JPH0580300A - Liquid crystal display device - Google Patents

Abstract

PURPOSE:To improve the reliability of the device by preventing the gradation in image quality in the initial period of use and during use and preventing the acceleration of the deterioration of a member disposed on the periphery and circuit while preventing the crytallization of a liquid crystal with the lower electric power consumption while the device is not used. CONSTITUTION:Temp. setting means 201, 203 by which the 1st set temp. to be used when the liquid crystal panel of the device is under use and the 2nd set temp. to be used when the liquid crystal panel is not in use are provided in the control circuit for controlling the heat generated by the plane heating element of the liquid crystal display device with the plane heating element and are used by changing over the 1st set temp. and the 2nd set temp. with a changeover means 205 according to whether the liquid crystal panel is under use or not in use.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display device having a flat heating element for controlling the temperature of a liquid crystal panel and a flat heating element control circuit. The present invention is particularly suitable for application to a liquid crystal display device using a ferroelectric liquid crystal.

[0002]

2. Description of the Related Art In recent years, a ferroelectric liquid crystal has been used for a liquid crystal display device having a large screen and a large capacity, in place of the nematic liquid crystal which has been frequently used. Ferroelectric liquid crystals have characteristics such as high-speed response and bistability, but also have the following characteristics that pose problems. Ferroelectric liquid crystals have a switching threshold value that changes significantly with temperature, and the lower the temperature, the slower the response speed. Ferroelectric liquid crystals have different structures depending on temperature and have a layered structure in the chiral smectic phase and have ferroelectricity, but in the low temperature region, the chiral smectic layer changes to a crystalline state. Once crystallized, it does not return to the original uniform layer structure even at room temperature and is not suitable for display.

Therefore, in order to solve the above problems, a liquid crystal display device having a flat heating element as shown in FIG. 5 has been conventionally used. In the figure, reference numeral 501 denotes a liquid crystal panel in which a ferroelectric liquid crystal is sealed, and an upper polarizing plate 502 and a lower polarizing plate 503 are fixed to both surfaces thereof via an adhesive,
It is supported on a support 509. Further, reference numeral 508 is a backlight for illuminating the liquid crystal panel 501 from the back side, and a flat heating element 505 is adhered and stuck to the surface thereof. The flat heating element 505 is formed by forming a transparent conductive layer on one surface of glass and providing extraction electrodes on both ends.
A circuit board 510 has a liquid crystal drive circuit and a planar heating element control circuit, and is connected to the liquid crystal panel 501 with leads 504.
Further, the lead 506 is connected to the flat heating element 505. The flat heating element control circuit of the circuit board 510 is the temperature detection element 5 attached to the liquid crystal panel 501.
The amount of heat generated by the flat heating element 505 is controlled by the signal from 07.

FIG. 3 shows an example of temperature characteristics of a liquid crystal scanning line writing frequency. The one scanning line writing frequency indicates the response speed of the liquid crystal, and the larger this value, the higher the image quality can be displayed. As can be seen from FIG. 3, the temperature characteristic of the liquid crystal has a tendency that the higher the temperature is, the higher the response speed becomes, and the image quality is improved. In order to fully exhibit the display capability of the liquid crystal display device, the flat heating element is controlled by setting a certain temperature to a set value.

[0005]

By the way, in the conventional liquid crystal device, in order to prevent the crystallization of the liquid crystal, the heater (planar heating element) is in the energized state even when the liquid crystal device is not in use, and the set temperature above a certain level is constantly maintained. Was kept at. Therefore, not only the liquid crystal but also the peripheral components and the electronic circuit that controls and drives the liquid crystal are constantly exposed to the same high temperature, which accelerates the deterioration of quality and shortens the life of the entire device. Was.

There is also a problem that a relatively large constant power is always consumed regardless of whether the display device is in use or not.

On the other hand, if the temperature is set lower by taking into consideration the reliability of the members and the control / driving circuit and the amount of power consumed by the heater, the response speed of the liquid crystal is reduced by that amount, and the image quality is deteriorated. Therefore, the ability of the liquid crystal display device cannot be fully exerted, and the original problem described above cannot be avoided.

The present invention has been made in view of the problems in the above-mentioned conventional example, and in a liquid crystal display device, the liquid crystal display device does not deteriorate in image quality at the initial use and during use, and consumes less power when not in use. It is an object of the present invention to provide a heating element control circuit capable of ensuring high reliability without accelerating the deterioration of members and circuits arranged in the periphery while preventing the crystallization of the heating element.

[0009]

In order to achieve the above object, in the present invention, two set temperatures are provided in a flat heating element control circuit of a liquid crystal display device with a flat heating element, and when the liquid crystal display device is used, the above-mentioned conventional method is used. The first set value set to the first temperature similar to the example is used, and the second set value set to a temperature lower than the first set temperature is used when not in use.

[0010]

According to the present invention, since the temperature of the liquid crystal is set high at the time of use, good image quality can be secured. Further, when not in use, the temperature of the liquid crystal is set to be low to suppress the heat generation of the flat heating element, so that it is possible to reduce the thermal stress on the members arranged around and the control drive circuit. It is possible to suppress the degree of circuit deterioration and ensure high reliability, and it is possible to prevent crystallization with less power consumption than during use.

[0011]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows the configuration of a liquid crystal display device according to an embodiment of the present invention. In FIG. 1, reference numeral 101 is a liquid crystal panel in which a ferroelectric liquid crystal is sealed, and an upper polarizing plate 1 is provided on both sides of the liquid crystal panel.
02 and the lower polarizing plate 103 are fixed to each other via an adhesive and are supported on the support base 109. Further, reference numeral 108 denotes a backlight for illuminating the liquid crystal panel 101 from the back side, and a flat heating element (heater) 105 is adhered and stuck to the surface thereof. The flat heating element 105 is formed by forming a transparent conductive layer on one surface of glass and providing extraction electrodes at both ends. A circuit board 110 has a liquid crystal drive circuit and a planar heating element control circuit, and is connected to the liquid crystal panel 101 by leads 104 and to the planar heating element 105 by leads 106. The planar heating element control circuit of the circuit board 510 controls the amount of heat generated by the planar heating element 105 based on a signal from the temperature detecting element 107 attached to the liquid crystal panel 101.

FIG. 2 shows the configuration of the planar heating element control circuit included in the circuit board 110 shown in FIG. Reference numeral 201 is a circuit for generating a signal corresponding to the first set temperature on the high temperature side, and the output signal (first set value signal) 201 is a signal from the temperature detection element 107 (FIG. 1) by the first comparator 202. Signal). Reference numeral 203 denotes a circuit for generating a signal corresponding to the second set temperature on the low temperature side, and an output signal (second set value signal) of the signal is generated by the second comparator 204 from the signal (temperature signal) from the temperature detecting element 107. Be compared. The comparison result by the first comparator 202 and the second
According to the comparison result by the comparator 204, one of them is selected by the selection circuit 205 according to the external signal, and the selected signal opens or closes the switch 206 of the flat heating element power supply.

According to experiments conducted by the present inventor, in the liquid crystal panel of this embodiment, practically sufficient image quality was obtained when the writing frequency for one scanning line was about 10 KHz or higher. FIG. 3 is a graph showing a temperature change in writing time of one scanning line of this liquid crystal panel. With reference to FIG. 3, it can be seen that in this liquid crystal panel, the image quality as a liquid crystal display device can be ensured by setting the liquid crystal temperature to 30 ° C. or higher in a low temperature environment.
That is, the temperature setting during use may be 30 ° C. Since the temperature rise due to the self-heating of the panel and the heating of the backlight is about 10 ° C, the temperature of the liquid crystal panel becomes 30 ° C or more when the environmental temperature exceeds 20 ° C, and the scanning line writing frequency exceeds 10 KHz. The image quality is improved.

The temperature when not in use is set in consideration of the temperature rise due to self-heating and the heat generation of the backlight and the allowable time to wait until the image quality is improved due to the temperature rise due to the heater. The increase was 15 ° C. At least one scanning line writing frequency that can be allowed at the beginning of use is 6KH
z is about 5 and the panel temperature for this is 17.5 ° C. is 5
It has been experimentally confirmed by the present inventor that it can be reached in about 5 minutes even in a temperature environment. FIG. 4 shows the time change of the liquid crystal panel temperature at the time of switching from the non-use state to the use state in this embodiment.

In this embodiment, there is a temperature difference of 15 ° C. between the set temperature when the liquid crystal display device is used and when it is not used. In the liquid crystal display device used in this embodiment, the temperature rise of the flat heating element required to raise the temperature setting of the liquid crystal panel by 1 ° C. is about 1 W, so that the flat heating element with the conventional single set temperature is used. It is possible to reduce the power consumption when not in use by about 15 W as compared with the control. In addition, resin materials are often used for supporting members and backlights of liquid crystal panels,
By lowering the set temperature when not in use by 15 ° C., deterioration of these resin materials due to heat can be prevented. In particular, the upper polarizing plate and the lower polarizing plate arranged in contact with the liquid crystal panel are weak against heat, and the present invention can remarkably improve the reliability.

[0017]

As described above, according to the present invention,
The image quality does not deteriorate in the initial stage of use, and the crystallization of the liquid crystal is prevented with low power consumption when not in use, and high reliability is ensured without accelerating the deterioration of peripheral components and circuits. It becomes possible.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a main part of a liquid crystal display device according to an embodiment of the present invention.

FIG. 2 is a configuration diagram of a control circuit for a planar heating element of the apparatus shown in FIG.

3 is a graph showing a temperature change in writing time of one scanning line of a liquid crystal panel used in the device of FIG.

FIG. 4 is a graph showing a temperature change of the liquid crystal panel when the apparatus of FIG. 1 is switched from a non-use state to a use state.

FIG. 5 is a cross-sectional view of a main part of a conventional liquid crystal display device incorporating a flat heating element.

[Explanation of symbols]

101: Liquid crystal panel, 105: Flat heating element, 107: Temperature detecting element, 110: Circuit board including control circuit for flat heating element, 201: First temperature setting signal generating circuit, 203:
Second temperature setting signal generation circuit, 202, 204: Comparator for comparing temperature setting signal and panel temperature signal, 20
5: a selection circuit for selecting one of the comparison results of the comparators 202 and 204, 206: a switch for a planar heating element power supply.

Claims (3)

[Claims] 1. A liquid crystal panel having a pair of substrates each having electrodes formed thereon and facing each other, and a liquid crystal disposed between the substrates, and a flat heating element provided near the panel. A liquid crystal display device comprising: a means for detecting the temperature of the panel; and a control circuit for comparing the output of the detecting means with a set temperature and controlling the heat generation amount of the heating element in accordance with the comparison result. Has a temperature setting means for setting, as the set temperature, a first set temperature used when the liquid crystal panel is in use and a second set temperature used when the liquid crystal panel is not in use, According to whether the liquid crystal panel is in use or not, the first set temperature and the second
A liquid crystal display device which is used by switching the set temperature of. 2. The liquid crystal display device according to claim 1, wherein the liquid crystal is a ferroelectric liquid crystal. 3. The liquid crystal display device according to claim 2, wherein the ferroelectric liquid crystal is a chiral smectic liquid crystal.