JP2001215810A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of stably carrying a recording material to a fixation nip while attracting the recording material to the carrying member without shortening a distance between a transfer nip and the fixation nip, when the length of the recording material is shorter than the distance between the transfer nip and the fixation nip, besides, the length of the recording material is longer than the distance between the recording material separation part of a belt-like recording material carrying member and the fixation nip. SOLUTION: The image forming device is provided with an intermediate transfer drum, and multiple color toner images primarily transferred from a photoreceptor drum to the intermediate transfer drum are secondarily transferred to the recording material, and then, fixed by a fixing unit. As for the length of the recording material, the recording material is shorter than the distance between the transfer nip and the fixation nip, but, longer than the distance between the recording material separation part of the secondary transfer belt and the fixation nip. At the point when the trailing end of the recording material passes through the transfer nip, the output T2 of a transfer high voltage power supply is switched from a transfer voltage V1=+1.5 kV to a voltage V2=+2.0 kV which is higher than the voltage V1 and has the same polarity as that of the voltage V1, then, applied on a transfer/ electrifying member, and the recording material is attracted to the transfer belt, so that the recording material is stably carried to the fixation nip.

Description

【発明の詳細な説明】DETAILED DESCRIPTION OF THE INVENTION

【０００１】[0001]

【発明の属する技術分野】本発明は、電子写真方式を用
いた画像形成装置に関し、特に第１の像担持体である感
光体に形成したトナー像を、一旦、第２の像担持体であ
る中間転写体に転写し、ついで中間転写体から記録材に
転写して、記録材に画像を得る複写機、プリンタ、ファ
ックス等の画像形成装置に関する。BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus using an electrophotographic system, and more particularly, to a method in which a toner image formed on a photosensitive member as a first image bearing member is temporarily used as a second image bearing member. The present invention relates to an image forming apparatus such as a copying machine, a printer, and a facsimile that transfers an image to an intermediate transfer member, and then transfers the image from the intermediate transfer member to a recording material to obtain an image on the recording material.

【０００２】[0002]

【従来の技術】転写ベルトを利用した画像形成装置は、
転写ベルトを像担持体または中間転写体がある装置では
中間転写体に密着させつつ、転写ベルトに記録媒体であ
る記録材（紙など）を吸着させて搬送することにより、
安定した記録材の搬送、画像の転写が可能であり、また
プロセスパーツを少なくすることができて、装置のコス
トダウンが可能である。2. Description of the Related Art An image forming apparatus using a transfer belt includes:
In a device having an image carrier or an intermediate transfer member, a transfer material is adsorbed and conveyed by a recording material (paper or the like) as a recording medium while the transfer belt is in close contact with the intermediate transfer member.
The recording material can be stably conveyed and the image transferred, and the number of process parts can be reduced, so that the cost of the apparatus can be reduced.

【０００３】転写ベルトおよび中間転写体を備えたフル
カラー画像形成装置を図６に示す。図６に示すように、
第１の像担持体としての感光ドラム（ドラム型電子写真
感光体）５１の周囲に、感光ドラム回転方向に沿って一
次帯電器５２、露光装置５３、固定式の現像器５４およ
び回転式の３個の現像器５５、ドラムクリーナ５９が配
置され、現像器とクリーナの間には第２の像担持体とし
てドラム状中間転写体、すなわち中間転写ドラム５６が
配置される。中間転写ドラム５６の周囲には、中間転写
ドラム回転方向に沿って感光ドラム５１よりも下流側に
転写ベルトを有する二次転写装置６０が配置され、必要
に応じてさらにクリーニング手段等が配置される。二次
転写装置６０の延長上には定着器５８が配置される。FIG. 6 shows a full-color image forming apparatus provided with a transfer belt and an intermediate transfer member. As shown in FIG.
Around a photosensitive drum (drum-type electrophotographic photosensitive member) 51 as a first image carrier, a primary charger 52, an exposure device 53, a fixed developing device 54, and a rotating A plurality of developing units 55 and a drum cleaner 59 are arranged, and a drum-shaped intermediate transfer body, that is, an intermediate transfer drum 56 is arranged as a second image carrier between the developing units and the cleaner. Around the intermediate transfer drum 56, a secondary transfer device 60 having a transfer belt downstream of the photosensitive drum 51 along the rotation direction of the intermediate transfer drum is arranged, and further, a cleaning unit and the like are arranged as necessary. . A fixing device 58 is disposed on an extension of the secondary transfer device 60.

【０００４】上記画像形成装置における画像形成プロセ
スを説明すると、感光ドラム５１の表面が、コロナ帯電
器やローラ帯電器などの一次帯電器５２によってたとえ
ば−５５０Ｖに一様に帯電される。レーザーなどを用い
た露光装置５３によって、帯電された感光ドラム５１表
面に画像パターンが露光されると、感光ドラム表面の露
光部の表面電位が−１５０Ｖ程度まで減衰し、露光部と
未露光部の間に電位差が生じて、感光ドラム表面に画像
パターンに応じた静電潜像が形成される。この静電潜像
を、現像器（ブラック（Ｋ））５４または現像器５５
（イエロー（Ｙ）、マゼンタ（Ｍ）、シアン（Ｃ））の
１つを用いてネガ帯電性のトナーで現像すると、ネガに
帯電されたトナーが感光ドラム１表面の露光部に付着し
て、潜像がトナー像として可視化される。The image forming process in the image forming apparatus will be described. The surface of the photosensitive drum 51 is uniformly charged to, for example, -550 V by a primary charger 52 such as a corona charger or a roller charger. When an image pattern is exposed on the surface of the charged photosensitive drum 51 by an exposure device 53 using a laser or the like, the surface potential of the exposed portion of the photosensitive drum surface is attenuated to about −150 V, and the exposed portion and the unexposed portion are exposed. A potential difference occurs between the two, and an electrostatic latent image corresponding to the image pattern is formed on the surface of the photosensitive drum. The electrostatic latent image is transferred to a developing device (black (K)) 54 or a developing device 55
(Yellow (Y), magenta (M), and cyan (C)), the negatively charged toner adheres to the exposed portion of the surface of the photosensitive drum 1 when developed with negatively charged toner. The latent image is visualized as a toner image.

【０００５】感光ドラム１上に形成されたトナー像は、
感光ドラム１と中間転写ドラム５６とが当接した一次転
写部で、中間転写ドラム５６にトナーの帯電極性とは逆
極性（正極性）の電圧（一次転写バイアスＴ１）、たと
えば＋３００Ｖを一定値で印加することにより、中間転
写ドラム５６の表面に転写される（一次転写）。[0005] The toner image formed on the photosensitive drum 1 is
At a primary transfer portion where the photosensitive drum 1 and the intermediate transfer drum 56 are in contact with each other, a voltage (primary transfer bias T1) having a polarity (positive polarity) opposite to the charged polarity of the toner, for example, +300 V, is fixed to the intermediate transfer drum 56 at a constant value. By being applied, it is transferred to the surface of the intermediate transfer drum 56 (primary transfer).

【０００６】フルカラーの画像形成では、この工程を複
数色分繰り返し、中間転写ドラム５６上で複数色のトナ
ー像を位置合わせしながら重畳転写する。中間転写ドラ
ム５６上に形成された複数色のトナー像は、中間転写ド
ラム５６と二次転写装置６０とが当接した二次転写部
で、二次転写装置６０にトナーの帯電極性と逆極性（正
極性）の電圧（二次転写バイアスＴ２）、たとえば＋
１．５ｋＶを一定値で印加することにより、二次転写部
に搬送された紙などの記録材に転写される（二次転
写）。二次転写装置６０の転写ベルト（二次転写ベル
ト）６１は、二次転写バイアスによって表面がプラスに
帯電することにより、記録材を吸着して定着器５８に送
り込む。In a full-color image formation, this process is repeated for a plurality of colors, and the toner images of a plurality of colors are superimposed and transferred on the intermediate transfer drum 56 while being aligned. The plurality of color toner images formed on the intermediate transfer drum 56 are applied to the secondary transfer unit where the intermediate transfer drum 56 and the secondary transfer device 60 are in contact with each other. (Positive polarity) voltage (secondary transfer bias T2), for example, +
By applying a constant value of 1.5 kV, the image is transferred onto a recording material such as paper conveyed to the secondary transfer section (secondary transfer). The transfer belt (secondary transfer belt) 61 of the secondary transfer device 60 attracts the recording material and sends it to the fixing device 58 when the surface thereof is positively charged by the secondary transfer bias.

【０００７】定着器５８は、一方または両方に加熱手段
を内蔵し、または外部に加熱手段を有する一対のローラ
からなり、一定の圧力で互いに圧接されて定着ニップを
形成している。記録材がこの一対のローラの間を通過す
ると、熱と圧力によってトナー像は混色と同時に記録材
に定着され、記録材にフルカラーの定着画像が得られ
る。[0007] The fixing device 58 comprises a pair of rollers having a heating means built in one or both, or having a heating means outside, and is pressed against each other at a constant pressure to form a fixing nip. When the recording material passes between the pair of rollers, the toner image is fixed on the recording material simultaneously with the color mixture by heat and pressure, and a full-color fixed image is obtained on the recording material.

【０００８】記録材は、通常、二次転写ニップで挟持搬
送して定着器５８に送り込まれ、続いて定着器５８のロ
ーラで挟持搬送して画像形成装置の機外に排出される。
たとえば高速タイプのＡ３サイズ用紙対応のフルカラー
プリンタでは、定着器５８に要求される熱量も多くな
り、定着器周辺の温度が必然的に高くなるが、中間転写
ドラム５６や二次転写ベルト６１への熱の影響を少なく
するために、中間転写ドラム５６や二次転写ベルト６１
を定着器５８に極端に近づけて配置することができな
い。Usually, the recording material is nipped and conveyed at the secondary transfer nip and sent to the fixing device 58. Subsequently, the recording material is nipped and conveyed by the rollers of the fixing device 58 and discharged out of the image forming apparatus.
For example, in a high-speed type full-color printer compatible with A3 size paper, the amount of heat required for the fixing device 58 also increases, and the temperature around the fixing device inevitably increases, but the heat applied to the intermediate transfer drum 56 and the secondary transfer belt 61 is increased. In order to reduce the influence of heat, the intermediate transfer drum 56 and the secondary transfer belt 61
Cannot be disposed extremely close to the fixing device 58.

【０００９】また定着器５８や二次転写ベルト６１は温
度変化による膨張収縮で回転速度にずれを生じることが
あり、相対的に定着器５８が速く回転すれば記録材を引
っ張ってしまい、相対的に二次転写ベルト６１が速く回
転すれば記録材は、二次転写ニップと定着ニップ間でル
ープができてしまい、記録材が折れ曲がってしまう。そ
こで実際には、二次転写ニップと定着ニップとは、これ
らの間にある程度の距離を置くように配置されている。The rotation speed of the fixing device 58 and the secondary transfer belt 61 may be deviated due to expansion and contraction due to a change in temperature. If the fixing device 58 rotates relatively fast, the recording material is pulled. If the secondary transfer belt 61 rotates rapidly, the recording material may form a loop between the secondary transfer nip and the fixing nip, and the recording material may be bent. Therefore, in practice, the secondary transfer nip and the fixing nip are arranged so as to keep a certain distance between them.

【００１０】つまり、二次転写ニップと定着ニップの間
で記録材が引っ張られないように、二次転写ベルト６１
による記録材の搬送速度ＶTと定着器５８側の送り速度
ＶFの関係を、ＶT＞ＶFとなるように構成した上で、そ
の装置の最大通紙サイズ（Ａ３プリンタなら４２０ｍ
ｍ）の記録材が通過する間に記録材が折れ曲がらずにル
ープで吸収できるように、転写ニップと定着ニップの間
にある程度の距離をおく。That is, the secondary transfer belt 61 is moved so that the recording material is not pulled between the secondary transfer nip and the fixing nip.
The relationship between the conveying speed VT of the recording material and the feed speed VF on the fixing device 58 side is such that VT> VF, and the maximum paper passing size of the apparatus (420 m for an A3 printer)
A certain distance is provided between the transfer nip and the fixing nip so that the recording material can be absorbed by the loop without being bent while the recording material passes through m).

【００１１】二次転写ベルト６１による記録材搬送時の
吸着力は、上記したように、二次転写ベルトに転写バイ
アスを印加することによって、表面がプラスに帯電され
ることにより発生している。二次転写ベルト６１の表面
抵抗値を高く設定すると、必要な転写電流を得るために
高い二次転写電圧を必要とするが、転写電圧が高すぎる
と、二次転写部で異常放電が起こって画像不良を招いた
り、中間転写ドラム５６への再転写によって、画像の濃
度低下を招く恐れがあるので、表面抵抗をなるべく抑え
ることが望ましい。As described above, the suction force at the time of conveying the recording material by the secondary transfer belt 61 is generated by applying a transfer bias to the secondary transfer belt to charge the surface positively. When the surface resistance of the secondary transfer belt 61 is set high, a high secondary transfer voltage is required to obtain a necessary transfer current. However, when the transfer voltage is too high, abnormal discharge occurs in the secondary transfer portion. Since there is a possibility that an image defect is caused or a density of an image is reduced by re-transfer to the intermediate transfer drum 56, it is desirable to suppress the surface resistance as much as possible.

【００１２】[0012]

【発明が解決しようとする課題】しかしながら、従来、
以下のような問題があった。However, conventionally,
There were the following problems.

【００１３】二次転写ニップと定着ニップ間の距離Ａに
対して記録材の長さａがａ＜Ａの場合、記録材先端が定
着ニップに到達するよりも前に記録材後端が二次転写ニ
ップを通過するため、二次転写ニップや定着ニップによ
る搬送力がないまま記録材が搬送される状態が生じる。When the length a of the recording material is a <A with respect to the distance A between the secondary transfer nip and the fixing nip, the rear end of the recording material is moved before the leading end of the recording material reaches the fixing nip. Since the recording material passes through the transfer nip, a state occurs in which the recording material is conveyed without the conveyance force due to the secondary transfer nip and the fixing nip.

【００１４】表面抵抗の低い二次転写ベルトを使用した
場合、記録材後端で二次転写が終了した時点で二次転写
バイアスをＯＦＦすると、二次転写ベルトの表面電位が
短時間で減衰してしまうので、二次転写ベルトへの吸着
力が得られなくなって、記録材は定着器まで搬送されず
に紙詰まりを生じる恐れがある。When a secondary transfer belt having a low surface resistance is used, when the secondary transfer bias is turned off at the time when the secondary transfer is completed at the rear end of the recording material, the surface potential of the secondary transfer belt attenuates in a short time. Therefore, there is a possibility that the recording material is not conveyed to the fixing device and a paper jam is caused because the attraction force to the secondary transfer belt cannot be obtained.

【００１５】また二次転写は、記録材の吸湿状態で最適
バイアス条件が異なり、低湿環境では高い転写電圧が、
高湿環境では低い転写電圧が設定されている。高い転写
電圧が設定されている場合は、仮に記録材後端で二次転
写終了後も二次転写バイアスを出力させ続ければ、吸着
力は得られる。しかし、高湿環境で低い転写電圧が設定
されている場合には、得られる吸着力も弱くなり、やは
り紙詰まりとなる恐れがあった。In the secondary transfer, the optimum bias condition is different depending on the moisture absorption state of the recording material.
In a high humidity environment, a low transfer voltage is set. When a high transfer voltage is set, if the secondary transfer bias is continuously output at the rear end of the recording material even after the end of the secondary transfer, the attraction force can be obtained. However, when a low transfer voltage is set in a high-humidity environment, the obtained attraction force is weakened, and there is a possibility that a paper jam may occur.

【００１６】本発明の目的は、転写ニップと定着ニップ
間の距離を短くしなくても、転写ニップと定着ニップ間
の距離よりも短い記録材を、これらニップ間に特別な搬
送補助手段を設けることなく安定して搬送可能とした画
像形成装置を提供することである。It is an object of the present invention to provide a recording material shorter than the distance between the transfer nip and the fixing nip, without providing a short distance between the transfer nip and the fixing nip, and to provide a special conveying assist means between the nips. An object of the present invention is to provide an image forming apparatus which can be stably conveyed without any trouble.

【００１７】[0017]

【課題を解決するための手段】上記目的は本発明に係る
画像形成装置にて達成される。要約すれば、本発明は、
像担持体と、ベルト状記録材搬送部材と、転写帯電部材
と、高圧電源と、定着手段とを有し、前記搬送部材上に
記録材を担持して、前記搬送部材を介して前記転写帯電
部材が前記像担持体と当接した転写ニップに搬送し、前
記高圧電源からトナーの帯電極性と逆極性の転写電圧を
出力して前記転写帯電部材に印加することにより、前記
像担持体上に形成されたトナー像を記録材に転写し、前
記トナー像が転写された記録材を前記搬送部材から分離
して前記定着手段に送り込み、前記定着手段の定着ニッ
プで定着する画像形成装置において、前記記録材の長さ
が、前記転写ニップと前記定着ニップとの間の距離より
も短く、かつ前記搬送部材の記録材分離部と前記定着ニ
ップとの間の距離よりも長い場合、前記記録材の後端が
前記転写ニップを通過したら、前記高圧電源の出力を転
写電圧からこれと同極性の高い電圧に切り替えて、前記
転写帯電部材に印加することを特徴とする画像形成装置
である。The above object is achieved by an image forming apparatus according to the present invention. In summary, the present invention provides:
An image carrier, a belt-shaped recording material conveying member, a transfer charging member, a high-voltage power supply, and a fixing unit; the recording material is carried on the conveying member, and the transfer charging is performed via the conveying member. The member is conveyed to a transfer nip in contact with the image carrier, and a high-voltage power supply outputs a transfer voltage having a polarity opposite to the charge polarity of the toner and applies the transfer voltage to the transfer charging member. An image forming apparatus that transfers the formed toner image to a recording material, separates the recording material onto which the toner image has been transferred from the transport member, sends the separated recording material to the fixing unit, and fixes the recording material at a fixing nip of the fixing unit. When the length of the recording material is shorter than the distance between the transfer nip and the fixing nip, and longer than the distance between the recording material separating portion of the conveying member and the fixing nip, The rear end is the transfer nip Filtered When the switches the output of the high-voltage power supply from the transfer voltage to the same polarity high voltage, an image forming apparatus and applying to said transfer charging member.

【００１８】本発明では、複数の像担持体を有すること
ができ、前記高圧電源の出力の切り替えを行う際の転写
ニップとして、前記搬送部材による記録材搬送方向最下
流の像担持体の転写ニップを使用する。また像担持体の
他に、中間転写体を備えることができ、前記記録材の長
さが、前記二次転写ニップと前記定着ニップとの間の距
離よりも短く、かつ前記搬送部材の記録材分離部と前記
定着ニップとの間の距離よりも長い場合に、二次転写電
圧を印加する二次高圧電源の出力について、上記と同様
にする。本発明によれば、ベルト状記録材搬送部材の表
面抵抗が１０¹⁴Ω／□以下である。前記中間転写体をド
ラム状に形成することができる。In the present invention, a plurality of image carriers can be provided, and the transfer nip for switching the output of the high-voltage power supply is used as a transfer nip of the image carrier at the most downstream direction in the recording material conveyance direction by the conveyance member. Use In addition to the image carrier, an intermediate transfer member may be provided, wherein the length of the recording material is shorter than the distance between the secondary transfer nip and the fixing nip, and the recording material of the conveying member is provided. When the distance is longer than the distance between the separation unit and the fixing nip, the output of the secondary high-voltage power supply for applying the secondary transfer voltage is the same as described above. According to the present invention, the surface resistance of the belt-shaped recording material conveying member is 10 ¹⁴ Ω / □ or less. The intermediate transfer member can be formed in a drum shape.

【００１９】[0019]

【発明の実施の形態】以下、本発明に係る実施例を図面
に則してさらに詳しく説明する。Embodiments of the present invention will be described below in more detail with reference to the drawings.

【００２０】実施例１ 図１は、本発明の画像形成装置の一実施例を示す概略断
面図である。Embodiment 1 FIG. 1 is a schematic sectional view showing an embodiment of the image forming apparatus of the present invention.

【００２１】本実施例の画像形成装置は、ネガプロセス
を用いたフルカラーレーザビームプリンタに構成されて
いる。The image forming apparatus of this embodiment is configured as a full-color laser beam printer using a negative process.

【００２２】図１に示すように、本画像形成装置は、第
１の像担持体としてドラム型帯電子写真感光体、すなわ
ち感光ドラム１を備え、この感光ドラム１は矢印方向に
回転し、その回転方向上流側から一次帯電器２、レーザ
ー露光装置３、固定式の現像器４および回転式の３個の
現像器５、ドラムクリーナ９が配置され、現像器とクリ
ーナの間には第２の像担持体としての中間転写ドラム
（ドラム状中間転写体）６が配置される。中間転写ドラ
ム６の周囲には、中間転写ドラム回転方向に沿って感光
ドラム１よりも下流側に転写ベルトを有する二次転写装
置（ユニット）１０が配置され、必要に応じてさらにク
リーニング手段等が配置される。二次転写装置１０の延
長上には定着器８が配置される。As shown in FIG. 1, the present image forming apparatus includes a drum type electrophotographic photosensitive member, that is, a photosensitive drum 1 as a first image carrier, and the photosensitive drum 1 rotates in a direction indicated by an arrow. A primary charger 2, a laser exposure device 3, a fixed developing device 4, three rotating developing devices 5, and a drum cleaner 9 are arranged from the upstream side in the rotation direction, and a second cleaning device is provided between the developing device and the cleaner. An intermediate transfer drum (drum-shaped intermediate transfer body) 6 as an image carrier is arranged. Around the intermediate transfer drum 6, a secondary transfer device (unit) 10 having a transfer belt on the downstream side of the photosensitive drum 1 along the rotation direction of the intermediate transfer drum is arranged. Be placed. A fixing device 8 is disposed on an extension of the secondary transfer device 10.

【００２３】二次転写装置１０は、転写ローラ１１、駆
動ローラ１２に転写ベルト１３を掛け回してなってお
り、転写ローラ１１のところで中間転写ドラム６に接離
自在に設置されている。この転写ローラ１１には二次転
写高圧電源１４が接続されている。The secondary transfer device 10 has a transfer belt 13 wrapped around a transfer roller 11 and a drive roller 12, and is installed at the transfer roller 11 so as to be able to freely contact and separate from the intermediate transfer drum 6. A secondary transfer high voltage power supply 14 is connected to the transfer roller 11.

【００２４】感光ドラム１の表面は、一次帯電器２によ
りたとえば−５５０Ｖに均一に一様帯電され、ついでレ
ーザー露光装置３によって画像パターンが露光され、感
光ドラム１の表面電位が、未露光部電位（ＶＤ）で−５
５０Ｖ、露光部電位（ＶＬ）で−１５０Ｖとなって、感
光ドラム１の表面に静電潜像が形成される。この静電潜
像を、現像器（ブラック（Ｋ））４または現像器５（イ
エロー（Ｙ）、マゼンタ（Ｍ）、シアン（Ｃ））の１つ
を用いてネガ帯電性のトナーで現像すると、ネガに帯電
されたトナーが感光ドラム１表面の露光部、すなわち電
位が低い部分（ＶＬ部）に付着して、潜像がトナー像と
して可視化される。The surface of the photosensitive drum 1 is uniformly and uniformly charged to, for example, -550 V by a primary charger 2, and then an image pattern is exposed by a laser exposure device 3, and the surface potential of the photosensitive drum 1 is changed to the unexposed portion potential. -5 in (VD)
The potential becomes 50 V and the exposure portion potential (VL) becomes -150 V, so that an electrostatic latent image is formed on the surface of the photosensitive drum 1. When this electrostatic latent image is developed with a negatively charged toner using one of the developing device (black (K)) 4 or the developing device 5 (yellow (Y), magenta (M), cyan (C)) The negatively charged toner adheres to an exposed portion of the surface of the photosensitive drum 1, that is, a portion having a low potential (VL portion), and the latent image is visualized as a toner image.

【００２５】中間転写ドラム６は、円筒状の金属の芯金
を導電性支持体として、その上にゴム、エラストマーも
しくは樹脂からなる弾性層を少なくとも有するローラか
らなり、さらには弾性層上には一層以上の被覆層を設け
ることができる。中間転写ドラム６は第一の転写部材を
兼ねていて、感光ドラムとほぼ等速で回転駆動されてい
る。The intermediate transfer drum 6 is composed of a roller having at least an elastic layer made of rubber, elastomer, or resin on a cylindrical metal core as a conductive support, and further having a single layer on the elastic layer. The above coating layer can be provided. The intermediate transfer drum 6 also serves as a first transfer member, and is driven to rotate at substantially the same speed as the photosensitive drum.

【００２６】中間転写ドラム６の芯金に一次転写バイア
ス（Ｔ１）を、＋３００Ｖで印加すると、感光ドラム１
と中間転写ドラム６とが当接した一次転写ニップ部にお
いて、感光ドラム１のＶＬ部と中間転写ドラム６との電
位差４５０Ｖによって、感光ドラム１上のトナー像は中
間転写ドラム６の表面に一次転写される。この工程をイ
エロー（Ｙ）、マゼンタ（Ｍ）、シアン（Ｃ）、ブラッ
ク（Ｋ）の４色分繰り返し、中間転写ドラム６上で４色
のトナー像を位置合わせしながら重畳転写する。When a primary transfer bias (T1) is applied to the core of the intermediate transfer drum 6 at +300 V, the photosensitive drum 1
The toner image on the photosensitive drum 1 is primarily transferred to the surface of the intermediate transfer drum 6 by the potential difference 450 V between the VL portion of the photosensitive drum 1 and the intermediate transfer drum 6 in the primary transfer nip portion where the toner and the intermediate transfer drum 6 abut. Is done. This process is repeated for four colors of yellow (Y), magenta (M), cyan (C), and black (K), and the toner images of four colors are superimposed and transferred on the intermediate transfer drum 6 while being positioned.

【００２７】つぎに二次転写ベルト１３を中間転写ドラ
ム６に加圧して、中間転写ドラム６との間に二次転写ニ
ップＮ２を形成し、中間転写ドラム６上の画像先端と同
期させて紙などの記録材Ｐを二次転写ニップＮ２に送り
込む。そして高圧電源１４から転写ローラ１１に二次転
写バイアス（Ｔ２）を、たとえば＋１．５ｋＶで印加
し、中間転写ドラム６上の４色のトナー像が一括して記
録材Ｐの表面に二次転写されていく。４色のトナー像が
転写された記録材Ｐは定着器８に送り込まれる。Next, the secondary transfer belt 13 is pressed against the intermediate transfer drum 6 to form a secondary transfer nip N2 between the secondary transfer belt 6 and the intermediate transfer drum 6. The recording material P is sent to the secondary transfer nip N2. Then, a secondary transfer bias (T2) is applied from the high-voltage power supply 14 to the transfer roller 11 at, for example, +1.5 kV, and the four-color toner images on the intermediate transfer drum 6 are collectively transferred onto the surface of the recording material P at the same time. Will be done. The recording material P to which the four color toner images have been transferred is sent to the fixing device 8.

【００２８】定着器８は、加熱ヒータ８ａを一方に内蔵
した（両方に内蔵してもよい）一対のローラからなり、
一定の圧力で互いに圧接されて定着ニップＮ３を形成し
ている。記録材Ｐはこの一対のローラの間を通過する間
に、熱と圧力によってトナー像が混色と同時に記録材に
定着され、記録材にフルカラーの定着画像が得られる。The fixing device 8 is composed of a pair of rollers having a heater 8a built in one side (or both may be built in).
The fixing nip N3 is formed by being pressed against each other at a constant pressure. While the recording material P passes between the pair of rollers, the toner image is fixed on the recording material simultaneously with the color mixture by heat and pressure, and a full-color fixed image is obtained on the recording material.

【００２９】本発明の目的は、記録材の長さが、転写ベ
ルトの記録材分離部と定着ニップとの間の距離よりも長
い場合に、転写ニップと定着ニップとの間の距離よりも
短くても、記録材を転写ベルトに安定に吸着、保持して
定着ニップに搬送させることにある。そのために、本発
明では、記録材の後端が転写ニップを抜けても転写電圧
を直ちに停止せず、電圧の印加によって記録材を転写ベ
ルトにしっかりと吸着させるようにした。An object of the present invention is to provide a recording medium having a length shorter than the distance between the transfer nip and the fixing nip when the length of the recording medium is longer than the distance between the recording material separating portion of the transfer belt and the fixing nip. In this case, the recording material is stably adsorbed and held on the transfer belt and transported to the fixing nip. Therefore, in the present invention, the transfer voltage is not immediately stopped even when the rear end of the recording material passes through the transfer nip, and the recording material is firmly attracted to the transfer belt by applying the voltage.

【００３０】本実施例において行った記録材搬送性の確
認実験について述べる。二次転写ベルト１３として表面
抵抗が１０¹⁰Ω／□のものを用い、二次転写高圧電源１
４から二次転写ローラ１１に、二次転写電圧Ｔ２の最適
値Ｖ１として低湿環境で＋２．０ｋＶ、通常環境で＋
１．５ｋＶ、高湿環境で＋０．９ｋＶを印加した。また
二次転写ニップＮ２と定着ニップＮ３との距離Ａは１９
０ｍｍとし、二次転写ベルト１３の記録材分離位置（ベ
ルト後端）から定着ニップＮ３までの距離は９０ｍｍで
あった。記録材Ｐとして長さ１４８ｍｍの普通紙を通紙
した。An experiment for confirming recording material transportability performed in this embodiment will be described. Used as a surface resistance of ¹⁰ 10 Ω / □ as a secondary transfer belt 13, a secondary transfer high-voltage power supply 1
4 to the secondary transfer roller 11, the optimum value V1 of the secondary transfer voltage T2 is +2.0 kV in a low humidity environment, and +2 kV in a normal environment.
1.5 kV and +0.9 kV were applied in a high humidity environment. The distance A between the secondary transfer nip N2 and the fixing nip N3 is 19
The distance from the recording material separation position (belt rear end) of the secondary transfer belt 13 to the fixing nip N3 was 90 mm. As the recording material P, plain paper having a length of 148 mm was passed.

【００３１】記録材（普通紙）Ｐの後端が二次転写ニッ
プＮ２を通過したら、二次転写電圧Ｔ２を電圧Ｖ１から
異なる電圧Ｖ２に切り替えて出力し、これを印加して記
録材の転写ベルト１３への吸着による搬送性を調べた。
電圧Ｖ２は種々に変更した。When the trailing edge of the recording material (plain paper) P passes through the secondary transfer nip N2, the secondary transfer voltage T2 is switched from the voltage V1 to a different voltage V2 and output, and is applied to transfer the recording material. The transportability by adsorption to the belt 13 was examined.
The voltage V2 was changed variously.

【００３２】その結果、記録材Ｐが二次転写ニップＮ２
で挟持されていない状態でも、二次転写ベルト１３に吸
着して安定して搬送されるには、Ｖ２の値を＋１．５ｋ
Ｖ以上、好ましくは＋２．０ｋＶ以上出力すればよいこ
とが分かった。As a result, the recording material P is moved to the secondary transfer nip N2
In order to stably adsorb and adhere to the secondary transfer belt 13 even when the sheet is not pinched, the value of V2 is set to +1.5 k.
It was found that the output should be at least V, preferably at least +2.0 kV.

【００３３】そこで、本実施例では、記録材Ｐが二次転
写ニップＮ２と定着ニップＮ３の距離Ａよりも短い場合
は、記録材Ｐの後端が二次転写ニップＮ２を通過後、記
録材Ｐの先端が定着ニップＮ３に到達するまでの時間だ
け、環境状態に関係なく、二次転写バイアスＴ２として
＋２．０ｋＶの電圧を出力させるようにした。Therefore, in the present embodiment, when the recording material P is shorter than the distance A between the secondary transfer nip N2 and the fixing nip N3, after the trailing end of the recording material P passes through the secondary transfer nip N2, A voltage of +2.0 kV was output as the secondary transfer bias T2 irrespective of the environmental condition only during the time until the tip of P reaches the fixing nip N3.

【００３４】図３は、高出力シーケンスを模式的に示す
図で、横軸が時間、縦軸が二次転写ローラに印加される
電圧である。プロセス速度を１００ｍｍ／秒としたと
き、長さａの記録材が二次転写ニップＮ２に通過するの
要する時間は、Ｔａ＝ａ／１００（秒）であり、前記の
ａ＝１４８ｍｍの場合、Ｔａ＝１４８／１００＝１．４
８秒である。記録材先端が二次転写ニップＮ２を通過し
てから定着ニップＮ３に到達するまでの時間はＴA＝Ａ
／１００（秒）であり、本実施例では、Ａ＝１９０ｍｍ
であるから、ＴA＝１９０／１００＝１．９秒である。
従来例では、時間Ｔａだけ二次転写バイアスＶ１を出力
させていたのに対し、本実施例では、時間Ｔａだけ二次
転写バイアスを出力させた後、時間ＴAになるまで出力
値をＶ２に切り替えて印加している。FIG. 3 is a diagram schematically showing a high output sequence, in which the horizontal axis represents time and the vertical axis represents the voltage applied to the secondary transfer roller. When the process speed is set to 100 mm / sec, the time required for the recording material having the length a to pass through the secondary transfer nip N2 is Ta = a / 100 (second). = 148/100 = 1.4
8 seconds. The time from when the leading edge of the recording material passes through the secondary transfer nip N2 to when it reaches the fixing nip N3 is TA = A
/ 100 (sec), and in this embodiment, A = 190 mm
Therefore, TA = 190/100 = 1.9 seconds.
In the conventional example, the secondary transfer bias V1 is output only for the time Ta. In the present embodiment, after the secondary transfer bias is output only for the time Ta, the output value is switched to V2 until the time TA is reached. Is applied.

【００３５】これにより、中間転写ベルト１３から記録
材Ｐへのトナー画像の二次転写は電圧Ｖ１によって各環
境に応じて適正に行われ、さらに電圧Ｖ２によって二次
転写ベルト１３と記録材Ｐの吸着力が確保され、二次転
写後も記録材Ｐを安定して搬送できるようになった。Thus, the secondary transfer of the toner image from the intermediate transfer belt 13 to the recording material P is appropriately performed according to each environment by the voltage V1, and further, the transfer of the secondary transfer belt 13 and the recording material P is performed by the voltage V2. The attraction force is secured, and the recording material P can be stably conveyed even after the secondary transfer.

【００３６】以上の実施例では、中間転写体として中間
転写ドラムを有するカラー画像形成装置を取り上げた
が、本発明は、感光ドラム等の画像形成手段を中間転写
ベルトに沿って複数組設置した形態のカラー画像形成装
置でもよく、同様に適用して同様な効果を得ることがで
きる。In the above embodiment, a color image forming apparatus having an intermediate transfer drum as an intermediate transfer member has been described. However, the present invention is directed to a form in which a plurality of image forming means such as photosensitive drums are installed along an intermediate transfer belt. The color image forming apparatus described above may be applied, and similar effects can be obtained by applying the same method.

【００３７】実施例２ 図４は、本発明の画像形成装置の他の実施例を示す概略
断面図である。Embodiment 2 FIG. 4 is a schematic sectional view showing another embodiment of the image forming apparatus of the present invention.

【００３８】本実施例の装置は、像担持体として複数の
感光ドラム１ａ〜１ｄを備え、各感光ドラム１（１ａ〜
１ｄ）の周囲には、回転方向上流から一次帯電器２（２
ａ〜２ｄ）、レーザー露光装置３（３ａ〜３ｄ）、現像
器４（４ａ〜４ｄ）、図示しないドラムクリーナ、およ
び転写ローラ２１（２１ａ〜２１ｄ）が配置され、感光
ドラム１〜転写ローラ２１の各組は、それぞれ画像形成
ステーションを構成している。The apparatus according to the present embodiment includes a plurality of photosensitive drums 1a to 1d as image carriers, and each photosensitive drum 1 (1a to 1d).
1d), the primary charger 2 (2
a to 2d), a laser exposure device 3 (3a to 3d), a developing device 4 (4a to 4d), a drum cleaner (not shown), and a transfer roller 21 (21a to 21d). Each set constitutes an image forming station.

【００３９】４つのステーションの現像器４ａ、４ｂ、
４ｃ、４ｄには、それぞれイエロー、マゼンタ、シア
ン、ブラックのトナーが収容されている。４つのステー
ションの感光ドラム１と転写ローラ２１の間には、これ
らに接するように転写ベルト２３が設置され、各ステー
ションの感光ドラム１と転写ベルト２３との間に転写部
が形成されている。この転写ベルト２３は従動ローラ２
４と駆動ローラ２５とに掛け回され、駆動ローラ２５に
より矢印方向に感光ドラム１とほぼ等速のプロセス速度
で回転駆動されている。転写ベルト２３には図示しない
カセットから供給された記録材が担持され、各ステーシ
ョンの転写部に順次搬送される。The developing devices 4a, 4b of the four stations,
4c and 4d contain yellow, magenta, cyan, and black toners, respectively. Transfer belts 23 are provided between the photosensitive drums 1 and the transfer rollers 21 of the four stations so as to be in contact therewith, and transfer portions are formed between the photosensitive drums 1 and the transfer belts 23 of the respective stations. This transfer belt 23 is driven roller 2
4 and the drive roller 25, and is driven by the drive roller 25 to rotate in the direction of the arrow at a process speed substantially equal to that of the photosensitive drum 1. A recording material supplied from a cassette (not shown) is carried on the transfer belt 23, and is sequentially conveyed to a transfer unit of each station.

【００４０】実施例１と同様、感光ドラム１に対する帯
電、露光、現像の工程を経て、第１のステーションにお
いて、感光ドラム１上に１色目のトナー像を形成し、こ
の画像と同期して転写ベルト２３上に担持した記録材を
第１ステーションの転写ニップに送り込む。これと同時
に転写ローラ２１に図示しない高圧電源から転写バイア
スを印加することにより、感光ドラム１上のトナー像が
記録材上に転写される。As in the first embodiment, a first color toner image is formed on the photosensitive drum 1 at the first station through the steps of charging, exposing, and developing the photosensitive drum 1 and transferred in synchronization with the image. The recording material carried on the belt 23 is sent to the transfer nip of the first station. At the same time, by applying a transfer bias to the transfer roller 21 from a high-voltage power supply (not shown), the toner image on the photosensitive drum 1 is transferred onto the recording material.

【００４１】このようにして記録材が第１〜第４ステー
ションでの転写工程を経ることにより、記録材上に４色
のトナー像を重畳したカラー画像が形成される。続いて
記録材は転写ベルト２３から分離されて定着器８に送ら
れ、定着されてフルカラーの定着画像が得られる。As described above, the recording material undergoes the transfer process at the first to fourth stations, whereby a color image in which four color toner images are superimposed on the recording material is formed. Subsequently, the recording material is separated from the transfer belt 23, sent to the fixing device 8, and fixed to obtain a full-color fixed image.

【００４２】本実施例では、転写ベルト２３に表面抵抗
が１０¹²Ω／□のものを用い、図５に示すように、第４
ステーションの転写ニップＮ１から定着ニップＮ３まで
の距離Ａを２００ｍｍ、転写ベルト２３の記録材分離部
（後端）から定着ニップＮ３までの距離を１００ｍｍと
した。In this embodiment, a transfer belt having a surface resistance of 10 ¹² Ω / □ is used, and as shown in FIG.
The distance A from the transfer nip N1 of the station to the fixing nip N3 was 200 mm, and the distance from the recording material separating portion (rear end) of the transfer belt 23 to the fixing nip N3 was 100 mm.

【００４３】今、記録材Ｐとしてこれに長さａ＝１４８
ｍｍの普通紙を通したとき、第４ステーションの高圧電
源２６ｄにより転写ローラ２１ｄに印加する最適転写バ
イアスＴ１がＶ１＝＋１．３ｋＶであるのに対し、記録
材の後端が第４ステーションの転写ニップＮ１を通過し
てから、記録材が定着器８まで安定に搬送されるにはＶ
２＝＋１．８ｋＶ以上必要であった。Now, as the recording material P, the length a = 148
mm plain paper, the optimum transfer bias T1 applied to the transfer roller 21d by the high voltage power supply 26d of the fourth station is V1 = + 1.3 kV, whereas the rear end of the recording material is transferred to the fourth station by the fourth station. In order for the recording material to be stably conveyed to the fixing device 8 after passing through the nip N1, V
2 = + 1.8 kV or more was required.

【００４４】そこで、本実施例では、記録材Ｐの後端が
第４ステーションの転写ニップＮ１を通過後、高圧電源
２６ｄの出力Ｔ１をＶ１＝＋１．３ｋＶからＶ２＝＋
１．８ｋＶに切り替えて、転写ローラ２１ｄに印加する
ようにした。Therefore, in this embodiment, after the rear end of the recording material P passes through the transfer nip N1 of the fourth station, the output T1 of the high voltage power supply 26d is changed from V1 = + 1.3 kV to V2 = +.
The voltage was switched to 1.8 kV to apply the voltage to the transfer roller 21d.

【００４５】これにより、第４ステーションでの感光ド
ラム１ｄからの記録材Ｐへのトナー画像の転写は電圧Ｖ
１によって適正に行われ、さらに電圧Ｖ２によって転写
ベルト２３と記録材Ｐの吸着力が確保され、転写後も記
録材Ｐを安定して搬送できるようになった。Thus, the transfer of the toner image from the photosensitive drum 1d to the recording material P at the fourth station is performed at the voltage V
1, the voltage V2 ensures the attraction between the transfer belt 23 and the recording material P, and the recording material P can be stably conveyed even after the transfer.

【００４６】以上の実施例では、いずれもカラーの画像
形成装置について説明したが、感光ドラム等の画像形成
手段を１組有する単色の画像形成装置についても本発明
を適用することができ、同様な効果を得ることができ
る。In each of the above embodiments, a color image forming apparatus has been described. However, the present invention can also be applied to a single color image forming apparatus having one set of image forming means such as a photosensitive drum. The effect can be obtained.

【００４７】[0047]

【発明の効果】以上説明したように、本発明によれば、
記録材の長さが、転写ニップと定着ニップとの間の距離
よりも短く、かつベルト状記録材搬送部材の記録材分離
部と定着ニップとの間の距離よりも長い場合に、記録材
の後端が転写ニップを通過した時点で、転写高圧電源の
出力を転写電圧からこれと同極性の高い電圧に切り替え
て、転写帯電部材に印加するようにしたので、転写ニッ
プと定着ニップ間の距離を短くしなくても、記録材を搬
送部材に吸着して安定に保持し、定着ニップに搬送する
ことができ、転写ニップと定着ニップ間に特別な搬送補
助手段を設ける必要もない。As described above, according to the present invention,
When the length of the recording material is shorter than the distance between the transfer nip and the fixing nip and longer than the distance between the recording material separating portion of the belt-like recording material conveying member and the fixing nip, When the rear end passed the transfer nip, the output of the transfer high-voltage power supply was switched from the transfer voltage to a voltage having the same polarity as the transfer voltage and applied to the transfer charging member, so that the distance between the transfer nip and the fixing nip was changed. The recording material can be stably held by being attracted to the conveying member without being shortened, and can be conveyed to the fixing nip, and there is no need to provide a special conveying auxiliary means between the transfer nip and the fixing nip.

【図面の簡単な説明】[Brief description of the drawings]

【図１】本発明に係る画像形成装置の一実施例を示す概
略断面図である。FIG. 1 is a schematic sectional view showing an embodiment of an image forming apparatus according to the present invention.

【図２】図１の画像形成装置の二次転写部から定着器ま
でを示す詳細図である。FIG. 2 is a detailed view illustrating a portion from a secondary transfer portion to a fixing device of the image forming apparatus of FIG. 1;

【図３】図１の実施例における転写バイアスの印加シー
ケンスを従来法と対比して示す図である。FIG. 3 is a diagram showing a transfer bias application sequence in the embodiment of FIG. 1 in comparison with a conventional method.

【図４】本発明の画像形成装置の他の実施例を示す概略
断面図である。FIG. 4 is a schematic sectional view showing another embodiment of the image forming apparatus of the present invention.

【図５】図４の画像形成装置の第４ステーションの転写
部から定着器まで示す詳細図である。FIG. 5 is a detailed view illustrating a portion from a transfer section to a fixing device of a fourth station of the image forming apparatus of FIG. 4;

【図６】従来の画像形成装置を示す概略断面図である。FIG. 6 is a schematic sectional view showing a conventional image forming apparatus.

【符号の説明】[Explanation of symbols]

１、１ｙ〜１ｋ 感光ドラム ４、４ａ〜４ｄ、５ 現像器 ８ 定着器 １０ 二次転写装置 １１ 二次転写ローラ １３ 二次転写ベルト １４、２６ 高圧電源 ２３ 転写ベルト ２１ａ〜２１ｄ 転写ローラ Ｎ１ 転写ニップ Ｎ２ 二次転写ニップ Ｎ３ 定着ニップ 1, 1y to 1k Photosensitive drum 4, 4a to 4d, 5 Developing device 8 Fixing device 10 Secondary transfer device 11 Secondary transfer roller 13 Secondary transfer belt 14, 26 High voltage power supply 23 Transfer belt 21a to 21d Transfer roller N1 Transfer nip N2 Secondary transfer nip N3 Fixing nip

Claims (7)

【特許請求の範囲】[Claims] 【請求項１】 像担持体と、ベルト状記録材搬送部材
と、転写帯電部材と、高圧電源と、定着手段とを有し、 前記搬送部材上に記録材を担持して、前記搬送部材を介
して前記転写帯電部材が前記像担持体と当接した転写ニ
ップに搬送し、前記高圧電源からトナーの帯電極性と逆
極性の転写電圧を出力して前記転写帯電部材に印加する
ことにより、前記像担持体上に形成されたトナー像を記
録材に転写し、前記トナー像が転写された記録材を前記
搬送部材から分離して前記定着手段に送り込み、前記定
着手段の定着ニップで定着する画像形成装置において、 前記記録材の長さが、前記転写ニップと前記定着ニップ
との間の距離よりも短く、かつ前記搬送部材の記録材分
離部と前記定着ニップとの間の距離よりも長い場合、前
記記録材の後端が前記転写ニップを通過したら、前記高
圧電源の出力を転写電圧からこれと同極性の高い電圧に
切り替えて、前記転写帯電部材に印加することを特徴と
する画像形成装置。An image carrier, a belt-shaped recording material conveying member, a transfer charging member, a high-voltage power supply, and a fixing unit, wherein the recording material is carried on the conveying member, and the conveying member is By transferring the transfer charging member to a transfer nip where the transfer charging member is in contact with the image carrier, and outputting a transfer voltage having a polarity opposite to the charging polarity of the toner from the high-voltage power supply and applying the transfer voltage to the transfer charging member, The image formed by transferring the toner image formed on the image carrier to a recording material, separating the recording material onto which the toner image has been transferred from the transporting member, feeding the separated recording material to the fixing unit, and fixing the toner image at a fixing nip of the fixing unit. In the forming apparatus, when the length of the recording material is shorter than a distance between the transfer nip and the fixing nip, and longer than a distance between a recording material separating unit of the conveying member and the fixing nip. , The rear end of the recording material is the front After passing through the transfer nip, the switches the output of the high-voltage power supply from the transfer voltage to the same polarity high voltage, an image forming apparatus and applying to said transfer charging member. 【請求項２】 複数の像担持体と、ベルト状記録材搬送
部材と、複数の転写帯電部材と、１つまたは複数の高圧
電源と、定着手段とを有し、 前記搬送部材上に記録材を担持して、前記搬送部材を介
して前記転写帯電部材が前記像担持体と当接した複数の
転写ニップに順次搬送し、前記高圧電源からトナーの帯
電極性と逆極性の転写電圧を出力して前記転写帯電部材
に印加することにより、前記複数の像担持体上に形成さ
れた複数色のトナー像を記録材に重ね合わせて転写し、
前記トナー像が転写された記録材を前記搬送部材から分
離して前記定着手段に送り込み、前記定着手段の定着ニ
ップで定着する画像形成装置において、 前記記録材の長さが、前記搬送部材による記録材搬送方
向最下流において、前記転写ニップと前記定着ニップと
の間の距離よりも短く、かつ前記搬送部材の記録材分離
部と前記定着ニップとの間の距離よりも長い場合、前記
記録材の後端が前記転写ニップを通過したら、前記高圧
電源の出力を転写電圧からこれと同極性の高い電圧に切
り替えて、前記転写帯電部材に印加することを特徴とす
る画像形成装置。2. A recording material having a plurality of image carriers, a belt-shaped recording material conveying member, a plurality of transfer charging members, one or a plurality of high-voltage power supplies, and a fixing unit. And the transfer charging member is sequentially transferred to a plurality of transfer nips in contact with the image carrier via the transfer member, and a transfer voltage having a polarity opposite to the charge polarity of the toner is output from the high-voltage power supply. By applying to the transfer charging member, a plurality of color toner images formed on the plurality of image carriers is transferred onto a recording material in a superimposed manner,
In an image forming apparatus, the recording material onto which the toner image has been transferred is separated from the transport member and sent to the fixing unit, and is fixed at a fixing nip of the fixing unit. At the most downstream in the material conveying direction, if the distance between the transfer nip and the fixing nip is shorter than the distance between the recording material separating portion of the conveying member and the fixing nip, When the rear end passes through the transfer nip, the output of the high-voltage power supply is switched from a transfer voltage to a voltage having the same polarity as the output voltage and is applied to the transfer charging member. 【請求項３】 像担持体と、中間転写体と、ベルト状記
録材搬送部材と、二次転写帯電部材と、二次高圧電源
と、定着手段とを有し、 前記像担持体上に形成されたトナー像を前記中間転写体
上に一次転写し、前記搬送部材上に記録材を担持して、
前記搬送部材を介して前記二次転写帯電部材が前記中間
転写体と当接した二次転写ニップに搬送し、前記高圧電
源からトナーの帯電極性と逆極性の二次転写電圧を出力
して前記転写帯電部材に印加することにより、前記中間
転写体上に転写されたトナー像を記録材に二次転写し、
前記トナー像が転写された記録材を前記搬送部材から分
離して前記定着手段に送り込み、前記定着手段の定着ニ
ップで定着する画像形成装置において、 前記記録材の長さが、前記二次転写ニップと前記定着ニ
ップとの間の距離よりも短く、かつ前記搬送部材の記録
材分離部と前記定着ニップとの間の距離よりも長い場
合、前記記録材の後端が前記二次転写ニップを通過した
ら、前記高圧電源の出力を二次転写電圧からこれと同極
性の高い電圧に切り替えて、前記転写帯電部材に印加す
ることを特徴とする画像形成装置。3. An image carrier, an intermediate transfer body, a belt-shaped recording material conveying member, a secondary transfer charging member, a secondary high voltage power supply, and a fixing unit, wherein the image carrier is formed on the image carrier. The transferred toner image is primarily transferred onto the intermediate transfer body, and a recording material is carried on the conveying member,
The secondary transfer charging member is transported to the secondary transfer nip in contact with the intermediate transfer body via the transport member, and outputs a secondary transfer voltage having a polarity opposite to the polarity of the charged toner from the high voltage power supply. By applying to the transfer charging member, the toner image transferred on the intermediate transfer body is secondarily transferred to a recording material,
In the image forming apparatus, the recording material onto which the toner image has been transferred is separated from the conveyance member, sent to the fixing unit, and fixed at a fixing nip of the fixing unit, wherein the length of the recording material is the secondary transfer nip. When the distance between the recording material separating portion of the conveyance member and the fixing nip is longer than the distance between the recording material separating portion and the fixing nip, the rear end of the recording material passes through the secondary transfer nip. Then, the output of the high-voltage power supply is switched from the secondary transfer voltage to a voltage having the same polarity as the secondary transfer voltage and applied to the transfer charging member. 【請求項４】 前記像担持体上に複数色のトナー像が順
次形成され、前記像担持体上に形成された複数色のトナ
ー像が前記中間転写体上に順次重ね合わせて転写される
請求項３の画像形成装置。4. A multi-color toner image is sequentially formed on the image carrier, and the multi-color toner images formed on the image carrier are sequentially superimposed and transferred on the intermediate transfer body. Item 3. The image forming apparatus according to Item 3. 【請求項５】 複数の像担持体と、中間転写体と、ベル
ト状記録材搬送部材と、二次転写帯電部材と、高圧電源
と、定着手段とを有し、 前記複数の像担持体上に形成された複数色のトナー像を
前記中間転写体上に重ね合わせて一次転写し、前記搬送
部材上に記録材を担持して、前記搬送部材を介して前記
二次転写帯電部材が前記中間転写体と当接した二次転写
ニップに搬送し、前記高圧電源からトナーの帯電極性と
逆極性の二次転写電圧を出力して前記転写帯電部材に印
加することにより、前記中間転写体上に転写された複数
色のトナー像を記録材に二次転写し、前記トナー像が転
写された記録材を前記搬送部材から分離して前記定着手
段に送り込み、前記定着手段の定着ニップで定着する画
像形成装置において、 前記記録材の長さが、前記二次転写ニップと前記定着ニ
ップとの間の距離よりも短く、かつ前記搬送部材の記録
材分離部と前記定着ニップとの間の距離よりも長い場
合、前記記録材の後端が前記二次転写ニップを通過した
ら、前記二次高圧電源の出力を二次転写電圧からこれと
同極性の高い電圧に切り替えて、前記転写帯電部材に印
加することを特徴とする画像形成装置。5. A method according to claim 1, further comprising a plurality of image carriers, an intermediate transfer member, a belt-shaped recording material conveying member, a secondary transfer charging member, a high voltage power supply, and a fixing unit. The toner image of a plurality of colors formed on the intermediate transfer member is superimposed on the intermediate transfer member and primary-transferred, a recording material is carried on the conveyance member, and the secondary transfer charging member is moved to the intermediate transfer member via the conveyance member. Conveyed to the secondary transfer nip in contact with the transfer body, and by outputting a secondary transfer voltage having a polarity opposite to the charge polarity of the toner from the high-voltage power supply and applying the same to the transfer charging member, the intermediate transfer body The transferred toner image of a plurality of colors is secondarily transferred to a recording material, and the recording material on which the toner image has been transferred is separated from the transport member, sent to the fixing unit, and fixed in a fixing nip of the fixing unit. In the forming apparatus, the length of the recording material is When the distance between the next transfer nip and the fixing nip is shorter than the distance between the recording material separating portion of the conveying member and the fixing nip, the trailing edge of the recording material is transferred to the secondary transfer nip. An image forming apparatus, wherein after passing through the nip, the output of the secondary high voltage power supply is switched from a secondary transfer voltage to a voltage having the same polarity as the secondary transfer voltage and applied to the transfer charging member. 【請求項６】 前記ベルト状記録材搬送部材の表面抵抗
が１０¹⁴Ω／□以下である請求項１〜５のいずれかの項
に記載の画像形成装置。6. The image forming apparatus according to claim 1, wherein the belt-shaped recording material conveying member has a surface resistance of 10 ¹⁴ Ω / □ or less. 【請求項７】 前記中間転写体がドラム状に形成された
請求項３〜６のいずれかの項に記載の画像形成装置。7. The image forming apparatus according to claim 3, wherein said intermediate transfer member is formed in a drum shape.