Information image synthesizing and copying method

An information image of a first original and an information image of a second original are synthesized on a photoconductor which includes a photoconductive layer having a spectral sensitivity to A-colored light but not having a spectral sensitivity to B-colored light, and a photoconductive layer having a spectral sensitivity to B-colored light, but not having a spectral sensitivity to A-colored light, which are formed in layers on a conductive base member, by taking the steps of charging the photoconductor to a predetermined polarity and then charging the photoconductor to reverse the original surface potential of the photoconductor, while retaining the charges applied to the photoconductor, to the extent that latent electrostatic images can be formed on the surface of the photoconductor, and exposing the photoconductor to an A-colored light image corresponding to the information image of the first original and a B-colored light image corresponding to the information image of the second originals simultaneously and or one after another to form the synthesized latent electrostatic images of the two originals on the photoconductor, and finally developing the synthesized latent electrostatic images by one or two types of developers.

BACKGROUND OF THE INVENTION 
The present invention relates to an information image synthesizing and 
copying method. 
The information image synthesizing and copying method is a method of 
synthesizing information image .alpha. of original I and information image 
.beta. of original II and copying the synthesized information images 
.alpha. and .beta. on one copying sheet C as shown in FIG. 1. This method 
serves to save the material necessary for copying and is useful for 
information processing. 
Conventionally, in one method of making synthesized copies, an original 
whose non-image portions are transparent is employed as the original I or 
the original II, and the original I and the original II are superimposed 
and copied. In another method, a latent electrostatic image corresponding 
to the original I and a latent electrostatic image corresponding to the 
original II are formed on two separate photoconductors and those latent 
electrostatic images are transferred to a recording sheet and the 
transferred latent electrostatic images are developed. In a further 
method, the latent electrostatic image of the original I is formed on one 
photoconductor and the electrostatic latent image is transferred to a 
recording sheet and the latent electrostatic image of the original II is 
formed on the same photoconductor and the electrostatic latent image is 
transferred to the same recording paper, and the transferred latent 
electrostatic images are developed. 
The first method has a shortcoming that a special transparent original is 
required as the original I or the original II. The second method requires 
two photoconductors and the copying apparatus employing this method is 
complicated in the mechanism. In the third method, a process of the 
formation of the latent electrostatic image and transfer thereof has to be 
repeated two times, which reduces the copying efficiency. 
SUMMARY OF THE INVENTION 
It is therefore an object of the present invention to provide and 
information image synthesizing and copying method capable of performing 
the synthesis of information images and copying of the synthesized 
information images simply and efficiently. 
According to the present invention, a photoconductor comprises a conductive 
base member, a first photoconductive layer formed on the conductive base 
and a second photoconductive layer formed on the first photoconductive 
layer. The first photoconductive layer has a spectral sensitivity to 
A-colored light but does not have a spectral sensitivity to B-colored 
light. On the other hand, the second photoconductive layer has a spectral 
sensitivty to B-colored light but does not have a spectral sensitivity to 
A-colored light. The photoconductor is charged to a predetermined polarity 
by a first charging in the dark or under uniform exposure using A-colored 
light or B-colored light. In one embodiment according to the present 
invention, charges in the polarity opposite to that of the first charging 
are then applied to the photoconductor to reverse the original polarity of 
the surface potential of the photoconductor, while retaining the charges 
applied to the photoconductor during the first charging to the extent that 
latent electrostatic images can be formed on the surface of the 
photoconductor. The photoconductor is then exposed to an A-colored light 
image corresponding to an information image .alpha. of a first original I 
and to a B-colored light image corresponding to an information image 
.alpha. of a second original II simultaneously or one after another to 
form the synthesized latent electrostatic images of the first original I 
and the second original II. The synthesized latent electrostatic images 
are developed by two types of toners which are charged in the opposite 
polarities.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring to FIG. 2, there is shown a photoconductor 1 which is employed in 
the present invention. 
The photoconductor 1 comprises a conductive base member 10 and 
photoconductive layers 11 and 12 formed on the conductive base member 10. 
The photoconductive layers 11 and 12 have different spectral 
sensitivities. For instance, the photoconductive layer 11 is sensitive to 
A-colored light, but is not sensitive to B-colored light. On the other 
hand, the photoconductor layer 12 is not sensitive to A-colored light, but 
it is sensitive to B-colored light. More specifically, in the present 
embodiment, the A-color is blue and the B-color is red, and the 
photoconductive layer 11 comprises selenium, while the photoconductive 
layer 12 comprises zinc oxide. 
The information image synthesizing and copying method according to the 
present invention starts with the step of electrically charging the 
surface of the photoconductor 1 to a predetermined polarity by a charger 
2. This charging process is referred to as a first charging. With respect 
to the polarity of the first charging, either positive polarity or 
negative polarity is selected. In the present embodiment, negative 
polarity is employed and the first charging is performed under uniform 
exposure of the photoconductor 1, using blue light. The blue light is 
transmitted through the photoconductive layer 12, without making the 
photoconductive layer 12 conductive and is absorbed by the photoconductive 
layer 11, making the photoconductive layer 11 conductive. 
The surface of the photoconductive layer 12 is charged uniformly by 
negative charges applied from the charger 2. Positive charges injected 
from the conductive base member 10 into the photoconductive layer 11 are 
moved through the photoconductive layer 11 by the induction of the 
negative charges on the upper surface of the photoconductive layer 12. As 
a result, positive charges are distributed in the interface where the 
photoconductive layers 11 and 12 meet. Since selenium is used as the 
photoconductive layer 11 and it has a characteristic that injection and 
movement of positive charges occur even in the dark, even if the first 
charging is performed in the dark, the same effect as mentioned above can 
be produced. 
After completion of the first charging, positive charges are applied to the 
surface of the photoconductor 1 by a charger 3. This charging is performed 
in the polarity opposite to that of the first charging and is referred to 
as a second charging step. The second charging is performed in such a 
manner that the polarity of the surface potential of the photoconductor 1 
is sufficiently reversed while retaining negative charges applied by the 
first charging on the surface of the photoconductor 1, to the extent that 
latent electrostatic images can be formed on the surface of the 
photoconductor 1. More specifically, as positive charges are applied to 
the photoconductor 1 by the charger 3, negative charges that have been 
applied by the first charging to the surface of the photoconductive layer 
12 are gradually neutralized and accordingly the surface potential of the 
photoconductor 1 is gradually decreased. With a furhter neutralization of 
negative charges, the surface potential of the photoconductor 1 becomes 
zero (0) and the polarity of the surface potential of the photoconductor 1 
is then reversed to positive by the effect of positive charges on the back 
or under side of the photoconductive layer 12. The surface potential of 
the photoconductor 1, being sufficiently reversed in polarity, signifies 
that the surface potential of the photoconductor 1, with its polarity 
reversed to positive, is sufficient for the formation of a electrostatic 
image on the surface of the photoconductor 1 and the sufficient retaining 
of negative charges signifies that the amount of negative charges is 
sufficient for the formation of an electrostatic image. 
In other words, when the second charging has been completed, the surface of 
the photoconductor 1 is charged by negative charges sufficiently capable 
of forming electrostatic images thereon, while the photoconductor 1, as a 
whole, has a sufficient positive surface potential for the formation of 
electrostatic images. 
Exposure of the photoconductor 1 to a blue light image of original I is 
then performed. This exposure can be performed by several methods. 
First, assume that original I is an information image .alpha. on white 
paper. The color of the information image .alpha. is not limited to black, 
but the complementary color of blue can be used. In one method for 
exposing the photoconductor 1 to the blue light image of the original I, 
the original I is directly illuminated by blue light and the 
photoconductor 1 is exposed to the reflected light from the original I. In 
another method, the original I is illuminated by white light and the 
reflected light from the original I is filtered through a blue color 
filter for color separation and the photoconductor 1 is exposed to the 
color separated light image of the original I. In a further method, the 
background of the original I is made blue in color and the information 
image is written using a complementary color of black or of blue. The thus 
formed original I is illuminated by white light or blue light and the 
photoconductor 1 is exposed to the reflected light from the original I. In 
any case, the photoconductor 1 is exposed to the blue light image of the 
original I. When the blue light image of the original I is projected onto 
the photoconductor 1, a portion of the photoconductor 1, corresponding to 
information image .alpha. of the original I, is not exposed to the blue 
light. Therefore, the surface potential of this portion remains positive 
in polarity and the value of the surface potential after the second 
charging is the same as before if the dark decay of the surface potential 
is negligible. On the other hand, the rest or remaining portion of the 
photoconductor 1, corresponding to the non-image or blank area of the 
original I, is exposed to the blue light and only the photoconductive 
layer 11 is made conductive, so that part of positive charges on the back 
side of the photoconductive layer 12 flows into the conductive base member 
10 and the rest of positive charges on the back side of the 
photoconductive layer 12 and the negative charges on the upper surface of 
the photoconductive layer 12 are balanced, whereby the polarity of the 
surface potential in this portion is again reversed to negative. As 
mentioned previously, the surface potential of the portion whose polarity 
is reversed to a negative polarity is high enough to form electrostatic 
images. 
The exposure using a red light image of an original II is then performed. 
In this exposure, exactly the same exposure method can be employed as in 
the case of the exposure using the blue light image of the original I. A 
portion of the photoconductor 1, corresponding to the information image 
.beta. of the red light image of the original II, is not exposed to the 
red light. Therefore, the surface potential of this portion remains in the 
negative polarity. The rest or remaining portion of the photoconductor 1, 
corresponding to the non-image or blank area of the original II, is 
exposed to the red light. The rest or remaining portion includes not only 
the blank or non-image portion common to the original I and the original 
II but also the portion corresponding to the information image .alpha. of 
the original I. 
When the red light image has not yet been projected onto the photoconductor 
1, positive charges and negative charges on both sides of the 
photoconductive layer 12 are balanced in the portion corresponding to the 
common blank portions of the original I and the original II. Therefore, 
when only the photoconductive layer 12 is made conductive by the 
projection of the red light image, the positive charges and the negative 
charges neutralize each other, so that these surface potential in the 
portions of the photoconductor 1 becomes zero (0). 
Furthermore, before the red light image is projected to the photoconductor 
1, the portion of the photoconductor 1, corresponding to the information 
image .alpha. of the original I retains the same charge distribution as 
that after the second charging. Therefore, when the photoconductor 1 is 
illuminated by the red light, negative charges on the surface of the 
photoconductive layer 12 are neutralized by part of positive charges on 
the back side of the photoconductive layer 12, whereby only the positive 
charges contribute to the surface potential of this portion of the 
photoconductor 1. As a result, after the exposure of the photoconductor 1 
to the red light image, the surface potential of this portion of the 
photoconductor 1 is positive in polarity and is increased further. A 
portion where the information image .alpha. and the information image 
.beta. are overlapped, if any, retains the same positive potential as that 
after the second charging. 
Thus, the surface potential of the portion of the photoconductor 1, 
corresponding to the blank or non-image portion common to the originals I 
and II, becomes zero (0) and the portion having the surface potential with 
positive polarity and the portion having the surface potential with 
negative polarity are distributed so that electrostatic latent image 
portions corresponding to the information images .alpha. and .beta. are 
formed. 
FIG. 3 shows the change of the surface potential of the photoconductor 1 
during this process. 
In the above-mentioned embodiment, the first charging is performed under 
uniform exposure using the blue light corresponding to the previously 
mentioned A-colored light. 
If the first charging is performed under uniform exposure using the red 
light corresponding to the previously mentioned B-colored light, the 
second charging can be performed to the extent that latent electrostatic 
images opposite in polarity to the first charging can be formed on the 
surface of the photoconductor 1, without reversing the polarity of the 
surface potential of the photoconductor 1. 
The synthesized latent electrostatic images formed on the surface of the 
photoconductor 1 are developed by two types of toners T1 and T2, which are 
charged in opposite polarities. The electrostatic latent image portion 
whose surface potential is in positive polarity is developed by negatively 
charged toner T1, so that a visible image of the the information image 
.alpha. is formed. On the other hand, the electrostatic latent image 
portion whose surface potential is in negative polarity is developed by 
positively charged toner T2, so that a visible image of the information 
image .beta. is formed. 
The synthesized latent electrostatic images can be developed by a single 
conductive developer instead of the two types of toners. 
The synthesized visible images of the information images .alpha. and .beta. 
formed on the photoconductor 1 are transferred to a recording sheet and 
fixed thereto, so that the synthetic information image copying process is 
completed. 
The photoconductor 1 can be formed into a sheet so that the synthesized 
visible image formed on the sheet-formed photoconductor can be fixed to 
the photoconductor. 
The following are the examples of the experiments conducted by the inventor 
of the present invention: 
EXPERIMENT 1 
An aluminum plate was employed as a conductive base member. Selenium with a 
purity of 99.99% was evaporated, to a thickness of 50.mu., onto the 
aluminum plate to form a first photoconductive layer. Onto the first 
photoconductive layer, a resin containing zinc oxide sensitized by 
methylene blue was coated with a thickness of 20.mu. to form a second 
photoconductive layer. The mixing ratio of methylene blue to zinc oxide 
was 0.0002 to 1 by weight, and the mixing ratio of zinc oxide to the resin 
was 2 to 1 by weight. 
The photoconductor was subjected to a first charging in the dark until the 
surface potential of the photoconductor became -800 volts. A second 
charging was then conducted in the dark until the surface potential of the 
photoconductor became 700 volts. 
An original bearing a black information image with white background was 
illuminated by blue light and the photoconductor was exposed to the blue 
light reflected from the original. The surface potential of the exposed 
area of the photoconductor became -320 volts, while the surface potential 
of the unexposed area of the photoconductor became +670 volts. 
Then a second original, which had a black information image with white 
background, in a portion corresponding to the blank or non-image area of 
the first original, was illuminated by red light and the photoconductor 
was exposed to the red light reflected from the second original. The 
surface potential of the portion of the photoconductor, corresponding to 
the information image of the first original, became +950 volts, while the 
surface potential of the portion of the photoconductor, corresponding to 
information image of the second original, became -290 volts, and the 
surface potential of the portion of the photoconductor, corresponding to 
the blank or non-image area common to the first and second originals, 
become -20 volts. The synthesized electrostatic latent images were 
developed by a negatively charged toner for use with a PPC-900 (trade 
name) Copying Machine manufactured by RICOH CO., LTD. and a polsitively 
charged toner for the U-Bix (trade name) Copying Machine manufactured by 
Konishiroku Co., Ltd. and clear synthesized information images were 
obtained with a high resolution. 
EXPERIMENT 2 
In Experiment 1, positively charged red toner prepared by the inventor of 
the present invention was used instead of the negatively charged toner for 
U-Bix Copying Machine. As a result, the information image of the first 
original was reproduced black in color while the information image of the 
second original was reproduced red in color and clearly with a high 
resolution. 
Thus, by use of two types of toners with different colors, each information 
image element of the synthesized information image can be copied with 
different colors. 
EXPERIMENT 3 
In Experiments 1 and 2, the photoconductor was exposed to the blue image of 
the first original and to the red light image of the second original 
simultaneously. The result was exactly the same as in Experiments 1 and 2. 
This indicates that the two exposures can be performed either separately 
or simultaneously, and when the two exposures are performed separately, 
the same result can be obtained regardless of the order of the two 
exposures. 
EXPERIMENT 4 
In Experiments 1 and 2, the first charging was conducted under uniform 
exposure using blue light. The result were exactly the same as in 
Experiments 1 and 2. 
EXPERIMENT 5 
In Experiments 1 and 2, the first charging was conducted under uniform 
exposure using red light. The results were almost the same as in 
Experiments 1 and 2.