JP3109283B2 - Liquid crystal display - Google Patents

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 device used as a display device of a workstation or a personal computer, and more particularly to a light receiving type display having a high reflection contrast, high resolution and high speed image display. The present invention relates to a novel liquid crystal display device capable of performing the following.

[0002]

2. Description of the Related Art In recent years, there has been an increasing demand for an electronic display device that is easy to see and handle for human eyes and that can display an image equivalent to a printer output. CR
Although a conventional light emitting display device represented by T can provide high contrast, eyes are more easily fatigued than a reflected image such as a character on paper. In addition, the characters and the like viewed on the electronic display device often have different images from those actually printed because the resolution of the display device is not sufficient compared with the printer.

In order to avoid these problems, a display device having a high reflection contrast and capable of displaying a high-definition image at a high speed is desired. In these demands, attention has been paid to a technique using a light scattering mode of a liquid crystal as a display material capable of obtaining a high reflection contrast. The display device in the light scattering mode mixes a liquid crystal and a transparent material having a refractive index substantially equal to that of the liquid crystal at the time of vertical alignment, and controls the alignment of the liquid crystal by heat or an electric field. This is a display technology that utilizes the fact that light is scattered and becomes opaque due to the difference in refractive index during random orientation. Since this display device does not require the use of a polarizing plate, a bright and high reflection contrast display can be obtained.

As a material technique used for such a light scattering mode display device, a method is known in which encapsulated liquid crystal is dispersed as liquid crystal droplets in a polymer to form a film (Japanese Patent Application Laid-Open No. 58-501631). Gazette, U.S. Pat. No. 4,435,047). In this technology, Nematic Curvilineear Ali
The liquid crystal sealed in the gneed phase (NCAP) shows a nematic phase having a positive dielectric anisotropy at an ambient temperature of use, and when placed in an electric field, its orientation vector is arranged in the direction of the electric field, and the refractive index of the liquid crystal is changed. When the refractive index np of the polymer becomes equal to n0, the film becomes transparent. On the other hand, when the electric field is removed, the liquid crystals are randomly arranged, and the light is scattered at the boundary between the liquid crystal droplets in the film and the transmitted light is transmitted. Is cut off, and the film becomes cloudy and displays recorded information. In addition, Tokuyo Sho 63
JP-A-501512 and JP-A-63-155022 disclose that a liquid crystal exhibiting a smectic phase at room temperature is used to impart a memory property to light modulation of a film.

Further, as an image writing method of a liquid crystal display device using these liquid crystal materials, the following is known. For example, as disclosed in JP-A-63-155022, a voltage is applied to a binder layer containing a microcapsule containing a numectic liquid crystal, and the liquid crystal is heated by a thermal head driven according to image information. It is known that the orientation of light is changed to control the transmission and non-transmission of light. Also, Japanese Patent Application Laid-Open No. 2-93432
As disclosed in Japanese Unexamined Patent Publication, a layer in which a nematic liquid crystal is irregularly dispersed in a polymer is sandwiched between matrix electrodes, and an electric field is applied thereto to control the orientation of the liquid crystal, thereby preventing light transmission and non-transmission. There is also a method of switching. Also,
As an image writing method for a liquid crystal display device using a liquid crystal material, as shown in FIG. 5, a laser beam from a semiconductor laser 100 is collimated via a collimator lens 101, and then two-dimensionally formed by a polygon mirror 102 and a galvanometer mirror 103. Polarization scanning, and forms an image on the photoconductive layer 106 of the liquid crystal cell 105 via the projection lens 104 (for example, JP-A-2-39018).
No.) etc. are known.

[0006]

However, for example, in the type disclosed in Japanese Patent Application Laid-Open No. 63-155022, an image is written using a thermal head, so that up to about 400 hard copies per inch are required. Although high resolution can be obtained, the display speed is limited by the heat transfer speed of the thermal head, and furthermore, for two-dimensional writing, the head or display medium must be mechanically scanned in one direction. In addition, there is a technical problem that high-speed display switching cannot be performed as in a normal display device.

In the type disclosed in Japanese Patent Application Laid-Open No. 2-93432, the orientation of liquid crystal is controlled not by heat but by an electric field, so that high-speed image rewriting is possible. It is necessary to form an electrode part for individually driving each one by fine processing, which leads to a complicated structure, and there is a limit in increasing the resolution in manufacturing.

Furthermore, as shown in FIG. 5, in the method of two-dimensionally exposing and scanning a photoconductive layer of a liquid crystal cell directly with a laser beam, writing with high resolution is possible, but the scanning range is wide. Has a limited writing speed.

As described above, the above-described liquid crystal display technologies achieve either high-speed display or high resolution equivalent to that of a printer output. Even when trying to combine them, it is practically difficult to achieve both high-speed display and high resolution equivalent to that of a printer output at the same time because the structure of each liquid crystal display device cannot be used at the same time.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned technical problems, and is intended to provide a high-speed display and printer in a light-receiving display device using a light scattering mode of a liquid crystal capable of obtaining a high reflection contrast. It is an object of the present invention to provide a liquid crystal display device which provides an image writing technique which makes it possible to achieve a resolution as high as an output, and which is easy to see for human eyes and can display an image equivalent to a printer output.

[0011]

That is, as shown in FIG. 1, a liquid crystal display device according to the present invention comprises an image writing means 1 for digitally writing an image in accordance with moving image information.
And an optical modulator 2 for holding the written image as a change in the optical state, and an optical image irradiating means 3 for reading out the image on the optical modulator 2 with light in an analog manner and enlarging and projecting the optical image. And a photoconductive layer 4a to be irradiated with an enlarged optical image from the optical image irradiation means 3 and a liquid crystal-polymer composite film 4b in which liquid crystal is dispersed in a polymer resin.
A liquid crystal cell 4 in which the orientation of the liquid crystal is controlled in accordance with the electric field pattern from the liquid crystal.
It is characterized in that it is set smaller than the cell (4) .

In such a technology, a transparent electrode is provided on the inner surface of the liquid crystal cell 4 as long as an electric field is applied according to an optical image from the optical image irradiating means 3. A transparent film in which a photoconductive layer 4a, a light blocking layer, and a liquid crystal-polymer composite film 4b are sequentially laminated may be sandwiched, or a charge may be generated by receiving light, and the charge may be transported. A layer in which a layer (corresponding to the photoconductive layer 4a), a liquid crystal-polymer composite film 4b, and a transparent electrode may be laminated.

From the viewpoint of simplification of the driving circuit of the liquid crystal cell 4, for example, the liquid crystal-polymer composite film 4b exhibits a nematic phase having a positive dielectric anisotropy at a use environment temperature. It is preferable to use a composite film in which liquid crystal is irregularly dispersed in a polymer resin, and to control light transmission and non-transmission (scattering) only by applying an electric field.

Further, from the viewpoint of facilitating image retention in the liquid crystal cell 4, for example, the liquid crystal-polymer composite film 4b of the liquid crystal cell 4 exhibits a smectic phase at room temperature and a nematic phase at room temperature or higher. It is preferable to use a composite film in which a liquid crystal exhibiting a phase is dispersed in a polymer resin, to have a memory property in the alignment state of the liquid crystal at normal temperature after writing, and to hold an image without power supply.

[0015]

According to the technical means described above, the image writing means 1 writes an image on the light modulator 2, and the scanning width on the light modulator 2 is limited to the liquid crystal cell 4 serving as a final display screen. The scanning time is short, and an image is written to the optical modulator 2 at high speed. Then, the image written on the light modulator 2 is instantaneously read out by analog light by the optical image irradiating means 3, and the optical image is enlarged and projected on the liquid crystal cell 4. At this time, the liquid crystal cell 4
Is a laminate of a liquid crystal-polymer composite film 4b in which liquid crystal is dispersed in a polymer resin and a photoconductive layer 4a, and an electric field corresponding to the projected optical pattern is applied to the liquid crystal through the photoconductive layer 4a. Since the voltage is applied to the polymer composite film 4b, the alignment of the liquid crystal is controlled according to the intensity of the electric field. That is, the portion of the liquid crystal that causes vertical alignment transmits light, and the portion where no alignment occurs becomes non-transmissive.
As a result, the reflection contrast is high on the liquid crystal cell 4,
In addition, a high-resolution image is written at a high speed.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to the embodiments shown in the accompanying drawings. Embodiment 1 FIG. 2 shows an embodiment of a liquid crystal display device to which the present invention is applied. In the figure, reference numeral 21 denotes an image signal generation circuit 10.
The emitted beam is collimated through a collimator lens 22 and then two-dimensionally deflected by a polygon mirror 23 and a galvanometer mirror 24 to be deflected by an optical signal 30. Is focused as a beam spot. Here, the polygon mirror 23 is used for horizontal scanning, for example, at a rotation speed of 360.
The one having 80 rpm and the number of faces is 80, and the galvanomirror 24 for vertical scanning vibrates at a frequency (indicating a display frame frequency) of 20 Hz, for example.

In this embodiment, the light modulator 30 has a structure similar to that used for a normal reflection type liquid crystal light valve, and includes a liquid crystal layer 31 exhibiting a nematic phase at room temperature, a dielectric ZnS / Mg as mirror
An F2 multilayer reflective film 32, a CdTe light shielding layer 33, and a photoconductive layer 34 composed of CdS are sequentially laminated,
The structure is such that a TO transparent electrode is sandwiched between a pair of glass 35 on which vapor deposition is performed. A power supply 36 is connected to the transparent electrode so that an AC voltage is applied. At this time, the laser beam, which is the image writing light, is
The light modulator 30 is 21 mm in width and 30 mm in height, and the size of the A4 size screen on which an image is finally displayed is just 10 mm. It is about one-third. Further, the spot diameter of the beam focused on the optical modulator 30 is 25 μm, the writing pitch is about 12 μm, and the resolution at this point is 2 μm.
000 DPI (Dots Per Inch). When an image is written in the optical modulator 30, the photoconductive layer 34 may be exposed to a laser beam while an AC voltage is applied from a power supply 36, and the image corresponding to the laser beam is a liquid crystal. High-resolution and high-speed writing is performed on the layer 31.

Reference numeral 40 denotes an optical image irradiation system. In this embodiment, a light from a high-intensity lamp (for example, a metal halide lamp in this embodiment) 41 is collected by a condensing lens 4.
2. Photo-conductivity of the light modulator 30 through a heat ray cut filter 43 and a half mirror 44 for preventing the light modulator 30 and the liquid crystal cell 50 from being heated by a heat ray (infrared ray) from the high-intensity lamp 41 and increasing the temperature. By irradiating from the opposite side of the layer 34, the image held in the light modulator 30 is read out as reflected light, and the reflected light is enlarged and projected ten times by the projection lens 45, and then is projected onto the liquid crystal cell 50 serving as a display screen. The image is formed with a resolution equivalent to 200 DPI.

In this embodiment, the liquid crystal cell 50
Is a mixture of 1 part of an acrylic photopolymerizable resin, 4 parts of a smectic A liquid crystal composition (“S2” manufactured by BDH), and 0.2 parts of a polymerization initiator (“Darocur 1116” manufactured by Merck). A molecular composite film 53 is uniformly applied on a PET film 51 provided with an ITO transparent electrode (also used as a heating electrode in this embodiment), cured by UV, and a light-shielding layer 54 made of CdTe is laminated thereon. A photoconductive layer 55 made of silicon is laminated, and another PET film 52 with an ITO transparent electrode is laminated thereon. The size of the liquid crystal cell 50 is 210 mm
X 300 mm, about A4 size.

Further, in this embodiment, the liquid crystal-polymer composite film 53 of the liquid crystal cell 50 is heated by flowing a heating current pulse (heating pulse) 61 to one of the ITO electrodes attached to the PET film. It has become. A liquid crystal phase detection sensor 62 for detecting a phase state of the liquid crystal is provided in a non-image portion of the liquid crystal cell 50 and in a part of the region where no electric field is applied.
Is attached. In this embodiment, the liquid crystal phase detection sensor 62 has a configuration in which a light emitting element 62a and a light receiving element 62b are provided with a liquid crystal cell 50 interposed therebetween. The operation of the liquid crystal phase detection sensor 62 will be briefly described below. Once the liquid crystal of the liquid crystal cell 50 is liquidized by heating, the liquid crystal phase detection sensor 62 receives the light from the light emitting element 62a while the light receiving element 62b constantly receives the light while the liquid crystal of the liquid crystal cell 50 is in the liquid phase and transparent state. ing. On the other hand, when the liquid crystal undergoes a phase transition from a liquid phase to a nematic phase due to natural cooling, an electric field is not applied to a region of the liquid crystal cell between the liquid crystal phase detection sensors 62, so that the orientation of the liquid crystal is disturbed and light is scattered. Light receiving element 62b
Light is blocked, and this change becomes a signal indicating a phase change.

Further, the timing control circuit 70 determines the generation timing of the heating pulse 61 and determines the timing of the writing scan of the optical image based on the phase change signal from the liquid crystal phase detection sensor 62.

Next, an image rewriting operation in the liquid crystal display device according to this embodiment will be described with reference to the timing chart of FIG. First, immediately before rewriting of an image in the liquid crystal cell 50 based on an image signal occurs, an image preparation signal S1 for notifying the rewriting is issued from the timing control circuit 70. In response to the signal S1, a DC heating pulse 61 is supplied to a heating electrode as a heating means from an external power supply (not shown). The width of the heating pulse 61 is about 10 ms.

In parallel with the operation, a power supply 56 is connected to a transparent electrode (also used as a heating electrode) of the liquid crystal cell 50 via a changeover switch 57, and is sufficient for aligning the liquid crystal. A voltage (here, 50 V) is applied. However, this voltage is not applied to the liquid crystal cell 50 until the photoconductive layer 55 is exposed. After the liquid crystal is once liquefied by Joule heat by the heating current pulse 61, it is transformed into a nematic phase by natural cooling. When the liquid crystal phase detection sensor 62 detects that the liquid crystal has transitioned from the liquid phase to the nematic phase, it receives the signal S2 and
(For example, about 1 ms), the semiconductor laser 2 is slightly delayed.
1 starts writing an image to the light modulator 30;
An optical image irradiation system 40 reads an image from the light modulator 30,
An image is irradiated on the photoconductive layer 55 side of the liquid crystal cell 50. At this time, since a voltage is applied to the electrodes of the liquid crystal cell 50 in advance, the electric field pattern according to the optical image is immediately given to the liquid crystal cell 50 by exposure by the optical image irradiation system 40, and the electric field pattern is applied. The liquid crystal is aligned. That is,
When the image is rewritten periodically, the above-described operation is performed continuously, and the image is rewritten according to the moving image information. The exposure and the application of the voltage are set in advance so that the liquid crystal is completed in sufficient time before the phase transition from the nematic phase to the smectic phase. In particular, in this embodiment, since the image writing operation is performed slightly after the detection signal S2 is output from the liquid crystal phase detection sensor 62, the phase change of the liquid crystal of the liquid crystal cell 50 is stable. Although the writing of the image is performed in the state in which the writing is performed in the state described above, the writing of the image is assured. No problem.

If the image is not rewritten, the heating pulse 61 is not applied after irradiating the photoconductive layer 55 with the last image to be written while applying the voltage of the power supply 56 in the nematic phase. In this case, the liquid crystal phase changes to a smectic phase (having a memory property at room temperature) while maintaining the alignment state according to the image. It will be retained even if it is not.

Embodiment 2 FIG. 4 shows another embodiment to which the present invention is applied. The same components as those in the first embodiment are denoted by the same reference numerals, and the detailed description thereof is omitted. In the drawing, since the writing area of the image to the optical modulator 30, that is, the scanning width is small, two ultrasonic deflectors (XY) are used instead of the mechanical scanning device used in the first embodiment. Direction) 81, 82
And the output light from the ultrasonic deflectors 81 and 82 is written into the optical modulator 30 via the reflection mirror 83. In this embodiment, as the ultrasonic deflectors 81 and 82, for example, a device in which TiNbO3 is joined as a transducer to a single crystal of TeO2 (Electrical Communication Society, Vol. 154 No99 / '71 "Commentary / Recent Advances in Optical Deflection Technology") P1266) can be used. According to this type, the scanning speed is higher than that of the mechanical scanning, and the reliability is higher than that of the first embodiment because no mechanical parts are used.

[0026]

As described above, according to the first aspect of the present invention, in a light receiving type display device utilizing a light scattering mode of a liquid crystal capable of obtaining a high reflection contrast, an image is temporarily formed on a light modulator. Since writing is performed at high speed and this image is enlarged and projected on the liquid crystal cell and displayed, the display and rewriting of the image can be performed at the same high speed as the electronic display device, and the display is the same as the printer output. High resolution can be obtained. Therefore, it is possible to provide an image writing technique that achieves both high-speed display and high resolution equivalent to that of printer output, and it is possible to realize display of an image that is easy to see for human eyes and equivalent to printer output. . According to the second aspect of the invention, light transmission and light transmission can be achieved only by applying an electric field at room temperature.
Since the opacity (scattering) can be controlled, the configuration of the apparatus can be controlled in an application requiring only display of a moving image.
The driving method can be simplified. Further, according to the third aspect of the present invention, after writing the image, the image can be held at room temperature without power supply, so that the displayed image can be grasped without restriction on the electrical connection, The display devices can be arranged side by side, and accordingly, a display device that can be handled like a paper document can be realized.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing a configuration of a liquid crystal display device according to the present invention.

FIG. 2 is an explanatory diagram showing Embodiment 1 of a liquid crystal display device to which the present invention is applied.

FIG. 3 is a timing chart illustrating an image rewriting operation according to the first embodiment.

FIG. 4 is an explanatory diagram showing a liquid crystal display device according to a second embodiment of the present invention;

FIG. 5 is an explanatory diagram illustrating an example of a conventional liquid crystal display device.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Image writing means, 2 ... Optical modulator, 3 ... Optical image irradiation means, 4 ... Liquid crystal cell, 4a ... Photoconductive layer, 4b ... Liquid crystal-polymer composite film

──────────────────────────────────────────────────続 き Continuation of front page (56) References JP-A-3-155525 (JP, A) JP-A-4-218020 (JP, A) JP-A-4-11218 (JP, A) JP-A-4- 75033 (JP, A) JP-A-4-70864 (JP, A) JP-A-3-17630 (JP, A) JP-A-4-86621 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G02F 1/135

Claims (3)

(57) [Claims] An image writing means (1) for digitally writing an image in accordance with moving image information, and an optical modulator (2) for holding the written image as a change in an optical state.
An optical image irradiating means (3) for reading out an image on the optical modulator (2) in analog form with light and enlarging and projecting the optical image, and an enlarged optical image from the optical image irradiating means (3). A photoconductive layer (4a) to be irradiated and a liquid crystal-polymer composite film (4b) in which liquid crystal is dispersed in a polymer resin are laminated, and the alignment of the liquid crystal is controlled according to an electric field pattern from the photoconductive layer (4a). and a liquid crystal cell (4), said optical modulator
A liquid crystal display device wherein the scanning width of (2) is set smaller than that of the liquid crystal cell (4) . 2. The liquid crystal cell-polymer composite film (4b) according to claim 1, wherein the liquid crystal exhibiting a nematic phase at room temperature is dispersed in a polymer resin. A liquid crystal display device characterized by the above-mentioned. 3. The liquid crystal cell (4) according to claim 1, wherein the liquid crystal-polymer composite film (4b) of the liquid crystal cell (4) exhibits a smectic phase at room temperature and a liquid crystal exhibiting a nematic phase at room temperature or higher. A liquid crystal display device comprising a composite film dispersed in a liquid crystal display.