JP2000193955A - Liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the response rate of a display in a low temp. atmosphere and to obtain a wide viewing angle by providing the device with a light diffusing plate which is produced by roughening at least one surface of a glass substrate to give specified scattering performance and forming a face heater on the roughened face into one body. SOLUTION: A liquid crystal cell 2 is produced by laminating a pair of transparent electrode substrates 21, 22 having transparent electrodes of indium tin oxide(ITO) formed on the inner surfaces facing each other with a peripheral sealing material, and then sealing a nematic liquid crystal (STN) with twisted orientation at 180 to 270 deg. angle in the cell gap. The light diffusing plate 4 has a glass substrate 40 the one surface 40a of which is roughened by frosting process. A face heater 41 is formed on the roughened surface. The scatting performance of the rough surface (light diffusing performance) is controlled to give 45 to 70% haze H. Thereby, decrease in the contrast in the horizontal direction of the display is prevented and good winwing angle characteristics can be obtd. without causing changes in colors.

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, and more particularly, to an STN type liquid crystal display device having a good display response speed even in a low-temperature atmosphere and having a wide viewing angle.

[0002]

2. Description of the Related Art In recent years, liquid crystal display devices have been widely used in portable information terminals, word processors, notebook computers, car navigation systems and the like. In particular, a vehicle-mounted liquid crystal display device such as a vehicle-mounted audio system and a vehicle-mounted navigation device performs a normal operation in a wide temperature range since it is used in a low temperature range (-30 ° C.) to a high temperature range (80 ° C.). A wide viewing angle is required so that it can be visually recognized from the driver's seat and the passenger's seat.

[0003] Liquid crystal display elements include an active matrix type using a TFT (thin film transistor) and a simple matrix type such as a super twisted nematic (STN). However, the manufacturing process of the TFT is complicated, and a variety of designs are required. It may not be applicable to applications that require customization and customization. On the other hand, S
The TN is widely used because it can perform multiplex driving at a high duty, has a simple manufacturing process, can cope with various designs, and can provide an inexpensive liquid crystal display device.

As a means for expanding the viewing angle of this STN type liquid crystal display element, an acrylic film having a diffraction grating arranged in multiple layers, or a light diffusing layer formed by dispersing beads having different refractive indices in a film is used. Are known.

[0005]

However, the means for widening the viewing angle by using a film has been difficult to apply to a liquid crystal display device used in a wide temperature range, such as for a vehicle. That is, at present, the reliability of the film has not reached the practical level. In particular, there is a problem that the film is easily peeled off at high temperature and high humidity, and a problem that the film is yellowed by irradiation with ultraviolet rays and the characteristic is apt to be deteriorated.

Further, since the viscosity of the liquid crystal increases at low temperatures, there is a problem that the response speed of the display becomes slow. To solve this, the physical properties of the liquid crystal (elastic constant,
(Dielectric anisotropy) to reduce the viscosity of the liquid crystal itself and narrow the gap of the liquid crystal cell.
It has not been resolved yet.

[0007]

SUMMARY OF THE INVENTION The present invention has been made to solve such a problem, and an object of the present invention is to provide a display having a good display response speed even in a low-temperature atmosphere and a wider viewing angle. It is an object of the present invention to provide a highly reliable STN type liquid crystal display device having the same.

According to the present invention, an object of the present invention is to provide a liquid crystal cell comprising a pair of transparent electrode substrates having transparent electrodes formed on opposing inner surfaces, and a nematic liquid crystal twisted at 180 to 270 ° being sandwiched between a pair of transparent electrode substrates. In a liquid crystal display device having a polarizing plate disposed on both sides of the liquid crystal cell, at least one surface is roughened between the liquid crystal cell and the one polarizing plate, and its scattering ability (haze) is increased. Value) is 45-
This is achieved by arranging a light diffusion plate integrally formed with a planar heater made of a transparent electrode and having voltage application terminals at both ends on a rough surface of a glass substrate of 70%.

Here, the haze value H is H = (diffuse transmittance /
(Total light transmittance) × 100%. When the haze value H exceeds 70%, the image starts to blur. On the other hand, if the haze value H is less than 45%, a desired wide viewing angle cannot be obtained.

Preferably, an optical retardation plate is provided on the surface of the glass substrate on the side opposite to the heater. In this case, the light diffusing plate is arranged so that its planar heater side faces the liquid crystal cell.

On the contrary, an optical retardation plate may be adhered on the planar heater. In this case, the other surface of the light diffusion plate on the side opposite to the planar heater faces the liquid crystal cell. Will be arranged as follows. This aspect is also included in the present invention.

The planar heater is preferably formed as a solid pattern over substantially the entire surface of the glass substrate. According to this, for example, since the resistance value is lower than that in the case of the stripe pattern, the heat generation efficiency is high. Also, there is no problem of so-called bone appearance.

As described above, when the planar heater is formed as a solid pattern of transparent electrodes, a plurality of blank portions are uniformly provided near the voltage application terminal in a direction substantially perpendicular to the lines of electric force flowing through the planar heater. By providing them at intervals, the lines of electric force flowing through the planar heater become substantially parallel, and it is possible to prevent the occurrence of heat unevenness. Note that the present invention does not exclude an aspect in which the planar heater has a stripe pattern.

[0014]

BRIEF DESCRIPTION OF THE DRAWINGS The invention will now be described with reference to an embodiment shown in the drawings. FIG. 1 is a cross-sectional view of the first embodiment in which components are separated.

According to this, the liquid crystal display element 1 comprises a liquid crystal cell 2, polarizing plates 3a and 3b disposed on both front and back sides of the liquid crystal cell 2, and a liquid crystal cell 2 and one of the polarizing plates 3a. And a light diffusion plate 4 to be disposed.

The liquid crystal cell 2 has an ITO (I
A pair of transparent electrode substrates 21 and 22 each having a transparent electrode made of ndium tin oxide are bonded to each other via a peripheral sealing material 23, and a nematic liquid crystal (180 ° to 270 °) twisted and aligned in the cell gap within the cell gap. STN) is enclosed.

The light diffusion plate 4 is, for example, 0.2 to 1.5 mm
The glass substrate 40 has a thickness of about one. In this embodiment, one surface 40a is roughened by frost processing, and an on-surface heater 41 is formed on the rough surface. Note that, unlike this embodiment, the other surface 4 of the glass substrate 40
The 0b side may be subjected to a surface roughening treatment.

In the present invention, the scattering ability (light diffusing ability) of the rough surface is in the range of 45 to 70% in haze value H. According to this, it is possible to obtain a good viewing angle characteristic without lowering the contrast of the display in the left-right direction and without a color change unique to the STN element. The haze value H
= (Diffuse transmittance / total light transmittance) x 100%, and when it exceeds 70%, the image starts to blur. On the other hand, if the haze value H is less than 45%, a desired wide viewing angle cannot be obtained.

The sheet heater 41 is made of ITO, like the transparent electrode of the liquid crystal cell 2. The forming method may be any of a sputtering method, a vapor deposition method, and an ion plating method. In this embodiment, as shown in FIG. 2, one surface 40a of the glass substrate 40 is roughened.
The planar heater 41 is formed in a solid pattern over substantially the entire surface of the substrate. Further, the light transmittance of the planar heater 41 including the glass substrate 40 is preferably 70% or more.

The planar heater 41 is provided with two voltage application terminals 42a and 42b for "+" and "-". At that position, non-display portions 41a, 41a at both left and right sides which do not cover the display area 2a of the liquid crystal cell 2 in FIG. 2 are selected.
In this embodiment, voltage application terminals 42a and 42b are provided at lower positions of the non-display portions 41a and 41a, respectively. These terminals 42a and 42b can be appropriately formed on the planar heater 41 by, for example, printing of silver paste or vapor deposition of copper.

Here, the voltage application terminal 42a side is "+",
When a voltage is applied from a heater power supply (not shown) to the voltage applying terminal 42b side as "-", electric lines of force (see arrows in the drawing) flow from the voltage applying terminal 42a side to the voltage applying terminal 42b side. In order to prevent heat unevenness from occurring, the present invention takes the following measures.

That is, each of the voltage application terminals 42a, 42b
, Preferably in the non-display portions 41a, 41a and at a position closer to the display region 2a side than the voltage application terminals 42a, 42b, a plurality of blank portions (hole portions) 43 are provided.
Are uniformly formed at predetermined intervals along a direction orthogonal to the lines of electric force.

For example, each blank portion 43 has a length of 5 mm to 10 mm.
The squares of mm are arranged at regular intervals within the range of 5 to 20 mm, whereby the lines of electric force flowing from the voltage application terminal 42a to the voltage application terminal 42b can be made substantially parallel.

The amount of heat Q generated by the planar heater 41
(Joule heat: Cal) is represented by Q = (V / R) × t, where V is an applied voltage, R is a resistance value, and t is a conduction time.

Therefore, the lower the resistance value of the planar heater 41 is, the higher the heat generation efficiency is and the lower the applied voltage can be. The film thickness of the planar heater 41 is relatively determined from the relationship between the calorific value to be obtained and the light transmittance (75% or more). For example, 100-200Ω / □ (film thickness 0.01-0.03
μm) is preferred.

As shown in this embodiment, if the sheet heater 41 has a solid pattern, there is little heat unevenness and there is no problem of so-called bone appearance, but the present invention is not limited to this. The planar heater 41 may have a stripe pattern.

Glass substrate 40 serving as base of light diffusion plate 4
The optical retardation plate 5 is adhered to the other surface 40b side (the opposite side of the heater). The light diffusing plate 4 is interposed between the liquid crystal cell 2 and one of the polarizing plates 3a. In this embodiment, the sheet heater 41 is opposed to the liquid crystal cell 2.

As shown in the second embodiment of FIG. 3, the light diffusing plate 4 may be arranged so that the other surface 40b faces the liquid crystal cell 2. In this case,
The optical retardation plate 5 is adhered on the planar heater 41.

[0029]

Example 1 A mixture ratio of NH ₄ F: H ₂ O: HF was adjusted as an etchant on one surface of a glass substrate having a thickness of 0.7 mm cut out to be almost the same size as a liquid crystal cell. Haze value H is 60
% Rough surface was obtained. And, I
TO is formed in a solid pattern with a thickness of 0.01 μm by sputtering, and a voltage application terminal is formed at both ends by printing silver paste, and a predetermined wiring is connected to the light diffusion terminal with a sheet heater. A plate was made. The light transmittance of this planar heater including the glass substrate was 80%. The resistance value of the sheet heater was 100Ω / □. After attaching one optical retardation plate to the opposite side (opposite heater side) of the light diffuser plate with the planar heater, the light diffuser plate is twisted at 240 ° to form an STN type liquid crystal cell. , So that the sheet heater side faces each other,
A polarizing plate was laminated on both sides to produce a liquid crystal display device.

<Comparative Example 1> Light consisting of beads having different refractive indexes dispersed in a film on the surface side of the same STN type liquid crystal cell twisted at 240 ° as used in Example 1 above. After adhering the diffusion plate, a liquid crystal display device was prepared by laminating polarizing plates on both surfaces.

In a low-temperature atmosphere of -30 ° C., each of the liquid crystal display devices of Example 1 and Comparative Example 1 was subjected to 1/200 Dut.
The liquid crystal was turned on (operated) at a liquid crystal driving voltage of y-1 / 15 Bias, and the response speed of the display was measured. Example 1
As for, the sheet heater was energized and the surface temperature of the liquid crystal cell during the operation was measured and found to be 0 ° C. The surface temperature of the liquid crystal cell of Comparative Example 1 was −30 ° C., the same as the ambient temperature.

As a result, the response speed of the display of the first embodiment is 5
Whereas the response speed of Comparative Example 1 was 7 ms.
000 ms. When the viewing angle characteristics were confirmed, each of the liquid crystal display elements exhibited good display without color change even when the liquid crystal display element was inclined by 45 ° in the left-right direction from the display front. After that, a high temperature and high humidity test (80 ° C., 90% RH)
A light fastness test (UV fade meter) was performed.

In the case of Example 1, the viewing angle characteristics did not change before and after the test, whereas in the case of Comparative Example 1, the light diffusion plate was peeled off after 288 hours of the high temperature and high humidity test.
After 100 hours from the light resistance test, the light diffusing plate was yellowed, and did not serve as the light diffusing plate.

[0034]

As described above, according to the present invention,
In the STN type liquid crystal display element, a glass substrate having a haze value of 45 to 70% is used as a light diffusion plate,
Since the sheet heater made of ITO is integrally formed on the rough surface, the response speed of display is good even in a low-temperature atmosphere, and a highly reliable S having a wider viewing angle is provided.
A TN liquid crystal display device is provided.

Further, since the heater for heating the liquid crystal cell is formed integrally with the light diffusing plate as a planar heater, the heater can be installed in the module without substantially affecting the overall thickness of the liquid crystal display element. Can be incorporated into

[Brief description of the drawings]

FIG. 1 is a schematic sectional view showing components of a first embodiment according to the present invention separately.

FIG. 2 is a plan view showing a planar heater applied to the first embodiment.

FIG. 3 is a schematic sectional view showing components of the second embodiment according to the present invention separately.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Liquid crystal display element 2 Liquid crystal cell 21, 22 Transparent electrode substrate 23 Peripheral sealing material 3a, 3b Polarizing plate 4 Light diffusing plate 40 Glass substrate 41 Planar heater 5 Optical retardation plate

Claims (4)

[Claims] 1. A liquid crystal cell comprising a pair of transparent electrode substrates each having a transparent electrode formed on opposing inner surfaces, and a nematic liquid crystal twisted at 180 to 270 ° interposed between the pair of transparent electrode substrates. A liquid crystal display device having a polarizing plate disposed thereon, wherein at least one surface is roughened and a transparent electrode is formed on a rough surface of a glass substrate having a scattering ability (haze value) of 45 to 70%. A liquid crystal display comprising a light diffusion plate integrally formed with a planar heater having voltage application terminals at both ends, wherein the light diffusion plate is disposed between the liquid crystal cell and the one polarizing plate. element. 2. An optical retardation plate is provided on the surface of the glass substrate on the side opposite to the planar heater, and the light diffusing plate is arranged such that the planar heater side faces the liquid crystal cell. The liquid crystal display device according to claim 1. 3. An optical retardation plate is provided on the planar heater, and the light diffusion plate is arranged such that the other surface on the side of the planar heater faces the liquid crystal cell. Item 2. A liquid crystal display device according to item 1. 4. The planar heater is formed as a solid pattern over substantially the entire surface of the glass substrate, and is provided in the vicinity of the voltage application terminal in a direction substantially orthogonal to a line of electric force flowing through the planar heater. 4. The liquid crystal display device according to claim 1, wherein a plurality of blank portions are provided at equal intervals.