JP2000267530A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce power consumption, needless to say, to prevent the occurrence of a transfer hysteresis by controlling a DC component of discharging provided with the DC component whose polarity is the same as the static charge characteristic of an image carrier in accordance with the output of a transfer means. SOLUTION: A photoreceptor drum 4 is driven to rotate, while the drum is rotating, a negative charging operation is executed by a primary charging scorotron 9 and an electrostatic latent image is formed by exposure light LB or the like. A destaticizing corotron 40 functioning as a 2nd destaticizing means for destaticizing by discharging the prescribed amount of static electricity from the surface of the photoreceptor drum 4 is arranged on the downstream side of a primary transfer roll 12 as a primary transfer means in the photoreceptor drum 4 moving direction, and also, arranged on the upstream side of an erasing lamp 31 as a 1st destaticizing means in the photoreceptor drum moving direction. As for the destaticizing corotron 40, discharging with a DC component of a negative polarity which is the same as the static charge characteristic of the photoreceptor drum 4 is executed, and also, the DC component of the destaticizing corotron 40 is controlled in accordance with the output of the primary transfer roll 12.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus using an electrophotographic process, such as an electrophotographic copying machine, a facsimile, a printer, etc., and more particularly to an output control technique of a charging means for removing static from a surface of an image carrier. It is about.

[0002]

2. Description of the Related Art Conventionally, as an image forming apparatus such as a copying machine or a printer utilizing the above-described electrophotographic process, for example, four colors of yellow, magenta, cyan and black of different colors sequentially formed on a photosensitive drum. The toner image of
There is a configuration in which a full-color or black-and-white image is formed by multiple transfer onto a transfer sheet held on the surface of a transfer drum. The transfer drum is configured to hold a transfer sheet on the surface of the transfer drum by forming a transfer film made of a dielectric into a cylindrical shape and electrostatically adsorbing the transfer sheet on the transfer film. I have.

In an image forming apparatus using such a transfer drum, transfer paper electrostatically attracted to a transfer film made of a dielectric material is separated from the photosensitive drum after a toner image is transferred from the photosensitive drum. A static elimination corotron has been used to suppress the influence of peeling discharge at that time and scattering of toner after transfer.

As an image forming apparatus using such a charge removing corotron, there are those disclosed in, for example, JP-A-3-87984 and JP-A-6-289557.

The image forming apparatus disclosed in Japanese Patent Application Laid-Open No. 3-88884 discloses an image carrier that moves endlessly, primary charging means for uniformly charging the image carrier, and a toner image on the image carrier as a recording material. An image forming apparatus having a transfer charging unit for transferring, wherein a discharging unit for performing a discharge biased to a polarity opposite to the transfer charging polarity is provided between the primary charging unit and the transfer charging unit.

The color image forming apparatus disclosed in Japanese Patent Application Laid-Open No. 6-289557 is a means for charging a photoreceptor,
A means for removing the charge of the photoconductor after transfer, a means for cleaning residual toner after transfer on the photoconductor, and an environment in the vicinity of the photoconductor, wherein a DC component of voltage or current is superimposed on an AC component of voltage or current. , A means for detecting the water content of the transfer material, and a means for controlling the current value of the minus DC component of the charge removing means based on the detection results of the two detecting means.

In the case of the image forming apparatus disclosed in JP-A-3-87984 or JP-A-6-289557, it is necessary to control the output of the charge removing means in accordance with the state of the transfer sheet. In addition, the environment near the photoconductor is detected by a humidity sensor or the like, and the amount of current of the charge removing unit is controlled based on the detection result.

[0008]

However, the above-mentioned prior art has the following problems. That is, Japanese Patent Application Laid-Open Nos.
In the case of the image forming apparatus disclosed in, for example, Japanese Patent No. 9557, the toner images of different colors are successively multiplex-transferred onto a transfer sheet held on a transfer drum or a transfer belt. It is necessary to control the output of the transfer charger according to the difference in thickness and material, but if the thickness or material of the transfer paper is significantly different, it is not possible to transfer multiple toner images on the transfer paper satisfactorily. However, there is a problem that it is difficult to form an image on the transfer paper satisfactorily.

In the above image forming apparatus, toner images of four different colors, yellow, magenta, cyan, and black, which are sequentially formed on a photosensitive drum, are temporarily formed on an intermediate transfer member such as an intermediate transfer belt. One that has been configured to form a color image by multiplex primary transfer and collectively secondary-transferring a plurality of color toner images multiplex-transferred onto the intermediate transfer body onto a transfer sheet is already available. Proposed.

In an image forming apparatus using such an intermediate transfer member, since the intermediate transfer member is a resistor and the transfer paper does not directly contact an image carrier such as a photoreceptor drum, the above-described humidity and the like are not considered. Control based on environmental changes is no longer required.

However, in the case of an image forming apparatus using the above-mentioned intermediate transfer member, since the intermediate transfer member is not a dielectric but a resistor, the toner image formed on an image carrier such as a photosensitive drum can be removed. When the primary transfer is performed on the intermediate transfer member by the transfer means, the transfer current easily flows into the image carrier through the intermediate transfer member which is a resistor, and a transfer history called “ghost” occurs. Was.

The mechanism of generating a transfer history called "ghost" will be further described. As shown in FIGS. 6 (a) to 6 (e), the surface of the photosensitive drum is set at a predetermined negative polarity potential by a primary charger. After the image is uniformly charged, the image is exposed by an image exposure method in which an image is exposed by an image exposure means, and an electrostatic latent image corresponding to the image is formed. At this time, as the photoreceptor drum, a photoreceptor drum using an organic photoconductor (OPC) is generally used due to various factors such as safety against human body, image quality, and cost. As shown in FIG. 7A, the photosensitive drum using the organic photoconductor (OPC) includes, for example, a charge transport layer (CTL) and a charge generation layer (CGL).
It is composed of a base material such as aluminum. The photosensitive drum using the organic photoconductor (OPC) uses a charge transport medium that transports a positive charge among positive and negative charges generated by the light exposure of the organic photoconductor (OPC). Therefore, as shown in FIGS. 7B to 7D, after uniformly charged to a negative polarity, the image is exposed to light to neutralize the charge in the exposed portion and form an electrostatic latent image. The electrostatic latent image formed on the photoreceptor drum is developed by a reversal developing method in which an area exposed by the developing means, that is, an area having a reduced negative potential is developed with toner charged to a negative polarity. Becomes The toner image formed on the photoconductor drum is primary-transferred onto the intermediate transfer member by receiving a positive polarity charge by a transfer unit including a transfer corotron and a transfer roll. At that time, the area other than the toner image on the photosensitive drum is in a state where positive charges flow through the intermediate transfer body which is a resistor and is biased to a positive polarity. Since the toner is a dielectric material, almost no electric charge flows into the toner, and the toner remains in a negative polarity. Then, after the residual toner and the like are removed by the cleaning unit, the surface of the photoreceptor drum is uniformly exposed to light by a neutralization unit such as a neutralization lamp or the like, and the surface is neutralized to prepare for the next image forming step.

By the way, in the case of the above-mentioned conventional image forming apparatus, when the surface of the photosensitive drum is uniformly exposed by a static elimination means such as a static elimination lamp or the like, static elimination is performed.
Since an organic photoconductor (OPC) using a charge transport medium that transports positive charges is used as the photosensitive drum,
The area of the surface of the photosensitive drum that has been charged to a negative polarity has a potential of 0 V by attracting and neutralizing the positive charge generated by exposure, but the area that has been charged to a positive polarity is Even if the organic photoconductor (OPC) shows conductivity, the charge is not removed and the organic photoconductor (OPC) remains charged to a positive polarity. Therefore, after the neutralization by the neutralization unit, the surface of the photosensitive drum is uniformly charged to a predetermined negative potential by the primary charging unit for the next image forming step, and the potential difference after the neutralization remains as it is. Thus, there is a problem that the previous image appears in the next image as a transfer history called "ghost".

In order to prevent the occurrence of such a transfer history called "ghost", the above-mentioned Japanese Patent Laid-Open Publication No. Hei 3-8788 is used.
As disclosed in Japanese Patent Application Laid-Open Publication No. 4 (1994) -294, Japanese Patent Application Laid-Open No. Hei 6-289957, and the like, a discharge means is provided between the primary charging means and the transfer charging means for performing a discharge biased to the opposite polarity to the transfer charging polarity. It is also possible.

However, in such a case, when a sufficiently high voltage or large current is applied to the charge removing means for removing charge from the image carrier so as to reliably prevent the occurrence of a transfer history called "ghost", the amount corresponding to that is reduced. However, the power consumed by the high-voltage power supply for the static elimination means increases, and there is a problem in that the cost and power consumption increase due to the limited power of the entire image forming apparatus. Also, in order to prevent the occurrence of a transfer history called "ghost" to some extent and to suppress an increase in power consumption, if the voltage applied to the discharging means for discharging the image carrier and the current flowing therethrough are limited to a small value, the "ghost" is obtained. A new problem arises in that it is not possible to reliably prevent the occurrence of a transfer history called “transfer history”.

Therefore, the present invention has been made to solve the above-mentioned problems of the prior art, and an object thereof is to surely prevent the occurrence of a transfer history called "ghost". Needless to say, it is an object of the present invention to provide an image forming apparatus capable of reducing power consumption.

[0017]

In order to solve the above-mentioned problems, the present invention is directed to an image carrier on which a toner image is formed after being uniformly charged by a charging means,
Transfer means for transferring the toner image formed on the image carrier to another member from the image carrier, and uniformly exposing the surface of the image carrier after the toner image transfer step is completed. A first discharging unit for discharging the surface of the image carrier by performing the operation, and a downstream side of the transfer unit in the moving direction of the image carrier, and an upstream of the first discharging unit in the moving direction of the image carrier. A second discharger disposed on the side of the image bearing member and performing a predetermined discharge on the surface of the image bearing member, wherein the second discharging member is configured to charge the image bearing member. A discharge having a DC component having the same polarity as the polarity is performed, and the DC component of the second charge removing unit is controlled according to the output of the transfer unit.

According to a second aspect of the present invention, there is provided an image bearing member on which a toner image is formed after being uniformly charged by charging means, and a toner image formed on the image bearing member. Primary transfer means for primary transfer from an image carrier to an intermediate transfer body, secondary transfer means for secondary transfer of a toner image transferred on the intermediate transfer body to a transfer member, and primary transfer of the toner image A first static eliminator for uniformly exposing the surface of the image carrier after the process is completed, and a downstream side of the primary transfer unit in the image carrier moving direction with respect to the primary transfer unit; And a second static eliminator disposed upstream of the first static eliminator in the moving direction of the image carrier and configured to perform a predetermined discharge on the surface of the image carrier to eliminate static. In the forming apparatus, the second charge removing unit is configured to charge the image carrier. Performs discharge having sex with the same polarity as the DC component, and is configured to DC components of the second discharging means so as to control in accordance with the output of the primary transfer unit.

[0019]

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

FIG. 2 is a schematic configuration diagram showing a color printer as an image forming apparatus according to the embodiment of the present invention.

In FIG. 2, reference numeral 1 denotes a main body of a color printer. Image data is input to the main body 1 of the color printer from an external image reading device or a personal computer (not shown). . Image data sent from an external image reading device, a personal computer, or the like (not shown) is input to the image processing device 2, and the image processing device 2 performs shading correction, position shift correction, Predetermined image processing such as brightness / color space conversion, gamma correction, frame erasure, color / movement editing, and the like are performed.

The image data subjected to the predetermined image processing by the image processing apparatus 2 as described above is yellow (Y),
ROS3 (R) is used as color material gradation data of four colors of magenta (M), cyan (C), and black (BK) (each of 8 bits).
master OutputScanner)
In this ROS 3, image exposure with laser light is performed according to the color material gradation data.

Inside the color printer body 1,
Image forming means A capable of forming a plurality of toner images of different colors
Are arranged. This image forming means A mainly includes
Photoconductor drum 4 as an image carrier on which an electrostatic latent image is formed
And a rotary developing device 5 as a developing means capable of developing an electrostatic latent image formed on the photosensitive drum 4 to form a plurality of toner images of different colors.

As shown in FIG. 2, the ROS 3 modulates a semiconductor laser (not shown) according to original color material gradation data, and emits a laser beam LB from the semiconductor laser according to the gradation data. The laser beam LB emitted from the semiconductor laser is deflected and scanned by the rotary polygon mirror 6, and is scanned and exposed on the photosensitive drum 4 as an image carrier via the f · θ lens 7 and the reflection mirror 8.

The photosensitive drum 4 on which the laser beam LB is scanned and exposed by the ROS 3 is driven to rotate at a predetermined speed in a direction indicated by an arrow by driving means (not shown). As the photoconductor drum 4, for example, a photoconductor drum using an organic photoconductor (OPC) is used. The surface of the photosensitive drum 4 is previously charged to a predetermined polarity (for example, a negative polarity) and a potential by a scorotron 9 for primary charging, and then scanned and exposed to a laser beam LB according to color material gradation data. This forms an electrostatic latent image. The electrostatic latent images formed on the photoreceptor drum 4 are four color developing units 5Y, 5M, 5M, 5Y, 5Y, 5Y, 5Y, 5Y (yellow (Y), magenta (M),
By a rotary developing device 5 rotatably provided with C and 5K, for example, the toner is charged in the negative polarity having the same polarity as the charged polarity of the photoconductor drum 4 and is reversely developed to form a toner image of a predetermined color. Incidentally, the toner image formed on the photosensitive drum 4 is charged with a negative polarity or the like by a pre-transfer charger 10 as necessary, and the charge amount is adjusted.

A toner image of each color formed on the photosensitive drum 4 is transferred onto an intermediate transfer belt 11 as an intermediate transfer member disposed below the photosensitive drum 4 by a primary transfer roll as a primary transfer means. 12 are multiplexed. The primary transfer means is not limited to a transfer roll, but may be a transfer corotron. The intermediate transfer belt 11 includes a driving roll 13, a tension roll 14a, a driven roll 14
The photoconductor drum 4 is supported rotatably in the direction of the arrow at the same moving speed as the peripheral speed of the photosensitive drum 4 by a backup roll 15 as an opposing roll constituting a part of the secondary transfer means b.

On the intermediate transfer belt 11, yellow (Y), magenta (M), cyan (C), and black (BK) are formed on the photosensitive drum 4 according to the color of the image to be formed. All or some of the toner images of the four colors are transferred by the primary transfer roll 12 while being sequentially superimposed. The toner image transferred onto the intermediate transfer belt 11 is transferred onto a transfer sheet 16 as a transfer member which is conveyed to a secondary transfer position at a predetermined timing.
The transfer is performed by the press-contact force and the electrostatic force of the backup roll 15 that supports the transfer roller 1 and the secondary transfer roll 17 that forms a part of the secondary transfer unit that presses against the backup roll 15. As shown in FIG. 2, the transfer paper 16 has a predetermined size from one of a plurality of paper feed cassettes 18, 19, and 20 as a plurality of transfer paper storage members disposed in the lower portion of the color printer main body 1. Is the feed roll 18
a, 19a, and 20a. The fed transfer paper 16 is transferred to the intermediate transfer belt 1 at a predetermined timing by a plurality of transport rolls 21 and registration rolls 22.
1 is transferred to the secondary transfer position. Then, as described above, the toner image of a predetermined color is collectively transferred from the intermediate transfer belt 11 to the transfer paper 16 by the backup roll 15 and the secondary transfer roll 17 as the secondary transfer means. It has become so.

The transfer paper 16 on which the toner image of a predetermined color has been transferred from the intermediate transfer belt 11 is separated from the intermediate transfer belt 11 and then conveyed to a fixing device 24 by a conveyance belt 23. The fixing device 24 fixes the toner image on the transfer paper 16 by heat and pressure, and discharges the toner image onto the discharge tray 25, thereby completing the color image recording process.

After the toner image transfer step is completed, the surface of the photosensitive drum 4 is cleaned by a cleaning device 26 to remove residual toner, paper dust, and the like. , And the residual charges are removed to prepare for the next image forming step.
Further, the cleaning device 27 removes residual toner, paper dust, and the like from the surface of the intermediate transfer belt 11 after the toner image transfer process is completed. The cleaning device 27 for the intermediate transfer belt comes into contact with and separates from the surface of the intermediate transfer belt 11 at a predetermined timing. FIG.
Reference numeral 29 denotes a manual feed tray.

FIG. 1 is a structural view showing the image forming means A of the color printer.

In this color printer, as described above, the surface of the photosensitive drum 4 is uniformly charged to a predetermined negative potential by the scorotron 9 for primary charging. In, an image corresponding to a predetermined color is exposed by the ROS 3, and an electrostatic latent image is formed. The electrostatic latent images formed for the respective colors on the surface of the photoconductor drum 4 correspond to the developing units 5Y, 5M,
5C and 5K, and a toner image T of a predetermined color is formed on the surface of the photosensitive drum 4.

For example, if the electrostatic latent image formed on the photosensitive drum 4 corresponds to a yellow color, the electrostatic latent image is developed by a yellow developing unit 5Y, and is developed. 4, a yellow toner image T is formed. Also, for the other magenta, cyan, and black colors, the corresponding color toner images T are sequentially formed on the photosensitive drum 4 by the same process.

The toner images T of the respective colors sequentially formed on the photosensitive drum 4 are transferred to the photosensitive drum 4 and the intermediate transfer belt 1.
In the primary transfer position where the photosensitive drum 4 contacts
The image is transferred onto the surface of the intermediate transfer belt 11 from above. This one
At the next transfer position, a semi-conductive primary transfer bias roll 12 is disposed on the back side of the intermediate transfer belt 11, and the intermediate transfer belt 11 is separated from the photosensitive drum 4 by the primary transfer bias roll 12. It comes in contact with the surface. A voltage having a polarity opposite to the charge polarity of the toner is applied to the bias roller 12 for primary transfer, and the toner image T formed on the photosensitive drum 4 is transferred to the intermediate transfer belt 11.
It is transferred onto the upper surface by a pressing force and an electrostatic force.

In the case of forming a monochromatic image, the toner image T of a predetermined color primary-transferred onto the intermediate transfer belt 11 is
Immediately after the secondary transfer onto the transfer paper 16, when forming a color image in which a plurality of color toner images T are superimposed, formation of a predetermined color toner image T on the photosensitive drum 4
The process of primary transfer of the toner image T onto the intermediate transfer belt 11 is repeated for a predetermined number of colors.

For example, when a full-color image is formed by superimposing four color toner images T of yellow (Y), magenta (M), cyan (C) and black (BK), the photosensitive drum 4 , For each rotation, yellow (Y), magenta (M), cyan (C), black (B
The toner images T of the respective colors K) are sequentially formed, and these four color toner images are sequentially primary-transferred onto the intermediate transfer belt 11 in a superimposed state.

At this time, the intermediate transfer belt 11 rotates at a period synchronized with the photosensitive drum 4 while holding the yellow unfixed toner image T that has been primarily transferred first. On the upper side, the magenta, cyan and black unfixed toner images T are transferred in a state of being sequentially superimposed on the yellow unfixed toner image T for each rotation.

The unfixed toner image T primarily transferred to the intermediate transfer belt 11 in this manner is transported to a secondary transfer position facing the transport path of the transfer paper 16 with the rotation of the intermediate transfer belt 11. You.

The transfer paper 16 is fed from predetermined paper feed cassettes 18, 19, 20 by feed rolls 18a, 19a, 20a and transported to the registration roll 22 by transport rolls 21 as described above. At a predetermined timing by the resist roll 22,
The paper is fed between the nip between the secondary transfer roll 17 and the intermediate transfer belt 11.

Further, on the back side of the intermediate transfer belt 11 at the secondary transfer position, a backup roll 15 which is a counter electrode of the secondary transfer roll 17 is provided. At the secondary transfer position, the semi-conductive secondary transfer roll 17 is pressed against the intermediate transfer belt 11 at a predetermined timing, and a voltage having a polarity opposite to the charging polarity of the toner is applied to the backup roll 15 to thereby perform the intermediate transfer. The unfixed toner image T transferred onto the belt 11 is secondarily electrostatically transferred onto the transfer paper 16 at the secondary transfer position.

In this embodiment, as shown in FIG.
Instead of directly applying a voltage having the same polarity as the charge polarity of the toner to the secondary transfer roll 17, the transfer bias is applied by the bias roll 30 to the backup roll 15 which is pressed against the secondary transfer roll 17 via the intermediate transfer belt 11. A voltage having the same polarity as the charging polarity of the toner is applied from a transfer bias high voltage power supply (not shown) as a voltage applying unit. However, a configuration may be employed in which a voltage having a polarity opposite to that of the toner is directly applied to the secondary transfer roll 17.

Then, the transfer paper 16 to which the unfixed toner image T has been transferred is separated from the intermediate transfer belt 11, sent to the fixing device 24 by the transport belt 23, and the unfixed toner image T is fixed.

As described above, in the above-described color printer, the photosensitive drum 4 is driven to rotate in the direction of the arrow, during which the negative charging by the scorotron 9 for primary charging, the formation of an electrostatic latent image by the exposure light LB, Developing device 5
Development, transfer to the intermediate transfer belt 11 rotating in the direction of the arrow by the primary transfer roll 12, cleaning of untransferred toner by the drum cleaning device 26, and the photosensitive drum 4 by the charge removing lamp 31 as the first charge removing means.
Image formation is performed by repeating the charge removal of the above residual potential. This cycle is based on 4 cycles of KYMC for one image.
The printing is performed for each color, and is sequentially stacked on the intermediate transfer belt 11 by the primary transfer roll 12. When the four colors overlap, the transfer paper 16 is transported in the direction of the arrow, and the secondary transfer roll 17
Is transferred from the intermediate transfer belt 11 to the transfer paper 16 by the secondary transfer means comprising

The surface of the intermediate transfer belt 11 is
After the final toner image transfer process is completed, the belt cleaning device 27 that has been separated from the surface of the intermediate transfer belt 11 until this time contacts the surface of the intermediate transfer belt 11 and 11 to clean the untransferred toner. The drum cleaning device 2
The untransferred toner scraped off by the belt cleaning device 6 and the belt cleaning device 27 is collected in a waste toner collecting bottle (not shown).

The intermediate transfer belt 11 is made of polyimide,
An appropriate amount of a conductive agent such as carbon black is dispersed in a synthetic resin such as polycarbonate, polyester, or polypropylene, or various rubbers, so that the volume resistivity is 10 ⁶ to 1.
Is formed by adjusting the film-like belt such that 0 ¹⁴ Ω · cm. The thickness of the intermediate transfer belt 11 is set to, for example, 0.1 mm. The circumference of the intermediate transfer belt 11 is set to an integral multiple (for example, three times) of the circumference of the photosensitive drum 4.

The secondary transfer roll 17 is disposed so as to be able to contact and separate from the intermediate transfer belt 11 as necessary. When a color image is formed, the unfixed toner image of the final color is formed. T is separated from the intermediate transfer belt 11 until T is primarily transferred onto the intermediate transfer belt 11.

Further, the secondary transfer roll 17 has a surface layer made of a urethane rubber tube in which carbon is dispersed, and an inner layer made of foamed urethane rubber in which carbon is dispersed. Is coated with fluorine. The secondary transfer roll 17 is formed such that its volume resistivity is set to 10 ³ to 10 ¹⁰ Ω · cm, and the roll diameter is φ28 mm.
The hardness is set to, for example, 30 ° (Asuka C).

On the other hand, the backup roll 15 has a surface layer composed of a tube of blended rubber of EPDM and NBR in which carbon is dispersed, and an internal layer composed of EPDM rubber, and has a surface resistivity of 10 ⁷ to 10 ⁷ . 10 ¹⁰ Ω
/ □, formed so that the roll diameter is φ28 mm,
The hardness is set to, for example, 70 ° (Asuka C).

By the way, in this embodiment, an image carrier on which a toner image is formed after being uniformly charged by the charging means, and a toner image formed on the image carrier are transferred to the image carrier. A primary transfer unit for primary transfer from the first transfer unit onto the intermediate transfer body, a secondary transfer unit for secondly transferring the toner image transferred on the intermediate transfer body onto a transfer member, and the primary transfer step of the toner image is completed. A first static eliminator for uniformly exposing the surface of the subsequent image carrier to neutralize the surface of the image carrier, and a first static eliminator downstream of the transfer unit in the image carrier moving direction; An image forming apparatus comprising: a second discharging unit disposed upstream of the one discharging unit in the moving direction of the image carrier and discharging the surface by performing a predetermined discharge on the surface of the image carrier. The second static eliminator has the same polarity as the charging polarity of the image carrier. Performs discharge with sexual DC component, and is configured to DC components of the second discharging means so as to control in accordance with the output of the primary transfer unit.

That is, in the color printer according to this embodiment, as shown in FIG. 1, the first transfer roller 12 as the primary transfer means is located on the downstream side in the moving direction of the photosensitive drum 4 and the first transfer means A static elimination corotron 40, which is disposed upstream of the erase lamp 31 as a static eliminator in the moving direction of the photosensitive drum 4 and removes static electricity by applying a predetermined discharge to the surface of the photosensitive drum 4. Are arranged. In addition, the static elimination corotron 4
Numeral 0 is configured to perform discharge having a negative DC component having the same polarity as the charging polarity of the photosensitive drum 4 and to control the DC component of the charge removing corotron 40 in accordance with the output of the primary transfer roll 12. ing.

FIG. 3 is a block diagram showing a control circuit of the color printer.

In FIG. 3, reference numeral 41 denotes a control device comprising an electronic circuit centered on a CPU for controlling an image forming operation of a color printer, and reference numeral 42 applies a high voltage of a predetermined polarity to the primary transfer roll 12 as a primary transfer means. The first high-voltage power supply 43 is a discharging corotron 4 as a second discharging means.
A second high-voltage power supply for applying a high voltage of a predetermined polarity to 0, 4
Reference numeral 4 denotes a memory in which a table for controlling at least one of a voltage and a current applied to the primary transfer roll 12 and the neutralizing corotron 40 is stored in advance.

In the above configuration, in the case of the color printer according to the present embodiment, the occurrence of a transfer history called "ghost" can be surely prevented as follows. It is possible to reduce power consumption.

That is, in the case of the above-described color printer, as shown in FIGS. 1 and 2, when a color or monochrome image is formed, the surface of the photosensitive drum 4 has a predetermined potential by a scorotron 9 for primary charging. Is uniformly charged. At this time, the surface of the photosensitive drum 4 is as shown in FIG.
As shown in (1), after being uniformly charged to a predetermined negative polarity potential by the scorotron 9 for primary charging, the ROS
An image is exposed by an image portion exposure method in which the image portion is exposed by 3 and an electrostatic latent image corresponding to the image is formed. At this time, the photosensitive drum 4 is made of an organic photoconductor (OP
C) is used. The photosensitive drum using the organic photoconductor (OPC) is uniformly charged to a negative polarity because the organic photoconductor (OPC) uses a charge transport medium that transports a positive charge. By exposing the image area, the exposed portion of the organic photoconductor becomes conductive and neutralizes negative charges, thereby forming an electrostatic latent image. The electrostatic latent image formed on the photosensitive drum 4 is developed by a reversal developing method in which a region exposed by the developing device 5, that is, a region where the negative potential is reduced, is developed by a toner charged to a negative polarity, It becomes a toner image. The toner image T formed on the photosensitive drum 4 is charged by the primary transfer roll 12 with a positive polarity, so that the intermediate transfer belt 1
1 is primarily transferred.

At this time, the resistance value of the primary transfer roll 12 changes depending on environmental conditions such as temperature and humidity, or usage conditions such as the usage amount, and an appropriate supply from the first high-voltage power supply 42 depends on the resistance value. Since the current values are different, the control device 41 detects the resistance of the primary transfer roll 12 at a certain interval, and determines an appropriate current value to be supplied to the primary transfer roll 12. The resistance of the primary transfer roll 12 is detected by outputting a constant current to the primary transfer roll 12 by the control device 41 via the first high-voltage power supply 42. By detecting the required voltage by the control device 41, the voltage is used as a substitute characteristic of the resistance value. As shown in FIG. 4, an appropriate transfer current value to be supplied to the primary transfer roll 12 is determined as a table in the memory 44 in advance in accordance with a voltage value (Vmonitor) as a substitute characteristic of a resistance value. This is performed by storing the data and making a selection with reference to the table.

The toner image T formed on the photosensitive drum 4 as described above is charged with a predetermined amount of positive polarity by the primary transfer roll 12 so that the intermediate transfer belt 1 is charged.
1 is primarily transferred. At this time, the photosensitive drum 4
Since the photosensitive drum 4 and the intermediate transfer belt 11 are in direct contact with each other in the area other than the upper toner image, a positive charge flowing from the primary transfer roll 12 through the intermediate transfer belt 11 that is a resistor is transferred to the photosensitive drum 4. The surface potential of the photosensitive drum 4 is biased to a positive polarity as shown in FIG. 5C. However, in the area where the toner image exists on the photosensitive drum 4, since the toner is a dielectric substance, almost no electric charge flows into the area, and the area remains charged to the negative polarity potential lowered by the image exposure.

Therefore, the step of transferring the toner image from the photosensitive drum 4 to the intermediate transfer belt 11 is completed as described above.
When the surface of the photosensitive drum 4 from which the residual toner and the like have been removed by the cleaning device 26 is subjected to uniform exposure by the charge removing lamp 31 as it is to remove the charge, as described in the related art, 4, the potential difference due to the presence or absence of the toner image remains, and during uniform charging by the primary charging scorotron 9 for the next image forming process, the potential difference after the charge removal is recharged as it is. That is, the previous image appears in the next image as a transfer history called "ghost".

Therefore, in this embodiment, FIG.
As shown in FIG. 5, the surface of the photoconductor drum 5 after the toner image transfer process is completed, the charge removing corotron 40 applies a negative polarity D having the same polarity as the charging polarity of the photoconductor drum 4 to the surface.
By performing discharge having the C component, the entire surface of the photosensitive drum 5 is shifted to a negative polarity.

Thus, even if a potential difference due to the presence or absence of the toner image remains on the surface of the photosensitive drum 4 after the toner image transfer process is completed, the photosensitive drum 4 is exposed by the charge removing corotron 40 thereafter. By performing a discharge having a negative DC component having the same polarity as the charging polarity of the body drum 4, the entire surface of the photosensitive drum 5 can be shifted to the minus polarity. Therefore,
By uniformly exposing the surface of the photosensitive drum 4 whose electric potential is shifted to the negative polarity side by the discharging lamp 31 to remove the electricity, the photosensitive drum 4
All negative charges can be eliminated through the organic photoconductor (OPC) whose surface is made conductive. Therefore, it is possible to uniformly remove the surface potential of the photosensitive drum 4 to 0 V. When the surface of the photosensitive drum 4 is uniformly charged by the scorotron 9 for primary charging for the next image forming step. In addition, the surface of the photosensitive drum 4 is uniformly charged to a predetermined potential as shown in FIG.
It is possible to reliably prevent the transfer history called "ghost" from appearing in the next image.

As described above, the "ghost"
In order to prevent the transfer history referred to as “transfer history”, before the charge is removed by the first charge removing means, the surface of the photosensitive drum 4 is charged with the charge polarity of the photosensitive drum 4 by the charge removing corotron 40 as the second charge removing means. What is necessary is just to charge uniformly to the negative polarity of the same polarity.

However, when the surface of the photosensitive drum 4 is uniformly charged to a negative polarity, the extent to which the area on the photosensitive drum 4 where no toner image is formed is shifted to the positive side depends on the primary degree. Since it changes depending on the transfer current flowing through the transfer roll 12, in order to surely prevent a transfer history called "ghost", it is necessary to supply a sufficient charge removing current to the charge removing corotron 40, which is the second charge removing means. Yes, power is unnecessarily consumed.

Therefore, in this embodiment, a discharge having a negative DC component having the same polarity as the charged polarity of the photosensitive drum 4 is performed to the charge removing corotron 40 as the second charge removing means. Forty DC components are controlled in accordance with the output of the primary transfer roll 12.

For example, when the value of 400 V is obtained as a result of the resistance detection of the primary transfer roll 12, the output of the primary transfer roll 12 is 30 μA from Table 1 in FIG. 4 and the output of the neutralizing corotron 40 is 300 μA from Table 2. Become.

As described above, the output of the primary transfer roll 12 is controlled based on the detection result of the resistance value of the primary transfer roll 12, as shown in Table 1 of FIG.
As shown in Table 2 of FIG. 4, the DC component of the static elimination corotron 40 is also controlled by the controller 41 according to the output of the primary transfer roll 12.
Control. Here, the DC component that is supplied to the neutralizing corotron 40 is the minimum necessary and sufficient to surely shift the surface of the photosensitive drum 4 that is deviated to the positive side by the output of the primary transfer roll 12 to the negative polarity side. It is set to the limit value.

As described above, in the above-described embodiment, not only the transfer history called “ghost” can be surely prevented, but also the output of the neutralizing corotron 40 can be suppressed to the minimum necessary. It can be reduced with respect to any of the power used, the generated discharge products, and the charging stress of the photosensitive drum 4.

In the above embodiment, for example, if a value of 400 V is obtained as a result of detecting the resistance value of the primary transfer roll 12, the output of the primary transfer roll is 30 μA from Table 1 in FIG. The output of the neutralizing corotron is 3
00 μA. In this case, the output of the primary transfer roll in Table 1 and the output of the primary transfer roll in Table 2 have the same value, but it is necessary to correct the output by a factor other than the resistance of the primary transfer roll 12, such as the film thickness of the photosensitive drum 4. May be configured to use the output of the primary transfer roll 12 corresponding to the correction value of the result obtained in Table 1 as the output of the primary transfer roll 21 in Table 2. For example, 94% of the output of the primary transfer roll 12 obtained in Table 1 of FIG.
When used as the output, the actual output is 28 μA with respect to 30 μA obtained in Table 1, so the output of the neutralizing corotron 40 may be controlled to be 280 μA from Table 2.

[0066]

As described above, according to the present invention, it is possible to surely prevent the occurrence of the transfer history called "ghost" and also to reduce the power consumption of the image. A forming device can be provided.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing an image forming unit of a color electrophotographic copying machine as an image forming apparatus according to Embodiment 1 of the present invention.

FIG. 2 is a configuration diagram showing a color electrophotographic copying machine as an image forming apparatus according to Embodiment 1 of the present invention.

FIG. 3 is a block diagram showing a control circuit.

FIG. 4 is a chart showing the output of a primary transfer roll and a discharging corotron.

FIGS. 5A to 5F are explanatory views showing image forming steps, respectively.

FIGS. 6A to 6E are explanatory views showing image forming steps in a conventional image forming apparatus.

FIGS. 7A to 7D are explanatory views showing the principle of forming an electrostatic latent image on an organic photoconductor.

[Explanation of symbols]

1: photosensitive drum (image carrier), 12: intermediate transfer belt, 13: primary transfer roll, 31: erase lamp (first charge removing means), 40: charge removing corotron (second charge removing means), 41: control Device, 42: first high-voltage power supply, 43:
Second high voltage power supply, 44: memory.

Claims (2)

[Claims] An image carrier on which a toner image is formed after being uniformly charged by a charging unit, and a toner image formed on the image carrier is transferred from the image carrier to another member. Transfer means for transferring, a first charge removing means for uniformly discharging the surface of the image carrier after the toner image transfer step is completed, and a charge removing means for removing the surface of the image carrier, and an image of the transfer means. A third discharger disposed downstream of the carrier moving direction and upstream of the first static eliminator in the moving direction of the image carrier and performing a predetermined discharge on the surface of the image carrier. In the image forming apparatus provided with the second charge removing means, the second charge removing means performs a discharge having a DC component having the same polarity as the charging polarity of the image carrier, and converts the DC component of the second charge removing means. That control is performed according to the output of the transfer means. An image forming apparatus symptoms. 2. An image bearing member on which a toner image is formed after being uniformly charged by charging means, and a toner image formed on the image bearing member are transferred from the image bearing member onto an intermediate transfer member. A primary transfer unit for primary transfer, a secondary transfer unit for secondary transfer of the toner image transferred on the intermediate transfer body to a transfer member, and an image carrier after the primary transfer step of the toner image is completed. A first discharging unit that neutralizes the surface of the image carrier by uniformly exposing the surface, and a downstream side of the primary transfer unit in the moving direction of the image carrier, and the first discharging unit includes: An image forming apparatus provided on the upstream side in the moving direction of the image carrier, and comprising a second static eliminator for eliminating static by applying a predetermined discharge to the surface of the image carrier; Is a discharge having a DC component having the same polarity as the charging polarity of the image carrier. Performs an image forming apparatus characterized by being configured to control in accordance with the output of the second primary transfer means the DC component of the charge eliminating unit.