JPS6250820B2 - - Google Patents

Description

[Detailed description of the invention] The present invention relates to a two-color electrophotographic copying method.

The two-color electrophotographic copying method uses an electrophotographic process to copy a document with an image written in black and chromatic color A on a white background, and then prints the black information part and the color A information part in two different colors on the copy. Due to their practicality, many methods have been proposed in recent years.

It is also an object of the present invention to provide a novel two-color electrophotographic reproduction method.

The present invention will be described below with reference to the drawings.

In FIG. 1, reference numeral 1 indicates the structure of a photoreceptor used for carrying out the present invention. That is, the photoreceptor 1 has a three-layer structure in which a charge generation layer 12 and a photoconductive layer 13 are laminated in this order on a conductive substrate 11.

The charge generation layer 12 is a thin layer made of a photoconductive material, and when it is irradiated with light, mobile charges are generated in the layer in the form of electron-hole pairs. This charge generation layer 12 preferably has panchromatic photosensitivity, but at least
It must have photosensitivity to the A color light that forms the image on the original.

The photoconductive layer 13 is made of a photoconductive material that does not have photosensitivity to A color light, has photosensitivity to at least B color light other than A color light, and transmits A color light. .

Furthermore, the photoreceptor 1 is required to have boss charge properties. That is, the photoreceptor 1 must be capable of charging the surface of the photoconductive layer 13 to either positive or negative polarity.

Further, as the photoconductive layer 13, a hole transfer type or an electron transfer type is used, that is, a layer having mobility for holes or electrons in the dark.

In the following, for the sake of concreteness of explanation, it is assumed that the color A is red. In other words, consider a two-color copy of an original document in which an image is written in two colors, black and red, on a white background. B
The color may be any color other than color A, but let us assume that it is blue. Further, it is assumed that the photoconductive layer 13 is of a hole movement type, that is, of a hole movement type. The charge generation layer 12 is assumed to have photosensitivity to red light and blue light.

Hereinafter, the process of the two-color electrophotographic method according to the present invention will be explained with reference to FIGS. 2 to 4.

First, the first step of the process is to uniformly charge the surface of the photoreceptor 1 with the charger 2. This charging process is called primary charging.

Next, the photoreceptor 1, which has been uniformly negatively charged by primary charging, is exposed to a color light image of the original. Then, in the area corresponding to the white background of the document,
The photoreceptor is exposed to white light, and areas corresponding to red information are exposed to red light.

In the portion of the photoreceptor 1 exposed to white light, pairs of holes and electrons are generated in the charge generation layer 12 .

There is no physical change in the photoconductive layer 13 in the part of the photoreceptor 1 exposed to red light, but since the charge generation layer 12 is photosensitized to red light, electrons and holes are generated in the same layer. Occur. However, since the photoconductive layer 13 is of the hole transport type, the charge generation layer 1
The holes generated at 2 move in the photoconductive layer 13 and cancel out the negative charges on the surface of the layer. Electrons generated in the charge generation layer 12 are dissipated into the conductive substrate 11. Therefore, even in the portion of the photoreceptor exposed to red light, the negative charge caused by the primary charging disappears. As a result, the negative charge caused by the primary charging remains only in the unexposed area of the photoreceptor, that is, the area corresponding to the black image.

Next, the surface of the photoreceptor 1 is secondarily charged to a positive polarity by the charger 3. Secondary charging is performed so as to satisfy the following conditions.

That is, in the areas exposed to white light and red light due to the above-mentioned exposure, negative charges have disappeared from the surface of the photoreceptor due to primary charging. , it is immediately positively charged, but the unexposed area remains negatively charged due to the primary charging, so
The positive charge generated by the charger 3 gradually cancels out the negative charge in this region.

Secondary charging is stopped when the electrical state of the surface of the photoreceptor reaches the following state. That is, 2
In the state where the next charging is completed, the areas exposed to white light and red light in the above exposure are positively charged to the extent that an electrostatic latent image can be formed, and the unexposed areas still have a sufficient amount of negative charges. That is, negative charges remain to the extent that an electrostatic latent image can be formed.

Subsequently, the photoreceptor 1 is re-exposed to the color light image of the original. This re-exposure is performed so that the light image is accurately superimposed on the light image irradiation portion during exposure.

Then, in the area exposed to white light,
The charge disappears, and the surface potential of the photoreceptor becomes 0 at this location.

In the photoconductor portion exposed to red light, electrons and holes are generated in the charge generation layer 12.
Since the photoconductive layer 13 is of the hole transfer type, electrons that should cancel out the positive charges on the surface of the photoreceptor are transferred to the photoconductive layer 13.
It cannot move inside, and the positive charge due to secondary charging remains in this region. Therefore, in this region, the polarity of the photoreceptor surface potential is positive.

In the unexposed area of the photoreceptor 1, the negative charge of the primary charge remains, which has been partially offset by the secondary charge, so the polarity of the photoreceptor surface potential is negative in this area. .

Thus, after re-exposure, the surface potential of the photoreceptor portion corresponding to the white background of the document becomes 0, and the electrostatic latent image portion corresponding to black information becomes red information due to the negative polarity photoreceptor surface potential distribution. Due to the photoconductor surface potential distribution where the corresponding electrostatic latent image portion has positive polarity,
Each is formed.

FIG. 3 shows a model of the changes in the photoreceptor surface potential in the process up to this point. In this figure, so-called dark decay is not taken into account.

When using an electron transfer type photoconductive layer 13, the polarity of the above-mentioned primary charging and secondary charging may be reversed. In this case, the electrostatic latent image portion corresponding to black information is composed of a positive photoreceptor surface potential distribution, and the electrostatic latent image portion corresponding to red information is composed of a negative photoreceptor surface potential distribution. Ru.

Next, as shown in Figure 4, the electrostatic latent image portion corresponding to red information is visualized using negatively charged red colored toner T _R , and the electrostatic latent image portion corresponding to black information is visualized. It may be visualized using toner T _B that is positively charged and colored black.

In this way, a two-color visible image corresponding to the image on the original is obtained on the photoreceptor 1.

When the photoreceptor 1 is in the form of a sheet and used as an image carrier as it is, the two-color visible image is a normal image and is fixed on the photoreceptor 1 by appropriate means. When a two-color visible image is transferred onto a recording sheet and then fixed onto the recording sheet, the two-color visible image is a mirror image. A two-color copy of the original is thus obtained.

FIG. 5 schematically shows only the essential parts of an example of an apparatus for carrying out the present invention. In order to avoid complication, the same reference numerals as in FIG. 2 are used for items that are considered to have no risk of confusion.

In the figure, 4 is an exposure optical system, 5 and 6 are developing devices, 7 is a precharger, 8 is a transfer charger, 9 is a static elimination charger, 10 is a cleaning device, and 14 is a static elimination lamp. .

We will briefly explain how the example described above is implemented by this device. The photoreceptor 1 is formed into a drum shape and rotates in the direction of the arrow, and is subjected to primary charging by a charger 2 and secondary charging by a charger 3 that irradiates a light image by an exposure optical system 4. The photoreceptor 1 continues to rotate further, but at this time, the developing devices 5 and 6 do not perform development. That is, at this time, the developing devices 5 and 6 are either retracted from the developing position, or are being applied with an extremely strong bias voltage having the same polarity as the electrostatic latent image portion to be developed. Similarly, a pre-charger 7, a transfer charger 8, a static elimination charger 9, a cleaning device 1
0, the static elimination lamp 14 is not activated, and the charger 1 does not discharge when the secondarily charged photoreceptor portion passes through the position of the primary charge. When the surface portion of the photoreceptor thus secondarily charged passes through the exposure section, re-exposure is performed by the exposure optical system 4. In this way, an electrostatic latent image corresponding to the original is formed on the photoreceptor 1. The charger 3 stops discharging after the secondary charging is completed, and the electrostatic latent image passes through the developing section of the developing device 5 without being affected by the charger 3.
During this time, an electrostatic latent image corresponding to red information is visualized by toner T _R . Next, the developing device 6 visualizes the electrostatic latent image portion corresponding to black information with toner T _B. The two-color visible image formed on the photoreceptor 1 in this way is transferred to the precharger 7.
The recording sheet S is recharged by the transfer charger 8, and then transferred onto the recording sheet S by positive electrostatic transfer by the transfer charger 8.

The two-color visible image transferred onto the recording sheet S is fixed onto the recording sheet by a fixing device (not shown), and the recording sheet S is ejected from the apparatus as a copy. After the visible image has been transferred, the photoreceptor 1 is neutralized by a static eliminating charger 9 and a static eliminating lamp 14, and residual toner is removed by a cleaning device 10. The copying process is thus completed. In short, photoreceptor 1
A two-color copying process is performed in two rotations.

2 of the manuscript with images written in two colors, red and black on a white background
When copying a color image using only red, first the photoreceptor 1 is charged with the charger 3, then the photoreceptor is further rotated to perform exposure, development is performed with the development device 6, and then the transfer is performed. The charger 8 may be used to transfer the image onto the recording sheet S. During this process, the charger 1 and the developing device 6 are not operated.

When performing ordinary black and white copying, the operation of the charger 3 and developing device 5 may be stopped and a normal electrophotographic copying process performed.

Finally, examples of experiments conducted by the present inventors will be described.

(Experimental example) A 1.0 μm thick selenium layer sensitized with tellurium was deposited on the circumferential surface of an aluminum drum to form a charge generation layer, and a 20 μm thick selenium layer sensitized with pyrylium salt was then deposited as a photoconductive layer. A drum-shaped photoreceptor was constructed by coating it with a film of polyvinyl carbazole, and this was assembled into an apparatus as shown in FIG.

After this photoreceptor was primarily charged with a discharge voltage of -6.5 KV, it was irradiated with a light image of a document with an image written in two colors, red and black, on a white background (the document was illuminated with a 100W halogen lamp). Next, perform secondary charging with a discharge voltage of +5.5KV, and perform both exposures under the same conditions as the exposure.
I developed it. Development was carried out using a magnetic brush development method using a developer that is a mixture of toner and a conductive magnetic carrier. In development using red toner, a bias voltage of +150V was applied to the development section. This is attached to the area corresponding to the white background on the photoreceptor.
This is because a potential of 50V remained.

Next, a visible image was charged with a Scorotron precharger at a discharge voltage of -4.5 KV, and a discharge voltage of -4.6 KV was applied to the transfer charger to perform electrostatic transfer. The transferred two-color visible image was fixed on the recording sheet by atmospheric fixing using an infrared lamp. The image density of the two-color copy thus obtained was 0.8 in the black part and 0.5 in the red part.

Finally, the concepts of black and white in this specification will be explained.
White light means light to which both the charge generation layer and the photoconductive layer have photosensitivity; therefore, the above-mentioned B color light is included in the white light category. Further, black includes a color in which neither the charge generation layer nor the photoconductive layer has photosensitivity. That is, even if the light is actually a chromatic color, light that is reflected by the photoconductive layer or light that does not act on either the charge generation layer or the photoconductive layer is included in the black category.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the configuration of a photoreceptor used for carrying out the present invention, FIGS. 2 to 4 are diagrams for explaining the present invention, and FIG. FIG. 2 is a front view schematically showing only important parts of one example. 1... Photoreceptor, 11... Conductive substrate, 12...
charge generation layer, 13... photoconductive layer, 2, 3... charger, T _R , T _B ... toner.

Claims (1)

[Scope of Claims] 1. A method of copying a document in which an image is written in black and chromatic color A on a white background, and reproducing the black information part and the color A information part of the image in different colors on the copy. a charge generation layer having photosensitivity to A color light and B color light on a conductive substrate; having no photosensitivity to A color light but having photosensitivity to B color light; A hole transfer type (or electron transfer type) photoconductive layer,
The surface of the photoreceptor, which is laminated in the above order from the conductive substrate side and can charge the surface of the photoconductive layer to any positive or negative polarity, is primarily charged to negative polarity (or positive polarity) in the dark; After exposure with the color light image of the original, secondary charging of positive polarity (or negative polarity) is performed, and while sufficient charge from the primary charging remains in the unexposed areas of the photoreceptor surface during the above exposure. ,
The surface of the photoreceptor in the exposure area is charged to a polarity opposite to the primary charge, and then re-exposure is performed using the color light image of the original to increase the surface potential of the photoreceptor at the portion of the photoreceptor that corresponds to the white background of the original. approximately 0, and an electrostatic latent image portion corresponding to the black information of the original and an electrostatic latent image portion corresponding to the A color image are formed by photoreceptor surface potential distributions of opposite polarity, and these electrostatic latent image portions are A two-color electrophotographic copying method, which is characterized in that the images are visualized using two types of toners charged with opposite polarities and colored in different colors.