JPS5934517A - Liquid crystal display device - Google Patents

Abstract

PURPOSE:To lessen the decrease in the writing grade in long-term use with reference to a liquid crystal display device utilizing the heat and electrooptic effect of a liquid crystal, by providing a heat sink consisting of metal on the rear of a substrate on a line electrode side. CONSTITUTION:While a liquid crystal display device using a thermotropic liquid crystal 62 changing from a smectic phase to a nematic phase and an isotropic state with an elevation in temp. has a large advantage, it has the disadvantage in that the entire part of the liquid crystal display panel heats up and decreases the display grade of picture quality upon long-term repetitive use. A heat sink consisting of metal is provided on the rear of the liquid crystal panel in order to lessen the elevation in the temp. Substrates 60, 61 consist usually of ordinary glass, and are joined to each other with a spacer 63. A metallic heat sink 64 is preferably larger in size than the substrate 60. While the above-mentioned liquid crystal display panel retains the initial writing grade of picture elements after 100,000 times, the conventional panel having no heat sink begins to lose the contrast in picture elements after 30,000 times.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a liquid crystal display device that utilizes the thermal and electro-optic effects of liquid crystal, and particularly relates to the structure of a liquid crystal display panel.

In recent years, supported by the development of semiconductor technology, information processing devices are rapidly becoming popular. Along with this, the demand for display devices as man-machine interfaces has also increased.
At the same time, the required performance is also becoming more sophisticated. Currently, CRTs have an overwhelming position as display devices that can meet these demands, but CRTs have a major drawback of being large in volume. In this respect, liquid crystal display devices have the advantage of being thin, but they have the disadvantage that it is difficult to increase basic display performance, such as display capacity (l), making it extremely difficult to compete with CRTs. Met.

The present invention relates to a liquid crystal display device based on a novel display method that overcomes the limitations of conventional liquid crystal display devices and has a high display capacity and high contrast. The display principle of the liquid crystal display device according to the present invention will be explained below.

FIG. 1 is a block diagram showing an example of the configuration of a liquid crystal display device according to the present invention. 11, 12, and 13 indicate row electrodes of the liquid crystal panel portion. 21, 22, and 23 indicate column electrodes. The two are substantially perpendicular to each other, and the intersection becomes a display pixel. The row electrode group and the column electrode group are each formed on the inner wall surface of a separate substrate, and are opposed to each other with a liquid crystal layer interposed therebetween. The substrate is omitted here. Further, in FIG. 1, there are only three row electrodes and three column electrodes for simplicity, but in reality, the number of these electrodes is usually larger depending on the display capacity required for the display device. The row electrodes are all connected at their right ends, so that they are usually all at the same potential. The column electrode group also includes column electrode drive circuits 41 and 4.
2 and 43, it is normally at the same potential as the row electrode group. Therefore, even in the liquid crystal layer sandwiched between the row and column electrodes,
Normally no electric field is applied.

There is a liquid crystal layer between the row electrode group and the column electrode group.

The liquid crystal used is a thermoto-3-robic liquid crystal which changes from a smectic phase to a nematic phase to an isotropic layer as the temperature rises. Further, the dielectric anisotropy of the liquid crystal must be positive. Examples of liquid crystals having such characteristics include [24 and 27 manufactured by BDH in the UK.

31 , 32 , and 33 are row electrode drive circuits, which are controlled by a row electrode drive control circuit 5 and a row electrode drive power supply 52
An electrical connection is made between the electrodes and each row of electrodes.

Column electrode drive circuits 41, 42, and 43 are controlled by a column electrode drive control circuit 53, and apply a signal from a column electrode drive power supply 54 to each column electrode, or apply a signal from a column electrode drive power supply 54 to the right end of a row electrode. This saves you the trouble of selecting whether to apply the same potential as.

Reference numeral 55 denotes a control circuit for the entire display apparatus, which receives and receives display data from a device external to p1, and performs a series of controls for displaying the data. A series of operations for actually performing the display will be explained below.

When the control circuit 55 receives a display command from an external device,
First, a symbol is output to the row electrode control circuit 51 to start driving the row electrodes. Upon receiving the request, the row electrode drive control circuit first puts the row electrode drive circuit 31 into an operating state.

As a result, a current flows through the row electrode 11 from the row electrode drive power source 52, generating heat, and the liquid crystal near the row electrode 11 is heated. Heating is continued for a sufficient period of time to bring the adjacent liquid crystal layer into an isotropic liquid phase. After this time has passed, the row electrode drive circuit 31 becomes inactive. At the same time, the V/c (-) row electrode drive circuit 32 becomes operational. Similarly, row electrode groups 11, 12, and 13 are driven in the same line sequential manner.

On the other hand, the temperature of the liquid crystal layer in the vicinity of the row electrode 11 that has been heated decreases, changing from an isotropic liquid phase to a nematic phase and a smectic phase. During this cooling, each pixel on the row electrode 11 is written. The data to be displayed is sent from an external device to the control circuit 55, and the control circuit 55
1 is being heated, the data of pixels on the row electrodes 11 is transferred to the column electrode control circuit 53. According to this data, the column electrode control circuit 53 controls the column electrode drive circuits 41 , 42 , 4
Control 3.

For example, when it is desired to turn on the pixel at the intersection with the column electrode 21, the column electrode drive circuit 41 applies the same potential as the right end of the row electrode. Then, no electric field is applied to the liquid crystal layer of the pixel at the intersection. When the temperature decreases in this state, the random state of the isotropic liquid phase is carried over to the smectic phase and stabilized. Such a random smectic phase exhibits a light scattering phenomenon and appears cloudy.

Further, for example, when it is desired to turn off a pixel at the intersection with the column electrode 22, the column electrode drive circuit 42 uses the column electrode drive power supply 54.
Apply a signal from Since the dielectric anisotropy of liquid crystal is positive,
When the liquid crystal layer is in the smectic phase, it becomes vertically aligned due to the electric field. When the temperature decreases to the sysmectic phase, the vertical alignment becomes stable. This state is transparent in appearance.

In this way, visually different states such as a cloudy state and a transparent state can be created, and display becomes possible. When the writing of the pixels on the row electrode 11 is completed by the above operations,
Thereafter, pixels on the row electrodes 12 and 13 are written in exactly the same manner.

The above is the display principle of the liquid crystal display device according to the present invention.

6. One of the advantages of the liquid crystal display device based on the above principle is that
The contrast of the display is essentially independent of the multiplicity of the multiplex drive.

This is a huge advantage compared to, for example, the conventional multiplex drive of twisted nematic liquid crystal display elements ('TN-LCD), in which the contrast ratio inevitably decreases as the multiplicity increases. .

However, on the other hand, problems that do not exist in conventional TN-LCDs also arise. One of these problems is that during long-term use, the temperature of the entire liquid crystal display panel increases and the pixel display quality deteriorates. This is due to the basic principle of the display device of the present invention, which requires heating every time a display is written. Moreover, the rate of temperature rise is high in the case of short repetition cycles.

The present invention has been made in consideration of these points, and is intended to reduce temperature rise by providing a heat sink made of metal on the back surface of a liquid crystal display panel.

Examples will be described below with reference to FIGS. 1 and 2. FIG. 2 is a sectional view showing the structure of the display panel of the liquid crystal display device of the present invention. 60 and 61 are substrates for holding the liquid crystal layer 62, which are usually made of transparent glass. 63
is a spacer that determines the liquid crystal layer thickness, and is 9.60, 61
964 connected via 63 is a metal heat sink,
Made of copper and copper alloys, aluminum and aluminum alloys, iron and iron alloys, which are inexpensive and have excellent thermal conductivity. Adhesives can be used to bond the glass substrate 60 and the metal heat sink 64, but an epoxy adhesive with good heat resistance is especially used. Further, the shape of the metal heat sink can be arbitrary, but it is desirable that it be larger than the glass substrate 60.

The liquid crystal display panel of the present invention obtained as described above and a conventional display panel that does not use a metal heat sink were filled with a mixed liquid crystal of 24 and 3Q manufactured by BDH, and the structure shown in FIG. 1 was obtained. Created a liquid crystal display device. Both row and column electrodes are closed. The row drive power supply 52 is 15V and the column drive power supply 54 is 20V.
When the writing quality of the pixels was compared by using a DC power supply for each row electrode and a heating time of 10 m8 per row electrode fin and writing between 8 and 108 ec, it was found that the structure of the present invention improved after 100,000 times. However, while the writing quality did not deteriorate, the pixel contrast of the conventional type without a heat sink began to deteriorate after 30,000 cycles.

As described above, the present invention aims to reduce the deterioration in writing quality during long-term use by providing a metal heat sink on the back surface of the display panel.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an example of the configuration of a liquid crystal display device according to the present invention. FIG. 2 is a sectional view showing an example of the structure of the display panel of the present invention. 11, 12, 13: Row electrodes 21, 22, 23: Column electrodes 31, 32, 33: Row electrode drive circuits 41, 42
, 43: Column electrode drive circuit 51: Row electrode drive control circuit 52: Row electrode drive power supply 53: Column electrode drive control circuit ~ 9-54: Column electrode drive power supply 55 2. Control circuit of liquid crystal display device 60. 61: Glass substrate 62: Liquid crystal 63 varnish spacer - 64: Metal heat sink or more Applicant: Suwa Seikosha Co., Ltd. Agent: Benri Toryu Kami-lr! −

Claims (1)

[Scope of Claims] At least a liquid crystal layer that changes from a smectic phase to a nematic phase to an isotropic liquid phase as the temperature rises, a pair of substrates sandwiching the liquid crystal layer, and one of the substrates. A group of row electrodes formed on the inner wall surface to generate heat as a current flows to heat a nearby liquid crystal layer, a row electrode drive circuit that supplies current to the group of row electrodes, and a group of row electrodes. A column electrode group is formed on the inner wall surface of the other substrate facing the substrate in a direction substantially perpendicular to the row electrode group, and a column electrode drive circuit that supplies display signals to the column electrode group. 1. A liquid crystal display device characterized in that a heat sink made of metal is provided on the back surface of the row electrode side substrate. 1-