JP3728382B2

JP3728382B2 - Wet image forming device

Info

Publication number: JP3728382B2
Application number: JP19674898A
Authority: JP
Inventors: 貞之岩井
Original assignee: Ricoh Co Ltd
Current assignee: Ricoh Co Ltd
Priority date: 1998-06-26
Filing date: 1998-06-26
Publication date: 2005-12-21
Anticipated expiration: 2018-06-26
Also published as: JP2000019859A

Description

【０００１】
【発明の属する技術分野】
本発明は、複写機、ファクシミリ、プリンタ等の画像形成装置に係り、詳しくは、液体現像剤を用いて像担持体上の静電潜像を現像する湿式現像装置と、該湿式現像装置で現像された像担持体上のトナー像を転写材に転写するための中間転写体とを備えた湿式画像形成装置に関するものである。
【０００２】
【従来の技術】
従来、像担持体としての感光体に形成された静電潜像を帯電粒子であるトナーで現像する湿式現像装置で、該湿式現像装置を小型化できるように、現像剤のトナー濃度を高めに設定した高濃度・高粘度の現像剤を用いることが提案されている。例えば、特開平７―２０９９２２号公報では、「画像支持体上に形成された静電潜像を、帯電した顕像化粒子であるトナーによって現像する静電潜像の液体現像方法であって、導電性を有する現像剤支持体上に塗布された絶縁性液体中にトナーが高濃度に分散された、１００〜１００００ｍＰａ・ｓの高粘度の液体現像剤を、前記画像支持体の潜像面に前記液体現像剤を供給する現像手段を備えることを特徴とする静電潜像の液体現像方法」が提案されている。
また、従来、上記中間転写体としての中間転写ベルトと、トナーが固体（粉体）の乾式現像剤を用いる乾式現像装置とを備えた乾式画像形成装置が提案されている。この乾式画像形成装置では、像担持体としての感光体ドラム上に形成されたトナー像を中間転写体としての中間転写ベルトに１回、あるいは複数回、転写し（１次転写）、上記中間転写ベルト上のトナー像を転写材に一括転写する（２次転写）。
【０００３】
上記中間転写ベルトは、体積抵抗で１０⁶Ωｃｍ以上、望ましくは、１０⁸〜１０⁹Ωｃｍの中間転写ベルトを用いるのが一般的である。これは、上記乾式画像形成装置では、トナーが粉体であり、中間転写ベルトの抵抗値が低すぎると、１次転写後にトナーのチリ（飛翔）という現象が発生してトナー像を乱すため、抵抗値を上げねばならなかったからである。上記中間転写ベルトの体積抵抗が、１０⁸〜１０⁹Ωｃｍ程度のいわゆる中抵抗である場合、該中間転写ベルトは環境にたいする抵抗の安定性にも問題を有していた。さらに、中間転写ベルトの抵抗値が高い場合、複数色のトナー像を重ね合わせる１次転写を行うと、１次転写の各色のトナー像の転写が行われる度ごとに１次転写電荷付与手段としての１次転写バイアスローラから中間転写ベルト裏面に電荷が付与され、中間転写ベルト表面の帯電量は、一次転写の回数に応じて大きくなっていき、複数色のトナー像の重ね合わせを行うときに各色において１次転写条件が異なってくる。この１次転写条件を揃えるためには中間転写ベルトの過剰帯電を除電する除電装置を設けたりする必要があり、これによるコストのアップ、また制御の困難さを有している。また、中間転写ベルトの抵抗値が高いと一次転写に必要な電荷量を付与することが困難になり、速い速度での１次転写に対する電荷量の供給が難しく、画像の輪郭だけが転写され、中程が転写されにくくなる現象が起こり、中間転写ベルトに印加する電圧も上げねばならなかった。
しかし、中間転写ベルトの抵抗値が低すぎる場合、トナー層にムラがあったり、感光体ドラムにキズがあったりすると、感光体ドラムにダメージを与える虞がある。このため、中間転写ベルトの体積抵抗の下限を、１０⁰Ωｃｍとする。
【０００４】
以上の点を考慮して、高粘性の液体現像剤を用いて小型化した湿式現像装置と、該湿式現像装置で現像された像担持体上のトナー像を転写材に転写するための中間転写体とを備えた湿式画像形成装置において、体積抵抗が１０⁰Ωｃｍ以上で１０³Ωｃｍ以下の低抵抗の中間転写ベルトを用いることにより、高価な除電装置や複雑な制御を必要とせず、高画質な画像を得ることができる。
【０００５】
【発明が解決しようとする課題】
しかしながら、中間転写体としてほとんど導体のような低抵抗の中間転写ベルトを用いた場合、中間転写ベルトの一部が感光体ドラムと接して転写バイアスが印加され１次転写が行われている最中に、同じ中間転写ベルトの他の部分が転写紙と接し、転写バイアスを印加して２次転写を行おうとすると、２次転写のために印加されている転写バイアスによるバイアス電流が１次転写側にまで回り込み、１次転写のバイアス電位が変動して、良好な画像の転写を阻害する虞れがある。
そのため、上述の湿式画像形成装置では、１次転写と２位転写を同時に行うことができないため、生産性が低いと共に、中間転写ベルトを感光体ドラムから接離する装置を必要とする不具合を有していた。
【０００６】
本発明は以上の問題点に鑑みなされたものであり、その目的とするところは、液体現像剤を用いた湿式現像装置と、低抵抗の中間転写体とを備えた湿式画像形成装置で、２次転写のバイアス電流の１次転写部分への回り込みをなくして、突入電流などによる１次転写のバイアス電位が変動しないようにする。これにより、１次転写と２次転写を同時に行っても、良好な１次転写ができるようにして、中間転写体を像担持体から接離するための複雑な可動装置を必要としない低コストで生産性の高い、かつ、高画質な画像が得られる湿式画像形成装置を提供することである。
【０００７】
【課題を解決するための手段】
上記目的を達成するために、請求項１の発明は、表面に静電潜像を形成する像担持体と、該像担持体上の静電潜像を高粘性液体現像剤で現像する湿式現像器と、該液体現像器で現像された前記像担持体上のトナー像が転写される中間転写体と、該中間転写体に転写されたトナー像が転写される転写材とを備え、前記像担持体上のトナー像を前記中間転写体上に転写する１次転写と、前記中間転写体上のトナー像を前記転写材上に転写する２次転写とを行う湿式画像形成装置において、前記中間転写体として、その体積抵抗が１０^０Ωｃｍ以上で１０^３Ωｃｍ以下の無端ベルトを用い、かつ、該無端ベルトに、前記１次転写側のバイアスを印加するためのバイアス電極と前記２次転写側のバイアスを印加するためのバイアス電極との間で、前記１次転写のバイアス電位と同電位を保持する電位保持手段を設け、前記無端ベルトの一部で前記像担持体から前記中間転写体への前記１次転写を行っている最中に、前記無端ベルトの他の一部で前記中間転写体から前記転写材への前記２次転写を行うことを特徴とするものである。
この請求項１の湿式画像形成装置では、低抵抗の無端ベルトに設けた電位保持手段により、２次転写バイアス電流の１次転写部分への回り込みによる１次転写のバイアス電位の変動がない。よって、１次転写と２次転写とを同時におこなっても、良好に１次転写ができる。また、無端ベルトを潜像担持体に接触させたままにしておける。
【０００８】
また、請求項２の発明は、請求項２の湿式画像形成装置において、前記電位保持手段の保持する電位は接地電位であることを特徴とするものである。
この請求項２の湿式画像形成装置では、電位を保持するための新たな電源等を必要としない。
【０００９】
また、請求項２の発明は、請求項１の湿式画像形成装置において、前記液体現像剤が、１００〜１００００ｍＰａ・ｓの高粘度の液体現像剤であることを特徴とするものである。
【００１１】
請求項３の発明は、請求項１、又は、２の湿式画像形成装置において、前記電位保持手段による所定電位の保持は、該無端ベルトを懸架するための懸架部材を介して行われることを特徴とするものである。
この請求項１の湿式画像形成装置では、電位の保持のために別部材を設ける必要がない。
【００１２】
上記感光体ドラム１０は矢印の時計方向に回転可能となっており、その回りには、帯電ローラ２０、湿式現像ユニット４０、中間転写ユニット５０、除電装置６０、感光体クリーニング装置７０及び不図示の露光装置等が配設されている。上記中間転写ユニット５０は、懸架ローラ５１、５２、５３、これらの懸架ローラ５１、５２、５３に張架された中間転写体としての中間転写ベルト５５、及びクリーニングブレードを有するクリーニング装置５９等から構成されている。上記紙転写ユニット８０は、２次転写電荷付与手段としての２次転写バイアスローラ８１及び該２次転写バイアスローラ８１に接続された２次転写電源８２等から構成されている（図２参照）。
【００１３】
上記トナー塗布装置９０は、液体現像剤を溜める現像タンク９２と、該現像タンク９２内の液体現像剤に浸漬するように配設された汲み上げローラ９３と、該汲み上げローラ９３から汲み上げられた液体現像剤を薄層化して現像ベルトに塗布する塗布ローラ９４等から構成されている。
上記液体現像剤は絶縁体溶媒であるキャリア液体中に顕像化粒子であるトナー粒子が高濃度に分散された高粘度の液体現像剤である。
上記現像ユニット４０は、複数のベルトローラと、これらのベルトローラに張架された現像剤担持体としての現像ベルト４１等から構成されており、該現像ベルト４１は前記塗布ローラ９４で液体現像剤が塗布されるようになっている。
【００１４】
図２は、中間転写ベルト、１次転写バイアスローラ及び２次転写バイアスローラ等の構成を説明する説明図である。
上記中間転写ベルト５５は、懸架部材としての懸架ローラ５１、懸架ローラ５２、懸架ローラ５３及び１次転写電荷付与手段としての１次転写バイアスローラ５４に所定の張力を有するように張架され、矢印の反時計方向に回転可能となっている。上記１次転写バイアスローラ５４は感光体ドラム１０に対向し、これら１次転写バイアスローラ５４と感光体ドラム１０との間に、中間転写ベルト５５を挟み込むような配置となっている。前記１次転写バイアスローラ５４は、１次転写バイアスを与える電極ともなっており、該１次転写バイアスローラ５４には１次転写電源５６から所定の転写バイアスが印加される。
なお、上記中間転写ベルト５５は、所定厚さの低抵抗の導電性部材の無端ベルトで、たとえば厚さが３０〜１５０μｍで、ポリイミドやＰＥＴ（ポリエチレンテレフタレート）、ＰＶＤＦ樹脂などに導電性の物質（カーボンや金属粉等）を一定割合で混入させたものである。上記中間転写ベルト５５は体積抵抗が１０⁰〜１０³Ωｃｍのものが主に用いられている。また、２次転写性を良くするために、該中間転写ベルト５５のトナー粒子が付着する側にフッ素系、もしくはシリコン系の導電性樹脂で１〜１０μｍ程度被覆して離型性を上げる場合もある。
前記懸架ローラ５３に対向して、２次転写電荷付与手段としての２次転写バイアスローラ８１が配設されており、該２次転写バイアスローラ８１は、２次転写バイアスを与える電極ともなっている。該２次転写バイアスローラ８１には２次転写電源８２から所定の転写バイアスが印加される。
【００１５】
次に、本実施形態に係る湿式電子写真複写機の動作について、図面に基づき説明する。
上述した低抵抗の中間転写ベルト５５を用いた湿式電子写真複写機で、図３に示すように、上記懸架ローラ５１、懸架ローラ５２及び懸架ローラ５３が電気的にフロートの場合に１次転写と２次転写とを同時に行おうとすると、２次転写バイアス電流が１次転写側にまで影響を及ぼし、たとえば、１次転写のバイアス電位が下がって、１次転写の転写条件を乱す虞れがある。
そこで、中間転写ベルト５５上に１次転写部分と２次転写部分との間で一定の電位を保持する電位保持点を設け、２次転写によるバイアス電流及び電位変動を吸収・調整し、１次転写部分に影響が及ばないようにする。また、中間転写ベルト５５上に電位保持点を設けると、完全な導体になっていない中間転写ベルト５５の低抵抗値により、１次転写バイアス電位と、懸架ローラ５１及び懸架ローラ５２における電位との電位差は一定となる。
以下、上記中間転写ベルト５５に電位保持点を設けた場合について、図１及び図４に基づいて説明する。図４は、中間転写ベルト５５を懸架する懸架ローラ５１及び懸架ローラ５２が接地されている場合に、１次転写と２次転写とを同時におこなったときの電流の流れを説明する説明図である。
図１に示すように、感光体ドラム１０を矢印方向に回転駆動しながら帯電ローラ２０で一様帯電した後、図示しない露光装置からの光３０を照射して感光体ドラム１０上に静電潜像を形成する。一方、現像タンク９２の高粘性液体現像剤に浸漬されているローラ９３に付着した液体現像剤は塗布ローラ９４を介して現像ベルト４１上に均一、たとえば、０．５〜２０μｍ程度の厚さに塗布される。
そして、上記感光体ドラム１０に現像ベルト４１を接触させ、該感光体ドラム１０の表面に形成された静電潜像に液体現像剤中のトナーを電界の力で移行させて現像し、トナー像を形成する。
【００１６】
ついで、該トナー像が形成された感光体ドラム１０を回転し、該感光体ドラム１０と中間転写ベルト５５とが当接する１次転写部分に移動する（図４参照）。そして、該１次転写部分で、上記中間転写ベルト５５裏面に１次転写バイアスローラ５４を介し、正極性トナーの逆極性である負極性バイアス電圧、たとえば、−３５０Ｖ程度を印加し、この印加電圧によって発生した電界で、上記感光体ドラム１０上のトナー像のトナーを、中間転写ベルト５５に引き寄せ、該中間転写ベルト５５上に転写する（１次転写）。
ついで、該１次転写で中間転写ベルト５５上にトナー像を転写しながら、トナー像の転写された中間転写ベルト５５を回転し、該中間転写ベルト５５と不図示の給紙部から矢印方向に搬送された転写紙１００とが当接する２次転写部分に移動する。この２次転写部分において、上記転写紙１００裏面に２次転写バイアスローラ８１を介して、負極性のバイアス電圧を印加し、この印加電圧によって発生した電界で、中間転写ベルト５５のトナーを転写紙１００に引き寄せ、該転写紙１００に転写する（２次転写）。該２次転写のとき、転写紙１００と中間転写ベルト５５との間の電位差は約３００Ｖで、２次転写側の方が低電圧になっている。また、上記２次転写を行うと、２次転写バイアスローラ８１から中間転写ベルト５５に電流が流れ込む構成になっている。なお、上記懸架ローラ５１及び懸架ローラ５２と１次転写バイアスローラ５４との電位差は−３００Ｖである。
上述のように懸架ローラ５１及び懸架ローラ５２が電気的に接地されている場合で１次転写と２次転写とを同時に行うとき、たとえば、２次転写バイアスローラ８１が中間転写ベルト５５に接触するときの突入電流の流れ込みによる電位変動、及び中間転写ベルト５５に流れた２次転写バイアス電流は、上記懸架ローラ５１及び懸架ローラ５２部分で吸収・調整されて１次転写側に影響が及ばない。
【００１７】
この後、トナー像が転写された転写紙１００は、不図示の分離装置により中間転写ベルト５５から分離され、不図示の定着装置で定着処理がなされた後に装置本体から排出される。一方、２次転写後の感光体ドラム１０は、除電装置６０で残留電荷が除電され、その表面がクリーニング装置７０よってクリーニングされ、未転写トナーが回収除去され、次の作像に備える。
なお、電位保持手段は、接地された懸架ローラ５１及び接地された懸架ローラ５２等からなる。
また、上述のように、体積抵抗が１０⁰Ωｃｍ以上で１０³Ωｃｍ以下の低抵抗の無端ベルトを用いることで、複雑な制御や高価な可動装置を用いずに高画質な画像をえることができる。
なお、体積抵抗の下限として１０⁰Ωｃｍ以上としたが、体積抵抗の下限は１０¹Ωｃｍ程度が望ましい。
【００１８】
ここで、上述の実施形態では、中間転写ベルト５５は低抵抗であるため、１次転写バイアス電源５６及び２次転写バイアス電源８２から、接地された懸架ローラ５１、５２に対して大きな電流が流れる可能性があり、これらの１次転写バイアス電源５６及び２次転写バイアス電源８２はともに容量の大きな電源が必要となる場合がある。だだし、中間転写ベルト５５の抵抗値に依存し、たとえば、体積抵抗が１０³Ωｃｍでローラ間の距離が長いと、問題ならないこともある。
そこで、図５に示すように、上記懸架ローラ５１に電源５７を、上記懸架ローラ５２に電源５８をそれぞれ接続し、これらの電源５７、電源５８の電位を１次転写バイアス電位と同電位にする。
これにより、中間転写ベルト５５の１次転写バイアスローラ５４と、懸架ローラ５１、５２との間で無駄に流れる電流を極力少なくするようにして、１次転写バイアスの安定度をさらに上げることができる。たとえ２次転写側で変動がおきた場合でも、これらの懸架ローラ５１の電源５７及び懸架ローラ５２の電源５８により変動分を吸収できるので、１次転写バイアス電位は常に一定に保持され、良好な転写ができる。
なお、電位保持手段は、懸架ローラ５１及び電源５７と、懸架ローラ５２及び電源５８等から構成される。
【００１９】
上述の実施形態では、図１に示すように、単色の作像器としたが、該実施形態を一部変更して、カラーの作像器を用いた場合のトナー塗布装置を並列したタイプ及び現像ユニットを並列したタイプについて説明する。なお、上述の実施形態と変更のない部材については、同一の符号を用いるものとする。
上記トナー塗布装置を並列したタイプは、図６に示すように、複数のベルトローラに懸架された現像ベルト１１０の展張部に対向し、複数のトナー塗布装置１０１を並列して配設する。各トナー塗布装置１０１は液体現像剤を溜める現像タンク１０２と、該現像タンク１０２内の液体現像剤に浸漬するように配設された汲み上げローラ１０３と、該汲み上げローラ１０３から汲み上げられた液体現像剤を現像ベルト１１０に塗布する塗布ローラ１０４等で構成し、上記現像ベルト１１０に前記塗布ローラ１０４が選択的に接触して液体現像剤が塗布できるようにする。
また、上述のトナー塗布装置を並列したタイプに代えて、現像ユニットを並列したタイプとすることもできる。図７に示すように、前記感光体ドラム１０に対向して複数の現像ユニット１０５を配設する。各現像ユニット１０５には、塗布ローラ１０６、現像ローラ１０７を配設し、上記塗布ローラ１０６で液体現像剤を現像ローラ１０７に塗布する。上記塗布ローラ１０６が前記感光体ドラム１０に選択的に接触して、感光体ドラム１０の表面に形成された静電潜像を液体現像剤中のトナーで現像し、トナー像を形成できるようにする。
なお、上述の実施形態では、２次転写電荷付与手段として２次転写バイアスローラ８１を用いたが、転写紙１００と中間転写ベルト５５を密着させた状態で電荷を付与できるものであればよい。
また、上述の実施形態では、現像剤担持体として現像ベルト４１はベルト状としたが、ローラ状でもよい。
また、１次転写バイアスローラ５４はバックアップローラ型としたが、図８で示すように、１次転写バイアスローラ５４ａ、５４ｂと分けて構成するようにしてもよい。
【００２０】
【発明の効果】
請求項１の発明によれば、低抵抗の無端ベルトに設けた電位保持手段により、２次転写のバイアス電流の１次転写部分への回り込みによる１次転写バイアス電位の変動が生じない。よって、１次転写と２次転写とを同時におこなっても、良好に１次転写ができる。したがって、１次転写及び２次転写に要する転写時間を大幅に減少させ、生産性を高めることができ、かつ良好な転写画像を得ることができる。また、無端ベルトを像担持体に接触させたままにしておける。よって、無端ベルトを潜像担持体から接離するための複雑な可動装置が必要がなく低コストの湿式画像形成装置とすることができるという優れた効果がある。
【００２１】
【発明の効果】
請求項１の発明によれば、低抵抗の無端ベルトに設けた電位保持手段により、２次転写のバイアス電流の１次転写部分への回り込みによる１次転写バイアス電位の変動が生じない。よって、１次転写と２次転写とを同時におこなっても、良好に１次転写ができる。したがって、１次転写及び２次転写に要する転写時間を大幅に減少させ、生産性を高めることができ、かつ良好な転写画像を得ることができる。また、無端ベルトを像担持体に接触させたままにしておける。よって、無端ベルトを潜像担持体から接離するための複雑な可動装置が必要がなく低コストの湿式画像形成装置とすることができる。更に、電位保持手段で保持する電位が、１次転写のバイアス電位と同電位であるため、１次転写バイアス電源にかかる負担が減少し、１次転写のバイアス電位が一層安定するので、さらに高画質の画像をえることができるという優れた効果がある。
【００２３】
また、請求項４の発明によれば、電位を保持するために別部材を設ける必要がないので、湿式画像形成装置のコストを抑えることができるという優れた効果がある。
【００２５】
また、請求項３の発明によれば、電位を保持するために別部材を設ける必要がないので、湿式画像形成装置のコストを抑えることができるという優れた効果がある。
【図面の簡単な説明】
【図１】本実施形態に係る湿式電子写真複写機の主要部である画像形成部の概略構成図。
【図２】同中間転写ベルト、１次転写バイアスローラ及び２次転写バイアスローラ等の構成を説明する説明図。
【図３】同懸架ローラ５１、懸架ローラ５２及び懸架ローラ５３が電気的にフロートである場合に、１次転写と２次転写を同時に行ったときの電流の流れを説明する説明図。
【図４】同懸架ローラ５１及び懸架ローラ５２が接地されている場合に、１次転写と２次転写とを同時におこなったときの電流の流れを説明する説明図。
【図５】同懸架ローラ５１及び懸架ローラ５２に一次転写バイアスと同電位である電源を接続し、１次転写と２次転写とを同時におこなったときの電流の流れを説明する説明図。
【図６】現像ベルト１１０の展張部に対向し、複数のトナー塗布装置１０１を並列して配置した場合の説明図。
【図７】感光体ドラム１０に対向し、複数の現像ユニット１０５を配設した場合の説明図。
【図８】同中間転写ベルトの他の構成を示す図。
【符号の説明】
１０感光体ドラム
２０帯電ローラ
４０湿式現像ユニット
４１現像ベルト
５０中間転写ユニット
５１懸架ローラ
５２懸架ローラ
５３懸架ローラ
５４１次転写バイアスローラ
５５中間転写ベルト
５６１次転写バイアス電源
５７電源
５８電源
６０除電装置
７０クリーニング装置
８０紙転写ユニット
８１２次転写バイアスローラ
８２２次転写バイアス電源
９０トナー塗布装置
９２現像タンク
９３汲み上げローラ
９４塗布ローラ
１００転写紙
１０１トナー塗布装置
１０２現像タンク
１０３汲み上げローラ
１０４塗布ローラ
１０５現像ユニット
１０６塗布ローラ
１０７現像ローラ
１１０現像ベルト[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an image forming apparatus such as a copying machine, a facsimile machine, and a printer. More specifically, the present invention relates to a wet developing apparatus that develops an electrostatic latent image on an image carrier using a liquid developer, and development using the wet developing apparatus. The present invention relates to a wet image forming apparatus provided with an intermediate transfer body for transferring a toner image on the image bearing member to a transfer material.
[0002]
[Prior art]
Conventionally, a wet developing device that develops an electrostatic latent image formed on a photoconductor as an image carrier with toner as charged particles, and the toner concentration of the developer is increased so that the wet developing device can be miniaturized. It has been proposed to use a developer having a set high density and high viscosity. For example, in Japanese Patent Laid-Open No. 7-209922, “a liquid developing method for an electrostatic latent image in which an electrostatic latent image formed on an image support is developed with toner that is a charged visualization particle, A liquid developer having a high viscosity of 100 to 10000 mPa · s, in which a toner is dispersed in a high concentration in an insulating liquid coated on a conductive developer support, is applied to the latent image surface of the image support. There has been proposed a “liquid developing method for an electrostatic latent image” comprising a developing means for supplying the liquid developer.
Conventionally, there has been proposed a dry image forming apparatus including an intermediate transfer belt as the intermediate transfer member and a dry developing device using a dry developer whose toner is solid (powder). In this dry image forming apparatus, a toner image formed on a photosensitive drum as an image carrier is transferred to an intermediate transfer belt as an intermediate transfer member once or a plurality of times (primary transfer), and the intermediate transfer is performed. The toner image on the belt is collectively transferred to a transfer material (secondary transfer).
[0003]
As the intermediate transfer belt, an intermediate transfer belt having a volume resistance of 10 ⁶ Ωcm or more, preferably 10 ⁸ to 10 ⁹ Ωcm is generally used. This is because, in the dry image forming apparatus, the toner is powder, and if the resistance value of the intermediate transfer belt is too low, the phenomenon of toner dust (flying) occurs after the primary transfer and disturbs the toner image. This is because the resistance value had to be increased. When the volume resistance of the intermediate transfer belt is a so-called medium resistance of about 10 ⁸ to 10 ⁹ Ωcm, the intermediate transfer belt has a problem in stability of resistance to the environment. Further, when the intermediate transfer belt has a high resistance value, primary transfer that superimposes toner images of a plurality of colors is performed as a primary transfer charge applying unit each time the toner image of each color of the primary transfer is transferred. A charge is applied from the primary transfer bias roller to the back surface of the intermediate transfer belt, and the amount of charge on the surface of the intermediate transfer belt increases as the number of times of primary transfer is performed. The primary transfer conditions differ for each color. In order to make this primary transfer condition uniform, it is necessary to provide a static eliminator for eliminating excessive charge of the intermediate transfer belt, which increases costs and makes control difficult. In addition, if the resistance value of the intermediate transfer belt is high, it becomes difficult to provide the charge amount necessary for the primary transfer, it is difficult to supply the charge amount for the primary transfer at a high speed, and only the contour of the image is transferred. A phenomenon that the intermediate transfer is difficult occurred, and the voltage applied to the intermediate transfer belt had to be increased.
However, if the resistance value of the intermediate transfer belt is too low, there is a risk of damage to the photosensitive drum if the toner layer is uneven or the photosensitive drum is scratched. For this reason, the lower limit of the volume resistance of the intermediate transfer belt is set to 10 ⁰ Ωcm.
[0004]
In consideration of the above points, a wet developing device miniaturized using a high-viscosity liquid developer and an intermediate transfer for transferring a toner image on an image carrier developed by the wet developing device to a transfer material In a wet image forming apparatus having a body, a low resistance intermediate transfer belt having a volume resistance of 10 ⁰ Ωcm or more and 10 ³ Ωcm or less is used, so that an expensive static eliminating device or complicated control is not required, and high image quality is achieved. Can be obtained.
[0005]
[Problems to be solved by the invention]
However, when a low resistance intermediate transfer belt such as a conductor is used as the intermediate transfer member, a part of the intermediate transfer belt is in contact with the photosensitive drum and a transfer bias is applied to perform primary transfer. In addition, when another portion of the same intermediate transfer belt is in contact with the transfer paper and a transfer bias is applied to perform the secondary transfer, the bias current due to the transfer bias applied for the secondary transfer is changed to the primary transfer side. The bias potential of the primary transfer may fluctuate and hinder good image transfer.
For this reason, the above-described wet image forming apparatus cannot perform the primary transfer and the second-position transfer at the same time, so that the productivity is low and there is a problem that a device for contacting and separating the intermediate transfer belt from the photosensitive drum is required. Was.
[0006]
The present invention has been made in view of the above problems, and an object, a wet image forming apparatus having a wet developing device, and an intermediate transfer body with a low resistance using the liquids developer, The bias current of the secondary transfer is prevented from flowing into the primary transfer portion so that the bias potential of the primary transfer due to the inrush current or the like does not fluctuate. Thereby, even if the primary transfer and the secondary transfer are performed simultaneously, a good primary transfer can be performed, and a low cost that does not require a complicated movable device for contacting and separating the intermediate transfer member from the image carrier. It is another object of the present invention to provide a wet image forming apparatus capable of obtaining an image with high productivity and high image quality.
[0007]
[Means for Solving the Problems]
In order to achieve the above object, the invention of claim 1 is directed to an image carrier that forms an electrostatic latent image on the surface, and wet development that develops the electrostatic latent image on the image carrier with a high-viscosity liquid developer. An image transfer device, an intermediate transfer member to which a toner image on the image carrier developed by the liquid developer is transferred, and a transfer material to which the toner image transferred to the intermediate transfer member is transferred. In the wet image forming apparatus that performs primary transfer for transferring a toner image on a carrier onto the intermediate transfer member and secondary transfer for transferring the toner image on the intermediate transfer member onto the transfer material. An endless belt having a volume resistance of 10 ⁰ Ωcm or more and 10 ³ Ωcm or less is used as a transfer body, and a bias electrode for applying a bias on the primary transfer side to the endless belt and the secondary transfer side bias between the bias electrode for applying a pre The potential holding means for holding the bias potential and the same potential of the primary transfer is provided, while said is a part of the endless belt from the image bearing member by performing the primary transfer onto the intermediate transfer member, the endless The secondary transfer from the intermediate transfer member to the transfer material is performed by another part of the belt.
In the wet image forming apparatus according to the first aspect, the potential holding means provided on the low-resistance endless belt does not change the bias potential of the primary transfer due to the secondary transfer bias current flowing into the primary transfer portion. Therefore, even if the primary transfer and the secondary transfer are performed simultaneously, the primary transfer can be performed satisfactorily. Further, the endless belt can be kept in contact with the latent image carrier.
[0008]
According to a second aspect of the present invention, in the wet image forming apparatus of the second aspect, the potential held by the potential holding unit is a ground potential.
The wet image forming apparatus according to the second aspect does not require a new power source or the like for holding the potential.
[0009]
Further, the invention of claim 2, in the wet image forming apparatus according to claim 1, wherein the liquid developer is characterized in that a liquid developer having a high viscosity of 100~10000mPa · s.
[0011]
According to a third aspect of the present invention, in the wet image forming apparatus according to the first or second aspect , the predetermined potential is held by the potential holding means via a suspension member for suspending the endless belt. It is what.
In wet-type image forming apparatus of the first aspect, there is no need to provide a separate member for holding the potential.
[0012]
The photosensitive drum 10 is rotatable in the clockwise direction indicated by an arrow, and around the charging roller 20, the wet developing unit 40, the intermediate transfer unit 50, the static eliminating device 60, the photosensitive member cleaning device 70, and a not-shown photosensitive member. An exposure device or the like is provided. The intermediate transfer unit 50 includes suspension rollers 51, 52, and 53, an intermediate transfer belt 55 as an intermediate transfer member stretched around the suspension rollers 51, 52, and 53, a cleaning device 59 having a cleaning blade, and the like. Has been. The paper transfer unit 80 includes a secondary transfer bias roller 81 as a secondary transfer charge applying unit, a secondary transfer power source 82 connected to the secondary transfer bias roller 81, and the like (see FIG. 2).
[0013]
The toner application device 90 includes a developing tank 92 for storing a liquid developer, a pumping roller 93 disposed so as to be immersed in the liquid developer in the developing tank 92, and a liquid developer pumped from the pumping roller 93. It is composed of a coating roller 94 and the like for thinning the agent and coating the developing belt.
The liquid developer is a high-viscosity liquid developer in which toner particles as visualized particles are dispersed at a high concentration in a carrier liquid that is an insulator solvent.
The developing unit 40 includes a plurality of belt rollers and a developing belt 41 as a developer carrying member stretched around these belt rollers. The developing belt 41 is a liquid developer formed by the application roller 94. Is to be applied.
[0014]
FIG. 2 is an explanatory diagram illustrating the configuration of the intermediate transfer belt, the primary transfer bias roller, the secondary transfer bias roller, and the like.
The intermediate transfer belt 55 is stretched so as to have a predetermined tension on a suspension roller 51 as a suspension member, a suspension roller 52, a suspension roller 53, and a primary transfer bias roller 54 as a primary transfer charge applying unit. It can be rotated counterclockwise. The primary transfer bias roller 54 is opposed to the photosensitive drum 10 and is arranged so that the intermediate transfer belt 55 is sandwiched between the primary transfer bias roller 54 and the photosensitive drum 10. The primary transfer bias roller 54 also serves as an electrode for applying a primary transfer bias, and a predetermined transfer bias is applied to the primary transfer bias roller 54 from a primary transfer power source 56.
The intermediate transfer belt 55 is an endless belt made of a low-resistance conductive member having a predetermined thickness. For example, the intermediate transfer belt 55 has a thickness of 30 to 150 μm and is electrically conductive with polyimide, PET (polyethylene terephthalate), PVDF resin, or the like ( Carbon, metal powder, etc.) are mixed at a certain ratio. As the intermediate transfer belt 55, one having a volume resistance of 10 ⁰ to 10 ³ Ωcm is mainly used. Also, in order to improve the secondary transfer property, the intermediate transfer belt 55 may be coated with about 1 to 10 μm of fluorine or silicon conductive resin on the side where the toner particles adhere to improve the releasability. is there.
A secondary transfer bias roller 81 as a secondary transfer charge applying unit is disposed opposite to the suspension roller 53, and the secondary transfer bias roller 81 also serves as an electrode for applying a secondary transfer bias. A predetermined transfer bias is applied from the secondary transfer power supply 82 to the secondary transfer bias roller 81.
[0015]
Next, the operation of the wet electrophotographic copying machine according to this embodiment will be described with reference to the drawings.
In the above-described wet electrophotographic copying machine using the low resistance intermediate transfer belt 55, as shown in FIG. 3, when the suspension roller 51, the suspension roller 52, and the suspension roller 53 are electrically floated, primary transfer is performed. If the secondary transfer is performed at the same time, the secondary transfer bias current affects the primary transfer side. For example, the primary transfer bias potential may be lowered to disturb the transfer conditions of the primary transfer. .
Therefore, a potential holding point for holding a constant potential between the primary transfer portion and the secondary transfer portion is provided on the intermediate transfer belt 55 to absorb and adjust the bias current and potential fluctuation due to the secondary transfer, and the primary transfer portion. Make sure that the transfer area is not affected. When a potential holding point is provided on the intermediate transfer belt 55, the primary transfer bias potential and the potentials at the suspension roller 51 and the suspension roller 52 are reduced due to the low resistance value of the intermediate transfer belt 55 that is not a perfect conductor. The potential difference is constant.
Hereinafter, a case where a potential holding point is provided on the intermediate transfer belt 55 will be described with reference to FIGS. FIG. 4 is an explanatory diagram illustrating the flow of current when primary transfer and secondary transfer are performed simultaneously when the suspension roller 51 and the suspension roller 52 that suspend the intermediate transfer belt 55 are grounded. .
As shown in FIG. 1, the photosensitive drum 10 is uniformly charged by the charging roller 20 while being driven to rotate in the direction of the arrow, and then light 30 from an exposure device (not shown) is irradiated to electrostatic latent image on the photosensitive drum 10. Form an image. On the other hand, the liquid developer adhering to the roller 93 immersed in the high-viscosity liquid developer in the developing tank 92 is uniformly formed on the developing belt 41 via the application roller 94, for example, to a thickness of about 0.5 to 20 μm. Applied.
Then, the developing belt 41 is brought into contact with the photosensitive drum 10, and the toner in the liquid developer is transferred to the electrostatic latent image formed on the surface of the photosensitive drum 10 by the force of an electric field and developed. Form.
[0016]
Next, the photosensitive drum 10 on which the toner image is formed is rotated and moved to a primary transfer portion where the photosensitive drum 10 and the intermediate transfer belt 55 are in contact (see FIG. 4). Then, at the primary transfer portion, a negative bias voltage having a polarity opposite to that of the positive toner, for example, about −350 V is applied to the back surface of the intermediate transfer belt 55 via the primary transfer bias roller 54. The toner of the toner image on the photosensitive drum 10 is attracted to the intermediate transfer belt 55 and transferred onto the intermediate transfer belt 55 (primary transfer).
Next, while transferring the toner image onto the intermediate transfer belt 55 in the primary transfer, the intermediate transfer belt 55 to which the toner image has been transferred is rotated, and the intermediate transfer belt 55 and a paper feeding unit (not shown) are moved in the direction of the arrow. It moves to the secondary transfer portion where the conveyed transfer paper 100 abuts. In this secondary transfer portion, a negative bias voltage is applied to the back surface of the transfer paper 100 via a secondary transfer bias roller 81, and the toner of the intermediate transfer belt 55 is transferred to the transfer paper by an electric field generated by the applied voltage. It is drawn to 100 and transferred onto the transfer paper 100 (secondary transfer). At the time of the secondary transfer, the potential difference between the transfer paper 100 and the intermediate transfer belt 55 is about 300 V, and the secondary transfer side has a lower voltage. Further, when the secondary transfer is performed, a current flows from the secondary transfer bias roller 81 to the intermediate transfer belt 55. The potential difference between the suspension roller 51 and suspension roller 52 and the primary transfer bias roller 54 is −300V.
When the primary transfer and the secondary transfer are performed simultaneously when the suspension roller 51 and the suspension roller 52 are electrically grounded as described above, for example, the secondary transfer bias roller 81 contacts the intermediate transfer belt 55. At this time, the potential fluctuation due to the inrush current flow and the secondary transfer bias current flowing through the intermediate transfer belt 55 are absorbed and adjusted by the suspension roller 51 and the suspension roller 52, and do not affect the primary transfer side.
[0017]
Thereafter, the transfer paper 100 onto which the toner image has been transferred is separated from the intermediate transfer belt 55 by a separation device (not shown), and after being subjected to a fixing process by a fixing device (not shown), is discharged from the apparatus main body. On the other hand, after the secondary transfer, the photosensitive drum 10 is charged with residual charges by the static eliminator 60, the surface thereof is cleaned by the cleaning device 70, and untransferred toner is collected and removed to prepare for the next image formation.
The potential holding means includes a grounded suspension roller 51 and a grounded suspension roller 52.
Further, as described above, by using a low-resistance endless belt having a volume resistance of 10 ⁰ Ωcm or more and 10 ³ Ωcm or less, high-quality images can be obtained without complicated control and expensive movable devices. it can.
Although the lower limit of the volume resistance is 10 ⁰ Ωcm or more, the lower limit of the volume resistance is preferably about 10 ¹ Ωcm.
[0018]
Here, in the above-described embodiment, since the intermediate transfer belt 55 has a low resistance, a large current flows from the primary transfer bias power supply 56 and the secondary transfer bias power supply 82 to the grounded suspension rollers 51 and 52. There is a possibility that both the primary transfer bias power source 56 and the secondary transfer bias power source 82 may require a power source having a large capacity. However, depending on the resistance value of the intermediate transfer belt 55, for example, if the volume resistance is 10 ³ Ωcm and the distance between the rollers is long, there may be no problem.
Therefore, as shown in FIG. 5, a power source 57 is connected to the suspension roller 51 and a power source 58 is connected to the suspension roller 52, and the potentials of the power source 57 and the power source 58 are set to the same potential as the primary transfer bias potential. .
As a result, it is possible to further increase the stability of the primary transfer bias by minimizing the wasteful current flowing between the primary transfer bias roller 54 of the intermediate transfer belt 55 and the suspension rollers 51 and 52. . Even if fluctuations occur on the secondary transfer side, the fluctuations can be absorbed by the power supply 57 of the suspension roller 51 and the power supply 58 of the suspension roller 52, so that the primary transfer bias potential is always kept constant and good. Can transfer.
The potential holding means includes a suspension roller 51 and a power source 57, and a suspension roller 52 and a power source 58.
[0019]
In the above-described embodiment, as shown in FIG. 1, a single color imager is used. However, the embodiment is a partly modified type in which toner imagers are used in parallel when a color imager is used. A type in which developing units are arranged in parallel will be described. In addition, the same code | symbol shall be used about the member which does not change with the above-mentioned embodiment.
As shown in FIG. 6, the type in which the toner application devices are arranged in parallel has a plurality of toner application devices 101 arranged in parallel so as to face the extended portion of the developing belt 110 suspended from a plurality of belt rollers. Each toner application device 101 includes a developing tank 102 for storing a liquid developer, a pumping roller 103 disposed so as to be immersed in the liquid developer in the developing tank 102, and a liquid developer pumped from the pumping roller 103. Is applied to the developing belt 110, and the application roller 104 is selectively brought into contact with the developing belt 110 so that the liquid developer can be applied thereto.
Further, instead of the above-described type in which the toner coating devices are arranged in parallel, a type in which the developing units are arranged in parallel may be employed. As shown in FIG. 7, a plurality of developing units 105 are disposed facing the photosensitive drum 10. Each developing unit 105 is provided with an application roller 106 and a development roller 107, and the application roller 106 applies a liquid developer to the development roller 107. The coating roller 106 is selectively brought into contact with the photosensitive drum 10 so that the electrostatic latent image formed on the surface of the photosensitive drum 10 is developed with toner in the liquid developer so that a toner image can be formed. To do.
In the above-described embodiment, the secondary transfer bias roller 81 is used as the secondary transfer charge applying unit. However, any device can be used as long as the transfer sheet 100 and the intermediate transfer belt 55 are in close contact with each other.
In the above-described embodiment, the developing belt 41 is a belt as the developer carrying member, but may be a roller.
Although the primary transfer bias roller 54 is a backup roller type, it may be configured separately from the primary transfer bias rollers 54a and 54b as shown in FIG.
[0020]
【The invention's effect】
According to the first aspect of the present invention, the potential holding means provided on the low-resistance endless belt does not cause a change in the primary transfer bias potential due to the secondary transfer bias current flowing into the primary transfer portion. Therefore, even if the primary transfer and the secondary transfer are performed simultaneously, the primary transfer can be performed satisfactorily. Therefore, the transfer time required for the primary transfer and the secondary transfer can be greatly reduced, the productivity can be improved, and a good transfer image can be obtained. Further, the endless belt can be kept in contact with the image carrier. Therefore, there is no need for a complicated movable device for contacting and separating the endless belt from the latent image carrier, and there is an excellent effect that a low-cost wet image forming apparatus can be obtained.
[0021]
【The invention's effect】
According to the first aspect of the present invention, the potential holding means provided on the low-resistance endless belt does not cause a change in the primary transfer bias potential due to the secondary transfer bias current flowing into the primary transfer portion. Therefore, even if the primary transfer and the secondary transfer are performed simultaneously, the primary transfer can be performed satisfactorily. Therefore, the transfer time required for the primary transfer and the secondary transfer can be greatly reduced, the productivity can be improved, and a good transfer image can be obtained. Further, the endless belt can be kept in contact with the image carrier. Therefore, Ru can be a low cost wet image forming apparatus is not necessary a complicated movable device for contact and separation of the endless belt from the image bearing member. Further, since the potential held by the potential holding means is the same as the bias potential of the primary transfer, the burden on the primary transfer bias power source is reduced, and the bias potential of the primary transfer is further stabilized. There is an excellent effect that an image of high image quality can be obtained.
[0023]
According to the fourth aspect of the present invention, there is no need to provide a separate member for maintaining the potential, so that there is an excellent effect that the cost of the wet image forming apparatus can be reduced.
[0025]
Further, according to the invention of claim 3 , since it is not necessary to provide a separate member for maintaining the potential, there is an excellent effect that the cost of the wet image forming apparatus can be suppressed.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram of an image forming unit which is a main part of a wet electrophotographic copying machine according to an embodiment.
FIG. 2 is an explanatory diagram illustrating configurations of the intermediate transfer belt, a primary transfer bias roller, a secondary transfer bias roller, and the like.
FIG. 3 is an explanatory diagram for explaining a current flow when primary transfer and secondary transfer are simultaneously performed when the suspension roller 51, the suspension roller 52, and the suspension roller 53 are electrically floated.
FIG. 4 is an explanatory diagram for explaining a current flow when primary transfer and secondary transfer are performed simultaneously when the suspension roller 51 and the suspension roller 52 are grounded.
FIG. 5 is an explanatory diagram for explaining a current flow when a power supply having the same potential as the primary transfer bias is connected to the suspension roller 51 and the suspension roller 52 and primary transfer and secondary transfer are performed simultaneously.
FIG. 6 is an explanatory diagram when a plurality of toner application devices 101 are arranged in parallel so as to face the extended portion of the developing belt 110;
FIG. 7 is an explanatory diagram when a plurality of developing units 105 are disposed opposite to the photosensitive drum 10;
FIG. 8 is a view showing another configuration of the intermediate transfer belt.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 Photosensitive drum 20 Charging roller 40 Wet developing unit 41 Developing belt 50 Intermediate transfer unit 51 Suspension roller 52 Suspension roller 53 Suspension roller 54 Primary transfer bias roller 55 Intermediate transfer belt 56 Primary transfer bias power source 57 Power source 58 Power source 60 Static elimination device 70 Cleaning Device 80 Paper Transfer Unit 81 Secondary Transfer Bias Roller 82 Secondary Transfer Bias Power Supply 90 Toner Application Device 92 Development Tank 93 Pumping Roller 94 Application Roller 100 Transfer Paper 101 Toner Application Device 102 Development Tank 103 Pumping Roller 104 Application Roller 105 Development Unit 106 Application roller 107 Development roller 110 Development belt

Claims

An image carrier that forms an electrostatic latent image on the surface;
Wet developing device for developing an electrostatic latent image on the image bearing member in liquids developer,
An intermediate transfer member to which a toner image on the image carrier developed by the liquid developer is transferred;
A transfer material onto which the toner image transferred to the intermediate transfer member is transferred,
In a wet image forming apparatus that performs primary transfer that transfers a toner image on the image carrier onto the intermediate transfer member and secondary transfer that transfers the toner image on the intermediate transfer member onto the transfer material,
As the intermediate transfer body, using an endless belt of the volume resistance of 10 ⁰ [Omega] cm or more at 10 ³ [Omega] cm or less, and the endless belt, the secondary bias electrode for applying a bias of the primary transfer side A potential holding means for holding the same potential as the bias potential of the primary transfer is provided between a bias electrode for applying a bias on the transfer side, and the intermediate transfer is performed from the image carrier by a part of the endless belt. A wet image forming apparatus, wherein the secondary transfer from the intermediate transfer body to the transfer material is performed by another part of the endless belt during the primary transfer to the body.

The wet image forming apparatus according to claim 1.
The wet image forming apparatus , wherein the liquid developer is a liquid developer having a high viscosity of 100 to 10,000 mPa · s .

The wet image forming apparatus according to claim 1 or 2 ,
The wet image forming apparatus is characterized in that holding of the potential by the potential holding means is performed via a suspension member for suspending the endless belt.