JPH09185031A - Liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make background color white in a color liquid crystal display device using birefringence effect by adding a dichroic dyestuff into a liquid crystal to allow the resulting liquid crystal layer to absorb light of specified wavelength and changing the absorption with the change in voltage value to be applied to the device. SOLUTION: In this display device, the product (Δn.d) of the refractive index anisotropy (birefringence, Δn) of a nematic liquid crystal 15 and the thickness (d) of a layer of the nematic liquid crystal 15 is adjusted to >=0.12μm and also, a dichroic dyestuff 17 is added to the nematic liquid crystal 15 in a 0.5 to 5wt.% ratio to the liquid crystal 15 to allow the resulting liquid crystal layer to absorb light of specified wavelength and to change the absorption by changing the voltage value to be applied to the device. At this time, the angle (made with the normal to the liquid crystal layer) of the major-axial direction of each of molecules of the dichronic dyestuff 17 added into the nematic liquid crystal 15, together with that of each of molecules of the liquid crystal 15, is changed with the change in voltage value applied to between electrode layers 12a and 12c and when the voltage is not applied, the absorption of light of specified wavelength by the liquid crystal layer becomes maximum and with the increase in applied voltage, the absorption is lowered. Thus, when the voltage is not applied, background color of the display can be made white.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thin liquid crystal display device used in systems such as computer terminals, image display devices and shutters.

[0002]

2. Description of the Related Art Conventionally, as shown in FIG. 3, in a thin display device, in this example, a liquid crystal display device, 11a and 11b are substrates made of glass, plastic or the like, and electrode layers 12a and 12b on the surface of which are oriented. Membrane layers 13a and 13b are provided. The electrode layer has a graphic pattern or a striped pattern for displaying characters and pictures. The alignment film is formed on almost the entire surface in contact with the liquid crystal material. The pair of substrates are installed so that the alignment film surfaces face each other. 14a and 14b are sealing agents for enclosing the liquid crystal 15. The liquid crystal 15 has a twisted helix structure of 180 degrees or more. A pair of polarizing plates 16a and 16b are provided outside the two substrates.

A driving voltage is applied to this liquid crystal display device,
Characters and pictures are displayed. The applied voltage is applied to the electrode layer 12
The potential difference between a and 12c is applied to the liquid crystal 15, and the angle of the liquid crystal material molecules changes. The liquid crystal device configured in this way is
Electrically Controlled B
Effect of irefence (RA Soref
and M.D. J. Rafuse, J. Appl. Phys
s. 43, 2029 (1972)), the refractive index anisotropy changes due to the angle change of the liquid crystal molecules controlled by voltage, and color display can be performed.

[0004]

However, when performing color display on the conventional liquid crystal display device, there is a problem that the background color is colored. Generally, a white background like copy paper is preferred. Therefore, an object of the present invention is to set a background color to white in a color liquid crystal display device using a birefringence effect in order to solve such a conventional problem.

[0005]

In order to solve the above problems, the present invention provides a product Δnd of the refractive index anisotropy Δn of a nematic liquid crystal and a thickness d of a nematic liquid crystal layer of 0.12 (μ
m) or more, a dichroic dye is added to the liquid crystal to absorb light of a specific wavelength, and the magnitude of the absorption is changed according to the magnitude of the voltage applied to the liquid crystal display device. Was added to the nematic liquid crystal in an amount of 0.5 to 5 (weight percent).

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION In a liquid crystal device configured as described above, a dichroic dye added to a nematic liquid crystal absorbs light of a specific wavelength to change the background color of the liquid crystal display device. You can

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a cross-sectional view illustrating the configuration of the liquid crystal display device of the present invention. Reference numerals 11a and 11b are substrates made of glass, plastic, or the like, on which electrode layers 12a and 12b and alignment film layers 13a and 13b are provided. ing. The electrode layer has a graphic pattern or a striped pattern for displaying characters and pictures. The alignment film is formed on almost the entire surface in contact with the liquid crystal material. The pair of substrates are installed so that the alignment film surfaces face each other. 14
Reference numerals a and 14b are sealing agents for enclosing the liquid crystal 15. A dichroic dye 16 is added to the liquid crystal 15. The liquid crystal 15 has a twisted helix structure of 180 degrees or more. A pair of polarizing plates 16a and 16a is provided outside the two substrates.
b is installed.

A driving voltage is applied to this liquid crystal display device,
Characters and pictures are displayed. The potential difference between the electrode layers 12a and 12c is applied to the liquid crystal 15, and the angle of the liquid crystal material molecules is changed by the voltage, so that display is performed. Reference numeral 17 is a dichroic dye added to the liquid crystal 15. The angle of the dichroic dye changes together with the nematic liquid crystal molecules depending on the applied voltage value. Absorption of a specific wavelength is maximum when no voltage is applied, and decreases as the voltage increases. Here, the measurement results of the liquid crystal display device according to the present invention will be described. FIG. 2 shows the chromaticity (x, y) of the transmitted light of the liquid crystal display device in this embodiment. In this case, the applied voltage is changed from no application to 2.5 (V
rms). The solid line shows the case of the liquid crystal display device of the present invention, and the dotted line shows the case of the conventional liquid crystal display device. Conventionally, it was separated from the white point (“x” in the figure) when no voltage was applied, but in the liquid crystal display device of the present invention, they are almost the same. As the voltage increases, the absorption by the dichroic dye decreases, and the difference in display color between the liquid crystal display device of the present invention and the conventional liquid crystal display device is almost eliminated. If the addition concentration of the dichroic dye is 0.5 (weight percent) or less, there is no effect, and if it is 0.5 (weight percent) or more, the dichroic dye cannot be completely dissolved in the nematic liquid crystal and there is a problem of precipitation.

The same effect can be obtained in the case of a liquid crystal display device having a retardation plate.

[0010]

The conventional liquid crystal display device has a problem that the background color is colored. As described above, the present invention has the effect of making the background color white.

[Brief description of the drawings]

FIG. 1 is an explanatory view showing a cross section of a liquid crystal display device of the present invention.

FIG. 2 is a graph showing the chromaticity of the display color of the liquid crystal display device of the present invention.

FIG. 3 is an explanatory diagram showing a cross section of a conventional liquid crystal display device.

[Explanation of symbols]

 11a, 11b Substrate 12a, 12b Electrode layer 13a, 13b Alignment film layer 14a, 14b Sealing agent 15 Liquid crystal 16a, 16b Polarizing plate 17 Dichroic dye

Claims (3)

[Claims] 1. A nematic liquid crystal having a positive dielectric constant anisotropy and an optical rotatory additive is enclosed between two substrates having a transparent electrode and an alignment film on their surfaces, the alignment films facing each other. Then, in a liquid crystal display device having a spiral structure twisted by 180 degrees or more in the thickness direction and having a pair of polarizing plates provided outside two substrates, the refractive index anisotropy Δn of the nematic liquid crystal and the nematic liquid crystal layer The product Δn · d of the thickness d is 0.12 (μm)
As described above, the liquid crystal device in which the dichroic dye is added to the liquid crystal. 2. The dichroic dye absorbs light of a specific wavelength,
The liquid crystal display device according to claim 1, wherein the magnitude of absorption changes depending on the magnitude of the voltage applied to the liquid crystal display device. 3. The liquid crystal display device according to claim 1, wherein the addition amount of the dichroic dye is 0.5 to 5 (weight percent) with respect to the nematic liquid crystal.