KR19990001276A - LCD and its manufacturing method - Google Patents

Abstract

Provided is a liquid crystal display device having excellent light efficiency by using a cholesteric polarizer and a liquid crystal layer whose phase difference is changed by λ / 2.

The method of manufacturing the liquid crystal display device includes the steps of providing first and second substrates, providing a cholesteric polarizer on the first and second substrates, and between the first and second substrates. Forming a liquid crystal layer for changing the phase difference of the light transmitted through by? / 2.

Description

LCD and its manufacturing method

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 using a liquid crystal layer which changes a phase difference by? / 2 with a cholesteric polarizer, and a manufacturing method thereof.

Liquid crystal display devices (Liquid Crystal Display device) is driven in a variety of operating modes, such as twisted nematic (TN) type, guest host (GH) type, and electrically controlled Birefringence (ECB) type.

1A and 1B illustrate a schematic structure of a general TN-LCD driven by NW display, in which a pair of transparent substrates, two polarizers having different polarization axes and attached to each substrate, and a liquid crystal layer therebetween. It consists of.

In the liquid crystal display having the above configuration, as shown in FIG. 1A, when no voltage is applied between the pixel electrode (not shown) and the counter electrode (not shown), the light (arrow) incident from the backlight (not shown) is removed. After filtering by one polarizer 10 and passing through the first substrate 11, the polarization direction is rotated by 90 ° by the TN-oriented liquid crystal molecules 14, and then passes through the second substrate 12. It is emitted through the polarizer 13. On the contrary, as shown in FIG. 1B, when a voltage is applied between the pixel electrode and the counter electrode, the incident light is filtered by the first polarizer 10 and passes through the first substrate 11, and then vertically in accordance with the application of the voltage. After passing through the second substrate 12 without changing the polarization state by the arranged liquid crystal molecules 14, the second polarizer 13 is blocked.

Conventional liquid crystal displays using two polarizers having different polarization axes have lowered light efficiency due to filtering of the polarizers. Therefore, recently, cholesteric polarizers that selectively reflect and transmit light have been used in liquid crystal display devices having very high light efficiency. The research is being actively conducted. One such attempt has been to replace the linear polarizer with a cholesteric polarizer and form a plate thereon that produces a phase difference of λ / 4. Such a liquid crystal display device is shown in FIG. Non-polarized light (arrow) incident through the backlight (not shown) passes through the cholesteric polarizer 114 while being converted into circularly polarized light while maintaining the amount of light as it is, Pass through 113). Thereafter, light linearly polarized by the thin plate 113 passes through the lower plate 111, the liquid crystal layer 115, and the upper plate 112, and then is blocked by the linear polarizer 110, or the linear polarizer 110 is blocked. It is emitted through. However, the liquid crystal display device is very advantageous in terms of light efficiency, but it requires a means for converting circularly polarized light into linearly polarized light, resulting in an increase in price due to the addition of process water.

The present invention is to solve the above-mentioned problems of the prior art, by using a liquid crystal layer that changes the phase difference between the cholesteric polarizer and the transmitted light by 90 degrees, without requiring a separate means for changing the phase difference light efficiency An object of the present invention is to provide a very high liquid crystal display device and a manufacturing method thereof.

In order to achieve the above object, the liquid crystal display device according to the present invention is a cholester that selectively reflects and transmits a light source, a pair of transparent upper and lower substrates, and light incident from the light source attached to each of the substrates. It consists of a liquid crystal layer which changes the phase difference of the light which is formed and transmitted between a Rick polarizer and said upper and lower substrates by 90 degrees.

In the liquid crystal display having the above-described configuration, unpolarized light incident through the backlight is converted into left-circular (or right-circular) polarized light while passing through the first polarizer, and passes through the liquid crystal layer through the first substrate. Thereafter, the right circularly polarized light by the liquid crystal layer is emitted through the second substrate and the second polarizer. Such a liquid crystal display device is very advantageous in terms of light efficiency, and does not require a means for converting circularly polarized light into linearly polarized light, thereby preventing a price increase due to the addition of process water.

In another embodiment of the present invention, there is provided a pair of parallel transparent substrates, a color filter for converting light transmitted and formed on one of the substrates into circularly polarized light, and a liquid crystal layer formed between the pair of substrates. When light is incident through the backlight, the light is passed through the color filter and becomes left circle (or right circle) polarized light. Such a color filter is a cholesteric color filter manufactured using a liquid crystal and a polymer, and the right circularly polarized light is selectively reflected by the characteristics thereof. The reflected right circle (or left circle) polarized light is again reflected by the backlight device and passes through the color filter as left circle (or right circle) polarized light. Eventually, the light projected from the backlight passes through the color filter. Subsequently, light passing through the color filter passes through the liquid crystal layer and is then emitted through the one substrate.

Such a color filter has a very high light efficiency compared to a conventional absorption type color filter.

1A and 1B are cross-sectional views showing a schematic structure of a typical TN-liquid crystal display device driven in a normally white (NW) display system.

Fig. 2 is a sectional view showing a schematic structure of a liquid crystal display device using a cholesteric polarizer and a λ / 4 retardation plate.

Fig. 3 is a cross-sectional view showing a schematic structure of a liquid crystal display device according to the present invention comprising a pair of cholesteric polarizers and a liquid crystal layer generating a phase difference of? / 2.

4 is a cross-sectional view showing a schematic structure of a liquid crystal display device according to the present invention comprising one cholesteric polarizer and a cholesteric color filter.

-Explanation of symbols for the main parts of the drawing-

211: first substrate 214: first polarizer

212: second substrate 210: second polarizer

215: liquid crystal layer 313: cholesteric color filter

Hereinafter, the configuration and operation of the liquid crystal display device according to the present invention will be described in detail with reference to the drawings.

3 is a view showing a liquid crystal display device according to the present invention, which is attached to a transparent first substrate 211 and a second substrate 212 and the first substrate 211 and is a backlight (not shown). A first cholesteric polarizer 214 (hereinafter referred to as a first polarizer) that selectively reflects or transmits light incident therefrom, and selectively reflects or transmits incident light attached to the second substrate 212. Liquid crystal layer 215 for changing the phase difference between the second cholesteric polarizer 210 (hereinafter referred to as a second polarizer) and the first and second substrates 211 and 212 to be transmitted by 90 °. It is composed of

Subsequently, the operation of the liquid crystal display device having the above-described configuration will be described. The unpolarized light (arrow) incident through the backlight passes through the first polarizer 214 and is changed to the left (or right) polarized light while maintaining the amount of light as it is, and then through λ / 2 through the first substrate 211. The liquid crystal layer 215 passes through the liquid crystal layer 215 for changing the phase difference. Thereafter, the right circularly polarized light by the liquid crystal layer 215 is emitted through the second substrate 212 and the second polarizer 210. At this time, if the second polarizer 210 is a polarizer that transmits only the left circularly polarized light, the display mode is NB (Normarry Black), and if the polarizer is a polarizer that transmits only the right circularly polarized light, the display mode is NW (Normarry White). The condition for changing the phase difference of the light transmitted through the liquid crystal layer 215 by λ / 2 may be satisfied using u = 2d · (Δn / λ). Where u is the compensation factor, d is the thickness of the liquid crystal layer, Δn is the refractive index anisotropy, and λ is the wavelength of incident light.

The liquid crystal display device using the cholesteric polarizer and the liquid crystal layer that changes the phase difference of λ / 2 is very advantageous in terms of light efficiency, and does not require any means for changing circularly polarized light into linearly polarized light. Additional price hikes can be prevented.

4 is a view showing another embodiment of the present invention, in which the apparatus is formed on (or irrelevant to, if formed on, the second substrate) the first substrate 311 and the second substrate 312 and the second substrate. A color filter 313 for changing the light into circularly polarized light, a cholesteric polarizer 314 formed on the second substrate 312, and between the first substrate 311 and the second substrate 312. And a liquid crystal layer 315 for converting the phase difference of the light transmitted and transmitted by? / 2.

In operation of the liquid crystal display having the above-described configuration, first, when light (arrow) is incident through a backlight (not shown), the light becomes a left circle (or right circle) polarized light while passing through the color filter 313. The color filter 313 is a cholesteric color filter manufactured by using a liquid crystal and a polymer, and the right or left polarized light is selectively reflected by the characteristics thereof. The reflected right circle (or left circle) polarized light is again reflected by the backlight device and passes through the color filter as left circle (or right circle) polarized light. As a result, the total amount of light incident from the backlight passes through the color filter 313. Subsequently, the left circle (or right circle) polarized light passing through the color filter 313 is polarized to the right circle (or left circle) after passing through the liquid crystal layer 315, and thus, the second substrate 312 and the cholesteric polarizer. 314 is emitted.

In the manufacturing method of the above-mentioned color filter, first, a material mixed with a liquid crystal and a polymer is mixed at an appropriate ratio and cured by ultraviolet irradiation, and then the liquid crystal and the polymer are made using the difference in the polymerization reaction rate and the diffusion rate of the liquid crystal. Has a partitioned internal structure. In addition, the wavelength region selects the wavelength region corresponding to each of R, G, and B, and adjusts the conditions such that a pitch gradient occurs within the same wavelength. Such a color filter has a very high light efficiency compared to a conventional absorption type color filter.

According to the liquid crystal display device according to the present invention, there is provided a means for converting circularly polarized light into linearly polarized light by forming a liquid crystal layer which varies the phase difference between at least one cholesteric polarizer and transmitted light by λ / 2. It is possible to maximize the light efficiency without the need.

In addition, by forming the polarizer and the cholesteric color filter in a single layer, the number of processes can be reduced to lower the manufacturing cost.

In addition, since the cholesteric color filter is installed on one substrate instead of the cholesteric polarizer, only one polarizer may be used, thereby reducing the manufacturing cost by reducing the number of processes.

Claims (12)

The first and second substrates, A cholesteric polarizer formed on the first substrate and the second substrate and filtering the transmitted light; And a liquid crystal layer for changing a phase difference of light transmitted between the first substrate and the second substrate by λ / 2. The liquid crystal display device of claim 1, wherein the material constituting the cholesteric polarizer is a material in which a polymer and a liquid crystal are mixed. The first and second substrates, A cholesteric color filter layer formed on the first substrate and filtering light transmitted therethrough; A cholesteric polarizer formed on the second substrate and filtering the transmitted light; And a liquid crystal layer for changing a phase difference of light transmitted through the color filter layer by λ / 2. 4. The liquid crystal display device according to claim 3, wherein the cholesteric color filter layer is formed on the second substrate, and the cholesteric polarizer is formed on the first substrate. The liquid crystal display device according to claim 3, wherein the material constituting the color filter layer is a mixture of a polymer and a liquid crystal. 4. The liquid crystal display device according to claim 3, wherein the color filter layer is formed by a difference between a polymerization reaction rate of a polymer and a diffusion rate of a liquid crystal. Providing first and second substrates, Providing a cholesteric polarizer on the first substrate and the second substrate; And forming a liquid crystal layer which varies the phase difference of the light transmitted between the first substrate and the second substrate by λ / 2. The method of claim 7, wherein the material constituting the cholesteric polarizer is a material in which a polymer and a liquid crystal are mixed. Providing first and second substrates, Forming a cholesteric color filter layer filtering light transmitted through the first substrate; Forming a cholesteric polarizer for filtering light transmitted through the second substrate; And forming a liquid crystal layer for changing the phase difference of the light transmitted through the color filter layer by λ / 2. The method of claim 9, wherein the cholesteric color filter layer is formed on the second substrate, and the cholesteric polarizer is formed on the first substrate. The method of claim 9, wherein the material constituting the color filter layer is a mixture of a polymer and a liquid crystal. The method of manufacturing a liquid crystal display device according to claim 9, wherein the color filter layer is formed by a difference between a polymerization reaction rate of a polymer and a diffusion rate of a liquid crystal.