JP3826594B2 - Image forming apparatus - Google Patents

Image forming apparatus Download PDF

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Publication number
JP3826594B2
JP3826594B2 JP36948598A JP36948598A JP3826594B2 JP 3826594 B2 JP3826594 B2 JP 3826594B2 JP 36948598 A JP36948598 A JP 36948598A JP 36948598 A JP36948598 A JP 36948598A JP 3826594 B2 JP3826594 B2 JP 3826594B2
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image
transfer material
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intermediate transfer
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JP2000194218A (en
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邦男 重田
洋太郎 佐藤
哲 羽根田
久喜 永瀬
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Konica Minolta Inc
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Konica Minolta Inc
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Description

【0001】
【発明の属する技術分野】
本発明は、像担持体の周辺に帯電手段と画像書込手段と現像手段とを配置して像担持体に形成したトナー像を転写材上に転写、定着する複写機、プリンタ、FAX等の電子写真方式の画像形成装置に関し、特に転写材の両面に画像を形成することができる画像形成装置に関する。
【0002】
【従来の技術】
従来、両面画像形成においては、像担持体上に形成した一方の面の画像を転写材上に転写、定着し、これを一旦両面反転給送装置に収納し、再び像担持体上に形成された画像とタイミングを合わせて両面反転給送装置より転写材を給送し、転写材上に他方の面の画像を転写、定着する方法がとられている。
【0003】
この両面画像形成装置では、上記の如く、両面反転給送装置への給送や定着装置を2度通す等の転写材の搬送が行われるので、転写材搬送の信頼性が低く、転写材のジャムやしわ等を引き起こす原因となっていた。
【0004】
これに対し、特公昭49−37538号公報、同54−28740号公報、特開平1−44457号公報や同4−214576号公報等により、像担持体と中間転写体とを用いて転写材の両面にトナー像を形成後、1回で定着を行うものが提案されている。
【0005】
また、本願発明者らは、感光体ドラム(像担持体)の周りに帯電手段、画像書込手段、現像手段等よりなるトナー像形成手段を複数組配置し、感光体ドラム上に形成した重ね合わせカラートナー像を一旦ベルト状の中間転写体に一括して転写した後、再度感光体ドラム上に重ね合わせカラートナー像を形成し、感光体ドラム上のトナー像及び中間転写体上のトナー像とタイミングを合わせて給送され、中間転写体により搬送される転写材の両面にそれぞれ、感光体ドラム上のトナー像を表面画像として転写し、また中間転写体上のトナー像を裏面画像として転写した後、中間転写体から転写材を分離し、転写材上のトナー像を定着して両面カラー画像を形成する画像形成装置や画像形成方法を特開平9−258492号公報や特開平9−258516号公報にて開示した。
【0006】
【発明が解決しようとする課題】
上記の如きベルト状の中間転写体を用いて転写材の両面に画像を形成する両面画像形成装置において、一対の定着部材(定着ローラ対)を用いて定着手段を構成し転写材上の表裏のトナー像を定着しているが、定着部材の抵抗が低かったり、定着部材が接地されたりしていると、定着手段を通して転写材から電荷がリークされ、転写材の裏面へのトナー像の転写が良好に行われないという問題が起こる。また、転写材が定着部材へと進入する際に、定着部材上に転写材上のトナーの鏡像電荷が発生し、鏡像電荷により転写材上の表裏のトナー像が乱され、良好な両面画像が形成されないという問題が起こる。
【0007】
また定着部材が絶縁部材で形成されている場合も、定着部材に電荷が蓄積され、蓄積された電荷により転写材上の表裏のトナー像が乱され、良好な両面画像が形成されないという問題が起こる。
【0008】
本発明は上記の問題点を解決し、転写材からのリークを防止して転写材裏面へのトナー像の転写を良好に行うと共に、定着手段による表裏のトナー像の乱れを防止し、良好な両面画像を形成する画像形成装置を提供することを目的とする。
【0009】
【課題を解決するための手段】
上記目的は、像担持体と、該像担持体上にトナー像を形成する手段と、前記像担持体上のトナー像が転写され、転写された該トナー像を表面に担持するとともに、転写材を支持搬送する無端ベルト状の中間転写体と、前記像担持体上のトナー像を前記中間転写体に転写する手段と、前記像担持体上のトナー像を前記転写材の表面に転写する手段と、前記中間転写体上のトナー像を前記転写材の裏面に転写する手段と、対となって回動する定着部材により前記転写材を挟持搬送して前記転写材の両面に転写されたトナー像を定着する手段とを有する画像形成装置において、前記転写材の表面側および裏面側の定着部材にはそれぞれ体積抵抗率が10 10 〜10 16 Ω・cmである高抵抗層けると共に、両面にトナー像が転写された前記転写材と同極性の電圧が印加され、前記転写材の表面側の定着部材に印加される電圧の絶対値は、前記転写材の裏面側の定着部材に印加される電圧の絶対値より高く設定されていることを特徴とする画像形成装置によって達成される(第1の発明)。
【0010】
また、上記目的は、第1の像担持体と、第2の像担持体と、前記第1の像担持体上にトナー像を形成する手段と、前記第2の像担持体上にトナー像を形成する手段と、前記第1の像担持体上のトナー像が転写され、転写された該トナー像を表面に担持するとともに、転写材を支持搬送する無端ベルト状の中間転写体と、前記第1の像担持体上のトナー像を前記中間転写体に転写する手段と、前記第2の像担持体上のトナー像を前記転写材の表面に転写する手段と、前記中間転写体上のトナー像を前記転写材の裏面に転写する手段と、対となって回動する定着部材により前記転写材を挟持搬送して前記転写材の両面に転写されたトナー像を定着する手段とを有する画像形成装置において、前記転写材の表面側および裏面側の定着部材にはそれぞれ体積抵抗率が10 10 〜10 16 Ω・cmである高抵抗層けると共に、両面にトナー像が転写された前記転写材と同極性の電圧が印加され、前記転写材の表面側の定着部材に印加される電圧の絶対値は、前記転写材の裏面側の定着部材に印加される電圧の絶対値より高く設定されていることを特徴とする画像形成装置によって達成される(第2の発明)。
【0011】
【発明の実施の形態】
以下、本発明の実施の形態を説明する。なお、本欄の記載は請求項の技術的範囲や用語の意義を限定するものではない。また、以下の、本発明の実施の形態における断定的な説明は、ベストモードを示すものであって、本発明の用語の意義や技術的範囲を限定するものではない。なお以下の実施形態の説明において、転写域において像担持体に対向する側の転写材の面を表面、転写材の他方の面すなわち中間転写体に対向する側の転写材の面を裏面といい、転写材の表面に転写される画像を表面画像、転写材の裏面に転写される画像を裏面画像という。
【0012】
本発明にかかわる画像形成装置の一実施形態の画像形成プロセス、各機構について、図1ないし図6を用いて説明する。図1は、本発明にかかわる画像形成装置の一実施形態を示すカラー画像形成装置の断面構成図であり、図2は、図1の像担持体の側断面図であり、図3は、本発明にかかわる画像形成装置におけるトナー像形成状態を示す図であり、図3(A)は、像担持体に形成した裏面画像を中間転写体上に転写するときのトナー像形成状態を示す図であり、図3(B)は、中間転写体上の裏面画像と同期して像担持体に表面画像を形成するときのトナー像形成状態を示す図であり、図3(C)は、転写材上への両面画像形成を示す図であり、図4は、定着手段に用いられる定着部材の構造と転写材上のトナー乱れを防止するための定着部材への電圧印加とを示す図であり、図5は、転写材の両面にトナー像を転写した後の転写材及び転写材上のトナーの荷電状態を示す図であり、図6は、転写材上のトナー乱れを防止する他の例を示す図である。
【0013】
図1において、10は像担持体である感光体ドラム、11は各色毎の帯電手段であるスコロトロン帯電器、12は各色毎の画像書込手段である露光光学系、13は各色毎の現像手段である現像器、14aは中間転写体である中間転写ベルト、14cは像担持体上のトナー像を中間転写体に転写する手段および像担持体上のトナー像を転写材の表面に転写する手段である転写器、14gは中間転写体上のトナー像を転写材の裏面に転写する手段である裏面転写器、14mは除電手段である除電器、150は転写材帯電手段である紙帯電器、14hは転写材分離手段である紙分離AC除電器、160は爪部材である分離爪210と拍車部材である拍車162とを有する搬送部、17は定着手段である定着装置である。
【0014】
像担持体である感光体ドラム10は、例えば、光学ガラスや透明アクリル樹脂等の透明部材によって形成される円筒状の基体の外周に、透明の導電層、a−Si層あるいは有機感光層(OPC)等の感光層を形成したものであり、導電層を接地した状態で図1の矢印で示す時計方向に、例えば80〜400mm/secの線速度にて回転される。
【0015】
感光体ドラム10は、図2に示すように、それを係合固定する両端部のフランジ部材10A及び10Bに嵌込まれたベアリングB1,B2により、装置本体に架設固定されるドラム軸30に対し軸受けされて回転自在に支持され、フランジ部材10Bの一体とする歯車Gが装置本体側の不図示の駆動歯車と噛合して駆動されることにより所定の方向に定速で回転される。
【0016】
像担持体上にトナー像を形成する手段は、帯電手段であるスコロトロン帯電器11、画像書込手段である露光光学系12及び現像手段である現像器13からなり、これらを1組として、イエロー(Y)、マゼンタ(M)、シアン(C)および黒色(K)の各色の画像形成プロセス用として4組設けられ、図1の矢印にて示す感光体ドラム10の回転方向に対して、Y、M、C、Kの順に配置される。
【0017】
各色毎の帯電手段であるスコロトロン帯電器11は、それぞれ所定の電位に保持された制御グリッドと例えば鋸歯状電極からなる放電電極11aとを有し、感光体ドラム10の感光層と対峙して取付けられ、トナーと同極性のコロナ放電によって帯電作用(本実施形態においてはマイナス帯電)を行い、感光体ドラム10に対し一様な電位を与える。放電電極11aとしては、その他ワイヤ電極や針状電極を用いることも可能である。
【0018】
各色毎の画像書込手段である露光光学系12は、感光体ドラム10上での露光位置が、前述した各色毎のスコロトロン帯電器11に対して感光体ドラム10の回転方向下流側に位置するようにして感光体ドラム10の内部に配置される。図2に示すように、それぞれの露光光学系12は、ドラム軸30と平行に主走査方向に配列された像露光光(画像書込光)の発光素子としてのLED(発光ダイオード)を複数個アレイ状に並べた線状の露光素子12aと、結像素子としての光集束性光伝送体(商品名:セルフォックレンズアレイ)12bと、レンズホルダ12cとで構成される露光用ユニットであり、保持部材20に取付けられる。保持部材20には各色毎の露光光学系12の他に転写同時露光器12d及び一様露光器12eが取付けられ、一体となって感光体ドラム10の透光性の基体内部に収容される。各色毎の露光光学系12は、別体の画像読取装置によって読み取られメモリに記憶された各色の画像データに従って感光体ドラム10の感光層を裏面から画像書込し、感光体ドラム10上に静電潜像を形成する。露光素子12aとしては、LEDの他、FL(蛍光体発光)、EL(エレクトロルミネッセンス)、PL(プラズマ放電)等の複数の発光素子をアレイ状に並べたものを用いることも可能である。像露光光(画像書込光)の発光素子の発光波長は、通常Y、M、Cのトナーに対して透過性の高い780〜900nmの範囲のものが用いられるが、本実施形態においては裏面から画像書込を行う方式であるため、カラートナーに対して透過性を十分に有しないこれより短い400〜780nmの波長でもよい。また、像露光光の80%以上は感光体ドラム10の感光層で吸収されることから、感光体ドラム10表面のカラートナーによる反射や吸収の影響は無視することができる。一般にカラートナーの現像順はトナー像や現像器13への混色の関係からY、M、C、Kの順が好ましい。なお図2において、WAは像露光光の発光素子(LED)よりのリード線である。
【0019】
各色毎の現像手段である現像器13は、感光体ドラム10の周面に対し所定の間隙を保ち、感光体ドラム10の回転方向と順方向に回転する例えば厚み0.5〜1mm、外径15〜25mmの円筒状の非磁性のステンレスあるいはアルミ材で形成された現像スリーブ131と、現像ケーシング138とを有し、現像ケーシング138の内部には、各々イエロー(Y)、マゼンタ(M)、シアン(C)および黒色(K)の一成分或いは二成分現像剤を収容している。それぞれの現像器13は不図示の突き当てコロにより感光体ドラム10と所定の間隙、例えば100〜500μmをあけて非接触に保たれており、現像スリーブ131に対して直流電圧と交流電圧を重畳した現像バイアスを印加することにより、非接触の反転現像を行い、感光体ドラム10上にトナー像を形成する。
【0020】
中間転写体である中間転写ベルト14aは体積抵抗率が108〜1012Ω・cmの無端ベルトであり、例えば変性ポリイミド、熱硬化ポリイミド、エチレンテトラフルオロエチレン共重合体、ポリフッ化ビニリデン、ナイロンアロイ等のエンジニアリングプラスチックに導電材料を分散した厚さ0.1〜1.0mmの半導電性フィルム基体の外側に、好ましくはトナーフィルミング防止層として厚さ5〜50μmのフッ素コーティングを行った2層構成のシームレスベルトである。中間転写ベルト14aの基体としては、この他に、シリコンゴム或いはウレタンゴム等に導電材料を分散した厚さ0.5〜2.0mmの半導電性ゴムベルトを使用することもできる。中間転写ベルト14aは、それぞれローラ部材である駆動ローラ14dとアースローラ14jと従動ローラ14eとガイドローラ14fとテンションローラ14iとに張架され、図1の矢印で示す反時計方向に回転される。ガイドローラ14f、従動ローラ14e、アースローラ14j及び駆動ローラ14dは固定して回転され、テンションローラ14iは不図示のバネ等の弾力により移動可能に支持されて回転される。不図示の駆動モータよりの駆動をうけて駆動ローラ14dが回転され、中間転写ベルト14aを駆動して回転させる。中間転写ベルト14aの回転によりアースローラ14j、従動ローラ14e、ガイドローラ14f及びテンションローラ14iが従動して回転される。回転中の中間転写ベルト14aのベルト弛みがテンションローラ14iにより緊張される。中間転写ベルト14aが従動ローラ14eに張架される位置に転写材である記録紙Pが供給され、中間転写ベルト14aによって搬送される。駆動ローラ14dに張架される中間転写ベルト14aの定着装置17側の端部の曲率部KTにおいて中間転写ベルト14aから記録紙Pが分離される。
【0021】
像担持体上のトナー像を中間転写体に転写する手段および像担持体上のトナー像を転写材の表面に転写する手段としての転写器14cは、中間転写ベルト14aを挟んで感光体ドラム10に対向して設けられるコロナ放電器であり、中間転写ベルト14aと感光体ドラム10との間に転写域14bを形成する。転写器14cにはトナーと反対極性(本実施形態においてはプラス極性)の直流電圧が印加され、感光体ドラム10上のトナー像を中間転写ベルト14a上または転写材である記録紙Pの表面に転写する。
【0022】
中間転写体上のトナー像を転写材の裏面に転写する手段である裏面転写器14gは好ましくはコロナ放電器により構成され、中間転写ベルト14aを挟んで転写器14cと駆動ローラ14dとの間に設けられるアースローラ14jに対向して設けられ、トナーと反対極性(本実施形態においてはプラス極性)の直流電圧が印加され、中間転写ベルト14a上のトナー像を記録紙Pの裏面に転写する。
【0023】
除電手段である除電器14mはコロナ放電器により構成され、中間転写ベルト14aの移動方向に対し、転写器14cの下流側に、転写器14cと並列して設けられ、交流電圧が印加され、転写器14cの電圧印加により荷電される中間転写ベルト14aの電荷を除電する。
【0024】
転写材帯電手段である紙帯電器150は好ましくは鋸歯状電極により構成され、中間転写ベルト14aを挟んで接地された従動ローラ14eと対向して設けられ、トナーと同極性(本実施形態においてはマイナス極性)の直流電圧が印加され、記録紙Pを帯電して中間転写ベルト14aに吸着させる。紙帯電器150としては鋸歯状電極の他に、コロナ放電器や中間転写ベルト14aに当接および当接解除可能な紙帯電ブラシや紙帯電ローラ等を用いることも可能である。
【0025】
転写材分離手段である紙分離AC除電器14hは好ましくはコロナ放電器により構成され、中間転写ベルト14aの定着装置17側端部に中間転写ベルト14aを挟んで接地された駆動ローラ14dに対向して設けられ、後述するように、裏面転写器14gに印加する直流電圧と同極性(本実施形態においてはプラス極性)の直流電圧を重畳した交流電圧が印加され、中間転写ベルト14aにより搬送される記録紙Pを除電して中間転写ベルト14aから分離する。
【0026】
搬送部160は爪部材である分離爪210と拍車部材である拍車162とを有し、中間転写ベルト14aの定着装置17側の端部の曲率部KTと定着装置17との間に設けられる。搬送部160は、定着装置17からの熱により、中間転写ベルト14aが変形したり、中間転写ベルト14aに担持されるトナー像が融着気味になって転写しにくくなったり、中間転写ベルト14a上にトナーが固着したりすることを防止する。
【0027】
爪部材である分離爪210は中間転写ベルト14aの曲率部KTに近接し、中間転写ベルト14aと所定の間隔、好ましくは0.1〜2.0mmを空けて支持軸221に固定されて設けられ、記録紙Pが中間転写ベルト14aより分離される際に、中間転写ベルト14a方向へ曲がって搬送されようとする記録紙Pの先端部を当接させ、記録紙Pの分離を補助する。
【0028】
拍車部材である拍車162は、周面に複数の突起部162aを有し、回転支持軸165を中心として回転自在に設けられる。拍車162は、記録紙Pの裏面側をガイドして記録紙Pを搬送し、両面にトナー像を有する記録紙Pの裏面トナー像の乱れを防止するとともに、記録紙Pの定着装置17への進入方向を一定にしながら記録紙Pを安定して定着装置17へと搬送する。
【0029】
分離爪210と拍車162とは、中間転写ベルト14a上の転写材搬送面或いはその延長面に対し、感光体ドラム10の反対側に配設される。転写材搬送面或いはその延長面の両側に拍車部材である拍車162を設けることも可能である。
【0030】
定着手段である定着装置17は、内部にヒータを有する第1定着ローラ17aと第2定着ローラ17bとの2本のローラ状の定着部材で構成され、第1定着ローラ17aと第2定着ローラ17bとの間のニップ部Tで記録紙Pを挟持搬送し、熱と圧力とをくわえることにより、ニップ部Tを搬送される記録紙P上のトナー像を定着する。第1定着ローラ17aと第2定着ローラ17bとにはそれぞれ、表面層として後段において詳述する高抵抗層173a,173bが設けられ、また後段において詳述するバイアス電圧が印加される。
【0031】
次に画像形成プロセスを説明する。
【0032】
画像記録のスタートにより不図示の感光体駆動モータの始動により感光体ドラム10が図1の矢印で示す時計方向へ回転され、同時にイエロー(Y)のスコロトロン帯電器11の帯電作用により感光体ドラム10に電位の付与が開始される。
【0033】
感光体ドラム10は電位を付与されたあと、Yの露光光学系12によって第1の色信号すなわちYの画像データに対応する電気信号による画像書込が開始され、感光体ドラム10の表面に原稿画像のYの画像に対応する静電潜像が形成される。
【0034】
前記の潜像はYの現像器13により非接触の状態で反転現像され、感光体ドラム10上にイエロー(Y)のトナー像が形成される。
【0035】
次いで感光体ドラム10は、Yのトナー像の上からマゼンタ(M)のスコロトロン帯電器11の帯電作用により電位が付与され、Mの露光光学系12によって第2の色信号すなわちMの画像データに対応する電気信号による画像書込が行われ、Mの現像器13による非接触の反転現像によって前記のイエロー(Y)のトナー像の上にマゼンタ(M)のトナー像が重ね合わせて形成される。
【0036】
同様のプロセスにより、シアン(C)のスコロトロン帯電器11、Cの露光光学系12およびCの現像器13によってさらに第3の色信号に対応するシアン(C)のトナー像が重ね合わせて形成され、更にその上に黒色(K)のスコロトロン帯電器11、Kの露光光学系12およびKの現像器13によって第4の色信号に対応する黒色(K)のトナー像が順次重ね合わせて形成され、感光体ドラム10の一回転以内にその周面上にイエロー(Y)、マゼンタ(M)、シアン(C)および黒色(K)の4色の重ね合わせカラートナー像が形成される。
【0037】
これらY、M、C及びKの露光光学系12による感光体ドラム10の感光層に対する画像書込はドラムの内部より前述した透光性の基体を通して行われる。従って第2、第3および第4の色信号に対応する画像の書込は何れも先に形成されたトナー像の影響を全く受けることなく行われ、第1の色信号に対応する画像と同等の静電潜像を形成することが可能となる。
【0038】
上記の画像形成プロセスによって像担持体である感光体ドラム10上に形成された裏面画像となる重ね合わせカラートナー像は、転写域14bにおいて、転写器14cによって、中間転写体である中間転写ベルト14a上に一括して転写される(図3(A))。この際、良好な転写がなされるように、感光体ドラム10の内部に設けた転写同時露光器12dによる一様露光が行われるようにしてもよい。また転写器14cにより荷電された中間転写ベルト14aの電荷は除電器14mにより除電される。
【0039】
転写後の感光体ドラム10の周面上に残ったトナーは感光体ドラムAC除電器16により除電を受けた後、像担持体クリーニング手段であるクリーニング装置19にいたり、感光体ドラム10に当接したゴム材から成るクリーニングブレード19aによってクリーニングされ、スクリュウ19bによって不図示の排トナー容器に回収される。また、感光体ドラム10の周面は、例えば発光ダイオードを用いた帯電前の一様露光器12eによる露光によって先の画像形成における感光体ドラム10の履歴が解消される。
【0040】
以上のようにして中間転写ベルト14a上に裏面画像となる重ね合わせカラートナー像が形成された後、感光体ドラム10上には上記のカラー画像形成プロセスと同様にして、引続き表面画像となる重ね合わせカラートナー像が形成される(図3(B))。この際、感光体ドラム10上に形成される表面画像は、前記感光体ドラム10上に形成した裏面画像に対して鏡像となるように画像データが変更される。
【0041】
感光体ドラム10上への表面画像形成にともなって転写材である記録紙Pが転写材収納手段である給紙カセット15より、送り出しローラ15aにより送り出され、転写材給送手段としてのタイミングローラ15bへ搬送され、タイミングローラ15bの駆動によって、感光体ドラム10上に形成される表面画像のカラートナー像と、中間転写ベルト14aに担持されている裏面画像のカラートナー像との同期がとられて転写域14bへ給送される。この際、給送される記録紙Pは、記録紙Pの表面側に設けられる転写材帯電手段である紙帯電器150によりトナーと同極性に帯電され、中間転写ベルト14aに吸着されて転写域14bへ搬送される。トナーと同極性に紙帯電を行うことにより、中間転写ベルト14a上のトナー像や感光体ドラム10上のトナー像と引き合うことを防止して、トナー像の乱れを防止している。
【0042】
転写域14bではトナーと反対極性(本実施形態においてはプラス極性)の電圧が印加される転写器14cによって感光体ドラム10上の表面画像が一括して記録紙Pの表面に転写される。このとき、中間転写ベルト14a上の裏面画像は記録紙Pに転写されないで中間転写ベルト14a上に存在する。この際、良好な転写がなされるように、転写域14bと対向して感光体ドラム10の内部に設けられた、例えば発光ダイオードを用いた転写同時露光器12dによる一様露光が行われるようにしてもよい。また転写器14cにより荷電された中間転写ベルト14aの電荷は除電器14mにより除電される。
【0043】
表面にカラートナー像が転写された記録紙Pは、トナーと反対極性(本実施形態においてはプラス極性)の電圧が印加される裏面転写器14gへと搬送され、裏面転写器14gにより中間転写ベルト14aの周面上の裏面画像が一括して記録紙Pの裏面に転写される(図3(C))。
【0044】
両面にカラートナー像が形成された記録紙Pは、中間転写ベルト14aの曲率部KTの曲率と、中間転写ベルト14aの端部に設けられる転写材分離手段としての紙分離AC除電器14hによる除電作用と、中間転写ベルト14aと所定の間隔を空けて搬送部160に設けられる分離爪210とにより、中間転写ベルト14aから分離され、搬送部160に設けられた拍車162を通して定着手段としての定着装置17へと搬送され、第1定着ローラ17aと第2定着ローラ17bとの間のニップ部T間を搬送され、ニップ部Tで熱と圧力とをくわえられることにより記録紙P上のトナー像が定着される。両面画像記録がなされた記録紙Pは表裏を反転されて送られ、排紙ローラ18により装置外部のトレイへ排出される。
【0045】
転写後の中間転写ベルト14aの周面上に残ったトナーは、中間転写ベルト14aを挟んでガイドローラ14fに対向して設けられ、支軸142を回転支点として中間転写ベルト14aに当接及び当接解除可能な中間転写体クリーニングブレード141を有する中間転写体クリーニング手段である中間転写体クリーニング装置140によりクリーニングされる。
【0046】
また、転写後の感光体ドラム10の周面上に残ったトナーは、感光体ドラムAC除電器16により除電を受けた後、クリーニング装置19によりクリーニングされ、帯電前の一様露光器12eにより先の画像形成における感光体ドラム10の履歴が解消されて、次の画像形成サイクルにはいる。
【0047】
上記の方法を用いることにより、重ね合わせカラートナー像を一括転写するので、中間転写ベルト14a上のカラー画像の色ズレやトナーの散りやこすれ等が起こりにくく、画像劣化が少ない良好な両面カラー画像形成がなされる。
【0048】
上記画像形成装置に用いられる定着手段である定着装置17に設けられる2本のロール状の定着部材である第1定着ローラ17aと第2定着ローラ17bの構造は、図4に示すように、記録紙P上の上側(表面側)のトナー像を定着するための第1定着ローラ17aと下側(裏面側)のトナー像を定着するための第2定着ローラ17bとはそれぞれ内部中心にハロゲンヒータHL1,HL2を設けた略同一構造の回転体である。中心部にハロゲンヒータHL1を有する第1定着ローラ17aは、例えばアルミ材を用いた円筒状の金属パイプ171aと、該金属パイプ171aの外周面に例えばシリコン材を用いた、1〜3mm厚の薄肉ゴム層よりなるゴムローラ層172aと、該ゴムローラ層172aの表面に、層厚(厚さ)0.05〜0.25mmで体積抵抗率が、前述した中間転写ベルト14aの体積抵抗率(108〜1012Ω・cm)や転写材である記録紙Pの体積抵抗率(中間転写ベルト14aと略同じ108〜1012Ω・cm)より高い1010〜1016Ω・cmのPFA、PTFE等のフッ素樹脂やシリコン樹脂等の耐熱性及び離型性を有する高抵抗層173aを形成したソフトローラとして構成される。同様に中心部にハロゲンヒータHL2を有する第2定着ローラ17bは、例えばアルミ材を用いた円筒状の金属パイプ171bと、該金属パイプ171bの外周面に例えばシリコン材を用いた、1〜3mm厚の薄肉ゴム層よりなるゴムローラ層172bと、該ゴムローラ層172bの表面に、層厚(厚さ)0.05〜0.25mmで体積抵抗率が1010〜1016Ω・cmのPFA、PTFE等のフッ素樹脂やシリコン樹脂等の耐熱性及び離型性を有する高抵抗層173bを形成したソフトローラとして構成される。定着装置17の定着部材に記録紙Pや中間転写ベルト14aより高い体積抵抗率を有する高抵抗層173a,173bを設けることにより、定着部材の抵抗が低かったり、定着部材が接地されたりしている場合に生じる、定着部材を通しての記録紙Pや中間転写ベルト14aからの電荷のリークが防止され、定着装置17の近くに配置される裏面転写器14gによる裏面トナー像の転写の際の、定着部材を通しての記録紙Pからの電荷のリークによる、裏面トナー像の転写が良好に行われないということを防止する。
【0049】
図4によれば、転写材である記録紙Pが感光体ドラム10上に形成される表面画像のカラートナー像(本実施形態においてはマイナス極性)と、中間転写ベルト14a上に担持されている裏面画像のカラートナー像(本実施形態においてはマイナス極性)との同期がとられて転写域14bへ給送され、転写域14bにおいてトナーと反対極性(本実施形態においてはプラス極性)の直流電圧が印加される転写器14cによって感光体ドラム10上の表面画像が一括して記録紙Pの表面に転写される。この際中間転写ベルト14a(体積抵抗率が108〜1012Ω・cm)を挟んで記録紙P上の表面トナー像が転写されるため、記録紙P上の表面トナー像は極性変換されずマイナス極性のままで保たれる。また、交流電圧が印加される除電器14mにより転写器14cによりプラス極性に荷電された中間転写ベルト14aの電荷が除電された後、さらに中間転写ベルト14a上の裏面トナー像をトナーと反対極性(本実施形態においてはプラス極性)の直流電圧が印加される裏面転写器14gにより記録紙Pの裏面に転写するが、裏面転写器14gを通過後の、図4の円(a)位置での表裏のトナー像と記録紙Pとの荷電状態は、図5に示すように、記録紙P上の裏面トナー像は極性変換されずマイナス極性のままで保たれるが、記録紙P上のマイナス極性の表面トナー像は、裏面転写器14gによるプラス極性の放電により極性変換されてプラス極性とされる。また裏面転写器14gによるプラス極性の放電により記録紙Pの表面側もプラス荷電され、記録紙Pの体積抵抗率は低いのでプラス電荷が記録紙Pの内部の中心部或いは裏側(裏面側)にも回っている。このとき記録紙Pの電位はプラス極性で1〜2kVまで荷電される。
【0050】
両面にカラートナー像が形成された記録紙Pは、中間転写ベルト14aの曲率部KTの曲率と、中間転写ベルト14aの端部に設けられ、裏面転写器14gに印加される直流電圧と同極性(図5にて前述したように本実施形態においてはプラス極性)の直流電圧を重畳した交流電圧が印加される転写材分離手段としての紙分離AC除電器14hによる除電作用と、分離爪210とにより、中間転写ベルト14aから分離され、拍車部材である拍車162を通して定着手段としての定着装置17へと搬送され、第1定着ローラ17aと第2定着ローラ17bとの間のニップ部T間を搬送され、ニップ部Tで挟持された状態で記録紙Pにループが形成されて、ニップ部Tで熱と圧力とをくわえられることにより記録紙P上のトナー像が定着されるが、紙分離AC除電器14hの除電作用により、前述した裏面転写器14gによるプラス極性の1〜2kVの記録紙P上の電位はプラス極性で500V程度まで除電される。
【0051】
前述したように、中間転写体である中間転写ベルト14aの体積抵抗率は108〜1012Ω・cmであり、転写材である記録紙Pの体積抵抗率は中間転写ベルト14aと略同じ108〜1012Ω・cmであり、定着手段である定着装置17に設けられる2本のロール状の定着部材である第1定着ローラ17aと第2定着ローラ17bには中間転写ベルト14aや記録紙Pの体積抵抗率より高い1010〜1016Ω・cmの高抵抗層173a,173bが設けられるが、定着装置17の定着部材に記録紙Pや中間転写ベルト14aより高い体積抵抗率を有する高抵抗層173a,173bを設けることにより、定着部材の抵抗が低かったり、定着部材が接地されたりしている場合に生じる、定着部材を通しての記録紙Pや中間転写ベルト14aからの電荷のリークが防止され、定着装置17の近くに配置される裏面転写器14gによる裏面トナー像の転写の際の、定着部材を通しての記録紙Pからの電荷のリークによる、裏面トナー像の転写が良好に行われないということを防止する。接地されるアースローラ14jや駆動ローラ14dは体積抵抗率が108〜1012Ω・cmの中間転写ベルト14aを介して設けられるので、アースローラ14jや駆動ローラ14dを通しての記録紙Pの電荷のリークは行われない。また、定着部材である第1定着ローラ17aと第2定着ローラ17bの体積抵抗率が低かったり、定着部材が接地されたりしていると、定着部材上に転写材上のトナーとの鏡像電荷が発生し、鏡像電荷により転写材上の表裏のトナー像が乱され、良好な両面画像が形成されないということを防止する。
【0052】
一方、定着部材が絶縁部材で形成されている場合は、定着部材に電荷が蓄積され、蓄積された電荷により転写材上の表裏のトナー像が乱され、良好な両面画像が形成されないという問題、いわゆる定着装置17による表裏のトナー像乱れを起こす。これを防止するため、表面側の定着部材としての第1定着ローラ17aには、ニップ部Tに進入される記録紙Pの極性と同極性(図5にて説明したように本実施形態においてはプラス極性)の直流電源E1により500〜1500Vの電圧を印加し、表面側の定着部材としての第1定着ローラ17aと裏面側の定着部材としての第2定着ローラ17bとの電圧差を200〜600V程度とするよう、裏面側の定着部材としての第2定着ローラ17bには直流電源E2によりプラスの100〜500Vの電圧を印加する。裏面側の第2定着ローラ17bに印加する電圧の極性をプラスとしたが、要は電圧差を200〜600V程度とすればよく、マイナス電圧或いはゼロ(V)電圧としてもよい。表裏の定着部材に電圧差を設けるのは、ベタトナー層電位が表裏(図5にて説明したように、表面トナー像はプラス極性、裏面トナー像はマイナス極性)で、絶対値で各々100〜200Vであるので、ベタ部電位差が表裏で200〜400V生じるので、表裏の定着部材に上記電圧差を設け、図4に点線矢印で示すような表面側の第1定着ローラ17aから裏面側の第2定着ローラ17bに向けての電界を生じさせ、表面側をプラス極性とする該電界により記録紙P上のプラス極性の表面トナー像を、また裏面側をマイナス極性とする該電界により記録紙P上のマイナス極性の裏面トナー像をそれぞれ記録紙P上に押さえ込むようにして記録紙P上に保持させ、飛散による定着部材へのトナーの付着や周囲の汚れを防止する。
【0053】
また直流電源E1,E2を用いず、図6に示すように、表面側の第1定着ローラ17aにツェナーダイオードZD1を、裏面側の第2定着ローラ17bにツェナーダイオードZD2をそれぞれ接続し、第1定着ローラ17aと第2定着ローラ17b間が、ニップ部Tにくわえられる記録紙Pと略同電位を保つ構成として、記録紙P上に表裏のトナー像を保持させ、飛散による定着部材へのトナーの付着や周囲の汚れを防止することも可能である。
【0054】
上記により、転写材からのリークが防止されて裏面トナー像の転写が良好に行われると共に、定着手段による表裏のトナー像の乱れや表裏のトナーの反撥が防止され、良好な両面画像が形成される。
【0055】
本発明にかかわる画像形成装置の他の実施形態について図7にて説明する。図7は、本発明にかかわる画像形成装置の他の実施形態を示すカラー画像形成装置の概要説明図である。
【0056】
本例の画像形成装置では、図7に示すように、裏面画像となるトナー像(裏面トナー像)を形成する第1の像担持体である感光体ドラム10bと、表面画像となるトナー像(表面トナー像)を形成する第2の像担持体である感光体ドラム10aとをそれぞれ別々に設け、感光体ドラム10bに形成した裏面トナー像を、トナーと反対極性(本実施形態においてはプラス極性)の電圧が印加される1次転写器114bにより中間転写体である中間転写ベルト114a上に転写した後、感光体ドラム10bと感光体ドラム10aとの間で中間転写ベルト114a上に転写材である記録紙Pを供給し、中間転写ベルト114aを挟んでアースローラ14kと対向して設けられる紙帯電器150の帯電により、記録紙Pを中間転写ベルト114aに吸着させて搬送し、感光体ドラム10a上に形成した表面トナー像を、トナーと反対極性(本実施形態においてはプラス極性)の電圧が印加される2次転写器114cにより記録紙Pの表面に転写した後、中間転写ベルト114a上の裏面トナー像を、トナーと反対極性(本実施形態においてはプラス極性)の電圧が印加される3次転写器114gにより記録紙Pの裏面に転写して、記録紙P上に表裏のトナー像を形成し、両面にカラートナー像が形成された記録紙Pを、中間転写ベルト114aの曲率部KTの曲率と、中間転写ベルト114aの端部に必要に応じて設けられる転写材分離手段としての紙分離AC除電器14hによる除電作用と、中間転写ベルト114aと所定の間隔を空けて搬送部160に設けられる分離爪210とにより、中間転写ベルト114aから分離し、搬送部160に設けられた拍車部材である拍車162を通して定着手段としての定着装置17へと搬送し、第1定着ローラ17aと第2定着ローラ17bとの間のニップ部Tで記録紙P上のトナー像を定着し、両面画像を得るようにするものである。
【0057】
本例の画像形成装置における感光体ドラム10a,10bや中間転写ベルト114aは、前記画像形成装置にて説明した感光体ドラム10や中間転写ベルト14aと同様な機能、構造のものが用いられる。中間転写ベルト114aは、それぞれローラ部材である駆動ローラ14dとアースローラ14jとアースローラ14kと従動ローラ14eとガイドローラ14fとテンションローラ14iとに内接して張架される。また、それぞれ除電手段である除電器114m,114nが、中間転写ベルト114aの移動方向に対し、1次転写器114b及び2次転写器114cの後に、1次転写器114b及び2次転写器114cと並列して設けられ、トナーと同極性または逆極性の直流電圧を重畳した交流電圧が印加され、1次転写器114b及び2次転写器114cの電圧印加により荷電される中間転写ベルト114aの電荷を除電する。
【0058】
裏面画像となるトナー像を第1の像担持体である感光体ドラム10bに形成する手段と表面画像となるトナー像を第2の像担持体である感光体ドラム10aに形成する手段とには、前述した画像形成装置にて用いられたと同様な、イエロー(Y),マゼンタ(M),シアン(C)および黒色(K)の画像形成プロセス用の4組の現像器13(現像手段)、スコロトロン帯電器11(帯電手段)、露光光学系12(画像書込手段)が感光体ドラム10b,10aに対してそれぞれに用いられ、裏面画像のトナー像と表面画像のトナー像とをそれぞれ形成する。
【0059】
また本例においても、ともに定着部材である第1定着ローラ17aと第2定着ローラ17bとは、図4にて説明したと同様な構造であり、第1定着ローラ17aと第2定着ローラ17bとにはそれぞれ表面層として、中間転写ベルト114aの体積抵抗率(108〜1012Ω・cm)や転写材である記録紙Pの体積抵抗率(中間転写ベルト114aと略同じ108〜1012Ω・cm)より高い1010〜1016Ω・cmのPFA、PTFE等のフッ素樹脂やシリコン樹脂等の耐熱性及び離型性を有する高抵抗層173a,173bが設けられる。定着装置17の定着部材に記録紙Pや中間転写ベルト114aより高い体積抵抗率を有する高抵抗層173a,173bを設けることにより、定着部材の抵抗が低かったり、定着部材が接地されたりしている場合に生じる、定着部材を通しての記録紙Pや中間転写ベルト114aからの電荷のリークが防止され、定着装置17の近くに配置される3次転写器114gによる裏面トナー像の転写の際の、定着部材を通しての記録紙Pからの電荷のリークによる、裏面トナー像の転写が良好に行われないということを防止する。
【0060】
転写材である記録紙Pが感光体ドラム10a上に形成される表面画像のカラートナー像(本実施形態においてはマイナス極性)と、中間転写ベルト114a上に担持されている裏面画像のカラートナー像(本実施形態においてはマイナス極性)との同期がとられて中間転写ベルト114a上へ給送され、転写域においてトナーと反対極性(本実施形態においてはプラス極性)の直流電圧が印加される2次転写器114cによって感光体ドラム10a上の表面画像が一括して記録紙Pの表面に転写される。この際中間転写ベルト114a(体積抵抗率が108〜1012Ω・cm)を挟んで記録紙P上の表面トナー像が転写されるため、記録紙P上の表面トナー像は極性変換されずマイナス極性のままで保たれる。また、交流電圧が印加される除電器114nにより2次転写器114cによりプラス極性に荷電された中間転写ベルト114aの電荷が除電された後、さらに中間転写ベルト114a上の裏面トナー像をトナーと反対極性(本実施形態においてはプラス極性)の直流電圧が印加される3次転写器114gにより記録紙Pの裏面に転写するが、3次転写器114g通過後の表裏のトナー像と記録紙Pとの荷電状態は、図5にて説明したと同様に、記録紙P上の裏面トナー像は極性変換されずマイナス極性のままで保たれるが、記録紙P上のマイナス極性の表面トナー像は、3次転写器114gによるプラス極性の放電により極性変換されてプラス極性とされる。また3次転写器114gによるプラス極性の放電により記録紙Pの表面側もプラス荷電され、また記録紙Pの体積抵抗率は低いのでプラス電荷が記録紙Pの内部の中心部或いは裏側(裏面側)にも回っている。このとき記録紙Pの電位はプラス極性で1〜2kVまで荷電される。
【0061】
両面にカラートナー像が形成された記録紙Pは、中間転写ベルト114aの曲率部KTの曲率と、中間転写ベルト114aの端部に設けられ、3次転写器114gに印加される直流電圧と同極性(図5にて前述したように本実施形態においてはプラス極性)の直流電圧を重畳した交流電圧が印加される転写材分離手段としての紙分離AC除電器14hによる除電作用と、分離爪210とにより、中間転写ベルト114aから分離され、拍車部材である拍車162を通して定着手段としての定着装置17へと搬送され、第1定着ローラ17aと第2定着ローラ17bとの間のニップ部T間を搬送され、ニップ部Tで挟持された状態で記録紙Pにループ(不図示)が形成されて、ニップ部Tで熱と圧力とをくわえられることにより記録紙P上のトナー像が定着されるが、紙分離AC除電器14hの除電作用により、前述した3次転写器114gによるプラス極性の1〜2kVの記録紙P上の電位はプラス極性で500V程度まで除電される。
【0062】
前例にて説明したと同様に、中間転写体である中間転写ベルト114aの体積抵抗率は108〜1012Ω・cmであり、転写材である記録紙Pの体積抵抗率は中間転写ベルト114aと略同じ108〜1012Ω・cmであり、定着手段である定着装置17に設けられる2本のロール状の定着部材である第1定着ローラ17aと第2定着ローラ17bには中間転写ベルト114aや記録紙Pの体積抵抗率より高い1010〜1016Ω・cmの高抵抗層173a,173bが設けられるが、定着装置17の定着部材に記録紙Pや中間転写ベルト114aより高い体積抵抗率を有する高抵抗層173a,173bを設けることにより、定着部材の抵抗が低かったり、定着部材が接地されたりしている場合に生じる、定着部材を通しての記録紙Pや中間転写ベルト114aからの電荷のリークが防止され、定着装置17の近くに配置される3次転写器114gによる裏面トナー像の転写の際の、定着部材を通しての記録紙Pからの電荷のリークによる、裏面トナー像の転写が良好に行われないということを防止する。接地されるアースローラ14jや駆動ローラ14dは体積抵抗率が108〜1012Ω・cmの中間転写ベルト114aを介して設けられるので、アースローラ14jや駆動ローラ14dを通しての記録紙Pの電荷のリークは行われない。また、定着部材である第1定着ローラ17aと第2定着ローラ17bの体積抵抗率が低かったり、定着部材が接地されたりしていると、定着部材上に転写材上のトナーとの鏡像電荷が発生し、鏡像電荷により転写材上の表裏のトナー像が乱され、良好な両面画像が形成されないということを防止する。
【0063】
一方、定着部材が絶縁部材で形成されている場合は、定着部材に電荷が蓄積され、蓄積された電荷により転写材上の表裏のトナー像が乱され、良好な両面画像が形成されないという問題、いわゆる定着装置17による表裏のトナー像乱れを起こす。これを防止するため、表面側の定着部材としての第1定着ローラ17aには、ニップ部Tに進入される記録紙Pの極性と同極性(図5にて説明したように本実施形態においてはプラス極性)の直流電源E1(図4参照、図7には不図示)により500〜1500Vの電圧を印加し、表面側の定着部材としての第1定着ローラ17aと裏面側の定着部材としての第2定着ローラ17bとの電圧差を200〜600V程度とするよう、裏面側の定着部材としての第2定着ローラ17bには直流電源E2(図4参照、図7には不図示)によりプラスの100〜500Vの電圧を印加する。裏面側の第2定着ローラ17bに印加する電圧の極性をプラスとしたが、要は電圧差を200〜600V程度とすればよく、マイナス電圧或いはゼロ(V)電圧としてもよい。表裏の定着部材に電圧差を設けるのは、ベタトナー層電位が表裏(図5にて説明したように、表面トナー像はプラス極性、裏面トナー像はマイナス極性)で、絶対値で各々100〜200Vであるので、ベタ部電位差が表裏で200〜400V生じるので、表裏の定着部材に上記電圧差を設け、図4にて説明したように、表面側の第1定着ローラ17aから裏面側の第2定着ローラ17bに向けての電界(図4参照、図7には不図示)を生じさせ、表面側をプラス極性とする該電界により記録紙P上のプラス極性の表面トナー像を、また裏面側をマイナス極性とする該電界により記録紙P上のマイナス極性の裏面トナー像をそれぞれ記録紙P上に押さえ込むようにして記録紙P上に保持させ、飛散による定着部材へのトナーの付着や周囲の汚れを防止する。
【0064】
また図6にて説明したように、表面側の第1定着ローラ17aにツェナーダイオードZD1(図6参照、図7には不図示)を、裏面側の第2定着ローラ17bにツェナーダイオードZD2(図6参照、図7には不図示)をそれぞれ接続し、第1定着ローラ17aと第2定着ローラ17b間が、ニップ部Tにくわえられる記録紙Pと略同電位を保つ構成として、記録紙P上に表裏のトナー像を保持させ、飛散による定着部材へのトナーの付着や周囲の汚れを防止することも可能である。
【0065】
上記により、転写材からのリークが防止されて裏面トナー像の転写が良好に行われると共に、定着手段による表裏のトナー像の乱れや表裏のトナーの反撥が防止され、良好な両面画像が形成される。
【0066】
なお、上記の画像形成装置の各例では像担持体上に直接トナー像を形成したが、像担持体とは別に像形成体を設け、該像形成体上に形成したトナー像を像担持体上に担持させてもよい。また、上記画像形成装置の各例としてカラー画像形成装置にて説明したが、本発明は必ずしもこれに限定されるものでなく、図1或いは図7にて説明したと同様のプロセスによるモノクロの画像形成装置にも適用されるものである。
【0067】
さらに、本発明の画像形成装置では、上述の各画像形成装置で説明したような転写材の両面に画像を形成する両面画像形成のほかに、転写材の表面または裏面のみの片側に画像を形成する片面画像形成もなされ得ることは勿論である。
【0068】
なお、上記図1或いは図7にて説明した両面用の画像形成装置を用いることにより、従来の両面反転給送装置を用いた両面画像形成装置における問題点、即ち、
●両面時の1stプリント速度が遅い。
【0069】
●用紙(転写材)搬送の信頼性が低く、ジャムが発生しやすい。
【0070】
●ジャムが発生した場合、通紙経路が長いため、無駄になる用紙が多く、ジャム処理も大変である。
【0071】
●適用できる紙種に制限があり、厚紙や薄紙、はがき等の小サイズ紙や不定形紙には対応できない。
【0072】
●定着オイルによって通紙経路が汚染され、特にカラーの場合に問題となる。
【0073】
●機内への熱の持ち込みがあり、プロセスが安定しない。
【0074】
等を解決し、以下の如き効果を奏する。
【0075】
○用紙(転写材)反転の待ち時間がないため、用紙両面への画像形成を続けて行うことが可能となり、両面時の1stプリント速度が速くなる。
【0076】
○定着手段通過後の用紙を再給紙する必要がないため、用紙の給送信頼性が大幅に向上する。また定着オイルによる通紙経路の汚染や機内への熱の持ち込みもない。
【0077】
○片面時と全く同じ給送系で両面プリントが可能であるため、転写材種類の制限がなくなる。
【0078】
○用紙反転経路がないため、ジャム発生時に無駄になる用紙が少なく、ジャム処理も容易である。
【0079】
○両面時に定着手段を通過する用紙の数は片面時の半分であるため、定着消費電力が低減される。
【0080】
【発明の効果】
本発明によれば、転写材からのリークが防止されて転写材裏面へのトナー像の転写が良好に行われると共に、定着手段による表裏のトナー像の乱れが防止され、良好な両面画像が形成される。
【図面の簡単な説明】
【図1】本発明にかかわる画像形成装置の一実施形態を示すカラー画像形成装置の断面構成図である。
【図2】図1の像担持体の側断面図である。
【図3】本発明にかかわる画像形成装置におけるトナー像形成状態を示す図である。
【図4】定着手段に用いられる定着部材の構造と転写材上のトナー乱れを防止するための定着部材への電圧印加とを示す図である。
【図5】転写材の両面にトナー像を転写した後の転写材及び転写材上のトナーの荷電状態を示す図である。
【図6】転写材上のトナー乱れを防止する他の例を示す図である。
【図7】本発明にかかわる画像形成装置の他の実施形態を示すカラー画像形成装置の概要説明図である。
【符号の説明】
10,10a,10b 感光体ドラム
11 スコロトロン帯電器
12 露光光学系
13 現像器
14a,114a 中間転写ベルト
14c 転写器
14g 裏面転写器
14h 紙分離AC除電器
14m,114m,114n 除電器
17 定着装置
17a 第1定着ローラ
17b 第2定着ローラ
114b 1次転写器
114c 2次転写器
114g 3次転写器
173a,173b 高抵抗層
E1,E2 直流電源
P 記録紙
[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a copying machine, a printer, a FAX, etc., in which a charging unit, an image writing unit, and a developing unit are arranged around an image carrier to transfer and fix a toner image formed on the image carrier onto a transfer material. The present invention relates to an electrophotographic image forming apparatus, and more particularly to an image forming apparatus capable of forming images on both sides of a transfer material.
[0002]
[Prior art]
Conventionally, in double-sided image formation, an image on one side formed on an image carrier is transferred and fixed on a transfer material, which is once stored in a double-sided reversal feeding device and formed again on the image carrier. A method is used in which a transfer material is fed from a double-sided reversal feeding device in synchronization with the transferred image, and the image on the other surface is transferred and fixed on the transfer material.
[0003]
In this double-sided image forming apparatus, as described above, the transfer material is conveyed such as feeding to the double-sided reversal feeding device and passing through the fixing device twice. It was the cause of jams and wrinkles.
[0004]
On the other hand, according to Japanese Patent Publication Nos. 49-37538, 54-28740, JP-A-1-44457, and 4-214576, etc., an image carrier and an intermediate transfer member are used to transfer a transfer material. It has been proposed to fix the toner image once after forming toner images on both sides.
[0005]
Further, the inventors of the present application have arranged a plurality of toner image forming means including charging means, image writing means, developing means, etc. around the photosensitive drum (image carrier), and formed an overlap formed on the photosensitive drum. The combined color toner image is once transferred to a belt-like intermediate transfer member in a lump, and then a color toner image is formed again on the photosensitive drum to form a toner image on the photosensitive drum and a toner image on the intermediate transfer member. The toner image on the photosensitive drum is transferred as a front image on both sides of the transfer material that is fed at the same time and conveyed by the intermediate transfer member, and the toner image on the intermediate transfer member is transferred as the back image. After that, an image forming apparatus and an image forming method for separating a transfer material from an intermediate transfer member and fixing a toner image on the transfer material to form a double-sided color image are disclosed in JP-A-9-258492 and JP-A-9-25. Disclosed in 516 JP.
[0006]
[Problems to be solved by the invention]
In a double-sided image forming apparatus that forms an image on both sides of a transfer material using a belt-like intermediate transfer member as described above, a fixing means is configured using a pair of fixing members (fixing roller pairs), and the front and back surfaces of the transfer material are Although the toner image is fixed, if the resistance of the fixing member is low or the fixing member is grounded, the charge is leaked from the transfer material through the fixing means, and the toner image is transferred to the back surface of the transfer material. The problem of not doing well occurs. Further, when the transfer material enters the fixing member, a mirror image charge of the toner on the transfer material is generated on the fixing member, and the toner images on the front and back surfaces of the transfer material are disturbed by the mirror image charge, and a good double-sided image is formed. The problem of not being formed occurs.
[0007]
Even when the fixing member is formed of an insulating member, charges are accumulated on the fixing member, and the accumulated charge disturbs the front and back toner images on the transfer material, resulting in a problem that a good double-sided image cannot be formed. .
[0008]
The present invention solves the above-described problems, prevents leakage from the transfer material, and transfers the toner image to the back surface of the transfer material satisfactorily. An object of the present invention is to provide an image forming apparatus that forms a double-sided image.
[0009]
[Means for Solving the Problems]
  The object is to provide an image carrier, a means for forming a toner image on the image carrier, a toner image on the image carrier is transferred, and the transferred toner image is carried on the surface and a transfer material. An endless belt-shaped intermediate transfer member that supports and conveys the toner, means for transferring the toner image on the image carrier to the intermediate transfer member, and means for transferring the toner image on the image carrier to the surface of the transfer material Toner transferred onto both surfaces of the transfer material by sandwiching and transporting the transfer material by a pair of rotating fixing members and means for transferring the toner image on the intermediate transfer member to the back surface of the transfer material In the image forming apparatus having the means for fixing the image, the fixing members on the front side and the back side of the transfer material are respectivelyVolume resistivity is 10 Ten -10 16 Ω · cmHigh resistance layerTheSettingKickIn addition, a voltage having the same polarity as that of the transfer material having the toner image transferred on both sides thereof is applied, and the absolute value of the voltage applied to the fixing member on the front surface side of the transfer material is the fixing member on the back surface side of the transfer material This is achieved by an image forming apparatus characterized in that it is set higher than the absolute value of the voltage applied to the first (first invention).
[0010]
  Further, the object is to provide a first image carrier, a second image carrier, means for forming a toner image on the first image carrier, and a toner image on the second image carrier. A toner image on the first image carrier, and an endless belt-like intermediate transfer member that supports and conveys the transfer material while the transferred toner image is carried on the surface, Means for transferring the toner image on the first image carrier to the intermediate transfer member; means for transferring the toner image on the second image carrier to the surface of the transfer material; Means for transferring the toner image onto the back surface of the transfer material; and means for fixing the toner image transferred on both sides of the transfer material by sandwiching and conveying the transfer material by a fixing member that rotates in pairs. In the image forming apparatus, the fixing members on the front surface side and the back surface side of the transfer material are respectively provided.Volume resistivity is 10 Ten -10 16 Ω · cmHigh resistance layerTheSettingKickIn addition, a voltage having the same polarity as that of the transfer material having the toner image transferred on both sides thereof is applied, and the absolute value of the voltage applied to the fixing member on the front surface side of the transfer material is the fixing member on the back surface side of the transfer material It is achieved by an image forming apparatus characterized in that it is set higher than the absolute value of the voltage applied to the second (second invention).
[0011]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below. The description in this column does not limit the technical scope of the claims or the meaning of terms. In addition, the following assertive description in the embodiment of the present invention shows the best mode, and does not limit the meaning or technical scope of the terms of the present invention. In the following description of the embodiments, the surface of the transfer material facing the image carrier in the transfer area is referred to as the front surface, and the other surface of the transfer material, that is, the surface of the transfer material facing the intermediate transfer member is referred to as the back surface. An image transferred onto the surface of the transfer material is referred to as a front image, and an image transferred onto the back surface of the transfer material is referred to as a back image.
[0012]
An image forming process and each mechanism of an embodiment of an image forming apparatus according to the present invention will be described with reference to FIGS. FIG. 1 is a cross-sectional configuration diagram of a color image forming apparatus showing an embodiment of an image forming apparatus according to the present invention, FIG. 2 is a side cross-sectional view of the image carrier of FIG. 1, and FIG. FIG. 3A is a diagram showing a toner image forming state in the image forming apparatus according to the invention, and FIG. 3A is a diagram showing a toner image forming state when a back image formed on the image carrier is transferred onto an intermediate transfer member. FIG. 3B is a diagram showing a toner image formation state when a front image is formed on the image carrier in synchronization with the back image on the intermediate transfer member, and FIG. FIG. 4 is a diagram showing the double-sided image formation on the top, and FIG. 4 is a diagram showing the structure of the fixing member used in the fixing unit and the voltage application to the fixing member to prevent toner disturbance on the transfer material; FIG. 5 shows the transfer material after transferring the toner image on both sides of the transfer material and the toner on the transfer material. A diagram illustrating a conductive state, FIG. 6 is a diagram illustrating another example of preventing toner disturbance on the transfer material.
[0013]
In FIG. 1, 10 is a photosensitive drum as an image carrier, 11 is a scorotron charger as charging means for each color, 12 is an exposure optical system as image writing means for each color, and 13 is developing means for each color. 14a, an intermediate transfer belt as an intermediate transfer member, 14c, means for transferring a toner image on the image carrier to the intermediate transfer member, and means for transferring the toner image on the image carrier to the surface of the transfer material. 14g is a back surface transfer device that is a means for transferring the toner image on the intermediate transfer member to the back surface of the transfer material, 14m is a charge removal device that is a charge removal means, 150 is a paper charger that is a transfer material charging means, Reference numeral 14h denotes a paper separating AC static eliminator serving as a transfer material separating unit, 160 denotes a conveying unit having a separating claw 210 serving as a claw member and a spur 162 serving as a spur member, and 17 denotes a fixing device serving as a fixing unit.
[0014]
A photosensitive drum 10 as an image carrier is formed on the outer periphery of a cylindrical substrate formed of a transparent member such as optical glass or transparent acrylic resin, for example, on a transparent conductive layer, an a-Si layer, or an organic photosensitive layer (OPC). ) And the like, and is rotated in the clockwise direction indicated by the arrow in FIG. 1 at a linear velocity of, for example, 80 to 400 mm / sec with the conductive layer grounded.
[0015]
As shown in FIG. 2, the photosensitive drum 10 is fixed to a drum shaft 30 installed and fixed to the apparatus main body by bearings B1 and B2 fitted into flange members 10A and 10B at both ends for engaging and fixing the photosensitive drum. The gear G, which is supported by the bearing and rotatably supported, and is integrated with the flange member 10B is engaged with a drive gear (not shown) on the apparatus main body side and driven to rotate in a predetermined direction at a constant speed.
[0016]
A means for forming a toner image on the image carrier comprises a scorotron charger 11 as a charging means, an exposure optical system 12 as an image writing means, and a developing device 13 as a developing means. Four sets are provided for the image forming process of each color of (Y), magenta (M), cyan (C), and black (K), and the rotation direction of the photosensitive drum 10 indicated by the arrow in FIG. , M, C, K.
[0017]
A scorotron charger 11 serving as a charging means for each color has a control grid held at a predetermined potential and a discharge electrode 11a made of, for example, a sawtooth electrode, and is mounted opposite to the photosensitive layer of the photosensitive drum 10. Then, a charging action (negative charging in the present embodiment) is performed by corona discharge having the same polarity as the toner, and a uniform potential is applied to the photosensitive drum 10. As the discharge electrode 11a, other wire electrodes or needle electrodes can be used.
[0018]
In the exposure optical system 12, which is an image writing unit for each color, the exposure position on the photosensitive drum 10 is located downstream in the rotation direction of the photosensitive drum 10 with respect to the aforementioned scorotron charger 11 for each color. In this way, it is arranged inside the photosensitive drum 10. As shown in FIG. 2, each exposure optical system 12 includes a plurality of LEDs (light emitting diodes) as light emitting elements for image exposure light (image writing light) arranged in parallel to the drum shaft 30 in the main scanning direction. An exposure unit composed of linear exposure elements 12a arranged in an array, a light converging light transmitter (trade name: Selfoc lens array) 12b as an imaging element, and a lens holder 12c. It is attached to the holding member 20. In addition to the exposure optical system 12 for each color, a simultaneous transfer exposure device 12 d and a uniform exposure device 12 e are attached to the holding member 20, and are integrally accommodated in the translucent substrate of the photosensitive drum 10. The exposure optical system 12 for each color writes an image on the photosensitive layer of the photosensitive drum 10 from the back according to the image data of each color read by a separate image reading device and stored in the memory, and is statically applied on the photosensitive drum 10. An electrostatic latent image is formed. As the exposure element 12a, a plurality of light emitting elements such as FL (phosphor light emission), EL (electroluminescence), and PL (plasma discharge) arranged in an array can be used in addition to the LED. The light emitting wavelength of the light emitting element for image exposure light (image writing light) is usually in the range of 780 to 900 nm, which is highly transmissive to Y, M, and C toners. Therefore, a shorter wavelength of 400 to 780 nm which does not have sufficient transparency to the color toner may be used. Since 80% or more of the image exposure light is absorbed by the photosensitive layer of the photosensitive drum 10, the influence of reflection and absorption by the color toner on the surface of the photosensitive drum 10 can be ignored. In general, the order of developing color toners is preferably Y, M, C, and K in order of the color mixture of the toner image and the developing device 13. In FIG. 2, WA is a lead wire from a light emitting element (LED) for image exposure light.
[0019]
The developing device 13 which is a developing unit for each color maintains a predetermined gap with respect to the peripheral surface of the photosensitive drum 10 and rotates in the forward direction and the rotating direction of the photosensitive drum 10, for example, a thickness of 0.5 to 1 mm, an outer diameter. A developing sleeve 131 made of 15-25 mm cylindrical non-magnetic stainless steel or aluminum material and a developing casing 138 are provided. Inside the developing casing 138, yellow (Y), magenta (M), Contains one-component or two-component developer of cyan (C) and black (K). Each developing device 13 is kept in contact with the photosensitive drum 10 with a predetermined gap, for example, 100 to 500 μm, by an abutting roller (not shown), and a DC voltage and an AC voltage are superimposed on the developing sleeve 131. By applying the developed bias, non-contact reversal development is performed, and a toner image is formed on the photosensitive drum 10.
[0020]
The intermediate transfer belt 14a, which is an intermediate transfer body, has a volume resistivity of 108-1012An endless belt of Ω · cm, for example, a thickness of 0.1 to 1.0 mm in which a conductive material is dispersed in engineering plastics such as modified polyimide, thermosetting polyimide, ethylene tetrafluoroethylene copolymer, polyvinylidene fluoride, nylon alloy, etc. A seamless belt having a two-layer structure in which a fluorine coating having a thickness of 5 to 50 μm is preferably provided on the outer side of the semiconductive film substrate as a toner filming prevention layer. As the base of the intermediate transfer belt 14a, a semiconductive rubber belt having a thickness of 0.5 to 2.0 mm in which a conductive material is dispersed in silicon rubber or urethane rubber can also be used. The intermediate transfer belt 14a is stretched around a driving roller 14d, a ground roller 14j, a driven roller 14e, a guide roller 14f, and a tension roller 14i, which are roller members, and is rotated counterclockwise as indicated by an arrow in FIG. The guide roller 14f, the driven roller 14e, the earth roller 14j, and the driving roller 14d are fixed and rotated, and the tension roller 14i is supported and rotated so as to be movable by an elastic force such as a spring (not shown). The drive roller 14d is rotated by driving from a drive motor (not shown), and the intermediate transfer belt 14a is driven to rotate. The ground roller 14j, the driven roller 14e, the guide roller 14f, and the tension roller 14i are driven and rotated by the rotation of the intermediate transfer belt 14a. The slack of the rotating intermediate transfer belt 14a is tensioned by the tension roller 14i. The recording paper P, which is a transfer material, is supplied to a position where the intermediate transfer belt 14a is stretched around the driven roller 14e, and is conveyed by the intermediate transfer belt 14a. The recording paper P is separated from the intermediate transfer belt 14a at the curvature portion KT at the end of the intermediate transfer belt 14a stretched around the drive roller 14d on the fixing device 17 side.
[0021]
A transfer unit 14c serving as a means for transferring the toner image on the image carrier to the intermediate transfer member and a means for transferring the toner image on the image carrier to the surface of the transfer material has the photosensitive drum 10 sandwiched by the intermediate transfer belt 14a. The transfer area 14b is formed between the intermediate transfer belt 14a and the photosensitive drum 10. A DC voltage having a polarity opposite to that of the toner (plus polarity in the present embodiment) is applied to the transfer device 14c, and the toner image on the photosensitive drum 10 is transferred onto the intermediate transfer belt 14a or the surface of the recording paper P as a transfer material. Transcript.
[0022]
The back surface transfer device 14g, which is a means for transferring the toner image on the intermediate transfer body to the back surface of the transfer material, is preferably constituted by a corona discharge device, and is interposed between the transfer device 14c and the driving roller 14d with the intermediate transfer belt 14a interposed therebetween. A DC voltage having a polarity opposite to that of the toner (in this embodiment, a positive polarity) is applied so as to face the provided earth roller 14j, and the toner image on the intermediate transfer belt 14a is transferred to the back surface of the recording paper P.
[0023]
The static eliminator 14m serving as a static eliminator is composed of a corona discharger, and is provided in parallel with the transfer unit 14c on the downstream side of the transfer unit 14c with respect to the moving direction of the intermediate transfer belt 14a. The charge of the intermediate transfer belt 14a charged by the voltage application of the device 14c is removed.
[0024]
The paper charger 150 serving as a transfer material charging unit is preferably formed of a sawtooth electrode, and is provided to face the driven roller 14e that is grounded with the intermediate transfer belt 14a interposed therebetween, and has the same polarity as the toner (in this embodiment, A negative polarity) DC voltage is applied to charge the recording paper P and attract it to the intermediate transfer belt 14a. As the paper charger 150, in addition to the sawtooth electrode, a corona discharger, a paper charging brush or a paper charging roller capable of coming into contact with and releasing from the intermediate transfer belt 14a can be used.
[0025]
The paper separating AC static eliminator 14h, which is a transfer material separating means, is preferably constituted by a corona discharger, and is opposed to a driving roller 14d that is grounded with the intermediate transfer belt 14a sandwiched between ends of the intermediate transfer belt 14a on the fixing device 17 side. As will be described later, an AC voltage superimposed with a DC voltage having the same polarity as the DC voltage applied to the back surface transfer device 14g (in this embodiment, a positive polarity) is applied and conveyed by the intermediate transfer belt 14a. The recording paper P is neutralized and separated from the intermediate transfer belt 14a.
[0026]
The transport unit 160 includes a separation claw 210 that is a claw member and a spur 162 that is a spur member, and is provided between the curvature portion KT at the end of the intermediate transfer belt 14 a on the fixing device 17 side and the fixing device 17. The transport unit 160 may cause the intermediate transfer belt 14a to be deformed by heat from the fixing device 17, or the toner image carried on the intermediate transfer belt 14a may become fused and difficult to transfer, or may be on the intermediate transfer belt 14a. The toner is prevented from adhering to the toner.
[0027]
The separation claw 210 as a claw member is provided close to the curvature portion KT of the intermediate transfer belt 14a and fixed to the support shaft 221 with a predetermined distance, preferably 0.1 to 2.0 mm, from the intermediate transfer belt 14a. When the recording paper P is separated from the intermediate transfer belt 14a, the leading edge of the recording paper P that is to be bent and conveyed in the direction of the intermediate transfer belt 14a is brought into contact with the recording paper P to assist the separation of the recording paper P.
[0028]
The spur 162, which is a spur member, has a plurality of protrusions 162a on the peripheral surface, and is provided so as to be rotatable about the rotation support shaft 165. The spur 162 guides the back side of the recording paper P and conveys the recording paper P to prevent the back side toner image of the recording paper P having a toner image on both sides from being disturbed and to fix the recording paper P to the fixing device 17. The recording paper P is stably conveyed to the fixing device 17 while keeping the entering direction constant.
[0029]
The separation claw 210 and the spur 162 are disposed on the opposite side of the photosensitive drum 10 with respect to the transfer material conveying surface on the intermediate transfer belt 14a or its extended surface. It is also possible to provide a spur 162 as a spur member on both sides of the transfer material conveying surface or its extended surface.
[0030]
The fixing device 17 serving as a fixing unit includes two roller-shaped fixing members including a first fixing roller 17a and a second fixing roller 17b each having a heater therein, and the first fixing roller 17a and the second fixing roller 17b. The recording paper P is nipped and conveyed at the nip portion T between the two and the toner image on the recording paper P conveyed through the nip portion T is fixed by adding heat and pressure. Each of the first fixing roller 17a and the second fixing roller 17b is provided with high resistance layers 173a and 173b, which will be described in detail later, as surface layers, and a bias voltage, which will be described in detail later, is applied.
[0031]
Next, the image forming process will be described.
[0032]
The photosensitive drum 10 is rotated in the clockwise direction indicated by the arrow in FIG. 1 by starting the photosensitive member driving motor (not shown) by the start of image recording, and at the same time, the photosensitive drum 10 is charged by the yellow (Y) scorotron charger 11. Application of a potential is started.
[0033]
After the photosensitive drum 10 is applied with an electric potential, image writing by an electric signal corresponding to the first color signal, that is, Y image data is started by the Y exposure optical system 12, and a document is formed on the surface of the photosensitive drum 10. An electrostatic latent image corresponding to the Y image of the image is formed.
[0034]
The latent image is reversely developed in a non-contact state by the Y developing device 13 to form a yellow (Y) toner image on the photosensitive drum 10.
[0035]
Next, a potential is applied to the photosensitive drum 10 from above the Y toner image by the charging action of the magenta (M) scorotron charger 11, and the M exposure optical system 12 applies a second color signal, that is, M image data. Image writing is performed by a corresponding electric signal, and a magenta (M) toner image is formed on the yellow (Y) toner image by non-contact reversal development by the M developing unit 13. .
[0036]
By a similar process, a cyan (C) toner image corresponding to the third color signal is further superimposed by a cyan (C) scorotron charger 11, a C exposure optical system 12, and a C developer 13. Further, a black (K) toner image corresponding to the fourth color signal is successively superimposed on the black (K) scorotron charger 11, the K exposure optical system 12, and the K developing device 13. Then, within one rotation of the photosensitive drum 10, a superimposed color toner image of four colors of yellow (Y), magenta (M), cyan (C) and black (K) is formed on the peripheral surface.
[0037]
Image writing to the photosensitive layer of the photosensitive drum 10 by the Y, M, C, and K exposure optical systems 12 is performed from the inside of the drum through the above-described translucent substrate. Therefore, writing of images corresponding to the second, third, and fourth color signals is performed without any influence from the previously formed toner image, and is equivalent to the image corresponding to the first color signal. It is possible to form an electrostatic latent image.
[0038]
The superimposed color toner image, which is the back image formed on the photosensitive drum 10 which is an image carrier by the above image forming process, is transferred to the intermediate transfer belt 14a which is an intermediate transfer member by the transfer device 14c in the transfer area 14b. The images are collectively transferred onto the top (FIG. 3A). At this time, uniform exposure may be performed by the simultaneous transfer exposure unit 12d provided inside the photosensitive drum 10 so that good transfer is performed. The charge on the intermediate transfer belt 14a charged by the transfer device 14c is discharged by the charge remover 14m.
[0039]
The toner remaining on the peripheral surface of the photosensitive drum 10 after the transfer is subjected to static elimination by the photosensitive drum AC static eliminator 16 and then enters the cleaning device 19 which is an image carrier cleaning means or abuts against the photosensitive drum 10. It is cleaned by the cleaning blade 19a made of the rubber material and collected in a waste toner container (not shown) by the screw 19b. Further, the history of the photosensitive drum 10 in the previous image formation is eliminated on the peripheral surface of the photosensitive drum 10 by exposure by the uniform exposure device 12e before charging using, for example, a light emitting diode.
[0040]
After the superimposed color toner image to be the back image is formed on the intermediate transfer belt 14a as described above, it is continuously superimposed on the surface of the photosensitive drum 10 in the same manner as the color image forming process described above. A combined color toner image is formed (FIG. 3B). At this time, the image data is changed so that the front surface image formed on the photoconductive drum 10 becomes a mirror image with respect to the back image formed on the photoconductive drum 10.
[0041]
Along with the surface image formation on the photosensitive drum 10, the recording paper P as a transfer material is sent out by a feed roller 15a from a paper feed cassette 15 as a transfer material storage means, and a timing roller 15b as a transfer material feeding means. By driving the timing roller 15b, the color toner image of the front image formed on the photosensitive drum 10 and the color toner image of the back image carried on the intermediate transfer belt 14a are synchronized. It is fed to the transfer area 14b. At this time, the fed recording paper P is charged to the same polarity as the toner by a paper charger 150 which is a transfer material charging means provided on the surface side of the recording paper P, and is attracted to the intermediate transfer belt 14a to be transferred to the transfer area. 14b. By charging the paper with the same polarity as the toner, the toner image is prevented from being attracted by being attracted to the toner image on the intermediate transfer belt 14a or the toner image on the photosensitive drum 10, thereby preventing the toner image from being disturbed.
[0042]
In the transfer area 14b, the surface image on the photosensitive drum 10 is collectively transferred onto the surface of the recording paper P by the transfer device 14c to which a voltage having a polarity opposite to that of the toner (plus polarity in this embodiment) is applied. At this time, the back image on the intermediate transfer belt 14a is not transferred to the recording paper P and exists on the intermediate transfer belt 14a. At this time, uniform exposure is performed by a transfer simultaneous exposure device 12d using, for example, a light-emitting diode, which is provided inside the photosensitive drum 10 so as to face the transfer region 14b so as to achieve good transfer. May be. The charge on the intermediate transfer belt 14a charged by the transfer device 14c is discharged by the charge remover 14m.
[0043]
The recording paper P on which the color toner image is transferred on the front surface is conveyed to a back surface transfer device 14g to which a voltage having a polarity opposite to that of the toner (positive polarity in the present embodiment) is applied, and the intermediate transfer belt by the back surface transfer device 14g. The back image on the peripheral surface 14a is transferred to the back surface of the recording paper P at once (FIG. 3C).
[0044]
The recording paper P on which the color toner images are formed on both sides is neutralized by the curvature of the curvature portion KT of the intermediate transfer belt 14a and the paper separation AC static eliminator 14h as a transfer material separation means provided at the end of the intermediate transfer belt 14a. The fixing device as a fixing means is separated from the intermediate transfer belt 14 a by the action and the separation claw 210 provided in the conveyance unit 160 with a predetermined distance from the intermediate transfer belt 14 a and through a spur 162 provided in the conveyance unit 160. 17, and is conveyed between the nip portion T between the first fixing roller 17 a and the second fixing roller 17 b, and heat and pressure are added in the nip portion T, whereby the toner image on the recording paper P is formed. It is fixed. The recording paper P on which double-sided image recording has been performed is sent with its front and back reversed and discharged by a paper discharge roller 18 to a tray outside the apparatus.
[0045]
The toner remaining on the peripheral surface of the intermediate transfer belt 14a after the transfer is provided so as to face the guide roller 14f with the intermediate transfer belt 14a interposed therebetween, and abuts against and contacts the intermediate transfer belt 14a with the support shaft 142 as a rotation fulcrum. Cleaning is performed by an intermediate transfer body cleaning device 140 that is an intermediate transfer body cleaning unit having an intermediate transfer body cleaning blade 141 that can be contacted and released.
[0046]
The toner remaining on the peripheral surface of the photosensitive drum 10 after the transfer is discharged by the photosensitive drum AC static eliminator 16 and then cleaned by the cleaning device 19, and is further cleaned by the uniform exposure unit 12e before charging. The history of the photoconductive drum 10 in the image formation is canceled, and the next image formation cycle is started.
[0047]
By using the above method, the superimposed color toner images are collectively transferred, so that color misregistration of the color image on the intermediate transfer belt 14a, toner scattering and rubbing are unlikely to occur, and good double-sided color image with little image deterioration Formation is made.
[0048]
As shown in FIG. 4, the structure of the first fixing roller 17a and the second fixing roller 17b which are two roll-shaped fixing members provided in the fixing device 17 which is a fixing means used in the image forming apparatus is a recording. The first fixing roller 17a for fixing the upper (front side) toner image on the paper P and the second fixing roller 17b for fixing the lower (back side) toner image are respectively halogen heaters at the inner center. A rotating body having substantially the same structure provided with HL1 and HL2. The first fixing roller 17a having the halogen heater HL1 in the center includes a cylindrical metal pipe 171a using, for example, an aluminum material, and a thin wall having a thickness of 1 to 3 mm using, for example, a silicon material on the outer peripheral surface of the metal pipe 171a. A rubber roller layer 172a made of a rubber layer, and a volume resistivity (10 mm) on the surface of the rubber roller layer 172a with a layer thickness (thickness) of 0.05 to 0.25 mm, the volume resistivity (108-1012Ω · cm) or volume resistivity of the recording paper P as a transfer material (approximately the same as the intermediate transfer belt 14a)8-101210 higher than Ω · cm)Ten-1016It is configured as a soft roller on which a high resistance layer 173a having heat resistance and releasability, such as fluororesin such as Ω · cm PFA and PTFE, and silicon resin is formed. Similarly, the second fixing roller 17b having the halogen heater HL2 at the center is formed of a cylindrical metal pipe 171b using, for example, an aluminum material, and a thickness of 1 to 3 mm using, for example, a silicon material on the outer peripheral surface of the metal pipe 171b. A rubber roller layer 172b made of a thin rubber layer and a surface of the rubber roller layer 172b having a layer thickness (thickness) of 0.05 to 0.25 mm and a volume resistivity of 10Ten-1016It is configured as a soft roller on which a high resistance layer 173b having heat resistance and releasability such as fluororesin such as Ω · cm PFA and PTFE and silicon resin is formed. By providing high resistance layers 173a and 173b having a higher volume resistivity than the recording paper P and the intermediate transfer belt 14a on the fixing member of the fixing device 17, the resistance of the fixing member is low, or the fixing member is grounded. In this case, the leakage of charge from the recording paper P and the intermediate transfer belt 14a through the fixing member is prevented, and the fixing member is transferred when the back surface toner image is transferred by the back surface transfer unit 14g disposed near the fixing device 17. The transfer of the back surface toner image due to the leakage of the charge from the recording paper P is prevented from being performed satisfactorily.
[0049]
According to FIG. 4, a recording paper P as a transfer material is carried on a color toner image (negative polarity in the present embodiment) of the surface image formed on the photosensitive drum 10 and the intermediate transfer belt 14a. The back side image is synchronized with the color toner image (negative polarity in the present embodiment) and fed to the transfer area 14b, and in the transfer area 14b, a DC voltage having a polarity opposite to that of the toner (positive polarity in the present embodiment). Is transferred to the surface of the recording paper P at a time by the transfer device 14c to which is applied. At this time, the intermediate transfer belt 14a (volume resistivity is 108-1012Since the surface toner image on the recording paper P is transferred across (Ω · cm), the polarity of the surface toner image on the recording paper P is not changed and is kept negative. In addition, after the charge of the intermediate transfer belt 14a charged to the positive polarity by the transfer device 14c is discharged by the charge remover 14m to which an AC voltage is applied, the back surface toner image on the intermediate transfer belt 14a has a polarity opposite to that of the toner ( In this embodiment, transfer is performed on the back surface of the recording paper P by the back surface transfer device 14g to which a DC voltage of positive polarity) is applied, but the front and back at the position of the circle (a) in FIG. 4 after passing through the back surface transfer device 14g. As shown in FIG. 5, the charge state between the toner image and the recording paper P is maintained at the negative polarity without being converted in polarity, but the negative polarity on the recording paper P is maintained. The front surface toner image is converted into a positive polarity by the polarity conversion by the positive polarity discharge by the back surface transfer device 14g. Further, the surface side of the recording paper P is positively charged by the positive polarity discharge by the back surface transfer device 14g, and the volume resistivity of the recording paper P is low, so that the positive charge is in the center or the back side (back side) of the recording paper P. It is also turning. At this time, the potential of the recording paper P is charged to 1 to 2 kV with a positive polarity.
[0050]
The recording paper P on which the color toner images are formed on both sides has the same polarity as the curvature of the curvature portion KT of the intermediate transfer belt 14a and the DC voltage applied to the end of the intermediate transfer belt 14a and applied to the back surface transfer device 14g. The neutralization action by the paper separation AC neutralizer 14h as a transfer material separation means to which an alternating voltage superimposed with a direct current voltage (positive polarity in the present embodiment as described above with reference to FIG. 5) is applied; Thus, the intermediate transfer belt 14a is separated from the intermediate transfer belt 14a, conveyed to a fixing device 17 as a fixing unit through a spur 162, which is a spur member, and conveyed between the nip portions T between the first fixing roller 17a and the second fixing roller 17b. Then, a loop is formed on the recording paper P while being nipped at the nip T, and the toner image on the recording paper P is fixed by adding heat and pressure at the nip T. By neutralizing the action of the paper separator AC discharger 14h, the potential on the recording paper P 1~2kV positive polarity by reverse side transfer device 14g as described above is discharged by the positive polarity to about 500V.
[0051]
As described above, the volume resistivity of the intermediate transfer belt 14a that is an intermediate transfer member is 10%.8-1012Ω · cm, and the volume resistivity of the recording paper P, which is a transfer material, is approximately the same as that of the intermediate transfer belt 14a.8-1012The volume resistance of the intermediate transfer belt 14a and the recording paper P is Ω · cm, and the first fixing roller 17a and the second fixing roller 17b, which are two roll-shaped fixing members provided in the fixing device 17 that is a fixing unit. 10 higher than rateTen-1016High resistance layers 173a and 173b of Ω · cm are provided. By providing high resistance layers 173a and 173b having a higher volume resistivity than the recording paper P and the intermediate transfer belt 14a on the fixing member of the fixing device 17, the fixing member is provided. Is prevented from leaking from the recording paper P and the intermediate transfer belt 14a through the fixing member, which occurs when the resistance of the fixing member is low, or the fixing member is grounded. When the back surface toner image is transferred by the transfer unit 14g, the back surface toner image is prevented from being transferred favorably due to leakage of charge from the recording paper P through the fixing member. The earth roller 14j and the drive roller 14d to be grounded have a volume resistivity of 108-1012Since it is provided via the Ω · cm intermediate transfer belt 14a, the charge of the recording paper P is not leaked through the ground roller 14j and the drive roller 14d. Further, if the volume resistivity of the first fixing roller 17a and the second fixing roller 17b, which are fixing members, is low, or if the fixing member is grounded, a mirror image charge of the toner on the transfer material is formed on the fixing member. This prevents the mirror image charges from disturbing the front and back toner images on the transfer material and preventing the formation of a good double-sided image.
[0052]
On the other hand, when the fixing member is formed of an insulating member, charges are accumulated in the fixing member, and the toner images on the front and back of the transfer material are disturbed by the accumulated charges, so that a good double-sided image cannot be formed. The so-called fixing device 17 causes the front and back toner images to be disturbed. In order to prevent this, the first fixing roller 17a as the fixing member on the front surface side has the same polarity as that of the recording paper P entering the nip portion T (in this embodiment, as described in FIG. 5). A voltage of 500 to 1500 V is applied from a positive polarity DC power source E1, and the voltage difference between the first fixing roller 17a as the fixing member on the front surface side and the second fixing roller 17b as the fixing member on the back surface side is 200 to 600V. A positive voltage of 100 to 500 V is applied to the second fixing roller 17b as the fixing member on the back surface side by the DC power source E2 so as to be approximately. Although the polarity of the voltage applied to the second fixing roller 17b on the back side is positive, in short, the voltage difference may be about 200 to 600V, and may be a negative voltage or a zero (V) voltage. A voltage difference is provided between the front and back fixing members because the solid toner layer potential is front and back (as described in FIG. 5, the front toner image has a positive polarity and the back toner image has a negative polarity), and each has an absolute value of 100 to 200 V. Therefore, since the solid portion potential difference is 200 to 400 V on the front and back sides, the above-described voltage difference is provided on the fixing members on the front and back sides, and the first fixing roller 17a on the front side as shown by the dotted arrow in FIG. An electric field is generated toward the fixing roller 17b, and the surface toner image having a positive polarity on the recording paper P is formed on the recording paper P by the electric field having a positive polarity on the front surface side. Are held on the recording paper P so as to be pressed onto the recording paper P, respectively, to prevent toner adhesion to the fixing member and surrounding contamination due to scattering.
[0053]
Further, without using the DC power sources E1 and E2, as shown in FIG. 6, the zener diode ZD1 is connected to the first fixing roller 17a on the front surface side, and the zener diode ZD2 is connected to the second fixing roller 17b on the back surface side. As a configuration in which the fixing roller 17a and the second fixing roller 17b maintain substantially the same potential as the recording paper P added to the nip portion T, toner images on the front and back surfaces are held on the recording paper P, and the toner on the fixing member due to scattering is retained. It is also possible to prevent adhesion and dirt around.
[0054]
As a result, leakage from the transfer material is prevented, and the transfer of the back toner image is performed well, and the front and back toner images are not disturbed by the fixing unit and the repelling of the toner on the front and back is prevented, and a good double-sided image is formed. The
[0055]
Another embodiment of the image forming apparatus according to the present invention will be described with reference to FIG. FIG. 7 is a schematic explanatory diagram of a color image forming apparatus showing another embodiment of the image forming apparatus according to the present invention.
[0056]
In the image forming apparatus of this example, as shown in FIG. 7, a photosensitive drum 10b, which is a first image carrier that forms a toner image (back surface toner image) to be a back image, and a toner image ( A photosensitive drum 10a, which is a second image carrier that forms a front surface toner image), is separately provided, and the back toner image formed on the photosensitive drum 10b is opposite in polarity to the toner (in this embodiment, a positive polarity). ) Is applied to the intermediate transfer belt 114a, which is an intermediate transfer member, by the primary transfer device 114b to which a voltage is applied, and then the transfer material is transferred onto the intermediate transfer belt 114a between the photosensitive drum 10b and the photosensitive drum 10a. A certain recording paper P is supplied, and the recording paper P is absorbed by the intermediate transfer belt 114a by charging of a paper charger 150 provided opposite to the earth roller 14k with the intermediate transfer belt 114a interposed therebetween. The surface toner image formed on the photosensitive drum 10a is transferred onto the surface of the recording paper P by the secondary transfer device 114c to which a voltage having a polarity opposite to that of the toner (plus polarity in this embodiment) is applied. After that, the back side toner image on the intermediate transfer belt 114a is transferred to the back side of the recording paper P by the tertiary transfer unit 114g to which a voltage having a polarity opposite to that of the toner (positive polarity in the present embodiment) is applied. The recording paper P in which the front and back toner images are formed on the paper P and the color toner images are formed on both sides is formed on the curvature of the curvature portion KT of the intermediate transfer belt 114a and the end of the intermediate transfer belt 114a as necessary. The neutralization action by the paper separation AC neutralizer 14h as the transfer material separation means provided, and the separation claw 210 provided in the transport unit 160 at a predetermined interval from the intermediate transfer belt 114a. The nip between the first fixing roller 17a and the second fixing roller 17b is separated from the intermediate transfer belt 114a and conveyed to a fixing device 17 as fixing means through a spur 162 which is a spur member provided in the conveying unit 160. The toner image on the recording paper P is fixed at the portion T to obtain a double-sided image.
[0057]
The photosensitive drums 10a and 10b and the intermediate transfer belt 114a in the image forming apparatus of this example have the same function and structure as the photosensitive drum 10 and the intermediate transfer belt 14a described in the image forming apparatus. The intermediate transfer belt 114a is stretched in contact with a driving roller 14d, a ground roller 14j, a ground roller 14k, a driven roller 14e, a guide roller 14f, and a tension roller 14i, which are roller members. Further, the static eliminators 114m and 114n serving as static eliminators are respectively connected to the primary transfer unit 114b and the secondary transfer unit 114c after the primary transfer unit 114b and the secondary transfer unit 114c in the moving direction of the intermediate transfer belt 114a. The charge of the intermediate transfer belt 114a, which is provided in parallel and charged by applying the voltage of the primary transfer device 114b and the secondary transfer device 114c, is applied with an AC voltage superimposed with a DC voltage of the same polarity or opposite polarity as the toner. Remove static electricity.
[0058]
Means for forming a toner image to be the back image on the photosensitive drum 10b as the first image carrier and means for forming the toner image to be the front image on the photosensitive drum 10a as the second image carrier. 4 sets of developing devices 13 (developing means) for the image forming process of yellow (Y), magenta (M), cyan (C) and black (K), similar to those used in the image forming apparatus described above. A scorotron charger 11 (charging means) and an exposure optical system 12 (image writing means) are used for the photosensitive drums 10b and 10a, respectively, to form a toner image of the back image and a toner image of the front image, respectively. .
[0059]
Also in this example, the first fixing roller 17a and the second fixing roller 17b, which are both fixing members, have the same structure as described in FIG. 4, and the first fixing roller 17a and the second fixing roller 17b Respectively, as a surface layer, the volume resistivity (108-1012Ω · cm) or volume resistivity of the recording paper P as a transfer material (approximately the same as the intermediate transfer belt 114a)8-101210 higher than Ω · cm)Ten-1016High resistance layers 173a and 173b having heat resistance and releasability such as fluororesins such as Ω · cm PFA and PTFE and silicon resins are provided. By providing high resistance layers 173a and 173b having a higher volume resistivity than the recording paper P and the intermediate transfer belt 114a on the fixing member of the fixing device 17, the resistance of the fixing member is low or the fixing member is grounded. In this case, charge leakage from the recording paper P or the intermediate transfer belt 114a through the fixing member is prevented, and fixing is performed when the back surface toner image is transferred by the tertiary transfer device 114g disposed near the fixing device 17. This prevents the back surface toner image from being transferred favorably due to charge leakage from the recording paper P through the member.
[0060]
A color toner image of the front surface image (negative polarity in the present embodiment) formed on the photosensitive drum 10a by the recording paper P as a transfer material, and a color toner image of the back surface image carried on the intermediate transfer belt 114a. (Negative polarity in this embodiment) is synchronized and fed onto the intermediate transfer belt 114a, and a DC voltage having a polarity opposite to that of the toner (positive polarity in this embodiment) is applied in the transfer area 2 The surface image on the photosensitive drum 10a is transferred to the surface of the recording paper P at a time by the next transfer device 114c. At this time, the intermediate transfer belt 114a (volume resistivity is 108-1012Since the surface toner image on the recording paper P is transferred across (Ω · cm), the polarity of the surface toner image on the recording paper P is not changed and is kept negative. Further, after the charge of the intermediate transfer belt 114a charged to the positive polarity by the secondary transfer device 114c is discharged by the discharger 114n to which an AC voltage is applied, the back surface toner image on the intermediate transfer belt 114a is opposite to the toner. The toner image is transferred to the back surface of the recording paper P by the tertiary transfer device 114g to which a DC voltage having a polarity (positive polarity in this embodiment) is applied. As in the case described with reference to FIG. 5, the back surface toner image on the recording paper P is kept in the negative polarity without being converted, but the negative polarity surface toner image on the recording paper P is The polarity is changed to positive polarity by positive polarity discharge by the tertiary transfer device 114g. Further, the surface side of the recording paper P is positively charged by the positive polarity discharge by the tertiary transfer device 114g, and the volume resistivity of the recording paper P is low, so that the positive charge is in the center or back side (back side) of the recording paper P. ). At this time, the potential of the recording paper P is charged to 1 to 2 kV with a positive polarity.
[0061]
The recording paper P on which the color toner images are formed on both sides is the same as the curvature of the curvature portion KT of the intermediate transfer belt 114a and the DC voltage applied to the end of the intermediate transfer belt 114a and applied to the tertiary transfer device 114g. The neutralization action by the paper separation AC neutralizer 14h as a transfer material separation means to which an alternating voltage superimposed with a direct current voltage of polarity (positive polarity in the present embodiment as described above in FIG. 5) is applied, and the separation claw 210 Are separated from the intermediate transfer belt 114a and conveyed to a fixing device 17 as fixing means through a spur 162, which is a spur member, and between the nip portions T between the first fixing roller 17a and the second fixing roller 17b. A loop (not shown) is formed on the recording paper P while being conveyed and nipped at the nip T, and heat and pressure are added to the recording paper P at the nip T, so -The image is fixed, but due to the neutralization action of the paper separation AC neutralizer 14h, the potential on the positive polarity 1-2kV recording paper P by the tertiary transfer device 114g is neutralized to about 500V with the positive polarity. .
[0062]
As described in the previous example, the volume resistivity of the intermediate transfer belt 114a that is an intermediate transfer member is 10%.8-1012The volume resistivity of the recording paper P, which is a transfer material, is approximately the same as that of the intermediate transfer belt 114a.8-1012The volume resistance of the intermediate transfer belt 114a and the recording paper P is Ω · cm, and the first fixing roller 17a and the second fixing roller 17b that are two roll-shaped fixing members provided in the fixing device 17 that is a fixing unit. 10 higher than rateTen-1016High resistance layers 173a and 173b of Ω · cm are provided. By providing high resistance layers 173a and 173b having higher volume resistivity than the recording paper P and the intermediate transfer belt 114a on the fixing member of the fixing device 17, the fixing member is provided. The leakage of electric charges from the recording paper P and the intermediate transfer belt 114a through the fixing member, which occurs when the resistance of the fixing member 17 is low or the fixing member is grounded, is prevented. When the back surface toner image is transferred by the next transfer unit 114g, the back surface toner image is prevented from being transferred favorably due to leakage of charge from the recording paper P through the fixing member. The earth roller 14j and the drive roller 14d to be grounded have a volume resistivity of 108-1012Since it is provided via the intermediate transfer belt 114a of Ω · cm, the charge of the recording paper P is not leaked through the ground roller 14j and the drive roller 14d. Further, if the volume resistivity of the first fixing roller 17a and the second fixing roller 17b, which are fixing members, is low, or if the fixing member is grounded, a mirror image charge of the toner on the transfer material is formed on the fixing member. This prevents the mirror image charges from disturbing the front and back toner images on the transfer material and preventing the formation of a good double-sided image.
[0063]
On the other hand, when the fixing member is formed of an insulating member, charges are accumulated in the fixing member, and the toner images on the front and back of the transfer material are disturbed by the accumulated charges, so that a good double-sided image cannot be formed. The so-called fixing device 17 causes the front and back toner images to be disturbed. In order to prevent this, the first fixing roller 17a as the fixing member on the front surface side has the same polarity as that of the recording paper P entering the nip portion T (in this embodiment, as described in FIG. 5). A positive polarity) DC power source E1 (see FIG. 4; not shown in FIG. 7) applies a voltage of 500 to 1500 V, and the first fixing roller 17a as the fixing member on the front side and the first fixing member as the fixing member on the back side. The second fixing roller 17b as a fixing member on the back side is positively charged 100 by a DC power source E2 (see FIG. 4, not shown in FIG. 7) so that the voltage difference with the two fixing rollers 17b is about 200 to 600V. Apply a voltage of ~ 500V. Although the polarity of the voltage applied to the second fixing roller 17b on the back side is positive, in short, the voltage difference may be about 200 to 600V, and may be a negative voltage or a zero (V) voltage. A voltage difference is provided between the front and back fixing members because the solid toner layer potential is front and back (as described in FIG. 5, the front toner image has a positive polarity and the back toner image has a negative polarity), and each has an absolute value of 100 to 200 V. Therefore, since the solid portion potential difference is 200 to 400 V on the front and back sides, the voltage difference is provided on the fixing members on the front and back sides, and as described with reference to FIG. 4, the first fixing roller 17a on the front side and the second side on the back side. An electric field (see FIG. 4; not shown in FIG. 7) is generated toward the fixing roller 17b, and a positive polarity surface toner image on the recording paper P is formed on the recording paper P by the electric field having a positive polarity on the front side. The negative polarity back toner image on the recording paper P is held on the recording paper P by the electric field having a negative polarity on the recording paper P, and the toner adheres to the fixing member due to scattering or the surroundings. Dirty The to prevent.
[0064]
As described with reference to FIG. 6, a zener diode ZD1 (see FIG. 6, not shown in FIG. 7) is provided on the first fixing roller 17a on the front surface side, and a zener diode ZD2 (see FIG. 6) on the second fixing roller 17b on the back surface side. 6 (not shown in FIG. 7) are connected, and the recording paper P is configured such that the first fixing roller 17a and the second fixing roller 17b maintain substantially the same potential as the recording paper P added to the nip portion T. It is also possible to hold toner images on the front and back and prevent toner adhesion to the fixing member and surrounding contamination due to scattering.
[0065]
As a result, leakage from the transfer material is prevented, and the transfer of the back toner image is performed well, and the front and back toner images are not disturbed by the fixing unit and the repelling of the toner on the front and back is prevented, and a good double-sided image is formed. The
[0066]
In each example of the image forming apparatus described above, the toner image is directly formed on the image carrier. However, the image carrier is provided separately from the image carrier, and the toner image formed on the image carrier is used as the image carrier. You may make it carry | support on. The color image forming apparatus has been described as each example of the image forming apparatus. However, the present invention is not necessarily limited to this, and a monochrome image by the same process as described in FIG. 1 or FIG. The present invention is also applied to a forming apparatus.
[0067]
Further, in the image forming apparatus according to the present invention, in addition to the double-sided image formation for forming images on both sides of the transfer material as described in each of the image forming apparatuses described above, an image is formed on only one side of the transfer material. Of course, single-sided image formation can also be performed.
[0068]
Incidentally, by using the double-sided image forming apparatus described with reference to FIG. 1 or FIG. 7, there is a problem in the double-sided image forming apparatus using the conventional double-sided reverse feeding apparatus,
● The 1st print speed is slow on both sides.
[0069]
● Paper (transfer material) transport is unreliable and jamming is likely to occur.
[0070]
● When a jam occurs, the paper passing route is long, so a lot of paper is wasted and jam handling is difficult.
[0071]
● There are restrictions on the types of paper that can be used, and it cannot be used for small-size paper such as thick paper, thin paper, and postcards, and irregular-size paper.
[0072]
● Fixing oil pollutes the paper path, especially in the case of color.
[0073]
● The process is not stable because heat is brought into the machine.
[0074]
The following effects are achieved.
[0075]
○ Since there is no waiting time for paper (transfer material) reversal, it is possible to continue image formation on both sides of the paper, and the 1st print speed on both sides is increased.
[0076]
○ Since it is not necessary to re-feed the paper after passing through the fixing means, the paper feeding reliability is greatly improved. In addition, there is no contamination of the paper path by fixing oil and no heat is brought into the machine.
[0077]
○ Since double-sided printing is possible with exactly the same feeding system as single-sided, there are no restrictions on the type of transfer material.
[0078]
○ Because there is no paper reversing path, less paper is wasted when a jam occurs, and jam handling is easy.
[0079]
○ Since the number of sheets passing through the fixing means on both sides is half that on one side, fixing power consumption is reduced.
[0080]
【The invention's effect】
According to the present invention, leakage from the transfer material is prevented and the transfer of the toner image onto the back surface of the transfer material is performed well, and the front and back toner images are prevented from being disturbed by the fixing unit, and a good double-sided image is formed. Is done.
[Brief description of the drawings]
FIG. 1 is a cross-sectional configuration diagram of a color image forming apparatus showing an embodiment of an image forming apparatus according to the present invention.
2 is a side sectional view of the image carrier in FIG. 1. FIG.
FIG. 3 is a diagram illustrating a toner image forming state in the image forming apparatus according to the present invention.
FIG. 4 is a diagram illustrating a structure of a fixing member used for fixing means and voltage application to the fixing member for preventing toner disturbance on a transfer material.
FIG. 5 is a diagram illustrating a transfer material after a toner image is transferred to both surfaces of the transfer material and a charged state of toner on the transfer material.
FIG. 6 is a diagram illustrating another example of preventing toner disturbance on a transfer material.
FIG. 7 is a schematic explanatory view of a color image forming apparatus showing another embodiment of the image forming apparatus according to the present invention.
[Explanation of symbols]
10, 10a, 10b Photosensitive drum
11 Scorotron charger
12 Exposure optics
13 Developer
14a, 114a Intermediate transfer belt
14c Transfer device
14g Back transfer device
14h Paper separation AC static eliminator
14m, 114m, 114n
17 Fixing device
17a First fixing roller
17b Second fixing roller
114b Primary transfer device
114c secondary transfer device
114g tertiary transfer device
173a, 173b High resistance layer
E1, E2 DC power supply
P Recording paper

Claims (7)

像担持体と、
該像担持体上にトナー像を形成する手段と、
前記像担持体上のトナー像が転写され、転写された該トナー像を表面に担持するとともに、転写材を支持搬送する無端ベルト状の中間転写体と、
前記像担持体上のトナー像を前記中間転写体に転写する手段と、
前記像担持体上のトナー像を前記転写材の表面に転写する手段と、
前記中間転写体上のトナー像を前記転写材の裏面に転写する手段と、
対となって回動する定着部材により前記転写材を挟持搬送して前記転写材の両面に転写されたトナー像を定着する手段とを有する画像形成装置において、
前記転写材の表面側および裏面側の定着部材にはそれぞれ体積抵抗率が10 10 〜10 16 Ω・cmである高抵抗層けると共に、両面にトナー像が転写された前記転写材と同極性の電圧が印加され、
前記転写材の表面側の定着部材に印加される電圧の絶対値は、前記転写材の裏面側の定着部材に印加される電圧の絶対値より高く設定されていることを特徴とする画像形成装置。
An image carrier;
Means for forming a toner image on the image carrier;
An endless belt-shaped intermediate transfer body that transfers the toner image on the image carrier, supports the transferred toner image on the surface, and supports and conveys the transfer material;
Means for transferring a toner image on the image carrier to the intermediate transfer member;
Means for transferring the toner image on the image carrier to the surface of the transfer material;
Means for transferring the toner image on the intermediate transfer member to the back surface of the transfer material;
In an image forming apparatus, the image forming apparatus includes: a fixing member that rotates as a pair; and a unit that fixes and transfers the toner image transferred to both surfaces of the transfer material by sandwiching and transferring the transfer material.
Front and each of the fixing member of the rear volume resistivity with kick set the high resistance layer is 10 10 ~10 16 Ω · cm of the transfer material, the said transfer material with the toner image transferred on both surfaces A polarity voltage is applied,
The absolute value of the voltage applied to the fixing member on the front side of the transfer material is set higher than the absolute value of the voltage applied to the fixing member on the back side of the transfer material. .
第1の像担持体と、
第2の像担持体と、
前記第1の像担持体上にトナー像を形成する手段と、
前記第2の像担持体上にトナー像を形成する手段と、
前記第1の像担持体上のトナー像が転写され、転写された該トナー像を表面に担持するとともに、転写材を支持搬送する無端ベルト状の中間転写体と、
前記第1の像担持体上のトナー像を前記中間転写体に転写する手段と、
前記第2の像担持体上のトナー像を前記転写材の表面に転写する手段と、
前記中間転写体上のトナー像を前記転写材の裏面に転写する手段と、
対となって回動する定着部材により前記転写材を挟持搬送して前記転写材の両面に転写されたトナー像を定着する手段とを有する画像形成装置において、
前記転写材の表面側および裏面側の定着部材にはそれぞれ体積抵抗率が10 10 〜10 16 Ω・cmである高抵抗層けると共に、両面にトナー像が転写された前記転写材と同極性の電圧が印加され、
前記転写材の表面側の定着部材に印加される電圧の絶対値は、前記転写材の裏面側の定着部材に印加される電圧の絶対値より高く設定されていることを特徴とする画像形成装置。
A first image carrier;
A second image carrier;
Means for forming a toner image on the first image carrier;
Means for forming a toner image on the second image carrier;
An endless belt-like intermediate transfer member that transfers the toner image on the first image carrier, supports the transferred toner image on the surface, and supports and conveys the transfer material;
Means for transferring a toner image on the first image carrier to the intermediate transfer member;
Means for transferring the toner image on the second image carrier to the surface of the transfer material;
Means for transferring the toner image on the intermediate transfer member to the back surface of the transfer material;
In an image forming apparatus, the image forming apparatus includes: a fixing member that rotates as a pair; and a unit that fixes and transfers the toner image transferred to both surfaces of the transfer material by sandwiching and transferring the transfer material.
Front and each of the fixing member of the rear volume resistivity with kick set the high resistance layer is 10 10 ~10 16 Ω · cm of the transfer material, the said transfer material with the toner image transferred on both surfaces A polarity voltage is applied,
The absolute value of the voltage applied to the fixing member on the front side of the transfer material is set higher than the absolute value of the voltage applied to the fixing member on the back side of the transfer material. .
前記定着部材に設けられる高抵抗層の抵抗値は前記中間転写体の抵抗値よりも高いことを特徴とする請求項1または2に記載の画像形成装置。  The image forming apparatus according to claim 1, wherein a resistance value of a high resistance layer provided on the fixing member is higher than a resistance value of the intermediate transfer member. 前記定着部材に設けられる高抵抗層の抵抗値は前記転写材の抵抗値よりも高いことを特徴とする請求項1〜3の何れか1項に記載の画像形成装置。  The image forming apparatus according to claim 1, wherein a resistance value of a high resistance layer provided on the fixing member is higher than a resistance value of the transfer material. 前記転写材の表面側の定着部材には500〜1500Vの電圧が印加されていることを特徴とする請求項1〜4の何れか1項に記載の画像形成装置。The image forming apparatus according to claim 1, wherein a voltage of 500 to 1500 V is applied to a fixing member on a surface side of the transfer material . 前記転写材の裏面側の定着部材には100〜500Vの電圧が印加されていることを特徴とする請求項1〜5の何れか1項に記載の画像形成装置。The image forming apparatus according to claim 1, wherein a voltage of 100 to 500 V is applied to a fixing member on a back surface side of the transfer material . 前記転写材の表面側の定着部材に印加される電圧と前記転写材の裏面側の定着部材に印加される電圧との差は200〜600Vであることを特徴とする請求項1〜6の何れか1項に記載の画像形成装置。Any of claims 1 to 6, wherein the difference between the voltage applied to the fixing member on the back side of the voltage applied to the fixing member of the surface side of the transfer material and the transfer material is 200~600V The image forming apparatus according to claim 1.
JP36948598A 1998-12-22 1998-12-25 Image forming apparatus Expired - Lifetime JP3826594B2 (en)

Priority Applications (2)

Application Number Priority Date Filing Date Title
JP36948598A JP3826594B2 (en) 1998-12-25 1998-12-25 Image forming apparatus
US09/468,500 US6205301B1 (en) 1998-12-22 1999-12-21 Two-sided image forming apparatus

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JP36948598A JP3826594B2 (en) 1998-12-25 1998-12-25 Image forming apparatus

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JP3826594B2 true JP3826594B2 (en) 2006-09-27

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JP2002123098A (en) * 2000-08-10 2002-04-26 Ricoh Co Ltd Heat resistant transfer belt and image forming device equipped therewith

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