KR20080038566A - Liquid crystal display device - Google Patents

Abstract

An LCD device is provided to enable cholesteric liquid crystal to pick a wavelength for reflecting light selectively according to a surrounding temperature and control liquid crystal alignment by changing an electric field applied to the cholesteric liquid crystal, thereby improving diffusion performance and light efficiency. An LCD(Liquid Crystal Display) device includes an LCD panel, a light source, and a light diffusion plate(30). The light source is positioned at the rear of the LCD panel. The light diffusion plate is positioned between the LCD panel and the light source. The light diffusion plate includes a first insulating plate(310), a second insulating plate(320) and a cholesteric liquid crystal layer(330). The second insulating plate is arranged to be opposite to the first insulating plate. The cholesteric liquid crystal layer is positioned between the first and second insulating plates. A thin film transistor(312) is formed on the first insulating plate, and an insulating film(313) covers the thin film transistor.

Description

Liquid crystal display {LIQUID CRYSTAL DISPLAY DEVICE}

1 is an exploded perspective view of a liquid crystal display according to a first embodiment of the present invention;

2 is a block diagram showing the configuration of a liquid crystal display according to a first embodiment of the present invention;

3 is a cross-sectional view of the diffusion plate in the liquid crystal display according to the first embodiment;

4 is a view for explaining the behavior of the cholesteric liquid crystal,

FIG. 5 illustrates luminance distribution for each zone of the diffusion plate in the liquid crystal display according to the first embodiment.

6 and 7 are cross-sectional views of main parts of the liquid crystal display according to the second and third embodiments of the present invention, respectively.

Explanation of Signs of Major Parts of Drawings

10 liquid crystal display panel 20 light source

30: diffusion plate 310: first substrate

320: second substrate 330: cholesteric liquid crystal layer

40: panel driver 50: image calculation unit

60: diffuser drive unit

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display device, and more particularly, to a liquid crystal display device having excellent diffusion performance and light efficiency by using a diffusion plate having a new configuration.

Recently, a flat panel display such as a liquid crystal display (LCD), a plasma display panel (PDP), or an organic light emitting diode (OLED) has been developed in place of the conventional CRT.

The liquid crystal display device includes a liquid crystal display panel and a backlight unit for supplying light to the liquid crystal display panel. Light transmitted from the backlight unit is adjusted according to the arrangement of liquid crystals.

A backlight plate is used for the backlight unit to diffuse the light of the light source over the entire surface of the liquid crystal display panel so that the light source is not recognized. The diffuser plate is mainly a transparent plate in which a diffuser is scattered.

However, when the conventional diffusion plate is used, there is a problem that the light efficiency is lowered by the diffusion agent. In particular, when a light emitting diode is used as a light source, color mixing for supplying white light is important, but there is a problem in that sufficient color mixing cannot be obtained with a conventional diffusion plate.

An object of the present invention is to provide a liquid crystal display device having excellent diffusion performance and light efficiency.

An object of the present invention is a liquid crystal display device comprising a liquid crystal display panel, a light source positioned behind the liquid crystal display panel, and a diffusion plate positioned between the liquid crystal display panel and the light source, wherein the diffusion plate comprises a first insulating layer. Board; A second insulating substrate disposed to face the first insulating substrate; It is achieved by including a cholesteric liquid crystal layer positioned between the first insulating substrate and the second insulating substrate.

In the cholesteric liquid crystal layer, it is preferable that the liquid crystal molecules have irregular alignment directions.

A first electrode is formed on the first insulating substrate and a second electrode is formed on the second insulating substrate. The diffusion plate driver is connected to the diffusion plate and controls an electric field between the first electrode and the second electrode. It is preferable to further include.

Preferably, the first electrode is formed over the entire first insulating substrate, and the second electrode is formed over the entire second insulating substrate.

The first electrode includes a plurality of sub-electrodes electrically separated from each other, the second electrode is formed over the entire second insulating substrate, and the first insulating substrate is connected to each of the sub-electrodes. It is preferable that a thin film transistor is formed.

And an image calculator for dividing the luminance applied to the liquid crystal display panel for each zone, wherein the diffusion plate driver adjusts an electric field between the first electrode and the second electrode based on the luminance value of the image calculator. It is preferable.

Preferably, the first insulating substrate faces the light source, and the second insulating substrate faces the liquid crystal display panel.

The light source preferably includes a light emitting diode.

The first electrode and the second electrode preferably include indium tin oxide (ITO) or indium zinc oxide (IZO).

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

In various embodiments, like reference numerals refer to like elements, and like reference numerals refer to like elements in the first embodiment and may be omitted in other embodiments.

The liquid crystal display according to the first embodiment of the present invention will be described with reference to FIGS. 1 to 5.

Referring to FIG. 1, the liquid crystal display device 1 is positioned between the liquid crystal display panel 10 and the light source 20 disposed behind the liquid crystal display panel 10, and between the liquid crystal display panel 10 and the light source 20. The diffusion plate 30 is included.

In another embodiment, the liquid crystal display device 1 may further include an optical film such as a diffusion film, a prism film, and a protective film positioned between the liquid crystal display panel 10 and the light source 20.

The light source 20 includes a plurality of light emitting diode groups 21, and the light emitting diode groups 21 are arranged in a matrix form over the entire rear surface of the liquid crystal display panel 10. In the drawing, the number of light emitting diode groups 21 is reduced for convenience of illustration, and in the actual LCD device, the number of light emitting diode groups 21 may be larger than that in the drawing. The light emitting diode group 21 is composed of three light emitting diodes emitting different colors.

In another embodiment, the light emitting diode group 21 may be composed of four light emitting diodes, and a lamp may be used as the light source 20.

Referring to FIG. 2, the liquid crystal panel 10 is driven by the panel driver 40, and the panel driver 40 modifies the image signals and voltages input from the outside and supplies them to the liquid crystal panel 10.

The image calculator 50 connected to the panel driver 40 calculates luminance for each area of the screen by using the input image signal. It is also possible that the image calculator 50 receives the image signal directly from the outside without being connected to the panel driver 40.

The diffuser plate 30 is driven by the diffuser plate driver 60, and the diffuser plate driver 60 drives the diffuser plate 30 based on the luminance calculation result of the image calculator 50.

Hereinafter, the configuration of the diffusion plate 30 and the driving of the diffusion plate 30 will be described with reference to FIGS. 3 to 5.

Referring to FIG. 3, the diffusion plate 30 may include a cholesteric liquid crystal layer 330 positioned between the first substrate 310 and the second substrate 320 facing each other, and the two substrates 310 and 320. Include.

The first substrate 310 is an insulating film covering the first insulating substrate 311 facing the light source 20, the thin film transistor 312 formed on the first insulating substrate 311, and the thin film transistor 312. 313 and a first electrode 314 connected to the thin film transistor 312.

The first insulating substrate 311 may be made of a transparent material such as glass or plastic. The diffusion plate driver 60 may adjust the voltage applied to the first electrode 314 by controlling the thin film transistor 312. The first electrodes 314 are provided in plural numbers separated from each other, and are arranged in a matrix form in plan view. The first electrode 314 is made of indium tin oxide (ITO) or indium zinc oxide (IZO), which are transparent conductive materials.

The second insulating substrate 321 facing the liquid crystal display panel 10 may also be made of a transparent material such as glass or plastic. The second electrode 322 is formed over the entire second insulating substrate 321 and is made of indium tin oxide (ITO) or indium zinc oxide (IZO), which are transparent conductive materials.

The liquid crystal molecules of the cholesteric liquid crystal layer 330 positioned between the two substrates 310 and 320 change in the alignment direction depending on the electric fields formed in the two electrodes 314 and 322.

A cholesteric liquid crystal is a liquid crystal having a twist due to a dopant in a nematic liquid crystal or a liquid crystal itself having a chiral structure. The cholesteric liquid crystal may selectively take the wavelength of reflecting light according to the ambient temperature, and may adjust the liquid crystal alignment by changing an electric field applied to the cholesteric liquid crystal.

The alignment state of the cholesteric liquid crystal will be described with reference to FIG. 4.

The cholesteric liquid crystal is oriented so that the twist axis (CHIRAL AXIS) is perpendicular to the liquid crystal panel 10 as shown in FIG. 4A when no electric field is applied. In the vertical alignment state, the cholesteric liquid crystal strongly reflects light corresponding to the pitch p, and passes light of different wavelengths as it is.

The reflected light is mainly light in the visible ray region, and infrared rays are transmitted through the cholesteric liquid crystal without being absorbed.

When an electric field is applied to the cholesteric liquid crystal, the axial axis (CHIRAL AXIS) is oriented parallel to the liquid crystal panel 10 as shown in FIG. In this state, the cholesteric liquid crystal passes the incident light as it is.

When the electric field is removed from the cholesteric liquid crystal, the alignment is disordered as shown in FIG. 4 (c), and the incident light is scattered and diffused.

The alignment state of the cholesteric liquid crystal according to the electric field described above may be variously modified according to the type and amount of the dopant.

Referring back to FIG. 2, the diffusion plate driver 60 adjusts an electric field formed between the two electrodes 314 and 322 so that the cholesteric liquid crystal repeats the three states described with reference to FIG. 4 over time. In another embodiment, the diffusion plate driver 60 may adjust the electric field so that the cholesteric liquid crystal repeats the (b) and (c) states of FIG. 4.

When the state (b) and (c) of FIG. 4 are repeated, permeation and diffusion (scattering) alternately occur in the diffusion plate 30. When the cholesteric liquid crystal is in the (b) state, it has a light extraction efficiency close to 100%. Accordingly, the diffusion plate 30 has excellent diffusion performance and good light efficiency. Simulation results confirmed that the light efficiency is increased by about 55% compared to the conventional diffusion plate.

The diffusion plate driver 60 may apply different voltages to the first electrodes 314 to cause the cholesteric liquid crystals corresponding to the first electrodes 314 to have different alignment states.

Light is supplied from the light source 20 in different colors. When the cholesteric liquid crystal is in the (c) state, the light is mixed and diffused in the diffusion plate 30.

As such, using the diffusion plate 30 according to the present invention, both light efficiency and color mixing (diffusion) are improved. On the other hand, even if the distance between the light source 20 and the diffusion plate 30 is reduced, sufficient diffusion performance can be obtained and the thickness of the liquid crystal display device 1 can be reduced.

As described above, according to the first exemplary embodiment, the diffusion plate 30 may control transmission and diffusion for each first electrode 314. By using these characteristics, the contrast ratio of the liquid crystal display device 1 may be increased, which will be described with reference to FIG. 5.

The image at any moment displayed on the liquid crystal display panel 10 has a dark portion and a bright portion according to the position of the screen. In the conventional liquid crystal display device, light having a constant luminance is continuously supplied from the rear surface of the liquid crystal display panel, and the liquid crystal layer serving as a shutter adjusts the amount of transmission to express various luminance. However, since there is a limit to blocking the light supplied from the back, it is difficult to increase the contrast ratio because the dark screen is not sufficiently dark.

According to the present exemplary embodiment, since the diffusion plate 30 may control transmission and diffusion characteristics for each region, as shown in FIG. 5, the diffusion plate 30 may have different transmittances for each region.

The image calculator 50 calculates luminance for each zone of the liquid crystal panel 10. The diffusion plate driver 60 has a low transmittance of a region of the diffusion plate 30 corresponding to the dark portion of the liquid crystal panel 10 according to the luminance calculation result, and thus the diffusion plate 30 corresponding to the light portion of the liquid crystal panel 10. The transmittance of the region is adjusted high. That is, as shown in FIG. 5, the partial region of the diffusion plate 30 is adjusted to have the maximum transmittance, and the partial region is adjusted so that light does not substantially transmit. Thereby, the contrast ratio of the liquid crystal display device 1 can be improved. In FIG. 5, the diffusion plate 30 is divided into nine regions arranged in 3 * 3, but the region division may be variously modified.

A second embodiment will be described with reference to FIG.

According to the second embodiment, the thin film transistor is not formed on the first substrate 310, and the first electrode 314 is integrally formed over the entire first insulating substrate 311. The diffusion plate 30 can not control the transmittance for each region as in the first embodiment, but may be repeated diffusion and transmission.

A third embodiment will be described with reference to FIG.

According to the third embodiment, no electrode is formed in the diffusion plate 30. Accordingly, the diffusion plate driver 60 of the liquid crystal display device 1 may be omitted.

The alignment layers 315 and 325 are formed on both substrates 310 and 320, and the liquid crystals of the cholesteric liquid crystal layer 330 have the irregular alignment as shown in FIG. 4C by the alignment layers 315 and 325. Perform the diffusion function.

Although some embodiments of the invention have been shown and described, those skilled in the art will recognize that modifications can be made to the embodiments without departing from the spirit or principles of the invention. . It is intended that the scope of the invention be defined by the claims appended hereto and their equivalents.

As described above, according to the present invention, a liquid crystal display device having excellent diffusion performance and light efficiency is provided.

Claims (9)

A liquid crystal display device comprising a liquid crystal display panel, a light source positioned behind the liquid crystal display panel, and a diffusion plate positioned between the liquid crystal display panel and the light source. The diffusion plate, A first insulating substrate; A second insulating substrate disposed to face the first insulating substrate; And a cholesteric liquid crystal layer disposed between the first insulating substrate and the second insulating substrate. The method of claim 1, The cholesteric liquid crystal layer is a liquid crystal display device characterized in that the liquid crystal molecules have an irregular orientation direction. The method of claim 1, A first electrode is formed on the first insulating substrate, and a second electrode is formed on the second insulating substrate; And a diffusion plate driver connected to the diffusion plate and configured to control an electric field between the first electrode and the second electrode. The method of claim 3, The first electrode is formed over the entire first insulating substrate, And the second electrode is formed over the entire second insulating substrate. The method of claim 3, The first electrode includes a plurality of sub electrodes electrically separated from each other. The second electrode is formed over the entire second insulating substrate, And a thin film transistor connected to each of the sub-electrodes. The method of claim 5, The apparatus may further include an image calculator which calculates the luminance applied to the liquid crystal display panel by division. And the diffusion plate driver adjusts an electric field between the first electrode and the second electrode based on a luminance value of the image calculator. The method according to claim 5 or 6, And the first insulating substrate faces the light source, and the second insulating substrate faces the liquid crystal display panel. The method according to any one of claims 1 to 6, The light source includes a light emitting diode. The method according to any one of claims 1 to 6, And the first electrode and the second electrode include indium tin oxide (ITO) or indium zinc oxide (IZO).

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