JPH0675218A - Liquid crystal panel - Google Patents

Abstract

PURPOSE:To make the thickness of a panel thinner and also to reduce a manufacture cost by providing a liquid crystal cell including liquid crystal capable of varying its state between a light transmissive state and a light scattering state in accordance with an impressed electric field and providing a light source attached to the side edge of the liquid crystal cell. CONSTITUTION:The liquid crystal cell 1 is formed by holding a liquid crystal layer 11 capable of varying its state between the light transmissive state and the light scattering state in accordance with the impressed electric field with transparent glass substrates 12 and 13. A common electrode 14 and a picture element electrode 15 for driving the picture element are formed on the substrates 12 and 13. On the side face of the liquid crystal cell 1, an illuminating light source 2 is arranged so that an optical coupling may be formed. On the main face of the liquid crystal cell 1 and opposite to an observer side, a microprism plate 3 is arranged, and a background plate 4 is arranged on the rear side of the plate 3. In the case of using the panel as a transmissive light mode type liquid crystal panel, the illuminating light source 2 is used. At this time, the liquid crystal cell 1 itself functions to scatter and guide the light. On the other hand, in the case of using the panel as a reflection mode type liquid crystal panel, the illuminating light source 2 is not used.

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 panel and, more particularly, to a liquid crystal display panel which can be used by switching between a transmission mode and a reflection mode, the light transmission state and the scattering state depending on an electric field. The present invention relates to a liquid crystal display panel that uses a liquid crystal whose state changes in.

Liquid crystal display panels are generally classified into a reflection mode type for displaying with reflected light and a transmission mode type for displaying with transmitted light. The reflection mode type uses the ambient light of the observer as a light source, the ambient light transmits through the liquid crystal cell, and is reflected by the reflection plate placed on the back surface of the liquid crystal cell to display, and the illumination device as a light source is not used. . On the other hand, the transmissive mode type uses an illuminating device as a backlight and transmits light from the backlight to the liquid crystal cell for display.

The liquid crystal display panel according to the present invention can be used for both modes. If an illuminating device is used, it becomes a transmissive liquid crystal display panel, and if no illuminating device is used, it becomes a reflective liquid crystal display panel. In this specification, this dual-mode liquid crystal display panel is referred to as a transflective liquid crystal display panel.

[0004]

2. Description of the Related Art The components of a transflective liquid crystal display panel are roughly divided into a backlight device, which is an illumination light source, and a backlight device that sufficiently transmits backlight light in a transmissive mode and transmits incident light in a reflective mode. It is composed of a diffusion plate that scatters and reflects, and a liquid crystal cell in which liquid crystal is sandwiched between transparent substrates. Hereinafter, the structure of the conventional transflective liquid crystal display panel will be described with reference to the external views of FIGS.

FIG. 4 is an external view of the most common backlight device. This backlight device is called an edge type and is convenient for obtaining a thin surface light source.
An elongated tubular illumination source 41, preferably a cold cathode white fluorescent lamp, is covered by a reflector 42 which is open at one end. The inner surface of the reflector 42 is a mirror surface and reflects the light of the illumination light source 41. The transparent end of the reflector 42 holds the transparent light guide plate 43.

The transparent light guide plate 43 is, for example, a transparent acrylic plate having a refractive index of light higher than that of air and having a value of about 1.5, which is close to that of glass. The light from the illumination light source 41 is guided by being totally reflected by the upper and lower surfaces of the transparent light guide plate 43 as shown by the arrow in FIG.

A first diffusion plate 44 is formed on the upper surface of the transparent light guide plate 43.
Are placed. The first diffusion plate 44 reflects about 50% of the light incident from the upper surface in the reflection mode, and transmits about 50% of the light incident from the transparent light guide plate 43 to the lower surface in the transmission mode. The material and composition are selected so that
For example, a transparent plate with dispersed scattering sources, a printed white pattern, or the like can be used.

A second diffusion plate 45 is formed on the lower surface of the transparent light guide plate 43.
Are placed. The second diffusion plate 45 is a transparent light guide plate 43.
It has a reflecting surface that scatters or reflects all the light that has passed through and is incident on the upper surface. This may use a metal plate.

When the backlight device of FIG. 4 is used in the reflection mode, the illumination light source 41 is not used and the first scattering plate 4 is not used.
4 and the second scattering plate 45 function as a reflection plate for incident light from above.

Next, FIG. 5 shows an external view of another backlight device. This is a structure in which a micro prism plate 46 is added to the configuration of the backlight device shown in FIG. As shown in the figure, the micro-prism plate 46 is formed by arranging a large number of mountain shapes each having a substantially triangular cross section in an array, and is made of a transparent or cloudless polycarbonate or acrylic material having a high refractive index. The pitch of the mountain is from 2 to 30 microns to 1
In the 00 micron range, the apex angle of each microprism is about 60-130 °.

The role of the micro prism plate 46 is as follows.
The brightness of reflected (refractive) light is enlarged for vertically incident light, and the brightness of reflected (refractive) light is reduced for light having a large incident angle (usually 45 ° or more) from the side. Therefore, although the directivity, that is, the viewing angle is narrowed, the utilization efficiency of light is increased and the brightness when viewed from the front is improved, and the display is easier to see.

Next, FIG. 6 is an external view of a transflective liquid crystal display panel using the backlight device and the liquid crystal cell 50 described in FIG. The transflective liquid crystal display panel using the backlight device described with reference to FIG. 4 is obtained by removing the micro prism plate 46 from the device of FIG.

The liquid crystal cell 50 has a liquid crystal layer 51 sandwiched between transparent glass substrates 52 and 53 and sealed. On the transparent glass substrates 52 and 53, electrodes for driving the pixels, driving elements, and an alignment film are formed, but they are not shown in the figure for simplicity.

Here, the types of liquid crystals that can be used in the liquid crystal layer 51 will be exemplified. There are various electro-optical effects of liquid crystals used in liquid crystal display panels, and they can be classified into the following types.

(1) Liquid crystals (twisted nematic (TN) type liquid crystal, super twisted nematic (STN) type liquid crystal, birefringence control (EC) which utilizes the display effect based on polarized light.
(B) type liquid crystal, surface-stabilized ferroelectric liquid crystal (SSFLC), etc.) (2) Dye light absorption effect Liquid crystal utilizing the so-called guest-host effect (Heilmeier type, white-tailor type) (3) Utilizing light scattering mode Liquid crystals (dynamic scattering mode (DSM), cholesteric / nematic phase transition mode (CNPT), polymer dispersed liquid crystal (PDL)
(C) etc.) In the case of a direct view type liquid crystal display panel, the above (1) and (2)
The liquid crystal of (3) is suitable, and the liquid crystal of the type (3) is suitable for the projection type liquid crystal display panel.

[0016]

Liquid crystal display panels are desired to be thin, lightweight, and inexpensive. In this respect, in the conventional transflective liquid crystal display device as described above, a linear light source as a backlight device, a light guide plate coupled to the linear light source, and two scattering plates coupled to the upper and lower surfaces of the light guide plate. The plate formed a thin surface light source. The backlight device and the liquid crystal cell are arranged so as to overlap each other, and the sum of the thicknesses thereof basically determines the thickness of the liquid crystal display panel.

Therefore, in order to further reduce the thickness of the liquid crystal display panel and further reduce its manufacturing cost, it is necessary to reexamine the structure of the liquid crystal display panel including the backlight device.

An object of the present invention is to provide a transflective liquid crystal display panel which can be made thinner and can be manufactured at a lower cost.

[0019]

A liquid crystal display panel of the present invention includes a liquid crystal cell containing a liquid crystal that changes its state between a light transmission state and a light scattering state in accordance with an applied electric field, and one of the liquid crystal cells. Of the liquid crystal cell and a light source that is coupled to the side edge of the liquid crystal cell and allows light to enter the liquid crystal cell.

Further, a micro prism can be arranged between the liquid crystal cell and the background plate.

[0021]

[Action]

(1) When used as a reflection mode type liquid crystal panel: When the liquid crystal is in a light transmitting state, the light incident on the liquid crystal cell is transmitted through the liquid crystal cell almost as it is without being scattered. The light transmitted through the liquid crystal cell reaches the background plate, where it is absorbed if the background plate is black, or only the light of that color is reflected if the background plate is colored. Therefore, the light-transmitting pixel appears to the observer as black or a background color. If there is a micro prism, directivity is added, but basically the same operation is performed.

When the liquid crystal is in the scattering state, the light incident on the liquid crystal cell is scattered by the liquid crystal molecules and reflected in all directions, so that the cell looks bright. Further, when the light is transmitted through the liquid crystal cell and reflected by the micro prism, the returned light is also scattered by the liquid crystal molecules. Therefore, if the incident light is white light, the pixels in the scattered state appear cloudy to the observer.

(2) When used as a transmission mode type liquid crystal panel: Light is incident from a light source coupled to the side edge of the liquid crystal cell. Instead of the conventional light scattering plate and light guide plate, the liquid crystal cell itself has the functions of scattering and light guiding.

That is, when the liquid crystal is in the light transmitting state, the light incident on the liquid crystal cell from the side surface from the light source is totally reflected inside the liquid crystal cell and does not go out of the liquid crystal cell. Therefore, the observer sees almost all the pixels in the light transmitting state as black or the background color.

When the liquid crystal is in a scattering state, the light incident from the light source to the liquid crystal cell from the side surface is scattered by the liquid crystal molecules and reflected in all directions to make the cell appear bright. Further, when the light is transmitted through the liquid crystal cell and reflected by the micro prism, the returned light is also scattered by the liquid crystal molecules. Therefore, if the incident light is white light, the pixels in the scattered state appear cloudy to the observer.

[0026]

1 is an external view of a transflective liquid crystal display panel according to an embodiment of the present invention. The components of the embodiment shown in FIG. 1 are roughly composed of a liquid crystal cell 1 that changes its state between a light transmitting state and a light diffusing state, and an illumination light source 2 arranged by forming an optical coupling on the side surface of the liquid crystal cell 1. The liquid crystal cell 1 comprises a micro prism plate 3 arranged on the side opposite to the observer side of the main surface, and a background plate 4 arranged on the back side of the micro prism plate 3.

The liquid crystal cell 1 is a liquid crystal cell which utilizes a light scattering mode, and a transparent glass substrate 1 has a liquid crystal layer 11 which changes between a light transmitting state and a light scattering state in accordance with an applied electric field.
It is sandwiched between 2 and 13. As such a liquid crystal, a liquid crystal utilizing the light scattering mode as described in the section (3) in the section of the conventional art is suitable.

These liquid crystals do not require an alignment film and do not require a polarizing plate. A common electrode 14 and a pixel electrode 15 made of ITO for driving a pixel are formed on the surfaces of the glass substrates 12 and 13 on the liquid crystal layer 11 side. Driving elements such as TFTs and other necessary members are also formed on the glass substrate, but the illustration thereof is omitted for simplicity in this drawing.

Since the liquid crystal cell 1 of this embodiment has a function as a light guide plate for the light from the illumination light source 2, it is necessary that the liquid crystal cell has a good transmittance. Therefore, it should be avoided to provide a layer having a high light absorption rate in the liquid crystal cell. It is desirable that the electrodes made of the ITO film formed on the glass substrates 12 and 13 also have a light transmittance of 90% or more.

Further, the glass substrates 12 and 13 must have a sufficient thickness so that the light is effectively introduced from the illumination light source 2 to the liquid crystal cell 1. The preferable thickness of the glass substrates 12 and 13 is 1 mm or more. Since the thickness of the glass substrate of the liquid crystal display panel currently used is 1.1 mm, this can be used. It may also be thicker than this.

Next, the illumination light source 2 is an edge type,
The fact that light is introduced from the side of the liquid crystal cell 1 is convenient for obtaining a thin surface light source like the conventional backlight shown in FIG. The light source itself has a configuration in which an elongated tubular lamp 21 such as a cold pole type white fluorescent lamp is covered with a reflector 22.

The inner surface of the reflector 22 is a mirror surface and the lamp 21
Reflects the light. The open ends of the reflector 22 sandwich the transparent glass substrates 12 and 13 so as to enclose the side edges of the liquid crystal cell. Although one lamp 21 is used in the embodiment, two lamps may be used, one on each side edge of the liquid crystal cell 1. In order to obtain uniform illuminance, a line light source is preferable to a point light source. Further, if a method of introducing light from the side edge of the liquid crystal cell 1 is adopted, an illumination method other than that shown in FIG. 1 may be used.

A characteristic point of this embodiment is that neither the light guide plate nor the two diffusion plates are required unlike the conventional backlight device shown in FIG. Therefore, the thickness of the liquid crystal display panel is correspondingly reduced, and the number of parts is reduced to reduce the manufacturing cost.

The micro-prism plate 3 is the same as that used in the prior art of FIG. 5, and a large number of chevrons each having a substantially triangular cross section are arranged in an array. As the material, polycarbonate or acrylic having a refractive index of about 1.5 can be used. When formed of these materials, the pitch of the peaks is in the range of 2,30 microns to several hundreds of microns.
By using the micro prism 3, the display brightness is improved and the display is easier to see.

The pitch of the peaks can be arbitrarily selected, but a fine pitch in the range of 20 to several hundreds of microns is preferable in order to avoid the moire fringe phenomenon due to pixels. Two micro prism plates may be stacked and used so that the directions of the prism arrays intersect each other. Further, as for the detailed specifications such as the shape of the micro prism and the direction of the apex angle, an appropriate one can be selected.

The background plate 4 is the color seen by the observer when the liquid crystal cell 1 is in the transmissive state. Therefore, the color of the surface facing the micro prism plate 3 should be dark. That is, a material having a low light reflectance is selected. The color is black in the case of a monochrome display panel. When the background of the color display panel is desired to be a desired color, the color of the background plate 4 is selected.

Next, the operation of the transflective liquid crystal display panel of this embodiment will be described below with reference to FIGS. 2 and 3 each show a cross section of one pixel of the liquid crystal cell 1. It is desirable that the color has high purity.

(1) When used as a reflection mode type liquid crystal panel (FIG. 2): The illumination light source 2 is not used in this mode. The light source is the light 31 from the observer 30 side. Figure 2
(A) is a case where the liquid crystal cell 1 is in a light transmitting state.
The light ray 31 passes through the transparent liquid crystal cell 1 in the light transmitting state as it is, and the direction of the light ray 31 does not change. The light ray 31 is incident on the micro-prism plate 3 and most of the light ray 3
2 passes through the microprism plate 3 (even if refracted) and is absorbed by the dark side of the background plate 4.

Light rays 31 reaching the micro-prism plate 3
The rest of the light is reflected as ray 33. The vertical reflection on the micro prism plate 3 is theoretically zero. However, in reality, although it is very small, it exists a little, and it is about 1/100 of the incident light on average in all directions.

If the background plate 4 is black, an observer who looks at the liquid crystal cell 1 from the front will see the light transmitting pixels as black. If the background plate 4 is colored, the color can be seen.

FIG. 2B shows the case where the liquid crystal is in the scattering state.
Is. The light ray 31 that has entered the liquid crystal cell 1 has liquid crystal molecules 16
Is scattered by and reflected in all directions. In addition, the liquid crystal cell 1
The light 34 that has passed through and reached the micro prism plate 3 is transmitted through the micro prism plate 3 and is absorbed by the dark background plate 4. The remaining light ray 35 is reflected by the micro prism plate 3, returns to the liquid crystal cell 1, and is scattered by the liquid crystal molecules 16 again.
Therefore, if the incident light is white light, the pixels in the scattered state appear cloudy to the observer 30.

(2) When used as a transmission mode type liquid crystal panel (FIG. 3): In this mode, the illumination light source 2 optically coupled to the side edge of the liquid crystal cell 1 is used. Instead of the conventional light scattering plate and light guide plate, the liquid crystal cell 1 itself has a function of scattering and guiding light.

FIG. 3A shows the case where the liquid crystal cell 1 is in the light transmitting state. When the liquid crystal 11 is in a light transmissive state, both the glass substrates 12 and 13 and the liquid crystal 11 are transparent with respect to light transmission and have a substantially uniform refractive index. The light is not scattered by the liquid crystal 11.

The light 36 incident from the side surface of the liquid crystal cell 1 from the illumination light source 2 is repeatedly totally reflected within the liquid crystal cell 1 as shown in FIG. Therefore, the pixels in the light transmitting state appear almost black to the observer 30.

FIG. 3B shows the case where the liquid crystal is in the scattering state.
Is. Light 36 incident on the liquid crystal cell 1 from the side of the illumination light source 2 is scattered by the liquid crystal molecules 16 and reflected in all directions. Light 37 reflected by the liquid crystal molecules 16 and incident on the micro prism plate 3 is transmitted through the micro prism plate 3 and absorbed by the dark background plate 4. The remaining light 38 is reflected by the micro prism plate 3, returns to the liquid crystal cell 1, and is scattered by the liquid crystal molecules 16 again. The micro prism plate 3 has a function of promoting light scattering and increasing the brightness of the screen.

Therefore, the entire liquid crystal cell 1 is bright and has uniform brightness. If the incident light is white light, the pixels in the scattered state appear cloudy to the observer 30. As described above, in the present embodiment, the light transmission of the liquid crystal cell 1 is performed both when used as the reflection mode type liquid crystal panel (FIG. 2) and when used as the transmission mode type liquid crystal panel (FIG. 3). The dark display and the bright display of the pixel can be obtained by selectively switching between the two states of the state and the light scattering state.

In the example of actually manufacturing the transflective liquid crystal display panel of the above embodiment, the following dimensions were obtained. Thickness of liquid crystal cell: 2.2 mm Thickness of micro prism plate: 0.5 mm Thickness of background plate: 0.2 mm Total: 2.9 mm In this case, the thickness was about half the thickness of the conventional transmissive liquid crystal display panel.

In the above embodiments, the micro prism is not an essential requirement. The configuration and operation when the micro prism is omitted will be obvious from the description of the above embodiment. In addition, the microprism 2
It may have a single-piece configuration.

Table 1 below shows a comparison of the display performances measured in the configuration examples of the conventional liquid crystal display panel and the liquid crystal display panel according to the embodiment of the present invention. According to the measurement results, the display performance of the conventional example and the display performance of the present example are almost the same. The measurement samples are as follows.

I. Conventional twisted nematic translucent liquid crystal display panel II. Transflective liquid crystal display panel IIa having a transmission state and a scattering state according to the configuration example of the embodiment of the present invention IIa: with edge light, without micro prism plate,
Polymer dispersed liquid crystal (PDLC) IIb: with edge light, 1 micro prism, P
DLC IIc: with edge light, 2 micro prisms (orthogonal), PDLC

[0051]

[Table 1] I 11a IIb IIc reflectance 25% 16% 40% 65% Contrast in reflection mode 10/1 9/1 10/1 12/1 Contrast in dark room (with edge light illumination) 100/1 15/1 20 / 1 20/1 bright room (with illumination edge light) contrast in 20/1 13/1 16/1 16/1 liquid crystal display panel of the present invention described above is not limited to the above embodiments, those skilled in the art If so, it will be clear that various changes and improvements can be made based on the content of the disclosure.

[0052]

According to the present invention, a liquid crystal cell that changes its state between a transmission state and a scattering state of light according to an applied electric field is used, and light is directly introduced into the cell from a side edge of the liquid crystal cell. By adopting the introduction method, the light guide plate and the light diffusing plate are not required, thus reducing the thickness of the liquid crystal display panel,
The number of parts is reduced, and the manufacturing cost can be reduced.

Further, since the scattering mode is used, an alignment film is unnecessary, and the number of manufacturing steps can be reduced. Further, since no polarizing plate is required, the utilization factor of the light source is high and a display screen with light brightness can be obtained.

[Brief description of drawings]

FIG. 1 is an external view showing a structure of a transflective liquid crystal display panel according to an embodiment of the present invention.

FIG. 2 is a cross-sectional view of a pixel for explaining an operation when a transflective liquid crystal display panel according to an exemplary embodiment of the present invention is used in a reflective mode.

FIG. 3 is a cross-sectional view of a pixel for explaining an operation when a transflective liquid crystal display panel according to an exemplary embodiment of the present invention is used in a transmissive mode.

FIG. 4 is an external view of an edge light type backlight device according to a conventional technique.

FIG. 5 is an external view showing a state in which a micro prism plate is stacked on a conventional backlight device.

FIG. 6 is an external view of a transflective liquid crystal display panel according to a conventional technique.

[Simple explanation of symbols]

 1. Liquid crystal cell 2. Illumination light source 3 Micro prism plate 4 Background plate 11 Liquid crystal 12, 13 Transparent Glass substrate 14 Common electrode 15 Pixel electrode 16 Liquid crystal molecule 21 Tubular lamp 22 Reflector 30 Observer 31 ~ 38 ...

Claims (11)

[Claims] 1. A liquid crystal cell containing a liquid crystal that changes its state between a transmission state and a scattering state of light in accordance with an applied electric field, and a background plate arranged to face one main surface of the liquid crystal cell. And a light source that is coupled to a side edge of the liquid crystal cell and can allow light to enter the liquid crystal cell. 2. The liquid crystal cell has two transparent substrates sandwiching the liquid crystal, and the transparent substrates are arranged so as to totally reflect the light from the light source on the substrate surface and guide the light to the liquid crystal. Item 3. A liquid crystal display panel according to item 1. 3. The light source has a tubular light emitting source arranged along a side edge of the liquid crystal cell, and a light reflecting surface surrounding the light emitting source and having a side edge of the liquid crystal cell as an open end. Item 2
The liquid crystal display panel described. 4. The liquid crystal display panel according to claim 1, wherein the background plate has a black surface, and the black surface faces the direction of the liquid crystal cell. 5. The background plate has a surface of a specific color, and the surface of the specific color faces the direction of the liquid crystal cell.
4. The liquid crystal display panel according to any one of 3 to 3. 6. The liquid crystal display panel according to claim 1, further comprising a transparent micro-prism plate arranged between the liquid crystal cell and the background plate. 7. The micro-prism plate is characterized in that each micro-prism has a triangular cross-sectional shape, and the apex angle of the triangle is substantially in the range of 60 ° to 130 °.
7. The liquid crystal display panel according to any one of 6. 8. The liquid crystal display panel according to claim 1, wherein the micro-prism plate has an arrangement pitch in the plane of the micro-prisms of 20 to several hundreds of microns. 9. The liquid crystal display panel according to claim 1, wherein the liquid crystal is a liquid crystal utilizing a dynamic scattering effect. 10. The liquid crystal display panel according to claim 1, wherein the liquid crystal is a liquid crystal that utilizes a phase transition effect between a cholesteric phase and a nematic phase. 11. The liquid crystal display panel according to claim 1, wherein the liquid crystal is a polymer dispersion type liquid crystal.