JPH02137816A - Liquid crystal display element - Google Patents

Abstract

PURPOSE:To make display of red disk colors so that the multicolor display is attained by specifying the product of the refractive index anisotropy and panel thickness of a nematic liquid crystal to a specific range. CONSTITUTION:Liquid crystal materials of a phase transfer type which are different in the product DELTAn.d of the refractive index anisotropy DELTAn and the panel thickness d are prepd. The hues in the display colors when a driving voltage is impressed are a linear relation when the relation is plotted by taking the DELTAn.d at the abscissa and the hue H deg. at the ordinate. The DELTAn.d of the range where the hue H deg. shows the red system colors (5R to 2.5RP hues in the Munsell system) shows an 800 to 950nm range. The product DELTAn.d of the refractive index anisotropy DELTAn and panel thickness d of the nematic liquid crystal is merely necessitated to be specified in the 800 to 950nm range in this way if the red system colors are desired to be obtd. as the colors to be projected and displayed. Since the display of the red system colors having a complementary color relation with a green is executed, the display of a black is possible as well. The multicolor display is thus obtd.

Description

[Detailed Description of the Invention] [Summary] An object of the present invention is to provide a liquid crystal display element capable of displaying red-based colors and realizing multi-color display. In a liquid crystal display element that utilizes the hysteresis loop of applied voltage and light transmittance drawn by a transition type liquid crystal, and selects and displays a transparent state and a cloudy state at the same voltage by changing the application conditions of the driving voltage,
The product of the refractive index anisotropy of the nematic liquid crystal and the panel thickness is 8
The wavelength is configured to be in the range of 00 to 950 nm.

[Industrial application field]

The present invention relates to a liquid crystal display element, and more particularly to a liquid crystal display element capable of displaying red-based colors.

In recent years, with the progress of office automation (OA), there has been a demand for liquid crystal display elements that perform projection-type display, and in such applications, for example, overhead projectors, slide projectors, etc. are used. However, rather than a projector that periodically changes information and displays it on a screen, there is a growing demand for a liquid crystal display element that inputs information in the form of a signal to the liquid crystal display element and can rewrite the content at will and display it on the screen. It's increasing.

[Conventional technology]

The conventional technology will be explained below.

As a projection type liquid crystal display, (1-1) the screen is bright and easy to see, (1-2) it can display a large screen with a large capacity, (1-3) the information can be rewritten,
(1-4) There is a demand for devices with performance such as being compact and inexpensive, and as a conventional projection type liquid crystal display element, TN (Twisted Nen+ati
c) Method, STN (Super Tiyisted)
Ne+watic) method and laser writing method are used, and projection type liquid crystal displays using these methods have been developed. However, TN system and ST
Since the N method requires a polarizing plate, there are problems in that light is cut by the polarizing plate, resulting in large optical loss, resulting in a dark screen, and in addition, the display capacity becomes small.

In addition, the laser writing method has the advantage of being able to solve the problem of the screen being dark and the display capacity being small, but since laser light is used to write on the liquid crystal panel, the laser light is directed at a predetermined position. An optical system having functions such as transfer is required, and this optical system becomes complicated and the device becomes large. Moreover, there is a problem that it is expensive, and it has not yet become popular.

Furthermore, in a projection type liquid crystal display, in order to perform color display, (2-1) RGB (Red GrB) is generally used.
A method of using a filter of een Blue),
Two methods are known: (2-2) a method in which light having different display colors transmitted through a plurality of liquid crystal panels is mixed by an optical system and projected onto a screen.

Here, in the method (2-1), since the RGB filter is used, the amount of projected light is reduced to less than 1/3, and a display with low contrast can only be obtained, and the resolution is also reduced to 1/3. be. In addition, with the method (2-2), it is possible to mix colors using a guichroic mirror, etc., but it requires filters to separate the colors and three liquid crystal panels for each color. There is a problem in that the device becomes larger and more expensive.

Therefore, the present inventors have been conducting research on nematic-cholesteric phase transition type liquid crystal display elements for some time. discovered that there is a wavelength dependence of light transmittance, and filed a patent application in 1983 for a projection color display system that utilizes this phenomenon.
This is proposed in the publication No.-194617.

Next, an outline of this projection type color display method will be explained.

Figure 5 is a diagram showing the display principle of a conventional liquid crystal display element, where the horizontal axis represents the applied voltage, and the vertical axis represents the light transmittance (unscattered transmittance) of incident light that has passed through the liquid crystal layer without being scattered. ). The liquid crystal here is a nematic-cholesteric phase transition type liquid crystal, and a chiral center (asymmetric carbon) is added to the nematic liquid crystal as a cholesteric liquid crystal.
It is a phase change type liquid crystal mixed with chiral nematic liquid crystal. When no voltage is applied or the applied voltage is low, this liquid crystal assumes a cloudy cholesteric phase with a spiral molecular arrangement, and the incident light is scattered and scattered outside the projection condensing lens. Therefore, less light passes through the condenser lens, resulting in a dark area on the screen.

On the other hand, when the applied voltage is high, the liquid crystal enters a transparent nematic phase state with molecules aligned in the direction of the electric field, and most of the incident light passes through 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 loop with respect to the applied voltage, as shown in FIG. By utilizing the hysteresis loop created by such an applied voltage vs. optical ratio curve, two states, a transparent nematic phase and a cloudy cholesteric phase, can be created at the same voltage (driving voltage Vd shown in FIG. 5), that is, an optical Two physically different states (transmission and scattering) can be stably obtained, and by utilizing this phenomenon, large-capacity display with no limit to the number of scanning lines is possible.

Here, the present inventors believe that in the cholesteric phase in a bistable state, there is refractive index modulation due to the spiral structure of the liquid crystal, and as a result, a type of diffraction grating is formed within the liquid crystal panel and light is diffracted. I focused on the points.

In other words, liquid crystal molecules have an elongated structure and there is anisotropy in the 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. are different. Therefore, in the scattering state, there is a refractive index modulation corresponding to the helical pitch of the liquid crystal, and a volume phase type diffraction grating is formed.

However, since the helical pitch varies to some extent and the direction of the fastening ring is not constant, the light is scattered on wide concentric circles.

Here, scattering efficiency is 1max (corresponding to light transmittance)
is approximated by the following equation under the condition of Bragg angle incidence.

ηIIIaχ=Sint (kπΔnd/λ)...
...(l,) where k is a constant, Δn is refractive index anisotropy,
d is the cell thickness and λ is the wavelength of light.

As can be seen from equation (1), the light transmittance (non-scattering transmittance), which corresponds to scattering efficiency, has a certain relationship with the wavelength of light, refractive index anisotropy, and cell thickness. Specifically, the light transmittance (He-Ne) increases by approximately 40% in proportion to the increase in cell thickness.
% to about 20%, and the cell thickness changes depending on the measurement wavelength so that the light transmittance becomes maximum or minimum.

The projection type color display system proposed by the present inventors utilizes such wavelength dependence of light transmittance to cause coloring in the image on the screen and perform color display.

[Problem to be solved by the invention]

However, although liquid crystal display elements using such projection color display methods utilize diffraction and scattering of liquid crystals, it is necessary to stack multiple liquid crystal panels with different display colors in order to perform multicolor display. Therefore, in order to perform color display, the present inventors have developed and proposed a liquid crystal material that can first display green, and then display other colors to achieve multicolor display. A liquid crystal material that can be used is needed. In particular, in order to perform the same display as a normal overhead projector, it is necessary to be able to display black, so the problem is that it must display a color that is complementary to the previously developed green color, that is, a color in the red family. was there.

Therefore, the present invention can display red-based colors,
The object of the present invention is to provide a liquid crystal display element that can realize multi-color display.

[Means to solve the problem]

In order to achieve the above object, the liquid crystal display element according to the present invention utilizes the hysteresis loop of applied voltage and light transmittance drawn by the nematic-cholesteric phase transition liquid crystal, and by changing the driving voltage application conditions, it can achieve a transparent state at the same voltage. In a liquid crystal display element that displays by selecting a cloudy state, the product of the refractive index anisotropy of the nematic liquid crystal and the panel thickness is 800.
950 nm.

[Effect]

The present invention is configured such that the product of the refractive index anisotropy of the nematic liquid crystal and the panel thickness is in the range of 800 to 950 nm.

Therefore, as shown in FIG. 2, the hue in the Munsell light color system falls within the range of 5R to 2.5RP, making it possible to display red-based colors.

〔Example〕

Hereinafter, the present invention will be explained based on the drawings.

1 and 2 are diagrams explaining one embodiment of a liquid crystal display element according to the present invention, FIG. 1 is a diagram showing the structural formula of a nematic liquid crystal used in the measurement of one embodiment, and FIG. is a diagram showing the relationship between Δnd shown in Table 1 and Ho shown in Table 2 in one embodiment.

First, the display conditions for a red-based color whose display color is complementary to green were determined as follows. This will be explained in detail below.

By newly mixing chiral nematic liquid crystal with a nematic liquid crystal whose main component is ethane-based liquid crystal as shown in Figure 1, five types of phase transition types with different product Δnd of refractive index anisotropy Δn and panel thickness d were created. Liquid crystal samples were prepared, and the driving voltage Vd, refractive index anisotropy Δn, and panel thickness d at 25"C were measured for each liquid crystal to determine the optical path difference. Table 1 shows the results.

Measured in Table 1. That is, L″a according to JIS-Z-8721
``b'' was determined, and Ho and C11 were calculated.

Table 2 shows the results. Here, L'' corresponds to lightness, Ho corresponds to hue (a measure of hue), and C1 corresponds to saturation.

Table 2 Next, the three elements of display color, brightness, hue, and saturation, are measured using a liquid crystal luminance meter (L
Table 2 shows the values of LゝH゛ and C''' for each of the five liquid crystals. , H”
(Hue) is -1 of lll15 than Nll of 65.0
It has changed significantly up to 06.2.

When plotted with Δnd on the horizontal axis and Ho on the vertical axis, it is shown that there is a linear relationship as shown in Figure 2, and Ho is in the range of red-based colors (5R in hue in the Munsell color system). ~2.5RP) Δnd is 800~
It was found that the wavelength was in the range of 950 nm. In the above embodiment, sample NQ4 can be displayed in a reddish color.

Therefore, if it is desired to obtain a red color as a projected display color, the product Δnd of the refractive index anisotropy Δn of the nematic liquid crystal and the panel thickness d should be in the range of 800 to 950 nm. Furthermore, since it is possible to display red-based colors that are complementary to green, black can also be displayed, making it possible to realize multi-color display.

In the above embodiment, the display conditions for red-based colors have been determined, but if the red-based colors are displayed under conditions that improve the saturation, the red-based colors can be displayed more preferably. This will be explained in detail below.

As shown in FIG. 3, a chiral nematic liquid crystal was newly mixed with a nematic liquid crystal mainly composed of ethane-based liquid crystal to prepare five types of phase transition type liquid crystal samples having different l group pitches.

Table 3 shows the relationship among the average refractive index n, panel d, L group pinch, and drive voltage Vd for each sample.

Table 3 Next, for each sample, the three elements of display color, brightness, hue, and saturation, were measured when driving voltage ■d was applied at 25°C. Table 4 shows the results. Here, Ll corresponds to brightness, Ho corresponds to hue, and C1 corresponds to saturation.

(This page, hereafter in the margin) Table 4 Also, FIG. 4 shows the relationship between the saturation C1 shown in Table 4 and the helical pitch. From Table 4 and Figure 4, sample size 1~
5, the brightness L''' and hue H° hardly change, but the saturation C6 improves as the spiral pinch becomes shorter.From Figure 4, Munsell color saturation is the best way to display red-based colors. It can be seen that the saturation is 4 or more (chroma C"16 or more), and the helical pitch should be 1.3 μm or less. For more favorable display, the helical pinch may be set to 0.8 μm or less.

Here, the reason why the condition for improving the saturation is defined as spiral is as follows.

In light scattering due to diffraction, it is known that the larger the diffraction efficiency, the higher the chroma, that is, the larger the value of the Q parameter expressed by the following equation, the higher the diffraction efficiency.

Q=2πλd/(nΔ”) ・−・(2) Here,
λ is the wavelength, d is the panel thickness, n is the average refractive index, and A is the spacing between the diffraction gratings.

From this equation (2), it can be seen that in order to increase the value of Q, it is effective to shorten the spacing (A) between the diffraction gratings, that is, the spacing between the helical pinches corresponding to the spacing between the diffraction gratings. Therefore, it is necessary to appropriately adjust the amount of chiral nematic liquid crystal mixed in the phase change liquid crystal to shorten the helical pitch (
Specifically, the problem can be solved by using a diameter of 1.3μ or less.

In each of the above embodiments, a case has been described in which an ethane liquid crystal is used as a nematic liquid crystal and a chiral nematic liquid crystal is used as a cholesteric liquid crystal constituting a nematic liquid crystal, but the present invention is limited to this. Specifically, for example, bicyclohexane-based liquid crystals, ester-based liquid crystals, etc. may be used as the nematic liquid crystal, and cholesteryl chloride, cholesteryl nanoate, etc. may be used as the cholesteric liquid crystal.

FIG. 4 is a diagram showing the relationship between the saturation C'' shown in Table 4 of another embodiment and the helical pitch, and FIG. 5 is a diagram showing the display principle of a conventional liquid crystal display element.

〔effect〕

According to the present invention, it is possible to perform display in red-based colors, and there is an effect that it is possible to realize multicolor display.

[Brief explanation of the drawing]

1 and 2 are diagrams explaining one embodiment of a liquid crystal display element according to the present invention. FIG. 1 is a diagram showing the structural formula of nematic liquid crystal used in the measurement of one embodiment, is a diagram showing the relationship between Δnd shown in Table 1 of one example and Ho shown in Table 2; FIG. 3 is a diagram showing the structural formula of the nematic liquid crystal used in the measurement of another example; Fig. showing the structural formula of the nematic liquid crystal used in the measurement of Other Example 3iIi Fig. showing the structural formula of the nematic liquid crystal used in the measurement of Other Example 9I Figure 4 shows the pitch relationship Figure 5 shows the display principle of a conventional liquid crystal display element

Claims (1)

[Claims] Utilizing the hysteresis loop of applied voltage and light transmittance drawn by a nematic-cholesteric phase transition type liquid crystal, by changing the driving voltage application conditions, a transparent state and a cloudy state can be selected and displayed at the same voltage. In a liquid crystal display element that performs
A liquid crystal display element characterized in that it is configured to have a wavelength in the range of 00 to 950 nm.