KR20090073867A - Wide viewing angle liquid crystal display device - Google Patents

Abstract

A wide viewing angle liquid crystal display device is provided to change a polarizing characteristic of light transmitting a liquid crystal display device through negative bi-axial films, thereby improving a characteristic in a diagonal direction. The first negative bi-axial film(242) is installed between an LCD(Liquid Crystal Display) panel(201) and the first polarizer(250). The second negative bi-axial film(244) is installed between the LCD panel and the second polarizer(260). In the second negative bi-axial film, a retardation value of a horizontal direction is 60~130nm. The retardation value of a thickness direction is 60~160nm. nx, ny and nz are respectively refractive indexes of an x axial direction, a y axial direction and a z axial direction. The first and second negative bi-axial films change a polarizing state of light.

Description

Wide viewing angle liquid crystal display device {LIQUID CRYSTAL DISPLAY DEVICE HAVING WIDE VIEWING ANGEL}

The present invention relates to a liquid crystal display device, and more particularly, to a liquid crystal display device having a plurality of biaxial optical films to improve viewing angle characteristics.

Recently, with the development of various portable electronic devices such as mobile phones, PDAs, and notebook computers, there is a growing demand for flat panel display devices for light and thin applications. Such flat panel displays are being actively researched, such as LCD (Liquid Crystal Display), PDP (Plasma Display Panel), FED (Field Emission Display), and VFD (Vacuum Fluorescent Display). Liquid crystal display devices (LCDs) are in the spotlight for reasons of implementation.

Such liquid crystal display devices have various display modes according to the arrangement of liquid crystal molecules. However, TN mode liquid crystal display devices are mainly used because of the advantages of easy monochrome display, fast response speed, and low driving voltage. In such a TN-mode liquid crystal display device, liquid crystal molecules oriented horizontally with respect to the substrate are almost perpendicular to the substrate when a voltage is applied. Therefore, there is a problem that the viewing angle is narrowed upon application of voltage due to the refractive anisotropy of the liquid crystal molecules.

In order to solve this viewing angle problem, liquid crystal display devices of various modes having wide viewing angle characteristics have recently been proposed, but among them, the liquid crystal display device of the lateral field mode (In Plane Switching Mode) is applied to actual production. It is produced. The IPS mode liquid crystal display device aligns liquid crystal molecules in a plane by forming at least one pair of electrodes arranged in parallel in a pixel to form a transverse electric field substantially parallel to the substrate.

FIG. 1 is a view showing the structure of a conventional IPS mode liquid crystal display device, in which FIG. 1 (a) is a plan view and FIG. 1 (b) is a sectional view taken along line II ′ of FIG. 1 (a). As shown in FIG. 1A, the pixels of the liquid crystal panel 1 are defined by gate lines 3 and data lines 4 arranged vertically and horizontally. Although only the (n, m) th pixels are shown in the drawing, in the liquid crystal panel 1, n and m gate lines 3 and data lines 4 are disposed, respectively, and thus the liquid crystal panel 1 is disposed. N x m pixels are formed throughout. The thin film transistor 10 is formed at the intersection 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 scan signal is applied from the gate line 3, and a semiconductor layer formed on the gate electrode 11 and activated as a scan signal is applied to form a channel layer. 12 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 image signal input from the outside is applied to the liquid crystal layer. do.

In the pixel, a plurality of common electrodes 5 and a pixel electrode 7 are arranged substantially parallel to the data line 4. In addition, 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. It overlaps with the common line 16. Storage capacitance is formed in the transverse electric field mode liquid crystal display by overlapping the common line 16 and the pixel electrode line 18.

As described above, in the configured IPS mode liquid crystal display device, the liquid crystal molecules are oriented substantially in parallel with the common electrode 5 and the pixel electrode 7. When the thin film transistor 10 is operated to apply a signal to the pixel electrode 7, a transverse electric field substantially parallel to the liquid crystal panel 1 is generated between the common electrode 5 and the pixel electrode 7. Since the liquid crystal molecules rotate on the same plane along the transverse electric field, gray level inversion due to the refractive anisotropy of the liquid crystal molecules can be prevented.

The conventional IPS mode liquid crystal display device having the above structure will be described in more detail with reference to the cross-sectional view of FIG.

As shown in FIG. 1B, a gate electrode 11 is formed on the first substrate 20, and a gate insulating layer 22 is stacked over the entire first substrate 20. The semiconductor layer 12 is formed on the gate insulating layer 22, and the source electrode 13 and the drain electrode 14 are formed thereon. In addition, a passivation layer 24 is formed over the entire first substrate 20, and a first alignment layer having an alignment direction for determining liquid crystal molecules in a specific direction by a method such as rubbing on the first substrate 20. 28a) is formed.

In addition, 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 to form the common electrode 5. The transverse electric field E is generated between the pixel electrodes 7.

The black matrix 32 and the color filter layer 34 are formed on the second substrate 30. The black matrix 32 is to prevent light leakage into an area where the liquid crystal molecules do not operate. As shown in the drawing, the black matrix 32 is formed between the region of the thin film transistor 10 and between the pixel and the pixel (ie, the gate line and the data line). Area). The color filter layer 34 is composed of R (Red), B (Blue), and G (Green) to realize actual colors. An overcoat layer 36 is formed on the color filter layer 34 to protect the color filter layer 34 and to improve flatness of the substrate, and a second alignment layer 28b having an alignment direction determined thereon is formed thereon. have.

The 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 device, 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, respectively. Since the liquid crystal molecules inside the liquid crystal layer 40 are rotated on a plane, gray level inversion due to refractive index anisotropy of the liquid crystal molecules can be prevented.

However, the IPS mode liquid crystal display device as described above has the following problems. That is, in the IPS mode liquid crystal display device, since the liquid crystal molecules rotate on the same plane along the transverse electric field, the gray scale inversion due to the refractive anisotropy of the liquid crystal molecules can be prevented, so that the viewing angle characteristic in the vertical direction or the left and right directions is improved. The viewing angle characteristic in the diagonal direction did not improve.

An object of the present invention is to provide a liquid crystal display device capable of improving the viewing angle characteristic in the diagonal direction by changing the polarization characteristics of light passing through the plurality of negative biaxial films through the liquid crystal display device. do.

In order to achieve the above object, a liquid crystal display device according to the present invention comprises a liquid crystal panel comprising a liquid crystal layer, a first polarizing plate and a second polarizing plate for polarizing the light incident to the upper and lower portions of the liquid crystal panel, the liquid crystal A first negative biaxial film provided between the panel and the first polarizing plate to change the polarization state of light and having a phase retardation value Re = 20 to 70 nm in a horizontal direction and a retardation value Rth = 30 to 100 nm in a thickness direction; It is provided between two polarizing plates to change the polarization state of light, and consists of a second negative biaxial film having a phase difference value Re = 60 to 130 nm in the horizontal direction and a phase difference value Rth = 60 to 160 nm in the thickness direction, wherein Re = (n _x -n _y ) d and Rth = (n _x -n _z ) d and n _x , n _y and n _z are the refractive indexes in the x-axis direction, the refractive index in the y-axis direction and the refractive index in the z-axis direction, respectively. .

Absorption axes of the first polarizing plate and the second polarizing plate are perpendicular to each other, the optical axis of the first negative biaxial film is perpendicular to the light absorption axis of the first polarizing plate, and the optical axis of the second negative biaxial film is the light absorption axis of the second polarizing plate And is vertical. Further, the rubbing direction of the liquid crystal panel is parallel or perpendicular to the light absorption axis of the first polarizing plate.

The present invention includes a negative biaxial film between the polarizing plate and the liquid crystal panel to change the polarization characteristics of the polarized light incident on the liquid crystal panel. By such a change in polarization characteristics, the optical axis of the light incident on the second polarizing plate coincides with the absorption axis of the second polarizing plate, thereby improving the viewing angle characteristic in the diagonal direction.

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

The reason why the viewing angle characteristic is deteriorated in the diagonal viewing angle direction of the liquid crystal display device is that light leakage occurs in the diagonal direction of the liquid crystal display device. As shown in FIG. 2, in a general IPS mode LCD, first and second polarizing plates 152 and 154 are attached to upper and lower portions of the liquid crystal panel 101 to be input and output to the liquid crystal panel 101. Linearly polarize

In the normally black mode, the polarization axes of the first polarizing plate 152 and the second polarizing plate 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 device. When no signal is applied to the liquid crystal panel, since the liquid crystal molecules 142 of the liquid crystal panel 101 are arranged in the x-axis direction, light incident on the liquid crystal panel 101 is linearly polarized along the x-axis direction. Through the liquid crystal panel 101. On the other hand, the polarization axis of the second polarizing plate 154 attached to the upper substrate is perpendicular to the polarization direction of the light transmitted through the liquid crystal layer, all the light is absorbed by the polarizing plate of the upper substrate to the outside of the second polarizing plate 152 Will not be displayed and the screen will be black.

However, when the liquid crystal display device as described above is viewed in a diagonal direction, the polarization directions of the first polarizing plate 152 and the second polarizing plate 154 are not substantially vertically disposed. That is, when viewed from the front of the liquid crystal display device 101, the polarization axes of the first polarizing plate 152 and the second polarizing plate 154 are disposed perpendicular to each other, but when viewed in a diagonal direction, the vertical polarization is broken.

FIG. 3A shows the arrangement of the polarization axes of the first polarizing plate 152 and the second polarizing plate 154 in the path of light transmitted perpendicularly to the screen of the liquid crystal display when viewed from the front, and FIG. 3B is a liquid crystal display. When the device is viewed diagonally, that is, the polarization axis of the first polarizing plate 152 and the second polarizing plate 154 in the path of light passing through the screen of the liquid crystal display device at a constant polar angle and azimuthal angle It is a batch. In this case, the dotted line in the drawing is the direction of the polarization axis (ie, 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.

As shown in FIG. 3A, the polarization axes of the first polarizing plate 152 and the second polarizing plate 154 when the liquid crystal display device is viewed from the front (that is, when light is transmitted perpendicularly to the screen of the liquid crystal display device). Are perpendicular to each other, but as shown in FIG. 3B, the first polarizing plate 152 and the second polarizing plate when the liquid crystal display device is viewed diagonally (when transmitted at a constant polar angle and azimuth angle with the screen of the liquid crystal display device). The polarization axis of 154 is disposed at a constant angle θ rather than vertical.

As described above, when the liquid crystal display is viewed in a diagonal direction, the polarization directions of the first polarizing plate 152 and the second polarizing plate 154 are not perpendicular to each other. The transmitted light is not all absorbed by the second polarizing plate 154, and a part of the light passes through the second polarizing plate 154. Therefore, even when the liquid crystal display device is viewed diagonally even in the normally black state, part of the light leaks, and thus, the black state cannot be maintained.

As such, when viewing the liquid crystal display device in a diagonal direction, the viewing angle characteristic is lowered, since the polarization directions of the first polarizing plate 152 and the second polarizing plate 154 are not perpendicular to each other, and thus the polarized light of the first polarizing plate 152. This is because part of the second polarizing plate 154 is not completely absorbed and leaks. Therefore, in order to improve the viewing angle characteristic when viewing the liquid crystal display device in a diagonal direction, all of the light polarized by the first polarizing plate 152 must be absorbed by the second polarizing plate 154. To this end, in the present invention, the polarization direction of the light incident on the second polarizing plate 154 is changed by changing the polarization direction of the light passing through the liquid crystal panel 101 using the compensation film (that is, the light absorption layer). ) To match.

Compensation films may be classified into uniaxial films and biaxial films. Uniaxial films are anisotropic birefringent films having only one optical axis and biaxial films are anisotropic birefringent films having two optical axes. Among such compensation films, uniaxial film may be classified into A-compensation film and C-compensation film according to the direction and size of optical axis. The refractive index characteristics of the A-compensation film and the C-compensation film are shown in FIGS. 4 and 5.

4A and 4B are diagrams showing a positive A-compensation film and a negative A-compensation film, respectively. As shown in FIGS. 4A and 4B, the A-compensation film has the same refractive index n _y in the y-axis direction and the refractive index n _{z in the} z-axis direction (n _y = n _z ) and refractive index (n _x) is the refractive index (n _z) and wherein the other of the passage ratio of y-axis direction _(y n), and z-axis directions _{(n x ≠ n y = n} z). As shown in FIG. 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, it is a positive A-compensation film and the refractive index n _{x in the} x-axis direction is the refractive index in the y-axis direction. If less than (n _y ) is a negative A-compensation film, these positive A-compensation film and negative A-compensation film, respectively defined by Equation 1 as follows.

n _x > n _y = n _z

n _x <n _y = n _z

5A and 5B are diagrams illustrating a positive C-compensation film and a negative C-compensation film, respectively. As shown in FIGS. 5A and 5B, the C-compensation film has the same refractive index (n _x ) in the x-axis direction and the refractive index (n _y ) in the y-axis direction (n _x = n _y ) and the z-axis direction. refractive index (n _z) this is the passage ratio (n _x) and refractive index (n _y) and different from one another in the y-axis direction along the x axis _{(n z ≠ n x = n} y). As shown in FIG. 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, it is a positive C-compensation film and is in the x-axis direction. If the refractive index (n _x ) and the refractive index (n _y ) in the _y- axis direction are larger than the refractive index (n _z ) in the z-axis direction, the negative C-compensation film and the negative C-compensation film and the negative C-compensation film are respectively If defined by 2, it is as follows.

n _x = n _y <n _z

n _x = n _y > n _z

In addition, the phase difference by the compensation film is determined by the refractive index (n _x ) in the x-axis direction, the refractive index (n _y ) in the _y- axis direction and the refractive index (n _z ) in the z-axis direction. The relationship between the refractive indices (n _x , n _y , n _z ) is shown.

Re = (n _x -n _y ) d

Rth = (n _x -n _z ) d

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

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

The biaxial film has different values of n _x , n _x , n _x , and is classified into a positive biaxial film, a negative biaxial film and a Z-axis biaxial film. Also the biaxial film having a refractive index in the x axis direction to 6 (nx) and the passage rate of the y-axis (n _y) and refractive index (n _z) in the z-axis direction is shown. The biaxial film has a refractive index in the x-axis direction (n _x) and a passage rate of the y-axis (n _y) and z-axis positive, the axis based on the size of the refractive index (n _z) in the direction of the film, the audio, the axis film and a Z-axis Stretched biaxial film is classified, these positive biaxial film, negative biaxial film and Z-axis biaxial film is defined by the following equation (4), respectively.

n _z > n _x > n _y

n _x > n _y > n _z

n _x > n _z > n _y

In addition, the biaxiality (Nz) of the biaxial film is defined as in Equation 5 below.

Nz = Rth / Re

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

By the definition of Equations 4 and 5, the negative biaxial film is Nz ≧ 1, the positive biaxial film is Nz <0, and the z-axis stretch biaxial film is 0 <Nz <1.

In the present invention, by providing a compensation film as described above the phase polarized light in the first polarizing plate 152 to make the polarization direction of the light completely perpendicular to the polarization direction of the second polarizing plate 154 second polarizing plate 154 Allow all light incident on the beam to be absorbed.

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

Since the Jones vector can represent only complete polarization, the Stokes parameter defined by Equation 6 below should be used to represent 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 관 계가 성립한다.Where: <> is the electric field component of the time it represents the average, E _x and E _x is the x-axis and y-axis directions, respectively. In this case, between these four variables

The inequality of is true, and this inequality is true only for complete polarization. That is, in the case of full polarization, the relationship of Equation 7 is established between the standardized variables s1, s2, and s3 obtained by dividing S1, S2, and S3 by the brightness S0 of light.

This is the equation of Poangcare sphere with radius 1 in three-dimensional space, where (s1, s2, s3) is the point of Cartesian coordinates.

In this case, all the points on the equator line in the Phang Nga district correspond to linearly polarized light, and the north pole corresponds to the right hand circularly polarized light and the south pole to the left hand circularly polarized light. All points in the northern hemisphere correspond to right-hand elliptical polarization, and all points in the southern hemisphere correspond to left-hand elliptical polarization.

7A and 7B are diagrams illustrating an arbitrary elliptical polarization and a corresponding poang curry vector in the rectangular coordinate system, respectively.

As shown in FIGS. 7A and 7B, the latitude angle of the Poang Cure vector P corresponding to the elliptically polarized light having the azimuthal angle of Ψ and the elliptic angle of x is 2x and the azimuth angle of the polarization ellipse is 2x. 2Ψ and the Cartesian coordinates are (cons (2Ψ) cons (2x), sin (2Ψ) cos (2x), sin (2x)). If this point is in the northern hemisphere, the direction of rotation of the electric field vector is clockwise; in the southern hemisphere, it is counterclockwise. At this time, the opposite points on the Poangaregu represent polarization states orthogonal to each other.

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

FIG. 8 is a view showing a Poang Karregu showing the polarization states of the first polarizing plate 152 and the second polarizing plate 154 when the IPS mode liquid crystal display device is viewed from the front as shown in FIG. 3A.

In the Poangcurry District, the anti-corrosive points represent polarization states orthogonal to each other, so that point A represents the light absorption axis of the first polarizing plate 152 and light transmission axis of the second polarizing plate 154, and the point B represents the first polarizing plate 152. ) And a light absorption axis of the second polarizing plate 154. As shown in FIG. 8, when the IPS mode liquid crystal display device is viewed from the front, the light transmission axis of the first polarizing plate 152 maintains the same linear polarization state as the light absorption axis of the second polarizing plate 154. This is because the light absorption axis of the first polarization plate 152 and the light absorption axis of the second polarization axis 154 are perpendicular to each other when the IPS mode liquid crystal display is viewed from the front. This is because the light absorption axes of the polarizing plates 154 are parallel to each other.

As such, the light transmission axis of the first polarizing plate 152 and the light absorption axis of the second polarizing plate 154 are parallel to each other, so that the light transmission axis of the first polarizing plate 152 and the light of the second polarizing plate 154 are located in Puang Cure. Since the absorption axes are 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 light is not transmitted to the outside of the second polarizing plate 154, and as a result, is normally In the black mode, when the IPS mode liquid crystal display device is viewed from the front, it is possible to maintain a completely black state.

On the other hand, Figure 9 is a diagram showing a Poincare sphere showing the polarization state of the light when viewing the liquid crystal display device in the diagonal direction in the IPS mode liquid crystal display device, as shown in Figure 3b.

In FIG. 9, the point A1 represents the light absorption axis of the first polarizing plate 152 and the point A2 opposite to the point represents the light transmission axis of the first polarizing plate 152 orthogonal to the light absorption axis. Further, point B1 represents the light transmission axis of the second polarizing plate 154 and point B2 represents the light absorption axis of the second polarizing plate 154. As shown in FIG. 3B, when the IPS mode liquid crystal display device is viewed from a diagonal direction, the polarization directions of the first polarizing plate 152 and the second polarizing plate 154 are not perpendicular to each other but at a predetermined angle θ. 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 interval of x means an angle between the light transmission axis of the first polarizing plate 152 and the light absorption axis of the second polarizing plate 154, and the light transmission axis of the first polarizing plate 152 and the second polarizing plate 154. As much as the angle corresponding to the angle between the light absorption axes of?) Is transmitted through the second polarizing plate 154. Accordingly, in order to prevent light leakage in the diagonal direction of the IPS mode liquid crystal display device, the light transmission axis of the first polarizing plate 152 and the light absorption axis of the second polarizing plate 154 are parallel to each other by matching the A2 and B2 points. Therefore, the light polarized by the first polarizing plate 152 must absorb all of the second polarizing plate 154.

In the present invention, by using a compensation film to change the polarization state of the linearly polarized light in the first polarizing plate 152 to match the point A2 and B2 on the Poincare sphere (that is, the light transmission axis of the first polarizing plate 152 and the first The light absorption axis of the second polarizing plate 154 is made in parallel) to prevent light leakage caused by light passing through the second polarizing plate 154.

Hereinafter, specific examples of the present invention will be described. In this case, the polarization state of the liquid crystal display device according to the exemplary 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 by changing the polarization state of the light using the biaxial film.

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

As shown in FIG. 10, the liquid crystal display device 200 according to the first exemplary embodiment of the present invention includes a liquid crystal panel 201 for implementing an image and attached to the lower and upper portions of the liquid crystal panel 201, respectively. A first compensation film 242 and a second compensation film 244, a first polarizing plate 250 attached to a lower portion of the first compensation film 242, and a second adhesion film attached to an upper portion of the second compensation film 244. It consists of two polarizing plates 260.

Although not shown in detail in the drawing, the liquid crystal panel 201 is formed of a liquid crystal layer formed between the first substrate and the second substrate and the first substrate and the second substrate, and the first substrate includes a thin film transistor, a gate line, Patterns such as data lines and various electrodes are formed, and on the second substrate, color matrices for real color and black matrices are formed to prevent light from leaking into an image non-display area and deteriorating image quality.

In particular, the liquid crystal panel of the present invention is an IPS mode liquid crystal panel. Accordingly, the common electrode and the pixel electrode are disposed parallel to each other on the first substrate to apply an electric field parallel to the surface of the substrate to the liquid crystal layer. In addition, the FFS (Fringe Field Switching) mode may be used as the liquid crystal panel of the present invention.

The first polarizer 250 includes a first polarizer 252 and a first support 254. The first polarizer 252 is a film that can convert natural light into any polarized light. In this case, when the first polarizer 252 divides incident light into two orthogonal polarization components, one polarization component of two polarization components passes and the other polarization component absorbs, reflects, or scatters light. Having can be used. Although there is no restriction | limiting in particular as an optical film used for a said 1st polarizing material, For example, the polymer film which consists mainly of polyvinyl alcohol (PVA) resin containing an iodine or a dichroic dye, a dichroic substance, The O-type polarizer which orientated the liquid crystalline composition containing a liquid crystalline compound to a fixed direction, and the E-type polarizer which orientated the lyotropic liquid crystal to a fixed direction can be used. The first support 254 is to protect the first polarizer 252 and is mainly formed in a film form. Therefore, any protective film may be used as long as the first polarizer 252 can be protected. For example, triacetylcellulose (TAC) or triacetylcellulose (zero retardation TAC) without phase difference (Rth) is mainly used.

In addition, the second polarizer 260 includes a second polarizer 262, a second support 264, and a third support 266. Like the first polarizer 252, the second polarizer 262 is made of polyvinyl alcohol-based resin, and the second support 264 uses triacetyl cellulose as a transparent protective film. In addition, the third support 266 is a transparent protective film that protects the second polarizer 262 and does not change the polarization state of the incident light, for example, there is no triacetyl cellulose or phase difference (Rth) Triacetylcellulose is used.

Meanwhile, in FIG. 10, the first polarizer 252 and the second polarizer 262 are in direct contact with the first compensation film 242 and the second compensation film 244, but the first polarizing plate 250 is not limited thereto. And a third support and a fourth support made of triacetylcellulose having no phase difference (Rth) on the second polarizing plate 260 so that the first polarizer 252 and the first compensation film 242 and the second polarizer are provided. The third support body and the fourth support body may be provided between the 262 and the second compensation film 244.

The first compensation film 242 and the second compensation film 244 are biaxial compensation films, and the retardation value Re in the horizontal direction of the first compensation film 242 is Re = 20 to 70 nm. And the retardation value Rth in the thickness direction is Rth = 30 to 100 nm. In the second compensation film 244, the retardation value Re in the horizontal direction is Re = 60 to 130 nm and the retardation value Rth in the thickness direction is Rth = 60 to 160 nm.

Therefore, the biaxiality Nz of the biaxial film of the first compensation film 242 is 1.0 <Nz <1.5 by Equation 5. In general, when the biaxiality (Nz) of the biaxial film is Nz> 1, the biaxial film is a negative biaxial film, and the refractive indices (n _x , n _y , n _z ) in the x, y and z axis directions are n _x > n. has a relationship of _y > n _z . In addition, when the biaxial film (Nz) of the biaxial film is Nz <0, the biaxial film is a positive biaxial film, the refractive index (n _x , n _y , n _z ) in the x, y, z axis direction is n _z > n has a relationship of _x > n _y . And, when the biaxiality (Nz) of the biaxial film is 0 <Nz <1, the biaxial film is a z-axis stretched biaxial film, the refractive index (n _x , n _y , n _z ) in the x, y, z axis direction is n _x > n _z > n _y . Accordingly, the first compensation film 242 is a negative biaxial film whose biaxiality Nz of the biaxial film is Nz> 1.

The biaxiality Nz of the second compensation film 244 is 1.0 <Nz <1.3, and the refractive indices n _x , n _y , n _z in the x, y, z axis directions are n _x > n _y > n _z. It is a negative biaxial film having a relationship of relationship.

The first compensation film 242 and the second compensation film 244, that is, the negative biaxial film is a UV curable liquid crystal film using a nematic liquid crystal (UV curable liquid crystal film) polycarbonate (polycarbonate), polyethylene terephthalate or polystyrene It may have a normal wavelength dispersion (flat wavelength dispersion) characteristics, flat wavelength dispersion (flat wavelength dispersion) characteristics and reverse wavelength dispersion (reverse wavelength dispersion) characteristics.

The absorption axis of the first polarizing plate 250 is disposed at an angle of 90 ° and the absorption axis of the second polarizing plate 260 is disposed at an angle of 0 °. In addition, the optical axis of the first compensation film 242 is arranged at 0 °, the second compensation film 244 is arranged at an angle of 90 °, the rubbing direction of the liquid crystal panel 201 is also made of 90 °.

The liquid crystal molecules of the liquid crystal layer of the liquid crystal panel 201 are disposed along the rubbing direction of the alignment layer in the off state of the liquid crystal panel 201. Accordingly, the optical axis of the liquid crystal molecules also forms 90 °. As described above, the liquid crystal panel 201 forms 90 ° in the rubbing direction for the following reason.

In general, in the IPS mode liquid crystal display, since the common electrode and the pixel electrode forming the horizontal electric field are arranged along the data line, the rubbing direction of the alignment layer is formed at an angle of about 15 ° to 45 °. However, in the present invention, the common electrode and the pixel electrode of the IPS mode liquid crystal display are bent at least once at a predetermined angle in one pixel, and the rubbing of the alignment layer is performed in the data line direction, that is, at an angle of 90 degrees.

As described above, the bending of the common electrode and the pixel electrode is intended to improve viewing angle characteristics of the liquid crystal display by forming a plurality of domains having different viewing angles in different directions in one pixel. Since the common electrode and the pixel electrode are formed at a predetermined angle with the data line and the rubbing direction of the alignment layer is made with the data line direction, the common electrode and the pixel electrode with the rubbing direction have a predetermined angle, for example, about 15 ° to about 45 °. It is made up of angles.

Of course, the present invention is not limited to the IPS mode liquid crystal display device having such a structure but may be applied to the FFS mode liquid crystal display device in which the rubbing direction is formed at 90 ° and the direction and the rubbing direction of the electrode are formed at a predetermined angle.

The polarization state of the liquid crystal display according to the present embodiment configured as described above will be described with reference to FIGS. 11A to 11C. 11A is a view showing a polarization state in each configuration in the liquid crystal display device according to the present invention, and FIG. 11B is a view showing a Poincare sphere showing a polarization state in the liquid crystal display device according to the present invention. Is a projection of the two-dimensional representation, ie Poincare sphere, of FIG. 11B.

As shown in FIG. 11A, a first compensation film 242 made of a negative biaxial film is disposed between the first polarizing plate 250 and the liquid crystal panel 201, wherein the optical of the first compensation film 242 is provided. The axis is perpendicular to the light absorption axis of the first polarizing plate 250 and the rubbing direction of the liquid crystal panel 201 (that is, the optical axis forms 0 °). In addition, the second polarizing plate 260 is disposed above the liquid crystal panel 201, where the light absorption axis of the second polarizing plate 260 is perpendicular to the rubbing direction of the liquid crystal panel 201 (that is, the light of the second polarizing plate). Absorption is formed at an angle of 0 °). In addition, the second compensation film 244 made of a negative biaxial film is disposed between the liquid crystal panel 201 and the second polarizing plate 260, wherein the optical axis of the second compensation film 244 is It is parallel to the rubbing direction and perpendicular to the light absorption axis of the second polarizing plate 260 (that is, the optical axis forms 90 °).

As shown in FIG. 11B, when the light that is not polarized from the backlight of the liquid crystal panel 201 is incident on the first polarizing plate 250, the light is linearly polarized. Most of the linearly polarized light is absorbed by the first polarizing plate 250. The polarization state of the light absorbed by the axis A1 and transmitted through the first polarizing plate 250 is positioned at A2. That is, the transmission axis of the first polarizing plate 250 is located at the point A2. At this time, the absorption axis of the second polarizing plate 260 is located at the point B2, and is spaced apart from the transmission axis of the first polarizing plate 250 by a predetermined distance.

When the linearly polarized light in the first polarizing plate 250 passes through the first compensation film 242 made of the negative biaxial film, the polarization state is rotated from the A2 point to the C1 point. In this case, since the first compensation film 242 is a negative biaxial film, its optical axis is present between the n _x axis and the n _z axis. Therefore, the polarization state of the light is rotated clockwise about the optical axis between the n _x axis and the n _z axis so that the polarization state is moved from the A2 point to the C1 point.

When the light whose polarization is changed as described above is transmitted through the liquid crystal panel 201, the alignment layer is rubbed at an angle of 90 °, and thus the polarization state of the liquid crystal panel 201 is positioned at the A1 point. Therefore, the light transmitted through the liquid crystal panel 201 is rotated clockwise around the A 2 O axis, so that the polarized state is moved from the C1 point to the C2 point. That is, the transmission axis of the light passing through the liquid crystal panel 201 is located at the point C2. In general, since the phase difference value of the liquid crystal panel 201 is 280 to 350 nm, the rotation angle of the polarization state becomes about 183 to 229 ° based on 550 nm, which is a green wavelength that affects luminance.

When the light transmitted through the liquid crystal panel 201 passes through the second compensation film 244 made of the negative biaxial film, the polarization state is rotated from the C2 point to the B2 point. At this time, since the second compensation film 244 is also a negative biaxial film, its optical axis is present between the n _x axis and the n _z axis, and thus the polarization state of the light is centered on the optical axis between the n _x axis and the n _z axis. The clockwise rotation causes the polarization state to move from the point C2 to the point B2. As a result, the light transmitted through the second compensation film 244 is changed into linearly polarized light having the same polarization axis as the absorption axis of the second polarizing plate 260, and the polarized light is absorbed by the second polarization 260. Therefore, light does not pass through the second polarizing plate 260.

As shown in FIG. 11C, the linearly polarized light in the first polarizing plate 250 is changed by the first and second compensation films 242 and 244 in the polarization state (corresponding to the point A2), and thus the final second polarizing film ( 244, that is, the polarization state of the negative biaxial film coincides with the B2 point, and the optical axis of the light incident on the second polarizing plate 260 coincides with the absorption axis of the second polarizing plate 260. All light polarized at 250 is absorbed by the second polarizing plate 260 to prevent light leakage in the diagonal direction.

12 is a diagram showing the structure of a liquid crystal display device 300 according to a second embodiment of the present invention. The liquid crystal display device having the structure shown in this embodiment is similar in structure to the liquid crystal display device shown in FIG. That is, the liquid crystal display device of this embodiment differs from the liquid crystal display device of the first embodiment only in the rubbing direction of the liquid crystal panel 301 but in the other structure. Therefore, the same configuration and function as the first embodiment will be described briefly.

As shown in FIG. 12, the liquid crystal display device 300 of this embodiment includes a liquid crystal panel 301 for implementing an image and a first compensation film 342 attached to the lower and upper portions of the liquid crystal panel 301, respectively. ) And a second compensation film 344, a first polarizing plate 350 attached to a lower portion of the first compensation film 342, and a second polarizing plate 360 attached to an upper portion of the second compensation film 344. It is composed. In this case, the first compensation film 342 and the second compensation film 344 is a negative biaxial film, the first compensation film 342 has a horizontal retardation value (Re) of Re = 60 ~ 130nm and the thickness direction The phase difference value Rth is Rth = 60 to 160 nm. In the second compensation film 344, the retardation value Re in the horizontal direction is Re = 20 to 70 nm and the retardation value Rth in the thickness direction is Rth = 30 to 100 nm. Accordingly, the first compensation film 342 is a negative biaxial film having a biaxiality (Nz) of 1.0 <Nz <1.3 and the second compensation film 344 is a negative biaxial film having a biaxiality (Nz) of 1.0 <Nz <1.5. .

The absorption axis of the first polarizing plate 250 is disposed at an angle of 90 ° and the absorption axis of the second polarizing plate 260 is disposed at an angle of 0 °. In addition, the optical axis of the first compensation film 242 is arranged at an angle of 0 °, the second compensation film 244 is arranged at an angle of 90 °, the rubbing direction of the liquid crystal panel 201 is an angle of 0 ° Is made of.

Hereinafter, the polarization state of the liquid crystal display according to the present exemplary embodiment configured as described above will be described with reference to FIGS. 13A and 13B.

As shown in FIG. 13A, a first compensation film 342 made of a negative biaxial film is disposed between the first polarizing plate 350 and the liquid crystal panel 301, wherein the optical of the first compensation film 342 is provided. The axis is perpendicular to the light absorption axis of the first polarizing plate 350 and parallel to the alignment direction of the liquid crystal panel 301 (that is, the optical axis forms 0 °). In addition, the second polarizing plate 360 is disposed above the liquid crystal panel 301, where the light absorption axis of the second polarizing plate 360 is parallel to the rubbing direction of the liquid crystal panel 301 (that is, the light of the second polarizing plate). Absorption is formed at an angle of 0 °). In addition, the second compensation film 344 made of a negative biaxial film is disposed between the liquid crystal panel 301 and the second polarizing plate 360, wherein the optical axis of the second compensation film 344 is the liquid crystal panel 301 The rubbing direction and the light absorption axis of the second polarizing plate 360 are perpendicular to each other (ie, the optical axis forms 90 °).

As shown in FIG. 13B, when the non-polarized light is incident on the first polarizing plate 350 from the backlight of the liquid crystal panel 301, the light is linearly polarized. Most of the linearly polarized light is absorbed by the first polarizing plate 350. The polarization state of the light absorbed by the axis A1 and transmitted through the first polarizing plate 350 is positioned at A2. That is, the transmission axis of the first polarizing plate 350 is located at the point A2. At this time, the absorption axis of the second polarizing plate 360 is located at the point B2, and is spaced apart from the transmission axis of the first polarizing plate 350 by a predetermined distance.

When the linearly polarized light from the first polarizing plate 350 passes through the first compensation film 342 made of the negative biaxial film, the polarization state is rotated from the A2 point to the C1 point. In this case, since the first compensation film 342 is a negative biaxial film, its optical axis is present between the n _x axis and the n _z axis. Therefore, the polarization state of the light is rotated clockwise about the optical axis between the n _x axis and the n _z axis so that the polarization state is moved from the A2 point to the C1 point.

When the light whose polarization is changed as described above is transmitted through the liquid crystal panel 301, the alignment layer is rubbed at an angle of 0 °, and thus the polarization state of the liquid crystal panel 301 is positioned at the A1 point. Accordingly, the light transmitted through the liquid crystal panel 301 is shifted from the C1 point to the C2 point in the polarization state. That is, the transmission axis of the light passing through the liquid crystal panel 301 is located at the point C2. When the light transmitted through the liquid crystal panel 301 passes through the second compensation film 344 made of the negative biaxial film, the polarization state is rotated from the C2 point to the B2 point. Accordingly, the light transmitted through the second compensation film 344 is changed into linearly polarized light having the same polarization axis as the absorption axis of the second polarizing plate 360, and the polarized light is absorbed by the second polarization 360. Therefore, light does not pass through the second polarizing plate 360.

As shown in FIG. 13C, the linearly polarized light in the first polarizing plate 350 is changed by the first and second compensation films 342 and 344 to change the polarization state (corresponding to the point A2). 344), ie, the polarization state of the negative biaxial film coincides with the B2 point, and the optical axis of the light incident on the second polarizing plate 360 is aligned with the absorption axis of the second polarizing plate 360. All light polarized at 350 is absorbed by the second polarizing plate 360 to prevent light leakage in the diagonal direction.

14A and 14B illustrate simulation results of luminance viewing angle characteristics in a normally black mode in a diagonal viewing direction of a conventional liquid crystal display device and a liquid crystal display device according to the present embodiment.

Here, the lower polarizing plate and the upper polarizing plate are arranged so that the light transmission axes are perpendicular to each other, and the optical axis of the liquid crystal layer is in a state parallel to the light transmission axis of the upper polarizing plate. 14A and 14B illustrate a liquid crystal display including a conventional liquid crystal display device and an optical compensation film according to the present invention at an inclination angle in the range of 0 ° to 80 ° with respect to all the mirror angles (or azimuth angles) when white light is used. This is the result of simulating contrast ratio for. 14A and 14B, the center of the circle is a case where the inclination angle is 0, indicating that the inclination angle increases as the radius of the circle increases, and the numerical values indicated along the circumference indicate the east angle.

When comparing the contrast ratio characteristics of the conventional liquid crystal display of FIG. 14A and the liquid crystal display according to the present invention of FIG. 14B, 45 degrees, 135 degrees, and 225 degrees corresponding to diagonal directions of the liquid crystal display panel in the normally black mode are compared. And it can be seen that the light leakage is significantly reduced at 315 degrees. At this time, while the maximum transmittance (Tmax) in the diagonal viewing angle direction in the conventional liquid crystal display device of FIG. 14A is Tmax = 0.00192, the diagonal viewing angle of the liquid crystal display device of the present invention having two negative biaxial films of FIG. 14B. The maximum transmittance (Tmax) in the direction is Tmax = 0.000716. Therefore, it can be seen that the transmittance in the diagonal viewing angle direction in the liquid crystal display device according to the present invention is significantly reduced compared to the conventional liquid crystal display device.

Many details are set forth in the foregoing description but should be construed as illustrative of preferred embodiments rather than to limit the scope of the invention. Therefore, the invention should not be defined by the described embodiments, but should be defined by the claims and their equivalents.

1A and 1B are views showing the structure of a general IPS mode liquid crystal display device.

Figure 2 is a simplified perspective exploded view showing the structure of a conventional liquid crystal display device.

Fig. 3A is a diagram showing an absorption axis of a vertical polarizer when the liquid crystal display device is viewed from the front.

Fig. 3B is a diagram showing the absorption axis of the vertical polarizer when the liquid crystal display element is viewed in the diagonal direction.

4A and 4B are graphs showing a refractive index relationship in an x-, y-, and z-axis directions of an A-compensation film.

5A and 5B are graphs showing refractive index relationships in x, y and z axis directions of a C-compensation film.

6 is a view showing a refractive index relationship in the x, y, z axis direction of a biaxial compensation film.

7A and 7B are diagrams illustrating elliptical polarizations of light and corresponding Poincare vectors, respectively.

Fig. 8 is a diagram showing the polarization state of light in Poincare sphere when the liquid crystal display device is seen from the front.

Fig. 9 is a diagram showing the polarization state of light in Poincare sphere when the liquid crystal display element is viewed from a diagonal direction.

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

11A is a view showing an optical axis of a liquid crystal display device according to a first embodiment of the present invention.

FIG. 11B is a view showing a Poang Karregu in which the polarization state of light in the liquid crystal display device according to the first embodiment of the present invention is displayed; FIG.

11C is a projection of FIG. 11B.

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

13A is a view showing an optical axis of a liquid crystal display device according to a second embodiment of the present invention.

FIG. 13B is a view showing a Poang Karregu in which a polarization state of light in a liquid crystal display device according to a second embodiment of the present invention is displayed; FIG.

13C is a projection of FIG. 13B.

14A and 14B are diagrams showing luminance viewing angle characteristics when the conventional liquid crystal display device and the liquid crystal display device according to the present invention are viewed in a diagonal direction, respectively.

* Description of the symbols for the main parts of the drawings *

200,300: liquid crystal display device 201,301: liquid crystal panel

242,244,342,344: negative biaxial film 250,260,350,360: polarizer

252,262,352,362 Polarizers 254,264,354,364 Support

Claims (23)

A liquid crystal panel including a liquid crystal layer; First and second polarizing plates positioned above and below the liquid crystal panel to polarize incident light; A first negative biaxial film provided between the liquid crystal panel and the first polarizing plate to change a polarization state of light, and having a phase retardation value Re = 20 to 70 nm in a horizontal direction and a retardation value Rth = 30 to 100 nm in a thickness direction; And It is provided between the liquid crystal panel and the second polarizing plate to change the polarization state of the light, and consists of a second negative biaxial film having a retardation value of Re = 60 ~ 130nm in the horizontal direction and Rth = 60 ~ 160nm in the thickness direction, Where Re = (n _x -n _y ) d and Rth = (n _x -n _z ) d and n _x , n _y and n _z are the refractive indices in the x-axis direction, the refractive indices in the y-axis direction and the z-axis direction, respectively. A liquid crystal display device characterized by the refractive index. The liquid crystal display of claim 1, wherein absorption axes of the first polarizing plate and the second polarizing plate are perpendicular to each other. The method of claim 1, wherein the first polarizing plate, A first support; And A liquid crystal display device, characterized in that one surface is formed of a first polarizer attached to the first support. The liquid crystal display device of claim 3, wherein the first support is made of a transparent protective film. The liquid crystal display device according to claim 4, wherein the transparent protective film is made of triacetyl cellulose or triacetyl cellulose having no phase difference (Rth). The liquid crystal display device according to claim 3, wherein the first polarizer is made of polyvinyl alcohol-based resin. The liquid crystal display device of claim 3, wherein the first polarizer further comprises a second support attached to the other surface of the first polarizer. The liquid crystal display device of claim 7, wherein the second support is made of a transparent protective film. The liquid crystal display device according to claim 8, wherein the transparent protective film is made of triacetyl cellulose or triacetyl cellulose having no phase difference (Rth). The method of claim 1, wherein the second polarizing plate, Third support; And A liquid crystal display device, characterized in that one surface is made of a second polarizer attached to the third support. The liquid crystal display device according to claim 10, wherein the third support is made of a transparent protective film. The liquid crystal display device according to claim 11, wherein the transparent protective film is made of triacetyl cellulose having no phase difference (Rth). The liquid crystal display device of claim 10, wherein the second polarizing plate further comprises a fourth support body attached to the other surface of the second polarizing body. The liquid crystal display of claim 13, wherein the second support is made of a transparent protective film. 15. The liquid crystal display device according to claim 14, wherein the transparent protective film is made of triacetyl cellulose or triacetyl cellulose having no phase difference (Rth). The liquid crystal display device according to claim 10, wherein the second polarizer is made of polyvinyl alcohol resin. The liquid crystal display device according to claim 1, wherein the negative biaxial film is made of a material selected from the group consisting of UV curable liquid crystal film, polycarbonate, polyethylene terephthalate and polystyrene. . The liquid crystal display of claim 1, wherein the optical axis of the first negative biaxial film is perpendicular to the light absorption axis of the first polarizing plate, and the optical axis of the second negative biaxial film is perpendicular to the light absorption axis of the second polarizing plate. device. The liquid crystal display of claim 1, wherein the rubbing direction of the liquid crystal panel is parallel to the light absorption axis of the first polarizing plate. The liquid crystal display of claim 1, wherein the rubbing direction of the liquid crystal panel is perpendicular to the light absorption axis of the first polarizing plate. The liquid crystal display of claim 1, wherein unpolarized light is incident through the first polarizing plate. The liquid crystal display of claim 1, wherein unpolarized light is incident through the second polarizing plate. The liquid crystal display device according to claim 1, wherein the liquid crystal panel is an IPS (In Plane Switching) mode liquid crystal panel or a FFS (Fringe Field Switching) mode liquid crystal panel.

Images