JPH0777703A - Liquid crystal display device - Google Patents

Abstract

PURPOSE:To make display with high resolution and to make exact gradation display by modulating the output light of an exposing means for exposing a photoconductive layer in accordance with a signal indicating the multiple gradation densities of images and controlling the light transmittance of the light controllable layer. CONSTITUTION:A voltage is applied by' a voltage source 3 to the light controllable layer 1 and photoconductive layer 2 having a light scattering state over the entire surface. The photoconductive layer 2 is irradiated with light from an exposure device 4 modulated in exposure time by a gradation controller 5 in accordance with the multiple gradation densities information of the writing images indicated by image density signals. The electric conductivity changes according to the degree of modulation in the exposed regions of the photoconductive layer 2 and the voltage of the quantity meeting the change is impressed to the light controllable layer 1. The transparency, i.e. degree of gradation, of the light controllable layer 1 is determined according to the voltage impression state. On the other hand, the electrical conductivity remains low in the unexposed regions of the photoconductive layer 2 and there is substantially no voltage to be impressed to the light controllable layer 1 and, therefore, the light scattering state is still maintained. As a result, the images of the multiple gradation densities are written on the light controllable layer 1.

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, and more particularly to an optical writing type liquid crystal display recording using liquid crystal, which is used for a recording device using a reversible recording medium, an image display device, an image storage device and the like. It relates to the device.

[0002]

2. Description of the Related Art JP-A-4-94281 and JP-A-4-13
0420, JP-A-4-136821, and JP-A-4-218.
In 021, a photoconductive layer and a light control layer are laminated, and the photoconductive layer is exposed based on image information while applying an electric field to both layers,
A display device is disclosed in which the orientation of the liquid crystal of the light control layer is controlled to write an image.

The features of the technology of the above-mentioned patent application will be individually described. The purpose of the technology of Japanese Patent Laid-Open No. 4-94281 is to obtain a high-resolution image at a low manufacturing cost.
The technique disclosed in Japanese Patent Laid-Open No. 136821 is to obtain a high-resolution image by adopting a structure in which multilayer dielectric mirrors are laminated. The technique disclosed in Japanese Patent Laid-Open No. 4-218021 has the same polarity as that at the time of writing. Apply a pulse voltage of magnitude,
In synchronization with this, a laser beam is irradiated under exactly the same conditions as during writing, thereby partially erasing while leaving necessary write information.

On the other hand, in recent years, from the viewpoint of improving the user interface, there is an increasing demand for electronic devices which are easy to see and handle for human eyes.
Among them, especially the electronic display is often used for work mainly for creating and displaying documents, so that it is possible to perform light receiving display that is easy on the eyes, has high reflection contrast, high-speed display, and memory property of display. The realization of a display that satisfies both requirements is desired. Several display technologies are currently being proposed to meet some of these needs. A display utilizing the light scattering mode of liquid crystal is known as one of them. In the light scattering mode display, a liquid crystal is mixed with a transparent material that has a refractive index almost equal to that of the liquid crystal when vertically aligned, and the liquid crystal is vertically or randomly aligned by controlling the liquid crystal orientation by heat or an electric field. . In such a display, light is transmitted at the time of vertical alignment, and at the time of random alignment, the light is scattered due to the difference in refractive index and becomes opaque.

As a material technology used for such a light-scattering mode display, Japanese Patent Publication No. 58-501631
Japanese Patent Publication No. 4,435,047,
A method is disclosed in which encapsulated liquid crystals are dispersed as liquid crystal droplets in a polymer to form a film. In this technique, for example, a liquid crystal encapsulated in a polymer exhibits 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 aligned in the direction of the electric field. When the refractive index of the liquid crystal and the refractive index of the polymer become equal and become transparent and the electric field is removed,
The liquid crystal molecules are randomly arranged, light is scattered at the interface between the liquid crystal and the capsule, the transmitted light is blocked, the film becomes cloudy, and the recorded information is displayed.

Further, in JP-A-63-501512 and JP-A-63-155022, a liquid crystal having a smectic phase at room temperature is used to impart a memory property to a film containing the liquid crystal. Is disclosed. When such a material is used, the image written by the memory property of the liquid crystal can be held in a non-powered state and the medium can be formed into a film, so that the display screen can be treated like a hard copy. Become.

Further, as a method of writing an image on a display device using these liquid crystal materials, for example, Japanese Patent Laid-Open No. 63-63 is available.
As disclosed in 155022, a voltage is applied to a binder layer containing a microcapsule containing a smectic liquid crystal, and heating is performed by a thermal head driven according to image information to change the orientation of the liquid crystal and transmit light. Those that control opacity are known.

The information recording medium disclosed in Japanese Patent Application Laid-Open No. 3-155525 is a photoconductive material composed of a polymer-liquid crystal composite film obtained by dispersing liquid crystal exhibiting a smectic phase at room temperature in a polymer matrix and amorphous silicon. Composed in combination with layers, the optical image is imaged on the photoconductive layer,
The electric field intensity distribution according to the exposure pattern is given to the polymer-liquid crystal composite film.

Further, in Japanese Patent Laid-Open No. 4-86618, a heating amount and a heating area are controlled for a recording medium in which a polymer-liquid crystal composite film in which liquid crystal is dispersed in a polymer material is attached to a substrate. , Gradation display is shown.

[0010]

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention
4281, JP-A-4-130420, and JP-A-4-136.
821, JP-A-4-218021 and JP-A-3-1552.
No technology relating to gradation display is disclosed in 525.

Further, the display device disclosed in JP-A-63-155022 and JP-A-4-86618, and the rewriting speed of the display depend on the heat transfer speed.
It is not possible to rewrite the display at high speed, and it is necessary to control the heating amount with high precision for gradation display, but since the characteristics of the heating element vary, accurate multi-gradation control is possible. Is difficult.

It is an object of the present invention to provide a liquid crystal display device capable of high-resolution display and accurate gradation display.

[0013]

In order to achieve the above-mentioned object, a liquid crystal display device of the present invention is provided with a dimming layer containing at least liquid crystal as a component and disposed on one side of the dimming layer. A photoconductive layer whose impedance changes according to light,
Voltage applying means for applying a voltage to the light control layer and the photoconductive layer,
Exposure means for writing an image on the light control layer by exposing the photoconductive layer, and controlling the light transmittance of the light control layer by modulating the output light of the exposure means based on a signal indicating the multi-tone density of the image Gradation control means for

[0014]

In the liquid crystal display device of the present invention having the above structure,
A voltage is applied by the voltage applying means to the light control layer and the photoconductive layer containing liquid crystal as a component whose entire surface is in a light scattering state. The output light of the exposure means is modulated by the gradation control means based on the multi-gradation density of the image to be written, and the modulated output light irradiates the photoconductive layer, and the irradiated area of the photoconductive layer. The impedance, that is, the conductivity changes according to the modulation degree of the output light from the exposure means, the voltage from the voltage applying means is applied to the dimming layer by an amount corresponding to this, and the impedance is changed according to the applied voltage. The light transmittance of the light control layer, that is, the gradation is determined. In the region of the photoconductive layer that does not receive light, the impedance of the photoconductive layer remains high, that is, the conductivity remains low, and almost no voltage is applied to the light control layer, so that the light scattering state is maintained. In this way, an image having multi-tone density is written in the light control layer.

[0015]

1 shows an embodiment of a liquid crystal display device of the present invention. This embodiment is an example in which the present invention is applied to a photo-writing type liquid crystal display device. The light control layer 1 is composed of a polymer-liquid crystal composite film in which liquid crystal is dispersed in a polymer resin. The liquid crystal of the polymer-liquid crystal composite film and the polymer resin are three-dimensionally connected to each other, and the liquid crystal is substantially evenly dispersed in the polymer resin to obtain strong light scattering and low driving voltage. Desirable above. In this example, the liquid crystal contained in the polymer-liquid crystal composite film has an ambient temperature of use (for example, 0 at an average temperature of 25 ° C.).
A liquid crystal that exhibits a smectic A phase at (° C. to 40 ° C.) and that undergoes a phase transition to a nematic phase at a temperature higher than the operating environment temperature is used.

On one of the light control layers 1, a photoconductive layer 2 whose impedance changes by receiving light is provided. The photoconductive layer 2 is characterized by being formed so that both electrons and holes are generated as carriers excited by exposure and these can move. As such a photoconductive layer, hydrogenated amorphous silicon is most preferable because it does not contain a toxic component and a high-speed response is possible.

Electrodes 31 and 32 are arranged so as to face each other so as to sandwich the light control layer 1 and the photoconductive layer 2. That is, the transparent electrode 31 is disposed on one side of the light control layer 1 and on the side opposite to the photoconductive layer 2, and on one side of the photoconductive layer 2 opposite to the light control layer 1. A transparent electrode 32 is provided on the side. ITO (indium tin oxide) is desirable as the material of the electrodes 31 and 32. The light control layer 1, the photoconductive layer 2, and the electrodes 31 and 32 form the display recording medium 100.

The voltage source 3 applies a voltage to the light control layer 1 and the photoconductive layer 2 via the transparent electrodes 31 and 32. The exposure device 4 is a device that writes an image on the light control layer 1 by exposing the photoconductive layer 2 in pixel units via the transparent electrode 32.

The gradation control device 5 is based on an image density signal indicating the multi-gradation density of the image to be written in the light control layer 1, and the exposure device 4 irradiates the photoconductive layer 2 with light per pixel. The light transmittance of the light control layer 1 is controlled by modulating the exposure time.

The heating device 6 is composed of, for example, a heating electrode for the light control layer 1, and heats the light control layer 1 (that is, the polymer-liquid crystal composite film) to a temperature higher than the ambient temperature for use to control the light control layer 1. The liquid crystal of is made into a liquid phase. The phase transition detection device 7 detects that the liquid crystal contained in the light control layer 1 has transitioned from a liquid phase to a nematic phase, and outputs a phase transition detection signal.

Next, the operation of the embodiment of FIG. 1 configured as described above will be described. First, the transparent electrodes 31 and 32 are formed on the light control layer 1 and the photoconductive layer 2 whose entire surfaces are in a light scattering state.
A voltage is applied from the voltage source 3 via. The photoconductive layer 2 is irradiated with the light from the exposure device 4 whose exposure time is modulated by the gradation control device 5 based on the multi-gradation density information of the written image indicated by the image density signal, whereby the photoconductive layer 2 is irradiated. 2 In the exposed region, the conductivity changes depending on the degree of modulation, and a voltage corresponding to this is applied to the light control layer 1, and the transparency of the light control layer 1 depends on the voltage application state, that is, Gradation is determined. On the other hand, in the non-exposed region of the photoconductive layer 2, the conductivity remains low and the voltage applied to the dimming layer 1 is almost zero, so that it remains in the light scattering state. In this way, the image having the multi-tone density indicated by the image density signal is written in the light control layer 1.

As described above, as the light control layer 1, a liquid crystal in which a liquid crystal exhibiting a smectic A phase at a use environment temperature and undergoing a phase transition to a nematic phase at a temperature higher than the use environment temperature is dispersed in a polymer resin is used. In this case, in order to bring the liquid into a light-scattering state, the liquid crystal is once heated by the heating device 6 to a temperature not lower than the transition point to the liquid phase and cooled to room temperature. During this cooling, the phase state detection device 7 detects that the liquid crystal contained in the light control layer 1 has changed from the liquid phase to the nematic phase, and outputs a phase change detection signal. The exposure device 4 receives the detection signal and receives the photoconductive layer 2
Exposure to. As described above, this exposure is gradation-controlled by the gradation control device 5 based on multi-gradation density information, and if the image is not rewritten, the light control layer 1 showing a gradation image. Is cooled as it is from the nematic phase to the smectic A phase while holding the image, and the image is held even without application of an electric field.

According to the embodiment of the invention of FIG. 1 described above,
Since the gradation control device 5 controls the light transmission state of the light control layer 1 by modulating the output light of the exposure device 4 based on the gradation density information of the image to be written, accurate gradation display can be performed. it can. Further, since the impedance of the photoconductive layer 2 is changed according to the modulation degree of the output light from the exposure device 4 and the voltage is applied to the light control layer 1 by an amount corresponding to this, high resolution display can be performed. it can.

Further, since the dimming layer 1 is composed of the polymer-liquid crystal composite film in which the liquid crystal is dispersed in the polymer resin, the dimming layer 1 can be made lightweight and flexible.

Further, since the liquid crystal contained in the light control layer 1 is a liquid crystal exhibiting a smectic A phase at a use environment temperature and exhibiting a phase transition to a nematic phase at a temperature higher than the use environment temperature, the liquid crystal is in a nematic phase state. The image can be written and rewritten at high speed by writing the image at a certain time, and since the liquid crystal exists in the state of a smectic phase having a memory property at the operating environment temperature, the last written image cannot be written. Can be held during a power outage.

Further, since the gradation control device 5 controls the exposure time for each pixel of the photoconductive layer 2 based on the multi-gradation density information, it is possible to perform gradation control with good linearity at high speed. .

Further, since the heating device 6 heats the light control layer 1 until the liquid crystal contained in the light control layer 1 becomes a liquid phase, an image can be written when the liquid crystal is in the nematic phase. The write drive voltage can be lowered.

Since the photoconductive layer 2 is exposed to light according to a detection signal indicating that the liquid crystal contained in the light control layer 1 has changed from the liquid phase to the nematic phase, the liquid crystal is in the nematic phase. When the image is sure, the light control layer 1
Can be written on.

FIG. 2 shows the display recording medium 10 shown in FIG.
A detailed configuration example of 0 is shown. First, a transparent electrode 32 made of indium tin oxide (ITO) is formed on one transparent substrate 34 made of polyimide by sputtering, and carrier injection is blocked on the transparent electrode 32 to prevent injection of carriers into the photoconductive layer. TaOx as the layer 36 is 0.1
The film was formed to a thickness of μm. Further, silane gas and hydrogen gas were used as raw materials for the photoconductive layer 2, and a small amount of boron was doped to form hydrogenated amorphous silicon as the photoconductive layer 2 by plasma CVD to a thickness of 5 μm. Then, a CdTe film, which is a carrier injection blocking layer 37 that also serves as a light-shielding layer, was deposited thereon with a thickness of 0.1 μm. The light shielding layer 37 originally has a function of absorbing light sensed by the photoconductive layer 2 and also has a function of a light absorbing layer for realizing a good direct-view black-and-white reflective display of black characters on a white background.

A cyanobiphenyl-based smectic liquid crystal mixture (for example, "S2" manufactured by BDH) was used as the liquid crystal material of the light control layer 1, and 80% by weight of this liquid crystal material and 1,6 hexanediol diacrylate as a polymer compound were used. (Kayalad HDDA manufactured by Nippon Kayaku Co., Ltd.) 11.6% by weight and urethane acrylate oligomer ("Evecryl 204" manufactured by Daicel UCB) 8% by weight, and 2-hydroxy-2-methyl-1 as a polymerization initiator. -Phenylpropan-1-one ("Darocur 1173" manufactured by Merck Japan Co., Ltd.) 0.4% by weight was mixed with a polymerizable composition. A spherical spacer having a diameter of 10 μm was added to this mixture (“Micropearl S” manufactured by Sekisui Fine Chemical Co., Ltd.).
P210 ") in a small amount and mixed with an ultrasonic cleaner,
The mixed solution was prepared by degassing. This mixed solution is applied between the carrier injection blocking layer 37 formed on the transparent substrate 34 side as described above and the transparent electrode 31 made of ITO formed on the transparent substrate 33 made of a PET (polyethylene terephthalate) film. The wavelength is 360nm evenly from the black lamp light source while sandwiching and keeping the whole at 25 ° C.
Curing was performed by irradiating a certain amount of ultraviolet rays for several seconds.

As shown in FIG. 2 and described above, the photoconductive layer 2
By disposing the carrier injection blocking phases 36 and 37 on both sides of, it is possible to prevent carrier injection into the photoconductive layer 2,
Since the dark current is suppressed low, the contrast and resolution of the image can be kept good.

Further, since the light-shielding layer 37 that absorbs light having a wavelength at which the photoconductive layer 2 has sensitivity is provided between the dimming layer 1 and the photoconductive layer 2, the writing light leaks to the dimming layer 1 side. Since this can be prevented, the safety of the eyes of the person who is looking at the display image is secured. Further, although the embodiments of FIGS. 1 and 2 assume a reflective display with a black character (the color of the layer below the transparent light control layer 1) on a white background (light scattering area), the light blocking layer 37 is used. Since it also serves as the light absorption layer viewed from the observation side (transparent substrate 33), good reflective display can be realized.

Since the layer 37 also serves as a carrier injection blocking layer and a light shielding layer, the structure of the display recording medium 100 can be simplified and the manufacturing cost can be reduced.

Further, in the photoconductive layer 2 made of hydrogen amorphous silicon, both electrons and holes are generated as carriers excited by exposure, and these are movable, so that space which causes an increase in residual charge and an afterimage is generated. Little charge is generated. Further, it is possible to make the light control layer 1 sufficiently transmissive with a low drive voltage, and it is possible to perform an AC operation in which a direct current component that deteriorates the liquid crystal of the light control layer 1 is difficult to flow.

FIG. 3 shows a concrete configuration example of the embodiment of the present invention shown in FIGS. In the example of FIG. 3, the exposure device 4 of FIG. 1 starts its operation in response to the exposure start signal from the timing control circuit 41, and the image signal and gradation control device 5
Laser driver 42 which outputs a laser drive signal according to the exposure time control signal from the semiconductor laser, semiconductor laser 43 which emits a laser beam having a wavelength of 690 nm according to the laser drive signal, and laser beam emitted from the semiconductor laser 43. The collimator lens 44 that narrows down the lens 4 and the lens 4 that is rotated by the driving device (not shown).
Laser beam sent from the display recording medium 10
The main scanning direction of 0, that is, the polygon mirror 45 that moves in the direction of the arrow A in FIG. 3, and the laser beam that is rotated by the drive device (not shown) and is sent from the polygon mirror 45, is the sub scanning direction of the display recording medium 100. A galvanometer mirror 46 that moves in the vertical direction (that is, the direction perpendicular to the main scanning direction),
It is configured to include an fθ focusing optical system 47 that focuses the laser beam reflected by the galvano mirror 46 into spot light and sends the spot light to the display recording medium 100.

In the specific example of FIG. 3, the heating device 6 of FIG. 1 is arranged in strips at intervals of, for example, 230 μm on the surface of the transparent substrate 34 on the side opposite to the transparent electrode 32 and has a width of, for example, 200 μm. A plurality of heating electrodes 60, a plurality of switches 60S connected to the heating electrodes 60 in series, respectively, and a series circuit of the above-mentioned plurality of heating electrodes 60 and a switch 60S connected in parallel via a switch 62. And a DC voltage source 64 that is generated.
The plurality of switches 60S are controlled by a control device (not shown) so that they are turned on immediately before the scanning is actually performed in synchronization with the laser beam scanning of the display recording medium 100.

In the specific example of FIG. 3, the phase transition detection device 7 of FIG. 1 is arranged so as to sandwich a non-image display area of the display recording medium 100, where transparent electrodes 31 and 32 do not apply an electric field. Light emitting element 72 and light receiving element 74
And a waveform shaping circuit 7 for shaping the output signal of the light receiving element 74 into a pulse-shaped signal having a sharp rise and fall.
6 is provided. The waveform shaping circuit 76 can be configured by, for example, a comparator that outputs an “H” signal when the level of the output signal of the light receiving element 74 is higher than the threshold value, and outputs an “L” signal when the level of the output signal is lower than the threshold value. While the liquid crystal contained in the light control layer 1 or the liquid phase is in a transparent state, the light receiving element 7
Reference numeral 4 always receives light from the light emitting element 72. When the liquid crystal undergoes a phase transition from the liquid phase to the nematic phase by natural cooling,
As described above, since the electric field is not applied to the liquid crystal in the region between the light emitting element 72 and the light receiving element 74, the alignment of the liquid crystal is disturbed and the light is scattered, and the light receiving element 74 causes the light from the light emitting element 72 to be scattered. I will not receive it. Therefore, the output signal level of the light receiving element 74 decreases, and the output of the waveform shaping circuit 76 also changes from "H" to "L".
Changes to.

The above-mentioned DC voltage source 64 is connected to the terminal 62A of the switch 62, and one terminal of the AC voltage source 66 is connected to the terminal 62B. AC voltage source 6
The other terminal of 6 is connected to the transparent electrode 62. Upon receiving the image rewriting preparation start signal S1 from the timing control circuit 41, the switch 62 puts the terminal 62A side into a connection state so that a heating pulse can be applied to the heating electrode 60 from the DC voltage source 64 via the switch 60S. To do. Further, the switch 62 is connected to the terminal 62B so that the AC voltage can be applied between the transparent electrodes 31 and 32 from the AC voltage source 66A when receiving the switch switching signal from the timing control circuit 41. To When the timing control circuit 41 receives from the waveform shaping circuit 76 the phase transition detection signal S2 indicating that the liquid crystal contained in the dimming layer 1 has undergone the phase transition from the liquid phase to the nematic phase, it outputs the above switch switching signal. .

FIG. 4 shows the operation timing of image rewriting in the concrete implementation of the optical writing type liquid crystal display recording apparatus of the present invention shown in FIG. The operation of the specific embodiment shown in FIG. 3 will be described below with reference to FIG. First, the timing control circuit 41 receives the image start signal and outputs the image rewrite preparation start signal S1 immediately before the image rewrite to the display recording medium 100 occurs. The switch 62 receives this signal S1 and puts the terminal 62A side into a connected state.
After that, the control circuit not disclosed includes a plurality of switches 60S '.
Are turned on before the laser beam scans the corresponding regions of the heating electrode 60. As a result, a DC current pulse is applied to the heating electrode 60 from the DC voltage source 64. The width of the current pulse is, for example, about 10 ms.

Next, the timing control circuit 41 outputs the image rewriting preparation start signal S1 and, after a predetermined time (this corresponds to immediately after the current pulse is supplied to the heating electrode 60), the switch changeover signal. Is supplied to the switch 62. The switch 62 accordingly connects the terminal 62B. As a result, the light control layer 1 is provided between the AC voltage source 66 and the transparent electrodes 31 and 32 of the display recording medium 100.
AC voltage (eg 30VRM) sufficient to orient the liquid crystal of
S) is applied. However, this voltage is not applied to the light control layer until the photoconductive layer 2 is exposed.

The liquid crystal is once liquefied by the Joule heat generated by the heating current pulse and then transitions to the nematic phase. When the liquid crystal transitions from the liquid phase to the nematic phase, the output of the waveform shaping circuit 76 changes from "H" to "L". That is,
The waveform shaping circuit 76 outputs the phase transition detection signal S2. The timing control circuit 41 receives the detection signal S2 and outputs an exposure start signal. This starts the exposure of the photoconductive layer 2 according to the image density information. For exposure of the photoconductive layer 2, a laser drive signal corresponding to the exposure time control signal is output from the laser driver 42 from the gradation control device 5, a laser beam corresponding to the laser drive signal is emitted from the semiconductor laser 43, and a laser beam is emitted. The beam emitted from 43 is collimated by a collimator 44, two-dimensionally deflected by a polygon mirror 45 and a galvanometer mirror 46, and then converged to a spot by an fθ focusing optical system 47.

At this time, when the on / off of the light emission of the laser driver 42 is controlled according to the image signal, the gradation control device 5 modulates the light emission time based on the image density signal at that time. 31 sandwiching the light control layer 1 and the photoconductive layer 2
Since a predetermined AC voltage is applied to the electrodes 32 and 32 in advance, a voltage pattern having a pulse width determined according to the density information is immediately applied to the light control layer 1 side by this exposure.

The timing control circuit 41 uses the above-mentioned switch so that the voltage application to the display recording medium 100 and the exposure to the photoconductive layer 2 are completed before the liquid crystal undergoes the phase transition from the nematic phase to the smectic phase. A switching signal and an exposure start signal are output. When image rewriting is performed periodically, the above-mentioned operation is performed continuously,
When there is no image switching, the liquid crystal is in the state of smectic A phase having a memory property at room temperature, and thus the last written image is held without power supply. In the case of "S2", the temperature of phase transition to Nemateikku phase from smectic A phase (S _A -N points) is 48 ° C, the temperature of phase transition to a liquid phase from the nematic phase (N-I point ) Is 49
° C.

FIG. 5 shows a specific example of the configuration of the gradation control device 5 shown in FIGS. The gradation control device of FIG.
For example, a latch circuit 52 that holds an image density signal, which is a digital signal represented by 256 gradations with 8 bits, according to a pixel clock, and the voltage application time of the light control layer 1 is corrected according to the nonlinearity of the light transmittance of the light control layer 1. A lookup table 54 that stores the value obtained in this manner in the form of a digital signal in association with the multi-tone density, and outputs a signal indicating the voltage application time corresponding to the image density signal held in the latch circuit 52; The D / A which outputs the signal indicating the charge application time output from the look-up table 54 by converting it into an analog signal indicating the emission pulse width of 256 gradations according to the pixel clock.
And a converter 56.

The operation of the concrete example of the gradation control device 5 of FIG.
It is as follows. That is, the 8-bit (256 gradation) image density signal is latched by the latch circuit 52 in synchronization with the pixel clock. Next, the non-linearity of the light control layer 1 with respect to the density of the latched image density signal is corrected by the look-up table 54, and the voltage application time of the light control layer 1 output from the look-up table 54 is D / A converter 56. Is converted into an analog signal having a light emission pulse width of 256 gradations, and this analog signal is given to the laser driver 42 as a drive current pulse.

FIG. 6 shows the change in light transmittance with respect to the voltage application time at the peak voltage of 30 V of the liquid crystal-polymer composite film used as the light control layer 1 in the above-mentioned embodiment. Since the light transmittance of the light control layer 1 can be considered as a substitute characteristic of the reflection image density, it can be seen from this figure that the gradation display with respect to the voltage application time is slightly non-linear.

FIG. 7 shows changes in voltage application time with respect to the input image density signal after correction by the look-up table 54.

FIG. 8 shows a result of actually writing an image by pulse-width-modulated exposure in terms of the relationship between the input image density signal and the light transmittance of the light control layer. It can be seen from FIG. 8 that good gradation characteristics excellent in linearity are obtained.

Although hydrogenated amorphous silicon is used as the photoconductive layer 2 in the above-described embodiments, other amorphous semiconductors such as amorphous selenium, amorphous selenium tellurium, amorphous hydrogenated silicon carbide, and selenium-arsenic are also used. It is also possible to use cadmium sulfide.

In the above embodiment, the transparent electrode 3
1 and was used ITO as 32 material, In addition, it is possible to use S _n O ₂ as an inorganic transparent material, it may be used organic transparent material such as an ion-doped polyacetylene.

In the above embodiment, the transparent substrate 3
PET was used as the material for item 3, but in addition to this, PES
An organic transparent material such as (polyether sulfone), polystyrene, or polyimide can be used, and an inorganic transparent material such as non-alkali glass can be used. Further, in the above embodiment, polyimide is used as the material of the transparent electrode 34, but the same material as the transparent substrate 33 can be used.

Further, in the above embodiment, the gradation control device 5 controls the light transmission state of the light control layer 1 by modulating the exposure time, but other factors of the output of the exposure device 4, for example, the exposure. The light transmission state of the light control layer 1 may be controlled by modulating or controlling the power or the number of exposure pulses. Even in this case, gradation control can be performed at high speed and with good linearity. For example, in the case of modulating the exposure power, the density information is converted into a laser drive current, the impedance of the photoconductive layer 2 is given a gradation, and the voltage dependence of the transmittance of the dimming layer 1 is used. Then, a gradation image may be displayed.

Further, in the above embodiment, the exposure device 4
A laser beam scanning device is used as this, but in addition to this, self-luminous image bars, liquid crystal shutter arrays, PLZT shutter arrays such as LED arrays, vacuum fluorescent tube arrays, plasma arrays, edge emitting EL arrays, etc. An optical shutter type image bar can also be used.

In the above embodiment, the heating device 6 is composed of the heating electrodes. However, an electromagnetic wave generation source for irradiating the light control layer 1 with infrared rays, and a heating laser for irradiating the light control layer 1 with a laser beam. The light source or the light control layer 1, that is, a microwave for generating a microwave for vibrating the polymer-liquid crystal composite film may be configured by a generation source or the like.

Further, in the above embodiment, the phase state detecting device 7 is composed of a set of a light emitting element and a light receiving element which are arranged so as to sandwich the display recording medium 100 including the light control layer 1 and the photoconductive layer 2. However, in addition to this, a monitor for monitoring the liquid crystal temperature or a detection device for detecting optical characteristics such as transmittance or refractive index may be used.

Further, in the above embodiment, the liquid crystal is heated until it becomes a liquid phase, but it may be heated at least until it becomes a nematic phase.

Although TaOx is used as the material of the carrier injection blocking layer 36 in the above embodiment, SiO ₂ , TiO ₂ , a-SiN or the like can also be used.

Further, in the above embodiment, CdTe is used as the material of the carrier injection blocking layer 37 which also serves as the light shielding layer, but other than this, a resin in which a pigment or carbon black is dispersed can be used.

[0059]

According to the liquid crystal display device of the present invention, the light transmittance of the light control layer is adjusted by modulating the output light of the exposure means based on the multi-tone density information of the image to be written by the tone control means. Since it is controlled, accurate gradation display can be performed. Further, since the impedance of the photoconductive layer is changed according to the degree of modulation of the output light from the exposure means and a voltage is applied to the light control layer by an amount corresponding to this, high resolution display can be performed.

[Brief description of drawings]

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

FIG. 2 is a cross-sectional view showing a specific configuration example of the liquid crystal display recording medium 100 of FIG.

FIG. 3 is a diagram showing a specific configuration example of an embodiment of the liquid crystal display device according to the present invention shown in FIG.

FIG. 4 is a timing chart showing operation timings of the specific configuration example of FIG.

5 is a block diagram showing a configuration example of a gradation control device 5 shown in FIGS. 1 and 3. FIG.

FIG. 6 is a graph showing changes in relative transmittance of the light control layer 1 shown in FIGS. 1, 2 and 3 with respect to voltage application time.

7 is a graph showing a change in voltage application time with respect to an input image density signal after correction by the lookup table 54 in FIG.

8 is a graph showing the relationship between the input image density signal and the relative transmittance of the light control layer 1 in the specific configuration example of the present invention of FIG. 3 when the gradation control device of the configuration of FIG. 5 is used. .

[Explanation of symbols]

 1 Light Control Layer 2 Photoconductive Layer 3 Voltage Source 4 Exposure Device 5 Gradation Control Device 6 Heating Device 7 Phase Transition Detection Device 31, 32 Transparent Electrode 33, 34 Transparent Substrate 36 Carrier Injection Blocking Layer 37 Light-shielding Layer and Carrier Injection Blocking Layer 52 latch circuit 54 look-up table 56 D / A converter 60 heating electrode 100 liquid crystal display recording medium

Claims (15)

[Claims] 1. A dimming layer containing at least liquid crystal as a component, a photoconductive layer disposed on one side of the dimming layer and having an impedance that changes according to received light, the dimming layer and the light. A voltage applying means for applying a voltage to a conductive layer, an exposing means for writing an image on the light control layer by exposing the photoconductive layer, and an exposing means for the exposing means based on a signal indicating a multi-tone density of the image. A liquid crystal display device comprising: a gradation control unit that controls the light transmittance of the light control layer by modulating output light. 2. The liquid crystal display device according to claim 1, wherein the light control layer comprises a composite film in which liquid crystal is dispersed in a polymer resin. 3. The liquid crystal contained in the light control layer is a liquid crystal exhibiting a smectic A phase at a use environment temperature and undergoing a phase transition to a nematic phase at a temperature higher than the use environment temperature. Liquid crystal display device. 4. The exposure means includes a light source capable of controlling exposure for each pixel, and the gradation control means exposes each pixel of the photoconductive layer on the basis of a signal indicating the multi-gradation density. The liquid crystal display device according to claim 1, wherein at least one of time, exposure power, and the number of exposure pulses is controlled. 5. The liquid crystal display device according to claim 3, further comprising heating means for heating the light control layer until the liquid crystal contained in the light control layer undergoes a phase transition to at least a nematic phase. 6. The liquid crystal display device according to claim 5, wherein the heating means heats the light control layer until the liquid crystal contained in the light control layer is in a liquid phase. 7. The liquid crystal display device further comprises detection means for detecting a transition of a liquid crystal contained in the light control layer from a liquid phase to a nematic phase and outputting a detection signal. 7. The liquid crystal display device according to claim 6, which is performed based on the above. 8. The carrier injection blocking layer according to claim 1, further comprising two carrier injection blocking layers disposed on both sides of the photoconductive layer to block injection of carriers into the photoconductive layer.
The described liquid crystal display device. 9. The light-shielding layer according to claim 1, further comprising a light-shielding layer that is disposed between the photoconductive layer and the light control layer and that absorbs light having a wavelength at which the photoconductive layer has sensitivity. Optical writing liquid crystal display device. 10. The carrier injection blocking layer disposed on the dimming layer side of the two carrier injection blocking layers,
9. The liquid crystal display device according to claim 8, wherein the photoconductive layer also serves as a light shielding layer that absorbs light having a wavelength having sensitivity. 11. The liquid crystal display device according to claim 1, wherein the photoconductive layer is a layer in which both electrons and holes are generated as carriers excited by the exposure, and these are movable. . 12. The liquid crystal according to claim 1, wherein the gradation control unit includes a correction unit that corrects non-linearity of light transmittance of the light control layer with respect to a voltage application time of the light control layer. Display device. 13. The memory for storing the value obtained by correcting the voltage application time of the light control layer according to the nonlinearity of the light transmittance of the light control layer in association with the multi-tone density. 13. The liquid crystal display device according to claim 12, further comprising means. 14. The liquid crystal display device according to claim 1, wherein the signal indicating the multi-tone density is a digital signal. 15. The gradation control means is a latch means for holding a signal indicating the multi-gradation density, which is the digital signal, and a voltage application time of the dimming layer and a light transmittance of the dimming layer. The value obtained by correcting in accordance with the non-linearity is stored in the form of a digital signal in association with the multi-tone density, and the voltage application time corresponding to the signal indicating the multi-tone density held in the latch means. Storage means for outputting a signal indicating
15. The liquid crystal display device according to claim 14, further comprising: a conversion unit that converts the signal indicating the voltage application time output from the storage unit into an analog signal.