JP3647409B2 - Charging device, process cartridge, image forming apparatus, roller-shaped charging member - Google Patents

Description

【００７９】
帯電ローラーが電子写真感光体に対して従動回転している場合は、両者の表面において速度差がない状態である。帯電ローラー周速は、感光体周速と同じ方向に移動するときを正とする。
【００８０】
速度差は−４００％以上−１００％未満が好ましい。速度差が−４００％未満の場合、帯電ローラーと被帯電体との摺擦によって被帯電体の寿命が低下する場合があり、また、速度差が−１００％、すなわち、帯電ローラーが回転しない場合、帯電ローラーと被帯電体が接している部分（ニップ部）に紙粉や残りトナーが堆積しやすく、帯電不良が発生する場合がある。
【００８１】
以上の構成をとることで、従来のローラー帯電では得られなかった高い帯電効率を得られ、帯電部材に印加した電位とほぼ同等の電位を感光ドラムに与えることができる。帯電に必要なバイアスは、感光ドラムに必要な電位相当の電圧で十分であり、放電現象を用いない安定かつ安全な帯電方式を実現する。
【００８２】
このように、帯電ローラー１０２１によって表面が均一帯電された電子写真感光体１０１は、次いで、スリット露光やレーザービーム走査露光などの露光手段（不図示）から出力される目的の画像情報の時系列電気デジタル画像信号に対応して強調変調された露光光１０Ｌを受ける。こうして電子写真感光体１０１の周面に対し、目的の画像情報に対応した静電潜像が順次形成されていく。
【００８３】
形成された静電潜像は、次いで、現像装置１０３によりトナー現像される。現像装置１０３は、マグネットロール１０３ｃを内包した現像スリーブ１０３ｂ、規制ブレード１０３ｄから構成される。現像装置内のトナー１０３ａは、スリーブ上を搬送される過程において、規制ブレード１０３ｄで層厚規制および電荷付与され、現像部位に導入され、電子写真感光体１０１上に形成された静電潜像を現像する。
【００８４】
次に、不図示の給紙部から電子写真感光体１０１と転写装置１０４との間に電子写真感光体１０１の回転と同期して取り出されて給紙された転写材１０Ｐに、電子写真感光体１０１の表面に形成担持されているトナー画像が転写装置１０４により順次転写されていく。
【００８５】
トナー画像の転写を受けた転写材１０Ｐは、電子写真感光体面から分離されて定着装置１０５へ導入されて像定着を受けることにより画像形成物（プリント、コピー）として装置外へプリントアウトされる。
【００８６】
像転写後の電子写真感光体１０１の表面は、クリーニング装置１０７によって転写残りトナーの除去を受けて清浄面化され、繰り返し画像形成に使用される。
【００８７】
本発明においては、本発明の帯電手段と、電子写真感光体１０１、現像装置１０３およびクリーニング装置１０７などの構成要素のうち、複数のものを容器に納めてプロセスカートリッジ１０６として一体に結合して構成し、このプロセスカートリッジ１０６を複写機やレーザービームプリンターなどの電子写真装置本体に対して着脱自在に構成してもよい。例えば、本発明の帯電装置と電子写真感光体１０１とを一体に支持してカートリッジ化して、装置本体のレールなどの案内手段（不図示）を用いて装置本体に着脱自在なプロセスカートリッジ１０６とすることができる。
【００８８】
また、露光光１０Ｌは、電子写真装置が複写機やプリンターである場合には、原稿からの反射光や透過光、あるいは、センサーで原稿を読取り、信号化し、この信号にしたがって行われるレーザービームの走査、ＬＥＤアレイの駆動および液晶シャッターアレイの駆動などにより照射される光である。
【００８９】
また、図２に本発明の帯電装置を有するプロセスカートリッジを用いた電子写真装置の別の概略構成を示す。
【００９０】
この図に示す画像形成装置は、クリーニング装置を装備することなく、トナーリサイクルを可能にしたクリーナーレスの画像形成装置である。
【００９１】
また、導電性粒子供給装置を有さず、代わりに導電性粒子を含有する現像剤（トナー）を有する点で、図１に示す画像形成装置と異なる。
【００９２】
このことにより、導電性粒子を供給する装置が必要なくなり、簡易な構成が実現できるため装置コストを安くすることができる。
【００９３】
図において、２０１は被帯電体としての電子写真感光体であり、矢印２０Ａの方向に所定の周速度で回転駆動される。電子写真感光体２０１は、回転過程において、本発明の帯電装置の帯電ローラー２０２１および帯電促進を目的とした導電性粒子２０２２によりその周面に帯電装置への印加電圧とほぼ同電位の均一帯電を受ける。
【００９４】
帯電ローラー２０２１は、芯金２０２１ａ上に弾性発泡体の中抵抗層２０２１ｂを形成することにより作製されている。
【００９５】
帯電ローラー２０２１によって表面が均一帯電された電子写真感光体２０１は、次いで、スリット露光やレーザービーム走査露光などの露光手段（不図示）から出力される目的の画像情報の時系列電気デジタル画像信号に対応して強調変調された露光光２０Ｌを受ける。こうして電子写真感光体２０１の周面に対し、目的の画像情報に対応した静電潜像が順次形成されていく。
【００９６】
形成された静電潜像は、次いで、現像装置２０３によりトナー現像される。現像装置２０３は、マグネットロール２０３ｃを内包した現像スリーブ２０３ｂ、規制ブレード２０３ｄから構成される。現像装置内のトナー２０３ａは、スリーブ上を搬送される過程において、規制ブレード２０３ｄで層厚規制および電荷付与され、現像部位に導入され、電子写真感光体２０１上に形成された静電潜像を現像する。
【００９７】
なお、トナー２０３ａは導電性粒子２０２２を含有しており、現像装置２０３からトナー２０３ａと共に供給された導電性粒子２０２２は電子写真感光体２０１の表面に移行し、その後、上記帯電装置に供給される。
【００９８】
次に、不図示の給紙部から電子写真感光体２０１と転写装置２０４との間に電子写真感光体２０１の回転と同期して取り出されて給紙された転写材２０Ｐに、電子写真感光体２０１の表面に形成担持されているトナー画像が転写装置２０４により順次転写されていく。
【００９９】
トナー画像の転写を受けた転写材２０Ｐは、電子写真感光体面から分離されて定着装置２０５へ導入されて像定着を受けることにより画像形成物（プリント、コピー）として装置外へプリントアウトされる。
【０１００】
本発明においては、本発明の帯電手段と、電子写真感光体２０１、現像装置０２３などの構成要素のうち、複数のものを容器に納めてプロセスカートリッジ２０６として一体に結合して構成し、このプロセスカートリッジ２０６を複写機やレーザービームプリンターなどの電子写真装置本体に対して着脱自在に構成してもよい。例えば、本発明の帯電装置と電子写真感光体２０１とを一体に支持してカートリッジ化して、装置本体のレールなどの案内手段（不図示）を用いて装置本体に着脱自在なプロセスカートリッジ２０６とすることができる。
【０１０１】
また、露光光２０Ｌは、電子写真装置が複写機やプリンターである場合には、原稿からの反射光や透過光、あるいは、センサーで原稿を読取り、信号化し、この信号にしたがって行われるレーザービームの走査、ＬＥＤアレイの駆動および液晶シャッターアレイの駆動などにより照射される光である。
【０１０２】
さて、現像により電子写真感光体上に得られた画像は転写材に転写されるが、トナーの一部は転写残りとして電子写真感光体上に残ることになる。従来、トナーは絶縁体であるため、電子写真感光体の帯電において著しい帯電不良が生じる。
【０１０３】
しかしながら、図２に示す画像形成装置においては、帯電ローラー２０２１の表面には、あらかじめ塗布された導電性粒子が存在することと、帯電装置からトナー２０３ａと共に供給された導電性粒子が存在することにより、帯電装置にトナーが混入した場合でも、導電性粒子の存在で電子写真感光体への接触性と接触抵抗を維持できるため直接注入による帯電を行うことができる。
【０１０４】
そして、混入した転写残りのトナーは、帯電ローラー２０２１内部に入り込むことなく、電子写真感光体２０１や導電性粒子２０２２との摩擦によってトナーが本来なるべき極性に帯電され、帯電ローラー２０２１の表面から排出され、次現像工程で現像装置にて再度回収あるいは現像される。
【０１０５】
以上の行程を繰り返すことにより、トナーリサイクルを可能にしながら、帯電ローラー表面が常に安定して接触帯電ができる状態にあるので、長期にわたり均一な帯電性が得られ良好な画像を維持することができる。
【０１０６】
なお、本発明のプロセスカートリッジおよび画像形成装置の構成はこれらに限定するものではない。
【０１０７】
次に、図３と図４を用いて、帯電ローラー表面のトナーの動きなどを説明する。ここでは、トナー３０３ａ、４０３ａをわかりやすくするため大きめに表示している。
【０１０８】
図３では、クリーニングをすり抜けたトナー３０３ａと電子写真感光体３０１上に残っている導電性粒子３０２２が、帯電ローラー３０２１と電子写真感光体３０１との接触部上流の領域Ｎｕに、電子写真感光体３０１の回転方向である矢印３０Ａの方向で突入してくる。一方、帯電ローラー３０２１は、矢印３０Ｂの方向に回転しているので、帯電ローラー３０２１のスポンジ状の中抵抗層３０２１ｂの表面の突起は、矢印３０Ｃの方向に圧を開放された形で広がり、このときに電子写真感光体３０１上のトナー３０３ａや導電性粒子３０２２をそれぞれ摩擦させ、トナーが本来持つべき帯電量に帯電する。よって、空孔率が大きく、空孔径が大きい方が、よりトナーの動きが大きくなる。
【０１０９】
図４は、帯電ローラー４０２１と電子写真感光体４０１との接触部下流の様子を示している。帯電ローラー４０２１のスポンジ状の中抵抗層４０２１ｂは、矢印４０Ｂの方向に移動しながら、帯電ローラー４０２１と電子写真感光体４０１との接触部下流領域Ｎｄに突入する。ここでは、トナーが十分に帯電されているために、帯電ローラー４０２１と電子写真感光体４０１の微小な電位差で電子写真感光体４０１上に排出され、かつ、帯電ローラー４０２１の表面の空孔が矢印４０Ｃの方向につぶされ、内部のトナーも排出されて、電子写真感光体４０１の表面に移り、現像装置に回収される。矢印４０Ａは電子写真感光体４０１の回転方向である。
【０１１０】
図５は、電子写真感光体の層構成の一例である。
【０１１１】
この図で例示する電子写真感光体は、アルミニウムなどの支持体５０１１上に下引き層５０１２、正電荷注入防止層５０１３、電荷発生層５０１４、電荷輸送層５０１５の順に重ねて塗工された一般的な有機電子写真感光体である。
【０１１２】
図６は、表面に電荷注入層を有する電子写真感光体の層構成の一例である。
【０１１３】
次に、図６を用いて、注入帯電効率が向上する電子写真感光体について説明する。
【０１１４】
具体的には、電子写真感光体の表面層の抵抗を調整することにより、さらに安定して均一に帯電を行う。つまり、帯電装置の性能が低下した場合でも、導電性粒子の介在と電子写真感光体側の表面抵抗を潜像形成可能な領域で低く設定することにより、一層効率良く電荷の授受を行うものである。以下に電荷注入層について詳しく述べる。
【０１１５】
図６に本実施例で用いた電子写真感光体の断面図を示す。
【０１１６】
電子写真感光体は、アルミニウムなどの支持体６０１１上に下引き層６０１２、正電荷注入防止層６０１３、電荷発生層６０１４、電荷輸送層６０１５の順に重ねて塗工された一般的な有機電子写真感光体ドラムに電荷注入層１６を塗布することにより、帯電性能を向上した電子写真感光体を用いた。
【０１１７】
電荷注入層は、光硬化型のアクリル樹脂にＳｎＯ_２超微粒子１６ａ（径が約０．０３μｍ）、ポリテトラフルオロエチレンなどの滑剤、重合開始剤などを混合分散し、塗工後、光硬化法により膜形成したものである。電荷注入層として重要な点は、表層の抵抗にある。電荷の直接注入による帯電方式においては、感光ドラム側の抵抗を下げることでより効率良く電荷の授受が行えるようになる。一方、電子写真感光体として用いる場合には、静電潜像を一定時間保持する必要があるため、最表面層、本実施例では電荷注入層１６の体積抵抗値が好ましくは１×１０^１４Ω・ｃｍ以下、特には１×１０^９〜１×１０^１４Ω・ｃｍの範囲であることが好ましい。つまり、電荷注入層を用いていない場合でも、電子写真感光体の最表面が上記抵抗範囲にある場合は同等の効果が得られる。例えば、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電子写真感光体などを用いても同様な効果が得られる。
【０１１８】
【実施例】
以下に、具体的な実施例を挙げて本発明をより詳細に説明するが、本発明はこれらの実施例により限定されるものではない。
【０１１９】
（実施例１）
本実施例では、キヤノン（株）製ＬＢＰ−１７６０（６００ＤＰＩ）に以下の改造を施した改造機、つまり、図１に示す構成を有する画像形成装置を用いて画像形成を行った。改造箇所は、帯電ローラーと導電性粒子供給手段である。
（改造前→改造後）
帯電部材：ＥＰ−５２帯電ローラー→本発明の帯電ローラー＋導電粒子
帯電部材の駆動：電子写真感光体に対して従動→周速差
粒子供給手段：なし→粒子供給手段あり
なお、ＥＰ−５２とは、上記ＬＢＰ１７６０用のカートリッジである。
【０１２０】
電子写真感光体は直径３０ｍｍのドラム状であり、図１中の矢印１０Ａの方向に９４ｍｍ／ｓの一定の周速で回転する。帯電ローラーは、ローラー表面が電子写真感光体と互いに逆方向に等速度で移動するよう１５０ｒｐｍで駆動する。ローラーの芯金に−６２０Ｖの直流電圧を印加した。
【０１２１】
帯電ローラーを、ＳＵＳ芯金上に弾性発泡体の中抵抗層を形成することにより作製した。中抵抗層は、ウレタン樹脂、導電性粒子としてのカーボンブラック、発泡剤などにより処方し、上記芯金上にローラー状に形成した。その後、表面を研磨して直径１２ｍｍ、母線方向長さ２００ｍｍの帯電ローラーを作製した。
【０１２２】
本実施例の帯電ローラー表面の空孔率は５７％、平均空孔径は１２０μｍであった。帯電ローラーの抵抗は１００ｋΩであった。
【０１２３】
導電性粒子として、体積抵抗値が１０^３Ω・ｃｍ、平均粒径１．５μｍの導電性酸化亜鉛粒子を帯電ローラー表面に均一に塗布した。
【０１２４】
導電性粒子は凝集体を構成しており、粒径は凝集体の平均粒径である。
【０１２５】
また、導電性粒子チップとして、導電性粒子を溶剤中で結着樹脂で結着したチップ状のものを用いた。具体的処方は次のとおりである。
【０１２６】
結着樹脂としてスチレンアクリル樹脂をエタノール中に５質量％の濃度で溶解し、質量にして結着樹脂に対して７倍の酸化亜鉛粒子を混合した。この溶液を型に入れて成形し、乾燥することで、酸化亜鉛をチップ状に結着固形化した形態の導電性粒子供給部材が得た。
【０１２７】
チップ用の導電性粒子としては、抵抗値が３×１０^３Ω・ｃｍ、平均粒径１．５μｍの導電性酸化亜鉛粒子を用いた。
【０１２８】
本実施例で使用した導電性チップは、ブロック状の形態をしており、カム式の機構が画像形成終了後に導電性チップが帯電ローラーに接し、画像形成開始前に帯電ローラーから離れ、帯電ローラー表面に導電粒子を供給している。
【０１２９】
上述の画像形成装置において画像形成を行い、初期（１枚目）、１００枚耐久後、５０００枚耐久後、１００００枚耐久後の画像評価を行った。評価方法は以下のとおりである。
【０１３０】
ａ）カブリ評価
カブリとは、本来印字しない白部（未露光部）において、トナーがわずかに現像され、地汚れのように現れる画像不良のことである。帯電不足のところがあると、本来の電位に比べて低くなるため、その場所はカブリとして現れる。カブリ量は光学反射率測定器（東京電色株式会社製ＴＣ−６ＤＳ）によりグリーンフィルタによる光学反射率を測定し記録紙のみに反射率から差し引いてカブリ分の反射率量を求めカブリ量として評価した。カブリ量は記録紙上を１０点以上測定しその平均値を求めた。
【０１３１】
評価基準は次のとおりである。
Ａ：カブリ量が２％未満である。
Ａ⁻：カブリ量が２〜１０％である。
Ｂ：カブリ量が１０％を超える。
【０１３２】
ｂ）中間調画像評価
微小領域の帯電不良、つまり帯電の不均一さは上述の白地部のカブリよりも、中間調で目立ちやすいため、白地部のカブリが良好であっても、中間調には微小な黒点または黒スジとして帯電不良が現れる場合がある。そこで、帯電均一性の評価として、異なる２水準の中間調で帯電均一性の評価を行った。用いた中間調は、６００ｄｐｉの横線の１ドット２スペースと、２ドット３スペースで、１ドット２スペースの方が帯電の不均一が目立ちやすい。
【０１３３】
評価基準は次のとおりである。
Ａ：黒点または黒スジが１ドット２スペースと、２ドット３スペースともに無い。
Ａ⁻：黒点または黒スジが２ドット３スペースに無く、１ドット２スペースにほとんど無い。
Ｂ：黒点または黒スジが１ドット２スペースと、２ドット３スペースともに有る。
なお、上記評価基準のうち、Ｂは本発明の効果が十分に得られていないと判断した。
【０１３４】
評価条件および評価結果を表１に示す。
【０１３５】
（実施例２〜１５、比較例１〜５）
画像形成装置、注入層の有無、帯電ローラーの空孔率および空孔径、帯電ローラーと電子写真感光体との速度差を表１に示すとおりにした以外は、実施例１と同様である。
【０１３６】
なお、実施例１０〜１５では、キヤノン（株）製ＬＢＰ−１７６０（６００ＤＰＩ）に以下の改造を施した改造機、つまり、図２に示す構成を有する画像形成装置を用いて画像形成を行った。改造箇所は、帯電ローラーと導電性粒子供給手段である。
（改造前→改造後）
帯電部材：ＥＰ−５２帯電ローラー→本発明の帯電ローラー＋導電粒子
帯電部材の駆動：電子写真感光体に対して従動→周速差
現像剤：ＥＰ−５２トナー→ＥＰ−５２トナーに導電粒子混合
クリーニング：あり→なし
なお、ＥＰ−５２とは、上記ＬＢＰ１７６０用のカートリッジである。
【０１３７】
また、実施例１〜１５および比較例１〜５の帯電ローラーの作製（表面の空孔径、空孔率の調整）は、以下の方法で行った。
・実施例１、６から１５、比較例５
あらかじめ導電性カーボンで抵抗調整し、発泡剤を含有した液状ウレタンを帯電ローラーの形状の型内に芯金も存在させて発泡させた後、表面研磨を行った。空孔径および空孔率は、発泡剤の量や粒径を変化させることで調整した。
・実施例２〜５、比較例１〜４
液体に可溶性の粒子をあらかじめカーボンで抵抗調整をしたウレタン樹脂に混合し、チューブ形状に成形した後、液体中に放置し、可溶性の粒子を溶出することで、チューブ形状の発泡体を得た。このチューブに芯金を圧入接着後、表面を研磨した。ここで、空孔率は可溶性粒子の混合量を変化させることで調整した。
【０１３８】
また、実施例１０〜１５で用いた図２で示す画像形成装置は、ＬＢＰ−１７６０およびそのカートリッジであるＥＰ−５２を以下のように改造した。
【０１３９】
評価条件および評価結果を表１に示す。
【０１４０】
【表１】

【０１４１】
本実施例では、１００００枚まで良好な画像を出力できることがわかった。
【０１４２】
【発明の効果】
以上説明したように、本発明によれば、表面の空孔率が高く、かつ、平均空孔径が微細な帯電ローラーを用いることで、常に帯電ローラー表面を汚染の少ない状態に維持できるため、放電生成物を発生しない注入帯電を安定して行い、長期使用においても安定した帯電性能および画像性能を維持できる画像形成装置を提供することが可能となった。
【０１４３】
また、特にクリーナーレスシステムを採用した画像形成装置においても、放電生成物を発生しない注入帯電を安定して行い、かつ長期の印字においても帯電ムラのない良好な画像を得ることが可能となった。
【図面の簡単な説明】
【図１】本発明の実施例１を実施した画像形成装置の構成図である。
【図２】本発明の実施例１の帯電ローラー表面のトナーの動きなどを説明する図である。
【図３】本発明の実施例１の帯電ローラー表面のトナーの動きなどを説明する別の図である。
【図４】本発明の実施例２を実施した画像形成装置の構成図である。
【図５】実施例１〜１４および比較例１〜５で用いた電子写真感光体の断面図である。
【図６】実施例１５で用いた電子写真感光体の断面図である。
【図７】注入帯電特性を示すグラフである。
【符号の説明】
１０１ 電子写真感光体
１０２１ 帯電ローラー
１０２１ａ 芯金
１０２１ｂ 中抵抗層
１０２２ 導電性粒子
１０３ 現像装置
１０３ａ トナー
１０３ｂ 現像スリーブ
１０３ｃ マグネットロール
１０３ｄ 規制ブレード
１０４ 転写装置
１０５ 定着装置
１０６ プロセスカートリッジ
１０７ クリーニング装置
１０８ 導電性粒子供給手段
１０８１ 導電性粒子供給部材
１０８２ 該導電性粒子供給部材の支持体１０８２
１０８３ 導電性粒子供給部材を収容させたハウジング
１０Ａ 電子写真感光体の回転方向
１０Ｂ 帯電ローラーの回転方向
１０Ｌ 露光光
１０Ｐ 転写材
１０Ｓ１ 帯電用電源
１０Ｓ２ 現像用電源
１０Ｓ３ 転写用電源
２０１ 電子写真感光体
２０２１ 帯電ローラー
２０２１ａ 中抵抗層
２０２１ｂ 中抵抗層
２０２２ 導電性粒子
２０３ 現像装置
２０３ａ トナー
２０３ｂ 現像スリーブ
２０３ｃ マグネットロール
２０３ｄ 規制ブレード
２０４ 転写装置
２０５ 定着装置
２０６ プロセスカートリッジ
２０Ａ 電子写真感光体の回転方向
２０Ｂ 帯電ローラーの回転方向
２０Ｌ 露光光
２０Ｐ 転写材
２０Ｓ１ 帯電用電源
２０Ｓ２ 現像用電源
２０Ｓ３ 転写用電源
３０１ 電子写真感光体
３０２１ 帯電ローラー
３０２１ｂ 中抵抗層
３０２２ 導電性粒子
３０３ａ トナー
３０Ａ 電子写真感光体の回転方向
３０Ｂ 帯電ローラーの回転方向
３０Ｃ 中抵抗層表面の突起の広がり方向
Ｎｕ 接触部上流の領域
４０１ 電子写真感光体
４０２１ 帯電ローラー
４０２１ｂ 中抵抗層
４０２２ 導電性粒子
４０３ａ トナー
４０Ａ 電子写真感光体の回転方向
４０Ｂ 帯電ローラーの回転方向
４０Ｃ 中抵抗沿う表面の突起の広がり方向
Ｎｄ 接触部下流の領域
５０１１ 支持体
５０１２ 下引き層
５０１３ 正電荷注入防止層
５０１４ 電荷発生層
５０１５ 電荷輸送層
６０１１ 支持体
６０１２ 下引き層
６０１３ 正電荷注入防止層
６０１４ 電荷発生層
６０１５ 電荷輸送層
６０１６ 電荷注入層
６０１６ａ 超微粒子
７０Ａ 接触帯電
７０Ｂ 直接注入帯電[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a charging device such as a copying machine or a printer, a process cartridge and an image forming apparatus having the charging device, and a roller-shaped charging member for the charging device.
[0002]
[Prior art]
In recent years, there are advantages such as low ozone and low power compared to corona charging devices. Therefore, a contact-type charging device (contact charging) that charges a charged object by contacting a charged member to which a voltage is applied to the charged object. Apparatus) has been put into practical use.
[0003]
The contact charging device contacts a charged member such as an image carrier with a conductive charging member such as a roller type (charging roller), a fur brush type, a magnetic brush type or a blade type, and this charging member (contact charging member) ) Is applied with a predetermined charging bias to charge the surface of the object to be charged to a predetermined polarity and potential.
[0004]
There are two types of contact charging mechanism (charging mechanism, charging principle): (1) discharge charging mechanism and (2) direct injection charging mechanism, depending on which is dominant. Each characteristic appears. FIG. 7 shows typical charging characteristics of each.
[0005]
(1) Discharge charging mechanism
This is a mechanism for charging the surface of the member to be charged by a discharge phenomenon that occurs in a minute gap between the contact charging member and the member to be charged.
[0006]
Since a discharge charging system such as corona charging has a constant discharge threshold value for the contact charging member and the member to be charged, it is necessary to apply a voltage larger than the charging potential to the contact charging member. Moreover, since the generation amount is remarkably smaller than that of a corona charging device, it is unavoidable in principle to generate a discharge product, and thus harmful effects due to active ions such as ozone are unavoidable.
[0007]
Among contact charging methods, a roller charging method using a charging roller as a contact charging member is preferable in terms of charging stability and is widely used, but in this roller charging, the charging mechanism is dominated by the discharge charging mechanism. is there.
[0008]
That is, the charging roller is manufactured using a conductive or medium resistance rubber material or foam. There are also those obtained by laminating these to obtain desired characteristics. The charging roller has elasticity to obtain a certain contact with the member to be charged, but has a large frictional resistance, and is often driven by the member to be charged or with a slight speed difference. Therefore, a non-contact state is unavoidable due to uneven shape on the roller and deposits on the object to be charged, so in conventional roller charging, the charging mechanism is dominant in the charging mechanism.
[0009]
More specifically, when the charging roller is pressed and brought into contact with an organic electrophotographic photosensitive member having a photosensitive layer thickness of 25 μm as a member to be charged, When a voltage of about 640 V or higher is applied, the surface potential of the electrophotographic photosensitive member starts to rise, and thereafter, the surface potential of the electrophotographic photosensitive member increases linearly with a slope of 1 with respect to the applied voltage.
[0010]
Hereinafter, this threshold voltage is defined as a charging start voltage (Vth) (dotted line 70A in FIG. 7).
[0011]
That is, in order to obtain the surface potential Vd of the electrophotographic photosensitive member required for electrophotography, the charging roller requires a DC voltage higher than that required, that is, Vd + Vth. A method for charging the image carrier by applying only the DC voltage to the contact charging member in this way is generally called a “DC charging method”.
[0012]
However, in the DC charging method, the resistance of the contact charging member fluctuates due to environmental fluctuations, etc., and Vth fluctuates when the thickness of the photosensitive layer changes due to the electrophotographic photosensitive member being scraped off. It was difficult to set the potential of the electrophotographic photosensitive member to a desired value.
[0013]
For this reason, as disclosed in Japanese Patent Laid-Open No. 63-149669, etc., in order to further equalize the charging, an AC having a peak-to-peak voltage more than twice Vth to a DC voltage corresponding to a desired Vd. A method generally referred to as an “AC charging method” is used in which an oscillating voltage in which components are superimposed is applied to a contact charging member to charge an object to be charged. This is for the purpose of smoothing the potential due to AC, and the potential of the charged body converges to Vd, which is the center of the peak of the AC voltage, and is not affected by disturbances such as the environment.
[0014]
However, even in such a contact charging device, the essential charging mechanism uses a discharge phenomenon from a charging member to an object to be charged. Therefore, as described above, the voltage required for charging is ( A value of (image carrier surface potential + discharge threshold value or more) is required, and a small amount of discharge product such as ozone is generated.
[0015]
In addition, when AC charging is performed for uniform charging, further generation of discharge products such as ozone, vibration noise (AC charging sound) between the contact charging member and the object to be charged due to the electric field of AC voltage, As a result, the deterioration of the surface of the member to be charged due to the discharge becomes remarkable, which is a new problem.
[0016]
(2) Direct injection charging mechanism
On the other hand, the direct injection charging mechanism is a mechanism for charging the surface of a charged body by directly injecting a charge from a contact charging member to the charged body, and is disclosed in Japanese Patent Laid-Open No. 6-3921, etc. .
[0017]
The medium-resistance contact charging member comes into contact with the surface of the member to be charged and directly injects charges into the surface of the member to be charged without going through a discharge phenomenon, that is, basically without using a discharge mechanism. Therefore, even if the voltage applied to the contact charging member is equal to or lower than the discharge threshold, the object to be charged can be charged to a potential corresponding to the applied voltage (solid line 70B in FIG. 7). Since this direct injection charging mechanism does not involve the generation of ions, no adverse effect due to the generation of discharge occurs.
[0018]
More specifically, a voltage is applied to a contact charging member such as a charging roller, a charging brush, or a charging magnetic brush, and a trap level on the surface of an object to be charged (image carrier) or conductive particles of a charge injection layer, etc. This mechanism directly injects and charges by injecting charges into the charge holding member. Since the discharge phenomenon is not dominant, the voltage required for charging is only the desired image carrier surface, and there is no generation of discharge products such as ozone.
[0019]
In particular, when the contact charging member is a porous roller such as a sponge roller coated with conductive fine particles, the contact between the contact charging member and the object to be charged can be made extremely dense. It was easy to obtain good chargeability.
[0020]
Furthermore, by rotating the charging member with a speed difference with respect to the surface of the object to be charged, there is no generation of discharge products such as ozone, and better chargeability can be obtained even in the injection charging which is a contact charging with a simple configuration. I was able to get it.
[0021]
[Problems to be solved by the invention]
However, even with such a configuration, the charging performance may deteriorate due to the toner passing through the cleaning gradually accumulating on the charging roller. In particular, a so-called cleaner that does not have an independent cleaning means for collecting and storing toner (transfer residual toner) remaining on a charged body after transfer before primary charging after transfer, and the developing means also serves as a substantial cleaning means. In the case of the less system, the accumulation of the transfer residual toner on the surface of the charging roller is more remarkable, and thus the charging performance is very easily deteriorated.
[0022]
Therefore, as a method for improving the above-mentioned problems, JP 2001-188404 A has a concave hole (cell) on the surface of the charging roller, and the edge length of the hole (cell) is 15 mm / mm. ² ~ 60mm / mm ² It is disclosed that the charging performance is improved. However, when charging is performed for a long time, further improvement in charging performance is required.
[0023]
An object of the present invention is to provide a contact charging type charging device which is excellent in charging uniformity and hardly generates discharge products such as ozone.
[0024]
Another object of the present invention is to use an injection charging method, which is a contact charging method, to maintain a stable charging performance even in long-term use, and to obtain a good image without uneven charging even in long-term printing. It is to provide a forming apparatus.
[0025]
[Means for Solving the Problems]
That is, the present invention is a charging device that charges a surface of a charged body by bringing a roller-shaped charging member to which a voltage is applied into contact with the charged body, and the surface layer of the charging member is an elastic foam, In the charging device in which the surface of the charging member has a speed difference with respect to the surface of the member to be charged, and conductive particles exist on the contact surface between the charging member and the member to be charged.
The porosity of the surface of the charging member is 50% or more and 90% or less,
The average pore diameter of the pores on the surface of the charging member is 5 μm or more and 150 μm or less.
This is a charging device.
[0026]
In addition, the present invention integrally supports an electrophotographic photosensitive member and a charging device that charges a surface of a member to be charged by bringing a roller-shaped charging member to which a voltage is applied into contact with the electrophotographic photosensitive member to form an image. A process cartridge that is detachable from the apparatus main body, wherein the surface layer of the charging member is an elastic foam, and the surface of the charging member has a speed difference with respect to the surface of the electrophotographic photosensitive member. In the process cartridge in which conductive particles exist on the contact surface between the charging member and the electrophotographic photosensitive member,
The porosity of the surface of the charging member is 50% or more and 90% or less,
The average pore diameter of the pores on the surface of the charging member is 5 μm or more and 150 μm or less.
This is a process cartridge.
[0027]
The present invention also provides an electrophotographic photosensitive member, a charging device for charging a surface of an object to be charged by bringing a roller-shaped charging member to which a voltage is applied into contact with the electrophotographic photosensitive member, and static exposure to the electrophotographic photosensitive member by exposure. An image forming apparatus comprising: an exposure unit that forms an electrostatic latent image; a developing unit that visualizes the electrostatic latent image with a developer; and a transfer unit that transfers an image visualized by the developing unit to a transfer material. The surface layer of the member is an elastic foam, the surface of the charging member has a speed difference with respect to the surface of the electrophotographic photosensitive member, and the contact surface between the charging member and the electrophotographic photosensitive member is electrically conductive. In an image forming apparatus in which particles exist,
The porosity of the surface of the charging member is 50% or more and 90% or less,
The average pore diameter of the pores on the surface of the charging member is 5 μm or more and 150 μm or less.
An image forming apparatus characterized by the above.
[0028]
The present invention also relates to a roller-shaped charging member for a charging device in which a roller-shaped charging member to which a voltage is applied is brought into contact with the member to be charged to charge the surface of the member to be charged, the surface layer of the charging member Is an elastic foam, the surface of the charging member has a speed difference with respect to the surface of the member to be charged, and the charging member and the member to be charged have conductive particles on the contact surface. In the roller-shaped charging member of
The surface porosity is 50% or more and 90% or less,
The average pore diameter of the surface pores is 5 μm or more and 150 μm or less,
This is a roller-shaped charging member.
[0029]
DETAILED DESCRIPTION OF THE INVENTION
In the present invention, a charging device is used that charges a surface of a member to be charged by bringing a roller-shaped charging member (charging roller) having a surface layer made of an elastic foam into contact with the member to be charged.
[0030]
Examples of the charged body whose surface is charged by the charging device of the present invention include an image carrier used in an electrophotographic apparatus, an electrostatic recording apparatus, a magnetic recording apparatus, and the like. When the electrophotographic photosensitive member used as the photosensitive member is applied as the member to be charged of the present invention, the effects of the present invention are particularly remarkably exhibited.
[0031]
The porosity of the surface of the charging member is 50% or more and 90% or less, but is particularly preferably 60% or more, and more preferably 70% or more. If it is less than 50%, the movement of the surface of the charging member is not dynamic, and when applied to electrophotography, the developer (toner) friction becomes insufficient. On the other hand, if it exceeds 90%, the material as the skeleton is reduced, and it becomes difficult for the foam to maintain the performance as the charging member.
[0032]
Further, in the cleanerless image forming apparatus described later, since the amount of transfer residual toner mixed into the charging device is large, if the porosity of the roller surface is less than 50%, the transfer residual toner cannot be retained sufficiently, and the transfer residual toner In some cases, the triboelectric charging of the resin becomes insufficient.
[0033]
The porosity of the surface of the charging member in the present invention is calculated by the area ratio of the hole portion and the portion other than the hole in the enlarged photograph (magnification 200 times) of the surface of the charging member.
[0034]
The average hole diameter of the holes on the surface of the charging member is 5 μm or more and 150 μm or less. When it is applied to electrophotography, if it is less than 5 μm, the developer (toner) and conductive particles cannot be sufficiently carried in the pores, and the chance of obtaining friction is reduced. Sufficient charge cannot be obtained by passing through the contact portion with the photoreceptor. On the other hand, when the thickness exceeds 150 μm, the contact uniformity with the electrophotographic photosensitive member becomes insufficient, and sufficiently uniform injection charging cannot be performed.
[0035]
Further, when the charging member is used in a cleaner-less image forming apparatus having a developing means that also serves as a means for collecting the developer remaining on the electrophotographic photosensitive member, which is a member to be charged, 20 μm or more and 100 μm or less is preferable. If it is less than 20 μm, it is difficult to sufficiently carry the transfer residual toner and conductive particles in the pores, the chance of obtaining friction is reduced, and the toner is sufficiently charged by passing through the contact portion between the roller and the drum once. It becomes difficult. In addition, since there is a large amount of untransferred toner in the cleaner-less configuration, if the hole diameter exceeds 100 μm, the contact uniformity with the electrophotographic photosensitive member becomes insufficient, and uniform injection charging becomes difficult.
[0036]
Examples of a method for obtaining such a foam having pores include the following method.
[0037]
A foam can be obtained by mixing particles soluble in a liquid with a polymer substance whose resistance has been adjusted in advance, forming the mixture, and then leaving it in the liquid to elute the soluble particles.
[0038]
Further, the resistance can be adjusted in advance, and a liquid polymer material containing a foaming agent can be poured into the mold and foamed to obtain a foam.
[0039]
Also, a foam can be obtained by mixing foamed particles in a polymer material to obtain a foam, or generating bubbles while stirring a liquid polymer material.
[0040]
Among these methods, the elution method makes it easy to obtain the desired pore size by adjusting the particle size of the particles to be eluted, and the method using a capsule also adjusts the pore size with the size of the capsule. Is easy.
[0041]
For the measurement of the hole diameter on the surface of the charging roller, 100 or more were extracted from observation with an optical or electron microscope, the hole diameter was calculated with the maximum chord length, and the average diameter on the basis of the number was defined as the average hole diameter.
[0042]
In addition, it is very difficult to form all the holes on the surface of the charging member in a perfect circle (average long / short axis ratio b / a = 1). In practice, the average long / short axis ratio b / a <1. Only the surface of the charging member can be obtained. However, from the viewpoint of injection charging properties, it is preferable that the holes are closer to a perfect circle, and specifically, the average major / minor axis ratio b / a is preferably 0.2 or more.
[0043]
Here, the average major / minor axis ratio b / a is defined as follows in the present invention.
[0044]
From observation with an optical or electron microscope, 100 or more holes are extracted, the maximum chord length of each hole is a, the minimum width of the ferret diameter is b, and the long / short axis ratio b / a is calculated. Was the average major / minor axis ratio b / a.
[0045]
Among the methods described above, the method using a capsule and the method of foaming in a mold tend to form pores having a shape that is relatively close to a perfect circle.
[0046]
As described above, the charging device of the present invention has a roller-shaped charging member (charging roller), and for the purpose of promoting charging, conductive particles are present on the contact surface between the charging member and the object to be charged. Yes. Conductive particles are coated on the surface of the charging roller in advance, and a charged object such as an electrophotographic photosensitive member is charged while the conductive particles are supported. Since conductive particles are interposed between the charging roller and the member to be charged and a speed difference is provided between them, high contactability can be obtained. For example, it is possible to adopt a configuration in which a speed difference is provided between the electrophotographic photosensitive member and the charging member by rotating or fixing the charging roller. The rotation direction of the charging member is preferably configured to be opposite to the moving direction of the surface of the electrophotographic photosensitive member.
[0047]
It is important that the charging roller functions as an electrode. In other words, it is necessary to have a sufficiently low resistance for charging a charged object such as an electrophotographic photosensitive member while at the same time providing elasticity and a sufficient contact state. On the other hand, when a defective portion such as a pinhole is present in the electrophotographic photosensitive member, it is necessary to prevent voltage leakage. Therefore, to obtain sufficient chargeability and leakage resistance, 10 ⁴ -10 ⁷ A resistance of Ω is preferred.
[0048]
The resistance of the charging roller was measured by applying 100 V to the core metal and the aluminum drum in a state where the core metal of the charging roller having a length of 200 mm was pressure-bonded to the aluminum drum with a diameter of 30 mm so that a total pressure of 1 kg was applied.
[0049]
If the hardness of the charging roller is too low, the shape will not be stable and the contact will be poor.If the hardness is too high, the contact portion between the charging roller and the charged object such as an electrophotographic photosensitive member cannot be secured. Since the micro contact property to the surface of the charged body is deteriorated, the preferred Asker C hardness is 25 to 50 degrees.
[0050]
When the charged body charged by the charging roller is an electrophotographic photosensitive member, usually a rubber elastic body, a foaming agent, a conductivity imparting agent, and, if necessary, a vulcanizing agent, a vulcanization accelerator, oil, It can be produced by forming into a roller shape using a so-called conductive rubber foam-forming material containing a rubber additive such as a plasticizer, zinc white, stearic acid, calcium carbonate, and magnesia.
[0051]
Examples of the rubber elastic body include EPDM rubber (ethylene propylene diene rubber), urethane rubber, nitrile rubber, silicone rubber, chloroprene rubber, epichlorohydrin rubber, butadiene rubber, styrene butadiene rubber, isoprene rubber, natural rubber, butyl rubber, and acrylic rubber. These may be used, and these may be used alone or in combination of two or more.
[0052]
The foaming agent can be appropriately selected from known inorganic foaming agents and organic foaming agents. Here, examples of the inorganic foaming agent include sodium hydrogen carbonate, ammonium hydrogen carbonate, sodium borohydride, and the like, and examples of the organic foaming agent include azodicarbonamide, azobisisobutyronitrile, barium azo Examples thereof include dicarboxylate, dinitropentamethylenetetramine, p, p′-oxybis (benzenesulfonylhydrazide), p-toluenesulfonylhydrazide and the like. These foaming agents may be used alone or in combination of two or more.
[0053]
Examples of the conductivity imparting agent include carbon black; metal powder such as nickel and copper; metal oxide powder such as tin oxide, titanium oxide and zinc oxide; and other conductive metal double oxide powder; It can be appropriately selected from ionic conductive agents such as chlorate, alkyl sulfate, carboxylate, and borofluoride. These conductivity-imparting agents may be used alone or in combination of two or more. Moreover, the compounding quantity can be suitably selected according to the kind of electroconductivity imparting agent so that the electroconductive rubber foam which has a desired specific resistance value is obtained.
[0054]
By appropriately selecting the type of material such as the foaming agent, foaming conditions, and the like, a charging roller having a predetermined hole on the surface can be formed.
[0055]
Moreover, in order to give the above-mentioned specific hole diameter to the charging roller, it can be formed by pouring material into a mold that can obtain a predetermined hole without using a foaming agent, but it gives elasticity to the entire charging roller. In order to do so, the method of producing using the said foaming agent is preferable.
[0056]
By adopting such a configuration, it was possible to obtain a high charging efficiency that could not be obtained by a method in which the surface of the charged body was charged by a discharge phenomenon that occurred in a minute gap between the contact charging member and the charged body, and applied to the charging member. A potential substantially equal to the potential can be applied to the photosensitive drum. As the bias necessary for charging, a voltage corresponding to the potential required for the electrophotographic photosensitive member is sufficient, and a stable and safe charging method using no discharge phenomenon is realized.
[0057]
The resistance value of the conductive particles used in the present invention is 1 × 10 in order to transfer charges through the particles. ¹² It is preferable that it is below Ω · cm.
[0058]
In the present invention, the resistance value is obtained by measuring and normalizing by the tablet method. Bottom area 2.26cm ² A 0.5 g powder sample was placed in the cylinder, and 15 kg of pressure was applied to the upper and lower electrodes. At the same time, a voltage of 100 V was applied, and the resistance value was measured.
[0059]
The particle diameter of the conductive particles is preferably not more than the hole diameter of the holes on the surface of the charging member in order to obtain good charging uniformity, and more preferably not more than 1/10 of the hole diameter.
[0060]
In order to obtain particles stably, the average particle size is preferably 10 nm or more, and more preferably 1/100 or more of the pore diameter in order to maintain good charging performance over long-term image formation. Is preferred.
[0061]
Further, the conductive particles are applied to an image forming apparatus having an exposure unit that scans and exposes a laser beam capable of digital exposure for each pixel to form an electrostatic latent image on the surface of an electrophotographic photosensitive member that is a charged body. When used, it is preferable that the average particle diameter of the conductive particles is not more than the diameter of one pixel. If it is larger than one pixel, light scattering by particles may occur during image exposure.
[0062]
In the present invention, the pixel size is obtained by dividing 1 inch by the resolution (DPI). For example, in the case of an image forming apparatus of 600 DPI, since 1 inch = 25400 μm, the pixel size in this image forming apparatus is
25400/600 = 42.33 μm
It becomes.
[0063]
In the present invention, the particle diameter when the particles constitute an aggregate is defined as the average particle diameter of the aggregate.
[0064]
For the measurement of the average particle diameter, 100 or more samples were extracted from observation with an optical or electron microscope, the particle diameter was calculated with the maximum chord length, and the average diameter based on the number was defined as the average particle diameter.
[0065]
Examples of the material for the conductive particles include conductive inorganic particles such as metal oxides and mixtures with organic substances, and various conductive particles obtained by subjecting them to surface treatment can be used.
[0066]
Furthermore, when the charging device is applied to electrophotography, colorless or white conductive particles are preferable in order not to disturb the latent image exposure.
[0067]
In particular, in the case of color image formation, colorless or white conductive particles are preferable in consideration of partial transfer of the conductive particles from the electrophotographic photosensitive member to the recording paper.
[0068]
In the present invention, as described above, the charging roller having the specific holes on the surface is used, a speed difference is provided between the charging roller and the member to be charged, and the contact surface between the charging roller and the member to be charged is provided. The above-mentioned effects can be obtained by the presence of conductive particles, and as long as these conditions are satisfied, the method and material for forming the charging roller, the type of conductive particles, etc. are not limited at all. Absent.
[0069]
On the other hand, the volume resistance value of the surface layer of the member to be charged used in the present invention is 1 × 10 in order to exchange charges through particles. ¹⁴ Ω · cm or less is preferable, and when the object to be charged is an electrophotographic photosensitive member that is an image carrier, it is necessary to hold the electrostatic latent image for a certain period of time. ⁹ It is preferable that it is Ω · cm or more.
[0070]
FIG. 1 shows a schematic configuration of an apparatus using a process cartridge having a charging device of the present invention.
[0071]
The image forming apparatus shown in FIG. 1 includes a charging device 2, an exposure light L, a developing device 3, a transfer charging device 4, a fixing device 5, and a cleaning device 7 arranged around the electrophotographic photoreceptor 1. Here, the photosensitive drum 1, the charging device 2, the developing device 3, and the cleaning device 7 are configured to be included in an integrated cartridge 6.
[0072]
The charging roller 1021 is manufactured by forming a middle resistance layer 1021b of an elastic foam on a cored bar 1021a, and conductive particles 1022 are coated on the surface in advance by the conductive particle supplying means 108. .
[0073]
The conductive particle supply means 108 includes a conductive particle supply member 1081, a support 1082 for the conductive particle supply member, a housing 1083 in which the conductive particle supply member is accommodated, and the like above the charging roller 1021. It is arranged so that the lower surface of the conductive particle supply member 1081 in the housing 1083 can be brought into contact with and separated from the upper surface of the charging roller 1021.
[0074]
The contact and separation of the conductive particle supply member 1081 can be performed by a cam type, an electromagnetic coil type, or the like, and the conductive particle supply member 1081 is formed within a certain time during which the charging roller 1021 rotates one or more times during non-image formation. In contact with the charging roller 1021 by a cam to supply particles. The conductive particles 1022 are supplied at the time of non-image formation. If the conductive particles 1022 are supplied at the time of image formation, the conductive particles 1022 are transferred from the charging roller 1021 onto the electrophotographic photosensitive member 101 when the conductive particles are excessively supplied. However, this is because there are problems such as light shielding in the exposure part and development leak in the development part. The conductive particle supply member 1081 is a member (conductive particle chip) obtained by binding and solidifying the conductive particles 1022 in a chip shape, and can be shaved like white ink by contact with the rotating charging roller 1021. A member that supplies and supplies conductive particles 1022 to the surface of the charging roller 1021.
[0075]
By carrying the conductive particles 1022 on the surface of the charging roller 1021, the driving torque with the electrophotographic photosensitive member can be reduced, and a speed difference can be provided between the charging roller 1021 and the electrophotographic photosensitive member. Due to this speed difference, high contact can be obtained between the conductive particles on the surface of the charging roller and the electrophotographic photosensitive member. As a specific configuration, the charging roller is rotationally driven or fixed to provide a speed difference between the electrophotographic photosensitive member and the charging roller.
[0076]
Hereinafter, the speed difference will be described.
[0077]
In the present invention, the speed difference is defined by the peripheral speed ratio as follows.
[0078]
[Outside 1]

[0079]
When the charging roller is driven to rotate with respect to the electrophotographic photosensitive member, there is no speed difference between both surfaces. The charging roller peripheral speed is positive when moving in the same direction as the photosensitive member peripheral speed.
[0080]
The speed difference is preferably −400% or more and less than −100%. When the speed difference is less than −400%, the life of the charged body may be shortened by rubbing between the charging roller and the charged body, and the speed difference is −100%, that is, the charging roller does not rotate. In addition, paper dust and remaining toner are likely to be deposited on the portion (nip portion) where the charging roller and the member to be charged are in contact, and charging failure may occur.
[0081]
By adopting the above configuration, it is possible to obtain high charging efficiency that cannot be obtained by conventional roller charging, and to apply a potential substantially equal to the potential applied to the charging member to the photosensitive drum. As the bias necessary for charging, a voltage corresponding to the potential required for the photosensitive drum is sufficient, and a stable and safe charging method using no discharge phenomenon is realized.
[0082]
As described above, the electrophotographic photosensitive member 101 whose surface is uniformly charged by the charging roller 1021 is then subjected to time series electricity of target image information output from exposure means (not shown) such as slit exposure or laser beam scanning exposure. The exposure light 10L that is enhanced and modulated corresponding to the digital image signal is received. In this way, electrostatic latent images corresponding to target image information are sequentially formed on the peripheral surface of the electrophotographic photosensitive member 101.
[0083]
The formed electrostatic latent image is then developed with toner by the developing device 103. The developing device 103 includes a developing sleeve 103b including a magnet roll 103c and a regulating blade 103d. The toner 103a in the developing device is subjected to layer thickness regulation and charge application by the regulation blade 103d in the process of being conveyed on the sleeve, introduced into the development site, and an electrostatic latent image formed on the electrophotographic photosensitive member 101. develop.
[0084]
Next, the electrophotographic photosensitive member is transferred to the transfer material 10P, which is taken out from the paper feeding unit (not shown) between the electrophotographic photosensitive member 101 and the transfer device 104 in synchronization with the rotation of the electrophotographic photosensitive member 101 and fed. The toner images formed and supported on the surface 101 are sequentially transferred by the transfer device 104.
[0085]
The transfer material 10P that has received the transfer of the toner image is separated from the surface of the electrophotographic photosensitive member, introduced into the fixing device 105, and subjected to image fixing, thereby being printed out as an image formed product (print, copy).
[0086]
The surface of the electrophotographic photosensitive member 101 after the image transfer is cleaned by the cleaning device 107 after the transfer residual toner is removed, and used repeatedly for image formation.
[0087]
In the present invention, the charging unit of the present invention and a plurality of components such as the electrophotographic photosensitive member 101, the developing device 103, and the cleaning device 107 are housed in a container and integrally coupled as a process cartridge 106. The process cartridge 106 may be configured to be detachable from an electrophotographic apparatus main body such as a copying machine or a laser beam printer. For example, the charging device of the present invention and the electrophotographic photosensitive member 101 are integrally supported to form a cartridge, and the process cartridge 106 is detachably attached to the apparatus main body using guide means (not shown) such as a rail of the apparatus main body. be able to.
[0088]
Further, when the electrophotographic apparatus is a copying machine or a printer, the exposure light 10L is a reflected light or transmitted light from the original, or a signal read from the original by a sensor and converted into a signal. The light is emitted by scanning, driving the LED array, driving the liquid crystal shutter array, and the like.
[0089]
FIG. 2 shows another schematic configuration of an electrophotographic apparatus using a process cartridge having the charging device of the present invention.
[0090]
The image forming apparatus shown in this figure is a cleanerless image forming apparatus that enables toner recycling without being equipped with a cleaning device.
[0091]
The image forming apparatus shown in FIG. 1 is different from the image forming apparatus shown in FIG. 1 in that it does not have a conductive particle supply device but instead has a developer (toner) containing conductive particles.
[0092]
This eliminates the need for a device for supplying conductive particles, and can realize a simple configuration, thereby reducing the device cost.
[0093]
In the figure, reference numeral 201 denotes an electrophotographic photosensitive member as a member to be charged, which is rotationally driven in the direction of arrow 20A at a predetermined peripheral speed. In the rotating process, the electrophotographic photosensitive member 201 is charged uniformly on the peripheral surface with the charging roller 2021 of the charging device of the present invention and the conductive particles 2022 for the purpose of promoting charging at substantially the same potential as the voltage applied to the charging device. receive.
[0094]
The charging roller 2021 is manufactured by forming an intermediate resistance layer 2021b of an elastic foam on a core metal 2021a.
[0095]
The electrophotographic photosensitive member 201 whose surface is uniformly charged by the charging roller 2021 is then converted into a time-series electric digital image signal of target image information output from exposure means (not shown) such as slit exposure or laser beam scanning exposure. Correspondingly enhanced exposure light 20L is received. In this way, electrostatic latent images corresponding to target image information are sequentially formed on the peripheral surface of the electrophotographic photosensitive member 201.
[0096]
The formed electrostatic latent image is then developed with toner by the developing device 203. The developing device 203 includes a developing sleeve 203b including a magnet roll 203c and a regulating blade 203d. The toner 203a in the developing device is subjected to layer thickness regulation and charge application by the regulation blade 203d in the process of being conveyed on the sleeve, introduced into the development site, and an electrostatic latent image formed on the electrophotographic photosensitive member 201 is formed. develop.
[0097]
The toner 203a contains conductive particles 2022, and the conductive particles 2022 supplied together with the toner 203a from the developing device 203 move to the surface of the electrophotographic photosensitive member 201 and are then supplied to the charging device. .
[0098]
Next, the electrophotographic photosensitive member is transferred to the transfer material 20 </ b> P that is taken out from the paper feeding unit (not shown) between the electrophotographic photosensitive member 201 and the transfer device 204 in synchronization with the rotation of the electrophotographic photosensitive member 201 and fed. The toner images formed and supported on the surface 201 are sequentially transferred by the transfer device 204.
[0099]
The transfer material 20P that has received the transfer of the toner image is separated from the surface of the electrophotographic photosensitive member, introduced into the fixing device 205, and subjected to image fixing to be printed out as an image formed product (print, copy).
[0100]
In the present invention, the charging unit of the present invention and a plurality of components such as the electrophotographic photosensitive member 201 and the developing device 023 are housed in a container and integrally combined as a process cartridge 206, and this process is performed. The cartridge 206 may be configured to be detachable from an electrophotographic apparatus main body such as a copying machine or a laser beam printer. For example, the charging device of the present invention and the electrophotographic photosensitive member 201 are integrally supported to form a cartridge, and the process cartridge 206 is detachably attached to the apparatus main body using guide means (not shown) such as a rail of the apparatus main body. be able to.
[0101]
Further, when the electrophotographic apparatus is a copying machine or a printer, the exposure light 20L is a reflected light or transmitted light from a document, or a signal is read from a document by a sensor, and a laser beam performed in accordance with this signal. Light emitted by scanning, driving of the LED array, driving of the liquid crystal shutter array, and the like.
[0102]
Now, the image obtained on the electrophotographic photosensitive member by the development is transferred onto the transfer material, but a part of the toner remains on the electrophotographic photosensitive member as a transfer residue. Conventionally, since toner is an insulator, significant charging failure occurs in charging the electrophotographic photosensitive member.
[0103]
However, in the image forming apparatus shown in FIG. 2, there are conductive particles applied in advance on the surface of the charging roller 2021 and conductive particles supplied together with the toner 203 a from the charging device. Even when toner is mixed in the charging device, the contact property and contact resistance to the electrophotographic photosensitive member can be maintained by the presence of the conductive particles, so that charging by direct injection can be performed.
[0104]
The mixed transfer residual toner does not enter the charging roller 2021, and is charged to a proper polarity by friction with the electrophotographic photosensitive member 201 and the conductive particles 2022, and is discharged from the surface of the charging roller 2021. Then, it is recovered or developed again by the developing device in the next development step.
[0105]
By repeating the above steps, the surface of the charging roller is always in a state where contact charging can be performed stably while enabling toner recycling, so that a uniform chargeability can be obtained over a long period and a good image can be maintained. .
[0106]
The configurations of the process cartridge and the image forming apparatus of the present invention are not limited to these.
[0107]
Next, the movement of toner on the surface of the charging roller will be described with reference to FIGS. Here, the toners 303a and 403a are displayed in a larger size for easy understanding.
[0108]
In FIG. 3, the toner 303 a that has passed through the cleaning and the conductive particles 3022 remaining on the electrophotographic photosensitive member 301 are placed in the region Nu upstream of the contact portion between the charging roller 3021 and the electrophotographic photosensitive member 301. It enters in the direction of arrow 30A, which is the rotation direction of 301. On the other hand, since the charging roller 3021 rotates in the direction of the arrow 30B, the protrusion on the surface of the sponge-like medium resistance layer 3021b of the charging roller 3021 spreads in a form in which the pressure is released in the direction of the arrow 30C. Occasionally, the toner 303a and the conductive particles 3022 on the electrophotographic photosensitive member 301 are rubbed to charge the toner to the charge amount that the toner should have. Therefore, the toner movement increases as the porosity increases and the hole diameter increases.
[0109]
FIG. 4 shows a state downstream of the contact portion between the charging roller 4021 and the electrophotographic photosensitive member 401. The sponge-like medium resistance layer 4021b of the charging roller 4021 enters the contact portion downstream region Nd between the charging roller 4021 and the electrophotographic photosensitive member 401 while moving in the direction of the arrow 40B. Here, since the toner is sufficiently charged, the toner is discharged onto the electrophotographic photosensitive member 401 by a small potential difference between the charging roller 4021 and the electrophotographic photosensitive member 401, and the holes on the surface of the charging roller 4021 are indicated by arrows. The toner is crushed in the direction of 40C, the toner inside is also discharged, moves to the surface of the electrophotographic photosensitive member 401, and is collected by the developing device. An arrow 40 </ b> A is the rotation direction of the electrophotographic photosensitive member 401.
[0110]
FIG. 5 shows an example of the layer structure of the electrophotographic photosensitive member.
[0111]
The electrophotographic photosensitive member illustrated in this figure is generally applied by laminating an undercoat layer 5012, a positive charge injection preventing layer 5013, a charge generation layer 5014, and a charge transport layer 5015 in this order on a support 5011 such as aluminum. Organic electrophotographic photoreceptor.
[0112]
FIG. 6 shows an example of the layer structure of an electrophotographic photosensitive member having a charge injection layer on the surface.
[0113]
Next, an electrophotographic photosensitive member with improved injection charging efficiency will be described with reference to FIG.
[0114]
Specifically, charging is performed more stably and uniformly by adjusting the resistance of the surface layer of the electrophotographic photosensitive member. In other words, even when the performance of the charging device is deteriorated, charges are transferred more efficiently by setting the interposition of conductive particles and the surface resistance on the electrophotographic photosensitive member side to be low in a region where a latent image can be formed. . The charge injection layer will be described in detail below.
[0115]
FIG. 6 shows a cross-sectional view of the electrophotographic photosensitive member used in this example.
[0116]
The electrophotographic photosensitive member is a general organic electrophotographic photosensitive member in which an undercoat layer 6012, a positive charge injection preventing layer 6013, a charge generation layer 6014, and a charge transport layer 6015 are sequentially laminated on a support 6011 such as aluminum. An electrophotographic photoreceptor having improved charging performance by applying the charge injection layer 16 to the body drum was used.
[0117]
The charge injection layer is made of SnO on a photocurable acrylic resin. ₂ Ultrafine particles 16a (diameter of about 0.03 μm), a lubricant such as polytetrafluoroethylene, a polymerization initiator and the like are mixed and dispersed, and after coating, a film is formed by a photocuring method. The important point as the charge injection layer is the resistance of the surface layer. In the charging method using direct injection of charges, charges can be exchanged more efficiently by reducing the resistance on the photosensitive drum side. On the other hand, when used as an electrophotographic photosensitive member, the electrostatic latent image needs to be held for a certain period of time. ¹⁴ Ω · cm or less, especially 1 × 10 ⁹ ~ 1x10 ¹⁴ A range of Ω · cm is preferred. That is, even when the charge injection layer is not used, the same effect can be obtained when the outermost surface of the electrophotographic photosensitive member is in the resistance range. For example, the volume resistance of the surface layer is about 10 ¹³ A similar effect can be obtained by using an amorphous silicon electrophotographic photosensitive member of Ω · cm.
[0118]
【Example】
Hereinafter, the present invention will be described in more detail with reference to specific examples, but the present invention is not limited to these examples.
[0119]
(Example 1)
In this embodiment, image formation was performed using a modified machine obtained by modifying the following LBP-1760 (600 DPI) manufactured by Canon Inc., that is, an image forming apparatus having the configuration shown in FIG. The modified parts are a charging roller and conductive particle supply means.
(Before modification → After modification)
Charging member: EP-52 charging roller → charging roller of the present invention + conductive particles
Charging member drive: Followed by electrophotographic photoreceptor → peripheral speed difference
Particle supply means: None → With particle supply means
Note that EP-52 is a cartridge for the LBP 1760.
[0120]
The electrophotographic photosensitive member has a drum shape with a diameter of 30 mm, and rotates at a constant peripheral speed of 94 mm / s in the direction of an arrow 10A in FIG. The charging roller is driven at 150 rpm so that the roller surface moves at the same speed in the opposite direction to the electrophotographic photosensitive member. A DC voltage of -620 V was applied to the roller core.
[0121]
A charging roller was prepared by forming a medium resistance layer of an elastic foam on a SUS mandrel. The middle resistance layer was formulated with a urethane resin, carbon black as conductive particles, a foaming agent, and the like, and formed in a roller shape on the core metal. Thereafter, the surface was polished to prepare a charging roller having a diameter of 12 mm and a length in the busbar direction of 200 mm.
[0122]
In this example, the porosity of the charging roller surface was 57%, and the average pore diameter was 120 μm. The resistance of the charging roller was 100 kΩ.
[0123]
As the conductive particles, the volume resistance value is 10 ³ Conductive zinc oxide particles having an Ω · cm and an average particle size of 1.5 μm were uniformly applied to the surface of the charging roller.
[0124]
The conductive particles constitute an aggregate, and the particle diameter is the average particle diameter of the aggregate.
[0125]
As the conductive particle chip, a chip-shaped chip in which conductive particles are bound with a binder resin in a solvent was used. The specific prescription is as follows.
[0126]
A styrene acrylic resin as a binder resin was dissolved in ethanol at a concentration of 5% by mass, and zinc oxide particles having a mass seven times that of the binder resin were mixed. The solution was put into a mold, molded, and dried to obtain a conductive particle supply member in a form in which zinc oxide was bound and solidified in a chip shape.
[0127]
As the conductive particles for the chip, the resistance value is 3 × 10 ³ Conductive zinc oxide particles having an Ω · cm and an average particle diameter of 1.5 μm were used.
[0128]
The conductive chip used in this example has a block shape, and the cam-type mechanism comes into contact with the charging roller after completion of image formation, and is separated from the charging roller before starting image formation. Conductive particles are supplied to the surface.
[0129]
Image formation was performed in the above-described image forming apparatus, and image evaluation was performed after initial (first sheet), endurance of 100 sheets, endurance of 5000 sheets, and endurance of 10,000 sheets. The evaluation method is as follows.
[0130]
a) Fog evaluation
The fog is an image defect in which a toner is slightly developed in a white portion (unexposed portion) which is not originally printed, and appears like a background stain. If there is an insufficiently charged part, it becomes lower than the original potential, and the place appears as fog. The amount of fog is measured with an optical reflectance meter (TC-6DS, manufactured by Tokyo Denshoku Co., Ltd.), and the amount of fog is measured by subtracting the reflectance from the reflectance only on the recording paper and evaluated as the amount of fog. did. The fog amount was measured at 10 or more points on the recording paper, and the average value was obtained.
[0131]
The evaluation criteria are as follows.
A: The fog amount is less than 2%.
A ⁻ : The fog amount is 2 to 10%.
B: The fog amount exceeds 10%.
[0132]
b) Halftone image evaluation
The charging failure in the micro area, that is, the non-uniformity of charging, is more noticeable in the halftone than in the above-mentioned fog on the white background. Therefore, even if the fog on the white background is good, the black As a result, a charging failure may appear. Therefore, as an evaluation of charging uniformity, charging uniformity was evaluated with two different levels of halftone. The halftone used is 1 dot 2 space of 600 dpi horizontal line and 2 dots 3 space, and the unevenness of charging is more conspicuous in 1 dot 2 space.
[0133]
The evaluation criteria are as follows.
A: There are no black dots or black stripes in both 1 dot 2 space and 2 dot 3 space.
A ⁻ : There are no black dots or black stripes in 2 dots and 3 spaces, and there are almost no 1 dots and 2 spaces.
B: There are black dots or black stripes in both 1 dot 2 space and 2 dot 3 space.
Of the above evaluation criteria, B judged that the effects of the present invention were not sufficiently obtained.
[0134]
Table 1 shows the evaluation conditions and the evaluation results.
[0135]
(Examples 2-15, Comparative Examples 1-5)
Example 1 is the same as Example 1 except that the image forming apparatus, the presence or absence of the injection layer, the porosity and hole diameter of the charging roller, and the speed difference between the charging roller and the electrophotographic photosensitive member are as shown in Table 1.
[0136]
In Examples 10 to 15, image formation was performed using a modified machine obtained by modifying the following LBP-1760 (600 DPI) manufactured by Canon Inc., that is, an image forming apparatus having the configuration shown in FIG. . The modified parts are a charging roller and conductive particle supply means.
(Before modification → After modification)
Charging member: EP-52 charging roller → charging roller of the present invention + conductive particles
Charging member drive: Followed by electrophotographic photoreceptor → peripheral speed difference
Developer: EP-52 toner → EP-52 toner mixed with conductive particles
Cleaning: Yes → No
Note that EP-52 is a cartridge for the LBP 1760.
[0137]
Moreover, preparation of the charging rollers of Examples 1 to 15 and Comparative Examples 1 to 5 (adjustment of surface pore diameter and porosity) was performed by the following method.
Examples 1 and 6 to 15, Comparative Example 5
The resistance was adjusted with conductive carbon in advance, and liquid urethane containing a foaming agent was foamed in the form of a charging roller in the form of a core metal, and then surface polishing was performed. The pore diameter and porosity were adjusted by changing the amount and particle size of the foaming agent.
-Examples 2-5, Comparative Examples 1-4
Particles soluble in liquid were mixed with urethane resin whose resistance was adjusted with carbon in advance, molded into a tube shape, and then left in the liquid to elute soluble particles to obtain a tube-shaped foam. The core metal was press-bonded to the tube and the surface was polished. Here, the porosity was adjusted by changing the mixing amount of the soluble particles.
[0138]
In the image forming apparatus shown in FIG. 2 used in Examples 10 to 15, LBP-1760 and its cartridge EP-52 were modified as follows.
[0139]
Table 1 shows the evaluation conditions and the evaluation results.
[0140]
[Table 1]

[0141]
In this embodiment, it was found that a good image can be output up to 10,000 sheets.
[0142]
【The invention's effect】
As described above, according to the present invention, by using a charging roller having a high surface porosity and a fine average pore diameter, the surface of the charging roller can always be maintained in a less contaminated state. It has become possible to provide an image forming apparatus capable of stably performing injection charging without generating a product and maintaining stable charging performance and image performance even during long-term use.
[0143]
In particular, even in an image forming apparatus adopting a cleanerless system, it is possible to stably perform injection charging without generating a discharge product and obtain a good image without charging unevenness even in long-term printing. .
[Brief description of the drawings]
FIG. 1 is a configuration diagram of an image forming apparatus that implements Embodiment 1 of the present invention.
FIG. 2 is a diagram illustrating toner movement on the surface of a charging roller according to the first exemplary embodiment of the present invention.
FIG. 3 is another diagram illustrating the movement of the toner on the surface of the charging roller according to the first exemplary embodiment of the present invention.
FIG. 4 is a configuration diagram of an image forming apparatus that implements Embodiment 2 of the present invention.
5 is a cross-sectional view of the electrophotographic photosensitive member used in Examples 1 to 14 and Comparative Examples 1 to 5. FIG.
6 is a cross-sectional view of an electrophotographic photosensitive member used in Example 15. FIG.
FIG. 7 is a graph showing injection charging characteristics.
[Explanation of symbols]
101 Electrophotographic photoreceptor
1021 Charging roller
1021a cored bar
1021b Medium resistance layer
1022 conductive particles
103 Developing device
103a toner
103b Development sleeve
103c Magnet roll
103d Regulating blade
104 Transfer device
105 Fixing device
106 Process cartridge
107 Cleaning device
108 Conductive particle supply means
1081 Conductive Particle Supply Member
1082 Support 1082 of the conductive particle supply member
1083 Housing housing conductive particle supply member
10A Rotation direction of electrophotographic photosensitive member
10B Direction of rotation of charging roller
10L exposure light
10P transfer material
10S1 Charging power supply
10S2 Development power supply
10S3 Transfer power supply
201 electrophotographic photoreceptor
2021 Charging roller
2021a Medium resistance layer
2021b Middle resistance layer
2022 conductive particles
203 Developing Device
203a Toner
203b Development sleeve
203c Magnet roll
203d Regulating blade
204 Transfer device
205 Fixing device
206 Process cartridge
20A Direction of rotation of electrophotographic photosensitive member
20B Charging roller rotation direction
20L exposure light
20P transfer material
20S1 Charging power supply
20S2 Development power supply
20S3 Transfer power supply
301 Electrophotographic photoreceptor
3021 Charging roller
3021b Medium resistance layer
3022 conductive particles
303a Toner
30A Rotation direction of electrophotographic photosensitive member
30B Charging roller rotation direction
30C Propagation direction of medium resistance layer surface
Nu upstream area
401 Electrophotographic photoreceptor
4021 Charging roller
4021b Middle resistance layer
4022 Conductive particles
403a Toner
Rotation direction of 40A electrophotographic photoreceptor
40B Rotation direction of charging roller
40C Spreading direction of surface protrusion along the middle resistance
Nd Contact area downstream
5011 Support
5012 Undercoat layer
5013 Positive charge injection preventing layer
5014 Charge generation layer
5015 Charge transport layer
6011 Support
6012 Undercoat layer
6013 Positive charge injection preventing layer
6014 Charge generation layer
6015 Charge transport layer
6016 charge injection layer
6016a Ultra fine particles
70A Contact charging
70B Direct injection charging

Claims (25)

A charging device for charging a surface of a charged body by bringing a roller-shaped charging member to which a voltage is applied into contact with the charged body, wherein the surface layer of the charging member is an elastic foam, and the surface of the charging member is In a charging device that has a speed difference with respect to the surface of the member to be charged, and in which conductive particles exist on the contact surface between the charging member and the member to be charged,
The porosity of the surface of the charging member is 50% or more and 90% or less,
The average pore diameter of the pores in the surface of the charging member is Ru der least 150μm below 5μm
A charging device, wherein the this. The charging device according to claim 1, wherein an average hole diameter of holes on the surface of the charging member is 20 μm or more and 100 μm or less. The charging device according to claim 1, wherein an average particle diameter of the conductive particles is 10 nm or more. The charging device according to claim 3, wherein an average particle diameter of the conductive particles is 1/100 or more of the average pore diameter. The charging device according to claim 1, wherein an average particle diameter of the conductive particles is equal to or less than the average pore diameter. The charging device according to claim 5, wherein an average particle diameter of the conductive particles is 1/10 or less of the average pore diameter. The charging device according to any one of claims 1 to 6 the resistance of the conductive particles is not more than 1 × 10 ¹² Ω · cm. The charging device according to any one of claims 1 to 7, wherein the charging member is rotated in the counter relative to the member to be charged. The charging device according to any one of claims 1-8 volume resistivity of the surface layer of the member to be charged is not more than 1 × 10 ¹⁴ Ω · cm. The charging device according to claim 1, wherein the member to be charged is an image carrier. The charging device according to claim 10, wherein the image carrier is an electrophotographic photosensitive member. An electrophotographic photosensitive member and a charging device that charges a surface of the electrophotographic photosensitive member by bringing a roller-shaped charging member to which a voltage is applied into contact with the electrophotographic photosensitive member are integrally supported and attached to and detached from the image forming apparatus main body. A process cartridge that is free, wherein the surface layer of the charging member is an elastic foam, and the surface of the charging member has a speed difference with respect to the surface of the electrophotographic photosensitive member. In the process cartridge in which conductive particles are present on the contact surface of the electrophotographic photosensitive member,
The process cartridge according to claim 11, wherein the charging device is the charging device according to claim 11 . The process cartridge according to claim 12 , wherein the volume resistance of the surface layer of the electrophotographic photosensitive member is 1 × 10 ⁹ Ω · cm to 1 × 10 ¹⁴ Ω · cm. The process cartridge according to claim 12, further comprising a developing unit having a developer containing the conductive particles. The process cartridge according to any one of claims 12 to 14 having a developing means which also serves as a means for recovering the developer remaining on the electrophotographic photoconductor. An electrophotographic photosensitive member, a charging device for charging a surface of the electrophotographic photosensitive member by bringing a roller-shaped charging member to which voltage is applied into contact with the electrophotographic photosensitive member, and exposing the electrostatic latent image to the electrophotographic photosensitive member An image forming apparatus comprising: an exposure unit for forming; a developing unit for visualizing the electrostatic latent image with a developer; and a transfer unit for transferring an image visualized by the developing unit to a transfer material, the surface layer of the charging member Is an elastic foam, the surface of the charging member has a speed difference with respect to the surface of the electrophotographic photosensitive member, and conductive particles are present on the contact surface of the charging member and the electrophotographic photosensitive member. In the image forming apparatus,
The image forming apparatus according to claim 11, wherein the charging apparatus is the charging apparatus according to claim 11 . The image forming apparatus according to claim 16 , wherein the volume resistance of the surface layer of the electrophotographic photosensitive member is 1 × 10 ⁹ Ω · cm to 1 × 10 ¹⁴ Ω · cm. The image forming apparatus according to claim 16, wherein the developing unit is a developing unit having a developer containing the conductive particles. The developing unit is an image forming apparatus according to any one of the electrophotographic on the photoreceptor is a developing means which also serves as a means for recovering the developer remaining claims 16-18. The exposure means is an exposure means for forming an electrostatic latent image on the surface of the electrophotographic photosensitive member by scanning exposure with a laser beam capable of digital exposure for each pixel, and the average particle diameter of the conductive particles is 1. the image forming apparatus according to any one of claims 16-19 or less the diameter of the pixel. A roller-shaped charging member for a charging device that charges a surface of a charged body by bringing a roller-shaped charging member to which a voltage is applied into contact with the charged body, and the surface layer of the charging member is an elastic foam The surface of the charging member has a speed difference with respect to the surface of the member to be charged, and the roller-shaped charging member for a charging device in which conductive particles are present on the contact surface between the charging member and the member to be charged. In
The surface porosity is 50% or more and 90% or less,
The average pore diameter of the pores in the surface Ru der least 150μm below 5μm
The roller-shaped charging member, wherein the this. The roller-shaped charging member according to claim 21 , wherein an average hole diameter of holes on the surface of the charging member is 20 µm or more and 100 µm or less. The roller-shaped charging member according to claim 21 or 22 , wherein an average particle diameter of the conductive particles is 1/100 or more of the average pore diameter. The roller-shaped charging member according to any one of claims 21 to 23 , wherein an average particle diameter of the conductive particles is equal to or less than the average pore diameter. The roller-shaped charging member according to claim 24 , wherein an average particle diameter of the conductive particles is 1/10 or less of the average pore diameter.

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