JP2002072705A - Wet image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a new image forming device capable of reducing the soiling of the back surface of transfer material due to reverse polarity toner. SOLUTION: This image forming device is provided with image carriers 11Y, 11M, 11C and 11K where a toner image consisting of electrified toner having a specified polarity is formed, a transferring member 60 whose surface is moved along an endless path including a transfer part opposed to the image carrier and which opposes the transfer material to the image carrier at the transfer part, and transfer electric field forming means 67Y, 67M, 67C, 67K, 9Y, 9M, 9C and 9K forming electric field in a direction where the toner having the specified polarity is moved to the transferring member side at the transfer part. In the device, a transfer electric field forming means is actuated at non- transfer time when the transfer material does not exist at the transfer part.

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 such as a copying machine, a printer, and a facsimile, and more particularly, to an image carrier on which a toner image composed of a charged toner having a predetermined polarity is formed, and an image carrier at a transfer section. The present invention relates to an image forming apparatus having a transfer member for causing a transfer material to face a carrier and a transfer electric field forming means for forming an electric field in a transfer section.

[0002]

2. Description of the Related Art Heretofore, the surface has moved along an endless path including an image carrier on which a toner image formed of a charged toner having a predetermined polarity is formed and a transfer section facing the image carrier, and the transfer section has a moving surface. A transfer member for causing a transfer material to face the image carrier; and a transfer electric field forming means for forming an electric field in the transfer section for moving the toner of the predetermined polarity from the image carrier to the transfer member side. Image forming apparatuses are known.

[0003]

In such an image forming apparatus, even if the surface of the image carrier is a non-image area where the toner image to be transferred to the transfer material is not formed, the developing member of the developing device can be used. The toner is transferred from the developing member to the image carrier due to a potential difference or mechanical contact between the toner and the image carrier, or toner adhered due to other causes. Such a toner is often charged to a polarity opposite to a predetermined charging polarity (hereinafter, referred to as a toner).
Reverse polarity toner). Then, there is a timing at which the transfer member directly faces the image carrier without a transfer material. Therefore, depending on the electrostatic state such as the potential of the image carrier surface at this timing and the electric field by the transfer electric field forming means, or the mechanical state such as direct contact or separation, the image carrier surface Is transferred to the surface of the transfer member. The transferred toner then adheres to the back surface of the transfer material facing the image carrier at the transfer portion by the transfer member, and generates so-called stain on the back surface of the transfer material.

The above-described stain on the back surface of the transfer material is caused by the image carrier on which the toner image formed of the charged toner having the predetermined polarity is formed, the first transfer portion facing the image carrier, and the first transfer portion facing the transfer material. An intermediate transfer member whose surface moves along an endless path including two transfer portions, and a transfer for forming an electric field in the first transfer portion in a direction for moving the toner having the predetermined polarity from the image carrier to the intermediate transfer member. This can also occur in an image forming apparatus having an electric field forming unit. At the non-transfer time when the transfer of the toner image on the image carrier is not performed in the first transfer portion, when the opposite polarity toner is transferred to the intermediate transfer member by mechanical contact or the like,
This is because there is a possibility that the toner may further transfer from the intermediate transfer member to the transfer member of the second transfer portion and adhere to the back surface of the transfer material.

SUMMARY OF THE INVENTION The present invention has been made in consideration of the above problems, and an object of the present invention is to provide a novel image forming apparatus capable of reducing the stain on the back surface of a transfer material caused by reverse polarity toner. It is.

[0006]

In order to achieve the above object, the invention according to claims 1 to 11 is directed to an image bearing member on which a toner image formed of a charged toner having a predetermined polarity is formed, and an image bearing member facing the image bearing member. A transfer member whose surface moves along an endless path including a transfer section to transfer a transfer material to the image carrier at the transfer section, and transfers the toner having the predetermined polarity from the image carrier to the transfer section. A transfer electric field forming means for forming an electric field in a direction to be moved toward the transfer member side, wherein a control means for operating the transfer electric field forming means at a non-transfer time when there is no transfer material in the transfer portion is provided. It is characterized by the following. The twelfth aspect of the present invention includes an image carrier on which a toner image composed of a charged toner having a predetermined polarity is formed, a first transfer unit facing the image carrier, and a second transfer unit facing the transfer material. An intermediate transfer member whose surface moves along an endless path; and a transfer electric field forming means for forming an electric field in the first transfer portion for moving the toner of the predetermined polarity from the image carrier to the intermediate transfer member. An image forming apparatus comprising: a control unit that operates the transfer electric field forming unit during a non-transfer period when the toner image on the image carrier is not transferred in the first transfer unit. .

[0007]

[Embodiment 1] Hereinafter, the present invention will be described.
An embodiment applied to an electrophotographic color laser printer (hereinafter, referred to as “laser printer”) as an image forming apparatus will be described. FIG. 2 is a schematic configuration diagram of the laser printer according to the present embodiment. This laser printer is
Four sets of toner image forming units 1Y, 1M, 1C, and 1K for forming images of each color of yellow (Y), magenta (M), cyan (C), and black (K) ,
M, C, and K are yellow, magenta, cyan,
Indicating that the member is for black). These are arranged in the above-described order from the upstream side along the moving direction of the transfer paper as the transfer material (the direction of arrow A in the figure). Each of the toner image forming units 1Y, 1M, 1C, and 1K is a photosensitive drum 11Y, 11M, 11C, 11 as an image carrier.
A photoconductor unit having K and a developing unit are provided. The rotation axes of the photoconductor drums in each photoconductor unit are parallel to each other, and are set at positions spaced at a predetermined pitch in the transfer paper moving direction.

The laser printer further includes a light source, a polygon mirror, an f-θ lens, a reflection mirror, and the like in addition to the toner image forming units 1Y, 1M, 1C, and 1K. 11Y, 11M, 11C,
An optical writing unit 2 for irradiating the surface of the 11K with a laser beam while scanning it is provided. Paper cassettes 3, 4,
The image forming apparatus includes a pair of registration rollers 5 and a transfer unit 6 as a belt device having a transfer conveyance belt 60 as a transfer member that carries the transfer paper and conveys the transfer paper so as to pass through the transfer position of each toner image forming unit. Further, a fixing unit 7 of a belt fixing type, a paper discharge tray 8, a manual feed tray (not shown), a toner supply container, a waste toner bottle, a duplex / reversing unit, a power supply unit, and the like are also provided.

The dashed line in FIG. 2 indicates the transfer path of the transfer paper. The transfer paper fed from the paper feed cassettes 3 and 4 is transported by transport rollers while being guided by a transport guide (not shown), and is transported to a temporary stop position where the registration roller pair 5 is provided. The transfer paper sent out by the registration roller pair 5 at a predetermined timing is carried by the transfer conveyance belt 60, and the toner image forming units 1Y, 1M, 1C,
The paper is conveyed so as to pass the 1K transfer position. The transfer paper on which the toner images of the respective toner image forming units 1Y, 1M, 1C, and 1K are transferred and the color image is formed is discharged onto a discharge tray 8 after the fixing unit 7 fixes the toner images.

FIG. 3 shows the toner image forming units 1Y, 1M,
FIG. 3 is an enlarged view showing a schematic configuration of a yellow toner image forming unit 1Y of 1C and 1K. Other toner image forming units 1M,
1C and 1K have the same configuration, respectively, and thus description thereof is omitted. In FIG. 3, the toner image forming unit 1Y includes the photoconductor unit 10Y and the developing unit 20Y as described above. Photoconductor unit 10
Y denotes a photosensitive drum 11Y, a brush roller 12Y for applying a lubricant to the photosensitive drum surface, a swingable counter blade 13Y for cleaning the photosensitive drum surface, and a uniform charging of the photosensitive drum surface. And a non-contact type charging roller 15Y. As the photoconductor drum of each photoconductor unit, a photoconductor drum having an organic photoconductor (OPC) layer on the surface and having a diameter of 30 mm was used. The developing unit 20Y uses a two-component developer including a magnetic carrier and a negatively charged toner having a desired charge polarity (hereinafter, referred to as a normal polarity). And
A developing roller 22Y as a developer carrier, which is disposed so as to be partially exposed from an opening on the photosensitive drum side of the developing case 21Y, transport screws 23Y and 24Y, a developing doctor 25Y, a toner density sensor (T sensor) 26Y , A powder pump 27Y and the like. The developer accommodated in the developing case 21Y is agitated and transported by the transporting screws 23Y and 24Y and is charged by friction. Then, a part of the developer is carried on the surface of the developing roller 22Y, and after the layer thickness is regulated by the developing doctor 25Y, the developer is conveyed to a developing position facing the photosensitive drum 11Y. At the developing position, the electrostatic latent image on the photosensitive drum 11Y is developed by the toner in the developer on the developing roller. The toner concentration of the developer in the developing case 21Y is detected by the toner concentration sensor 26Y, and toner is supplied by a powder pump 27Y as needed.

In the toner image forming section having the above structure, the light is applied to the surface of the photosensitive drum 11Y, which is uniformly charged to minus 700 volts having the same polarity as the normal polarity of the toner by the charging roller 15Y to which the AC voltage is applied. When the laser beam modulated and deflected by the writing unit 2 is irradiated while being scanned, an electrostatic latent image is formed on the surface of the photosensitive drum 11Y. The electrostatic latent image on the photoreceptor drum 11Y is reversely developed using the negatively charged toner in the developing unit 20Y to be a yellow toner image. Transfer conveyance belt 60
At the transfer position Pt where the upper transfer paper 100 passes, the toner image on the photosensitive drum 11Y is transferred to the transfer paper 100. The surface of the photoconductor drum 11Y after the transfer of the toner image is coated with a predetermined amount of lubricant by the brush roller 12Y, and then cleaned by the counter blade 13Y to prepare for the formation of the next electrostatic latent image.

FIG. 1 is a schematic structural view of the transfer unit 6. The transfer / transport belt 60 used in the transfer unit 6 has a temperature of 10 degrees Celsius and a humidity of 15% to 30 degrees Celsius.
Change in volume resistivity in degrees and humidity 90% of the environmental change is endless single layer belt fit in ¹ × 10 9 ~1 × 10 1 ¹ range. The material is, for example, PVDF (polyvinylidene fluoride). This transfer conveyance belt 60 is
Photosensitive pair drums 11Y, 11M, 11 of each toner image forming unit
C and 11K are wound around four grounded support rollers 61 to 64 so as to pass through each transfer position in contact with and opposed to 11K. The exit roller 62 on the downstream side in the transfer paper moving direction is a drive roller that frictionally drives the transfer conveyance belt 60, and is connected to a drive source (not shown).

An electrostatic attraction roller 65 is opposed to the entrance roller 61 of the support rollers 61 to 64 on the upstream side in the transfer paper moving direction. This electrostatic attraction roller 65
Is obtained by forming a conductive foamed elastic layer on a cored bar. As the elastic layer material, for example, a specific resistivity of 10 ⁵
Ωcm chloroprene rubber is used. The roller 65 includes a power supply 65a for suction and a power supply 65 for reverse polarity.
The voltage is selectively applied from b. The power supply 65a for suction is for applying a charge of positive polarity opposite to the normal polarity of the toner to the transfer paper, and uses, for example, a constant current power supply of +15 μA. The transfer paper passing between the electrostatic attraction 65 and the entrance roller 61 in a state where power is supplied from the attraction power supply 65 a is electrostatically attracted onto the transfer conveyance belt 60. Power supply 65 for reverse polarity
b increases the charge of the negatively charged toner having the normal polarity on the transfer / transport belt 60, inverts the positively charged opposite polarity toner to the positive polarity, and applies the toner to the surface of the electrostatic attraction roller 65. This is for transferring the attached negatively charged toner to the surface of the transfer / conveying belt 60. For example, a constant voltage power supply of minus 2 KV is used. Switching of the voltage applied to the electrostatic attraction roller 65 is performed by a main body control plate (not shown). The control by the main body control plate will be described later in detail.

Further, as a transfer electric field forming means for forming a transfer electric field at each transfer position, a transfer bias is applied so as to come into contact with the back surface of the transfer carrying belt 60 which is in contact with and opposes the photosensitive drum and forms a transfer nip. Member 67Y, 6
7M, 67C and 67K are provided. The transfer bias applying members 67Y, 67M, 67C, and 67K are fixed brushes made of a conductive mylar.
Transfer bias is applied from Y, 9M, 9C, 9K.
By the transfer bias applied by the transfer bias applying member, a transfer charge is applied to the transfer / conveyance belt 60, and a transfer electric field having a predetermined strength is formed between the transfer / conveyance belt 60 and the surface of the photosensitive drum at each transfer position. You. In the present embodiment, the transfer bias power supplies 9Y, 9M, 9
As C and 9K, a constant current power supply having a positive polarity, which is a polarity opposite to the normal polarity of the toner, is used. Among them, the transfer bias power supply 9K corresponding to the black photosensitive member 9K located at the most downstream in the moving direction of the transfer conveyance belt 60 in the transfer paper conveyance range is configured to be able to switch the current value between, for example, +15 μA and +10 μA. I have. The ON / OFF of each transfer bias power supply and the switching of the current value of the black transfer bias power supply 9K are also controlled by the main body control plate. The control by the main body control plate will be described later in detail.

Each of the photosensitive drums 11Y, 11M, 1
Backup rollers 68Y and 68 pressing the transfer conveyance belt 60 toward the photosensitive drum corresponding to 1C and 11K.
M, 68C and 68K are provided. Each of the backup rollers 68Y, 68M, 68C, and 68K partially winds the transfer conveyance belt 60 around the peripheral surface of the photosensitive drum 11Y on the upstream side of the transfer position in the transfer sheet moving direction. This allows
The contact pressure between the transfer paper 100 and each photosensitive drum at the transfer nip is increased, and the transfer efficiency at the transfer position is increased.

A stretched portion between the support rollers 63 and 64 of the transfer / conveyance belt 60 on the side where the transfer paper is not conveyed,
A cleaning device 70 for cleaning toner adhered to the surface of the transfer conveyance belt 60 is provided. The cleaning device 70 includes a cleaning roller 71 made of metal as a conductive cleaning member disposed so as to be in contact with the surface of the transfer conveyance belt, and a conductive roller disposed opposite to the cleaning roller 71 via the transfer conveyance belt 60. And a cleaning electric field forming means for forming a cleaning electric field between the cleaning roller 71 and the material of the opposing roller 73. In this example, the opposing roller 73 is formed of a sponge roller having an elastic foam layer made of a conductive sponge material on a cored roller. The cleaning electric field forming means includes a cleaning roller 71 having the conductivity, and a cleaning bias power source 7 serving as a voltage applying means for applying a voltage to the cleaning roller 71.
5 and the opposite roller 63 connected to the ground, and a voltage having a polarity (plus) opposite to the normal polarity (minus) of the toner is applied to the cleaning roller 71 by the power supply 75. As a result, an electric field is generated in the cleaning nip, which is the contact portion between the transfer conveyance belt 60 and the cleaning roller 71, such that the negatively charged toner moves from above the transfer conveyance belt 60 to the cleaning roller 71 side. The toner attached to the transfer / transport belt 60 is moved toward the cleaning roller 71 by this electric field, and the toner is removed from the surface of the transfer / transport belt 60. The toner that has moved to the cleaning roller 71 side is
2 and is removed from the surface of the roller 71.

FIGS. 4A and 4B are enlarged views of the transfer unit 6 when executing the full color mode and the monochrome mode, respectively. The transfer unit 6 according to the present embodiment includes a transfer unit main body 600 fixedly arranged with respect to the apparatus main body, and a transfer subunit 601 swingable about a swing shaft 602 provided on the transfer unit main body side. . The transfer unit main body 600 includes a transfer bias applying member 67K for black and a backup roller 68.
K, support rollers 61 to 64, an eccentric cam 603 for swinging the transfer subunit 601 and the like are supported.
On the other hand, the transfer subunit 601 supports color transfer bias applying members 67Y, 67M, 67C, backup rollers 68Y, 68M, 68C, and the like. Further, between the swing end of the transfer subunit 601 and the transfer unit main body 600, the transfer subunit 601 is provided.
A spring is provided as urging means for urging the photoconductor drums 11Y, 11M, and 11C apart from each other. The eccentric cam 603 is attached so as to be in contact with the lower surface of the swinging end of the transfer subunit 601, and is driven to rotate by a driving device (not shown).
When the color mode shown in FIG. 4A is executed, the eccentric cam 603 is rotated to a position where the lower surface of the swing end of the transfer subunit 601 is pushed up against the urging force of the spring 604. As a result, the transfer / conveying belt 60 comes into contact with all the photosensitive drums, and the toner images of each color on each of the photosensitive drums can be transferred to the transfer paper on the transfer / conveying belt 60 in a superimposed manner. When the monochrome mode shown in FIG. 4B is executed, the eccentric cam 603 is rotated to a position where the lifting force on the swing end of the transfer subunit 601 is released. As a result, the swinging end of the transfer subunit 601 is pushed down by the urging force of the spring 604, and the transfer / conveyance belt 60 and the photosensitive drums 11Y and 1
1M and 11C are separated from each other, and only the black toner image on the photosensitive drum 11K can be transferred to the transfer paper on the transfer / conveyance belt 60. Further, in the present embodiment, only the black photosensitive drum 11K contacts the transfer conveyance belt 60 at the time of the initial operation immediately after the power of the laser printer is turned on or at the time of the cleaning operation of the transfer conveyance belt 60 which is appropriately performed. Take the state of b).

FIG. 5 is a timing chart showing an example of timing control of the laser printer controlled by the control unit during the initial operation. The photosensitive drum and the transfer bias applying member in the figure are for black. At the time of this initial operation, as described above, only the black photosensitive drum 11 in FIG.
The photoreceptor drum for color remains non-rotating, and the bias application to the transfer bias applying member remains off. In addition,
These controls are performed by the main body control plate. When the power of the laser printer is turned on, the drive motor of the photosensitive drum 11K is turned on to rotate the photosensitive drum 11K, and at the same time, the rotational drive of the transfer conveyance belt 60, the cleaning roller 66, and the suction roller 65 is started. Is done.
Further, in synchronization with this, a positive voltage for cleaning is applied to the cleaning roller 66. Thereby, for a while after the power is turned on, the transfer / conveyance belt 6
Cleaning of the normal polarity (minus) charged toner attached to 0 is performed. At this time, the toner having the normal polarity (minus) charged on the transfer conveyance belt is
In order to facilitate the transfer to the transfer roller, a negative voltage having a polarity opposite to that of the transfer material suction voltage is applied to the suction roller 65. The transfer bias applying member 67 transfers the toner in the image forming operation so that the toner charged to the opposite polarity (plus) attached to the surface of the photosensitive drum 11 is less likely to be transferred to the surface of the transfer conveyance belt 60. The same positive voltage as the transfer bias at the time is applied. This positive voltage may be controlled at a constant current of +15 μA as in the case of transfer described later. However, in the present embodiment, in order to reduce the potential history on the photoconductor due to the application of the transfer bias without the transfer paper interposed. The current is controlled at a constant current of -10 μA to make the transfer electric field weaker. The application of the voltage to the transfer bias applying member 68 is started with a delay of T1 after the drive motor of the photosensitive drum 11 is turned on. The delay time T1 is a time required for the drive motor of the photosensitive drum 11K to rise.

After the cleaning of the transfer conveyance belt 60 has been performed for a predetermined time, a positive voltage and a negative voltage are alternately applied to the suction roller 65 for a predetermined time t in order to clean the suction roller 65. In the example of FIG. 5, the time t corresponds to the time corresponding to two rotations of the suction roller 65, and is 20 μm.
A is a constant current controlled positive voltage and a negative voltage of 2 kV.
The main body control plate controls which of the suction power supply 65a and the power supply 65b for reverse polarity to apply the voltage so that the voltage is applied four times alternately by the rotation time t.
As a result, the negatively charged toner and the positively charged toner attached to the suction roller 65 can be alternately transferred from the suction roller 65 onto the transfer conveyance belt 60, and the suction roller 65 can be cleaned.

During the cleaning of the suction roller 65 in this manner, and for a predetermined time after the completion of the cleaning, the cleaning roller 66 is controlled so as to continuously apply a positive voltage for cleaning.
Thus, the negatively charged toner transferred from the suction roller 65 to the transfer conveyance belt 60 is cleaned.
The control unit includes the photosensitive drum 11, the cleaning roller 66, the suction roller 65, and the transfer conveyance belt 6.
0 at the same time as the cleaning bias power supply 6
6a, power supplies 65a, 65b connected to the suction roller 65
Then, the transfer bias power supply 9K is turned off to terminate the initial operation. In the example of FIG. 5, the above initial operation is performed for a time corresponding to three rotations of the transfer / conveyance belt 60.

FIG. 6 is a timing chart showing an example of timing control of the laser printer during the image forming operation in the mono-color mode. This timing chart is based on the assumption that the same black image is continuously printed on two sheets (A4 horizontal size). When an external print start signal is input, first, the drive motor of the photosensitive drum 11K is turned on to rotate the photosensitive drum 11K, and at the same time, the transfer conveyance belt 60, the cleaning roller 66, and the suction roller 65 are driven. The rotation drive is also started.
Further, in synchronization with this, a positive voltage for cleaning is applied to the cleaning roller 66, and the negatively charged toner on the transfer conveyance belt is easily transferred to the cleaning roller 66 by the suction roller 65 as described above. Is applied from the power supply 65b having the opposite polarity. Next, voltage application to the charging roller 15K is started with a delay of T1. This delay time T1 is
The time required for the drive motor of the photosensitive drum 11K to rise. After the voltage is applied to the charging roller 15K, the transfer bias application to the transfer bias applying member 67K is started with a delay of T2. This transfer bias is controlled at a constant current of −10 μA in order to reduce the potential history on the photoreceptor due to the application of the transfer bias in the state where the transfer paper is not interposed, in order to reduce the transfer electric field similarly to the above-mentioned initial operation. . The delay time T2 is a time required for the charged area of the photosensitive drum 11K to move to the transfer position.

After a lapse of a predetermined time, a registration clutch (not shown) for operating the registration roller pair 5 (see FIG. 1) is turned on at a predetermined timing, and at the same time, the suction roller 6 is turned on.
5 is switched to the power supply 65a for suction.
A constant current controlled positive voltage of 5 μA is applied. In the present embodiment, the time T3 from when the registration clutch is turned on to when the leading end of the transfer paper 100 reaches the opposing portion between the transfer conveyance belt 60 and the suction roller 65 is at least one rotation of the suction roller 65. It has such a configuration. Therefore, the control unit controls the switching from the reverse polarity power supply 65b to the suction power supply 65a at least before a time corresponding to at least one rotation of the suction roller 65 when the leading end of the transfer paper 100 reaches the opposing portion. With such control,
The negatively charged toner still adhering after the cleaning of the suction roller 65 is transferred to the transfer conveyance belt 60 as much as possible, and the transfer of the toner to the transfer material due to the subsequent application of the positive voltage for suctioning the transfer material can be reduced. . And 15
While the positive voltage controlled at a constant current of μA is continuously applied to the attraction roller 65, a charge is applied to the transfer paper 100 that reaches and passes through the opposing portion, and the transfer paper 100 is electrostatically attracted to the transfer conveyance belt 60. Let it. Subsequently, the transfer conveyance belt 6
At the timing T4 immediately before the leading edge of the transfer paper on the transfer paper reaches the transfer position, the constant current control value of the transfer bias is increased to 15
Switch to μA.

After the formation of the first image is completed, the formation of the second image is also performed continuously. Immediately after the rear end of the first transfer paper 100 passes through the facing portion,
The voltage applied to the attraction roller 65 is switched from the plus voltage from the attraction power supply 65a to the minus voltage from the reverse polarity power supply 65b, and then, at the timing when the leading end of the second transfer paper 100 reaches the facing portion, Power supply 65 for suction again
Switch to positive voltage from a. That is, in the inter-paper period T5, a negative voltage is applied to the suction roller 65 from the power supply 65b for reverse polarity. Also, the transfer bias is controlled by a constant current of 10 .mu.A, which is relatively low, in the period T6 between sheets in order to make the transfer electric field weak. During the period of facing the second transfer sheet, the voltage from the suction power supply 65a is continuously applied to the suction roller 65 in the same manner as the first sheet, and the transfer bias is continuously controlled at a relatively high 15 μA. For a while after the completion of the second image formation, the cleaning roller 6
While continuing to apply a positive voltage for cleaning to 6,
The application of the negative voltage that has been switched in accordance with the passage of the trailing edge of the second transfer sheet is continued to be applied. Next, the photosensitive drum 11K, the cleaning roller 66, the suction roller 65, and the transfer conveyance belt 60 are stopped, and the voltage application to the charging roller 15K, the cleaning roller 66, and the suction roller 65 is also stopped. In the illustrated example, the transfer bias is turned off in accordance with the rear end of the second transfer sheet passing through the transfer position. However, in accordance with this passage, the transfer bias is switched to a weaker transfer electric field.
This weak transfer electric field may be continuously applied for a while.

In this embodiment, the black photosensitive member 11K is used in the initial operation or in the mono-color mode as shown in FIG.
Only the transfer conveyor belt 60 is brought into contact,
At the time of the initial operation or the mono-color mode, a state in which all the photoconductors are in contact with the transfer conveyance belt as shown in FIG. In this case, all the photosensitive drums in contact with the transfer / conveyance belt 60 may be driven to rotate, and the transfer bias may be applied to all of the photosensitive drums in a state where the transfer sheet is not interposed at the transfer position. However, the transfer bias may be applied only to the photoconductor 11K for black located at the most downstream position. It is desirable to apply the transfer bias only to the black photoconductor 11K from the viewpoint of reducing the potential history of the photoconductor by applying the transfer bias without the transfer paper. Moreover,
Even if reversely charged toner (positive) transfer from the upstream photosensitive drums 11Y, 11M, and 11C to the transfer / conveying belt 60 occurs, the transfer from the transfer / conveying belt 60 is performed at the transfer position of the blackest photosensitive drum 11K on the lowermost stream. Photosensitive drum 11K for black
Therefore, the purpose of removing the oppositely charged toner from the transfer conveyance belt 60 can be achieved. The oppositely charged toner transferred from the transfer conveyance belt 60 to the photoconductor drum 11 is removed from the surface of the photoconductor drum by the photoconductor cleaning device 10.

[Second Embodiment] In the first embodiment, the present invention is applied to an image forming apparatus for transferring a toner image on a photosensitive drum onto a transfer sheet carried on a transfer / conveying belt as a transfer member. However, the present invention can also be applied to an image forming apparatus that transfers a toner image on a so-called intermediate transfer member onto transfer paper on a transfer member. FIG. 7 shows a configuration example of an intermediate transfer unit 200 as a belt device in a laser printer using a belt-shaped intermediate transfer belt 201. In this laser printer, the intermediate transfer belt 201 is wound around a plurality of support rollers 202 to 205 and is driven to rotate in a direction indicated by an arrow in FIG. The toner images formed on the photoconductor drums 11Y, 11M, 11C, and 11K of the respective toner image forming units are transferred to primary transfer rollers 206Y, which are provided to face the photoconductor drums with the intermediate transfer belt 201 interposed therebetween. 206M, 206C, 206K and 1
Next transfer bias power supplies 209Y, 209M, 209C,
The image is sequentially transferred onto the intermediate transfer belt 201 by the primary transfer electric field formed at 209K. Then, the color images on the intermediate transfer belt 201 are collectively transferred onto the transfer paper 100 carried on the transfer / conveyance belt 60 in a secondary transfer unit provided near the black toner image forming unit for the fourth color. Is secondarily transferred. The transfer conveyance belt 60 employs a cleaning device 70 of a bias cleaning type and uses an attraction roller 65, similarly to the transfer conveyance belt 60 in the printer of the first embodiment. Corresponding members have the same reference characters allotted, and description thereof will not be repeated. Also in the present embodiment, if at least one of the primary transfer bias and the secondary transfer bias is biased to the polarity opposite to the normal polarity toner at the non-transfer time, the transfer source member (the photosensitive member in the primary transfer) 11. In the secondary transfer, the opposite polarity toner adhering to the intermediate transfer belt 201 is transferred to a member on the transfer destination side (the intermediate transfer belt 201 in the primary transfer, and the transfer transport in the secondary transfer). Transfer to the belt 60) and contamination can be reduced. Further, as shown in the example of the drawing, when a bias cleaning type cleaning device is used as a cleaning device for the transfer destination side member, the opposite polarity toner which is difficult to clean by the bias cleaning type is transferred from the transfer source member. This can be suppressed, which is preferable. Then, the suction roller 65 is also used as a charge-up unit, the application of a voltage from the suction power supply 65a to the suction roller 65 before the transfer paper is opposed to the suction roller 65, or the most downstream photosensitive drum among the plurality of photosensitive drums. If the transfer bias is applied only when the transfer bias is not transferred during the non-transfer, the same advantage as that of the first embodiment is obtained.

[0026]

According to the first to eleventh aspects of the present invention, the transfer electric field forming means is operated by the control means at a non-transfer time when there is no transfer material in the transfer section, and a transfer electric field is formed in the transfer section. The transfer electric field exerts an electrostatic force from the surface of the image carrier toward the surface of the transfer member for the toner of a predetermined polarity, and an opposite electrostatic force for the toner of the opposite polarity. Therefore, by forming a transfer electric field in the transfer portion during the non-transfer period in which the transfer member and the image carrier directly face each other without the intermediary of the transfer material, the opposite polarity toner adhering to the surface of the image carrier is transferred. Transfer to the surface of the member. Therefore, it is possible to achieve a specific effect that the back stain of the transfer material due to the opposite polarity toner can be reduced.

In particular, according to the second aspect of the present invention, charged toner of a predetermined polarity is sucked toward the cleaning member between the surface of the transfer member and the cleaning member opposed thereto by the cleaning electric field forming means. A cleaning electric field is formed. By this cleaning electric field,
The charged toner having a predetermined polarity attached to the surface of the transfer member is transferred to the cleaning member by electrostatic force to clean the surface of the transfer member. Since the electrostatic force is used as described above, for example, when a cleaning member such as a cleaning blade that cleans only with a mechanical force such as a mechanical rubbing force or a toner damping force is used, a transfer member is used. There is little mechanical damage to the member surface and the lining member. On the other hand, in the cleaning using the cleaning electric field, the opposite polarity toner adhered to the transfer member cannot be cleaned. Therefore, by using in combination with the configuration for reducing the transfer of the opposite polarity toner to the surface of the transfer member as described above with reference to claim 1, the back contamination of the transfer material by the opposite polarity toner can be reduced, and the transfer member surface and It is possible to provide a specific effect that the deterioration of the lining member due to mechanical damage and the burden of replacing the member due to the deterioration can be reduced.

According to the third aspect of the present invention, the toner adhering to the surface of the transfer member is given a charge of a predetermined polarity and charged up by the toner charge-up means. By this charge application, the charged toner of a predetermined polarity increases the charge amount, and the polarity of the opposite polarity toner attached to the surface of the transfer member is inverted to a predetermined polarity. Thereby, the toner adhering to the surface of the transfer member can be easily cleaned by the cleaning electric field.

According to the fourth aspect of the present invention, a charge having a polarity opposite to the predetermined polarity is applied to the transfer material on the transfer member by the suction means, and the transfer material is suctioned to the transfer member. This stabilizes the transfer of the transfer material at the transfer unit, and reduces transfer failure due to a relative positional shift between the image carrier and the transfer material. Furthermore, during the period when the transfer material does not exist in the transfer member,
The polarity of the applied charge can be switched by setting the applied charge polarity of the adsorption means to a predetermined polarity and operating the toner to charge the toner on the transfer member surface to a predetermined polarity. In this way, by using the suction means also as the toner charge-up means, the number of parts and the cost can be reduced, or the size of the apparatus can be reduced.

According to the fifth aspect of the present invention, the transfer of the transfer material in the transfer section is stabilized by using the suction means in the same manner as described above in the fourth aspect, so that the relative position between the image carrier and the transfer material can be improved. Transfer defects due to misalignment are reduced. In this case, since the suction means uses the electrode member arranged in contact with the transfer material, there is a possibility that charged toner of a predetermined polarity adhering to the surface of the transfer member is transferred to the surface of the electrode member. is there. This transition is caused by an arrangement setting (for example, an arrangement setting in which the electrode member and the transfer member are in contact with each other in a state where the transfer material is not interposed) and a setting of the mutual electric potential state.
This is caused by directly facing the surface of the transfer member when the transfer material is not interposed. When such a transfer of the charged toner having the predetermined polarity to the surface of the electrode member occurs, the transferred charged toner having the predetermined polarity is transferred to the surface of the transfer material that comes into contact with the electrode member, and the toner on the surface of the transfer material is transferred. It causes dirt. Therefore, in the invention of claim 5, when the transfer material is supplied to the transfer member by the transfer material supply means, the transfer material from the transfer material supply means reaches a contact portion with the electrode member. Before that, the operation of applying the charge of the predetermined polarity is performed to the adsorption means configured to be able to switch the polarity of the applied charge. By this charge application, the charged toner having a predetermined polarity attached to the electrode member is transferred from the electrode member to the transfer member, and the electrode member is cleaned. This reduces toner contamination on the surface of the transfer material that comes into contact with the electrode member thereafter.

In the sixth aspect of the present invention, the electrode function is exhibited while the roller member as the electrode member is not rotated. For this reason, it is possible to replace the contact portion with the transfer material on the transfer member, for example, compared with the case of using a fixing member such as a brush or a resin film, it is possible to suppress the aging of the electrode member due to the contact, The life of the electrode member can be extended. Since the operation of applying the electric charge having the predetermined polarity is performed for one or more rotations of the roller member, before the transfer material from the transfer material supply unit reaches the contact portion with the roller member as the electrode member. The cleaning can be performed on the entire circumference of the roller member.

According to the seventh aspect of the present invention, similarly to the second aspect of the present invention, by using the cleaning electric field forming means and the cleaning member, the cleaning member for cleaning only by mechanical force can be provided. As compared with the case where the transfer member is used, deterioration due to mechanical damage to the surface of the transfer member and the cleaning member, and a member replacement work load due to the deterioration can be reduced. In addition, since the cleaning electric field forming means suctions the toner to the charged toner cleaning member having a predetermined polarity, the toner having the predetermined polarity transferred from the electrode member to the transfer member along with the cleaning of the electrode member can be removed. Then, the transfer member can be cleaned.

Further, in the invention according to claim 8, the transfer material is carried and transferred by the transfer member, and a plurality of transfer electric fields are formed by the transfer electric field forming means provided for each of the plurality of image carriers. And the toner images on the plurality of image carriers are transferred to a transfer material. The control for operating the transfer electric field forming means at the non-transfer time as described in claim 1 is performed by controlling the transfer electric field forming means corresponding to the image carrier located at the most downstream position in the endless movement direction of the transfer member. Let only do it. If the transfer electric field forming means corresponding to the most downstream image carrier is actuated, even if the opposite polarity toner is mechanically transferred from the image carrier on the more upstream side to the transfer member in the same direction, the reverse is performed. The polar toner can be transferred to the most downstream image carrier and removed from the transfer member. In addition, since the image carrier on the upstream side is not controlled to operate the transfer electric field forming means at the non-transfer time, the transfer electric field formation at the non-transfer time without the transfer material is performed for these image carriers. By operating the means, it is possible to prevent the deterioration of the image carrier due to charging and the unevenness of the image density due to the potential unevenness of the image carrier.

In the ninth aspect of the present invention, the reverse polarity toner attached to the surface of the intermediate transfer member as the image carrier is transferred to the surface of the transfer member in the same manner as described above. This can reduce the stain on the back side of the transfer material caused by the transfer.

In the tenth aspect of the present invention, the operating condition of the transfer electric field forming means in the non-transfer period corresponds to an electric field intensity smaller than the electric field intensity in the period when the transfer material exists in the transfer portion. Therefore, compared to the case where the transfer unit is operated under the operation condition corresponding to the electric field strength at the time when the transfer material is present in the transfer unit, the deterioration due to the charge of the image carrier due to the formation of the transfer electric field without the transfer material interposed therebetween And image density unevenness caused by potential unevenness of the image carrier can be reduced.

According to the eleventh aspect of the present invention, since the transfer member having a volume resistivity in a predetermined range is used, the transfer member has a higher resistivity than the range. Charge-up of the transfer member due to repeated exposure of the member to the transfer electric field can be sufficiently suppressed by a simple static elimination structure in which a support member for supporting the transfer member is formed of a conductor and grounded.

In a twelfth aspect of the present invention, the control means activates the transfer electric field forming means at a non-transfer time when the toner image on the image carrier is not transferred in the first transfer section, and To form a transfer electric field. The transfer electric field exerts an electrostatic force from the surface of the image carrier toward the surface of the intermediate transfer member for the toner of a predetermined polarity, and an opposite electrostatic force for the toner of the opposite polarity. Therefore, by forming a transfer electric field in the transfer portion during the non-transfer period, the opposite polarity toner adhered to the surface of the image carrier is less likely to be transferred to the surface of the intermediate transfer member. Therefore, a unique effect can be achieved in that the reverse polarity toner is transferred to the intermediate transfer member, and further, the back contamination of the transfer material, which is generated by transferring from the intermediate transfer member to the transfer member of the second transfer portion, can be reduced. .

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of a transfer unit of a laser printer according to an embodiment.

FIG. 2 is a schematic configuration diagram of the laser printer.

FIG. 3 is an enlarged view showing a schematic configuration of a toner image forming unit of the laser printer.

FIG. 4A is an enlarged view of the transfer unit 6 at the time of executing the full color mode. FIG. 4B is an enlarged view of the transfer unit 6 when executing the monochrome mode.

FIG. 5 is a timing chart illustrating an example of timing control of the laser printer during an initial operation.

FIG. 6 is a timing chart illustrating an example of timing control of a laser printer during an image forming operation.

FIG. 7 is a schematic configuration diagram of an intermediate transfer unit of a laser printer according to another embodiment.

[Explanation of symbols]

 Reference Signs List 1 toner image forming unit 6 transfer unit 9 transfer bias power supply 10 photoreceptor unit 11 photoreceptor drum 20 developing unit 60 transfer / transport belt 61-64 support roller 70 cleaning device 71 cleaning roller 73 opposing roller 75 cleaning bias power supply 100 transfer paper 200 intermediate Transfer unit 201 Intermediate transfer belt 202-205 Support roller 210 Cleaning device 211 Cleaning roller 213 Opposing roller

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2H030 AA06 AB02 AD03 BB27 BB44 BB46 BB52 BB54 2H032 AA05 BA04 BA18 BA30 CA01 CA11 2H074 AA03 BB60 CC21

Claims (12)

[Claims] An image bearing member on which a toner image formed of a charged toner having a predetermined polarity is formed, and a surface moves along an endless path including a transfer portion facing the image bearing member, and the image bearing member moves on the transfer portion. Image forming apparatus comprising: a transfer member for causing a transfer material to face a body; and a transfer electric field forming means for forming an electric field in the transfer portion for moving the toner having the predetermined polarity from the image carrier to the transfer member side. The image forming apparatus according to claim 1, further comprising control means for operating said transfer electric field forming means at a non-transfer time when there is no transfer material in said transfer section. 2. The image forming apparatus according to claim 1, wherein said cleaning member opposing a surface of said transfer member, and said charged toner having a predetermined polarity is interposed between said cleaning member and said transfer member. And a cleaning electric field forming means for forming a cleaning electric field to be attracted to the cleaning member side. 3. The image forming apparatus according to claim 2, further comprising a toner charge-up means for applying a charge of the predetermined polarity to the toner attached to the surface of the transfer member to charge up the toner. Image forming device. 4. An image forming apparatus according to claim 3, further comprising: suction means for applying a charge having a polarity opposite to the predetermined polarity to the transfer material on the transfer member and sucking the transfer material on the transfer member.
An image forming apparatus, wherein the polarity of the charge applied by the suction means is switchable, and the suction means is also used as the toner charge-up means. 5. An image forming apparatus according to claim 1, wherein said transfer material is supplied to said transfer member by a transfer material supply means, and said electrode member is in contact with said transfer material supplied on said transfer member. An adsorbing means for applying an electric charge having a polarity opposite to the polarity and adsorbing the electric charge on the transfer member, the adsorbing means being configured to be able to switch the polarity of the applied electric charge, and When the transfer material is supplied to the contact member, before the transfer material from the transfer material supply unit reaches the contact portion with the electrode member, the operation of applying the charge of the predetermined polarity is performed by the suction unit. Characteristic image forming apparatus. 6. The image forming apparatus according to claim 5, wherein a rotatable roller member is used as the electrode member, and the operation of applying the charge of the predetermined polarity is performed for at least one rotation of the roller member. Characteristic image forming apparatus. 7. The image forming apparatus according to claim 5, wherein
A cleaning member facing the surface of the transfer member, and a cleaning electric field for attracting the charged toner having the predetermined polarity to the cleaning member side between the cleaning member and the transfer member. An image forming apparatus comprising an electric field forming means. 8. The image forming apparatus according to claim 1, wherein a plurality of said image carriers are provided, and each of said plurality of image carriers is opposed to each of said plurality of image carriers as said transfer member. The transfer surface forming means is provided for each of the plurality of image carriers using a member whose surface moves along an endless path including a plurality of transfer portions. An image forming apparatus characterized in that only the one corresponding to the image carrier located at the most downstream position in the endless movement direction is operated at the non-transfer timing. 9. The method of claim 1, 2, 3, 4, 5, 6, 7 or 8.
The image forming apparatus according to claim 1, wherein the image carrier is an intermediate transfer member to which a toner image is transferred from another image carrier on which a toner image is formed. 10. The method of claim 1, 2, 3, 4, 5, 6, 7, or 8.
Alternatively, in the image forming apparatus according to the ninth aspect, the operating condition of the transfer electric field forming means in the non-transfer period corresponds to an electric field intensity smaller than the electric field intensity when the transfer material exists in the transfer portion. Image forming device. 11. The method of claim 1, 2, 3, 4, 5, 6, 7,
8. The image forming apparatus according to 8, 9, or 10, wherein the transfer member is a belt rotatably supported by two or more support members, wherein the transfer member is 10 degrees Celsius and 15% humidity to 30 degrees Celsius and 90% humidity. An image forming apparatus characterized in that a change in volume resistivity within the range of 1 × 10 ⁹ to 1 × 10 ¹¹ within the environmental fluctuation is used. 12. An endless path including an image carrier on which a toner image composed of a charged toner having a predetermined polarity is formed, and a first transfer section facing the image carrier and a second transfer section facing the transfer material. Image forming apparatus, comprising: an intermediate transfer member having a surface that moves in a vertical direction; and a transfer electric field forming unit that forms an electric field in the first transfer portion in a direction to move the toner having the predetermined polarity from the image carrier to the intermediate transfer member. 2. The image forming apparatus according to claim 1, further comprising control means for operating the transfer electric field forming means at a non-transfer time when the toner image on the image carrier is not transferred by the first transfer portion.