JPH1096915A - Liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve availability of light emitted from a backlight and to improve contrast and visibility by arranging so that an axis of polarization of a polarizing plate is nearly parallel to the axis of polarization of a polarizing beam splitter. SOLUTION: The light outgoing from a light source 8 is made incident on a light transmission layer 9, and reflects repeatedly by boundaries in the light transmission layer 9 to arrive at a scatter pit 13. Since a refractive index difference between the light transmission layer 9 and a scatter pit boundary is remarkably small on the scatter pit 13, light scatter occurs. The light is scattered to a panel side mainly to go out from the light transmission layer 9 to the outside. One polarization transmits through the polarizing beam splitter 5, and is scattered by a scatter layer, and transmits through the polarizing plate 3 to be modulated by a liquid crystal panel 2. On the other hand, the polarization not transmmitting through the polarizing beam splitter 5 is reflected by the polarizing beam splitter 5, and transmits through the light transmission layer 9, and transmits through a 1/4 wavelength plate 6 to be reflected by a reflection plate 7, and transmits again through the 1/4 wavelength plate 6, the light transmission layer 9, and is twisted by 90 deg. in its polarization direction to transmit through the polarizing beam splitter 5.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a structure of a liquid crystal display device used for a direct-view and projection type display as a terminal of an information device, a television, a projector or a bulletin board.

[0002]

2. Description of the Related Art In recent years, as information devices have become smaller and lighter,
The displays mounted on them are also required to save power. A liquid crystal display device using the TN method is used for the small display capacitance device, a liquid crystal display device using the FTN method is used for the medium display capacitance device, and a T device using an active element is used for the large display capacitance device.
A liquid crystal display device of the N type is used. In particular, recently, a large-capacity color display with a backlight has been demanded, and applications of using an information input device such as a tablet on these displays have been expanding. In addition, these information devices are often required to be portable, and are necessarily driven by a battery. For this reason, brightness as a liquid crystal display device with backlight,
Low power consumption is eagerly desired.

Further, from the viewpoint of low power consumption, a device has been devised which is usually used as a reflection type liquid crystal display device without using a backlight, and is used in a dark use environment.

[0004]

However, in a conventional TN or FTN liquid crystal display device using a polarizing plate, only half of the light emitted from the backlight can be used because the polarizing plate is used. The display was dark. Therefore, half of the power consumption of the backlight was discarded. In order to solve such a situation, in Japanese Patent Application Laid-Open No. 05-119293, the backlight is arranged so that the optical axis of the backlight and the normal line of the liquid crystal panel form an angle near the Brewster angle. In addition, Japanese Patent Application Laid-Open
In Japanese Patent No. 027420, a polarizing beam splitter is provided in place of a polarizing plate disposed on the back side of a liquid crystal panel to divide light from a light source into two polarized lights, one polarized light is incident on the liquid crystal panel, and the other polarized light is halved. The light is incident on the liquid crystal panel with the polarization direction twisted by 90 degrees by the wave plate. In each case, the utilization efficiency of the light source approaches 100% by these measures.

However, the former method requires a collimator light source as a light source, and it is disadvantageous in terms of space to arrange a liquid crystal panel obliquely with respect to this light source. In the latter case, the size of the light source unit becomes extremely large, which is not practical in terms of space. Further, in the latter case, when applied to a direct-view type liquid crystal display panel, there is a problem that when the liquid crystal panel is viewed from the front side of the liquid crystal panel, the mirror surface of the polarizing beam splitter is visible, and visibility is reduced.

According to Japanese Patent Application Laid-Open No. Hei 6-19012, a projector using a cholesteric liquid crystal cell as a polarizing beam splitter is disclosed. According to this, it is possible to avoid an increase in the size of the device as in the former case.
However, if this principle is applied to a direct-view type liquid crystal display panel as it is, the mirror surface of the polarizing beam splitter can be seen, and there is a problem that visibility is reduced.

In a liquid crystal display device using both a reflection type and a backlight, the reflectance is low because the reflection plate disposed on the back side of the liquid crystal panel is a transflective type, and the display is dark when used as a reflection type. Also, when a backlight is used, the liquid crystal panel cannot be sufficiently illuminated because the light is somewhat absorbed and reflected by the semi-transmissive reflection plate, and the display becomes dark.

Accordingly, the liquid crystal display device of the present invention solves such a problem.
It is an object of the present invention to provide a liquid crystal display device which can utilize nearly 100% of light emitted from a backlight and has good contrast and visibility. Another object of the present invention is to provide a liquid crystal display device that can use nearly 100% of light emitted from a backlight and can be used as a reflection type in a bright place.

[0009]

A liquid crystal display device according to the present invention comprises a liquid crystal panel having a liquid crystal layer sandwiched between a pair of substrates having electrodes on inner surfaces facing each other, and a liquid crystal panel disposed on the back of the one substrate. In a liquid crystal display device having a backlight, a first polarizing plate is provided on an outer surface of the other substrate, and a second polarizing plate is provided on a surface of the one substrate on which the backlight is provided, A polarization beam splitter, a light guide plate or a light source, a quarter-wave plate, and a reflection layer are arranged, and a polarization axis of the second polarization plate and a polarization axis of the polarization beam splitter are arranged substantially aligned. It is characterized by the following.

According to this configuration, one of the polarized lights out of the light from the light source is directly or reflected by the reflective layer, passes through the plane-type polarizing beam splitter and the polarizing plate 2, and is modulated by the liquid crystal panel. Of the light from the light source, the component orthogonal to the previous polarized light is reflected by the plane-type polarizing beam splitter, passes through the quarter-wave plate, is reflected by the reflective layer, passes through the quarter-wave plate again, and has the polarization axis. Is rotated by 90 degrees and enters the polarization beam splitter. This time, since the polarization axis is rotated by 90 degrees, it is transmitted through the polarization beam splitter and the polarizing plate 2 and modulated by the liquid crystal panel.

As described above, since the light of the light source is effectively modulated by the liquid crystal panel almost 100%, the light of the conventional backlight is reduced.
Double brightness can be realized. In addition, power consumption can be reduced by half in order to make the brightness equal to the conventional brightness. Further, the polarizing plate 2
Not really necessary. If the polarizing plate 2 is removed, when the display is viewed from the front, the reflection of the polarizing beam splitter rides on a portion where black is originally displayed, and the contrast is reduced in a bright place.

In the present invention, by inserting the polarizing plate 2, the reflection of the polarizing beam splitter can be absorbed, and the contrast when viewed in a bright place can be remarkably improved. In this configuration, the visibility can be improved by disposing a non-glare plate on the surface and / or performing the anti-reflection treatment.

The present invention also provides a liquid crystal display device in which a liquid crystal layer is sandwiched between two substrates with transparent electrodes and a backlight is disposed on the back surface of the substrate.
It has a structure in which a polarizing plate, two substrates sandwiching liquid crystal, a planar polarizing beam splitter, a light source or a light guide layer, a quarter-wave plate, and a reflective layer are stacked. With this configuration, when used in the reflection type, light incident from the table is transmitted through the light scattering plate and the polarizing plate, is modulated by the liquid crystal panel, and reaches the polarizing beam splitter. One polarized light is reflected and the other polarized light is transmitted according to the degree of modulation in the liquid crystal panel. The reflected polarized light is modulated again by the liquid crystal panel, analyzed by the polarizing plate, and scattered by the light scattering plate. In the case of displaying with a backlight, the light from the light source is polarized in almost the same direction, enters the liquid crystal panel, is modulated, and transmits through the polarizing plate and the light scattering plate according to the principle described above. As described above, it is possible to realize a liquid crystal display device having both the reflection type and the backlight type without deteriorating the performance of each. In this configuration, visibility can be improved by performing anti-reflection treatment on the surface.

Further, the second liquid crystal display device of the present invention is characterized in that there is provided a means for inverting display data applied to the liquid crystal layer between black and white when using as a reflection type and when using a backlight. Thereby, it is possible to prevent the contrast from being inverted between the case of using the reflection type and the case of using the transmission type (backlight).

[0015]

Embodiments of the present invention will be described below with reference to the drawings.

(Embodiment 1) In this embodiment, a non-glare plate (14), a polarizing plate (1), a liquid crystal panel (2), a liquid crystal panel (2), and a thin backlight from which light enters the light guide layer from the side are used. A polarizing plate (3), a light scattering plate (4), a planar polarizing beam splitter (5), a light source (8), or a light guide layer (9), a quarter-wave plate (6), and a reflecting plate (7) An example is shown in which the polarizing plate 3 and the planar polarizing beam splitter have a superposed structure, and the polarizing plates 3 and the planar polarization beam splitters are arranged so as to align the polarization axes with respect to the transmitted light. FIG. 1 shows a simple sectional view of the liquid crystal display device of the present embodiment. In the figure, points ← → and ○ indicate the polarization direction.

The principle will be described with reference to FIG. Light emitted from the light source is incident on the light guide layer, and is repeatedly reflected at the interface in the light guide layer to reach the scattering pits (13). Then, in the scattering pit, since the difference in refractive index between the light guide layer and the scattering pit interface is extremely small, light enters the scattering pit, and light scattering occurs. The light is mainly scattered to the panel side and exits from the light guide layer. One polarized light is transmitted by the polarization beam splitter, scattered by the scattering layer, transmitted through the polarizing plate, and modulated by the liquid crystal panel.

On the other hand, the polarized light that has not passed through the polarizing beam splitter is reflected by the polarizing beam splitter, passes through the light guide layer, passes through the quarter-wave plate, and is reflected by the reflector.
Again, the light passes through the quarter-wave plate and the light guide layer and is twisted by 90 degrees in the polarization direction, and then passes through the polarization beam splitter.

In a conventional liquid crystal display device using a backlight, display brightness was 200 cd / cm 2, but when the same light source was used, the liquid crystal display device of this embodiment had a brightness of 35 cd / cm 2.
0 cd / cm2 was realized. When the brightness was the same as before, the power consumption was reduced to about half.

As the non-glare plate, a plate manufactured by Nitto Denko Corporation was used. However, the use of a non-glare plate having a surface provided with an anti-reflection coating improves visibility. Of course, it is not necessary to use it.

The polarizing plate used was manufactured by Nitto Denko Corporation.
A commonly used polarizing plate can be used. The polarization direction of the polarizing plate may be optimized by the structure and arrangement of the liquid crystal panel used.

Although a color liquid crystal panel using a TFT element is used as a liquid crystal panel, an active type liquid crystal panel using an MIM element or the like, a liquid crystal panel such as an STN, a normal TN type liquid crystal panel, or the like is used in the display principle. Any material that requires polarized light can be used.

The light scattering plate is necessary to hide the shape of the light source, but care must be taken in selecting the light scattering plate because if the scattering property is too high, the polarization axis is disturbed. Further, if the light scattering plate has a refractive index anisotropy, the degree of polarization is also lowered. Therefore, it is desirable to use a light scattering plate having as little refractive index anisotropy as possible. In the case where a material having a refractive index anisotropy is unavoidably used, it is preferable that the anisotropic direction coincides with or is perpendicular to the polarization axis. Further, a prism lens array may be inserted at this position in order to optimize the light scattering direction. As a method of increasing the contrast, as shown in FIG. 5, if the light scattering plate is removed and this light scattering plate is used instead of the non-glare plate (14), the scatterer can be removed from the polarizing optical system, and the contrast can be reduced. Improved. When the surface of the light scattering plate was subjected to anti-reflection treatment, reflection of the surrounding scenery was reduced, and visibility was extremely improved.

The light scattering plate can be used even if the scattering degree is reduced by optimizing the size and arrangement of the scattering pits (for example, by making them extremely fine).
In extreme cases, it can be removed.

As the plane-type polarizing beam splitter, one having a structure in which a cholesteric cell in which a cholesteric liquid crystal is sealed in a glass cell is sandwiched between two quarter-wave plates is used. This planar polarization beam splitter reflects one circularly polarized light component of the incident light on the cholesteric layer, transmits another circularly polarized light component, and converts the transmitted circularly polarized light into linearly polarized light by a quarter wavelength plate. Configuration. The reflected circularly polarized light is converted into linearly polarized light by the quarter-wave plate on the reflected light side and emitted. As the cholesteric cell, a film-type cholesteric film using a polymer liquid crystal or the like can be used in addition to a liquid crystal sealed in the cell.

The planar polarizing beam splitter used in the present invention may have a function as a planar polarizing beam splitter, and its structure is not limited to that shown here. Regarding the relationship between the polarization direction of the polarizing beam splitter and the arrangement of the light sources, the arrangement shown in FIG. 1 has the best polarization separation property and the brightest display, but not limited to this arrangement, a display that is much brighter than before can be obtained. Can do it.

The quarter-wave plate is arranged so that its extending direction forms an angle of about 45 degrees with the polarization direction of the polarizing beam splitter. Also, as the quarter wavelength plate,
Any material having the function can be used, and any material having good transparency can be used. The insertion position may be right below the polarizing plate 2.

As the reflection plate, a silver film or a silver vapor-deposited plate having a high reflectance is preferable, but other materials having a high reflectance can be used.

As a light source, it is ideally desirable that the light be incident on the polarizing beam splitter at an incident angle close to the vertical. Therefore, a planar light source is preferable. However, in this embodiment, a cold cathode tube was used. Therefore, the light source and the polarization beam splitter are arranged as shown in FIG. 1 in consideration of the incident angle dependence of the polarization characteristics of the polarization beam splitter.

The positional relationship between the polarizing plate (1) and the polarizing plate (3) changes depending on the twist angle, arrangement, and display (ie, normally black or normally white) of the liquid crystal panel used when an electric field is applied. In the embodiment, the liquid crystal panel is 90
As a twist orientation, the polarizing directions of the polarizing plates 1 and 2 were further aligned to obtain a normally black display.

(Embodiment 2) In this embodiment, a non-glare plate (14), a polarizing plate (1), a liquid crystal panel (2), a polarizing plate are used from the front side using a backlight from which light enters from the center of the light guide layer. (3) a structure in which a light scattering plate (4), a planar polarization beam splitter (5), a light source (8) or a light guide layer (9), a quarter-wave plate (6), and a reflection layer (7) are stacked. An example is shown in which the polarizing plate (3) and the plane-type polarizing beam splitter are arranged so as to overlap with each other with the polarization axes for the transmitted light being aligned. FIG. 2 shows the liquid crystal display device of the present embodiment. Although the position of the light source (8) and the structure of the light guide layer (9) are different from those of the first embodiment, the basic principle of polarization is the same.

With this principle and structure, it is possible to realize 1.5 times the brightness of the conventional liquid crystal display device with a backlight.

The light-scattering plate (4) is necessary to hide the shape of the light source, but care must be taken in selecting the light-scattering plate (4) because too high scattering properties will disturb the polarization axis. If the light scattering plate has a refractive index anisotropy, the degree of polarization is also lowered. Therefore, it is desirable to use a light scattering plate having as little refractive index anisotropy as possible. In the case where a material having a refractive index anisotropy is unavoidably used, it is preferable that the anisotropic direction coincides with or is perpendicular to the polarization axis. Further, a prism lens array may be inserted at this position in order to optimize the light scattering direction.

As a method for increasing the contrast, as shown in FIG. 5, if the light scattering plate is removed and this light scattering plate is used instead of the non-glare plate, the scatterer can be removed from the polarizing optical system, and the contrast can be reduced. Improved. When the surface of the light scattering plate was subjected to anti-reflection treatment, reflection of the surrounding scenery was reduced, and visibility was extremely improved.

The position of the quarter-wave plate may be between the light guide layer (9) and the polarizing beam splitter (5). Also, this 1 /
Even if the four-wavelength plate is removed, a brighter display can be performed as compared with the related art. Because 13. This is because there is a light scattering portion such as a scattering pit, and the polarization of the reflected light from the polarizing beam splitter changes in this portion.

Other characteristics required for each member are the same as those in the first embodiment.

(Embodiment 3) In this embodiment, an example will be described in which a flat light source is used and the configuration is the same as that of the first embodiment. FIG. 3 shows a simple sectional view of the liquid crystal display device of this embodiment. The configuration will be described with reference to FIG. The non-glare plate (14), the polarizing plate (1), the liquid crystal panel (2), the polarizing plate (3), the flat polarizing beam splitter (5), and the quarter-wave plate (6) are the same as those described in the first embodiment. Can be used. An EL element was used as the flat light source (10). Further, the reflection layer (7) on the back side can also serve as a reflective electrode of the flat light source.

In this embodiment, an organic EL is used as a flat light source.
An element was used. When a flat light source is used, a light scattering plate, which is necessary for hiding the shape of the light source in the first and second embodiments, is not required, so that the polarization efficiency is increased.

The organic EL used here uses an aluminum quinolinium complex for the light emitting layer. However, in order to increase the efficiency of the backlight, the structure shown in FIG.
The transparency of the organic EL layer is important. Therefore, an EL element having a highly transparent light-emitting layer is most suitable. With such a configuration, light emitted from the flat light source is directly or reflected by the reflection electrode, passes through the quarter-wave plate, enters the polarization beam splitter, transmits one polarized light, and is orthogonal to this. Polarized light is reflected. The reflected polarized light is a 波長 wavelength plate,
The light passes through the flat light source and is reflected by the reflection plate. The light again passes through the flat light source and the quarter-wave plate, and its polarization direction is twisted by 90 degrees, enters the polarization beam splitter, and passes through.

Even if the quarter-wave plate is removed, a brighter display can be performed as compared with the conventional case. This is because there is a light scattering portion such as a flat light source, and the polarization of the light reflected from the polarizing beam splitter changes in this portion.

Although an organic EL is used in this embodiment, an inorganic EL having high transparency can be used. Further, other light sources such as a VFD, a micro vacuum element, and a plasma light source can be used.

(Embodiment 4) In this embodiment, a light scattering plate (4), a polarizing plate (1), a liquid crystal panel (2), a planar polarizing beam splitter (5), a light source (8), or a light guide from the front side. An example of a liquid crystal display device having a configuration in which a layer (9), a quarter-wave plate (6), and a reflective layer (7) are stacked is shown. FIG. 4 shows a simple sectional view of the liquid crystal display device of this embodiment. With this configuration, when used in the reflection type, light incident from the table is transmitted through the light scattering plate and the polarizing plate, is modulated by the liquid crystal panel, and reaches the polarizing beam splitter. One polarized light is reflected and the other polarized light is transmitted according to the degree of modulation in the liquid crystal panel. The transmitted light is 1 /
The polarization direction is twisted by 90 degrees by the four-wavelength plate and the reflection plate, and attempts to enter the polarization beam splitter again. However, since the polarization directions are orthogonal to each other, the light cannot be transmitted. On the other hand, the polarized light reflected by the polarizing beam splitter with the light incident from the front side is modulated again by the liquid crystal panel, analyzed by the polarizing plate, scattered by the light scattering plate, and the display becomes easy to see. In the case of displaying with a backlight, the light from the light source is polarized in almost the same direction, enters the liquid crystal panel, is modulated, and transmits through the polarizing plate and the light scattering plate according to the principle described above. The thus manufactured liquid crystal display device is 50% brighter when used as a reflection type liquid crystal display than a conventional reflection type liquid crystal display device, and 50% brighter when used as a backlight type liquid crystal display device. I found it bright.

In this embodiment, the structure of the light guide layer used in the first embodiment is advantageous because the shape of the light source becomes difficult to see together with the light scattering plate.

The light scattering plate has a different role from the light scattering plates of the other embodiments, and plays a role of scattering the light reflected by the polarizing beam splitter to provide a white display. Further, since it is outside the polarization optical system, the degree of scattering can be optimized only from the viewpoint of visibility. When the surface of the light scattering plate was subjected to anti-reflection treatment, reflection of the surrounding scenery was reduced, and visibility was extremely improved.

(Embodiment 5) This embodiment shows an example in which a means for inverting the display data applied to the liquid crystal layer between black and white is provided in the case of the reflection type and the case of using the backlight in the fourth embodiment. Specifically, if the display is bright manually or in accordance with the surrounding brightness, the backlight is turned off and the display is performed in a reflection type. FIG. 6 shows a conceptual diagram of an apparatus for automatically switching between the reflection type and the backlight type. If the surroundings are dark,
The backlight is turned on and the data signal input to the data driver of the liquid crystal panel is inverted between black and white.
For this purpose, it is possible to select whether or not to insert an inverter between data signal lines to a data driver by a backlight control signal.

The reason why such an inverting circuit is necessary is that the liquid crystal display device shown in the fourth embodiment has a structure in which the reflection type and the transmission type (backlight) are used. This is because the polarization direction of the plate changes by 90 degrees. That is, the normally black mode and the normally white mode are switched. Therefore, with the configuration shown in this embodiment, it is possible to prevent the contrast from being inverted between the case of using the reflection type and the case of using the transmission type.

[0047]

As described above, according to the present invention, by combining a plane-type polarizing beam splitter and a polarizing plate, nearly 100% of the light emitted from the backlight can be used, and the contrast when viewed in a bright place is greatly increased. Can be improved. Further, a liquid crystal display device which can be used both as a reflection type and a backlight type, which is much brighter than the conventional one, can be realized. Further, since power consumption can be easily reduced, it can be mounted on a small information device.

[Brief description of the drawings]

FIG. 1 is a simple sectional view of a liquid crystal display device according to a first embodiment.

FIG. 2 is a simple sectional view of a liquid crystal display device according to a second embodiment.

FIG. 3 is a simple sectional view of a liquid crystal display device according to a third embodiment.

FIG. 4 is a simple sectional view of a liquid crystal display device according to a fourth embodiment.

FIG. 5 is a simple cross-sectional view of the liquid crystal display device according to the first embodiment.

FIG. 6 is a simple block diagram illustrating a circuit of a liquid crystal display device according to a fifth embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Polarizer 1 2 Liquid crystal panel 3 Polarizer 2 4 Light scattering plate 5 Polarizing beam splitter 6 1/4 wavelength plate 7 Reflector 8 Light source 9 Light guide layer 10 Flat light source 13 Scattering pit 14 X driver 15 Sensor circuit 16 Optical sensor 17 Backlight circuit 18 Driver circuit

Claims (6)

[Claims] 1. A liquid crystal display comprising a liquid crystal panel having a liquid crystal layer sandwiched between a pair of substrates having electrodes on opposing inner surfaces, and a liquid crystal display having a backlight disposed on the back of said one substrate. A first polarizing plate is disposed on an outer surface of the substrate, and a second polarizing plate, a polarizing beam splitter, a light guide plate or a light source, and a 、 A liquid crystal display device comprising a wavelength plate and a reflection layer, wherein a polarization axis of the second polarizing plate and a polarization axis of the polarization beam splitter are substantially aligned. 2. The liquid crystal display device according to claim 1, wherein
A non-glare layer is disposed on a surface of the liquid crystal display device. 3. The liquid crystal display device according to claim 2, wherein
A liquid crystal display device having its surface subjected to anti-reflection treatment. 4. A liquid crystal display device in which a liquid crystal layer is sandwiched between two substrates with transparent electrodes and a backlight is arranged on the back surface of the substrate, wherein a light scattering plate, a polarizing plate, and a liquid crystal are sandwiched from the front side. Sheets, a plane-type polarizing beam splitter,
A liquid crystal display device having a configuration in which a light source or a light guide layer, a quarter-wave plate, and a reflective layer are stacked. 5. The liquid crystal display device according to claim 4, wherein
A liquid crystal display device, wherein a surface of the liquid crystal display device is subjected to a reflection reducing process. 6. The liquid crystal display device according to claim 4, wherein
What is claimed is: 1. A liquid crystal display device comprising: means for inverting display data applied to a liquid crystal layer between black and white when a reflective type is used and when a backlight is used.