JPH11202312A - Liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To respectively provide the reflection type liquid crystal display device of a high contrast ratio and the liquid crystal display device provided with the two forms of a reflection type and a transmission type capable of separately using them as needed. SOLUTION: As this liquid crystal display device of the reflection type, a polarizing plate 3 is disposed on the surface side of a liquid crystal cell 1 in which liquid crystal 12 is enclosed between a pair of glass substrates 2 and 4 and a film, changeable in light transmissivity and light reflectivity, composed by laminating a 1/4 wavelength film 6 and a cholesteric liquid crystal film 7 and a light adsorption film 13 are disposed on the back surface side of the liquid crystal cell 1. Also, as the liquid crystal display device, instead of the light adsorption film 13 of the liquid crystal display device of the reflection type, the transmission type liquid crystal display device B formed by enclosing the liquid crystal 23 between a pair of the glass substrates 21 and 22 and a back light C are successively laminated.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reflection type liquid crystal display device having a high contrast ratio and two types of reflection type and transmission type, and the display type can be changed as required. The present invention relates to a liquid crystal display device.

[0002]

2. Description of the Related Art In general, display modes of a liquid crystal display device include:
There are a transmission type having a backlight and a reflection type having a reflector instead of the backlight. Since the transmission type liquid crystal display device illuminates the display surface with a backlight, the display surface has high luminance and is suitable for display requiring high definition and high image quality such as a television image. On the other hand, a reflection type liquid crystal display device uses only external light such as sunlight and illumination light to perform display without a backlight, and consumes little power. For example, a portable information terminal that is required to be thin and lightweight. It is often used for such purposes.

[0003]

By the way, since the reflection type liquid crystal display device uses only external light, the display surface is inevitably dark and a high contrast ratio cannot be obtained. In addition, since the reflection type liquid crystal display device uses a pair of polarizing plates via a liquid crystal layer, the absorption of light per polarizing plate is 5 to 10%, and the contrast ratio is 3%.
It was as low as ~ 4.

Further, the conventional liquid crystal display device is of either a transmission type or a reflection type, and therefore, it is not possible to use both types as needed. However, for example, when operating an information terminal device such as a personal computer, there are cases where data such as characters and numbers are processed and cases where an image such as a moving image is processed. Thus, the display screen may have low image quality. That is, if the liquid crystal display device can be selectively used as a transmissive type or a reflective type in response to a demand for image quality, power consumption can be reduced, and the utility value as a portable terminal is particularly improved.

The present invention has been made in view of the above circumstances, and has a reflective liquid crystal display device having a high contrast ratio, and two types of a reflective type and a transmissive type. It is an object to provide each of the liquid crystal display devices described above.

[0006]

According to the liquid crystal display device of the present invention, a polarizing plate is disposed on a front side of a liquid crystal cell in which liquid crystal is sealed between a pair of glass substrates, and a polarizing plate is disposed on a rear side of the liquid crystal cell.
The present invention is characterized in that a light-absorbing film and a film formed by laminating a four-wavelength film and a cholesteric liquid crystal film to change light transmittance and light reflectance are provided. That is, the film that changes the light transmittance and the light reflectance can reflect light that is circularly polarized in a specific direction and can also transmit light that is circularly polarized in another specific direction. Can function as

In the liquid crystal display device of the present invention, a polarizing plate is disposed on the front side of a liquid crystal cell in which liquid crystal is sealed between a pair of glass substrates, and a quarter-wave film and a cholesteric liquid crystal are disposed on the back side of the liquid crystal cell. A reflective liquid crystal display device in which a film that changes the light transmittance and light reflectance formed by laminating a film is disposed, and a transmissive liquid crystal display device in which liquid crystal is sealed between a pair of glass substrates. , And a backlight. Therefore, it is possible to arbitrarily select a reflection type or a transmission type as a display mode depending on required image quality.

Further, in the liquid crystal display device of the present invention, the transmission type liquid crystal display device comprises a TFT type transmission type liquid crystal display device. With such a configuration, the transmission type liquid crystal display device can be adapted to large-capacity image display.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the liquid crystal display device of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic sectional view of the reflection type liquid crystal display device.
A polarizing plate 3 laminated on an upper glass substrate 2 of the liquid crystal cell 1; and a film 5 provided outside the lower glass substrate 4 of the liquid crystal cell 1 for changing light transmittance and light reflectance.
(Hereinafter, referred to as a polarization conversion film) and a light absorbing film 13 made of a black sheet such as carbon paper. The polarization conversion film 5 is made of a polymer material 1 /
It is formed by laminating a four-wavelength film 6 and a cholesteric liquid crystal film 7 made of a cholesteric polymer material, and has a function of reflecting transparent but circularly polarized light in a specific direction.

In the liquid crystal cell 1, transparent electrodes 8 and 9 made of ITO or the like and alignment films 10 and 11 made of a polymer film such as polyimide are sequentially provided on opposing upper and lower glass substrates 2 and 4, respectively. And a nematic liquid crystal 12 having a twist angle of 90 degrees between the alignment films 10 and 11.
(TN) is enclosed.

Next, the operation of the liquid crystal display device will be described. Figure 2 is intended for explaining the relationship between the optical axis of the quarter wave film 6 of the polarization conversion film 5 to the polarization axis of the polarizing plate 3 of the reflection type liquid crystal display device, the polarization axis P ₁ of the polarizing plate 3 and 1 The angle θ ₁ formed between the 波長 wavelength film 6 and the optical axis L is set to −45 degrees in advance.

[0012] Therefore, if the transparent electrodes 8 and 9 of the liquid crystal cell 1 is not applied a voltage, light incident on the surface of the liquid crystal display device from the outside is linearly polarized in the direction of the polarization axis P ₁ by the polarizing plate 3 further, when passing through the liquid crystal 12 of the liquid crystal cell 1, the polarization direction of the light is rotated 90 degrees along the twist of the liquid crystal molecules, the direction of the dashed arrow P _2. As a result, the angle θ ₂ between the linear polarization direction P _{2 of} the light transmitted through the liquid crystal cell 1 and the optical axis L of the 波長 wavelength film 6 is +45 degrees.

[0013] Figure 3 is obtained by describing the state of the light passing through the polarization conversion film 5 from the liquid crystal cell 1 side, the light incident L ₁
When the linear polarization direction P ₂ (shown in parallel with the drawing) is +45 degrees with the optical axis L of the 波長 wavelength film 6, the light transmitted through the ４ wavelength film 6 becomes left-handed circularly polarized light. Is totally reflected by the next cholesteric liquid crystal film 7. Since the reflected light L ₂ exits the polarizing plate 3 along the original path,
A white display is obtained.

[0014] Next, when a voltage is applied to the transparent electrodes 8 and 9 of the liquid crystal cell 1, polarization axes P ₁ direction of light linearly polarized by the polarizing plate 3 is not rotated by the liquid crystal 12, as the liquid crystal cell 1 is transmitted. Accordingly, the polarization direction P ₁ (shown perpendicularly to the drawing) of the light L ₃ incident on the quarter-wave film 6 is １ ／
The angle formed between the wavelength film 6 and the optical axis L is −45 degrees. In this case, the light transmitted through the 膜 wavelength film 6 becomes right-handed circularly polarized light, transmitted through the next cholesteric liquid crystal film 7,
Absorbed by the light absorbing film 13 disposed on the back side,
Since light does not return to the display surface, black display can be performed.
As described above, the present liquid crystal display device uses a polarization conversion film and has a display function as a reflection type using only one polarizing plate, so that high contrast can be obtained.

Next, another embodiment of the liquid crystal display device of the present invention will be described with reference to FIG. FIG. 4 is a schematic sectional view, in which a reflective liquid crystal display device A, a transmission liquid crystal display device B, and a backlight C are sequentially laminated.

The reflection type liquid crystal display device A has exactly the same structure as that of the reflection type liquid crystal display device described with reference to FIG. 1 except that the light absorbing film 13 is removed. Detailed description is omitted. That is, the liquid crystal cell 1 includes a polarizing plate 3 laminated on the upper glass substrate 2 of the liquid crystal cell 1, and a polarization conversion film 5 provided outside the lower glass substrate 4 of the liquid crystal cell 1. .

Next, the transmission type liquid crystal display device B is of an active matrix type, is laminated on the polarization conversion film 5 side of the reflection type liquid crystal display device A, and has a pair of glass substrates 2.
The liquid crystal cell 20 includes a TN type nematic liquid crystal 23 sealed between the liquid crystal cells 1 and 22, and a pair of upper and lower polarizers 24 and 25 disposed with the liquid crystal cell 20 interposed therebetween. On one (lower) glass substrate 22, a TFT (thin film transistor) 26 as an active element is provided.
And pixel electrodes 27 are arranged in a matrix, and an alignment film 28 is provided thereon. The TFT 26 has a gate electrode 29 formed on the glass substrate 22 and a gate electrode 2
9, a gate insulating film 30 formed on the gate insulating film 30 so as to face the gate electrode 29, a source electrode 32 and a drain electrode 33 connected to the semiconductor layer 31, It is composed of On the other (upper) glass substrate 21, a counter electrode 34 facing the pixel electrode 27 and an alignment film 35 formed on the counter electrode 34 are formed. The pixel electrode 27 and the counter electrode 34 are made of ITO.
And the alignment films 28 and 35 are made of a polymer material such as polyimide.

Although not shown, in order to apply the transmissive liquid crystal display device B to color display, for example, three primary colors of red, blue and green are provided between the upper glass substrate 21 and the counter electrode 34. What is necessary is just to form a color filter. The backlight C includes a light source such as a fluorescent tube and an electroluminescent device (EL).

As described above, the liquid crystal display device of the present invention comprises a reflection type liquid crystal display device A, a transmission type liquid crystal display device B, and a backlight C which are sequentially laminated, respectively.
Next, the operation principle of the liquid crystal display device will be described. First, an operation when the liquid crystal display device is used as a reflection type will be described. In this case, only the reflection type liquid crystal display device A is driven, and the backlight C is not lit.
The operation is as described with reference to FIGS. 2 and 3, and there is no difference except that the light absorbing film 13 is replaced with the transmissive liquid crystal display device B.

Next, when the liquid crystal display device is used as a transmission type, a voltage is applied to the transparent electrodes 8 and 9 of the liquid crystal cell 1 of the reflection type liquid crystal display device A so that the device A transmits light. While driving the transmissive liquid crystal display device B,
In addition, the backlight C is turned on. The polarization axis of the upper polarizing plate 24 of the transmission type liquid crystal display device B and the lower polarizing plate 2
Although the polarization axis is orthogonal to the polarization axis of 5, the polarization axis of the upper polarizing plate 24 may be oriented in any direction with respect to the reflective liquid crystal display device A.

The operation principle of the transmission type liquid crystal display device B itself is as follows.
The operation is performed based on whether or not a voltage between the pixel electrode 27 and the counter electrode 34 of the liquid crystal cell 20 is present or not, and whether or not the light of the backlight C can pass through the upper polarizing plate 24, as in the generally performed operation. When light passes through the upper polarizing plate 24, white display is performed, and when light is not transmitted, black display is performed.

On the other hand, the linearly polarized light transmitted through the upper polarizing plate 24 becomes right-handed circularly polarized light when transmitted through the cholesteric liquid crystal film 7 of the polarization conversion film 5 thereon. 6 and becomes linearly polarized light. The polarization direction of the linearly polarized light coincides with the direction of polarization axis P ₁ of the polarizing plate 3 of the reflection type liquid crystal display device A side, therefore, it is transmitted through the liquid crystal cell 1 in the ON state, the polarizing plate 3 By emitting, white display (or color display)
Is obtained. Regardless of the direction of the polarization axis of the upper polarizing plate 24 with respect to the reflective liquid crystal display device A, the polarization direction of the linearly polarized light when transmitted through the polarization conversion film 5 is changed to the polarizing plate. 3 always coincides with the polarization axis P ₁ and can be transmitted.

As described above, the liquid crystal display device of the present invention
When used as a reflection type, the reflection type liquid crystal display device A
The display can be performed by driving only the backlight C, and the power consumption can be reduced without using the backlight C, which is suitable for outdoor use. When used as a transmissive liquid crystal display, the backlight C is turned on and the transmissive liquid crystal display B is driven, so that the reflective liquid crystal display A on top applies a voltage to the transparent electrodes 8 and 9 thereof. By setting it in a state, it substantially acts as a transparent body, so that the display of the transmission type liquid crystal display device B can be displayed as it is,
It is suitable for high-quality display such as image processing.

[0024]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the liquid crystal display device of the present invention will be described, but the present invention is not limited to only these embodiments. (Example 1) In a reflection type liquid crystal display device, AL-8 (trade name, manufactured by Sanritz) was used as a polarizing plate. The liquid crystal cell has upper and lower glass substrates made of soda-lime glass, and has a thickness of 0.1 mm and a size of 50 mm ² , and transparent electrodes and an alignment film JALS171 (made of ITO) are formed on opposing surfaces of the upper and lower glass substrates. (Trade name, manufactured by Japan Synthetic Rubber Co., Ltd.). The liquid crystal of the liquid crystal cell is a nematic liquid crystal ZLI-4 having a twist orientation of 90 degrees.
792 (trade name, manufactured by Merck Japan) was sealed between the upper and lower alignment films.

The polarization conversion film constituting the reflector includes 1
A Transmax Film (trade name, manufactured by Merck Japan Ltd.) in which a と wavelength film and a cholesteric liquid crystal film were laminated was used. The light-absorbing film was formed by depositing (2 nm) a carbon black agent of CFPR BK-7085 of Tokyo Ohka Co., Ltd. on a glass substrate, and was heated at 100 ° C. × 1 minute and 200 ° C.
What was fired for 30 minutes was used.

The electro-optical response characteristics of the liquid crystal display of the first embodiment will be described with reference to FIG. In the figure, light emitted from an external light source onto a display surface at an incident angle of 30 degrees is detected by a detector arranged at a position orthogonal to the display surface, and the reflected light is detected. The light is applied to a transparent electrode of a liquid crystal display device. The change of the reflectance with respect to the applied voltage is shown by a graph. Compared with the conventional reflection type liquid crystal display device, it had a high reflectance and a high contrast, and a contrast ratio of 5 to 8 was obtained. In the figure, the reflectance was measured using a liquid crystal panel evaluation device (LCD 5000 model manufactured by Otsuka Electronics Co., Ltd.) and a white plate (Mg).
This is a value expressed as a percentage (%) by dividing the output of the reflected light by the above-mentioned reference output with reference to the output of the reflected light when irradiating the plate having an O standard white surface at an incident angle of 30 degrees.

(Embodiment 2) In a liquid crystal display device in which a reflection type liquid crystal display device and a transmission type liquid crystal display device are combined, the polarizing plate and the upper and lower polarizing plates are made of AL-8 as in the case of the first embodiment.
(Trade name, manufactured by Sanritz), the upper and lower glass substrates of both liquid crystal cells were 0.1 mm in thickness and 50 m in size.
m ² soda-lime glass was used. The transparent electrode, pixel electrode and counter electrode on the opposing surfaces of the upper and lower glass substrates are I
By TO, the alignment film was formed by applying JALS171 (trade name, manufactured by Nippon Synthetic Rubber Co., Ltd.). The TFT was formed by a general film forming technique. A nematic liquid crystal ZLI having a 90-degree twist alignment between the upper and lower alignment films of each liquid crystal cell.
-4792 (trade name, manufactured by Merck Japan Ltd.) was respectively enclosed.

The polarization conversion film constituting the reflector of the reflection type liquid crystal display device was a Transmax Film (trade name, manufactured by Merck Japan), and the backlight was LTU01 manufactured by Nippon Miyuki Seiki Co., Ltd.

The electro-optical response characteristics of the liquid crystal display device according to the second embodiment will be described with reference to the drawings. Note that the measuring method is the same as that in Example 1. Further, when the liquid crystal display device is used as a reflection type, the change in reflectance with respect to the voltage applied to the transparent electrode of the reflection type liquid crystal display device has the same result as that of FIG. The transmissive liquid crystal display device located on the back side absorbs light similarly to the light absorbing film, and provides high reflectance and high contrast.

FIG. 6 shows a case where the liquid crystal display device is used as a transmissive type, in which the backlight is turned on, and the transmittance of light from the backlight with respect to the voltage between the pixel electrode and the counter electrode of the transmissive type liquid crystal display device. Is shown in a graph. As is clear from the figure, a display function as a transmissive liquid crystal display device is sufficiently provided.

[0031]

As described above, in the liquid crystal display device of the present invention, a polarizing plate is disposed on the front side of a liquid crystal cell in which liquid crystal is sealed between a pair of glass substrates, and on the rear side of the liquid crystal cell. 1 /
A polarization conversion film formed by laminating a four-wavelength film and a cholesteric liquid crystal film, and a light absorption film are disposed. The polarization conversion film reflects light circularly polarized in a specific direction, and includes one polarizing plate. Since this configuration is used, a remarkable effect that high contrast can be obtained is achieved.

Further, in the liquid crystal display device of the present invention, a polarizing plate is disposed on a front side of a liquid crystal cell in which liquid crystal is sealed between a pair of glass substrates, and a quarter-wave film is provided on a rear side of the liquid crystal cell. A reflection type liquid crystal display device in which a polarization conversion film formed by laminating a cholesteric liquid crystal film is disposed, a transmission type liquid crystal display device in which liquid crystal is sealed between a pair of glass substrates, and a backlight. In the case where the display is stacked and low-quality display such as data processing is required, driving the reflective liquid crystal display device without turning on the backlight can reduce power consumption.

On the other hand, when display such as image processing requires high image quality, the backlight can be turned on and the transmission type liquid crystal display device can be driven to satisfy the demand. It can be changed and is very economical. Further, if the transmission type liquid crystal display device is a TFT type transmission type liquid crystal display device in which a thin film transistor is formed on one of the glass substrates, it is suitable for enlargement of the screen.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view of a reflection type liquid crystal display device of the present invention.

FIG. 2 is an explanatory diagram illustrating the relationship between the polarization axis of a polarizing plate of the reflective liquid crystal display device of the present invention and the optical axis of a quarter-wave film of a polarization conversion film.

FIG. 3 is an explanatory diagram illustrating a state of light passing through the polarization conversion film of the present invention.

FIG. 4 is a schematic cross-sectional view of a liquid crystal display device according to the present invention, which serves both as a reflection type and a transmission type.

FIG. 5 is a graph showing an electro-optical response characteristic of the reflective liquid crystal display device according to the first embodiment of the present invention.

FIG. 6 is a graph showing electro-optical response characteristics when the liquid crystal display device according to the second embodiment of the present invention is used as a transmission type.

[Explanation of symbols]

Reference Signs List A reflective liquid crystal display device B transmissive liquid crystal display device C backlight 1 liquid crystal cell 2 upper glass substrate 3 polarizing plate 4 lower glass substrate 5 film (polarization conversion film) 6 for changing light transmittance and light reflectance 6 1/4 wavelength film 7 Cholesteric liquid crystal film 12 Liquid crystal 13 Light absorbing film 20 Liquid crystal cell 21 Upper glass substrate 22 Lower glass substrate 23 Liquid crystal 24 Upper polarizing plate 25 Lower polarizing plate 26 TFT

Claims (3)

[Claims] 1. A polarizing plate is disposed on the front side of a liquid crystal cell in which liquid crystal is sealed between a pair of glass substrates, and a quarter-wave film and a cholesteric liquid crystal film are laminated on the back side of the liquid crystal cell. A reflective liquid crystal display device, comprising a film for changing light transmittance and light reflectance, and a light absorbing film. 2. A polarizing plate is disposed on the front side of a liquid crystal cell in which liquid crystal is sealed between a pair of glass substrates, and a quarter-wave film and a cholesteric liquid crystal film are laminated on the back side of the liquid crystal cell. A reflective liquid crystal display device in which a film that changes light transmittance and light reflectance is disposed, and a transmissive liquid crystal display device in which liquid crystal is sealed between a pair of glass substrates,
A liquid crystal display device characterized by sequentially laminating a backlight. 3. The liquid crystal display device according to claim 2, wherein the transmission type liquid crystal display device comprises a TFT type transmission type liquid crystal display device.