JP2004117517A - Contact electrifier and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To safely and efficiently apply a voltage by defining the magnitude of a protective resistance connected in series by a mathematical formula, in a contact electrification system. <P>SOLUTION: The apparatus has at least one of contact electrifying means 2, 6, and 7 which abut on the surface of a body 1 to be electrified and electrifies the surface. When applying a voltage V1 to a circuit in which the contact electrifying means and a resistance circuit Rh (protective resistance 27) are connected in series, the apparatus satisfies a numerical expression as shown, in relation to the heat quantity Wb with which the constituent member of the contact electrifying means starts burning. <P>COPYRIGHT: (C)2004,JPO

Description

【００２４】
となる。ここで、保護抵抗ＲｈをＲｂに比べて非常に大きくすると、上記のような導電性繊維の抵抗ムラに対する電流量Ｉｃの変化は小さくなり、導電性繊維の燃焼を防ぐことができる。
【特許文献１】
特開２００１―２１５７９８号公報
【特許文献２】
特開平５−１５０６１２号公報
【００２５】
【発明が解決しようとする課題】
しかしながら、接触帯電部材に過電流防止の保護抵抗を接続した画像形成装置において、以下のような問題が生じた。
【００２６】
接触帯電部材に導電性樹脂繊維を用いる場合、導電性樹脂繊維は安価で抵抗調整の容易性等から扱いやすいが、この抵抗値は温度、湿度といった環境に大きく左右される上に、製造上のばらつきも大きい。このため、過電流による燃焼の恐れを無くすためには、保護抵抗はある程度大きなものを接続する必要があった。しかしながら、大きな保護抵抗Ｒｈを接続すると回路電流Ｉｃが小さくなってしまい、帯電や現像剤帯電量制御といった接触帯電部材に求められる機能が低下してしまった。このため、保護抵抗の値は必要最小限に抑えたいが、ブラシの保護と機能性とを両立させる保護抵抗値を選ぶことは困難であった。
【００２７】
本発明は上記に鑑みて提案されたもので、接触帯電方式において、接触帯電手段に直列に接続された保護抵抗の大きさを印加した高圧に対して最も機能を発揮できる適切なものにすることを可能にして、安全かつ効率的に電圧を印加することを目的としている。
【００２８】
【課題を解決するための手段】
本発明は下記の構成を特徴とする、接触帯電装置および画像形成装置である。
【００２９】
（１）被帯電体面に接触して被帯電体面を帯電する接触帯電手段（接触帯電部材）をひとつあるいは複数手段有する接触帯電装置において、
前記接触帯電手段と抵抗回路Ｒｈとが直列に接続された回路に対して電圧Ｖ１を印加する際に、前記接触帯電手段の構成部材が燃焼を開始する熱量Ｗｂに対して
【００３０】
【数４】

【００３１】
の関係を満たすことを特徴とした接触帯電装置。
【００３２】
（２）前記接触帯電手段のひとつあるいは複数手段あるいは全手段を被帯電体面に接触する導電性繊維ブラシ部材で構成することを特徴とする（１）に記載の接触帯電装置。
【００３３】
（３）前記接触帯電手段のひとつあるいは複数手段に振動電界を印加することを特徴とする請求項１または２に記載の接触帯電装置。
【００３４】
（４）像担持体と、像担持体面に接触して像担持体面を帯電する接触帯電手段をひとつあるいは複数手段有し、帯電処理された前記像担持体に静電潜像を形成する情報書き込み手段と、前記静電潜像に所定の極性の現像剤を供給し静電潜像を可視化する現像手段と、可視化した現像剤像を転写材に転写する転写手段とを有する画像形成装置において、
前記接触帯電手段と抵抗回路Ｒｈとが直列に接続された回路に対して電圧Ｖ１を印加する際に、前記接触帯電手段の構成部材が燃焼を開始する熱量Ｗｂに対して
【００３５】
【数５】

【００３６】
の関係を満たすことを特徴とした画像形成装置。
【００３７】
（５）前記接触帯電手段のひとつあるいは複数手段あるいは全手段を像担持体に接触する導電性繊維ブラシ部材で構成することを特徴とする（４）に記載の画像形成装置。
【００３８】
（６）前記接触帯電手段のひとつあるいは複数手段に振動電界を印加することを特徴とする（４）または（５）に記載の画像形成装置。
【００３９】
（７）前記情報書き込み手段は露光手段であることを特徴とする（４）ないし（６）のいずれかに記載の画像形成装置。
【００４０】
（８）前記情報書き込み手段よりも像担持体回転方向上流側に主の接触帯電手段を有し、該主の接触帯電手段よりも像担持体回転方向上流側かつ前記転写手段よりも像担持体回転方向下流側に、帯電処理された像担持体上の残留現像剤を正規極性に帯電処理する現像剤帯電量制御手段としての補助接触帯電手段を有することを特徴とする（４）ないし（８）いずれかに記載の画像形成装置。
【００４１】
（９）前記転写手段よりも像担持体回転方向下流側かつ前記現像剤帯電量制御手段としての補助接触帯電手段よりも像担持体回転方向上流に、前記現像剤像を転写材に転写した後の像担持体上に残留する残留現像剤を均一化する残留現像剤均一化制御手段としての第２の補助接触帯電手段を有することを特徴とする（８）に記載の画像形成装置。
【００４２】
〈作　用〉
すなわち本発明は、接触帯電手段に対し、被帯電体（像担持体）のピンホール等に過電流が流れるのを防止する高抵抗を直列に接続する際に、適正な抵抗の大きさを式より算出することによって、燃焼等の恐れがなく、より効率的に接触帯電手段を機能させることが可能となった。
【００４３】
【発明の実施の形態】
（１）画像形成装置例
１）全体的な概略説明
図１は本実施の形態に係る画像形成装置の概略構成図である。この画像形成装置は、転写方式電子写真プロセス、接触帯電方式、反転現像方式、クリーナレス方式、最大通紙サイズＡ３サイズで、第１から第４の４つの画像形成部を有し、各画像形成部の第１の像担持体である回転ドラム型の電子写真感光体に形成した１色目から４色目（イエロー、マゼンタ、シアン、ブラック）のトナー画像を一旦第２の像担持体である中間転写ベルト（中間転写体）に連続的に多重転写し、フルカラープリント画像を得る４連ドラム方式（インライン）のフルカラーレーザプリンタである。
【００４４】
Ｙ、Ｍ、Ｃ、Ｂｋはそれぞれイエロー、マゼンタ、シアン、ブラックの色トナー画像を形成する第１から第４の４つの画像形成部である。
【００４５】
各画像形成部Ｙ、Ｍ、Ｃ、Ｂｋはそれぞれ、第１の像担持体としての回転ドラム型の電子写真感光体（以下、感光ドラム）１と、主の接触帯電手段としての帯電ローラ２と、情報書き込み手段としてのレーザビームスキャナ３と、現像装置４と、現像剤供給ユニット５と、補助接触帯電手段としての第１と第２の２つの接触帯電ブラシ６・７等、からなるクリーナレス方式の電子写真プロセス機構である。
【００４６】
図２は第１の画像形成部Ｙ部分の拡大模型図であり、第２から第４の画像形成部Ｍ、Ｃ、Ｂｋもこれと同様の機構構成である。ただし、第１から第４の各画像形成部Ｙ、Ｍ、Ｃ、Ｂｋの現像装置４と現像剤供給ユニット５に収納のトナーはそれぞれイエロートナーｔ（Ｙ）、マゼンタトナーｔ（Ｍ）、シアントナーｔ（Ｃ）、ブラックトナーｔ（Ｂｋ）である。
【００４７】
各画像形成部Ｙ、Ｍ、Ｃ、Ｂｋにおいて、感光ドラム１、帯電ローラ２、現像装置４、第１と第２の２つの接触帯電ブラシ６・７は一括して画像形成装置本体に対して着脱区間交換自在なプロセスカートリッジ（Ｐ−ＣＲＧ）８としてある。
【００４８】
９は第２の像担持体としての中間転写ベルトであり、駆動ローラ９ｅ、テンションローラ９ｆ及び２次転写対向ベルト１０ａの３つのローラ間に懸回張設してある。上記第１から第４の４つの画像形成部Ｙ、Ｍ、Ｃ、Ｂｋは、テンションローラ９ｆと駆動ローラ９ｅとの間の水平の中間転写ベルト部分の上側に図面上左側から右側に一定の間隔をおいて順に一列に配置してある。
【００４９】
この中間転写ベルト９は駆動ローラ９ｅが不図示の駆動系により回転駆動されることで矢印の時計方向に所定のプロセス速度で回転駆動される。
【００５０】
各画像形成部Ｙ、Ｍ、Ｃ、Ｂｋの感光ドラム１の下面には中間転写ベルト９を介して１次転写ローラ９ｇを圧接させて配設して、それぞれ感光ドラム１と中間転写ベルト９との間で１次転写ニップ部ｄを形成させている。
【００５１】
１０は２次転写ローラであり、２次転写対向ローラ１０ａに対して中間転写ベルト９を挟ませて圧接させて配設して、中間転写ベルト９と２次転写対向ローラ１０との間で２次転写ニップ部ｇを形成させている。
【００５２】
画像形成動作開始信号（プリント開始信号）が発せられると、各画像形成部Ｙ、Ｍ、Ｃ、Ｂｋの感光ドラム１が矢印の反時計方向に、また中間転写ベルト９が矢印の時計方向に、所定のプロセス速度で回転駆動される。本実施例では、感光ドラム１と中間転写ベルト９は同じ周速で回転駆動される。
【００５３】
各画像形成部Ｙ、Ｍ、Ｃ、Ｂｋの感光ドラム１は、それぞれ帯電部ａにおいて主の接触帯電手段としての帯電ローラ２によって本実施例では負極性の所定の電位に一様に接触帯電される。
【００５４】
そして、各画像形成部Ｙ、Ｍ、Ｃ、Ｂｋのレーザビームスキャナ３はフルカラー画像情報の色分解デジタル画像信号に対応して変調されたレーザビームＬを出力して各感光ドラム１の一様帯電処理面を露光部ｂにおいて走査露光する。これにより各感光ドラム１にはそれぞれフルカラー画像の色分解画像パターン（本実施例では、第１の色成分＝イエロー、第２の色成分＝マゼンタ、第３の色成分＝シアン、第４の色成分＝ブラック、の各画像パターン）に対応した静電潜像が形成される。
【００５５】
各感光ドラム１上の静電潜像は対応の現像装置４により現像部ｃにおいて同一極性（本例では負極性）に帯電されたトナーにより反転現像される。すなわち各感光ドラム１にはそれぞれフルカラー画像の色分解画像パターンであるイエロートナー像、マゼンタトナー像、シアントナー像、ブラックトナー像が形成される。
【００５６】
そして、各１次転写ニップ部ｄにおいて中間転写体である中間転写ベルト９上に各感光ドラム１上の上記イエロートナー像、マゼンタトナー像、シアントナー像、ブラックトナー像を順次に重畳転写してフルカラートナー画像を合成する。
【００５７】
中間転写ベルト９と各感光ドラム１のなす各１次転写ニップ部ｄでは、中間転写ベルト６の背面に接している１次転写ローラ９ｇに対してそれぞれ電源９ａ〜９ｄから印加された、トナーと逆極性の正の１次転写バイアスにより、各感光ドラム１側から中間転写ベルト６側にトナー像が１次転写される。
【００５８】
中間転写ベルト６が最後の第４の画像形成部Ｂｋの感光ドラム１との１次転写ニップ部ｄを通過した段階でフルカラートナー画像が中間転写ベルト９上に重畳合成形成されて担持され、１次転写行程は完了する。
【００５９】
そして、中間転写ベルト９上のフルカラートナー画像の先端が２次転写ニップ部ｇに到達するタイミングに合わせて、不図示の給紙手段部より記録媒体としての転写材Ｐが１枚給送され、レジストローラ対１２で同期取りされて、２次転写ニップ部ｇに導入される。この時、２次転写ローラ１１にはトナーと逆極性の正の２次転写バイアスが電源１０ｂより印加され、フルカラートナー画像は中間転写ベルト９から転写材Ｐに一括２次転写される。
【００６０】
２次転写ニップ部ｇを出た、未定着フルカラートナー画像を載せた転写材Ｐは、不図示の定着装置へ搬送導入されて未定着フルカラートナー画像が永久固着画像として定着される。
【００６１】
フルカラートナー画像を転写材Ｐに一括２次転写し終えた中間転写ベルト９の表面はベルトクリーニング装置１１によって転写残トナーが除去されて清掃され、繰返して作像に供される。
【００６２】
モノクロ画像形成モードは、上記第１〜第４の４つの画像形成部Ｙ、Ｍ、Ｃ、Ｂｋのうちブラックのトナー画像を形成する第４の画像形成部Ｂｋのみが作像動作することで実行される。
【００６３】
第１〜第４の各画像形成部Ｙ、Ｍ、Ｃ、Ｂｋはクリーナレスであり、１次転写ニップ部ｄにおいて中間転写ベルト９の面に転写されずに感光ドラム１面に残留した転写残トナーは、引き続く感光ドラム１の回転にともない、残留現像剤均一化制御手段としての第２の補助接触帯電手段である第２の接触帯電ブラシ７と感光ドラム１との接触部ｆに持ち運ばれて第２の接触帯電ブラシ７によって均一化され、次いで現像剤帯電量制御手段としての第１の補助接触帯電手段である第１の接触帯電ブラシ６と感光ドラム１との接触部ｅに持ち運ばれて第１の接触帯電ブラシ６によって正規極性に帯電処理され、更に主の接触帯電手段である接触帯電ローラ２と感光ドラム１との接触部である帯電部ａ、および露光部ｂを通って現像部ｃに持ち運ばれて現像装置４により現像同時クリーニングされて、現像装置４に回収・再用される。
【００６４】
２）感光ドラム１
各画像形成部Ｙ、Ｍ、Ｃ、Ｂｋの感光ドラム１は、有機光導電体（ＯＰＣ）ドラムで、外径５０ｍｍであり、中心支軸を中心に１００ｍｍ／ｓｅｃのプロセススピード（周速度）をもって矢示の時計方向に回転駆動されている。この感光ドラム１は、アルミニウム製シリンダ（導電性ドラム基体）の表面に、光の干渉を抑え、上層の接着性を向上させる下引き層と、光電荷発生層と、電荷輸送層（厚さ２０μｍ）の３層を下から順に塗り重ねた構成をしている。
【００６５】
３）帯電ローラ２
各画像形成部Ｙ、Ｍ、Ｃ、Ｂｋにおける主の接触帯電手段としての帯電ローラ２の長手長さは３２０ｍｍであり、芯金（支持部材）２ａの外回りに、下層２ｂと、中間層２ｃと、表面層２ｄを下から順次に積層した３層構成としている。下層２ｂは帯電音を低減するための発泡スポンジ層であり、中間層２ｃは帯電ローラ全体として均一な抵抗を得るための抵抗層であり、表層２ｄは感光ドラム１上にピンホール等の欠陥があってもリークが発生するのを防止するために設けている保護層である。本例の帯電ロ一ラ２は芯金２ａとして直径６ｍｍのステンレス丸棒を用い、表層としてフッ素樹脂にカーボンを分散させており、ローラとしての外径は１４ｍｍ、ローラ抵抗は１０^４Ω〜１０^７Ωとしている。
【００６６】
この帯電ロ一ラ２は、芯金２ａの両端部をそれぞれ軸受け部材により回転自在に保持させると共に押し圧ばねによって感光ドラム１方向に付勢して感光ドラム１の表面に対して所定の押圧力をもって圧接させており、感光ドラム１の回転に従動して回転する。該帯電ロ一ラ２と感光ドラム１との圧接部が帯電部（帯電ニップ部）ａである。そして電源２５から直流電圧に周波数ｆの交流電圧を重畳した所定の振動電圧（バイアス電圧Ｖｄｃ＋Ｖａｃ）が芯金２ａを介して帯電ローラ２に印加されることで、回転する感光ドラム１の周面が所定の電位に帯電処理される。
【００６７】
本実施例においては直流電圧；−５００Ｖ、交流電圧；周波数ｆ＝１１５０Ｈｚ、ピーク間電圧Ｖｐｐ＝１４００Ｖ、正弦波とを重畳した振動電圧であり、感光ドラム１の周面は−５００Ｖ（暗電位Ｖｄ）に一様に接触帯電処理される。
【００６８】
２ｆは帯電ローラクリーニング部材であり、本例では可撓性を持つクリーニングフィルムである。このクリーニングフィルム２ｆは帯電ローラ２の長手方向に対し平行に配置され且つ同長手方向に対し一定量の往復運動をする支持部材２ｇに一端を固定され、自由端側近傍の面において帯電ローラ２と接触ニップを形成するよう配置されている。支持部材２ｇがプリンタの駆動モーターによりギア列を介して長手方向に対し一定量の往復運動駆動されて帯電ローラ表層２ｄがクリーニングフィルム２ｆで摺擦される。これにより帯電ローラ表層２ｄの付着汚染物（微粉トナー、外添剤など）の除去がなされる。
【００６９】
４）レーザビームスキャナ３
感光ドラム１は帯電ローラ２により所定の極性・電位に一様に帯電処理されたのちは、画像露光手段（カラー原稿画像の色分解・結像露光光学系、画像情報の時系列電気デジタル画素信号に対応して変調されたレーザビームを出力するレーザスキャンによる走査露光系等）による画像露光Ｌを受けることにより目的のカラー画像における色成分像（イエロー成分像）に対応した静電潜像が形成される。
【００７０】
本実施例では各画像形成部Ｙ、Ｍ、Ｃ、Ｂｋにおける露光装置として半導体レーザを用いたレーザビームスキャナ３を用い、不図示の画像読み取り装置等のホスト装置からプリンタ側に送られた画像信号に対応して変調されたレーザ光Ｌを出力して回転感光ドラム１の一様帯電処理面をレーザ走査露光（イメージ露光）する。このレーザ走査露光Ｌにより感光ドラム１面のレーザ光で照射されたところの電位が低下することで回転感光ドラム１面には走査露光した画像情報に対応した静電潜像が形成されていく。本実施例においては露光部電位を−１５０Ｖとしている。
【００７１】
５）現像装置４
本実施例では各画像形成部Ｙ、Ｍ、Ｃ、Ｂｋにおける現像装置４は２成分接触現像装置（２成分磁気ブラシ現像装置）である。
【００７２】
４０は現像容器、４１は非磁性の現像スリーブであり、内部に固定配置された不図示のマグネットローラを有している。この現像スリーブ４１はその外周面の一部を外部に露呈させて現像容器４０内に回転可能に配設してある。４２は現像剤規制ブレード、４６は現像容器４０に収容したトナーと磁性キャリアの混合物である二成分現像剤、４３、４４は現像容器４０内の底部側に配設した現像剤攪拌部材である。
【００７３】
現像スリーブ４１には所定間隙を有して、現像剤規制ブレード４２が設けられ、現像スリーブ４１の矢印の反時計方向への回転に伴い、現像スリーブ４１上に現像剤薄層を形成する。
【００７４】
現像スリーブ４１は感光ドラム１との最近接距離（Ｓ−Ｄｇａｐと称する）を３５０μｍに保たせて感光ドラム１に近接させて対向配設してある。この感光ドラム１と現像スリーブ４１との対向部が現像部ｃである。現像スリーブ４１は現像部ｃにおいて感光ドラム１の進行方向とは逆方向に回転駆動される。現像スリーブ４１上の現像剤薄層は現像部ｃにおいて感光ドラム１の面に対して接触して感光ドラム面を適度に摺擦する。現像スリーブ４１には電源４ａから所定の現像バイアスが印加される。本例において、現像スリーブ４１に対する現像バイアス電圧は直流電圧（Ｖｄｃ）と交流電圧（Ｖａｃ）とを重畳した振動電圧である。より具体的には、Ｖｄｃ＝−３５０Ｖ、Ｖａｃ＝１８００Ｖ、周波数＝２３００Ｈｚとを重畳した振動電圧である。
【００７５】
而して、回転する現像スリーブ４１の面に薄層としてコーティングされ、現像部ｃに搬送された現像剤中のトナーが現像バイアスによる電界によって感光ドラム１面に静電潜像に対応して選択的に付着することで静電潜像がトナー画像として現像される。本例の場合は感光ドラム１面の露光明部にトナーが付着して静電潜像が反転現像される。
【００７６】
現像部ｃを通過した現像スリーブ４１上の現像剤薄層は引き続く現像スリーブの回転に伴い現像容器４０内の現像剤溜り部に戻される。
【００７７】
現像容器４０内には、現像剤攪拌用の撹拌スクリュー４３、４４があり、スリーブ回転と同期して回転し、補給されたトナーとキャリアを攪拌しトナーに所定のトリボを与える機能を有している。
【００７８】
現像装置４のスクリュー４４の上流側壁面には、現像剤の透磁率変化を検出して現像剤中のトナー濃度を検知するセンサー（不図示）を設けられており、そのセンサーのやや下流側にトナー補給開口４５が設けられている。現像動作を行った後に現像剤がセンサー部に運ばれここでトナー濃度を検知し、その検知結果に応じて現像剤４６中のトナー濃度を一定に維持するために、適宜現像剤供給ユニット（Ｔ−ＣＲＧ）５中のスクリュー５１の回転により、現像剤供給ユニット５から現像装置４の開口４５を通して現像装置４内へのトナーｔの補給が行われる。補給されたトナーｔはスクリュー４４・４３により搬送され、キャリアと混ざり合い適度なトリボを付与された後にスリーブ４１近傍に運ばれ、現像スリーブ４１上で薄層形成され現像に供される。
【００７９】
本実施の形態においてトナーｔとして、平均粒径６μｍのネガ帯電トナーを用い、キャリアとしては飽和磁化が２０５ｅｍｕ／ｃｍ^３の平均粒径３５μｍの磁性キャリアを用いた。また、トナーとキャリアを重量比６：９４で混合したものを現像剤４６として用いた。
【００８０】
そして感光ドラム上に現像されたトナーの帯電量は−２５μＣ／ｇである。
【００８１】
６）中間転写ベルト９
各画像形成部Ｙ、Ｍ、Ｃ、Ｂｋにおける１次転写ニップ部（ポート）ｄでは中間転写ベルト９の裏側に転写ローラ９ｇを所定の押圧力をもって圧接させている。転写ローラ９ｇには各１次転写ニップ部ｄで独立にバイアス印加可能とするため、１次転写バイアス源９ａ〜９ｄを有している。中間転写ベルト９は第１の画像形成部Ｙの１次転写部ｄで１色目であるイエロートナー像を転写し、次いで第２から第４の画像形成部Ｍ、Ｃ、Ｂｋの１次転写部ｄで順次２色目から４色目であるマゼンタトナー像、シアントナー像、ブラックトナー像の各色トナー像を多重転写する。
【００８２】
本実施例においては露光部Ｖｌ部（電位−１５０Ｖ）に現像されたトナーに対する転写効率を考慮し、１次転写バイアスとして、１色目〜４色目まですべて＋３５０Ｖの電圧を印加した。
【００８３】
中間転写ベルト９上で形成された４色フルカラー画像は、次いで２次転写ニップ部ｇに対してレジストローラ対１２により導入された転写材Ｐに２次転写ローラ１０により一括転写される。２次転写ローラ１０には電源１０ｂから正極性の２次転写バイアスが印加される。２次転写ニップ部ｇを出た転写材Ｐは中間転写ベルト９の面から分離され、不図示の定着装置に搬送導入されてトナー画像の溶融定着を受け、カラープリント画像を得る。
【００８４】
中間転写ベルト９上に残留する２次転写残トナーは、中間転写ベルトクリーナ１１でブレードクリーニングされ、次作像工程に備える。
【００８５】
上記転写ベルト９の材質の選定としては、各色の１次転写ニップ部ｄでのレジストレーションを良くするため、伸縮する材料は望ましくなく、樹脂系或いは、金属芯体入りのゴムベルト、樹脂＋ゴムベルトが望ましい。
【００８６】
本実施例ではＰＩ（ポリイミド）にカーボン分散し、体積抵抗を１０^８Ωｃｍオーダーに制御した樹脂ベルトを用いた。その厚さは８０μｍ、長手方向３２０ｍｍ、全周は９００ｍｍである。
【００８７】
また１次転写ローラ９ｇとしては、導電性スポンジからなり。その抵抗は１０^６Ω以下、外径は１６ｍｍ、長手長さは３１５ｍｍとしている。
【００８８】
７）クリーナレスシステム
図１・図２において、通常であればクリーニングブレードが配置されているところに、現像剤帯電量制御手段としての第１の補助接触帯電手段６と、残留現像剤均一化制御手段としての第２の補助接触帯電手段をそれぞれ感光ドラム１に当接させて配設してある。両者６・７ともに本実施例では導電性の繊維からなるブラシ部材を用いている。
【００８９】
すなわち、現像剤帯電量制御手段（以下、トナー帯電量制御手段と記す）６と残留現像剤均一化制御手段（以下、残留トナー均一化手段と記す）７は帯電部ａと一次転写ニップ部ｄとの間において、現像剤帯電量制御手段６は一次転写ニップ部ｄよりも感光ドラム回転方向上流側に、また残留現像剤均一化制御手段７はこの現像剤帯電量制御手段６よりも更に感光ドラム回転方向上流側に位置させてある。
【００９０】
具体的には、トナー帯電量制御手段６（第１ブラシ）は横長の電極板６２にブラシ部６１を具備させたものであり、また残留トナー均一化手段７（第２ブラシ）についても同様に電極板７２にブラシ部７１を具備させてなる。
【００９１】
そして、それぞれブラシ部６１及び７１を感光ドラム１面に当接させて固定支持させて配設している。ブラシ部６１及び７１はレーヨン、アクリル、ポリエステル等の繊維にカーボンや金属粉を含ませて抵抗値を制御したものである。ブラシ部６１、７１は、感光ドラム表面及び転写残トナーに均一に接触できるように、太さとしては３０デニール以下、密度としては１〜５０万本／ｉｎｃｈ^２以上が好ましい。本実施例では、ブラシ部６１、７１ともに６デニール、１０万本／ｉｎｃｈ^２、毛足の長さ５ｍｍで、ブラシの抵抗は６×１０^３Ω・ｃｍとした。これらのトナー帯電量制御手段６と残留トナー均一化手段７をブラシ部６１、７１が感光ドラム１面に対して侵入量１ｍｍとなるように当接させ、感光ドラム１との当接ニップ部幅は５ｍｍとした。
【００９２】
上記のトナー帯電量制御手段６と残留トナー均一化手段７によって本実施例のクリーナレスシステムは実現している。
【００９３】
クリーナレスシステムは、転写後の感光ドラム１面上に残った転写残トナーを帯電部ａ、露光部ｂを通過させて、現像装置３により現像同時クリーニング（回収）させるシステムである。
【００９４】
感光ドラム１面上の転写残トナーは露光部ｂを通るので露光工程はその転写残トナー上からなされるが、転写残トナーの量は少ないため、大きな影響は現れない。
【００９５】
転写残トナーには帯電極性が正規極性のもの、逆極性のもの（反転トナー）、帯電量が少ないものが混在しており、その内の反転トナーや帯電量が少ないトナーが帯電部ａを通過する際に帯電ローラ２に付着することで帯電ローラが許容以上にトナー汚染して帯電不良を生じることになる。
【００９６】
また、感光ドラム１面上の転写残トナーの現像装置４による現像同時クリーニングを効果的に行なわせるためには、現像部ｃに持ち運ばれる感光ドラム上の転写残トナーの帯電極性が正規極性であり、かつその帯電量が現像装置４によって感光ドラム１の静電潜像を現像できるトナーの帯電量であることが必要である。反転トナーや帯電量が適切でないトナーについては感光ドラム１上から現像装置４に除去・回収できず、不良画像の原因となってしまう。
【００９７】
また、近年のユーザニーズの多様化に伴い、写真画像などといった高印字率な画像などの連続の印字動作などにより、一度に大量の転写残トナーの発生により、上述のような問題を更に助長させてしまうのである。
【００９８】
そこで、一次転写ニップ部ｄよりも感光ドラム回転方向下流側で帯電部ａよりも上流側の位置に、感光ドラム１上の転写残トナーを均一化し、転写残トナーの帯電極性を正規極性である負極性に揃えるために、残留トナー均一化手段７とトナー帯電量制御手段６を設けている。
【００９９】
残留トナー均一化手段７は正極性の電圧（ポジバイアス＝＋３５０Ｖ）が電源２５より保護抵抗２７を介して印加されている。
【０１００】
転写残トナーの中には、逆極性のものや、ほとんど極性を持たないものが混在しているが、その中のゼロ近傍〜負極性に帯電されているトナーは、電気的、物理的な力によってこの残留トナー均一化手段７に吸引される。そして、残留トナー均一化手段７のポジバイアスによって逆極性（正極性）となり、徐々にトナーが離脱して感光ドラム１面に再付着して搬送される。この作用により、感光ドラム１上のトナーの分布が均一化され、一度に大量のトナーが下流のトナー帯電量制御手段６に流れ込まないようになる。また、また感光ドラム上の電位は０Ｖ付近になる。転写残トナーを逆極性（正極性）にし、感光ドラム１上の電位を０Ｖ付近にすることで、後述するように、トナー帯電量制御手段６がトナーに対して充分に電荷付与を行なえるようにする役目も果たしている。
【０１０１】
トナー帯電量制御手段６は負極性の電圧（ネガバイアス＝−８００Ｖ）が電源２５より保護抵抗２７を介して印加されている。
【０１０２】
トナー帯電量制御手段６を通過すると、感光ドラム１上の転写残トナーはその帯電極性が正規極性である負極性に揃えられる。上記のようにトナー均一化手段７で、トナーは正極性に揃えられており、また感光ドラム上の電位も０Ｖ付近になっているため、より効果的に強い負極性に揃えることができる。
【０１０３】
このトナー帯電量制御手段６で、転写残トナーの帯電極性を正規極性である負極性に揃えることにより、さらに下流に位置する帯電部ａで、該転写残トナーの上から感光ドラム１面上を帯電処理する際に、感光ドラム１への鏡映力が大きくなり、転写残トナーの帯電ローラ２への付着を防止するのである。
【０１０４】
そして、帯電ローラ２に付着せずに通過したトナーは現像装置４において現像同時クリーニングされ回収される。
【０１０５】
このような方法で、感光ドラム１上の転写残トナーを現像装置４に回収するためには、適正なトナー帯電量であることが必要である。しかしながら、上述したように帯電ローラ２へのトナー付着を防止するために、トナー帯電量制御手段６によって負極性に大きく帯電された転写残トナーを、現像装置４において回収させるためには、除電を行なう必要がある。
【０１０６】
トナー帯電量制御手段６によって負極性に大きく帯電された転写残トナーが、帯電ローラ２に印加された交流電圧（周波数ｆ１１５０Ｈｚ、Ｖｐｐ１４００Ｖ）により交流除電され、帯電部ａを通過後のトナー帯電量は現像トナーの帯電量とほぼ同じとなる。
【０１０７】
そして、現像工程において、トナーが現像されるべきではない未露光部の感光体ドラム１上の転写残トナーは、完全に負極性に揃い、帯電ローラ２により適度に除電され感光ドラム１との鏡映力を減じることが出来ていることから、前述したドラム電位−５００Ｖと現像バイアスのＤＣ成分の−３５０Ｖとの関係で確実に現像装置内に回収される。本実施例においては現像装置４の現像スリーブ４１は前述したように現像部ｃにおいて、感光ドラム１面の進行方向とは逆方法に回転させており、これは感光ドラム１上の転写残トナーの回収に有利となる。
【０１０８】
（２）保護抵抗２７の抵抗値の必要最小値算出方法
次に、本発明の特徴である保護抵抗２７のの抵抗値必要最小値の算出方法について述べる。
【０１０９】
この実施の形態において、感光ドラム１にピンホール等の欠陥のない部分に対するトナー帯電量制御手段６と残留トナー均一化手段７のブラシ６１（７１）の等価回路は図３の（ａ）であり、感光ドラム１のピンホールなどの欠陥のある部分に対するブラシ６１（７１）の等価回路は図３の（ｂ）である。以下、この等価回路を元に計算を進める。
【０１１０】
感光ドラム１のピンホール部にブラシ素材が接触した際には図３の（ｂ）により、ブラシ部分の発熱量Ｗは下式（１）のようになる。
【０１１１】
【数６】

【０１１２】
ここで、ブラシに過電流が流れたときにも燃焼しないようにするためには、ブラシが燃焼する熱量をＷｂとすると、
【０１１３】
【数７】

【０１１４】
を常に満たさなければならない。このとき、変数Ｒｂに対してＷの一次導関数をＷ’とすると、Ｗが最大になる点において、
【０１１５】
【数８】

【０１１６】
を満たす。つまり、Ｒｂ＝Ｒｈである１点においてＷは最大値をとり、その値Ｗ_ＭＡＸは
【０１１７】
【数９】

【０１１８】
である。式（２）（４）より、
【０１１９】
【数１０】

【０１２０】
となり、式（５）を満たすように保護抵抗Ｒｈを定めれば良い。
【０１２１】
図４はブラシの抵抗とそのブラシにおける消費電力との関係を示すグラフである。本実施の形態において、ブラシの抵抗のばらつきの範囲は、１０^４〜１０^８程度であり、（１）式はこの範囲においてグラフ上で頂点をひとつだけ持ち、Ｒｂ＝Ｒｈとなる点でＷが最大となっていることがわかる。
【０１２２】
以上の結果に基づき、本実施の形態ではＷｂは約０．２Ｗ程度、Ｖ１＝８００Ｖであるため、全てのブラシ抵抗のばらつきに対して式（２）が成立するように、保護抵抗Ｒｈは２．２ＭΩのものを用いた。このときＷ_ＭＡＸは０．０７Ｗであり、Ｗｂを超えず、燃焼することは無い。
【０１２３】
回路に充分に電流Ｉｃを流すことができないと、残留トナー均一化手段７とトナー帯電量制御手段６は感光ドラム１上の現像剤に充分な電荷を付与することができないが、上記の手法で保護抵抗２７の値Ｒｈを決定することで、ブラシの安全性を保障しつつ必要最小限の保護抵抗値を選ぶことができる。
【０１２４】
本実施の形態においては、室温、湿度の異なる環境下で実際に印字動作を６００００枚行った後においても、ブラシが損傷せず、機能にも問題なく、鮮明な印刷画像が得られた。
【０１２５】
このように、残留トナー均一化手段７とトナー帯電量制御手段６の機能に対して充分な回路電流Ｉｃを得ながら、接触帯電部材の燃焼を防止することが可能となった。
【０１２６】
（３）その他
１）主の接触帯電手段２は可撓性の帯電ローラの他に、ファーブラシ、フェルト、布などの形状・材質のものも使用可能である。また各種材質のものの組み合わせでより適切な弾性（可撓性）、導電性、表面性、耐久性のものを得ることもできる。この主の接触帯電手段２にも保護抵抗２７を設けて、その際に、Ｗｂ＞Ｖ１^２／４Ｒｈの関係を用いることで本発明を適用できることは勿論である。
【０１２７】
２）補助接触帯電手段としての残留トナー均一化手段７とトナー帯電量制御手段６は、本実施例では固定のブラシ状部材であるが、ブラシ回転体、弾性ローラ体、シート状部材など任意の形態の部材にすることができる。
【０１２８】
３）また被帯電体としての像担持体は表面抵抗が１０^９〜１０^１４Ω・ｃｍの電荷注入層を設けた直接注入帯電性のものであってもよい。電荷注入層を用いていない場合でも、例えば電荷輸送層が上記の抵抗範囲にある場合も同等の効果がえられる。表層の体積抵抗が約１０^１３Ω・ｃｍであるアモルファスシリコン感光体でもよい。
【０１２９】
４）また接触帯電部材や現像部材に印加する振動電界の交番電圧成分（ＡＣ成分、周期的に電圧値が変化する電圧）の波形としては、正弦波、矩形波、三角波等適宜使用可能である。直流電源を周期的にオン／オフすることによって形成された矩形波であってもよい。
【０１３０】
５）更に像担持体としての感光体の帯電面に対する情報書き込み手段としての像露光手段は実施例のレーザ走査手段以外にも、例えば、ＬＥＤのような固体発光素子アレイを用いたデジタル露光手段であってもよい。ハロゲンランプや蛍光灯等を原稿照明光源とするアナログ的な画像露光手段であってもよい。要するに、画像情報に対応した静電潜像を形成できるものであればよい。
【０１３１】
６）像担持体は静電記録誘電体などであってもよい。この場合は、該誘電体面を一様に帯電した後、その帯電面を除電針ヘッドや電子銃等の除電手段で選択的に除電して目的の画像情報に対応した静電潜像を書き込み形成する。
【０１３２】
７）静電潜像のトナー現像方式・手段は任意である。反転現像方式でも正規現像方式でもよい。
【０１３３】
一般的に、静電潜像の現像方法は、非磁性トナーについてはこれをブレード等でスリーブ等の現像剤担持搬送部材上にコーティングし、磁性トナーについてはこれを現像剤担持搬送部材上に磁気力によってコーティングして搬送して像担持体に対して非接触状態で適用し静電潜像を現像する方法（１成分非接触現像）と、上記のように現像剤担持搬送部材上にコーティングしたトナーを像担持体に対して接触状態で適用し静電潜像を現像する方法（１成分接触現像）と、トナー粒子に対して磁性のキャリアを混合したものを現像剤（２成分現像剤）として用いて磁気力によって搬送して像担持体に対して接触状態で適用し静電潜像を現像する方法（２成分接触現像）と、上記の２成分現像剤を像担持体に対して非接触状態で適用し静電潜像を現像する方法（２成分非接触現像）との４種顛に大別される。
【０１３４】
８）画像形成装置は実施形態例の中間転写体を用いたフルカラー画像形成装置に限られず、単色画像形成装置であっても勿論よいし、転写手段もローラ転写、ブレード転写、ベルト転写、その他の接触転写帯電方式であってもよいし、コロナ帯電器を使用した非接触転写帯電方式でもよい。
【０１３５】
９）本発明の接触帯電装置は画像形成装置の像担持体の帯電装置としてばかりでなく、広く被帯電体の接触帯電装置として有効に使用できることは勿論である。
【０１３６】
【発明の効果】
以上説明したように本発明によれば、接触帯電手段に高電圧を印加する回路に保護抵抗を設ける際に、Ｗｂ＞Ｖ１^２／４Ｒｈの関係を用いることで、被帯電体のピンホール等に対して接触帯電手段から過電流が流れて燃焼するのを防止することが可能となった。また、印加した高圧に対して最も機能を発揮できる適切な保護抵抗を選ぶことが可能となった。
【０１３７】
これにより、像担持体の帯電処理に接触帯電装置を用いた画像形成装置においては、常時、高画質画像を安定して提供できるようになった。
【図面の簡単な説明】
【図１】実施例の画像形成装置の概略構成模型図
【図２】部分拡大図
【図３】接触帯電装置の等価回路図
【図４】実施例におけるブラシ抵抗と発熱量の関係図
【符号の説明】
１は感光体（被帯電体、像担持体）、２は帯電ローラ（主の接触帯電手段）、３は画像露光装置、４は現像装置、５は現像剤供給ユニット、６は現像剤帯電量制御手段（第１の補助接触帯電手段）、７は転写残現像剤像均一化手段（第２の補助接触帯電手段）、８はプロセスカートリッジ、９は中間転写ベルト、１０は２次転写ローラ、１１は中間転写ベルトクリーナ、１２はレジストローラ対（給紙ローラ）、２５，４ａ，９ａ〜９ｄ，１０ｂは電源[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a contact charging device, and an image forming process such as an electrophotographic method or an electrostatic recording method using the contact charging device as a charging device for an image carrier such as an electrophotographic photosensitive member or an electrostatic recording dielectric. And an image forming apparatus such as a copier, a printer, a facsimile, etc.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, a transfer type image forming apparatus such as a copying machine, a printer, a facsimile or the like using a transfer type electrophotographic method has a photoreceptor which is a rotating drum type image carrier in general, and the photoreceptor has a predetermined polarity. A charging device for uniformly charging to a potential (a charging process); an exposure device as information writing means for forming an electrostatic latent image on the charged photoconductor (exposure process); and an electrostatic device formed on the photoconductor. A developing device that develops the latent image with toner as a developer (developing process), a transfer device that transfers the toner image from the photoconductor surface to a transfer material such as paper, and a transfer device that transfers the toner image onto the photoconductor after the transfer process The cleaning device includes a cleaning device (cleaning process) for cleaning the photoreceptor surface by removing a small amount of remaining toner, and a fixing device (fixing process) for fixing the toner image on the transfer material. True process (charging, exposure, development, transfer and cleaning) is applied is used for image formation.
[0003]
Conventionally, a corona charger has been used as a charging means. However, the charging potential of the organic photoreceptor has a negative polarity. ₃ Or NO _x Occurs more or less.
[0004]
In contrast, contact charging methods such as a roller charging method using a conductive roller and a brush charging method using a conductive brush hardly generate ozone or the like. I have.
[0005]
By the way, the cleaning device is provided with a waste toner collecting container for storing the toner remaining on the photoconductor removed from the photoconductor surface in the cleaning device. Therefore, in order to obtain a device having a long service life, it is necessary to increase the size of the container, which is disadvantageous in terms of miniaturization of the device.
[0006]
Therefore, the cleaning device having a waste toner collection container was abolished, and the transfer residual toner on the photoconductor after the transfer process was removed and collected from the photoconductor by the “simultaneous development cleaning” in the developing device and reused. There is an image forming apparatus of a system.
[0007]
In the simultaneous cleaning with development, the transfer residual toner on the photoreceptor after the transfer is used in the subsequent development process, that is, the photoreceptor is subsequently charged and exposed to form an electrostatic latent image. The fogging bias (fogging potential difference Vback, which is a potential difference between the DC voltage applied to the developing device and the surface potential of the photoreceptor) during the process, causes the surface of the photoreceptor not to be developed with toner to be developed (non-image portion). In this method, the remaining transfer residual toner is collected in the developing device. According to this method, since the transfer residual toner is collected in the developing device and reused for the development of the electrostatic latent image in the next and subsequent steps, waste toner is eliminated, and maintenance work is reduced. And the absence of a waste toner container is advantageous for downsizing the image forming apparatus.
[0008]
In a cleaner-less image forming apparatus that removes and collects transfer residual toner on a photoconductor after a transfer process by simultaneous development and cleaning in a developing device, when the contact charging device described above is used as a photoconductor charging device, When the transfer residual toner on the photoreceptor passes through the charging portion, which is the contact nip portion of the photoreceptor and the contact charging device, the toner in the transfer residual toner, in particular, the charge polarity of which is reversed to the opposite polarity to the normal polarity. The toner adheres to the contact charging device and undesirably contaminates the contact charging device with toner, thereby causing charging failure.
[0009]
This is due to the fact that the toner as the developer contains a small amount of toner whose charge polarity is originally reversed to the opposite polarity from the normal polarity, or that the charge polarity is the normal polarity. This is because, even with toner, there is a toner whose charge polarity is inverted due to an influence of a transfer bias or a peeling discharge, or a toner whose charge amount is reduced due to charge removal.
[0010]
In other words, the transfer residual toner includes a toner having a normal charge polarity, a reverse toner having a reverse polarity, and a toner having a small charge amount. Is easily attached to the contact charging device when passing through the charging portion which is the contact nip portion.
[0011]
Also, in order to remove and collect the transfer residual toner on the photoreceptor by simultaneous cleaning with the developing device, the charge polarity of the transfer residual toner on the photoreceptor carried through the charging unit to the developing unit is regulated. It is necessary that the charge amount is a polarity and the charge amount of the toner is such that the electrostatic latent image on the photosensitive member can be developed by the developing device. Inverted toner and toner with an inappropriate charge amount cannot be removed and collected from the photoreceptor to the developing device, causing a defective image.
[0012]
Therefore, the present applicant has proposed an image forming apparatus in which a transfer residual toner uniforming unit is provided downstream of the transfer unit, and a developer charge amount control unit is provided further downstream and upstream of a charging unit for charging the photoconductor. For example, see Patent Document 1).
[0013]
In this image forming apparatus, the transfer residual toner equalizing means disperses and distributes the pattern-like residual toner image on the image carrier carried from the transfer section to the developer charge amount control means section on the image carrier surface. And means for non-patterning. Specifically, the residual developer image pattern is scraped or disturbed by rubbing the image carrier surface with a rubbing member, thereby dispersing and distributing the developer on the image carrier surface.
[0014]
The presence of the transfer residual toner uniformizing means ensures that the entire normal polarity charging process for the transfer residual toner by the developer charge amount control means to which the next normal polarity is applied is always sufficiently performed, and the transfer residual toner is The adhesion to the charging means is effectively prevented. Further, the ghost image of the residual toner image pattern is prevented from being generated by erasing the residual toner image pattern.
[0015]
That is, when there is no means for equalizing the residual developer image, for example, when the transferability of the developer image is poor, such as a vertical line pattern developer image, environment, paper type (transfer paper), color secondary color, etc. The number of transfer residual toner images in the form of a pattern on the body also increases, and the transfer residual toner image is carried to the developer charge amount control unit as it is, and the developer is concentrated on a part of the developer charge amount control unit. As a result, a phenomenon that the charge amount of the residual developer cannot be completely controlled by a part of the developer charge amount control means (toner charging failure phenomenon) occurs. As a result, contamination of the charging member → poor charging → fogging image is caused, or a ghost image is generated with a residual toner image pattern remaining.
[0016]
By providing the residual toner image uniforming means, as described above, the pattern-shaped transfer residual toner image on the image carrier carried from the transfer section to the developer charge amount control means section has a large developer amount. Since the developer is distributed and distributed on the surface of the image carrier and is non-patterned, the developer does not concentrate on a part of the developer charge amount control means, and the transfer residual by the developer charge amount control means is prevented. The entire normal polarity charging process of the developer is always sufficiently performed, and the adhesion of the transfer residual developer to the charging unit is effectively prevented. Generation of a ghost image of the residual developer image pattern is also strictly prevented.
[0017]
The photosensitive member is charged to a predetermined potential by the charging means, and at the same time, the charge amount of the transfer residual toner having the regular polarity by the developer charge amount control means is charged by the developing device to the electrostatic latent image on the photosensitive drum. Is controlled to an appropriate charge amount that can be developed. As a result, the transfer residual toner was efficiently collected in the developing device, and a good image free of ghost and charging failure was obtained.
[0018]
Auxiliary charging means such as a residual developer uniformizing means and a developer charge amount controlling means also employ a contact charging method so as not to generate environmental pollutants such as ozone.
[0019]
However, the image forming apparatus using the contact charging system has the following problems.
[0020]
When a conductive resin fiber, for example, a conductive rayon brush is used for the contact charging member, a leak occurs when the rayon yarn comes into contact with the ground potential conductive substrate exposed by the pinhole of the image carrier, which is the member to be charged. As a result, an undesired overcurrent may flow through the conductive fibers, causing the bristles to burn and spread to other bristles.
[0021]
Therefore, when a voltage is normally applied to the conductive resin fiber, a protection resistor 27 is provided between the brush fiber 61 and the power supply 25 as shown in FIG. When the conductive substrate is exposed on the image carrier 1 by a pinhole or the like, its equivalent circuit is as shown in FIG.
[0022]
Here, the power supply voltage is V1, the conductive fiber resistance is Rb, and the protection resistance is Rh. The current Ic flowing through the circuit in FIG.
[0023]
[Equation 3]

[0024]
It becomes. Here, when the protection resistance Rh is much larger than Rb, the change in the current amount Ic with respect to the resistance unevenness of the conductive fiber as described above becomes small, and the burning of the conductive fiber can be prevented.
[Patent Document 1]
JP 2001-215798 A
[Patent Document 2]
JP-A-5-150612
[0025]
[Problems to be solved by the invention]
However, in an image forming apparatus in which a protection resistor for preventing overcurrent is connected to a contact charging member, the following problem occurs.
[0026]
When a conductive resin fiber is used for the contact charging member, the conductive resin fiber is inexpensive and easy to handle due to ease of resistance adjustment, but this resistance value is greatly affected by the environment such as temperature and humidity. The variation is large. For this reason, in order to eliminate the risk of combustion due to overcurrent, it is necessary to connect a protection resistor having a relatively large resistance. However, when the large protection resistor Rh is connected, the circuit current Ic becomes small, and functions required for the contact charging member such as charging and developer charge amount control are reduced. For this reason, the value of the protection resistor is desired to be minimized, but it has been difficult to select a protection resistor value that achieves both protection and functionality of the brush.
[0027]
The present invention has been proposed in view of the above, and in a contact charging method, an appropriate one capable of exerting the highest function at a high voltage applied with the magnitude of a protection resistor connected in series to a contact charging means is provided. And to apply the voltage safely and efficiently.
[0028]
[Means for Solving the Problems]
The present invention is a contact charging device and an image forming apparatus having the following configurations.
[0029]
(1) In a contact charging device having one or a plurality of contact charging means (contact charging members) for charging a surface of a charged object by contacting the surface of the charged object,
When a voltage V1 is applied to a circuit in which the contact charging means and the resistance circuit Rh are connected in series, the amount of heat Wb at which the constituent members of the contact charging means start burning is reduced.
[0030]
(Equation 4)

[0031]
A contact charging device characterized by satisfying the following relationship:
[0032]
(2) The contact charging device according to (1), wherein one or more or all of the contact charging units are formed of a conductive fiber brush member that comes into contact with the surface of the member to be charged.
[0033]
(3) The contact charging device according to claim 1 or 2, wherein an oscillating electric field is applied to one or more of the contact charging units.
[0034]
(4) Information writing for forming an electrostatic latent image on the charged image carrier, the image carrier having one or more contact charging means for charging the image carrier surface by contacting the image carrier surface. Means, a developing means for supplying a developer of a predetermined polarity to the electrostatic latent image and visualizing the electrostatic latent image, and an image forming apparatus having a transfer means for transferring the visualized developer image to a transfer material,
When a voltage V1 is applied to a circuit in which the contact charging means and the resistance circuit Rh are connected in series, the amount of heat Wb at which the constituent members of the contact charging means start burning is reduced.
[0035]
(Equation 5)

[0036]
An image forming apparatus characterized by satisfying the following relationship:
[0037]
(5) The image forming apparatus according to (4), wherein one or more or all of the contact charging means are constituted by a conductive fiber brush member which is in contact with the image carrier.
[0038]
(6) The image forming apparatus according to (4) or (5), wherein an oscillating electric field is applied to one or more of the contact charging units.
[0039]
(7) The image forming apparatus according to any one of (4) to (6), wherein the information writing unit is an exposure unit.
[0040]
(8) Main contact charging means is provided upstream of the information writing means in the direction of rotation of the image carrier, and the image carrier is further upstream of the main contact charging means in the direction of rotation of the image carrier and further than the transfer means. An auxiliary contact charging means as a developer charge amount control means for charging the residual developer on the charged image carrier to a normal polarity on the downstream side in the rotation direction is provided (4) to (8). The image forming apparatus according to any one of the above.
[0041]
(9) After transferring the developer image to the transfer material downstream of the transfer unit in the image carrier rotation direction and upstream of the auxiliary contact charging unit as the developer charge amount control unit in the image carrier rotation direction. (8) The image forming apparatus according to (8), further including a second auxiliary contact charging unit as a residual developer uniforming control unit that uniformizes the residual developer remaining on the image carrier.
[0042]
<Operation>
That is, according to the present invention, when a high resistance for preventing an overcurrent from flowing into a pinhole or the like of a member to be charged (image carrier) is connected in series to the contact charging means, the magnitude of the appropriate resistance is calculated by the following equation. By performing the calculation, there is no danger of combustion or the like, and the contact charging unit can be functioned more efficiently.
[0043]
BEST MODE FOR CARRYING OUT THE INVENTION
(1) Example of image forming apparatus
1) Overall description
FIG. 1 is a schematic configuration diagram of an image forming apparatus according to the present embodiment. This image forming apparatus is a transfer type electrophotographic process, a contact charging type, a reversal developing type, a cleanerless type, a maximum paper passing size A3 size, and has four image forming units from first to fourth. The first to fourth color (yellow, magenta, cyan, and black) toner images formed on the rotating drum-type electrophotographic photosensitive member as the first image carrier of the image forming section are temporarily transferred to the intermediate image as the second image carrier. This is a four-drum type (in-line) full-color laser printer that continuously performs multiple transfer onto a belt (intermediate transfer member) to obtain a full-color print image.
[0044]
Y, M, C, and Bk are first to fourth four image forming units that form yellow, magenta, cyan, and black color toner images, respectively.
[0045]
Each of the image forming units Y, M, C, and Bk includes a rotating drum type electrophotographic photosensitive member (hereinafter, photosensitive drum) 1 as a first image carrier, and a charging roller 2 as a main contact charging unit. A cleaner-less system including a laser beam scanner 3 as information writing means, a developing device 4, a developer supply unit 5, and first and second two contact charging brushes 6 and 7 as auxiliary contact charging means. This is an electrophotographic process mechanism.
[0046]
FIG. 2 is an enlarged model diagram of the first image forming unit Y, and the second to fourth image forming units M, C, and Bk have the same mechanical configuration. However, the toners stored in the developing device 4 and the developer supply unit 5 of each of the first to fourth image forming units Y, M, C, and Bk are yellow toner t (Y), magenta toner t (M), and cyan, respectively. The toner t (C) and the black toner t (Bk).
[0047]
In each of the image forming units Y, M, C, and Bk, the photosensitive drum 1, the charging roller 2, the developing device 4, and the first and second two contact charging brushes 6 and 7 are collectively attached to the image forming device main body. It is a process cartridge (P-CRG) 8 which can be replaced in a detachable section.
[0048]
Reference numeral 9 denotes an intermediate transfer belt as a second image carrier, which is suspended between three rollers of a driving roller 9e, a tension roller 9f and a secondary transfer opposing belt 10a. The first to fourth four image forming units Y, M, C, and Bk are arranged at a predetermined distance from the left to the right in the drawing above the horizontal intermediate transfer belt portion between the tension roller 9f and the driving roller 9e. Are arranged in a line in order.
[0049]
The intermediate transfer belt 9 is rotated at a predetermined process speed in a clockwise direction indicated by an arrow by rotating a driving roller 9e by a driving system (not shown).
[0050]
A primary transfer roller 9g is disposed on the lower surface of the photosensitive drum 1 of each of the image forming units Y, M, C, and Bk in pressure contact with the intermediate transfer belt 9 therebetween. The primary transfer nip d is formed between the two.
[0051]
Reference numeral 10 denotes a secondary transfer roller, which is disposed in such a manner that the intermediate transfer belt 9 is sandwiched and pressed against a secondary transfer opposing roller 10a, and a secondary transfer roller 10a is disposed between the intermediate transfer belt 9 and the secondary transfer opposing roller 10. The next transfer nip g is formed.
[0052]
When an image forming operation start signal (print start signal) is issued, the photosensitive drums 1 of the image forming units Y, M, C, and Bk move counterclockwise as indicated by arrows, and the intermediate transfer belt 9 moves clockwise as indicated by arrows. It is driven to rotate at a predetermined process speed. In this embodiment, the photosensitive drum 1 and the intermediate transfer belt 9 are driven to rotate at the same peripheral speed.
[0053]
In the present embodiment, the photosensitive drums 1 of the image forming units Y, M, C, and Bk are uniformly contact-charged to a predetermined negative potential in this embodiment by a charging roller 2 as a main contact charging unit in a charging unit a. You.
[0054]
The laser beam scanner 3 of each of the image forming units Y, M, C, and Bk outputs a laser beam L modulated according to a color-separated digital image signal of full-color image information to uniformly charge each photosensitive drum 1. The processing surface is scanned and exposed in the exposure section b. As a result, each photosensitive drum 1 has a color separation image pattern of a full-color image (in this embodiment, the first color component = yellow, the second color component = magenta, the third color component = cyan, the fourth color An electrostatic latent image corresponding to each image pattern (component = black) is formed.
[0055]
The electrostatic latent image on each photosensitive drum 1 is reversely developed by a corresponding developing device 4 in a developing section c with toner charged to the same polarity (in this example, negative polarity). That is, a yellow toner image, a magenta toner image, a cyan toner image, and a black toner image, which are color separation image patterns of a full-color image, are formed on the respective photosensitive drums 1.
[0056]
Then, the yellow toner image, the magenta toner image, the cyan toner image, and the black toner image on each photosensitive drum 1 are sequentially superimposedly transferred onto the intermediate transfer belt 9 as an intermediate transfer body at each primary transfer nip d. Synthesize a full-color toner image.
[0057]
In each primary transfer nip d formed by the intermediate transfer belt 9 and each photosensitive drum 1, the toner applied to the primary transfer roller 9g in contact with the back surface of the intermediate transfer belt 6 from the power sources 9a to 9d respectively. The toner image is primarily transferred from each photosensitive drum 1 side to the intermediate transfer belt 6 side by the positive primary transfer bias having the opposite polarity.
[0058]
At the stage when the intermediate transfer belt 6 has passed the primary transfer nip d with the photosensitive drum 1 of the last fourth image forming unit Bk, a full-color toner image is superimposed and formed on the intermediate transfer belt 9 and carried. The next transfer process is completed.
[0059]
Then, one sheet of the transfer material P as a recording medium is fed from a paper supply unit (not shown) at the timing when the leading end of the full-color toner image on the intermediate transfer belt 9 reaches the secondary transfer nip g. Synchronized by the pair of registration rollers 12 and introduced into the secondary transfer nip g. At this time, a positive secondary transfer bias having a polarity opposite to that of the toner is applied to the secondary transfer roller 11 from the power supply 10b, and the full-color toner image is collectively and secondarily transferred from the intermediate transfer belt 9 to the transfer material P.
[0060]
The transfer material P, on which the unfixed full-color toner image has been placed and has exited the secondary transfer nip portion g, is transported and introduced to a fixing device (not shown), and the unfixed full-color toner image is fixed as a permanently fixed image.
[0061]
The surface of the intermediate transfer belt 9 on which the full-color toner image has been secondarily transferred onto the transfer material P at a time is cleaned by removing the transfer residual toner by the belt cleaning device 11, and is repeatedly used for image formation.
[0062]
The monochrome image forming mode is executed when only the fourth image forming unit Bk that forms a black toner image among the first to fourth image forming units Y, M, C, and Bk performs an image forming operation. Is done.
[0063]
The first to fourth image forming units Y, M, C, and Bk are cleaner-less, and the transfer residue remaining on the surface of the photosensitive drum 1 without being transferred to the surface of the intermediate transfer belt 9 in the primary transfer nip d. With the subsequent rotation of the photosensitive drum 1, the toner is carried to the contact portion f between the second contact charging brush 7, which is the second auxiliary contact charging means as the residual developer uniforming control means, and the photosensitive drum 1. And then carried to a contact portion e between the first contact charging brush 6, which is a first auxiliary contact charging device as a developer charging amount control device, and the photosensitive drum 1. It is charged by the first contact charging brush 6 to have a regular polarity, and further passes through the charging section a, which is the contact section between the contact charging roller 2 and the photosensitive drum 1, which are the main contact charging means, and the exposure section b. Carried to the developing unit c Is cleaning simultaneous with developing by the developing device 4, is use recovered and re-developing apparatus 4.
[0064]
2) Photosensitive drum 1
The photosensitive drum 1 of each of the image forming units Y, M, C, and Bk is an organic photoconductor (OPC) drum having an outer diameter of 50 mm and a process speed (peripheral speed) of 100 mm / sec around a central support shaft. It is driven to rotate clockwise as indicated by the arrow. The photosensitive drum 1 has a subbing layer for suppressing light interference and improving the adhesiveness of an upper layer, a photocharge generation layer, and a charge transport layer (thickness of 20 μm) on the surface of an aluminum cylinder (conductive drum base). ) Are applied in order from the bottom.
[0065]
3) Charging roller 2
The longitudinal length of the charging roller 2 as a main contact charging unit in each of the image forming units Y, M, C, and Bk is 320 mm, and the lower layer 2b, the intermediate layer 2c, and the outer circumference of the cored bar (supporting member) 2a. , A surface layer 2d is sequentially laminated from the bottom to form a three-layer structure. The lower layer 2b is a foamed sponge layer for reducing charging noise, the intermediate layer 2c is a resistance layer for obtaining uniform resistance as a whole of the charging roller, and the surface layer 2d has defects such as pinholes on the photosensitive drum 1. This is a protective layer provided to prevent the occurrence of a leak even if it is present. The charging roller 2 of this example uses a stainless steel round bar having a diameter of 6 mm as a cored bar 2a, carbon is dispersed in a fluororesin as a surface layer, the outer diameter of the roller is 14 mm, and the roller resistance is 10 ⁴ Ω-10 ⁷ Ω.
[0066]
The charging roller 2 holds both ends of the cored bar 2a rotatably by bearing members, and urges in the direction of the photosensitive drum 1 by a pressing spring to apply a predetermined pressing force to the surface of the photosensitive drum 1. And rotates following the rotation of the photosensitive drum 1. The pressure contact portion between the charging roller 2 and the photosensitive drum 1 is a charging portion (charging nip portion) a. Then, a predetermined vibration voltage (bias voltage Vdc + Vac) obtained by superimposing an AC voltage having a frequency f on a DC voltage is applied from the power supply 25 to the charging roller 2 via the metal core 2a, so that the peripheral surface of the rotating photosensitive drum 1 is rotated. It is charged to a predetermined potential.
[0067]
In this embodiment, a DC voltage is -500 V, an AC voltage is a frequency f = 1150 Hz, a peak-to-peak voltage Vpp = 1400 V, and a vibration voltage in which a sine wave is superimposed. The peripheral surface of the photosensitive drum 1 is -500 V (dark potential Vd ) Is uniformly contact-charged.
[0068]
A charging roller cleaning member 2f is a flexible cleaning film in this example. The cleaning film 2f is arranged in parallel with the longitudinal direction of the charging roller 2 and has one end fixed to a supporting member 2g that reciprocates a fixed amount in the longitudinal direction. It is arranged to form a contact nip. The support member 2g is driven by the drive motor of the printer in a reciprocating motion by a fixed amount in the longitudinal direction via a gear train, and the charging roller surface layer 2d is rubbed by the cleaning film 2f. As a result, contaminants (fine powder toner, external additives, and the like) attached to the surface layer 2d of the charging roller are removed.
[0069]
4) Laser beam scanner 3
After the photosensitive drum 1 is uniformly charged to a predetermined polarity and potential by the charging roller 2, image exposure means (a color separation / imaging exposure optical system for a color original image, a time-series electric digital pixel signal of image information) An image forming apparatus according to the present invention receives an image exposure L by a scanning exposure system using a laser scan that outputs a laser beam modulated in accordance with an image forming method, thereby forming an electrostatic latent image corresponding to a color component image (yellow component image) in a target color image. Is done.
[0070]
In this embodiment, a laser beam scanner 3 using a semiconductor laser is used as an exposure device in each of the image forming units Y, M, C, and Bk, and an image signal transmitted from a host device such as an image reading device (not shown) to the printer side. The laser beam L modulated in accordance with (1) is output to perform laser scanning exposure (image exposure) on the uniformly charged surface of the rotary photosensitive drum 1. By the laser scanning exposure L, the potential of the surface of the photosensitive drum 1 irradiated with the laser light is reduced, so that an electrostatic latent image corresponding to the scanned and exposed image information is formed on the surface of the rotating photosensitive drum 1. In this embodiment, the potential of the exposed portion is set to -150V.
[0071]
5) Developing device 4
In this embodiment, the developing device 4 in each of the image forming units Y, M, C, and Bk is a two-component contact developing device (two-component magnetic brush developing device).
[0072]
Numeral 40 denotes a developing container, and numeral 41 denotes a non-magnetic developing sleeve, which has a magnet roller (not shown) fixed and disposed inside. The developing sleeve 41 is rotatably disposed in the developing container 40 with a part of the outer peripheral surface exposed to the outside. 42 is a developer regulating blade, 46 is a two-component developer which is a mixture of toner and magnetic carrier contained in the developing container 40, and 43 and 44 are developer stirring members arranged on the bottom side inside the developing container 40.
[0073]
A developer regulating blade 42 is provided on the developing sleeve 41 with a predetermined gap, and a thin developer layer is formed on the developing sleeve 41 with the rotation of the developing sleeve 41 in the counterclockwise direction indicated by the arrow.
[0074]
The developing sleeve 41 is opposed to the photosensitive drum 1 while keeping the closest distance (referred to as S-Dgap) to the photosensitive drum 1 at 350 μm. The facing portion between the photosensitive drum 1 and the developing sleeve 41 is a developing portion c. The developing sleeve 41 is driven to rotate in a direction opposite to the traveling direction of the photosensitive drum 1 in the developing section c. The thin developer layer on the developing sleeve 41 contacts the surface of the photosensitive drum 1 in the developing section c and rubs the photosensitive drum surface appropriately. A predetermined developing bias is applied to the developing sleeve 41 from the power supply 4a. In this embodiment, the developing bias voltage for the developing sleeve 41 is an oscillating voltage obtained by superimposing a DC voltage (Vdc) and an AC voltage (Vac). More specifically, it is an oscillating voltage in which Vdc = −350 V, Vac = 1800 V, and frequency = 2300 Hz are superimposed.
[0075]
Thus, the surface of the rotating developing sleeve 41 is coated as a thin layer, and the toner in the developer conveyed to the developing section c is selected on the surface of the photosensitive drum 1 by the electric field due to the developing bias in accordance with the electrostatic latent image. As a result, the electrostatic latent image is developed as a toner image. In the case of this example, the toner adheres to the exposed light portion on the surface of the photosensitive drum 1 and the electrostatic latent image is reversely developed.
[0076]
The developer thin layer on the developing sleeve 41 that has passed the developing section c is returned to the developer reservoir in the developing container 40 with the subsequent rotation of the developing sleeve.
[0077]
In the developing container 40, there are stirring screws 43 and 44 for stirring the developer, which are rotated in synchronization with the rotation of the sleeve, and have a function of stirring the replenished toner and the carrier and giving a predetermined tribo to the toner. I have.
[0078]
A sensor (not shown) for detecting a change in the magnetic permeability of the developer to detect a toner concentration in the developer is provided on an upstream side wall surface of the screw 44 of the developing device 4, and a sensor is provided slightly downstream of the sensor. A toner supply opening 45 is provided. After the developing operation is performed, the developer is carried to the sensor unit, where the toner concentration is detected. In order to maintain the toner concentration in the developer 46 constant according to the detection result, the developer supply unit (T The rotation of the screw 51 in (−CRG) 5 causes the toner supply unit 5 to supply the toner t into the developing device 4 through the opening 45 of the developing device 4. The replenished toner t is conveyed by the screws 44 and 43, mixed with the carrier and provided with an appropriate tribo, is conveyed to the vicinity of the sleeve 41, formed into a thin layer on the developing sleeve 41, and used for development.
[0079]
In the present embodiment, a negatively charged toner having an average particle diameter of 6 μm is used as the toner t, and the carrier has a saturation magnetization of 205 emu / cm. ³ Of a magnetic carrier having an average particle size of 35 μm. A mixture of the toner and the carrier at a weight ratio of 6:94 was used as the developer 46.
[0080]
The charge amount of the toner developed on the photosensitive drum is −25 μC / g.
[0081]
6) Intermediate transfer belt 9
In the primary transfer nip (port) d in each of the image forming units Y, M, C, and Bk, a transfer roller 9g is pressed against the back side of the intermediate transfer belt 9 with a predetermined pressing force. The transfer roller 9g has primary transfer bias sources 9a to 9d so that a bias can be applied independently at each primary transfer nip d. The intermediate transfer belt 9 transfers the first color yellow toner image at the primary transfer section d of the first image forming section Y, and then the primary transfer sections of the second to fourth image forming sections M, C, and Bk. In step d, the magenta toner image, the cyan toner image, and the black toner image, which are the second to fourth colors, are sequentially multiplex-transferred.
[0082]
In the present embodiment, a voltage of +350 V was applied to all of the first to fourth colors as the primary transfer bias in consideration of the transfer efficiency with respect to the toner developed at the exposed portion V1 (potential -150 V).
[0083]
The four-color full-color image formed on the intermediate transfer belt 9 is then collectively transferred by the secondary transfer roller 10 to the transfer material P introduced into the secondary transfer nip g by the registration roller pair 12. A positive secondary transfer bias is applied to the secondary transfer roller 10 from a power supply 10b. The transfer material P that has exited the secondary transfer nip g is separated from the surface of the intermediate transfer belt 9, conveyed to a fixing device (not shown), and subjected to fusion and fixing of the toner image to obtain a color print image.
[0084]
The secondary transfer residual toner remaining on the intermediate transfer belt 9 is blade-cleaned by the intermediate transfer belt cleaner 11 to prepare for the next image forming process.
[0085]
In selecting the material of the transfer belt 9, a material that expands and contracts is not desirable in order to improve the registration at the primary transfer nip portion d of each color, and a resin-based or rubber belt containing a metal core or a resin + rubber belt is preferable. desirable.
[0086]
In this embodiment, carbon is dispersed in PI (polyimide) and the volume resistance is 10 ⁸ A resin belt controlled to the order of Ωcm was used. The thickness is 80 μm, the longitudinal direction is 320 mm, and the entire circumference is 900 mm.
[0087]
The primary transfer roller 9g is made of a conductive sponge. Its resistance is 10 ⁶ Ω or less, the outer diameter is 16 mm, and the longitudinal length is 315 mm.
[0088]
7) Cleanerless system
1 and 2, where a cleaning blade is normally disposed, a first auxiliary contact charging means 6 as a developer charge amount control means and a second auxiliary contact charging means 6 as a residual developer uniformization control means are provided. Are provided in contact with the photosensitive drum 1, respectively. In both the embodiments 6 and 7, the present embodiment uses a brush member made of conductive fiber.
[0089]
That is, the developer charge amount control means (hereinafter, referred to as toner charge amount control means) 6 and the residual developer uniformization control means (hereinafter, referred to as residual toner uniformity means) 7 are composed of a charging section a and a primary transfer nip section d. The developer charge amount control means 6 is located upstream of the primary transfer nip d in the photosensitive drum rotation direction, and the residual developer uniformization control means 7 is more photosensitive than the developer charge amount control means 6. It is located on the upstream side in the drum rotation direction.
[0090]
More specifically, the toner charge amount control means 6 (first brush) includes a horizontally long electrode plate 62 provided with a brush portion 61, and the remaining toner uniforming means 7 (second brush) also has the same configuration. An electrode plate 72 is provided with a brush portion 71.
[0091]
The brush portions 61 and 71 are disposed so as to be in contact with and fixedly supported by the surface of the photosensitive drum 1. The brush portions 61 and 71 are made of fibers such as rayon, acryl, polyester and the like containing carbon or metal powder to control the resistance value. The brush portions 61 and 71 have a thickness of 30 denier or less and a density of 100,000 to 500,000 brushes / inch so that the brush portions 61 and 71 can uniformly contact the photosensitive drum surface and transfer residual toner. ² The above is preferable. In this embodiment, both the brush portions 61 and 71 are 6 denier and 100,000 brushes / inch. ² The length of the bristle feet is 5mm and the brush resistance is 6 × 10 ³ Ω · cm. The toner charge amount control means 6 and the residual toner uniforming means 7 are brought into contact with each other so that the brush portions 61 and 71 have an intrusion amount of 1 mm with respect to the surface of the photosensitive drum 1, and the width of the contact nip with the photosensitive drum 1 is set. Was 5 mm.
[0092]
The cleanerless system of the present embodiment is realized by the toner charge amount control means 6 and the residual toner uniformity means 7.
[0093]
The cleaner-less system is a system in which the transfer residual toner remaining on the surface of the photosensitive drum 1 after the transfer passes through the charging unit a and the exposure unit b, and is simultaneously cleaned (collected) by the developing device 3 during development.
[0094]
Since the transfer residual toner on the surface of the photosensitive drum 1 passes through the exposure portion b, the exposure process is performed on the transfer residual toner. However, since the amount of the transfer residual toner is small, no significant effect appears.
[0095]
The transfer residual toner includes a toner having a normal polarity, a toner having a reverse polarity (inverted toner), and a toner having a small charge amount, of which the inverted toner and the toner having a small charge amount pass through the charging portion a. When the charging roller 2 adheres to the charging roller 2, the charging roller is unnecessarily contaminated with toner, resulting in poor charging.
[0096]
Further, in order to effectively carry out simultaneous cleaning of the transfer residual toner on the surface of the photosensitive drum 1 by the developing device 4, the charge polarity of the transfer residual toner on the photosensitive drum carried to the developing section c is a normal polarity. It is necessary that the charge amount is a charge amount of the toner that can develop the electrostatic latent image on the photosensitive drum 1 by the developing device 4. Inverted toner and toner with an inappropriate charge amount cannot be removed / recovered from the photosensitive drum 1 to the developing device 4 and cause a defective image.
[0097]
In addition, with the diversification of user needs in recent years, continuous printing operations such as high-printing-rate images such as photographic images have caused a large amount of untransferred toner to be generated at a time, thereby further promoting the above-described problems. It will be.
[0098]
Therefore, the transfer residual toner on the photosensitive drum 1 is made uniform at a position downstream of the primary transfer nip d in the photosensitive drum rotation direction and upstream of the charging unit a, and the charge polarity of the transfer residual toner is the normal polarity. In order to make the negative polarity uniform, a residual toner uniforming means 7 and a toner charge amount controlling means 6 are provided.
[0099]
A positive polarity voltage (positive bias = + 350 V) is applied to the residual toner uniforming means 7 from the power supply 25 via the protection resistor 27.
[0100]
Transfer residual toner includes toner of opposite polarity and toner having almost no polarity. Among them, the toner charged near zero to negative polarity has electrical and physical force. Is sucked by the residual toner uniforming means 7. Then, the toner becomes reverse polarity (positive polarity) due to the positive bias of the residual toner uniforming means 7, and the toner is gradually separated, re-adhered to the surface of the photosensitive drum 1, and transported. By this operation, the distribution of the toner on the photosensitive drum 1 is made uniform, so that a large amount of toner does not flow into the toner charge amount control means 6 at a time. Further, the potential on the photosensitive drum is near 0V. By setting the transfer residual toner to the opposite polarity (positive polarity) and setting the potential on the photosensitive drum 1 to around 0 V, the toner charge amount control unit 6 can sufficiently charge the toner as described later. Also plays a role.
[0101]
A negative voltage (negative bias = −800 V) is applied to the toner charge amount control unit 6 from the power supply 25 via the protection resistor 27.
[0102]
After passing through the toner charge amount control means 6, the transfer residual toner on the photosensitive drum 1 is adjusted to have a negative polarity whose charging polarity is a normal polarity. As described above, the toner is made uniform in the positive polarity by the toner uniforming means 7 and the potential on the photosensitive drum is also around 0 V, so that the toner can be more effectively made uniform in the negative polarity.
[0103]
By adjusting the charge polarity of the transfer residual toner to the negative polarity which is the normal polarity by the toner charge amount control means 6, the charging unit a located further downstream moves the transfer residual toner from above the transfer residual toner onto the surface of the photosensitive drum 1. During the charging process, the mirror force on the photosensitive drum 1 is increased, and the transfer residual toner is prevented from adhering to the charging roller 2.
[0104]
Then, the toner that has passed without adhering to the charging roller 2 is cleaned and collected simultaneously with the development in the developing device 4.
[0105]
In order to recover the transfer residual toner on the photosensitive drum 1 to the developing device 4 by such a method, the toner charge amount needs to be appropriate. However, as described above, in order to prevent the toner from adhering to the charging roller 2, in order to collect in the developing device 4 the transfer residual toner that has been largely charged to the negative polarity by the toner charge amount control unit 6, it is necessary to perform charge elimination. I need to do it.
[0106]
The transfer residual toner charged to a large negative polarity by the toner charge amount control means 6 is subjected to AC charge removal by an AC voltage (frequency f 1150 Hz, Vpp 1400 V) applied to the charging roller 2, and the toner charge amount after passing through the charging unit a is This is almost the same as the charge amount of the developing toner.
[0107]
In the developing step, the transfer residual toner on the unexposed portion of the photosensitive drum 1 where the toner should not be developed is completely negatively aligned, is appropriately neutralized by the charging roller 2, and is mirrored with the photosensitive drum 1. Since the imaging power can be reduced, the drum is reliably collected in the developing device in the relationship between the drum potential of -500 V and the DC component of the developing bias of -350 V. In the present embodiment, the developing sleeve 41 of the developing device 4 is rotated in the developing section c in the opposite direction to the traveling direction of the surface of the photosensitive drum 1 as described above. This is advantageous for recovery.
[0108]
(2) Calculation method of minimum required resistance value of protection resistor 27
Next, a description will be given of a method of calculating a necessary minimum resistance value of the protection resistor 27, which is a feature of the present invention.
[0109]
In this embodiment, the equivalent circuit of the brush 61 (71) of the toner charge amount control means 6 and the residual toner uniforming means 7 for a portion where the photosensitive drum 1 has no defect such as a pinhole is (a) of FIG. FIG. 3B shows an equivalent circuit of the brush 61 (71) for a defective portion such as a pinhole of the photosensitive drum 1. Hereinafter, the calculation will proceed based on this equivalent circuit.
[0110]
When the brush material comes into contact with the pinhole portion of the photosensitive drum 1, the calorific value W of the brush portion is expressed by the following equation (1) according to FIG.
[0111]
(Equation 6)

[0112]
Here, in order to prevent the brush from burning even when an overcurrent flows, if the amount of heat that the brush burns is Wb,
[0113]
(Equation 7)

[0114]
Must always be satisfied. At this time, assuming that the first derivative of W with respect to the variable Rb is W ′, at the point where W becomes maximum,
[0115]
(Equation 8)

[0116]
Meet. That is, at one point where Rb = Rh, W takes the maximum value and the value W _MAX Is
[0117]
(Equation 9)

[0118]
It is. From equations (2) and (4),
[0119]
(Equation 10)

[0120]
Thus, the protection resistance Rh may be determined so as to satisfy Expression (5).
[0121]
FIG. 4 is a graph showing the relationship between the resistance of the brush and the power consumption of the brush. In the present embodiment, the range of variation in brush resistance is 10 ⁴ -10 ⁸ It can be seen that equation (1) has only one vertex on the graph in this range, and that W is maximum at the point where Rb = Rh.
[0122]
Based on the above results, in the present embodiment, Wb is about 0.2 W and V1 = 800 V. Therefore, the protection resistance Rh is set to 2 so that the equation (2) holds for all the brush resistance variations. .2 MΩ. At this time, W _MAX Is 0.07 W, does not exceed Wb, and does not burn.
[0123]
If the current Ic cannot be sufficiently supplied to the circuit, the residual toner equalizing means 7 and the toner charge amount controlling means 6 cannot apply sufficient charge to the developer on the photosensitive drum 1, but the above-described method is used. By determining the value Rh of the protection resistor 27, it is possible to select the minimum necessary protection resistance value while ensuring the safety of the brush.
[0124]
In this embodiment, even after actually performing the printing operation of 60000 sheets under the environment of different room temperature and humidity, a clear printed image was obtained without any damage to the brush and no problem in the function.
[0125]
As described above, it is possible to prevent the contact charging member from burning while obtaining a sufficient circuit current Ic for the functions of the residual toner equalizing means 7 and the toner charge amount controlling means 6.
[0126]
(3) Other
1) In addition to the flexible charging roller, the main contact charging means 2 may be of a shape or material such as a fur brush, felt, or cloth. In addition, it is possible to obtain more appropriate elasticity (flexibility), conductivity, surface properties and durability by combining various materials. This main contact charging means 2 is also provided with a protection resistor 27, in which case Wb> V1 ² Needless to say, the present invention can be applied by using the relationship of / 4Rh.
[0127]
2) The residual toner equalizing means 7 and the toner charge amount controlling means 6 as auxiliary contact charging means are fixed brush-like members in the present embodiment, but are arbitrary such as a brush rotating body, an elastic roller body, and a sheet-like member. It can be in the form of a member.
[0128]
3) The image bearing member as a member to be charged has a surface resistance of 10 ⁹ -10 ¹⁴ It may be of a direct injection charging type provided with a charge injection layer of Ω · cm. Even when the charge injection layer is not used, the same effect can be obtained, for example, when the charge transport layer is in the above resistance range. The surface volume resistance is about 10 ^Thirteen It may be an amorphous silicon photoreceptor of Ω · cm.
[0129]
4) As a waveform of an alternating voltage component (AC component, a voltage whose voltage value changes periodically) of the oscillating electric field applied to the contact charging member or the developing member, a sine wave, a rectangular wave, a triangular wave, or the like can be used as appropriate. . It may be a rectangular wave formed by periodically turning on / off a DC power supply.
[0130]
5) Further, the image exposure means as information writing means on the charged surface of the photoreceptor as the image carrier may be a digital exposure means using a solid light emitting element array such as an LED in addition to the laser scanning means of the embodiment. There may be. An analog image exposure unit using a halogen lamp, a fluorescent lamp, or the like as a document illumination light source may be used. In short, any device that can form an electrostatic latent image corresponding to image information may be used.
[0131]
6) The image carrier may be an electrostatic recording dielectric or the like. In this case, after uniformly charging the dielectric surface, the charged surface is selectively discharged by a discharging means such as a discharging needle head or an electron gun to write and form an electrostatic latent image corresponding to target image information. I do.
[0132]
7) The toner developing method and means of the electrostatic latent image are arbitrary. A reversal development system or a regular development system may be used.
[0133]
In general, a method of developing an electrostatic latent image is to coat a non-magnetic toner on a developer carrying member such as a sleeve with a blade or the like, and to coat a magnetic toner on a developer carrying member such as a sleeve. A method of developing the electrostatic latent image by applying it in a non-contact state to the image carrier by coating and conveying by force (one-component non-contact development), and coating the developer carrying member as described above A method of developing an electrostatic latent image by applying toner in a contact state to an image carrier (one-component contact development), and a developer in which a magnetic carrier is mixed with toner particles (a two-component developer) A method of developing the electrostatic latent image by applying a magnetic force to the image carrier in a contact state (two-component contact development), and a method of applying the two-component developer to the image carrier. Apply in the contact state to create an electrostatic latent image Is roughly divided into four 顛 the method (two-component non-contact development) to the image.
[0134]
8) The image forming apparatus is not limited to the full-color image forming apparatus using the intermediate transfer member of the embodiment, but may be a single-color image forming apparatus, and the transfer means may be roller transfer, blade transfer, belt transfer, or other transfer. A contact transfer charging method or a non-contact transfer charging method using a corona charger may be used.
[0135]
9) The contact charging device of the present invention can be effectively used not only as a charging device for an image carrier of an image forming apparatus but also widely as a contact charging device for a member to be charged.
[0136]
【The invention's effect】
As described above, according to the present invention, when providing a protection resistor in a circuit for applying a high voltage to the contact charging means, Wb> V1 ² By using the relationship of / 4Rh, it is possible to prevent an overcurrent from flowing from the contact charging means to a pinhole or the like of the member to be charged and burn it. In addition, it has become possible to select an appropriate protection resistor that can exhibit the most function with respect to the applied high voltage.
[0137]
As a result, in an image forming apparatus using a contact charging device for charging an image carrier, a high-quality image can always be stably provided.
[Brief description of the drawings]
FIG. 1 is a schematic configuration model diagram of an image forming apparatus according to an embodiment.
FIG. 2 is a partially enlarged view
FIG. 3 is an equivalent circuit diagram of the contact charging device.
FIG. 4 is a diagram illustrating a relationship between a brush resistance and a calorific value in the embodiment.
[Explanation of symbols]
1 is a photoconductor (charged member, image carrier), 2 is a charging roller (main contact charging means), 3 is an image exposure device, 4 is a developing device, 5 is a developer supply unit, and 6 is a developer charging amount. Control means (first auxiliary contact charging means), 7 is a transfer residual developer image uniforming means (second auxiliary contact charging means), 8 is a process cartridge, 9 is an intermediate transfer belt, 10 is a secondary transfer roller, 11 is an intermediate transfer belt cleaner, 12 is a pair of registration rollers (feed roller), 25, 4a, 9a to 9d and 10b are power supplies

Claims (9)

In a contact charging device having one or a plurality of contact charging means for charging the charged body surface in contact with the charged body surface,
When a voltage V1 is applied to a circuit in which the contact charging means and the resistance circuit Rh are connected in series, the amount of heat Wb at which the constituent members of the contact charging means start burning is reduced.

A contact charging device characterized by satisfying the following relationship: 2. The contact charging device according to claim 1, wherein one or more or all of the contact charging units are formed of a conductive fiber brush member that comes into contact with the surface of the member to be charged. The contact charging device according to claim 1, wherein an oscillating electric field is applied to one or a plurality of the contact charging units. An image carrier, having one or more contact charging means for charging the image carrier surface by contacting the image carrier surface, and an information writing device for forming an electrostatic latent image on the charged image carrier; A developing unit that supplies a developer having a predetermined polarity to the electrostatic latent image to visualize the electrostatic latent image, and an image forming apparatus that includes a transfer unit that transfers the visualized developer image to a transfer material.
When a voltage V1 is applied to a circuit in which the contact charging means and the resistance circuit Rh are connected in series, the amount of heat Wb at which the constituent members of the contact charging means start burning is reduced.

An image forming apparatus characterized by satisfying the following relationship: 5. The image forming apparatus according to claim 4, wherein one or a plurality of the contact charging units or all of the contact charging units are formed by a conductive fiber brush member that contacts the image carrier. The image forming apparatus according to claim 4, wherein an oscillating electric field is applied to one or more of the contact charging units. 7. The image forming apparatus according to claim 4, wherein the information writing unit is an exposure unit. A main contact charging unit upstream of the information writing unit in the rotation direction of the image carrier; an upstream side of the main contact charging unit in the rotation direction of the image carrier; and a downstream side of the transfer unit in the rotation direction of the image carrier. 9. An auxiliary contact charging means as a developer charge amount control means for charging the residual developer on the charged image carrier to a normal polarity on the side. Image forming apparatus. The image carrier after transferring the developer image to the transfer material, downstream of the transfer unit in the image carrier rotation direction and upstream of the auxiliary contact charging unit as the developer charge amount control unit in the image carrier rotation direction. 9. The image forming apparatus according to claim 8, further comprising a second auxiliary contact charging unit serving as a residual developer uniforming control unit for uniformizing the residual developer remaining on the body.

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