JPH06258619A - Liquid crystal display device - Google Patents

Abstract

PURPOSE:To prevent the steepness of light transmissivity-applied voltage characteristics at a low temperature from decreasing with respect to the two- layered type STN liquid crystal display device which uses liquid crystal cells for display and liquid crystal cells for optical compensation. CONSTITUTION:The liquid crystal cells for optical compensation are provided with heating means 30 and 40 and heated so that the liquid crystal cells (3, 4, and 12) for optical compensation are nearly equal to in temperature or higher than the liquid crystal cells for display. Consequently, the difference in nd between the liquid crystal cells for display and liquid crystal cells for optical compensation is controlled to prevent the steepness of the light transmissivity- applied voltage characteristics at a low temperature from decreasing.

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 of STN type, which is constructed by using a liquid crystal cell for optical compensation.

[0002]

2. Description of the Related Art Liquid crystal display devices using liquid crystals have been put to practical use in various fields such as office automation equipment, liquid crystal televisions, and liquid crystal viewfinders. Among these liquid crystal display devices, the STN type liquid crystal display device in which the twist angle of liquid crystal molecules is large is widely used as a display device capable of high contrast.

When the voltage is applied to the liquid crystal cell of the negative type liquid crystal display device to change the transmittance, the maximum transmittance is 100%.
And the voltage showing 50% transmittance is V50, and the transmittance is 1
If the voltage indicating 0% is defined as V10, V50 / V10
The ratio is the steepness of the electro-optical characteristics (hereinafter simply referred to as steepness)
Represents an index indicating the degree of. If this ratio is small, the steepness is high.

S with a liquid crystal molecule twist angle of 180 ° or more
The TN type liquid crystal display device has a T angle of 90 °.
The steepness is higher than that of the N-type liquid crystal display device, and the number of scanning electrodes can be increased without sacrificing contrast. Further, the improvement of the steepness leads to the improvement of the on-display transmittance in the time-division driving, and a bright display screen can be obtained.

However, the STN type display liquid crystal cell is colored by the birefringence action, and therefore an optical compensating member must be used together in order to eliminate this coloring. The coloring phenomenon is related to the retardation value (hereinafter referred to as Δnd) which is the product of the birefringence Δn of the liquid crystal substance and the thickness d of the substance.
An optical compensating member is used to compensate for the above.

The retardation value of the liquid crystal cell for display is Δn
d1 and the retardation value of the optical compensation member is Δnd
If (Δnd1-Δnd2) is defined as Δnd difference as 2, the coloring phenomenon can be compensated by reducing this Δnd difference, but if the Δnd difference is reduced, the steepness tends to decrease. , Usually set to an appropriate positive value.
That is, the Δnd difference is set in a range such that (Δnd1−Δnd2)> 0.

As described above, the optical compensating member has the property of changing the steepness of the light transmittance-applied voltage characteristic of the liquid crystal display device while simultaneously compensating the color of the display liquid crystal cell. By setting the nd difference to an appropriate value, it is possible to obtain a high-quality display device having high steepness and no coloring.

As the optical compensating member, an optical compensating liquid crystal cell or a retardation film is used. However, the retardation film does not have twist like liquid crystal molecules or has a small wavelength dispersion property. The degree of optically compensating the display liquid crystal cell is not sufficient as compared with the liquid crystal cell.

On the other hand, the STN type liquid crystal display device generally requires a time required for switching the screen display (hereinafter referred to as a response time).
Tends to be slow. This tendency becomes more remarkable as the twist angle of the display liquid crystal cell increases.

Moreover, the response time of the liquid crystal cell has temperature dependency, and it tends to be faster at higher temperatures but slower at lower temperatures, so that it can be used at room temperature but has satisfactory response time characteristics at low temperatures. In many cases, it will not be obtained. Since the response time is related only to the temperature dependence of the display cell, raising the temperature of the display liquid crystal cell is one of the effective means for solving the above problem.

The conventional example for raising the temperature of the liquid crystal cell for display is
Japanese Utility Model Laid-Open No. 59-156225 or JP-A-61
-47933. Actual development Sho 59-1562
No. 25, the liquid crystal display for display is formed by forming a resistance layer on the surface of the upper substrate and the surface of the lower substrate of a TN type liquid crystal display element for display, and supplying a current to at least one of the resistance layers. An example of heating the element is shown. Further, Japanese Patent Laid-Open No. 61-47933 discloses an example in which a heater is provided on the back surface of a liquid crystal display element for display for the purpose of correcting the transmittance due to the visual angle difference.

FIG. 5 shows an ST using a conventional retardation film.
FIG. 11 is a cross-sectional view showing an N-type liquid crystal display device using the above-described conventional technique. The substrates 1 and 2 are adhered with a sealant 5 while keeping a constant space with a spacer 9 made of a transparent glass fiber, a resin ball or the like, and a liquid crystal 11 is enclosed in the liquid crystal 11 (hereinafter referred to as a display cell). ) Get. The substrate 1 of the display cell is provided with a heating unit 30 and a polarizing plate 32, and the substrate 2 is provided with a heating unit 3.
0, the retardation film 31, and the polarizing plate 32 are provided to constitute a liquid crystal display device. Actually, on the substrates 1 and 2, an electrode layer for applying a voltage to the liquid crystal 11, an alignment layer for aligning the liquid crystal 11, and a color filter layer as necessary are formed. Omitted. When the ambient temperature of the liquid crystal display device becomes low, the heating means 30 heats the substrates 1 and 2 of the display cell to raise the temperature of the liquid crystal 11, and the temperature dependence of the display cell is used to increase the temperature of the liquid crystal. It is possible to prevent the response time of the display device from increasing.

Next, FIG. 6 is a cross-sectional view showing an STN type liquid crystal display device using a liquid crystal cell for optical compensation instead of the retardation film 31 shown in FIG. is there. The substrate 1 of the display cell in FIG. 6 is provided with the heating means 30 and the polarizing plate 32, and the substrate 2 is provided with the heating means 30.

On the other hand, in the optically compensating liquid crystal cell (hereinafter referred to as compensating cell), the substrates 3 and 4 on which an alignment layer (not shown) for orienting the liquid crystal 12 is formed are spacers 10 such as glass fibers and resin balls. The sealant 6 is adhered to the substrate 4 while maintaining a constant interval, and the liquid crystal 12 is sealed therein, and the polarizing plate 32 is arranged on the substrate 4. Then, the display cell and the compensation cell are arranged so as to overlap each other to form a liquid crystal display device. In this case, the compensation cell does not apply a drive voltage, so
Unlike the display cell, no electrode layer is provided.

In the liquid crystal display device of FIG. 6, since the response time is related only to the temperature dependence of the display cell, when the ambient temperature becomes low, the substrates 1 and 2 of the display cell are heated by the heating means 30 to cause the liquid crystal display. By increasing the temperature of only 11, it is possible to prevent an increase in response time as in the case of the liquid crystal display device using the retardation film shown in FIG.

[0016]

However, in the liquid crystal display device using the compensation cell of FIG. 6, when the temperature of only the liquid crystal 11 is raised by the heating means 30 formed in the display cell to reduce the response time, Responsiveness is improved, but other problems arise.

That is, the birefringence Δn of the liquid crystal substance has temperature dependence, and in general, the change of Δn of the liquid crystal with temperature tends to be small when the temperature rises and large when the temperature falls. Therefore, when only the display cell is heated by the heating means 30 having the configuration shown in FIG. 6 at a low temperature, the change in Δnd1 of the display cell is small and the heating means 3 is used for the compensation cell.
Since 0 is not provided, Δnd2 maintains the low temperature state.
Therefore, the Δnd difference between the display cell and the compensation cell, that is, (Δnd1−Δnd2), becomes small, and the steepness decreases. As a result, there arises a problem that the screen display becomes dark due to the decrease in the transmittance in the on-display, or the contrast is lowered when trying to maintain the brightness.

Further, when the response is not a problem, it is not necessary to provide the heating means 30 in the display cell. In this case, since the Δnd difference between the display cell and the compensation cell does not change, the steepness also changes. Should not. However, in reality, the steepness tends to decrease due to the temperature characteristics of the physical constants other than Δnd of the liquid crystal substance.

Therefore, an object of the present invention is to solve the above problems and control Δnd2 of the liquid crystal cell for optical compensation at a low temperature to prevent the steepness of the light transmittance-applied voltage characteristic from decreasing.
An object is to provide a liquid crystal display device capable of displaying high-quality images.

[0020]

Means for solving the problems used by the present invention to achieve the above object are as follows: the temperature of the display cell and the compensation cell are substantially equal to each other, or the temperature of the compensation cell is the temperature of the display cell. It is to heat so that it will be higher than.

[0021]

If the display cell and the compensating cell are heated so that their temperatures are substantially equal to each other, the Δnd difference does not change, so that the steepness can be prevented from lowering. If the temperature of the compensating cell is heated to be higher than that of the display cell, the Δ
It is possible to compensate for the decrease in steepness due to the temperature characteristics of physical property constants other than nd.

[0022]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a sectional view showing the configuration of the first embodiment of the present invention. The display cell is configured by bonding the substrates 1 and 2 with a sealant 5 while keeping a constant space with a spacer 9 made of transparent glass fiber, resin balls or the like, and enclosing a liquid crystal 11 therein. Actually, an electrode layer for applying a voltage to the liquid crystal 11, an alignment layer for orienting the liquid crystal 11, and a color filter layer, etc., are formed on the substrates 1 and 2, if necessary, but not shown for simplicity. To do. Compensation cell is liquid crystal 1
Substrates 3 and 4 on which an alignment layer (not shown) for orienting 2 is formed are bonded with a sealant 6 while keeping a constant distance with a spacer 10 such as glass fiber or resin balls,
The liquid crystal 12 is enclosed in the structure. And the substrate 1
A liquid crystal display device is configured by arranging a display cell provided with a heating unit 30 and a polarizing plate 32 thereon and a compensation cell provided with a heating unit 40 and a polarizing plate 32 on the substrate 4 so as to overlap each other.

In the embodiment of FIG. 1, when the ambient temperature becomes low, the display cell and the compensation cell are heated by the heating means 30 and the heating means 40 to raise the temperature of the liquid crystals 11 and 12. As the temperature rises, the response time of the display cell becomes faster. At this time, Δn of the liquid crystal 11 becomes small and Δn
Although nd1 decreases, Δnd2 also decreases because the temperature of the liquid crystal 12 in the compensation cell also increases at the same time. Therefore, the .DELTA.nd difference between the display cell and the compensation cell hardly changes, so that the steepness of the light transmittance-applied voltage characteristic in the liquid crystal display device can be maintained.

In FIG. 1, the display cell heating means 30 may be either the substrate 1 or the substrate 2, and the compensation cell heating means 40 may be either the substrate 3 or the substrate 4. . These settings are heating means 30,
The heating capacity of the heating means 40 should be taken into consideration.

FIG. 2 is a sectional view showing the structure of another embodiment of the present invention. In FIG. 2, the heating means 50 is provided between the display cell and the compensation cell so as to simultaneously heat the display cell and the compensation cell. In this embodiment, at least one of the display cell heating means 30 and the compensation cell heating means 40 can be omitted.

FIG. 3 is a sectional view showing the structure of still another embodiment of the present invention, which has a structure in which the heating means 40 is provided only in the compensation cell in order to prevent the steepness from being lowered due to the low temperature. It is a liquid crystal display device. In FIG. 3, only one of the heating means 40 can be used.

In FIG. 3, the heating means 40 is used at a low temperature.
Thereby heating the compensation cell to raise the temperature of the liquid crystal 12. Along with this, the Δn of the liquid crystal 12 becomes smaller, and the Δnd2 of the compensation cell also decreases. On the other hand, △ of the display cell
Since n does not change, Δnd1 of the display cell does not change.
Therefore, a change occurs such that the Δnd difference between the display cell and the compensation cell becomes large, and the steepness of the light transmittance-applied voltage characteristic due to the temperature characteristic of the physical constant other than the Δnd difference is prevented from decreasing. Can be done.

In the embodiment based on FIGS. 1, 2 and 3, it is desirable that the heating degree of the heating means 30, 40, 50 for raising the temperature of the display cell and the compensation cell can be automatically controlled. For that purpose, it is necessary to use a temperature sensor to detect the temperature of the display cell or the compensation cell or the ambient temperature. In the embodiment based on FIGS. 1 and 2, the display cell temperature for detecting the temperature of the display cell is used. It is desirable to provide separate compensation cell temperature sensors that sense the temperature of the sensor and the compensation cell.

FIG. 4 is a block diagram of heating control showing an embodiment of the present invention, in which a display cell temperature sensor 63 for detecting the temperature of the display cell and a compensation cell temperature sensor 64 for detecting the temperature of the compensation cell are separately provided. , Display cell temperature sensor 6
3 and the compensation cell temperature sensor 64 are connected to the heating control means 61, and the heating control means 61 is connected to the display cell temperature sensor 63.
The display cell is heated by energizing the heating means 30 for the display cell on the basis of the temperature information from the compensator, and the compensation is performed by energizing the heating means 40 for the compensation cell on the basis of the temperature information from the compensation cell temperature sensor 64. Heat the cell. The heating means 50 shared by the display cell and the compensation cell is controlled based on temperature information from the display cell temperature sensor 63 and / or the compensation cell temperature sensor 64.

Of course, when heating only the compensation cell as in the embodiment of FIG. 3, the display cell temperature sensor 63 is not necessary, and only the heating means 50 shared by the display cell and the compensation cell in the embodiment of FIG. 2 is used. When providing, only one common temperature sensor may be used.

When the liquid crystal display device is driven by a battery, it may be desirable to limit the electric power for heating in order to extend the operation time. It is desirable to provide a heating setting means for such a purpose. Heating setting means 6 in FIG.
2 is, for example, to set a heating temperature, or heating means 30, 40
Alternatively, among 50, it is possible to set only specific heating means to operate, or to set a part of each heating means to operate.

Heating means 30, 40, 50 used in the present invention
For this, a transparent resistance layer provided directly on the substrate surface of the liquid crystal cell by a vapor deposition method, a sputtering method, or the like can be used, or a heating sheet having a transparent resistance layer provided on a transparent film can also be used. Particularly in the case of the heating means 50 shown in FIG. 2, it is preferable to use a heating sheet.

As described above, since the compensation cell does not apply a driving voltage, it does not originally have an electrode layer unlike the display cell. Therefore, the heating means 40 of the compensation cell can be provided with a transparent electrode layer on the inner surface of the substrate 3 or 4 of the compensation cell, and this electrode layer can be used as a heating resistor.

When the liquid crystal display device has a lighting means, the heating means 3 is considered in consideration of the temperature rise due to heat from the lighting means and the heating capacity of the heating means 30, 40, 50.
It is necessary to determine the installation position and the number of 0, 40, 50.

[0035]

As described above, according to the present invention, in the two-layer STN display device having the compensation cell for color compensation, the heating means 40 or 5 for heating the compensation cell is used.
Since 0 is provided, it is possible to prevent a decrease in contrast when the display cell is heated in order to improve the response at low temperature. Further, the responsiveness at a low temperature does not pose a problem, and even when it is not necessary to heat the display cell, it is possible to prevent the contrast from being lowered at a low temperature. Therefore, there is a great effect in providing a high-quality liquid crystal display device.

[Brief description of drawings]

FIG. 1 is a sectional view showing a first embodiment of the present invention.

FIG. 2 is a sectional view showing a second embodiment of the present invention.

FIG. 3 is a sectional view showing a third embodiment of the present invention.

FIG. 4 is a block diagram showing a heating control system of the present invention.

FIG. 5 is a sectional view showing a conventional technique.

FIG. 6 is a cross-sectional view showing a conventional technique.

[Explanation of symbols]

 1, 2, 3, 4 Substrate 11, 12 Liquid Crystal Layer 30 Heating Means 40 Heating Means 50 Heating Means 32 Polarizing Plate 61 Heating Control Means 62 Heating Setting Means 63 Display Cell Temperature Sensor 64 Compensation Cell Temperature Sensor

Claims (8)

[Claims] 1. A liquid crystal display device comprising a display liquid crystal cell and an optical compensation cell for color-compensating a color generated from the display liquid crystal cell, wherein the optical compensation cell is provided with heating means. Liquid crystal display device characterized by 2. The liquid crystal display device according to claim 1, wherein the display liquid crystal cell is provided with heating means. 3. The liquid crystal display device according to claim 1, wherein the display liquid crystal cell and the optical compensation cell are brought into close contact with each other via a heating means. 4. The liquid crystal display device according to claim 1, wherein the transparent electrode provided on the inner surface of the optical compensation cell serves as a heating means. 5. A temperature sensor and heating control means for controlling the heating means are provided.
The liquid crystal display device according to claim 2, claim 3, or claim 4. 6. The display cell temperature sensor for detecting the temperature of the display liquid crystal cell and the compensation cell temperature sensor for detecting the temperature of the compensation liquid crystal cell are provided.
The liquid crystal display device according to item 1. 7. A heating setting means for setting a heating control condition of the heating control means is provided.
The liquid crystal display device according to item 1. 8. The liquid crystal display device according to claim 6, wherein heating is controlled so that the temperatures of the display liquid crystal cell and the optical compensation cell are substantially equal to each other.