KR20050000958A - In Plane Switching mode Liquid Crystal Display Device - Google Patents

Abstract

PURPOSE: An in-plane switching mode LCD device is provided to improve light leakage under the black state by further forming a discotic layer between an upper polarizer or a lower polarizer and an LCD panel. CONSTITUTION: An in-plane switching mode LCD device includes an LCD panel(60) having a first substrate(61) with pixel electrodes and common electrodes alternately formed, a second substrate(62) opposing the first substrate, and a liquid crystal layer(63) formed between the first and second substrates, first and second polarizers(70,80) respectively corresponding to outer sides of the first and second substrates, and a discotic layer(64) formed between the LCD panel and the first or second polarizer.

Description

Transverse type liquid crystal display device {In Plane Switching mode Liquid Crystal Display Device}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display device. In particular, a transverse field type liquid crystal display device using a general polarizer but having a discotic layer further formed between an upper polarizer or a lower polarizer and a liquid crystal panel to improve light leakage in a black state. It is about.

As the information society develops, the demand for display devices is increasing in various forms, and in recent years, liquid crystal display devices (LCDs), plasma display panels (PDPs), electro luminescent displays (ELD), and vacuum fluorescent (VFD) Various flat panel display devices such as displays have been studied, and some of them are already used as display devices in various devices.

Among them, LCD is the most widely used as the substitute for CRT (Cathode Ray Tube) for mobile image display device because of its excellent image quality, light weight, thinness, and low power consumption. In addition to the use of the present invention has been developed in various ways such as a television and a computer monitor for receiving and displaying broadcast signals.

In order to use such a liquid crystal display as a general screen display device in various parts, it is a matter of how high quality images such as high definition, high brightness and large area can be realized while maintaining the characteristics of light weight, thinness and low power consumption. Can be.

A general liquid crystal display device may be largely divided into a liquid crystal panel displaying an image and a driving unit for applying a driving signal to the liquid crystal panel, wherein the liquid crystal panel includes first and second glass substrates bonded to each other with a predetermined space; It consists of a liquid crystal layer injected between the said 1st, 2nd glass substrate.

Here, the first glass substrate (TFT array substrate) has a plurality of gate lines arranged in one direction at regular intervals, a plurality of data lines arranged at regular intervals in a direction perpendicular to the gate lines, A plurality of pixel electrodes formed in a matrix form in each pixel region defined by crossing a gate line and a data line, and a plurality of thin film transistors switched by signals of the gate line to transfer the signal of the data line to each pixel electrode. Is formed.

The second glass substrate (color filter substrate) includes a light shielding layer for blocking light in portions other than the pixel region, an R, G, and B color filter layers for expressing color colors, and a common electrode for implementing an image. Is formed.

The driving principle of the general liquid crystal display device uses the optical anisotropy and polarization property of the liquid crystal. Since the liquid crystal is thin and long in structure, the liquid crystal has directivity in the arrangement of molecules, and the direction of the arrangement of molecules can be controlled by artificially applying an electric field to the liquid crystal.

Therefore, when the molecular arrangement direction of the liquid crystal is arbitrarily adjusted, the molecular arrangement of the liquid crystal is changed, and light is refracted in the molecular arrangement direction of the liquid crystal by optical anisotropy, thereby representing image information.

Currently, an active matrix LCD, in which a thin film transistor and pixel electrodes connected to the thin film transistor are arranged in a matrix manner, is attracting the most attention due to its excellent resolution and ability to implement video.

The above-mentioned liquid crystal display device drives the liquid crystal by an electric field applied up and down, and thus has excellent characteristics such as transmittance and aperture ratio, and the common electrode of the upper substrate serves as a ground to prevent destruction of the liquid crystal cell due to static electricity. have.

However, the liquid crystal drive by the electric field applied up-down has a disadvantage that the viewing angle characteristics are not excellent.

Accordingly, in order to overcome the above disadvantages, a new technology, that is, a liquid crystal display device having an in-plane switching mode, has been proposed.

Hereinafter, a conventional transverse electric field type liquid crystal display device will be described with reference to the accompanying drawings.

1 is a schematic cross-sectional view illustrating a general transverse electric field type liquid crystal display device and an electric field formed when a voltage is applied thereto.

As shown in FIG. 1, in the general transverse electric field type liquid crystal display, the common electrode 13 and the pixel electrode 15 are formed on the same plane on the lower substrate 10. In addition, the liquid crystal 3 formed between the lower substrate 10 and the upper substrate 20 bonded to the lower substrate 10 may have an electric field between the common electrode 13 and the pixel electrode 15 on the lower substrate 10. Drive by.

That is, when the common electrode 13 and the pixel electrode 15 are placed side by side at an interval of 1 to 2 times the thickness of the liquid crystal cell on the same plane, and a voltage is applied, the voltage distribution curve is the common electrode 13 and Parallel to the plane to which the pixel electrode 15 belongs, and fall away from the plane becomes a little parabolic.

In such a transverse electric field type liquid crystal display, the pretilt angle is parallelly aligned at 1 to 2 degrees. When a voltage greater than the threshold is applied on the common electrode 13 and the pixel electrode 15, if the dielectric anisotropy of the liquid crystal is negative, the short axis of the liquid crystal molecule is parallel to the electric field, and if the positive axis of the liquid crystal molecule is arranged parallel to the electric field. .

On the other hand, the transmission axis of the upper and lower polarizing plates are orthogonal, and the transmission axis of the lower polarizing plate is parallel to the rubbing direction of the lower polarizing plate so as to be normally black. Since the transmission axis of the lower polarizer when driven darkest coincides with the long axis of the liquid crystal oriented in parallel, the light passing in the vertical and horizontal directions of the liquid crystal does not change polarization, and thus contrast in a relatively wide range (above, right, left, 80 ° or more) Screen of 10 or more can be realized.

2 is a plan view illustrating a conventional transverse electric field type liquid crystal display device.

As shown in FIG. 2, in the conventional transverse electric field type liquid crystal display device, a gate line 11 and a data line 12 are formed on the lower substrate 10 so as to intersect longitudinally and horizontally to define a pixel area. The common electrode 13 and the pixel electrode 15 are formed spaced apart from each other at predetermined intervals.

The gate electrode 11a protruding from the gate line 11 and a gate insulating film (see 14 in FIGS. 3 and 4) are formed on the entire surface of the lower substrate 10 including the gate electrode 11a. The semiconductor layer 18 overlapping the gate electrode 11a, the source electrode 12a protruding from the data line 12 on both sides of the semiconductor layer 18, and the drain electrode 12b spaced apart from the predetermined distance. A thin film transistor TFT is formed. The drain electrode 12b of the thin film transistor TFT is connected to the pixel electrode 15.

The common electrode 13 is formed to be spaced apart from the pixel electrode 15 by a predetermined interval, and simultaneously formed when the gate line 11 or the data line 12 is formed. In the figure shown, the common electrode 13 is formed on the same layer as the data line 12.

Further, a passivation layer 16 is further deposited between the data line 12 and the pixel electrode 15, wherein the passivation layer (see 16 in FIGS. 3 and 4) is made of the same component as the gate insulating layer 14. An inorganic insulating film such as SiNx or SiOx, or an organic insulating film of acryl, polyimide, BCB (BenzoCycloButene), or photopolymer is used.

In addition, the common electrode 13 receives a voltage signal from the common line 19, and when a voltage signal is applied to each pixel electrode 15 through the drain electrode 12b, a horizontal electric field is formed to drive the liquid crystal. .

Hereinafter, a conventional transverse electric field type liquid crystal display device will be described in terms of voltage application.

FIG. 3 is a cross-sectional view illustrating the alignment of the liquid crystal before voltage application on the line II ′ of FIG. 2, and FIG. 4 is a cross-sectional view illustrating the alignment of the liquid crystal after voltage application on the line II ′ of FIG. 2.

First, as shown in FIGS. 3 and 4, on the upper substrate 20 corresponding to the lower substrate 10 of the conventional transverse electric field type liquid crystal display device described above, the light is prevented from leaking to an area other than the pixel region. A light blocking layer 21 and a color filter layer 22 for implementing color hues R, G, and B are formed.

On the front surfaces of both substrates 10 and 20, a first having a rubbing direction (arrow direction) which is twisted by 45 ° with respect to the longitudinal direction of the common electrode 13 and the pixel electrode 15 so as to define the initial orientation of the liquid crystal. , Second alignment layers 17 and 23 are formed.

As shown in FIG. 3, the liquid crystal before voltage application is defined according to the rubbing directions (arrow directions) of the first and second alignment layers 17 and 23 formed on the lower substrate 10 and the upper substrate 20, respectively. Therefore, as shown in the drawing, when the liquid crystal is observed in a direction perpendicular to the common electrode 13 and the pixel electrode 15, the shape of the liquid crystal becomes nearly circular.

As described above, in the general transverse electric field-type optical mode, light is not transmitted before voltage is applied to normally black.

As shown in FIG. 4, when a voltage is applied to the pixel electrode 15 and the common electrode 13, an electric field is formed between two electrodes 13 and 15 formed on the same substrate, and the two electrodes 13 and 15. The liquid crystal is aligned along the electric field formed between the layers.

In this case, when the liquid crystal has a positive dielectric anisotropy, in the rubbing direction of the first and second alignment layers 17 and 23, a horizontal plane in the electric field direction formed between the common electrode 13 and the pixel electrode 15, that is, in a clockwise direction. The liquid crystal is aligned by rotating on (In-plane).

At this time, when observing the liquid crystal in the direction perpendicular to the common electrode 13 and the pixel electrode 15, the liquid crystal is located in the direction in which the electric field is formed, so that it is seen as a long ellipse which is the shape of the original liquid crystal.

On the other hand, when the dielectric anisotropy of the liquid crystal is negative, the liquid crystal is oriented perpendicular to the electric field, and thus, in the rubbing direction of the first and second alignment layers 17 and 23 in the longitudinal direction of the common electrode 13 and the pixel electrode 15. That is, the liquid crystal is aligned by rotating counterclockwise.

After the voltage is applied, internal light is transmitted along the liquid crystal to display a white state.

Here, since the liquid crystal corresponding to the portion where the pixel electrode 15 and the common electrode 13 are formed is located in a region where an electric field is divided, it is not easy to move in a specific direction when voltage is applied to each electrode. Therefore, when the display is performed, the pixel becomes a portion where foreground lines are formed, and light is not transmitted through the pixel electrode 15 and the formation region of the common electrode 13 so that the pixel electrode 15 and the common electrode ( 13) is formed of metal or deposited by alloy of ITO / metal to prevent light leakage phenomenon.

5 is a schematic cross-sectional view illustrating a liquid crystal panel and a vertical polarizer in a conventional transverse electric field type liquid crystal display device.

As illustrated in FIG. 5, the conventional transverse electric field type liquid crystal display device attaches the upper polarizing plate 35 and the lower polarizing plate 30 to the top and bottom of the manufactured liquid crystal panel 1, as shown in FIG. 3.

The upper and lower polarizing plates 35 and 30 are made of a polymer capable of mass-producing a large area, which is a needle-shaped halogen salt crystal such as iodine on the polyvinyl alcohol (PVA) film (32, 37). After adsorbing, the PVA films 32 and 37 were stretched between two rollers having different rotational speeds to align the needle-shaped crystals side by side, thereby making them dichroic. To the PVA films 32 and 37, cellulose triacetate (hereinafter referred to as TAC: Tri-Acetyl Cellulose) films 31, 33, 36 and 38 are attached to both surfaces. The use of dichroic dyes in place of iodine crystals shows polarization characteristics for certain colors. As such, the manufactured polarizing plate may be viewed as a uniaxial film having an optical tilt angle of 0 and a refractive index of a complex number.

In an ideal polarizer, the imaginary part of the complex refractive index in the ideal optical axis direction is so large that all light polarized in this direction is absorbed and all components perpendicular to it are transmitted.

FIG. 6 is a diagram illustrating the degree of brightness according to the viewing angle in the black state in the transverse electric field type liquid crystal display of FIG. 5.

In the above-described conventional transverse electric field type liquid crystal display device, the longitudinal direction of the common electrode 13 and the pixel electrode 15 is assumed as the x-axis, and passes through the liquid crystal panel 1 and the upper and lower polarizing plates 35 and 30. In the case of converting the change of polarization state into the Poincare Sphere, which is geometrically expressed, the angle of incidence decreases as the angle between the transmission axes of the two polarizers decreases, resulting in leakage light. Do not.

Therefore, when there is an incident angle when the angle between the x-axis and the transmission axes of the upper and lower polarizers 35 and 30 is ± 45 °, the absorption axis of the upper and lower polarizers 35 and 30 approaches optically in the y-axis direction and the transmission axis This light is not orthogonal and leakage light is generated.

In particular, the site where such leakage light (light leakage) occurs severely passes at an angle compared to when light passes vertically, that is, as shown in FIG. 6, the azimuth angles are 45 °, 135 °, 225 °, and 315 °. In the black state near 40 degrees of latitude, the degree of brightness increases, indicating that light leakage is more severe than other parts.

In the above-described conventional transverse electric field type liquid crystal display device, the upper and lower polarizing plates 35 and 30 are arranged to be orthogonal to each other, and the upper and lower polarizing plates 35 and 30 are disposed with respect to the longitudinal direction of the common electrode 13 and the pixel electrode 15. Transmission axis is twisted ± 45 °. As described above, since a common electrode and a pixel electrode are disposed in the conventional transverse type liquid crystal display device to form a transverse electric field, light leakage phenomenon is severe around the electrode in a black state, and thus there is a problem in functioning as a display device.

Therefore, another conventional transverse field type liquid crystal display device in which an optical compensation film is formed to compensate for light leakage phenomenon of the conventional transverse field type liquid crystal display device described above will be described.

7 is a cross-sectional view illustrating a conventional transverse electric field type liquid crystal display device to which the optical compensation film of FIG. 7 is applied.

As shown in FIG. 7, a conventional transverse electric field type liquid crystal display device to which an optical compensation film is applied is a liquid crystal layer 43 formed between an upper substrate 41, a lower substrate 42, and upper and lower substrates 41 and 42 facing each other. The liquid crystal panel 40, upper and lower polarizers 50 and 55 positioned above and below the liquid crystal panel 40, and between the liquid crystal panel 40 and the upper polarizer 50 or the lower polarizer 55. It consists of two layers of uniaxial (n _x = n _y > n _z ) films 44 and 45.

In FIG. 7, the uniaxial films 44 and 45 are formed on the upper polarizer 50. As such, although the optical compensation films 44 and 45 are illustrated as two layers as uniaxial films, the two layers of uniaxial films 44 and 45 are formed as a single layer biaxial ( n _x ≠ n _y ≠ n _z ) may be replaced with a film.

In addition, the upper and lower polarizers 50 and 55 are polarizers in which the TAC film is removed at a portion corresponding to the liquid crystal panel 40, and the upper polarizers 50 are sequentially connected from the top to the TAC film 51 and the PVA film 52. The lower polarizer 55 is composed of a PVA film 56 and a TAC film 57 in order from above.

In the transverse electric field type liquid crystal display of FIG. 7 of FIG. 8, it is a figure which shows the brightness | luminance according to the viewing angle in a black state.

As shown in FIG. 8, assuming that the uniaxial films 44 and 45 are applied to one of the upper and lower polarizing plates 50 and 55, and the angle between the x-axis and the transmission axis of the upper and lower polarizing plates 50 and 55 is ± 45 °, the predetermined Even in the viewing angle at the position of, the uniaxial films 44 and 45 compensate for the occurrence of leakage light. That is, azimuth angles at which light leakage defects are severe when the uniaxial films 44 and 45 are not used are 45 °, 135 °, 225 °, and 315 °, and the uniaxial films 44 and 45 are disposed at a viewing angle near 40 ° or more of latitude. To compensate, the brightness of the light in the black state (usually in the transverse normalized black mode, thus the black state before voltage application) is significantly lower, indicating that light leakage is almost prevented in the black state.

Therefore, it can be seen that the light leakage phenomenon is remarkably improved in the transverse electric field type liquid crystal display device to which the uniaxial films 44 and 45 are applied.

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

Due to orthogonality of the upper and lower polarizers, light leakage occurs at a predetermined viewing angle in a black state.

Therefore, in order to compensate for such light leakage, an optical compensation film (two uniaxial films or one biaxial film) is applied to one substrate of the transverse field-type liquid crystal display device. It is inconvenient to remove the TAC film of the portion corresponding to the liquid crystal panel among the upper and lower polarizers manufactured by the process of. The process cost is increased because a separate process is required for this, and the PVA film of the dyed polarizing plate is directly surfaced during the process. There is a problem that the stain phenomenon occurs by exposure to.

The present invention has been made to solve the above problems, but generally using a polarizing plate, a discotic layer is further formed between the upper polarizer or the lower polarizer and the liquid crystal panel to improve the light leakage phenomenon in the black state. It is an object to provide an electric field type liquid crystal display device.

1 is a schematic cross-sectional view illustrating a general transverse electric field type liquid crystal display device and an electric field formed when a voltage is applied thereto.

2 is a plan view showing a conventional transverse electric field type liquid crystal display device

FIG. 3 is a cross-sectional view illustrating the alignment of liquid crystals before voltage application on the line II ′ of FIG. 2.

FIG. 4 is a cross-sectional view illustrating the alignment of liquid crystals after voltage application on the line II ′ of FIG. 2.

5 is a schematic cross-sectional view showing a liquid crystal panel and a vertical polarizer in a conventional transverse electric field type liquid crystal display device.

FIG. 6 is a diagram illustrating a brightness degree according to a viewing angle in a black state in the transverse electric field type liquid crystal display of FIG.

7 is a cross-sectional view of a conventional transverse electric field type liquid crystal display device to which an optical compensation film of FIG. 7 is applied.

In the transverse electric field type liquid crystal display of FIG. 7 of FIG. 8, the brightness degree according to the viewing angle in a black state is shown with a contour line.

9A to 9B are cross-sectional views showing a transverse electric field type liquid crystal display device of the present invention.

10A and 10B are exploded perspective views illustrating each layer related to light transmission, a transmission axis, and an optical axis of the layer in the transverse electric field type liquid crystal display of FIGS. 9A and 9B.

11 is a view showing a change in the optical axis when passing through each layer of the transverse field type liquid crystal display device according to Poincare analysis (Poincare)

FIG. 12 is a diagram illustrating a brightness degree according to a viewing angle in a black state in the transverse electric field type liquid crystal display of FIG.

13 is a view showing a change in the optical axis for each predetermined visible light when passing through each layer of the transverse field-type liquid crystal display of the present invention according to Poangkare analysis

14 is a cross-sectional view of a transverse electric field type liquid crystal display device according to another exemplary embodiment of the present invention.

FIG. 15 is a view illustrating a change in optical axes for predetermined visible light when passing through each layer of the transverse electric field type liquid crystal display of FIG.

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

60: liquid crystal panel 61: upper substrate

62: lower substrate 63: liquid crystal layer

64: discotic layer 70: upper polarizing plate

71, 73, 81, 83: TAC film 72, 82: PVA film

74, 84: biaxial film

In order to achieve the above object, a transverse electric field type liquid crystal display device of the present invention alternately includes a first substrate on which a pixel electrode and a common electrode are formed, a second substrate opposed thereto, and a liquid crystal layer formed between the first and second substrates. And a discotic layer further formed between the first and second polarizing plates corresponding to the outer surfaces of the first and second substrates, and the liquid crystal panel and the first or second polarizing plate, respectively. There is a characteristic.

The discotic layer includes a discotic liquid crystal (n _x = n _y > n _z ) having a predetermined optical axis and arranged in one direction.

The discotic liquid crystal of the discotic layer is formed by curing in one direction.

The discotic layer is formed such that an optical axis of a liquid crystal having a disk shape therein is perpendicular to a liquid crystal array direction before voltage application of the liquid crystal layer in an in-plane of the first substrate or the second substrate.

The discotic layer is integrally formed with the first polarizing plate or the second polarizing plate.

An adhesive layer is interposed between a surface of the discotic layer and the first substrate or the second substrate.

The discotic layer is formed in a film type.

The discotic layer has a retardation (Δnd) of 50 nm to 150 nm.

The transmission axes of the first polarizing plate and the second polarizing plate are perpendicular to each other.

The said 1st, 2nd polarizing plate is an optical film and the upper and lower base materials for protection are formed above and below the optical film, respectively.

The optical film is made of a dye-treated PVA film, the protective upper and lower substrates are made of a TAC film.

The TAC film has a retardation value of R _th = {(n _x + n _y ) / 2-n _z } of 30 nm to 150 nm in the thickness direction.

The first and second polarizing plates each include an optical film, a biaxial film formed on one side of the optical film so as to correspond to the first substrate or the second substrate, and a TAC film formed on the other side of the optical film. Is done.

The biaxial film has a retardation value of 10 nm ≦ (n _× n _y ) d ≦ 90 nm and 40 nm ≦ (n _x −n _z ) d ≦ 200 nm.

The TAC film has a retardation value of R _th = {(n _x + n _y ) / 2-n _z } of 30 nm to 150 nm in the thickness direction.

The inner side surface of the said 1st board | substrate or a 2nd board | substrate further includes the alignment film which defines the orientation of the liquid crystal of an initial state.

In addition, a transverse electric field type liquid crystal display device of the present invention for achieving the same object is a first substrate in which the pixel electrode and the common electrode are alternately formed, the second substrate and the liquid crystal layer formed between the first and second substrate A first liquid crystal panel formed of a TAC film / PVA film / TAC film corresponding to an outer surface of the first and second substrates, and between the liquid crystal panel and the first polarizing plate or the second polarizing plate, respectively. Another feature is that it comprises a discotic layer further formed on.

In addition, a transverse electric field type liquid crystal display device for achieving the same purpose is a liquid crystal composed of a first substrate in which a pixel electrode and a common electrode are alternately formed to each other, a second substrate opposed thereto and a liquid crystal layer formed between the first and second substrates. The first and second polarizing plates and the liquid crystal panel and the first and second polarizing plates each including a panel and a biaxial film / PVA film / TAC film in order from the surface corresponding to the outer surface of the first and second substrates, respectively. Another feature is that it comprises a discotic layer further formed between the polarizing plate or the second polarizing plate.

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

9A to 9B are cross-sectional views illustrating a transverse electric field type liquid crystal display device of the present invention.

The transverse field type liquid crystal display device of the present invention includes a liquid crystal panel 60 including an upper substrate 61 facing each other, a lower substrate 62 and a liquid crystal layer 63 formed between the two substrates 61 and 62, and Discotic layers formed between the upper polarizing plate 70 and the lower polarizing plate 80 and the liquid crystal panel 60 and the upper polarizing plate 70 or the lower polarizing plate 80 respectively positioned above and below the liquid crystal panel 60 ( 64).

In the drawing, the discotic layer 64 is formed on the upper polarizer 70 or the lower polarizer 80, but one polarizer of the liquid crystal panel 60 and the upper and lower polarizers 70 and 80 in the form of a single layer film. The form interposed in between is also possible.

In this case, a color filter array (not shown) is formed on the upper substrate 61 of the liquid crystal panel 60, and the lower substrate 62 is a TFT array (not shown), a pixel electrode (not shown), and a common electrode ( Not shown) is formed.

The disc-shaped liquid crystal, that is, the discotic liquid crystal (the optical axis is perpendicular to the disc surface, n _x = n _y > n _z ) corresponding to any one of the upper and lower polarizing plates 70 and 80 is The discotic layer 64 is arranged to have an optical axis that is orthogonal to each other in the plane direction (in-plane) of the upper and lower substrates 61 and 62 and the liquid crystal array direction before the voltage application of the liquid crystal layer 64 (black state). Is formed.

The discotic layer 64 may be integrally formed with the upper polarizing plate 70 or the lower polarizing plate 80 to be formed on a side where the polarizing plates 70 and 80 meet the liquid crystal panel 60 for the convenience of manufacture. It is formed on the back of the upper substrate 61 or the lower substrate 62 in the form of a film. Here, the discotic layer 64 is attached to the liquid crystal panel 60 through an adhesive layer (not shown) on the surface where the liquid crystal panel 60 and the discotic layer 64 meet each other.

As shown in FIG. 9A, in the transverse electric field type liquid crystal display according to the first exemplary embodiment, the discotic layer 64 is formed on the upper polarizing plate 70 so as to correspond to an outer surface of the upper substrate 61. As described above, in the transverse electric field type liquid crystal display according to the second exemplary embodiment, the discotic layer 64 is formed on the lower polarizing plate 80 so as to correspond to an outer surface of the lower substrate 62.

The discotic layer 64 has a retardation (Δnd) of 50 nm to 150 nm. More preferably, the retardation of the discotic layer has a value of 60 nm to 130 nm.

The upper polarizer 70 and the lower polarizer 80 are each made of a polymer capable of mass production of a large area, which is a needle such as iodine in the poly-vinyl alcohol (hereinafter referred to as PVA) films 72 and 82. After adsorbing the halogen crystals of the shape, the PVA membranes 72 and 82 were stretched between two rollers having different rotational speeds to align the needle-shaped crystals side by side, thereby making them dichroic. First and second Tri-Acetyl Cellulose (TAC) films 71 and 73 and third and fourth TAC films 81 and 83 are attached to both surfaces of the PVA films 72 and 82 as protective layers.

That is, the upper polarizing plate 70 includes first and second TAC films 71 and 73 at upper and lower portions of the PVA film 72, and the lower polarizing plate 80 is disposed at upper and lower parts of the PVA 82 film. And third and fourth TAC films 81 and 83, respectively.

The second and third TAC films 73 and 81 positioned between the liquid crystal panel 60 and the PVA films 72 and 82 serving as optical functions of the upper and lower polarizing plates 70 and 80 are C-plates (n _x = n). _y > n _z ), even if the transmission axes of the upper and lower polarizing plates 70 and 80 are arranged to cross 90 ° to each other, the viewing angle viewed through the light passes through the second and third TAC films 73 and 81. It is observed that the polarization directions of the PVA films 72 and 82 are out of the polarity depending on the position of.

Here, the first to fourth TAC films have a retardation value of R _th = {(n _x + n _y ) / 2-n _z } of 30 nm to 150 nm in the thickness direction.

At this time, the discotic layer 64 compensates for the movement of the optical axis according to the viewing angle so that the optical axes of the light traveling through the lower polarizing plate 80 and pass through the upper polarizing plate 70 cross each other by 90 ° regardless of the viewing angle. To compensate.

Hereinafter, in the transverse electric field type liquid crystal display device of the present invention illustrated in FIGS. 9A to 9B, the transmission axis of the polarizing plate and the optical axis of the film will be described.

10A and 10B are exploded perspective views illustrating each layer related to light transmission, a transmission axis, and an optical axis of the layer in the transverse electric field type liquid crystal display of FIGS. 9A and 9B.

The change in the optical axis during the propagation of light is only affected by the layers between the PVA films 72 and 82 having the actual polarization function in the polarizing plates 70 and 80, so that the first and fourth TAC films 71 and 83 are used here. Will be omitted.

As shown in FIG. 10A, when the discotic layer 64 is formed between the liquid crystal panel 60 and the upper polarizer 70 according to the first embodiment of the present invention, the discotic layer 64 is in an initial state (black). Disc-shaped discotic liquid crystals having optical axes orthogonal to each other with respect to the liquid crystal alignment direction of the state-normally black mode) are arranged in an array.

Here, assuming that the transmission axis direction of the lower polarizing plate 80 and the PVA film 82 is 0 ° on a plane (xy two-dimensional coordinate), the transmission axis of the PVA film 72 of the upper polarizing plate 70 perpendicularly intersecting with this is 90 °. Becomes

The liquid crystal alignment in the black state (in the case of normally black mode before voltage application) is determined according to the alignment direction of the lower substrate 61, and when the alignment direction is a direction orthogonal to the transmission axis of the lower polarizing plate 80. The arrangement direction of the liquid crystal layer 63 is thus 90 °.

In this case, the liquid crystal layer 63 is made of a rod-type nematic liquid crystal, and its arrangement varies depending on whether voltage is applied.

In addition, since the discotic liquid crystal of the discotic layer 64 has optical axes perpendicular to each other in a plane with respect to the arrangement direction of the liquid crystal layer 63, the discotic liquid crystal has an optical axis of 0 ° and is arranged so as not to be inclined in the z-axis direction. In-Plane). The discotic layer 64 is a film that maintains an initial state without changing a discotic liquid crystal therein depending on whether voltage is applied.

As shown in FIG. 10B, when the discotic layer 64 is formed between the liquid crystal panel 60 and the lower polarizer 80 according to the second embodiment of the present invention, the discotic layer 64 is in an initial state (black). Disc-shaped discotic liquid crystals having optical axes orthogonal to each other with respect to the liquid crystal alignment direction of the state-normally black mode) are arranged in an array.

In this case, the transmission axis of the lower polarizing plate 80 is 90 °, the transmission axis of the upper polarizing plate 70 is 0 °, and the point where the discotic layer 64 and the liquid crystal layer 63 are inverted with each other. Except for the same optical effects as shown in Fig. 10A, the same reference numerals are given.

Hereinafter, the transverse field type liquid crystal display device of the present invention is applied to a Poangcare sphere to look at the geometrical change of the polarization state when passing through each layer.

FIG. 11 is a view illustrating a change in an optical axis when passing through each layer of the transverse electric field type liquid crystal display device according to Poincare analysis.

Here, the second and third TAC films 73 and 81 positioned between the liquid crystal panel 60 and the PVA films 72 and 82 serving as optical functions of the upper and lower polarizing plates 70 and 80 are C-plates (n _x). = n _y > n _z ).

When there is a light source on the lower side of the liquid crystal panel, and the light propagates from the lower side to the upper side, when the change of the optical axis in each layer is shown through the Poangkar sphere, the transmission axis of each of the polarizing plates 70 and 80 is actually 90 °. 11, when the polarization directions of the PVA films 72 and 82 are not optically opposite to each other due to observation from the angle between the two transmission axes even though they are arranged in a distorted manner, the predetermined polarization directions (arrow directions at 82) After the optical axis shift from the PVA film 82 of the lower polarizing plate having the third polarization plate 81 through the third TAC film 81, the liquid crystal layer 63 is rotated, the discotic layer 64 is subjected to a predetermined compensation, and then again. The optical axis moves in the second TAC film 73 of the upper polarizer to pass light in the polarization direction (arrow direction 72) of the PVA film 72 of the upper polarizer.

Here, the discotic layer 64 serves to compensate for the optical axis shift in the second and third TAC films 81, and when the light incident in any direction is optically analyzed, the lower polarizer 80 The light passes through the transmission axes orthogonal to each other between the PVA film 82 of the PVA film 72 and the PVA film 72 of the upper polarizing plate 70.

On the other hand, when the liquid crystal layer 63 and the discotic layer 64 are upside down (second), the optical axis shifts from the PVA film 82 to the third TAC film 81, and immediately after the discotic layer ( 64, and after the rotation conversion in the liquid crystal layer 63, the optical axis shift is finally performed in the second TAC film 73 and passes through the transmission axis of the PVA film 72.

FIG. 12 is a diagram illustrating a brightness degree according to a viewing angle in a black state in the transverse electric field type liquid crystal display of FIG. 9.

As shown in FIG. 12, the transverse electric field type liquid crystal display device of the present invention includes a discotic layer 64 having an optical compensation function, and uses a polarizing plate having a general TAC film above and below the PVA film, and has a predetermined viewing angle in brightness in a black state. Even at a certain value can be maintained to prevent light leakage defects. In particular, it can be seen that there is almost no leakage light in the black state since the brightness is less than 0.2 even in the vicinity of 40 ° of 45 °, 135 °, 225 °, and 315 ° of the azimuth 45 °, 135 °, 315 °, where conventional light leakage defects are mainly observed.

In FIG. 12, the effect of blocking leakage light is lowered at the viewing angle of 35 ° to 135 ° than when using two conventional uniaxial films. However, two conventional uniaxial films were actually used. In addition, there is a problem in that a polarizing plate in which a TAC film is removed from a portion corresponding to the liquid crystal panel is additionally used, and since the manufacturing of the polarizing plate in which a part of the TAC film is removed is practically restricted, the transverse field type liquid crystal display device of the present invention is meaningful. Has

13 is a view showing a change in the optical axis for each predetermined visible light when passing through each layer of the transverse field-type liquid crystal display of the present invention according to Poangkare analysis.

The change in the optical axis shown in FIG. 11 illustrates a change in polarization characteristics of green light. When the change in the optical axis for each layer is represented by visible light according to each color, it may be illustrated as shown in FIG. 13.

At this time, the discotic layer 64 normally compensates for the green light, but the remaining red light or blue light shows a different polarization state from the green light, so that the optical axis shifts. This can be done differently to indicate color deviation.

Accordingly, the second polarizing plate 73 and the third polarizing plate 81 corresponding to the liquid crystal panels 60 of the upper and lower polarizing plates 70 and 80 are formed as biaxial films, respectively, to provide red light having different polarization characteristics. A transverse field type liquid crystal display device according to another embodiment for compensating for blue light is also proposed.

14 is a cross-sectional view illustrating a transverse electric field type liquid crystal display device according to another exemplary embodiment of the present invention.

As illustrated in FIG. 14, a transverse electric field type liquid crystal display according to another exemplary embodiment of the present invention includes an upper substrate 61 facing each other, a lower substrate 62, and a liquid crystal layer 63 formed between the two substrates 61 and 62. It consists of a liquid crystal panel 60, an upper polarizing plate 70, and a lower polarizing plate 80 which are respectively positioned on the upper and lower portions of the liquid crystal panel 60.

In this case, a color filter array (not shown) is formed on the upper substrate 61 of the liquid crystal panel 60, and the lower substrate 62 is a TFT array (not shown), a pixel electrode (not shown), and a common electrode ( Not shown) is formed. Discotic liquid crystals (discotic liquid crystals, optical axes perpendicular to the disk plane, n _x = n _y > n _z ) to the liquid crystal panel 60 and the upper polarizer 70 or the lower polarizer 80. A discotic layer 64 is formed which is arranged with this predetermined optical axis. Here, the discotic layer 64 may be formed between the liquid crystal panel 60 and the upper polarizer 70 or the lower polarizer 80 in a separate film type.

And, the film of the surface corresponding to the liquid crystal panel 60 of the upper and lower polarizing plates 70 and 80 is optically biaxial film (biaxial film, n _x ≠ n _y ≠ n _z , n _x > n _y > n _z (74, 84).

That is, the upper polarizing plate 70 is composed of a TAC film 71, a dye-treated PVA film 82, and a biaxial film 74 in order from above, and the lower polarizing plate 80 is a biaxial film in order from above. (84), a dye-treated PVA film (82), and a TAC film (83).

In this case, the discotic layer 64 is formed by being attached to any one of the biaxial films 74 and 84. In this case, a double-sided adhesive layer (not shown) is further interposed on the surface where the discotic layer 64 meets the liquid crystal panel 60.

The biaxial films 74 and 84 have a retardation value of 10 nm ≦ (n _× n _y ) d ≦ 90 nm and 40 nm ≦ (n _x −n _z ) d ≦ 200 nm.

In addition, the TAC films 71 and 83 have the characteristics of C plate (n _x = n _y > n _z ), respectively, and the phase difference value in the thickness direction is R _th = {(n _x + n _y ) / 2-n _z } to be 30 nm to 150 nm.

FIG. 15 is a view illustrating a change in an optical axis when passing through each layer of the transverse electric field type liquid crystal display of FIG. 14 according to a Poangare analysis.

As illustrated in FIG. 15, the biaxial films 74 and 84 provided in the upper and lower polarizing plates 70 and 80 each have a compensation function according to a polarization state of a predetermined light, and optically each of the PVA films 72 and 82 of the upper and lower polarizing plates. The transmission axes of are perpendicular to each other.

That is, when there is a light source on the lower side of the liquid crystal panel, and the light propagates from the lower side to the upper side, when the change of the optical axis in each layer is shown through the Poangcurry sphere, the predetermined transmission axis (arrow direction in 82) is indicated. After the optical axis shift of each predetermined color of visible light is performed from the PVA film 82 of the lower polarizing plate to have a predetermined color, it is rotated in the liquid crystal layer 63 and the predetermined compensation is performed in the discotic layer 64. Afterwards, the optical axis of the visible light of a predetermined color is moved again in the biaxial film 74 of the upper polarizing plate, and light passes through the transmission axis (arrow direction 72) of the PVA film 72 of the upper polarizing plate of the predetermined visible light.

In this case, the biaxial films 74 and 84 may have different birefringence values for each visible light of a predetermined color, thereby minimizing the change in polarization state for each color. That is, since the polarization dispersion characteristics of the liquid crystals vary according to the wavelength of light, the biaxial films 74 and 84 compensate for the occurrence of color difference (Bluish or Yellowish) in the viewing angle direction, thereby minimizing the change in polarization state for each color. can do.

In addition, as in the above-described first and second embodiments, the discotic layer 64 serves to compensate for optical axis movement in the second and third TAC films 81, so that any light incident in any direction When optically analyzed, the transmission axes of the PVA film 82 of the lower polarizer 80 and the PVA film 72 of the upper polarizer 70 are orthogonal to each other.

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

Applying a discotic layer to either side of the upper and lower substrates of the liquid crystal panel, and using a polarizing plate made of a TAC film / PVA film / TAC film or a TAC film / PVA film / biaxial film without removing some film layers of the polarizing plate, In any state, light leakage can be minimized by reducing leakage light at any viewing angle in any direction.

Claims (18)

A liquid crystal panel comprising a first substrate alternately formed with a pixel electrode and a common electrode, a second substrate facing the substrate, and a liquid crystal layer formed between the first and second substrates; First and second polarizing plates corresponding to outer surfaces of the first and second substrates, respectively; And And a discotic layer further formed between the liquid crystal panel and the first polarizing plate or the second polarizing plate. The method of claim 1, The discotic layer of the transverse electric field liquid crystal display, characterized in that the discotic liquid crystal (n _x = n _y > n _z ) is arranged in one direction with a predetermined optical axis. The method of claim 2, And the discotic liquid crystals of the discotic layer are arranged in one direction and cured. The method of claim 2, The discotic layer is formed such that the optical axis of the liquid crystal having a disk shape therein is orthogonal to each other in the plane direction (In-plane) of the liquid crystal array direction before the voltage is applied to the liquid crystal layer in the plane direction (In-plane) of the first substrate or the second substrate. Transverse electric field liquid crystal display device. The method of claim 1, And the discotic layer is formed integrally with the first polarizing plate or the second polarizing plate. The method of claim 5, And a bonding layer interposed between the discotic layer and the first substrate or the second substrate. The method of claim 1, And the discotic layer is formed in a film type. The method of claim 1, And the discotic layer has a retardation (Δnd) of 50 nm to 150 nm. The method of claim 1, And a transmission axis of the first polarizing plate and the second polarizing plate is perpendicular to each other. The method of claim 1, The first and second polarizing plates are optical film and a transverse electric field liquid crystal display device, characterized in that upper and lower protective substrates are formed above and below the optical film, respectively. The method of claim 10, The optical film is made of a dye-treated PVA film, and the upper and lower substrates for protection are made of a TAC film. The method of claim 11, And the TAC film has a retardation value in the thickness direction of R _th = {(n _x + n _y ) / 2-n _z } of 30 nm to 150 nm. The method of claim 1, The first and second polarizing plates each include an optical film, a biaxial film formed on one side of the optical film so as to correspond to the first substrate or the second substrate, and a TAC film formed on the other side of the optical film. Transverse electric field liquid crystal display device characterized in that consisting of. The method of claim 13, The biaxial film has a phase difference value of 10 nm≤ (n _x -n _y ) d≤90 nm and 40nm≤ (n _x -n _z ) d≤200 nm. The method of claim 13, And the TAC film has a retardation value in the thickness direction of R _th = {(n _x + n _y ) / 2-n _z } of 30 nm to 150 nm. The method of claim 1, The inner side surface of the said 1st board | substrate or a 2nd board | substrate further equipped with the orientation film which defines the orientation of the liquid crystal of an initial state, The transverse electric field type liquid crystal display device characterized by the above-mentioned. A liquid crystal panel comprising a first substrate alternately formed with a pixel electrode and a common electrode, a second substrate facing the substrate, and a liquid crystal layer formed between the first and second substrates; First and second polarizing plates corresponding to the outer surfaces of the first and second substrates, respectively, including a TAC film / PVA film / TAC film; And And a discotic layer further formed between the liquid crystal panel and the first polarizing plate or the second polarizing plate. A liquid crystal panel comprising a first substrate alternately formed with a pixel electrode and a common electrode, a second substrate facing the substrate, and a liquid crystal layer formed between the first and second substrates; First and second polarizing plates each having a biaxial film / PVA film / TAC film in order from the surfaces corresponding to the outer surfaces of the first and second substrates, respectively; And And a discotic layer further formed between the liquid crystal panel and the first polarizing plate or the second polarizing plate.