JP3874128B2

JP3874128B2 - Proximity charging device

Info

Publication number: JP3874128B2
Application number: JP09684097A
Authority: JP
Inventors: 富啓安
Original assignee: Ricoh Co Ltd
Current assignee: Ricoh Co Ltd
Priority date: 1997-04-15
Filing date: 1997-04-15
Publication date: 2007-01-31
Anticipated expiration: 2017-04-15
Also published as: JPH10288881A

Description

【０００１】
【発明の属する技術分野】
本発明は、静電複写機，レーザープリンター等の電子写真プロセスを用いる画像形成装置に用いられる近接帯電装置に関する。
【０００２】
【従来の技術】
図８は従来より使用されている電子写真プロセスを用いる画像形成装置の一例を示す概略図である。感光体ドラム１は、導体１ａの表面に感光層１ｂを塗布することによって形成され、図示しない駆動手段により図８中の点線矢印方向に回転駆動される。帯電ロ−ラ２は、感光体ドラム１表面の感光層１ｂを所望の電位に帯電する。画像露光器５は、帯電した感光層１ｂ上に露光して、所望の画像に対応する静電潜像を形成する。現像器６は、感光層１ｂ上につくられた静電潜像を、トナーによって現像し、感光層１ｂ上にトナー像を形成する。転写器７は、感光層１ｂ上に現像されたトナー像を、図示しない搬送手段によって搬送される紙などの転写媒体８上に転写する。転写器７によって、トナー像を転写された転写媒体８は、図示しない定着器へと搬送され、定着器でトナーが加熱および加圧され、転写媒体８上に定着される。クリーニング装置９は、転写器７で転写媒体８上に転写されず感光体１ｂ上に残ったトナーを清掃する。感光体ドラム１は図２中の点線矢印の方向に回転するため、上記の処理を繰り返すことによって、次々に送り込まれる転写媒体８上に所望の画像が形成される。
【０００３】
この様な画像形成装置に使用される帯電器（２）としては、従来からスコロトロンなどのコロナ帯電装置のほかに、いわゆる接触帯電ロ−ラがある。コロナ帯電装置の場合には、印加電圧を高く（５〜７ｋＶ）する必要があり、そのため発生するオゾンが多い等の問題があった。接触帯電ロ−ラ２は、コロナ帯電装置での上記問題を改善することができる。このため、低速，中速の電子写真方式の画像形成装置での帯電器として広く用いられている。接触帯電ロ−ラ２は、導電体（金属）の芯金を抵抗層で被覆したものであり、被帯電体である感光体（以下、単に感光体と略す）に接触した抵抗層に芯金を介して電圧を印加することによって感光体の帯電を行う。
【０００４】
図９に、従来の帯電ロ−ラの一例を横断面で示す。帯電ローラ２は直径５〜２０ｍｍ、長さ約３００ｍｍであり、導体（芯金）２ａの上に弾性層（抵抗層）２ｂを形成してある。感光体ドラム１は直径３０〜８０ｍｍ、長さ約３００ｍｍであり、アルミニウム筒１ａの外表面上に有機感光体１ｂを形成してある。帯電ロ−ラ２は、回転する感光体ドラム１に対して接触し、従動回転する。帯電ロ−ラ２の弾性層（抵抗層）２ｂは、抵抗率が１０⁷〜１０⁹Ωｃｍの材料から構成される。また、帯電ロ−ラ２の表面（弾性層の表面）には、膜厚が１０〜２０μｍｍ程度の表面保護層が形成されている場合もある。帯電ロ−ラ２には電源３によって電圧を印加し、感光体１ｂの帯電を行う。印加電圧は、直流で−１．０〜−１．５ｋＶである。
【０００５】
しかし、接触帯電装置では、帯電ロ−ラ２が直接感光体１ｂと接触しているために、感光体１ｂ上のトナーなどが帯電ロ−ラ２に付着することによる帯電性能の低下，帯電ロ−ラ２を構成している物質の感光体１ｂへの付着，感光体１ｂを長期停止したときに生じる、帯電ロ−ラ２の永久変形等の問題が発生する。
【０００６】
このような問題を解決する方法として、帯電部材を非接触に感光体に近接させる近接帯電装置が考案されている。この種の近接帯電装置は、帯電部材を、感光体との最近接部での距離が０．００５〜０．３０ｍｍになるように近接して感光体と対向させ、帯電部材に電圧を印加することによりコロナ放電を生じさせ、感光体の帯電を行う。
【０００７】
例えば、特公平６−９０５６８号公報に提示された帯電装置は、固定電極板（帯電部材）と電荷受容体（感光体）との間に間隙が存在する非接触な近接帯電装置に関するもので、この固定電極板の抵抗率が１０⁶〜１０¹³Ωｃｍ、かつ表面抵抗が１０⁶Ω以上であり、前記の間隙幅が５００μｍ以下であることが特徴である。近接帯電装置をこのような構成にすることによって、固定電極板と電荷受容体との間の空隙で火花放電が起こることなく、均一な帯電が可能となる。また固定電極板は板状であるため、電荷受容体と対向する面の平面性が高精度で得られるとしている。
【０００８】
近接帯電装置では、帯電部材と感光体とが接触していないために、接触帯電装置で問題となる「帯電部材を構成している物質の感光体への付着」、「感光体を長期停止したときに生じる永久変形」は問題とはならない。また、「感光体上のトナーなどが帯電部材に付着することによる帯電性能の低下」に関しても、帯電部材に付着するトナーが少なくなるため、近接帯電装置の方が優れている。
【０００９】
図１０は、従来考えられていた近接帯電装置の一例であり、その断面図を表している。帯電ロ−ラ２は、直径５〜２０ｍｍ、長さ約３００ｍｍであり、導体２ａの上に抵抗層２ｂを形成してある。感光体ドラム１は直径３０〜８０ｍｍ、長さ約３００ｍｍであり、導体１ａ上に感光体１ｂを形成してある。帯電ロ−ラ２は回転させてもよいし、回転させなくてもよい。帯電ロ−ラ２は回転する感光体ドラム１に対して、最近接部での距離（図１０中の点Ａと点Ｂ間の距離Ｇ）が０．００５〜０．３０ｍｍになるような位置に配置される。帯電ロ−ラ２の抵抗層２ｂは、抵抗率が１０⁷〜１０⁹Ωｃｍの材料から構成される。帯電ロ−ラ２には、電源３によって電圧を印加し、感光体１ｂの帯電を行う。印加電圧は、直流で−１．５〜−２．０ｋＶである。
【００１０】
接触帯電，非接触（近接）帯電にかかわらず、帯電ロ−ラを長時間使用した場合には、ローラの表面がトナーなどによって汚れ帯電能力が低下する。その対策として、従来ではブレードを適当な押圧下で帯電ローラに当接させてトナーを除去し、除去したトナーを専用の容器に収容していた。しかし、このような方法では、除去トナーを収容する容器が必要なため装置の小型化が困難であったり、また、除去トナーを収容する容器に貯まったトナーを処理する必要があるなどの問題があった。
【００１１】
特開平６−１４９０２０号公報は、帯電ローラをクリーニングするクリーニング装置に関するもので、帯電ローラに接触させるブレードの位置を工夫している。すなわち帯電ローラに当接するブレードの配設位置および姿勢を、かきとったトナーが重力により感光体表面に落下、付着するように工夫している。感光体上に落下した除去トナーは、感光体の回転にともなって次行程に運ばれるので、従来のように、除去トナーを収容する容器が不要となる。
【００１２】
この様にブレードを帯電ローラに当接させてトナーを除去する近接帯電装置においても、接触帯電装置に比べれば少量ではあるが、長時間の使用によって、帯電部材の表面にトナーなどが付着する。帯電部材の表面がトナー等で汚れた状態で感光体の帯電を行った場合には、感光体の帯電電位が低下する，感光体の帯電電位が不均一になるなどの問題が発生する。このような状態で画像の形成を行った場合には、白地部にトナーが付着したり（反転現像時）、画像濃度が均一でなくなるなどの問題が発生する。
【００１３】
帯電部材の表面が汚れることの影響を防止する方法として、帯電部材の表面を移動させながら（例えば帯電ローラを回転させながら）、感光体の帯電を行う方法が提案されている。このような方法では、帯電部材の表面積が実質的に拡大されるため付着するトナーが分散されるので、帯電部材の汚れによる影響を小さくすることができる。移動する帯電部材の表面にブレード（クリーニング部材）を当接することによって、帯電部材の表面上に付着したトナーを除去する方法も提案されている（特開平６−１４９０２０号公報）。
【００１４】
また、特開平７−７２７０４，７２７０５，７２７０６号公報には、移動可能な被帯電体と、被帯電体に接触する導電性の帯電部材をもち、被帯電体の移動方向に対して上流側の前記帯電部材と前記被帯電体とによって挾まれた空間内にブレードを配置した帯電装置が提案されている。前記帯電部材には直流電圧を印加し、前記ブレードは直流電圧を印加するかまたは接地する。ブレードにより、帯電部材と被帯電体とが徐々に近づく領域で、被帯電体への放電が規制されるので、帯電むらがなくなり均一帯電が可能になると説明されている。
【００１５】
【発明が解決しようとする課題】
しかしながら、上述のような帯電部材の表面を移動させながら感光体の帯電を行うタイプの近接帯電装置では、帯電部材を静止させて感光体の帯電を行うタイプの近接帯電装置に比べて、帯電むらが発生しやすいという問題がある。帯電むらとは感光体の帯電が均一になされない状態のことであり、感光体の表面電位が場所によって、高くなったり、低くなったりしている状態のことである。近接帯電装置で現れるこのような帯電むらは、ピッチ（空間周期）が０．１〜１ｍｍ程度と小さいため、いわゆる表面電位計（例えばＴrek model 344 など）では検出することができない（表面電位計の空間分解能は、５ｍｍ程度であり、このような小さな帯電むらは平均化されてしまい検出することができない）。しかし実際に、近接帯電装置によって感光体を帯電させたのち、感光体上に画像を形成した場合、画像上にまだ班点状の帯電むらが現れる。例えば反転現像（ネガポジ）を行った場合には、白地部にトナーが付着したり、黒地部でトナーの付着が少ない箇所が現れる。
【００１６】
本発明は、帯電部材と感光体の表面間距離が０．１〔ｍｍ〕以上の非接触である近接帯電装置において、帯電部材を回転させた場合でも、帯電むらを生じないようにすることを目的とする。
【００１７】
【課題を解決するための手段】
（１）本発明は、被帯電体(1)の移動可能な被帯電面(1b)に対して、帯電部材(2)の帯電面(2c)が非接触に対向し、この帯電部材(2)に電圧を印加することにより、前記帯電面(2c)と前記被帯電体(1)との間で直接放電を起こさせ、前記被帯電面(1b)を帯電する近接帯電装置において、
前記被帯電面(1b)を帯電する間に前記帯電面(2c)が移動し、前記帯電面(2c)と前記被帯電面(1b)との距離が、最も小さい最近接部(A-B)においても0.1[mm]以上であり、該最近接部 (A-B) において前記被帯電面 (1b) と前記帯電面 (2c) が移動する向きが同じであって、前記帯電面(2c)が移動する向きに対して、前記最近接部(A-B)よりも上流側の、前記帯電面(2c)に対向する位置に、該対向帯電面を放電させて該対向帯電面の表面電位を下げる予備放電部材(4)を配置してある、ことを特徴とする。
【００１８】
なお、理解を容易にするためにカッコ内には、図面に示し後述する実施例の対応要素の符号または対応事項の記号を、参考までに付記した。
【００１９】
予備放電部材(4)がない場合を、図１０の示す近接帯電装置を参照して説明すると、帯電ロ−ラ２は、図の実線矢印方向に回転するので、帯電面２ｃの或る一点Ｐは回転に伴い次第にＡ点（感光体１ｂとの最接近点）に接近する。即ち感光体１ｂのＢ点（抵抗層２ｂとの最接近点）に接近する。感光体１ｂは除電された後にＢ点に近づいて来るので、帯電面（２ｂの表面）と被帯電面（１ｂの表面）との電位差Ｖｄは大略電源３の電圧に等しい。この様に被帯電面と帯電面が次第に近接して行くような場合には、放電は被帯電面と帯電面が最近接する点（Ａ−Ｂ）よりも上流側で、電位差Ｖｄが放電開始電圧を越えた部分（ギャップＧが比較的大きい部分）で始まる。放電が始まると被帯電面は帯電されるので次第に電位が上昇し、帯電面と被帯電面との電位差Ｖｄは減少する。従って上流側のギャップＧが小さくなる部分では、電位差Ｖｄが放電持続しきい値を下まわり放電は終了する。この放電開始直後の領域では放電に伴って移動する電荷量は大きく、その結果、放電の跡が帯電むらとして観察される。
【００２０】
一方本発明のように、予備放電部材(4)を配置した場合には、上述と同様な放電が、まず帯電面(1b)と予備放電部材(4)間で発生するので、帯電面(1b)の電位は電源(3)により印加された電位よりも低くなる。例えば帯電面(2c)の或る一点Ｐは、まず予備放電部材(4)間で放電開始するので、点Ｐの電位は電源(3)により印加された電位よりも低くなっている。点Ｐが帯電部材(2)の回転によって、被帯電面(1b)との間で放電が起こる領域に移動してきたときにも、点Ｐと被帯電面(1b)との電位差は予備放電部材(4)がない場合にくらべて小さくなり、点Ｐと被帯電面(1b)との間で起こる放電にともなって移動する電荷量も小さくなる。その結果、放電跡が帯電むらとして観察されることはなく、均一な帯電がなされる。
帯電部材(2)を移動させず静止させた場合でも、上記の様に帯電面(2c)と被帯電面(1b)との間の電位差が小さく、このため帯電むらは発生しない。しかし、帯電部材(2)を静止させた場合には、従来技術の項で指摘したように、被帯電面(1b)の帯電のために使われる帯電部材(2)の帯電面(2c)表面積が小さいので、帯電時の電位低下，帯電不均一などの問題が発生する。このため、帯電部材(2)及び帯電面(2c)が移動するタイプの近接帯電装置の方が優れている。
【００２１】
このように、本発明の近接帯電装置においては、帯電面(2c)を移動させた場合でも、従来問題となっていた帯電むらが発生しない。そして、帯電部材の帯電面(2c)を移動させることが可能なため、帯電部材の帯電面(2c)を固定させるタイプの近接帯電装置に比べて、帯電面(2c)上に付着したトナーの影響を小さくすることができる。
【００２２】
【発明の実施の形態】
（２）前記最近接部(A-B)での前記帯電面(2c)と前記被帯電面(1b)との移動速度(Va,Vb)が異なることを特徴とする。
これによれば、帯電面(2c)の移動する速度(Va)を、被帯電面(1b)の移動する速度（Vb；画像プロセス速度）に関係なく決めることができる。従って帯電部材(2)を必要以上に速く回転させる必要がなくなり、帯電部材(2)の軸や、帯電部材(2)を支持する軸受けなどの磨耗を少なくすることができる。また軸受け部分で発生する熱量を小さくすることができる。
【００２３】
（３）予備放電部材(4)の表面が中抵抗の材料(4b)で被覆してあることを特徴とする。
予備放電部材(4)の表面を絶縁体のような高抵抗の材料で被覆した場合には、予備放電部材(4)と帯電部材(2)との間で放電が起こらなくなり、予備放電部材(4)を配置した効果がなくなる。また予備放電部材(4)の表面を金属のような低抵抗の材料で被覆した場合には、帯電部材(2)に抵抗が小さい欠陥が存在する場合、そこから予備放電部材(4)に対し大きな電流が流れ、その結果予備放電部材(4)や帯電部材(2)が劣化し、機能が損なわれることがある。
これに対し、中抵抗の材料(4b)で被覆してあるので、予備放電機能が損なわれることがなく、又予備放電部材(4)が劣化することがない。
【００２４】
（４）予備放電部材(4)に、帯電部材(2)に印加する電圧とは反対の極性の電圧を印加することを特徴とする。
これによれば、予備放電部材(4)と帯電部材(2)との間には、予備放電部材(4)に電圧を印加しない場合に比べて、より大きな電位差が生じる。この結果、予備放電部材(4)と帯電部材(2)との間に発生する放電規模がより大きく、従って帯電部材(2)上に蓄積される電荷量が多くなる。帯電部材表面により多くの電荷が蓄積されると、帯電部材表面(2c)の電位は印加した電位に比べてより下がるため、この部分が帯電部材(2)の回転によって帯電部材表面(2c)と被帯電面(1b)との間で放電が起きる領域に移動してきた場合、帯電部材表面(2c)と被帯電面(1b)との間の電位差が小さくなり、帯電むらが発生しにくくなる。このように、予備放電部材(4)の効果がより大きく、帯電むら解消効果がより高い。
【００２５】
（５）予備放電部材(4)が帯電部材(2)に接触していることを特徴とする。これによれば、予備放電部材(4)が帯電部材(2)に接触すれば良いので、予備放電部材(4)の取り付け精度はそれほど高くなくてもよい。これにより予備放電部材(4)を搭載する近接帯電装置の作成が容易となり、予備放電部材(4)を搭載してもコストを引き上げる要因にはならない。
【００２６】
（６）予備放電部材(4)が帯電部材(2)の表面をクリーニングする機能を有することを特徴とする。
【００２７】
これによれば、帯電部材(2)の表面(2c)がトナーなどによって汚れた場合でも、予備放電部材(4c)によりクリーニングされるため、長期間にわたって安定して、被帯電体(1)を均一に帯電することが可能である。また、予備放電部材(4c)とクリーニング部材が兼用されるため、装置の構成が複雑になることはない。帯電部材(2)は長期間にわたって安定して、被帯電体(1)を均一に帯電することが可能であり、さらに装置の構成が複雑にならない。
【００２８】
本発明の他の目的及び特徴は、図面を参照した以下の実施例の説明より明らかになろう。
【００２９】
【実施例】
−第１実施例−
図１は、本発明の第１実施例の近接帯電装置の概略構成を示す断面図である。ローラ形状で実線矢印の方向に回転する帯電ロ−ラ２は、導体２ａ（芯金）上に抵抗層２ａを設け、その表面に形成した表面層２ｃから構成され、導体２ａ（芯金）には電源３から直流電圧が供給される。筒状で点線矢印の方向に回転する感光体ドラム１は、接地した導体１ａと、その表面に形成した感光体１ｂで構成されている。図１に示す様に、帯電ロ−ラ２は感光体１と非接触で対向している。帯電ロ−ラ２には、接地されている予備放電部材４が非接触で対向している。
【００３０】
この第１実施例の近接帯電装置と従来の帯電装置との違いは、
・帯電ロ−ラ２と感光体１との距離は、最も小さい最近接部Ａ−Ｂでも０．１ｍｍ以上である；
・帯電ロ−ラ２が回転する。すなわち、帯電ロ−ラ２の表面（以下単に帯電面２ｃと略す）が移動する；
・帯電面２ｃの移動する向きに対して、帯電ロ−ラ２と感光体１との最近接部Ａ−Ｂよりも上流側の、帯電面２ｃと対向する位置に予備放電部材４を配置してある；
の３点である。
【００３１】
第１実施例の近接帯電装置では、帯電ロ−ラ２はローラ形状で、直径１５ｍｍ、長さ３００ｍｍであり、導体２ａの上に３ｍｍの厚さを有する抵抗層２ｂが形成してある。抵抗層２ｂは、ＮＢＲ系のゴム材料にハロゲン化物（イオン性化合物）を添加して、導電性を付与した材料によって構成され、抵抗率が、１０⁸Ωｃｍに調整してある。この抵抗層２ｂの表面を、イオン性化合物を添加して導電性を付与したフッ素系の樹脂で被覆し、表面層２ｃを形成してある。この表面層２ｃの抵抗率は１０¹⁰Ωｃｍになるように調整してある。
【００３２】
抵抗層２ｂを構成する材料としては、上記のほか各種ゴム又は樹脂などの高分子材料にイオン性化合物を添加することによって導電性を付与した材料（いわゆるイオン性導電化材料），イオン性化合物の代わりにカーボンを高分子材料中に分散させた材料（いわゆる電子性導電化材料），金属酸化物（セラミックス）などのほか、いわゆる中程度の抵抗率をしめす材料であればどのようなものであってもよい。しかし帯電むらを発生させずに、感光体１を帯電するためには、抵抗層は１０⁷〜１０⁹Ωｃｍでなけれなばならない。また表面については、表面層２ｃを形成しても、しなくてもよく、上述の材料以外のもので表面層２ｃを形成してもよい。
【００３３】
また、第１実施例の近接帯電装置では、帯電ロ−ラ２は、図１中の実線矢印の向きに、駆動源（図示せず）によって駆動されて回転する。回転の速度は、帯電面２ｃ上の一点が移動する速さ（周速）が、１５ｍｍ／ｓｅｃになるように調整してある。感光体１も図１中の点線矢印の向きに、駆動源（図示せず）によって駆動されて回転する。帯電ロ−ラ２の回転の向きは、図１中に示したように、帯電ロ−ラ２と感光体１との距離が最も小さくなる最近接部Ａ−Ｂにおいて、帯電ロ−ラ２，感光体１それぞれの表面が移動する向きが同じである。帯電ロ−ラ２の帯電面２ｃが移動する速さは、上記以外の値でもよい。
【００３４】
帯電ロ−ラ２は、感光体１にたいして、最近接部Ａ−Ｂでの距離が０．１ｍｍ以上になるように対向させて配置されている。帯電ロ−ラ２の導体部分２ａには電源３によって電圧が印加され、感光体１の帯電を行う。印加電圧は、直流で−１．５〜−２．０ｋＶである。
【００３５】
予備放電部材４の配置位置は、帯電面２ｃの移動する向きに対して、帯電ロ−ラ２と感光体１との最近接部Ａ−Ｂよりも上流側で、帯電面２ｃに対向する位置である。また予備放電部材４と帯電面２ｃとの距離がもっとも小さいところで、０．１ｍｍである。予備放電部材４と帯電部２との距離は、必ずしも０．１ｍｍでなくてもよいが、後述するように、予備放電部材４との間で放電が起こるような距離である必要がある。
【００３６】
実施例１の近接帯電装置では、予備放電部材４は接地された金属であり、帯電ロ−ラ２の帯電面２ｃとこの予備放電部材４との間で放電が起こる。予備放電部材４は、必ずしも金属でなくてもよく、帯電面２ｃとの間で継続して放電が起こることが可能な導電性の材料であればよい。つまり、導電性のプラスチック，フィルムなどであってもかまわない。
【００３７】
このほか、第１実施例の近接帯電装置では、帯電ロ−ラ２はローラ形状であるが、ベルト状であってもよい。図２は帯電ロ−ラ２がベルト状である場合の、近接帯電装置の概略図である。
【００３８】
−第２実施例−
図３に、本発明の第２実施例の近接帯電装置の概略構成を示す。第２実施例の近接帯電装置と第１実施例の近接帯電装置との違いは、
・帯電面２ｃと感光体１ｂとの最近接部Ａ−Ｂでの、帯電面２ｃと感光体１ｂとの移動する速度が異なる；
点である。
【００３９】
第２実施例の近接帯電装置でも第１実施例の場合と同じように、帯電ロ−ラ２は不図示の駆動源によって図３中の実線矢印の向きに回転しており、また感光体ドラム１は不図示の駆動源によって図３中の点線矢印の向きに回転している。ただし、第２実施例の場合には、帯電ロ−ラ２と感光体ドラム１との最近接部Ａ−Ｂでの、帯電面２ｃの移動する速度Ｖａ（ベクトル）と感光体１ｂ表面の移動する速度Ｖｂ（ベクトル）とが異なるように、帯電ロ−ラ２の回転の速さを調整している。つまり、Ｖａ ≠ Ｖｂとなるように、帯電ロ−ラ２の回転速度を制限する。第２実施例の近接帯電装置では、帯電面２ｃの移動する速さは１５mm／secである。それに対して感光体１ｂの移動する速さは１８０mm／secである。帯電面２ｃの移動する速さは、上述の値でなくてもよく、帯電ロ−ラ２が回転していればよい。ただし、１０〜１００mm／sec程度の比較的小さい値の方が、帯電ロ−ラ２の軸の磨耗が少ないなどの点を考えると望ましい。
【００４０】
第２実施例の近接帯電装置の、帯電面２が移動する速さと感光体ドラム１が移動する速さとが異なる点以外は、第１実施例の近接帯電装置と同じである。
【００４１】
−第３実施例−
図４に、本発明の第３実施例の近接帯電装置の概略構成を示す。第３実施例の近接帯電装置と第１実施例の近接帯電装置との違いは、
・予備放電部材４の表面が中抵抗の材料４ｂで被覆してある；
点である。
【００４２】
第３実施例の近接帯電装置では、予備放電部材４の基板導体４ａの表面を、抵抗率を１０⁸Ωｃｍに調整した中抵抗の樹脂層４ｂで被覆してある。使用した被覆材料は、イオン性化合物を添加して導電性を付与したフッ素系の樹脂である。
被覆材料の抵抗率は、上述の値でなくてもよい。ただし、被覆材料の抵抗率が大きい（１０¹⁰Ωｃｍ超）場合には、予備放電部材の樹脂層４ｂ表面上に電荷が蓄積されるため、帯電部材２と樹脂層４ｂとの間で放電が起こらなくなってしまい、予備放電部材４を配置した効果がなくなってしまう。また、被覆材料の抵抗率が小さい（１０⁵Ωｃｍ未満）場合には、帯電部材２に欠陥（抵抗が局所的に小さい部分）があると、その部分を介して、帯電部材２から樹脂層４ｂに大きな電流が流れ、帯電部材４や予備放電部材４の樹脂層４ｂが劣化し、その機能を果たさなくなる。このため、予備放電部材４の導電性樹脂層４ｂとしては、中抵抗の抵抗率（１０⁶〜１０⁹Ωｃｍ）を持つ材料を使用する必要がある。
【００４３】
被覆材料は上述のもの以外でも、抵抗率を上述の様に中抵抗の領域に調整できるようなものであれば使用してよい。第３実施例の近接帯電装置では、予備放電部材４の表面が中抵抗の材料で被覆されていること以外は、第１実施例の近接帯電装置と同じである。
【００４４】
−第４実施例−
図５に、本発明の第４実施例の近接帯電装置の概略構成を示す。第４実施例の近接帯電装置と実施例１の近接帯電装置との違いは、
・予備放電部材に、帯電部材に印加する電圧とは反対の極性の電圧を印加する；点である。
第４実施例の近接帯電装置では、帯電部材２には、帯電部材用電源３ａから−２．０ｋＶの電圧を印加して、感光体１の帯電を行なう。そして、予備放電部材４には、予備放電部材用電源３ｂから＋０．５ｋＶの電圧を印加する。予備放電部材４に印加する電圧は上述の値でなくてもよいが、ただし、０．５ｋＶを越えるような正極性の電圧を印加すると、予備放電部材４と感光体層１ｂとの間で放電が起こる可能性がある。そしてこの場合には、画像に放電の跡がみられるようになるなどの問題が発生する。また、予備放電部材４と感光体層１ｂとの間で起こる放電を防止するために、絶縁体を配置することなども考えられるが、帯電装置全体が複雑な構成になってしまうという問題がある。このため、予備放電部材４に印加する電圧は＋０．５ｋＶを越えないような値である方が望ましい。
【００４５】
第４実施例の近接帯電装置は、予備放電部材４に、帯電部材２に印加する電圧とは反対の極性の電圧を印加すること以外は、第１実施例の近接帯電装置と同じである。
【００４６】
−第５実施例−
図６に、本発明の第５実施例の近接帯電装置の概略構成を示す。第５実施例の近接帯電装置と第１実施例の近接帯電装置との違いは、
・接地した予備放電部材が、帯電部材に接触している；
点である。
第５実施例の近接帯電装置では、予備放電部材４は導電性のポリカーボネートフィルムである。ただし予備放電部材４としては、上述の材料以外のものでもよく、各種導電性フィルムやゴムなどで、帯電部材２に接触させることができるようなものであればどのようなものであってもよい。
【００４７】
また第５実施例の近接帯電装置では、帯電装置を使用している時でも使用していない時でも、予備放電部材４が帯電部材２に接触している。しかし、接離機構を設けて、帯電装置を使用していないときには、予備放電部材４を帯電部材２から離すようにしてもよい。
【００４８】
第５実施例の近接帯電装置では、予備放電部材４が、少くとも帯電処理期間は帯電部材２に接触していること以外は、実施例１の帯電装置と同じである。
【００４９】
−第６実施例−
図７に、本発明の第６実施例の近接帯電装置の概略構成を示す。第６実施例の近接帯電装置と第１実施例の近接帯電装置との違いは、
・予備放電部材４ｃが、帯電部材２の表面をクリーニングする機能を有する；点である。
第６実施例の近接帯電装置では、予備放電部材４ｃは導電性の繊維を寄り合わせたブラシである。ただし予備放電部材４ｃとしては、上述のブラシ以外のものでもよく、フィルムや弾性ブレードなど、帯電部材２の表面に付着するトナーなどの汚れを取り除くことができるようなものであればどのようなものであってもよい。また上記の予備放電部材４ｃを構成するブラシ，フィルム，弾性ブレード等に導電性を持たせて、更にそこに電圧を印加して、トナーなどの除去能力を高めたものであってもよい。
【００５０】
第６実施例の近接帯電装置は、予備放電部材４ｃが、帯電部材２の表面をクリーニングする機能を有すること以外は、第１実施例の近接帯電装置と同じである。
【図面の簡単な説明】
【図１】本発明の第１実施例の主要部の断面図である。
【図２】第１実施例の変形例の断面図であり、ベルト状の帯電部材２を備える態様を示す。
【図３】本発明の第２実施例の主要部の断面図であり、帯電部材２と感光体ドラム１の表面速度が異なる態様を示す。
【図４】本発明の第３実施例の主要部の断面図であり、予備放電部材４の表面を導電性の樹脂層４ｂで被覆した態様を示す。
【図５】本発明の第４実施例の主要部の断面図であり、予備放電部材４に帯電部材２に印加した電圧と異なる極性の電圧を加える態様を示す。
【図６】本発明の第５実施例の主要部の断面図であり、予備放電部材４が帯電部材２に接触する態様を示す断面図である。
【図７】本発明の第６実施例の主要部の断面図であり、予備放電部材４が帯電部材２をクリ−ニングする機能を兼ね備える態様を示す。
【図８】従来の画像形成装置の構成の一例を、断面で示すブロック図である。
【図９】従来の接触帯電装置の構成の一例を、断面で示すブロック図である。
【図１０】従来の近接帯電装置の構成の一例を、断面で示すブロック図である。
【符号の説明】
１：感光体ドラム１ａ：感光体
１ｂ：導体２：帯電部材
２ａ：導体２ｂ：抵抗層（弾性層）
２ｃ：表面層３：電源
３ａ：帯電部材用電源３ｂ：予備放電部材用電源
４：予備放電部材４ａ：導体
４ｂ：導電性の樹脂層４ｃ：クリ−ナ兼予備放電部材
５：静電潜像形成手段６：現像手段
７：転写手段８：転写体（紙）
９：クリーニング手段Ａ：帯電部材表面層最近接位置
Ｂ：感光体最近接位置Ｇ：Ａ−Ｂ間ギャップ[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a proximity charging device used in an image forming apparatus using an electrophotographic process such as an electrostatic copying machine or a laser printer.
[0002]
[Prior art]
FIG. 8 is a schematic view showing an example of an image forming apparatus using an electrophotographic process conventionally used. The photosensitive drum 1 is formed by applying the photosensitive layer 1b on the surface of the conductor 1a, and is driven to rotate in the direction of the dotted arrow in FIG. 8 by a driving means (not shown). The charging roller 2 charges the photosensitive layer 1b on the surface of the photosensitive drum 1 to a desired potential. The image exposure unit 5 exposes the charged photosensitive layer 1b to form an electrostatic latent image corresponding to a desired image. The developing device 6 develops the electrostatic latent image formed on the photosensitive layer 1b with toner, and forms a toner image on the photosensitive layer 1b. The transfer unit 7 transfers the toner image developed on the photosensitive layer 1b onto a transfer medium 8 such as paper conveyed by a conveyance unit (not shown). The transfer medium 8 onto which the toner image has been transferred by the transfer unit 7 is conveyed to a fixing unit (not shown), and the toner is heated and pressurized by the fixing unit and fixed on the transfer medium 8. The cleaning device 9 cleans the toner that is not transferred onto the transfer medium 8 by the transfer unit 7 and remains on the photoreceptor 1b. Since the photosensitive drum 1 rotates in the direction of the dotted arrow in FIG. 2, a desired image is formed on the transfer medium 8 that is successively fed by repeating the above processing.
[0003]
As a charger (2) used in such an image forming apparatus, there is a so-called contact charging roller in addition to a corona charging device such as a scorotron. In the case of the corona charging device, it is necessary to increase the applied voltage (5 to 7 kV), which causes problems such as a large amount of ozone generated. The contact charging roller 2 can improve the above problem in the corona charging device. For this reason, it is widely used as a charger in low- and medium-speed electrophotographic image forming apparatuses. The contact charging roller 2 is a conductor (metal) cored bar coated with a resistance layer, and a cored bar is placed on the resistance layer in contact with a photosensitive body (hereinafter simply referred to as a photosensitive body) that is a charged body. The photosensitive member is charged by applying a voltage via.
[0004]
FIG. 9 shows an example of a conventional charging roller in cross section. The charging roller 2 has a diameter of 5 to 20 mm and a length of about 300 mm, and an elastic layer (resistance layer) 2b is formed on the conductor (core metal) 2a. The photoconductor drum 1 has a diameter of 30 to 80 mm and a length of about 300 mm, and an organic photoconductor 1b is formed on the outer surface of the aluminum cylinder 1a. The charging roller 2 is in contact with the rotating photosensitive drum 1 and is driven to rotate. The elastic layer (resistive layer) 2b of the charging roller 2 has a resistivity of 10⁷-10⁹Consists of Ωcm material. Further, a surface protective layer having a thickness of about 10 to 20 μm may be formed on the surface of the charging roller 2 (surface of the elastic layer). A voltage is applied to the charging roller 2 by the power source 3 to charge the photoreceptor 1b. The applied voltage is -1.0 to -1.5 kV in direct current.
[0005]
However, in the contact charging device, since the charging roller 2 is in direct contact with the photoreceptor 1b, the charging performance is reduced due to the toner on the photoreceptor 1b adhering to the charging roller 2, and the charging roller. -Problems such as adhesion of substances constituting the roller 2 to the photosensitive member 1b and permanent deformation of the charging roller 2 that occur when the photosensitive member 1b is stopped for a long time occur.
[0006]
As a method for solving such a problem, a proximity charging device has been devised in which a charging member is brought close to a photoconductor in a non-contact manner. In this type of proximity charging device, the charging member is placed close to the photosensitive member so that the distance at the closest part to the photosensitive member is 0.005 to 0.30 mm, and a voltage is applied to the charging member. As a result, corona discharge is generated, and the photosensitive member is charged.
[0007]
For example, the charging device presented in Japanese Patent Publication No. 6-90568 relates to a non-contact proximity charging device in which a gap exists between a fixed electrode plate (charging member) and a charge receptor (photosensitive member). The resistivity of this fixed electrode plate is 10⁶-10¹³Ωcm and surface resistance of 10⁶It is characteristic that it is Ω or more and the gap width is 500 μm or less. By adopting such a configuration of the proximity charging device, uniform charging can be performed without causing spark discharge in the gap between the fixed electrode plate and the charge receptor. Further, since the fixed electrode plate has a plate shape, the flatness of the surface facing the charge acceptor can be obtained with high accuracy.
[0008]
In the proximity charging device, since the charging member and the photoconductor are not in contact with each other, there is a problem with the contact charging device such as “adhesion of a substance constituting the charging member to the photoconductor”, “the photoconductor has been stopped for a long time. “Permanent deformation sometimes occurs” is not a problem. Further, with respect to “decrease in charging performance due to adhesion of toner or the like on the photosensitive member to the charging member”, the proximity charging device is superior because less toner adheres to the charging member.
[0009]
FIG. 10 is an example of a proximity charging device conventionally considered, and shows a cross-sectional view thereof. The charging roller 2 has a diameter of 5 to 20 mm and a length of about 300 mm, and a resistance layer 2b is formed on the conductor 2a. The photoreceptor drum 1 has a diameter of 30 to 80 mm and a length of about 300 mm, and a photoreceptor 1b is formed on a conductor 1a. The charging roller 2 may be rotated or may not be rotated. The charging roller 2 is positioned such that the distance (the distance G between point A and point B in FIG. 10) at the closest point to the rotating photosensitive drum 1 is 0.005 to 0.30 mm. Placed in. The resistance layer 2b of the charging roller 2 has a resistivity of 10⁷-10⁹Consists of Ωcm material. A voltage is applied to the charging roller 2 by the power source 3 to charge the photoreceptor 1b. The applied voltage is -1.5 to -2.0 kV in direct current.
[0010]
Regardless of contact charging or non-contact (proximity) charging, when the charging roller is used for a long time, the surface of the roller is contaminated with toner or the like and the charging capability of the dirt is lowered. As a countermeasure, conventionally, the blade is brought into contact with the charging roller under an appropriate pressure to remove the toner, and the removed toner is accommodated in a dedicated container. However, such a method requires a container for storing the removed toner, so that it is difficult to reduce the size of the apparatus, and it is necessary to process the toner stored in the container for storing the removed toner. there were.
[0011]
Japanese Patent Laid-Open No. 6-149020 relates to a cleaning device for cleaning a charging roller, and devise the position of a blade to be brought into contact with the charging roller. That is, the arrangement position and posture of the blade that contacts the charging roller are devised so that the scraped toner falls and adheres to the surface of the photoreceptor due to gravity. The removed toner that has fallen on the photosensitive member is carried to the next step as the photosensitive member rotates, so that a container for storing the removed toner is not required as in the prior art.
[0012]
Even in the proximity charging device that removes the toner by bringing the blade into contact with the charging roller in this way, the toner adheres to the surface of the charging member after a long period of use, although the amount is smaller than that of the contact charging device. When the photosensitive member is charged while the surface of the charging member is contaminated with toner or the like, problems such as a decrease in the charging potential of the photosensitive member or an uneven charging potential of the photosensitive member occur. When an image is formed in such a state, problems such as toner adhering to a white background (during reversal development) and non-uniform image density occur.
[0013]
As a method for preventing the influence of the surface of the charging member from becoming dirty, a method of charging the photosensitive member while moving the surface of the charging member (for example, rotating the charging roller) has been proposed. In such a method, since the surface area of the charging member is substantially enlarged, the adhering toner is dispersed, so that the influence of contamination of the charging member can be reduced. There has also been proposed a method of removing toner adhering to the surface of the charging member by bringing a blade (cleaning member) into contact with the surface of the moving charging member (Japanese Patent Laid-Open No. 6-149020).
[0014]
Japanese Laid-Open Patent Publication No. 7-72704, 72705, 72706 has a movable object to be charged and a conductive charging member in contact with the object to be charged, which is upstream of the moving direction of the object to be charged. There has been proposed a charging device in which a blade is disposed in a space sandwiched between the charging member and the member to be charged. A DC voltage is applied to the charging member, and the blade is applied with a DC voltage or grounded. It is described that since the discharge to the charged body is regulated in a region where the charging member and the charged body are gradually approached by the blade, there is no uneven charging and uniform charging is possible.
[0015]
[Problems to be solved by the invention]
However, in the proximity charging device of the type that charges the photosensitive member while moving the surface of the charging member as described above, the charging unevenness is smaller than that of the proximity charging device that charges the photosensitive member with the charging member stationary. There is a problem that is likely to occur. Uneven charging is a state in which the photosensitive member is not uniformly charged, and the surface potential of the photosensitive member is increased or decreased depending on the location. Such charging unevenness appearing in the proximity charging device cannot be detected by a so-called surface electrometer (for example, Trek model 344) because the pitch (space period) is as small as about 0.1 to 1 mm. The spatial resolution is about 5 mm, and such small charging unevenness is averaged and cannot be detected. However, when an image is formed on the photosensitive member after the photosensitive member is actually charged by the proximity charging device, spot-like charging unevenness still appears on the image. For example, when reversal development (negative-positive) is performed, a toner adheres to a white background or a portion where the toner adheres less in a black background.
[0016]
In the proximity charging device in which the distance between the surface of the charging member and the photosensitive member is 0.1 [mm] or more, even if the charging member is rotated, uneven charging is prevented. Objective.
[0017]
[Means for Solving the Problems]
(1) In the present invention, the charging surface (2c) of the charging member (2) is opposed to the movable surface (1b) to which the charged body (1) is movable, and this charging member (2 In the proximity charging device that causes a direct discharge between the charged surface (2c) and the charged body (1) by applying a voltage to the charged surface (1b),
  The charged surface (2c) moves while the charged surface (1b) is charged, and the distance between the charged surface (2c) and the charged surface (1b) is the smallest at the closest portion (AB). Is also 0.1 [mm] or more,The closest part (AB) In the charged surface (1b) And the charged surface (2c) Are moving in the same direction,The counter charging surface is discharged to a position facing the charging surface (2c) upstream of the closest portion (AB) with respect to the direction of movement of the charging surface (2c). A preliminary discharge member (4) for lowering the surface potential of the surface is arranged.
[0018]
In addition, in order to make an understanding easy, the code | symbol of the corresponding element or the code | symbol of a corresponding matter of the Example shown in drawing and mentioned later in parentheses was added for reference.
[0019]
The case where the preliminary discharge member (4) is not provided will be described with reference to the proximity charging device shown in FIG. 10. Since the charging roller 2 rotates in the direction of the solid line arrow in the figure, a certain point P on the charging surface 2c. Gradually approaches point A (the closest point to the photoreceptor 1b) as it rotates. That is, it approaches the point B (the closest point to the resistance layer 2b) of the photoreceptor 1b. Since the photosensitive member 1b approaches point B after being neutralized, the potential difference Vd between the charged surface (the surface of 2b) and the charged surface (the surface of 1b) is approximately equal to the voltage of the power source 3. In this way, when the surface to be charged and the surface to be charged gradually approach each other, the discharge is upstream of the point (AB) where the surface to be charged and the charging surface are closest to each other, and the potential difference Vd is the discharge start voltage. It begins with the part beyond (the gap G is relatively large). When the discharge starts, the charged surface is charged, so that the potential gradually increases, and the potential difference Vd between the charged surface and the charged surface decreases. Accordingly, in the portion where the upstream gap G becomes smaller, the potential difference Vd falls below the discharge duration threshold value, and the discharge is terminated. In the region immediately after the start of the discharge, the amount of charge that moves with the discharge is large, and as a result, the trace of the discharge is observed as uneven charging.
[0020]
On the other hand, when the preliminary discharge member (4) is arranged as in the present invention, the discharge similar to that described above first occurs between the charging surface (1b) and the preliminary discharge member (4). ) Is lower than the potential applied by the power source (3). For example, since a certain point P on the charging surface (2c) starts to discharge between the preliminary discharge members (4), the potential at the point P is lower than the potential applied by the power source (3). Even when the point P moves to a region where discharge occurs between the charged surface (1b) and the charged surface (1b), the potential difference between the point P and the charged surface (1b) is a preliminary discharge member. Compared to the case where there is no (4), the charge is smaller, and the amount of charge that moves with the discharge that occurs between the point P and the surface to be charged (1b) is also smaller. As a result, the discharge trace is not observed as uneven charging, and uniform charging is performed.
Even when the charging member (2) is stationary without moving, the potential difference between the charged surface (2c) and the surface to be charged (1b) is small as described above, and hence uneven charging does not occur. However, when the charging member (2) is stationary, as pointed out in the prior art section, the charging surface (2c) surface area of the charging member (2) used for charging the charged surface (1b) Therefore, problems such as potential drop during charging and non-uniform charging occur. For this reason, the proximity charging device of the type in which the charging member (2) and the charging surface (2c) move is superior.
[0021]
As described above, in the proximity charging device of the present invention, even when the charging surface (2c) is moved, charging unevenness which has been a problem in the past does not occur. Since the charging surface (2c) of the charging member can be moved, the toner adhering to the charging surface (2c) can be moved compared to a proximity charging device of a type that fixes the charging surface (2c) of the charging member. The influence can be reduced.
[0022]
DETAILED DESCRIPTION OF THE INVENTION
(2) The moving speed (Va, Vb) between the charged surface (2c) and the charged surface (1b) at the closest portion (A-B) is different.
According to this, the moving speed (Va) of the charged surface (2c) can be determined irrespective of the moving speed (Vb; image process speed) of the charged surface (1b). Accordingly, it is not necessary to rotate the charging member (2) faster than necessary, and wear of the shaft of the charging member (2) and the bearing supporting the charging member (2) can be reduced. Further, the amount of heat generated at the bearing portion can be reduced.
[0023]
(3) The surface of the preliminary discharge member (4) is covered with a medium resistance material (4b).
When the surface of the preliminary discharge member (4) is coated with a high resistance material such as an insulator, no discharge occurs between the preliminary discharge member (4) and the charging member (2), and the preliminary discharge member ( The effect of placing 4) is lost. Further, when the surface of the preliminary discharge member (4) is coated with a low resistance material such as a metal, if there is a defect having a small resistance in the charging member (2), the preliminary discharge member (4) is A large current flows, and as a result, the preliminary discharge member (4) and the charging member (2) may be deteriorated and the function may be impaired.
On the other hand, since it is covered with the medium resistance material (4b), the preliminary discharge function is not impaired and the preliminary discharge member (4) is not deteriorated.
[0024]
(4) A voltage having a polarity opposite to the voltage applied to the charging member (2) is applied to the preliminary discharge member (4).
According to this, a larger potential difference is generated between the preliminary discharge member (4) and the charging member (2) than when no voltage is applied to the preliminary discharge member (4). As a result, the scale of discharge generated between the preliminary discharge member (4) and the charging member (2) is larger, and thus the amount of charge accumulated on the charging member (2) is increased. When more charge is accumulated on the surface of the charging member, the potential of the surface of the charging member (2c) is lower than the applied potential, so this portion is referred to as the surface of the charging member (2c) by the rotation of the charging member (2). When moving to a region where discharge occurs between the surface to be charged (1b), the potential difference between the surface of the charging member (2c) and the surface to be charged (1b) becomes small, and uneven charging becomes difficult to occur. Thus, the effect of the preliminary discharge member (4) is greater, and the effect of eliminating the uneven charging is higher.
[0025]
(5) The preliminary discharge member (4) is in contact with the charging member (2). According to this, since the preliminary discharge member (4) only needs to contact the charging member (2), the mounting accuracy of the preliminary discharge member (4) may not be so high. This facilitates the creation of a proximity charging device on which the preliminary discharge member (4) is mounted, and mounting the preliminary discharge member (4) does not increase the cost.
[0026]
(6) The preliminary discharge member (4) has a function of cleaning the surface of the charging member (2).
[0027]
According to this, even when the surface (2c) of the charging member (2) is soiled with toner or the like, it is cleaned by the preliminary discharge member (4c). It is possible to charge uniformly. Further, since the preliminary discharge member (4c) and the cleaning member are used together, the configuration of the apparatus is not complicated. The charging member (2) is stable over a long period of time and can uniformly charge the object (1) to be charged, and further, the configuration of the apparatus is not complicated.
[0028]
Other objects and features of the present invention will become apparent from the following description of embodiments with reference to the drawings.
[0029]
【Example】
-1st Example-
FIG. 1 is a cross-sectional view showing a schematic configuration of a proximity charging device according to a first embodiment of the present invention. The charging roller 2 that rotates in the direction of the solid arrow in the shape of a roller is provided with a resistance layer 2a on a conductor 2a (core metal) and is composed of a surface layer 2c formed on the surface thereof. Is supplied with a DC voltage from the power source 3. The photosensitive drum 1 which is cylindrical and rotates in the direction of a dotted arrow is composed of a grounded conductor 1a and a photosensitive member 1b formed on the surface thereof. As shown in FIG. 1, the charging roller 2 is opposed to the photoreceptor 1 in a non-contact manner. The charging roller 2 is opposed to the grounded preliminary discharge member 4 in a non-contact manner.
[0030]
The difference between the proximity charging device of the first embodiment and the conventional charging device is as follows:
The distance between the charging roller 2 and the photosensitive member 1 is 0.1 mm or more even at the shortest closest portion AB;
-The charging roller 2 rotates. That is, the surface of the charging roller 2 (hereinafter simply referred to as the charging surface 2c) moves;
A preliminary discharge member 4 is disposed at a position facing the charging surface 2c upstream of the closest portion AB of the charging roller 2 and the photosensitive member 1 with respect to the moving direction of the charging surface 2c. Is;
The three points.
[0031]
In the proximity charging device of the first embodiment, the charging roller 2 has a roller shape, a diameter of 15 mm, a length of 300 mm, and a resistance layer 2b having a thickness of 3 mm is formed on the conductor 2a. The resistance layer 2b is made of a material obtained by adding a halide (ionic compound) to an NBR rubber material to impart conductivity, and has a resistivity of 10⁸It is adjusted to Ωcm. The surface of the resistance layer 2b is covered with a fluorine-based resin added with conductivity by adding an ionic compound to form a surface layer 2c. The resistivity of the surface layer 2c is 10^TenIt is adjusted to be Ωcm.
[0032]
As the material constituting the resistance layer 2b, in addition to the above, a material imparted with conductivity by adding an ionic compound to various polymer materials such as rubber or resin (so-called ionic conductive material), ionic compound Instead, any material that exhibits a moderate resistivity, such as a material in which carbon is dispersed in a polymer material (so-called electronic conductive material), metal oxide (ceramics), etc. May be. However, in order to charge the photoreceptor 1 without causing uneven charging, the resistance layer is 10⁷-10⁹Must be Ωcm. Further, the surface layer 2c may or may not be formed on the surface, and the surface layer 2c may be formed of a material other than the above-described materials.
[0033]
  In the proximity charging device of the first embodiment, the charging roller 2 is driven and rotated by a driving source (not shown) in the direction of the solid line arrow in FIG. The rotation speed is adjusted so that the speed (peripheral speed) at which one point on the charging surface 2c moves is 15 mm / sec. The photoconductor 1 is also rotated by being driven by a drive source (not shown) in the direction of the dotted arrow in FIG. As shown in FIG. 1, the rotation direction of the charging roller 2 is such that the charging roller 2 in the closest portion AB where the distance between the charging roller 2 and the photosensitive member 1 is the smallest. The direction in which the surface of each photoreceptor 1 moves is the same.The bandThe speed at which the charging surface 2c of the electric roller 2 movesIsOther values than the above may be used.
[0034]
The charging roller 2 is disposed so as to face the photoreceptor 1 so that the distance at the closest portion AB is 0.1 mm or more. A voltage is applied to the conductor portion 2 a of the charging roller 2 by the power source 3 to charge the photoreceptor 1. The applied voltage is -1.5 to -2.0 kV in direct current.
[0035]
  The arrangement position of the preliminary discharge member 4 is a position facing the charging surface 2c on the upstream side of the closest portion AB between the charging roller 2 and the photosensitive member 1 with respect to the moving direction of the charging surface 2c. It is. The distance between the preliminary discharge member 4 and the charging surface 2c is 0.1 mm at the shortest distance. The distance between the preliminary discharge member 4 and the charging unit 2 is not necessarily 0.1 mm. However, as described later, the distance between the preliminary discharge member 4 and the charging unit 2 needs to be a distance at which discharge occurs between the preliminary discharge member 4 and the preliminary discharge member 4.The
[0036]
In the proximity charging device of the first embodiment, the preliminary discharge member 4 is a grounded metal, and discharge occurs between the charging surface 2 c of the charging roller 2 and the preliminary discharge member 4. The preliminary discharge member 4 does not necessarily have to be a metal, and may be any conductive material that can continuously discharge from the charging surface 2c. That is, it may be a conductive plastic or film.
[0037]
In addition, in the proximity charging device of the first embodiment, the charging roller 2 has a roller shape, but may have a belt shape. FIG. 2 is a schematic view of the proximity charging device when the charging roller 2 has a belt shape.
[0038]
-Second Example-
FIG. 3 shows a schematic configuration of the proximity charging device according to the second embodiment of the present invention. The difference between the proximity charging device of the second embodiment and the proximity charging device of the first embodiment is as follows.
The moving speed of the charging surface 2c and the photosensitive member 1b at the closest part A-B between the charging surface 2c and the photosensitive member 1b is different;
Is a point.
[0039]
In the proximity charging device of the second embodiment, as in the case of the first embodiment, the charging roller 2 is rotated in the direction of the solid line arrow in FIG. 1 is rotated in the direction of a dotted arrow in FIG. 3 by a drive source (not shown). However, in the case of the second embodiment, the speed Va (vector) at which the charging surface 2c moves and the movement of the surface of the photosensitive member 1b at the closest portion AB between the charging roller 2 and the photosensitive drum 1. The speed of rotation of the charging roller 2 is adjusted so that the speed Vb (vector) to be operated is different. In other words, the rotation speed of the charging roller 2 is limited so that Va ≠ Vb. In the proximity charging device of the second embodiment, the moving speed of the charging surface 2c is 15 mm / sec. On the other hand, the moving speed of the photosensitive member 1b is 180 mm / sec. The speed at which the charging surface 2c moves may not be the above-mentioned value, as long as the charging roller 2 is rotating. However, a relatively small value of about 10 to 100 mm / sec is desirable in view of the fact that the shaft of the charging roller 2 is less worn.
[0040]
The proximity charging device of the second embodiment is the same as the proximity charging device of the first embodiment, except that the speed at which the charging surface 2 moves and the speed at which the photosensitive drum 1 moves are different.
[0041]
-Third Example-
FIG. 4 shows a schematic configuration of a proximity charging device according to a third embodiment of the present invention. The difference between the proximity charging device of the third embodiment and the proximity charging device of the first embodiment is as follows.
The surface of the pre-discharge member 4 is coated with a medium resistance material 4b;
Is a point.
[0042]
In the proximity charging device of the third embodiment, the resistivity of the surface of the substrate conductor 4a of the preliminary discharge member 4 is 10%.⁸It is coated with a medium resistance resin layer 4b adjusted to Ωcm. The coating material used is a fluorine-based resin to which conductivity is imparted by adding an ionic compound.
The resistivity of the coating material may not be the above value. However, the resistivity of the coating material is large (10^TenIn this case, since charges are accumulated on the surface of the resin layer 4b of the preliminary discharge member, no discharge occurs between the charging member 2 and the resin layer 4b, and the effect of arranging the preliminary discharge member 4 is achieved. Will disappear. Also, the resistivity of the coating material is small (10^FiveIf the charging member 2 has a defect (part where the resistance is locally small), a large current flows from the charging member 2 to the resin layer 4b through the part, and the charging member 4 or preliminary discharge The resin layer 4b of the member 4 deteriorates and does not perform its function. For this reason, as the conductive resin layer 4b of the preliminary discharge member 4, the resistivity (10⁶-10⁹It is necessary to use materials with Ωcm).
[0043]
Other than the above-described coating materials, any coating materials may be used as long as the resistivity can be adjusted to the medium resistance region as described above. The proximity charging device of the third embodiment is the same as the proximity charging device of the first embodiment except that the surface of the preliminary discharge member 4 is coated with a medium resistance material.
[0044]
-Fourth embodiment-
FIG. 5 shows a schematic configuration of a proximity charging device according to a fourth embodiment of the present invention. The difference between the proximity charging device of the fourth example and the proximity charging device of Example 1 is as follows.
A voltage having a polarity opposite to the voltage applied to the charging member is applied to the preliminary discharge member;
In the proximity charging apparatus of the fourth embodiment, the charging member 2 is charged with the voltage of −2.0 kV from the charging member power source 3 a to charge the photosensitive member 1. Then, a voltage of +0.5 kV is applied to the preliminary discharge member 4 from the preliminary discharge member power source 3b. The voltage applied to the preliminary discharge member 4 may not be the above-mentioned value. However, if a positive voltage exceeding 0.5 kV is applied, a discharge occurs between the preliminary discharge member 4 and the photoreceptor layer 1b. Can happen. In this case, there arises a problem that a trace of discharge is seen in the image. Moreover, in order to prevent the electric discharge which occurs between the preliminary discharge member 4 and the photoreceptor layer 1b, it is conceivable to arrange an insulator. However, there is a problem that the entire charging device has a complicated configuration. . For this reason, it is desirable that the voltage applied to the preliminary discharge member 4 is a value that does not exceed +0.5 kV.
[0045]
The proximity charging device of the fourth embodiment is the same as the proximity charging device of the first embodiment, except that a voltage having a polarity opposite to the voltage applied to the charging member 2 is applied to the preliminary discharge member 4.
[0046]
-Fifth embodiment-
FIG. 6 shows a schematic configuration of a proximity charging device according to a fifth embodiment of the present invention. The difference between the proximity charging device of the fifth embodiment and the proximity charging device of the first embodiment is as follows:
The grounded pre-discharge member is in contact with the charging member;
Is a point.
In the proximity charging device of the fifth embodiment, the preliminary discharge member 4 is a conductive polycarbonate film. However, the preliminary discharge member 4 may be other than the above-described materials, and may be any material as long as it can be brought into contact with the charging member 2 with various conductive films, rubber, or the like. .
[0047]
In the proximity charging device of the fifth embodiment, the preliminary discharge member 4 is in contact with the charging member 2 whether the charging device is used or not. However, the preliminary discharge member 4 may be separated from the charging member 2 when a contact / separation mechanism is provided and the charging device is not used.
[0048]
The proximity charging device of the fifth embodiment is the same as the charging device of the first embodiment except that the preliminary discharge member 4 is in contact with the charging member 2 for at least the charging process period.
[0049]
-Sixth Example-
FIG. 7 shows a schematic configuration of a proximity charging device according to a sixth embodiment of the present invention. The difference between the proximity charging device of the sixth embodiment and the proximity charging device of the first embodiment is as follows.
The preliminary discharge member 4c has a function of cleaning the surface of the charging member 2;
In the proximity charging device of the sixth embodiment, the preliminary discharge member 4c is a brush in which conductive fibers are brought together. However, the pre-discharge member 4c may be other than the above-mentioned brush, and any material can be used as long as it can remove dirt such as a toner adhering to the surface of the charging member 2, such as a film or an elastic blade. It may be. Further, the brush, film, elastic blade or the like constituting the preliminary discharge member 4c may be made conductive, and a voltage may be applied to the brush, film, elastic blade or the like to enhance the removal capability of toner or the like.
[0050]
The proximity charging device of the sixth embodiment is the same as the proximity charging device of the first embodiment except that the preliminary discharge member 4c has a function of cleaning the surface of the charging member 2.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view of a main part of a first embodiment of the present invention.
FIG. 2 is a cross-sectional view of a modified example of the first embodiment, showing an aspect including a belt-shaped charging member 2;
FIG. 3 is a cross-sectional view of the main part of a second embodiment of the present invention, showing a mode in which the surface speeds of the charging member 2 and the photosensitive drum 1 are different.
FIG. 4 is a cross-sectional view of the main part of a third embodiment of the present invention, showing a state in which the surface of the preliminary discharge member 4 is covered with a conductive resin layer 4b.
FIG. 5 is a cross-sectional view of the main part of a fourth embodiment of the present invention, showing a mode in which a voltage having a polarity different from that applied to the charging member 2 is applied to the preliminary discharge member 4;
6 is a cross-sectional view of a main part of a fifth embodiment of the present invention, showing a state in which a preliminary discharge member 4 is in contact with the charging member 2. FIG.
FIG. 7 is a cross-sectional view of the main part of a sixth embodiment of the present invention, showing a mode in which the preliminary discharge member 4 also has a function of cleaning the charging member 2;
FIG. 8 is a block diagram showing a cross-sectional view of an example of the configuration of a conventional image forming apparatus.
FIG. 9 is a block diagram showing, in section, an example of the configuration of a conventional contact charging device.
FIG. 10 is a block diagram showing, in section, an example of the configuration of a conventional proximity charging device.
[Explanation of symbols]
1: Photoconductor drum 1a: Photoconductor
1b: Conductor 2: Charging member
2a: Conductor 2b: Resistance layer (elastic layer)
2c: Surface layer 3: Power supply
3a: Power supply for charging member 3b: Power supply for preliminary discharge member
4: Predischarge member 4a: Conductor
4b: Conductive resin layer 4c: Cleaner and preliminary discharge member
5: Electrostatic latent image forming means 6: Developing means
7: Transfer means 8: Transfer body (paper)
9: Cleaning means A: Charging member surface layer closest position
B: Photoconductor closest position G: A-B gap

Claims

The charging surface of the charging member faces non-contact with the surface to be charged, which is movable, and a voltage is applied to the charging member to directly connect the charging surface and the body to be charged. In the proximity charging device that causes discharge and charges the charged surface,
Wherein said charged surface during the charging of the charged surface to move, the distance between the charging surface and the object to be charged surface, it is also 0.1 [mm] or more in the smallest closest unit, outermost proximal part The charged surface and the charging surface move in the same direction, and the charging surface moves in a position facing the charging surface upstream of the closest portion with respect to the moving direction. A proximity charging device, comprising: a pre-discharge member that discharges the opposing charging surface to lower the surface potential of the opposing charging surface.

The proximity charging device according to claim 1, wherein moving speeds of the charged surface and the charged surface at the closest portion are different.

2. The proximity charging device according to claim 1, wherein the surface of the preliminary discharge member is coated with a medium resistance material.

The proximity charging device according to claim 1, wherein a voltage having a polarity opposite to a voltage applied to the charging member is applied to the preliminary discharge member.

The proximity charging device according to claim 1, wherein the preliminary discharge member is in contact with the charging member.

The proximity charging device according to claim 1, wherein the preliminary discharge member has a function of cleaning a surface of the charging member.