JP2004061908A

JP2004061908A - Transfer device

Info

Publication number: JP2004061908A
Application number: JP2002220874A
Authority: JP
Inventors: Hiromi Ogiyama; 荻山　宏美; Ryuta Takechi; 武市　隆太; Takeshi Sakashita; 坂下　武司; Yuji Sawai; 澤井　雄次
Original assignee: Ricoh Co Ltd
Current assignee: Ricoh Co Ltd
Priority date: 2002-07-30
Filing date: 2002-07-30
Publication date: 2004-02-26

Abstract

<P>PROBLEM TO BE SOLVED: To provide a transfer device free from the occurrence of toner scattering to a transfer entrance guide plate, and free from staining on the edge and rear faces of a wide paper even after continuously forming an image on a narrow paper. <P>SOLUTION: As for the transfer device comprising a primary transfer process of transferring a toner image charged with a desired polarity from an image carrier to an intermediate transfer member and a secondary transfer process of transferring the toner image from the intermediate transfer member to a recording medium, the transfer device is provided with voltage applying means (7f and 31) for applying a voltage whose polarity is opposite to that of the toner image on this side of the secondary transfer process and behind the intermediate transfer member 6. <P>COPYRIGHT: (C)2004,JPO

Description

【０００１】
【発明の属する技術分野】
この発明は、カラー電子写真装置など画像形成装置に用いられる転写装置に関するものである。
【０００２】
【従来の技術】
この種の装置として、本出願人は先に画像形成装置として特願２００２−１３２０６５を提案した。これは中間転写体としての中間転写ベルトを巻きつけているローラ部位で中間転写ベルトから記録媒体としての転写紙へ２次転写を行う装置で、２次転写ニップ部位の直ぐ上流に中間転写ベルトと転写紙を密着させる密着手段を設け、プレ転写（転写チリ）を防止したものである。
【０００３】
【発明が解決しようとする課題】
ところで、前記の装置では転写入口ガイド板と固定摺動部材位置での中間転写ベルトが近接するために、中間転写ベルト上のトナーの一部が転写入口ガイド板に飛散する。飛散トナー量は僅かで、１枚作像動作では問題となる量ではない。しかし、巾の狭い紙を繰り返し作像している間に、巾の狭い紙の通過しない領域の転写入口ガイド板に飛散トナーが堆積する。そして、次に大きな巾の紙を通紙したときは、この飛散トナーの堆積領域を紙が通過するので、この領域に合った紙のコバ面とウラ面が汚れる問題がある。
【０００４】
そこでこの発明は、前記のような従来のものが有する問題点を解決し、転写入口ガイド板へのトナー飛散がなく、巾の狭い紙で作像を続けた後でも、巾の広い紙のコバ面やウラ面の汚れがない転写装置を提供することを目的とする。
【０００５】
【課題を解決するための手段】
前記目的を達成するために、請求項１に記載の発明は、所望の極性に帯電されたトナー像を像担持体から中間転写体に転写する１次転写工程と、中間転写体から記録媒体にトナー像を転写する２次転写工程を有する転写装置において、２次転写工程の手前で中間転写体の背面にトナー像と逆極性の電圧を印可する電圧印加手段を具えたことを特徴とする。
【０００６】
請求項２に記載の発明は、請求項１において、電圧印加手段が、中間転写体の背面に接触して設けられた密着部材と、該密着部材にトナー像と逆極性の電圧を印可する電源とを有する。請求項３に記載の発明は、請求項２において、密着部材が、中間転写体の張架部材の１つである固定摺動部材である。請求項４に記載の発明は、請求項２において、密着部材が、中間転写体の張架部材の１つである密着ローラである。この密着ローラは、中間転写体と連れ回りするようにするのが望ましい。
【０００７】
請求項５に記載の発明は、請求項３又は４において、中間転写体と２次転写ローラで２次転写工程が行われ、該２次転写ローラにトナー像と逆極性の電圧が印可される。
【０００８】
【発明の実施の形態】
この発明の実施の形態を、添付図面を参照して説明する。この実施の形態では転写装置の２次転写部周辺の構成を含むその特徴とするほとんどの構成が先願である前記特願２００２−１３２０６５に記載したものと同様であるので、以下には相違する構成を中心に説明する。
【０００９】
図１は画像形成装置に設置された転写装置の２次転写部周辺の概略構成図で、図示省略の接離機構により接離可能となった２次転写ローラ１１が中間転写ベルト６に当接しているときの状態を示す。前記転写装置は所望の極性に帯電されたトナー像を図示省略の第１の像担持体としての感光体ドラムから中間転写ベルト６に転写する１次転写工程と、無端ベルト状の第２の像担持体としての中間転写ベルト６から転写紙にトナー像を転写する２次転写工程を有している。中間転写ベルト６は図示した２次転写対向ローラ７ｄと固定摺動部材７ｆを含む複数の張架部材に張架されて、矢印で示すように移動可能に配設されている。
【００１０】
２次転写対向ローラ７ｄと固定摺動部材７ｆは、いずれも中間転写ベルト６の背面に接触して配設されている。２次転写ローラ１１は中間転写ベルト６に当接した状態で２次転写ニップを形成し、該ニップ部で２次転写工程を行う。この２次転写工程に際し、固定摺動部材７ｆは２次転写工程の手前、すなわち中間転写ベルト６の移動方向に沿う２次転写ニップ部上流側の位置で、中間転写ベルト６と２次転写ローラ１１を密着させる部材（密着部材）としての機能を果たす。
【００１１】
固定摺動部材７ｆは導電性または半導電性で筐体アースからは絶縁され、電源３１からトナー像と逆極性の電圧が印可されるようになっている。固定摺動部材７ｆと電源３１は電圧印加手段を構成する。固定摺動部材７ｆには中間転写ベルト６との摺擦面が鏡面に仕上げられたステンレスを用いている。ステンレスを用いたのは導電性であること、錆びないこと、アルミニウムでは自らが磨耗して磨耗紛が中間転写ベルト６のウラ面を傷つけるがステンレスではそれが起きないこと、等からである。しかし、長期使用の間には中間転写ベルト６のウラ面が磨耗するので、導電フィラを含んだナイロン、テフロン（登録商標）など摺動性の良い樹脂ブラシを板金の上に接着したものとし、中間転写ベルト６にはブラシが接触するようにするが望ましい。２次転写ローラ１１は固定摺動部材７ｆと同様に別の電源３２からトナー像と逆極性の電圧が印可されるようになっている。また２次転写対向ローラ７ｄは接地されている。
【００１２】
図１で１０は転写紙、１２は紙除電チャージャ、１７は転写紙搬送ベルトである。また、２１は上ガイド板、２２は下ガイド板、２３は入口ガイドマイラーで、これらで転写入口ガイド板を構成する。
【００１３】
固定摺動部材７ｆに電源３１からトナー像と逆極性の電圧を印可すると、中間転写ベルト６上では転写ニップ手前でトナー像を中間転写ベルト６に引き付ける電界が生じるので、転写入口ガイド板へのトナー飛散がなくなる。したがって、巾の狭い転写紙で作像を続けた後に、巾の広い転写紙の作像を行ってもそのコバ面やウラ面の汚れがなくなる。固定摺動部材７ｆへの印加に際しては、２次転写ローラ１１にも別の電源３２からトナー像と逆極性の電圧を印加するのが好ましい。
【００１４】
図２は別の実施の形態を示す。この実施の形態は、さらに長期使用に耐えるようにするために密着部材である固定摺動部材７ｆをローラタイプとし、この密着ローラ７ｒが中間転写ベルト６と連れ回ることにより摺擦を避けるようにしている。そのほかの構成は前記実施の形態と同様である。
【００１５】
ところで、前記のような密着ローラ７ｒタイプにおいては、径が過度に小さいと、強度不足によるローラの撓みが生じて、ローラ中央部が逃げ、転写紙１０の中央が撓むこととなるので、転写紙１０と中間転写ベルト６の密着性が悪くなったり、撓んだ転写紙１０が転写ニップに進入してシワの原因となる。一方、径が大きくなると、２次転写対向ローラ７ｄと密着ローラ７ｒを近接させても、中間転写ベルト６の巻き付き部同士は更に両ローラの半径分遠ざかるので、密着ローラ７ｒを転写ニップに近接できない。すると、転写紙１０が中間転写ベルト６に密着する距離が長くなり、一度中間転写ベルト６に接触した転写紙がニップまで接触状態が保てず、途中で接触不良となる不具合がある。
【００１６】
しかし、密着ローラ７ｒに電源３１からトナー像と逆極性の電圧を印可すると、中間転写ベルト６上では転写ニップ手前でトナー像を中間転写ベルト６に引き付ける電界が生じるので、転写入口ガイド板へのトナー飛散がなくなる。したがって、巾の狭い転写紙で作像を続けた後に、巾の広い転写紙の作像を行ってもそのコバ面やウラ面の汚れがなくなる。そこで強度の得られる密着ローラ径であれば、中間転写ベルト６のウラ面の削れによる寿命の低下も、ローラ撓みにより転写紙が撓んで転写ニップに進入することによるシワの発生も、転写紙１０と中間転写ベルト６の密着不良による転写チリの発生も、防止できる。密着ローラ７ｒへの印加に際しては、前記と同様に２次転写ローラ１１にも別の電源３２からトナー像と逆極性の電圧を印加するのが好ましい。
【００１７】
この実施の形態の密着ローラ７ｒをφ１６のステンレスムクであるが、耐高電圧性や放電に対して弱い中間転写ベルト６に対しては、密着ローラ７ｒを芯金の周りに中抵抗な樹脂やゴムを用いても良い。
【００１８】
密着部材（固定摺動部材７ｆ、密着ローラ７ｒ）への印加電圧と転写入口ガイド板へのトナー飛散量について以下に説明する。三菱化学製ハイレスタＡＰ、印可電圧１００Ｖ、測定持時間１０秒の測定で、体積抵抗率１０^９Ωｃｍ、ウラ面の表面抵抗率１０^８Ω／□、オモテ面の表面抵抗率１０^９Ω／□、厚さ１００μｍの中間転写ベルト６では、密着ローラ７ｒの電圧によらずほとんど飛散しない。しかし、この抵抗の低いベルトでは転写電圧に対して放電が発生し易く、このため放電跡と思われる小粒な白抜け画像や、放電によるトナー帯電量の低下が原因と思われる転写チリの発生がある。
【００１９】
三菱化学製ハイレスタＡＰ、印可電圧５００Ｖ、測定持時間１０秒の測定で、体積抵抗率１０^１３Ωｃｍ、ウラ面の表面抵抗率１０^９Ω／□、オモテ面の表面抵抗率１０^１４Ω／□（測定可能巾のほぼ限界付近）、厚さ１５０μｍの中間転写ベルト６では前記の低い抵抗による異常画像は発生しない。しかし、固定摺動部材７ｆや密着ローラ７ｒから転写入口ガイド板へのトナー飛散が生じた。密着ローラ７ｒに印可する電圧を横軸に、一定パターンで一定枚数巾の狭い紙で作像を続けたときの転写入口ガイド板の汚れを縦軸にとったものが図３である。トナーはマイナス極性である。密着ローラ７ｒに印可する電圧がトナーと反対極性のプラスに大きくなるほどにトナー飛散量は減少して、１．２ｋＶ付近より高い電圧では全く飛散しないことがわかった。
【００２０】
これから次のことを考察することができる。抵抗の低い中間転写ベルトでは中間転写ベルト上のトナーは中間転写ベルトとの鏡像力によりトナーが中間転写ベルトに引き付けられてトナー飛散しない。抵抗の高い中間転写ベルトではこの鏡像力が小さくトナー飛散がし易い。中間転写ベルトのウラ面に反対極性の電圧を印可することにより、中間転写ベルトのオモテ面にトナーを引き付ける電界が生じて、トナーが飛散しなくなる。
【００２１】
前記各実施の形態で示した密着部材としての固定摺動部材７ｆ、密着ローラ７ｒは好ましい一例を示したにすぎず、これ以外の形状等の密着部材を排除するものではない。また、電圧印加手段の具体的な構成を含め、その実際の実施に際しては請求項に記載した技術的事項の範囲内で種々の設計的な変更や修正ができることは言うまでもない。
【００２２】
【発明の効果】
請求項１ないし３の発明は、前記のようであって、電圧印加手段により２次転写工程の手前で中間転写ベルトの背面にトナー像と逆極性の電圧を印加するので、中間転写体上のトナーを中間転写体に引き付ける電界が生じ、転写入口ガイド板へのトナー飛散がなくなり、巾の狭い紙で作像を続けた後でも、巾の広い紙のコバ面やウラ面の汚れがなくなる。
【００２３】
請求項４の発明は、さらに転写ニップより手前にトナーを中間転写体に引き付ける電界が生じているので、転写チリに余裕度ができる。従来では、記録媒体が中間転写体に密着する距離が長くなり、一度中間転写体に接触した記録媒体がニップまで接触状態が保てず、途中で接触不良となり、転写チリに余裕のなかった密着ローラでも転写チリが低減できた。また密着ローラでは中間転写体のウラ面の汚れがなくなるので、従来両立の困難であった中間転写体の長寿命化と転写チリの低減の両立が可能となった。請求項５の発明は、２次転写ローラからもトナー像と逆極性の電圧が印加されるので、転写入口ガイド板へのトナーの飛散と転写チリをより効果的に低減することができる。
【図面の簡単な説明】
【図１】この発明の一実施の形態における２次転写部周辺の概略構成図で、２次転写ローラが中間転写ベルトに当接しているときの状態を示す。
【図２】別の実施の形態における図１と対応する概略構成図である。
【図３】密着部材への印加電圧と転写入口ガイド板へのトナー飛散量について説明するグラフである。
【符号の説明】
６　中間転写ベルト（中間転写体）
７ｄ　２次転写対向ローラ
７ｆ　固定摺動部材（密着部材）
７ｒ　密着ローラ（密着部材）
１０　転写紙（記録媒体）
１１　２次転写ローラ
１２　紙除電チャージャ
１７　転写紙搬送ベルト
２１　上ガイド板
２２　下ガイド板
３１，３２　電源[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a transfer device used for an image forming apparatus such as a color electrophotographic apparatus.
[0002]
[Prior art]
As an apparatus of this type, the present applicant has previously proposed Japanese Patent Application No. 2002-132665 as an image forming apparatus. This is a device that performs secondary transfer from the intermediate transfer belt to transfer paper as a recording medium at a roller portion around which an intermediate transfer belt as an intermediate transfer member is wound. A pre-transfer (transfer dust) is prevented by providing a contact means for bringing the transfer paper into close contact.
[0003]
[Problems to be solved by the invention]
In the above-described apparatus, since the transfer entrance guide plate and the intermediate transfer belt at the position of the fixed sliding member are close to each other, a part of the toner on the intermediate transfer belt scatters on the transfer entrance guide plate. The amount of scattered toner is small, and is not an amount that causes a problem in an image forming operation for one sheet. However, scattered toner accumulates on the transfer entrance guide plate in an area where the narrow paper does not pass while the narrow paper is repeatedly imaged. Then, when the next wide paper is passed, the paper passes through the area where the scattered toner is accumulated, and there is a problem that the edge surface and the back surface of the paper corresponding to this area are stained.
[0004]
Therefore, the present invention solves the above-mentioned problems of the related art, and there is no toner scattering on the transfer entrance guide plate, and even after the image is continuously formed on a narrow paper, the edge of the wide paper is covered. It is an object of the present invention to provide a transfer device free from surface and back surface contamination.
[0005]
[Means for Solving the Problems]
In order to achieve the above object, the invention according to claim 1 includes a primary transfer step of transferring a toner image charged to a desired polarity from an image carrier to an intermediate transfer body, and a method of transferring the toner image from the intermediate transfer body to a recording medium. In a transfer apparatus having a secondary transfer step for transferring a toner image, a voltage applying means for applying a voltage having a polarity opposite to that of the toner image is provided on the back surface of the intermediate transfer member before the secondary transfer step.
[0006]
According to a second aspect of the present invention, in the first aspect, the voltage applying means is a contact member provided in contact with the back surface of the intermediate transfer member, and a power supply for applying a voltage having a polarity opposite to that of the toner image to the contact member. And According to a third aspect of the present invention, in the second aspect, the close contact member is a fixed sliding member that is one of the tension members of the intermediate transfer member. According to a fourth aspect of the present invention, in the second aspect, the close contact roller is one of the tension members of the intermediate transfer member. It is desirable that the close contact roller rotates together with the intermediate transfer member.
[0007]
According to a fifth aspect of the present invention, in the third or fourth aspect, a secondary transfer step is performed by the intermediate transfer member and the secondary transfer roller, and a voltage having a polarity opposite to that of the toner image is applied to the secondary transfer roller. .
[0008]
BEST MODE FOR CARRYING OUT THE INVENTION
Embodiments of the present invention will be described with reference to the accompanying drawings. In this embodiment, most of the features including the configuration around the secondary transfer portion of the transfer apparatus are the same as those described in the above-mentioned Japanese Patent Application No. 2002-132665. The configuration will be mainly described.
[0009]
FIG. 1 is a schematic configuration diagram of the vicinity of a secondary transfer portion of a transfer device installed in an image forming apparatus. A secondary transfer roller 11 that can be separated and moved by an unillustrated contact and separation mechanism contacts an intermediate transfer belt 6. Shows the state when it is running. The transfer device transfers a toner image charged to a desired polarity from a photosensitive drum as a first image carrier (not shown) to the intermediate transfer belt 6, and an endless belt-shaped second image. There is a secondary transfer step of transferring a toner image from the intermediate transfer belt 6 as a carrier to transfer paper. The intermediate transfer belt 6 is stretched around a plurality of stretching members including the illustrated secondary transfer facing roller 7d and the fixed sliding member 7f, and is movably disposed as indicated by arrows.
[0010]
Both the secondary transfer opposing roller 7d and the fixed sliding member 7f are disposed in contact with the back surface of the intermediate transfer belt 6. The secondary transfer roller 11 forms a secondary transfer nip in a state in which the secondary transfer roller 11 is in contact with the intermediate transfer belt 6, and performs a secondary transfer process at the nip portion. In the secondary transfer step, the fixed sliding member 7f is positioned between the intermediate transfer belt 6 and the secondary transfer roller at a position before the secondary transfer step, that is, at a position upstream of the secondary transfer nip along the moving direction of the intermediate transfer belt 6. It functions as a member (close contact member) that makes 11 closely contact.
[0011]
The fixed sliding member 7f is conductive or semiconductive and is insulated from the housing ground, so that a voltage having a polarity opposite to that of the toner image is applied from the power supply 31. The fixed sliding member 7f and the power supply 31 constitute voltage applying means. As the fixed sliding member 7f, stainless steel whose surface rubbing with the intermediate transfer belt 6 is mirror-finished is used. The reason why stainless steel is used is that it is conductive, does not rust, and that aluminum wears itself and abrasion powder damages the back surface of the intermediate transfer belt 6, but does not occur with stainless steel. However, since the back surface of the intermediate transfer belt 6 wears out during long-term use, a resin brush having good slidability such as nylon or Teflon (registered trademark) containing a conductive filler is adhered to the sheet metal. It is desirable that the brush be in contact with the intermediate transfer belt 6. The secondary transfer roller 11 is configured to apply a voltage having a polarity opposite to that of the toner image from another power source 32 similarly to the fixed sliding member 7f. The secondary transfer opposing roller 7d is grounded.
[0012]
In FIG. 1, 10 is a transfer paper, 12 is a paper discharging charger, and 17 is a transfer paper transport belt. Further, 21 is an upper guide plate, 22 is a lower guide plate, and 23 is an entrance guide mylar, and these constitute a transfer entrance guide plate.
[0013]
When a voltage having a polarity opposite to that of the toner image is applied from the power supply 31 to the fixed sliding member 7f, an electric field is generated on the intermediate transfer belt 6 to attract the toner image to the intermediate transfer belt 6 just before the transfer nip. Elimination of toner scattering. Therefore, even if an image is formed on a wide transfer paper after the image formation is continued on a narrow transfer paper, the edge surface and the back surface are not stained. When the voltage is applied to the fixed sliding member 7f, it is preferable to apply a voltage having a polarity opposite to that of the toner image to the secondary transfer roller 11 from another power source 32.
[0014]
FIG. 2 shows another embodiment. In this embodiment, in order to withstand long-term use, the fixed sliding member 7f, which is a close contact member, is of a roller type, and the close contact roller 7r rotates along with the intermediate transfer belt 6 so as to avoid rubbing. ing. Other configurations are the same as those of the above embodiment.
[0015]
In the above-mentioned close contact roller 7r type, if the diameter is excessively small, the roller is bent due to insufficient strength, the roller central portion escapes, and the center of the transfer paper 10 bends. The adhesion between the paper 10 and the intermediate transfer belt 6 may be deteriorated, or the bent transfer paper 10 may enter the transfer nip and cause wrinkles. On the other hand, if the diameter becomes large, even if the secondary transfer opposing roller 7d and the close contact roller 7r are brought close to each other, the wrapped portion of the intermediate transfer belt 6 is further away by the radius of both rollers, so that the close contact roller 7r cannot approach the transfer nip. . Then, the distance in which the transfer paper 10 comes into close contact with the intermediate transfer belt 6 becomes long, and the transfer paper once in contact with the intermediate transfer belt 6 cannot maintain the contact state up to the nip, and there is a problem that a contact failure occurs halfway.
[0016]
However, when a voltage having a polarity opposite to that of the toner image is applied from the power supply 31 to the contact roller 7r, an electric field is generated on the intermediate transfer belt 6 to attract the toner image to the intermediate transfer belt 6 just before the transfer nip. Elimination of toner scattering. Therefore, even if an image is formed on a wide transfer paper after the image formation is continued on a narrow transfer paper, the edge surface and the back surface are not stained. Therefore, if the contact roller diameter is strong, the life of the intermediate transfer belt 6 is reduced due to the scraping of the back surface, the transfer paper is bent due to the roller bending, and wrinkles are generated due to entering the transfer nip. The occurrence of transfer dust due to poor adhesion between the belt and the intermediate transfer belt 6 can also be prevented. Upon application to the contact roller 7r, it is preferable to apply a voltage having a polarity opposite to that of the toner image to the secondary transfer roller 11 from another power source 32 as described above.
[0017]
Although the contact roller 7r of this embodiment is made of stainless steel of φ16, for the intermediate transfer belt 6 which is resistant to high voltage and discharge, the contact roller 7r is made of a resin having a medium resistance around the cored bar. Rubber may be used.
[0018]
The voltage applied to the contact member (fixed sliding member 7f, contact roller 7r) and the amount of toner scattered on the transfer entrance guide plate will be described below. Measured by Mitsubishi Chemical Hiresta AP, applied voltage 100 V, measurement duration 10 seconds, volume resistivity 10 ⁹ Ωcm, surface resistivity of back surface 10 ⁸ Ω / □, surface resistivity of front surface 10 ⁹ Ω / □, The intermediate transfer belt 6 having a thickness of 100 μm hardly scatters regardless of the voltage of the close contact roller 7r. However, discharge is likely to occur with respect to the transfer voltage in the belt having a low resistance, and therefore, a small white image which is considered to be a discharge mark, and transfer dust which is considered to be caused by a decrease in the toner charge amount due to the discharge are generated. is there.
[0019]
Measured by Mitsubishi Chemical Hiresta AP, applied voltage 500 V, measurement duration 10 seconds, volume resistivity 10 ¹³ Ωcm, back surface surface resistivity 10 ⁹ Ω / □, front surface surface resistivity 10 ¹⁴ Ω / □ ( The abnormal image due to the low resistance does not occur in the intermediate transfer belt 6 having a thickness near the limit of the measurable width and a thickness of 150 μm. However, toner was scattered from the fixed sliding member 7f and the close contact roller 7r to the transfer entrance guide plate. FIG. 3 shows the voltage applied to the contact roller 7r on the horizontal axis and the transfer entrance guide plate stain when the image formation is continued on a narrow sheet of paper in a fixed pattern on a vertical axis. The toner has a negative polarity. It was found that as the voltage applied to the close contact roller 7r becomes larger to the opposite polarity to that of the toner, the amount of scattering of the toner decreases, and the voltage does not scatter at a voltage higher than about 1.2 kV.
[0020]
From this, the following can be considered. In an intermediate transfer belt having a low resistance, the toner on the intermediate transfer belt is attracted to the intermediate transfer belt by the mirror image force of the intermediate transfer belt and does not scatter. In an intermediate transfer belt having a high resistance, the mirror image force is small and toner is easily scattered. By applying a voltage of the opposite polarity to the back surface of the intermediate transfer belt, an electric field that attracts the toner to the front surface of the intermediate transfer belt is generated, and the toner does not scatter.
[0021]
The fixed sliding member 7f and the close contact roller 7r as the close contact members described in each of the above embodiments are merely preferred examples, and do not exclude other close contact members having other shapes. In addition, it goes without saying that various design changes and modifications can be made within the scope of the technical matters described in the claims, including the specific configuration of the voltage applying means.
[0022]
【The invention's effect】
According to the first to third aspects of the present invention, since a voltage having a polarity opposite to that of the toner image is applied to the back surface of the intermediate transfer belt by the voltage application means before the secondary transfer process, An electric field that attracts the toner to the intermediate transfer member is generated, so that the toner does not scatter to the transfer entrance guide plate, and the edge of the wide paper and the back surface of the wide paper are not stained even after the image is formed on the narrow paper.
[0023]
According to the fourth aspect of the present invention, an electric field for attracting the toner to the intermediate transfer body is generated before the transfer nip. Conventionally, the distance that the recording medium adheres to the intermediate transfer body increases, and the recording medium that once contacts the intermediate transfer body cannot maintain the contact state up to the nip, resulting in poor contact in the middle, leaving no room for transfer dust. The transfer dust was reduced even with the roller. Further, since the back surface of the intermediate transfer member is not stained with the contact roller, it is possible to achieve both a longer life of the intermediate transfer member and a reduction in transfer dust, which have been difficult to achieve in the past. According to the fifth aspect of the present invention, since a voltage having a polarity opposite to that of the toner image is also applied from the secondary transfer roller, scattering of the toner on the transfer entrance guide plate and transfer dust can be more effectively reduced.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram around a secondary transfer unit according to an embodiment of the present invention, showing a state when a secondary transfer roller is in contact with an intermediate transfer belt.
FIG. 2 is a schematic configuration diagram corresponding to FIG. 1 in another embodiment.
FIG. 3 is a graph illustrating a voltage applied to a contact member and an amount of toner scattered on a transfer entrance guide plate.
[Explanation of symbols]
6 Intermediate transfer belt (intermediate transfer body)
7d Secondary transfer opposed roller 7f Fixed sliding member (close contact member)
7r contact roller (contact member)
10 Transfer paper (recording medium)
11 Secondary Transfer Roller 12 Paper Charger 17 Transfer Paper Conveying Belt 21 Upper Guide Plate 22 Lower Guide Plates 31, 32 Power Supply

Claims

所望の極性に帯電されたトナー像を像担持体から中間転写体に転写する１次転写工程と、前記中間転写体から記録媒体にトナー像を転写する２次転写工程を有する転写装置において、２次転写工程の手前で前記中間転写体の背面にトナー像と逆極性の電圧を印可する電圧印加手段を具えたことを特徴とする転写装置。In a transfer apparatus having a primary transfer step of transferring a toner image charged to a desired polarity from an image carrier to an intermediate transfer body and a secondary transfer step of transferring a toner image from the intermediate transfer body to a recording medium, A transfer device comprising a voltage applying means for applying a voltage having a polarity opposite to that of the toner image to the back surface of the intermediate transfer member before the next transfer step.

電圧印加手段が、中間転写体の背面に接触して設けられた密着部材と、該密着部材にトナー像と逆極性の電圧を印可する電源とを有する請求項１記載の転写装置。2. The transfer device according to claim 1, wherein the voltage applying means includes a contact member provided in contact with the back surface of the intermediate transfer member, and a power supply for applying a voltage having a polarity opposite to that of the toner image to the contact member.

密着部材が、中間転写体の張架部材の１つである固定摺動部材である請求項２記載の転写装置。3. The transfer device according to claim 2, wherein the contact member is a fixed sliding member that is one of the tension members of the intermediate transfer member.

密着部材が、中間転写体の張架部材の１つである密着ローラである請求項２記載の転写装置。The transfer device according to claim 2, wherein the contact member is a contact roller that is one of tension members of the intermediate transfer body.

中間転写体と２次転写ローラで２次転写工程が行われ、該２次転写ローラにトナー像と逆極性の電圧が印可される請求項３又は４記載の転写装置。5. The transfer device according to claim 3, wherein a secondary transfer step is performed by the intermediate transfer member and the secondary transfer roller, and a voltage having a polarity opposite to that of the toner image is applied to the secondary transfer roller.