Information recording method having a liquid crystal substrate

Changes-with-time in the voltages of exposed and unexposed portions of a liquid crystal recording layer with respect to a photoconductive layer having a varying dark current value are found by varying an applied voltage, and the applied voltage and the value of a dark current through the photoconductive layer are determined such that when the voltage of the unexposed portion of the liquid crystal recording layer reaches the threshold voltage of the liquid crystal recording layer, the difference in voltage between the exposed and unexposed portions of the liquid crystal recording layer reaches a maximum, so that information is recorded with the photoconductive layer and at the applied voltage, where a potential difference is obtained, which is at least one half of the difference (maximum contrast) in the voltages applied on the liquid crystals at the exposed and unexposed portions of the liquid crystal recording layer.

BACKGROUND OF THE INVENTION 
The present invention relates to a method for recording information on an 
integrated type of information recording system comprising a photoelectric 
sensor and a liquid crystal recording medium stacked on each other. 
There has so far been known an integrated type of information recording 
system which comprises a liquid crystal recording medium including on an 
electrode a liquid crystal-polymer composite layer with polymer balls 
filled in a liquid crystal phase and a photoelectric sensor including a 
photoconductive layer on an electrode layer, both stacked on each other, 
and which is exposed to light at an applied voltage to record an image 
thereon. 
Such an integrated type of information recording system is schematically 
shown in FIG. 1. More specifically, this system is broken down into two 
types, the first type wherein a liquid crystal medium 20 is directly 
stacked on a photoelectric sensor 10 as shown in FIG. 1(a), and the second 
type wherein an interlayer 24 made up of a transparent dielectric material 
(transmission type) or a dielectric mirror (reflection type) is interposed 
between them, as shown in FIG. 1(b). In the photoelectric sensor 10 a 
transparent electrode 12 and a photoconductive layer 13 are successively 
stacked on a transparent substrate 11, and in the liquid crystal recording 
medium 20 a liquid crystal-polymer composite layer 23 is stacked on a 
transparent electrode 22. When the photoconductive layer 13 used has a 
single-layer structure, amorphous selenium, amorphous silicon and so on 
may be used in the form of an inorganic photoconductive layer, and 
polyvinyl carbazole may be used with trinitrofluorenone added thereto in 
the form of an organic photoconductive layer. Alternatively, use may also 
be made of a composite photoconductive layer comprising a carrier 
generation layer having an azo dye dispersed in resin such as polyvinyl 
butyral and a carrier transport layer having a hydrazone derivative mixed 
with resin such as polycarbonate, both layers stacked on each other. 
When such an integrated type of information recording system is irradiated 
with recording light in the form of visible light with voltage applied 
from a power source 30 across the electrodes 12 and 22 thereof, as shown 
in FIG. 2, there is a change in the conductivity of the photoconductive 
layer 13 depending on the intensity of visible light. This change in turn 
causes an electric field applied on the liquid crystal layer 23 to change, 
resulting in a change in the orientation of liquid crystals. Even after 
removal of the electric field by putting off the application of voltage, 
this state is so maintained that image information can be recorded. 
To read out the thus recorded image information, the liquid crystal 
recording medium 20 is irradiated with reading light which emanates from a 
light source 60 and is selected in terms of wavelength through a filter 
70, as shown in FIG. 3(a) (transmission type) and FIG. 3(b) (reflection 
type). The incident light is modulated by the orientation of liquid 
crystals in the liquid crystal recording medium, while the transmitted (or 
reflected) light is converted by an photoelectric converter 80 into an 
electrical signal, which may be outputted through a printer or CRT, if 
required. The light source 60 used may be a white light source such as a 
xenon or halogen lamp, or laser light. 
However, a problem with recording an image with an integrated type of 
liquid crystal recording system is that, although depending on the 
characteristics of the photoelectric sensor, the quantity of exposure 
light (light intensity.times.exposure time) required for image recording 
often becomes too large, or no image can be recorded at all. A liquid 
crystal recording layer has a certain threshold voltage. As can be 
understood from FIG. 4 illustrating the range of modulation of liquid 
crystals, when the voltage applied on the liquid crystal layer is within 
the range of 200 V to 250 V for example, recording can be made depending 
on the quantity of exposure light. At lower than 200 V, however, no image 
can be recorded because the liquid crystals are hardly oriented. At higher 
than 250 V, no image can again be recorded because of saturated 
orientation. 
SUMMARY OF THE INVENTION 
It is thus one object of the present invention to provide an information 
recording method using an integrated type of information recording system 
including a dielectric interlayer. 
Another object of the present invention is to enable the optimum 
photoelectric sensor to be specified, even when there are changes in the 
values of the capacity and resistance of a dielectric interlayer, and the 
values of the capacity, resistance and threshold voltage of a liquid 
crystal recording layer. 
Still another object of the present invention is to enable the optimum 
photoelectric sensor to be so specified that information can be recorded 
at the optimum applied voltage for the optimum voltage applying time. 
More specifically, the present invention provides an information recording 
method using an integrated type of information recording system having a 
photoconductive layer, a dielectric interlayer, a liquid crystal recording 
layer and an electrode layer stacked on a transparent electrode in the 
described order, wherein the photoconductive layer is exposed to 
information light with voltage applied across both electrodes of the 
system so that the liquid crystals are oriented to record image 
information depending on the quantity of the exposure light, characterized 
in that: 
from the following equations: 
##EQU1## 
where V.sub.AP is the voltage applied across both electrodes; C.sub.S, 
C.sub.L and C.sub.M are the capacities of the photo conductive layer, the 
liquid crystal recording layer and the interlayer, respectively; V.sub.S, 
V.sub.L and V.sub.M are the voltages applied on the respective layers; 
I.sub.S, I.sub.L and I.sub.M are the currents flowing through the 
respective layers; and V.sub.S (0), V.sub.M (0) and V.sub.L (0) are the 
voltages applied on the respective layers just after the application of 
voltages, changes-with-time in the voltages of exposed and unexposed 
portions of the liquid crystal recording layer with respect to the 
photoconductive layer having a varying dark current value are found by 
varying the applied voltage, and the applied voltage and the value of the 
dark current through the photoconductive layer are determined such that 
when the voltage of the unexposed portion of the liquid crystal recording 
layer reaches the threshold voltage of the liquid crystal recording layer, 
the difference in voltage between the exposed and unexposed portions of 
the liquid crystal recording layer reaches a maximum, so that information 
is recorded with the photoconductive layer and at the applied voltage, 
where a potential difference is obtained, which is at least one half of 
the difference (maximum contrast) in the voltages applied on the liquid 
crystals at the exposed and unexposed portions of the liquid crystal 
recording layer.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
An account will now be given of how to calculate changes in the voltages 
applied on an integrated type of information recording system comprising 
three layers, a photoelectric sensor, a liquid crystal recording layer and 
an interlayer, i.e., in the voltages applied on the liquid crystal 
recording layer and interlayer thereof. 
The integrated type of information recording system is represented by an 
equivalent circuit shown in FIG. 5. Here let C.sub.S, C.sub.L and C.sub.M 
denote the capacities of the photoelectric sensor, liquid crystal 
recording layer and interlayer, respectively, and V.sub.AP represent the 
power source voltage. Then, the voltages V.sub.S (0), V.sub.L (0) and 
V.sub.M (0) distributed to the photoelectric sensor, liquid crystal 
recording layer and interlayer just after the application of voltage are 
respectively given by: 
##EQU2## 
Thereafter, currents flow through the resistance components of the layers, 
so that there are changes in the voltages of the layers. At this time, the 
following differential equation holds: 
##EQU3## 
Here, 
EQU V.sub.S +V.sub.M +V.sub.L =V.sub.AP (1-5) 
EQU dV.sub.S /dt+dV.sub.M /dt+dV.sub.L /dt=0 (1-6) 
I.sub.S, I.sub.M and I.sub.L are the values of the currents through the 
photoelectric sensor, interlayer and liquid crystal recording layer, 
respectively. As already proposed (JP-A 6(1994)-88200), the value of the 
current through a photoelectric sensor differs at bright and dark portions 
and depends on voltage and time. This will now be briefly explained below. 
Shown in FIG. 6 is a photo-induced current as measured when the 
photoelectric sensor of 10 .mu.m in thickness is exposed to light at an 
intensity of 20 Lux for 33 msec and at an applied voltage of 300 V, with 
the time after the start of irradiation with light as abscissa. The dark 
current I.sub.d of the photoelectric sensor is defined as a current value 
at t=0, and the photo-induced current as a difference .DELTA.I between the 
measured current value and the dark current. 
As shown by a broken line in FIG. 6, the dark current I.sub.d is kept 
constant while voltage is applied to the photoelectric sensor, and the 
photo-induced current continues to flow even after the irradiation with 
light is put off. Now consider the case where a constant voltage V is 
applied to the photoelectric sensor. Then, the current flowing through the 
photoelectric sensor can be divided to a base current portion that flows 
regardless of irradiation with light and an incremental portion caused by 
irradiation with light. The base current is measured as a dark current in 
the absence of light, and when a constant voltage is applied to the 
photoelectric sensor, a current as represented by Eq. (2-1) flows through 
it. 
EQU Id=.alpha.V.sub.p.sup.2 (2-1) 
where I.sub.d is the base (dark) current, .alpha. is a constant, and 
V.sub.p is the voltage of the photoelectric sensor. 
When the photoelectric sensor is irradiated with light having constant 
intensity for a constant time, its current value varies with time, as 
shown in FIG. 6. The current value measured upon the start of irradiation 
with light is the base current given by Eq. (2-1). The photo-induced 
current portion is divided into a component upon irradiation with light 
and a component after the completion of irradiation with light. 
The change in the photo-induced current cannot precisely be expressed by a 
simple equation. In a region having a field intensity (of 5 to 49 
V/.mu.m), a low exposure light intensity (of up to 50 Lux) and a short 
exposure time (of up to 100 msec), however, that change can be linearly 
approximated, as represented by Eq. (2-2). 
EQU .DELTA.I(t).apprxeq.kV.sub.p T(0&lt;t.ltoreq.t.sub.1) (2-2) 
After the conclusion of irradiation with light, the photo-induced current 
attenuates at a time constant of 200 to 500 msec, as approximated by Eq. 
(2-3). 
EQU .DELTA.I(t).apprxeq.kV.sub.p t.sub.1 exp{(t.sub.1 -t)/.tau.}(t.sub.1 
&lt;t)(2-3) 
where .DELTA.I(t)=the photo-induced current, 
k=a constant (proportional to light intensity), 
t.sub.1 =the time at which the irradiation with light is put off, and 
.tau.=a time constant (200 to 500 msec). 
In a photoelectric sensor whose dark current value is in proportion to the 
applied voltage, the dark current value I.sub.d corresponding to the base 
current is given by 
EQU I.sub.d =.alpha.'V.sub.p (2-4) 
Accordingly, the current value I.sub.p of the photoelectric sensor at the 
bright portion is represented by the following equations with respect to 
during and after irradiation with light, respectively. 
EQU I.sub.p (V.sub.p, t).apprxeq..alpha.V.sub.p.sup.2 +kV.sub.p t.sub.1 
(0&lt;t.ltoreq.t.sub.1) (2-5) 
EQU I.sub.p (V.sub.p, t).apprxeq..alpha.V.sub.p.sup.2 +kV.sub.p t.sub.1 
exp{(t.sub.1 -t)/.tau.}(t.sub.1 &lt;t) (2-6) 
In a photoelectric sensor whose dark current value is proportional to 
voltage, the base current portion is proportional to voltage and the 
photo-induced current is proportional to the one-second power of voltage, 
as given by 
EQU I.sub.p (V.sub.p, t)=.alpha.'V.sub.p (I.sub.p, t)+k'V.sub.p.sup.1/2 
t(0&lt;t.ltoreq.t1) (2-7) 
EQU I.sub.p (V.sub.p, t)=.alpha.'V.sub.p (I.sub.p, t)+k'V.sub.p.sup.1/2 t.sub.1 
exp{(t.sub.1 -t)/.tau.}(t.sub.1 &lt;t) (2-8) 
On the other hand, the currents of the liquid crystal recording layer and 
interlayer are proportional to voltage, as given by 
EQU I.sub.M =V.sub.M /R.sub.M (3-1) 
EQU I.sub.L =V.sub.L /R.sub.L (3-2) 
Here, R.sub.M and R.sub.L are the resistance components of the interlayer 
and liquid crystal recording layer. From Eqs. (1-4) and (1-6), 
##EQU4## 
By substituting Eqs. (3-1) to (3-4) for the following equations, it is 
possible to find the voltages of the interlayer and liquid crystal 
recording layer. 
EQU V.sub.M (t+.DELTA.t)=V.sub.M (t)+(dV.sub.M /dt).DELTA.t (3-5) 
EQU V.sub.L (t+.DELTA.t)=V.sub.L (t)+(dV.sub.L /dt).DELTA.t (3-6) 
When the interlayer is made up of two or more stacked layers different from 
each other in terms of resistivity and dielectric constant, the equivalent 
circuit is represented in FIG. 7. In this case, the voltage of each layer 
must be calculated depending on the structure of that layer. In what 
follows, an account will be given of how to calculate the voltage of an 
interlayer, when it is made up of two or more layers stacked one upon 
another. 
When the interlayer is made up of n layers, the capacity C.sub.t of an 
integrated type of information recording system is given by 
EQU C.sub.t =1/{(1/C.sub.S)+(1/C)+(1/C.sub.1)+(1/C.sub.2) . . . . }(4-1) 
provided that the capacities and resistance of the layers are represented 
by C.sub.n (n=1, 2, 3, . . . . ). 
At an initial stage of application of voltage, the voltages distributed to 
the photoelectric sensor, liquid crystal recording layer and interlayer 
are given by 
##EQU5## 
As in the case where the interlayer is made up of a single layer, voltage 
changes occur after the application of voltage because of currents flowing 
through the resistance components of the layers. The differential equation 
in this transient state is given by 
##EQU6## 
Here, 
EQU V.sub.S +V.sub.L +V.sub.1 +V.sub.2 . . . . .=V.sub.AP (4-4) 
EQU dV.sub.S /dt+dV.sub.L /dt+dV.sub.1 /dt+dV.sub.2 /dt=0 (4-5) 
The voltages of the liquid crystal recording layer and interlayer can be 
calculated from the following equations: 
##EQU7## 
From the above-described equations, the voltages applied on the liquid 
crystal recording layer and interlayer of an integrated type of 
information recording system can be calculated. Shown in FIG. 8 are the 
voltages applied on the liquid crystal recording layer and interlayer, as 
calculated from Eqs. (3-5) and (3-6). Set out below are the physical 
characteristic values of the photoelectric sensor, liquid crystal 
recording layer and interlayer used for calculation. 
Capacity of the photoelectric sensor: 310 pF/cm.sup.2 
Dark current value of the photoelectric sensor: 5.0.times.10.sup.-7 
A/cm.sup.2 (at an applied voltage of 100 V) 
Capacity of the liquid crystal recording layer: 950 pF/cm.sup.2 
Resistance of the liquid crystal recording layer: 160 M.OMEGA./cm.sup.2 
Capacity of the interlayer: 2,000 pF/cm.sup.2 
Resistance of the interlayer: 64 M.OMEGA./cm.sup.2 
Applied voltage: 430 V 
Thickness of the photoelectric sensor: 10 .mu.m 
Thickness of the liquid crystal medium: 6 .mu.m 
Thickness of the interlayer: 1.5 .mu.m 
In FIG. 8(a), curves L.sub.L and L.sub.D represent the voltages applied on 
the bright and dark portions of the liquid crystal recording layer, 
respectively, and curves M.sub.L and M.sub.D indicate the voltages applied 
on those of the interlayer. Immediately after the application of voltage, 
the voltages distributed to the liquid crystal recording layer and 
interlayer are about 95 V and about 45 V, respectively. Thereafter, the 
voltages applied on the liquid crystal recording layer and interlayer 
change because of currents flowing through the resistance components 
thereof. At the bright portion rather than at the dark portion, the 
voltage applied on the liquid crystal recording layer becomes excessive 
because the photoelectric sensor can have a higher conductivity. 
FIG. 8(b) shows a voltage difference between the bright and dark portions 
of the liquid crystal recording layer. This voltage difference increases 
with time and, in the instant example, reaches a maximum at about 100 
msec. According to the recording system of the present invention, it is 
preferable to record an image thereon when the voltage difference between 
the bright and dark portions reaches a maximum. It is then desired that 
the voltage to be applied be controlled such that the voltage of the 
liquid crystal recording layer at the dark portion reaches the threshold 
voltage. This is because when the voltage of the liquid crystal recording 
layer exceeds the threshold voltage, the orientation of liquid crystals 
occurs regardless of exposure, and at lower than the threshold voltage the 
liquid crystals do not work (orient); in either case, no image of good 
quality can be recorded. 
Shown in FIG. 9, on the other hand, are the results of calculation of the 
voltages applied on the liquid crystal recording layer and interlayer 
while the dark current value (conductivity) of the photoelectric sensor 
and the resistivity of the interlayer were varied (with increases in the 
dark current value and the resistivity of the interlayer). Set out below 
are the physical characteristic values used for calculation. 
Capacity of the photoelectric sensor: 310 pF/cm.sup.2 
Dark current value of the photoelectric sensor: 1.0.times.10.sup.-6 
A/cm.sup.2 (at an applied voltage of 100 V) 
Capacity of the liquid crystal recording layer: 950 pF/cm.sup.2 
Resistance of the liquid crystal recording layer: 160 M.OMEGA./cm.sup.2 
Capacity of the interlayer: 2,000 pF/cm.sup.2 
Resistance of the interlayer: 160 M.OMEGA./cm.sup.2 
Applied voltage: 390 V 
Thickness of the photoelectric sensor: 10 .mu.m 
Thickness of the liquid crystal medium: 6 .mu.m 
Thickness of the interlayer: 1.5 .mu.m 
From FIG. 9(a), it can be seen that the voltage applied on the liquid 
crystal recording layer is about 90 V immediately after the application of 
voltage, then increases because of a current flowing through the 
resistance component of the photoelectric sensor, then reaches a maximum 
after about 100 msec, and finally decreases. This phenomena take place 
because the voltage across the interlayer increases due to the large 
resistance value thereof. From FIG. 9(b), on the other hand, it can be 
seen that the voltage difference between the bright and dark portions of 
the liquid crystal recording layer reaches a maximum at about 75 msec. 
This time is shorter as compared with FIG. 8(b) due to an increase in the 
dark current value of the photoelectric sensor. 
In some cases, the voltage of the liquid crystal recording layer reaches a 
maximum at a certain time depending on the conductivity of the 
photoelectric sensor and the resistivity of the liquid crystal recording 
layer, and thereafter decreases. It is then required that when the voltage 
of the dark portion reaches a maximum before the voltage difference 
between the bright and dark portions reaches a maximum, an image be 
recorded before the voltage of the dark portion reaches a maximum. In 
other words, it is required that the applied voltage be such that the 
maximum voltage of the dark portion becomes slightly higher than the 
threshold voltage of liquid crystals, so that an image can be recorded at 
a potential difference (contrast potential) between the bright and dark 
portions. In the process during which the voltage of the liquid crystal 
recording layer decreases, no image can be recorded because no further 
orientation of liquid crystal takes place. This would be true of even when 
the potential difference between the bright and dark portions reaches a 
maximum in the process during which the voltage of the dark portion 
reaches a maximum and then decreases. In such a case, it is required that 
the recording of an image be finished when the voltage of the dark portion 
reaches a maximum. 
In a simulation of calculation of the voltage applied on the liquid crystal 
recording layer using a photoelectric sensor having a varying dark current 
value (while the coefficient .alpha. in Eq. (2-1) was varied), the maximum 
values of the voltages of the bright and dark portions and the optimum 
value for the voltage applying time were calculated at the applied voltage 
preset such that the voltage of the liquid crystal recording layer at the 
dark portion reaches the threshold voltage at the time when the potential 
difference between the dark and light portions reaches a maximum. For 
instance, where the voltage of the liquid crystal recording layer at the 
dark portion has a maximum value (as shown in FIG. 9), t.sub.2 at which 
the voltage of the liquid crystal recording layer at the dark portion 
reaches a maximum is often shorter than t.sub.1 at which the potential 
difference between the bright and dark portions reaches a maximum. It is 
then time t.sub.2 that is the optimum value for the voltage applying time. 
For this reason, the simulation was done under the conditions that the 
potential difference between the bright and dark portions reaches a 
maximum and the voltage of the dark portion reaches a maximum. Set out 
below are the physical characteristic values used for the simulation. 
Capacity of the photoelectric sensor: 310 pF/cm.sup.2 
Capacity of the liquid crystal recording layer: 950 pF/cm.sup.2 
Resistance of the liquid crystal recording layer: 160 M.OMEGA./cm.sup.2 
Capacity of the interlayer: 2,000 pF/cm.sup.2 
Resistance of the interlayer: 160 M.OMEGA./cm.sup.2 
Thickness of the photoelectric sensor: 10 .mu.m 
Thickness of the liquid crystal medium: 6 .mu.m 
Thickness of the interlayer: 1.5 .mu.m 
Shown in FIG. 10 is the relation between the applied voltage and the dark 
current density when the dark current value of the photoelectric sensor 
was varied. A solid line indicates the applied voltage at which the 
potential difference between the bright and dark portions reaches a 
maximum, and a broken line represents the applied voltage preset under the 
condition that the voltage of the dark portion reaches a maximum (the 
threshold voltage). It should here be noted that calculation was made 
assuming that the applied voltage is within the range of 200 V to 800 V, 
because at an applied voltage exceeding 800 V an initial voltage 
distributed to the liquid crystal recording layer is lower than the 
threshold voltage. 
As can be seen from FIG. 10, a photoelectric sensor, if its dark current is 
lower than 5.times.10.sup.-8 A/cm.sup.2, cannot be applied to the present 
system, because the applied voltage exceeds 800 V. 
Shown in FIG. 11 is the relation between the initial voltage distributed to 
the liquid crystal recording layer and the dark current. As can be seen 
from FIG. 11, it is required that the initial voltage be lower than the 
threshold voltage. If the threshold voltage is of the order of about 180 
V, it is then somehow possible to use a photoelectric sensor of 
1.0.times.10.sup.-7 A/cm.sup.2. Since the initial voltage is preferably at 
most one half of the threshold voltage, however, FIG. 11 teaches that it 
is preferable to use a photoelectric sensor having a dark current value of 
at least 8.times.10.sup.-7 A/cm.sup.2. 
The relation between the potential difference between the bright and dark 
portions and the dark current value of the photoelectric sensor is shown 
in FIG. 12, wherein a solid line indicates the potential difference found 
under the condition that the potential difference between the bright and 
dark portions reaches a maximum, and a broken line represents the 
potential difference found under the condition that the voltage of the 
dark portion reaches a maximum. Referring here to how to find the broken 
line, the applied voltage and the voltages distributed to the layers are 
determined, as shown in FIGS. 11 and 12. Then, the voltage applied on the 
liquid crystal recording layer is found from Eqs. (3-1) to (3-6). Thus, 
the broken line is found in the form of the potential difference between 
the bright and dark portions when the solid line in the form of the 
maximum value of the potential difference between the bright and dark 
portions represents that the voltage of the dark portion reaches a maximum 
(threshold voltage). 
As shown by the solid line in FIG. 12, the maximum value of 34 V for the 
potential difference is obtained at a dark current value of 
5.times.10.sup.-8 A/cm.sup.2. Under the condition that the voltage of the 
dark portion shown by the broken line reaches a maximum (threshold 
voltage), the potential difference between the bright and dark portions is 
25 V. This indicates that when the potential difference between the bright 
and dark portions reaches a maximum, the voltage of the liquid crystal 
recording layer at the dark portion is decreasing after already reached a 
maximum. This voltage decreasing process can also be seen from FIG. 13 
showing the relation between the dark current value and the voltage 
applying time. In FIG. 13, too, the conditions for finding the solid and 
broken lines are the same as explained in connection with FIG. 12. When 
the dark current value is 5.times.10.sup.-8 A/cm.sup.2, the broken line 
lies beneath the solid line, indicating that the time the potential of the 
dark portion reaches a maximum is shorter than the time the potential 
difference between the bright and dark portions reaches a maximum. 
Referring again to FIG. 13, it should be noted that for a dark current 
value represented by a broken line portion lying above the solid line, the 
potential of the dark portion does not reach a maximum even when the 
potential difference between the bright and dark portions has already 
reached a maximum. 
In such a voltage decreasing process, no image can be recorded, and so the 
maximum value for the potential difference is 32 V under the condition 
that the dark current value of the photoelectric sensor is 
8.0.times.10.sup.-8 A/cm.sup.2, as shown by the broken line in FIG. 12. 
This value is the maximum value for the potential difference, with the 
potential difference decreasing regardless of a conductivity increase or 
decrease. To record an image of good quality, as large a potential 
difference as possible is needed between the bright and dark portions. In 
other words, it is desired that the potential difference be at least one 
half of this maximum value of 32 V and that the dark current value of the 
photoelectric sensor used be within the range of 4.0.times.10.sup.-8 
A/cm.sup.2 to 2.0.times.10.sup.-6 A/cm.sup.2. 
As can be seen from FIG. 13 showing the relation between the dark current 
value and the voltage applying time, the voltage applying time may be up 
to 200 msec, but should preferably be up to 100 msec. As can thus be 
understood from FIG. 13, it is preferable to use a photoelectric sensor 
having a dark current value of at least 3.0.times.10.sup.-7 A/cm.sup.2. 
The foregoing is one exemplary simulation. By simulation, the optimum 
photoelectric sensor can be achieved even when there are variations in the 
thickness of a photoelectric sensor and liquid crystal recording medium, 
the thickness, capacity and resistance of an interlayer, and the capacity, 
resistance and threshold electrode of a liquid crystal recording layer. 
EXAMPLE 1 
Three (3) parts of a fluorenone azo dye acting as a carrier generation 
substance and having the following structural formula (1) and 1 part of a 
polyester resin were mixed with 196 parts of a mixed solvent of dioxane 
and cyclohexanone at 1:1, and the mixture was then sufficiently kneaded 
together in a mixer to prepare a coating solution. 
##STR1## 
This solution was coated on the side of a glass substrate on which an ITO 
transparent electrode (of 500 .ANG. in thickness and 80 .OMEGA./ in 
resistance) was formed, and dried at 100.degree. C. for 1 hour to form a 
carrier generation layer of 0.3 .mu.m in thickness. 
Then, 3 parts of p-dimethylstilbene acting as a carrier transport substance 
and having the following structural formula (2) and 1 part of a 
polystyrene resin were mixed with and dissolved in 180 parts of a mixed 
solvent of dichloromethane and 1,1,2-trichloroethane at 68:102 to prepare 
a coating solution. 
##STR2## 
This solution was coated on the above-described carrier generation layer, 
and dried at 80.degree. C. for 2 hours to form a carrier transport layer, 
thereby preparing a photoelectric sensor of 10 .mu.m in thickness. 
EXAMPLE 2 
Three (3) parts of the fluorenone azo dye acting as a carrier generation 
substance and having the above formula (1) and 1 part of a polyvinyl 
formal resin were mixed with 180 parts of a mixed solvent of dioxane and 
cyclohexanone at 1:1, and the mixture was then sufficiently kneaded 
together in a mixer to prepare a coating solution. 
This solution was coated on the side of a glass substrate on which an ITC 
transparent electrode (of 500 .ANG. in thickness and 80 .OMEGA./ in 
resistance) was formed, and dried at 100.degree. C. for 1 hour to form a 
carrier generation layer of 0.3 .mu.m in thickness. 
Then, 3 parts of p-dimethylstilbene acting as a carrier transport substance 
and having the above formula (2) and 1 part of a polystyrene resin were 
mixed with and dissolved in 180 parts of a mixed solvent of 
dichloromethane and 1,1,2-trichloroethane at 68:102 to prepare a coating 
solution. This solution was coated on the above-described carrier 
generation layer, and dried at 80.degree. C. for 2 hours to form a carrier 
transport layer, thereby preparing a photoelectric sensor of 10 .mu.m in 
thickness. 
EXAMPLE 3 
Three (3) parts of the azo dye acting as a carrier generation substance and 
having the above formula (1) and 1 part of a polyvinyl formal resin were 
mixed with 202 parts of a mixed solvent of dioxane and cyclohexanone at 
1:1, and the mixture was then sufficiently kneaded together in a mixer to 
prepare a coating solution. This solution was coated on the side of a 
glass substrate on which an ITO transparent electrode (of 500 .ANG. in 
thickness and 80 .OMEGA./ in resistance) was formed, and dried at 
100.degree. C. for 1 hour to form a carrier generation layer of 0.3 .mu.m 
in thickness. 
Then, 3 parts of 4-methyltriphenylamine acting as a carrier transport 
substance and 1 part of a polycarbonate resin were mixed with and 
dissolved in 180 parts of a mixed solvent of dichloromethane and 
1,1,2-trichloroethane at 68:102 to prepare a coating solution. This 
solution was coated on the above-described carrier generation layer, and 
dried at 80.degree. C. for 2 hours to form a carrier transport layer, 
thereby preparing a photoelectric sensor of 10 .mu.m in thickness. 
EXAMPLE 4 
By vapor evaporation, a gold electrode was formed over an area of 4 
mm.times.4 mm on the carrier transport layer of each of the photoelectric 
sensors prepared in Examples 1-3. In a dark place, a voltage of 100 V was 
applied across the transparent and gold electrodes while the transparent 
electrode was kept positive. The current value was then measured 500 msec 
after the application of voltage. The respective current values were 
8.0.times.10.sup.-7 A/cm.sup.2, 2.4.times.10.sup.-8 A/cm.sup.2, and 
3.6.times.10.sup.-5 A/cm.sup.2. 
EXAMPLE 5 
Five (5) parts of polyvinyl alcohol were dissolved in 95 parts of pure 
water to prepare a coating solution, which was in turn spin-coated on each 
of the carrier transport layers of the photoelectric sensors prepared in 
Examples 1-3, and then vacuum-dried at 80.degree. C. for 2 hours to form 
an interlayer of 1.5 .mu.m in thickness. 
EXAMPLE 6 
A liquid crystal recording layer of 6 .mu.m in thickness was stacked on 
each of the interlayers of the photoelectric sensors prepared in Examples 
1-3 and 5. The liquid crystal recording layer was prepared as follows. 
A mixture consisting of 4 parts of dipentaerythritol hexaacrylate, smectic 
liquid crystals ("S6" made by Merck), 0.2. parts of a fluorine surfactant 
("Florado FC-430" made by 3M), and 0.2 parts of a photopolymerization 
initiator ("Dalocure 1173" made by Merck) was controlled to a solid 
content of 30% with the use of xylene. The resulting solution was coated 
on the side of a glass substrate on which an ITO transparent electrode (of 
500 .ANG. in thickness and 80 .OMEGA./ in resistance) was formed, using a 
blade coater having a gap thickness of 50 .mu.m, retained at 50.degree. 
C., and irradiated with UV light at 0.3 J/cm.sup.2 to prepare a liquid 
crystal recording layer of about 6 .mu.m in thickness. Using hot methanol, 
liquid crystals were extracted from a section of this liquid crystal 
recording layer, dried, and internally observed under a scanning electron 
microscope of 10,000 magnifications ("S-800" made by Hitachi, Ltd.). As a 
result, it was found that the layer is covered thereon with an UV cured 
type resin of 0.6 .mu.m in thickness and filled therein with resin 
particles of 0.1 .mu.m in diameter. 
After the liquid crystal recording layer had been formed in this way, an 
ITO electrode of about 1,000 .ANG. in thickness was formed thereon by 
sputtering. 
EXAMPLE 7 
An integrated type of information recording system constructed using the 
photoelectric sensor obtained in Example 1 was irradiated with image 
carrying light from the transparent side of the photoelectric sensor for 
33 msec, while a voltage of 420 V was applied across both electrodes for 
80 msec, with the photoelectric sensor kept positive. After the 
application of voltage, the information recording system was irradiated 
with blue light to read the transmitted light by means of a CCD sensor. As 
a result, an image signal of high contrast was obtained. 
EXAMPLE 8 
An integrated type of information recording system constructed using the 
photoelectric sensor obtained in Example 2 was irradiated with image 
carrying light from the transparent side of the photoelectric sensor for 
33 msec, while a voltage of 420 V was applied across both electrodes for 
80 msec, with the photoelectric sensor kept positive. After the 
application of voltage, the information recording system was observed, but 
no change was found. 
EXAMPLE 9 
An integrated type of information recording system constructed using the 
photoelectric sensor obtained in Example 2 was irradiated with image 
carrying light from the transparent side of the photoelectric sensor for 
33 msec, while a voltage of 850 V was applied across both electrodes for 
80 msec, with the photoelectric sensor kept positive. After the 
application of voltage, the information recording system was observed. As 
a result, it was found that the liquid crystal recording layer was overall 
oriented regardless of the image exposed to light. 
EXAMPLE 10 
An integrated type of information recording system constructed using the 
photoelectric sensor obtained in Example 3 was irradiated with image 
carrying light from the transparent side of the photoelectric sensor for 
33 msec, while a voltage of 320 V was applied across both electrodes for 
50 msec, with the photoelectric sensor kept positive. After the 
application of voltage, the information recording system was irradiated 
with blue light to read the transmitted light by means of a CCD sensor. As 
a result, the obtained image signal was found to be of low contrast. 
The present invention as above explained provides an integrated type of 
information recording system including a dielectric interlayer, which 
enables the optimum photoelectric sensor to be specified even when there 
are changes in the capacity and resistance of the dielectric interlayer 
and the capacity, resistance and threshold voltage of the liquid crystal 
recording layer, and enables information to be recorded at the optimum 
applied voltage for the optimum voltage applying time.