JPH0447823B2 - - Google Patents

Description

[Detailed description of the invention] (Technical field) The present invention relates to a two-color electrophotographic copying apparatus.

(Prior art) Two layers are placed on a drum-shaped or belt-shaped conductive substrate.
A photoreceptor is prepared by laminating photoconductive layers such that one photoconductive layer mainly becomes a conductor when irradiated with light of a specific color. A two-color electrophotographic method is known which includes steps of applying primary and secondary charging (see, for example, Japanese Patent Laid-Open No. 56445/1983).

Furthermore, recently, a two-color electrophotographic system has been proposed that uses the above-mentioned photoreceptor and a normal electrophotographic photoreceptor.

FIG. 1 schematically shows only the main parts of an example of such a two-color electrophotographic copying apparatus using two photoreceptors.

Since the present invention relates to at least a two-color electrophotographic copying apparatus using a photoreceptor having the above-mentioned two photoconductive layers, the following will be explained based on the example shown in FIG. The two-color copying process will be briefly explained, and the problems to be solved by the present invention will also be discussed. Note that for the sake of concreteness of the explanation, the colors of the image to be copied in two colors are black and red.

In the figure, numeral 1 is a document placement glass, numeral 2 is a lamp, numerals 3, 4, 5, 6, 7, 8 are mirrors, numeral L is a lens, numeral 9 is a half mirror, numeral FR
indicates a red filter, and symbol FC indicates a red cut filter.

Further, reference numeral 10 indicates a photoreceptor for black images, and reference numeral 20 indicates a photoreceptor for red images.

The photoreceptor 10 is an ordinary photoreceptor for electrophotography, and has a structure in which one photoconductive layer is provided on a conductive substrate. Further, the photoreceptor 20 has a structure in which two photoconductive layers are provided on a conductive substrate.

Around the photoreceptor 10, reference numeral 11 indicates a charger, reference numeral 12 indicates a developing device, and reference numeral 13 indicates a cleaner.

Around the photoreceptor 20, reference numeral 21 indicates a charger for primary charging, reference numeral 22 a charger for secondary charging, reference numeral 23 a developing device, and reference numeral 24 a cleaner.

Further, reference numeral 30 is a transfer belt, and reference numerals 31, 3
2, 33, and 34 are chargers, and 35 is a fixing device.

Further, the symbol O indicates a red/black two-color original, and the symbol S indicates a recording medium, for example, plain paper.

The half mirror 9 has the attitude indicated by the solid line in the figure,
The posture shown by the broken line can be selectively taken. Further, the red filter FR and the red cut filter FC can be selectively set in the optical path.

Now, as shown in FIG. 1, with the half mirror 9 in the position shown by the solid line and the red filter FR in the optical path, the original O is placed on the original placing glass 1 and the lamp 2 is turned on. , the reflected light from the original O passes through the mirrors 3, 4, 5 and the lens L, and reaches the half mirror 9. The half mirror 9 splits the light into two optical paths, and one passes through the red filter FR and the mirror 6. One reaches the photoreceptor 10, and the other reaches the photoreceptor 20 via mirrors 7 and 8. Then, by the action of the lens L, a slit-shaped image of the original O is formed on each photoreceptor 10, 20.

Therefore, while rotating the photoreceptors 10 and 20 in the directions of the arrows, the lamp 2 and mirror 3 are integrally moved in the direction of the arrows, that is, to the right in FIG. 1, to slit scan the original O. At the same time, if the mirrors 4 and 5 are moved as one unit to the right at a speed that is half the moving speed of the mirror 3, the photoreceptors 10 and 20 can be subjected to slit exposure at the same time.

Prior to slit exposure, the photoreceptor 10 is uniformly charged to a predetermined polarity, for example negative polarity, by a charger 11, and then subjected to slit exposure.
The light that exposes the photoreceptor 10 is red light because it passes through the red filter FR.
When an image is formed on the photoreceptor 10, the red image on the original O blends into the background. Therefore, due to this slit exposure, the original O
An electrostatic latent image corresponding only to the upper black image is formed.

This electrostatic latent image is then processed by the developing device 12.
Developed with positively charged black toner. Thus, a visible black image corresponding to the black image on the original O is obtained on the photoreceptor 10.

On the other hand, as shown in FIG. 2, the photoreceptor 20 has photoconductive layers P1, P
It has a structure in which 2 layers are laminated. photoconductive layer P1,
P2 have different sensitivities, and when the photoreceptor 20 is irradiated with red light, only the photoconductive layer P1 is mainly made into a conductor.

Between the conductive base BS and the photoconductive layer P1,
It has rectifying properties for holes. Therefore, when negative primary charging is performed by the charger 21 shown in FIG. 1, an electric double layer is formed via the photoconductive layer P2, as shown in FIG. 2(). This state is referred to as the photoconductive layer P2 being charged. Subsequently, when the photoconductive layers P1 and P2 are positively charged by the charger 22 shown in FIG. 1, a state is realized in which the photoconductive layers P1 and P2 are charged in opposite directions, as shown in FIG. 2(). The directions are said to be opposite to each other because the directions of the dipole moment vectors in the electric double layer formed via each photoconductive layer are opposite.

The surface potential of the photoreceptor 20 is negative after primary charging, but after secondary charging, the secondary charging is adjusted so that it is close to O or slightly reversed to positive polarity. For the sake of simplicity, it is assumed here that the surface potential of the photoreceptor is 0 after secondary charging. This means that the absolute values of the charging potentials of each photoconductive layer are equal to each other.

Subsequently, the photoreceptor 20 is subjected to slit exposure, and this state is shown in FIG. 2(). The part of the document O corresponding to the black image N is not exposed, and therefore,
The surface potential of this portion remains at 0 potential after secondary charging. A portion of the document O corresponding to the white background portion W is exposed to white light, the charged state of each photoconductive layer P1, P2 is eliminated, and the surface potential of this portion is zero. on the other hand,
The area corresponding to the red image R is exposed to red light, the charged state of the photoconductive layer P1 is released, and the surface potential becomes negative in this area. This means that an electrostatic latent image corresponding only to the upper red image R has been formed.

Therefore, this electrostatic latent image is transferred to the developing device 23 (first
(Figure 2), the positively charged red toner TR (Figure 2)
If the original is developed with
A red visible image corresponding only to the upper red image is obtained (FIG. 2()).

Thus, on the photoreceptors 10 and 20, respectively,
A black visible image and a red visible image are obtained.

These black and red visible images are transferred onto the recording medium S in mutual alignment.

That is, the recording medium S is conveyed from the right side in FIG. 1, and when it is placed on the transfer belt 30, it is electrostatically attached to the transfer belt 30 by the charger 31. The transfer belt 30 conveys the recording medium while rotating counterclockwise.

The red visible image on the photoreceptor 20 is first transferred onto the recording medium S by the charger 32, and then the black visible image on the photoreceptor 10 is transferred by the charger 33.

The recording medium S to which the two-color visible image has been transferred is separated from the transfer belt 30 by a separating device (not shown), the two-color visible image is fixed by a fixing device 35, and is discharged from the apparatus.

After the visible image has been transferred, residual toner is removed from the photoreceptors 10 and 20 by cleaners 13 and 24, respectively. On the other hand, the transfer belt 30 is
The static electricity is removed by 4.

In this way, a two-color copy corresponding to the two-color original O is obtained.

In addition, instead of the red filter FR, a red cut filter FC is placed in the optical path, and the rotation of the photoreceptor 20,
and stop the operation of equipment around the photoreceptor 20,
If the copying process is carried out in the remaining part of the device,
A two-color red/black image on the original O can be copied using only one color, black.

By the way, the problem is as follows. That is, the photoreceptor 20 having two photoconductive layers is charged with primary and secondary charges with opposite polarities, but what will happen if an abnormality occurs in these primary and secondary charges?

Suppose that the process proceeds without secondary charging for some reason. In this case, the photoreceptor 20 changes from the state shown in FIG.
As a result of sudden image exposure, negative electrostatic latent images corresponding to the black image N and red image R on the original O are formed as shown in FIG. , as shown in FIG. 2(), a red visible image corresponding to the black image N and the red image R is formed. Then, the black image corresponding image of the copied image obtained on the recording medium becomes a mixture of red toner and black toner, resulting in an extremely unsightly color. Not only that, but on the photoreceptor 20,
The red toner that forms the red visible image corresponding to the black image will be wasted in vain.

Conversely, what happens when the process progresses without primary charging and only secondary charging occurs?
In this case, since the positive electrostatic latent image formed on the photoreceptor 20 and the red toner have the same polarity, no development is performed. However, if the developer is a two-component powder, the toner The carrier, which is charged with the opposite polarity, adheres to the photoreceptor.

A portion of this carrier is transferred onto the recording medium S and enters the fixing device, causing damage to the device. In addition, some of the particles may enter the cleaner and impair its function, or may enter between the blade and the photoreceptor and damage the photoreceptor.

In the method disclosed in JP-A-54-5644, that is, when only a photoreceptor having two photoconductive layers is used, electrostatic latent images of opposite polarity are formed on the same photoreceptor. Since this is developed with two types of toner that are charged with opposite polarities, the carriers are also charged with positive and negative polarities. , primary charging, and secondary charging may occur.

(Objective) Therefore, it is an object of the present invention to provide a two-color electrophotographic copying apparatus that can effectively prevent the occurrence of such problems.

(Structure) The present invention will be explained below. The present invention can also be applied to a two-color electrophotographic method using only a photoreceptor having two photoconductive layers, and as in the example of FIG.
It can also be applied to a two-color electrophotographic method using a book photoreceptor.

In any case, a photoreceptor having at least two photoconductive layers is used.

The two-color electrophotographic copying apparatus of the present invention includes first and second detection means, charging stop means for stopping primary and secondary charging, and optical charge removal means.

The first detection means detects the charging current of primary charging, and the second detection means detects the charging current of secondary charging.

The charging stop means stops the power supply to each charger for primary and secondary charging when at least one of the current values detected by the first and second detection means differs from a set value, and stops the primary and secondary charging. Both stop.

The optical charge eliminating means is disposed at a position that does not interfere with image exposure between the secondary charging section, that is, the area where secondary charging is performed and the developing section, and the optical charge eliminating means is disposed at a position where image exposure is not hindered. , charging current abnormality,
That is, when a difference from the set value is detected, the portion of the photoreceptor where the charging abnormality has occurred is uniformly irradiated in a slit shape.

Hereinafter, description will be given based on specific examples.

FIG. 3 schematically shows only the parts necessary for explanation regarding an embodiment in which the present invention is applied to the system shown in FIG. 1. The same symbols as in Figure 1 are used for the same equipment. Also, parts not shown, such as the optical system, the photoreceptor 10 and its peripheral equipment, are the same as in FIG. To explain the newly appearing symbols in FIG. 3, the symbol E1 is the power source of the charger 21 for primary charging, and the symbol E2 is the power source of the charger 21 for secondary charging.
2, the reference numeral E3 is a power supply for the static elimination lamp 303 as an optical static elimination means, the reference numeral D2 is a current detection circuit as a first detection means, the reference numeral D2 is a current detection circuit as a second detection means, The code 300 is
Current value discrimination circuit, code 301 is a control circuit, code 3
02 indicates an abnormality indicator, and symbol M indicates a drive motor.

The power supplies E1, E2, E3, the abnormality indicator 302, the motor M, etc. are controlled by the control circuit 301.

Current detection circuits D1 and D2 detect charging currents for primary charging and secondary charging, respectively.

The current value discrimination circuit 300 includes a current detection circuit D ₁ ,
The detected current value detected by D ₂ is compared with the set value of the charging current for primary and secondary charging, and it is determined whether the detected current value and the set value are different.

The current value discrimination circuit 300 and the control circuit 301 are
This constitutes charging stopping means.

Now, how to implement the present invention will be explained with reference to FIG.

The left half of FIG. 4 shows normal timing. The primary and secondary charging control signals are issued by the control circuit 301 and control the power supply to the chargers 21 and 22 by the power sources E1 and E2. It goes without saying that the state in which it is standing up means that it is on. Note that the time T represents the time of one copy cycle.

The detection signal is a signal indicating the charging current detected by the current detection circuits D1 and D2.

Now, let's consider an abnormal case in which the wire of the charger 22 for secondary charging breaks during discharge, and therefore secondary charging is interrupted midway.The timing in this case is shown in Figure 4. shown on the right half.

First, an abnormality in the secondary charging current is detected by the fall of the detection signal, and as a result, the control circuit immediately turns off the primary and secondary charging control signals and turns on the static elimination lamp control signal. Also, at the same time,
Also turn on the error indicator control signal. As a result, power supply to the chargers 21 and 22 for primary and secondary charging is stopped, both primary and secondary charging are stopped, and an abnormality display is displayed on the abnormality display 302.

Further, the static elimination lamp 303 is turned on, and uniformly irradiates the abnormally charged photoreceptor portion to optically eliminate static electricity. This also prevents wasteful consumption of toner or adhesion of carrier.

When an abnormality occurs, the recording medium is generally already in the process of being transported, so the drive motor M of the device continues to operate for one copy cycle, ejects the recording medium, and completes the specified copying process. After completing the process, the device is deactivated. Note that an erase lamp can also be used as the static elimination lamp 303. In that case, all erase lamps are turned on in case of abnormality.

(Effects) As described above, in the two-color electrophotographic copying apparatus according to the present invention, unnecessary consumption of toner and adhesion of carrier to the photoreceptor due to abnormalities in primary and secondary charging are prevented.

[Brief explanation of the drawing]

1 and 2 are diagrams for explaining a two-color electrophotographic process; FIG. 3 is a front view schematically showing only the parts necessary for explaining one embodiment of the present invention; FIG. 4 is a timing chart for explaining the above embodiment. 21... Charger for primary charging, 22...
Charger for secondary charging, E1, E2, E3...
...Power supply, D1, D2...Power supply detection circuit, 300...
...Current value discrimination circuit, 301...Control circuit, 303
...Static electricity removal lamp.

Claims (1)

[Claims] 1. Two photoconductive layers are laminated on a drum-shaped or belt-shaped conductive substrate, and one of the photoconductive layers mainly becomes a conductor when irradiated with light of a specific color. A two-color copying device, which uses at least a photoreceptor prepared in the above-mentioned method, and has a step of applying primary and secondary charges of opposite polarity to the photoreceptor, the method comprising: When at least one of the current values detected by the first detection means for detecting current, the second detection means for detecting the charging current of the secondary charging, and the first and second detection means differs from a set value. , a means for stopping both the primary and secondary charging, and a means provided between the secondary charging section and the developing section, and when an abnormality in the charging current is detected, the portion of the photoconductor where the charging abnormality has occurred is slit. 1. A two-color electrophotographic copying apparatus, comprising: an optical charge eliminating means for uniformly irradiating the image.