JP2005189687A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electrophotographic image forming apparatus in which copying can be started upon a series of instructions to start copying and soiling of the back of a transfer material can be prevented when copying is re-started. <P>SOLUTION: The image forming apparatus X includes an image forming part A which has a photoreceptor 1 for forming an electrostatic latent image on its surface; a developing part B which develops the electrostatic latent image on the photoreceptor 1 with electrified toner T; a transfer part C which transfers the toner image on the photoreceptor 1 to a transfer material P with a transfer belt 6 by the application of a transfer bias; and a cleaning part D which removes residual toner T' on the transfer belt 6 after the transfer. The image forming apparatus X further includes a power source device 14 capable of applying a bias voltage between the surface and back of the transfer belt 6; and a transfer belt erasing means 141a which, after the transfer belt 6 is stopped due to the end of an image forming operation, erases the transfer belt 6 while maintaining the bias voltage applied by the power source device 14. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention includes an image forming unit having an image carrier on which an electrostatic image is formed on a surface, a developing unit that visualizes the electrostatic image on the image carrier with charged toner, and a transfer bias. The present invention relates to an image forming apparatus provided with a transfer unit that transfers a toner image on the image carrier onto a transfer material by a transfer belt, and a cleaning unit that removes residual toner on the transfer belt after transfer.

  In an electrophotographic image forming apparatus such as an electrostatic copying machine, an electrostatic printing machine, a laser printer, or a facsimile machine, an electrostatic image formed on the peripheral surface of an image carrier is visualized with a charged toner and visualized. The imaged toner image is transferred to a transfer material at the transfer portion.

In an image forming apparatus provided with this type of transfer belt, the back stain generated on the first copy or the like is a problem, and this back stain is known to occur in the following situation.
During the copying operation, a transfer bias is applied to a transfer bias roller attached to the transfer belt. Here, the bias applied to the transfer belt for transferring the toner image on the image carrier onto the transfer material is usually opposite in polarity to the charge polarity of the image carrier and toner.
When the application of the transfer bias is stopped and the drive of the transfer belt is stopped in the end operation of the series of copying operations, the application of the cleaning bias applied to the cleaning unit is also stopped in synchronization with this.

  When the charge polarity of the image carrier and toner is positive, when the transfer belt stops driving, the transfer belt surface is on the positive side (back surface is negative) due to the transfer bias, and the reversely charged toner is on the belt. If reversely charged toner remains on the brush provided in the cleaning unit, this type of reversely charged toner adheres to the transfer belt and is transported to the transfer unit when the copying operation is resumed. Back stains occur on the material.

  As a countermeasure against this type of problem, in an apparatus having a charge applying member (transfer process) for applying charge to the transfer belt, a charge removing member for removing charge from the transfer belt, and a cleaning device for cleaning the surface of the transfer belt, There is one that performs the above operation (Patent Document 1).

  In the technique disclosed in Patent Document 1, as a cleaning device, a main cleaning mechanism including a blade and a cleaning member using an electric field (member 12 in Patent Document 1) are provided as sub-cleaning mechanisms. While rotating the belt, an electric field having a polarity opposite to the electric field applied by the charge applying means is applied to the cleaning member using the electric field (this operation is referred to as reverse polarity application). In this technique, when the transfer to the transfer material is sequentially performed, the main cleaning mechanism works, and therefore, an electric field of reverse polarity is not applied.

FIG. 3 shows a timing chart for driving the transfer belt and applying reverse polarity in this prior art. In this chart, t2 to t3 are times when the transfer is actually performed on the photosensitive material, t1 to t2 are reverse polarity application periods at the start of copying, and t3 to t4 are reverse polarity applications accompanying the end of copying. Indicates the period.
In this technique, the transfer belt is rotated over the entire period from t1 to t4, and no operation is performed after the transfer belt is stopped.
Accordingly, the entire period from t1 to t4 is necessary for the copying operation as a series.

On the other hand, in this type of apparatus having a transfer belt and a cleaning unit for the transfer belt as shown in FIG. 1, the transfer belt is sandwiched between the cleaning unit or the cleaning unit even during a copying operation. The drive roller arranged in (1) is known to be in a predetermined charge application state.
Usually, the polarity applied to this type of drive roller is opposite to the transfer bias.
The bias application during the copying operation to the cleaning unit and the driving roller is synchronized with the operation of the transfer belt as described above, and when the rotation of the transfer belt is stopped as the copying operation ends. At the same time, bias application was stopped.
This technique is a technique that has been performed in the past, and no prior literature can be shown.

Japanese Patent Laid-Open No. 7-168454 (refer to claims 0006 to 0012, FIG. 4 etc.)

The above prior art has the following problems.
1 Problems in the technology disclosed in Patent Document 1 In this technology, in order to perform a series of copying operations, reverse polarity application is performed while rotating the transfer belt at both the start time and the end time. That amount of time is not available for actual copying. In particular, since this is done at the start, the start of copying is delayed.
Further, since the transfer belt is rotated when the transfer onto the transfer material is not performed, there is a case where interference with devices arranged around the transfer belt may occur, which is not preferable.

2 Problems in the technology for stopping the application of the cleaning unit or the driving roller in synchronization with the stoppage of the rotation of the transfer belt In this case, the problem of the back dirt described so far occurs as it is.

  SUMMARY OF THE INVENTION An object of the present invention is to provide an electrophotographic image forming apparatus that can immediately start copying in response to a series of copying start commands, and can prevent the occurrence of back contamination of a transfer material at the restart. There is.

(Configuration 1)
In order to achieve the above object, a first characteristic configuration of an image forming apparatus according to the present invention includes an image forming unit having an image carrier on which an electrostatic image is formed on the surface, and a charged toner on the image carrier. A developing unit that visualizes the electrostatic image, a transfer unit that applies a transfer bias to transfer the toner image on the image carrier onto a transfer material by a transfer belt, and residual toner on the transfer belt after transfer. In the image forming apparatus provided with a cleaning unit to be removed,
A bias application mechanism capable of applying a bias voltage across the front and back surfaces of the transfer belt;
After the transfer belt is stopped upon completion of the image forming operation, there is provided a transfer belt neutralizing unit that neutralizes the transfer belt while maintaining a bias voltage application state by the bias application mechanism.

In the image forming apparatus having this configuration, the transfer belt is neutralized by maintaining the bias voltage application state by the bias application mechanism even after the transfer belt stops rotating when the copying operation is completed. be able to.
Here, static elimination means that the charge on the transfer belt is reduced or eliminated by neutralizing the charge from the charged surface of the transfer belt.
Therefore, even if the transfer belt is started to resume copying to the next transfer material in this state, the above-described reversely charged toner is conveyed along with the rotation of the transfer belt and adheres to the back surface of the transfer material. Can be prevented in advance.

Here, as shown in the prior art, it is considered that even if the timing for discharging the transfer belt is set immediately before the start of the copying operation, the backside contamination can be prevented. However, in this case, since it takes time to neutralize the transfer belt before the start of copying, the timing until the image is transferred to the transfer material is delayed, which is not preferable.
Therefore, the image forming apparatus according to the present invention can prevent the occurrence of back stain on the transfer material without delaying the timing from the start of copying to the transfer of the image to the transfer material.

(Configuration 2)
A second characteristic configuration of the image forming apparatus according to the present invention is that a maintenance time for maintaining the application state of the bias voltage by the bias application mechanism is set to 1 second or more after the transfer belt is stopped. .

The inventors examined the occurrence of back-stain on the transfer material when the maintenance time for maintaining the bias voltage application state by the bias application mechanism was variously changed after the transfer belt was stopped (see Table 1). As a result, it was confirmed that when the maintenance time was 1 second or longer, there was almost no stain on the transfer material. Therefore, if the maintenance time is 2 seconds or more, it is considered that the back stain on the transfer material is eliminated.
Further, it is preferable that the maintenance time is 120 seconds or less, because sufficient neutralization of the transfer belt can be expected and deterioration of the transfer belt due to such bias application can be suppressed.
Therefore, a preferable range of the maintenance time can be set to 2 to 120 seconds, for example.
Therefore, the image forming apparatus described in the second characteristic configuration of the present invention can secure a sufficient time for removing the charge over the entire length of the transfer belt. Therefore, it is possible to reliably prevent the reversely charged toner from adhering to the transfer belt from the cleaning unit, and it is possible to provide an image forming apparatus that is less likely to cause back transfer stains.

(Configuration 3)
A third characteristic configuration of the image forming apparatus according to the present invention is configured such that a conductive member that rotates in synchronization with the rotation of the transfer belt is disposed opposite to the cleaning unit via the transfer belt,
The bias applying mechanism is an applying mechanism that applies the bias voltage between the conductive member and the cleaning unit, and applies a cleaning bias voltage during an image forming operation.

In the image forming apparatus according to the third characteristic configuration of the present invention, for example, an existing drive roller that rotates in synchronization with the rotation of the transfer belt is used as the conductive member, so that the conductive member and the cleaning unit A cleaning bias voltage can be applied between them. That is, at the time of actual copying, a predetermined bias can be applied after the transfer belt is stopped by using a conductive member or the like that works for applying a cleaning bias.
Therefore, it is not necessary to add a configuration such as a corona discharge means particularly for cleaning on the transfer belt, so that the configuration of the image forming apparatus can be simplified and generation of harmful substances such as ozone due to the corona discharge. Can be suppressed.

(Configuration 4)
A fourth characteristic configuration of the image forming apparatus according to the present invention is that the bias applying mechanism applies a bias voltage having the same polarity as the transfer bias to the cleaning unit.

  As described above, due to the influence of the transfer bias, when the transfer belt is stopped, the surface side of the transfer belt is charged with a polarity opposite to that of the transfer bias, and the cleaning unit located on the surface side of the transfer belt is Thus, the transfer belt can be neutralized by applying a bias voltage having the same polarity as that of the transfer bias (the transfer bias reverses the direction of the voltage applied to the transfer belt). As a result, the back stain can be reduced.

(Configuration 5)
A fifth characteristic configuration of the image forming apparatus according to the present invention is that the bias applying mechanism applies a bias voltage having a polarity opposite to the transfer bias to the conductive member.

  As described above, due to the influence of the transfer bias, when the transfer belt is stopped, the surface side of the transfer belt is charged with the opposite polarity to the transfer bias, and the conductive member located on the back side of the transfer belt On the other hand, the transfer belt can be neutralized by applying a bias voltage having a polarity opposite to that of the transfer bias (the direction of the voltage applied to the transfer belt is opposite to that of the transfer bias). As a result, the back stain can be reduced.

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is a schematic diagram showing an example of a main part of an image forming apparatus for carrying out the present invention.
The image forming apparatus X includes an image forming unit A having a photoreceptor 1 that is an image carrier on which an electrostatic image is formed, and development that visualizes the electrostatic image on the photoreceptor 1 with charged toner T. Part B, a transfer part C for applying a transfer bias to transfer the toner image on the photosensitive member 1 to the transfer material P by the transfer belt 6, and a cleaning part for removing the residual toner T ′ on the transfer belt 6 after the transfer. D is provided.

The photosensitive member 1 provided in the image forming unit A rotates in the clockwise direction. Around the photosensitive member 1, there are a charging unit 2, exposure units 18 to 19, a developing unit B, a transfer unit C, and a drum cleaning unit 5 for removing the toner T adhering to the surface of the photosensitive unit 1. It is provided.
In the present application, an amorphous silicon drum that can be positively charged as the photosensitive member 1, a reversal development as a developing method, and a toner that is positively charged as a toner T can be applied, but are not limited thereto.

The transfer unit C is configured to press the transfer belt 6, the drive roller 7 that rotates the transfer belt 6 counterclockwise, the driven roller 8 that stretches the transfer belt 6, and the transfer belt 6 against the photoreceptor 1. A transfer roller 9 for applying a transfer voltage, and rollers A11 and B12 for maintaining a nip 10 between the transfer belt 6 and the photosensitive member 1 are provided.
Here, the drive roller 7 is composed of a conductive member in order to perform cleaning bias application. On the other hand, the transfer belt 6 made of urethane rubber, having a surface coat of GLS-213, and a volume resistivity of 10 to the 11.5th power can be applied, but is not limited thereto.

  In this configuration, a transfer bias can be applied between the photosensitive member 1 and the transfer roller 9 with the transfer belt 6 interposed therebetween, and a cleaning bias can be applied between the driving roller 7 and the fur brush 13 provided in the cleaning unit D. It can be applied.

For this purpose, the transfer section C is provided with a power supply device 14.
The power supply device 14 includes a power supply 15 for applying a voltage (minus side) to the transfer roller 9 when transferring the toner T from the photosensitive member 1 to the transfer material P, and a voltage (positive side) of the same polarity as the toner T for the driving roller 7. ) And a power source 16 for facilitating cleaning of the toner on the transfer belt 6 with the fur brush 13 using electrostatic repulsive force, and the transfer roller 9 and the drive via the switching mechanism 140. The roller 7 is set to a predetermined voltage application state.
The movement of the power supply device 14 is controlled by a controller 141 provided in the power supply device 14, and the controller 141 is provided with a transfer belt charge eliminating means 141a as referred to herein. . This transfer belt neutralizing means 141a is software stored in the controller 141, and by its function, after the transfer belt is stopped upon completion of the image forming operation, the voltage applied to the drive roller 7 is maintained and transferred. The belt 6 is neutralized.

The control command from the controller 141 is for a plurality of components of the image forming apparatus, and the main items related to the present application are shown in the timing chart shown in FIG.
FIG. 2 is a timing chart including the main charging, the developing bias, the transfer belt drive, the transfer bias, and the cleaning bias before and after the copy operation from the top.
The transfer belt neutralizing unit 141a that performs the operation unique to the present application is a unit that maintains the bias application state in the time zone indicated by T4 in FIG.

  The cleaning unit D includes a fur brush 13 that cleans the transfer belt 6, a SUS plate 3, and a toner collection container 4. The residual toner T ′ removed from the transfer belt 6 by the fur brush 13 is accommodated in the toner collecting container 4 by hitting the fur brush 13 with the SUS plate 3.

Next, the operation of each unit will be described using FIG. 1 as an example of the image forming apparatus.
a Copy Operation When image formation is started, first, the photoreceptor 1, the developing roller 17, and the transfer belt 6 start to circulate, and at the same time, a developing bias voltage is applied to the developing roller 17. Next, the charging unit 2 starts to uniformly charge (main charge) the photoconductor 1, and image exposure is started on the photoconductor 1 by the exposure units 18-19. The surface of the photosensitive member 1 that has undergone image exposure circulates in a state where the surface potential of the non-image portion is lowered, and the toner T adheres to the image portion of the photosensitive member 1 by contact with the developer 20 on the developing roller 17. Then, the toner is transferred to the nip 10 with the transfer belt 6.

On the other hand, the transfer material P is supplied from a paper feed unit (not shown), and the toner image on the photoconductor 1 is positioned between the photoconductor 1 and the transfer belt 6 (in FIG. 1) in accordance with the timing toward the transfer unit C. Inserted from the right). The transfer material P is inserted into the nip 10 while being conveyed on the transfer belt 6, and the toner T reaches the transfer roller 9 while contacting the upper surface of the sheet at the nip 10 by the rotation of the photoreceptor 1. At this time, a voltage having a polarity opposite to that of the toner T is applied to the transfer roller 9, whereby the toner T of the photoreceptor 1 is attracted toward the transfer material P, and the transfer material P is applied to the transfer belt 6 together with the toner T. While being attracted, it is conveyed on the transfer belt 6 in the left direction of the drawing.
A thermal fixing device 21 is disposed on the left side of the transfer portion C in the drawing, and the toner T is thermally fused to the transfer material P when the transfer material P on which the toner T is placed passes through the transfer portion P.

  On the other hand, the fur brush 13 rotates counterclockwise while contacting the transfer belt 6. When scattered toner or the like in the apparatus adheres to the transfer belt 6, the transfer belt 6 is subjected to electrostatic repulsion by the driving roller 7 to which a voltage having the same polarity as the residual toner T ′ on the transfer belt 6 is applied. The residual toner T ′ is removed from the transfer belt 6 by repeatedly brushing with the fur brush 13 around the transfer belt 6 while the residual toner T ′ is floated from the transfer belt 6.

b After Copying Operation The surface state of the transfer belt 6 at the end of the copying operation is charged to the plus side particularly between the driving roller 7 and the transfer roller 9. In this state, the drive of the transfer belt 6 is started to copy to the next transfer material P, and when the toner collection container 4 is reached, the transfer belt 6 charged to the positive side is reversely charged. The adhesion force of the toner is maintained, and the reversely charged toner (uncharged toner) recovered in the toner recovery container 4 is easily attached. As a result, the reversely charged toner adheres to the surface of the transfer belt 6, which causes back contamination of the transfer material P, which is a problem of the present application.

  Therefore, as described above, in the present application, the transfer belt neutralizing means 141a is provided, and as shown in FIG. 2, the drive roller (conductive member) 7 is provided even after the transfer belt 6 has finished rotating. The voltage application to is continued. That is, in the period T4 shown in the bottom column of FIG. 2, application of the same polarity as that during the copy operation (when applying the cleaning bias) is continued. The effect of this application appears as charge removal of the transfer belt 6, as will be described later.

[Results of demonstration test]
After the transfer belt 6 was stopped, the state of occurrence of back contamination in the transfer material P when the maintenance time for maintaining the bias application state (FIG. 2: T4) was variously changed was examined. The results are shown in Table 1.
The bias voltage maintaining time was measured after the transfer belt 6 stopped driving. In the table, “XX” indicates that a plurality of backside stains were observed after resuming copying to the transfer material P, and “X” indicates that only one backside soiling was observed after copying to the transfer material P was resumed. “Δ” indicates that the back stain is recognized, but it is hardly noticeable, and “◯” indicates that there is no back stain.
Furthermore, the main charge was +400 V, the development bias was +300 V, the paper gap was −200 V, the transfer bias was −50 μA with constant current control, and the cleaning bias was +10 μA with constant current control (in this state, driving was performed). The roller 7 maintains a voltage application state).

As a result, it was recognized that the back-stain on the transfer material P is almost eliminated if the maintenance time for maintaining the bias voltage application state is 1 second or longer after the transfer belt 6 is stopped. If it was 3 seconds or more, it was confirmed that the transfer material P had no backside contamination. Therefore, if the maintenance time is 2 seconds or longer, it is considered that the back stain on the transfer material is eliminated. This is considered to be because if the maintenance time of the bias voltage is 1 second or longer, the charge can be removed over the entire length of the transfer belt 6 even when the transfer belt 6 is stopped.
Further, if the bias voltage maintaining time is 120 seconds or less, it is possible to expect sufficient charge removal of the transfer belt 6 and it is possible to suppress the deterioration of the transfer belt 6 due to such bias application.

[Another embodiment]
(1) In the above embodiment, in the mechanism for applying the cleaning bias, after the cleaning at the time of copying is completed, the application to the driving roller 7 is maintained and the transfer belt 6 is neutralized. This type of structure in which the transfer belt 6 is sandwiched may be provided with a different bias applying mechanism.
(2) In the above embodiment, a bias voltage having a polarity opposite to the transfer bias is applied to the driving roller 7 and the applied state is maintained even after the belt is stopped to remove the belt. For example, the belt may be neutralized by applying a bias having the same polarity as the transfer bias to the fur brush.

Schematic of the image forming apparatus of the present invention The figure which showed the timing chart of the image forming apparatus of this invention The figure which showed the timing chart of belt drive and cleaning bias application of the conventional image forming device

Explanation of symbols

X Image forming apparatus A Image forming section B Developing section C Transfer section D Cleaning section P Transfer material T Toner T 'Residual toner 1 Photoconductor 6 Transfer belt 14 Power supply device 141a Transfer belt neutralizing means

Claims (5)

An image forming unit having an image carrier on which an electrostatic image is formed on the surface, a developing unit for visualizing the electrostatic image on the image carrier with charged toner, and applying the transfer bias to the image carrier. In an image forming apparatus provided with a transfer unit that transfers a toner image on a body to a transfer material by a transfer belt, and a cleaning unit that removes residual toner on the transfer belt after transfer,
A bias application mechanism capable of applying a bias voltage across the front and back surfaces of the transfer belt;
An image forming apparatus comprising: a transfer belt neutralizing unit that neutralizes the transfer belt while maintaining a bias voltage application state by the bias application mechanism after the transfer belt is stopped upon completion of an image forming operation.   The image forming apparatus according to claim 1, wherein after the transfer belt is stopped, a maintenance time for maintaining the application state of the bias voltage by the bias application mechanism is set to 1 second or more. A conductive member that rotates in synchronization with the rotation of the transfer belt is configured to be opposed to the cleaning unit via the transfer belt,
The image according to claim 1, wherein the bias applying mechanism is an applying mechanism that applies the bias voltage between the conductive member and the cleaning unit, and applies a cleaning bias voltage during an image forming operation. Forming equipment.   The image forming apparatus according to claim 3, wherein the bias applying mechanism applies a bias voltage having the same polarity as the transfer bias to the cleaning unit. The image forming apparatus according to claim 3, wherein the bias applying mechanism applies a bias voltage having a polarity opposite to the transfer bias to the conductive member.

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