JPH02165122A - Liquid crystal light valve - Google Patents

Abstract

PURPOSE:To obtain the light valve which has a less secular change by switching the state of a ferroelectric liquid crystal at every prescribed time while the device is not in use. CONSTITUTION:The ferroelectric liquid crystal is crimped between substrates 1 and 2 having electrodes on opposite surfaces and a means of applying a prescribed voltage via the electrodes to the ferroelectric liquid crystal is provided. The state of the liquid crystal while this device is not in use is alternately switched at every prescribed time. Namely, the secular change of the characteristics of the ferroelectric liquid crystal panel begins to take place in about 3,000 hours and the matrix driving becomes infeasible in 1,000 hours according to experiment, but the characteristics change less and there is no influence on display if the stable state is switched within 300 hours. Only the stability of the state of the characteristics is improved in this way and the infeasibility of the display writing is prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a liquid crystal light valve having a ferroelectric liquid crystal as a liquid crystal layer, and a display device, a printing device, and an optical logic operator using the ferroelectric liquid crystal light valve. It is.

2. Prior Art Conventional ferroelectric liquid crystal light valves include, for example, the fifth
It consists of a liquid crystal panel and a drive circuit as shown in the figure. A pair of substrates with a transparent electrode, an electrical insulating film, and an alignment film on glass are separated by a spacer from 1.5 μm to 5 μm.
They are placed facing each other at a certain interval of about m, and ferroelectric liquid crystal is injected and aligned between them. As the alignment film, there are cases where a thin film made of an organic substance is formed and then subjected to a rubbing treatment, and cases where an inorganic substance such as SIO is vapor-deposited from an oblique direction. As described above, when the thickness of the liquid crystal layer is reduced, the helical structure originally possessed by the ferroelectric liquid crystal becomes stable in several states as shown in the schematic diagram of FIG. The liquid crystal molecules 60 shown with diagonal lines move on the side surface of the cone 61, FIG. 6(a)
5 (b) is a state in which the directions of the liquid crystal molecules are almost aligned, and at this time the spontaneous polarization is directed upward and downward to the normal line of the substrate.

FIG. 6(C) shows a state in which the liquid crystal molecules are twisted in the normal direction of the substrate, and there also exists a state in which the twisting direction is reversed.

Depending on the type of alignment film, the angle of inclination of the liquid crystal molecules on the substrate and the way the liquid crystal layer is bent may differ from Figure 6, but this schematic diagram basically represents the stable state of the liquid crystal molecules. Figures (a), (b), and (C) are plan views of the liquid crystals in Figures 6 (a) and (bL (c), respectively, viewed from the upper substrate. By sandwiching a liquid crystal cell between them, it is possible to create brightness and darkness using the --like states shown in Figures 7 (a) and (b).
When the liquid crystal molecules have a twisted structure as shown in Figure (C), the display becomes gray. A thin ferroelectric liquid crystal panel has such a stable state, and the transition between these states occurs very rapidly depending on the applied voltage, and the characteristics of the applied voltage and amount of transmitted light have a steep dark value. Show characteristics. Therefore, it is possible to obtain a high-capacity, high-contrast display using only electrodes in a simple matrix configuration, without providing a nonlinear element such as a thin film transistor.

The scanning side and signal side drivers are connected to this liquid crystal panel, and information is written to the panel using the voltage/timing control circuit and line memory.

Invention tries to solve! ! ! We found that if a ferroelectric liquid crystal panel is left in a stable state, the stability of the left state gradually increases and other states become unstable, making it impossible to write the display using matrix drive. The time it took for 0 display to become impossible, as determined by the experiment, was about 1000 hours, although it varied depending on the panel configuration, ie, the liquid crystal material, alignment film, etc. Such changes in properties over time have been observed in addition to our experiments, such as Yamanaka, Horiguchi, Kobayashi et al., "Electro-optical properties of ferroelectric liquid crystal elements subjected to current-carrying alignment treatment", Lecture at the 14th Liquid Crystal Symposium. There are also some reports in the preliminary lecture collection, page 133.

Once the changes described above occur over time, they cannot easily return to their original state.
The product lacks credibility.

Means for Solving the Problems In order to solve the above problems, the liquid crystal light valve of the present invention has a ferroelectric liquid crystal sandwiched between substrates having electrodes on opposing surfaces, and a predetermined voltage is applied to the liquid crystal light valve through the electrodes. By providing means for applying an electric current to the ferroelectric liquid crystal, and by alternating the state of the liquid crystal at predetermined time intervals when the device is not in use, the stability of the characteristic state is increased;
This prevents the display from becoming impossible to write.

Effect: According to our experiments, the characteristics of the ferroelectric liquid crystal panel begin to change over time after about 300 hours, and matrix driving becomes impossible after 1000 hours. If the stable state is changed every 300 hours, the change in characteristics will be small and there will be no effect on the display.In particular, in order to obtain high contrast display, it is necessary to change the stable state in a state in which the direction of the liquid crystal molecules in the normal direction of the substrate is almost uniform. It is preferable to switch between the states shown in Figure (a), [Yes].

Further, if a specific pattern is left written, the pattern may become fixed due to changes over time, so it is desirable to keep the state of all pixels constant.

EXAMPLE Hereinafter, a liquid crystal light pulp according to an example of the present invention will be explained with reference to the drawings.

FIGS. 2 and 3 are optical characteristic diagrams of a ferroelectric liquid crystal panel. The panel used was a ferroelectric liquid crystal matrix panel with a 2.5 pm thick surface electrified ferroelectric liquid crystal layer using ester-based 131x conductive liquid crystal. Then, an alignment film was formed. A voltage was applied to the panel with a fixed pulse width of 100 μs, and the brightness in the maintained state after the voltage application was finished was measured. Figure 2 shows the panel immediately after it was created, and Figure 3 shows the same panel with a dark display. 5
It is a characteristic diagram after being left for 00 hours. In Fig. 2, the dark value voltage from bright display to dark display and from dark display to bright display is about 15 volts, and at 14 volts, Fig. 7 (C1, (d)
It becomes a twisted state like , and takes an intermediate brightness. At this time, when the panel was driven using a matrix drive waveform as shown in FIG. 4, a display with a contrast of 20 was obtained. Fourth
In the figure, the horizontal axis is time, (a) in Fig. 4 is the scanning waveform, (b) in Fig. 4 is the signal voltage waveform, and (C) in Fig. 4 is the voltage waveform applied to the picture element. In Figure 4, (cut) is the brightness of the picture element.

Looking at the optical characteristic diagram of FIG. 3 when the dark display is left for 500 hours, the dark value voltage of the dark display increases and the dark value voltage of the bright display decreases. At this time, when driven using the driving method shown in FIG. 4, the bright display written during the selection period became distorted due to the crosstalk voltage, and the contrast decreased to about 1O. Furthermore, when the panel was left in a dark state for too long, the stable state was only a dark display, with no contrast at all.

However, when a ferroelectric liquid crystal panel with the same configuration is left unused and switched between bright and dark alternately within 300 hours, the dark value voltage changes only slightly from when the panel was made, and even after 3000 hours, the contrast in matrix drive remains about 20. Met.

Therefore, in the liquid crystal light valve of the present invention, by changing the left state of the liquid crystal panel for a predetermined period of 300 hours or less using the simple configuration shown in FIG. 1, the change in the liquid crystal panel over time is suppressed and the reliability is improved. It was very successful. When the switch 9 is on, power is supplied from an external power source or a storage battery 10, and data supplied from the outside via the line memory 7 is written to the liquid crystal panel by the drive circuits 5 and 6 by normal matrix driving. When the use is finished and switch 9 is turned off, the contents of the flag memory are checked.
After the screen is set to either bright or dark state, power supply to the drive circuit is stopped.

The timer counts the time or the elapsed time since the device was left unattended, and if it exceeds the specified time,
When the output 13 is turned on and the logical product 14 with the negative logic of the switch 9 is 1, the timing/voltage control circuit 8 drives the liquid crystal panel to display either bright or dark according to the data in the frang memory 12. The circuit is activated, and after the rewriting is completed, the drive circuit is stopped and the flag memory 12 is inverted. Since the response speed of ferroelectric liquid crystals changes depending on the temperature, the panel temperature is measured and the pulse width is adjusted appropriately depending on the temperature. With this configuration, even when the light bulb is not used for a long time, it can be used with just the power of the storage battery.
There was no deterioration of the display even under various environmental conditions for more than 1,000 hours.

If a highly reliable light valve as described above is used, it becomes possible to realize a high-speed and inexpensive printing device in addition to a display device, and a large-capacity parallel optical logic operator using a single layer of light valves.

Effects of the Invention The liquid crystal light valve of the present invention switches the state of the ferroelectric liquid crystal at predetermined intervals when the device is not in use, thereby producing a highly reliable ferroelectric liquid crystal light with extremely small changes over time. It provides a valve.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an embodiment of the present invention, and FIGS. 2 and 3 are optical diagrams of a ferroelectric liquid crystal panel. te sex diagram, figure 4 is matori,
FIG. 5 is a block diagram of a conventional ferroelectric liquid crystal panel, and FIGS. 6 and 7 are schematic diagrams of stable states of the ferroelectric liquid crystal. 3...Signal electrode, 4...Scanning electrode, 5
... Scanning measurement drive circuit, 6 ... Shinto side drive circuit, 8 ... Timing, voltage control circuit, 9 ... Switch 10 ...・Battery, 11...Timer, I2...Flag memory, 13...Temperature sensor Name of agent Patent attorney Shigetaka Awano 1 person Bad figure 13 - Digestion Zensar diagram diagram diagram diagram diagram 56--Saihyakuten diagram diagram (αp (b) 60--R6 欁chi

Claims (8)

[Claims] (1) A ferroelectric liquid crystal is sandwiched between substrates having electrodes on opposing surfaces, and means is provided for applying a predetermined voltage to the ferroelectric liquid crystal via the electrodes, and the device is not used by the means. A liquid crystal light valve characterized in that the state of the liquid crystal is alternately switched at predetermined time intervals. (2) A storage battery and a timer or counter are provided, and the timer or counter measures the predetermined time, and when the device is not in use, power is supplied from the storage battery to the voltage application means only when changing the state of the liquid crystal. The liquid crystal light valve according to claim 1, characterized in that: (3) Claim (1) characterized in that the state of the liquid crystal when the device is not in use is a memory state in which the directions of liquid crystal molecules are almost uniformly aligned, and all pixels are brought into the same state.
) LCD light bulb as described. (4) The liquid crystal light valve according to claim (2), wherein the electrodes on the opposing surfaces form pixels in a matrix. (5) The liquid crystal light valve according to claim (1), wherein the predetermined time is 1000 hours or less. (6) The liquid crystal light valve according to claim (1), wherein the predetermined time is 300 hours or less. (7) A printing device comprising the liquid crystal light valve according to claim (1), and comprising means for converting an image on the liquid crystal light valve into a latent image on paper or a resin film. (8) An optical logic operator comprising the liquid crystal light valve according to claim (1).