KR100322697B1 - Polymer-dispersed liquid crystal display - Google Patents

Abstract

PURPOSE: A polymer-dispersed liquid crystal display is provided to improve deterioration in chrominance of red in a long wavelength of 550-700m and raise reliability of the display. CONSTITUTION: An electrode layer(5) and a thin film transistor are formed on the first substrate. An electrode layer, a black matrix(6) and a color filter are formed on the second substrate. Polymer-dispersed liquid crystal is interposed between the first and second substrates. The color filter contains red pigment grains having the size of 0.5-1micrometers in the concentration of 10-20%. The size and concentration of the red pigment grains used for the color filter are controller based on light transmissivity of the polymer-dispersed liquid crystal layer.

Description

Polymer liquid crystal composite liquid crystal display device

The present invention relates to a liquid crystal display device of a projection polymer liquid crystal composite, and more particularly, to a liquid crystal display device using a polymer liquid crystal composite as a liquid crystal material and a thin film transistor as a driving device, the red chromaticity at a wavelength of 550-700 nm is used. An improved polymer liquid crystal composite liquid crystal display device is provided.

TN (Twisted Nematic) active matrix thin transistor (LCD) liquid crystal displays, which are currently the mainstream of projection displays, have low luminance and poor surface orientation due to the low utilization efficiency of light due to the use of polarizing plates. In order to overcome these drawbacks, a polymer-dispersed liquid crystal display using a polymer liquid crystal composite film that does not use a polarizing plate has been developed. In the case of PDLCD, since the polarizer is not used, the luminance is improved and the alignment process of the liquid crystal is unnecessary.

The display using the polymer liquid crystal composite membrane uses light scattering and permeation due to an electric field, and the higher the light scattering, the higher the contrast can be obtained. These light scattering characteristics depend on the size of the liquid crystal quadrature or three-dimensional network. Generally, the smaller the size of the liquid crystal quadrature or three-dimensional network is, the larger the light scattering becomes. When color display is implemented by using a polymer liquid crystal composite as a liquid crystal material and a thin film transistor as a driving device, a color filter is used to display red, blue, and green colors by mixing a dichroic dye into a liquid crystal. In general, color is good due to high light scattering at short wavelengths such as blue and green, but is poor in color due to light scattering at a long wavelength of red.

One type of display device of a color implementation method using conventional light scattering is disclosed in US Pat. No. 5,307,185. According to this device, since the dichroic dye is mixed and used in the liquid crystal, the dye is also aligned when the electric field is applied, and the color is not realized. When the electric field is removed, the dye absorbs the incident light to implement the color. However, in this apparatus, the dichroic dye and the liquid crystal are mixed to drive the liquid crystal and the dye at the same time, so that the driving voltage is high and the response speed is slow. In addition, even when the premise is applied and the liquid crystal and the dye are aligned, a small amount of the pigment absorbs light and thus has poor chromaticity, and in the case of a short wavelength, absorption of light causes deterioration of the liquid crystal due to heat generation of the panel or absorption of ultraviolet rays.

As another type of conventional color display method, there is a device that expresses color by separating incident light according to a wavelength to be incident on each panel and mixing the light on a screen through light transmission or light scattering (US Patent No. 5,150,232). ). This type requires a device (beam splitter) for separating incident light, which not only complicates the optical device but also requires three panels, which increases the volume and weight of the device and increases the cost of the display. .

SUMMARY OF THE INVENTION An object of the present invention is to solve the above problems and to relate to a polymer liquid crystal display liquid crystal display device having improved red color deterioration at a long wavelength (especially 550-700 nm).

In order to achieve the above object, in the present invention, an electrode layer, a thin film transistor, an electrode layer, a black matrix, and a color filter are formed on a first substrate, and a polymer liquid crystal composite is inserted between the first and second substrates. In the liquid crystal display device of claim 1, wherein the liquid crystal sphere of the polymer liquid crystal complex is 1-2 μm, and the color filter contains the red pigment particles having a size of 0.5-1 μm at a concentration of 10-20%. A composite liquid crystal display device is provided.

That is, once the light transmittance of the polymer liquid crystal composite membrane is determined by the size of the liquid crystal sphere or the three-dimensional network, the light transmittance of the color filter is controlled by adjusting the particle size and concentration of the red pigment used in the color filter accordingly. It is a polymer liquid crystal composite liquid crystal device.

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

1 is a block diagram of a thin film transistor PDLCD panel using the polymer liquid crystal composite of the present invention. An active circuit (thin film transistor and capacitor layer) and an indium tin oxide (ITO) pixel electrode are formed on the substrate. On the opposite substrate, a black mask is formed on the opposite substrate to prevent degradation of the thin film transistor and to reduce the contrast caused by the light transmitted through the thin film transistor, and a color filter and an ITO common electrode are sequentially formed thereon. The panel is finally obtained through the injection process and the curing process of the polymer liquid crystal complex. The method for producing the polymer liquid crystal composite used in the present invention may use any of phase separation methods such as a method of forming a liquid crystal sphere and a method of forming a three-dimensional network.

Phase separation conditions such as temperature, UV intensity, solvent evaporation rate, etc. are changed by changing the content ratio or constituents of the liquid crystal and polymer of the polymer liquid crystal complex to adjust the phase separation characteristics of the polymer liquid crystal complex so that light scattering can be maintained at 550-700 nm. It is necessary to adjust. By adjusting the above conditions, the liquid crystal quadrature and the size of the three-dimensional network of the polymer liquid crystal complex are made into 1-2 μm. When the liquid crystal quadrature or the size of the three-dimensional network of the polymer liquid crystal composite is smaller than 1 μm, light scattering characteristics are good, but when the driving voltage is high and when larger than 2 μm, the driving voltage is low but light scattering characteristics tend to be worse.

The dependence of light scattering on the wavelength of the polymer liquid crystal composite prepared by the above method is shown in FIG. 2. Light scattering is largely maintained below 550 nm, but in the 550-700 nm range, the increase in light transmission decreases the contrast in red, resulting in deteriorated image quality. Therefore, in order to improve the chromaticity of the red color, it is necessary to adjust the light transmission characteristics of the color filter related to chromaticity compensation and adjustment. In general, the light transmittance of the color filter depends on the wavelength of each color, which is 95% for red, 80% for blue, and 70% for green. Therefore, when the polymer liquid crystal complex is used, the transmittance of the red portion is high, resulting in a problem of low contrast.

As a method of adjusting the light transmittance of the color filter, there is a method of controlling the thickness of the color filter, the concentration of pigment to be dispersed, and the particle size. The method of controlling the thickness of the color filter is not preferable because the thickness difference between the red, blue, and green color filters is generated. Therefore, it is desirable to control the concentration and particle size of the pigment.

Pigment particles are made to a size of 0.5-1 μm, preferably 0.5-0.8 μm, by a ball mill so that light scattering may occur at 550-700 nm, and a binder such as an acrylic ester, a diluent such as an acrylic monomer, and benzophenone It is mixed with photoinitiators, such as these, and solvent, such as cyclohexanone. As a pigment, red pigments, such as diamino dianthraquinone, are mixed 10-20%, Preferably it is 10-15%. In this case, when the particle size is small (0,5μm), 15% is mixed, and when the particle size is large (0.8μm), 10% is mixed by spin coating to make a thickness of 1.2μm. The coated film is baked at 25 ° C. and then photocured by irradiation with ultraviolet light.

Since the image quality of the screen is affected by the light transmittance and the brightness of the screen, it is necessary to properly combine the light transmittance of the color filter and the light transmittance of the polymer liquid crystal composite membrane. When the light transmittance of the polymer liquid crystal composite when the electric field is applied is 80% The light transmittance of the preferred color filter is 70-85%, more preferably about 80-85%.

The light scattering dependence according to the wavelength of the polymer liquid crystal composite improved by the above method is shown in FIG. 3. Since the light scattering property is uniform with respect to the electric field, it is possible to realize an improved image quality than in the related art.

Hereinafter, the present invention will be described in detail with reference to Examples and Comparative Examples, but the present invention is not limited thereto.

Example 1

20% of PN393 (Merck) as a polymer material and 80% of TL205 (Merck) as a liquid crystal material were mixed and injected between two ITO substrates, and then cured for 3 minutes using 30mW / cm² ultraviolet light. At this time, the reaction temperature was maintained at 22 ° C. After preparing the polymer liquid crystal composite membrane, the light transmittance according to the wavelength was measured. Diaminodianthraquinone pigment is made into a size of 0.7μm and mixed with a binder such as acrylic ester, diluent such as acrylic monomer, photoinitiator such as benzophenone and solvent such as cyclohexanone so as to have a concentration of about 12%. Prepared to a thickness of 1.2 μm. The coated film was baked at 250 ° C. and then irradiated with ultraviolet light and photocured to form a color filter. The light transmittance of the glass plate in which the color filter was formed was measured. The said polymeric material was inject | poured between the glass plates in which the said color filter was formed, and contrast was measured.

Example 2

20% of PN393 (Merck) as a polymer material and 80% of TL203 (Merck) as a liquid crystal material are mixed and injected between two ITO substrates and cured for 3 minutes using 30mW / cm² ultraviolet light. At this time, the reaction temperature is maintained at 22 ° C. After preparing the polymer liquid crystal composite membrane, the light transmittance according to the wavelength was measured. After diaminodianthraquinone pigment is made into 0.8μm size, spin coating after mixing with binder such as acrylic ester, diluent such as acrylic monomer, photoinitiator such as benzophenone and solvent such as cyclohexanone to have a concentration of about 10% To a thickness of 1.2 μm. The coated film was baked at 250 ° C. and then irradiated with ultraviolet light and photocured to form a color filter. The light transmittance of the glass plate in which the color filter was formed was measured. The said polymeric material was inject | poured between the glass plates in which the said color filter was formed, and contrast was measured.

Comparative Example 1

A polymer liquid crystal composite film was prepared in the same manner as in Example 1. After diaminodianthraquinone pigment is 0.2μm in size and mixed with a binder such as acrylic ester, diluent such as acrylic monomer, photoinitiator such as benzophenone, and solvent such as cyclohexanone to have a concentration of about 20%, spin coating To a thickness of 1.2 μm. The coated film was baked at 250 ° C. and then irradiated with ultraviolet light and photocured to form a color filter. The light transmittance of the glass plate in which the color filter was formed was measured. The said polymeric material was inject | poured between the glass plates in which the said color filter was formed, and contrast was measured.

Comparative Example 2

A polymer liquid crystal composite film was prepared in the same manner as in Example 1. After diamino diantriquinone pigment is made into 0.2μm size, spin coating after mixing with a binder such as acrylic ester, diluent such as acrylic monomer, photoinitiator such as benzophenone and solvent such as cyclohexanone to have a concentration of about 15% To a thickness of 1.2 μm. The coated film was baked at 250 ° C. and then irradiated with ultraviolet light and photocured to form a color filter. The light transmittance of the glass plate in which the color filter was formed was measured. The said polymeric material was inject | poured between the glass plates in which the said color filter was formed, and contrast was measured.

Light transmittance and contrast measurements of the polymer liquid crystal composite membrane and the color filter of Examples and Comparative Examples are shown in Table 1 below.

Table 1

As shown in Table 1 above, when the particle size and concentration of the pigment were adjusted so that the light transmittance of the color filter was maintained at about 80% when the light transmittance of the polymer liquid crystal composite membrane during electric field application was 80% (Example 1 And Example 2) When the contrast of the screen is 30 or more and the quality of the image quality is good, but the light transmittance of the color filter is 80% or more (Comparative Example 1 and Comparative Example 2), the contrast of the screen is low to about 20-25, The quality of was bad.

The liquid crystal display device of the polymer liquid crystal composite according to the present invention has improved driving characteristics and no deterioration of the liquid crystal due to light absorption as compared with the conventional liquid crystal device, thereby improving display reliability and image quality. In addition, unlike conventional liquid crystal displays using three panels by separating incident light by wavelength, a liquid crystal display is simple and inexpensive by implementing a color display using one panel.

1 is a block diagram of a thin film transistor panel using a polymer liquid crystal composite,

2 is a graph showing the wavelength of light transmittance according to the wavelength of a conventional polymer liquid crystal composite,

3 is a graph showing the light transmittance according to the wavelength of the polymer liquid crystal composite of the present invention.

* Description of the main parts of the drawing

1: spacer 2: thin film transistor

3: liquid crystal mixture 4: sealing agent

5: ITO 6: Black Matrix

Claims (1)

In the liquid crystal display device in which an electrode layer, a thin film transistor, an electrode charge, a black matrix, and a color filter are formed on a first substrate, and a polymer liquid crystal composite is inserted between the first and second substrates. A liquid crystal display device having a liquid crystal composition of the polymer liquid crystal composite, wherein the color filter contains red pigment particles having a size of 0.5-1 μm at a concentration of 10-20%.