JP2006154058A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus in which toner is electrostatically collected, collection efficiency is increased by making a moving speed difference between a member to be cleaned and a collection roller, a wave height value of an AC bias to be applied is decreased, and a power supply cost is reduced. <P>SOLUTION: The image forming apparatus includes a body to be cleaned having a surface to which toner may be stuck, collection members allowed to be abutted on the surface of the body to be cleaned to collect toner stuck to the surface and a bias application means for applying bias to the collection members, wherein the plurality of toner collection members are provided and the bias application means applies a DC bias to which an AC bias is superposed to the plurality of toner collection members in respectively different conditions. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an image forming apparatus using an electrophotographic system such as a printer, a copying machine, or a facsimile, and more particularly to an image forming apparatus having a borderless printing function.

  Conventionally, in an inkjet or electrophotographic image forming apparatus, an image is recorded with a margin margin at the periphery of a recording sheet.

  However, with the colorization of image forming apparatuses, there is an increasing demand for so-called borderless printing that can record an image without blank spaces over the entire area of the recording paper, similar to the printing of silver halide photographs. In the inkjet image forming apparatus, products capable of borderless printing have already been put on the market, and an electrophotographic image forming apparatus has also been proposed as in Patent Document 1.

  In the case of an electrophotographic color image forming apparatus employing an intermediate transfer body method, a toner image formed on the intermediate transfer body is transferred onto a recording sheet by a transfer device. Therefore, when borderless printing is performed in an intermediate transfer body type color image forming apparatus, a toner image having the same size as the recording paper may be formed on the intermediate transfer body.

  However, when the size of the toner image is the same as the size of the recording paper, a margin is generated at the upper end of the recording paper if the feeding timing of the recording paper is slightly early, and a margin is generated at the lower end if it is slightly late. In order to transfer the toner image onto the recording paper without a margin, perfect paper feeding accuracy is required. However, the paper should be fed perfectly in response to changes in the recording paper material, moisture absorption state, atmosphere environment, etc. It is difficult.

  Therefore, when performing borderless printing, a toner image that is slightly larger than the recording paper is formed on the intermediate transfer member, and even if the recording paper is fed slightly shifted from front to back and left and right, the toner image on the recording paper is There are no images.

JP 2004-005559 A

  When transferring toner from the intermediate transfer member onto the recording paper, it is common to adopt a roller transfer system using a rubber roller in order to form a stable transfer electric field while performing stable paper conveyance. .

  However, when borderless printing is performed, since the size of the toner image is larger than the size of the recording paper, a large amount of toner that is not transferred onto the recording paper during the secondary transfer is deposited on the rubber roller. The rubber roller to which the toner has adhered causes stains on the back of the paper. Therefore, although a cleaning means for the rubber roller is required, it is difficult to clean the toner adhering to the rubber by a system in which the toner adhering to the rubber roller is physically scraped with a general blade or brush. In order to facilitate cleaning, a resin layer or the like may be provided on the rubber surface to improve toner releasability. However, if toner releasability is improved, the frictional force between the recording paper and the transfer roller decreases. Paper stability is lost.

  Further, in the system in which the toner is physically scraped with a blade, a brush, or the like, a problem of surface scraping occurs because the surface is rubbed continuously.

  SUMMARY OF THE INVENTION The present invention has been made in view of the above-described problems, and an object of the present invention is to collect toner by electrostatically collecting toner and providing a moving speed difference between a member to be cleaned and a collecting roller. An object of the present invention is to provide an image forming apparatus capable of increasing the efficiency, suppressing the peak value of the AC bias to be applied, and reducing the power supply cost.

  In order to achieve the above object, the invention according to claim 1 is a cleaning object to which toner can adhere to a surface, a recovery member that contacts the surface of the cleaning object and collects the toner attached to the surface; In the image forming apparatus having a bias applying unit that applies a bias to the collecting member, the DC includes a plurality of the toner collecting members, and the bias applying unit superimposes an AC bias on the plurality of toner collecting members. The bias is applied under different conditions.

  According to a second aspect of the present invention, when a DC bias superimposed with an AC bias is applied to the plurality of toner collecting members by the bias applying unit under different conditions, the different conditions are DC bias values. It is characterized by.

  According to a third aspect of the present invention, when a DC bias superimposed with an AC bias is applied to the plurality of toner collecting members under different conditions by the bias applying means, the different conditions are the duty ratio of the AC bias. It is characterized by being.

  The invention according to claim 3 is characterized in that the duty ratio of the AC bias applied by the bias applying means is different.

  The invention according to claim 4 is characterized in that a surface layer of the object to be cleaned is rubber.

  The invention according to claim 5 is characterized in that the rubber of the surface layer of the object to be cleaned is foamed rubber.

  The invention according to claim 6 is characterized in that the toner recovery member is a conductive roller.

  The invention according to claim 7 is characterized in that the conductive roller is a metal roller.

  The invention according to claim 8 is characterized in that the surface layer of the toner recovery member is a resin layer having toner releasability.

  The invention according to claim 9 is characterized in that the resin on the surface of the toner recovery member is a urethane resin, a fluororesin, a nylon resin, or a polyimide resin.

  The invention described in claim 10 is characterized in that the member to be cleaned and the toner collecting member are moved with a speed difference on the surface where the member to be cleaned and the toner collecting member abut.

  According to an eleventh aspect of the present invention, a plurality of movement speed differences between the cleaning object and the toner recovery member are set on a surface where the cleaning object and the toner recovery member contact each other.

  According to a twelfth aspect of the present invention, in an image forming apparatus having means for forming toner images of a plurality of colors on an image carrier, a full color mode for forming toner images of a plurality of colors on the image carrier, and the image carrier In the mono mode in which only one color toner image is formed thereon, a plurality of settings of the moving speed difference between the object to be cleaned and the toner recovery member are changed.

  According to a thirteenth aspect of the present invention, there is provided an image forming apparatus having a mode in which at least one of a width or a length of a toner image formed on an image carrier is longer than a width or a length of the recording material. A plurality of settings of the moving speed difference between the object to be cleaned and the toner collecting member are changed between the mode to be shortened and the mode to be shortened.

  According to a fourteenth aspect of the present invention, in a mode in which at least one of the width or length of the toner image formed on the image carrier is longer than the width or length of the recording material, the width or length of the recording member is greater. A plurality of settings of the moving speed difference between the object to be cleaned and the toner collecting member are changed by a long toner image.

  The invention according to claim 15 is an image forming apparatus comprising: an image carrier on which a toner image is formed; and a transfer member that transfers the toner image on the image carrier to a recording material. It is a body.

  According to the present invention, when toner adheres to the surface of the member to be cleaned, two toner recovery rollers are brought into contact with the surface of the member to be cleaned, and the DC bias in which the AC bias is superimposed on each recovery roller is different. By applying it under conditions, it becomes possible to collect toner electrostatically. Further, by providing a moving speed difference between the member to be cleaned and the collection roller, it is possible to increase the collection efficiency, to suppress the peak value of the AC bias to be applied, and to reduce the power supply cost.

  Embodiments of the present invention will be described below with reference to the accompanying drawings.

<Embodiment 1>
The configuration of the image forming apparatus of the present embodiment will be described with reference to a schematic cross-sectional view of the full-color electrophotographic image forming apparatus shown in FIG. Here, as the first image carrier, a plurality of photosensitive drums 11a corresponding to respective color toners of the first color: yellow, the second color: magenta, the third color: cyan, and the fourth color: black. 11b, 11c, and 11d, and an intermediate transfer belt 1 that is in contact with each of the photosensitive drums 11a, 11b, 11c, and 11d at each primary transfer portion as a second image carrier.

  Each photosensitive drum is a first color (yellow) photosensitive drum 11a positioned at the most upstream position along the moving direction of the intermediate transfer belt 1, and a second color positioned closest to the downstream side of the photosensitive drum 11a. (Magenta) photosensitive drum 11b, third color (cyan) photosensitive drum 11c located closest to the downstream side of the photosensitive drum 11b, and fourth color positioned closest to the downstream side of the photosensitive drum 11c. (Black) photosensitive drums 11d are arranged in this order.

  The photosensitive drums 11a, 11b, 11c, and 11d in the present embodiment have an outer diameter of 30.0 mm and have a layer in which a photosensitive material is applied on an aluminum cylinder.

  The intermediate transfer belt 1 includes a resin film such as a urethane resin, a fluorine resin, a nylon resin, and a polyimide resin, a resin film in which carbon or conductive powder is dispersed in these resins, or a resistance adjustment, or urethane rubber. Further, an elastomer sheet having a multi-layer structure in which a resin layer such as a urethane resin, a fluorine resin, a nylon resin, or a polyimide resin is formed as a release layer on the toner carrier surface side of a base layer sheet such as NBR may be used. it can.

The intermediate transfer member belt 1 used in the present embodiment is formed on the belt 1 in a transfer process or the like by dispersing carbon in polyimide and adjusting the medium resistivity of the surface resistivity ρs = 1 × 10 ¹² Ω. The added charge can be attenuated without providing a special static elimination mechanism. The intermediate transfer belt 1 is a single-layer endless belt having a circumferential length of 1000 mm and a thickness of 100 μm.

  The surface resistivity measurement is based on JIS-K6911. After obtaining good contact between the electrode and the belt surface by using conductive rubber as an electrode, an ultra-high resistance resistance meter (R8340 manufactured by Advantest) is used. Measured. The measurement conditions were applied voltage = 100 V and voltage application time = 30 s.

  As shown in FIG. 1, the intermediate transfer belt 1 is suspended by three rollers including a drive roller 1a, a support roller 1b, and a separation roller 1c included in the intermediate transfer belt 1. The drive roller 1a, the support roller 1b, and the separation roller 1c are electrically grounded.

The driving roller 1a and the separation roller 1c are rollers having an outer diameter of 29.8 mm composed of an aluminum cored bar having a diameter of 24.0 mm and a hydrin rubber layer having a layer thickness of 2.9 mm, and the resistance is adjusted by adjusting the resistance of the hydrin rubber. The resistance value is 1 × 10 ⁶ Ω.

  The support roller 1b is an aluminum roller having a diameter of 29.8 mm.

  The roller resistance value was measured using an ultra-high resistance resistance meter (R8340 manufactured by Advantest) while the roller to be measured was brought into contact with an aluminum cylinder having a diameter of 30 mm and rotated following the aluminum cylinder. The measurement conditions were applied voltage = 100 V, voltage application time = 30 s, contact force = 9.8 N, and rotational peripheral speed = 117 mm / s.

  The intermediate transfer belt 1 is rotated at a predetermined process speed (117.0 mm / s in this embodiment) by a driving device (not shown) in the direction of the arrow. Each of the photosensitive drums 11a, 11b, 11c, and 11d is 99.0% of the moving speed of the intermediate transfer belt 1 in the same direction as the moving direction of the intermediate transfer belt 1 (115.8 mm / s in this embodiment). ) By a driving device (not shown). The primary transfer efficiency is improved by giving a speed difference ΔVa to the moving speed of each of the photosensitive drums 11a, 11b, 11c, 11d and the intermediate transfer belt 1. However, as the speed difference ΔVa between the moving speeds of the photosensitive drums 11a, 11b, 11c, and 11d and the intermediate transfer belt 1 is larger, the photosensitive drums 11a, 11b, 11c, and 11d are caused by the friction with the intermediate transfer belt 1. The occurrence of wear and scratches is promoted. Therefore, in this embodiment, the speed difference ΔVa is set to 1.5% of the process speed (1.8 mm / s in this embodiment) in order to achieve both the primary transfer efficiency and the degree of wear and scratches on the photosensitive drum. .

  The photosensitive drums 11a, 11b, 11c, and 11d are uniformly charged by the contact charging rollers 12a, 12b, 12c, and 12d, and lasers from the scanners 13a, 13b, 13c, and 13d modulated by the exposure information signal. An electrostatic latent image is created with light.

  The image information signal sent from the host computer is processed by the controller so as to obtain a desired image size. When performing borderless printing, the toner image on the intermediate transfer belt 2 is converted into an exposure information signal that is larger than the recording material. When printing with margins, the intensity of the laser beam and the irradiation spot diameter converted into an exposure information signal that makes the toner image on the intermediate transfer belt 2 smaller than the recording material depend on the resolution of the image forming apparatus and the desired image density. The electrostatic latent images on the respective photoconductive drums 11a, 11b, 11c, and 11d are set appropriately, and the portion irradiated with the laser light is at the bright portion potential VL (about −150 V), and the other portion is primary charged. It is formed by being held at the dark portion potential VD (about −650 V) charged by the contact charging rollers 12 a, 12 b, 12 c, and 12 d, which are containers.

  The electrostatic latent image reaches the facing portion of each developing unit 14a, 14b, 14c, 14d by the rotation of each photosensitive drum 11a, 11b, 11c, 11d, and has the same polarity as the surface of the photosensitive drum (in this example, A developer (toner) charged to a negative polarity is supplied to be visualized to form a developer image (toner image).

  The developing device 14 in this case is a developing device adopting a two-component developing method. The developing bias in this case is a DC bias on which an AC bias having a waveform: a rectangular wave, an offset DC value: -400 V, a peak value: 1.5 kV, and a frequency: 3 kHz is superimposed.

  The toner images formed on the photosensitive drums 11a, 11b, 11c, and 11d are in the primary transfer nips that are the proximity or contact portions between the intermediate transfer belt 1 and the photosensitive drums 11a, 11b, 11c, and 11d. The primary transfer bias applied to the primary transfer rollers 15a, 15b, 15c, and 15d in contact with the back surface of the intermediate transfer belt 1 from the primary transfer bias sources 16a, 16b, 16c, and 16d (in this embodiment, a constant voltage of +400 V). The image is transferred onto the intermediate transfer belt 1 by the control. When the intermediate transfer belt 1 passes through the primary transfer nip with the photosensitive drum 11d, the formation of the four-color image on the intermediate transfer belt 1 is completed, and the primary transfer process is completed.

  On the other hand, the surface of each of the photosensitive drums 11a, 11b, 11c, and 11d after the primary transfer of the toner image is subjected to removal of primary transfer residual toner and the like by a drum cleaning device 17a, 17b, 17c, and 17d formed of a urethane rubber blade. It is cleaned and prepared for the next image forming process.

  Next, one sheet of recording paper P is taken out from the recording paper cassette 5 by the paper feeding means 6, and is a portion between the separation roller 1c and the secondary transfer roller 2 as a transfer member with the intermediate transfer belt 1 interposed therebetween. Inserted into the secondary transfer nip.

  At this time, the secondary transfer roller 2 has a polarity opposite to that of the toner, and an optimum bias determined in accordance with the temperature and humidity in the image forming apparatus detected by the temperature and humidity sensor (in this embodiment, 15 ° C./10% R.D.). H. + 20 μA, 23 ° C./50% RH, +30 μA, 30 ° C./80% RH, +35 μA constant current control) is applied by the secondary transfer bias source 21, and the toner image is transferred to the intermediate transfer belt. Secondary transfer from 1 to the recording paper P is performed.

The secondary transfer roller 2 in the present embodiment is a sponge roller having an outer diameter of 22.0 mm constituted by an aluminum core having a diameter of 14.0 mm and a foamed hydrin rubber layer having a thickness of 4 mm, and adjusts the resistance of the hydrin rubber. Therefore, the roller resistance value is set to 1 × 10 ⁸ Ω. The hardness of the secondary transfer roller 2 is 35 ° (ASKER-C).

  The secondary transfer roller 2 is rotated at a substantially constant speed with the intermediate transfer belt 1 by a driving device (not shown) in the direction of the arrow, so that the recording paper P can be fed at a predetermined process speed (the actual speed) regardless of the amount of toner on the intermediate transfer belt 1. In the embodiment, the image is stably conveyed at 117.0 mm / s), and an image size on the recording sheet equal to the image size formed on the intermediate transfer belt 1 is obtained regardless of the image pattern. .

  The toner adhering to the secondary transfer roller 2 is cleaned by the two collection rollers 22 and 23 installed for cleaning the secondary transfer roller, thereby preventing the toner from adhering to the back surface of the recording paper P.

  The recording paper P on which the unfixed toner image that has passed through the secondary transfer nip portion reaches the fixing device 3 and is heated and pressurized to obtain a permanent fixed image. The recording paper P discharged from the fixing device 3 is transported by a transport means 7 to a paper discharge tray 8 outside the device.

  After the transfer of the toner image onto the recording paper P, the surface of the intermediate transfer belt 1 is cleaned of secondary transfer residual toner by an intermediate transfer body cleaner 4 having a cleaning blade made of urethane rubber.

  When forming images on both sides of the recording paper P, the recording paper P discharged from the fixing device 3 through the first image forming process is conveyed again to the paper feeding means 6 by the conveying means 7 and After being discharged from the fixing device 3 through the second image forming process, the paper is conveyed by a conveying means 7 to a paper discharge tray 8 outside the apparatus.

  Next, cleaning of the secondary transfer roller 2 will be described in detail.

  The feature of the present invention is that two recovery rollers 22 and 23 for cleaning contacting the secondary transfer roller 2 are provided, and the AC bias is applied to each of the recovery rollers 22 and 23 to electrostatically clean the secondary transfer roller 2. In the point.

  Recovery rollers 22 and 23 for electrostatically recovering toner adhering to the secondary transfer roller 2 in contact with the surface of the secondary transfer roller 2 and urethane rubber for scraping the recovered toner from the recovery rollers 22 and 23 The cleaning blades 221 and 231 are made of toner, waste toner containers 222 and 232 for storing scraped toner, and cleaning bias power supplies 223 and 232 for applying a cleaning bias to the collection rollers 22 and 23. In the present embodiment, SUS rollers having a diameter of 10 mm are used as the collection rollers 22 and 23.

  In the above-described configuration, the relationship between the bias applied to the collection rollers 22 and 23 and the paper back stain when performing borderless printing was examined. The image at the time of borderless printing was a magenta solid black image. The test environment was a temperature of 23 ° C. and a humidity of 60%. In each table, ◯ indicates no occurrence of paper stains, Δ indicates slight occurrence, × indicates occurrence, XX indicates occurrence of paper stains continuously, and xxx indicates continuous occurrence of paper stains of bad level.

  First, the case where only a DC bias was applied to each roller was examined. The toner on the intermediate transfer belt 1 is negatively charged, and the toner adhering to the secondary transfer roller 2 is almost negatively charged. Therefore, it was considered that a plus bias should be applied to the collection roller 22 arranged at the upstream position. The toner that cannot be collected by the collection roller 22 is considered to be positively charged toner. Therefore, it was considered that a minus bias should be applied to the collection roller 23 arranged at the downstream position. Table 1 shows the results.

表１に示したように、ＤＣバイアス印加の場合、紙裏汚れが連続発生してクリーニング性が悪いことが分かった。但し、回収ローラ２２への印加バイアスはプラスバイアスが大きいほどクリーニング性が良化する傾向にあり、回収ローラ２３への印加バイアスは−５００V 付近が最適であることが分かった。

As shown in Table 1, it was found that when the DC bias was applied, stains on the back of the paper occurred continuously and the cleaning property was poor. However, the bias applied to the collecting roller 22 tends to improve the cleaning property as the positive bias is increased, and it is found that the optimum bias applied to the collecting roller 23 is around −500V.

  Thus, the paper back contamination level when a DC bias of −500 V was applied to the collection roller 23 and an AC bias was applied to the collection roller 22 was examined.

  First, the frequency dependence was examined. As the AC bias applied to the collection roller 22, the waveform: rectangular wave, peak value: 3 kV, offset DC value: 1.5 kV, duty ratio: + 50% were set as common conditions, and only the frequency was varied. The results are shown in Table 2.

表１から分かるように、紙裏汚れはＮＧであったが、周波数は１．０ｋＨｚ〜２．０ｋＨｚで良化するという結果となった。

As can be seen from Table 1, the paper back stain was NG, but the frequency was improved at 1.0 kHz to 2.0 kHz.

  Next, the offset DC value dependency was examined. As the bias applied to the collection roller 22, the common conditions were: waveform: rectangular wave, frequency: 1.5 kHz, peak value: 3 kV, duty ratio: + 50%, and only the offset DC value was varied. The results are shown in Table 3.

表３から分かるように、オフセットＤＣ値を大きく取ることで紙裏汚れのレベルが良化するという結果となった。

As can be seen from Table 3, when the offset DC value was increased, the level of paper back contamination was improved.

  Next, the peak value dependency was examined. As a bias applied to the collection roller 22, the waveform: rectangular wave, frequency: 1.5 kHz, offset DC value: 1.5 kV, duty ratio: + 50% were set as common conditions, and only the peak value was varied. The results are shown in Table 4.

表４から分かるように、波高値を大きくとることで紙裏汚れのレベルが良化するという結果となった。

As can be seen from Table 4, increasing the peak value improved the level of dirt on the back of the paper.

  Next, the duty ratio dependency was examined. As the bias applied to the collection roller 22, the common conditions were: waveform: rectangular wave, offset DC value: 1.5 kV, frequency: 1.5 kHz, peak value: 3 kV, and only the duty ratio was varied. The results are shown in Table 5.

表５から分かるように、プラス側のデューティー比を大きく取ることで紙裏汚れのレベルが良化するという結果であった。

As can be seen from Table 5, the result was that the level of dirt on the back of the paper was improved by increasing the duty ratio on the plus side.

  As described above, by changing the AC bias condition applied to the collecting roller 22, the level of dirt on the back of the paper could be improved, but the level of OK could not be reached completely.

  Then, next, a DC bias of +2000 V was applied to the collection roller 22, and the paper back contamination level when an AC bias was applied to the collection roller 23 was examined.

  First, the frequency dependence was examined. As the bias applied to the collection roller 23, the waveform: rectangular wave, peak value: 3 kV, offset DC value: -0.5 kV, duty ratio: + 50% were set as common conditions, and only the frequency was varied. The results are shown in Table 6.

表６から分かるように、周波数は１．０ｋＨｚ〜２．０ｋＨｚで良化するという結果となった。

As can be seen from Table 6, the frequency was improved at 1.0 kHz to 2.0 kHz.

  Next, the peak value dependency was examined. As the bias applied to the collection roller 23, the waveform: rectangular wave, frequency: 1.5 kHz, offset DC value: -0.5 kV, duty ratio: + 50% were set as common conditions, and only the peak value was varied. The results are shown in Table 7.

表７から分かるように、波高値を大きく取ることで紙裏汚れのレベルが良化するという結果となった。

As can be seen from Table 7, increasing the crest value improved the level of dirt on the back of the paper.

  Next, the duty ratio dependency was examined. As the bias applied to the collection roller 23, the waveform: rectangular wave, offset DC value: -0.5 kV, frequency: 1.5 kHz, peak value: 3 kV were set as common conditions, and only the duty ratio was varied. The results are shown in Table 8.

表８から分かるように、プラス側のデューティー比を小さくすることで紙裏汚れのレベルが良化するという結果となった。

As can be seen from Table 8, reducing the duty ratio on the plus side improved the level of paper back contamination.

  Next, the offset DC value dependency was examined. As the bias applied to the collection roller 23, the waveform: rectangular wave, duty ratio: + 30%, frequency: 1.5 kHz, peak value: 3 kV were set as common conditions, and only the offset DC value was varied. The results are shown in Table 9.

表９から分かるように、−５００Ｖ前後のオフセットＤＣ値で紙裏汚れのレベルが良化するという結果となった。

As can be seen from Table 9, the result was that the level of stains on the back of the paper improved with an offset DC value around −500V.

  From the above results, it was confirmed that application of an AC bias to either of the collecting rollers 22 and 23 improved the cleaning property, but it did not reach a level that completely removes paper back stains.

  In view of this, the case where an AC bias is applied to both the collecting rollers 22 and 23 was examined. The condition of the bias applied to the collection roller 22 is considered to be optimal from the above examination results, and the waveform: rectangular wave, frequency: 1.5 kHz, peak value: 3 kV, offset voltage: +1.5 kV, duty ratio: + 70% . The condition of the bias applied to the collection roller 23 is considered to be optimal from the above examination results, and the waveform is a rectangular wave, the frequency is 1.5 kHz, the peak value is 3 kV, the offset voltage is −0.5 kV, and the duty ratio is + 30%. did.

  Under the above bias condition, the paper back stain was not generated even when a magenta solid black image was output. Further, even when a magenta and yellow two-color solid image was output as an image, the paper back was not stained.

  Here, even if the AC bias waveform is not a rectangular wave but a triangular wave or a SIN wave, even if a magenta and yellow two-color overlapping solid image is output, the paper back stain does not occur.

  Based on the above results, two inexpensive metal rollers for cleaning that contact the secondary transfer roller 2 are provided, and the secondary transfer roller 2 is electrostatically cleaned by applying an AC voltage to each roller. Can now be prevented.

  In the present embodiment, the toner attached to the surfaces of the collection rollers 22 and 23 is cleaned by the blade cleaning method. However, the present invention is not limited to this, and cleaning may be performed by using a web or the like.

  In this embodiment, metal rollers made of SUS are used as the collection rollers 22 and 23. However, the material is not limited to SUS, and any roller that has conductivity even if it is not metal. Any roller can be used. In addition, if a surface layer that ensures releasability from the toner is provided, such as a urethane resin, a fluorine resin, a nylon resin, a polyimide resin, etc., may be coated on the collection rollers 22 and 23 or covered with a tube. Cleaning on the collection rollers 22 and 23 is facilitated.

<Embodiment 2>
Next, a second embodiment of the present invention will be described.

  FIG. 2 is a schematic sectional view of the electrophotographic image forming apparatus according to the first embodiment. Constituent elements similar to those of the first embodiment are denoted by the same reference numerals and description thereof is omitted.

  A feature of this embodiment is that when the secondary transfer roller 2 is cleaned by the collection rollers 22 and 23, a difference is provided between the circumferential speed of the collection rollers 22 and 23 and the circumferential speed of the secondary transfer roller 2. It is in the point.

  The conditions of the bias applied to the collection roller 22 were a rectangular wave, frequency: 1.5 kHz, peak value: 2 kV, offset voltage: +1.5 kV, and duty ratio: + 50%. The conditions of the bias applied to the collection roller 231 were a rectangular wave, frequency: 1.5 kHz, peak value: 2 kV, offset voltage: −0.5 kV, and duty ratio: + 50%.

  As an image at the time of borderless printing, evaluation was performed using a two-color overlapping solid image of magenta and yellow. The test environment was a temperature of 23 ° C. and a humidity of 60%. Table 10 shows the result of examining the level of paper back contamination by varying the peripheral speed difference provided between the collection rollers 22 and 23 and the secondary transfer roller 2 under the above conditions. In each table, ◯ indicates no occurrence of stains on the back of the paper, Δ indicates slight occurrence, and × indicates occurrence.

表１０から分かるように、回収ローラ２２，２３に印加したＡＣバイアスの波高値を２ｋＶとしているため、周速差が無い場合には紙裏汚れが発生しているが、周速差を設けることで紙裏汚れが良化し、６０％以上の周速差では紙裏汚れが発生しなくなった。

As can be seen from Table 10, the crest value of the AC bias applied to the collecting rollers 22 and 23 is 2 kV, so that there is a paper back stain when there is no peripheral speed difference, but a peripheral speed difference is provided. As a result, the stain on the back of the paper improved, and the stain on the back of the paper did not occur when the peripheral speed difference was 60% or more.

  Therefore, in this embodiment, when the secondary transfer roller 2 is cleaned by the collection rollers 22 and 23, a difference is provided between the circumferential speed of the collection rollers 22 and 23 and the circumferential speed of the secondary transfer roller 2. As a result, by suppressing the crest value to a low level, it was possible to reduce the cost of the cleaning bias power supplies 223 and 233 and to suppress the occurrence of paper back contamination.

<Embodiment 3>
Next, a third embodiment of the present invention will be described.

  FIG. 3 is a schematic cross-sectional view of the electrophotographic image forming apparatus according to the third embodiment. Constituent elements similar to those of the first and second embodiments are denoted by the same reference numerals and description thereof is omitted.

  In the second embodiment, it was shown that the cleaning performance is improved by providing a difference between the peripheral speed of the collection rollers 22 and 23 and the peripheral speed of the secondary transfer roller 2.

  However, when the peripheral speed difference is set to ± 70% or more and the paper is continuously passed, a phenomenon occurs in which the surface of the secondary transfer roller 2 is scraped by rubbing. In order to reduce the peak value of the AC bias applied to the collection rollers 22 and 23 and to keep the cost of the cleaning bias power supplies 223 and 233 low, it is better to increase the peripheral speed difference, but the secondary transfer roller 2 is scraped. There is a risk that image defects will occur within the durable life of the main body.

  Therefore, in this embodiment, a mechanism for separating the collection rollers 22 and 23 from the secondary transfer roller 2 is provided, and when performing borderless printing, the collection rollers 22 and 23 come into contact with each other to perform the secondary transfer roller cleaning. Thus, the recovery rollers 22 and 23 are separated from the secondary transfer roller 2 when normal printing with margins is performed.

  By doing so, even if there is a large peripheral speed difference between the collection rollers 22 and 23 and the secondary transfer roller 2, it is possible to suppress the scraping of the secondary transfer roller 2.

<Embodiment 4>
Next, a fourth embodiment of the present invention will be described. Constituent elements similar to those in the first to third embodiments are given the same reference numerals and explanations thereof are omitted.

  In the third embodiment, a separation mechanism is provided between the collection rollers 22 and 23 and the secondary transfer roller 2, and the separation rollers 22 and 23 are separated from the secondary transfer roller 2 for normal margin printing. When performing borderless printing, the recovery rollers 22 and 23 are brought into contact with the secondary transfer roller 2 to show that the scraping of the secondary transfer roller 2 can be suppressed to a minimum.

  However, there are also users who perform only marginless printing. In this case, the amount of scraping of the secondary transfer roller 2 increases, and image defects may occur.

  Therefore, in the present embodiment, the peripheral speed difference provided between the collection rollers 22 and 23 and the secondary transfer roller 2 is varied. Then, when performing borderless printing, if it is known in advance that the amount of toner used in the edge portion is small, the peripheral speed difference provided between the collection rollers 221 and 231 and the secondary transfer roller 2 is reduced.

  When performing borderless printing, an example of a case where it is known in advance that the amount of toner used in the edge portion is small is a monocolor printing mode. In the case of mono-color printing, only one toner color is used, so the maximum toner usage is less than in the full-color printing mode. Therefore, the back of the paper in the monochrome printing mode was examined.

  The conditions of the bias applied to the collection roller 22 were a rectangular wave, frequency: 1.5 kHz, peak value: 2 kVpp, offset voltage: +1.5 kVdc, and duty ratio: + 50%. The conditions of the bias applied to the collection roller 23 were a rectangular wave, frequency: 1.5 kHz, peak value: 2 kVpp, offset voltage: −0.5 kVdc, and duty ratio: + 50%. As an image at the time of borderless printing, a black solid image was evaluated. The test environment was a temperature of 23 ° C. and a humidity of 60%. Table 11 shows the results of examining the level of paper back contamination by varying the peripheral speed difference provided between the collection rollers 22 and 23 and the secondary transfer roller 2 under the above conditions.

  In each table, ◯ indicates no occurrence of stains on the back of the paper, Δ indicates slight occurrence, and × indicates occurrence.

表から分かるように、周速差が４０％程度でも紙裏汚れは発生しなかった。

As can be seen from the table, no stain on the back of the paper occurred even when the peripheral speed difference was about 40%.

  Even when borderless printing is performed by full-color printing, there is an image with a small amount of toner used in the edge portion. When the amount of toner used in the edge portion was 100% or less, when the difference in peripheral speed was reduced to 50%, no stain on the back of the paper occurred.

  That is, when borderless printing is performed, when an image information signal is sent from the host computer, the controller processes so that a toner image slightly larger than the recording paper is formed on the intermediate transfer belt 2. And the peripheral speed difference may be varied according to the Max toner amount of the edge image.

  This embodiment will be described with reference to the flowchart of FIG.

  An image information signal is transferred from the host computer to the controller, and printing is started. At that time, an information signal for instructing whether to perform marginless printing or marginal printing is also sent. When performing borderless printing, the controller converts the image information signal into an exposure information signal so that the toner image on the intermediate transfer belt 2 is larger than the recording paper. When printing with margins, the controller converts the image information signal into an exposure information signal so that the toner image on the intermediate transfer belt 2 is smaller than the recording paper.

In the case of bordered printing, since the secondary transfer roller cleaning is unnecessary, the peripheral speed difference provided between the collection rollers 22 and 23 and the secondary transfer roller 2 is set to ± 0%. In the case of borderless printing, the secondary transfer roller needs to be cleaned, so that a peripheral speed difference is set. However, the toner amount at the image edge portion is estimated from the transferred image, and the peripheral amount provided according to the toner amount is set. Variable speed difference. In this embodiment, the peripheral speed difference is 40% when the toner amount is 100% or less, the peripheral speed difference is 60% when the toner amount is 100% to 150%, and the peripheral speed difference is 80 when the toner amount is 150% or more. Control to be%.

  As described above, the toner image formed on the intermediate transfer belt 2 is secondarily transferred onto the recording paper while controlling the peripheral speed difference. The toner attached on the secondary transfer roller 2 is collected by the collection rollers 22 and 23.

  As described above, the crest value of the AC bias applied to the collection rollers 22 and 23 is kept small, thereby reducing the cost of the cleaning bias power supplies 223 and 233 and generating backside stains even when performing borderless printing. As a result, the scraping of the secondary transfer roller 2 can be further reduced.

  The description has been given of the case of the color image forming apparatus adopting the intermediate transfer belt method, but the same applies to the intermediate transfer drum method. Further, the present invention was an invention related to cleaning of a sponge roller that is extremely difficult to clean, but it is considered to be a particularly effective cleaning method for a member that requires cleaning but is difficult to clean. It is considered that the present invention can also be applied to the cleaning of a rubber intermediate transfer member surface and a transfer conveyance belt.

It is a figure explaining the image forming apparatus which concerns on Embodiment 1 of this invention. It is a figure explaining the image forming apparatus which concerns on Embodiment 2 of this invention. It is a figure explaining the image forming apparatus which concerns on Embodiment 3 of this invention. It is a figure explaining Embodiment 3 of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Intermediate transfer belt 2 Secondary transfer roller 5 Recording paper cassette 6 Paper feeding device 7 Conveying device 8 Paper discharge tray 22 Collection roller 23 Collection roller P Recording paper

Claims (15)

An image having an object to be cleaned to which toner can adhere to the surface, a recovery member that contacts the surface of the object to be cleaned and collects the toner attached to the surface, and a bias applying unit that applies a bias to the recovery member In the forming device,
An image forming apparatus, comprising: a plurality of toner collecting members, wherein the bias applying unit applies a DC bias superimposed with an AC bias to the plurality of toner collecting members under different conditions.   2. The DC bias value is different when each of the plurality of toner collecting members is applied with a DC bias superimposed with an AC bias under different conditions by the bias applying unit. Image forming apparatus.   The AC bias duty ratio is different when a DC bias superimposed with an AC bias is applied to the plurality of toner collecting members by the bias applying unit under different conditions, respectively. The image forming apparatus according to 1 or 2.   The image forming apparatus according to claim 1, wherein a surface layer of the object to be cleaned is rubber.   The image forming apparatus according to claim 4, wherein the rubber of the surface layer of the object to be cleaned is foamed rubber.   The image forming apparatus according to claim 1, wherein the toner collecting member is a conductive roller.   The image forming apparatus according to claim 6, wherein the conductive roller is a metal roller.   8. The image forming apparatus according to claim 6, wherein a surface layer of the toner recovery member is a resin layer having toner releasability.   9. The image forming apparatus according to claim 8, wherein the resin on the surface of the toner collecting member is a urethane resin, a fluororesin, a nylon resin, or a polyimide resin.   10. The image forming apparatus according to claim 1, wherein the member to be cleaned and the toner collecting member are moved with a speed difference on a surface where the member to be cleaned and the toner collecting member are in contact with each other. .   The image forming apparatus according to claim 10, wherein a plurality of moving speed differences between the cleaning object and the toner recovery member are set on a surface where the cleaning object and the toner recovery member contact each other.   In an image forming apparatus having means for forming a toner image of a plurality of colors on an image carrier, a full color mode for forming a toner image of a plurality of colors on the image carrier and only one color toner image on the image carrier 12. The image forming apparatus according to claim 11, wherein a plurality of settings of a difference in moving speeds of the object to be cleaned and the toner recovery member are changed in the mono mode for forming the image.   In an image forming apparatus having a mode in which at least one of the width or length of a toner image formed on an image carrier is longer than the width or length of the recording material and a mode in which the toner image is shortened, The image forming apparatus according to claim 11, wherein a plurality of settings of a difference in moving speed between the object to be cleaned and the toner collecting member are changed.   In a mode in which at least one of the width or length of the toner image formed on the image carrier is longer than the width or length of the recording material, the toner image is formed by a portion of the toner image longer than the width or length of the recording member. The image forming apparatus according to claim 13, wherein a plurality of settings of the moving speed difference between the cleaning body and the toner collecting member are changed.   An image forming apparatus comprising: an image carrier on which a toner image is formed; and a transfer member that transfers the toner image on the image carrier to a recording material, wherein the transfer member is the object to be cleaned. The image forming apparatus according to claim 1.

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