JPH07244435A - Color electrophotographic device - Google Patents

Abstract

PURPOSE:To provide a color electrophotographic device having facility for maintenance. CONSTITUTION:The color electrophotographic device is provided with a photoreceptor drum 11, an electrifier disposed on the circumference of the drum 11 and charging its surface, an optical writing device disposed on the circumference of the drum 11 and forming an electrostatic latent image, plural developing devices 14-17 disposed on the circumference of the drum 11 and sequentially forming the toner images of each color, an intermediate transfer body 18 disposed in contact with the drum 11 and forming the color toner images in such a manner that a transfer voltage is applied and the toner images of each color are successively transferred, a transfer device transferring the color toner images formed on the intermediate transfer body 18 onto a transfer material 20 altogether and moreover, a polarity switching means changing the polarity of the transfer voltage applied to the intermediate transfer body 18. At this time, toner transferred to the intermediate transfer body is attracted to a developing device 14 via the photoreceptor drum 11.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a color electrophotographic apparatus.

[0002]

2. Description of the Related Art Conventionally, in a color electrophotographic apparatus such as a color printer or a color copying machine which forms a color image using an electrophotographic recording system, a plurality of developing devices form toner images of respective colors on a photosensitive drum. In the first transfer step, the color toner images are transferred to the intermediate transfer body to form color toner images, and the color toner images formed in the intermediate transfer body are collectively transferred to the transfer material in the second transfer step. To form a color image.

Therefore, a charging device, an optical writing device, a developing device for yellow, magenta, cyan and black, and an intermediate transfer drum as an intermediate transfer member are arranged around the photosensitive drum. Then, the surface of the photosensitive drum charged by the charging device is exposed by the optical writing device to form an electrostatic latent image. The electrostatic latent image is developed by each developing device for yellow, magenta, cyan and black to become a toner image for yellow, magenta, cyan and black.

Then, in the first transfer step, the toner images of the respective colors formed on the photosensitive drum are sequentially transferred to the intermediate transfer drum to form a color toner image. Subsequently, in the second transfer step, the color toner images formed on the intermediate transfer drum are collectively transferred to the transfer material. For that purpose, a transfer device is disposed so as to face the intermediate transfer drum, and a color toner image is transferred onto a transfer material that enters between the intermediate transfer drum and the transfer device.

The color toner image thus formed on the transfer material is sent to a fixing device and fixed on the transfer material to form a color image. By the way, when the toner images of the respective colors formed on the photosensitive drum are transferred to the intermediate transfer drum, the toner remains on the photosensitive drum. Therefore, in order to remove and collect the residual toner, a cleaning device is arranged facing the photosensitive drum.

When the color toner image formed on the intermediate transfer drum is transferred to the transfer material, the toner also remains on the intermediate transfer drum. Therefore, in order to remove and collect the residual toner, a cleaning device is arranged facing the intermediate transfer drum.

[0007]

However, in the above-mentioned conventional color electrophotographic apparatus, the toner remaining on the photosensitive drum and the intermediate transfer drum is removed by the cleaning device and collected in the cleaning device. Therefore, it is necessary to periodically discard the collected toner, which makes maintenance and management troublesome.

An object of the present invention is to solve the problems of the conventional color electrophotographic apparatus and to provide a color electrophotographic apparatus which is easy to maintain and manage.

[0009]

Therefore, in the color electrophotographic apparatus of the present invention, a photosensitive drum, and a charging device which is arranged around the photosensitive drum and charges the surface of the photosensitive drum, An optical writing device is provided around the photosensitive drum to form an electrostatic latent image, and a plurality of developing devices are provided around the photosensitive drum to sequentially form toner images of respective colors. .

An intermediate transfer member, which is disposed in contact with the photosensitive drum, is applied with a transfer voltage and sequentially transfers toner images of respective colors to form color toner images, and the intermediate transfer member is formed on the intermediate transfer member. And a transfer device that collectively transfers the color toner images onto the transfer material. Further, it has a polarity switching means for changing the polarity of the transfer voltage applied to the intermediate transfer member.

[0011]

According to the present invention, as described above, in the color electrophotographic apparatus, the photosensitive drum, the charging device disposed around the photosensitive drum and charging the surface of the photosensitive drum, and the photosensitive drum It has an optical writing device arranged around the body drum to form an electrostatic latent image, and a plurality of developing devices arranged around the photosensitive drum to sequentially form toner images of respective colors.

An intermediate transfer member, which is disposed in contact with the photosensitive drum, is applied with a transfer voltage and sequentially transfers toner images of respective colors to form color toner images, and the intermediate transfer member is formed on the intermediate transfer member. And a transfer device that collectively transfers the color toner images onto the transfer material. Therefore, the surface of the photosensitive drum is charged by the charging device, and then,
The optical writing device irradiates the photosensitive drum with light to expose it, and an electrostatic latent image is formed on the photosensitive drum.

Subsequently, the developing device is placed at the developing position, and the electrostatic latent image is developed with toner of a predetermined color to be visualized, and a toner image is formed on the photosensitive drum. Then, a transfer voltage is applied to the intermediate transfer body at a predetermined timing, and the toner image on the photosensitive drum is transferred to the intermediate transfer body. The developing devices of the respective colors sequentially form the toner images of the respective colors, and the toner images of the respective colors are sequentially transferred to the intermediate transfer member to form the color toner images.

Subsequently, the color toner images are collectively transferred onto a transfer material by a transfer device. Further, it has a polarity switching means for changing the polarity of the transfer voltage applied to the intermediate transfer member. Therefore, the toner remaining on the intermediate transfer member is sucked into the developing device via the photosensitive drum.

[0015]

Embodiments of the present invention will now be described in detail with reference to the drawings. FIG. 1 is a schematic diagram of a color image forming apparatus according to an embodiment of the present invention. In the figure, 11
Is a photosensitive drum formed in a drum shape, in which a photoconductive layer is formed on a conductive support, and an organic optical semiconductor can be used. Then, a charging roller 12 as a charging device is arranged so as to face the photoconductor drum 11, and charges the surface of the photoconductor drum 11 uniformly and uniformly.

The LED array head 13 as an optical writing device irradiates the photosensitive drum 11 with light corresponding to an image signal to expose the photosensitive drum 11 to form an electrostatic latent image for each color. Further, developing devices 14 to 17 for accommodating the toners of the respective colors of black (B), cyan (C), magenta (M) and yellow (Y) in the toner container are provided. Each of the developing devices 14 to 17 is arranged from the upstream side to the downstream side along the rotation direction of the photoconductor drum 11, and operates by selecting the developing device containing the toner of the color necessary for forming the toner image. Can be made.

Therefore, each of the developing devices 14 to 17 can be independently moved in the direction of the arrow, and when a toner image of a predetermined color is formed, the developing device corresponding to the color is developed. The apparatus is advanced toward the photosensitive drum 11 and placed at the developing position. Meanwhile, the developing devices for the other colors are placed in the retracted position apart from the photoconductor drum 11 during that time. An actuator (not shown) is used to move the developing devices 14 to 17 forward and backward, respectively. The actuator biases the developing devices 14 to 17 in the direction to retract the developing device, and the developing device 1 against the biasing force of the springs.
It consists of a solenoid for advancing 4-17.

Each of the developing devices 14 to 17 adsorbs toner on the surface of each toner carrier and conveys it, develops the electrostatic latent image formed on the photoconductor drum 11, and visualizes it. A toner image of each color is formed on the photoconductor drum 11.
Further, an intermediate transfer drum 18 as an intermediate transfer member is arranged so as to face the photoconductor drum 11 and rotate in contact with the photoconductor drum 11. To form a transfer portion TR1 for. The intermediate transfer drum 18 electrostatically transfers toner, and is formed by coating the surface of a metal drum such as aluminum with a resin such as polyamide or silicone rubber. A high voltage power supply device 25 is connected to the metal drum of the intermediate transfer drum 18, and the high voltage power supply device 25
Applies a required transfer voltage to the intermediate transfer drum 18 in the first transfer step.

Further, a transfer roller 19 as a transfer device is disposed so as to face the intermediate transfer drum 18, and a transfer portion TR2 for the second transfer step is formed between the transfer roller 19 and the intermediate transfer drum 18. The transfer roller 19 can be moved in the direction of arrow A, and the transfer roller 19 is moved in the second transfer step.
It is possible to press the transfer material 20 against the intermediate transfer drum 18 by advancing it toward and placing it at the transfer position. A high voltage power supply device 26 is connected to the transfer roller 19, and the high voltage power supply device 26 applies a necessary transfer voltage to the transfer roller 19 in the second transfer process.

Further, the transfer roller 19 is retracted at a position other than the second transfer step and is placed at the retracted position. An actuator (not shown) is used to move the transfer roller 19 back and forth. The actuator biases the transfer roller 19 in a direction to move it backward, and moves the transfer roller 19 forward against the biasing force of the spring. It consists of a solenoid.

Then, a fixing device (not shown) is disposed downstream of the second transfer portion TR2 in the transfer direction of the transfer material 20. The fixing device is composed of a heating roller and a pressure roller which are arranged to face each other with the transfer material 20 interposed therebetween. Next, the operation of the color electrophotographic apparatus having the above structure will be described with reference to FIG.

FIG. 2 is a time chart of the color electrophotographic apparatus in the embodiment of the present invention. In the figure, (a) shows the operating states of the developing devices 14 to 17, and (b) shows the intermediate transfer drum 1.
8 shows the transfer voltage applied to the transfer roller 8, and (c) shows the transfer voltage applied to the transfer roller 19. Based on a start signal for image formation from a control device (not shown), the photosensitive drum 11 and the intermediate transfer drum 18 are rotated at a constant peripheral speed in the arrow direction by a driving means (not shown). The surface of the photosensitive drum 11 is uniformly and evenly charged by the charging roller 12.

Next, the image signal is the LED array head 13
The LED array head 13 irradiates the photoconductor drum 11 with light corresponding to the image signal to expose the photoconductor drum 11 to form an electrostatic latent image on the photoconductor drum 11. Subsequently, at timing t1, the developing device 17 is advanced and placed at the developing position, the electrostatic latent image is developed with yellow toner to be visualized, and a yellow toner image is formed on the photosensitive drum 11. . Then, a transfer voltage having a positive polarity is applied at timing t1 to the intermediate transfer drum 18 arranged so as to face the photoconductor drum 11 and rotate in contact with it.

Therefore, in the first transfer step, the yellow toner image on the photosensitive drum 11 is electrostatically transferred to the intermediate transfer drum 18. The outer peripheral length of the intermediate transfer drum 18 is set to be equal to or longer than the image length. Next, at timing t2, the developing device 17 is retracted to the retracted position, and the developing device 16
Are advanced to the developing position, the electrostatic latent image is developed with magenta toner to be visualized, and a magenta toner image is formed on the photoconductor drum 11. in this case,
The exposure and development device 16 by the LED array head 13 so that the head of the yellow toner image and the head of the magenta toner image formed on the intermediate transfer drum 18 may coincide with each other.
And the transfer by the intermediate transfer drum 18 are performed.

Next, at the timing t3, the developing device 1
6 is retracted to the retracted position, and the developing device 15 is advanced to the developing position to develop the electrostatic latent image with cyan toner to make it a visible image. A cyan toner image is formed. In this case, exposure by the LED array head 13, development by the developing device 15, and intermediate transfer drum so that the heads of the yellow and magenta toner images and the heads of the cyan toner images formed on the intermediate transfer drum 18 coincide with each other. Transfer by 18 is performed.

Then, at the timing t4, the developing device 15 is moved back to the retracted position, and the developing device 14 is moved forward to the developing position to develop the electrostatic latent image with black toner. A visible toner image is formed and a black toner image is formed on the photosensitive drum 11. In this case, exposure by the LED array head 13, development by the developing device 14, and intermediate processing are performed so that the heads of the yellow, magenta, and cyan toner images formed on the intermediate transfer drum 18 and the heads of the black toner images coincide with each other. Transfer is performed by the transfer drum 18.

In this way, a color toner image is formed on the intermediate transfer drum 18. Further, the timing t
In 4, the transfer material 20 is sucked by a suction device (not shown) and is conveyed to the transfer portion TR2 between the intermediate transfer drum 18 and the transfer roller 19. Then, the timing t4
At a timing t5 after a lapse of time Δt, the transfer roller 19 is moved forward and placed at the transfer position, and the transfer voltage is applied to the transfer roller 19, so that the color toner images are collectively transferred to the transfer material 20. In the second transfer step, the transfer material 20 is conveyed so that the print start position of the transfer material 20 reaches when the head of the color toner image formed on the intermediate transfer drum 18 reaches the transfer portion TR2. Timing is set.

Timing t6 when the second transfer process is completed
At, the transfer voltage applied to the transfer roller 19 is set to "0", and the transfer roller 19 is retracted to the retracted position. Then, the transfer material 20 on which the color toner image is transferred is conveyed to a fixing device, and the color toner image is fixed on the transfer material 20 by the fixing device, and a color image is formed on the transfer material 20.

By the way, at the timing t6,
The transfer voltage applied to the intermediate transfer drum 18 is changed to a negative polarity. Therefore, the high-voltage power supply device 25 has a polarity switching unit (not shown), and the polarity switching unit changes the polarity of the transfer voltage applied to the intermediate transfer drum 18. By doing so, the toner remaining on the intermediate transfer drum 18 after the second transfer process can be attached to the photosensitive drum 11. The toner adhering to the photosensitive drum 11 from the intermediate transfer drum 18 reaches the developing device 14 through the space between the charging roller 12 and the LED array head 13 as the photosensitive drum 11 rotates. The developing device 14 sucks the toner, and the photosensitive drum 11
Clean the surface of.

By the way, in the developing devices 14 to 17, reversal development is performed, the surface of the photosensitive drum 11 and the toner are charged to the same polarity, and the L of the photosensitive drum 11 is charged.
Toner is attached to the portion exposed by the ED array head 13. Therefore, if there is no exposed portion on the photoconductor drum 11, the toner in the developing devices 14 to 17 will not be attached to the photoconductor drum 11.

Therefore, for example, after a black toner image is formed on the photosensitive drum 11 by the developing device 14,
When the surface of the photoconductor drum 11 is uniformly charged by the charging roller 12 in a state where the developing device 14 is placed at the developing position as it is, the toner attached to the photoconductor drum 11 from the intermediate transfer drum 18 is removed from the photoconductor drum 11. It is sucked by the developing device 14 with the rotation of 11.

As described above, when the intermediate transfer drum 18 is rotated once, the cleaning is completed, and the toner remaining on the intermediate transfer drum 18 is transferred to the developing device 1 through the photosensitive drum 11.
4 is sucked and collected. Therefore, at the timing t7, the negative polarity applied voltage applied by the high-voltage power supply device 25 is set to "0". The charging roller 12 is set so that the photoconductor drum 11 is always charged.

The toner collected by the developing device 14 is mixed into the black toner and used again as the black toner. In this embodiment, the developing device 14 for forming a black toner image.
Since the toner remaining on the photoconductor drum 11 and the toner remaining on the intermediate transfer drum 18 are sucked and collected, the image quality may deteriorate even if the collected toner is mixed with the black toner. There is no such thing. On the other hand, in a color electrophotographic apparatus that does not use black toner, the toner remaining on the photosensitive drum 11 and the toner remaining on the intermediate transfer drum 18 may be sucked and collected by a developing device of another color. it can.

In that case, the toner collected by the developing device is mixed with the toner of the developing device. Therefore, the developing device is selected so that the image quality does not deteriorate due to the mixing of the toner. Further, in the present embodiment, yellow, magenta, cyan and black toner images are sequentially formed. However, the arrangement of the developing devices 14 to 17 may be changed or the operation order may be changed. The order in which toner images are formed can be changed by.

Further, in this embodiment, after the first transfer step and the second transfer step are completed and the color toner image is transferred to the transfer material 20, the photosensitive drum 11 and the intermediate transfer drum 18 are cleaned. However, each time the toner image of each color is transferred to the intermediate transfer drum 18 in the first transfer step, the photosensitive drum 11 is transferred to the photosensitive drum 11 without forming an electrostatic latent image on the photosensitive drum 11. The photosensitive drum 11 can also be cleaned by rotating it.

By the way, when the electrostatic latent image on the photosensitive drum 11 is developed by the developing devices 14 to 17, toner adheres to the exposed portion of the electrostatic latent image to form a toner image of each color. A small amount of toner may adhere to the exposed portion, that is, the background portion. Since the toner attached to the background portion is charged to the opposite polarity to the toner charged by the original developing devices 14 to 17, it is not transferred to the intermediate transfer drum 18 and is transferred to the transfer portion TR1. It passes and is attracted by the charging roller 12. In this case, since the charging roller 12 directly contacts the photosensitive drum 11 to charge the photosensitive drum 11, if toner adheres to the charging roller 12, charging failure will occur.

Therefore, a cleaning device is provided so that the toner adhering to the charging roller 12 can be removed. FIG. 3 is a diagram showing a charging roller cleaning device according to an embodiment of the present invention. As shown in the figure,
The cleaning roller 3 is brought into contact with the charging roller 12
The cleaning roller 31 removes the toner and collects it in the toner recovery box 32.

In this embodiment, the charging roller 12 is arranged so that the toner on the charging roller 12 can be sucked.
A voltage having the same polarity as is applied to the cleaning roller 31. The cleaning roller 31 is composed of a metal roller,
The toner attached to the charging roller 12 is scraped off by the blade 34 of the toner recovery box 32.
In this case, the amount of toner adhering to the background is extremely small,
Even if the capacity of the toner recovery box 32 is reduced, it can be used for a sufficiently long period.

Further, the charging roller 12 is formed of a semiconductive rubber roller or the like, and is rotated at a peripheral speed different from the peripheral speed of the photosensitive drum 11, so that the toner can be efficiently collected in the developing device 14 (FIG. 1). You can That is, when the toner adheres to the photoconductor drum 11 and passes between the photoconductor drum 11 and the charging roller 12, there is a difference between the peripheral speed of the photoconductor drum 11 and the peripheral speed of the charging roller 12. It moves slightly on the drum 11.
As a result, it is possible to charge the portion of the photosensitive drum 11 on which the toner is attached.

Therefore, when the developing device 14 collects the toner, the Coulomb force is sufficiently applied to the toner, and the developing device 14 strongly sucks the toner. Further, when spherical toner is used, the contact area between the photosensitive drum 11 and the toner is reduced, and the mechanical adhesive force is reduced, so that the toner suction force in the developing device 14 can be increased.

It should be noted that the present invention is not limited to the above-described embodiments, but various modifications can be made based on the spirit of the present invention, and they are not excluded from the scope of the present invention.

[0042]

As described above in detail, according to the present invention, in the color electrophotographic apparatus, the photosensitive drum and the peripheral surface of the photosensitive drum are provided to charge the surface of the photosensitive drum. A charging device, an optical writing device that is arranged around the photosensitive drum to form an electrostatic latent image, and a plurality of developing devices that are arranged around the photosensitive drum and sequentially form toner images of respective colors. And a device.

Then, an intermediate transfer member, which is disposed in contact with the photosensitive drum, is applied with a transfer voltage and sequentially transfers the toner images of the respective colors to form color toner images, and the intermediate transfer member is formed on the intermediate transfer member. And a transfer device that collectively transfers the color toner images onto the transfer material. Further, it has a polarity switching means for changing the polarity of the transfer voltage applied to the intermediate transfer member. In this case, the toner transferred to the intermediate transfer body is sucked into the developing device via the photosensitive drum.

Therefore, since the toner remaining on the photosensitive drum and the intermediate transfer drum can be sucked and collected without using a cleaning device, it is not necessary to periodically discard the toner. As a result, maintenance and management of the color electrophotographic apparatus becomes easy.

[Brief description of drawings]

FIG. 1 is a schematic diagram of a color image forming apparatus according to an embodiment of the present invention.

FIG. 2 is a time chart of the color electrophotographic apparatus according to the embodiment of the present invention.

FIG. 3 is a diagram illustrating a cleaning device for a charging roller according to an exemplary embodiment of the present invention.

[Explanation of symbols]

 11 Photoreceptor Drum 12 Charging Roller 13 LED Head 14 to 17 Developing Device 18 Intermediate Transfer Drum 19 Transfer Roller 20 Transfer Material 31 Cleaning Roller 32 Toner Collection Box

Claims (5)

[Claims] 1. A photosensitive drum, (a) a charging device (b) disposed around the photosensitive drum and charging a surface of the photosensitive drum, and (c) a charging device disposed around the photosensitive drum. An optical writing device provided to form an electrostatic latent image; (d) a plurality of developing devices arranged around the photoconductor drum to sequentially form toner images of respective colors; and (e) the photoconductor. An intermediate transfer member which is disposed in contact with the drum and which sequentially transfers toner images of respective colors to which a transfer voltage is applied to form a color toner image; and (f) a color toner image formed on the intermediate transfer member. And (g) polarity switching means for changing the polarity of the transfer voltage applied to the intermediate transfer member, and a color electrophotographic apparatus. 2. The color electrophotographic apparatus according to claim 1, wherein the charging device comprises a charging roller which is disposed in contact with the photosensitive drum and which constantly charges the photosensitive drum. 3. The color electrophotographic apparatus according to claim 2, wherein the charging device includes a cleaning device for cleaning the charging roller. 4. The color electrophotographic apparatus according to claim 2, wherein the charging roller is rotated at a peripheral speed different from the peripheral speed of the photosensitive drum. 5. The color electrophotographic apparatus according to claim 1, wherein the developing device uses spherical toner.