JPH0128380B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for forming positive and negative electrostatic latent images on a photoreceptor according to two types of optical images suitable for two-color recording.

An example of a conventional multicolor recording technique using electrophotography is a method in which a latent image forming step and a developing step are repeated for a desired number of colors on one photoreceptor. In this method, the developed image is transferred to a recording medium such as paper each time to obtain a record by overlapping colors, or the photoreceptor is developed each time to obtain a multicolor record on the photoreceptor, and then the image is transferred to the recording medium. Records were obtained by transcribing the documents. In this method, the time required for recording in two colors was twice as long as in the case of one color, and there was a problem in speeding up the recording. Another example is a system in which a plurality of photoreceptors are used to form and develop latent images, and the images are superimposed and transferred onto a recording medium to obtain a multicolor recording. This method has the drawback that in the case of two colors, two devices are required for the conventional single color device, making it difficult to downsize. For these reasons, the development of a fast and simple two-color recording method has been awaited.

The purpose of the present invention is to solve the drawbacks of the prior art,
The object of the present invention is to provide a new electrophotographic method that allows high-speed and simple two-color recording.

According to the present invention, there is a primary charging step in which an electrophotographic photoreceptor having a surface insulating layer, a photoconductive layer, and a conductive substrate as its basic constituents is uniformly charged; A first optical image of positive image information and a second optical image of negative image information are formed on the electrophotographic photoreceptor.
By sequentially performing a secondary charging step of irradiating an optical image of An electrophotographic method is obtained which is characterized in that charge images of different polarities are generated to form a composite image latent image of the first and second optical images.

The present invention will be explained in detail below with reference to the drawings.

FIG. 1 is a diagram showing the basic structure of a photoreceptor used in the present invention. The photoreceptor 1 consists of a conductive support base 2 in which a conductive layer such as S _o O ₂ , In ₂ O ₃ or a metal thin film is formed on the surface of metal or glass, and a photoconductive substance (for example, S _e , C _d S, It is made by sequentially laminating a photoconductive layer 3 made of C _d S _e , Z _o O, organic semiconductor, etc.) and an insulating layer 4 made of fluororesin, polyester resin, etc.

2 to 4 schematically illustrate the electrostatic latent image forming process and the charge distribution on the photoreceptor according to the present invention.

First, as shown in FIG. 2, the surface of the insulating layer 4 of the photoreceptor 1 is primarily charged by a charging means such as a corona discharger 5. At this time, it is desirable that the charging polarity be negative if the photoconductive layer is an N-type semiconductor, or negative if the photoconductive layer is a p-type semiconductor. This figure shows a case where an N-type semiconductor such as C _d S is used. Due to this primary charging, negative charges 7 corresponding to the positive charges 6 are transferred to the photoconductive layer 3 and the insulating layer 4.
is trapped at the interface of the photoconductive layer 3 or near the insulating layer 4 of the photoconductive layer 3. When the charge injected from the conductive support substrate 2 in the primary charging process is small and a sufficient amount of charge is not captured at or near the interface between the photoconductive layer 3 and the insulating layer 4, it is possible to shorten the charge by using full-surface exposure at the time of charging. The required amount of primary charging can be performed in a short amount of time.

Next, as shown in FIG. 3, positive image A (image light 9)
While exposing the negative image B (image light 10), secondary charging with a polarity opposite to the primary charging is performed using a corona discharger 8 or the like. The image lights 9 and 10 shown here correspond to the bright parts of a positive image A and a negative image B, an example of which is shown in FIGS. 7a and 7b, respectively. however,
In the figure, the shaded areas are dark areas, and the other areas are bright areas. When such a positive image A and a negative image B are exposed by superimposing them, an exposure pattern as shown in FIG. 7c is obtained. Then, in the area A where neither the image lights 9 nor 10 are irradiated, the resistance of the photoconductive layer is high and the trapped charges 7 are hardly released, so that the positive charges 6 due to the primary charging are partially discharged due to the opposite polarity charging. However, most of the positive charges 11 remain. In addition, in the areas B and C irradiated with the image light 10, by increasing the exposure amount of the image light 10 sufficiently, the photoconductive layer 3
is made conductive by light, and the captured negative charges 7 are easily released to the conductive support base 2 due to reverse charging. At this time, the positive charges 6 due to the primary charging are removed from the insulating layer 4, and negative charges 12 are given by continuing the charging. Next, in the area D (corresponding to the background area of the positive image A and the negative image B) where only the image light 9 is irradiated, by adjusting the exposure amount of the image light 9, the primary charge on the surface of the insulating layer 4 can be adjusted. When the charge 6 is removed, the amount of charge on the surface of the insulating layer changes to other areas A,
It should be sufficiently smaller than B and C and almost zero. As described above, when overlapping exposure and secondary charging are performed using the positive image A and the negative image B, an electrostatic latent image having a charge distribution as shown in FIG. 7d is formed on the photoreceptor. In this explanation, positive image A
Although the case where the positive image A and the negative image B are exposed at the same time is shown, the exposure of the positive image A and the negative image B may be performed before or after the exposure during the secondary charging process.

FIG. 4 shows the entire surface exposure process. When the photoreceptor 1 is irradiated with light 13, the photoconductor layer becomes conductive, and the charges captured in the photoconductive layer 3 are released to the conductive support base 2, leaving behind an amount corresponding to the charges on the insulating layer 4. As a result, the surface potential of each region increases positively in region A, the negative potential due to secondary charging hardly changes in regions B and C, and the surface potential in region D is sufficiently small to be almost zero. Becomes a bolt. In this way, a positive electrostatic latent image is obtained for the positive image A, and a negative electrostatic latent image is obtained for the negative image B.

FIG. 5 shows changes in surface potential of each region during the latent image forming process.

In the above description of the latent image forming process, for the sake of brevity, the area B irradiated with only the image light 10 and the area B irradiated with the image light 9
It was assumed that the amounts of negative charges in the area C and the area C irradiated with the image light 10 were equal. However, in reality, since there is a difference in the amount of exposure in each region, a difference occurs in the amount of charge charged. For example, when the image light 9 and the image light 10 have approximately the same exposure amount, the amount of charge in the region B becomes almost zero like the region D. When the amount of exposure by the image light 10 is smaller than that by the image light 9, the area B becomes a positive charge image,
On the other hand, if it is large, it becomes a negative charge image. In this way, in the area (area B) where the dark area of positive image A and the bright area of negative image B, which are positive charge images and negative charge images of the two optical images, overlap, the exposure amount of image lights A and B is Accordingly, one of the information is given priority. Which one to give priority to is selected depending on the content of the optical information. In the explanation of the latent image forming process shown above, the case where the image light B is prioritized is shown.

In addition, in the above explanation, for the sake of brevity, the potential of the latent image is referred to as a positive predetermined potential, zero, and a negative predetermined potential.
Although the exposure level is divided into two levels, it is also possible to record intermediate tones by changing the exposure amount between 0 and the maximum exposure amount.

The positive and negative latent images formed on the photoreceptor as described above are visualized as follows. For example, when a latent image is developed using cyan negatively charged toner and black positively charged toner, the negatively charged toner adheres to the positively charged areas of the latent image, and the positively charged toner adheres to the negatively charged areas. In this way, a two-color image of cyan for the positive image A and black for the negative image B is obtained. By transferring this onto a recording medium such as paper, a two-color recording can be obtained. Of course, the toner colors may be used in other combinations or may be the same color.

FIG. 6 is a schematic diagram illustrating an example of a case where the latent image forming process according to the present invention is applied to a two-color recording apparatus. In the figure, a photosensitive drum 101
has the laminated structure described in FIG. 1 above, and is formed into a drum shape with an insulating layer on the outside, and is provided to rotate in the direction of the arrow. A corona discharger 1 for primary charging is provided around the photoreceptor drum 101.
02, Corona discharger 103 that performs discharge at the same time as image irradiation, First optical information irradiation means 104, Second optical information irradiation means 105, Lamp 106 for full-surface exposure, Two types of electrostatic charges: positive and negative A developing means 107 for developing a latent image with two types of toner particles having different polarities, a transfer means 109 for transferring the toner image onto a recording medium 108 such as paper, and a means for fixing the toner image transferred onto the recording medium. The fixing means 110 of the photosensitive drum 10 after the toner image transfer
Cleaning means 111 are arranged for removing toner particles remaining on the toner particles.

This example shows a case where n-type C _d S is used as the photoconductor. Recording can be performed in the same manner when using other N-type photoconductors, and recording can be performed in the same manner when using a P-type photoconductor by reversing the polarity of the corona dischargers 102 and 103.

When the photosensitive drum 101 rotates, it is first uniformly and primarily charged with a positive charge by the corona discharger 102 . At this time, the old electrostatic latent image remaining on the surface of the photosensitive drum 101 is also erased. Also, if the entire surface of the photoreceptor drum is exposed to light at the same time as this charging,
More uniform primary charging can be performed.

Next, a first optical information irradiation means 104 using a micro film projector or the like is applied to the surface of the photoreceptor drum 101.
While irradiating a positive image with a laser beam or a negative image with a second optical information irradiation means 105 such as a CRT display device, at the same time secondary charging with a negative charge is performed using a corona discharger 103.
Charging is performed so that the surface potential of the photosensitive drum 101 becomes a predetermined negative potential. In addition, in the figure, as an example, the light source 15 is used as the first optical information irradiation means 104.
1. It consists of a positive film 152 that moves in synchronization with the photosensitive drum, a lens system 153, and a mirror 154, and as a second optical information irradiation means, a laser light source 155, a modulator 156, a control unit 157, a rotating polygon mirror 158, A case is shown in which the lens system 159 and the mirror 160 are included.

In this example, the positive film 152 is suitable for providing form information, and the second optical information irradiation means is suitable for providing data information. Here, the positive film 152 represents a positive image as shown in FIG. 7a, and for example, in the case of information such as a contour line, the contour line portion becomes a dark portion.

At this time, the exposure amount corresponding to the background part of the first optical information is adjusted to remove the positive charge caused by the primary charging on the photoreceptor surface by secondary charging, so that the amount of charge on the surface of the insulating layer becomes almost zero. .

Next, when the entire surface of the photoreceptor drum 101 is exposed by the lamp 106, a positive and negative potential distribution corresponding to each optical image is formed on the photoreceptor drum 101.

The positive and negative electrostatic latent images thus formed are processed by the developing means 107 using a well-known technique, that is,
A toner image is obtained which is developed using a one-bath two-color development method or a two-bath two-color development method and is divided into two colors according to the first and second optical information. The one-bath two-color development method uses a carrier such as iron powder or glass beads, and a developer that is a mixture of toner particles that are positively charged and toner particles that are negatively charged due to friction. The latent images can be developed simultaneously. When this developing method is used, fogging in the background area can be reduced by applying the potential of the background area of the latent image, that is, the ground potential, to the developing electrode. Of course, a bias voltage may be applied to the developing electrode depending on the characteristics of the developer. In addition, the two-bath two-color development method uses a conventional two-component developer, one in which the toner particles are positively charged and the other in which the toner particles are negatively charged, to separately develop positive and negative latent images. It is something.

Next, this two-color toner image is transferred to a recording medium 108 such as paper by a transfer means 109. The transfer method consists of first charging a toner image with a different polarity using a corona discharger 162 so as to have the same polarity, and then pressing a recording medium 108 such as paper against this toner image using a grounding or bias roller 163. This method allows a two-color toner image to be transferred well, but if the transfer speed is high or the paper is thick, corona discharge with the opposite polarity to the toner image is performed from behind the paper before separating it with the roller 163. This ensures good transfer.

Next, this toner image is fixed onto the recording medium by a fixing means 110 such as a heat roller, a hot plate, an infrared heater, a pressure roller, etc. to obtain a record.

Toner particles remaining on the photoreceptor drum 101 after transfer are removed by a cleaning means 111 consisting of, for example, a blade or a brush. At this time, cleaning can be facilitated by removing static electricity from the toner particles using an AC corona charger (not shown) or the like to reduce the electrostatic attraction between the toner particles and the photoreceptor drum. With the above steps, the recording process is completed, and the next recording can be performed again.

As described above, this apparatus is capable of two-color printing with a configuration comparable to that of conventional printing apparatuses. Furthermore, since recording can be performed continuously, two-color recording can be performed even on long continuous paper.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the basic structure of the photoreceptor used in the present invention, and FIGS. 2, 3, and 4 schematically show the electrostatic latent image forming process and the charge distribution of the photoreceptor according to the present invention. Figure 5 is a diagram showing changes in the surface potential of each region during the latent image formation process.
FIG. 6 is a schematic diagram for explaining an example of a two-color recording device to which the present invention is applied. Figure 7 a, b,
c and d are diagrams showing an example of a positive image A, a negative image B, an overlapping pattern of the positive image A and the negative image B, and an electrostatic latent image pattern, respectively. In the figure, 1 is a photoreceptor, 2 is a conductive support substrate, 3 is a photoconductive layer, 4 is an insulating layer, 5 and 8 are corona dischargers, 6 is a positive charge due to primary charging, and 7 is a photoconductor in which The captured negative charge, 9 is the image light of positive image A,
10 is the image light of the negative image B, 11 is the positive charge remaining in area A after the secondary charging process, 12 is the negative charge charged in areas B and C after secondary charging, 13 is the light, 101
102, 103 and 162 are corona dischargers, 104 is a first optical information irradiation means, 105 is a second optical information irradiation means, 106 is a lamp, 107 is a developing means, 108 is a recording medium,
109 is a transfer means, 110 is a fixing means, 111 is a cleaning means, 151 is a light source, 152 is a positive film, 153 is a lens system, 154 is a mirror,
155 is a laser light source, 156 is a modulator, 157
is a control unit, 158 is a rotating polygon mirror, 159 is a lens system, 160 is a mirror, 161 is a bias power source,
163 indicates a roller.

Claims (1)

[Claims] 1. A primary charging step of uniformly charging an electrophotographic photoreceptor whose basic components are a surface insulating layer, a photoconductive layer, and a conductive substrate, and then charging the electrophotographic photoreceptor with a polarity opposite to that of the primary charging. The electrophotographic process is performed by sequentially performing a secondary charging step of irradiating a first optical image of positive image information and a second optical image of negative image information, and then a step of exposing the entire surface of the electrophotographic photoreceptor to light. The first and second
An electrophotographic method characterized in that a composite image latent image of the first and second optical images is formed by generating charge images of different polarities depending on the optical images of the first and second optical images.