compensation film

212 ', 312', 414, 512 ', 612': a fourth support

512 ", 614: fifth support

Claims (24)

A liquid crystal display panel including a liquid crystal layer; A first polarizer located at a lower portion of the liquid crystal display panel, the first polarizer comprising a first support and a second support, and a first polarizer disposed between the first and second supports; And A second polarizing plate located on the liquid crystal display panel and including a third support, first and second optical compensation films, and a second polarizing element positioned between the third support and the first and second optical compensation films, &Lt; / RTI & Wherein the first optical compensation film is defined by -8.0 <Nz <0, where Nz = Rth / Re, Re = (nx-ny) d and Rth = (nx-nz) nz denotes the refractive index in the x direction, the y direction and the z direction, respectively, and d denotes the thickness of the film), and the second optical compensation film is made of a negative C plate-like film And the first optical compensation film is positioned between the second optical compensation film and the liquid crystal display panel. The optical compensation film according to 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, and the optical axis of the liquid crystal layer is parallel to the absorption axis of the first polarizing element The liquid crystal display device comprising: The liquid crystal display device according to 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, and the optical axis of the liquid crystal layer is parallel to the absorption axis of the second polarizing element Liquid crystal display device. The transverse electric field type liquid crystal display device according to claim 1, wherein the first and third supports are made of a protective film having no phase delay. The transverse electric field type liquid crystal display device according to claim 4, wherein the protective film comprises triacetyl cellulose (TAC). The transverse electric field type liquid crystal display device according to claim 1, wherein the second support comprises a protective film without phase retardation. 7. The transverse electric field type liquid crystal display device according to claim 6, wherein the protective film comprises 0-RT (modified TAC with Rth approaching 0 nm) or TAC. The transverse electric field type liquid crystal display device according to claim 1, wherein the positive biaxial film has a Re retardation value of about 50 to 180 nm. The transverse electric field type liquid crystal display device according to claim 1, wherein the positive biaxial film has a retardation value of Rth of about -400 to 0 nm. The transverse electric field type liquid crystal display device according to claim 1, wherein the negative C plate-like film has a Re value of 0 and a retardation value of Rth of about 0 to 400 nm. The positive biaxial film according to claim 1, wherein the positive biaxial film has a retardation value of Re and Rth of 120 nm and -24 nm, respectively, and the negative C plate-like film has a retardation value of Re of 0 and Rth of 90 nm The liquid crystal display device comprising: a liquid crystal layer; The transverse electric field system according to claim 1, wherein the light passing through the positive biaxial film and the negative C plate-like film has a polarization state coinciding with an absorption axis of the second polarizing element Liquid crystal display device. The transverse electric field type liquid crystal display device according to claim 1, wherein TAC is used in place of the negative C plate similar film. The transverse electric field type liquid crystal display device according to claim 1, further comprising a fourth support positioned between the second polarizing element and the second optical compensation film. 15. The transverse electric field type liquid crystal display device according to claim 14, wherein the fourth support is made of TAC. 15. The transverse electric field type liquid crystal display device according to claim 14, wherein the fourth support comprises 0-RT. 14. The transverse electric field type liquid crystal display device according to claim 13, further comprising a fourth support positioned between the second polarizing element and a TAC used in place of the negative C plate similar film . The transverse electric field type liquid crystal display device according to claim 17, wherein the fourth support is made of TAC. The transverse electric field type liquid crystal display device according to claim 17, wherein the fourth support comprises 0-RT. A liquid crystal display panel including a liquid crystal layer; A first polarizer located at a lower portion of the liquid crystal display panel, the first polarizer comprising a first support and a second support, and a first polarizer disposed between the first and second supports; And A second polarizing plate located on the liquid crystal display panel and including a third support, first and second optical compensation films, and a second polarizing element positioned between the third support and the first and second optical compensation films, &Lt; / RTI & Wherein the first optical compensation film is made of a positive biaxial film and the second optical compensation film is made of a negative C plate similar film and the first optical compensation film is positioned between the second optical compensation film and the liquid crystal display panel Wherein the liquid crystal display device is a liquid crystal display device. 21. The film according to claim 20, wherein the positive biaxial film is defined as -8.0 < Nz < 0, wherein Nz = Rth / Re, Re = (nx-ny) d and Rth = (nx- Wherein nx, ny and nz denote the refractive index in the x direction, the y direction and the z direction, respectively, and d denotes the thickness of the film). Liquid crystal display device. The transverse electric field type liquid crystal display device according to claim 21, wherein the positive biaxial film has a Re retardation value of about 50 to 180 nm. The transverse electric field type liquid crystal display device according to claim 21, wherein the positive biaxial film has a retardation value of Rth of about -400 to 0 nm. The transverse electric field type liquid crystal display device according to claim 21, wherein the negative C plate-like film has a Re value of 0 and a retardation value of Rth of about 0 to 400 nm.

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