JP3581525B2

JP3581525B2 - Image forming device

Info

Publication number: JP3581525B2
Application number: JP18284197A
Authority: JP
Inventors: 誠陣在
Original assignee: Canon Inc
Current assignee: Canon Inc
Priority date: 1997-07-08
Filing date: 1997-07-08
Publication date: 2004-10-27
Anticipated expiration: 2017-07-08
Also published as: JPH1124431A

Description

【０００１】
【発明の属する技術分野】
本発明は、電子写真方式、静電記録方式等によって画像形成を行う複写機、プリンター、ファクシミリ等の画像形成装置に関し、特に、像担持体に形成された静電潜像と同極性の電荷をもつ現像剤で反転現像して顕像化する画像形成装置に関する。
【０００２】
【従来の技術】
電子写真方式、静電記録方式等によって画像形成を行う複写機、プリンター、ファクシミリ等の画像形成装置では、従来より、像担持体の表面に形成された静電潜像と同極性の電荷をもつ現像剤で反転現像して顕像化するタイプの画像形成装置が提案されている。
【０００３】
図６は反転現像を用いた従来の画像形成装置を示す概略構成図である。この図において、１は像担持体としてのドラム型の電子写真感光体（以下、感光体という）であり、１次帯電器２により規定の正電位に帯電される。そして、半導体レーザー装置等を有する露光装置３により表面が帯電処理された感光体１上に静電潜像を形成し、該静電潜像は現像装置４によりレーザー露光部分が正極性の現像剤（トナー）で顕像化される。
【０００４】
一方、転写材Ｐは転写ガイド５に導かれて感光体１と対向する転写帯電器６、分離帯電器７との間の転写部位に進入し、電界が印加された転写帯電器６により転写材Ｐ上に前記顕像化された現像剤（トナー）画像が転写される。そして、この転写材Ｐは分離帯電器７の除電作用により感光体１から静電分離された後、定着器（不図示）により定着処理されて画像形成が終了する。なお、図中、８は分離補助のための転写前露光装置、９はバリスタ素子である。
【０００５】
図７は、上記した画像形成の工程を示したものであり、まず、１次帯電器２による帯電工程で感光体１を正電位に帯電後、露光装置３による露光工程で画像部のみレーザ露光を行い、いわゆる井戸型の静電電位を形成する。次に、現像装置４による現像工程で前記静電電位が形成する電界、及び現像装置４と潜像電位による電界に従って、正極性の現像剤が前記静電潜像を現像し顕像化する。そして、転写帯電器６による転写工程で前記顕像化された現像剤（トナー）画像は、転写材Ｐに電界転写される。そして、分離帯電器７による分離工程で転写材Ｐは静電分離される。
【０００６】
また、上記した反転現像を用いた従来の画像形成における転写材Ｐの分離において、図８に示すように、非画像部（白地部）が高電位部側になるため、転写材Ｐと感光体１間の静電吸着力（Ｆ１、Ｆ２、Ｆ３）が大きくなり、分離性が悪くなる。このため、図６、図９に示したように、現像後及び転写、分離工程前に、非画像部の電位を低減させることを目的として、ＬＥＤ素子等の転写前露光装置８で転写前露光を行うようにしている。
【０００７】
また、図８に示すように、上記画像形成装置では感光体１上に付着する現像剤（トナー）の静電着力として、Ｆ１（潜像電位電界によるクーロン力）、Ｆ２（現像剤の電荷量による鏡映力）、Ｆ３（現像剤と感光体１の局所電界によるクーロン力）等が挙げられるが、特にＦ３（現像剤と感光体１の局所電界によるクーロン力）の局所電界が、感光体１の表面電位と現像剤の極性が同極性（正極性）により正規現像に比べて極めて小さいため、現像剤の感光体１との付着力が弱く、転写ガイド５に浮遊現像剤が付着して汚れを発生する。
【０００８】
このため、従来、図１０に示すように、転写ガイド５に電源１１から現像剤と同極性（正極性）の直流バイアスを印加して、転写ガイド５の現像剤の付着による汚れを防止する手段等が提案されている。
【０００９】
【発明が解決しようとする課題】
しかしながら、図６に示した従来の画像形成装置では、転写前露光装置８で転写前露光を行うことによって、図８に示したように、現像剤と感光体１上の静電付着力（Ｆ１；潜像電位電界によるクーロン力）が減少することにより、特にベタ黒とベタ白の境界部分の文字の周辺や、ラインの周辺での画像飛び散りが発生しやすいという問題点があった。この画像飛び散り現象は、特に低湿環境で顕著に発生する。
【００１０】
また、図１０に示した従来の画像形成装置では、転写ガイド５の汚れを防止するために転写ガイド５に現像剤と同極性（正極性）の直流バイアスを印加することにより、図１１に示すように、転写電流の転写材Ｐを介して転写ガイド５側への漏れ電流ｉによって、転写不良が発生するという問題点があった。この漏れ電流ｉによる転写不良現象は、特に高湿環境で顕著に発生する。
【００１１】
そこで、本発明は、画像飛び散りを防止し、かつ、現像剤による転写ガイド汚れの防止と、転写電流の漏れによる転写不良を防止することができる画像形成装置を提供することを目的とする。
【００１３】
【課題を解決するための手段】
請求項１に係る発明は、像を担持する像担持体と、該像担持体を帯電する帯電手段と、前記像担持体上に静電潜像を形成する露光手段と、前記静電潜像と同極性をもつ現像剤で該静電潜像を反転現像して現像剤画像を形成する現像手段と、該現像手段による現像工程後に前記像担持体表面を露光してその表面電位を低減させる転写前露光手段と、前記現像剤画像を転写部位において転写材へ転写する転写手段と、前記転写材を前記転写部位へ導くとともに前記現像剤と同極性の直流バイアスが印加される転写ガイドとを備えた画像形成装置において、環境湿度を検出する湿度検出手段と、該湿度検出手段から入力される湿度情報に基づいて前記転写前露光手段による前記像担持体への転写前露光量、及び前記転写ガイドに印加する直流バイアス値を制御する制御手段とを備え、前記制御手段は、低湿環境では前記転写前露光量と前記転写ガイドに印加する直流バイアス値を大きめに設定するよう制御し、高湿環境では前記転写前露光量と前記転写ガイドに印加する直流バイアス値を小さめに設定するよう制御することを特徴としている。
【００１４】
請求項２に係る発明は、像を担持する像担持体と、該像担持体を帯電する帯電手段と、前記像担持体上に静電潜像を形成する露光手段と、前記静電潜像と同極性をもつ現像剤で該静電潜像を反転現像して現像剤画像を形成する現像手段と、該現像手段による現像工程後に前記像担持体表面を露光してその表面電位を低減させる転写前露光手段と、前記現像剤画像を転写部位において転写材へ転写する転写手段と、前記転写材を前記転写部位へ導くとともに前記現像剤と同極性の直流バイアスが印加される転写ガイドとを備えた画像形成装置において、両面画像形成または多重画像形成可能な転写材給紙手段と、前記転写材への１回目の画像形成と２回目以降の画像形成時とで前記転写前露光手段による前記像担持体への転写前露光量、及び前記転写ガイドに印加する直流バイアス値を切り替えるよう制御する制御手段とを備え、前記制御手段は、１回目の画像形成時よりも２回目以降での画像形成時に、前記転写前露光量と前記転写ガイドに印加する直流バイアス値を大きめに設定するよう制御することを特徴としている。
【００１５】
請求項３に係る発明は、像を担持する像担持体と、該像担持体を帯電する帯電手段と、前記像担持体上に静電潜像を形成する露光手段と、前記静電潜像と同極性をもつ現像剤で該静電潜像を反転現像して現像剤画像を形成する現像手段と、該現像手段による現像工程後に前記像担持体表面を露光してその表面電位を低減させる転写前露光手段と、前記現像剤画像を転写部位において転写材へ転写する転写手段と、前記転写材を前記転写部位へ導くとともに前記現像剤と同極性の直流バイアスが印加される転写ガイドとを備えた画像形成装置において、前記転写材の水分量を検出する水分量検出手段と、該水分量検出手段から入力される水分量情報に基づいて前記転写前露光手段による前記像担持体への転写前露光量、及び前記転写ガイドに印加する直流バイアス値を制御する制御手段とを備え、前記制御手段は、前記転写材の水分量が少ない場合には前記転写前露光量と前記転写ガイドに印加する直流バイアス値を大きめに設定するよう制御し、前記転写材の水分量が多い場合には前記転写前露光量と前記転写ガイドに印加する直流バイアス値を小さめに設定するよう制御することを特徴としている。
【００１６】
（作用）
本発明者は鋭意検討した結果、上記した問題点は以下のメカニズムで発生していると考察している。
【００１７】
まず、転写前露光装置８の転写前帯電による画像飛び散りは、上述したように現像剤と感光体１間の静電付着力が減少し、感光体１と転写材Ｐの接触領域の正規の転写位置前で転写材Ｐに転写が起こり始める、いわゆるプレ転写現象が発生するためである。この現象は特に、転写領域前で転写材Ｐと感光体１間の電界作用によることが判明し、特に、転写材Ｐが現像剤（トナー）と反対電荷に帯電している場合に顕著に発生した。特には、１回目の画像形成後、２回目の画像形成時及び、低湿環境で顕著に発生した。
【００１８】
しかしながら、この現象は転写ガイド５に現像剤と同極性の直流バイアスを印加し、現像剤への転写ガイド５からの反発電界を与えることにより、プレ転写を防ぐことで簡単に回避できることが判明した。また、転写材Ｐの感光体１からの分離に関しては、低湿環境が厳しいことが一般的に知られている。
【００１９】
一方、転写ガイド５の汚れ対策の弊害によって発生する転写漏れ電流ｉによる転写不良に関しては、転写ガイド５に印加する直流バイアス値を大きくする程顕著に発生し、また、転写材Ｐの水分量にも大きく依存していることが明確になっている。また、一方で、転写ガイド５の汚れに関しても環境依存性は顕著で、特に、低湿環境で顕著だった。こらは、現像剤（トナー）の凝集性に依存する傾向と考察されており、凝集傾向にある高湿環境では、転写ガイド５はさほど汚れなかった。
【００２０】
このように、低湿環境では転写材Ｐの分離性補助のために転写前露光量を大きめに設定して分離性を補助する一方、弊害として悪化する画像飛び散りは転写ガイド５に印加する直流バイアス値を大きめに設定することで対策できる。一方、高湿環境では転写電流漏れ電流を防ぐ目的で、転写ガイド５に印加する直流バイアス値を小さめに設定し、さらに転写前露光量を小さめに設定することにより画像飛び散りを抑制することができる。
【００２１】
【発明の実施の形態】
以下、図面に基づいて本発明の実施の形態について説明する。
【００２２】
（第１の実施の形態）
図１は、本実施の形態に係る画像形成装置を示す概略構成図である。なお、従来例と同一部材には同一符号を付し、重複する説明は省略する。
【００２３】
この画像形成装置は、ドラム状のａ−Ｓｉ等からなる感光体１、一次帯電器２、露光装置（スキャナ装置）３、現像装置４、転写ガイド５、転写帯電器６、分離帯電器７、転写前露光装置８を備えている。
【００２４】
現像装置４は、感光体１の表面に形成される静電潜像を、その静電潜像と同極性の電荷をもつ現像剤で反転現像して顕像化する。
【００２５】
次に、上記した画像形成装置の画像形成動作について説明する。
【００２６】
画像形成時には、感光体１は駆動手段（不図示）により所定のプロセススピードで回転駆動され、所定の帯電バイアスが印加された一次帯電器２により約＋４００Ｖに帯電される。そして、帯電された感光体１上に露光装置３によりレーザ光による画像データ出力に対応した画像露光が与えられて、正極性の静電潜像が形成される。上記レーザ光による画像露光によって感光体１上の露光部は約＋５０Ｖに電位が低下する。
【００２７】
そして、現像装置４により静電潜像は正極性現像剤によって上記露光部に現像され、反転現像して顕像化される。
【００２８】
そして、感光体１は、ＬＥＤで構成される転写前露光装置８により転写前露光される。ここで簡単に転写前露光装置８によるＬＥＤ露光前後の感光体１の表面電位の変化について説明する。まず、転写前露光の直前においては、白地部電位は暗減衰により約＋３５０Ｖであったが、この転写前露光の作用で約＋１００Ｖに調整される。一方、画像部は現像後において、感光体１が現像剤で転写前露光が遮蔽されることにより、電位は変化せず約＋３０Ｖだった。
【００２９】
そして、転写材Ｐは、転写ガイド５によって感光体１と転写帯電器６との隙間の転写部位へ搬送され、転写帯電器６に印加される負極性の転写バイアスにより、感光体１上の現像剤は転写材Ｐに転写される。この際、転写ガイド５には、電源１０より現像剤と同極性（正極性）の＋５００Ｖの直流バイアスが印加される。
【００３０】
そして、現像剤が転写された転写材Ｐは、分離帯電器７に印加される正極性の直流電圧に交流電圧を重畳した分離バイアスにより静電的に除電されて、感光体１より分離される。感光体１より分離された転写材Ｐは定着装置（不図示）に搬送され、定着装置（不図示）により現像剤画像が転写材Ｐ上に永久固着画像として定着されて排出される。
【００３１】
本実施の形態と、図６、図１０に示した従来例（図６の従来例を従来例１、図１０の従来例を従来例２とする）とにおいて、画像評価（画像飛び散り、転写ガイド５の汚れ、転写抜け）と分離性評価（感光体１からの転写材Ｐの分離性）を行った。表１は、これらの評価結果を示したものである。
【００３２】
【表１】

本実施の形態は、転写ガイド５に＋５００Ｖの直流バイアスを印加し、転写前露光を行った（露光後電位は＋２００Ｖ）。従来例１は、転写前露光の設定条件は本実施の形態と同一条件（露光後電位は＋２００Ｖ）で、転写ガイド５は＋５００Ｖのバリスタ素子９で接地した。この場合、実際の画像形成時に、転写ガイド５には転写の負極性電荷が転写材Ｐを介して流入し、約−５００Ｖになっていた。一方、従来例２は、転写前露光はなく（露光後電位は＋３５０Ｖ）、転写ガイド５には本実施の形態と同様＋５００Ｖの直流バイアスを印加した。これらの評価は常温常湿で行った（２０℃、６０％）。他の基本条件は同一である。
【００３３】
表１に示す評価結果から明らかなように、本実施の形態では、画像飛び散り、転写ガイド５の汚れ、転写抜けのいずれもなく（○）、また、感光体１からの転写材Ｐの分離性も良好（○）であった。
【００３４】
一方、従来例１では転写抜けはなく（○）、感光体１からの転写材Ｐの分離性は良好（○）であったが、画像飛び散り、転写ガイド５の汚れが発生した（×）。また、従来例２では画像飛び散り、転写ガイド５の汚れ、転写抜けはいずれもなかった（○）が、感光体１からの転写材Ｐの分離性は良くなかった（×）。
【００３５】
このように、本実施の形態では、反転現像によって画像形成を行う画像形成装置で必然的にもっていた転写材Ｐの感光体１からの分離性を向上させ、さらにこのとき弊害として存在する、画像飛び散り、転写ガイド５の汚れ、転写抜けも同時に防止することができる。
【００３６】
（第２の実施の形態）
図２は、本実施の形態に係る画像形成装置を示す概略構成図である。
【００３７】
本実施の形態では、装置内に環境湿度センサー１２と制御装置（ＣＰＵ）１３を備え、制御装置（ＣＰＵ）１３は、環境湿度センサー１２から入力される湿度情報に基づいて転写前露光装置８の電源９を制御して感光体１への転写前露光量、及び転写ガイド５の電源１１を制御して転写ガイド５に印加する直流バイアス値をそれぞれ適正制御する構成とした。即ち、低湿環境では、転写前露光量と転写ガイド５に印加する直流バイアス値を大きめに設定し、高湿環境では、転写ガイド５に印加する直流バイアス値を小さめに設定するよう制御する。他の構成は第１の実施の形態と同様である。
【００３８】
図３は、環境湿度に対する転写前露光後の感光体１の白地部電位（露光後電位）と通紙時の転写ガイド５に印加する直流バイアス値（通紙時転写ガイド電位）の切り替え条件を示した図であり、図中Ａは通紙時の転写ガイド５の電位、図中Ｂは転写前露光後の電位である。
【００３９】
この切り替え条件は、上記したように低湿環境では、転写材Ｐの分離性を優先として転写前露光の値を大きめに設定し、弊害として存在する画像飛び散りの悪化に対しては、転写ガイド５に印加する直流バイアス値を大きめに設定した。一方、高湿環境では、転写材Ｐと転写ガイド５を介しての転写電流の漏れを防ぐために、転写ガイド５に印加する直流バイアス値を小さめに設定した。
【００４０】
本実施の形態（第２の実施の形態（ａ）〜（ｄ））と、比較例（比較例１〜４）とにおいて、画像評価（画像飛び散り、転写ガイド５の汚れ、転写抜け）と分離性評価（感光体１からの転写材Ｐの分離性）を行った。表２は、これらの評価結果を示したものである。
【００４１】
【表２】

本実施の形態（ａ），（ｂ）の低湿環境（湿度５％、３０％）では、転写前露光量を大きめ（露光後電位は＋１００Ｖ、＋１４０Ｖ）に設定し、転写ガイド５に印加する直流バイアス値を大きめ（通紙時電位は＋７００Ｖ、＋６００Ｖ）に設定した。また、本実施の形態（ｃ），（ｄ）の高湿環境（湿度６０％、８０％）では、転写ガイド５に印加する直流バイアス値を小さめ（通紙時電位は＋５００Ｖ、＋２００Ｖ）に設定した。なお、このときの露光後電位は＋２００Ｖ、＋２５０Ｖにそれぞれ設定した。
【００４２】
一方、比較例１〜４では、それぞれ湿度５％、３０％、６０％、８０％を変化させた条件においても転写前露光量、及び転写ガイド５に印加する直流バイアス値を固定値とした。このときの露光後電位は＋２００Ｖ、通紙時電位は＋５００Ｖに設定した。
【００４３】
表２に示す評価結果から明らかなように、本実施の形態（第２の実施の形態（ａ）〜（ｄ））では、画像飛び散り、転写ガイド５の汚れ、転写抜けのいずれもなく（○）、また、感光体１からの転写材Ｐの分離性も良好（○）であった。
【００４４】
一方、比較例１では転写抜けはなかった（○）が、画像飛び散り、転写ガイド５の汚れが少し発生し（△）、感光体１からの転写材Ｐの分離性もやや悪かった（△）。比較例２では画像飛び散り、転写抜けはなかった（○）が、転写ガイド５の汚れが少し発生し（△）、感光体１からの転写材Ｐの分離性もやや悪かった（△）。また、比較例４では画像飛び散り、転写ガイド５の汚れ、感光体１からの転写材Ｐの分離性は良好（○）であったが、転写抜けがやや悪かった（△）。なお、比較例３は本実施の形態（ｃ）と同じ設定条件である。
【００４５】
このように、本実施の形態では、低湿環境での画像飛び散り、転写ガイド５の汚れを防止して、感光体１からの転写材Ｐの分離性を向上させ、高湿環境での転写抜けを防止することができる。
【００４６】
（第３の実施の形態）
本実施の形態においては、図１に示した画像形成装置に両面または多重画像形成のための転写材給紙手段（不図示）を備えた場合であり、転写材Ｐへの１回目の画像形成後に再度２回目の画像形成が可能である。上記転写材給紙手段（不図示）としては公知のものを用いることができる。
【００４７】
このような画像形成装置では、転写材は一般に１回目の画像形成終了後に含まれている水分の一部が蒸発し、その電気抵抗値も大きくなる。したがって、この場合、環境湿度だけでは上記した転写前露光量、及び転写ガイドに印加する直流バイアス値の最適値は決まらず、画像形成モードによって設定条件を切り替える必要がある。
【００４８】
表３は、本実施の形態と比較例における各設定条件を示したものである。
【００４９】
【表３】

本実施の形態では、１回目の画像形成時には、転写前露光量は露光後電位が＋２００Ｖになるよう設定し、転写ガイド５に印加する直流バイアス値は通紙時電位が＋５００Ｖになるように設定した。そして、２回目の画像形成時には、転写前露光量は露光後電位が＋１００Ｖになるよう設定し、転写ガイド５に印加する直流バイアス値は通紙時電位が＋７００Ｖになるように設定した。
【００５０】
一方、比較例では、１回目、２回目の画像形成時の転写前露光量は露光後電位が＋２００Ｖになるよう設定し、転写ガイド５に印加する直流バイアス値は通紙時電位が＋５００Ｖになるように設定して、設定条件の切り替えは行わなかった。なお、本実施の形態と比較例における画像形成は、環境湿度６０％で行った。
【００５１】
そして、本実施の形態と比較例とにおいて、画像評価（画像飛び散り、転写ガイド５の汚れ、転写抜け）と分離性評価（感光体１からの転写材Ｐの分離性）を行った結果、１回目と２回目の画像形成時に、転写前露光量と転写ガイド５に印加する直流バイアス値の設定条件を切り替えた本実施の形態の場合には、画像飛び散り、転写ガイド５の汚れ、転写抜けもなく、また、感光体１からの転写材Ｐの分離性も良好であった。
【００５２】
一方、比較例では、２回目の画像形成時に画像飛び散りが発生した。
【００５３】
このように、本実施の形態では、両面または多重画像形成可能な画像形成装置において、１回目の画像形成後に再度２回目の画像形成を行う場合でも、転写材Ｐの感光体からの分離性が良好で、かつ画像飛び散り、転写ガイドの汚れ、転写抜けも同時に防止することができる。
【００５４】
また、本実施の形態においても、第２の実施の形態で述べた環境湿度による転写前露光量、及び転写ガイド５に印加する直流バイアス値の制御を組み合わせることも可能である。
【００５５】
（第４の実施の形態）
図４は、本実施の形態に係る画像形成装置を示す概略構成図である。
【００５６】
本実施の形態では、両面または多重画像形成のための転写材給紙手段（不図示）を備え、装置内に給紙される転写材Ｐの水分量を検出する水分量検出センサー１４と制御装置（ＣＰＵ）１３を備えている。上記転写材給紙手段（不図示）としては公知のものを用いることができる。
【００５７】
制御装置（ＣＰＵ）１３は、水分量検出センサー１４から入力される転写材Ｐの水分量情報に基づいて転写前露光装置８の電源９を制御して感光体１への転写前露光量、及び転写ガイド５の電源１１を制御して転写ガイド５に印加する直流バイアス値をそれぞれ適正制御する構成とした。即ち、転写材Ｐの水分量が少ない場合には、転写前露光量と転写ガイド５に印加する直流バイアス値を大きめに設定し、転写材Ｐの水分量が多い場合には、転写ガイド５に印加する直流バイアス値を小さめに設定するよう制御する。他の構成は第１の実施の形態と同様である。
【００５８】
図５は、転写材Ｐの水分量に対する転写前露光後の感光体１の白地部電位（露光後電位）と通紙時の転写ガイド５に印加する直流バイアス値（通紙時転写ガイド電位）の切り替え条件を示した図であり、図中Ａは通紙時の転写ガイド５の電位、図中Ｂは転写前露光後の電位である。
【００５９】
この切り替え条件は、上記したように転写材Ｐの水分量が少ない場合には、転写材Ｐの分離性を優先として転写前露光の値を大きめに設定し、弊害として存在する画像飛び散りの悪化に対しては、転写ガイド５に印加する直流バイアス値を大きめに設定した。一方、転写材Ｐの水分量が多い場合には、転写材Ｐと転写ガイド５を介しての転写電流の漏れを防ぐために、転写ガイド５に印加する直流バイアス値を小さめに設定した。
【００６０】
そして、前記同様に本実施の形態での画像評価（画像飛び散り、転写ガイド５の汚れ、転写抜け）と分離性評価（感光体１からの転写材Ｐの分離性）を行った結果、１回目の画像形成後の２回目の画像形成時に、図５に示した転写材Ｐの水分量切り替え条件に基づいて転写前露光量（露光後電位）と転写ガイド５に印加する直流バイアス値（通紙時の転写ガイド５の電位）の設定条件を切り替えることによって、画像飛び散り、転写ガイド５の汚れ、転写抜けもなく、また、感光体１からの転写材Ｐの分離性も良好であった。
【００６１】
このように、本実施の形態では、両面または多重画像形成可能な画像形成装置において、１回目の画像形成後に再度２回目の画像形成を行う場合でも、転写材Ｐの水分量に応じて転写前露光量と転写ガイド５に印加する直流バイアス値を適正に設定することにより、転写材Ｐの感光体からの分離性が良好で、かつ画像飛び散り、転写ガイドの汚れ、転写抜けも同時に防止することができる。
【００６２】
【発明の効果】
以上説明したように本発明によれば、転写後の転写材の像担持体からの分離性の向上を図ることができ、かつ画像飛び散り、転写ガイドの汚れ、転写抜けを防止することができるので、良好な画像形成を行うことができる。
【図面の簡単な説明】
【図１】本発明の第１の実施の形態に係る画像形成装置を示す概略構成図。
【図２】本発明の第２の実施の形態に係る画像形成装置を示す概略構成図。
【図３】本発明の第２の実施の形態における環境湿度切り替え条件を示す図。
【図４】本発明の第４の実施の形態に係る画像形成装置を示す概略構成図。
【図５】本発明の第４の実施の形態における転写材水分量切り替え条件を示す図。
【図６】第１の従来例に係る画像形成装置を示す概略構成図。
【図７】画像形成の工程を示す図。
【図８】画像形成時の転写材と感光体間の静電吸着力を示す図。
【図９】転写前露光がある場合の画像形成の工程を示す図。
【図１０】第２の従来例に係る画像形成装置を示す概略構成図。
【図１１】第２の従来例に係る画像形成装置での転写漏洩れ電流を説明した図。
【符号の説明】
１感光体（像担持体）
２一次帯電器（帯電手段）
３露光装置（露光手段）
４現像装置（現像手段）
５転写ガイド
６転写帯電器（転写手段）
７分離帯電器
８転写前露光装置（転写前露光手段）
１２環境湿度センサー（湿度検出手段）
１３制御装置（制御手段）
１４水分量検出センサー（水分量検出手段）[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an image forming apparatus such as a copying machine, a printer, and a facsimile that forms an image by an electrophotographic method, an electrostatic recording method, and the like.In particular, an electric charge having the same polarity as an electrostatic latent image formed on an image carrier is generated. The present invention relates to an image forming apparatus for reversal developing with a developer and developing the image.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, image forming apparatuses such as copiers, printers, and facsimiles that form an image by an electrophotographic method, an electrostatic recording method, and the like have electric charges of the same polarity as an electrostatic latent image formed on the surface of an image carrier. 2. Description of the Related Art An image forming apparatus of a type in which an image is developed by reversal development with a developer is proposed.
[0003]
FIG. 6 is a schematic configuration diagram showing a conventional image forming apparatus using reversal development. In FIG. 1, reference numeral 1 denotes a drum-type electrophotographic photosensitive member (hereinafter, referred to as a photosensitive member) as an image carrier, which is charged to a specified positive potential by a primary charger 2. Then, an electrostatic latent image is formed on the photoreceptor 1 whose surface is charged by an exposure device 3 having a semiconductor laser device or the like. (Toner).
[0004]
On the other hand, the transfer material P is guided by the transfer guide 5 and enters a transfer portion between the transfer charger 6 facing the photoreceptor 1 and the separation charger 7, and is transferred by the transfer charger 6 to which an electric field is applied. The developed developer (toner) image is transferred onto P. Then, after the transfer material P is electrostatically separated from the photoconductor 1 by the static elimination action of the separation charger 7, a fixing process is performed by a fixing device (not shown), and the image formation is completed. In the drawing, reference numeral 8 denotes a pre-transfer exposure device for assisting separation, and 9 denotes a varistor element.
[0005]
FIG. 7 shows the above-described image forming process. First, the photosensitive member 1 is charged to a positive potential in a charging process by the primary charger 2, and then only the image portion is exposed to laser by the exposure process by the exposure device 3. To form a so-called well-type electrostatic potential. Next, in accordance with the electric field formed by the electrostatic potential in the developing step by the developing device 4 and the electric field generated by the developing device 4 and the latent image potential, a developer having a positive polarity develops the electrostatic latent image to make it visible. The developer (toner) image visualized in the transfer step by the transfer charger 6 is transferred to the transfer material P by electric field. Then, the transfer material P is electrostatically separated in a separation step by the separation charger 7.
[0006]
In addition, in the separation of the transfer material P in the conventional image formation using the reversal development described above, as shown in FIG. 8, the non-image portion (white background portion) is on the high potential portion side. The electrostatic attraction force (F1, F2, F3) between the two increases, and the separability deteriorates. For this reason, as shown in FIGS. 6 and 9, before the development and before the transfer and separation processes, in order to reduce the potential of the non-image portion, the pre-transfer exposure device 8 such as an LED element is used. To do.
[0007]
As shown in FIG. 8, in the above-described image forming apparatus, F1 (Coulomb force due to a latent image potential electric field) and F2 (charge amount of the developer) are used as electrostatic force of the developer (toner) adhering to the photoreceptor 1. And the local electric field of F3 (the Coulomb force due to the local electric field between the developer and the photoreceptor 1). Since the surface potential of the developer 1 and the polarity of the developer are the same (positive) and extremely small as compared with the normal development, the adhesion of the developer to the photoconductor 1 is weak, and the floating developer adheres to the transfer guide 5. Generates dirt.
[0008]
Conventionally, as shown in FIG. 10, a DC bias having the same polarity (positive polarity) as the developer is applied to the transfer guide 5 from the power supply 11 to prevent the transfer guide 5 from being stained due to the adhesion of the developer. Etc. have been proposed.
[0009]
[Problems to be solved by the invention]
However, in the conventional image forming apparatus shown in FIG. 6, by performing the pre-transfer exposure by the pre-transfer exposure device 8, as shown in FIG. A decrease in the Coulomb force due to the latent image potential electric field) causes a problem that the image is liable to be scattered particularly around the character at the boundary between the solid black and the solid white and around the line. This image scattering phenomenon occurs remarkably especially in a low humidity environment.
[0010]
In the conventional image forming apparatus shown in FIG. 10, a DC bias having the same polarity (positive polarity) as that of the developer is applied to the transfer guide 5 to prevent the transfer guide 5 from being stained. As described above, there is a problem that a transfer failure occurs due to the leakage current i of the transfer current to the transfer guide 5 side via the transfer material P. The transfer failure phenomenon due to the leakage current i occurs remarkably especially in a high humidity environment.
[0011]
SUMMARY OF THE INVENTION It is an object of the present invention to provide an image forming apparatus capable of preventing image scattering, preventing transfer guide contamination by a developer, and preventing transfer failure due to transfer current leakage.
[0013]
[Means for Solving the Problems]
The invention according to claim 1 is an image carrier that carries an image, a charging unit that charges the image carrier, an exposure unit that forms an electrostatic latent image on the image carrier, and the electrostatic latent image. Developing means for inverting the electrostatic latent image with a developer having the same polarity as above to form a developer image, and exposing the surface of the image carrier after the developing step by the developing means to reduce the surface potential thereof A pre-transfer exposure unit, a transfer unit that transfers the developer image to a transfer material at a transfer site, and a transfer guide that guides the transfer material to the transfer site and applies a DC bias having the same polarity as the developer. An image forming apparatus comprising: a humidity detecting unit for detecting environmental humidity; an exposure amount before transfer to the image carrier by the pre-transfer exposure unit based on humidity information input from the humidity detecting unit; DC via applied to guide And control means for controlling a value, said control means, in a low humidity environment is controlled to larger setting the DC bias value to be applied to the transfer guide and the pre-transfer exposure, the pre-transfer exposure in high humidity environment The amount and the DC bias value applied to the transfer guide are controlled to be set to be smaller.
[0014]
The invention according to claim 2 is an image carrier that carries an image, a charging unit that charges the image carrier, an exposure unit that forms an electrostatic latent image on the image carrier, and the electrostatic latent image. Developing means for inverting the electrostatic latent image with a developer having the same polarity as above to form a developer image, and exposing the surface of the image carrier after the developing step by the developing means to reduce the surface potential thereof A pre-transfer exposure unit, a transfer unit that transfers the developer image to a transfer material at a transfer site, and a transfer guide that guides the transfer material to the transfer site and applies a DC bias having the same polarity as the developer. An image forming apparatus comprising: a transfer material feeding unit capable of forming a double-sided image or a multiplex image; and the pre-transfer exposure unit configured to perform the first image formation and the second and subsequent image formations on the transfer material. Exposure amount before transfer to image carrier and before Control means for controlling switching of a DC bias value to be applied to the transfer guide, wherein the control means controls the exposure amount before transfer and the transfer guide during the second and subsequent image forming than the first image forming. Is characterized in that the DC bias value to be applied to is controlled to be set relatively large.
[0015]
The invention according to claim 3 is an image carrier that carries an image, a charging unit that charges the image carrier, an exposure unit that forms an electrostatic latent image on the image carrier, and the electrostatic latent image. Developing means for inverting the electrostatic latent image with a developer having the same polarity as above to form a developer image, and exposing the surface of the image carrier after the developing step by the developing means to reduce the surface potential thereof A pre-transfer exposure unit, a transfer unit that transfers the developer image to a transfer material at a transfer site, and a transfer guide that guides the transfer material to the transfer site and applies a DC bias having the same polarity as the developer. An image forming apparatus comprising: a water amount detecting unit for detecting a water amount of the transfer material; and a transfer to the image carrier by the pre-transfer exposure unit based on water amount information input from the water amount detecting unit. Pre-exposure amount and mark on the transfer guide Control means for controlling a DC bias value to be applied, wherein the control means sets the DC exposure value to be applied to the transfer guide and the exposure amount before transfer when the water content of the transfer material is small. When the moisture content of the transfer material is large, control is performed so that the exposure amount before transfer and the DC bias value applied to the transfer guide are set to be small.
[0016]
(Action)
As a result of intensive studies, the present inventor considers that the above-mentioned problem occurs by the following mechanism.
[0017]
First, the image scattering due to the pre-transfer charging of the pre-transfer exposure device 8 reduces the electrostatic adhesion between the developer and the photoconductor 1 as described above, and causes the regular transfer of the contact area between the photoconductor 1 and the transfer material P. This is because a so-called pre-transfer phenomenon occurs in which transfer starts to be performed on the transfer material P before the position. It has been found that this phenomenon is caused by an electric field between the transfer material P and the photoconductor 1 before the transfer area. In particular, this phenomenon occurs remarkably when the transfer material P is charged to a charge opposite to that of the developer (toner). did. In particular, it occurred remarkably during the second image formation after the first image formation and in a low humidity environment.
[0018]
However, it has been found that this phenomenon can be easily avoided by applying a DC bias having the same polarity as the developer to the transfer guide 5 and applying a repulsive electric field from the transfer guide 5 to the developer, thereby preventing pre-transfer. . Further, regarding the separation of the transfer material P from the photoconductor 1, it is generally known that a low humidity environment is severe.
[0019]
On the other hand, the transfer failure caused by the transfer leakage current i caused by the adverse effect of the transfer guide 5 against contamination becomes more prominent as the DC bias value applied to the transfer guide 5 is increased. It has been clarified that he is also heavily dependent. On the other hand, the stain on the transfer guide 5 is also significantly dependent on the environment, particularly in a low humidity environment. It is considered that these tend to depend on the cohesiveness of the developer (toner), and the transfer guide 5 was not so contaminated in a high-humidity environment where there was a tendency for cohesion.
[0020]
As described above, in a low-humidity environment, the exposing amount before transfer is set to a large value to assist the separability of the transfer material P, and the separability is assisted. It can be countermeasured by setting a large value. On the other hand, in a high-humidity environment, image scattering can be suppressed by setting a small DC bias value applied to the transfer guide 5 and setting a small exposure amount before transfer in order to prevent a transfer current leakage current. .
[0021]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[0022]
(First Embodiment)
FIG. 1 is a schematic configuration diagram illustrating an image forming apparatus according to the present embodiment. The same members as those in the conventional example are denoted by the same reference numerals, and overlapping description will be omitted.
[0023]
This image forming apparatus includes a drum-shaped photosensitive member 1 made of a-Si or the like, a primary charger 2, an exposure device (scanner device) 3, a developing device 4, a transfer guide 5, a transfer charger 6, a separation charger 7, A pre-transfer exposure device 8 is provided.
[0024]
The developing device 4 reversely develops the electrostatic latent image formed on the surface of the photoconductor 1 with a developer having the same polarity as that of the electrostatic latent image to visualize the image.
[0025]
Next, an image forming operation of the above-described image forming apparatus will be described.
[0026]
At the time of image formation, the photoconductor 1 is driven to rotate at a predetermined process speed by a driving unit (not shown), and is charged to about +400 V by the primary charger 2 to which a predetermined charging bias is applied. Then, an image exposure corresponding to the image data output by the laser beam is given to the charged photoreceptor 1 by the exposure device 3, and a positive electrostatic latent image is formed. The potential of the exposed portion on the photoconductor 1 is reduced to about +50 V by the image exposure using the laser light.
[0027]
Then, the developing device 4 develops the electrostatic latent image on the exposed portion with a positive polarity developer, and reversely develops the image to make it visible.
[0028]
Then, the photoreceptor 1 is subjected to pre-transfer exposure by a pre-transfer exposure device 8 including an LED. Here, the change in the surface potential of the photoconductor 1 before and after the LED exposure by the pre-transfer exposure device 8 will be briefly described. First, immediately before the pre-transfer exposure, the white background potential was about +350 V due to dark decay, but is adjusted to about +100 V by the action of the pre-transfer exposure. On the other hand, the potential of the image portion was about +30 V without being changed because the pre-transfer exposure was blocked by the developer on the photosensitive member 1 after the development.
[0029]
Then, the transfer material P is conveyed by the transfer guide 5 to a transfer portion in a gap between the photoconductor 1 and the transfer charger 6, and is developed on the photoconductor 1 by a negative transfer bias applied to the transfer charger 6. The agent is transferred to the transfer material P. At this time, a DC bias of +500 V having the same polarity (positive polarity) as the developer is applied to the transfer guide 5 from the power supply 10.
[0030]
The transfer material P onto which the developer has been transferred is electrostatically neutralized by a separation bias in which an AC voltage is superimposed on a positive DC voltage applied to the separation charger 7, and is separated from the photoreceptor 1. . The transfer material P separated from the photoreceptor 1 is transported to a fixing device (not shown), and the developer image is fixed on the transfer material P as a permanently fixed image by the fixing device (not shown) and is discharged.
[0031]
In this embodiment and the conventional example shown in FIGS. 6 and 10 (the conventional example of FIG. 6 is referred to as Conventional Example 1 and the conventional example of FIG. 10 is referred to as Conventional Example 2), image evaluation (image scattering, transfer guide 5 and the evaluation of separation (separation of transfer material P from photoreceptor 1). Table 1 shows these evaluation results.
[0032]
[Table 1]

In this embodiment, a DC bias of +500 V is applied to the transfer guide 5 to perform the pre-transfer exposure (the post-exposure potential is +200 V). In Conventional Example 1, the setting conditions of the pre-transfer exposure were the same as those of the present embodiment (the post-exposure potential was +200 V), and the transfer guide 5 was grounded by a varistor element 9 of +500 V. In this case, at the time of actual image formation, the negative charge of the transfer flowed into the transfer guide 5 via the transfer material P, and became about -500V. On the other hand, in Conventional Example 2, there was no pre-transfer exposure (the post-exposure potential was +350 V), and a DC bias of +500 V was applied to the transfer guide 5 as in the present embodiment. These evaluations were performed at normal temperature and normal humidity (20 ° C., 60%). Other basic conditions are the same.
[0033]
As is clear from the evaluation results shown in Table 1, in the present embodiment, there is no image scattering, no stain on the transfer guide 5 and no transfer omission (○), and the separation property of the transfer material P from the photoreceptor 1. Was also good (○).
[0034]
On the other hand, in the conventional example 1, there was no transfer omission (）), and the separation property of the transfer material P from the photoreceptor 1 was good (○), but the image was scattered and the transfer guide 5 was stained (（). Further, in Conventional Example 2, there was no image scattering, no contamination of the transfer guide 5, and no transfer omission (いずれ), but the separation of the transfer material P from the photoreceptor 1 was not good (×).
[0035]
As described above, in the present embodiment, the separability of the transfer material P from the photoreceptor 1, which is inevitable in an image forming apparatus that forms an image by reversal development, is improved. Scattering, contamination of the transfer guide 5 and transfer omission can also be prevented at the same time.
[0036]
(Second embodiment)
FIG. 2 is a schematic configuration diagram illustrating the image forming apparatus according to the present embodiment.
[0037]
In the present embodiment, the apparatus includes an environmental humidity sensor 12 and a control device (CPU) 13, and the control device (CPU) 13 controls the pre-transfer exposure device 8 based on the humidity information input from the environmental humidity sensor 12. The power supply 9 is controlled to control the exposure amount before transfer to the photoconductor 1 and the power supply 11 of the transfer guide 5 to appropriately control the DC bias value applied to the transfer guide 5. That is, in a low humidity environment, the exposure amount before transfer and the DC bias value applied to the transfer guide 5 are set to be relatively large, and in a high humidity environment, the DC bias value applied to the transfer guide 5 is controlled to be set to be small. Other configurations are the same as those of the first embodiment.
[0038]
FIG. 3 shows the switching condition of the white background potential (post-exposure potential) of the photoreceptor 1 after the pre-transfer exposure and the DC bias value (transfer guide potential at the time of paper passing) applied to the transfer guide 5 at the time of paper passing. In the drawing, A indicates the potential of the transfer guide 5 when the paper is passed, and B indicates the potential after exposure before transfer.
[0039]
As described above, in the low humidity environment, the value of the pre-transfer exposure is set to be large in order to give priority to the separability of the transfer material P in the low-humidity environment. The applied DC bias value was set large. On the other hand, in a high-humidity environment, the DC bias value applied to the transfer guide 5 was set to be small in order to prevent the transfer current from leaking through the transfer material P and the transfer guide 5.
[0040]
In this embodiment (second embodiments (a) to (d)) and comparative examples (comparative examples 1 to 4), image evaluation (image scattering, dirt on transfer guide 5, transfer omission) and separation are performed. Evaluation (separability of transfer material P from photoreceptor 1) was performed. Table 2 shows these evaluation results.
[0041]
[Table 2]

In the low humidity environment (humidity 5%, 30%) of the embodiments (a) and (b), the exposure amount before transfer is set to a relatively large value (post-exposure potential is +100 V, +140 V), and the DC voltage applied to the transfer guide 5 The bias value was set to a relatively large value (the potential at the time of paper passing was +700 V, +600 V). In the high-humidity environment (humidity 60%, 80%) of the embodiments (c) and (d), the DC bias value applied to the transfer guide 5 is set to a small value (potential during sheet passing is +500 V, +200 V). did. The post-exposure potential at this time was set to +200 V and +250 V, respectively.
[0042]
On the other hand, in Comparative Examples 1 to 4, the exposure amount before transfer and the DC bias value applied to the transfer guide 5 were fixed values even when the humidity was changed to 5%, 30%, 60%, and 80%, respectively. At this time, the potential after exposure was set to +200 V, and the potential at the time of paper passing was set to +500 V.
[0043]
As is clear from the evaluation results shown in Table 2, in the present embodiment (second embodiment (a) to (d)), there is no image scattering, no stain on the transfer guide 5, and no transfer omission (抜け). ) Also, the separability of the transfer material P from the photoreceptor 1 was good (○).
[0044]
On the other hand, in Comparative Example 1, there was no transfer omission (○), but the image was scattered, the transfer guide 5 was slightly stained (△), and the separation of the transfer material P from the photoreceptor 1 was slightly poor (△). . In Comparative Example 2, there was no image scattering and no transfer omission (○), but the transfer guide 5 was slightly stained (△), and the separability of the transfer material P from the photoreceptor 1 was slightly poor (△). Further, in Comparative Example 4, the image was scattered, the transfer guide 5 was stained, and the separation property of the transfer material P from the photoreceptor 1 was good (○), but the transfer omission was slightly poor (△). Note that Comparative Example 3 has the same setting conditions as those of the embodiment (c).
[0045]
As described above, in the present embodiment, the image scattering in a low humidity environment and the contamination of the transfer guide 5 are prevented, the separability of the transfer material P from the photoconductor 1 is improved, and the transfer omission in a high humidity environment is prevented. Can be prevented.
[0046]
(Third embodiment)
In the present embodiment, the image forming apparatus shown in FIG. 1 is provided with a transfer material feeding unit (not shown) for double-sided or multiple image formation. Later, the second image formation can be performed again. As the transfer material feeding means (not shown), a known means can be used.
[0047]
In such an image forming apparatus, generally, a part of the moisture contained in the transfer material after the completion of the first image formation evaporates, and its electric resistance value also increases. Therefore, in this case, the optimum value of the exposure amount before transfer and the DC bias value to be applied to the transfer guide are not determined only by the environmental humidity, and the setting conditions need to be switched depending on the image forming mode.
[0048]
Table 3 shows each setting condition in the present embodiment and the comparative example.
[0049]
[Table 3]

In the present embodiment, at the time of the first image formation, the exposure amount before transfer is set so that the potential after exposure is +200 V, and the DC bias value applied to the transfer guide 5 is set so that the potential during paper passing is +500 V. did. At the time of the second image formation, the exposure amount before transfer was set so that the potential after exposure was +100 V, and the DC bias value applied to the transfer guide 5 was set so that the potential at the time of paper passing was +700 V.
[0050]
On the other hand, in the comparative example, the exposure amount before transfer at the time of the first and second image formation is set so that the potential after exposure is +200 V, and the DC bias value applied to the transfer guide 5 is +500 V at the time of paper passing. And the setting conditions were not switched. Note that the image formation in this embodiment and the comparative example was performed at an environmental humidity of 60%.
[0051]
In this embodiment and the comparative example, image evaluation (image scattering, dirt on the transfer guide 5, transfer omission) and separation property evaluation (separation property of the transfer material P from the photoreceptor 1) were performed. In the case of the present embodiment in which the setting conditions of the exposure amount before transfer and the DC bias value applied to the transfer guide 5 are switched at the time of the second and the second image formation, image scattering, dirt on the transfer guide 5 and transfer omission may also occur. In addition, the separation property of the transfer material P from the photoreceptor 1 was good.
[0052]
On the other hand, in the comparative example, image scattering occurred during the second image formation.
[0053]
As described above, in the present embodiment, in the image forming apparatus capable of forming a double-sided or multiple image, even when the second image formation is performed again after the first image formation, the separation property of the transfer material P from the photoconductor is improved. In addition, it is possible to prevent image scattering, transfer guide contamination, and transfer omission at the same time.
[0054]
Also in the present embodiment, it is possible to combine the control of the exposure amount before transfer based on the environmental humidity and the control of the DC bias value applied to the transfer guide 5 described in the second embodiment.
[0055]
(Fourth embodiment)
FIG. 4 is a schematic configuration diagram illustrating the image forming apparatus according to the present embodiment.
[0056]
In the present embodiment, a moisture detecting sensor 14 that includes a transfer material feeding unit (not shown) for forming double-sided or multiple images, detects the moisture content of the transfer material P fed into the apparatus, and a control device (CPU) 13. As the transfer material feeding means (not shown), a known means can be used.
[0057]
The control device (CPU) 13 controls the power supply 9 of the pre-transfer exposure device 8 based on the water content information of the transfer material P input from the water content detection sensor 14, and controls the pre-transfer exposure amount to the photoconductor 1, and The power supply 11 of the transfer guide 5 is controlled to appropriately control the DC bias value applied to the transfer guide 5. That is, when the moisture content of the transfer material P is small, the exposure amount before transfer and the DC bias value applied to the transfer guide 5 are set to be relatively large. Control is performed so that the DC bias value to be applied is set smaller. Other configurations are the same as those of the first embodiment.
[0058]
FIG. 5 shows the potential of the white background of the photoreceptor 1 after exposure before transfer (potential after exposure) and the DC bias value applied to the transfer guide 5 during paper passing (transfer guide potential during paper passing) with respect to the water content of the transfer material P. In the figure, A represents the potential of the transfer guide 5 when the paper is passed, and B represents the potential after exposure before transfer.
[0059]
As described above, when the amount of water in the transfer material P is small as described above, the value of the pre-transfer exposure is set to a relatively large value with priority given to the separability of the transfer material P. On the other hand, the DC bias value applied to the transfer guide 5 was set relatively large. On the other hand, when the water content of the transfer material P is large, the DC bias value applied to the transfer guide 5 is set to be small in order to prevent the transfer current from leaking through the transfer material P and the transfer guide 5.
[0060]
In the same manner as described above, image evaluation (image scattering, dirt on the transfer guide 5, transfer omission) and separation property evaluation (separation property of the transfer material P from the photoconductor 1) in the present embodiment were performed. In the second image formation after the image formation, the exposure amount before transfer (potential after exposure) and the DC bias value (paper passing) to be applied to the transfer guide 5 based on the water content switching condition of the transfer material P shown in FIG. By changing the setting conditions of the transfer guide 5 at the time, the image was not scattered, the transfer guide 5 was not stained, and the transfer was not removed, and the separation property of the transfer material P from the photoreceptor 1 was good.
[0061]
As described above, in the present embodiment, even when the second image formation is performed again after the first image formation in the image forming apparatus capable of forming a double-sided or multiple image, the transfer before the transfer is performed according to the water content of the transfer material P. By properly setting the exposure amount and the DC bias value applied to the transfer guide 5, the separation property of the transfer material P from the photoconductor is good, and the scattering of the image, the contamination of the transfer guide, and the transfer omission are simultaneously prevented. Can be.
[0062]
【The invention's effect】
As described above, according to the present invention, it is possible to improve the separability of the transfer material after transfer from the image carrier, and it is possible to prevent image scattering, transfer guide dirt, and transfer omission. And good image formation can be performed.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram illustrating an image forming apparatus according to a first embodiment of the present invention.
FIG. 2 is a schematic configuration diagram illustrating an image forming apparatus according to a second embodiment of the present invention.
FIG. 3 is a diagram showing environmental humidity switching conditions according to a second embodiment of the present invention.
FIG. 4 is a schematic configuration diagram illustrating an image forming apparatus according to a fourth embodiment of the present invention.
FIG. 5 is a diagram illustrating a transfer material moisture amount switching condition according to a fourth embodiment of the present invention.
FIG. 6 is a schematic configuration diagram showing an image forming apparatus according to a first conventional example.
FIG. 7 is a view showing an image forming process.
FIG. 8 is a diagram illustrating an electrostatic attraction force between a transfer material and a photosensitive member during image formation.
FIG. 9 is a diagram showing an image forming process when there is exposure before transfer.
FIG. 10 is a schematic configuration diagram showing an image forming apparatus according to a second conventional example.
FIG. 11 is a diagram illustrating a transfer leakage current in an image forming apparatus according to a second conventional example.
[Explanation of symbols]
1 Photoconductor (image carrier)
2 Primary charger (charging means)
3 Exposure equipment (exposure means)
4 Developing device (developing means)
5 Transfer guide 6 Transfer charger (transfer means)
7 Separator charger 8 Pre-transfer exposure device (pre-transfer exposure means)
12 Environmental humidity sensor (humidity detecting means)
13 control device (control means)
14 Water content detection sensor (water content detection means)

Claims

An image carrier for carrying an image, charging means for charging the image carrier, exposure means for forming an electrostatic latent image on the image carrier, and a developer having the same polarity as the electrostatic latent image Developing means for inverting and developing the electrostatic latent image to form a developer image; exposing means for exposing the surface of the image carrier after the developing step by the developing means to reduce the surface potential thereof; Transfer means for transferring a developer image to a transfer material at a transfer site, and an image forming apparatus including a transfer guide to which the transfer material is guided to the transfer site and a DC bias having the same polarity as the developer is applied.
Humidity detecting means for detecting environmental humidity, an exposure amount before transfer to the image carrier by the pre-transfer exposure means based on humidity information inputted from the humidity detecting means, and a DC bias value applied to the transfer guide Control means for controlling the exposure amount before transfer and the DC bias value applied to the transfer guide in a low humidity environment to be relatively large, and the exposure amount before transfer in a high humidity environment . And controlling the DC bias value to be applied to the transfer guide to be set smaller.
An image forming apparatus comprising:

An image carrier for carrying an image, charging means for charging the image carrier, exposure means for forming an electrostatic latent image on the image carrier, and a developer having the same polarity as the electrostatic latent image Developing means for inverting and developing the electrostatic latent image to form a developer image; exposing means for exposing the surface of the image carrier after the developing step by the developing means to reduce the surface potential thereof; Transfer means for transferring a developer image to a transfer material at a transfer site, and an image forming apparatus including a transfer guide to which the transfer material is guided to the transfer site and a DC bias having the same polarity as the developer is applied.
A transfer material feeding unit capable of forming a double-sided image or a multiplex image, and a transfer before the transfer to the image carrier by the pre-transfer exposure unit during the first image formation and the second and subsequent image formation on the transfer material Control means for controlling the exposure amount and a DC bias value to be applied to the transfer guide, wherein the control means performs the pre-transfer exposure during the second and subsequent image forming than the first image forming. Control to set the amount and the DC bias value applied to the transfer guide to be relatively large,
An image forming apparatus comprising:

An image carrier for carrying an image, charging means for charging the image carrier, exposure means for forming an electrostatic latent image on the image carrier, and a developer having the same polarity as the electrostatic latent image Developing means for inverting and developing the electrostatic latent image to form a developer image; exposing means for exposing the surface of the image carrier after the developing step by the developing means to reduce the surface potential thereof; Transfer means for transferring a developer image to a transfer material at a transfer site, and an image forming apparatus including a transfer guide to which the transfer material is guided to the transfer site and a DC bias having the same polarity as the developer is applied.
A water amount detecting means for detecting the water amount of the transfer material; an exposure amount before transfer to the image carrier by the pre-transfer exposure means based on the water amount information inputted from the water amount detecting means; Control means for controlling a DC bias value applied to the guide, wherein the control means increases the amount of exposure before transfer and the DC bias value applied to the transfer guide when the moisture content of the transfer material is small. Control to set, when the water content of the transfer material is large, control to set the DC bias value applied to the pre-transfer exposure amount and the transfer guide to be smaller,
An image forming apparatus comprising: