JP4294714B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus such as a copying machine, a printer, and a facsimile machine. More specifically, the present invention relates to an image carrier on which a toner image made of a charged toner having a predetermined polarity is formed, and a transfer material is opposed to the image carrier in a transfer unit. The present invention relates to an image forming apparatus having a transfer member to be transferred and a transfer electric field forming means for forming an electric field in a transfer portion.

  Conventionally, a surface moves along an endless path including an image carrier on which a toner image made of charged toner of a predetermined polarity is formed and a transfer unit facing the image carrier, and is transferred to the image carrier by the transfer unit. 2. Description of the Related Art An image forming apparatus having a transfer member that opposes a material and a transfer electric field forming unit that forms an electric field in a direction to move the toner of the predetermined polarity from the image carrier to the transfer member side in the transfer portion is known. It has been.

In such an image forming apparatus, even in a non-image area where a toner image to be transferred to a transfer material is not formed on the surface of the image carrier, the potential difference between the developing member of the developing device and the surface of the image carrier There is toner that has been transferred from the developing member to the image carrier by mechanical contact, or adhered for other reasons . Their to said transfer member is a timing opposite to the image carrier directly without the intervention of the transfer material. Therefore, depending on the electrostatic state such as the potential of the surface of the image carrier at this timing and the electric field generated by the transfer electric field forming unit, or the mechanical state of direct contact or separation, the surface of the image carrier belt toner adhering to is transferred to the transfer member surface.
Also, the image forming apparatus has an adsorbing unit that applies an electric charge having a polarity opposite to a predetermined polarity via an electrode member that contacts the transfer material supplied on the transfer member, and adsorbs the transfer material to the transfer member There is. By using the suction unit, the transfer material conveyance at the transfer unit is stabilized, and transfer defects due to the relative displacement between the image carrier and the transfer material are reduced. In such an image forming apparatus, since the adsorbing means uses an electrode member arranged in contact with the transfer material, there is a possibility that the charged toner having a predetermined polarity attached to the transfer member surface may be transferred to the electrode member surface. . 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 no transfer material is present) and a potential state of each other, and the transfer member surface is not in the period when the transfer material is not present. It is caused by directly facing each other. When the 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 then the toner on the surface of the transfer material. It will cause dirt.

  The above-described backside contamination of the transfer material is caused by an image carrier on which a toner image made of charged toner of 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 body whose surface moves along an endless path including the transfer field, and a transfer electric field forming means for forming an electric field in a direction for moving the toner of the predetermined polarity from the image carrier to the intermediate transfer body side in the first transfer portion It can also occur in an image forming apparatus having When the reverse polarity toner is transferred to the intermediate transfer member by mechanical contact or the like at a non-transfer time when the toner image on the image carrier is not transferred by the first transfer unit, this is further transferred from the intermediate transfer member to the second transfer member. This is because it may be transferred to the transfer member of the transfer portion and attached to the back surface of the transfer material.

The present invention has been made in view of the above problems, and the object of the present invention is to transfer a charged toner of a predetermined polarity attached to an electrode member by applying a charge to the surface of a transfer material that contacts the electrode member thereafter. Thus, it is an object of the present invention to provide a novel image forming apparatus capable of reducing the occurrence of toner contamination on the surface of a transfer material .

In order to achieve the above object, the inventions of claims 1 to 3 are arranged along an endless path including an image carrier on which a toner image made of charged toner of a predetermined polarity is formed and a transfer portion facing the image carrier. A transfer member that causes the transfer surface to move the transfer material to face the image carrier at the transfer portion, and an electric field that moves the toner of the predetermined polarity from the image carrier to the transfer member side at the transfer portion. And a transfer material supply means for supplying a transfer material to the transfer member, and an electrode that is a rotating body that contacts the transfer material supplied on the transfer member member and the predetermined polarity is provided a suction means for attracting the said transfer Utsushiyo member transfer material by applying a reverse polarity of the bias, the transfer material that is fed subjected to the transfer member in the transfer material supply means before reaching the contact portion between the electrode member, A bias having the same polarity as that of the predetermined polarity is applied to the electrode member over a time equal to or longer than one rotation of the electrode member, and then the electrode member is moved more than the time when the transfer material reaches the contact portion with the electrode member. The bias applied to the electrode member is switched from the predetermined polarity to a polarity opposite to the predetermined polarity at a time point before the rotation time .

In the first to third aspects of the present invention, when the transfer material is supplied to the transfer member by the transfer material supply means, before the transfer material from the transfer material supply means reaches the contact portion with the electrode member. In addition, an operation of applying the charge of the predetermined polarity is performed on the suction means configured to be able to switch the polarity of the applied charge. Due to 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 to clean the electrode member. As a result, it is possible to achieve a specific effect that toner contamination on the surface of the transfer material that subsequently contacts the electrode member can be reduced.

In particular, such rotate the rotating member as the upper Symbol electrode member, because that Ru is exhibited electrode function can swap a region of contact between the transfer material on the transfer member, for example, fixed, such as a brush or a resin film Compared with the case of using a member, the electrode member can be prevented from being deteriorated with time by the contact, and the life of the electrode member can be extended.
And, since the operation of applying the charge of the predetermined polarity is performed for a time of one rotation or more of the rotating body, before the transfer material from the transfer material supply means reaches the contact portion with the rotating body as the electrode member, The cleaning can be performed on the entire circumference of the rotating body.
Further, since the transfer material from the top Symbol transfer material supply means reaches the contact portion between the electrode member, before or one revolution time of the electrode the electrode member, said predetermined charge to be applied by the suction means Switch to the opposite polarity of the polarity.

In the invention of 請 Motomeko 2, the cleaning electric field forming unit, between the cleaning member to the surface facing thereto of the transfer member, the electric field for cleaning for sucking the charged toner of a predetermined polarity to the cleaning member side Form. By this electric field for cleaning, 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 in this manner, for example, the cleaning member is used for transfer as compared with the case where a cleaning member such as a cleaning blade or a member that cleans only with a mechanical force such as a toner damming force is used. There is little mechanical damage to the surface of the member or the member for craning.

In the invention of 請 Motomeko 3, the toner is in a manner similar to that described above for claim 1 adhered to the surface of the intermediate transfer member as an image bearing member is transferred to the transfer member surface, the electrode in the charge imparting It can be reduced that the charged toner having a predetermined polarity attached to the member is transferred to the surface of the transfer material that comes into contact with the electrode member and becomes a toner stain on the surface of the transfer material.

Embodiment 1
Hereinafter, an embodiment in which the present invention is 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 includes four toner image forming units 1Y, 1M, 1C, 1K (hereinafter referred to as “yellow” (Y), magenta (M), cyan (C), and black (K)). The subscripts Y, M, C, and K of each symbol indicate yellow, magenta, cyan, and black members, respectively). These are arranged in the order described above 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 includes a photoconductor unit having photoconductor drums 11Y, 11M, 11C, and 11K as image carriers, and a developing unit. The rotation axes of the photosensitive drums in the respective photosensitive units are parallel to each other, and are set at positions spaced by a predetermined pitch in the transfer paper moving direction.

  In addition to the toner image forming units 1Y, 1M, 1C, and 1K, the laser printer includes a light source, a polygon mirror, an f-θ lens, a reflection mirror, and the like, and the photosensitive drums 11Y and 11M are based on image data. , 11C, 11K are provided with an optical writing unit 2 that irradiates the laser beam while scanning it. Further, as a belt device having a transfer conveyance belt 60 as a transfer member that carries the sheet feeding cassettes 3 and 4, the registration roller pair 5, and transfer paper and conveys it so as to pass the transfer position of each toner image forming unit. A transfer unit 6 is provided. Furthermore, a belt fixing type fixing unit 7, 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.

  A one-dot chain line in FIG. 2 represents a transfer paper conveyance path. The transfer paper fed from the paper feed cassettes 3 and 4 is conveyed by a conveyance roller while being guided by a conveyance guide (not shown), and is sent to a temporary stop position where the registration roller pair 5 is provided. The transfer paper sent at a predetermined timing by the registration roller pair 5 is carried by the transfer conveyance belt 60 and conveyed so as to pass through the transfer positions of the toner image forming portions 1Y, 1M, 1C, and 1K. The transfer paper on which the toner images of the respective toner image forming portions 1Y, 1M, 1C, and 1K are transferred to form a color image is discharged onto the paper discharge tray 8 after the toner image is fixed by the fixing unit 7.

FIG. 3 is an enlarged view showing a schematic configuration of the yellow toner image forming unit 1Y among the toner image forming units 1Y, 1M, 1C, and 1K. Since the other toner image forming units 1M, 1C, and 1K have the same configuration, their descriptions are omitted.
In FIG. 3, the toner image forming unit 1Y includes the photosensitive unit 10Y and the developing unit 20Y as described above.
In addition to the photosensitive drum 11Y, the photosensitive unit 10Y includes a brush roller 12Y that applies a lubricant to the surface of the photosensitive drum, a swingable counter blade 13Y that cleans the surface of the photosensitive drum, and a surface of the photosensitive drum. A non-contact type charging roller 15Y that is uniformly charged is provided. As the photoreceptor drum of each photoreceptor unit, a photoreceptor drum having a diameter of 30 mm and having an organic photoreceptor (OPC) layer on the surface thereof was used.
The developing unit 20Y uses a two-component developer containing a negatively charged toner having a magnetic carrier and a desired charged polarity (hereinafter referred to as normal polarity). Then, the developing roller 22Y as a developer carrying member disposed so as to be partially exposed from the opening on the photosensitive drum side of the developing case 21Y, the conveying screws 23Y and 24Y, the developing doctor 25Y, a toner concentration sensor (T sensor). ) 26Y, powder pump 27Y and the like. The developer accommodated in the developing case 21Y is frictionally charged by being agitated and conveyed by the conveying screws 23Y and 24Y. A part of the developer is carried on the surface of the developing roller 22Y, the layer thickness is regulated by the developing doctor 25Y, and then conveyed to the developing position facing the photosensitive drum 11Y. At the development position, the electrostatic latent image on the photosensitive drum 11Y is developed by the toner in the developer on the development roller. The toner density of the developer in the developing case 21Y is detected by the toner density sensor 26Y, and the toner is replenished by the powder pump 27Y as necessary.

  In the toner image forming unit having the above configuration, the optical writing unit is formed on the surface of the photosensitive drum 11Y uniformly charged to minus 700 volts, which is the same polarity as the normal polarity of the toner, by the charging roller 15Y to which an AC voltage is applied. When the laser beam modulated and deflected by 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 photoconductive drum 11Y is reversely developed using negatively charged toner in the developing unit 20Y to become a yellow toner image. At the transfer position Pt where the transfer paper 100 on the transfer conveyance belt 60 passes, the toner image on the photosensitive drum 11Y is transferred to the transfer paper 100. After the toner image is transferred, the surface of the photosensitive drum 11Y 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 configuration diagram of the transfer unit 6. The transfer conveyance belt 60 used in the transfer unit 6 has a volume resistivity change of 1 × 10 ⁹ to 1 × 10 ¹¹ Ω · within an environmental variation of 10 degrees Celsius and 15 percent humidity to 30 degrees Celsius and 90 percent humidity. It is an endless single-layer belt that falls within the range of cm . The material is, for example, PVDF (polyvinylidene fluoride). The transfer / conveying belt 60 is wound around four grounded support rollers 61 to 64 so as to pass through the transfer positions in contact with and opposed to the photosensitive drums 11Y, 11M, 11C, and 11K of the toner image forming units. ing. 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 attracting roller 65 is disposed opposite to the inlet roller 61 on the upstream side of the support rollers 61 to 64 in the transfer sheet moving direction. The electrostatic attraction roller 65 has a conductive foam elastic body layer formed on a cored bar. For example, chloroprene rubber having a specific resistivity of 10 ⁵ Ωcm is used as the elastic layer material. The electrostatic attraction roller 65 is selectively applied with a voltage from an attraction power source 65a and a reverse polarity power source 65b. The power source 65a for adsorption is for applying a positive polarity charge opposite to the normal polarity of the toner to the transfer paper. For example, a constant current power source of plus 15 μA is used. The transfer paper that has passed between the electrostatic attraction roller 65 and the entrance roller 61 in a state where power is supplied from the attraction power source 65 a is electrostatically adsorbed on the transfer conveyance belt 60. The power supply 65b for reverse polarity increases the charge of negatively charged toner, which is the normal polarity on the transfer conveyance belt 60, reverses positively charged reverse polarity toner to positive polarity, This is for transferring the negatively charged toner adhering to the surface of the roller 65 to the surface of the transfer / conveying belt 60. For example, a constant voltage power source of minus 2 KV is used. The voltage applied to the electrostatic attraction roller 65 is switched by a main body control plate (not shown). The control by the main body control plate will be described in detail later.

Further, as a transfer electric field forming means for forming a transfer electric field at each transfer position, the transfer bias applying member 67Y, so as to come into contact with the back surface of the transfer conveyance belt 60 that forms a transfer nip in contact with the photosensitive drum. 67M, 67C, and 67K are provided. The transfer bias applying members 67Y, 67M, 67C, and 67K are fixed brushes made of conductive mylar, and transfer bias is applied from the transfer bias power supplies 9Y, 9M, 9C, and 9K. The transfer bias applied by the transfer bias applying member applies a transfer charge 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. The
In this embodiment, as the transfer bias power supplies 9Y, 9M, 9C, and 9K, constant current power supplies having a positive polarity that is opposite to the normal polarity of the toner are used. Among these, the transfer bias power supply 9K corresponding to the black photoconductor 9K located at the most downstream side in the moving direction of the transfer conveyance belt 60 in the transfer sheet conveyance range is configured such that the current value can be switched between, for example, plus 15 μA and plus 10 μA. Yes. The main body control plate also controls the on / off of each transfer bias power source and the current value switching of the black transfer bias power source 9K. The control by the main body control plate will also be described in detail later.

  Further, backup rollers 68Y, 68M, 68C, and 68K that press the transfer / conveying belt 60 toward the photosensitive drum are provided corresponding to the photosensitive drums 11Y, 11M, 11C, and 11K. Each of the backup rollers 68Y, 68M, 68C, and 68K partially wraps the transfer conveyance belt 60 around the circumferential surface of the photosensitive drum 11Y on the upstream side of the transfer position in the transfer sheet moving direction. Thereby, the contact pressure between the transfer paper 100 and each photosensitive drum in the transfer nip is increased, and the transfer efficiency at the transfer position is increased.

A cleaning device 70 that cleans the toner adhering to the surface of the transfer conveyance belt 60 is disposed on the 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. 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 property 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 counter roller 73 material. In this example, the opposing roller 73 is constituted by a sponge roller having an elastic foam layer made of a conductive sponge material on a core metal roller. Further, as the cleaning electric field forming unit, a cleaning roller 71 having the conductivity, the cleaning bias power source 75 is a voltage applying means for applying a voltage to the cleaning roller 71, and the counter roller 7 3 connected to ground The power supply 75 applies a voltage having a polarity (plus) opposite to the normal polarity (minus) of the toner to the cleaning roller 71. As a result, an electric field is formed in the cleaning nip, which is a contact portion between the transfer conveyance belt 60 and the cleaning roller 71, so that the negatively charged toner moves from the transfer conveyance belt 60 to the cleaning roller 71 side. The toner attached to the transfer conveyance belt 60 by this electric field is moved to the cleaning roller 71 side, and the toner is removed from the surface of the transfer conveyance belt 60. The toner moved to the cleaning roller 71 side is scraped off by the cleaning blade 72 and removed from the surface of the roller 71.

4A and 4B are enlarged views of the transfer unit 6 when the full color mode is executed and when the monochrome mode is executed, respectively. The transfer unit 6 according to the present embodiment includes a transfer unit main body 600 that is fixedly arranged with respect to the apparatus main body, and a transfer subunit 601 that can swing around a swing shaft 602 provided on the transfer unit main body side. . The transfer unit main body 600 supports a black transfer bias applying member 67K, a backup roller 68K, support rollers 61 to 64, an eccentric cam 603 for swinging the transfer subunit 601, and the like. 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, as an urging means for urging the transfer subunit 601 to be separated from the color photosensitive drums 11Y, 11M, and 11C between the swing end portion of the transfer subunit 601 and the transfer unit main body 600. A spring is attached. The eccentric cam 603 is attached so as to be in contact with the lower surface of the swing end portion of the transfer subunit 601 and is rotationally driven 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 oscillating end of the transfer subunit 601 is pushed up against the urging force of the spring 604. As a result, the transfer conveyance belt 60 and all the photosensitive drums come into contact with each other, and each color toner image on each photosensitive drum can be transferred onto the transfer paper on the transfer conveyance belt 60 in an overlapping manner.
When the monochrome mode shown in FIG. 4B is executed, the eccentric cam 603 is rotated to a position where the push-up force with respect to the swing end of the transfer subunit 601 is released. As a result, the oscillating end of the transfer subunit 601 is pushed down by the urging force of the spring 604, the transfer conveyance belt 60 and the color photosensitive drums 11Y, 11M, and 11C are separated from each other, and the black on the photosensitive drum 11K. Only the toner image can be transferred onto the transfer paper on the transfer conveyance belt 60.
Further, in the present embodiment, during the initial operation immediately after the laser printer is turned on or during the cleaning operation of the transfer / conveying belt 60 that is appropriately performed, only the black photosensitive drum 11K contacts the transfer / conveying belt 60 (FIG. 4). The state of b) is taken.

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. During this initial operation, as described above, only the black photosensitive drum 11 shown in FIG. 4B is in contact with the transfer conveyance belt 60, so that the color photosensitive drum remains non-rotated and is applied to the transfer bias applying member. The bias application is still off. 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 driving of the transfer conveyance belt 60, the cleaning roller 71 , and the suction roller 65 is started. Is done. In synchronization with this, a cleaning positive voltage is applied to the cleaning roller 71 . As a result, for a while after the power is turned on, the normal polarity (minus) charged toner adhering to the transfer conveyance belt 60 is cleaned. At this time, in order to facilitate transfer of the normal polarity (minus) charged toner on the transfer conveyance belt to the cleaning roller 71 , a negative voltage having a polarity opposite to the transfer material suction voltage is applied to the suction roller 65. . Further, the transfer bias applying member 67 is provided with a transfer in the image forming operation so that the toner charged to the reverse polarity (plus) attached to the surface of the photosensitive drum 11 is not easily transferred to the surface of the transfer conveyance belt 60. The same plus voltage as the transfer bias at the time is applied. This positive voltage may be controlled at a constant current of plus 15 μA as in the later-described transfer. However, in this embodiment, in order to reduce the potential history on the photosensitive member due to the transfer bias applied without the transfer paper interposed. The constant current is controlled at minus 10 μA so as to make the transfer field weaker. The voltage application 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. This delay time T1 is a time required for the drive motor of the photosensitive drum 11K to rise.

  Then, after the transfer / conveying belt 60 is cleaned for a predetermined time, in order to clean the suction roller 65, a positive voltage and a negative voltage are alternately applied to the suction roller 65 for each predetermined time t. In the example of FIG. 5, the time t corresponds to the time for two rotations of the suction roller 65, and a positive voltage controlled at a constant current of 20 μA and a negative voltage of 2 kV are alternately four times for each time t for the two rotations. The main body control plate switches and controls which of the power source 65a for adsorption and the power source 65b for reverse polarity is applied from the main body control plate. Thereby, the negatively charged toner and the positively charged toner adhering 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.

The cleaning roller 71 is controlled so that a positive voltage for cleaning is continuously applied to the cleaning roller 71 during the cleaning of the suction roller 65 and for a predetermined time after the cleaning is completed. As a result, the negatively charged toner transferred from the suction roller 65 to the transfer conveyance belt 60 is cleaned. The control unit stops the photosensitive drum 11, the cleaning roller 71 , the suction roller 65, and the transfer conveyance belt 60, and at the same time, the cleaning bias power source 75 , the power sources 65a and 65b connected to the suction roller 65, and the transfer bias. The power supply 9K is turned off and the initial operation is terminated. 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.

Figure 6 is a timing chart showing an example of a timing control of the laser printer during the image forming operation of the monochrome mode. This timing chart assumes that two identical black images (A4 horizontal size) are printed continuously.
When an external print start signal is input, first, the drive motor for the photoconductive drum 11K is turned on and the photoconductive drum 11K is driven to rotate. At the same time, the transfer conveyance belt 60, the cleaning roller 71 , and the suction roller 65 Rotational driving is also started. In synchronization with this, with a positive voltage for cleaning is applied to the cleaning roller 71, the suction roller 65, to easily transfer the negatively charged toner on the transfer conveyor belt, as described above the cleaning roller 71 Minus 2 KV is applied from the power supply 65b having the reverse polarity. Next, voltage application to the charging roller 15K is started with a delay of T1. This delay time T1 is a time required for the drive motor of the photosensitive drum 11K to rise. Further, 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. As in the initial operation, the transfer bias is controlled at a constant current of minus 10 μA so that a weak transfer electric field is applied in order to reduce a potential history on the photosensitive member due to the transfer bias applied without the transfer paper interposed. . 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 predetermined time has elapsed, a registration clutch (not shown) that operates the registration roller pair 5 (see FIG. 1) is turned on at a predetermined timing. At the same time, the voltage applied to the suction roller 65 is switched to the suction power supply 65a, and 15 μA A positive voltage controlled at a constant current is applied to. In the present embodiment, at least the attraction roller 65 rotates at least once during the time T3 from when the registration clutch is turned on until the leading edge of the transfer paper 100 reaches the facing portion between the transfer conveyance belt 60 and the attraction roller 65. It has a configuration like this. Therefore, the control unit performs switching control from the reverse polarity power source 65b to the suction power source 65a at least before the time corresponding to one rotation of the suction roller 65 when the leading edge of the transfer paper 100 reaches the facing portion. By such control, the negatively charged toner that still adheres 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 following the application of a positive voltage for attracting the transfer material thereafter. Can be reduced. Then, while a positive voltage controlled at a constant current of 15 μA is continuously applied to the suction roller 65, a charge is applied to the transfer paper 100 that reaches and reaches the facing portion, and the transfer paper 100 is statically applied to the transfer conveyance belt 60. Electroadsorb. Subsequently, at a timing T4 immediately before the leading edge of the transfer paper on the transfer conveyance belt 60 reaches the transfer position, the constant current control value of the transfer bias is switched to a stronger value of 15 μA.

After the first image is formed, the second image is continuously formed. Immediately after the rear end of the first transfer paper 100 passes through the opposing portion, the main body control plate changes the voltage applied to the suction roller 65 from the positive voltage from the suction power source 65a to the reverse polarity power source 65b. After switching to the negative voltage, at the timing when the leading edge of the second transfer paper 100 reaches the facing portion, the voltage is switched again to the positive voltage from the suction power source 65a. That is, a negative voltage from the power supply 65b for reverse polarity is applied to the suction roller 65 during the paper interval T5. Further, the transfer bias is also controlled at a constant current during the period T6 between the sheets at a weak 10 μA so as to make the transfer 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 constant current control is continued at a strong transfer bias of 15 μA. For a while after the image formation of the second sheet is completed, the positive voltage for cleaning is continuously applied to the cleaning roller 71 and the negative voltage switched in accordance with the passage of the trailing edge of the second sheet of transfer paper is continuously applied. Next, the photosensitive drum 11K, the cleaning roller 71 , the suction roller 65, and the transfer conveyance belt 60 are stopped, and the voltage application to the charging roller 15K, the cleaning roller 71 , and the suction roller 65 is also stopped. In the illustrated example, the transfer bias is turned off as the trailing edge of the second transfer sheet passes through the transfer position. However, the weak transfer electric field is switched to a weak transfer electric field in accordance with this passage. May be applied for a while.

In the present embodiment, although take the state where the initial contact operation or monochrome mode in the photosensitive member 11K only transfer conveyance belt 60 for black as shown in FIG. 4 (b), the initial operation or monochrome mode Sometimes, as shown in FIG. 4A, all the photoconductors may be brought into contact with the transfer conveyance belt. In this case, all the photosensitive drums in contact with the transfer conveyance belt 60 may be rotationally driven, and transfer bias application may be performed on all of these photosensitive drums without the transfer paper interposed at the transfer position. However, the transfer bias may be applied only to the black photoconductor 11K located on the most downstream side. 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 interposed. Moreover, even if the reversely charged toner (plus) transfer from the upstream photosensitive drums 11Y, 11M, and 11C to the transfer conveyance belt 60 occurs, the transfer conveyance belt at the transfer position of the most downstream black photosensitive drum 11K. Since the toner can be transferred from 60 to the black photosensitive drum 11K, the purpose of removing the reversely charged toner from the transfer conveyance belt 60 can be achieved. The reversely charged toner transferred from the transfer conveyance belt 60 to the photosensitive drum 11 is removed from the surface of the photosensitive drum by the photosensitive member cleaning device 10.

[Embodiment 2]
In Embodiment 1 described above, the present invention is applied to an image forming apparatus that transfers a toner image on a photosensitive drum onto a transfer sheet carried on a transfer conveyance belt as a transfer member. 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 a transfer sheet 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-like 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 the arrow direction in the figure. The toner images formed on the photoconductive drums 11Y, 11M, 11C, and 11K of the respective toner image forming units are primary transfer rollers 206Y provided so as to face the photoconductive drums with the intermediate transfer belt 201 interposed therebetween. The images are sequentially transferred onto the intermediate transfer belt 201 by a primary transfer electric field formed by 206M, 206C, 206K and primary transfer bias power supplies 209Y, 209M, 209C, 209K. The color image on the intermediate transfer belt 201 is collected on the transfer paper 100 carried on the transfer conveyance belt 60 in the secondary transfer unit provided in the vicinity of the fourth color black toner image forming unit. Secondarily transferred. Similar to the transfer and transport belt 60 in the printer of the first embodiment, this transfer and transport belt 60 employs a cleaning device 70 of a bias cleaning system, and uses a suction roller 65. Corresponding members are denoted by the same reference numerals and description thereof is omitted.
Also in this embodiment, if at least one of the primary transfer bias and the secondary transfer bias is biased to a polarity opposite to that of the normal polarity toner at the non-transfer timing, each of the transfer source members (photoconductor for primary transfer) 11. For secondary transfer, reverse polarity toner adhering to the intermediate transfer belt 201) is a transfer destination side member (intermediate transfer belt 201 for primary transfer, transfer conveyance for secondary transfer). The transfer to the belt 60) and contamination can be reduced. Also, as shown in the example, when a bias cleaning type cleaning device is used as a cleaning device for the transfer destination side member, the reverse polarity toner is difficult to clean by this bias cleaning method and is transferred from the transfer source member. This is preferable because it can be suppressed.
Then, the suction roller 65 is also used as a charge-up unit, voltage application from the suction power source 65a is started before the transfer paper is opposed to the suction roller 65, and the most downstream photosensitive drum among the plurality of photosensitive drums. If only the transfer bias is applied at the time of non-transfer, the same advantage as in the first embodiment is obtained.

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. 2 is an enlarged view showing a schematic configuration of a toner image forming unit of the laser printer. (A) is an enlarged view of the transfer unit 6 when the full color mode is executed. FIG. 6B is an enlarged view of the transfer unit 6 when the monochrome mode is executed. 3 is a timing chart showing an example of laser printer timing control during initial operation. 4 is a timing chart showing an example of laser printer timing control during an image forming operation. FIG. 6 is a schematic configuration diagram of an intermediate transfer unit of a laser printer according to another embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Toner image formation part 6 Transfer unit 9 Transfer bias power supply 10 Photoconductor unit 11 Photoconductor drum 20 Developing unit 60 Transfer conveyance belt 61-64 Support roller 70 Cleaning device 71 Cleaning roller 73 Opposite roller 75 Cleaning bias power supply 100 Transfer paper 200 Intermediate Transfer unit 201 Intermediate transfer belt 202 to 205 Support roller 210 Cleaning device 211 Cleaning roller 213 Opposing roller

Claims (3)

The surface moves along an endless path including an image carrier on which a toner image made of charged toner of a predetermined polarity is formed and a transfer portion facing the image carrier, and the transfer material is transferred to the image carrier at the transfer portion. In the image forming apparatus, comprising: a transfer member to be opposed; and a transfer electric field forming unit that forms an electric field in a direction in which the toner of the predetermined polarity is moved from the image carrier to the transfer member side in the transfer portion.
Transfer material supply means for supplying a transfer material to the transfer member;
An adsorbing means for applying a bias having a polarity opposite to the predetermined polarity to the electrode member , which is a rotating body that contacts the transfer material supplied on the transfer member, to adsorb the transfer material to the transfer member is provided. ,
Before the transfer material which is fed subjected to the transfer member in the transfer material supply means reaches the contact portion between the electrode member, the predetermined polarity and the polarity of the bias across one rotation or more times of the electrode member Is applied to the electrode member, and a bias applied to the electrode member is then applied at a time more than a time equivalent to one rotation of the electrode member before the transfer material reaches the contact portion with the electrode member. An image forming apparatus, wherein the predetermined polarity is switched to a polarity opposite to the predetermined polarity . The image forming apparatus 請 Motomeko 1,
A cleaning member that faces the surface of the transfer member, and a cleaning electric field that forms a cleaning electric field between the cleaning member and the transfer member for sucking the charged toner of the predetermined polarity toward the cleaning member. An image forming apparatus comprising an electric field forming unit. The image forming apparatus according to claim 1 or 2 ,
An image forming apparatus, 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.

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