JPH0611727A - Method for exposing liquid crystal recording medium by impression of voltage - Google Patents

Abstract

PURPOSE:To improve a contrast and to obtain good responsiveness by impressing successively increasing voltages between a photosensitive body and a liquid crystal recording medium thereby applying the voltage increase-components on a liquid crystal layer and increasing the modulation degree of a liquid crystal. CONSTITUTION:The photosensitive body 1 laminated with a photoconductive layer 13 on a transparent conductive layer 12 and the recording medium 2 laminated with the liquid crystal layer 21 on the transparent conductive layer 22 are disposed to face each other. A voltage is impressed between the two conductive layers to expose the layers with images, by which the orientation of the liquid crystal layer 21 is modulated and the images are recorded. The voltage to be impressed between the two conductive layers is gradually increased. Namely, the initial voltage is distributed at the volumetric ratio between the photosensitive body 1 and the recording medium 2 when the voltage of a prescribed gradient is impressed, but the voltage to be distributed to the liquid crystal of exposed parts is increased when the conductive layers are exposed with the images while the voltage is gradually increased. The best contrast is obtd. when the image exposing is executed at the timing at which the potential difference between the exposed parts and the unexposed parts is maximized.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a voltage application exposure method for a liquid crystal recording medium in which the orientation of liquid crystal is modulated by image exposure to record an image.

[0002]

2. Description of the Related Art Conventionally, it has been proposed to use a polymer-dispersed liquid crystal in which a liquid crystal is dispersed in a resin body as an image recording medium and modulate the orientation of the liquid crystal by voltage application exposure to record an image.

FIG. 7 is a diagram for explaining such image recording. The transparent support 11, the transparent conductive layer 12 and the photoconductive layer 13 are shown in FIG.
And a recording medium 2 composed of a liquid crystal layer 21, a transparent conductive layer 22, and a transparent support 23 are arranged to face each other, and a voltage is applied between the transparent conductive layers 12 and 22 by a power source 3 to the photosensitive body side. , Or image exposure from the recording medium side,
The exposed portion of the photoconductive layer 13 becomes conductive, discharge is generated between the photoconductor 1 and the recording medium 2 and a strong electric field is applied to the liquid crystal layer,
As a result, the orientation of the liquid crystal dispersed in the resin body changes, and a visible image is recorded. In the case where the liquid crystal dispersed in the resin body is a smectic liquid crystal, the memory property is particularly large, and even if the electric field is removed, the modulated orientation is maintained as it is, and the image can be read even if left for a long time. This visualized image is erased by heating it to a temperature near the isotropic phase transition of the liquid crystal, so that it can be reused.

[0004]

By the way, when the photoconductor and the recording medium are respectively represented by a resistor R1, a capacitor C1, a resistor R2, and a capacitor C2, in the arrangement relationship in FIG.
Since discharge occurs in the gap in the exposed portion, the gap resistance can be ignored, and the impedance of the photoconductor and the recording medium are connected in series, and the voltage (V-Vg) obtained by subtracting the discharge voltage Vg of the gap from the power supply voltage V Can be represented by an equivalent circuit as shown in FIG. Therefore, when the switch S is turned on and the voltage is applied stepwise in the configuration of FIG. 7, the voltage distribution to the photoconductor and the recording medium immediately after the voltage application is determined by the ratio of the reciprocal of the capacitances C1 and C2. When the capacity of the medium is about four times the capacity of the photoconductor, a voltage of about ⅕ of the applied voltage is applied to the liquid crystal layer. As time passes, the capacitors C1 and C2 are charged, and finally the voltage distribution between the photoconductor and the recording medium is determined by the ratio of the resistors R1 and R2. For example, as shown in FIG. The voltage applied to the layer is as shown in characteristic B.

However, since the resistance R2 of the liquid crystal layer is not so large, the voltage finally applied to the liquid crystal layer cannot be so large that the modulation degree cannot be increased, and as shown in FIG. The rising curve is extremely gentle, and the state in which the difference between this voltage and the dark potential of the unexposed area is large is the optimal state for image recording. There was a problem that it was not good. Therefore, it is possible to increase the power supply voltage, but if the power supply voltage is set so that the initial distribution voltage of the recording medium exceeds the threshold value of the liquid crystal, the liquid crystal will be modulated regardless of the image information. It is not desirable because it will happen. Therefore, there is a limit to increase the power supply voltage.

The present invention is intended to solve the above problems. Even if the initial potential applied to the liquid crystal is small, the voltage finally applied is increased to increase the modulation degree of the liquid crystal, improve the contrast, and further improve the response. It is an object of the present invention to provide a voltage application exposure method for a liquid crystal recording medium, which can improve the property.

[0007]

SUMMARY OF THE INVENTION According to the present invention, a photoconductor having a photoconductive layer laminated on a transparent conductive layer and a recording medium having a liquid crystal layer laminated on the transparent conductive layer are arranged so as to face each other. A method of image-recording by modulating the orientation of a liquid crystal layer by applying a voltage between layers to perform image exposure is characterized in that the voltage applied between both conductive layers is gradually increased.

Further, the present invention is characterized in that image exposure is carried out at a predetermined timing after voltage application.

[0009]

According to the present invention, a voltage which is gradually increased is applied between the photoconductor and the liquid crystal recording medium in which the liquid crystal layer is laminated on the transparent conductive layer so that a large amount of voltage increase is applied to the liquid crystal layer. As a result, even if the initial voltage applied to the liquid crystal layer is small, it is possible to increase the effective voltage applied to the liquid crystal layer by increasing the voltage increase rate, increase the modulation degree to improve the contrast, and improve the responsiveness. It will be possible.

[0010]

FIG. 1 is a diagram showing an embodiment of the present invention. In the figure, 1 is a photoconductor, 11 is a transparent support, 12 is a transparent conductive layer, 13 is a photoconductive layer, 2 is a liquid crystal recording medium, 21 is a liquid crystal layer, 22 is a transparent conductive layer, and 23 is a transparent support. Is the power supply.

The photoconductor 1 has a structure in which a transparent conductive layer 12 such as ITO and a photoconductive layer 13 are sequentially laminated on a transparent support 11 such as glass. The liquid crystal recording medium 2 arranged facing the photoconductor has a structure in which a transparent conductive layer 22 such as ITO and a liquid crystal layer 21 are sequentially laminated on a transparent support 23 such as glass.

The liquid crystal layer 21 is a polymer dispersed liquid crystal layer,
A low molecular weight liquid crystal material dispersed and fixed in a resin body.
Liquid crystal materials include smectic liquid crystals, nematic liquid crystals,
A cholesteric liquid crystal or a mixture thereof can be used, but it is preferable to use a smectic liquid crystal from the viewpoint of a memory property that retains the alignment of the liquid crystal and permanently retains a recorded image. As the resin body, it is desirable to use an ultraviolet curable resin which is compatible with the liquid crystal material in a monomer or oligomer state or compatible with a common solvent. Even if a large amount of liquid crystal is contained by crosslinking using UV curable resin, phenomena such as liquid crystal bleeding are suppressed, and conductivity is reduced due to cracking of the transparent electrode layer laminated on the recording layer surface. Can be prevented.

The mixing ratio of the liquid crystal material and the resin body may be such that the content of the liquid crystal material is 10% by weight to 90% by weight, preferably 40% by weight to 80% by weight, and the mixing ratio is less than 10% by weight. If so, the liquid crystal layer has a high transmittance (in an OFF state) before alignment and cannot obtain a contrast, and if it exceeds 90% by weight, the film strength becomes unfavorable. By containing a large amount of liquid crystal in the resin, the contrast ratio can be improved and the operating voltage can be lowered.

In the present invention, a ramp-shaped voltage having a predetermined inclination is applied by the power supply 3 between the conductive layers of the photoconductor 1 and the liquid crystal recording medium 2. As described above, the initial voltage in this case is distributed according to the capacity ratio between the photoconductor 1 and the liquid crystal recording medium, but at this time, the voltage applied to the liquid crystal layer is set to be lower than the threshold value of the liquid crystal. Then, when image exposure is performed while gradually increasing the voltage, the voltage distributed to the liquid crystal in the exposed portion increases, and as the voltage is further increased, a dark current also flows in the unexposed portion and the dark potential also rises. Then, the best contrast can be obtained when the image exposure is performed at the timing when the potential difference between the exposed portion and the unexposed portion becomes maximum.

Next, the present invention will be described in detail by the simulation of FIG.

In FIG. 2, a power source 31 is for applying a constant voltage in a stepwise manner, and a power source 32 is for applying a voltage that increases at a constant rate from the initial voltage in a ramp shape. This voltage is switched by the switch S1 and applied to the liquid crystal element 10 through the parallel circuit of the capacitor 40PF and the resistor 250 MΩ or 300 MΩ. 40PF is the capacity of the photoconductor, and 250MΩ and 300MΩ correspond to the resistances of the photoconductors in the exposed portion and the unexposed portion, respectively, which are switched by the switch S2. Then, the modulation degree when a voltage is applied to the liquid crystal element 10 is obtained by detecting light from the light source 12 through the liquid crystal element by the photoelectric detector 13 and measuring the waveform by the oscilloscope 11. The modulation degree M is defined by the following equation when the amount of transmitted light when no voltage is applied is T _OFF , the amount of transmitted light when voltage is applied is T _ON , and the amount of transmitted light when voltage is V is T. .

[0017] First, as shown in FIG.
V constant (characteristic V1), initial voltage 400 by power supply 32
When a ramp-shaped voltage (characteristic V2) that rises to 500 V in 0.5 seconds is applied, the effective voltage applied to the liquid crystal is as shown in characteristics L1 and L2, respectively, as shown in FIG. It was In this case, the average value of the applied voltage is 45
Although it is the same as 0V, the effective voltage applied to the liquid crystal has already exceeded at the time of 0.1 seconds when the ramp voltage is lower than the step voltage, which shows the superiority of applying the ramp voltage. There is.

Further, the modulation degree when the step-like voltage is applied and when the ramp-like voltage is applied is obtained by the equation (1), and the current (charge amount) flowing through the circuit is obtained with respect to the modulation degree. A result like 4 was obtained. In the figure, □ indicates the case of applying the step voltage, and ◯ indicates the case of applying the ramp voltage.

From the figure, it can be seen that the current flowing to achieve a modulation of 90% requires a stepwise voltage that is about 1.5 times larger than the ramp voltage. Therefore, in the case of the step-like voltage, a photosensitive member with a large performance that the resistance value changes largely due to the exposure is required to obtain the same degree of modulation as the ramp-like voltage. In addition, since the effective voltage applied to the liquid crystal can be made large, it is possible to perform appropriate recording even if the photoconductor characteristics are not so good.

FIG. 5 shows time-dependent modulation factor characteristics when a step-like voltage and a ramp-like voltage are applied.

In FIG. 5A, the characteristic M1 is 200 m.
When the voltage is increased from 400 V to 500 V in sec, the characteristic M2 is increased from 400 V to 500 V in 500 msec, and the characteristic M3 is 470 V constant. The characteristic M1 has a steeper rise than the characteristic M2,
It can be seen that it is better to increase the voltage increase speed, that is, the slope of the voltage.

Further, in FIG. 5 (b), M2 and M3 are the same as those in FIG. 5 (a) except that the time span is expanded to 0.5 seconds, and the characteristic M4 is a constant 450V. . From this figure, the modulation degree saturates in the case of the characteristics M3 and M4, whereas the modulation degree 1 in the case of the characteristic M2.
Can be achieved. Therefore, the contrast can be made sufficiently large, and recording with high image quality can be performed. Further, the characteristic M2 is steeper than the characteristic M3, which is advantageous in achieving high contrast.

FIG. 6 shows the modulation characteristic in the case of 250 MΩ and 300 MΩ.

In the figure, P1 and D1 are ramp voltages (400
250 when applying V → 500V / 0.5 sec)
Degree of modulation at MΩ and 300MΩ, P2 and D2 are 250M when a step voltage (450V constant) is applied.
6 shows the degree of modulation at Ω and 300 MΩ.
(A) and (b) are the same except that the time span is different.

From the figure, when the ramp voltage is applied, the difference between the characteristics P1 and D1 is larger than that when the step voltage is applied. For example, the difference between P1 and D1 is the largest at the timing of about 0.3 seconds. Therefore, if image exposure is performed at this timing, image recording with good contrast can be obtained. On the other hand, in the case of the step-like voltage, it takes time to increase the degree of modulation, and the difference between P2 and D2 cannot be made large, so that the contrast is not good.

In the above-mentioned embodiment, the voltage is raised at a constant inclination, but the inclination ratio may be changed by changing with time, and the liquid crystal recording medium is a transmissive type. However, the present invention can be similarly applied to the case of the reflection type.

[0027]

As described above, according to the present invention, by applying a gradually increasing voltage between the photoconductor and the liquid crystal recording medium, a large amount of voltage increase is applied to the liquid crystal layer, and the effective voltage applied to the liquid crystal layer is reduced. It is possible to increase the degree of modulation to increase the contrast and improve the responsiveness.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of the present invention.

FIG. 2 is a diagram illustrating a simulation of the present invention.

FIG. 3 is a diagram showing effective voltage characteristics with respect to time of a liquid crystal.

FIG. 4 is a diagram showing the relationship between the degree of modulation and the amount of charge that flows.

FIG. 5 is a diagram showing a time modulation factor characteristic.

FIG. 6 is a diagram showing time-dependent modulation factor characteristics of an exposed portion and an unexposed portion.

FIG. 7 is a diagram illustrating conventional voltage application exposure.

FIG. 8 is a diagram showing an equivalent circuit.

FIG. 9 is a diagram showing voltages applied to a photoconductor and liquid crystal.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Photosensitive material, 11 ... Transparent support body, 12 ... Transparent conductive layer, 1
3 ... Photoconductive layer, 2 ... Liquid crystal recording medium, 21 ... Liquid crystal layer, 22
... transparent conductive layer, 23 ... transparent support, 3 ... power supply.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Internal reference number FI Technical display location G09G 3/18 7319-5G G11C 11/42

Claims (2)

[Claims] 1. A photosensitive member having a photoconductive layer laminated on a transparent conductive layer and a recording medium having a liquid crystal layer laminated on the transparent conductive layer are arranged to face each other, and a voltage is applied between the conductive layers to form an image. A method for exposing a voltage of a liquid crystal recording medium, wherein a voltage applied between both conductive layers is gradually increased in the method of exposing and modulating the orientation of the liquid crystal layer to record an image. 2. The liquid crystal recording medium voltage application exposure method according to claim 1, wherein image exposure is performed at a predetermined timing after voltage application.