JP2004233553A - Image forming apparatus and processing cartridge - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus and a processing cartridge which prevent adverse effect on images in various conditions, and output a satisfactory image free of a re-transfer ghost. <P>SOLUTION: The developer carrier 5 is capable of recovering residual developer from an image carrier 1 while a development operation is performed. The direction of the movement of the developer carrier 5 is reverse of the direction of the image carrier 1 in a development position. The position of the developer carrier is in the fourth quadrant with respect to the center of the image carrier 1 rotated counterclockwise. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

【００６２】
これをみると再転写トナー量０．４（ｍｇ／ｃｍ^２）以上になると、色味違いゴーストが発生してしまう。通常、現像ニップ部では、トナーたまりがありバッファーの役目をして再転写トナーを現像器に回収している。またこのトナーたまりは図７（ａ）に示すように現像ローラと感光体ドラムの接触によってできている。これが、現像ローラ逆方向回転では、重力方向に対して現像ローラが下にある方が回収しやすくなる。また、それとは逆に図７（ｂ）に示すように、現像ローラ逆方向回転では、ドラムが下にあるため、ドラム上に再転写トナーが残りやすく再転写ゴーストが現れやすい。表１に示した結果は、第１象限に現像ローラが位置したときの結果である。この場合、大量に再転写トナーがおそったときは、再転写トナーを完全に回収できずに色味違いゴーストが発生してしまう。
【００６３】
そこで、現像位置を感光ドラムの回転方向に対して、図８に示すように各象限の位置で配置し、再転写トナー量と色味違いゴーストレベルを検討した。
その結果を表２に示す。
【００６４】
【表２】

【００６５】
これより、第３，４象限に現像部を配置した系では、色味違いのゴーストを確認することはできなかった。これは、重力を利用し現像ローラ側に落下する構成にすることによって大量の再転写トナーが突入してきても確実に現像部に回収できるからである。
【００６６】
ただし、第３象限に関しては、重力を利用しているもののトナーだまりができにくく、トナー飛散してしまう弊害があるため、第４象限のみが好ましいということがわかった。
【００６７】
このように、感光ドラムの回転方向に対して現像位置を第四象限に配置した方が、色味の弊害もなく良好な画像が得られた。
【００６８】
上述したように、本実施の形態では、クリーナレス方式のカラー画像形成において転写直後帯電前にブラシなどの補助部材を用いることなく、現像ローラと感光ドラムの対向部において、現像ローラ表面を感光ドラム表面の移動方向に対して逆方向に移動させる。結果、機械的にニップ前で再転写トナーをせき止めて、再転写トナーの進行を阻害させ、トナーたまりを作ることで再転写トナーを確実に現像装置に再転写トナーを回収させる。これにより、シンプルなカラークリーナレスシステムにおいて、再転写トナーの影響をなくした高画質な画像が得ることができた。
【００６９】
なお、本実施の形態では、帯電装置、現像装置、感光ドラムが一体型になったプロセスカートリッジを使用したが、帯電装置もしくは現像装置を画像形成装置本体に具備してもよく、また各々の感光ドラムを画像形成装置本体に具備してもよい。
【００７０】
また、上記画像形成装置にスキャナー等の画像入力手段と、コンピュータやサーバ等の制御手段を組み合わせた画像システムとしてもよい。
【００７１】
（第２の実施形態）
図９には、第２の実施の形態が示されている。第２の実施の形態において、画像形成装置構成、現像装置構成は、第１の実施の形態と同一なので、同一の構成部分については同一の符号を付して、その説明は簡略し、本発明の特徴的な構成について説明を行う。
【００７２】
第１の実施の形態では、帯電装置として感光ドラムに対して従動で回転する帯電ローラを用いた構成であった。しかし、本実施の形態においては、所定の周速度で回転する感光ドラムの表面に対して帯電ローラ表面を接触させ、さらに順方向に回転させてかつ周速度を異なるようにするか、又は逆方向に回転させる構成で行うものとする。
【００７３】
このような構成においては、帯電ローラに転写残トナーが付着しても転写残トナーに対する帯電性能は劣化せず、長期間にわたって安定して転写残トナーを所望の極性に摩擦帯電させやすくなるため、再転写ゴースト等の画像弊害を生じることもない。本発明者の実験においては、１％以上の周速差を付けることで効果があることがわかっており、以上述べた周速差とは、周速度で１％以上の差のことをさすものである。
【００７４】
第２の実施の形態では、帯電ローラ２ｙは感光ドラムの回転方向に対して順方向で回転させ、感光ドラムの周速に対して１２０％の周速で回転させた。このように、感光ドラム表面と帯電ローラ表面との間に周速差を設けることによって、帯電ローラ表面のトナーなどの汚染物を摺擦させ、摩擦帯電によってマイナスに帯電することが有効に行なえる。
【００７５】
次に本実施の形態の構成について説明する。
【００７６】
図９の装置本体の概略図に示すように、プロセスカートリッジＰ２１、Ｐ２２、Ｐ２３、Ｐ２４は、感光ドラム、帯電ローラ、現像ローラ、トナー容器を一体的に収納したものである。
【００７７】
帯電ローラ２２は感光ドラムの回転方向に対して順方向で回転させ、感光ドラムの周速に対して１２０％の周速で回転させた。このように、感光ドラム表面と帯電ローラ表面との間に周速差を設けることによって、帯電ローラ表面のトナーなどの汚染物を摺擦させ、摩擦帯電によってマイナスに帯電することが有効に行なえる。ここで、マイナスに帯電したトナーはある程度、帯電ローラと感光ドラムの電位差（例えば、帯電ローラ印加電圧１２５０Ｖ、感光ドラム電位−７００Ｖ）によって感光ドラム表面に移動する。なお、実施例１と同様に帯電ローラは放電を用いて感光ドラムを帯電するものであり、この放電によってもトナーは強くマイナスに帯電されやすくなる。
【００７８】
マイナスに帯電された転写残トナー（最転写トナーを含む）は、感光ドラム表面の移動方向に対し逆方向で回転する現像ローラに回収され、現像容器内に収容し撹拌部材でトナーが撹拌される。なお、再転写トナーは、非常に少ないため、現像装置内で混合されることで画像上問題ないレベルとなる。
【００７９】
使用している部材は第２の実施の形態と同様なものを使用しているものとする。このような構成をとることによって第１の実施の形態と同様な効果が得られた。
【００８０】
これにより、シンプルなカラークリーナレスシステムにおいて、帯電ローラへの転写残トナーによる汚染をも防止し、かつ、再転写トナーの影響をなくした高画質な画像が得ることができた。
【００８１】
以上の実施の形態においては、全ての画像形成ステーションにおいて、同じ現像装置としていたが、１色目の画像形成ステーションにおいては、通常、再転写トナーが付着しにくいので、１色目の画像形成ステーションの現像装置においては上記現像装置に限られることもない。
【００８２】
すなわち、１色目の画像形成ステーションにおいて、感光体の回転方向に対して現像ローラを順方向に回転することもできるし、感光体と現像ローラとを非接触として現像時に現像ローラ上のトナーを感光体へ飛翔させることもできる。
【００８３】
ただし、転写ベルトによって１色目の像担持体に他の色のトナーが搬送されやすく１色目の像担持体に再転写トナーが付着しやすい場合には、実施の形態１、２のように１色目の画像形成ステーションの現像装置も他のステーションの現像装置と同じにすることが有効である。
【００８４】
以上の実施の形態において、受像部材は転写材であり、転写材を転写ベルトで担持して各画像形成ステーションに搬送したが、受像部材を中間転写ベルトとして、各画像形成ステーションから中間転写ベルトに各色トナー像を重畳転写した後、中間転写ベルトから転写材へ重畳トナー像を一括転写するようにしても良い。
【００８５】
以上説明したように、現像同時回収を行うシンプルなカラークリーナレスシステムにおいて、像担持体表面の移動方向に対し現像剤担持体を逆方向に回転させることで、再転写ゴースト等の画像弊害をなくすことが可能となる。
【００８６】
本発明は以上の実施の形態に限定されるものではなく、本発明の技術思想の範囲内においてあらゆる変形が可能である。
【００８７】
【発明の効果】
以上の説明で明らかなように、前記第１の現像剤担持体は、前記第１の像担持体上の残留現像剤を、前記第１の現像剤担持体と前記第１の像担持体とのニップ部の前でせき止めることによって前記第１の現像剤担持体へ回収し、前記第２の現像剤担持体は、前記第２の像担持体上の前記残留現像剤を、前記第２の現像剤担持体と前記第２の像担持体とのニップ部の前でせき止めることによって前記第２の現像剤担持体へ回収し、また、現像剤担持体位置は、像担持体の中心から、像担持体の回転方向に対して第四象限の位置にあることで、現像ニップ部で残留現像剤のたまりを作り、現像剤担持体側に重力を利用して自然に落下する構成にすることにより、回収を確実におこなうことができ、大量の再転写トナーが突入してきたときでも、現像剤担持体へ確実に回収することにより、現像時の混色を防止した画像形成装置及びプロセスカートリッジを提供できる。
【００８８】
更に、再転写ゴーストを防止した画像形成装置及びプロセスカートリッジを提供することができる。
【００８９】
更に、専用のクリーナをもたないクリーナレス方式に適した画像形成装置及びプロセスカートリッジを提供することができる。
【００９０】
更に、像担持体上の残留現像剤を現像時に残らず除去するようにした画像形成装置及びプロセスカートリッジを提供することができる。
【図面の簡単な説明】
【図１】従来の画像形成装置の概略断面図である。
【図２】カラー電子写真システムの２次色目のステーションにおける転写残トナーの機構について示したものである。
【図３】第１の実施の形態に係る画像形成装置の断面図である。
【図４】第１の実施の形態に係る画像形成装置における再転写トナーの回収の様子を示した模式図である。
【図５】画像弊害を確認するためのパターン画像を示した図である。
【図６】再転写ゴーストが現れたパターン画像を示した図である。
【図７】ドラムと現像のニップ部を表した図である。
【図８】現像位置とドラム位置を示した図である。
【図９】第２の実施の形態に係る画像形成装置の断面図である。
【符号の説明】
１，１ｙ，１ｍ，１ｃ，１ｋ 感光ドラム（像担持体）
２，２ｙ，２ｍ，２ｃ，２ｋ 帯電ローラ（帯電部材）
３，３ｙ，３ｍ，３ｃ，３ｋ 露光手段
４，４ｙ，４ｍ，４ｃ，４ｋ 現像装置（現像手段）
５，５ｙ，５ｍ，５ｃ，５ｋ 現像ローラ（現像剤担持体）
６，６ｙ，６ｍ，６ｃ，６ｋ 感光ドラム
７ トナー供給ローラ
８ 転写材
９ 転写ベルト
１０ 吸着ローラ
１２ 定着装置
１３ 摺擦部材
Ｐ１，Ｐ２，Ｐ３，Ｐ４ プロセスカートリッジ[0001]
TECHNICAL FIELD OF THE INVENTION
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a color image forming apparatus such as a laser beam printer or an electrophotographic copying machine, and a process cartridge detachably mountable to a main body of the apparatus, and more particularly to a cleanerless color image forming apparatus having a plurality of developing devices. And a process cartridge.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, in an image forming apparatus such as an electrophotographic copying machine or a laser beam printer, generally, a charging process for uniformly and uniformly charging an image carrier such as a photosensitive drum is performed. An exposure process for writing a latent image, a development process for attaching toner to an electrostatic latent image to develop it as a toner image, a transfer process for transferring a toner image on an image carrier to a transfer material such as paper, and a toner image on a transfer material The image is formed by a series of image forming processes including a fixing process for fixing the toner image, a cleaning process for removing a residue such as a transfer residual toner remaining on the surface of the image carrier after the transfer of the toner image, and the like.
[0003]
In the above-described cleaning process, the transfer residual toner collected by the cleaning device is stored in a container for disposal, and then disposed.
[0004]
Therefore, in recent years, a cleaner-less process has been proposed in which the image forming apparatus is reduced in size by omitting the above-described cleaning device, and maintenance such as discarding transfer residual toner is not required. In one embodiment of the cleanerless process, the developing device attaches the toner to the exposed portion of the image carrier whose surface potential is attenuated by reversal development, and simultaneously removes the residue remaining in the non-exposed portion. We are collecting.
[0005]
Specifically, in the case of a one-component developer composed of a negatively chargeable toner, the image carrier is uniformly charged to −600 V in the charging step, and a portion corresponding to the image portion of the image carrier is exposed in the exposure step. Exposure is performed to attenuate the surface potential so that the exposed portion becomes -200 V. If a DC voltage of -400 V is applied to the developer carrier as a developing bias in the developing process, the negatively charged residual toner is removed from the image portion. In the exposed portion corresponding to the above, the toner remains on the image carrier as it is, but in the non-exposed portion, the toner is collected by the developing device due to the back contrast. It can be used again.
[0006]
In the recent laser beam printer market, color laser printers have become mainstream.
[0007]
What is needed is an inexpensive and compact color printer as well as a monochrome printer. Therefore, it has become necessary to construct a simple electrophotographic system.
[0008]
[Problems to be solved by the invention]
However, when the cleanerless system used in the monochrome electrophotographic system in the related art as described above is applied to a full-color electrophotographic system, the following problems occur.
[0009]
In the color electrophotographic system, a plurality of colors are used, so that there is a problem of a difference in color of the transfer residual toner. FIG. 1 shows the mechanism of the transfer residual toner in the second color image forming station of the color electrophotographic system.
[0010]
In a color electrophotographic system, a toner image formed on a photosensitive drum in each image forming station is sequentially transferred onto a transfer material (for example, paper or an OHP sheet) carried and conveyed by a belt-shaped transfer material conveying means. It is something to do.
[0011]
In the image forming apparatus having such a configuration, for example, the so-called re-transfer, in which the toner transferred on the transfer material in the previous station adheres to the photosensitive drum of the next station when it reaches the next station. May occur and may be included in the transfer residual toner of the next station (in FIG. 1, the toner having the positive polarity on the drum after the transfer corresponds).
[0012]
The transfer toner of the previous station is, of course, a toner of a different color (the transfer toner of the previous station is hereinafter referred to as retransfer toner). These are negatively charged by removing the charging device, and the toner remaining in the non-image area is collected by the developing device, but the re-transferred toner of a different color remaining in the image area on the photosensitive drum is collected by the developing unit. Instead, it remains in the image portion and is developed, and appears in the image as a ghost having a different color.
[0013]
In order to collect the toner, the developing roller was rotated in the opposite direction to the photosensitive drum, and all of the toner was collected in the developing nip.However, when a large amount of retransferred toner entered the developing position, the developing nip was stopped. There was a problem that retransfer ghosts appeared because they could not be accumulated at the portion.
[0014]
An object of the present invention is to provide an image forming apparatus and a process cartridge capable of outputting a good image without image harm under all conditions and without retransfer ghosts. That is.
[0015]
Another object of the present invention is to provide an image forming apparatus and a process cartridge in which a retransfer ghost is prevented.
[0016]
It is another object of the present invention to provide an image forming apparatus and a process cartridge suitable for a cleanerless system having no dedicated cleaner.
[0017]
Another object of the present invention is to provide an image forming apparatus and a process cartridge in which a residual developer on an image carrier is completely removed during development.
[0018]
[Means for Solving the Problems]
In order to solve the above problems, the present invention has the following means.
That is, the image forming apparatus of the present invention transfers the image of the developer of the first color to the image receiving member at the first image forming station, and then transfers the image of the second color to the image receiving member at the second image forming station. Transfer means for transferring the image of the developer,
The first image forming station has a first image carrier, a first charging unit for charging the first image carrier, and a carrier for carrying the first color developer. A first developer carrier for developing the electrostatic image formed on the first image carrier with the developer of the first color;
The second image forming station carries a second image carrier, a second charging unit for charging the second image carrier, and carries and transports the developer of the second color. And a second developer carrier for developing the electrostatic image formed on the second image carrier with the developer of the second color.
The second developer carrier can collect the residual developer from the second image carrier at the same time as the developing operation,
The direction of movement of the second developer carrier is opposite to the direction of movement of the second image carrier at the development position,
The position of the second developer carrier is such that the second image carrier rotates clockwise and is located in a fourth quadrant with respect to the center of the second image carrier.
[0019]
According to this configuration, the first developer carrier removes the residual developer on the first image carrier into a nip portion between the first developer carrier and the first image carrier. And collects the residual developer on the second image carrier by the second developer carrier by collecting the first developer carrier by damming in front of the second developer carrier. The developer is recovered to the second developer carrier by damping in front of a nip portion between the image carrier and the second image carrier, and the position of the developer carrier is moved from the center of the image carrier to the image carrier. Is located in the fourth quadrant with respect to the rotation direction of the developer, a pool of the residual developer is formed in the developing nip portion, and the developer is naturally dropped by using gravity on the developer carrier side, so that the recovery is performed. It can be performed reliably, and even when a large amount of retransfer toner enters, the developer carrier By reliably collected, it is possible to provide an image forming apparatus and a process cartridge to prevent color mixing at the time of development.
[0020]
Further, in the image forming apparatus of the present invention, the second charging unit includes a second charging member that can contact the second image carrier.
The second charging member frictionally charges the residual developer on the second image carrier to a regular polarity.
[0021]
Further, in the image forming apparatus according to the present invention, it is preferable that the image forming apparatus further includes a transport unit that transports the image receiving member from the first image forming station to the second image forming station.
[0022]
Further, in the image forming apparatus of the present invention, it is preferable that the second developer carrier is provided in contact with the second image carrier.
[0023]
Further, in the image forming apparatus of the present invention, it is preferable that the second charging member is applied with a DC voltage without being applied with an AC voltage. This is because, if the applied voltage is a superimposed voltage of the AC voltage and the DC voltage, the residual toner is removed by the action of the AC voltage.
[0024]
Further, in the image forming apparatus of the present invention, it is preferable that the second charging member is rotatable with a peripheral speed difference with respect to the second image carrier. By doing so, a peripheral speed difference is provided between the surface of the image carrier and the surface of the developer carrier, and a nip pressure is provided, so that the retransfer toner is mechanically damped before the nip to advance the retransfer toner. And cause the developing device to collect re-transferred toner of a different color from the previous station.
[0025]
Further, the process cartridge of the present invention further comprises a second image forming station which transfers the first color developer image to the image receiving member at the first image forming station, and then transfers the second color developer image to the image receiving member at the second image forming station. A process cartridge detachable from the second image forming station of an image forming apparatus main body including a transfer unit for transferring an image,
The process cartridge carries and conveys an image carrier, a charging unit for charging the image carrier, and a developer of the second color, and transfers the electrostatic image formed on the image carrier to the second color. A developer carrying member for developing with a developer of a color of
The developer carrier can collect the residual developer from the image carrier at the same time as the developing operation,
The moving direction of the developer carrier is opposite to the moving direction of the image carrier at the developing position,
The developer carrier is located at the center of the image carrier and in the fourth quadrant with respect to the rotation direction of the image carrier.
[0026]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. However, the dimensions, materials, shapes, relative arrangements, and the like of the components described in this embodiment are not intended to limit the technical scope of the present invention to them unless otherwise specified. Not something. Further, in the following drawings, the same members as those described in the drawings used in the description of the related art described above are denoted by the same reference numerals.
[0027]
(1st Embodiment)
An image forming apparatus and a process cartridge according to the first embodiment will be described with reference to FIGS.
[0028]
FIG. 3 shows a schematic configuration of a tandem type color laser beam printer having a plurality of developing devices as an example of the image forming apparatus according to the present invention. FIG. 1 is a longitudinal sectional view of the transfer material 8 as an image receiving member, taken along the transport direction.
[0029]
Referring to FIG. 3, the color image forming apparatus is configured to transfer an endless transfer belt 9 which is a transfer material transporting unit for carrying and transporting a transfer material 8 and a toner image of a different color in a moving direction of the transfer belt 9. Process cartridges P1, P2, P3, and P4 as image forming stations to be formed are arranged in series. In each process cartridge (image forming unit), the toner contained in the developing devices 4y, 4m, 4c, and 4k is of a different color, but the basic configuration and operation remain unchanged. The process cartridge is configured to be detachable from the image forming apparatus main body.
[0030]
Here, the process cartridges P1 to P4 as image forming means are constituted by four image forming units of yellow (Y), magenta (M), cyan (C), and black (Bk). Each of the image forming units has a configuration in which photosensitive drums 1y, 1m, 1c, and 1k, which are image carriers, are arranged, and a yellow toner, a magenta toner, and a cyan toner, each of which is a one-component developer, are provided on the outer periphery thereof. , Developing devices (developing means) 4y, 4m, 4c, 4k provided with developing rollers 5y, 5m, 5c, 5k as developer carrying members for storing black toner and transporting the toners, and 3y as exposure means , 3m, 3c, and 3k, and charging rollers 2y, 2m, 2c, and 2k as charging means (charging members) are provided. Further, transfer rollers 6y, 6m, 6c, and 6k as transfer means are disposed at portions opposed to the respective photosensitive drums 1 with the transfer belt 9 interposed therebetween.
[0031]
The transfer material transporting means in this image forming apparatus is an electrostatic transfer belt 9 which runs while being suspended by a suitable plurality of rollers. Inside and around the electrostatic transfer belt 9, a transfer roller 6, a suction roller 10 It has. A plurality of transfer rollers 6 are provided as a part of a plurality of image forming units described later.
[0032]
The attraction roller 10 of the electrostatic transfer belt 9 electrostatically attracts the transfer material 8 conveyed from the paper supply unit onto the electrostatic transfer belt 9 prior to image formation. The image forming units P1 to P4 sequentially move the yellow toner image, the magenta toner image, the cyan toner image, and the like at predetermined positions on the transfer material 8 as the transfer material 8 electrostatically attracted onto the electrostatic transfer belt 9 travels. An image is formed at a timing so that the black toner images overlap, and the images are sequentially superimposed and transferred.
[0033]
Hereinafter, the image forming procedure will be described focusing on a process cartridge (also referred to as an image forming unit) P1 as an image forming station.
[0034]
The surface photosensitive layer of the photosensitive drum 1y rotated and driven by a driving unit (not shown) is uniformly charged by the charging roller 2y to which a charging bias of -1150V is applied. The charging bias was a DC voltage without an AC voltage, and the surface potential of the photosensitive drum 1y was -600 V. That is, the photosensitive drum 1y is charged to a potential of approximately (applied DC voltage-discharge start voltage) by a discharge phenomenon in a minute gap between the drum 1y and the roller 2y. In this embodiment, the discharge starting voltage was about 550V. An image forming signal based on a yellow component is projected from the laser scanner on the charged surface of the photosensitive drum 1y, and an electrostatic latent image is formed.
[0035]
When this electrostatic latent image reaches the developing site with the rotation of the photosensitive drum 1y, a yellow toner having a negative charge polarity is applied to the latent image from the developing roller 4y by the developing bias, and the latent image is reversely developed as a yellow toner image. . This yellow toner image is further sent to the above-described transfer portion as the photosensitive drum 1y rotates.
[0036]
The transfer material 8 electrostatically attracted onto the transfer belt 9 in advance is conveyed in synchronization with the timing at which the yellow toner image reaches the transfer portion, and the transfer bias (positive polarity) applied to the transfer roller 7y causes the transfer material 8 to become yellow. The toner image is transferred (transferred) onto the transfer material 8. The residual toner remaining on the image carrier 1 without contributing to the transfer is charged by the charging roller 2y to a normal polarity (minus polarity) that can be collected by the developing device. The photosensitive drum is also negatively charged. Many of the residual toner on the photosensitive drum after the transfer has a polarity opposite to the normal polarity (minus polarity). However, since the charging roller 2y is charged using discharge, the toner is strongly charged to a negative polarity. Is done.
[0037]
The voltage applied to the charging roller 2y is preferably a DC voltage without an AC voltage in order to strongly negatively charge the residual toner. This is because, if the applied voltage is a superimposed voltage of the AC voltage and the DC voltage, the residual toner is removed by the action of the AC voltage.
[0038]
Further, in order to more reliably negatively charge the residual toner on the photosensitive drum, the surface layer of the charging roller 2y preferably has a frictional charging polarity for frictionally charging the toner negatively. That is, it is preferable to select the material of the surface layer of the charging roller 2y and the material of the toner such that the toner is negatively frictionally charged by the charging roller.
[0039]
Thereafter, the photosensitive drum is irradiated with light according to image information by a laser scanner while the residual toner remains on the photosensitive drum. At the same time as the developing device develops the latent image, the residual toner charged to the normal polarity by the charging roller 2y is collected by the developing device.
At that time, the photosensitive drum 1y has already entered the next image forming operation.
[0040]
The transfer material 8 onto which the yellow toner image has been transferred is conveyed to a process cartridge (image forming unit) P2 as the transfer belt 9 moves. Before the transfer material 8 reaches the image forming portion P2, a magenta toner image is formed on the photosensitive drum 1m by the laser scanner 3m and the developing roller 5m in the same manner as described above, and the toner image is formed by the transfer roller 6m. The image is superimposed and transferred onto the yellow toner image. The transfer material 8 on which the superimposed toner image has been transferred is transported to a process cartridge (image forming unit) P3.
[0041]
Similarly, in the image forming units P3 and P4, a cyan toner image and a black toner image are formed on the photosensitive drums 1c and 1k by the laser scanners 3c and 3k and the developing rollers 5c and 5k, and are formed by the transfer rollers 6c and 6k. Are sequentially superimposed and transferred onto the superimposed toner image, thereby completing the transfer process.
[0042]
After the transfer, the transfer material 8 reaches the fixing device 12, where it is heated and pressed to melt and mix the toner image to form a color image. After being fixed and fixed to the transfer material 8, it is discharged outside the machine. You.
[0043]
The photosensitive drum 1y is configured by providing a photosensitive layer (for example, an organic optical semiconductor, amorphous silicon, or the like) on the surface of a conductive cylindrical drum base. The photosensitive drum 1 is driven to rotate by driving means (not shown), and its surface moves (rotates) in a direction indicated by an arrow at a predetermined surface moving speed (hereinafter abbreviated as a peripheral speed).
[0044]
The charging roller 2y has a configuration in which the outer peripheral surface of a cored bar is covered with an elastic body, and is arranged such that the surface of the elastic body is in contact with the surface of the photosensitive drum 1y.
[0045]
The developing device 4y includes a developing roller 5y that is driven to rotate, a developing blade that regulates a layer thickness of the toner carried on the surface of the developing roller 5y, and an old toner from the developing roller 5y while supplying new toner to the developing roller 5y. In order to peel off the toner, a toner supply roller 7 (see FIG. 4) that rotates the counter with respect to the developing roller is arranged in the developing device 4y. The toner supply roller is provided in pressure contact with the developing roller.
[0046]
As the toner, either magnetic or non-magnetic toner can be used, and the production method thereof may be either polymerization or pulverization. The toner used in the exemplary embodiment is a negatively chargeable toner that is normally negatively charged by friction.
[0047]
The toner applied to the surface of the developing roller 5y and the layer thickness of which is regulated by the developing blade is applied to the developing roller 5y by a power source (not shown) to apply a developing bias (DC voltage) of -400V to the photosensitive drum 1y. The toner adheres to the exposed portion, whereby the electrostatic latent image is developed as a toner image.
[0048]
On the other hand, residues on the photosensitive drum such as transfer residual toner remaining on the surface of the photosensitive drum after the transfer of the toner image are removed as follows.
[0049]
The toner attached to the surface of the photosensitive drum from the developing device during the development is negatively charged. The back surface of the transfer material is positively charged by the transfer roller 4 during transfer, and is transferred onto the transfer material by the electric field.
[0050]
At this time, since the photosensitive drum is also positively charged, a part of the toner is positively charged, and as a result, the toner remains on the photosensitive drum without being transferred to the transfer material.
[0051]
Some of the residues on the photosensitive drum 1 remaining on the surface of the photosensitive drum 1 without being transferred onto the transfer material 8 are positively and negatively charged. Those negatively charged are collected during development.
[0052]
However, in order to recover the positively charged residue on the photosensitive drum by the back contrast during development, it is necessary to negatively charge the residue on the photosensitive drum. This is performed at the same time as the surface of the photosensitive drum is negatively charged by the charging roller. In this way, the residue on the photosensitive drum is recovered to the original developing device.
[0053]
However, at the secondary color and tertiary color stations, when the developing roller rotates in the forward direction with respect to the photosensitive drum, as shown in FIG. This will cause the image to be adversely affected.
[0054]
Therefore, in the present embodiment, the simultaneous recovery of the re-transferred toner is carried out as follows.
[0055]
That is, in the present embodiment, as shown in FIG. 4, the photosensitive drum 1 and the developing roller 5 are provided in contact with each other, and the photosensitive drum 1 And the developing roller 5 is rotated in the opposite direction (arrow direction) at the contact portion.
[0056]
In this embodiment, the developing roller is rotated in the opposite direction (counter direction) at a peripheral speed of 170% of the peripheral speed of the photosensitive drum. By doing so, as shown in FIG. 4, a peripheral speed difference is provided between the surface of the photosensitive drum 1 and the surface of the developing roller 5 and a nip pressure is applied to mechanically dampen the retransfer toner before the nip. Then, the progress of the retransfer toner is inhibited, and the retransfer toner is collected by the developing device.
[0057]
The residue on the photosensitive drum collected by the developing roller 5 is agitated in the developing device 4 by the agitating member and mixed with other toner for reuse. (Toner) is very small, and is mixed in the developing device to a level at which there is no problem on the image.
[0058]
Next, Table 1 shows the relationship between the retransfer toner amount and the rank of the ghost having a different color.
[0059]
A pattern image as shown in FIG. 5 was used as a sample image for evaluating a different color ghost. This is an image in which a 4 cm square solid black image is written in the area A and a halftone pattern is written in the area B. In the area A, a yellow-only image forming pattern was formed in the primary color, and in the area B, a magenta-only image forming pattern was formed in the secondary color.
[0060]
As a result, when the yellow toner is not collected in the development, the image pattern of the area A appears in the area B, which causes an image problem. Therefore, images were output when the developing roller was rotated in the forward direction with respect to the photosensitive drum and when the developing roller was rotated in the reverse direction. It should be noted that the image adverse effects can be recognized as shown in FIG. 6, and the images were compared based on the density of the area C and the difference in the color of the area D. In Table 1, ○ indicates a rank in which a difference in color is not recognized, Δ indicates a rank in which a difference in color is slightly generated, and X indicates a rank in which a difference in color is clearly recognized.
[0061]
[Table 1]

[0062]
It can be seen that the retransfer toner amount is 0.4 (mg / cm ² Above), ghosts with different colors are generated. Normally, in the developing nip portion, there is a pool of toner, which serves as a buffer and collects the retransferred toner to the developing device. This toner accumulation is formed by the contact between the developing roller and the photosensitive drum as shown in FIG. However, when the developing roller is rotated in the reverse direction, it is easier to collect when the developing roller is below the direction of gravity. On the contrary, as shown in FIG. 7B, when the developing roller is rotated in the reverse direction, the retransfer toner tends to remain on the drum because the drum is below, and a retransfer ghost is likely to appear. The results shown in Table 1 are obtained when the developing roller is located in the first quadrant. In this case, when a large amount of retransferred toner is used, the retransferred toner cannot be completely recovered, and a ghost with a different color is generated.
[0063]
Therefore, the developing position was arranged at each quadrant position as shown in FIG. 8 with respect to the rotation direction of the photosensitive drum, and the retransfer toner amount and the color difference ghost level were examined.
Table 2 shows the results.
[0064]
[Table 2]

[0065]
As a result, in the system in which the developing units were arranged in the third and fourth quadrants, it was not possible to confirm ghosts with different colors. This is because, by employing a configuration in which the toner is dropped to the developing roller using gravity, even if a large amount of retransfer toner enters, the toner can be reliably collected in the developing unit.
[0066]
However, in the third quadrant, it was found that only the fourth quadrant was preferable because gravity was used, but there was a problem that toner accumulation was difficult and toner was scattered.
[0067]
As described above, when the developing position was arranged in the fourth quadrant with respect to the rotation direction of the photosensitive drum, a good image was obtained without any adverse effect on the tint.
[0068]
As described above, in the present embodiment, in the cleanerless color image formation, the surface of the developing roller is contacted with the photosensitive drum at the opposing portion between the developing roller and the photosensitive drum without using an auxiliary member such as a brush immediately before transfer and before charging. Move in the opposite direction to the direction of surface movement. As a result, the retransferred toner is mechanically damped before the nip to hinder the progress of the retransferred toner, and the toner is formed, so that the retransferred toner is reliably collected by the developing device. As a result, in a simple color cleanerless system, a high-quality image free of the influence of retransfer toner could be obtained.
[0069]
In the present embodiment, the process cartridge in which the charging device, the developing device, and the photosensitive drum are integrated is used. However, the charging device or the developing device may be provided in the main body of the image forming apparatus. The drum may be provided in the image forming apparatus main body.
[0070]
Further, an image system in which the image forming apparatus is combined with an image input unit such as a scanner and a control unit such as a computer or a server may be used.
[0071]
(Second embodiment)
FIG. 9 shows a second embodiment. In the second embodiment, since the configuration of the image forming apparatus and the configuration of the developing apparatus are the same as those of the first embodiment, the same components are denoted by the same reference numerals, and the description thereof will be simplified. The characteristic configuration of will be described.
[0072]
In the first embodiment, the charging device is configured to use a charging roller that rotates following the photosensitive drum. However, in the present embodiment, the surface of the charging roller is brought into contact with the surface of the photosensitive drum rotating at a predetermined peripheral speed, and is further rotated in the forward direction and the peripheral speed is changed, or It is assumed that the rotation is performed in the following manner.
[0073]
In such a configuration, even if the transfer residual toner adheres to the charging roller, the charging performance for the transfer residual toner does not deteriorate, and it becomes easy to stably frictionally charge the transfer residual toner to a desired polarity over a long period of time. No adverse effects such as retransfer ghosts occur. In experiments conducted by the present inventor, it has been found that providing a peripheral speed difference of 1% or more is effective, and the peripheral speed difference described above refers to a difference of 1% or more in peripheral speed. It is.
[0074]
In the second embodiment, the charging roller 2y is rotated in the forward direction with respect to the rotation direction of the photosensitive drum, and is rotated at a peripheral speed of 120% with respect to the peripheral speed of the photosensitive drum. By providing the peripheral speed difference between the photosensitive drum surface and the charging roller surface, contaminants such as toner on the charging roller surface can be rubbed and negatively charged by frictional charging. .
[0075]
Next, the configuration of the present embodiment will be described.
[0076]
9, the process cartridges P21, P22, P23, and P24 integrally house a photosensitive drum, a charging roller, a developing roller, and a toner container.
[0077]
The charging roller 22 was rotated in a forward direction with respect to the rotation direction of the photosensitive drum, and was rotated at a peripheral speed of 120% with respect to the peripheral speed of the photosensitive drum. By providing the peripheral speed difference between the photosensitive drum surface and the charging roller surface, contaminants such as toner on the charging roller surface can be rubbed and negatively charged by frictional charging. . Here, the negatively charged toner moves to the surface of the photosensitive drum to some extent due to the potential difference between the charging roller and the photosensitive drum (for example, a charging roller applied voltage of 1250 V and a photosensitive drum potential of -700 V). Note that, similarly to the first embodiment, the charging roller uses a discharge to charge the photosensitive drum, and the discharge also tends to strongly negatively charge the toner.
[0078]
The negatively charged transfer residual toner (including the most-transferred toner) is collected by a developing roller that rotates in a direction opposite to the direction of movement of the photosensitive drum surface, is accommodated in a developing container, and is stirred by a stirring member. . Since the amount of retransferred toner is very small, the retransferred toner is mixed in the developing device to a level at which there is no problem on the image.
[0079]
It is assumed that the same members as those used in the second embodiment are used. With such a configuration, the same effect as in the first embodiment is obtained.
[0080]
As a result, in a simple color cleaner-less system, it was possible to prevent contamination of the charging roller by toner remaining after transfer, and to obtain a high-quality image without the influence of retransfer toner.
[0081]
In the above embodiment, the same developing device is used in all the image forming stations. However, in the first color image forming station, the re-transfer toner is usually difficult to adhere, so The device is not limited to the developing device.
[0082]
That is, in the image forming station for the first color, the developing roller can be rotated in the forward direction with respect to the rotating direction of the photoconductor, or the toner on the developing roller is exposed at the time of development by leaving the photoconductor and the developing roller out of contact. You can also fly to the body.
[0083]
However, when the toner of another color is easily transported to the image carrier of the first color by the transfer belt and the retransfer toner easily adheres to the image carrier of the first color, the first color image carrier is used as in the first and second embodiments. It is effective to make the developing device of the image forming station the same as the developing devices of the other stations.
[0084]
In the above embodiment, the image receiving member is a transfer material, and the transfer material is carried on the transfer belt and conveyed to each image forming station. After the respective color toner images are superimposedly transferred, the superimposed toner images may be collectively transferred from the intermediate transfer belt to the transfer material.
[0085]
As described above, in a simple color cleanerless system for simultaneous recovery of development, by rotating the developer carrier in a direction opposite to the moving direction of the image carrier surface, image harm such as retransfer ghost is eliminated. It becomes possible.
[0086]
The present invention is not limited to the above embodiments, and various modifications are possible within the scope of the technical idea of the present invention.
[0087]
【The invention's effect】
As is apparent from the above description, the first developer carrier carries the residual developer on the first image carrier with the first developer carrier and the first image carrier. The first developer carrier is collected by damming in front of the nip portion, and the second developer carrier transfers the residual developer on the second image carrier to the second image carrier. The developer carrier and the second image carrier are collected in the second developer carrier by damming in front of the nip portion, and the position of the developer carrier is from the center of the image carrier, By being in the fourth quadrant position with respect to the rotation direction of the image carrier, a pool of residual developer is formed at the developing nip portion, and the structure is such that the developer drops naturally using gravity on the developer carrier side. Can be reliably collected, and even when a large amount of retransfer toner enters, the current Agent by reliably collected into carrier, it is possible to provide an image forming apparatus and a process cartridge to prevent color mixing at the time of development.
[0088]
Further, it is possible to provide an image forming apparatus and a process cartridge in which a retransfer ghost is prevented.
[0089]
Further, it is possible to provide an image forming apparatus and a process cartridge suitable for a cleanerless system having no dedicated cleaner.
[0090]
Further, it is possible to provide an image forming apparatus and a process cartridge in which the residual developer on the image carrier is completely removed during development.
[Brief description of the drawings]
FIG. 1 is a schematic sectional view of a conventional image forming apparatus.
FIG. 2 illustrates a mechanism of a transfer residual toner in a station of a secondary color of a color electrophotographic system.
FIG. 3 is a cross-sectional view of the image forming apparatus according to the first embodiment.
FIG. 4 is a schematic view showing a state of collecting retransfer toner in the image forming apparatus according to the first embodiment.
FIG. 5 is a diagram showing a pattern image for confirming an image defect.
FIG. 6 is a diagram illustrating a pattern image in which a retransfer ghost appears.
FIG. 7 is a diagram illustrating a nip portion of a drum and a development.
FIG. 8 is a diagram showing a developing position and a drum position.
FIG. 9 is a sectional view of an image forming apparatus according to a second embodiment.
[Explanation of symbols]
1,1y, 1m, 1c, 1k Photosensitive drum (image carrier)
2,2y, 2m, 2c, 2k Charging roller (charging member)
3,3y, 3m, 3c, 3k Exposure means
4,4y, 4m, 4c, 4k developing device (developing means)
5,5y, 5m, 5c, 5k developing roller (developer carrier)
6,6y, 6m, 6c, 6k photosensitive drum
7 Toner supply roller
8 Transfer material
9 Transfer belt
10 Suction roller
12 Fixing device
13 Sliding member
P1, P2, P3, P4 Process cartridge

Claims (7)

Transfer means for transferring the first color developer image to the image receiving member at the first image forming station, and then transferring the second color developer image to the image receiving member at the second image forming station; ,
The first image forming station has a first image carrier, a first charging unit for charging the first image carrier, and a carrier for carrying the first color developer. A first developer carrier for developing the electrostatic image formed on the first image carrier with the developer of the first color;
The second image forming station carries a second image carrier, a second charging unit for charging the second image carrier, and carries and transports the developer of the second color. And a second developer carrier for developing the electrostatic image formed on the second image carrier with the developer of the second color.
The second developer carrier can collect the residual developer from the second image carrier at the same time as the developing operation,
The direction of movement of the second developer carrier is opposite to the direction of movement of the second image carrier at the development position,
The second developer carrier is located in a fourth quadrant with respect to the center of the second image carrier when the second image carrier rotates clockwise. apparatus. The second charging unit includes a second charging member that can contact the second image carrier,
The image forming apparatus according to claim 1, wherein the second charging member frictionally charges the residual developer on the second image carrier to a normal polarity. The image forming apparatus according to claim 1, further comprising a conveying unit configured to convey the image receiving member from the first image forming station to the second image forming station. The image forming apparatus according to claim 1, wherein the second developer carrier is provided in contact with the second image carrier. The image forming apparatus according to claim 1, wherein a DC voltage is applied to the second charging member without applying an AC voltage. The image forming apparatus according to claim 1, wherein the second charging member is rotatable with a peripheral speed difference with respect to the second image carrier. An image including transfer means for transferring a developer image of a first color to an image receiving member at a first image forming station and then transferring a developer image of a second color to the image receiving member at a second image forming station; A process cartridge detachable from the second image forming station of the forming apparatus main body;
The process cartridge carries and conveys an image carrier, a charging unit for charging the image carrier, and a developer of the second color, and transfers the electrostatic image formed on the image carrier to the second color. A developer carrying member for developing with a developer of a color of
The developer carrier can collect the residual developer from the image carrier at the same time as the developing operation,
The moving direction of the developer carrier is opposite to the moving direction of the image carrier at the developing position,
The process cartridge according to claim 1, wherein the developer carrier is located at a center of the image carrier and in a fourth quadrant with respect to a rotation direction of the image carrier.

Images