JPS637385B2 - - Google Patents

Description

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

Recently, various two-color electrophotographic copying methods using a composite photoreceptor having two photoconductive layers have been proposed.

The present invention utilizes such a two-color electrophotographic copying method and aims to provide a three-color electrophotographic copying method that is one step further.

The present invention will be explained below.

According to this invention, by copying a three-color original having three-color images of A, B, and black on a white background, it is possible to reproduce the three-color images in mutually different colors on the copy.
That is, a three-color copy image can be obtained corresponding to a three-color image.

In its simplest configuration, the photoreceptor has two photoconductive layers and a conductive substrate, and the two photoconductive layers are laminated on the conductive substrate. In more complex configurations of photoreceptors, between the two photoconductive layers,
An intermediate layer for charge trapping is provided, an insulating transparent thin layer is provided on the surface of the two photoconductive layers,
An insulating thin layer may be provided between the photoconductive layer and the conductive substrate, or the intermediate layer, an insulating transparent thin layer,
Two or more of the thin insulating layers may be provided simultaneously.

The properties of the two photoconductive layers are determined depending on the two chromatic colors A and B out of the three colors constituting the three-color image.
That is, if one of the two photoconductive layers is called the first photoconductive layer, this first photoconductive layer is insensitive to A color light and sensitive to B color light. I have to. The other photoconductive layer, that is, the second photoconductive layer, is selected to be sensitive to A color light and also sensitive to B color light. However, the sensitivity of the second photoconductive layer to B color light must be relatively weak compared to the sensitivity of the first photoconductive layer to B color light.

For such photoreceptors, the charge is at least 2
The polarity is alternately reversed twice, and the first photoconductive layer and the second photoconductive layer are charged in opposite directions. This process of charging the first and second photoconductive layers in opposite directions differs depending on the configuration of the photoreceptor, ie, whether there is an insulating transparent thin layer or not. However, although the above processes differ from each other depending on the configuration of the photoreceptor, they include the above two charging processes as the greatest common divisor.

Charging the first and second photoconductive layers in opposite directions is exactly the same as in the two-color electrophotographic reproduction method. Since such methods have already been proposed for each photoreceptor structure, they may be applied as appropriate in the case of the present invention depending on the specific structure of the photoreceptor.

Now, the two photoconductive layers are charged in opposite directions, and at this time, the surface potential of the photoreceptor is set to a value relatively close to 0 after this charging.
Adjust the amount of charge.

Next, the photoreceptor is exposed to light using the light image of the three-color original, and the following state is achieved for the photoreceptor.

That is, regarding the correspondence between the exposed photoreceptor and the three-color original, the surface potential of the photoreceptor at the portion corresponding to the white background of the original is approximately 0, and the electrostatic latent image portions corresponding to the A color image and the B color image are They are formed by the photoreceptor surface potential distribution having opposite polarities. The surface potential of the photoreceptor in the area corresponding to the black image is maintained approximately at the same level as before exposure.

Next, the electrostatic latent image portions corresponding to the A color image and B color image are visualized using two types of toners charged with opposite polarities and colored in α and β colors, respectively.

Thereafter, the photoreceptor is uniformly irradiated with B color light, reversing the magnitude relationship between the photoreceptor surface potential in the area corresponding to the black image and the photoreceptor surface potential in the area corresponding to the B color image, and increasing the difference between the two as much as possible. urge

The difference in sensitivity to B color light in the two photoconductive layers makes this process possible. The above conditions of sensitivity in the photoconductive layer are necessary to make this process possible.

Then, by developing the area corresponding to the black image using toner charged to a predetermined polarity and colored in γ color, a three-color visible image corresponding to the three-color image is obtained on the surface of the photoreceptor.

The three-color electrophotographic copying process is completed by fixing this visible image on a photoreceptor (if the photoreceptor is in the form of a sheet) or transferring and fixing it onto a suitable recording sheet.

The three colors A, B, and black on a three-color original are α, β, and γ.
It corresponds to each of the three colors. There is no necessity in principle to make A and α colors, B colors and β colors, and black and γ colors the same color, but from a practical standpoint, it is not common to make them the same color. Probably.

Hereinafter, the present invention will be explained in more detail with reference to specific examples.

As the three-color original, one having three-color images of red, blue, and black on a white background is selected. When actually realizing three-color copying, such a three-color original is considered to be the most common three-color original.

If we compare the above A and B, red is color A,
Blue corresponds to color B.

Now, as a photoreceptor, I made the following prototype.

An aluminum plate is used as a conductive base, and on this,
Se-Te alloy (Te content: 6% by weight) was heated to
It was deposited at 70°C to a thickness of 30μ. This Se-Te alloy layer is insensitive to red light and has good sensitivity to blue light. That is, this photoconductive layer is the first photoconductive layer. After forming the first photoconductive layer, place it in a dark place for 1
After leaving it for a week to let the characteristics drop, we applied eutectic OPC to a thickness of 22 μm on top of this layer by dipping.
was coated to form a second photoconductive layer. In fact, this second photoconductive layer exhibits good sensitivity to red light but not very good sensitivity to blue light.

This photoreceptor is designated by the reference numeral 1 in FIG. In the photoreceptor 1, reference numeral 11 denotes a conductive substrate, and reference numeral 1
Reference numeral 2 indicates a first photoconductive layer, and reference numeral 13 indicates a second photoconductive layer. Also, in Figure 2, curve 2-1 is the first
Curve 2-2 shows the spectral sensitivity of the Se-Te alloy layer as the material for the second photoconductive layer, curve 2-2 shows the spectral sensitivity of the eutectic OPC layer as the material for the second photoconductive layer, and curve 2-3 shows the spectral sensitivity of the eutectic OPC layer as the material for the second photoconductive layer. , shows the spectral transmittance of the eutectic OPC layer. As is clear from the spectral transmittance of the eutectic OPC layer, the eutectic OPC layer does not transmit red light.
This means that even if the photoreceptor 1 is irradiated with color light, this red light does not reach the photoconductive layer 12, and therefore,
Even if the photoconductive layer 12 as a material is sensitive to red light, the photoreceptor 1 is insensitive to red light.

The conditions of the first and second photoconductive layers in the photoreceptor must therefore be understood from this perspective. That is, the first and second photoconductive layers must satisfy the above-mentioned conditions regarding sensitivity when forming a photoreceptor. In other words, in the case of a photoreceptor prepared for use in the practice of the present invention, when it is irradiated with A color light, only the second photoconductive layer becomes a conductor, and when it is irradiated with B color light,
Although both photoconductive layers become conductive, the degree of conductivity in the second photoconductive layer is weaker than that in the first photoconductive layer.

Now, let's go back to Figure 1.

When the photoreceptor 1 is positively charged while being uniformly irradiated with red light, the photoconductive layer 13 has become a conductor, so the first
An electric double layer as shown in the figure is formed. This state is referred to as the photoconductive layer 12 being charged.

Next, when the photoconductive layers 12 and 13 are negatively charged in the dark, a state is realized in which the photoconductive layers 12 and 13 are charged in opposite directions, as shown in FIG. At this time, each polarity is charged so that the surface potential of the photoreceptor takes a value relatively close to 0.

In the experiment, the surface potential of the photoreceptor was first set to +2200 V by positive charging, and then the surface potential was set to -110 V by negative charging. of course,
At this time, the conductive base 11 is grounded.

Then, as shown in FIG. 1, the photoreceptor 1 was exposed to the light image of the three-color original O. Due to this exposure, the photoconductor portion corresponding to the white background W of the original O is
The areas exposed to white light LW and corresponding to red image area R and blue image area B are exposed to red light, respectively.
LR, exposed by blue light LB. The region corresponding to the black image N is not exposed.

In the area exposed to white light LW,
Both photoconductive layers 12 and 13 are made into conductors, and these two
The charged state of the layer is eliminated, and the surface potential of the photoreceptor becomes approximately zero. In the area exposed to red light LR, the photoconductive layer 1
When only the photoreceptor 3 becomes a conductor and its charged state is eliminated, the surface potential of the photoreceptor at this portion becomes positive. In the area exposed to blue light LB, the photoconductive layer 1
Although both 2 and 13 become conductive, due to the difference in their sensitivity to B color light, the photoconductive layer 1 is mainly
The charging state No. 2 is eliminated, and the surface potential of the photoreceptor becomes negative at this location. Exposure by the original light image must be stopped in this state.

In the experiment, when exposure was performed for 0.7 seconds with the irradiation energy per unit area being 5.5μWsec/cm ² at the white light irradiation area, the photoreceptor surface potential was +20V at the area corresponding to the white background, and 20V at the area corresponding to the black image. -110V at the part, +400V at the part corresponding to the red image,
The voltage was -650V at the part corresponding to the blue image.

In this state, the negatively charged red toner T _R
The electrostatic latent image portions corresponding to the red and blue images were visualized using a positively charged blue toner T _B (FIG. 1). Development is performed using a magnetic brush development method using a two-component developer, with a bias voltage of +50V applied for development using red toner and -150V for development using blue toner.
A bias voltage of was applied. This is to prevent the background area and the area corresponding to the black image from being developed. If the potential of the area corresponding to the black image is high, the bias potential during development with blue toner must be set high, which results in a decrease in the image density of the blue visible image. This is why the surface potential of the photoreceptor before exposure is set relatively close to 0.

Next, as shown in FIG. 1, the photoreceptor 1 is uniformly irradiated with blue light LB. Then, the photoreceptor surface potential attenuates to 0 at the portion corresponding to the red image. This is because the blue light turns the photoconductive layer 12 into a conductor. Even in the area corresponding to the blue image, the photoconductive layer 13 becomes a conductor to some extent, so the surface potential gradually decreases to zero. On the other hand, in the black image corresponding area, the photoreceptor surface potential increases in a negative direction due to the effect of blue light irradiation, and eventually the magnitude relationship of the photoreceptor surface potentials in the black image corresponding area and the blue image corresponding area is reversed. Then, this uniform irradiation process using blue light is stopped when the difference in the photoreceptor surface potential becomes maximum.

In the experiment, blue light obtained by filtering white light with a Kodatsu Ratten Filter B47 was used to
Photoreceptor 1 was exposed to light at a light intensity of 2.1μWsec/ ^cm2 ,
The photoreceptor surface potentials at the photoreceptor parts corresponding to the white background, black, red, and blue image areas are -20V, respectively.
-650V, +30V, -390V. In this state,
The black image corresponding area is developed with positively charged black toner T _N (Fig. 1 ()), and then the three-color visible image obtained on the photoreceptor 1 is transferred onto the recording sheet S (the first
Figure ()), when fixed, high quality 3 with no color mixture
A color copy was obtained. Incidentally, development with the black toner was also carried out by a magnetic brush development method using a two-component developer, and a bias voltage of -420V was applied during development. Further, prior to the transfer, positive polarity corona discharge was applied to the visible image to align the polarity of the toner in the visible image to positive polarity, and the transfer was performed by negative polarity electrostatic transfer. During transfer, the discharge voltage applied to the transfer corona charger was -5.5 KV.

FIG. 3 shows a model of the change in the surface potential of the photoreceptor during the process of the three-color electrophotographic copying method according to the present invention. In the figure, numbers 3-1, 3-
The time regions indicated by 2 indicate positive and negative charging steps, respectively, and the time regions indicated by 3-3 and 3-4 respectively indicate image exposure and uniform exposure with blue light steps. Curves 3-W, 3-N, 3-R, and 3-B in areas 3-3 and 3-4 represent exposure to photoreceptor parts corresponding to the white background, black image, red image, and blue image area, respectively. It shows changes in body surface potential.

Now, as is clear from the above explanation, the main feature of the present invention is that after imagewise exposure is performed on the photoreceptor, uniform irradiation with B color light is performed to correspond to the black image area and the B color image area. The purpose of this method is to reverse the magnitude relationship of the photoreceptor surface potential at a certain location and further increase the difference between the two as much as possible.

This means that when the photoreceptor is continuously irradiated with blue light after the two photoconductive layers have been charged in opposite directions, the surface potential of the photoreceptor changes as shown in Figure 4. However, this means that a peak appears in the surface potential at a certain amount of exposure. In actual experiments, the surface potential of the photoreceptor behaves like this. This is explained as follows. That is, since the two photoconductive layers have a difference in response to B color light, when the charge state in each photoconductive layer is canceled by irradiation with B color light, the charge state in the first photoconductive layer is quickly released, and the second photoconductive layer is Since the gradual dissolution in the photoconductive layer continues and the direction of charge in both layers is opposite, the peak of the photoreceptor surface potential occurs at the time when the charge in the first photoconductive layer is substantially dissipated. It happens.

For example, the bright attenuation characteristic of the photoconductive layer 12 of the photoreceptor 1 for blue light is as shown by curve 5-1 in FIG. 5, and that of the photoconductive layer 13 is as shown by curve 5-2. Therefore, if each photoconductive layer of the photoreceptor 1 is charged as described above and irradiated with blue light, the change in the surface potential of the photoreceptor 1 will be as shown by the curve 5--, which is a combination of the curves 5-1 and 5-2. It is given by 3.

Therefore, when performing image exposure, the exposure amount is adjusted so that the surface potential of the photoreceptor in the area corresponding to the B color image occupies a value near the peak of the surface potential, and when performing uniform irradiation with B color light, The exposure amount may be adjusted so that the surface potential of the photoreceptor in the area corresponding to the black image reaches the peak of the surface potential.

FIG. 6 schematically shows only the essential parts of an example of an apparatus for carrying out the present invention. The experiments in the example described above were conducted with such a device.

The photoreceptor 1 is formed into a drum shape, and around it,
Chargers 21, 22, exposure section, developing device 2
3, 24 Blue light irradiation device 25, developing device 26, pre-charger 27, transfer charger 28, fixing device 29, cleaning device 30, static eliminator 3
1 is deployed.

The charger 21 is for positive charging and is equipped with a red light lamp 20. The charger 22 is for negative charging. Developing devices 23, 24, 26
are for red toner, blue toner, and black toner, respectively.

While rotating in the direction of the arrow, the photoreceptor 1 is positively charged by a charger 21 while being irradiated with red light from a red light lamp 20 . Then, after being negatively charged by the charger 22, it is exposed to a light image of the document in an exposure section. When the electrostatic latent image portions corresponding to the red image and the blue image are sequentially visualized by the developing devices 23 and 24, the photoreceptor 1 is exposed to the blue light irradiation device 25.
The area corresponding to the black image is then uniformly irradiated with blue light and then developed by the developing device 26.

The three-color visible image thus formed on the surface of the photoreceptor is charged in a positive polarity by the precharger 27, and transferred onto the recording sheet S by negative electrostatic transfer by the transfer charger 28.

The transferred visible image is fixed onto the recording sheet S by the fixing device 29, and the fixed recording sheet S is discharged from the apparatus as a copy.

The photoreceptor 1 after the visible image transfer is transferred to a cleaning device 3
0, and then the static eliminator 31
The entire process of three-color copying is completed.

[Brief explanation of the drawing]

FIGS. 1 to 5 are diagrams for explaining the present invention, and FIG. 6 is an illustration of an apparatus for carrying out the present invention.
FIG. 2 is a front view schematically showing only the main parts of an example. DESCRIPTION OF SYMBOLS 1... Photoreceptor, O... 3-color original, 11... Conductive substrate, 12... 1st photoconductive layer, 13... 2nd photoconductive layer.

Claims (1)

[Scope of Claims] 1. A first photoconductive layer that is insensitive to A color light and sensitive to B color light; and a first photoconductive layer that is insensitive to A color light and sensitive to B color light; For a photoreceptor comprising at least a second photoconductive layer having a sensitivity lower than that of the second photoconductive layer and a conductive substrate, the first and second photoconductive layers being laminated on the conductive substrate, Charging is performed at least twice with the polarities alternately reversed to charge the first and second photoconductive layers in opposite directions, and to bring the surface potential of the photoreceptor to a value relatively close to zero. Then, the photoreceptor is exposed to light using a light image of a three-color original having three-color images of A, B, and black on a white background, and the surface potential of the photoreceptor at a portion corresponding to the white background is set to approximately 0.
The electrostatic latent image portions corresponding to the A-color image and the B-color image are formed by photoreceptor surface potential distributions of opposite polarity, and the photoreceptor surface potential at the portion corresponding to the black image is maintained approximately at the photoreceptor surface potential before exposure. , Visualize the electrostatic latent image portions corresponding to the A color image and B color image using two types of toners charged with opposite polarities and colored in α color and β color respectively, and further exposed to B color light. After uniform exposure is performed to reverse the magnitude relationship between the photoreceptor surface potential in the area corresponding to the black image and the photoreceptor surface potential in the area corresponding to the B color image, and to increase the difference between the two as much as possible, a predetermined A three-color electrophotographic copying method characterized in that a portion corresponding to a black image is developed using a toner that is polar-charged and colored in gamma color.