KR20150080234A - In-Plane Switching Mode Liquid Crystal Display Device - Google Patents

Abstract

The present invention relates to an in-plane switching mode liquid crystal display device which solves a problem of contrast ratio and color shift vulnerable to a diagonal direction by changing the application of an optical compensation film. It include an in-plane switching mode liquid crystal; a first optical compensation film which comprises a positive B-plate of which a refractive index anisotropy (Nz) is defined as a value of -7.5 to -1.0 (here, Nz=Rth/Re +0.5, Re=(nx-ny)*d, Rth=((nx+ny)/2-nz)*d). nx, ny, nz are refractive indexes in x, y, and z directions. d is the thickness of a film; a second optical compensation film which is located on the first optical compensation film and comprises a negative inverse dispersion plate; and a second polarizing plate which is located on the second optical compensation film and includes a second polarizing device and a second support body.

Description

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

BACKGROUND OF THE INVENTION 1. Field of the Invention 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 which solves a problem of a weak contrast ratio and color shift in a diagonal direction by applying an optical compensation film.

As the era of informationization becomes full-scale, the display field for visually displaying electrical information signals is rapidly developing. Accordingly, studies have been continuing to develop performance such as thinning, lightening, and low power consumption for various flat display devices.

Typical examples of such flat panel display devices include a liquid crystal display device (LCD), a plasma display panel (PDP), a field emission display (FED) An electroluminescence display device (ELD), an electro-wetting display device (EWD), and an organic light emitting display device (OLED).

Such flat panel display devices commonly include flat panel display panels for realizing images. A flat panel display panel is a structure in which a pair of substrates sandwiching a unique light emitting material or a polarizing material are face-to-face bonded.

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 separating light passing through the liquid crystal layer and shielding light transmitted 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.

 The above-mentioned 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 a substrate. The liquid crystal display device of this type has a viewing angle of about 90 degrees It has a drawback that it is narrow. 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.

An IPS (In Plane Switching Mode) liquid crystal display device has been proposed in which liquid crystal molecules are driven in a horizontal direction with respect to a substrate to improve a viewing angle to 170 degrees or more.

However, in the transverse electric-field liquid crystal display device, the phase delay of the liquid crystal different from the voltage is small and the optical axis of the upper and lower polarizers maintains the vertical state in the up-and-down and left-right directions. The light leakage occurs in the diagonal direction where the image is distorted, causing deterioration of image quality.

The conventional transverse electric field type liquid crystal display device has the following problems.

There is a problem that the optical axis in the diagonal direction is broken and the light leakage occurs in the black state. Currently, the polarizer is composed of the protective film of the PVA optical layer and the TAC (triacetyl cellulose) above and below the optical axis. It is impossible to solve the deterioration in picture quality due to the above.

It is an object of the present invention to provide a transverse electric field type liquid crystal display device which solves the problem of a weak contrast ratio and a color shift in a diagonal direction by applying different optical compensation films.

According to an aspect of the present invention, there is provided a transverse electric field type liquid crystal display comprising: a transverse electric field type liquid crystal panel; a first polarizer disposed under the transverse electric field type liquid crystal panel, the first polarizer including a first support and a first polarizer; (Nz = Rth / Re + 0.5, Re = (nx-ny) * d, Rth = (nx + ny) / 2-nz) * d where nx, ny and nz are refractive indices in the x, y and z directions, respectively, and d is the thickness of the film) A second optical compensation film located on the first optical compensation film and made of a negative reverse dispersion A plate and a second optical compensation film positioned on the second optical compensation film, The second polarizing plate including the second polarizing plate.

Here, the first optical compensation film has a refractive index characteristic of nz > nx > ny.

The second optical compensation film preferably has an Nz value of 1.0 to 1.3. In this case, it is preferable that the second optical compensation film has a refractive index condition of nx > ny = nz.

Here, the first and second polarizing elements have absorption axes perpendicular to each other.

The optical axis of the transverse electric field type liquid crystal panel coincides with the absorption axis of either the first polarizing element or the second polarizing element.

The light having passed through the first polarizing element, the liquid crystal panel, and the first and second optical compensation films in order can have a polarization state coinciding with the absorption axis of the second polarizing element.

The first and second supports may be made of triacetyl celluose or cycloolefin polymer (COP) without phase retardation.

In this case, the transverse electric field type liquid crystal panel includes: first and second substrates facing each other; a gate line and a data line crossing each other on the first substrate to define a plurality of pixel regions; A data line and a thin film transistor formed on the second substrate in correspondence with the gate line, the data line, and the thin film transistor, a thin film transistor formed at a crossing portion of the data line, A color filter layer formed on the second substrate to correspond to the pixel regions; And a liquid crystal layer between the first and second substrates.

The above-described transverse electric field type liquid crystal display device of the present invention has the following effects.

The transverse electric field type liquid crystal display device according to the present invention prevents defects in a dark state in a diagonal direction to prevent color shift and ultimately improves the image quality. To this end, a liquid crystal panel and an upper polarizing element Polarizing elements) of the first and second optical compensation films.

That is, the first optical compensation film closest to the liquid crystal panel has a refractive index anisotropy Nz value in the range of -7.5 to -1.0 and is a biaxial positive birefringent plate, and the second optical compensation film has an Nz value of refractive index anisotropy of 1.0 to 1.3 And a negative A plate having an inverse wavelength dispersion characteristic. As a result, incident light of all colors passes through the second polarizing element (upper polarizing element) and collects on the absorption axis, thereby blocking the light leakage in an optically dark state.

1 is a cross-sectional view showing a transverse electric field type liquid crystal display device of the present invention
Fig. 2 is a plan view of the liquid crystal panel of Fig.
3 is a cross-sectional view taken along line I-I '
4A is an exemplary diagram schematically showing light transmission axes of first and second polarizing elements which are orthogonal to each other when viewed from the front;
4B is an exemplary diagram schematically showing the light transmission axes of the first and second polarizing elements which are orthogonal to each other when viewed from the diagonal direction
5A and 5B are diagrams showing arbitrary polarizations in a rectangular coordinate system and corresponding Poincare vectors;
Figure 6 is a plot of the light path of a comparative example of the present invention in a Poincare vector
Fig. 7 is a graph showing the light-diffusing properties of the A-plate having the optical path L2 of Fig. 6
8 is a graph comparing the optical dispersibility of the second optical compensation film of the liquid crystal display device of the present invention and the A-plate of the comparative example by wavelength
9 is a graph showing the optical path of light passing through the liquid crystal panel in the liquid crystal display of the present invention,
Figs. 10A and 10B are views for explaining the optical compensation path in two dimensions in the comparative example and the embodiment of the present invention
11A and 11B are simulation diagrams showing the luminance viewing angle characteristics of the dark state in the comparative example and the embodiment of the present invention

Hereinafter, a transverse electric field type liquid crystal display device of the present invention will be described in detail with reference to the accompanying drawings.

1 is a cross-sectional view showing a transverse electric field type liquid crystal display device of the present invention.

1, a transverse electric field type liquid crystal display device according to the present invention includes a liquid crystal panel 100 and a liquid crystal panel 100 which is disposed under the liquid crystal panel 100 and includes a first support 112 and a first polarizer 111 A first polarizing plate 110 and a first optical compensation film 121 disposed directly on the liquid crystal panel 100 and made of a positive B plate having a refractive index anisotropy Nz of -7.5 to -1.0, A second optical compensation film 122 which is located on the first optical compensation film 121 and is composed of a negative reverse dispersion A plate and a second polarizing element 123 which is located on the second optical compensation film 122, And a second polarizer (120) including a second support (124).

In general, Nz representing the refractive index anisotropy of the first and second optical compensation films 121 is calculated as Nz = Rth / Re +0.5. Re denotes the in-plane phase retardation value of the optical compensation film, and is obtained by the following equation (1). Rth denotes the phase retardation value in the thickness direction of the optical compensation film, Loses.

[Equation 1]

Re = (nx-ny) * d

&Quot; (2) "

Rth = ((nx + ny) / 2-nz) * d

Here, nx, ny, and nz are refractive indices in the x, y, and z directions, respectively, and d represents the thickness of the optical compensation film, respectively.

On the other hand, the first optical compensation film 121 is a biaxial film having different refractive indices in the x, y, and z directions, and has a refractive index relationship of nz> nx> ny.

The second optical compensation film 122 is characterized in that the refractive indexes in the y and z directions are approximately the same (ny = nz) and the refractive index nx in the x direction is larger than the refractive indexes ny and nz. Here, ny = nz includes not only cases where ny and nz are numerically completely identical but also substantially the same case.

The first optical compensation film 121 may be a biaxial optical film made of a cycloolefin polymer (COP), a polynorbornene (PNB), a polycarbonate (PC), a biaxial liquid crystal film, or the like .

In this case, the second optical compensation film 122 has a Nz value indicating the degree of refractive index anisotropy of 1.0 to 1.3. In this case, the second optical compensation film 122 has an inverse wavelength dispersion characteristic. For example, when the refractive index is expressed by a refractive index, the refractive index of a long wavelength is higher than the refractive index of a short wavelength (? N (450 nm) ? N (550 nm) <? N (650 nm). In this case, the second optical compensation film 122 may consist of an olefin polymer, a stretched polycarbonate film, or a UV cured film type horizontally aligned liquid crystal film in a stretched state in a uniaxial state.

The first and second polarizing elements 111 and 123 have absorption axes perpendicular to each other.

In this case, the optical axis of the liquid crystal panel 100 and the absorption axis of one of the first polarizing element 111 and the second polarizing element 123 coincide with each other.

The transverse electric field type liquid crystal display device of the present invention having such a characteristic is characterized in that light passing through the first polarizing element 111 and the liquid crystal panel 100 and the first and second optical compensation films 121 and 122, It is possible to have a polarization state that coincides with the absorption axis of the second polarizing element 123 without color difference.

The first and second supports 112 and 124 may be formed of a protective film such as triacetyl celluose or cycloolefin polymer (COP) without phase retardation.

The first and second polarizing elements 111 and 123 are not limited to any particular optical film. For example, the first and second polarizing elements 111 and 123 may be a stretched film of a polymer film containing a PVA-based resin containing iodine or dichromatic dye as a main component, An O-type polarizing element in which a liquid crystal composition containing a 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.

Hereinafter, the internal structure of the liquid crystal panel of the transverse electric field type liquid crystal display device of the present invention will be briefly described.

Fig. 2 is a plan view of the liquid crystal panel of Fig. 1, and Fig. 3 is a cross-sectional view taken along line I-I 'of Fig.

In an actual transverse electric field type liquid crystal display device, N number of gate lines and M number of data lines intersect to form MxN pixels. However, in order to simplify the description, one pixel will be described.

The liquid crystal panel 100 of the transverse electric field type liquid crystal display device includes first and second substrates 10 and 5 opposed to each other and first and second substrates 10 and 5, A gate line 16 and a data line 17 defining a plurality of pixel regions, a thin film transistor T formed at the intersection of the gate line 16 and the data line 17, A data line 17 and a black matrix T formed in correspondence with the gate line 16, the data line 17 and the thin film transistor T on the second substrate 5, , A color filter layer (7) formed on the second substrate (5) corresponding to the pixel regions, and a liquid crystal layer (30) between the first and second substrates (10, 5) .

 The first and second substrates 10 and 5 are made of a transparent substrate and the light incident through the transmission axis of the lower first polarizing element 111 is incident on the liquid crystal panel 100 in a white state, And transmitted through the transmission axis of the second polarizing element 123 through the first and second optical compensation films 121 and 122 to be displayed.

The thin film transistor T includes a gate electrode 21 connected to the gate line 16, a source electrode 22 connected to the data line 17, and a drain electrode 23 spaced apart from the source electrode. Here, the drain electrode 23 is integrally connected to the pixel electrode line 181 connecting the branched pixel electrodes 18.

The thin film transistor T includes a first insulating layer 15a for insulation between the gate electrode 21 and the source and drain electrodes 22 and 23. The source electrode 22 and the drain electrode 23 between the first insulating layer 15a and the source / drain electrodes 22, 23. The first insulating layer 15a and the source / drain electrodes 22, 23 form a conductive channel.

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

 In this pixel region, a common line 81 and a storage electrode 18s are arranged in a direction parallel to the gate line 16, and a transverse electric field 90 is generated in the pixel region to form liquid crystal molecules (not shown) A plurality of common electrodes 8 and pixel electrodes 18 are arranged in a direction parallel to the data lines 17 for switching 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.

In the liquid crystal panel 100 constructed as described above, an alignment film (not shown) for determining the initial alignment direction of the liquid crystal molecules on the upper surface of the first and second substrates 10 and 5, respectively, Respectively.

The first polarizing element 111 is formed on the outer surface of the second substrate 5 so as to be in direct contact with the outer surface of the first substrate 10 with the external configuration of the liquid crystal panel, (121) are directly in contact with each other.

The liquid crystal panel 100 having the above structure is formed by arranging the common electrode 8 and the pixel electrode 18 on the same first substrate 10 to generate a transverse electric field, And is arranged in parallel with the transverse electric field parallel to the surface of the substrate. Therefore, the viewing angle can be improved.

However, in the liquid crystal panel 100 of the transverse electric field system, light leakage occurs in a diagonal direction when a black state is displayed, and a problem that a low contrast ratio is exhibited when applied to the liquid crystal panel 100 itself have.

On the other hand, the liquid crystal layer 30 may include a liquid crystal that is uniformly oriented in a state in which no electric field exists (light state (white state)). In this case, the liquid crystal layer 30 has a structure of nx> ny = Refractive index characteristics. However, the refractive index in the plane is nx and ny, and the refractive index in the thickness direction is nz. In this case, ny = nz includes not only numerically perfect identical but also substantially equal cases.

In the transverse electric field system, by using an electronically controlled birefringence (ECB) effect, a liquid crystal uniformly aligned in a state in which no electric field exists is used as a transverse electric field element provided between the pixel electrode and the common electrode Thereby driving the liquid crystal layer.

Fig. 4A is a diagram schematically showing the light transmission axes of the first and second polarizing elements which are orthogonal to each other when viewed from the front, Fig. 4B is a view showing, in a diagonal direction, Fig. 8 is an exemplary diagram schematically showing a light transmission axis of a polarizing element. Fig.

As shown in FIG. 4A, when the liquid crystal panel is viewed from the front, the light absorption axes of the first and second polarizing elements located at the lower and upper portions of the liquid crystal panel are 90 °, When the liquid crystal panel is viewed in the diagonal direction as shown in FIGS. 4A and 4B, the difference between the light absorption axes of the first and second polarizing elements is observed at 90 degrees or more. When viewed in the diagonal direction, Light leakage occurs because orthogonality is broken.

As described above, in the transverse electric field type liquid crystal display device, the retardation change of the liquid crystal depending on the voltage is small in the manner that the transverse electric field is applied to the liquid crystal layer, and the optical axis of the upper and lower polarizers maintains the vertical state in the up, However, in the diagonal direction in which the vertical state of the optical axis of the first and second polarizing elements is broken, light leakage occurs, which may result in image quality deterioration.

In order to improve the image quality degradation in the diagonal direction, an optical compensation film should be applied. The present protective layer (mainly a TAC layer) for protecting the optical layer (PVA layer) of the polarizing plate itself is compensated .

Hereinafter, the principle of the first and second optical compensation films for preventing light leakage in the diagonal direction of the present invention will be described with reference to a pouincure sphere.

In order to geometrically analyze the optical properties of a transparent medium such as a liquid crystal, the expression of the pungent curie in the 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 3 below, is used to represent more general partial polarized light.

&Quot; (3) &quot;

In this case, <> represents the time average, and the inequality between these four variables holds, and the equation applies only to the complete polarization.

In the case of perfectly polarized light, the relationship of the following equation (4) is established between normalized variables s1, s2 and s3 obtained by dividing S ₁ , S ₂ and S ₃ by the light brightness S 0.

&Quot; (4) &quot;

This is an equation of a sphere with a radius of one in three-dimensional space, and a sphere consisting of points with (s1, s2, s3) as orthogonal coordinates means the Poincare sphere.

At this time, all the points on the equator line in the Pouincare 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. 5A and 5B are diagrams showing arbitrary elliptical polarized light in the orthogonal coordinate system and corresponding pouinc curry vectors. Fig.

As shown in the figure, the latitude angle of the puang curley 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, Is. 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 puang curle sphere show polarized states perpendicular to each other.

In addition, the Unitary Jones matrix describing the change of the polarization state when the light passes through the transparent medium can be interpreted as a rotation transformation on the pouinc curry sphere.

In the following, the change of the optical path shift according to the static dispersion and reverse dispersion characteristics applied to the optical compensation film is examined.

6 is a diagram showing a light path of a comparative example of the present invention in a Pouinc curry vector. 7 is a graph showing the light-splitting property of the A-plate having the optical path L2 of FIG. 6 for each wavelength. In the comparative examples shown in Figs. 6 and 7, the first and second optical compensation films have common positive dispersion characteristics, and the first optical compensation film on the liquid crystal panel is a positive B plate, Has the characteristics of a negative A plate. The first and second optical compensation films have the refractive index anisotropy (Nz) characteristic described in Fig.

As shown in Fig. 6, in a comparative example, in Pouincare sphere, P represents the absorption axis of the lower polarizing element (first polarizing element), and its opposite point S on the equatorial plane represents the transmission axis of the lower polarizing element. Further, A is the absorption axis of the upper polarizing element (second polarizing element) when the liquid crystal panel is viewed from the diagonal direction, and the opposite point of the equatorial plane is the transmission axis of the upper polarizing element. The absorption axis P of the lower polarizing element and the absorption axis A of the upper polarizing element are not completely at 90 degrees because they are viewed from the diagonal direction.

Therefore, the light incident on the liquid crystal panel through the lower polarizing element is at the point S of the pouincere sphere, and the absorption axis of the upper polarizing element is at point A. Without the optical compensation film, the transmitted light is not completely blocked by the absorption axis, The transverse electric field type liquid crystal display device of the present invention has the first optical compensation film having the optical path L1 so as to change the light of the point S to the latitude of the southern hemisphere and the optical path L2 that moves elliptically to the point A at the point D And a second optical compensation film. 7, when the first optical compensation film is a positive B type plate and the second optical compensation film has a positive dispersion characteristic (the phase delay value is low as the wavelength becomes large) in FIG. 7, The red (R), green (B), and blue (B) colors do not reach the point A and the point A, respectively. Color shift phenomenon can be expected to occur.

Particularly, the phase retardation (retardation) during the movement of the elliptically polarized light is more affected by the wavelength of the incident light than the wavelength dispersion of the compensation film itself, resulting in a difference in the phase delay value of the incident light by wavelength. In this case, the optical path of a short wavelength at the point A becomes longer and the color difference is generated by the RGB dispersion, and color shift is visually recognized.

The transverse electric field type liquid crystal display device of the present invention is formed by forming a negative A plate having reverse dispersion wavelength characteristics in order to solve the phase delay problem of each color in the second optical compensation film of the above-mentioned comparative example.

FIG. 9 is a graph comparing the optical dispersibility of the second optical compensation film of the liquid crystal display device of the present invention and the A-plate of the comparative example on a wavelength-by-wavelength basis. FIG. And the light path is shown in the Pouinc curry vector.

8, an inverse dispersion negative A plate is applied to the second optical compensation film that performs the optical path L2, so that the elliptical movement of R, G, and B is the same, This is to allow L2 movement of color.

As shown in Fig. 8, in the transverse electric field type liquid crystal display device according to the present invention, the wavelength dispersion of the first optical compensation film in contact with the second substrate surface of the liquid crystal panel is controlled by a function of the positive dispersion (in the case of a long wavelength, Positive B plate, and the second optical compensation film thereon is a negative dispersion A negative plate.

At this time, as shown in Fig. 9, the light which has exited the liquid crystal panel and moved to the southern hemisphere from the point S via the first optical compensation film moves from point S to point D, passes through the second optical compensation film to the optical path The phase delay of the red light is reduced by reducing the phase delay of the blue light and the light of the red, green and blue is collected at the point A do. Thus, the color shift problem can be prevented, and the light passing through the second optical compensation film can be gathered at the absorption axis of the upper polarizing element, and the light leakage can be prevented in the black state.

 FIGS. 10A and 10B are views for two-dimensionally describing the optical compensation paths of the comparative example and the embodiment of the present invention. FIGS. 11A and 11B are graphs showing simulation results showing the luminance viewing angle characteristics of the dark state of the comparative example and the embodiment of the present invention .

FIGS. 10A and 10B illustrate the optical compensation paths of the comparative example and the embodiment of the present invention two-dimensionally, respectively.

10A, when the incident light Tin is positioned on the s2 axis and moves along the s3 axis through the first optical compensation film and travels through the second optical compensation film on the s3 axis, (G) light is collected on the absorption axis A of the upper polarizing element, but the phase retardation of the red (R) light does not reach the absorption axis of the upper polarizing element and the phase delay of the blue (B) The absorption axis of the upper polarizing element is exceeded, and light of exactly each color does not gather on the absorption axis A of the upper polarizing element.

This results in a color shift when viewed in the diagonal direction.

 On the other hand, in the case of FIG. 10B, the optical compensation path of the embodiment of the present invention is such that the incident light Tin is positioned on the s2 axis, moves through the first optical compensation film to the s3 axis L1, Green, and blue (R, G, and B) light are transmitted through the same L2 optical path shift to match the phase delay values of the R, G, and B colors, Absorbing axis (A). This is because the incident light is gathered on the absorption axis to show an excellent dark state in the black state.

Thus, according to the embodiment of the present invention, it is possible to view an image without color shift even when viewed in the diagonal direction.

In the black state of FIGS. 11A and 11B, when the luminance viewing angle characteristics of the comparative example and the embodiment of the present invention are examined, it is observed that the degree of light leakage is reduced in the embodiment of the present invention.

On the other hand, Table 1 shows an experiment in which the values of the refractive index anisotropy (Nz) of the first and second optical compensation films are different in the transverse electric field type liquid crystal display device of the present invention.

The first optical compensation film (Nz) The second optical compensation film (Nz) Color shift prevention characteristic The first experiment -4.0 1.2 Good Second experiment -1.0 1.3 Good Third experiment -7.5 1.0 Good

As shown in Table 1, in the first experiment, the Nz value of the first optical compensation film is -4.0 and the Nz value of the second optical compensation film is 1.2. In this case, it can be seen that the color shift is prevented.

In the second experiment, it is shown that the Nz value of the first optical compensation film is -1.0 and the Nz value of the second optical compensation film is 1.3, and in this case, the color shift is prevented.

In the third experiment, it is shown that the Nz value of the first optical compensation film is -7.5 and the Nz value of the second optical compensation film is 1.0, and in this case, the color shift is prevented.

The Nz value of the first optical compensation film can be selected from a value of -7.5 to -1.0 and the Nz value of the second optical compensation film is selected to be in the range of 1.0 to 1.3 And the like.

The transverse electric field type liquid crystal display device according to the present invention prevents defects in a dark state in a diagonal direction to prevent color shift and ultimately improves the image quality. To this end, a liquid crystal panel and an upper polarizing element Polarizing elements) of the first and second optical compensation films.

That is, the first optical compensation film closest to the liquid crystal panel has a refractive index anisotropy Nz value in the range of -7.5 to -1.0 and is a biaxial positive birefringent plate, and the second optical compensation film has an Nz value of refractive index anisotropy of 1.0 to 1.3 And a negative A plate having an inverse wavelength dispersion characteristic. As a result, incident light of all colors passes through the second polarizing element (upper polarizing element) and collects on the absorption axis, thereby blocking the light leakage in an optically dark state.

While the present invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims. Will be apparent to those of ordinary skill in the art.

100: liquid crystal panel 110: first polarizer plate
111: first polarizing element 112: first support
120: second polarizer 121: first optical compensation film
122: second optical compensation film 123: second polarizing element
124: second support

Claims (9)

A transverse electric field type liquid crystal panel;
A first polarizer positioned under the transverse electric liquid crystal panel and including a first support and a first polarizer;
And a refractive index anisotropy (Nz) of -7.5 to -1.0 (where Nz = Rth / Re + 0.5, Re = (nx-ny) * d, Rth = ny) / 2-nz) * d, where nx, ny and nz are refractive indices in the x, y and z directions and d is the thickness of the film);
A second optical compensation film positioned on the first optical compensation film and consisting of a negative inverse dispersion A plate; And
And a second polarizer disposed on the second optical compensation film, the second polarizer including a second polarizer and a second support. The method according to claim 1,
Wherein the first optical compensation film has a refractive index characteristic of nz > nx > ny. The method according to claim 1,
And the second optical compensation film has an Nz value of 1.0 to 1.3. The method of claim 3,
Wherein the second optical compensation film has a refractive index condition of nx > ny = nz. The method according to claim 1,
Wherein the first and second polarizing elements have absorption axes perpendicular to each other. 6. The method of claim 5,
Wherein the optical axis of the transverse electric field type liquid crystal panel and the absorption axis of either the first polarizing element or the second polarizing element coincide with each other. The method according to claim 6,
Wherein the light passing through the first polarizing element, the liquid crystal panel, and the first and second optical compensation films in turn has a polarization state coinciding with an absorption axis of the second polarizing element. The method according to claim 1,
Wherein the first and second supports are made of triacetyl celluose or cycloolefin polymer (COP) having no phase retardation. The method according to claim 1,
In the transverse electric field type liquid crystal panel,
First and second substrates facing each other;
A gate line and a data line crossing each other on the first substrate to define a plurality of pixel regions;
A thin film transistor formed at an intersection of the gate line and the data line;
A pixel electrode and a common electrode alternately formed in the pixel regions;
A black matrix layer formed on the second substrate so as to correspond to the gate line, the data line, and the thin film transistor;
A color filter layer formed on the second substrate corresponding to the pixel regions; And
And a liquid crystal layer between the first and second substrates.

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