JP5197066B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus that uses an electrophotographic recording system such as a laser printer, a copying machine, or a facsimile.

  In image forming apparatuses such as copying machines, printers, and fax machines, an electrophotographic system using toner as a developer is often used.

  These image forming apparatuses have a transfer process as described below. It is a recording material carried on a recording material conveyance body in which a toner image as a developer image carried on a photosensitive drum as an image carrier is applied to a transfer means by applying an electric field having a polarity opposite to the charged polarity of the toner to the transfer means. Alternatively, it is a transfer step for electrostatically transferring the surface of the intermediate transfer member.

  In this transfer step, a transfer bias applying means for providing a necessary bias is provided for electrostatically transferring the toner, and the transfer means connected to the high voltage power source has the following configuration. Is often used. It is positioned opposite to the photosensitive drum (the back side of the recording material conveyance belt or intermediate transfer belt) with the recording material conveyance body (hereinafter referred to as recording material conveyance belt) or the intermediate transfer body (hereinafter referred to as intermediate transfer belt) interposed therebetween. A contact transfer member such as a transfer roller is arranged.

  However, when a transfer roller is used as the transfer means, image quality degradation such as so-called scattering may occur. This is because the toner image on the photosensitive drum is pre-transferred onto the recording material carried on the recording material conveyance belt or the intermediate transfer belt by the transfer electric field formed by the transfer bias applied to the transfer roller.

  As a countermeasure, a configuration using a sheet-like member or a brush-like member as a transfer means has been proposed (Patent Documents 1 and 2).

  By using a sheet-like member or a brush-like member as the transfer means, it is possible to suppress the influence of the transfer electric field formed by the transfer bias, and it is possible to prevent so-called image quality deterioration such as scattering. As described above, the common point of the configuration using the sheet-like member or the brush-like member as the transfer means is that the transfer means is in contact with and sliding with the recording material conveying belt or the intermediate transfer belt.

  In addition, there is an image forming apparatus including a cleaning process for cleaning the recording material conveyance belt or the intermediate transfer belt. Contrary to the transfer process described above, this cleaning process applies unnecessary toner remaining on the recording material conveyance belt or the intermediate transfer belt to the transfer means by applying an electric field having the same polarity as the toner charging polarity to the photosensitive drum. Electrostatic reverse transfer is performed on the top.

  As a conventional example of an image forming apparatus provided with such a cleaning process, an operation of the image forming apparatus for electrostatically cleaning unnecessary toner remaining on the intermediate transfer belt as the second image carrier will be described. FIG. 10 is an example of an image forming apparatus using a four-color full-color electrophotographic system in which four process stations as image forming units are arranged side by side, and schematically shows an image forming apparatus adopting a so-called inline configuration. It is sectional drawing.

2. Description of the Related Art Conventionally, in an electrophotographic image forming apparatus, for example, a developing device including a negative organic photoreceptor as a photosensitive drum 101 and a negative toner as a developer is used. For this reason, a positive transfer bias is applied to the transfer member 110 by the bias power sources 122a to 122d during transfer.

  On the other hand, in the following cases, in order to clean unnecessary toner remaining on the intermediate transfer belt 113, a negative cleaning bias is applied to the transfer member 110 by the bias power sources 122a1 to 122d1. . That is, when secondary transfer residual toner remains on the intermediate transfer belt 113 after the secondary transfer, or when a jam occurs or a registration mark or density detection pattern is directly formed on the intermediate transfer belt 113, this is detected. This is the case after using the correct system.

  Further, in the case where the intermediate transfer belt 113 is electrostatically cleaned by a so-called in-line method, it is important to distribute unnecessary toner to a plurality of waste toner containers 103 for collection. This is because if unnecessary toner is continuously collected in only one waste toner container, the waste toner leaks when the maximum value of the collection amount is exceeded, and a defect that stains an image occurs.

  Therefore, as a conventional example, a method of cleaning the intermediate transfer belt 113 while distributing unnecessary toner on the intermediate transfer belt 113 to a plurality of waste toner containers will be described with reference to FIG. 11 in addition to FIG.

  FIG. 11 is a diagram for explaining a conventional cleaning operation for sorting and collecting unnecessary toner on the intermediate transfer belt 113. In this example, unnecessary toner on the intermediate transfer belt 113 is collected by being divided into four waste toner containers 103a to 103d.

  When collecting unnecessary toner on the intermediate transfer belt 113, the transfer members 110a, 110b, and 110c have positive polarity until the head of the unnecessary toner reaches the contact portion between the photosensitive drum 101d and the intermediate transfer belt 113. The transfer bias is applied. This is to prevent unnecessary toner on the intermediate transfer belt 113 from being reversely transferred to the photosensitive drums 101a, 101b, and 101c.

  Next, the head of unnecessary toner on the intermediate transfer belt 113 reaches the contact portion between the photosensitive drum 101d and the intermediate transfer belt 113, and the bias applied to the transfer members 110a to 110d is changed from the positive transfer bias to the negative polarity. Switch to the cleaning bias. Then, unnecessary toner on the intermediate transfer belt 113 starts to be reversely transferred to the photosensitive drums 101a to 101d.

  By applying a negative bias to the transfer members 110a to 110d until the intermediate transfer belt 113 advances by a distance equal to the interval between adjacent photosensitive drums, unnecessary toner in the region 1 shown in FIG. The containers 103a to 103d are sorted and collected.

  At the same time as all unnecessary toner in the region 1 is collected, the bias applied to the transfer members 110a to 110d is switched from the negative cleaning bias to the positive transfer bias. Then, unnecessary toner on the intermediate transfer belt 113 starts to advance to the contact portion between the photosensitive drum 101d and the intermediate transfer belt 113 without being reversely transferred to the photosensitive drums 101a, 101b, and 101c.

Next, at the same time that the head of the region 2 shown in FIG. 11 reaches the contact portion between the photosensitive drum 101d and the intermediate transfer belt 113, the bias applied to the transfer members 110a to 110d is changed from the positive transfer bias to the negative cleaning. Switch to bias. Then, the unnecessary toner in the area 2 is also distributed to the waste toner containers 103a to 103d in the same manner as the unnecessary toner in the area 1.

By repeating this process, unnecessary toner on the intermediate transfer belt 113 can be distributed to the waste toner containers 103a to 103d, and an excessive amount of waste toner can be prevented from being collected in a single waste toner container. Can do.
Japanese Patent No. 3388535 JP 05-127546 A

  However, in the conventional example as described above, there has been a concern that the intermediate transfer belt may be defective in a system in which the intermediate transfer belt and the transfer member slide. This is because a negative cleaning bias is simultaneously applied to a plurality of transfer members at the time of cleaning the intermediate transfer belt, so that the total amount of attracting force between the intermediate transfer belt and the transfer member becomes extremely large. Is due to.

  This problem generally relates to the fact that the magnitude of the cleaning bias is larger than the magnitude of the transfer bias and the cleaning bias applied to the transfer member.

  For example, in the case of the apparatus described in JP-A-2005-242178, the transfer bias is +1 kv, whereas the cleaning bias is -2.5 kv, and there is a difference of 1.5 kv in size. Due to the difference in applied voltage, the suction force generated between the belt and the electrophotographic member during cleaning becomes larger. For this reason, if a cleaning bias is applied to a plurality of transfer members at the same time, the sum of the attractive forces between the intermediate transfer belt and the transfer member increases, and as a result, there is a possibility that the intermediate transfer belt may malfunction. is there.

  The above-described problem has been described for the case of the image forming apparatus using the intermediate transfer belt, but the same applies to the case of the image forming apparatus using the recording material carrier that conveys the recording material while it is being carried.

  The present invention has been made in view of the above circumstances, and the adsorption generated between a plurality of transfer members sliding on an intermediate transfer member (recording material carrier) and the intermediate transfer member (recording material carrier). An object is to prevent problems occurring in the intermediate transfer member (recording material carrier) by reducing the total force.

In order to achieve the above object, the present invention provides:
An image forming apparatus for forming an image on a recording material by performing a secondary transfer of the developer image primarily transferred onto the intermediate transfer body onto the recording material.
Forming an image bearing member for bearing a developer image, an intermediate transfer member the developer image on the image bearing member is primarily transferred, the said image carrier via the intermediate transfer member and the two-up portion a transfer member, a plurality of image forming units provided before and cleaning means for removing the developer on Kizo carrier, and
Bias applying means for applying a bias to the plurality of transfer members;
Control means for controlling the bias applying means,
By applying a cleaning bias having the same polarity as the charging polarity of the developer image to the transfer member by the bias applying means, the residual developer remaining on the intermediate transfer member is reversely transferred onto the image carrier to In the image forming apparatus for removing from the image carrier by a cleaning unit ,
It said control means does not overlap the application time of the cleaning bias to the plurality of transcription members to each other and, one image forming unit cleaning region in the plurality of image forming portion to which the residual developer is present as divided into areas for removing the residual developer on each, and wherein the benzalkonium controls the bias applying means.

An image forming apparatus for forming an image on a recording material by transferring a developer image on the image bearing member to a recording material carried and conveyed by the recording material carrier,
A recording material carrier for carrying and conveying the recording material;
An image bearing member for bearing a developer image, a transfer member forming the image bearing member and two-up unit through the recording material bearing member, and cleaning means for removing developer on said image bearing member, a plurality of image forming unit comprising,
Bias applying means for applying a bias to the plurality of transfer members;
Control means for controlling the bias applying means;
Have
By applying a cleaning bias having the same polarity as the charging polarity of the developer image to the transfer member by the bias applying means, the residual developer remaining on the recording material carrier is reversely transferred onto the image carrier. In the image forming apparatus for removing from the image carrier by the cleaning unit,
It said control means does not overlap the application time of the cleaning bias to the plurality of transcription members to each other and, one image forming unit cleaning region in the plurality of image forming portion to which the residual developer is present It characterized the Turkey controls the bias applying means to be divided into areas for removing the residual developer on each.
An image forming apparatus that forms an image on a recording material by collectively transferring the developer image primarily transferred onto the intermediate transfer member to the recording material.
An image carrier that carries a developer image, an intermediate transfer member on which the developer image on the image carrier is primarily transferred, and a transfer member that forms a nip portion with the image carrier via the intermediate transfer member A plurality of image forming units, and a cleaning unit that removes the developer on the image carrier,
Bias applying means for applying a bias to the plurality of transfer members;
Control means for controlling the bias applying means,
By applying a cleaning bias having the same polarity as the charging polarity of the developer image to the transfer member by the bias applying means, the residual developer remaining on the intermediate transfer member is reversely transferred onto the image carrier to In the image forming apparatus for removing from the image carrier by a cleaning unit,
Two of the plurality of image forming units are biased to each of the transfer members by the same bias applying unit,
The control means prevents a cleaning bias from being simultaneously applied to three or more transfer members among the plurality of transfer members, and a cleaning region where the residual developer exists is present in the plurality of image forming units. The bias applying unit is controlled to be divided into regions where the residual developer is removed for each image forming unit.
An image forming apparatus that forms an image on a recording material by collectively transferring the developer image primarily transferred onto the intermediate transfer member to the recording material.
An image carrier that carries a developer image, an intermediate transfer member on which the developer image on the image carrier is primarily transferred, and a transfer member that forms a nip portion with the image carrier via the intermediate transfer member A plurality of image forming units, and a cleaning unit that removes the developer on the image carrier,
Bias applying means for applying a bias to the plurality of transfer members;
Control means for controlling the bias applying means,
By applying a cleaning bias having the same polarity as the charging polarity of the developer image to the transfer member by the bias applying means, the residual developer remaining on the intermediate transfer member is reversely transferred onto the image carrier to In the image forming apparatus for removing from the image carrier by a cleaning unit,
The plurality of image forming units are arranged in parallel at equal intervals in one direction,
Three adjacent image forming units among the plurality of image forming units are arranged in order from the upstream side toward the downstream side in the conveyance direction by the nip unit, in order, the first image forming unit, the second image forming unit, and the third image forming unit. In this case, the second image forming unit and the third image forming unit are biased to the respective transfer members by the same bias applying unit,
The control means includes
Of the cleaning area where the residual developer is present, the time required for the leading end downstream in the conveyance direction by the nip portion to pass between two adjacent image forming units is t, and a is a natural number. If
By the bias applying means for a time t with respect to the first image forming unit at a timing after time t × (3a−2) has elapsed since the leading end has passed through the first image forming unit. Control to perform the application operation of the cleaning bias,
At the timing after time t × (3a-1) has elapsed since the leading end has passed through the first image forming unit, the second image forming unit and the third image forming unit are in a time period of 2t. The bias applying means controls the cleaning bias to be applied.

  According to the present invention, it is possible to reduce the total of the attractive forces generated between the plurality of transfer members sliding on the intermediate transfer member (recording material carrier) and the intermediate transfer member (recording material carrier). In addition, it is possible to prevent problems that occur in the intermediate transfer member (recording material carrier).

  The best mode for carrying out the present invention will be exemplarily described in detail below with reference to the drawings. However, the dimensions, materials, shapes, and relative arrangements of the components described in this embodiment should be appropriately changed according to the configuration of the apparatus to which the invention is applied and various conditions. It is not intended to limit the scope to the following embodiments.

  FIG. 1 is a schematic cross-sectional view illustrating an image forming apparatus according to Embodiment 1 of the present invention.

  Hereinafter, the image forming operation of the image forming apparatus will be described in detail with reference to FIG. In this embodiment, an image forming apparatus including four image forming units as a plurality of image forming units will be described. In the following description, the four image forming units (hereinafter referred to as “stations”) are respectively yellow (Y) for the first station, magenta (M) for the second station, cyan (C) for the third station, and black for the fourth station. (K).

  In the first station, a photosensitive drum (OPC photosensitive drum) 1a as an image carrier, a charging roller 2a as a charging unit, a cleaning unit 3a, and a developing unit 8a as a developing unit constitute an integrated process cartridge 9a. doing. Here, the developing unit 8a includes a developing sleeve 4a, a non-magnetic one-component developer (hereinafter referred to as toner) 5a, and a developer coating blade 7a. The cleaning unit 3a constitutes a cleaning unit, and cleans the transfer residual toner (residual developer) on the photosensitive drum 1a (on the image carrier).

  An exposure unit 11a is constituted by a scanner unit or LED array that scans laser light with a polygon mirror, and irradiates the photosensitive drum 1a with a scanning beam 12a that is modulated based on an image signal.

  Next, an image forming operation will be described.

  When the image forming operation is started, the photosensitive drum 1a, the intermediate transfer belt 13 as an intermediate transfer member, and the like start to rotate at a predetermined process speed in the arrow direction shown in the drawing. The photosensitive drum 1a is uniformly charged to a negative polarity by a charging roller 2a to which a voltage is applied from a power source 20a, and then an electrostatic latent image according to image information is formed by a scanning beam 12a from the exposure device 11a. .

  The toner 5a in the developing unit 8a is charged to a negative polarity by the developer applying blade 7a and applied to the developing sleeve 4a. A bias is supplied to the developing sleeve 4a from a developing bias power source 21a.

  When the photosensitive drum 1a rotates and the electrostatic latent image formed on the photosensitive drum 1a reaches the developing sleeve 4a, the electrostatic latent image is visualized by the negative polarity toner, and the first image is displayed on the photosensitive drum 1a. A toner image (developer image) of color (in this embodiment, Y) is formed.

  Although the first station has been described above, the second to fourth stations have the same configuration as that of the first station and perform the same image forming operation, and thus the description thereof is omitted.

  On the other hand, the intermediate transfer belt 13 which is a toner image carrier is disposed so as to abut against all the four photosensitive drums 1a to 4d.

  The intermediate transfer belt 13 is supported by three rollers, that is, a secondary transfer counter roller 24, a driving roller 15, and a tension roller 14 as a stretching member, so that an appropriate tension is maintained. By driving the driving roller 15, the intermediate transfer belt 13 rotates in the direction of the arrow shown in the figure (clockwise in FIG. 1), and the intermediate transfer belt 13 is substantially the same speed in the forward direction with respect to the photosensitive drums 1a to 4d. Moving.

  A primary transfer member 10a as a transfer member is disposed on the opposite side of the photosensitive drum 1a with the intermediate transfer belt 13 interposed therebetween so as to form a nip portion with the photosensitive drum 1a. The primary transfer member 10 a slides with respect to the intermediate transfer belt 13 while the intermediate transfer belt 13 is rotating (moving).

  The charging roller 2a is connected to a charging bias power source 20a as a voltage supply unit to the charging roller 2a, and the developing sleeve 4a is connected to a developing bias power source 21a as a voltage supply unit to the developing sleeve 4a. The primary transfer member 10a is connected to a primary transfer bias power source 22a as voltage supply means for applying a transfer bias to the primary transfer member 10a, and the secondary transfer roller 25 is connected to a secondary transfer bias power source 26. ing. Here, the primary transfer bias power source 22a constitutes a bias applying unit together with a cleaning bias power source 22a1 described later.

  The primary transfer members 10a to 10d are disposed around the intermediate transfer belt 13 and opposed to the photosensitive drums 1a to 1d in correspondence with the photosensitive drums 1a to 1d.

Depending on the distance between the primary transfer positions of each color (between the nip portions), each photosensitive drum 1a to 1d converts the electrostatic latent image by exposure while delaying a write signal from a controller (not shown) at a certain timing for each color. Form on top. Then, a DC bias (transfer bias) having a polarity opposite to that of the toner is applied from the primary transfer bias power sources 22a to 22d to the primary transfer members 10a to 10d, respectively. In a state where the transfer bias is applied, the intermediate transfer belt 13 is nipped and conveyed by a nip portion constituted by the primary transfer members 10a to 10d and the photosensitive drums 1a to 1d.

  Through the above steps, the toner image is primarily transferred from the first station to the intermediate transfer belt 13 in order from the first station toward the fourth station toward the downstream side in the rotation direction of the intermediate transfer belt 13 (downstream in the conveyance direction by the nip portion). Multiple images are formed on the transfer belt 13.

  Thereafter, the recording material P loaded on the recording material cassette 16 is picked up by the feeding roller 17 and conveyed to the registration roller 18 by a conveyance roller (not shown) in accordance with the electrostatic latent image formed by exposure. . The recording material P conveyed to the registration roller 18 is formed by the intermediate transfer belt 13 and the secondary transfer roller 25 by the registration roller 18 so as to synchronize with the toner image on the intermediate transfer belt 13 (on the intermediate transfer body). It is conveyed to the contact part.

  Thereafter, a bias having a polarity opposite to that of the toner is applied to the secondary transfer roller 25 by a secondary transfer bias power source 26, and a four-color multiple toner image carried on the intermediate transfer belt 13 on the recording material P is formed. Secondary transfer is performed at once.

In this embodiment, the secondary transfer roller 25 is a nickel-plated steel rod having a diameter of ⁸ mm and covered with a foamed NBR foam having a resistance value of 10 ⁸ Ω and a thickness of 5 mm. The secondary transfer roller 25 is brought into contact with the intermediate transfer belt 13 with a linear pressure of about 5 to 15 g / cm, and rotates at a substantially constant speed in the forward direction with respect to the moving direction of the intermediate transfer belt 13. Arranged to be.

  After the completion of the secondary transfer, the recording material P is conveyed to the fixing unit 19, receives the toner image fixing, and is discharged out of the image forming apparatus as an image formed product (print, copy).

The intermediate transfer belt 13 is made of PVDF (polyvinylidene fluoride) having a thickness of 100 μm and a volume resistivity of 10 ¹¹ Ωcm.

  The primary transfer members 10a to 10d have a sheet member and an elastic body, and the sheet member is sandwiched between the intermediate transfer belt 13 and the elastic body. In this embodiment, a conductive sheet is used as the sheet member, and an ultra high molecular conductive polyethylene sheet having a thickness of 200 μm is used as the conductive sheet. As the elastic body, a urethane foam sponge-like elastic body having a substantially rectangular parallelepiped shape with a thickness of 2 mm, a width of 5 mm, and a length of 230 mm is used. The sheet member is pressed against the intermediate transfer belt 13 by the elastic body with a total pressure of 4.9 N, and slides on the intermediate transfer belt 13 when the intermediate transfer belt 13 moves.

  The tension roller 14 as a tension member uses an Al metal rod of φ18.6 mm, and the tension is set to a total pressure of 58.8N.

The driving roller 15 as a stretching member is a roller having a diameter of 25 mm and covered with EPDM rubber (ethylene propylene rubber) having a resistance of 10 ⁴ Ω and a thickness of 1.0 mm in which carbon is dispersed in an Al core metal as a conductive agent.

The secondary transfer counter roller 24 as a stretching member is a roller having a diameter of 25 mm coated with EPDM rubber having a resistance of 10 ⁴ Ω and a thickness of 1.5 mm in which carbon is dispersed in an Al core metal.

  Hereinafter, features of the present embodiment will be described.

  When a jam occurs or when a registration mark or density detection pattern is formed, toner adheres to the intermediate transfer belt 13 and therefore needs to be cleaned. In this embodiment, in order to remove the unnecessary toner (residual developer), cleaning bias power sources 22a1 to 22d1 for applying a cleaning bias having the same polarity as the charging polarity of the toner to the primary transfer members 10a to 10d are provided. Yes.

  By applying a cleaning bias having the same polarity as the charging polarity of the toner to the primary transfer members 10a to 10d, unnecessary toner on the intermediate transfer belt 13 can be reversely transferred to the photosensitive drums 1a to 1d, and the cleaning unit 3a. Can be removed in ~ 3d. Thereby, the intermediate transfer belt 13 can be cleaned. At the same time, unnecessary toner can be sorted and collected in waste toner containers provided in the cleaning units 3a to 3d, respectively. This embodiment is characterized in that, when performing this cleaning, it is avoided to apply a cleaning bias to a plurality of transfer members simultaneously.

  A method for cleaning the intermediate transfer belt 13 performed by the control unit of the image forming apparatus will be specifically described below.

  FIG. 2 is a diagram for explaining a cleaning operation for sorting and collecting unnecessary toner on the intermediate transfer belt 13 in this embodiment. FIG. 3 is a diagram for explaining biases applied to the primary transfer members 10a to 10d from the cleaning bias power sources 22a1 to 22d1 in the cleaning operation of the present embodiment, respectively. In this embodiment, contact portions (nip portions) between the photosensitive drums 1a to 1d and the intermediate transfer belt 13 are arranged in parallel so as to be equally spaced in one direction (the rotation direction of the intermediate transfer belt 13).

  On the horizontal axis in FIG. 3, a reference time 0 is defined as the time when the leading (tip) portion of unnecessary toner reaches the contact portion between the photosensitive drum 1 a and the intermediate transfer belt 13. Further, on the horizontal axis in FIG. 3, the intermediate transfer belt 13 advances (passes) a quarter of the area (cleaning area, area where unnecessary toner exists) shown in area 1 in FIG. The time required for this is u seconds.

  First, a cleaning bias (−1300 V) is applied to the primary transfer member 10a from the reference time 0 to u seconds. Thus, unnecessary toner in the area 1-1 on the intermediate transfer belt 13 is reversely transferred to the photosensitive drum 1a and removed from the intermediate transfer belt 13.

  Here, the absolute value of the cleaning bias is set larger than the absolute value of the bias at the time of transfer. This is because, when a voltage that is too large is applied during transfer, the transferred toner image may be disturbed, whereas the reversely transferred toner image during cleaning needs to be aware of such points. Because there is no. In addition, cleaning requires moving a toner having a low charge amount, so that it is necessary to form a strong electric field.

  Next, a cleaning bias (−1300 V) is applied to the primary transfer member 10b for u seconds after 0 u from the reference time. As a result, unnecessary toner in the region 1-2 on the intermediate transfer belt 13 is reversely transferred to the photosensitive drum 1b and removed from the intermediate transfer belt 13.

  Next, after 4 u seconds from the reference time, a cleaning bias (−1300 V) is applied to the primary transfer member 10 c for u seconds. As a result, unnecessary toner in the area 1-3 on the intermediate transfer belt 13 is reversely transferred to the photosensitive drum 1c and removed from the intermediate transfer belt 13.

Next, after 6 u seconds from the reference time, a cleaning bias (−1300 V) is applied to the primary transfer member 10 d for u seconds. As a result, unnecessary toner in the region 1-4 on the intermediate transfer belt 13 is reversely transferred to the photosensitive drum 1d and removed from the intermediate transfer belt 13.

  In this way, the primary transfer member is cleaned for each station in order from the first station toward the downstream side in the rotation direction of the intermediate transfer belt 13 (from the upstream side to the downstream side in the conveyance direction by the nip portion). A bias application operation is performed.

  By performing the cleaning method as described above, unnecessary toner in the region 1 on the intermediate transfer belt 13 is sequentially distributed to the photosensitive drums 1a, 1b, 1c, and 1d and removed from the intermediate transfer belt 13.

  In the present embodiment, a voltage of 300V is applied to the primary transfer members 10a to 10d when the cleaning bias (-1300V) is not applied.

  Next, the operation of this embodiment will be described.

  In this embodiment, as described above, the cleaning bias (-1300 V) having the same polarity as the charging polarity of unnecessary toner on the intermediate transfer belt 13 is applied to the primary transfer members 10a to 10d. As a result, unnecessary toner is reversely transferred to the photosensitive drums 1 a to 1 d to clean the intermediate transfer belt 13.

  At this time, the present embodiment is characterized in that the cleaning bias (-1300 V) is not simultaneously applied to the primary transfer members 10a to 10d. As a result, the total electrostatic attraction force generated between the intermediate transfer belt 13 and the primary transfer members 10a to 10d can be reduced. As a result, since the total tension force applied to the intermediate transfer belt 13 is reduced, it is possible to prevent the intermediate transfer belt 13 from being defective when an excessive tension force is applied to the intermediate transfer belt 13. it can.

[Evaluation of Examples]
In order to investigate the effect of the image forming apparatus of this example, evaluation was performed together with Comparative Example 1 shown below using an image forming apparatus having a process speed of 100 mm / sec. The evaluation was performed with respect to the value of the driving torque of the intermediate transfer belt and the breaking state of the intermediate transfer belt after 200 times and 400 times of cleaning of the intermediate transfer belt in the initial stage. The frequency of cleaning is once for every 50 sheets, and when the 200th cleaning is performed, it corresponds to when the durable sheet number of the image forming apparatus main body reaches 10,000 sheets.

[Comparative Example 1]
The cleaning operation of the intermediate transfer belt in Comparative Example 1 will be described with reference to FIGS.

  FIG. 4 is a diagram for explaining a cleaning operation for sorting and collecting unnecessary toner on the intermediate transfer belt 13 in this comparative example. FIG. 5 is a diagram for explaining the bias applied to the primary transfer members 10a to 10d by the cleaning operation of this comparative example.

  When collecting unnecessary toner on the intermediate transfer belt 13, the time at which the head of the unnecessary toner reaches the contact portion between the photosensitive drum 1 a and the intermediate transfer belt 13 is the reference time 0, and the station where the intermediate transfer belt 13 is adjacent. The time taken to move by the distance of the interval is assumed to be t seconds.

  In this comparative example, a cleaning bias (-1300 V), which is a bias having the same polarity as that of unnecessary toner, is simultaneously applied to the primary transfer members 10a, 10b, 10c, and 10d for t seconds when 3 t seconds have elapsed from the reference time. To do.

  Then, among the unnecessary toners in the area 1 on the intermediate transfer belt 13, the unnecessary toner in the area 1-1 is reversely transferred to the photosensitive drum 1d, and the unnecessary toner in the area 1-2 is reversely transferred to the photosensitive drum 1c. The Unnecessary toner in the area 1-3 is reversely transferred to the photosensitive drum 1b, and unnecessary toner in the area 1-4 is reversely transferred to the photosensitive drum 1a.

  In this way, unnecessary toner in the region 1 on the intermediate transfer belt 13 is distributed to the photosensitive drums 1a, 1b, 1c, and 1d and removed from the intermediate transfer belt 13.

  In addition, by repeating the control from the reference time 0 to 4 tsec after the elapse of 4 tsec from the reference time 0, unnecessary toner after the area 2 on the intermediate transfer belt 13 is also removed from the photosensitive drums 1a and 1b. , 1c, 1d and removed from the intermediate transfer belt 13.

  In this comparative example, as in Example 1, a voltage of 300 V is applied to the primary transfer members 10a to 10d when no cleaning bias (-1300 V) is applied.

[Evaluation results]
The evaluation results are shown in FIG. This evaluation was performed by paying attention to the driving torque of the intermediate transfer belt 13 and the state (failure status) of the intermediate transfer belt 13 when unnecessary toner on the intermediate transfer belt 13 is being cleaned. Further, 4024 basis weight 75 g / m ² manufactured by Xerox Co. was used as a paper passing durability test.

  In the configuration of this embodiment, the maximum value of the driving torque of the intermediate transfer belt 13 when cleaning unnecessary toner on the intermediate transfer belt 13 is 3.0 kgf · cm after 800 cleanings. Yes, the intermediate transfer belt 13 was not broken, and good results were obtained.

  In Comparative Example 1, the maximum value of the drive torque value of the intermediate transfer belt 13 when cleaning the unnecessary toner on the intermediate transfer belt 13 is 5.0 kgf · cm after 400 cleanings. At this time, the intermediate transfer belt 13 was broken. (Here, 3.0 kgf · cm is 29.4 N · cm, and 5.0 kgf · cm is 49 N · cm.)

  As described above, in this embodiment, unnecessary toner is applied to the photosensitive drum by applying a cleaning bias having the same polarity as the charging polarity of unnecessary toner on the intermediate transfer belt 13 to the plurality of primary transfer members. The intermediate transfer belt is cleaned by reverse transfer. When such cleaning is performed, a cleaning bias is not simultaneously applied to a plurality of primary transfer members.

  Thereby, the collection of unnecessary toner can be distributed to a plurality of waste toner containers, and at the same time, the total electrostatic attraction force generated between the intermediate transfer belt 13 and the primary transfer members 10a to 10d can be reduced. As a result, since the total tension force applied to the intermediate transfer belt 13 is reduced, it is possible to prevent the intermediate transfer belt 13 from malfunctioning when an excessive tension force is applied to the intermediate transfer belt 13.

In the present embodiment, an image forming apparatus provided with four stations as a plurality of image forming units has been described. However, the present invention is not limited to this. That is, even when five or more stations are provided, the first transfer member is sequentially transferred from the first station toward the downstream side in the rotation direction of the intermediate transfer belt 13 for each primary transfer member. A cleaning bias application operation may be performed. By such control, it is possible to prevent a problem from occurring in the intermediate transfer belt when an excessive tension force is applied to the intermediate transfer belt.

  In the present embodiment, the image forming apparatus using the intermediate transfer belt 13 has been described. However, the present invention is not limited to this, and the image forming apparatus using a recording material carrier (transfer belt) that conveys the recording material while carrying it. In addition, the present invention can be preferably applied. Here, the recording material carrier is provided so as to be sandwiched and conveyed by a plurality of nip portions formed between the photosensitive drum and the transfer member, and is attached to the recording material carried and conveyed by the recording material carrier. The toner image on the photosensitive drum is transferred to form an image on the recording material. In the image forming apparatus that cleans the recording material carrier by reversely transferring unnecessary toner remaining on the recording material carrier onto the photosensitive drum, the same effect as described above can be obtained by performing the above-described control. be able to.

  The second embodiment of the present invention will be described below.

  FIG. 7 is a schematic cross-sectional view showing the image forming apparatus according to the present embodiment. FIG. 8 is a diagram for explaining a cleaning operation for sorting and collecting unnecessary toner on the intermediate transfer belt 13 in this embodiment. FIG. 9 is a diagram for explaining a bias applied to the primary transfer members 10a to 10d by the cleaning operation of this embodiment. Note that the configuration of the image forming apparatus applied in the present embodiment is the same as that of the first embodiment described above, and the same components as those in the first embodiment are denoted by the same reference numerals and the description thereof is omitted.

  Hereinafter, features of the present embodiment will be described.

  The image forming apparatus according to the present embodiment eliminates the bias power supplies 22c, 22c1, and 22d1 that apply a bias to the primary transfer member for the purpose of reducing the cost as compared with the image forming apparatus according to the first embodiment. In the second and third stations (second image forming unit and third image forming unit), the primary transfer members 10b and 10c are shared by a common (same) bias power source (bias power sources 22b and 22b1). A bias is applied. Further, when unnecessary toner on the intermediate transfer belt 13 is cleaned, the unnecessary toner is distributed and collected in three waste toner containers provided in the cleaning units 3a to 3c, respectively.

  In this embodiment, when the intermediate transfer belt 13 is cleaned, a cleaning bias is not simultaneously applied to three or more primary transfer members.

  The method for cleaning the intermediate transfer belt 13 in this embodiment will be specifically described below.

  When collecting unnecessary toner on the intermediate transfer belt 13, the time at which the head of the unnecessary toner reaches the contact portion between the photosensitive drum 1 a and the intermediate transfer belt 13 is the reference time 0, and the station where the intermediate transfer belt 13 is adjacent. The time taken to move by the distance of the interval is assumed to be t seconds.

  First, after a reference time of 0 seconds from the reference time, a cleaning bias (−1300 V) that is a bias having the same polarity as that of unnecessary toner is applied to the primary transfer member 10a of the first station (first image forming unit) for t seconds.

  As a result, unnecessary toner in the region 1-2 on the intermediate transfer belt 13 is reversely transferred to the photosensitive drum 1a and removed from the intermediate transfer belt 13.

Next, a cleaning bias (-1300 V) is applied to the primary transfer members 10b and 10c for 2t seconds after 2t seconds from the reference time.

  Then, of the 2t seconds, unnecessary toner in the area 1-1 on the intermediate transfer belt 13 is reversely transferred to the photosensitive drum 1c for the first t seconds, and on the intermediate transfer belt 13 for the second t seconds. Unnecessary toner in the area 1-3 is reversely transferred to the photosensitive drum 1b. As a result, unnecessary toner in the area 1-1 on the intermediate transfer belt 13 and unnecessary toner in the area 1-3 are removed from the intermediate transfer belt 13.

  By the control from t seconds to 4 t seconds, unnecessary toner in the region 1 on the intermediate transfer belt 13 is distributed to the photosensitive drums 1a, 1b, and 1c and removed from the intermediate transfer belt 13.

Further, even after the elapse of 4 t seconds from the reference time 0, by repeating the above control from t seconds to 4 t seconds, unnecessary toners after the region 2 on the intermediate transfer belt 13 are also exposed to the photosensitive drums 1a and 1b. , 1c and removed from the intermediate transfer belt 13. Here, regarding the repetition of the control from t seconds to 4 t seconds, when a is a natural number, the following (1) and (2) can be indicated.
(1) At the timing after time t × (3a-2) has elapsed, a cleaning bias (−1300 V), which is a bias having the same polarity as that of unnecessary toner, is applied to the primary transfer member 10a for a time t.
(2) A cleaning bias (-1300 V) is applied to the primary transfer members 10b and 10c for a time 2t at a timing after the time t × (3a-1) has elapsed.

  In this embodiment, a voltage of 300 V is applied to the primary transfer members 10a to 10d when the cleaning bias (-1300 V) is not applied.

  Next, the operation of this embodiment will be described.

  In this embodiment, the cost can be reduced by reducing the number of bias power supplies for applying a bias to the primary transfer member 10, and at the same time, three or more 1s can be used when cleaning unnecessary toner on the intermediate transfer belt 13. A cleaning bias is not simultaneously applied to the next transfer member. For this reason, the total of the electrostatic attraction force generated between the intermediate transfer belt 13 and the primary transfer members 10a to 10d is greater than when the cleaning bias (-1300V) is not applied to all the primary transfer members 10 simultaneously. Will get bigger.

  However, in this embodiment, the number of primary transfer members 10 to which the cleaning bias is applied simultaneously is set to two or less. As a result, the total of the electrostatic attraction force generated between the intermediate transfer belt 13 and the primary transfer members 10a to 10d is not so large as to cause a problem in the intermediate transfer belt 13. ing.

  For this reason, it is possible to prevent a problem from occurring in the intermediate transfer belt when an excessive tension force is applied to the intermediate transfer belt 13 at the same time as realizing cost reduction.

  As described above, in this embodiment, by providing a bias power source that applies a bias to the two primary transfer members in common, the cost can be reduced, and at least three primary transfer members can be used for cleaning. The cleaning bias is not simultaneously applied to the members.

As a result, the total of the electrostatic attraction force generated between the intermediate transfer belt 13 and the primary transfer members 10 a to 10 d can be made smaller than the value when a problem occurs in the intermediate transfer belt 13. As a result, it is possible to prevent the intermediate transfer belt 13 from malfunctioning when an excessive tension force is applied to the intermediate transfer belt 13.

  In the present embodiment, an image forming apparatus provided with four stations as a plurality of image forming units has been described. However, the present invention is not limited to this. That is, even when five or more stations are provided, when the above-described control is performed on three adjacent stations, an excessive tension force is applied to the intermediate transfer belt. It is possible to prevent the intermediate transfer belt from being defective.

1 is a schematic cross-sectional view illustrating an image forming apparatus according to Embodiment 1. FIG. FIG. 6 is a view for explaining sorting and collection by the cleaning operation of the first embodiment. FIG. 6 is a diagram for explaining a bias applied to the primary transfer member by the cleaning operation of the first embodiment. The figure for demonstrating the distribution collection | recovery by the cleaning operation | movement of the comparative example 1. FIG. FIG. 6 is a diagram for explaining a bias applied to a primary transfer member by a cleaning operation of Comparative Example 1; The figure which shows the evaluation result of Example 1. FIG. FIG. 3 is a schematic cross-sectional view illustrating an image forming apparatus according to a second embodiment. FIG. 10 is a diagram illustrating sorting and collection by a cleaning operation according to the second embodiment. FIG. 10 is a diagram for explaining a bias applied to a primary transfer member by a cleaning operation according to a second embodiment. FIG. 10 is a schematic cross-sectional view showing a conventional image forming apparatus. The figure for demonstrating the distribution collection | recovery by the conventional cleaning operation | movement.

Explanation of symbols

1a to 1d Photosensitive drum 3a to 3d Cleaning unit 10a to 10d Primary transfer member 13 Intermediate transfer belt 22a to 22d Primary transfer bias power source 22a1 to 22d1 Cleaning bias power source

Claims (5)

An image forming apparatus for forming an image on a recording material by performing a secondary transfer of the developer image primarily transferred onto the intermediate transfer body onto the recording material.
Forming an image bearing member for bearing a developer image, an intermediate transfer member the developer image on the image bearing member is primarily transferred, the said image carrier via the intermediate transfer member and the two-up portion a transfer member, a plurality of image forming units provided before and cleaning means for removing the developer on Kizo carrier, and
Bias applying means for applying a bias to the plurality of transfer members;
Control means for controlling the bias applying means,
By applying a cleaning bias having the same polarity as the charging polarity of the developer image to the transfer member by the bias applying means, the residual developer remaining on the intermediate transfer member is reversely transferred onto the image carrier to In the image forming apparatus for removing from the image carrier by a cleaning unit ,
It said control means does not overlap the application time of the cleaning bias to the plurality of transcription members to each other and, one image forming unit cleaning region in the plurality of image forming portion to which the residual developer is present as divided into areas for removing the residual developer on each, images forming device wherein that control bias applying means. An image forming apparatus that forms an image on a recording material by transferring a developer image on the image bearing member to a recording material carried and conveyed by the recording material carrier,
A recording material carrier for carrying and conveying the recording material;
An image bearing member for bearing a developer image, a transfer member forming the image bearing member and two-up unit through the recording material bearing member, and cleaning means for removing developer on said image bearing member, a plurality of image forming unit comprising,
Bias applying means for applying a bias to the plurality of transfer members;
Control means for controlling the bias applying means;
Have
By applying a cleaning bias having the same polarity as the charging polarity of the developer image to the transfer member by the bias applying means, the residual developer remaining on the recording material carrier is reversely transferred onto the image carrier. In the image forming apparatus for removing from the image carrier by the cleaning unit,
It said control means does not overlap the application time of the cleaning bias to the plurality of transcription members to each other and, one image forming unit cleaning region in the plurality of image forming portion to which the residual developer is present the residual developer said bias application means that controls the images forming apparatus as divided into areas to remove the every. It said control means to said plurality of image forming portions, sequentially toward the downstream side from the upstream side by the nip portion, for each one of the image forming section, so as to perform the application operation before Symbol cleaning bias The image forming apparatus according to claim 1 , wherein the bias applying unit is controlled . An image forming apparatus for forming an image on a recording material by performing a secondary transfer of the developer image primarily transferred onto the intermediate transfer body onto the recording material.
An image carrier that carries a developer image, an intermediate transfer member on which the developer image on the image carrier is primarily transferred, and a transfer member that forms a nip portion with the image carrier via the intermediate transfer member A plurality of image forming units, and a cleaning unit that removes the developer on the image carrier,
Bias applying means for applying a bias to the plurality of transfer members;
Control means for controlling the bias applying means,
By applying a cleaning bias having the same polarity as the charging polarity of the developer image to the transfer member by the bias applying means, the residual developer remaining on the intermediate transfer member is reversely transferred onto the image carrier to In the image forming apparatus for removing from the image carrier by a cleaning unit,
Two of the plurality of image forming units are biased to each of the transfer members by the same bias applying unit,
The control means prevents a cleaning bias from being simultaneously applied to three or more transfer members among the plurality of transfer members , and a cleaning region where the residual developer exists is present in the plurality of image forming units. It said bias application means that controls the images forming apparatus as divided into areas for removing the residual developer on each single image forming unit. An image forming apparatus for forming an image on a recording material by performing a secondary transfer of the developer image primarily transferred onto the intermediate transfer body onto the recording material.
An image carrier that carries a developer image, an intermediate transfer member on which the developer image on the image carrier is primarily transferred, and a transfer member that forms a nip portion with the image carrier via the intermediate transfer member A plurality of image forming units, and a cleaning unit that removes the developer on the image carrier,
Bias applying means for applying a bias to the plurality of transfer members;
Control means for controlling the bias applying means,
By applying a cleaning bias having the same polarity as the charging polarity of the developer image to the transfer member by the bias applying means, the residual developer remaining on the intermediate transfer member is reversely transferred onto the image carrier to In the image forming apparatus for removing from the image carrier by a cleaning unit,
The plurality of image forming units are arranged in parallel at equal intervals in one direction,
Three adjacent image forming units among the plurality of image forming units are arranged in order from the upstream side toward the downstream side in the conveyance direction by the nip unit, in order, the first image forming unit, the second image forming unit, and the third image forming unit. In this case, the second image forming unit and the third image forming unit are biased to the respective transfer members by the same bias applying unit,
The control means includes
Of the cleaning area where the residual developer is present, the time required for the leading end downstream in the conveyance direction by the nip portion to pass between two adjacent image forming units is t, and a is a natural number. If
By the bias applying means for a time t with respect to the first image forming unit at a timing after time t × (3a−2) has elapsed since the leading end has passed through the first image forming unit. Control to perform the application operation of the cleaning bias,
At the timing after time t × (3a-1) has elapsed since the leading end has passed through the first image forming unit, the second image forming unit and the third image forming unit are in a time period of 2t. , images forming device you and controls so as to perform the operation of applying the cleaning bias by the bias applying means.

Images