JPH10319390A - Color liquid crystal display - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize color display with good display quality by using a temperature compensated phase difference plate where a retardation value gets smaller with the rise of temperature. SOLUTION: This color liquid crystal display device is provided with a liquid crystal cell 1, polarizing plates 2 and 3, a reflection plate 4 and the phase difference plate 5 where the retardation value is changed according to temperature. Since the phase difference plate where the retardation value gets smaller with the rise of the temperature similarly to liquid crystal, concretely, the phase difference plate where the ratio of the retardation value at 70 deg.C to the retardation value at 25 deg.C is >=0.70 and <=0.99 is used, a difference between the retardation values of the liquid crystal at the respective temperatures gets small and matching with the liquid crystal is improved. Especially, it is effective because the white color of a background is not changed according to the temperature in the case of a positive type, and the black color of the background is not changed according to it in the case of a negative type. When the white color and the black color of the background are not changed according to the temperature in such a way, a hue at each voltage is stable and vivid color display is synthetically realized.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a color liquid crystal display device using retardation.

[0002]

2. Description of the Related Art In recent years, liquid crystal display devices have been widely used in various fields as flat type displays. Liquid crystal display devices have begun to be commercialized from calculators, watches, and the like because of their thinness, light weight, low power consumption, and easy colorization, and recently have been commercialized as large displays for word processors and personal computers.

In these liquid crystal display devices, the tendency of colorization has been remarkable in recent years, and as a method of colorization, a method using a color filter (CF) is generally used. In this method, a vivid color image can be expressed by using CF, but on the other hand, since the CF itself realizes a color by absorption, the reflection type is dark and cannot be used.
For this reason, at present, a color liquid crystal display device is usually used as a transmission type having a backlight on the back side of a liquid crystal display panel.

On the other hand, a liquid crystal display device is used in portable devices such as calculators and mobile phones because of little power consumption even in a driving state and low power consumption. However, in the case of color display, a backlight is necessary for the above-mentioned reason. In this case, the power consumption of the backlight is very large, so that the battery cannot be driven for a long time, and the weight of the battery increases the weight of the battery so that it is not portable. There was a problem of becoming unsuitable.

As a means for solving this problem, a color liquid crystal display device utilizing the retardation of a liquid crystal and a retardation plate has been proposed (see Japanese Patent Application Laid-Open No. 8-292434). In this system, the retardation value is changed by controlling the voltage applied to the liquid crystal display device, thereby realizing color display. For this reason C
Since F is unnecessary, and inexpensive and bright color display is possible, a low power consumption type color liquid crystal display device that does not require a backlight can be realized.

[0006]

In this system, colorization is realized by using the retardation of the liquid crystal and the retardation plate, and the balance of these retardation values is very important. Generally, the retardation value of a liquid crystal changes with temperature, and decreases as the temperature increases. on the other hand,
The retardation value of the phase difference plate does not change in a practical temperature range. For this reason, even if a beautiful hue is exhibited near room temperature, the matching of the retardation between the liquid crystal and the retardation plate becomes poor at low or high temperatures, and there has been a problem that a vivid color cannot be realized.

[0007]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and comprises an optically rotatory substance between two substrates each having a transparent electrode and an alignment film and arranged substantially in parallel. A nematic liquid crystal having a positive dielectric anisotropy is sandwiched therein, and the twist angle of the liquid crystal according to the alignment direction of the liquid crystal molecules formed by the alignment film of each substrate is 160 to 300 °,
The refractive index anisotropy (Δn ₁ ) of the liquid crystal layer and the thickness (d
₁ ) and (Δn ₁ · d ₁ ) at 25 ° C.
A color liquid crystal display device having a thickness of 2.5 μm, at least one polarizing plate and at least one retardation plate provided outside the liquid crystal layer, and a driving circuit for applying a driving voltage between the transparent electrodes; It is another object of the present invention to provide a color liquid crystal display device, wherein a temperature-compensated retardation plate whose retardation value decreases with increasing temperature is used as the retardation plate.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In a color liquid crystal display device of the present invention, it is important to use a temperature compensation type retardation plate whose retardation value becomes smaller as the temperature rises.

The present invention will be described below with reference to the drawings. FIG. 1 schematically shows the configuration of a color liquid crystal display device of the present invention, taking a reflection type as an example. In FIG. 1, reference numeral 1 denotes a liquid crystal cell, 2 denotes a front polarizing plate, 3 denotes a back polarizing plate, 4 denotes a reflecting plate, and 5 denotes a phase difference plate whose retardation value changes with temperature.

Conventionally, a color liquid crystal display device having the same configuration as that of FIG. 1 except that a retardation plate made of a polymer material such as polycarbonate (PC) is used is known. However, in such an apparatus, as shown in FIG.
Is that the retardation value of the liquid crystal cell is constant in a practical temperature range, while the retardation value Δn ₁ · d ₁ of the liquid crystal cell changes with the temperature and becomes smaller as the temperature becomes higher. And the color matching becomes worse, especially at high temperatures compared to room temperature.

On the other hand, in the present invention, since a retardation plate whose retardation value becomes smaller as the temperature rises is used like the liquid crystal, the difference between the retardation value of the liquid crystal at each temperature becomes smaller and the matching with the liquid crystal becomes smaller. Will be better. In particular, in the case of the positive type, the background white color does not change with temperature in the case of the negative type, which is effective. If the white or black background does not change with temperature,
The hue at each voltage is also stable, and a vivid color display can be obtained comprehensively.

As the retardation plate in the present invention, various materials can be used as long as the retardation value changes with temperature. Industrially, a polymer liquid crystal which is solid but has liquid crystal properties is the most simple. If it is difficult to form a film using only the polymer liquid crystal, a mixed system with another polymer material is also possible. The optical characteristics need not be uniaxial, but may be a biaxial or a three-dimensional retardation plate that draws a spiral like a cholesteric liquid crystal. Here, the temperature change of the retardation value of the retardation plate does not need to completely match that of the liquid crystal cell, and is appropriately selected in consideration of the balance of each color.

Specifically, the retardation plate has a ratio of the retardation value at 70 ° C. to the retardation value at 25 ° C. of preferably 0.70 to 0.99, more preferably 0.80 to 0.98. Is used, a color display with a small color change based on a temperature change can be performed.

In the present invention, the twist angle of the liquid crystal molecules between the two electrodes may be set to 160 to 300 °. This is 16
When the angle is less than 0 °, a change in the state of the liquid crystal during time-division driving at a high duty ratio requiring a sharp change in transmittance is small, and when it exceeds 300 °, hysteresis and a domain that scatters light are easily generated. .

Also, the refractive index anisotropy (Δn) of the liquid crystal in the liquid crystal layer
₁ ) and the thickness Δn ₁ · d _{1 of the} liquid crystal layer (d ₁ )
Is set to 1.2 to 2.5 μm. This is because when the voltage is less than 1.2 μm, the change in the state of the liquid crystal when a voltage is applied is small, and when it is more than 2.5 μm, it is difficult to display an achromatic color, and the viewing angle and the response are poor. In particular, Δn ₁ · d ₁ of the liquid crystal layer is 1.3 to 1.8 μm in order to enable achromatic color development and increase color change with respect to voltage.
It is preferable that

It is preferable that the range of Δn ₁ · d ₁ is satisfied within the operating temperature range of the liquid crystal display device, and a beautiful display can be obtained within the operating temperature range. However, due to performance requirements for outdoor use,
This relationship may be satisfied only in a part of the operating temperature range. In this case, in a temperature range in which the range of Δn ₁ · d ₁ is out of the above range, the display color may be out of the desired one or the viewing angle characteristics may be deteriorated.

Next, the overall configuration of the color liquid crystal display device of the present invention will be described. A film of polyimide, polyamide, or the like is provided on the surface of a substrate such as a plastic or glass substrate provided with a transparent electrode such as ITO (In ₂ O ₃ —SnO ₂ ) or SnO ₂ patterned into a desired pattern, and the surface is rubbed. Or a liquid crystal layer having a twist of 160 to 300 ° made of a nematic liquid crystal having a positive dielectric anisotropy is sandwiched between substrates having a transparent electrode on which an alignment control film is formed by obliquely depositing SiO or the like. To be.

As a typical example, there is a dot matrix liquid crystal display device having a large number of matrix-shaped electrodes formed thereon. For example, 640 stripe-shaped electrodes are formed on one substrate, and the other substrate is formed on the other substrate. 40 perpendicular to this
0 stripe-shaped electrodes are formed, and 640 × 400
The display is like a dot. Usually, the size of one pixel forming a dot is about 270 μm × 270 μm, and the gap between the pixels is about 30 μm.

When performing multiplex driving, the minimum effective voltage applied to the pixel is V _OFF . It is preferable to design so that white display can be performed when the V _OFF voltage is applied. In order to realize this, it is sufficient to design the liquid crystal to slightly rise up by a retardation plate. In this way, bright white can be obtained when multiplex driving is performed.

The color liquid crystal display device of the present invention is capable of carrying out a bright display with low power consumption and is suitable for carrying. Especially when used as a reflection type, the effect is very large, but is limited to this. Not EL, C
The present invention can also be applied to a transmission type or a semi-transmission type provided with a backlight such as FL. Even in these cases, an inexpensive color display element that does not use CF can be realized, so that the range of application is wide.

In the case of the transmission type, it is preferable to cover a background portion other than the pixel with a light-shielding film by printing or the like, so that the color contrast can be improved. The material of the reflective film when used as a reflective type is not limited, but a silver reflective film can be preferably used because it has a reflectivity about 20% higher than that of aluminum and improves light use efficiency. In this case, silver and aluminum have different wavelength dependencies at the time of reflection.In general, the reflection of silver has a low reflectance in the blue wavelength range and the reflected light has a yellow tint. The overall display characteristics are improved by adopting a specification that is entirely toward the blue side, and a bright and high-color display can be obtained.

The liquid crystal display device of the present invention includes a personal computer, a word processor, a fish finder, an instrument panel for car use, an information terminal, and an information display device for industrial use [for example, an operation status display (copy red) on an operation panel of a copy machine. Medium, number of sheets is displayed in green, line is displayed in blue, background is displayed in white) or
Driving display of power equipment (background color is white, driving state is green, danger display is red), etc., various dot matrix display devices for consumer use [audio equipment, clocks, game equipment,
Display of amusement, communication equipment, car navigation, camera, TV phone, calculator].

In particular, since the color liquid crystal display device of the present invention can be used with low power consumption, portable electronic devices such as a mobile phone, an electronic notebook, an electronic book, an electronic dictionary, a PDA (personal digital assistant), When used as a pager (pager), it exhibits high functionality in combination with its high visibility and expressive power.

Further, the present invention can be applied to various applications as long as the effect is not impaired. For example, in the case of the reflection type, a method in which the back side polarizing plate 3 is unnecessary in FIG. 1 is also possible.
In this case, a brighter color liquid crystal display device is possible. In addition, the temperature compensation type retardation plate in the present invention does not need to be one, and a plurality of the temperature compensation type retardation plates may be laminated on one or both sides of the liquid crystal cell, or their optical axes may be shifted from each other if necessary. .

[0025]

【Example】

[Examples 1-3 and Comparative Example 1] In the configuration of FIG.
Δn ₁ · d at a liquid crystal twist angle of 240 ° and 25 ° C
₁ using a liquid crystal cell of 1. 27μm. The transition temperature of the used liquid crystal is 99.2 ° C. On the other hand, a thin film of a polymer liquid crystal is formed on a liquid crystal panel as a temperature compensation type retardation plate, and its retardation value at room temperature is approximately 1.39 μm.
And

By changing the material of the polymer liquid crystal, three kinds (Examples 1 to 3) of different retardations of the polymer liquid crystal having different temperatures were prepared. Also made up of Table 1 shows the temperature dependence of the retardation value of each of the retardation plates. In the table, R _70/25 indicates the ratio of the retardation value at 70 ° C. to the retardation value at 25 ° C.

Using these four types of retardation plates, a reflection type color liquid crystal display device as shown in FIG. 1 was prepared, and the color change at 25 ° C. and 50 ° C. was measured under a driving condition of 1/64 duty. FIG. 3 shows the results arranged on the (x, y) chromaticity diagram. In the figure, the data at 25 ° C. was concentrated on almost the same point in each case, and therefore, the data of Example 1 was represented to avoid complication.

As is clear from FIG. 3, at 25 ° C., a sufficient color difference was obtained in each case of white and red-orange, blue, and green, whereas at 50 ° C., as in Comparative Example 1, When a retardation plate having no temperature dependence in the retardation value is used, the color difference of each color decreases. In particular, the change in white as the background color is remarkable, and in Comparative Example 1, the color difference between white and red-orange is small and it is difficult to distinguish colors.

On the other hand, in the case of Examples 1 to 3 using the temperature compensation type retardation plate, a sufficient hue change is obtained between the colors because the hue change of the background white is small even at 50 ° C. .
However, in the retardation plate having a greater temperature dependency than in the first embodiment, the color difference between blue and green is small, and therefore, there is an optimum value for the temperature dependency. A great effect was obtained. However, since this optimum value changes depending on the physical property value of the liquid crystal used, the display mode, or the driving conditions, it is desirable to determine the optimum value according to each.

[0030]

[Table 1]

Examples 4 to 6 and Comparative Example 2 In the configuration of FIG. 1, a liquid crystal cell having a twist angle of liquid crystal of 240 ° and Δn ₁ · d _{1 at} 25 ° C. of 1.36 μm was used. The transition temperature of the used liquid crystal is 94.1 ° C. On the other hand, a thin film of a polymer liquid crystal is formed on a liquid crystal panel as a temperature compensation type retardation plate, and the retardation value at room temperature is approximately 1.
It was 47 μm.

By changing the material of the polymer liquid crystal in the same manner as in the above-described example, three types of retardation plates of the polymer liquid crystal having different temperature dependences of the retardation values (Examples 4 to 6) were used. ) And Comparative Example 2 made of polycarbonate.

Using these four types of retardation plates, a reflection type color liquid crystal display device as shown in FIG. 1 was prepared, and color changes at 25 ° C. and 50 ° C. were measured under a driving condition of 1/240 duty. FIG. 4 shows the results arranged on the (x, y) chromaticity diagram. In this case as well, the data at 25 ° C. was concentrated on almost the same point, so that the data of Example 4 was represented to avoid complication. As in the case of FIG. 3, the use of a temperature-compensating retardation plate has the characteristic that the change in hue at high temperatures is small, and particularly the change in background color is small.

[0034]

[Table 2]

[Embodiment 7] A negative-type reflective color display device was prepared by rotating the rear polarizing plate 3 by 90 ° and removing the reflector from the panel under the conditions of Example 2, and installing a white backlight instead. did. In this case, the background is black, and red-orange, blue, and green colors can be displayed on a black background.
Also in this case, compared with the element using the conventional PC, 50 ° C.
In this case, display with a small change in black hue was possible.

[0036]

In the color liquid crystal display device of the present invention, it is possible to suppress a change in hue at a high temperature or a low temperature by using a temperature compensation type retardation plate. On the other hand, in a negative panel, the color change of the background black can be minimized, and a color display with good display quality can be realized.

[Brief description of the drawings]

FIG. 1 is a schematic cross-sectional view illustrating a configuration of a color liquid crystal display device of the present invention.

FIG. 2 is a graph showing a temperature change of a retardation value of a liquid crystal cell and a retardation plate.

FIG. 3 is a (x, y) chromaticity diagram of Examples 1 to 3 and Comparative Example 1.

FIG. 4 is an (x, y) chromaticity diagram of Examples 4 to 6 and Comparative Example 2.

[Explanation of symbols]

 1: liquid crystal cell 2: front side polarizing plate 3: back side polarizing plate 4: reflective plate 5: retardation plate

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Masao Ozeki 1150 Hazawacho, Kanagawa-ku, Yokohama-shi, Kanagawa Prefecture Asahi Glass Co., Ltd. Central Research Laboratory

Claims (3)

[Claims] A nematic liquid crystal containing an optical rotatory substance and having a positive dielectric anisotropy is sandwiched between two substrates, each having a transparent electrode and an alignment film, and arranged substantially in parallel. The twist angle of the liquid crystal according to the orientation direction of the liquid crystal molecules formed is 160 to 300 °, and the product (Δn ₁ ) of the refractive index anisotropy (Δn ₁ ) of the liquid crystal layer and the thickness (d ₁ ) of the liquid crystal layer.
D ₁ ) is set to be 1.2 to 2.5 μm at 25 ° C.
A color liquid crystal display device provided with at least one polarizing plate and at least one retardation plate outside the liquid crystal layer, and a driving circuit for applying a driving voltage between transparent electrodes, wherein the retardation plate is A color liquid crystal display device using a temperature-compensating retardation film whose retardation value decreases with increasing temperature. 2. The color liquid crystal display device according to claim 1, wherein the ratio of the retardation value at 70 ° C. to the retardation value at 25 ° C. of the retardation plate is 0.70 or more and 0.99 or less. 3. A color liquid crystal display device according to claim 1, wherein a pair of polarizing plates is arranged outside the liquid crystal layer.