JPH06308543A - Display device - Google Patents

Abstract

(57) [Summary] [Object] To provide a display device which has less light loss, is brighter, has a faster response speed, is easy to manufacture, and has a simple device configuration as compared with a conventional liquid crystal display device. [Structure] A ferroelectric liquid crystal layer capable of responding to an electric field is adjacently arranged on a lower surface of a light guide plate having a light source on a side surface, and an alternating current near a relaxation frequency of a Goldstone mode of the liquid crystal is formed on the ferroelectric liquid crystal layer. A display device that displays an image by adjusting light emitted from the upper surface of the light guide plate by scattering of light by a disclination line that appears when an electric field is applied.

Description

Detailed Description of the Invention

[0001]

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

[0002]

2. Description of the Related Art Liquid crystal display devices are thin and lightweight, and are widely used in portable televisions, word processors and the like. However, generally, in these devices, the light loss due to the polarizing plate is large, and even the TN (twisted nematic) and STN (super twisted nematic) systems, which have the highest light utilization efficiency, have about 60% light loss. Therefore, in the transmissive liquid crystal display device having particularly good visibility, the burden of the backlight used on the back surface thereof is large.

As a display device for solving the problem of light loss,
In Japanese Unexamined Patent Publication No. 4-352129, a liquid crystal layer whose refractive index is changed by an electric field is superposed on a transparent plate having a predetermined refractive index, and light is irradiated from the side surface of the transparent plate to form a transparent plate and a liquid crystal layer. A device that displays by controlling the total reflection and transmission of light at the interface is described, but in order to transmit light, the transparent plate and the liquid crystal must have the same refractive index. However, since switching between total reflection and transmission of light is used, there is a problem that strong directivity occurs in the direction of light transmission and the viewing angle becomes narrow.

Further, in Japanese Laid-Open Patent Publication No. 5-2908, a plurality of light guide plates having different lengths are laminated, an inclined reflector is provided on the end face on the stairs, and a dimming liquid crystal plate is provided on the opposite face. Although the light distribution variable illumination device provided is described, there is a problem that the device becomes large in size when a large number of light guide plates have to be stacked when a so-called display is performed with various light distributions. Further, since the conventional dimming liquid crystal plate uses nematic liquid crystal, there is a problem that the applied voltage is high and a power supply circuit such as an inverter is required.

[0005]

SUMMARY OF THE INVENTION The present invention solves the above problems and provides a display device with less light loss than the conventional liquid crystal display device, which is bright and has a fast response speed and is manufactured. It is an object of the present invention to provide a display device that is easy to operate and has a simple device configuration.

[0006]

As a result of intensive studies to solve the above problems, the present inventor has found that a light guide plate having a light source on the side surface and a ferroelectric liquid crystal layer are arranged adjacent to each other to improve the ferroelectricity. A display device that applies an AC electric field in the vicinity of the relaxation frequency of the Goldstone mode of the liquid crystal to the liquid crystal layer and adjusts the amount of light emitted from the upper surface of the light guide plate by scattering of the disclination lines that appear is used for display. The inventors have found that they are bright and have a fast response speed, and have completed the present invention based on this finding.

That is, according to the present invention, a ferroelectric liquid crystal layer capable of responding to an electric field is disposed adjacently on the lower surface of a light guide plate having a light source on its side surface, and the ferroelectric liquid crystal layer has a Goldstone mode of this liquid crystal. A display device characterized by displaying an image by adjusting light emitted from the upper surface of a light guide plate by scattering of light by a disclination line that appears when an AC electric field near the relaxation frequency is applied. .

The structure and operating principle of the display device of the present invention will be described below with reference to FIG. FIG. 1 is a sectional view of an example of the display device of the present invention. A light source 2 used as a side light is provided at one end or both ends of the light guide plate 1. A ferroelectric liquid crystal layer 4 capable of responding to an electric field is arranged adjacent to the light guide plate 1. In the device of FIG. 1, an electrode 5 for applying an electric field is provided between the light guide plate 1 and the ferroelectric liquid crystal layer 2.
This electrode may be provided on the lower surface of the electrode supporting substrate 6 in advance, or may be directly provided on the lower surface of the light guide plate 1. In the device of FIG. 1, the ferroelectric liquid crystal layer 4
An electrode 5'and an electrode supporting substrate 6'are provided on the surface opposite to the surface facing the light guide plate 1.

In order to improve the utilization efficiency of light, the light source 2
A reflection plate 7 may be provided below the reflection plate 3 for use in and the ferroelectric liquid crystal layer 4 capable of responding to an electric field. In this case, the lower electrode 5'may also serve as a reflector. Further, a light diffusion plate 8 may be provided on the light guide plate 1 in order to improve the viewing angle characteristic of the display.

The light incident on the light guide plate 1 from the light source 2 usually has a higher refractive index than the outside air, so that most of the light propagates while being repeatedly reflected inside the light guide plate 1. In this case, if there is an object that scatters light on the surface where the light is reflected, the light is scattered here, and the light that has not been reflected on the inner surface goes out. By utilizing this, light is applied to one surface of the light guide plate, and unevenness is applied to the surface so that the light can be emitted relatively uniformly over the entire surface. .

In the present invention, a ferroelectric liquid crystal is used as this scatterer. Usually, a ferroelectric liquid crystal is used for display by combining it with a polarizing plate in the form of a surface-stabilized cell exhibiting a memory property, and the present inventor has disclosed it in JP-A-3-228019.
As proposed in the publication, by applying an AC electric field having a frequency close to the relaxation frequency of the Goldstone mode of the ferroelectric liquid crystal itself, a structure similar to the spiral structure is created even in the thin cell in which the spiral is unwound. The light is scattered by the disclination line that appears at this time.

In the display device of the present invention, such a ferroelectric liquid crystal layer is installed adjacent to the lower surface of the light guide plate to control the emission of light from the upper surface of the light guide plate to display an arbitrary image. is there.

The light guide plate 1 may be made of transparent plastic such as acrylic resin, polycarbonate, polyvinyl chloride, or glass. If a relatively thin plastic plate or the like is used, the entire device can be made flexible and curved surface display can be performed.

The light source 2 is not particularly limited, but is preferably an elongated hot cathode tube or cold cathode tube which does not require any light collecting means because light is incident from the end surface of the light guide plate 1. The light source 2 may be provided on only one end face as shown in FIG. 1, or may be provided on the left and right two end faces or more end faces.

In order to improve the incidence efficiency of the light source 2, the light source reflection plate 3 may be used. This only needs to reflect the light emitted from the light source 2. For example, a white polyester film, a metal vapor deposition film, a metal plate or the like is wound around the light source 2 to be used. In the present invention, bistability (memory property) is not used for display. Therefore, any ferroelectric liquid crystal can be used as the ferroelectric liquid crystal of the ferroelectric liquid crystal layer 4. Above all, when a liquid crystal composition containing a ferroelectric polymer liquid crystal is used, it is easy to manufacture the cell portion and increase the area thereof. The thickness of the ferroelectric liquid crystal layer is usually preferably 1 μm or more and 10 μm or less. If it is less than 1 μm, it may not be possible to sufficiently scatter light, or it may be difficult to manufacture a cell.
If it exceeds μm, a high voltage may be required as the applied voltage.

There is no particular limitation on the method of manufacturing the cell portion,
A known injection method or a method of laminating after coating and film formation can be used. The ferroelectric liquid crystal does not necessarily have to be aligned because it utilizes the scattered and non-scattered (transparent) states, but it is preferable that the liquid crystal be horizontally aligned in the plane in order to improve the contrast.

As the electrodes 5 and 5 ', at least the upper electrode 5 is transparent. The lower electrode 5'is not necessarily required to be transparent, but may be used also as the auxiliary reflector 7 using a metal electrode. The upper electrode 5 may be provided directly on the lower surface of the light guide plate 1. The electrode pattern may be a dot-matrix type using a striped pattern or a segment type having a shape to be displayed.

The electrode supporting substrates 6 and 6'are not particularly limited in material such as glass plate and plastic plate, but those having transparency on the upper side are used. However, it is not necessary when the electrodes are directly provided on the lower surface of the light guide plate 1 as described above. Preferably, a plastic plate is used together with the light guide plate, or a structure in which an electrode is directly provided on the lower surface of the light guide plate made of a plastic plate can impart flexibility to the entire device, and the application is expanded.

When light is scattered by the ferroelectric liquid crystal layer 4 provided under the light guide plate 1, the scattered light goes out not only upward but also downward. Therefore, when it is desired to use the light more efficiently, the reflector 7 is arranged in the lowest layer. The reflection plate may be a metal plate of aluminum, iron or the like, or a plate in which metal layers are vapor-deposited or laminated, or may be a sheet of white paper, plastic, or the like. Further, it may be integrated with the lower electrode support substrate 6, or the metal reflection layer may also serve as the lower electrode.

In order to improve the visibility of the light emitted from the upper surface of the light guide plate 1, the light diffusion plate 8 may be arranged on the uppermost surface.
This can improve the display change depending on the viewing angle of the observer. As the light diffusing plate, a plastic plate having irregularities on its surface, clouded glass, a flat plate provided with fine projections by printing or the like is used.

The constituent elements of the display device of the present invention may be colored if necessary, and so-called color filters may be laminated anywhere between the layers.

In order to generate a disclination line which causes light scattering in the ferroelectric liquid crystal layer 4, an electrode 5,
A voltage having an AC component whose frequency is in the vicinity of the relaxation frequency of the Goldstone mode of thermal fluctuation of liquid crystal molecules is applied between 5 '. As a result, a repeating structure similar to a spiral structure is generated in the liquid crystal, and many disclination lines corresponding to the pitch are generated. Since this pitch changes depending on the frequency of the applied voltage and the voltage, the degree of scattering can be adjusted.

The apparent frequency of the relaxation frequency of the Goldstone mode changes depending on the thickness of the liquid crystal layer and the state of the interface between the electrodes and the alignment film. Also, although it varies depending on the liquid crystal material, in many cases, it is usually between several tens Hz and several tens KHz.

[0024]

EXAMPLES The present invention will now be described in detail based on examples, but the present invention is not limited thereto.

Example 1 In FIG. 1, the light guide plate 1 has a length of 370 mm and a width of 15 mm.
A 0 mm, 2 mm thick transparent acrylic plate is used, and cold cathode fluorescent tubes 2 (Harrison Electric Co., Ltd.) are provided on both short sides of the light guide plate.
A normal tube made of aluminum and a 0.5 mm thick aluminum plate is bent to cover the outside with a light source reflection plate 3 so that light enters from both ends of the light guide plate 1 (in FIG. 1, the light source is one side). Only shown).

Next, the following ferroelectric liquid crystal and molecular weight 3300
A mixture of polymethylmethacrylate of 0 in a weight ratio of 95: 5 was dissolved in toluene to obtain a 20% by weight solution.

[0027]

[Chemical 1] (Iso: isotropic phase, SmA: smectic A phase, SmC
^* : Chiral smectic C phase, Glass: glass phase) This solution was applied to a polyethersulfone substrate (6, 5) (width 1) having stripe-shaped ITO electrodes with a pitch of 1.0 mm.
50 mm, length 50 m, thickness 100 μm: Sumilite FST manufactured by Sumitomo Bakelite Co., Ltd. was applied to form a film using a roll coater, and the solvent was dried to form a ferroelectric liquid crystal layer 4. On the liquid crystal surface of this ferroelectric liquid crystal layer,
Substrates (6 ', 5') of the same type with no coating (ITO
(Only the direction of stripes is shifted in the right angle direction)
Was laminated.

From the laminate obtained above, a length of 350 m
Cut out m parts and apply AC voltage 20 between the upper and lower electrodes 5, 5 '.
While applying Hz and 40 V, the entire element was flexibly deformed and oriented. From the transmission spectrum measurement under crossed Nicols, the thickness of the ferroelectric liquid crystal layer 4 was 4.7 μm. In addition, it was confirmed under a microscope that there was no helical structure in this state.

This element is arranged directly on the lower surface of the light guide plate 1 without a polarizing plate interposed therebetween, and an aluminum foil is further laminated under the reflection plate 7 with a polyethylene terephthalate film laminated thereon.
(Panak Kogyo Alpet) was placed.

The two cold cathode fluorescent tubes 2 were turned on, and a drive waveform (pulse width 1 ms) of a normal nematic liquid crystal of the 1/3 bias method was applied to the liquid crystal element section. 30V pulse voltage
When set to, the selected pixel became cloudy and scattered light strongly.
When observed under a microscope, a disclination line as shown in FIG. 2 was formed in the pixel which became cloudy.

In the non-selected pixels, there was no disclination line, and the spiral structure remained unsolved. In this way, display by the dot matrix system was possible.

[0032]

The display device of the present invention has the features that it has a simpler device structure, is easier to manufacture, has less optical loss, and has a faster response speed than the conventional device. It has high practical value.

[Brief description of drawings]

FIG. 1 is an explanatory cross-sectional view of a display device of the present invention.

FIG. 2 is a front view showing the shape of a disclination line.

[Explanation of symbols]

 1 Light guide plate 2 Light source 3 Reflector for light source 4 Ferroelectric liquid crystal layer 5 Electrode 5'electrode 6 Electrode supporting substrate 6'Electrode supporting substrate 7 Reflector 8 Light diffusing plate

Claims (4)

[Claims] 1. A ferroelectric liquid crystal layer capable of responding to an electric field is disposed adjacent to a lower surface of a light guide plate having a light source on its side surface,
An image is displayed by adjusting the light emitted from the upper surface of the light guide plate by scattering of light by the disclination line that appears when an AC electric field near the relaxation frequency of the Goldstone mode of this liquid crystal is applied to the ferroelectric liquid crystal layer. A display device characterized by the above. 2. The ferroelectric liquid crystal layer has a thickness of 1 μm or more and 10 or more.
The display device according to claim 1, wherein the display device has a thickness of not more than μm. 3. The display device according to claim 1, wherein the light guide plate and the ferroelectric liquid crystal layer are supported by a plastic substrate. 4. The display device according to claim 1, 2 or 3, wherein a light diffusion layer is arranged on the upper surface of the light guide plate.