JP2004029054A

JP2004029054A - Image forming device

Info

Publication number: JP2004029054A
Application number: JP2002180661A
Authority: JP
Inventors: Daijiro Kato; 加藤　大二郎
Original assignee: Canon Inc
Current assignee: Canon Inc
Priority date: 2002-06-21
Filing date: 2002-06-21
Publication date: 2004-01-29

Abstract

【課題】中間転写体から転写材へトナー像を転写する際に飛び散りによる画像欠陥の発生を防止し、かつ２次転写ニップ部における中間転写体から転写材へのトナー像の良好な転写効率を得ることができるようにする。
【解決手段】中間転写ベルト８を張架する複数のローラ部材のうち、第１、第２の２次転写対向ローラ１０ａ，１０ｂを中間転写ベルト８を介して２次転写ローラ１３と圧接するように配置し、中間転写ベルト８の第１、第２の２次転写対向ローラ１０ａ，１０ｂ間で張架されている部分が２次転写ローラ１３表面に巻き付くようにして２次転写ニップ部Ｎを形成することにより、２次転写ニップ部Ｎにおける中間転写ベルト８上のトナー像と転写材Ｐとの密着度が高まり、高い転写効率を得ることができる。
【選択図】　　　図２An image forming apparatus includes: a transfer unit configured to transfer a toner image from an intermediate transfer member to a transfer material; To be able to get.
SOLUTION: Among a plurality of roller members for stretching an intermediate transfer belt 8, first and second secondary transfer opposed rollers 10a and 10b are pressed against a secondary transfer roller 13 via the intermediate transfer belt 8. And a portion of the intermediate transfer belt 8 stretched between the first and second secondary transfer opposed rollers 10a and 10b is wound around the surface of the secondary transfer roller 13 so that the secondary transfer nip portion N Is formed, the degree of adhesion between the toner image on the intermediate transfer belt 8 and the transfer material P in the secondary transfer nip N is increased, and high transfer efficiency can be obtained.
[Selection] Fig. 2

Description

【０００１】
【発明の属する技術分野】
本発明は、電子写真方式などによって画像形成を行う複写機、プリンタ、ファクシミリ等の画像形成装置に関し、特に像担持体上に担持した現像剤像を一旦ベルト状の中間転写体上に１次転写した後、該中間転写体に転写されたトナー画像を転写材へ２次転写部材により２次転写して画像形成を行う画像形成装置に関する。
【０００２】
【従来の技術】
近年、電子写真方式でデジタル方式の複数色又はフルカラーの画像形成装置ととして、各色毎に応じて感光ドラムを複数配置し、各感光ドラム上に形成された各色のトナー像を中間転写体としての中間転写ベルト上に順次重ね合わせてカラー画像を形成する画像形成装置（複写機やレーザビームプリンタなど）が実用化されている。
【０００３】
図４は、中間転写体を有する従来例における画像形成装置を示す概略構成図である。
【０００４】
この画像形成装置では、画像形成動作開始信号が発せられると、所定のプロセススピードで回転駆動される各画像形成部１Ｙ、１Ｍ、１Ｃ、１Ｋの各感光ドラム２ａ、２ｂ、２ｃ、２ｄは、それぞれ帯電ローラ３ａ、３ｂ、３ｃ、３ｄによって一様に帯電される。そして、各露光装置６ａ、６ｂ、６ｃ、６ｄは、入力される画像情報に対応してカラー色分解された時系列電気デジタル画素信号に変調し、変調された光信号であるレーザ光を、帯電された各感光ドラム２ａ、２ｂ、２ｃ、２ｄ上にそれぞれ走査露光して静電潜像を形成する。
【０００５】
そして、先ず感光ドラム２ａ上に形成された静電潜像に、感光ドラム２ａの帯電極性と同極性の現像バイアスが印加された現像装置４ａによりイエローのトナーを付着させて、トナー像として可視像化する。このイエローのトナー像は、１次転写部にて１次転写バイアス（トナーと逆極性の電圧）が印加された１次転写ローラ５ａにより、移動（回転）している中間転写体としての中間転写ベルト８上に１次転写される。中間転写ベルト８は、駆動ローラ９と２次転写対向ローラ１０とテンションローラ１１によって張架されており、駆動ローラ９の回転駆動によって矢印方向に移動（回転）される。
【０００６】
イエローのトナー像が転写された中間転写ベルト８は、駆動ローラ９の駆動によって画像形成部１Ｍ側に移動される。そして、画像形成部１Ｍにおいても、同様にして感光ドラム２ｂ上に形成されたマゼンタのトナー像が、１次転写部にて１次転写バイアス（トナーと逆極性の電圧）が印加された１次転写ローラ５ｂにより、中間転写ベルト８上のイエローのトナー像上に重ね合わせて転写される。
【０００７】
以下、同様にして中間転写ベルト８上に重畳転写されたイエロー、マゼンタのトナー像上に、画像形成部１Ｃ、１Ｋの感光ドラム２ｃ、２ｄで形成されたシアン、ブラックのトナー像を、各１次転写部にて１次転写バイアス（トナーと逆極性の電圧）が印加された１次転写ローラ５ｃ、５ｄにより、順次重ね合わせて転写してフルカラーのトナー像を中間転写ベルト８上に形成する。
【０００８】
そして、中間転写ベルト８上のフルカラーのトナー像先端が、２次転写ローラ１３と２次転写対向ローラ１０との間の２次転写ニップ部Ｎに移動されるタイミングに合わせて、カセット（不図示）から給紙された用紙などの転写材Ｐを２次転写ニップ部Ｎに搬送して、この転写材Ｐに、２次転写バイアス電源１４から２次転写バイアス（トナーと逆極性の電圧）が印加された２次転写ローラ１３によりフルカラーのトナー像が一括して転写（２次転写）される。
【０００９】
そして、フルカラーのトナー像が形成された転写材Ｐは搬送ベルト１５によって定着装置１６に搬送され、定着装置１６の定着ローラ１６ａと加圧ローラ１６ｂ間の定着ニップ部でフルカラーのトナー像を加熱、加圧して転写材Ｐ表面に熱定着した後に外部に排出して、一連の画像形成動作を終了する。
【００１０】
なお、上記した１次転写時において、各感光ドラム２ａ、２ｂ、２ｃ、２ｄ上に残留している１次転写残トナーは、ドラムクリーニング装置７ａ、７ｂ、７ｃ、７ｄによって除去されて回収される。また、２次転写後に中間転写ベルト８表面に残留している２次転写残トナーは、ベルトクリーニング装置１２によって除去されて回収される。
【００１１】
【発明が解決しようとする課題】
上述した従来例における図４の画像形成装置では、２次転写ローラ１３と、中間転写ベルト８を張架しているローラのうちの２次転写対向ローラ１０とを中間転写ベルト８を介して圧接するように対向配置して２次転写ニップ部Ｎを形成して、この２次転写ニップ部Ｎで中間転写ベルト８及び転写材Ｐを挟持搬送することにより、２次転写ローラ１３に印加した２次転写バイアスの印加によって発生する転写電界と、２次転写対向ローラ１０と２次転写ローラ１３との間に作用する圧接力によって、中間転写ベルト８上のフルカラーのトナー像が転写材Ｐに一括転写（２次転写）される。
【００１２】
ところで、上述した従来例の画像形成装置では、２次転写対向ローラ１０と２次転写ローラ１３とを圧接対向することで２次転写ニップ部Ｎを形成しているため、この２次転写ニップ部Ｎの転写材移動方向における転写領域の幅が小さく、転写材の搬送速度が速い場合や転写材の種類などによっては転写不良が発生する可能性があった。
【００１３】
このような問題を防止するために、例えば特開２００１−１６６６１１号公報に開示されているように、２次転写ニップ部を、２つの支持ローラ間に張架されている中間転写体（中間転写ベルト）の張架部に２次転写ローラが巻き付くことで形成し、かつ上記支持ローラのうち、例えば中間転写体の移動方向上流側に配設される一方の支持ローラと２次転写ローラとの圧接力が最大となるよう圧接して２次転写ニップ部に転写電界を付与するようにした構成が提案されている。
【００１４】
しかしながら、このような構成の画像形成装置では、中間転写体の移動方向上流側で圧接力が最大となるよう２次転写ローラに転写バイアス電圧を印加して、中間転写体の移動方向上流側の圧接部周辺にて転写電界が最大となるよう発生させるため、２次転写ニップ部に進入しようとする転写材が、前記一方の支持ローラ近傍にて発生する転写電界を帯び、中間転写体上のトナー像が２次転写ニップ部に到達しない上流側にて転写材に引き寄せられるなどの飛び散りによる画像欠陥を生じるおそれがあった。
【００１５】
そこで本発明は、２次転写ローラの中間転写体への圧接及び２次転写ニップ部への転写バイアス印加を適切に行い、中間転写体から転写体へトナー像を転写する際に飛び散りによる画像欠陥の発生を防止し、かつ２次転写ニップ部における中間転写体から転写材へのトナー像の良好な転写性を得ることができる画像形成装置を提供することを目的とする。
【００１６】
【課題を解決するための手段】
上記目的を達成するために本発明は、現像剤像が担持される像担持体と、前記像担持体と１次転写部にて当接し、複数のローラ部材で移動自在に張架された無端ベルト状の中間転写体と、前記１次転写部にて前記中間転写体を介して前記像担持体に当接し、１次転写バイアスの印加により前記像担持体上に担持された現像剤像を前記中間転写体上に１次転写する１次転写部材と、２次転写部にて２次転写バイアスの印加により前記中間転写体上に１次転写された現像剤像を転写材に２次転写する回転自在な２次転写部材と、を備えた画像形成装置において、前記複数のローラ部材のうち、少なくとも２つのローラ部材が前記中間転写体を介して前記２次転写部材と圧接するように配置され、前記中間転写体の前記２つのローラ部材間で張架されている現像剤像担持面側の部分が前記２次転写部材表面に巻き付くことにより前記２次転写部が形成されることを特徴としている。
【００１７】
また、前記２次転写部材は、弾性を有する導電性部材からなるローラ部材であることを特徴としている。
【００１８】
また、２次転写時に前記２次転写部材に２次転写バイアスを印加した際において、前記２次転写部における転写電界を、前記２次転写部に対して前記中間転写体の移動方向下流側に位置する前記２つのローラ部材のうちの一方のローラ部材と前記中間転写体を介して前記２次転写部材が当接する近傍で最大となるようにしたことを特徴としている。
【００１９】
また、前記２つのローラ部材のうち、少なくとも前記２次転写部に対して前記中間転写体の移動方向下流側に位置する一方のローラ部材の径が、前記２次転写部材の径よりも小径であることを特徴としている。
【００２０】
また、前記２つのローラ部材のうちの、少なくとも前記２次転写部に対して前記中間転写体の移動方向下流側に位置する一方のローラ部材の前記２次転写部と反対側の表面に、前記一方のローラ部材を前記中間転写体を介して前記２次転写部材に押圧するためのローラ部材を配置したことを特徴としている。
【００２１】
【発明の実施の形態】
以下、本発明を図示の実施の形態に基づいて説明する。
【００２２】
〈実施の形態１〉
図１は、本発明の実施の形態１に係る画像形成装置（本実施の形態では、電子写真方式のフルカラープリンタ等の画像形成装置）を示す概略構成図である。なお、図４に示した従来例の画像形成装置と同一機能を有する部材には同一符号を付して説明する。
【００２３】
この画像形成装置は、イエロー色のトナー像を形成する画像形成部１Ｙと、マゼンタ色のトナー像を形成する画像形成部１Ｍと、シアン色のトナー像を形成する画像形成部１Ｃと、ブラック色のトナー像を形成する画像形成部１Ｋの４つの画像形成部（画像形成ユニット）を備えており、これらの４つの画像形成部は一定の間隔をおいて一列に配置されている。
【００２４】
各画像形成部１Ｙ、１Ｍ、１Ｃ、１Ｋには、それぞれ像担持体としての感光ドラム２ａ、２ｂ、２ｃ、２ｄが設置されている。各感光ドラム２ａ、２ｂ、２ｃ、２ｄの周囲には、帯電ローラ３ａ、３ｂ、３ｃ、３ｄ、現像装置４ａ、４ｂ、４ｃ、４ｄ、転写ローラ５ａ、５ｂ、５ｃ、５ｄ、ドラムクリーニング装置７ａ、７ｂ、７ｃ、７ｄがそれぞれ設置されており、帯電ローラ３ａ、３ｂ、３ｃ、３ｄと現像装置４ａ、４ｂ、４ｃ、４ｄ間の上方には露光装置６ａ、６ｂ、６ｃ、６ｄがそれぞれ設置されている。
【００２５】
感光ドラム２ａ、２ｂ、２ｃ、２ｄは、本実施の形態では負帯電の有機感光ドラムで、アルミニウム等のドラム基体上にＯＰＣ感光層を有しており、駆動装置（不図示）によって矢印方向（反時計方向）にそれぞれ所定の周速度（プロセススピード）で回転駆動される。
【００２６】
接触帯電手段としての帯電ローラ３ａ、３ｂ、３ｃ、３ｄは、それぞれ感光ドラム２ａ、２ｂ、２ｃ、２ｄに所定の圧接力で接触し、帯電バイアス電源（不図示）から印加される帯電バイアスによって各感光ドラム２ａ、２ｂ、２ｃ、２ｄ表面を負極性の所定電位に均一に帯電する。
【００２７】
現像装置４ａ、４ｂ、４ｃ、４ｄは、本実施の形態では２成分現像方式であり、現像バイアス電源（不図示）から印加される現像バイアスによって各感光ドラム２ａ、２ｂ、２ｃ、２ｄ上に形成される静電潜像にトナーを付着させて、トナー像として反転現像する。各現像装置４ａ、４ｂ、４ｃ、４ｄには、それぞれイエロートナー、シアントナー、マゼンタトナー、ブラックトナーが収納されている。
【００２８】
接触転写手段としての転写ローラ５ａ、５ｂ、５ｃ、５ｄは、中間転写体としての無端ベルト状の中間転写ベルト８を介して各感光ドラム２ａ、２ｂ、２ｃ、２ｄ表面に所定の押圧力で接触し、各１次転写バイアス電源（不図示）から印加される前記トナーとは逆極性の１次転写バイアスにより、感光ドラム２ａ、２ｂ、２ｃ、２ｄと転写ローラ５ａ、５ｂ、５ｃ、５ｄ間の各一次転写部で、各感光ドラム２ａ、２ｂ、２ｃ、２ｄ表面の各色のトナー像を、移動する中間転写ベルト８上に順次重ね合わせて転写（１次転写）する。
【００２９】
露光装置６ａ、６ｂ、６ｃ、６ｄは、ホストコンピュータ（不図示）からそれぞれ入力される画像情報の時系列電気デジタル画素信号に対応して変調されたレーザ光で各感光ドラム２ａ、２ｂ、２ｃ、２ｄ表面を画像露光することにより、各帯電ローラ３ａ、３ｂ、３ｃ、３ｄで帯電された各感光ドラム２ａ、２ｂ、２ｃ、２ｄ表面に画像情報に応じた静電潜像を形成する。
【００３０】
中間転写ベルト８は、駆動ローラ９と２つの第１、第２の２次転写対向ローラ１０ａ，１０ｂとテンションローラ１１によって張架されており、駆動ローラ９の回転駆動によって、感光ドラム２ａ、２ｂ、２ｃ、２ｄの回転に同期して矢印方向に移動（回転）される。中間転写ベルト８として、ウレタン系樹脂、フッ素系樹脂、ナイロン系樹脂、ポリイミド樹脂のものや、シリコーンゴムやヒドリンゴム等の弾性材料や、これらにカーボンや導電粉体を分散させ抵抗調整を行ったもの等を用いることができる。
【００３１】
第１、第２の２次転写対向ローラ１０ａ，１０ｂは、中間転写ベルト８を介して２次転写ローラ１３に接して２次転写ニップ部Ｎを形成している。また、２次転写対向ローラ１０ｂは、圧接するバックアップローラ１０ｃによって中間転写ベルト８を介して２次転写ローラ１３に押圧されている（本発明の特徴である、２次転写ニップ部Ｎ近傍における中間転写ベルト８に対する２つの２次転写対向ローラ１０ａ，１０ｂ、２次転写ローラ１３の構成については後述する）。
【００３２】
次に、上記した本実施の形態の画像形成装置による画像形成動作について説明する。
【００３３】
画像形成動作開始信号が発せられると、所定のプロセススピードで回転駆動される画像形成部１Ｙ、１Ｍ、１Ｃ、１Ｋの各感光ドラム２ａ、２ｂ、２ｃ、２ｄは、それぞれ帯電ローラ３ａ、３ｂ、３ｃ、３ｄによって一様に本実施の形態では負極性の所定電位に帯電される。そして、露光装置６ａ、６ｂ、６ｃ、６ｄは、ホストコンピュータ（不図示）から入力されるカラー色分解された画像信号を光信号にそれぞれ変換し、変換された光信号であるレーザ光を帯電された各感光ドラム２ａ、２ｂ、２ｃ、２ｄ上にそれぞれ走査露光して静電潜像を形成する。
【００３４】
そして、先ず感光ドラム２ａ上に形成された静電潜像に、感光ドラム２ａの帯電極性（負極性）と同極性の現像バイアスが印加された現像装置４ａによりイエローのトナーを付着させて反転現像を行い、トナー像として可視像化する。そして、このイエローのトナー像を、１次転写部にて転写バイアス電源（不図示）から１次転写バイアスが印加された１次転写ローラ５ａにより、移動（回転）している中間転写ベルト８上に１次転写する。
【００３５】
イエローのトナー像が転写された中間転写ベルト８は、駆動ローラ９の駆動によって画像形成部１Ｍ側に移動される。そして、画像形成部１Ｍにおいても、同様にして感光ドラム２ｂ上に形成されたマゼンタのトナー像が、１次転写部にて転写バイアス電源（不図示）から１次転写バイアスが印加された１次転写ローラ５ｂにより、中間転写ベルト８上のイエローのトナー像上に重ね合わせて転写される。
【００３６】
以下、同様にして中間転写ベルト８上に重畳転写されたイエロー、マゼンタのトナー像上に、画像形成部１Ｃ、１Ｋの感光ドラム２ｃ、２ｄで形成されたシアン、ブラックのトナー像を、各１次転写部にて各転写バイアス電源（不図示）から１次転写バイアスが印加された１次転写ローラ５ｃ、５ｄにより、順次重ね合わせて転写してフルカラーのトナー像を中間転写ベルト８上に形成する。
【００３７】
そして、中間転写ベルト８上のフルカラーのトナー像先端が、２次転写ローラ１３と２つの２次転写対向ローラ１０ａ，１０ｂとの間の２次転写ニップ部Ｎに移動されるタイミングに合わせて、搬送された用紙などの転写材Ｐをこの２次転写ニップ部Ｎに搬送して、２次転写バイアス電源１４からトナーと逆極性の２次転写バイアスが印加された２次転写ローラ１３により、転写材Ｐ上にフルカラーのトナー像が一括して転写（２次転写）される。
【００３８】
そして、フルカラーのトナー像が形成された転写材Ｐは搬送ベルト１５を介して定着装置１６に搬送され、定着装置１６の定着ローラ１６ａと加圧ローラ１６ｂ間の定着ニップ部でフルカラーのトナー像を加熱、加圧して転写材Ｐ表面に熱定着した後に外部に排出して、一連の画像形成動作を終了する。
【００３９】
なお、上記した１次転写時において、感光ドラム２ａ、２ｂ、２ｃ、２ｄ上に残留している転写残トナーは、ドラムクリーニング装置７ａ、７ｂ、７ｃ、７ｄによってそれぞれ除去されて回収される。また、２次転写後に中間転写ベルト８表面に残った残トナーは、ベルトクリーニング装置１２によって除去されて回収される。
【００４０】
次に、２次転写ニップ部Ｎ近傍における中間転写ベルト８に対する第１、第２の２次転写対向ローラ１０ａ，１０ｂ、２次転写ローラ１３の構成について説明する。
【００４１】
図１、図２に示すように、第１の２次転写対向ローラ１０ａは２次転写ニップ部Ｎに対して中間転写ベルト８の移動方向上流側に配設され、第２の２次転写対向ローラ１０ｂは中間転写ベルト８の移動方向に対して２次転写対向ローラ１０ａの下流側に配設されており、第１、第２の２次転写対向ローラ１０ａ，１０ｂは回転自在に支持されている。
【００４２】
２次転写ローラ１３は、その表面部が弾性体なる導電性部材（抵抗値１０^６〜１０^７Ω）から形成されており、中間転写ベルト８を介して第１、第２の２次転写対向ローラ１０ａ，１０ｂに所定の圧力にて圧接するように配設されている。これにより、第１の２次転写対向ローラ１０ａと第２の２次転写対向ローラ１０ｂ間に張架されている中間転写ベルト８のトナー像担持面側の張架部分が、２次転写ローラ１３表面に巻き付くとともに、第１、第２の２次転写対向ローラ１０ａ，１０ｂと２次転写ローラ１３とが中間転写ベルト８を介して対向かつ圧接して、２次転写ニップ部Ｎが形成される。また、２次転写ローラ１３は、中間転写ベルト８に対して当接離間自在に配設されており、２次転写時に中間転写ベルト８を介して第１、第２の２次転写対向ローラ１０ａ，１０ｂに圧接する。
【００４３】
なお、本実施の形態における２次転写ニップ部Ｎの領域は、中間転写ベルト８の移動方向に沿って２次転写ローラ１３表面の第１の２次転写対向ローラ１０ａと２次転写ローラ１３が中間転写ベルト８を介して当接する部分から第２の２次転写対向ローラ１０ｂと２次転写ローラ１３が中間転写ベルト８を介して当接する部分である。
【００４４】
また、本発明の実施の形態１では、２次転写バイアス電源１４から２次転写バイアスを２次転写ローラ１３に２次転写バイアスを印加した際に、第２の２次転写対向ローラ１０ｂと２次転写ローラ１３との圧接部、即ち、２次転写ニップ部Ｎの下流側にて転写電界が最大となるように構成されている。
【００４５】
更に、本実施の形態では、図２に示すように第２の２次転写対向ローラ１０ｂの直径ｄは、２次転写ローラ１３の直径Ｄに比べて小径となるように形成されており、２次転写ニップ部Ｎの最下流側における中間転写ベルト８の曲率を高めることによって、２次転写ニップ部Ｎを抜けた転写材Ｐと中間転写ベルト８との分離性の向上を図ることができる。なお、第１の２次転写対向ローラ１０ａの直径も、第２の２次転写対向ローラ１０ｂの直径と略同じである。
【００４６】
また、第２の２次転写対向ローラ１０ｂの２次転写ニップ部Ｎと反対側の表面には、回転自在に支持されたバックアップローラ１０ｃが圧接するように配設されている。バックアップローラ１０ｃが２次転写ニップ部Ｎと反対側から第２の２次転写対向ローラ１０ｂの周面を押圧することにより、第２の２次転写対向ローラ１０ｂの軸方向に沿った撓みが抑制されることによって、軸方向にわたって２次転写ローラ１３との圧接力が均一化され、転写むらの発生を防止することができる。
【００４７】
本実施の形態に係る画像形成装置の２次転写ニップ部Ｎ近傍における中間転写ベルト８に対する第１、第２の２次転写対向ローラ１０ａ，１０ｂ、２次転写ローラ１３は上記のように構成されており、２次転写ニップ部Ｎにおいて、第１、第２の２次転写対向ローラ１０ａ，１０ｂによって中間転写ベルト８が２次転写ローラ１３表面に巻き付くように圧接することによって、２次転写ニップ部Ｎにおける中間転写ベルト８上のトナー像と転写材Ｐとの密着度が高まり、更に、この状態で転写電界が２次転写ニップ部Ｎの下流側にて最大に作用するため、高い転写効率を得ることができた。
【００４８】
また、上記した本実施の形態においては、２次転写ニップ部Ｎの上流側にて過度の転写電界を発生させることなく転写材Ｐが２次転写ニップ部Ｎに進入されることにより、中間転写ベルト８上のトナー像が、２次転写ニップ部Ｎに到達しない２次転写ニップ部Ｎの上流側にて転写材Ｐに引き寄せられるなどの飛び散りによる画像欠陥を発生させることなく、２次転写ニップ部Ｎで中間転写ベルト８上のトナー像を転写材Ｐへ確実に密着させ、２次転写ニップ部Ｎの下流側にて中間転写ベルト８上のトナー像を転写材Ｐへ確実に転写することができた。
【００４９】
〈実施の形態２〉
実施の形態１では、第２の２次転写対向ローラ１０ｂの２次転写ニップ部Ｎと反対側の表面にバックアップローラ１０ｃを圧接するように配設した構成であったが、本実施の形態では、図３に示すように、第１の２次転写対向ローラ１０ａ側にも２次転写ニップ部Ｎと反対側の表面にバックアップローラ１０ｄを圧接するように配設した構成である。他の構成は実施の形態１の画像形成装置と同様であり、本実施の形態ではそれらの説明は省略する。
【００５０】
このように本実施の形態では、実施の形態１で得られる効果以外に、２次転写ニップ部Ｎにおける中間転写ベルト８上のトナー像と転写材Ｐとの密着度をさらに高めることができ、より高い転写効率を得ることができる。
【００５１】
【発明の効果】
以上説明したように請求項１に記載の発明によれば、中間転写ベルト８を張架する複数のローラ部材のうち、少なくとも２つのローラ部材を中間転写体を介して２次転写部材と圧接するように配置し、中間転写体の２つのローラ部材間で張架されている現像剤像担持面側の部分が２次転写部材表面に巻き付くようにして２次転写部を形成したことにより、２次転写部における中間転写体上の現像剤像と転写材との密着度が高まり、高い転写効率を得ることができる。
【００５２】
また、請求項３に記載の発明は、２次転写部における転写電界を、２次転写部に対して中間転写体の移動方向下流側に位置する２つのローラ部材のうちの一方のローラ部材と中間転写体を介して２次転写部材が当接する近傍で最大となるようにしたことにより、中間転写体から転写材への転写過程において異常画像を発生することなく、良好な転写性を得ることができる。
【図面の簡単な説明】
【図１】本発明の実施の形態１、２に係る画像形成装置を示す概略構成図。
【図２】本発明の実施の形態１における２次転写ニップ部近傍を示す図。
【図３】本発明の実施の形態２における２次転写ニップ部近傍を示す図。
【図４】従来例における画像形成装置を示す概略構成図。
【符号の説明】
１Ｙ、１Ｍ、１Ｃ、１Ｋ　　　　画像形成部
２ａ、２ｂ、２ｃ、２ｄ　　　　感光ドラム（像担持体）
３ａ、３ｂ、３ｃ、３ｄ　　　　帯電ローラ
４ａ、４ｂ、４ｃ、４ｄ　　　　現像装置
５ａ、５ｂ、５ｃ、５ｄ　　　　転写ローラ
６ａ、６ｂ、６ｃ、６ｄ　　　　露光装置
７ａ、７ｂ、７ｃ、７ｄ　　　　ドラムクリーニング装置
８　　　　中間転写ベルト（中間転写体）
９　　　　駆動ローラ
１０ａ　　第１の２次転写対向ローラ（ローラ部材）
１０ｂ　　第２の２次転写対向ローラ（ローラ部材）
１０ｃ、１０ｄ　　　　バックアップローラ（ローラ部材）
１１　　　テンションローラ
１２　　　ベルトクリーニング装置
１３　　　２次転写ローラ（２次転写部材）
１４　　　２次転写バイアス電源
１５　　　搬送ベルト
１６　　　定着装置
１６ａ　　定着ローラ
１６ｂ　　加圧ローラ
Ｎ　　　　２次転写ニップ部（２次転写部）[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an image forming apparatus such as a copier, a printer, a facsimile, etc., which forms an image by an electrophotographic method or the like, and more particularly to a primary transfer of a developer image carried on an image carrier onto a belt-shaped intermediate transfer body. Then, the present invention relates to an image forming apparatus for forming an image by secondary-transferring the toner image transferred to the intermediate transfer member to a transfer material by a secondary transfer member.
[0002]
[Prior art]
In recent years, as an electrophotographic multi-color or full-color image forming apparatus, a plurality of photosensitive drums are arranged in accordance with each color, and a toner image of each color formed on each photosensitive drum is used as an intermediate transfer member. 2. Description of the Related Art An image forming apparatus (such as a copying machine or a laser beam printer) for sequentially forming a color image by superimposing on an intermediate transfer belt has been put to practical use.
[0003]
FIG. 4 is a schematic configuration diagram showing a conventional image forming apparatus having an intermediate transfer member.
[0004]
In this image forming apparatus, when an image forming operation start signal is issued, each of the photosensitive drums 2a, 2b, 2c, and 2d of each of the image forming units 1Y, 1M, 1C, and 1K, which is driven to rotate at a predetermined process speed, respectively. It is uniformly charged by the charging rollers 3a, 3b, 3c, 3d. Each of the exposure devices 6a, 6b, 6c, and 6d modulates the color-separated time-series electric digital pixel signals corresponding to the input image information, and charges the modulated laser light, which is a light signal. Each of the photosensitive drums 2a, 2b, 2c, and 2d is scanned and exposed to form an electrostatic latent image.
[0005]
First, a yellow toner is made to adhere to the electrostatic latent image formed on the photosensitive drum 2a by the developing device 4a to which a developing bias having the same polarity as the charging polarity of the photosensitive drum 2a is applied, so that a visible toner image is obtained. Image. This yellow toner image is transferred (rotated) by a primary transfer roller 5a to which a primary transfer bias (a voltage having a polarity opposite to that of the toner) is applied in an intermediate transfer member as an intermediate transfer member. The primary transfer is performed on the belt 8. The intermediate transfer belt 8 is stretched by a driving roller 9, a secondary transfer opposing roller 10, and a tension roller 11, and is moved (rotated) in the direction of the arrow by the rotation of the driving roller 9.
[0006]
The intermediate transfer belt 8 to which the yellow toner image has been transferred is moved to the image forming section 1M side by driving of the driving roller 9. In the image forming section 1M, the magenta toner image similarly formed on the photosensitive drum 2b is similarly transferred to the primary transfer section by applying a primary transfer bias (a voltage having a polarity opposite to that of the toner) to the primary transfer section. The transfer roller 5b superimposes and transfers the toner image on the yellow toner image on the intermediate transfer belt 8.
[0007]
Thereafter, the cyan and black toner images formed by the photosensitive drums 2c and 2d of the image forming units 1C and 1K are respectively transferred onto the yellow and magenta toner images superimposedly transferred on the intermediate transfer belt 8 in the same manner. A primary transfer roller (5c, 5d) to which a primary transfer bias (a voltage having a polarity opposite to that of the toner) is applied in the secondary transfer portion, and the images are sequentially superimposed and transferred to form a full-color toner image on the intermediate transfer belt 8. .
[0008]
Then, the cassette (not shown) is synchronized with the timing at which the leading end of the full-color toner image on the intermediate transfer belt 8 is moved to the secondary transfer nip N between the secondary transfer roller 13 and the secondary transfer opposing roller 10. ) Is transferred to the secondary transfer nip N, and a secondary transfer bias (a voltage having a polarity opposite to that of the toner) from the secondary transfer bias power supply 14 is applied to the transfer material P. The full-color toner image is collectively transferred (secondarily transferred) by the applied secondary transfer roller 13.
[0009]
Then, the transfer material P on which the full-color toner image is formed is conveyed to the fixing device 16 by the conveyance belt 15, and the full-color toner image is heated at a fixing nip portion between the fixing roller 16a and the pressure roller 16b of the fixing device 16, After being pressurized and thermally fixed on the surface of the transfer material P, it is discharged to the outside, and a series of image forming operations is completed.
[0010]
At the time of the primary transfer, the primary transfer residual toner remaining on each of the photosensitive drums 2a, 2b, 2c and 2d is removed and collected by the drum cleaning devices 7a, 7b, 7c and 7d. . Further, the secondary transfer residual toner remaining on the surface of the intermediate transfer belt 8 after the secondary transfer is removed and collected by the belt cleaning device 12.
[0011]
[Problems to be solved by the invention]
In the image forming apparatus shown in FIG. 4 in the conventional example described above, the secondary transfer roller 13 and the secondary transfer opposing roller 10 of the rollers on which the intermediate transfer belt 8 is stretched are pressed through the intermediate transfer belt 8. The intermediate transfer belt 8 and the transfer material P are nipped and conveyed in the secondary transfer nip N so that the secondary transfer nip N is applied to the secondary transfer roller 13. A full-color toner image on the intermediate transfer belt 8 is collectively transferred onto the transfer material P by the transfer electric field generated by the application of the next transfer bias and the pressing force acting between the secondary transfer opposing roller 10 and the secondary transfer roller 13. Transfer (secondary transfer) is performed.
[0012]
By the way, in the above-described conventional image forming apparatus, since the secondary transfer nip N is formed by pressing the secondary transfer opposing roller 10 and the secondary transfer roller 13 against each other, the secondary transfer nip N is formed. When the width of the transfer area in the transfer direction of N is small and the transfer speed of the transfer material is high, or depending on the type of the transfer material, a transfer failure may occur.
[0013]
In order to prevent such a problem, for example, as disclosed in Japanese Patent Application Laid-Open No. 2001-166611, an intermediate transfer member (intermediate transfer member) in which a secondary transfer nip portion is stretched between two support rollers. The secondary transfer roller is formed by winding a secondary transfer roller around a stretched portion of the belt, and one of the support rollers, for example, one of the support rollers disposed on the upstream side in the moving direction of the intermediate transfer member and the secondary transfer roller Has been proposed in which a transfer electric field is applied to a secondary transfer nip by press-contacting such that the press-contact force becomes maximum.
[0014]
However, in the image forming apparatus having such a configuration, the transfer bias voltage is applied to the secondary transfer roller so that the pressing force is maximized on the upstream side in the moving direction of the intermediate transfer body, and the transfer bias voltage is applied on the upstream side in the moving direction of the intermediate transfer body. In order to generate the transfer electric field around the pressure contact portion so that the transfer electric field is maximized, the transfer material that is going to enter the secondary transfer nip portion is borne by the transfer electric field generated near the one support roller, and There is a possibility that an image defect may occur due to scattering such as the toner image being attracted to the transfer material on the upstream side where the toner image does not reach the secondary transfer nip portion.
[0015]
In view of the above, the present invention appropriately performs the pressing of the secondary transfer roller against the intermediate transfer member and the application of the transfer bias to the secondary transfer nip portion, and the image defect due to scattering when transferring the toner image from the intermediate transfer member to the transfer member. It is an object of the present invention to provide an image forming apparatus capable of preventing occurrence of toner image and obtaining good transferability of a toner image from an intermediate transfer body to a transfer material at a secondary transfer nip portion.
[0016]
[Means for Solving the Problems]
In order to achieve the above object, the present invention provides an image carrier on which a developer image is carried, and an endless end which abuts the image carrier at a primary transfer portion and is movably stretched by a plurality of roller members. A belt-shaped intermediate transfer member, and a developer image that is brought into contact with the image carrier at the primary transfer section via the intermediate transfer member and is applied on the image carrier by application of a primary transfer bias. A primary transfer member for primary transfer onto the intermediate transfer member, and a secondary transfer of a developer image primarily transferred onto the intermediate transfer member by application of a secondary transfer bias at a secondary transfer portion to a transfer material And a rotatable secondary transfer member, wherein at least two of the plurality of roller members are arranged to be in pressure contact with the secondary transfer member via the intermediate transfer member. Being stretched between the two roller members of the intermediate transfer member. By which are part of the developer image carrying surface side is wound on the secondary transfer member surface is characterized in that the secondary transfer portion is formed.
[0017]
Further, the secondary transfer member is a roller member made of a conductive member having elasticity.
[0018]
Further, when a secondary transfer bias is applied to the secondary transfer member at the time of secondary transfer, the transfer electric field in the secondary transfer portion is shifted downstream of the intermediate transfer member in the moving direction of the intermediate transfer member with respect to the secondary transfer portion. It is characterized in that the maximum value is obtained near one of the two roller members located in contact with the secondary transfer member via the intermediate transfer member.
[0019]
Further, among the two roller members, at least one of the roller members located on the downstream side in the moving direction of the intermediate transfer member with respect to the secondary transfer portion has a smaller diameter than the diameter of the secondary transfer member. It is characterized by having.
[0020]
Further, of the two roller members, at least a surface of one of the roller members located on the downstream side in the moving direction of the intermediate transfer member with respect to the secondary transfer portion is opposite to the secondary transfer portion. A roller member for pressing one roller member against the secondary transfer member via the intermediate transfer member is provided.
[0021]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, the present invention will be described based on the illustrated embodiments.
[0022]
<Embodiment 1>
FIG. 1 is a schematic configuration diagram showing an image forming apparatus according to Embodiment 1 of the present invention (in this embodiment, an image forming apparatus such as an electrophotographic full-color printer). Members having the same functions as those of the conventional image forming apparatus shown in FIG.
[0023]
This image forming apparatus includes an image forming section 1Y for forming a yellow toner image, an image forming section 1M for forming a magenta toner image, an image forming section 1C for forming a cyan toner image, and a black color image. The image forming unit 1K includes four image forming units (image forming units) for forming the toner images, and these four image forming units are arranged in a line at a predetermined interval.
[0024]
In each of the image forming units 1Y, 1M, 1C, and 1K, photosensitive drums 2a, 2b, 2c, and 2d as image carriers are provided, respectively. Around each photosensitive drum 2a, 2b, 2c, 2d, a charging roller 3a, 3b, 3c, 3d, a developing device 4a, 4b, 4c, 4d, a transfer roller 5a, 5b, 5c, 5d, a drum cleaning device 7a, Exposure devices 6a, 6b, 6c, and 6d are provided above the charging rollers 3a, 3b, 3c, and 3d and the developing devices 4a, 4b, 4c, and 4d, respectively. I have.
[0025]
In the present embodiment, the photosensitive drums 2a, 2b, 2c, and 2d are organic photosensitive drums that are negatively charged, have an OPC photosensitive layer on a drum substrate such as aluminum, and are driven by a driving device (not shown) in the direction of the arrow (not shown). Each of them is rotationally driven at a predetermined peripheral speed (process speed) in a counterclockwise direction.
[0026]
The charging rollers 3a, 3b, 3c, and 3d as contact charging means contact the photosensitive drums 2a, 2b, 2c, and 2d, respectively, with a predetermined pressure contact force, and each of them is charged by a charging bias applied from a charging bias power supply (not shown). The surfaces of the photosensitive drums 2a, 2b, 2c and 2d are uniformly charged to a predetermined negative potential.
[0027]
The developing devices 4a, 4b, 4c, and 4d are of the two-component developing type in the present embodiment, and are formed on the respective photosensitive drums 2a, 2b, 2c, and 2d by a developing bias applied from a developing bias power supply (not shown). The toner is attached to the formed electrostatic latent image, and the image is reversely developed as a toner image. The developing devices 4a, 4b, 4c, and 4d store yellow toner, cyan toner, magenta toner, and black toner, respectively.
[0028]
The transfer rollers 5a, 5b, 5c, and 5d as contact transfer units contact the surfaces of the photosensitive drums 2a, 2b, 2c, and 2d with a predetermined pressing force via an endless belt-shaped intermediate transfer belt 8 as an intermediate transfer body. Then, a primary transfer bias having a polarity opposite to that of the toner applied from each primary transfer bias power source (not shown) causes a transfer between the photosensitive drums 2a, 2b, 2c, 2d and the transfer rollers 5a, 5b, 5c, 5d. In each primary transfer unit, the toner images of each color on the surface of each of the photosensitive drums 2a, 2b, 2c, and 2d are sequentially superimposed on the moving intermediate transfer belt 8 and transferred (primary transfer).
[0029]
Each of the exposure devices 6a, 6b, 6c, and 6d receives a corresponding one of the photosensitive drums 2a, 2b, 2c, and 2C by using a laser beam modulated according to a time-series electric digital pixel signal of image information input from a host computer (not shown). By performing image exposure on the 2d surface, an electrostatic latent image corresponding to the image information is formed on the surface of each of the photosensitive drums 2a, 2b, 2c, 2d charged by each of the charging rollers 3a, 3b, 3c, 3d.
[0030]
The intermediate transfer belt 8 is stretched by a driving roller 9, two first and second secondary transfer opposing rollers 10a and 10b, and a tension roller 11, and the rotation of the driving roller 9 causes the photosensitive drums 2a and 2b to rotate. , 2c and 2d are moved (rotated) in the direction of the arrow in synchronization with the rotation. The intermediate transfer belt 8 is made of a urethane resin, a fluorine resin, a nylon resin, a polyimide resin, an elastic material such as silicone rubber or hydrin rubber, or a material obtained by dispersing carbon or conductive powder in these materials and adjusting the resistance. Etc. can be used.
[0031]
The first and second secondary transfer facing rollers 10a and 10b are in contact with the secondary transfer roller 13 via the intermediate transfer belt 8 to form a secondary transfer nip N. Further, the secondary transfer opposing roller 10b is pressed against the secondary transfer roller 13 via the intermediate transfer belt 8 by the backup roller 10c that is in pressure contact with the secondary transfer opposing roller 10b (the intermediate transfer near the secondary transfer nip N, which is a feature of the present invention). The configuration of the two secondary transfer opposing rollers 10a and 10b for the transfer belt 8 and the configuration of the secondary transfer roller 13 will be described later.
[0032]
Next, an image forming operation performed by the image forming apparatus according to the present embodiment will be described.
[0033]
When the image forming operation start signal is issued, the photosensitive drums 2a, 2b, 2c, and 2d of the image forming units 1Y, 1M, 1C, and 1K, which are driven to rotate at a predetermined process speed, respectively charge the charging rollers 3a, 3b, and 3c. In this embodiment, the electrode is uniformly charged to a predetermined negative potential by 3d. The exposure devices 6a, 6b, 6c, and 6d convert the color-separated image signals input from the host computer (not shown) into optical signals, respectively, and are charged with the laser light as the converted optical signals. Each of the photosensitive drums 2a, 2b, 2c, and 2d is scanned and exposed to form an electrostatic latent image.
[0034]
First, yellow toner is adhered to the electrostatic latent image formed on the photosensitive drum 2a by the developing device 4a to which a developing bias having the same polarity as the charging polarity (negative polarity) of the photosensitive drum 2a is applied, and reverse developing is performed. And a visible image is formed as a toner image. Then, the yellow toner image is transferred (rotated) on the intermediate transfer belt 8 by the primary transfer roller 5a to which a primary transfer bias is applied from a transfer bias power supply (not shown) at the primary transfer portion. First transfer.
[0035]
The intermediate transfer belt 8 to which the yellow toner image has been transferred is moved to the image forming section 1M side by driving of the driving roller 9. In the image forming section 1M, the magenta toner image formed on the photosensitive drum 2b in the same manner is applied to the primary transfer section by applying a primary transfer bias from a transfer bias power supply (not shown) to the primary transfer section. The transfer roller 5b superimposes and transfers the toner image on the yellow toner image on the intermediate transfer belt 8.
[0036]
Thereafter, the cyan and black toner images formed by the photosensitive drums 2c and 2d of the image forming units 1C and 1K are respectively transferred onto the yellow and magenta toner images superimposedly transferred on the intermediate transfer belt 8 in the same manner. The primary transfer rollers 5c and 5d to which primary transfer biases are applied from respective transfer bias power sources (not shown) at the secondary transfer unit are sequentially superimposed and transferred to form a full-color toner image on the intermediate transfer belt 8. I do.
[0037]
Then, in accordance with the timing at which the leading end of the full-color toner image on the intermediate transfer belt 8 is moved to the secondary transfer nip N between the secondary transfer roller 13 and the two secondary transfer opposed rollers 10a and 10b, The transferred transfer material P such as paper is transferred to the secondary transfer nip N, and transferred by the secondary transfer roller 13 to which a secondary transfer bias having a polarity opposite to that of the toner is applied from a secondary transfer bias power supply 14. A full-color toner image is collectively transferred (secondarily transferred) onto the material P.
[0038]
Then, the transfer material P on which the full-color toner image is formed is transported to the fixing device 16 via the transport belt 15, and the full-color toner image is formed at the fixing nip portion between the fixing roller 16a and the pressure roller 16b of the fixing device 16. After heating and pressurizing to thermally fix the surface of the transfer material P, the sheet is discharged to the outside, and a series of image forming operations is completed.
[0039]
In the above-described primary transfer, the transfer residual toner remaining on the photosensitive drums 2a, 2b, 2c, and 2d is removed and collected by the drum cleaning devices 7a, 7b, 7c, and 7d, respectively. Further, residual toner remaining on the surface of the intermediate transfer belt 8 after the secondary transfer is removed and collected by the belt cleaning device 12.
[0040]
Next, the configuration of the first and second secondary transfer opposing rollers 10a and 10b and the secondary transfer roller 13 for the intermediate transfer belt 8 near the secondary transfer nip N will be described.
[0041]
As shown in FIGS. 1 and 2, the first secondary transfer opposing roller 10 a is disposed on the upstream side in the moving direction of the intermediate transfer belt 8 with respect to the secondary transfer nip portion N, and The roller 10b is disposed downstream of the secondary transfer facing roller 10a with respect to the moving direction of the intermediate transfer belt 8, and the first and second secondary transfer facing rollers 10a and 10b are rotatably supported. I have.
[0042]
The surface of the secondary transfer roller 13 is formed of an elastic conductive member (resistance value of 10 ⁶ to 10 ⁷ Ω), and the first and second secondary transfer opposed members are provided via the intermediate transfer belt 8. The rollers 10a and 10b are disposed so as to be pressed against the rollers 10a and 10b with a predetermined pressure. As a result, the portion of the intermediate transfer belt 8 stretched between the first secondary transfer facing roller 10a and the second secondary transfer facing roller 10b on the toner image bearing surface side is moved to the secondary transfer roller 13 While being wound around the surface, the first and second secondary transfer opposing rollers 10a and 10b and the secondary transfer roller 13 are opposed and pressed against each other via the intermediate transfer belt 8 to form a secondary transfer nip portion N. You. Further, the secondary transfer roller 13 is disposed so as to be able to come into contact with and separate from the intermediate transfer belt 8, and the first and second secondary transfer opposed rollers 10 a via the intermediate transfer belt 8 during the secondary transfer. , 10b.
[0043]
Note that, in the area of the secondary transfer nip portion N in the present embodiment, the first secondary transfer opposing roller 10a and the secondary transfer roller 13 on the surface of the secondary transfer roller 13 move along the moving direction of the intermediate transfer belt 8. The portion where the second secondary transfer facing roller 10b and the secondary transfer roller 13 abut via the intermediate transfer belt 8 from the portion where the intermediate transfer belt 8 abuts.
[0044]
In the first embodiment of the present invention, when the secondary transfer bias is applied from the secondary transfer bias power supply 14 to the secondary transfer roller 13, the second secondary transfer opposing rollers 10b and 2 The transfer electric field is maximized at a pressure contact portion with the next transfer roller 13, that is, at a downstream side of the secondary transfer nip portion N.
[0045]
Further, in the present embodiment, as shown in FIG. 2, the diameter d of the second secondary transfer opposing roller 10b is formed to be smaller than the diameter D of the secondary transfer roller 13; By increasing the curvature of the intermediate transfer belt 8 at the most downstream side of the next transfer nip portion N, it is possible to improve the separability between the transfer material P having passed through the secondary transfer nip portion N and the intermediate transfer belt 8. The diameter of the first secondary transfer facing roller 10a is also substantially the same as the diameter of the second secondary transfer facing roller 10b.
[0046]
A backup roller 10c, which is rotatably supported, is disposed on the surface of the second secondary transfer opposed roller 10b opposite to the secondary transfer nip portion N so as to be pressed against the surface. The backup roller 10c presses the peripheral surface of the second secondary transfer opposed roller 10b from the side opposite to the secondary transfer nip N, thereby suppressing the bending of the second secondary transfer opposed roller 10b along the axial direction. By doing so, the pressure contact force with the secondary transfer roller 13 is made uniform in the axial direction, and the occurrence of transfer unevenness can be prevented.
[0047]
The first and second secondary transfer opposed rollers 10a, 10b and the secondary transfer roller 13 for the intermediate transfer belt 8 near the secondary transfer nip N in the image forming apparatus according to the present embodiment are configured as described above. In the secondary transfer nip portion N, the intermediate transfer belt 8 is pressed against the surface of the secondary transfer roller 13 by the first and second secondary transfer opposing rollers 10a and 10b so that the secondary transfer is performed. Since the degree of adhesion between the toner image on the intermediate transfer belt 8 and the transfer material P at the nip N is increased, and in this state, the transfer electric field acts maximally on the downstream side of the secondary transfer nip N, so that high transfer is achieved. Efficiency could be obtained.
[0048]
In the above-described embodiment, the transfer material P enters the secondary transfer nip N without generating an excessive transfer electric field on the upstream side of the secondary transfer nip N, whereby the intermediate transfer is performed. The secondary transfer nip is performed without causing image defects due to scattering such as the toner image on the belt 8 being drawn to the transfer material P on the upstream side of the secondary transfer nip N that does not reach the secondary transfer nip N. The toner image on the intermediate transfer belt 8 is securely adhered to the transfer material P at the portion N, and the toner image on the intermediate transfer belt 8 is reliably transferred to the transfer material P downstream of the secondary transfer nip portion N. Was completed.
[0049]
<Embodiment 2>
In the first embodiment, the backup roller 10c is disposed so as to be in pressure contact with the surface of the second secondary transfer opposing roller 10b on the side opposite to the secondary transfer nip N. However, in the present embodiment, As shown in FIG. 3, a backup roller 10d is also provided on the first secondary transfer opposing roller 10a side so as to be in pressure contact with the surface opposite to the secondary transfer nip portion N. Other configurations are the same as those of the image forming apparatus according to the first embodiment, and a description thereof will be omitted in the present embodiment.
[0050]
As described above, in the present embodiment, in addition to the effects obtained in the first embodiment, the degree of adhesion between the toner image on the intermediate transfer belt 8 and the transfer material P in the secondary transfer nip portion N can be further increased. Higher transfer efficiency can be obtained.
[0051]
【The invention's effect】
As described above, according to the first aspect of the present invention, among the plurality of roller members that stretch the intermediate transfer belt 8, at least two roller members are pressed against the secondary transfer member via the intermediate transfer member. And the secondary transfer portion is formed such that the portion on the developer image carrying surface side stretched between the two roller members of the intermediate transfer member is wound around the secondary transfer member surface. The degree of adhesion between the developer image on the intermediate transfer member and the transfer material in the secondary transfer portion is increased, and high transfer efficiency can be obtained.
[0052]
According to a third aspect of the present invention, the transfer electric field in the secondary transfer unit is controlled by one of the two roller members located downstream of the secondary transfer unit in the moving direction of the intermediate transfer member. Good transfer performance is obtained without causing an abnormal image in the process of transfer from the intermediate transfer member to the transfer material by having the maximum value near the contact of the secondary transfer member via the intermediate transfer member. Can be.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram showing an image forming apparatus according to Embodiments 1 and 2 of the present invention.
FIG. 2 is a diagram showing the vicinity of a secondary transfer nip according to the first embodiment of the present invention.
FIG. 3 is a diagram showing the vicinity of a secondary transfer nip according to a second embodiment of the present invention.
FIG. 4 is a schematic configuration diagram showing an image forming apparatus in a conventional example.
[Explanation of symbols]
1Y, 1M, 1C, 1K Image forming units 2a, 2b, 2c, 2d Photosensitive drum (image carrier)
3a, 3b, 3c, 3d Charging rollers 4a, 4b, 4c, 4d Developing devices 5a, 5b, 5c, 5d Transfer rollers 6a, 6b, 6c, 6d Exposure devices 7a, 7b, 7c, 7d Drum cleaning device 8 Intermediate transfer belt (Intermediate transfer member)
9 drive roller 10a first secondary transfer facing roller (roller member)
10b Second secondary transfer facing roller (roller member)
10c, 10d Backup roller (roller member)
11 tension roller 12 belt cleaning device 13 secondary transfer roller (secondary transfer member)
14 Secondary transfer bias power supply 15 Conveyor belt 16 Fixing device 16a Fixing roller 16b Pressure roller N Secondary transfer nip (secondary transfer)

Claims

An image carrier on which a developer image is carried, an endless belt-shaped intermediate transfer body that abuts on the image carrier at a primary transfer portion and is movably stretched by a plurality of roller members; A transfer unit that abuts on the image carrier via the intermediate transfer body and primary-transfers a developer image carried on the image carrier by application of a primary transfer bias onto the intermediate transfer body; A secondary transfer member, and a rotatable secondary transfer member that secondary-transfers a developer image primarily transferred onto the intermediate transfer member by applying a secondary transfer bias in a secondary transfer unit to a transfer material. In the image forming apparatus provided with
At least two of the plurality of roller members are disposed so as to be in pressure contact with the secondary transfer member via the intermediate transfer member, and are stretched between the two roller members of the intermediate transfer member. The secondary transfer portion is formed by winding a portion of the developer image carrying surface side around the surface of the secondary transfer member.
An image forming apparatus comprising:

The secondary transfer member is a roller member made of a conductive member having elasticity,
The image forming apparatus according to claim 1, wherein:

When a secondary transfer bias is applied to the secondary transfer member at the time of secondary transfer, the transfer electric field in the secondary transfer portion is located on the downstream side in the moving direction of the intermediate transfer member with respect to the secondary transfer portion. One of the two roller members and the intermediate transfer member via the intermediate transfer member so that the maximum is in the vicinity of the secondary transfer member abuts,
The image forming apparatus according to claim 1, wherein:

Among the two roller members, at least one of the roller members located on the downstream side in the moving direction of the intermediate transfer member with respect to the secondary transfer portion has a smaller diameter than the diameter of the secondary transfer member.
The image forming apparatus according to claim 2, wherein:

Of the two roller members, at least one of the two roller members located on the downstream side in the moving direction of the intermediate transfer member with respect to the secondary transfer portion, on the surface opposite to the secondary transfer portion, A roller member for pressing a roller member against the secondary transfer member via the intermediate transfer member was disposed,
The image forming apparatus according to any one of claims 2 to 4, wherein: