JP2860806B2 - LCD color display - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to a color display device using a liquid crystal.

[Prior art] Liquid crystal display devices include TN type liquid crystal display devices that have been used in watches and calculators and STN type liquid crystal display devices that have recently been used in slightly large display devices such as word processors. There is a device, and a ferroelectric liquid crystal display device with a high response speed, which is currently under research.

The TN type liquid crystal display device has a structure in which a liquid crystal to which a light-emitting substance is added is injected between a pair of electrode substrates having surfaces subjected to an alignment treatment. At this time, the alignment processes of the substrates are almost mutually
With a 90 ° angle, the liquid crystal molecules have a 90 ° twist orientation.

This TN type liquid crystal display device has a drawback that the contrast with respect to the applied voltage of the liquid crystal is not clear, so that the contrast is reduced when the number of scanning lines is increased.

The STN type liquid crystal display has a structure almost similar to that of the TN type, but the twist angle of the liquid crystal is 90 ° or more.
It has a twist angle of 180 ° to 270 °, and the threshold value of the applied voltage is clearer than that of the TN type. However, since the display is performed using the refractive index anisotropy, white-black display cannot be performed. Therefore, conventionally, the display was once corrected to white-black display using an optical compensation panel or the like.
Then, a method of controlling an applied voltage to perform a gradation display is used.

When color display is performed in the case of the STN type, a color filter is usually added to this white-black display panel to add color.

[Problems of conventional technology]

In general, a printing method or a photolithography method can be considered as a method of manufacturing a color filter, but the yield in manufacturing three types of (R, G, B) filters is poor when either method is used. Manufacturing costs increase. In addition, there is an adverse effect such that the produced filter fades in color while being used for a long period of time.
Therefore, there has been a demand for a device capable of performing color display without using a filter.

Further, a liquid crystal color display device using a color filter has a disadvantage that a change in color tone when the ambient temperature changes cannot be corrected. Explaining this point, the refractive index anisotropy of the liquid crystal generally tends to increase as the temperature increases. Since the thickness of the panel is almost constant with temperature change, the retardation (Δn × d) of the liquid crystal increases as the ambient temperature increases, so that the light transmittance changes and the color tone of the color display changes. It will be.

[Object of the invention]

In order to solve the above-mentioned problems, the present invention proposes a liquid crystal display device which performs color display without using a color filter and further enables gray scale display. In addition, the present invention proposes a liquid crystal display device capable of performing stable color display with respect to a change in ambient temperature.

[Configuration of the invention]

In order to achieve the above object, the present invention provides a light source and a nematic liquid crystal having a positive dielectric anisotropy and having a light-emitting substance added thereto, which is sandwiched between a pair of upper and lower electrode substrates which are arranged to face each other,
A display panel having a twisted spiral structure in the range of 180 degrees to 270 degrees in the thickness direction, a means for color-compensating the display panel, and a positive dielectric between the pair of upper and lower electrode substrates. A liquid crystal color display device having a color panel in which isotropic and homogeneously aligned liquid crystal is interposed and a polarizing means for distinguishing a plurality of states of the liquid crystal.

In the present invention, the display panel has a nematic liquid crystal containing a chiral component having a twist orientation of 180 to 270 degrees interposed between a pair of transparent substrates on which transparent electrodes are formed, similarly to a normal STN type liquid crystal display device. The structure shall be stiff.
Since white-black display cannot be performed as it is, white-black display is not possible.
Optical compensation means for performing black display, for example, a liquid crystal panel twisted in the opposite direction to the display panel, or a polymer film having a refractive index anisotropy is placed above or below the display panel. Alternatively, they are arranged both above and below.

A liquid crystal device including a display panel and an optical compensator has been conventionally used.
Black display and gradation display are possible. In the present invention, by adding a color panel to this structure, a color display without using a color filter is made possible.

The color panel has a structure in which a homogeneously oriented liquid crystal having a positive dielectric anisotropy is interposed between a pair of substrates on which transparent electrodes are formed. The shape of the transparent electrodes formed on the color display panel may be in the form of a matrix, but one may be in the form of stripes and the other may be unpatterned, that is, one surface may be in the form of one electrode. However, in this case, it is necessary that the width of the stripe-shaped electrode and the width of the electrode of the display panel substantially match. When driving the color panel, it is not necessary to use time-division driving, and static driving can be used.

In the present invention, both the display panel and the color panel may have a liquid crystal alignment means on the surface of the substrate in contact with the liquid crystal.

In the present invention, a total of four polarizing means may be used on both sides of the display panel and on both sides of the color panel. However, since only one polarizing means is sufficient between the display panel and the color panel, three polarizing means are convenient. Is good.

Further, the type of the display panel of the present invention is not limited to the STN type, and a normal TN type or a ferroelectric liquid crystal type can also be used. However, when a normal TN type is used, there is also a disadvantage that the contrast is reduced when a large display is manufactured. In the case of using a ferroelectric liquid crystal type, it is difficult at present to realize the ferroelectric liquid crystal panel due to a low production yield. However, the performance of color panels is sufficient.

Hereinafter, the principle of performing color display using the present invention will be described with reference to FIG. 1 and FIG.

FIG. 1 is a schematic view of a cross section of a liquid crystal color display device according to the present invention, and FIG. 2 is a schematic view showing a state of liquid crystal molecules when a voltage is applied to a color panel.

 First, the light (2) emitted from the light source (1) passes through the polarizing plate (3).
It passes through to become linearly polarized light. And the display panel (4)
pass. Normal yellow when passing through the display panel (4)
Mode or blue mode can be displayed.
Become. However, color display cannot be performed as it is, so light
Compensation means (optical compensation film in FIG. 1)
(5)) is provided, and light passes through the
Black display is possible for a while, and light passes through the polarizing plate (6).
As a result, the display becomes color-black. After that, light is applied to the color panel
(7). The color panel (7) is striped
The substrate on which the electrode is formed and the transparent electrode (common electrode)
(Homogeneous) orientation between the substrates on which the poles are formed.
Because it has a matte liquid crystal, it has a common electrode and stripe shape
By adjusting the voltage applied between the electrode and the
Set the state of the molecule to one of three types (A, B, C)
be able to. However, if a DC voltage is applied to the liquid crystal for a long time,
Doing so adversely affects the liquid crystal,
It is preferably used. The three states (A, B,
C) has different angles of the liquid crystal molecules to the substrate surface.
The apparent refractive index anisotropy of the molecule (Δn = n -N_⊥)
Is different. The color tone of light passing through the liquid crystal panel is
(Δn × d; d is the thickness of the liquid crystal layer)
Color of light passing through the liquid crystal in three states (A, B, C)
Each key is different. Therefore, pass through A, B, C
Color can be set to red, green, and blue respectively.
You. Then, one color display image is formed by three pixels of the display panel.
Display the elementary components (that is, three pixels of red, green, and blue
To display one pixel for white display). In this way,
-Display is now possible.

Also, when the ambient temperature changes, the apparent refractive index anisotropy of the liquid crystal can be changed by changing the value of the voltage applied to the stripe electrode of the color panel,
As a result, a change in color tone due to a change in temperature can be corrected.

Further, by finely adjusting the voltage applied to the color panel (which is possible because of static driving), color display with one pixel of the display panel is also possible.

 Embodiments of the present invention will be described below.

Example 1 First, the manufacture of a display panel will be described.

In FIG. 1, the display panel (4) is used as a transparent electrode.
After ITO is formed on soda glass by a sputtering method, a substrate (13) on which a polyimide thin film is formed as a liquid crystal alignment film, a transparent electrode (ITO) and a liquid crystal alignment film are formed on soda glass, and a spacer ( (Not shown in the drawing) A substrate (14) on which spraying was performed was bonded, and a liquid crystal was injected between the substrates. However, the surfaces of both substrates are 240
The rubbing treatment was performed so that the angle was ゜.

The color panel (7) is composed of a substrate (11) having a transparent electrode and a liquid crystal alignment film formed on soda glass and a substrate (12) having a transparent electrode and a liquid crystal alignment film formed on soda glass. Liquid crystal was injected between the substrates. Here, the transparent electrode was formed as a whole electrode without patterning on the substrate (11) side, and formed in a stripe-like structure with the same width as the electrode of the display cell on the substrate (12) side.

Further, the polarizing plates (3) and (8) are arranged outside the substrate (13),
It is located outside the substrate (12). Further, a polarizing plate (6) is arranged between the display panel (4) and the color panel (7). In this embodiment, it is arranged below the color panel (7).

In this structure, the polarizing plate (3) disposed below the display panel (4) may be provided directly on the light source (1), and may be provided between the display panel (4) and the color panel (7). The arranged polarizing plate may be arranged below the color panel (7).

In using the configuration of FIG. 1 which is an example of the present invention,
Light passing through the display panel (4) and passing through the optical compensation film (5) and the polarizing plate (6) enters the color panel (7). Here, pulse voltages (frequency: 70 Hz) of OV, ± 1.5 V, and ± 2.4 V are applied to each of the three stripe electrodes of the color panel. By doing so, it is considered that the liquid crystal molecules to which the respective voltages are applied are as shown in A, B, and C in FIG.

In these three states, the apparent refractive index anisotropy of each molecule is different, so that the color of light passing through the three striped electrodes can be red, green, and blue, respectively.

3 (a) to 3 (c) show light transmittance curves in the respective states A, B and C of FIG.

In FIG. 3A, there is a peak around 640 to 650 nm, indicating red light. This is because the apparent retardation of the liquid crystal (Δn × d; d is the thickness of the liquid crystal layer) is 1000 nm in a state where no voltage is applied to the liquid crystal.

In FIG. 3 (b), there is a peak near 540 nm, indicating that the light is green light. This has a retardation of 800 nm in a state where a voltage of ± 1.5 V is applied to the liquid phase.

In FIG. 3 (c), the peak is around 400 nm, indicating that the light is blue light. This is a retardation of 600 nm when a voltage of ± 2.4 V is applied to the liquid crystal.

FIG. 4 shows the transmittance with respect to the applied voltage of red (640 nm), green (540 nm), and blue (440 nm) light.

As described above, 0 is applied to the continuous stripe electrodes.
By applying V, ± 1.5V, ± 2.4V, 0V, ± 1.5V, ± 2.4V ..., it passes through the optical compensation film as red, green, blue, red, green, blue, ... After that, the white-black display could be colored.

In this example, a vivid color display without abnormal color tone was obtained at an ambient temperature of 10 ° C. to 20 ° C.

In this example, optical compensation was performed using one polymer film for optical compensation. If necessary, a more vivid color display can be obtained by using a plurality of optical compensation films.

Example 2 First, the manufacture of a display panel will be described.

In FIG. 5, the display panel (4) is used as a transparent electrode.
After forming ITO on soda glass using a sputtering method, a substrate (13) on which a polyimide thin film is formed as a liquid crystal alignment film, a transparent electrode (ITO) and a liquid crystal alignment film are formed on soda glass, and the diameter is 6 μm. Sio ₂ particles (spacer;
(Not shown in the drawing) A substrate (14) on which spraying was performed was bonded, and a liquid crystal was injected between the substrates. However, both substrates were rubbed so that their surfaces were at an angle of 240 ° to each other.

The color panel (7) is composed of a substrate (11) having a transparent electrode and a liquid crystal alignment film formed on soda glass and a substrate (12) also having a transparent electrode and a liquid crystal alignment film formed on soda glass. A liquid crystal was injected between them. Here, the transparent electrode was formed as a whole electrode without patterning on the substrate (11) side, and was formed in a stripe shape on the substrate (12) side with the same width as the electrode of the display panel.

Further, the polarizing plates (8) and (3) are arranged outside the substrate (12),
It is arranged outside the substrate (13). Further, a polarizing plate (6) is arranged between the display panel (4) and the color panel (7). In this embodiment, it is arranged below the color panel (7).

In this embodiment, a liquid crystal panel (20) for optical compensation is arranged between the display panel (4) and the color panel (7). This optical compensation panel (20) has substantially the same configuration as the display panel (4), but does not apply any voltage to the liquid crystal, so that no electrodes are formed. The twist orientation of the liquid crystal was reversed from that of the display panel. further,
In FIG. 5, the rubbing direction of the substrate (14) of the display panel and the substrate (16) of the optical compensation panel (20) are almost 90.
Degree.

When a polymer film is used as the optical compensator as in Example 1, when the ambient temperature changes, light passing through the display panel and the optical compensator is slightly colored, and the Accuracy decreases. This is thought to be due to the expansion or shrinkage of the film and the change in the refractive index anisotropy of the liquid crystal. On the other hand, by using the liquid crystal panel as the optical compensation means, even if the ambient temperature changes and affects the display panel, the optical compensation panel is also affected at the same time and compensates each other. As a result, a clear color display could be obtained in a wide temperature range without deteriorating the accuracy of optical compensation of light passing through the display panel. In fact, in this embodiment, 0
A vivid color display without abnormal color tone was obtained at a temperature of from 25 ° C to 25 ° C.

Embodiment 3 First, the manufacture of a display panel will be described.

As in the second embodiment, the display panel is formed by forming ITO as a transparent electrode on soda glass using a sputtering method, and then forming a polyimide thin film as a liquid crystal alignment film, a transparent electrode (ITO) on the soda glass and a liquid crystal. Forming an alignment film,
Attach the substrate on which the SiO ₂ particles with a diameter of 6 μm have been sprayed,
Liquid crystal was injected between the substrates. However, both substrates were rubbed so that their surfaces were at an angle of 240 ° to each other.

As in the case of Example 2, the color panel was bonded to a substrate having a transparent electrode and a liquid crystal alignment film formed on soda glass and a substrate having a transparent electrode and a liquid crystal alignment film formed on soda glass. It was configured by injecting liquid crystal. Here, one of the transparent electrodes was formed as a full-surface electrode without patterning, and the other was formed in a stripe shape with the same width as the electrode of the display panel. Thereafter, a polarizing plate was disposed in the same manner as in Example 2.

Also in this example, a liquid crystal panel for optical compensation was arranged between the display panel and the color panel.

In the second embodiment, by using a liquid crystal panel as the optical compensation means, a clear color display can be obtained in a wide temperature range even if the ambient temperature changes and affects the display panel. In this embodiment,
By controlling the voltage applied to the stripe-shaped electrodes of the color panel, the value of the apparent refractive index anisotropy of the liquid crystal of the color panel is controlled. In this way, stable color display can be performed. Actually, as long as the liquid crystal used in the liquid crystal color display device of the present invention does not undergo phase transition, a vivid color display without abnormal color tone can be obtained.

Actually change the ambient temperature artificially and apply the pulse voltage applied to obtain the ambient temperature and the red, green, and blue displays when performing color display (frequency 70 Hz in each case)
Are shown in Table 1.

[Effects] As described above, by using the configuration of the present invention, color display can be easily performed without using a color filter, and further, gradation display can be realized, and furthermore, it is extremely resistant to ambient temperature changes. A stable color display can be obtained.

Further, since the liquid crystal color display device of the present invention does not use a color filter, a color panel is manufactured using the same device as a display panel manufacturing device without the need for a device for producing a color filter during mass production. As a result, significant cost reduction can be realized.

In this specification, the case where the display panel is arranged between the color panel and the light source is described. However, for the purpose of the invention, the color panel can be provided between the display panel and the light source. it is obvious.

[Brief description of the drawings]

1 and 5 show schematic cross sections of a liquid crystal color display device according to the present invention. FIG. 2 schematically shows the state of liquid crystal molecules when a voltage is applied to a color panel which is a part of the structure of the present invention. 3 (a) to 3 (c) show the transmittance with respect to the applied voltage of light. FIG. 4 shows the transmittance of light when a voltage is applied to the color panel. DESCRIPTION OF SYMBOLS 1 ... Light source 3, 6, 8 ... Polarizing plate 4 ... Display panel 5 ... Optical compensation film 7 ... Color panel 20 ... Optical compensation panel

Claims (1)

(57) [Claims] 1. A display panel comprising: a light source; and a nematic liquid crystal to which a light-emitting substance is added, sandwiched between a first pair of substrates on which electrodes are formed, and having a twist alignment of 180 to 270 degrees. A means for optically compensating the display panel; and a color panel in which a liquid crystal having a positive dielectric anisotropy and having a homogeneous alignment is interposed between a second pair of substrates having electrodes formed thereon. A liquid crystal color display device comprising: polarizing means.