JPS5919325B2 - Guest/host liquid crystal display element - Google Patents

Description

[Detailed description of the invention] The present invention relates to a liquid crystal display element.

More specifically, a display cell is filled with a liquid crystal that undergoes a phase transition from a cholesteric phase to a nematic phase when an electric field is applied, to which a pleochroic dye is added, and the hue is controlled by applying an electric field. The present invention relates to a positive type guest-host liquid crystal display device. An object of the present invention is to obtain a clear display element with low power consumption. There are several display principles for liquid crystal displays. Among them, the ones that are in practical use are the DSM method, which utilizes the clouding phenomenon of liquid crystal due to the movement of ions in the liquid crystal, and the DSM method, which uses an electric field to twist-aligned liquid crystal molecules. This is an FEM method that aligns the cells and displays their state changes in brightness and darkness through a deflection filter.

Among these, the DSM method has a simple structure, but has the disadvantages that the display is difficult to judge, the drive voltage and power consumption are rather high, and the service life is not very long. Further, the FEM method is an excellent display method because it has a low driving voltage, extremely low power consumption, and has a long life, but it has the disadvantage that the viewing angle is narrow and the display is not very clear. Another problem was that although it had a clear threshold voltage, the rise was not very steep, so the response speed was not very fast.
Although conventional liquid crystal display methods, especially the FEM method, have certain advantages, they have shortcomings in viewing angle, clarity, responsiveness, etc., and there is a need for new display methods that improve these points. was.

The liquid crystal display element of the present invention satisfies these demands. The liquid crystal display element according to the present invention belongs to the so-called guest-host effect in principle.
The guest-host effect can be displayed in any color by selecting dyes, and the viewing angle can be widened. Furthermore, since the structure does not require a polarizing plate and has the same structure as the DSM method, it is easy to manufacture. The conventional guest-host effect used a nematic liquid crystal as the host.

Conventionally, a method for obtaining a positive display in a guest-host liquid crystal display device is to vertically align a liquid crystal with negative dielectric anisotropy, but there is no negative liquid crystal with large dielectric anisotropy, and the driving voltage is high. There was a drawback. On the other hand, the display of the present invention differs from the conventional guest-host effect in that a liquid crystal that undergoes a phase transition from a cholesteric phase to a nematic phase upon application of an electric field is used as a host. There are several methods for producing a liquid crystal exhibiting such a nematic cholesteric phase transition. For example, a nematic liquid crystal exhibiting optical activity is mixed into one nematic liquid crystal.

2.Cholesteric liquid crystal is mixed into nematic liquid crystal.

and so on.

In either case, the dielectric anisotropy of the resulting liquid crystal must be positive. A dye is added as a guest to this host liquid crystal, and the dyes shown in Table 1 are available as the dye. FIGS. 1 and 2 show the state in which the liquid crystal to which this dye has been added is sealed in a cell. FIG. 1a shows the case of encapsulation in a cell treated for homogeneous alignment, and FIG. 2a shows the case of encapsulation in a cell treated for homeotropic alignment. In either case, the liquid crystal has a helical structure, and the long axes of individual liquid crystal molecules are oriented in various directions, and the dyes mixed in the liquid crystal are oriented in various directions. absorbs light of a specific wavelength and becomes colored. Next, when an electrolytic voltage is applied to this liquid crystal layer, when the voltage exceeds a certain level, the liquid crystal layer enters a nematic liquid crystal state with a homeotropic alignment as shown in FIGS. 1b and 2b in both cases. At this time, the long axis of the dye is also oriented perpendicular to the substrate, so the color becomes invisible and becomes transparent. Electro-optical display is therefore possible. In this way, in the liquid crystal display element of the present invention, the voltage application part is transparent, so when forming transparent electrodes like in the conventional display element, the display pattern of numbers or letters is colored in the background.
Or the color of the reflector) will make it stand out. However, when using this method, the total amount of reflected light is small, so when actually viewed with the naked eye, the entire display appears dim, which is not very desirable. Therefore, in the present invention, the third
As shown in the figure or Fig. 4, by covering the area other than the display pattern with a transparent electrode and applying a voltage, the background is made colorless (or the color of the reflector), and the display pattern develops color and floats within it. The clarity is increased by making the display brighter. FIG. 3 shows a cross section of a portion where the transparent conductive film 1 of the display pattern section and the conductive film 3 as a lead on the opposite side of the substrate 2 are electrically connected by a conductive substance 4. .

Further, FIG. 4 shows a cross section passing through the display pattern part of a part other than the display pattern part 6 covered with a transparent conductive film 8 via a transparent or opaque insulating film 7. A feature is that the conductive film 6 and the transparent conductive film 8 form multilayer wiring. When driving a liquid crystal display cell with electrodes configured in this way, it was found that the conventional DSM or F
A brighter and clearer display was obtained compared to the EM type liquid crystal display cell.

In both FIGS. 3 and 4, the opposing electrodes do not need to have a display pattern, and may be formed by uniformly forming a conductive film on the surface of the substrate. In addition, the effect obtained is the same regardless of whether the electrode having the structure shown in FIGS. 3 or 4 or the counter electrode is placed on the front side of the display cell, and the polarizing plate is not required. It is possible to easily change the cell structure by using an opaque material with high reflectance on one side as a reflector, or using an opaque counter electrode treated to arrange liquid crystals in a homogeneous or homeotropic alignment as a reflector. . As mentioned above,
According to the present invention, a bright and clear display can be obtained, and the structure can be simplified with low power, which is of great value.

[Brief explanation of drawings]

Figure 1 A, b, a liquid crystal cell with homogeneous alignment. Figure 2 A, b, liquid crystal cell with homeotropic alignment. FIGS. 3 and 4 show cross sections of display pattern parts in the present invention. 1...Display pattern section, 2...
・Substrate, 3... Lead part, 4... Conductive material, 5, 8... Electrode provided to apply voltage to areas other than the display pattern part, 6... . . . Display pattern portion, 7 . . . Insulating film.

Claims (1)

[Claims] 1. A cholesteric liquid crystal material with positive dielectric anisotropy to which a pleochroic dye is added is filled between a pair of substrates held at a constant distance, and A transparent conductive film corresponding to the desired display pattern is formed on the surface, and by applying a voltage between the transparent conductive films, the liquid crystal molecules exhibit a nematic phase in which they are oriented perpendicularly to the electrode surface. In a guest-host liquid crystal display device that performs display by changing the direction of the colored dye and, as a result, changing the hue of the area to which an electric field is applied, a transparent conductive film is provided to apply voltage to areas other than the display pattern area. A guest-host liquid crystal display element characterized by: 2 A transparent conductive film is provided in a portion other than the display pattern portion, and a lead portion that applies an electric field to the back shadow portion and a voltage to the display pattern portion passes through the substrate and comes out to the back side, and is wired on the back side of the substrate. A guest-host liquid crystal display device according to claim 1. 3. The guest-host liquid crystal display according to claim 1, wherein a portion other than the display pattern portion is coated with an insulating film and a transparent conductive film, and the lead portion of the display pattern is a multilayer wiring. element.