KR100735195B1 - Color liquid crystal display - Google Patents

Abstract

The present invention discloses a color liquid crystal display capable of realizing full color. The disclosed color liquid crystal display device includes: an array substrate having a thin film transistor and a pixel electrode; A transparent electrode substrate disposed to face the array substrate; And a polymer dispersed liquid crystal layer interposed between the array substrate and the transparent electrode substrate and including a polymer mixture, a liquid crystal added with a dichroic dye, and a pigment. A color liquid crystal display device having such a configuration has a characteristic that black is expressed by the dichroic dye in an off state (blocking state), and color can be expressed by a pigment in an on state (transmission state).

Description

Color liquid crystal display {COLOR LIQUID CRYSTAL DISPLAY}

1 is a schematic diagram illustrating a color liquid crystal display according to an exemplary embodiment of the present invention.

<Description of the symbols for the main parts of the drawings>

100: array substrate 110: first transparent substrate

115: sealing member 120: pixel electrode

150: transparent electrode substrate 160: second transparent substrate

170: common electrode 190: polymer dispersed liquid crystal layer

192: polymer mixture 194: dichroic dye (bold line)

196: liquid crystal (thin line) 198: pigment

The present invention relates to a liquid crystal display, and more particularly, to a color liquid crystal display including a polymer dispersed liquid crystal layer capable of realizing full color.

In general, a polymer dispersed liquid crystal (PDLC) display includes two transparent substrates facing each other and a polymer dispersed liquid crystal layer interposed between the substrates. At this time, the polymer dispersed liquid crystal layer is sealed between the two transparent substrates so as not to contact with oxygen and moisture which may chemically damage the liquid crystal.

An example of the polymer dispersed liquid crystal technique is disclosed in P. S. Drzaic's Liquid Crystal Kispersions (1995).

Typically, the polymer dispersed liquid crystal is composed of micron sized droplets of small molecular weight nematic liquid crystal dispersed in a polymer binder. Nematic droplets scatter light strongly, causing the material to have a white opaque or opaque appearance (blocked state). Then, if a voltage difference occurs between the two electrodes provided on each transparent substrate (transmission state), the electric field aligns the droplets so that the normal refractive index of the liquid crystal almost matches the refractive index of the isotropic polymer matrix, and the scattering power of the droplets is substantially reduced. This is reduced to allow light to pass through. Thus, the cell in the transmissive state, which is on, appears clear or transparent, and opaque in the blocked state, which is off.

In a guest-host polymer dispersed liquid crystal display, a dye, in particular a polychromatic or dichroic dye, is added to the liquid crystal to make a color display. For example, if a dichroic dye having a bar-shaped structure is added to a polymer dispersed liquid crystal, the dichroic dye molecules have a characteristic of being oriented parallel to the polymer dispersed liquid crystal molecules, and thus are faced with each other. When the molecular direction of the liquid crystal is changed by applying an electric field to both electrodes, the direction of the dichroic dye molecule also changes. Since the dichroic dye is made without coloring or depending on the alignment direction, switching between the off state and the 'on state' is possible. It is apparent to those skilled in the art that the dichroic dye is used in a guest-host polymer dispersed liquid crystal display to improve the color ratio.

In addition, the polymer dispersed liquid crystal display may be classified into a transmissive liquid crystal display or a reflective liquid crystal display.

The transmissive polymer dispersed liquid crystal display has an internal light source. When a voltage is applied to the anode, light may pass through the polymer dispersed liquid crystal layer. The transmissive liquid crystal display device is difficult to implement black due to the scattering characteristics of the polymer dispersed liquid crystal, and thus requires a light control layer in addition to the backlight. However, the viewing angle is limited by the light adjusting film.

The reflective liquid crystal display typically includes a reflective black or colored filter that is visible in a transparent state. However, since the reflective liquid crystal display device operates in the black state in the off state and in the transmissive state in the on state, the luminance increases but it is difficult to express black color. In addition, only when using a polymer dispersed liquid crystal containing a dichroic dye has a problem that only a single color expression.

Accordingly, an object of the present invention is to provide a color liquid crystal display including a polymer dispersed liquid crystal layer capable of realizing full color.

A color liquid crystal display according to a preferred embodiment of the present invention for achieving the above object is an array substrate having a thin film transistor and a pixel electrode; A transparent electrode substrate disposed to face the array substrate; And a polymer dispersed liquid crystal layer interposed between the array substrate and the transparent electrode substrate and including a polymer mixture, a liquid crystal added with a dichroic dye, and a pigment.

The dichroic dye is a blackish dye,

Examples of the pigments include red pigments, blue pigments, green pigments, and the like.

The liquid crystal is dispersed in a droplet state in the polymer mixture, and the pigment is dispersed in the polymer mixture.

The backlight unit may further include a backlight unit or a reflection unit provided under the array substrate.

As described above, the color liquid crystal display device of the present invention includes a liquid crystal containing a dichroic dye and a polymer dispersed liquid crystal layer containing the pigment, so that black color is caused by the dichroic dye in an off state (blocking state). It has the characteristic of expressing color by a pigment in an on state (transmission state). In other words, not only the implementation of full color is possible but also the contrast ratio and the resolution of the color are improved.

In addition, the color liquid crystal display of the present invention as described above may have an improved brightness, color implementation degree and viewing angle compared to the conventional liquid crystal display due to being combined with the reflection unit or the backlight unit.

(Example)

Hereinafter, a color liquid crystal display according to an exemplary embodiment of the present invention will be described in detail with reference to the accompanying drawings. The invention is not limited to the embodiments described herein but may be embodied in other forms. Rather, the embodiments introduced herein are provided to make the disclosed content more complete, and to fully convey the spirit of the present invention to those skilled in the art.

1 is a schematic diagram illustrating a color liquid crystal display according to the present invention.

Referring to FIG. 1, a color liquid crystal display according to the present invention includes an array substrate 100, a transparent electrode substrate 150, a sealing member 115 defining an accommodating area of a polymer dispersed liquid crystal, the array substrate 100, or the like. A column spacer (not shown) formed on the transparent electrode substrate 150 to define a cell gap of the polymer dispersed liquid crystal layer, and a polymer dispersed liquid crystal layer interposed between the array substrate 100 and the transparent electrode substrate 150 ( 190).

The array substrate 100 includes a first transparent substrate 110 and a pixel electrode 120, and although not shown, a thin film transistor, a source line, a gate wiring, a gate insulating film, an organic film, and the like. It includes.

Specifically, the first transparent substrate 110 is a glass substrate of a transparent material that can pass light. The glass substrate has an alkali free property. If the glass substrate has an alkali property, alkali ions are eluted from the glass into the polymer dispersed liquid crystal layer, and the elution of the alkali ions leads to a decrease in the resistivity of the polymer dispersed liquid crystal layer, as well as the sealing member 115, that is, It reduces the adhesion between the sealant and the glass substrate and adversely affects the operation of the thin film transistor. Therefore, the glass substrate uses an alkali-free one.

The thin film transistor is formed in each pixel area of the first transparent substrate 110 and is formed at the intersection of the gate line and the data line. In particular, the thin film transistor includes a data electrode including a gate electrode, a gate insulating film, a channel film, a source electrode, and a drain electrode.

The gate electrode is formed on the first transparent substrate 110 and is connected to the gate wiring. The gate insulating layer is formed on the gate line including the gate electrode, and serves to prevent the gate electrode from being shorted in contact with another conductive pattern. In particular, the gate insulating film is silicon nitride (SiNx).

The channel film is disposed on the top surface of the gate electrode in an insulated state from the gate electrode. Specifically, the channel film preferably comprises an amorphous silicon film and an n + amophous silicon film disposed on an upper surface of the amorphous silicon film. The channel film is disposed on the gate insulating film, and when the selection signal is applied to the gate electrode, current flows between the source electrode and the drain electrode through the channel film. The n + amorphous silicon thin film is formed in two parts on the surface of the amorphous silicon thin film.

The source electrode is connected to each data line, and the source electrode is in contact with one of two n + amorphous silicon thin films. The drain electrode is in contact with the other of the two divided n + amorphous silicon thin films.

The organic layer includes a contact hole exposing a drain electrode of the thin film transistor.

The pixel electrode 120 is a transparent electrode formed on the organic layer and is electrically connected to the drain electrode through the contact hole. The pixel electrode 120 may be a conductive oxide film such as indium tin oxide (ITO), indium zinc oxide (IZO), or zinc oxide (ZO). Is formed. In addition, the pixel electrode 120 controls the liquid crystal in the polymer dispersed liquid crystal layer 190 by the voltage applied between the common electrode 170 and the transparent electrode substrate 150 to adjust the light transmittance.

The transparent electrode substrate 150 includes a second transparent substrate 160 and a common electrode 170. The second transparent substrate 160 is a glass substrate of a transparent material that can pass light. The glass substrate has an alkali free property. The common electrode 170 is formed of a transparent conductive material such as ITO, IZO, or ZO.

The sealing member 115 is formed along the outside of the substrates 100 and 150 to secure the storage space of the polymer dispersed liquid crystal, and has a closed curve shape. As the sealing member 115, a UV curable sealant that is cured by ultraviolet rays or a heat curable sealant that is cured by heat may be used.

The column spacer serves to separate the array substrate 100 from the transparent electrode substrate 150. Specifically, it serves to maintain a cell gap in which the polymer dispersed liquid crystal layer 190 is formed. For example, the column spacer may be formed in a pixel region of the array substrate 100, and may be formed in an area of the transparent electrode substrate 150 corresponding to the pixel region of the array substrate 100. The column spacer may be formed by performing a process of forming a general photoresist pattern.

The polymer dispersed liquid crystal layer 190 is interposed between the array substrate 100 and the transparent electrode substrate 150 spaced apart by the column spacer, and the storage space is defined by the sealing member 115.

In particular, the polymer dispersed liquid crystal layer 190 includes a polymer mixture 192, a liquid crystal 196 and a pigment 198 to which a dichroic dye 194 is added. The polymer dispersed liquid crystal layer 190 according to the present embodiment is characterized in that the dye 194 and the pigment 198 added to the liquid crystal 196 are not mixed with each other.
For example, the polymer dispersed liquid crystal layer 190 of the present invention is manufactured as follows.
First, a liquid crystal 196 in which dichroic dye 194 is mixed by about 1 wt% is manufactured. M-TL TL203 is used as the liquid crystal 196, and M-S-428 is used as the dichroic dye 194. Here, S-428 is a black color dye having high dichroic ratio, high solubility and high light fastness. Subsequently, 80 wt% of the liquid crystal 196 mixed with the dichroic dye 194 prepared as described above and 20 wt% of the polymer mixture are mixed. The polymer mixture is PN393 from M Company.
Then, 2wt% red (or green or blue) pigment 198 is mixed with the mixture thus prepared to prepare a final mixture, and then the mixture is placed on a substrate, that is, on the first transparent substrate 110. After coating, it is cured to prepare the polymer dispersed liquid crystal layer 190 of the present invention.

In the polymer dispersed liquid crystal layer 190, the liquid crystal 196 is dispersed in a droplet state in the polymer mixture and is driven by an electric field formed by the pixel electrode 120 and the common electrode 170. The dichroic dye 194 added to the liquid crystal 196 is a black dichroic dye. In particular, the black dichroic dye is driven together with the liquid crystal 196 by an electric field formed by the pixel electrode 120 and the common electrode 170. In particular, the dichroic dye of black serves to improve the characteristics of brightness and color reproducibility by making the on state (transmission state) applicable to the color state. In addition, the pigment 198 is dispersed in the polymer mixture 192 and includes a red pigment, a blue pigment, a green pigment, and the like. The pigment 198 may be used alone or in combination.

The pigment 198 is included in the polymer dispersed liquid crystal layer 190 to enable full color implementation of the liquid crystal display. That is, the color liquid crystal display according to the present invention including the polymer dispersed liquid crystal layer 190 has a characteristic that black is expressed by the dichroic dye 194 in an off state (blocking state), and is in an on state. In the (transmission state), the pigment 198 has the characteristic of expressing color. That is, not only the implementation of full color is possible, but also the contrast ratio and the resolution of the color are improved.

Although not shown, the color liquid crystal display of the present invention may further include a backlight unit and a reflection unit to further improve its characteristics. The color liquid crystal display device to which the backlight unit is applied may be applied as a transmissive color liquid crystal display device. That is, it is driven in black in the off state and driven in the color state in the on state. In addition, the color liquid crystal display device to which the reflection unit is applied may be applied as a reflective color liquid crystal display device. That is, it is driven in black in the off state and driven in the color state in the on state.

As described above, the color liquid crystal display device according to the present invention includes a polymer mixture, a liquid crystal containing a dichroic dye, and a polymer dispersed liquid crystal layer including the pigment. Therefore, the color liquid crystal display of the present invention has a characteristic that black is expressed by the dichroic dye in the off state (blocking state), and color can be expressed by the pigment in the on state (transmission state). In other words, not only full color can be realized but also the contrast ratio and resolution of the color are improved. In addition, since the color liquid crystal display of the present invention is combined with the reflection unit or the backlight unit, the color liquid crystal display may have improved characteristics such as brightness, degree of color implementation, viewing angle, and the like compared to the conventional liquid crystal display.

Although described above with reference to the embodiments, those skilled in the art can be variously modified and changed within the scope of the present invention without departing from the spirit and scope of the invention described in the claims below. I can understand.

Claims (7)

An array substrate having a thin film transistor and a pixel electrode; A transparent electrode substrate disposed to face the array substrate; And And a polymer dispersed liquid crystal layer interposed between the array substrate and the transparent electrode substrate and including a polymer mixture, a liquid crystal added with a dichroic dye, and a pigment. The color liquid crystal display of claim 1, wherein the dichroic dye is a dye having a black color. The color liquid crystal display of claim 1, wherein the pigment is any one selected from the group consisting of a red pigment, a blue pigment, and a green pigment. The color liquid crystal display of claim 1, wherein the liquid crystal is dispersed in a droplet state in the polymer mixture. The color liquid crystal display device according to claim 1, wherein the pigment is dispersed in a polymer mixture. The color liquid crystal display of claim 1, further comprising a backlight unit disposed under the array substrate. The color liquid crystal display device of claim 1, further comprising a reflection unit disposed under the array substrate.

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