KR101891540B1 - Liquid crystal display device having wide viewing angle - Google Patents

Abstract

The present invention relates to a liquid crystal display device having improved viewing angle characteristics, and more particularly, to a liquid crystal display device including a liquid crystal panel including a liquid crystal layer; A first polarizing plate and a second polarizing plate positioned at upper and lower portions of the liquid crystal panel to polarize incident light; The retardation value Re in the horizontal direction is in the range of 40 to 60 nm and the retardation value Rth in the thickness direction is Rth = A first biaxial film of -110 to-130 nm; A first C-film disposed between the first biaxial film and the liquid crystal panel to change light transmitted through the first biaxial film and having a retardation value (Rth) in the thickness direction of Rth = 55 to 75 nm; A second C-film disposed between the liquid crystal panel and the second polarizing plate to change the light transmitted through the liquid crystal panel and having a thickness retardation value (Rth) of Rth = 55 to 75 nm; And a polarizing state of light passing through the second C-film is changed between the second C-film and the second polarizing plate, and the retardation value Re in the horizontal direction is Re = 40 to 60 nm and the retardation value in the thickness direction ) consists of a second biaxial film having Rth = 110~130nm, wherein _{Re = (n x -n y)} d and _{Rth = ((n x + n} z) / 2-n z) d and n _x, n _y and n _z are respectively the refractive index in the x-axis direction, the refractive index in the y-axis direction, and the refractive index in the z-axis direction.

Description

TECHNICAL FIELD [0001] The present invention relates to a liquid crystal display (LCD)

The present invention relates to a vertical transverse electric field mode liquid crystal display element, and more particularly to a vertical transverse electric field mode liquid crystal display element having a compensation film and improved viewing angle characteristics.

2. Description of the Related Art Recently, various portable electronic devices such as a mobile phone, a PDA, and a notebook computer have been developed. Accordingly, there is a growing need for a flat panel display device for a light and small size. As such flat panel display devices, a liquid crystal display (LCD), a plasma display panel (PDP), a field emission display (FED) and a vacuum fluorescent display (VFD) have been actively studied. However, Because of its implementation, liquid crystal display devices (LCDs) are now spotlighted.

Although these liquid crystal display devices have various display modes depending on the arrangement of liquid crystal molecules, liquid crystal display devices of TN mode are mainly used because of their advantages of easy monochrome display, quick response speed and low driving voltage. In such a TN mode liquid crystal display element, liquid crystal molecules aligned horizontally with the substrate are oriented substantially perpendicular to the substrate when a voltage is applied. Therefore, there is a problem that the viewing angle is narrowed when the voltage is applied due to the refractive index anisotropy of the liquid crystal molecules.

In order to solve such a viewing angle problem, liquid crystal display devices of various modes having a wide viewing angle characteristic have been proposed. Among them, liquid crystal display devices of a transverse electric field mode (In Plane Switching Mode) . The IPS mode liquid crystal display element forms at least one pair of electrodes arranged in parallel in a pixel to form a transversal electric field substantially parallel to the substrate, thereby aligning the liquid crystal molecules in a plane.

In particular, in recent years, in order to improve the contrast ratio, which is a disadvantage of the IPS mode liquid crystal display device, and to improve the switching speed, the initial liquid crystal molecules are oriented perpendicularly to the substrate, and the liquid crystal molecules are aligned horizontally A vertical IPS mode liquid crystal display element has been proposed.

1 is a plan view of a general vertical IPS mode liquid crystal display device. FIG. 1 (a) is a plan view and FIG. 1 (b) is a cross-sectional view taken along line I-I 'of FIG.

As shown in Fig. 1 (a), the pixels of the liquid crystal panel 1 are defined by the gate line 3 and the data line 4 arranged vertically and horizontally. Although only the (n, m) -th pixel is shown in the figure, n and m of the gate line 3 and the data line 4 are arranged in the liquid crystal panel 1, N x m pixels are formed over the entire area. A thin film transistor 10 is formed in a crossing region of the gate line 3 and the data line 4 in the pixel. The thin film transistor 10 includes a gate electrode 11 to which a scanning signal is applied from a gate line 3 and a semiconductor layer which is formed on the gate electrode 11 and is activated by a scanning signal to form a channel layer And a source electrode 13 and a drain electrode 14 formed on the semiconductor layer 12 and to which an image signal is applied through the data line 4. The liquid crystal layer 40 .

In the pixel, a plurality of common electrodes 5 and pixel electrodes 7 arranged substantially in parallel with the data lines 4 are arranged. A common line 16 connected to the common electrode 5 is disposed in the middle of the pixel and a pixel electrode line 18 connected to the pixel electrode 7 is disposed on the common line 16, And overlaps with the common line 16. A storage capacitance is formed in the transverse electric field mode liquid crystal display element by overlapping the common line 16 and the pixel electrode line 18. [

The liquid crystal molecules of the liquid crystal layer 40 are negative liquid crystal molecules. Therefore, in the vertical IPS mode liquid crystal display device constructed as described above, the liquid crystal molecules are oriented substantially perpendicular to the common electrode 5 and the pixel electrode 7. [ A horizontal electric field substantially parallel to the liquid crystal panel 1 is generated between the common electrode 5 and the pixel electrode 7 when the thin film transistor 10 is operated and a signal is applied to the pixel electrode 7. [ The liquid crystal molecules are rotated in parallel with the liquid crystal panel 1 along the transverse electric field, so that the grayscale inversion due to the refractive index anisotropy of the liquid crystal molecules can be prevented.

A conventional IPS mode liquid crystal display device having the above structure will be described in more detail with reference to the sectional view of FIG. 1 (b).

1 (b), a gate electrode 11 is formed on the first substrate 20, and a gate insulating layer 22 is laminated over the entire first substrate 20. A semiconductor layer 12 is formed on the gate insulating layer 22 and a source electrode 13 and a drain electrode 14 are formed thereon. A passivation layer 24 is formed on the entire surface of the first substrate 20 and a first alignment layer (not shown) is formed on the first substrate 20 to align the liquid crystal molecules in a specific direction 28a are formed.

A plurality of common electrodes 5 are formed on the first substrate 20 and a pixel electrode 7 and a data line 4 are formed on the gate insulating layer 22. The common electrode 5, A transverse electric field E is generated between the pixel electrodes 7.

On the second substrate 30, a black matrix 32 and a color filter layer 34 are formed. The black matrix 32 serves to prevent light from leaking into a region where the liquid crystal molecules do not operate. As shown in the figure, the black matrix 32 is formed between the pixel region and the pixel (that is, the gate line and the data line Region). The color filter layer 34 is formed of R (Red), B (Blue), and G (Green) to realize actual colors. An overcoat layer 36 for protecting the color filter layer 34 and improving the flatness of the substrate is formed on the color filter layer 34 and a second alignment layer 28b having an alignment direction is formed thereon have.

A liquid crystal layer 40 is formed between the first substrate 20 and the second substrate 30 to complete the liquid crystal panel 1.

As described above, in the IPS mode liquid crystal display element, a transverse electric field is generated inside the liquid crystal layer 40 by the common electrode 5 and the pixel electrode 7 formed on the substrate 20 and the gate insulating layer 22 The liquid crystal molecules in the liquid crystal layer 40 are rotated in a planar state perpendicular to the substrates 20 and 30 so that the grayscale inversion due to the refractive index anisotropy of the liquid crystal molecules can be prevented.

However, the vertical IPS mode liquid crystal display device has the following problems. That is, in the vertical IPS mode liquid crystal display device, since the liquid crystal molecules rotate parallel to the plane of the substrate in the vertical direction along the transverse electric field, it is possible to prevent the grayscale inversion due to the refractive index anisotropy of the liquid crystal molecules, There is a problem that the viewing angle characteristics in the diagonal direction of the screen are not improved.

An object of the present invention is to provide a liquid crystal display element capable of improving viewing angle characteristics in the diagonal direction by changing polarization characteristics of light transmitted through a liquid crystal panel by a compensation film.

According to an aspect of the present invention, there is provided a liquid crystal display device including: a liquid crystal panel including a liquid crystal layer; A first polarizing plate and a second polarizing plate positioned at upper and lower portions of the liquid crystal panel to polarize incident light; The retardation value Re in the horizontal direction is in the range of 40 to 60 nm and the retardation value Rth in the thickness direction is Rth = A first biaxial film of -110 to-130 nm; A first C-film disposed between the first biaxial film and the liquid crystal panel to change light transmitted through the first biaxial film and having a retardation value (Rth) in the thickness direction of Rth = 55 to 75 nm; A second C-film disposed between the liquid crystal panel and the second polarizing plate to change the light transmitted through the liquid crystal panel and having a thickness retardation value (Rth) of Rth = 55 to 75 nm; And a polarizing state of light passing through the second C-film is changed between the second C-film and the second polarizing plate, and the retardation value Re in the horizontal direction is Re = 40 to 60 nm and the retardation value in the thickness direction ) consists of a second biaxial film having Rth = 110~130nm, wherein _{Re = (n x -n y)} d and _{Rth = ((n x + n} z) / 2-n z) d and n _x, n _y and n _z are respectively the refractive index in the x-axis direction, the refractive index in the y-axis direction, and the refractive index in the z-axis direction.

The optical axis of the first biaxial film is perpendicular to the optical absorption axis of the first polarizing plate and the optical axis of the second biaxial film is perpendicular to the optical absorption axis of the second polarizing plate . The rubbing direction of the liquid crystal panel is parallel to the light absorption axis of the first polarizing plate.

The liquid crystal panel includes a vertical IPS (Vertical In Plane Switching) mode liquid crystal panel, an IPS mode liquid crystal panel, and a FFS (Fringe Field Swiching) mode liquid crystal panel.

The present invention provides a compensation film between a polarizing plate and a liquid crystal panel to change polarization characteristics of light incident on the liquid crystal panel. By changing the polarizing characteristic, the optical axis of the light incident on the second polarizing plate coincides with the absorption axis of the second polarizing plate, so that the viewing angle characteristics in the diagonal direction can be improved.

1A and 1B are diagrams showing the structure of a general IPS mode liquid crystal display element.
2 is a simplified exploded view showing the structure of a conventional liquid crystal display device.
3A is a diagram showing the absorption axes of the upper and lower polarizing plates when the liquid crystal display element is viewed from the front;
Fig. 3B is a diagram showing the absorption axes of the upper and lower polarizing plates when the liquid crystal display element is viewed diagonally. Fig.
4A and 4B are diagrams showing refractive index relationships in the x, y and z axial directions of the A-compensation film.
Figs. 5A and 5B are diagrams showing refractive index relationships in the x, y and z axial directions of a C-compensation film. Fig.
6 is a view showing a refractive index relationship in the x, y and z axial directions of the biaxial compensation film.
7A and 7B are diagrams showing elliptically polarized light and corresponding Poincare vectors, respectively.
8 is a view showing a polarization state of light in a Poincare sphere when the liquid crystal display element is viewed from the front;
9 is a diagram showing a polarization state of light in a Poincare sphere when the liquid crystal display element is viewed in a diagonal direction;
10 is a view showing the structure of a liquid crystal display element according to an embodiment of the present invention.
11 is a sectional view showing the structure of a liquid crystal panel according to the present invention.
12A is a view showing an optical axis of a liquid crystal display element according to an embodiment of the present invention.
12B is a view showing a Pujiang curry sphere in which the polarization state of light in the liquid crystal display element according to the embodiment of the present invention is indicated.
FIG. 12C is a projection view of FIG. 12B. FIG.
13A and 13B are diagrams showing luminance viewing angle characteristics when viewing a conventional liquid crystal display element and a liquid crystal display element according to an embodiment of the present invention, respectively, in a diagonal direction.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will now be described in detail with reference to the accompanying drawings.

The reason why the viewing angle characteristic decreases in the diagonal viewing angle direction of the liquid crystal display element is that light leakage occurs in the diagonal direction of the liquid crystal display element. 2, in a general vertical IPS mode liquid crystal display device, a first polarizer 152 and a second polarizer 154 are attached to upper and lower portions of a liquid crystal panel 101 and are input to and output from the liquid crystal panel 101 The light is linearly polarized.

In the normally black mode, the polarization axes of the first polarizer 152 and the second polarizer 154 attached to the upper and lower substrates are perpendicular to each other. Therefore, the light transmitted through the first polarizing plate 152 is linearly polarized in the x-axis direction and input to the liquid crystal display element. When no signal is applied to the liquid crystal panel, the liquid crystal molecules 142 of the liquid crystal panel 101 are arranged in the z-axis direction, i.e., perpendicular to the liquid crystal panel, so that light incident on the liquid crystal panel 101 is linearly polarized Through the liquid crystal panel 101 as shown in Fig. On the other hand, the polarization axis of the second polarizing plate 154 attached to the upper substrate is completely absorbed by the polarizing plate of the upper substrate perpendicular to the polarization direction of the light transmitted through the liquid crystal layer, And the screen is displayed in black.

However, when the above liquid crystal display element is viewed diagonally, the polarization directions of the first polarizing plate 152 and the second polarizing plate 154 are not arranged substantially vertically. That is, when viewed from the front side of the liquid crystal display element 101, the polarization axes of the first polarizing plate 152 and the second polarizing plate 154 are vertically aligned with each other, but they are broken when viewed diagonally.

3A shows the arrangement of the polarization axes of the first polarizing plate 152 and the second polarizing plate 154 in the light path passing through the liquid crystal display element in the front view, that is, in the direction perpendicular to the screen of the liquid crystal display element, The polarization axis of the first polarizing plate 152 and the polarizing axis of the second polarizing plate 154 in the path of the light passing through the screen of the liquid crystal display element at a constant polar angle and azimuthal angle when the device is viewed diagonally Layout. Here, the dotted line in the drawing is the direction of the polarization axis (i.e., the light absorption axis) in the first polarizing plate 152 and the solid line is the direction of the light absorption axis in the second polarizing plate 152.

3A, when the liquid crystal display element is viewed from the front (that is, when light is vertically transmitted through the screen of the liquid crystal display element), the polarization axes of the first polarizer 152 and the second polarizer 154 The first polarizer 152 and the second polarizer 152 of the liquid crystal display device when viewed in a diagonal direction (when transmitting the liquid crystal display device at a certain polar angle and azimuth angle with the screen of the liquid crystal display device) The polarization axes of the light guide plate 154 are arranged at a constant angle?

When the liquid crystal display element is viewed in the diagonal direction, the polarizing directions of the first polarizing plate 152 and the second polarizing plate 154 are not perpendicular to each other. Therefore, the first polarizing plate 152 linearly polarizes the liquid crystal panel 101, Is partially absorbed by the second polarizing plate 154 without being completely absorbed by the second polarizing plate 154. Therefore, when the liquid crystal display element is viewed in the diagonal direction even in the normally black state, a part of the light leaks and the black state can not be maintained completely.

As described above, the viewing angle characteristics are degraded when the liquid crystal display element is viewed in the diagonal direction because the polarizing directions of the first polarizing plate 152 and the second polarizing plate 154 are not perpendicular to each other, Is not completely absorbed by the second polarizing plate 154, and a part thereof is leaked. Therefore, in order to improve the viewing angle characteristics when viewing the liquid crystal display element in the diagonal direction, the polarized light from the first polarizing plate 152 must be absorbed by the second polarizing plate 154. For this purpose, in the present invention, the compensation film is used to change the polarization direction of the light transmitted through the liquid crystal panel 101 so that the optical axis of the light incident on the second polarizing plate 154 is changed in the direction of polarization of the second polarizing plate 154 ).

The compensation film can be classified into a uniaxial film and a biaxial film. The uniaxial film is an anisotropic birefringent film having only one optical axis and the biaxial film is an anisotropic birefringent film having two optical axes. Among these compensation films, the uniaxial film can be classified into an A-compensation film and a C-compensation film depending on the direction and size of the optical axis. The refractive index characteristics of such an A-compensation film and a C-compensation film are shown in Figs. 4 and 5. Fig.

4A and 4B are views showing a positive A-compensation film and a negative A-compensation film, respectively. As shown in FIGS. 4a and 4b, A- compensation film is a refractive index in the y-axis direction _(y n) and the refractive index of the z-axis (n _z) is equal to (n _y = n _z) in the x-axis direction to each other refractive index (n _x) is the refractive index (n _z) and wherein the other of the refractive index (n _y) and z-axis direction of the y-axis _{(n x ≠ n y = n} z). 4A, when the refractive index n _{x in the x-} axis direction is larger than the refractive index n _{y in the} y-axis direction, the refractive index n _{x in the} x-axis direction is the refractive index in the y- (n _y ), the positive A-compensation film and the negative A-compensation film are defined by the following Equation 1, respectively.

5A and 5B are views showing a positive C-compensation film and a negative C-compensation film, respectively. 5A and 5B, the C-compensation film has the same refractive index n _x in the x-axis direction and refractive index n _{y in the} y-axis direction (n _x = n _y ) The refractive index n _z is different from the refractive index n _{x in the} x-axis direction and the refractive index n _{y in the} y-axis direction (n _z ≠ n _x = n _y ). 5A, when the refractive index n _{x in the} x-axis direction and the refractive index n _{y in the y-} axis direction are smaller than the refractive index n _{z in the} z-axis direction, the positive C- refractive index (n _x) and y inde-axis refractive index (n _y) is greater than the negative C- compensation film, the refractive index (n _z) in the z-axis direction, respectively, the expression of these positive and negative compensation film C- C- compensation film 2 is defined as follows.

Further, the phase difference due to the compensating film is determined by the refractive index (n _z) of the refractive index (n _x) of the x-axis direction, refractive index in the y-axis (n _y) and z-axis direction, the phase difference and the equation (3) Refractive index (n _x , n _y , n _z ).

Here, Re is the retardation value in the horizontal direction, Rth is the retardation value in the thickness direction, and d is the thickness of the compensation film.

The A-compensation film and the C-compensation film mainly use a cycloolefin polymer film or a polycarbonate film, a UV curable horizontal or horizontal alignment liquid crystal film, polystyrene resin, and polyethylene terephthalate.

The biaxial films are classified into positive biaxial films, negative biaxial films and Z-axis oriented biaxial films in which n _x , n _y and n _z are different values. Also the biaxial film having a refractive index in the x axis direction to 6 (nx) and the refractive index in the y-axis (n _y) and refractive index (n _z) in the z-axis direction is shown. The biaxial film is positive, the axis loaded, and voice, the axis film and a Z-axis oriented according to the magnitude of the refractive index (n _x) of the x-axis direction and the refractive index in the y-axis (n _y) and the refractive index in the z direction (n _z) These positive biaxial films, negative negative biaxial films and Z-axis oriented biaxial films are defined by the following Equation 4, respectively.

Further, the biaxiality (Nz) of the biaxial film is defined by the following equation (5).

As defined in Equation (3), Re is the retardation value in the horizontal direction, Rth is the retardation value in the thickness direction, and d is the thickness of the compensation film.

According to the definition of Equations (4) and (5), the negative biaxial film has Nz? 1 and the positive biaxial film has Nz < 0, and the z axis stretched biaxial film has 0 < Nz <

In the present invention, by providing the compensation film as described above, the polarized light of the linearly polarized light is phase-transformed by the first polarizing plate 152 to make the polarizing direction of the light completely perpendicular to the polarizing direction of the second polarizing plate 154, Thereby absorbing all the light incident on the light emitting device.

The polarization state of light can be analyzed by a Jones matrix. In the Jones operation, the Jones matrix representing the polarization transmission characteristics of a transparent medium is a unitary matrix because it neglects the reflection of light at the interface. Can be represented by the Poincare shpere.

Since the Jones vector can represent only the full polarization, the Stokes parameter defined by the following equation (6) must be used to express the partial polarization.

의 부등식이 성립하는데, 이 부등식은 완전편광에서만 맞는다. 즉, 완전편광의 경우, S1, S2 및 S3를 빛의 밝기 S0로 나눈 규격화된 변수 s1, s2 및 s3 사이에는 다음의 수학식 7의 관계가 성립한다.Here, <> represents time average, and E _x and E _x are electric field components in the x-axis and y-axis directions, respectively. At this time, among these four variables

This inequality is only true for perfect polarization. That is, in the case of perfect polarization, the relationship of Equation (7) is established between normalized variables s1, s2 and s3 obtained by dividing S1, S2 and S3 by the light brightness S0.

This is an equation of Poincare Sphere with a radius of 1 in three-dimensional space, and (s1, s2, s3) is the point of Cartesian coordinates of the Poincare sphere.

At this time, all the points on the equator line in the Pujiang Curve correspond to linearly polarized light, the north pole corresponds to the right-handed circular polarization, and the south polarization corresponds to the left-handed 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 elliptic polarized light in the orthogonal coordinate system and corresponding pouinc curves, respectively.

As shown in Figs. 7A and 7B, the latitude angle of the puang curry 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 and the azimuth angle is (2x) cons (2x), sin (2ψ) cos (2x), and sin (2x). 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. At this time, the opposite points on the Pujiang Curve show polarized states orthogonal 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 Pujiang curry sphere.

Fig. 8 is a view showing a Poincare sphere showing the polarization states of the first polarizing plate 152 and the second polarizing plate 154 when the IPS mode liquid crystal display element is viewed from the front as shown in Fig. 3A.

The point A represents the light absorption axis of the first polarizer 152 and the light transmission axis of the second polarizer 154 and the point B represents the light absorption axis of the first polarizer 152 ) And the light absorption axis of the second polarizing plate 154. [ 8, when the IPS mode liquid crystal display element is viewed from the front, the light transmission axis of the first polarizing plate 152 maintains the same linearly polarized light state as the light absorption axis of the second polarizing plate 154. As shown in FIG. This is because the optical absorption axis of the first polarizing plate 152 and the optical absorption axis of the second polarizing axis 154 are perpendicular to each other when viewed from the front of the IPS mode liquid crystal display element, This is because the light absorption axes of the polarizing plate 154 are parallel to each other.

As described above, the light transmission axis of the first polarizer 152 and the light absorption axis of the second polarizer 154 are parallel to each other so that the light transmission axis of the first polarizer 152 and the light of the second polarizer 154 Since the absorption axis is located at the same point, the linearly polarized light transmitted through the first polarizing plate 152 is absorbed by the second polarizing plate 154, so that no light is transmitted to the outside of the second polarizing plate 154, When the IPS mode liquid crystal display element is viewed from the front in the black mode, it is possible to maintain a completely black state.

9 is a view showing a Poincare sphere showing the polarization state of light when the liquid crystal display element is viewed in the diagonal direction in the IPS mode liquid crystal display element as shown in FIG. 3B.

In FIG. 9, the point A1 represents the light absorption axis of the first polarizer 152, and the point A2 opposite thereto represents the light transmission axis of the first polarizer 152 orthogonal to the light absorption axis. The point B1 represents the light transmission axis of the second polarizing plate 154 and the point B2 represents the light absorption axis of the second polarizing plate 154. [ 3B, when the IPS mode liquid crystal display element is viewed diagonally, the polarization directions of the first polarizing plate 152 and the second polarizing plate 154 are not perpendicular to each other, Therefore, the point A2, which is the light transmission axis of the first polarizing plate 152, and the point B2, which is the light absorption axis of the second polarizing plate 154, do not coincide with each other but are spaced apart by x. The distance x is the angle between the light transmission axis of the first polarizer 152 and the light absorption axis of the second polarizer 154. The distance between the light transmission axis of the first polarizer 152 and the light transmission axis of the second polarizer 154 ) Of the first polarizing plate 154 transmits the light corresponding to the angle between the light absorption axes of the first polarizing plate 154 and the second polarizing plate 154. Accordingly, in order to prevent the light leakage in the diagonal direction of the IPS mode liquid crystal display element, the A2 point and the B2 point are aligned so that the light transmission axis of the first polarizer 152 and the light absorption axis of the second polarizer 154 are parallel So that the polarized light from the first polarizing plate 152 must be absorbed by the second polarizing plate 154.

In the present invention, the polarizing state of the linearly polarized light in the first polarizing plate 152 is changed by using the compensation film so that the point A2 and the point B2 on the Poincare sphere are made to coincide (that is, the light transmitting axis of the first polarizing plate 152 and Polarizing plate 154 is parallel to the light-absorbing axis of the second polarizing plate 154).

Hereinafter, a specific embodiment of the present invention will be described. At this time, the polarization state of the liquid crystal display according to the embodiment of the present invention will be described using the Poincare sphere. As described above, in the present invention, it is possible to prevent light leakage in the diagonal direction of the liquid crystal display element by changing the polarization state of light by using a compensation film.

10 is a view showing a structure of a liquid crystal display device according to an embodiment of the present invention.

10, a liquid crystal display device 200 according to an embodiment of the present invention includes a liquid crystal panel 201 that implements an image, a first compensation film attached to the lower portion of the liquid crystal panel 201, A third compensating film 246 and a fourth compensating film 248 attached to the upper portion of the liquid crystal panel 201 and a second compensating film 244 And a second polarizing plate 260 attached on the fourth compensating film 248. The first polarizing plate 250 and the second polarizing plate 260 are attached to each other.

Although not shown in detail in the drawing, the liquid crystal panel 201 is formed of a first substrate and a second substrate, and a liquid crystal layer formed between the first substrate and the second substrate. The first substrate includes a thin film transistor, A data line pattern, and various electrodes are formed on the second substrate, and a black matrix is formed on the second substrate to prevent light from being leaked to the image non-display area to deteriorate image quality.

In particular, the liquid crystal panel of the present invention is a vertical IPS mode liquid crystal panel. Therefore, the common electrode and the pixel electrode are arranged on the first substrate in parallel with each other, and an electric field parallel to the surface of the substrate is applied to the liquid crystal layer. The liquid crystal layer of the liquid crystal panel 201 uses a negative nematic liquid crystal having a retardation value (Rth) of about 450 nm.

In addition, the present invention can be applied not only to the vertical IPS mode liquid crystal panel but also to the IPS mode liquid crystal panel and the FFS (Fringe Field Swiching) mode liquid crystal panel.

The first polarizer 250 includes a first polarizer 252, a first support 254, and a second support 256. The first polarizer 252 is a film that can convert natural light into arbitrary polarized light. At this time, the first polarizer 252 functions to transmit one polarized light component of two polarized light components and to absorb, reflect or scatter other polarized light components when the incident light is divided into two polarized light components orthogonal to each other May be used. The optical film used for the first polarizer is not particularly limited, and for example, a polymer film containing as a main component a polyvinyl alcohol (PVA) based resin containing iodine or a dichroic dye, An O-type polarizer in which a liquid crystal composition containing a liquid crystal compound is aligned in a certain direction, and an E-type polarizer in which a lyotropic liquid crystal is aligned in a certain direction. The first support 254 serves to protect the first polarizer 252 and is formed of a general protection film having no retardation. Any of these protective films can be used, but mainly triacetylcellulose (TAC) is used.

The first and second supports 254 and 256 may be formed of a general protective film having no phase retardation in order to protect the first polarizer 252. For example, 0-RT (where Rth is 0 nm TAC), COP (Cyclo-olefin-Polymer), and the like. 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 second polarizer 260 also includes a second polarizer 262, a third support 264, and a fourth support 266. The second polarizer 262 is made of a polyvinyl alcohol resin like the first polarizer 252 and triacetylcellulose is used as a transparent protective film for the third and fourth supports 264 and 266 .

10, a second support member 223 made of triacetyl cellulose having no retardation Rth between the first polarizer 252, the liquid crystal panel 201, the second polarizer 262, and the liquid crystal panel 201, The second support member 256 and the fourth support member 266 are removed so that the first polarizer 252 and the second polarizer 262 are directly disposed on the liquid crystal panel 252. [ (Not shown).

The second compensation film 244 and the third compensation film 246 are uniaxial compaction films, which are negative C-films. The negative C film is mainly formed by using a cycloolefin polymer film or a polycarbonate film, a UV curable horizontal or horizontal alignment liquid crystal film, polystyrene resin, or polyethylene terephthalate. At this time, the retardation value (Rth) in the thickness direction of the second compensation film 244 and the third compensation film 246, which are the negative C films, is Rth = 55 to 75 nm.

The first compensation film 242 and the fourth compensation film 248 are respectively a positive biaxial compensation film and a negative biaxial compensation film. In the case of a positive biaxial film, the retardation value Re in the horizontal direction is Re The retardation value Re in the thickness direction is Rth = -110 to -130 nm, the retardation value Re in the horizontal direction is Re = 40 to 60 nm in the case of the negative biaxial film and the retardation value (Rth ) Is Rth = 110 to 130 nm.

Accordingly, the biaxiality Nz of the first compensation film 246 is -1.8 < Nz < -3.2 by the equation (5). Typically <If 0, biaxial film as a positive biaxial film that x, y, the refractive index in the z-axis direction (n _x, n _y, n _z) is n _z> biaxial (Nz) of the biaxial film Nz n _x & gt _; n.

Further, the biaxiality Nz of the fourth compensation film 248 is 1.8 < Nz < 3.2 according to Equation (5). Typically, if a biaxially (Nz) of the biaxial film is a Nz> 1, biaxial film is a refractive index _{(n x, n y, n} z) in the x, y, z-axis direction as a negative biaxial film is n _x> n _y > _z .

The first compensation film 242 and the fourth compensation film 248, that is, the biaxial film may be a UV curable liquid crystal film using nematic liquid crystal, polycarbonate, polyethylene terephthalate, polystyrene, Uniaxial stretched TAC (uniaxial stretched TAC), uniaxially stretched PNB (Polynorbonene), biaxially stretched PC (polycarbonate), biaxially stretched COP, and biaxial LC film are used. a normal wavelength dispersion characteristic, a flat wavelength dispersion characteristic, and a reverse wavelength dispersion characteristic.

The absorption axis of the first polarizer 250 is arranged at an angle of 90 ° and the absorption axis of the second polarizer 260 is arranged at an angle of 0 °. The direction of the refractive index n _{x in} the x-axis direction of the first compensation film 244 is arranged at 90 ° and the direction of the second compensation film 246 is arranged at 0 ° in the n _x direction, 201 also have a rubbing direction of 90 degrees.

The liquid crystal molecules of the liquid crystal layer of the liquid crystal panel 201 are arranged along the rubbing direction of the alignment film when the liquid crystal panel 201 is in the off state. Therefore, the optical axis of the liquid crystal molecules also forms 90 degrees. The reason why the liquid crystal panel 201 is formed at an angle of 90 DEG in the rubbing direction is as follows.

Since the common electrode and the pixel electrode forming the horizontal electric field in the IPS mode liquid crystal display device are arranged along the data line, the rubbing direction of the alignment film is formed at an angle of about 15 to 45 degrees.

11, in the present invention, the common electrode 205 and the pixel electrode 207 of the IPS mode liquid crystal panel 201 are formed in a pixel defined by the gate line 203 and the data line 204 And the rubbing of the alignment film is performed in the data line direction, that is, at an angle of 90 [deg.]. That is, the direction of the electrodes 205 and 207 and the alignment direction are formed at a certain angle?.

The common electrode 205 and the pixel electrode 207 are bent in such a manner that a plurality of domains having main viewing angles in different directions are formed in one pixel to improve the viewing angle characteristics of the liquid crystal display device will be. Since the common electrode 205 and the pixel electrode 207 are formed at a certain angle with the data line 204 and the rubbing direction of the alignment film is in the data line direction, ), For example, at an angle of about 15 deg. To 45 deg.

Of course, the present invention can be applied not only to the IPS mode liquid crystal display device having such a structure but also to the FFS mode liquid crystal display device in which the rubbing direction is formed at 90 degrees and the electrode direction and the rubbing direction are formed at a certain angle.

The polarization state of the liquid crystal display according to the present embodiment having the above-described structure will now be described with reference to FIGS. 12A to 12C. 12A is a diagram showing a polarization state in each constitution of the liquid crystal display element according to the present invention, Fig. 12B is a view showing a Poincare sphere showing a polarization state in the liquid crystal display element according to the present invention, and Fig. 12C Is a two-dimensional representation of Fig. 12B, that is, a projection of a Poincare sphere.

12A, the first polarizing plate 250 is disposed below the liquid crystal panel 201, and the light absorption axis of the first polarizing plate 250 is perpendicular to the rubbing direction of the liquid crystal panel 201 That is, the light absorption of the first polarizing plate is formed at an angle of 90 degrees). A first compensation film 242 made of a positive biaxial film and a second compensation film 244 made of a negative C film are disposed between the liquid crystal panel 201 and the first polarizer 250, n _x direction of the first compensation film 242 is composed of a rubbing direction and the vertical of the first polarizing plate 250, the light absorption axes and liquid crystal panel 201 (i.e., the n _x direction to form a 0 °).

The second polarizing plate 260 is disposed on the liquid crystal panel 201 and the light absorption axis of the second polarizing plate 260 is perpendicular to the rubbing direction of the liquid crystal panel 201 Absorption is formed at an angle of 0 DEG). The third compensation film 246 made of the negative C film and the fourth compensating film 248 made of the negative biaxial film are disposed between the liquid crystal panel 201 and the second polarizer 260, The n _x direction of the compensation film 246 is parallel to the rubbing direction of the liquid crystal panel 201 and perpendicular to the light absorption axis of the second polarizer 260 (i.e., the n _x direction forms 90 °) .

12B, when the unpolarized light is incident on the first polarizer 250 from the backlight of the liquid crystal panel 201, the light is linearly polarized. Most of the linearly polarized light is absorbed by the first polarizer 250 The polarized state of light absorbed by the axis (point A1) and transmitted through the first polarizing plate 250 is located at point A2. That is, the transmission axis of the first polarizer 250 is located at the point A2. At this time, the absorption axis of the second polarizer 260 is located at the point B2, and is spaced apart from the transmission axis of the first polarizer 250 by a certain distance.

When the first compensation film 242 made of a linearly polarized positive biaxial film is transmitted through the first polarizer 250, the polarization state thereof is rotated from the A2 point to the C1 point. At this time, the first compensation film 242 is present between the positive because biaxial film, the optical axis is n _y-axis, and n _z-axis, so that the polarization state of the light with an optical axis center between n _y-axis, and n _z axis So that the polarization state is shifted from the point A2 to the point C1 to be elliptically polarized light. In this case, since the retardation value (Rth) of the positive biaxial film is Rth = 110 to 130 nm, the rotation angle of the polarization state is about 72 to 85 degrees when the wavelength of 550 nm, which is a green wavelength affecting the brightness, .

Then, when the elliptically polarized light is polarized by the first compensation film 242 and transmitted through the second compensating film 244 made of the negative C film, the polarization state is rotated counterclockwise about the S1 axis, The polarization state is rotated from point C1 to point C2. At this time, the point C2 is positioned on the quadrant of the quadrangle of the puang curlephere to maintain the elliptically polarized state.

When the voice C- film second compensation film 244, the elliptically polarized light transmitted through the transmission composed of the back of the liquid crystal panel 201, since the alignment film is rubbed at an angle of 90 °, the polarization state is A ₂ - O axis and the polarization state of the liquid crystal panel 201 is located at the point C3. At this time, since the retardation value of the liquid crystal layer of the liquid crystal panel 201 is about 450 nm, the light passing through the liquid crystal panel 201 rotates clockwise at an angle of about 294 degrees about the S ₂ -O axis. At this time, the polarization state of the light maintains the elliptically polarized state located on the fourth quadrant of the Poincare sphere.

When the light transmitted through the liquid crystal panel 201 is transmitted through the third compensation film 246 made of the negative C-film, the polarization state rotates counterclockwise about the S1 axis, Rotation to the point. At this time, the polarization state of the light maintains the elliptically polarized state located on the fourth quadrant of the Poincare sphere.

When the light transmitted through the third compensation film 246 is transmitted through the fourth compensation film 248 made of a negative biaxial film, the polarization state thereof is rotated from C4 to B2. At this time, since the fourth compensation film 248 is a negative biaxial film, its optical axis exists between the n _x axis and the n _z axis. Thus, the polarization state of the light is rotated in the counterclockwise direction around the optical axis between n _x and n _z-axis shaft, wherein a phase difference value (Rth) of the negative biaxial film, the rotation angle of the polarization state by Rth = 110~130nm The polarization state of the light is shifted from the point C4 to the point B2.

As a result, the light transmitted through the fourth compensation film 248 is changed into linearly polarized light having the same polarization axis as the absorption axis of the second polarizer 260, and the polarized light is absorbed in the second polarized light 260 So that the light can not pass through the second polarizer 260.

12C, the linearly polarized light in the first polarizing plate 250 is changed after the polarized state (corresponding to the point A2) is changed by the positive biaxial film, the negative C-film, the liquid crystal panel, and the negative C-film The polarizing state of the polarized light is made to coincide with the position B2 of the final negative biaxial film, that is, the third compensation film 248, and the optical axis of the light incident on the second polarizer 260 is aligned with the absorption axis of the second polarizer 260 So that all the light polarized in the first polarizer 250 is absorbed by the second polarizer 260 to prevent light leakage in the diagonal direction.

13A is a graph showing a result of simulating the luminance viewing angle characteristics in the normally black mode in the diagonal viewing direction of the conventional liquid crystal display device, and FIG. 13B is a graph showing the result of simulation in the normal black mode in the diagonal viewing direction of the liquid crystal display according to the present invention FIG. 8 is a graph showing the simulation result of the luminance viewing angle characteristics in the case of FIG.

Here, the lower polarizer and the upper polarizer are arranged such that the light transmission axes thereof are orthogonal to each other, and the optical axis of the liquid crystal layer is parallel to the light transmission axis of the lower polarizer. 13A and 13B illustrate a conventional liquid crystal display device and a liquid crystal display device including an optical compensation film according to the present invention at an inclination angle of 0 to 80 degrees with respect to all the long axis angles (or azimuth angles) when white light is used. Which is the result of simulating the contrast ratio characteristics. In FIGS. 13A and 13B, 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.

When comparing the contrast ratio characteristics of the conventional liquid crystal display device of FIG. 13A and the liquid crystal display device of the present invention of FIG. 13B, in the normally black mode, the angle of 45 degrees, 135 degrees, and 225 degrees corresponding to the diagonal direction of the liquid crystal display panel And the light leakage at 315 degrees is remarkably reduced. Accordingly, it can be seen that the transmittance in the diagonal viewing angle direction in the liquid crystal display according to the present invention is significantly reduced as compared with the conventional liquid crystal display device.

On the other hand, in the detailed description of the present invention described above, when light is incident through the first polarizing plate and the polarized state of the light passes through the positive biaxial film, the negative C-film, the liquid crystal layer, the negative C- All the light is absorbed by the light absorption axis of the polarizing plate and the light is not transmitted through the second polarizing plate in the normally black mode, but the same effect can be obtained even if the above configuration is reversed. That is, light is incident through the second polarizing plate and the incident light is transmitted through the negative biaxial film, the negative C-film, the liquid crystal layer, the negative C-film, and the positive biaxial film, I will not.

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. Accordingly, the invention is not to be determined by the embodiments described, but should be determined by equivalents to the appended claims and the appended claims.

200: liquid crystal display element 201: liquid crystal panel
242: Positive biaxial film 244, 246
Negative C-film 248: negative biaxial film
250, 260: polarizer

Claims (16)

A liquid crystal panel including a liquid crystal layer;
A first polarizing plate and a second polarizing plate positioned at upper and lower portions of the liquid crystal panel to polarize incident light;
The retardation value Re in the horizontal direction is in the range of 40 to 60 nm and the retardation value Rth in the thickness direction is Rth = A first biaxial film of -110 to-130 nm;
A first C-film disposed between the first biaxial film and the liquid crystal panel to change a polarization state of light transmitted through the first biaxial film and having a thickness retardation value (Rth) of Rth = 55 to 75 nm;
A second C-film disposed between the liquid crystal panel and the second polarizing plate to change a polarization state of light transmitted through the liquid crystal panel and having a thickness retardation value (Rth) of Rth = 55 to 75 nm; And
Film is provided between the second C-film and the second polarizing plate to change the polarization state of light transmitted through the second C-film, the retardation value Re in the horizontal direction is Re = 40 to 60 nm and the retardation value (Rth) Is composed of a second biaxial film having Rth = 110 to 130 nm,
Wherein _{Re = (n x -n y)} d and _{Rth = ((n x + n} z) / 2-n z) d and n _x, n _y and n _z is the refractive index, y-axis direction of the x-axis direction, respectively Refractive index and refractive index in the z-axis direction, and d is a thickness of the first biaxial film, the second biaxial film, the first C-film, and the second C-film. The liquid crystal display of claim 1, wherein the absorption axes of the first polarizing plate and the second polarizing plate are perpendicular to each other. The liquid crystal display according to claim 1,
A first polarizer; And
And a first support and a second support attached to the upper surface of the first polarizer. The liquid crystal display according to claim 3, wherein the first and second supports are transparent protective films. The liquid crystal display according to claim 4, wherein the transparent protective film is made of triacetyl cellulose or triacetyl cellulose having no retardation (Rth). The liquid crystal display element according to claim 3, wherein the first polarizer is made of a polyvinyl alcohol-based resin. The liquid crystal display according to claim 1, wherein the second polarizer comprises:
A second polarizer; And
And a third support and a fourth support attached to the upper and lower surfaces of the second polarizer. The liquid crystal display device according to claim 7, wherein the third and fourth supports are transparent protective films. The liquid crystal display according to claim 8, wherein the transparent protective film is made of triacetyl cellulose having no retardation (Rth). The liquid crystal display element according to claim 7, wherein the second polarizer is made of a polyvinyl alcohol-based resin. The method according to claim 1, wherein the first and second biaxial films are made of a material selected from the group consisting of a UV curable liquid crystal film, polycarbonate, polyethylene terephthalate, and polystyrene . The liquid crystal display of claim 1, wherein the optical axis of the first biaxial film is perpendicular to the optical absorption axis of the first polarizer, and the optical axis of the second biaxial film is perpendicular to the optical absorption axis of the second polarizer. The liquid crystal display element according to claim 1, wherein a rubbing direction of the liquid crystal panel is parallel to a light absorption axis of the first polarizing plate. The liquid crystal display element according to claim 1, wherein unpolarized light is incident through the first polarizing plate. The liquid crystal display element according to claim 1, wherein unpolarized light is incident through the second polarizer plate. The liquid crystal display of claim 1, wherein the liquid crystal panel comprises a vertical IPS mode liquid crystal panel, an IPS mode liquid crystal panel, and a FFS mode liquid crystal panel.

Images