JP2007121657A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a cleanerless type image forming apparatus, capable of suppressing residual transfer toner from entering into a recovery member during recovery mode and smoothly discharging the recovered toner to an image carrier during discharge mode, thereby forming satisfactory images. <P>SOLUTION: The cleanerless type image forming apparatus, having a toner recovery discharge device 16 on the upstream side of a charging device 12 for charging the surface of the image carrier 11 is provided with a brush roller 161 disposed in contact with the surface of the image carrier; a bias application electrode 162 disposed in contact with the roller; and a bias application power source device PW2, which applies the recovery bias for recovering the transfer residual toner to the roller 161 in the toner recovery mode and the discharge bias for discharging the toner on the roller 161 to the image carrier 11 in the toner discharge mode, respectively, to the roller 161 via the electrode 162. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an image forming apparatus using an electrophotographic system, an electrostatic recording system, or the like, such as a copying machine, a printer, a facsimile machine, or a multi-function machine combining two or more of these.

  In an electrophotographic image forming apparatus, usually, the surface of an image carrier such as a photoconductor is charged by a charging device, and the charging area is exposed according to an image to be formed from an exposure device, and electrostatically charged. A latent image is formed, the electrostatic latent image is developed by a developing device to form a visible toner image, and the visible toner image is transferred to a transfer target.

  In an electrostatic recording type image forming apparatus, for example, the surface of an image carrier such as an electrostatic recording dielectric is charged by a charging device, and an electrostatic recording device is used to charge the charged area in accordance with an image to be formed. The electrostatic latent image is formed to form an electrostatic latent image, the electrostatic latent image is developed by a developing device to form a visible toner image, and the visible toner image is transferred to a transfer target.

  In any type of image forming apparatus, the transfer target is a normal recording medium in a monochrome image forming apparatus, and the transferred toner image is fixed on the recording medium. In a color image forming apparatus, the transfer target is generally an intermediate transfer member, and the toner image primarily transferred to the intermediate transfer member is further secondarily transferred to a recording medium and fixed.

  In any type of image forming apparatus, the transfer residual toner remaining on the image carrier after the visible toner image formed on the image carrier is transferred to the transfer target is cleaned by a cleaning unit.

  As such a cleaning means, one using a cleaning blade arranged in contact with the surface of the image carrier is widely known. For example, as described in JP-A-9-50218, an image is formed together with a cleaning blade. In some cases, a foreign matter cleaning brush roller provided on the surface of the carrier is employed. A bias for collecting foreign matters such as paper dust charged to a polarity opposite to the normal charging polarity of the toner is applied to the foreign matter cleaning brush roller. There is also known a so-called cleanerless type image forming apparatus that does not have such a cleaning-specific cleaner.

  The cleaner-less type image forming apparatus will be further described. This type of image forming apparatus aims to reduce waste toner or reduce the size of the image forming apparatus. The latent image development and toner image transfer processes are executed. After transfer, the untransferred toner is charged and scattered by a charge control member disposed upstream of the charging device and passes through the charging device. Thereafter, the toner is collected simultaneously with the development in the developing device.

  In such a cleanerless type image forming apparatus, if an excessive amount of toner is discharged from the charge control member onto the image carrier during image formation, so-called exposure is performed in image exposure for forming an electrostatic latent image, for example. Or toner recovery failure occurs in the developing device, and image noise occurs.

  Therefore, a part or all of the transfer residual toner is collected by the charge control member at the time of image formation, and the collected toner is discharged to the image carrier at a timing that does not interfere with image formation such as non-image formation and collected by the developing device. Alternatively, for example, in a color image forming apparatus, it has been proposed to discharge from an image carrier to an intermediate transfer member.

  For example, in Japanese Patent Laid-Open No. 9-325607, a rotating member for disturbing a transfer residual toner that contacts an image carrier is disposed upstream of a charging device, and the rotating member to which a toner recovery bias is applied during image formation. Describes that toner remaining after transfer is collected and discharged from the rotating member to which a toner discharge bias is applied during non-image formation. In this case, the transfer residual toner disturbance rotating member functions as a toner collecting member.

Japanese Patent Laid-Open No. 9-50218 JP 9-325607 A

  However, in such a configuration that the transfer residual toner is collected during image formation by this toner collecting member and the collected toner is discharged during non-image formation, the collecting member is refreshed by discharging the collected toner, and the function can be maintained. However, if the transfer residual toner enters the inside of the collecting member at the time of collecting the toner, the toner that has entered the toner cannot be discharged sufficiently at the time of discharging, and the collecting member deteriorates its function.

  Accordingly, the present invention provides an image carrier, a charging device that charges the surface of the image carrier, and an electrostatic latent image forming device that forms an electrostatic latent image on the image carrier charged by the charging device. A developing device that develops an electrostatic latent image on the image carrier into a visible toner image, a transfer device that transfers the visible toner image on the image carrier to a transfer target, and A toner recovery mode that includes a toner recovery member provided upstream of the charging device and downstream of the transfer device in the surface movement direction, and recovers at least a portion of the transfer residual toner on the image carrier during image formation In the toner discharge mode in which the transfer residual toner on the image carrier is collected by the toner collecting member and the collected toner is discharged from the toner collecting member onto the image carrier at a timing that does not hinder image formation. The collected toner is A cleanerless type image forming apparatus that discharges from a recovery member onto the image carrier, wherein the toner recovered by the toner recovery member in the toner recovery mode is less likely to enter the recovery member, and the toner discharge It is an object of the present invention to provide an image forming apparatus that can be sufficiently discharged in the mode, thereby suppressing a decrease in the toner collecting function of the toner collecting member, and thus forming a good image.

The present inventor has conducted research to solve the above-mentioned problems and has come to know the following.
When collecting the transfer residual toner on the toner collecting member, it is only necessary to apply a toner collecting bias to the toner collecting member as in the conventional case. When discharging the collected toner, the toner collecting bias is applied to the toner collecting member. do it.

  The toner collecting member is preferably a brush roller from the viewpoint of easy retention of the collected toner, charge control of the toner, reduction of stress on the surface of the image carrier, and the like. However, if the brush roller is used, the toner enters the brush roller, and unless some contrivance is made, it becomes difficult to smoothly discharge the toner, resulting in a problem that the toner collecting function of the brush roller is lowered.

  In this regard, the application of toner recovery bias and toner discharge bias to the brush roller is not applied to the brush roller shaft (core metal) as is generally considered, but to the brush roller image carrier. A separate bias applying electrode may be brought into contact with a portion opposite to the roller diameter direction from the facing portion, and this may be performed through the electrode. The shaft (core metal) of the brush roller may be electrically floated.

By doing so, when a bias for collecting the transfer residual toner is applied, the applied effective bias differs between the electric field application nip between the brush and the image carrier and the electric field application nip between the brush and the electrode. In the electric field application nip portion between the brush and the image carrier, a bias is applied so that the toner on the image carrier moves into the brush, but in the electric field application nip portion between the brush and the electrode, the toner moves from the inside of the brush to the outside of the brush. A bias that moves is applied.
Therefore, excessive toner can be prevented from entering the brush, and the toner collected by the brush can be discharged sufficiently smoothly when the toner is discharged. Such smooth toner discharge suppresses toner accumulation on the brush roller, undesirable toner spillage caused by the toner accumulation, and deterioration of the toner recovery function of the brush roller.

  A similar effect can be achieved by applying a voltage to each of the shaft (core metal) and the electrode of the brush roller. However, with the above configuration, the power supply device can be reduced, and the image forming apparatus can be reduced in size and reduced accordingly. Pricing is possible.

Based on this finding, the present invention
An image carrier, a charging device for charging the surface of the image carrier, an electrostatic latent image forming device for forming an electrostatic latent image on the image carrier charged by the charging device, and the image carrier A developing device that develops the electrostatic latent image on the image to form a visible toner image, a transfer device that transfers the visible toner image on the image carrier to a transfer target, and the charging in the surface movement direction of the image carrier. An image carrier in a toner collection mode that includes a toner collection member provided on the upstream side of the apparatus and on the downstream side of the transfer apparatus, and collects at least a part of the transfer residual toner on the image carrier during image formation. In the toner discharge mode in which the toner remaining on the upper transfer is collected by the toner collecting member, and the collected toner is discharged from the toner collecting member onto the image carrier at a timing that does not hinder image formation, the collected toner is used as the toner. The image from the recovery member A cleanerless type image forming apparatus for discharging onto a holder, wherein a brush roller disposed in contact with the surface of the image carrier is employed as the toner collecting member, and a portion of the brush roller that contacts the image carrier; Has a bias applying electrode in contact with a portion on the opposite side of the roller diameter direction, and in the toner recovery mode, a recovery bias for recovering the transfer residual toner on the image carrier to the brush roller via the electrode. An image forming apparatus provided with a bias applying power supply device that applies a discharge bias to the brush roller via the electrode, which is applied to the roller and discharges the toner collected on the brush roller to the image carrier in the toner discharge mode. I will provide a.

  According to the image forming apparatus of the present invention, the transfer residual toner on the image carrier is recovered to the brush roller by applying the recovery bias to the brush roller in the toner recovery mode during image formation. However, since it is applied via a bias application electrode disposed in contact with the portion of the brush roller that is in contact with the image bearing member, the toner roller is prevented from excessively entering the brush roller. In other words, the toner is collected so that the subsequent toner discharge is smooth and easy.

The toner collected on the brush roller is smoothly and sufficiently discharged onto the image carrier by applying a discharge bias to the brush roller via the electrode in a toner discharge mode at a timing that does not interfere with image formation. Then, the brush roller is brought into a state where it can be used again for toner recovery.
As a result, a good image can be formed accordingly.

  Here, the “cleanerless type image forming apparatus” does not have a cleaning cleaner such as a cleaner having a cleaning blade in contact with the surface of the image carrier as a means for cleaning the transfer residual toner on the surface of the image carrier. An image forming apparatus, for example, for causing the developing device to collect toner discharged from the brush roller onto the image carrier, or for transferring toner discharged from the brush roller onto the image carrier (for example, And the like to be discharged to an intermediate transfer member in a color image forming apparatus.

  Examples of “timing that does not hinder image formation” include ““ between images ”and“ after image formation ”when a plurality of images are formed.

  The electric field application nip width between the brush roller and the electrode may be made larger than the electric field application nip width between the brush roller and the image carrier. As a result, it is possible to extend the time during which the bias for moving the toner from the inside of the brush roller to the outside of the brush roller is applied, and to suppress the accumulation of toner inside the brush roller.

  A representative example of the electrode is one having a shape curved along the outer periphery of the brush roller.

Examples of the “electrostatic latent image forming apparatus” include an electrostatic recording apparatus in the case where the image forming apparatus is of an electrostatic recording type employing an electrostatic recording dielectric as an image carrier. Examples of the image carrier that employs a photoreceptor include an image exposure apparatus.
The image forming apparatus according to the present invention may be either a monochrome image forming apparatus or a color image forming apparatus.
Examples of the transfer medium include a recording medium such as recording paper in a monochrome image forming apparatus, and an intermediate transfer body that primarily transfers a toner image formed on an image carrier in a color image forming apparatus. Can do.

  As described above, according to the present invention, an image carrier, a charging device that charges the surface of the image carrier, and an electrostatic image that forms an electrostatic latent image on the image carrier charged by the charging device. A latent image forming device; a developing device that develops an electrostatic latent image on the image carrier to form a visible toner image; a transfer device that transfers the visible toner image on the image carrier to a transfer target; Including a toner recovery member provided upstream of the charging device and downstream of the transfer device in the surface movement direction of the image carrier, and collects at least a portion of the transfer residual toner on the image carrier during image formation In the toner collecting mode, the toner remaining on the image carrier is collected by the toner collecting member, and the toner is discharged from the toner collecting member onto the image carrier at a timing that does not hinder image formation. In mode, the recovered A cleanerless type image forming apparatus that discharges toner from the toner collecting member onto the image carrier, and makes it difficult for the toner collected by the toner collecting member to enter the inside of the collecting member in the toner collecting mode. Therefore, it is possible to provide an image forming apparatus that can sufficiently discharge in the toner discharge mode, thereby suppressing a decrease in the toner recovery function of the toner recovery member, and thus can form a better image.

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 shows an example of an image forming apparatus according to the present invention.
The image forming apparatus shown in FIG. 1 is a tandem type full color printer. This printer has an endless intermediate transfer belt 3 wound around a driving roller 21 and a roller 22 facing the driving roller 21. The transfer belt 3 can be rotated counterclockwise in the figure (arrow direction in the figure) by a driving roller 21 driven by a belt driving unit (not shown).

  The drive roller 21 is faced with a cleaner 4 for cleaning the secondary transfer residual toner on the transfer belt 3 and the secondary transfer roller 5 is faced. The toner or the like collected by the cleaner 4 is sent to a waste container by a conveying means (not shown).

  The surface layer portion of the secondary transfer roller 5 is formed of an elastic material, and is pressed against the intermediate transfer belt 3 by a pressing unit (not shown) to form a nip portion between the intermediate transfer belt 3 and the intermediate transfer belt 3. , Or following the movement of the recording medium S fed into the nip as will be described later. A secondary transfer bias voltage can be applied to the secondary transfer roller 5 from a secondary transfer bias application power supply device (not shown).

  A fixing device 6 is disposed above the intermediate transfer belt 3 and the secondary transfer roller 5, and a timing roller pair 7 is disposed below the intermediate transfer belt 3 and the secondary transfer roller 5. A recording medium storage cassette that stores the medium is disposed.

The fixing device 6 includes a fixing roller incorporating a heat source such as a halogen lamp heater (not shown) and a pressure roller pressed against the fixing roller.
The recording medium S stored in a recording medium storage cassette (not shown) can be pulled out one by one by a medium supply roller (not shown) and supplied to the timing roller pair 7.

  Between the rollers 21 and 22 around which the intermediate transfer belt 3 is wound, the yellow image forming unit Y, the magenta image forming unit M, the cyan image forming unit C, and the rollers 21 to 22 along the transfer belt 3. Black image forming portions K are arranged in this order.

  Each of the image forming units Y, M, C, and K includes a drum-type photoconductor 11 as an electrostatic latent image carrier, and a charging device 12, an image exposure device 13, and a developing device 14 are provided around the photoconductor. The primary transfer roller 15 and a toner collection / discharge device 16 for collecting and discharging the primary transfer residual toner on the photosensitive member are arranged in this order.

The primary transfer roller 15 faces the photoconductor 11 with the transfer belt 3 in between, and rotates as the belt travels. A primary transfer bias voltage for primary transfer of the toner image formed on the photoreceptor 11 to the belt 3 can be applied to the primary transfer roller 15 from a power supply device for primary transfer bias application (not shown).
The exposure device 13 can perform image exposure on the photoconductor 11 using a laser beam in accordance with image information provided from a personal computer (not shown) or the like.

The photoconductor 11 in each image forming unit is a negatively chargeable photoconductor here, and can be driven to rotate clockwise in the drawing by a photoconductor drive motor (not shown).
As shown in FIG. 2, the charging device 12 in each image forming unit has a charging roller 121 disposed in contact with the surface of the photoconductor 11 as a charging member, and the charging bias applying power supply device PW1 is connected to the charging roller 121. A charging bias voltage can be applied at a predetermined timing. In this example, the charging bias voltage is a voltage obtained by superimposing an AC voltage on a DC voltage.

  The developing device 14 in each image forming unit is not limited thereto, but in this example, a negatively chargeable toner is used, and an electrostatic latent image formed on the photoconductor 11 is converted into a developing bias applying power supply device. Reversal development can be performed by a developing roller 141 to which a developing bias voltage is applied from PW3 (see FIG. 2).

  As shown in FIG. 2, the toner collecting and discharging device 16 in each image forming unit includes a brush roller 161 disposed in contact with the photoconductor 11 and a contact portion of the roller 161 with the photoconductor 11 opposite to the roller diameter direction. And a bias applying power supply device PW2 for applying a toner recovery bias or a toner discharge bias to the electrode 162. The brush roller cored bar (shaft) 161a is electrically floated.

  In this example, the power supply device PW2 can apply, to the electrode 162, a voltage obtained by superimposing an AC voltage on a DC voltage for collecting the primary transfer residual toner on the photoconductor 11 to the brush roller 161 as a toner recovery bias. As a toner discharge bias, a DC voltage for discharging the toner collected by the brush roller 161 to the photoconductor 11 can be applied to the electrode 162.

  The width N2 in the roller circumferential direction of the electric field application nip between the brush roller 161 and the electrode 162 (in other words, the contact nip width N2 between the roller 161 and the electrode 162) is equal to the electric field application nip between the brush roller 161 and the photoconductor 11. It is desirable that the width is set to be larger than the width N1 in the roller circumferential direction (in other words, the contact nip width N1 between the roller 161 and the photoconductor 11).

According to this printer, an image can be formed using one or more of the Y, M, C, and K image forming units.
Taking a case where a full color image is formed using all of the image forming portions Y, M, C, and K as an example, first, a yellow toner image is formed in the yellow image forming portion Y, and this is formed on the transfer belt 3 as a primary. Transcript.

  That is, in the yellow image forming portion Y, the photosensitive member 11 is rotated in the clockwise direction in the drawing, and the image exposure device is applied to the charged area of the photosensitive member 11 whose surface is uniformly charged to a predetermined potential by the charging device 12. 13, yellow image exposure is performed, and a yellow electrostatic latent image is formed on the photoreceptor 11. The electrostatic latent image is developed by a developing roller 141 to which a developing bias of a developing device 14 having yellow toner is applied to become a visible yellow toner image, and the toner image is transferred onto the transfer belt 3 by a primary transfer roller 15. Primary transfer is performed. At this time, a primary transfer bias voltage is applied to the primary transfer roller 15 from a power supply device (not shown).

  Similarly, a magenta toner image is formed in the magenta image forming unit M and transferred to the transfer belt 3, a cyan toner image is formed in the cyan image forming unit C and transferred to the transfer belt 3, and in the black image forming unit K. A black toner image is formed and transferred to the transfer belt 3.

Yellow, magenta, cyan, and black toner images are formed at a timing at which these toner images are transferred onto the intermediate transfer belt 3 in an overlapping manner.
Thus, the multiple toner images formed on the transfer belt 3 are moved toward the secondary transfer roller 5 by the rotation of the transfer belt 3.

  On the other hand, the recording medium S is pulled out by a medium supply roller from a recording medium storage cassette (not shown), supplied to the timing roller pair 7 and is on standby.

  Thus, the recording medium S waiting at the timing roller pair 7 is supplied to the nip portion between the transfer belt 3 and the secondary transfer roller 5 in accordance with the multiple toner image sent by the intermediate transfer belt 3. The multiple toner image is secondarily transferred onto the recording medium S by a secondary transfer roller 5 to which a secondary transfer bias voltage is applied from a power supply device (not shown). Thereafter, the recording medium S is passed through the fixing device 6 where the multiple toner images are fixed on the recording medium S under heat and pressure. The recording medium S is continuously discharged to a discharge tray by a pair of discharge rollers (not shown).

The image is formed as described above. In this image forming apparatus, the toner collection / discharge device 16 in each image forming unit is operated as follows.
During image formation, the apparatus 16 is in a toner recovery mode. In the toner recovery mode, a toner recovery bias is applied from the power supply device PW2 to the brush roller 161 via the electrode 162, thereby at least on the photoconductor 11. The primary transfer residual toner is collected on the brush roller 161.

  In the toner recovery mode, the recovery bias is applied to the brush roller 161 via the electrode 162 from the opposite side of the brush roller 161 from the contact portion with the photosensitive member 11. The effective bias applied differs between the electric field application nip and the electric field application nip between the brush roller 161 and the electrode 162. Therefore, a bias is applied at the nip portion between the brush roller 161 and the photosensitive member 11 so that the toner on the photosensitive member 11 moves into the brush roller, and the toner on the photosensitive member 11 is smoothly collected by the roller 161. At the nip portion between the roller 161 and the electrode 162, a bias is applied to move the toner from the inside of the brush roller to the outside of the brush roller.

  Thus, excessive toner can be prevented from entering the brush roller, and the toner collected on the brush roller can be discharged sufficiently smoothly when the toner is subsequently discharged. Such smooth toner discharge suppresses accumulation of toner on the brush roller 161, undesirable toner spillage resulting therefrom, and a decrease in the toner recovery function of the brush roller 161.

  On the other hand, the toner discharge mode is set at a predetermined timing (in this example, between images when a plurality of images are formed and after image formation) at which there is no hindrance in image formation. A toner discharge bias is applied to the brush roller 161 via 162, whereby at least the primary transfer residual toner collected by the brush roller 161 is discharged onto the photoconductor 11. The toner discharged on the photoreceptor 11 is collected by the developing device 14 or discarded on the transfer belt 3.

  Next, a specific example of toner collection and discharge by the toner collection and discharge device 16 of the image forming unit in the image forming apparatus of FIG. 1 will be described. In the following description, Vdc indicates a DC voltage, and Vpp is a peak-to-peak voltage for AC voltage.

The brush roller 161 was provided with brush hair having a bristle length of 2.5 mm on a core metal (shaft) 161a, and had an outer diameter of 12 mm. The contact nip width N1 between the brush roller 161 and the photoconductor 11 was set to 5 mm, and the contact nip width N2 between the brush roller 161 and the electrode 162 was set to 6 mm. The relationship between N1 and N2 is not limited to this.
The rotation direction of the brush roller 161 was set so as to move in the same direction as that of the photoconductor 11, in other words, in the contact portion between them, in the opposite directions (counter direction). The rotation direction of the brush roller 161 is not limited to this.

  In both the toner recovery mode and the toner discharge mode, the charging bias by the charging device 12 is a bias in which an AC voltage (Vpp = 1200 V, frequency 2 kHz) is superimposed on a DC voltage (Vdc = −550 V). The development bias in was a bias (rectangular wave with 60% positive ratio (Duty)) in which an AC voltage (Vpp = 1600 V, frequency 2 kHz) was superimposed on a DC voltage (Vdc = −400 V). By applying the charging bias Vdc, the photoconductor 11 is charged to a surface potential of about −500V. An electrostatic latent image can be formed by subjecting the charged area to image exposure from the exposure device 13 and reducing the surface potential of the exposed portion to about −100.

<Toner recovery mode>
Toner recovery bias applied to the brush roller 161 via the electrode 162:
The whole is a rectangular wave voltage (duty 50%)
DC voltage Vdc = -300V AC voltage Vpp = 1000V, 1000Hz

The developing device 14 uses a negatively chargeable toner. The DC voltage at the toner recovery bias is set to a negative voltage because the transfer residual toner on the photoconductor 11 is a toner charged to a reverse polarity (positive polarity). Because there are many.
When Vdc = −300 V, Vmin is −800 V and Vmax is +200 V, and both the positive side and the negative side are applied to the unexposed portion (−500 V) and the exposed portion (−100 V) on the photosensitive member. Therefore, it is possible to collect the toner having both the normal charging polarity and the reverse charging polarity.

<Toner discharge mode>
Toner discharge bias applied to the brush roller 161 via the electrode 162:
A DC voltage Vdc = + 500V is applied between the images,
After image formation (job end), DC voltages Vdc = + 500 V and Vdc = −500 V were sequentially applied for the same time.

  By applying Vdc = + 500V between the images, the positively charged toner on the brush roller 161 collected during the image formation is ejected onto the photoconductor, and Vdc = + 500V and Vdc = −500V are sequentially applied after the image formation. As a result, both the positively charged toner and the negatively charged toner on the brush roller 161 are discharged onto the photosensitive member.

  When the effective voltage of the photosensitive member surface portion in contact with the cored bar 161a and the brush roller 161 when a bias was applied to the electrode 162 was measured, the toner recovery mode was as shown in FIG. Vpp in the bias applied to the surfaces of the electrode 162, the core metal 161a, and the photoreceptor 11 was 1000V, 800V, and 600V, and Vdc was −300V, −250V, and −200V. That is, the voltage decreased in the order of electrode> core metal> photoreceptor surface.

  Therefore, an electric field is generated between the photoconductor 11 and the brush roller 161 so that the plus toner moves into the brush, and a bias is applied between the photoconductor 11 and the electrode 162 so that the plus toner moves from the inside of the brush to the outside of the brush. .

  Further, when the toner is discharged between the images, +500 V is applied to the electrode 162. At this time, the voltages applied to the surfaces of the core metal 161a and the photoconductor 11 are +400 V and +300 V, respectively. Then, plus toner is discharged to the photoreceptor 11. That is, an electric field is generated between the photoconductor 11 and the brush roller 161 so that plus toner moves from the inside of the brush to the outside of the brush, and a bias is applied between the photoconductor 11 and the electrode 162 so that the plus toner moves into the brush. The toner attached to the electrode 162 can be transferred to the brush at the time of discharge.

  In order to apply such a bias, as shown in FIG. 5, there is a method in which a bias is applied to each of the electrode 162 and the cored bar 161a by further using a power supply device PW4. The number of power supply devices can be reduced, which is also preferable for downsizing the image forming apparatus.

In the image forming apparatus of FIG. 1, only black image forming portion K was used, and 10,000 sheets were printed at 5% B / W, and an experiment was performed to measure the amount of toner accumulated on brush roller 161 in image forming portion K.
In any experiment, the brush roller 161 was 2.5 mm in bristle length and 12 mm in outer diameter, as in the above specific example. The contact nip width N1 between the roller 161 and the photosensitive member 11 was set to 5 mm. The roller 161 was rotated in the same direction as the photoconductor 11.

The peripheral speed (system speed) of the photosensitive member was set to 100 mm / sec, and the peripheral speed of the roller 161 was set to 100 mm / sec.
Further, the charging bias by the charging device 12 is a bias in which an AC voltage (Vpp = 1200 V, frequency 2 kHz) is superimposed on a DC voltage (Vdc = −550 V), and a developing bias is a DC voltage (Vdc = −400 V). A bias (rectangular wave with a 60% positive ratio (Duty)) on which an alternating voltage (Vpp = 1600 V, frequency 2 kHz) was superimposed was used.

The toner discharge bias was set to Vdc = + 500 V between images in all experiments, and Vdc = + 500 V and −500 V in order after image formation.
The contact nip width N2 between the toner recovery bias application electrode and the brush roller was varied in each experiment as follows.

(Experimental example 1)
A bias was directly applied to the cored bar 161a without using an electrode (the same applies to the toner discharge bias).
Recovery bias: Vdc = −250V Vpp = 800V

(Experimental example 2)
A bias was applied to the electrode 162.
Recovery bias: Vdc = −300V, Vpp = 1000V, duty 50% rectangular wave bias Nip width between electrode and brush N2 = 4 mm <N1 = 5 mm

(Experimental example 3)
A rectangular wave bias of Vdc = −300V, Vpp = 1000V, duty 50% is applied to the electrode 162, and a rectangular shape with Vdc = −250V, Vpp = 800V, duty 50% is applied to the cored bar 161a as shown in FIG. A wave bias was applied.
The electrode-brush nip width N2 was set to 4 mm <N1 = 5 mm.
In the above experimental examples 1, 2, and 3, the voltage applied to the core 161a was set to be the same.

(Experiment 4)
A bias was applied to the electrode 162.
Recovery bias: Vdc = −300V, Vpp = 1000V, duty 50% rectangular wave bias Nip width between electrode and brush N2 = 6 mm> N1 = 5 mm

(Experimental example 5)
Instead of the electrode 162, a curved electrode 162 ′ along the circumferential surface of the brush roller 161 was employed as shown in FIG.
A bias was applied to the electrode 162 ′.
Recovery bias: Vdc = −300V, Vpp = 1000V, duty 50% rectangular wave bias Nip width between electrode and brush N2 = 8 mm> N1 = 5 mm

The following table shows the toner accumulation amount of the brush roller 161 in each experiment.

Presence of electrodes Electrode contact nip width N2 Number of power supply units Toner accumulation amount (g)
Experimental Example 1 None 1 2.1
Experimental example 2 Yes 4mm 1 0.8
Experimental Example 3 Yes 4mm 2 0.9
Experimental Example 4 Yes 6mm 1 0.6
Experimental Example 5 Yes 8mm 1 0.4

  As can be seen from the above experimental examples, the amount of toner accumulated in the brush roller 161 decreased with the electrode compared to when there was no bias application electrode. This is presumably because different biases are applied to the electrode and the brush core 161a, so that the toner moves from the inside of the brush to the surface between the brush roller and the electrode, and is easily discharged during discharge.

In Experimental Examples 2 and 3, there was no significant difference in the toner adhesion amount. However, in Experimental Example 2, it can be seen that one power supply device functions as two power supply devices in Experimental Example 3.
The toner accumulation amount decreases in the order of Experimental Examples 2, 4, and 5, and the accumulation decreases as the contact nip width N2 between the brush roller and the electrode increases. As in Experimental Examples 4 and 5, it can be said that the contact nip width between the brush roller and the electrode is preferably wider than the contact nip width between the brush roller and the photosensitive member. Further, since the contact area is enlarged when the contact surface is curved as illustrated in FIG. 4, a more preferable result is obtained. In short, it is more effective that the contact area between the electrode and the brush roller is wider than the contact area between the photoreceptor and the brush roller.

  The color image forming apparatus has been described above as an example, but the present invention can also be applied to a monochrome image forming apparatus.

  According to the present invention, in a cleanerless type image forming apparatus, it is possible to suppress the transfer residual toner on the image carrier from reaching the charging device of the image carrier during the image formation, thereby forming a better image. Can be used to make

1 is a diagram illustrating a schematic configuration of an example (color printer) of an image forming apparatus according to the present invention. FIG. 2 is an enlarged view showing a part of an image forming unit in the printer of FIG. 1. It is a figure which shows the measurement result of the effective voltage of the part relevant to a toner collection | recovery discharge apparatus. FIG. 3 is a diagram illustrating a case where a bias application electrode in the toner recovery and discharge apparatus is replaced with a curved electrode in FIG. 2. FIG. 3 is a diagram showing a case where a bias is also applied to a brush roller core in FIG. 2 as a reference.

Explanation of symbols

Y Yellow image forming portion M Magenta image forming portion C Cyan image forming portion K Black image forming portion 11 Photoconductor 12 Charging device 121 Charging roller 13 Image exposure device 14 Developing device 141 Developing roller 15 Primary transfer roller 16 Toner recovery and discharge device 161 Brush roller 161a Metal core 162 Bias application electrode PW1 Power supply device PW2 for charging bias application Power supply device PW3 for toner recovery and discharge bias application Power supply device PW4 for development bias application Power supply device N1 for applying bias to the brush roller metal brush and photosensitive Contact nip (electric field application nip) width N2 between the bodies Contact nip (electric field application nip) width 21 between the brush roller and the electrode 21 Driving roller 22 Opposing roller 3 Intermediate transfer belt 4 Cleaner 5 Secondary transfer roller 6 Fixing device 7 Timing roller pair S Recording medium

Claims (4)

  An image carrier, a charging device for charging the surface of the image carrier, an electrostatic latent image forming device for forming an electrostatic latent image on the image carrier charged by the charging device, and the image carrier A developing device that develops the electrostatic latent image on the image to form a visible toner image, a transfer device that transfers the visible toner image on the image carrier to a transfer target, and the charging in the surface movement direction of the image carrier. An image carrier in a toner collection mode that includes a toner collection member provided on the upstream side of the apparatus and on the downstream side of the transfer apparatus, and collects at least a part of the transfer residual toner on the image carrier during image formation. In the toner discharge mode in which the toner remaining on the upper transfer is collected by the toner collecting member, and the collected toner is discharged from the toner collecting member onto the image carrier at a timing that does not hinder image formation, the collected toner is used as the toner. The image from the recovery member A cleanerless type image forming apparatus for discharging onto a holder, wherein a brush roller disposed in contact with the surface of the image carrier is employed as the toner collecting member, and a portion of the brush roller that contacts the image carrier; Has a bias applying electrode in contact with a portion on the opposite side of the roller diameter direction, and in the toner recovery mode, a recovery bias for recovering the transfer residual toner on the image carrier to the brush roller via the electrode. A bias applying power supply device is provided that applies a discharge bias to the brush roller via the electrode, which is applied to the roller and discharges the toner collected on the brush roller to the image carrier in the toner discharge mode. An image forming apparatus.   The image forming apparatus according to claim 1, wherein an electric field application nip width between the brush roller and the bias application electrode is larger than an electric field application nip width between the brush roller and the image carrier.   The image forming apparatus according to claim 1, wherein the bias applying electrode has a curved shape along an outer periphery of the brush roller. The image forming apparatus according to claim 1, wherein the developing device collects toner discharged from the brush roller onto an image carrier.