JP5171223B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus such as a copying machine, a printer, and a facsimile machine that performs image formation.

Conventionally, as an image forming apparatus such as a copying machine, a printer, or a facsimile, an image forming apparatus having a configuration using an intermediate transfer member (moving member) is known. As described in Patent Document 1 (Japanese Patent Application Laid-Open No. 09-44007) as a cleaning device for an intermediate transfer member, a predetermined charge is applied to secondary transfer residual toner (residual toner) remaining on the intermediate transfer member. Some are provided with charging means.

The secondary transfer residual toner to which a predetermined charge is applied is reversely transferred from the intermediate transfer member to the photosensitive drum in the subsequent primary transfer portion, and is collected by the photosensitive drum cleaning device.

An in-line type color printer having a charging member that imparts a predetermined charge to the secondary transfer residual toner remaining on the intermediate transfer member is also known.

However, in the case of the in-line method, as described in Patent Document 2 (Japanese Patent Application Laid-Open No. 2004-21134), in the color mode, only at the first image forming station downstream of the charging member in the rotation direction of the intermediate transfer member. Most of the residual toner is collected.

Therefore, in the inline image forming apparatus, a charging / toner holding member (charging means) that holds a predetermined amount of the secondary transfer residual toner remaining on the intermediate transfer body and applies a predetermined charge to the secondary transfer residual toner. A color printer having a configuration has been proposed.

In the color printer having the charging / toner holding member, the secondary transfer residual toner held on the charging / toner holding member is transferred onto the intermediate transfer member at a predetermined timing such as when the post-rotation is performed after printing (hereinafter, referred to as “transferring toner”) , Called exhaling). This discharge is performed by alternately applying a DC bias of both polarities to the charging / toner holding member.

Here, since the charging / toner holding member applies a positive bias to collect the negative secondary transfer residual toner, most of the discharged toner has a negative polarity (the normal polarity is positive). is there. Control is performed so that the discharged toner is not transferred to the photosensitive drum in the first image forming station. Accordingly, the secondary transfer residual toner can be collected at an image station other than the first image station, and the collection of the secondary transfer residual toner at the first image station can be suppressed.

As a method of preventing the secondary transfer residual toner from being transferred to the photosensitive drum, there is a method of separating a transfer roller facing an image station that is not desired to be transferred. In addition, a positive transfer bias is applied to the transfer roller facing the image station that is not desired to be transferred, and a negative bias is applied to the charge roller of the image station that is not desired to be transferred. There is a method in which the image is not transferred to the photosensitive drum.

JP 09-44007 A Japanese Patent Laid-Open No. 2004-21134

However, in the conventional method, a series of cleaning operations during printing is completed, and the rotation of the intermediate transfer member is stopped while the secondary transfer residual toner is held on the charging / toner holding member. At the same time as the rotation of the intermediate transfer member was stopped, the bias applied to the charging / toner holding member was turned off.

For this reason, a part of the secondary transfer residual toner held on the charging / toner holding member is discharged onto the intermediate transfer member due to the physical vibration of the intermediate transfer member accompanying the rotation stop.

Further, the rotation of the intermediate transfer member is started from the state where the rotation of the intermediate transfer member is stopped and the toner is held on the charging / toner holding member. A bias is applied to the charging / toner holding member simultaneously with the start of rotation of the intermediate transfer member.

For this reason, a portion of the secondary transfer residual toner held on the charging / toner holding member is discharged onto the intermediate transfer member due to physical vibration of the intermediate transfer member accompanying the start of rotation.

The secondary transfer residual toner is discharged onto the intermediate transfer member on the downstream side from the position (charging / toner holding nip) where the charging / toner holding member and the intermediate transfer member face each other. The discharge is significant when the amount of secondary transfer residual toner held by the residual toner charging brush exceeds a predetermined amount or when the charge amount of the secondary transfer residual toner is insufficient.

Here, when an image forming operation is started in the image forming station, a positive bias is applied to the primary transfer roller, and a negative bias is applied to the charging roller. Most of the discharged secondary transfer residual toner has a negative polarity. For this reason, the discharged secondary transfer residual toner and an electric field in a direction repelling from the photosensitive drum are received, and remain on the intermediate transfer body without being transferred and collected on the photosensitive drum.

As a result, the discharged secondary transfer residual toner is transferred together with the output image from the intermediate transfer member to the recording material at the secondary transfer position. Further, the discharged secondary transfer residual toner adheres to the secondary transfer roller and stains the back side of the recording material.

Therefore, the present invention can suppress the discharge of residual toner to the moving body and suppress image defects caused by the discharged toner in an image forming apparatus having a charging unit that temporarily holds the residual toner attached to the moving body. An object is to provide an image forming apparatus.

In order to solve the above problems, a typical configuration of an image forming apparatus according to the present invention includes an image carrier that carries a toner image, and a movable body that transfers the toner image carried by the image carrier to a recording material. and Do mobile, said having contact with the moving body and a charging means for charging the deposited toner adhering to the movable body, and a voltage applying means for applying a voltage to the charging means, the toner by said voltage applying means The adhering toner is charged by the charging means to which a first voltage having a reverse polarity to the charging polarity is applied, and the adhering toner is moved from the moving body to the image carrier, whereby the adhering toner is removed from the moving body. In the image forming apparatus to be collected , the moving body is in contact with the charging unit before starting to move, and the charging unit has the same polarity as the first voltage and a smaller absolute value than the first voltage. Second Characterized in that it starts moving in a state where pressure is applied.

According to the present invention, in an image forming apparatus having a charging unit that temporarily holds residual toner attached to a moving body, the residual toner is prevented from being discharged to the moving body, and image defects caused by the discharged toner are suppressed. it can.

[ Reference example ]
A reference example of an image forming apparatus according to the present invention will be described with reference to the drawings.

(Image forming device)
FIG. 1 is a configuration diagram showing a color image forming apparatus according to this reference example (in this embodiment, an electrophotographic intermediate transfer type full-color printer).

As shown in FIG. 1, a color image forming apparatus 100 includes four image forming units (image forming units) 1Y, 1M, 1C, and 1Bk that form yellow, magenta, cyan, and black images. ). The four image forming units 1Y to 1Bk are arranged in a line at a constant interval.

Photosensitive drums 2a, 2b, 2c, and 2d as image carriers are installed in the image forming units 1Y, 1M, 1C, and 1Bk, respectively.

Around the photosensitive drums 2a to 2d, there are charging rollers 3a to 3d, developing devices 4a to 4d as developing means, transfer rollers 5a, 5b, 5c and 5d as transferring means, drum cleaning devices 6a, 6b and 6c, 6d is installed. Exposure devices 7a, 7b, 7c, and 7d are installed above the charging rollers 3a, 3b, 3c, and 3d and the developing devices 4a, 4b, 4c, and 4d, respectively.

The developing devices 4a to 4d contain yellow toner, magenta toner, cyan toner, and black toner. This reference example will be described using a toner having a negative charge.

The photoreceptor drums 2a to 2d are negatively charged organic photoreceptors and have a photosensitive layer on an aluminum drum base. The photosensitive drums 2a to 2d are rotationally driven in a direction indicated by an arrow (clockwise) at a predetermined process speed by a driving device (not shown).

The charging rollers 3a to 3d are in contact with the photosensitive drums 2a to 2d with a predetermined pressure contact force, and a desired charging bias is applied by a charging bias power source (not shown) so that the surfaces of the photosensitive drums 2a to 2d are predetermined. Charge uniformly to potential (negative polarity in this reference example ).

The exposure devices (laser scanner devices) 7a to 7d receive laser light modulated in accordance with time-series electric digital pixel signals of image information respectively input from a host computer (not shown) from a laser output unit (not shown). Output. The output laser light exposes the surfaces of the photosensitive drums 2a to 2d through respective reflecting mirrors (not shown), whereby image information is applied to the surfaces of the photosensitive drums 2a to 2d charged by the charging rollers 3a to 3d. An electrostatic latent image corresponding to the above is formed.

The developing devices 4a to 4d use a contact developing method as a developing method, and have a developing roller as a developer carrier. The toner carried on a thin layer on the developing roller is transported to a portion (developing portion) facing the photosensitive drums 2a to 2d as the developing roller is rotated by a developing driving means (not shown).

The electrostatic latent image formed on the photosensitive drum in the developing unit is developed (reversed development) as a toner image by a developing bias applied to the developing roller by a developing voltage applying unit (not shown).

The intermediate transfer belt (intermediate transfer member) 20 is formed in an endless belt shape in which a rubber base layer is coated with a dispersion of a fluorine resin such as PTFE. The rubber base layer is formed of PVdF (vinylidene fluoride resin), ETFE (tetrafluoroethylene-ethylene copolymer resin), polyimide, PET (polyethylene terephthalate), a resin such as polycarbonate, EPDM, or the like.

The transfer rollers 5a to 5d for primary transfer are made of an elastic member such as sponge rubber, and are transferred to the photosensitive drums 2a to 2d via the intermediate transfer belt (moving body) 20 at the primary transfer nip N. Abutting and rotating following the intermediate transfer belt 20. Primary transfer power sources 40a, 40b, 40c, and 40d are connected to the transfer rollers 5a to 5d, respectively, and a primary transfer bias is applied thereto.

The toner images developed on the photosensitive drums 2a to 2d are primarily transferred onto the rotating intermediate transfer belt 20 by transfer rollers 5a to 5d to which a primary transfer bias is applied.

The secondary transfer counter roller 23 is in contact with the secondary transfer roller 24 via the intermediate transfer belt 20 to form a secondary transfer portion M. The secondary transfer roller 24 is installed so as to be able to contact and separate from the intermediate transfer belt 20.

Further, the residual toner charging brush (charging means) 10 contacts the intermediate transfer belt 20 on the downstream side in the rotation direction of the intermediate transfer belt 20 with respect to the secondary transfer nip portion M and on the upstream side with respect to the primary transfer nip N. It is arranged in the state. The residual toner charging brush 10 removes and collects the transfer residual toner remaining on the surface of the intermediate transfer belt 20.

The material of the remaining toner charging brush 10 is nylon, the fineness is 300 T / 50 F, and the pile length is 5 mm. The brush width is 5 mm, the density is 80 KF / inch 2, and the resistance is 6.5 × 10 6. The material of the remaining toner charging brush 10 may be a synthetic fiber such as rayon, polyester, aramid, acrylic, modacrylic, vinylon, or the like.

A fixing device 12 having a fixing roller 12a and a pressure roller 12b is installed on the downstream side of the secondary transfer portion M in the conveyance direction of the recording material P.

(Image forming operation by color image forming apparatus)
Next, an image forming operation by the color image forming apparatus of the present embodiment will be described.

When the image forming operation start signal is issued, the photosensitive drums 2a to 2d of the image forming units 1Y to 1Bk that are rotationally driven at a predetermined process speed are uniformly charged by the charging rollers 3a to 3d, respectively (in this embodiment, Negatively charged).

Then, the exposure devices 7a to 7d respectively convert the input color-separated image signals into optical signals by a laser output unit (not shown). Then, each of the charged photosensitive drums 2a to 2d is scanned and exposed to laser light, which is a converted optical signal, to form an electrostatic latent image.

The developing device 4a, to which a developing bias having the same polarity as the charging polarity (negative polarity) of the photosensitive drum 2a is applied, applies yellow toner on the photosensitive drum 2a on which the electrostatic latent image is formed according to the charging potential on the surface of the photosensitive member. The electrostatic latent image is visualized and developed into a developed image.

This yellow toner image is primary-transferred onto the rotating intermediate transfer belt 20 by a transfer roller 5a to which a primary transfer bias (polarity opposite to the toner (positive polarity)) is applied at the primary transfer portion N. Is done. The intermediate transfer belt 20 to which the yellow toner image has been transferred is rotated toward the image forming unit 1M.

Also in the image forming unit 1M, the magenta toner image formed on the photosensitive drum 2b in the same manner as described above is superimposed on the yellow toner image on the intermediate transfer belt 20 and transferred by the primary transfer unit N. Is done.

Thereafter, cyan and black toner images formed by the photosensitive drums 2c and 2d of the image forming units 1C and 1Bk are primary-transferred onto the yellow and magenta toner images superimposed and transferred onto the intermediate transfer belt 20 in the same manner. Overlapping is performed sequentially at part N. As a result, a full-color toner image is formed on the intermediate transfer belt 20.

Then, the recording material P is conveyed to the secondary transfer portion M by the feeding roller (registration roller) 13 in accordance with the timing at which the front end of the full color toner image on the intermediate transfer belt 20 is moved to the secondary transfer portion M. The conveyed recording material P is subjected to secondary transfer of a full-color toner image at once by a secondary transfer roller 24 to which a secondary transfer bias (opposite polarity (positive polarity) to toner) is applied.

The recording material P on which the full-color toner image is formed is conveyed to the fixing device 12 and heated and pressed at the fixing nip portion between the fixing roller 12a and the pressure roller 12b to thermally fix the full-color toner image. . The recording material P on which the toner image is thermally fixed on the surface of the recording material P is discharged to the outside, and a series of image forming operations is completed.

During the primary transfer described above, the primary transfer residual toner remaining on the photosensitive drums 2a to 2d is removed and collected by the drum cleaning devices 6a to 6d.

Further, the secondary transfer residual toner remaining on the intermediate transfer belt 20 after the secondary transfer is charged to a polarity (positive polarity) opposite to the normal charging characteristic (negative polarity) by the residual toner charging brush 10, and the primary transfer. Collected on the photosensitive drum 2a at the nip N <cleaning operation during printing>.

The residual toner charging brush 10 has a function of collecting and temporarily holding a part of the secondary transfer residual toner, and transferring the collected and held toner onto the intermediate transfer belt 20 at a predetermined timing such as post-rotation. (Hereinafter referred to as spitting). The remaining toner charging brush 10 charges the collected and retained toner to a negative polarity. As a result, the secondary transfer residual toner is not collected by the image forming unit 1Y, and a negative bias is applied to the primary transfer rollers 5b and 5c of the image forming units 1M and 1C, so that the waste toner of the image forming units 1M and 1C is applied. <Discharge operation> to selectively collect in a container.

<Cleaning operation during printing>
Hereinafter, the secondary transfer residual toner collecting operation by the residual toner charging brush 10 will be described in detail.

Since the toner having normal charging characteristics (negative polarity) before the secondary transfer is transferred onto the recording material in the secondary transfer process, the secondary transfer residual toner has a polarity opposite to that of the normal charging characteristics (negative polarity). Many are positively charged.

However, not all secondary transfer residual toners are positively charged, and some toners are neutralized and have no charge, and some toners maintain negative polarity.

A positive bias (about 1300 V in this reference example , hereinafter referred to as a residual toner charging bias) is applied to the remaining toner charging brush 10 by a power source (voltage applying means) 14. At the charging nip W formed by the residual toner charging brush 10 and the intermediate transfer belt 20, discharge occurs between the residual toner charging brush 10 and the intermediate transfer belt 20. Due to the discharge, the secondary transfer residual toner on the intermediate transfer belt is charged with a polarity (positive polarity) opposite to the normal charging characteristics.

When the secondary transfer residual toner moves to the charging nip W, the residual toner charging brush 10 charges the secondary transfer residual toner positively and at the same time electrostatically collects a part of the secondary transfer residual toner. -Hold and physically collect and hold.

The secondary transfer residual toner charged positively without being collected and held by the residual toner charging brush 10 at the charging nip portion W remains on the intermediate transfer belt 20 and is primarily transferred at the image forming portion 1Y. Move to nip N.

Here, as described above, a positive bias (about 500 V in this reference example ) is applied to the primary transfer roller 5a during image formation. Therefore, the developed image (negative polarity) formed on the photosensitive drum 2a is transferred onto the intermediate transfer belt 20 by electrostatic force, and at the same time, most of the secondary transfer residual toner (positive polarity) is transferred. The image is reversely transferred onto the photosensitive drum 2a by an electrostatic force.

The secondary transfer residual toner reversely transferred onto the photosensitive drum 2a is scraped off from the photosensitive drum 2a by the cleaning blade 6a and collected in the waste toner box 8a, and a series of collecting operations is completed.

<Discharge operation>
Next, the discharging operation of the secondary transfer residual toner by the residual toner charging brush 10 will be described in detail.

Since the secondary transfer residual toner of positive polarity is collected by the cleaning operation during printing, a part (mostly negative polarity) of the secondary transfer residual toner is collected and held in the residual toner charging brush 10. . That is, most of the toner collected and held by the remaining toner charging brush 10 is charged to a negative polarity, but a part is also charged to a positive polarity.

Therefore, in order to discharge the collected and held residual transfer residual toner onto the intermediate transfer belt 20, a bipolar DC bias is alternately applied to the residual toner charging brush by a power source (not shown). That is, when a positive bias is applied to the residual toner charging brush 10, a positive secondary transfer residual toner is discharged onto the intermediate transfer belt 20, and when a negative bias is applied, a negative secondary transfer residual toner is discharged onto the intermediate transfer belt 20. .

The toner discharged on the intermediate transfer belt 20 is conveyed to the primary transfer nip N of the yellow image forming unit 1Y as the intermediate transfer belt 20 rotates.

Before the toner discharged on the intermediate transfer belt 20 reaches the primary transfer nip N, a positive bias (about +400 V in this reference example ) is applied to the primary transfer roller 5a. As a result, most of the secondary transfer residual toner charged to the negative polarity remains on the intermediate transfer belt 20 without being transferred and collected to the photosensitive drum 2a by electrostatic force. On the other hand, a part of the positive transfer residual toner having a positive polarity is transferred and collected on the photosensitive drum 2a by electrostatic force.

The toner remaining on the intermediate transfer belt 20 is conveyed to the primary transfer nip N of the magenta image forming unit 1M as the intermediate transfer belt 20 rotates.

Before the toner discharged on the intermediate transfer belt 20 reaches the primary transfer nip portion N of the magenta image forming unit 1M, a negative bias (about −400 V in this reference example ) is applied to the primary transfer roller 5b. To do. As a result, the secondary transfer residual toner is collected on the photosensitive drum 2b by electrostatic force.

The secondary transfer residual toner discharged onto the intermediate transfer belt 20 is exposed to light by applying a positive bias to the primary transfer rollers 5a and 5b and applying a negative bias to the primary transfer roller 5c. You may transfer and collect | recover to the drum 2c.

By performing the control as described above, the secondary transfer residual toner collected and held by the residual toner charging brush 10 during the printing cleaning operation can be selectively collected by the image forming unit other than the specific image forming unit. it can. Accordingly, it is possible to suppress the secondary transfer residual toner from being concentrated in the waste toner box of the specific image forming unit.

In addition, by performing the above discharging operation at a predetermined timing such as post-rotation after printing, the residual toner remaining in the residual toner charging brush 10 exceeds the limit of the recovery capability, and the secondary transfer residual toner is discharged. Reduction in charging ability can be suppressed.

Next, various timings in the cleaning operation during printing will be described in comparison with various conventional timings.

≪Timing chart-Conventional example≫
FIG. 2 is a timing chart of the conventional cleaning operation during printing.

As shown in FIG. 2, before starting the cleaning operation during printing, the intermediate transfer belt 20 is in a stopped state, and the residual toner charging brush 10 is in a state in which bias application from a power source (not shown) is turned off. At this time, the residual toner charging brush 10 holds the secondary transfer residual toner collected during the previous cleaning operation during printing.

When a print signal is received from the host computer, a cleaning operation during printing is started, and the intermediate transfer belt 20 starts to rotate (t1). At the same time, a positive residual toner charging bias (about 1300 V) is applied (ON) to the residual toner charging brush 10 by a power source (not shown).

As the intermediate transfer belt 20 starts to rotate, the remaining toner charging brush 10 physically vibrates. For this reason, a portion of the secondary transfer residual toner held on the residual toner charging brush 10 may be discharged from the residual toner charging brush 10 onto the intermediate transfer belt 20. This is remarkable when the amount of secondary transfer residual toner held by the residual toner charging brush 10 exceeds a predetermined amount or when the charge amount of the secondary transfer residual toner is insufficient. This phenomenon is particularly noticeable when the process speed is high.

In the conventional example, in the final step of the cleaning operation during printing, the rotation of the intermediate transfer belt 20 is stopped and the application of the residual toner charging bias is turned off (t2).

As the intermediate transfer belt 20 stops, the remaining toner charging brush 10 physically vibrates. For this reason, a portion of the secondary transfer residual toner held on the residual toner charging brush 10 may be discharged from the residual toner charging brush 10 onto the intermediate transfer belt 20.

Here, since the residual toner charging brush 10 applies a positive bias and collects negative secondary transfer residual toner, most of the toner discharged from the residual toner charging brush 10 onto the intermediate transfer belt 20 is Has negative polarity. Therefore, when image formation is started in the image forming units 1Y to 1Bk and a positive bias (about 500V) is applied to the primary transfer rollers 5a to 5d, the secondary transfer residual toner is repelled from the photosensitive drums 2a to 2d. Receive the force in the direction to do. For this reason, the discharged secondary transfer residual toner remains on the intermediate transfer belt 20 without being transferred onto the photosensitive drum 2a.

Since a positive bias (+200 V in this reference example ) is applied to the secondary transfer roller 24, the discharged secondary transfer residual toner is transferred from the intermediate transfer belt 20 to the recording material at the secondary transfer portion M. Transferred to P together with the output image. In addition, when the recording material P is in the secondary transfer portion M, the discharged secondary transfer residual toner adheres to the secondary transfer roller 24 and stains the back side of the recording material P that is conveyed later.

≪Timing chart- Reference example≫
FIG. 3 is a timing chart at the time of the cleaning operation during printing according to this reference example .

As shown in FIG. 3, the intermediate transfer belt 20 is in a stopped state and the remaining toner charging brush 10 is in a state in which bias application from a power source (not shown) is turned off before the cleaning operation during printing is started, as in the conventional example. It is. At this time, the residual toner charging brush 10 holds the secondary transfer residual toner collected during the previous cleaning operation during printing.

In this reference example , when a print signal is received from the host computer, a cleaning operation during printing is started, and a positive residual toner charging bias (about 1300 V) is applied (ON) to the residual toner charging brush 10 by a power source (not shown). (T1). Then, 200 ms after the bias application, the intermediate transfer belt 20 starts to rotate (ta).

As described above, by applying a positive bias to the residual toner charging brush 10 before starting the intermediate transfer belt 20, the negative secondary transfer residual toner held on the residual toner charging brush 10 is electrostatically charged. Is attracted to the remaining toner charging brush 10 by an effective force. For this reason, even if the residual toner charging brush 10 is physically vibrated as the intermediate transfer belt 20 is started, the negative secondary transfer residual toner held on the residual toner charging brush 10 is discharged onto the intermediate transfer belt 20. I can't. Accordingly, image defects caused by the discharged toner can be suppressed.

In the final step of the cleaning operation during printing, first, the rotation of the intermediate transfer belt 20 is stopped (tb). Then, 200 ms after the rotation of the intermediate transfer belt 20 is stopped, the application of the residual toner charging bias is turned off (t2).

As described above, after the rotation of the intermediate transfer belt 20 is stopped, the bias application to the residual toner charging brush 10 is turned off, whereby the negative secondary transfer residual toner held on the residual toner charging brush 10 is electrostatically charged. Is attracted to the remaining toner charging brush 10 by a strong force. Therefore, even if the residual toner charging brush 10 is physically vibrated as the intermediate transfer belt 20 is stopped, the negative secondary transfer residual toner held by the residual toner charging brush 10 is discharged onto the intermediate transfer belt 20. I can't. Accordingly, image defects caused by the discharged toner can be suppressed.

In this reference example , the bias application to the residual toner charging brush 10 is turned ON / OFF 200 ms before the rotation start of the intermediate transfer belt 20 and 200 ms after the rotation stop. However, the present invention is not limited to 200 ms. Even if the residual toner charging brush 10 is physically vibrated as the intermediate transfer belt 20 is started, the secondary transfer residual toner is held in the residual toner charging brush 10. It may be a predetermined time. That is, the bias application to the residual toner charging brush 10 may be turned on and off a predetermined time before the rotation start of the intermediate transfer belt 20 and a predetermined time after the rotation stop.

Note that the positive secondary transfer residual toner held on the residual toner charging brush 10 may be partially ejected onto the intermediate transfer belt 20 due to physical vibration accompanying the start-up of the intermediate transfer belt 20. . However, when image formation is started and a positive bias (about 500 V) is applied to the primary transfer roller 5a, the positive secondary transfer residual toner is electrostatically transferred and collected to the photosensitive drum 2a. It does not cause problems such as image defects.

In this reference example , the intermediate transfer type image forming apparatus has been described. However, the present invention is not limited to this. For example, the image forming apparatus may employ a method in which a toner image on a photosensitive drum is directly transferred onto a recording material sucked and conveyed on a transfer conveyance belt (moving body). Such an image forming apparatus can obtain the same effect by performing the same control.

[ First embodiment]
Next, a first embodiment of an image forming apparatus according to the present invention will be described with reference to the drawings. The same reference numerals as those in the above-described reference example are given the same reference numerals, and the description thereof is omitted. FIG. 4 is a timing chart during the cleaning operation during printing in the first embodiment.

As shown in FIG. 4, the image forming apparatus according to the present embodiment performs stepwise application of a bias to the remaining toner charging brush 10 at the start of the cleaning operation during printing in the image forming apparatus of the reference example . Further, turning off the bias application to the remaining toner charging brush 10 at the end of the cleaning operation during printing is ended stepwise.

<< Timing chart-this embodiment >>
Similar to the conventional example and the above-described reference example , before starting the cleaning operation during printing, the intermediate transfer belt 20 is in a stopped state, and the residual toner charging brush 10 is in a state in which bias application from a power source (not shown) is turned off. At this time, the residual toner charging brush 10 holds the secondary transfer residual toner collected during the previous cleaning operation during printing.

In this embodiment, when a print signal is received from the host computer, a cleaning operation during printing is started, and first, a positive bias of about 300 V is applied to the remaining toner charging brush 10 from a power source (not shown) (t1). .

Then, 200 ms later, the intermediate transfer belt 20 starts to rotate, and simultaneously with the start of the rotation of the intermediate transfer belt 20, a positive polarity bias of about 1300 V is applied to the remaining toner charging brush 10 from a power source (not shown) ( ta).

In the final cleaning process, first, the rotation of the intermediate transfer belt 20 is stopped, and the residual toner charging bias is switched to about +300 V simultaneously with the stop of the rotation of the intermediate transfer belt 20 (tb). Then, 200 ms after the rotation of the intermediate transfer belt 20 is stopped, the application of the residual toner charging bias is turned off (t2).

The bias (+300 V in this embodiment) applied to the remaining toner charging brush 10 while the intermediate transfer belt 20 is stopped is optimized according to the surface potential of the intermediate transfer belt 20 (about +50 to +200 V in this embodiment). It should be. This is because when the bias is lower than the surface potential of the intermediate transfer belt 20, an electrostatic force acts in the direction of discharging negative secondary transfer residual toner from the residual toner charging brush 10 to the intermediate transfer belt side. It is because it ends up. Therefore, the bias applied to the remaining toner charging brush 10 while the intermediate transfer belt 20 is stopped needs to be 100 to 250 V higher than the surface potential of the intermediate transfer belt 20.

By performing the control described above, it is possible to suppress the secondary transfer residual toner from being discharged from the residual toner charging brush 10 when the intermediate transfer belt 20 is started and stopped as in the above-described reference example . Accordingly, image defects caused by the discharged toner can be suppressed.

In the reference example , when the intermediate transfer belt 20 is started and stopped, a positive bias of about 1300 V is applied for 200 ms while the intermediate transfer belt 20 is stopped. Therefore, depending on the material of the intermediate transfer belt 20 and the resistance value, a leak site is formed in the intermediate transfer belt 20, and the intermediate transfer belt 20 has a hole, which may cause a transfer failure corresponding to the leak site.

In contrast, in the present embodiment, a high bias that leaks to the intermediate transfer belt 20 is not applied to the remaining toner charging brush 10 while the intermediate transfer belt 20 is stopped. For this reason, in the reference example , a belt material and a resistance value that cannot be used due to leakage of the intermediate transfer belt 20 can be adopted, and the degree of freedom in selecting the material of the intermediate transfer belt 20 is increased.

[ Second Embodiment]
Next, a second embodiment of the image forming apparatus according to the present invention will be described with reference to the drawings. The same reference numerals as those in the above-described reference example are given the same reference numerals, and the description thereof is omitted. FIG. 5 is a configuration diagram of the image forming apparatus according to the present embodiment.

As shown in FIG. 5, the image forming apparatus of this embodiment uses a residual toner charging roller (charging means) 11 instead of the residual toner charging brush 10 of the image forming apparatus of the first embodiment. .

The residual toner charging roller 11 is a charging member for charging the secondary transfer residual toner to a reverse polarity and collecting it in the image forming unit. The residual toner charging roller 11 is a residual toner charging roller having an outer diameter of 20 mm in which a sponge-like elastic body is provided in a roll shape around an axis. The foamable elastic body is made of silicon rubber having a resistance adjusted to about 107 Ωcm and having a firing cell of 50 to 300 μm.

The remaining toner charging roller 11 is brought into contact with the intermediate transfer belt 20 with a pressing force of a total pressure of 1 Kgf, and rotates following the intermediate transfer belt 20. Note that the residual toner charging roller 11 may be driven and rotated to provide a peripheral speed difference from the intermediate transfer belt 20.

A positive bias (about 1500 V in the present embodiment, hereinafter referred to as a residual toner charging bias) is applied to the remaining toner charging roller 11 by a power source (not shown).

In the charging nip portion X formed by the residual toner charging roller 11 and the intermediate transfer belt 20, discharge occurs in the minute gaps on the upstream side and the downstream side in the rotation direction of the intermediate transfer belt 20. Is charged to the opposite polarity (ie, positive polarity) side.

When the secondary transfer residual toner moves to the charging nip portion, the residual toner charging roller 11 charges the secondary transfer residual toner positively, and at the same time, electrostatically collects and holds a part of the secondary transfer residual toner. In addition to physical collection and retention.

By performing the control described in the first embodiment using the remaining toner charging roller 11, the secondary transfer from the remaining toner charging roller 11 is performed when the intermediate transfer belt 20 is started and stopped, as in the first embodiment. The remaining toner can be prevented from being discharged. Accordingly, image defects caused by the discharged toner can be suppressed.

Further, using the residual toner charging roller 11, by the control of the residual toner charging bias as described above first embodiment, as in the first embodiment, increasing the degree of freedom in selecting the material of the intermediate transfer belt 20 .

The toner collection / holding amount of the remaining toner charging roller 11 depends largely on the outer diameter and the firing cell diameter of the roller. Generally, the larger the outer diameter and the firing cell diameter of the roller, the higher the collection / holding ability. However, since increasing the outer diameter of the roller affects the size of the main body, it cannot be increased unnecessarily.

In addition, when the firing cell system is enlarged, the recovery / holding capability is increased, but when the secondary transfer residual toner is discharged onto the intermediate transfer belt 20, the secondary transfer residual toner is likely to remain in the cell. -It is necessary to select the balance after considering the balance between retention capacity and discharge capacity.

1 is a configuration diagram illustrating an image forming apparatus according to a reference example . It is a timing chart at the time of cleaning operation during printing of a conventional example. 6 is a timing chart during a printing cleaning operation of a reference example . 6 is a timing chart during a cleaning operation during printing according to the first embodiment. It is a block diagram of the image forming apparatus which concerns on 2nd embodiment.

M ... secondary transfer portion N ... primary transfer nip portion P ... recording material W, X ... charging nip portion 1 ... image forming portion 2 ... photosensitive drum (image carrier) )
3 ... Charging roller 4 ... Developing device 5 ... Transfer roller 6 ... Drum cleaning device 7 ... Exposure device 8 ... Waste toner box 10 ... Remaining toner charging brush (charging means)
11: Residual toner charging roller (charging means)
12 ... Fixing device 14 ... Power supply (voltage applying means)
20 ... Intermediate transfer belt (moving body)
23 ... Secondary transfer counter roller 24 ... Secondary transfer roller 40 ... Primary transfer power supply 100 ... Color image forming apparatus

Claims (6)

An image carrier for carrying a toner image;
A movable body for transferring a toner image carried by the image carrier to a recording material;
A charging unit that charges the adhering toner adhering to the moving body in contact with the moving body,
Voltage applying means for applying a voltage to the charging means,
The voltage of the first charge polarity and reverse polarity toner is charged to the adhering toner by the applied said charging means by said voltage applying means, wherein by moving the image bearing member the deposited toner from the mobile In an image forming apparatus for collecting the adhered toner from a moving body ,
The moving body is in contact with the charging unit before starting to move, and a second voltage having the same polarity as the first voltage and having an absolute value smaller than the first voltage is applied to the charging unit. Image forming apparatus characterized in that movement starts in a touched state The image forming apparatus according to claim 1, wherein the second voltage is larger than an absolute value of a surface potential of the moving body. 3. The image formation according to claim 1, wherein the second voltage is applied to the charging unit during a predetermined time after the rotation of the moving body is stopped. apparatus. 4. The image forming apparatus according to claim 1, wherein the moving body is an intermediate transfer belt on which a toner image is primarily transferred from the image carrier. 5. The adhering toner is charged to the reverse polarity by the charging means to which the first voltage is applied, and a toner image is primarily transferred from the image carrier to the intermediate transfer belt and simultaneously from the intermediate transfer belt to the The image forming apparatus according to claim 4, wherein the image forming apparatus moves to the image carrier. The image forming apparatus according to claim 1, wherein the charging unit is a charging brush.

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