JPH01200327A - Projection type color liquid crystal display device - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Summary] Regarding a projection type color display device using a phase change type liquid crystal, the present invention aims to display color in a simple manner by using a plurality of electrode pieces constituting one side of a liquid crystal display panel. A projection type color liquid crystal display device is constructed by providing electrode terminals at both ends of each electrode piece, applying current between the electrode terminals of the required electrode pieces, and heating the electrode pieces to locally change the temperature of the liquid crystal.

[Industrial application field]

The present invention relates to a projection type color display device using a phase change type liquid crystal.

As a projection display method, twisted nematic effect (Twi
T using sted nematic effect)
N display is performed, but since it requires a polarizing plate, there is a large optical loss and it is difficult to obtain a bright display.

On the other hand, a nematic-cholesteric phase change type liquid crystal display is characterized in that it does not use a polarizing plate, so it can provide a bright and easy-to-see display, and it can provide a large-capacity display with a simple matrix configuration.

Next, the following two methods are known as projection type color display methods.

■ Method using RGB (Red-Green-Blue) filters.

■ A method in which the light that passes through different liquid crystal layers is mixed and projected onto a screen using an optical system.

Here, the method (2) has a problem in that when the image is projected onto a screen, the amount of projected light is less than 173 in the case of a monochrome image.

In addition, method (2) has the problem of increasing the size of the device and increasing costs.

Due to these reasons, none of them have been put into practical use.

[Conventional technology]

The inventors have been researching nematic-cholesteric phase transition type liquid crystal displays for some time, and have discovered that the light transmittance becomes wavelength-dependent due to diffraction and scattering caused by the helical structure of the cholesteric phase in the cloudy state of the liquid crystal. We have proposed a projection-type color display method using . (Patent Application No. 1986-194617, filed on August 7, 1988) The outline is as follows.

Figure 4 shows the display principle of a nematic-cholesteric phase change liquid crystal, with the horizontal axis representing the applied voltage and the vertical axis representing the light transmittance (non-scattered transmittance).

In other words, in a liquid crystal composition that is a mixture of nematic liquid crystal and cholesteric liquid crystal, when no voltage is applied or when the applied voltage is low, the liquid crystal assumes a cholesteric phase with a spiral molecular arrangement, and light is scattered and focused for projection. Since the light is scattered outside the lens, the light transmittance is low, resulting in a dark area on the screen.

Furthermore, when the voltage is high, the liquid crystal becomes a nematic phase in which molecules are aligned in the direction of the electric field, and the light enters the condenser lens without being scattered, resulting in a bright area on the screen.

The phase transition between the cholesteric phase and the nematic phase draws a hysteresis curve with respect to the applied voltage, as shown in the figure.

This indicates that optically different bistable states can be achieved with the same driving voltage (Vd), and this phenomenon is utilized to perform large-capacity displays.

Here, the inventors focused on the fact that scattering in the cholesteric phase in a bistable state is caused by the helical structure of the liquid crystal, but that light is diffracted by refractive index modulation corresponding to the helical pitch.

In other words, liquid crystal molecules have an elongated structure and have anisotropy in refractive index, so the refractive index is different where the liquid crystal molecules are aligned perpendicularly to the substrate and where they are aligned horizontally. .

Therefore, there is a refractive index modulation corresponding to the helical pitch, and a volume phase type diffraction grating is formed.

However, since there is some variation in the helical pitch and the direction of the helical axis is not constant, the light is scattered on wide concentric circles.

Here, the scattering efficiency η□ is approximated by the following equation under the condition of Black angle incidence.

W+sax=sin”(kπδ11d/λ)
・(1) However, δ, ... refractive index anisotropy d ... cell thickness λ ... wavelength of light As can be seen from equation (1), light transmittance has dependence on wavelength and cell thickness. Experimentally, the light transmittance changes periodically in the range of about 40% to about 2% in proportion to the increase in cell thickness, and the repetition period changes depending on the measurement wavelength.

The projection type color display method proposed by the inventors performs color display by utilizing the fact that images on a screen are colored due to the wavelength dependence of light transmittance.

However, it has been found that such color display is sensitively affected by the temperature of the liquid crystal forming the display device.

That is, the light transmittance of a cholesteritter nematic liquid crystal in a bistable state has not only wavelength dependence but also remarkable temperature dependence.

Therefore, in order to perform color display, the liquid crystal must be kept at a predetermined temperature and used for one cycle, which is a hassle.

[Problem to be solved by the invention]

As mentioned above, cholesteric in a bistable state
The problem is that the light transmittance of nematic liquid crystals has both wavelength dependence and remarkable temperature dependence, and temperature control is important for stable color display.

[Means to solve the problem]

The above problem is solved by providing electrode terminals at both ends of each of the plurality of electrode pieces that make up one side of the liquid crystal display panel, and by passing electricity between the electrode terminals of the required electrode pieces, the temperature of the liquid crystal increases as the electrode pieces are heated. This problem can be solved by a projection-type color liquid crystal display device that displays colors by locally changing the color.

[Effect]

The present invention uses the fact that the color of an image projected on a screen changes due to temperature changes to perform color display in a projection type liquid crystal display device.

- As an example, the temperature dependence of a cholesteric-nematic liquid crystal composition consisting of five components shown in FIG. 2 will be explained.

Among the components shown in FIG. 2, ethane, bicyclohexane, and biphenyl liquid crystals are nematic liquid crystals, and chiral nematic liquid crystals are cholesteric liquid crystals.

This mixed liquid crystal is mixed above the uniform edge transition temperature to create a phase transition type liquid crystal, which is injected into a liquid crystal cell with a panel thickness of 6 μm to create a cloudy liquid crystal panel. Light is incident vertically and the temperature of the liquid crystal is 10 to 50℃.
Figure 3 shows the results of measuring the three elements of color, Munsell saturation (purity), Munsell hue, and Munsell brightness (brightness), using a liquid crystal luminance meter while changing stepwise within the range.

The present invention takes advantage of the fact that the displayed color differs markedly depending on the temperature of the liquid crystal, and on the contrary actively changes the temperature of the liquid crystal to perform color projection display.

〔Example〕

FIG. 1 is a schematic diagram showing the structure of the electrodes of a liquid crystal display panel employing the segment method, and shows the structure of the upper electrode and the lower electrode.

Here, the electrode is composed of a transparent electrode made of a solid solution of 5yJ oxide (SnO 2, 2' are provided, and each electrode piece 1 is configured to be heated by passing current through the terminal 3, 3' which is patterned up to the electrode terminal 2, 2' of each electrode piece 1. It is.

Note that the driving voltage applied to each electrode piece 1 is
This is done between one of the terminals 3, 3' (for example 3) leading to the terminal 3 and the terminal 4 of the lower electrode which is the common electrode.

Then, a driving voltage (Vd) is applied between the electrode piece 1 to be displayed and the lower electrode, and at the same time, a current necessary for developing each color is passed through the electrode piece 1 to heat the electrode piece 1.

By using such a method, color display can be performed.

〔Effect of the invention〕

By carrying out the present invention, which performs color display by changing the temperature of the phase change liquid crystal, multicolor color projection display becomes possible with a simple method.

[Brief explanation of the drawing]

Figure 1 is a diagram of the electrode configuration of a liquid crystal panel. Figure 2 is the composition of the liquid crystal used. Figure 3 is the temperature dependence of projected display color. Figure 4 is the relationship between light transmittance and applied voltage for phase change type liquid crystal. Figure, is. In the figure, 1 is an electrode piece, 2.2' is an electrode terminal, 3.3
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Claims (1)

[Scope of Claims] In a projection type color display device using a phase change type liquid crystal, electrode terminals are provided at both ends of each of a plurality of electrode pieces constituting one side of a liquid crystal display panel, and the electrode terminals of the necessary electrode pieces are provided. 1. A projection type color liquid crystal display device, characterized in that a color display is performed by locally changing the temperature of a liquid crystal by applying electricity between the electrode pieces and heating the electrode pieces.