JP3585202B2

JP3585202B2 - Image forming device

Info

Publication number: JP3585202B2
Application number: JP10821497A
Authority: JP
Inventors: 治司水石; 勝田中; 俊隆山口; 滋渡邊; 謙三巽; 武男須田; 洋吉永; 賢雨宮; 真由美大堀
Original assignee: Ricoh Co Ltd
Current assignee: Ricoh Co Ltd
Priority date: 1997-04-10
Filing date: 1997-04-10
Publication date: 2004-11-04
Anticipated expiration: 2017-04-10
Also published as: JPH10282798A

Description

【０００１】
【発明の属する技術分野】
本発明は、回転駆動されながら表面にトナー像が形成される像担持体と、該像担持体の表面に当接しながら、その当接部において、像担持体表面の移動方向とほぼ同一方向に送られる転写材の表面に、像担持体表面に形成されたトナー像を静電的に移行させて転写する転写装置と、該転写装置により像担持体表面のトナー像を転写材の表面に転写する転写部よりも、転写材の移動方向下流側に位置し、かつ転写部を通過した転写材の裏面に対して離間した状態で、当該裏面の側に配置されると共に、転写材の移動方向に対してほぼ直交する向きに長く延び、前記像担持体表面に形成されたトナー像のトナーと同極性の電圧を印加されて転写材を除電する除電装置と、該除電装置を保持するホルダとを具備する画像形成装置に関する。
【０００２】
【従来の技術】
電子複写機、プリンタ、ファクシミリ或いはこれらの少なくとも２つの機能を備えた複合機などとして構成される上記形式の画像形成装置は従来より周知である。
【０００３】
この形式の画像形成装置においては、像担持体表面に形成されたトナー像のトナーと逆極性の電圧を転写装置に印加し、これにより像担持体表面と転写装置の間に電界を形成し、像担持体表面のトナー像を転写材の表面に静電的に移行させてトナー像を転写している。またトナー像転写後の転写材に対し、除電装置によって、トナーと同極性の電荷を付与し、転写材の像担持体表面からの分離性を高めている。
【０００４】
このような除電装置として、従来、その長手方向に配列された複数の針状突起を有する除電針部材が用いられ、その針状突起の尖端から転写材の裏面に向く放電によって、転写材に対してトナーと同極性の電荷を付与している。これによって、像担持体表面に対する転写材の密着力をなくし、或いはその密着力を弱めて転写材を像担持体表面から確実に分離させている。
【０００５】
ところで、像担持体表面から転写材にトナー像を転写する転写部においては、上述のように、転写材に対し、トナーの帯電極性と逆極性の電荷が付与されるので、像担持体表面から離れた直後の転写材の表面に担持されたトナー像と、そのまわりの転写材表面、すなわち地肌部との間に電界が形成され、これによってトナー像を形成するトナーの一部がトナー像近傍の地肌部に静電的に移行することがある。このような現象は、一般に「トナー散り」と称せられているが、かかる現象が発生すると、転写材上に転写されたトナー像が不鮮明となり、その画質が劣化する。
【０００６】
上述の欠点を除去するには、除電装置の針状突起の尖端を転写装置に近づけ、転写部により近い部分で転写材を除電する方法が考えられる。このようにすれば、転写部を通過した直後の転写材を除電できるので、上述したトナー散り現象の発生を防止できる。ところが、この構成によると、除電装置の針状突起尖端が転写装置に近づくので、その両者間に、例えば放電による電流のリークが発生し、これによって転写装置の電位が低下し、像担持体から転写材へのトナー像の転写効率が低下する。
【０００７】
そこで、転写装置へ印加する電圧の値を高め、転写効率の低下を補うようにすることも考えられるが、除電装置と転写装置との間に流れるリーク電流の値は、湿度などの周囲の環境条件によって大きく左右されるので、転写装置への印加電圧の値を画一的に高めてしまうと、例えば低湿度時には、その電圧値が過多となり、これによって転写部に存する転写材上のトナーに対し、その本来の極性と逆極性の電荷が注入され、当該トナーの帯電極性が反転することがある。このようになれば、極性の反転したトナーが像担持体の表面に再付着するので、転写材へのトナー像の転写効率が低下し、転写材に転写されたトナー像の画質が劣化する不具合を免れない。
【０００８】
一方、像担持体から転写材を分離するときの分離性はできるだけ高いことが望ましい。このように転写材の分離性を高めるには、除電装置に印加する電圧を高めればよい。ところが、除電装置への印加電圧の極性は、転写材表面に転移したトナーの極性と同極性であるため、除電装置に対して高い電圧を印加すると、転写材表面のトナーが像担持体表面に静電的に移行して再付着し、転写材表面のトナー像の画質が劣化するおそれを免れない。
【０００９】
【発明が解決しようとする課題】
本発明は、上述した新規な認識に基づきなされたものであって、その目的とするところは、前述のトナー散り現象の発生を防止できると共に、除電装置と転写装置との間の電流のリークに基づく転写効率の低下を阻止でき、しかも支障なく像担持体表面からの転写材の分離性を高めることのできる冒頭に記載した形式の画像形成装置を提供することにある。
【００１０】
【課題を解決するための手段】
本発明は、上記目的を達成するため、冒頭に記載した形式の画像形成装置において、前記除電装置が、前記転写部よりも転写材の移動方向下流側の転写材裏面部分に向けて先細に形成され、かつ当該除電装置の長手方向に配列された複数の第１の針状突起と、該第１の針状突起よりも前記転写部寄りの転写材裏面部分に向けて先細に形成され、かつ当該除電装置の長手方向に配列された複数の第２の針状突起を有し、前記ホルダが絶縁体より成ると共に、該ホルダの内側の空間内に前記第１の針状突起と第２の針状突起が配置され、転写材の移動方向における前記空間の幅が、転写材の裏面に近づくに従って拡大していることを特徴とする画像形成装置を提案する（請求項１）。
【００１１】
同じく、本発明は、上記目的を達成するため、冒頭に記載した形式の画像形成装置において、前記除電装置が、前記転写部よりも転写材の移動方向下流側の転写材裏面部分に向けて先細に形成され、かつ当該除電装置の長手方向に配列された複数の第１の針状突起と、該第１の針状突起よりも前記転写部寄りの転写材裏面部分に向けて先細に形成され、かつ当該除電装置の長手方向に配列された複数の第２の針状突起を有し、前記第１の針状突起と第２の針状突起とのなす角度であって、第１の針状突起から、転写材の移動方向上流側へ向けて計った角度が１０°乃至４０°に設定されていることを特徴とする画像形成装置を提案する（請求項２）。
【００１２】
また、本発明は、上記目的を達成するため、冒頭に記載した形式の画像形成装置において、前記除電装置が、前記転写部よりも転写材の移動方向下流側の転写材裏面部分に向けて先細に形成され、かつ当該除電装置の長手方向に配列された複数の第１の針状突起と、該第１の針状突起よりも前記転写部寄りの転写材裏面部分に向けて先細に形成され、かつ当該除電装置の長手方向に配列された複数の第２の針状突起を有し、前記第１の針状突起の尖端から転写材の裏面までの距離よりも、第２の針状突起の尖端から転写材の裏面までの距離が大きく設定されていることを特徴とする画像形成装置を提案する（請求項３）。
【００１３】
さらに、上記請求項１乃至３のいずれかに記載の画像形成装置において、前記除電装置が１枚の除電針部材を有し、該除電針部材に、前記第１の針状突起と第２の針状突起が共に形成されていると有利である（請求項４）。
【００１４】
また、上記請求項１乃至３のいずれかに記載の画像形成装置において、前記除電装置が第１及び第２の少なくとも２枚の除電針部材を有し、その第１の除電針部材に前記第１の針状突起が形成され、第２の除電針部材に前記第２の針状突起が形成されていると有利である（請求項５）。
【００１８】
【発明の実施の形態】
以下、本発明の実施形態例を図面に従って説明し、併せて前述の従来の欠点を図面に即してより具体的に明らかにする。
【００１９】
図１は本発明一実施形態例の画像形成装置の内部を正面側から示した概略断面図であり、その画像形成装置本体１には、作像ユニット２が着脱可能に装着されていると共に、転写ユニット３が組込まれている。ここに示した画像形成装置は複写機として構成され、この複写機にプリンタやファクシミリなどの機能をもたせることもできる。作像ユニット２は画像形成装置本体１の手前側から画像形成装置本体に対して着脱される。画像形成装置の正面側ないしは手前側とは、通常オペレータがその画像形成装置を操作するとき位置する側であり、その反対側が画像形成装置の奥側である。
【００２０】
図２は作像ユニット２と転写ユニット３とを正面側から見たときの拡大断面図である。図１及び図２に示すように、作像ユニット２はユニットケース４を有し、このケース４の内部には像担持体の一例であるドラム状の感光体５と、帯電装置の一例である帯電ローラ６がそれぞれ回転自在に組付けられている。
【００２１】
画像形成動作時に、感光体５は、図示していない駆動装置によって図２における時計方向に回転駆動され、このとき除電光Ｌ１によって感光体表面が基準電位に除電される。帯電ローラ６は感光体５の表面に圧接しながら従動回転し、感光体表面を所定の極性、本例ではマイナス極性に一様に帯電する。このように帯電された感光体５の表面部分には、原稿からの光像又は光変調されたレーザＬ２が照射され、これによって感光体５上に所定の静電潜像が形成される。光を照射された感光体表面部分の表面電位が低下し、これが静電潜像を形成する。光の当てられない感光体表面部分は、実質的に電位は低下せず、これが地肌部を形成する。
【００２２】
一方、ユニットケース４には、図２に示すように現像装置７の現像ローラ８が回転自在に支持され、本例の現像ローラ８には、感光体の帯電極性と同極性のバイアス電圧が印加される。またユニットケース４の一部によって構成された現像ケース９には、粉体状の現像剤Ｄが収容され、この現像剤Ｄは、反時計方向に回転駆動される現像ローラ８上に担持されて搬送される。かかる搬送現像剤が感光体５と現像ローラ８との間に至ったとき、現像剤中のトナーが感光体５に形成された静電潜像に静電的に移行し、その潜像がトナー像として可視像化される。本例では、トナーが、感光体５の帯電極性と同極性のマイナス極性に帯電され、かかるトナーが光の当てられた感光体表面部分、すなわち静電潜像に静電的に付着する。所謂、反転現象が行われるのである。
【００２３】
転写ユニット３は、図３及び図４にも示すように、転写装置の一構成例である転写ローラ１１と、除電装置１４と、この除電装置１４を保持する絶縁体より成るホルダ１５と、これらを支持する保持体１３とを有し、転写ローラ１１と除電装置１４は感光体５に対して平行に延びている。本例の転写ローラ１１は、導電性材料、例えば金属より成る中心軸３８と、そのまわりに固設された中抵抗体より成る弾性体３９を有し、その弾性体３９の体積固有抵抗率は、例えば１０^６乃至１０^９Ωｃｍ程度である。かかる転写ローラ１１は、図２に示した状態で、感光体５の表面に対向して圧接しながら、図示していない駆動装置によって反時計方向に回転駆動される。転写ローラ１１は、感光体５との当接部において、当該転写ローラの表面が、感光体５の表面の移動方向と同じ方向に移動する向きに回転駆動されるのである。
【００２４】
一方、図１に示した複数の給紙装置１６，１７，１８，１９のうちの選択された給紙装置から、転写材の一例である転写紙Ｐが感光体５と転写ローラ１１の間の転写部２０へ矢印Ａで示すように搬送される。そして、転写紙Ｐが転写部２０を通過するとき、転写ローラ１１に印加された転写電圧の作用によって、感光体５の表面に形成されたトナー像が転写紙Ｐ上に転写される。転写紙Ｐは、感光体５の表面に当接しながら、その当接部において、感光体５の表面の移動方向とほぼ同一方向に送られ、このとき、図５に示すように、転写ローラ１１の中心軸３８には、電源１０によって、感光体表面に形成されたトナー像のトナーの帯電極性と逆極性、本例ではプラス極性の電圧が印加される。これによって転写ローラ１１と感光体５の間の転写部２０には、感光体５上のトナーが転写紙Ｐの表面に移行する向きの電界が形成され、そのトナー像が転写紙Ｐの表面に転写される。
【００２５】
一方、除電装置１４は、図５から明らかなように、感光体表面のトナー像を転写紙Ｐの表面に転写する転写部２０よりも転写紙Ｐの移動方向下流側に位置し、しかも転写部２０を通過した転写紙Ｐの裏面に対して離間した状態で、その裏面の側に配置され、転写紙Ｐの移動方向Ａに対してほぼ直交する向き、すなわち感光体５の軸方向に長く延びている。かかる除電装置１４は、導電性材料、例えば金属の薄い板材より成る除電針部材２８により構成され、図５に示すように、この除電装置１４に対して、電源１２によって、感光体表面に形成されたトナー像のトナーの帯電極性、並びに感光体表面の帯電極性と同極性、本例ではマイナス極性の電圧が印加される。除電装置１４の構成に関しては後に詳しく説明する。
【００２６】
このようにして、転写部２０を通過した転写紙Ｐは、除電装置１４からのマイナス電荷の放電作用を受けながら感光体５から分離される。除電装置１４は、転写装置によって帯電された転写材の電荷、本例ではプラス極性の電荷を除去し、ないしはその電荷量を少なくし、像担持体からの転写材の分離性を高める用をなす。感光体５を離れた転写紙Ｐは、図１に示すように、定着装置２１の定着ローラ２１Ａと加圧ローラ２１Ｂの間を通り、このとき転写紙上のトナー像が熱と圧力の作用によって転写紙上に定着される。次いで、この転写紙Ｐはトナー像より成る記録画像の形成されたコピー紙として画像形成装置本体外に排出され、排紙トレイ２２上にスタックされる。
【００２７】
転写紙Ｐの搬送方向に関し、定着装置２１の上流側の部位には、例えば除電ブラシ５０より成る導電性の除電部材が設けられ、この除電ブラシ５０は、定着装置２１へ進入する前の転写紙Ｐの裏面に接触すると共に、図２に示すようにアースされている。
【００２８】
トナー像転写後に感光体５上に残留しているトナーは、クリーニング装置２３のクリーニング部材２４によって感光体表面から除去され、ユニットケース４の一部によって構成されたクリーニングケース２５内に落下する。
【００２９】
図３は転写ユニット３の斜視図であり、図４はその分解斜視図であるが、これらの図と図２に示すように、転写装置の一例である転写ローラ１１を保持する保持体１３は、第１保持部材２６と第２保持部材２７とを有し、第１保持部材２６はその基端側が画像形成装置本体１の各側板３０，３１に支持され、通常は画像形成装置本体１に付設された支持部材４９に支持されて、図２に示した姿勢を保つ。また、第１及び第２保持部材２６，２７は、例えば硬質の合成樹脂により構成され、これらは互いに連結されている。これらの保持部材２６，２７を一体に構成することもできる。
【００３０】
図２及び図４に示すように、転写ローラ１１は、その中心軸３８の手前側と奥側の部位が、軸受４０，４１にそれぞれ回転自在に支持され、各軸受４０，４１は第２保持部材２７にそれぞれ一体に形成された軸受保持部４２，４３に保持され、各軸受４０，４１と第２保持部材２７との間には、それぞれ圧縮ばね４４，４５が圧装されている。
【００３１】
また図４に示すように、転写ローラ１１の中心軸手前側にはギア４６が当該中心軸３８に対して相対回転不能に嵌合し、中心軸３８の前後の端部には突き当てローラ４７，４８がそれぞれ回転自在に嵌合している。ギア４６に、図示していない駆動ギアが噛み合い、これらのギアを介して、転写ローラ１１が駆動装置によって回転駆動される。このとき、突き当てローラ４７，４８が感光体５の表面に突き当てられ、感光体５に対して転写ローラ１１が位置決めされる。また図４に示すように、第２保持部材２７の除電装置取付部５７に、除電装置１４のホルダ１５が着脱可能に装着されている。
【００３２】
以上のように、図示した画像形成装置は、回転駆動されながら表面にトナー像が形成される感光体５として構成された像担持体と、像担持体の表面に当接しながら、その当接部において、像担持体表面の移動方向とほぼ同一方向に送られる転写紙Ｐより成る転写材の表面に、像担持体表面に形成されたトナー像を静電的に移行させて転写する転写ローラ１１として構成された転写装置と、その転写装置により像担持体表面のトナー像を転写材の表面に転写する転写部２０よりも、転写材の移動方向下流側に位置し、かつ転写部２０を通過した転写材の裏面に対して離間した状態で、その裏面の側に配置されると共に、転写材の移動方向に対してほぼ直交する向きに延び、像担持体表面に形成されたトナー像のトナーと同極性の電圧を印加されて転写材を除電する除電装置１４と、その除電装置１４を保持するホルダ１５とを具備している。ここでは、便宜上、像担持体からトナー像を転写される側の転写材の面を表面と称し、これと反対側の面を裏面と称していることは上記説明から明らかである。
【００３３】
上述した構成自体は、従来の画像形成装置と異なるところはない。その際、従来のこの種の画像形成装置においては、その除電装置１４が図１４及び図１５に示すように、転写紙Ｐの移動方向Ａに対してほぼ直交する方向に延び、その長手方向に多数の針状突起２９ａが形成された導電性の除電針部材２８ａにより構成されていた。かかる除電針部材２８ａに、前述のようにトナーの帯電極性と同極性の電圧が印加され、その各針状突起２９ａの尖端からのマイナス電荷の放電によって、転写材Ｐに電荷が付与される。
【００３４】
その際、図１４に模式的に示し、かつ先に説明したように、転写ローラ１１には、感光体５上のトナーＴと逆極性のプラスの電圧が印加され、これによって感光体表面のマイナス極性のトナーＴが転写紙Ｐの表面に静電的に移行するのであるが、このとき、転写ローラ１１に当接した転写紙Ｐの裏面は、転写ローラ１１に印加された電圧の作用によりプラス極性に帯電する。このような転写紙Ｐの裏面に対し、除電装置１４の針状突起２９ａからの放電によって、転写紙Ｐの裏面にマイナスの電荷が付与され、これにより転写紙Ｐのプラスの電荷が除去され、ないしは減少する。このようにして、感光体５の表面に対する転写紙Ｐの密着力が除去ないしは軽減され、転写紙Ｐが感光体５の表面に付着したままとなることが阻止され、転写紙Ｐはその自重によって曲面状の感光体５の表面から分離される。
【００３５】
ところが、図１４に示すように、感光体５から離れた直後の転写紙Ｐの表面にはマイナス極性のトナーが担持され、その裏面はプラス極性に帯電しているので、転写紙Ｐの表面に担持されたトナー像のトナーＴと、そのまわりの転写紙表面部分、すなわち地肌部との間に、図１４に矢印Ｅで示す電界が形成される。これによって、そのトナー像の一部のトナーが当該トナー像の近傍の転写紙表面部分に静電的に移行する。これが「トナー散り」現象であり、この現象は転写紙Ｐの移動方向Ａにおけるトナー像の前方領域と後方領域に生じやすい。かかるトナー散り現象が発生すると、転写紙Ｐに転写されたトナー像が不鮮明となり、その画質が劣化する。
【００３６】
上述した欠点を除去する方法として、図１６に示すように、除電装置１４の針状突起２９ａの尖端を転写部２０に近づけ、その針状突起２９ａからのマイナス電荷の放電により、転写紙表面のトナーが地肌部に散る前に、転写紙Ｐを除電することが考えられる。このようにすれば、転写部２０を通過した直後の転写紙Ｐを除電できるので、感光体表面から分離した直後の転写紙Ｐの裏面のプラス電荷をなくし、或いはその電荷量を少なくできるので、図１４に示した電界Ｅが形成されることを防止でき、トナー散りの発生を阻止することができる。
【００３７】
ところが、除電装置１４と転写ローラ１１を図１６に示すように近づけると、これらには互いに逆極性の高い電圧が印加されているので、両者の間に、例えば放電による電流のリークが発生する。特に湿度の高い環境下においては、リーク現象が発生しやすくなる。このような電流のリーク現象が発生すれば、転写ローラ１１の電位が低下し、これによって感光体５から転写紙Ｐへのトナー像の転写効率が低下する。
【００３８】
そこで、転写ローラ１１に対し、より高い電圧を印加し、上述した転写効率の低下を補うようにしたとすると、転写ローラ１１と除電装置１４との間に流れるリーク電流の値は環境条件によって異なるため、例えば低湿度時には、転写ローラ１１への印加電圧値が過多となり、これによって転写部２０に存する転写紙上のトナーにプラスの電荷が注入され、その極性がプラスに反転し、これが感光体表面に再付着するおそれを免れない。
【００３９】
また図２を参照して先に説明したように、定着装置２１へ送られる前の転写紙Ｐの裏面に、アースされた除電ブラシ５０を接触させているが、これは、除電装置１４からの放電によって、転写紙Ｐの裏面がマイナス極性に帯電したときも、その転写紙Ｐの裏面を除電し、定着ローラ２１Ａと加圧ローラ２１Ｂの間に転写紙Ｐが挟まれたとき、転写紙Ｐの表面のトナーが静電的に定着ローラ２１Ａの表面に付着することを防止するための対策である。
【００４０】
このような構成を採用した場合、図１６に示したように除電装置１４の針状突起尖端を転写部２０に近づけ、除電装置１４と感光体５との間の距離を小さくすると、除電装置１４による放電によって転写紙Ｐの裏面が強くマイナスに帯電する。このマイナスの電荷は、図１６に示すように除電ブラシ５０によって除電されるが、このときその電荷量が多いと、当該電荷が除電ブラシ５０に流れるとき、転写紙Ｐの表面に担持されたトナー像のトナーに静電的な影響を与え、これによって一部のトナーが、その周辺の地肌部に散る。この現象は、文字などのトナー像のまわりにトナーが散ることから、文字散りと称せられているが、かかる現象が発生すれば、そのトナー像の画質が劣化する。
【００４１】
また、図１４に示した従来の構成において、転写紙Ｐを感光体５から効率よく分離するには、除電装置１４に印加する電圧の値を高くする必要がある。ところがこのようにすると、この印加電圧の極性と、感光体５から離れた直後の転写紙Ｐ上の表面に担持されたトナーＴの帯電極性は同極性であるため、一部のトナーＴが静電的に転写紙Ｐの表面から離れ、これが感光体５の表面に再付着するおそれがあり、これによって当該トナー像の画質が劣化する。また除電装置１４への印加電圧を高めると、転写紙Ｐの裏面のマイナス帯電量が増えるため、その電荷を除電ブラシ５０によって除去するときに、前述の文字散り現象が発生しやすくなる。
【００４２】
なお、図１４及び図１６において、転写紙Ｐの裏面側に付した「＋」及び「−」の符号は、その帯電極性を示しており、またこれらの図にはトナーの粒子を模式的に拡大して示してあるが、その各トナーＴに付した符号「−」もその帯電極性を示している。これは図５及び図７においても同様である。
【００４３】
上述した各種欠点を除去するため、本例の画像形成装置においては、図５及び図６に示すように、前述の除電装置１４が、その長手方向に配列された複数の第１の針状突起２９と、同じく除電装置１４の長手方向に配列された複数の第２の針状突起３２を有している。ここに示した例では、除電装置１４が金属板などの導電性材料より成る１枚の除電針部材２８を有し、その除電針部材２８に、多数の第１の針状突起２９と多数の第２の針状突起３２が共に形成されている。
【００４４】
各第１の針状突起２９は、転写部２０よりも、転写紙Ｐより成る転写材の移動方向下流側の転写材裏面部分に向けて先細に形成され、各第２の針状突起３２は、第１の針状突起２９よりも転写部２０寄りの転写材裏面部分に向けて先細に形成されている。各第１の針状突起２９と各第２の針状突起３２が、除電針部材２８の延在方向に交互に配置され、これらが互いに０°より大なる角度をなして感光体５に向けて突出しているのである。図６には、第１及び第２の針状突起２９，３２を拡大して示してあるが、その各針状突起２９，３２の根元部の除電装置長手方向の幅Ｗは、例えば２ｍｍ程に設定される。
【００４５】
このように形成された除電装置１４に、前述の如く電源１２によってトナーと同極性のマイナスの電圧が印加されるのであるが、このとき、除電装置１４は、転写紙Ｐの移動方向Ａに対してその下流側の部位を向いた第１の針状突起２９と、これよりも上流側の部位を向いた第２の針状突起３２を有し、その各尖端からの放電によって転写紙Ｐの裏面にマイナスの電荷を付与する。第２の針状突起３２が転写部２０の近傍に位置し、第１の針状突起２９が、転写部２０よりも転写紙搬送方向下流側の部位を向き、図示した例では第１の針状突起２９が、転写紙Ｐの裏面に対して垂直な方向に突出している。
【００４６】
上記構成により、転写紙Ｐは、その送り方向Ａの広い範囲Ｓ（図５）に亘って、マイナス電荷の放電作用を受ける。転写紙Ｐは、従来よりも長い時間に亘って放電による除電作用を受けるのである。このため、除電装置１４に印加する電圧値を従来より大きく下げることができる。除電装置に印加する電圧値の絶対値が従来より低いのであるが、転写紙Ｐを長い時間をかけて除去するので、その除電効果が低下することはない。第２の針状突起３２の尖端は、転写部２０の近くに位置し、転写ローラ１１に極く接近して位置しているので、図１６を参照して先に説明したように、トナー散り現象の発生を阻止でき、しかも除電装置１４に印加される電圧値が低く抑えられるので、除電装置１４と転写ローラ１１との間のリーク電流の発生を防止でき、転写ローラ１１への印加電圧の値を特に高めなくとも、トナー像転写効率の低下を阻止することができ、感光体５へのトナーの再付着を防止できるのである。
【００４７】
また、除電装置１４に印加する電圧値を上述のように下げても、転写紙Ｐを長い時間をかけて除電するので、その除電効果を高めることができ、これによって、除電後の転写紙Ｐの裏面がマイナス極性に帯電しても、その帯電量を下げることができる。これによっても、転写紙Ｐ上のトナーが感光体５に向けて再付着する現象の発生を阻止でき、さらに除電ブラシ５０による除電後の文字散り現象の発生も防止できる。このようにして、転写紙Ｐを感光体５から効率よく分離させ、しかも転写紙Ｐ上に高品質なトナー像を形成することができるのである。なお、除電装置１４の放電によって、転写紙Ｐの裏面がマイナス極性に帯電しても、その帯電極性は感光体表面の帯電極性と同極性であるので、その帯電によって転写紙Ｐの感光体表面からの分離性が低下することはなく、むしろ、その分離性が高められる。
【００４８】
ところで、除電装置１４を保持するホルダ１５は絶縁体より成るが、図５に示すように、除電装置１４の基端側１４Ａが、ホルダ１５の一対の壁部１５Ａ，１５Ｂによって挟持され、これによって除電装置１４がホルダ１５に保持されている。またホルダ１５の両壁部１５Ａ，１５Ｂは、転写紙Ｐの側に近づくに従って互いに離間し、ここに空間Ｇが形成されている。このようなホルダ１５の内側の空間Ｇ内に、除電装置１４の第１の針状突起２９と第２の針状突起３２が配置されている。これらの針状突起２９，３２がホルダ１５の空間Ｇから外部に突出していると、これらの針状突起２９，３２に転写紙Ｐが接触するおそれがあるので、これら針状突起を空間Ｇ内に収めたのである。転写紙Ｐがホルダ１５の壁部先端に軽く接するようなことがあっても、ホルダ１５は絶縁体であるため何ら支障を生じることはない。
【００４９】
ホルダ１５を上述のように構成した場合、そのホルダ１５の空間Ｇの幅を転写紙Ｐの側に向けて漸次拡大させる必要がある。転写紙Ｐより成る転写材の移動方向Ａにおける空間Ｇの幅が、転写材の裏面に近づくに従って拡大するように、ホルダ１５を構成するのである。かかる構成により、第１の針状突起２９と第２の針状突起３２によって、広い範囲Ｓに亘り、転写紙Ｐに対して除電作用を与える前述の作用を保証することができる。
【００５０】
図５及び図６に示した例では、除電装置１４が１枚の除電針部材２８を有し、これに第１の針状突起２９と第２の針状突起３２を共に形成したため、除電装置１４の部品点数が増大することを阻止できる。これにより、除電装置の構造を簡素化できる利点が得られる。ところが、その反面、１枚の除電針部材２８に、互いに角度をもった第１の針状突起２９と第２の針状突起３２を交互に形成することは、その加工が難しく、これによってその製造コストが上昇するおそれがある。
【００５１】
これに対し、図７及び図８に示す例においては、除電装置１４が、第１及び第２の少なくとも２枚の導電性除電針部材１２８，２２８を有し、その第１の除電針部材１２８に前述の第１の針状突起２９が形成され、第２の除電針部材２２８に第２の針状突起３２が形成されている。図７では、第１の除電針部材１２８と第２の除電針部材２２８を互いにわずかなスペースをあけて離間させているが、これらを互いに重ね合せ、またその両者を貼り合せるようにしてもよい。図７に示したように、両除電針部材１２８，２２８を互いに離したときは、その両者に対してそれぞれ電源１２によって所定の電圧を印加する必要がある。図７及び図８に示した例の他の構成は、図１乃至図６に示した構成と変りはない。
【００５２】
除電装置を複数の除電針部材によって構成し、そのそれぞれに第１の針状突起２９と第２の針状突起３２を形成すれば、その各除電針部材の製造が簡単となり、その総コストを低減できる。
【００５３】
ところで、図９の（ａ）は、除電装置１４の第１の針状突起２９と第２の針状突起３２のなす角度θであって、第１の針状突起２９から、転写紙Ｐの移動方向Ａの上流側へ向けて計った角θを示す説明図である。ここに示した例では、第１の針状突起２９が、転写部を通過した後の転写紙Ｐに対して直交する向きに突出している。
【００５４】
これに対し、図９の（ｂ）は、従来の除電装置１４の除電針部材２８ａと、その針状突起２９ａの傾き状態を説明する図であり、除電針部材２８ａの基端側部分を転写紙Ｐに向けて延長した線Ｂに対して針状突起２９ａがなす角度をθとしている。
【００５５】
図１０は、図９の（ａ），（ｂ）に示した角度θを変化させたときに、前述のトナー散りと文字散りがどのように現われるかを示したグラフであり、直線Ｑ１は従来の構成によるトナー散りの発生状況を示し、直線Ｑ２は同じく従来の構成による文字散りの発生状況を示している。このグラフ中の「良」は文字散り及びトナー散りの発生が少ないことを示し、「不良」はその発生が著しいことを示している。
【００５６】
この図から判るように、従来の構成によると、角度θが小さくなるに従ってトナー散りの発生が著しくなり、逆に角度θが大きくなるに従って文字散りの発生が著しくなる。
【００５７】
これに対し、直線Ｑ３は、図１乃至図８に示した画像形成装置によるトナー散りと文字散りの発生状況を示している。これから判るように、角度θが１０°乃至４０°のいずれの値をとったときも、トナー散りと文字散りの発生が共に抑えられる。
【００５８】
また、第１の針状突起２９と第２の針状突起３２のなす角度θは、ゼロよりも大なる適宜な角度に設定できるが、図１０から判るように、この角度θが１０°乃至４０°であると有利である。すなわち、第１の針状突起２９と第２の針状突起３２とのなす角度であって、第１の針状突起２９から、転写材の移動方向上流側へ向けて計った角度θが１０°乃至４０°に設定されていると、トナー散りと文字散りの発生を効果的に抑えることができるのである。
【００５９】
ところで、図５及び図７に示した除電装置１４の第１及び第２の針状突起２９，３２の尖端から転写紙Ｐまでの距離Ｘ１，Ｘ２は、適宜設定することができるが、第２の針状突起３２の尖端から転写紙Ｐまでの距離Ｘ２をあまり小さく設定すると、その尖端からの放電の影響が転写部２０にまで及び、転写紙Ｐへのトナー像の転写効率が低下するおそれがある。このため、この距離Ｘ２は、上述の不具合が発生しないように、比較的大きく設定する必要がある。ところが、このようにすると、転写紙Ｐに対する除電機能が低下する。
【００６０】
一方、第１の針状突起２９は、元々、転写部２０から比較的大きく離れているので、その尖端から転写紙Ｐまでの距離Ｘ１を小さく設定しても、その放電による影響が転写部２０にまで及ぶことはない。
【００６１】
図５及び図７に示した例では、上述した点に着目し、第１の針状突起２９の尖端から転写紙Ｐより成る転写材の裏面までの距離Ｘ１よりも、第２の針状突起３２の尖端から転写材の裏面までの距離Ｘ２が大きく設定されている。かかる構成により、第２の針状突起３２からの放電の影響が転写部２０にまで及ぶことを阻止でき、トナー像の転写効率の低下を防止できると共に、第１の針状突起２９の尖端を転写紙に近づけることによって、転写紙Ｐに対する除電機能の低下を阻止することができる。
【００６２】
ところで、この種の画像形成装置においては、比較的紙厚の大なる転写紙から、比較的紙厚の小なる転写紙まで、各種の転写紙Ｐが使用される。ここで、紙厚の大なる転写紙に対し、図１１においては符号Ｐ_１を付し、紙厚の小なる転写紙には符号Ｐ_２を付してある。紙厚の大なる転写紙を厚紙、紙厚の小なる転写紙を薄紙と称することにすると、厚紙Ｐ_１は薄紙Ｐ_２よりも腰が強く、従って厚紙Ｐ_１は図１１に示すように感光体５から分離しやすい。これに対し、腰の弱い薄紙Ｐ_２は、図１１に破線で示すように感光体５から分離し難い。
【００６３】
従って、転写紙Ｐとして薄紙Ｐ_２が用いられたときは、図１１に示すように第１の針状突起２９の尖端を感光体５の表面に近づけ、トナー像転写後の薄紙Ｐ_２に対する除電効率を高め、薄紙Ｐ_２を感光体５から確実に分離できるようにすることが望ましい。ところが、第１の針状突起２９をこのように構成すると、転写紙Ｐとして厚紙Ｐ_１を用いたときは、その厚紙Ｐ_１は元々感光体５から分離しやすくなっているので、図１１に示すようにその厚紙Ｐ_１が第１の針状突起２９やホルダ１５に突き当り、転写紙の搬送トラブルが発生するおそれがある。
【００６４】
そこで、図１２及び図１３に示す例の画像形成装置においては、第１の針状突起２９の尖端から、感光体５より成る像担持体の表面までの距離を調整すべく、除電装置１４を調整動させる駆動装置３３が設けられている。より具体的に示すと、ホルダ１５の一方の壁部１５Ｂの先端部がピン３４を介して画像形成装置本体に対して揺動可能に枢支され、そのホルダ１５の基端側の部分にソレノイド３５のプランジャが可撓性部材３６を介して連結され、その他側に引張ばね３７の一端が係止され、そのばね３７の他端は画像形成装置本体側に係止されている。図１２及び図１３に示した画像形成装置の他の構成は先に説明した各例と変りはない。
【００６５】
転写紙として厚紙Ｐ_１が使用されるときは、図１２に示すように、ソレノイド３５はオフされ、第１の針状突起２９の尖端が感光体５の表面から比較的大きく離れた位置を占める。このため、トナー像転写後の厚紙Ｐ_１が感光体５から離れたとき、これが第１の針状突起２９やホルダ１５に突き当ることはなく、その搬送トラブルが発生することはない。第１の針状突起２９は感光体５の表面から比較的大きく離れているが、厚紙Ｐ_１は元々感光体５から分離されやすいものであるから、厚紙Ｐ_１に対する除電不足に基づく感光体５からの分離性が低下することはない。
【００６６】
一方、転写紙として薄紙Ｐ_２が使用されるときは、図１３に示すように、図示していない制御装置からの指令により、ソレノイド３５がオンし、そのプランジャが引かれる。これにより、ホルダ１５はピン３４のまわりに回動し、第１の針状突起２９の尖端が感光体５の表面に近づく。このため、除電装置１４による薄紙Ｐ_２に対する除電機能が高められ、薄紙Ｐ_２を感光体５から確実に分離させることができる。またこのとき、薄紙Ｐ_２は元々感光体５から分離し難いものであるため、第１の針状突起２９の尖端から大きく離れた経路を通して移動する。これにより、第１の針状突起２９が感光体表面に近づいても、薄紙Ｐ_２が第１の針状突起２９に接触したり、ホルダ１５に突き当って搬送トラブルを生じるおそれはない。
【００６７】
上述した構成によって、転写紙が厚紙Ｐ_１であるときも、またこれが薄紙Ｐ_２であるときも、搬送トラブルを起こすことなく、これらの転写紙を効率よく感光体５の表面から分離させることができる。
【００６８】
また図１２及び図１３に示した例では、除電装置１４を調整動させる駆動装置３３が、除電装置１４を保持するホルダ１５を揺動させる駆動装置として構成されており、かかる構成によると、その駆動装置の構成を簡素化できると共に、ホルダ１５がいずれの姿勢をとったときも、第２の針状突起３２の尖端から感光体５ないしは転写部２０までの距離が、全く、或いはほとんど変化しないようにすることができ、これによって転写部２０に対し、放電による悪影響を与える不具合を阻止できる。
【００６９】
以上説明した実施形態例では、除電装置に第１及び第２の２列の針状突起２９，３２を設けたが、その数は３列以上であってもよい。また、本発明は図示した形式以外の各種形式の画像形成装置にも適用できるものである。例えば、転写装置として、像担持体表面から離間したコロナ放電器、転写ブラシ又は転写ブレードなどを用いる画像形成装置や、ベルト状感光体を用いる画像形成装置などにも本発明を広く適用できる。さらに、感光体表面に形成したトナー像をベルト又はドラムなどから成る中間転写体に一次転写し、次いでそのトナー像を最終転写材である転写紙などに二次転写する画像形成装置も公知であるが、その中間転写体より成る像担持体に形成されたトナー像を最終転写材に転写する構成にも本発明を支障なく適用できる。
【００７０】
【発明の効果】
請求項１に記載の構成によれば、トナー散り現象の発生を防止し、かつ除電装置と転写装置との間の電流のリークに基づくトナー像転写効率の低下を阻止し、しかも像担持体からの転写材の分離性を高めることができ、転写材が除電装置に接触することを防止できる。
【００７２】
請求項２に記載の構成によれば、トナー散り現象の発生を防止し、かつ除電装置と転写装置との間の電流のリークに基づくトナー像転写効率の低下を阻止し、しかも像担持体からの転写材の分離性を高めることができる。
【００７３】
請求項３に記載の構成によれば、トナー散り現象の発生を防止し、かつ除電装置と転写装置との間の電流のリークに基づくトナー像転写効率の低下を阻止し、しかも像担持体からの転写材の分離性を高めることができ、さらに転写効率の低下を招くことを阻止できると共に、転写材に対する除電効果を高め、像担持体からの転写材の分離性を一層高めることができる。
【００７４】
請求項４に記載の構成によれば、除電装置の部品点数の増大を阻止し、その構成を簡素化できる。
【００７５】
請求項５に記載の構成によれば、除電装置の製造が容易となり、そのコストの低減を達成できる。
【図面の簡単な説明】
【図１】画像形成装置の全体構成を示す概略断面図である。
【図２】作像ユニットと転写ユニットの断面図である。
【図３】転写ユニットの斜視図である。
【図４】転写ユニットの分解斜視図である。
【図５】感光体と転写ローラと除電装置との相対位置を示す説明図である。
【図６】除電装置の部分斜視図である。
【図７】除電装置が２枚の除電針部材より成る例を示す、図５と同様な説明図である。
【図８】図７に示した除電針部材の部分斜視図である。
【図９】除電装置の針状突起の角度を示す説明図である。
【図１０】本発明実施形態例の除電装置と従来の除電装置の機能の相違を示すグラフである。
【図１１】厚紙と薄紙の感光体からの分離性の相違を説明する図である。
【図１２】除電装置を調整動させる駆動装置を設けた例を示す、図５と同様な説明図である。
【図１３】図１２に示したホルダが傾動したときの様子を示す、図１２と同様な説明図である。
【図１４】従来の除電装置の一例を示す、図５と同様な説明図である。
【図１５】従来の除電装置の斜視図である。
【図１６】従来の他の例を示す、図５と同様な説明図である。
【符号の説明】
１４除電装置
１５ホルダ
２０転写部
２８除電針部材
２９第１の針状突起
３２第２の針状突起
３３駆動装置
１２８除電針部材
２２８除電針部材
Ａ移動方向
Ｇ空間
Ｘ１距離
Ｘ２距離
θ 角度[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention provides an image carrier on which a toner image is formed on its surface while being driven to rotate, and abutting on the surface of the image carrier, at an abutting portion thereof, in a direction substantially the same as the moving direction of the image carrier surface. A transfer device that electrostatically transfers the toner image formed on the image carrier to the surface of the transferred transfer material and transfers the toner image on the image carrier to the surface of the transfer material by the transfer device Is located on the downstream side of the transfer material in the moving direction of the transfer material, and is spaced from the back surface of the transfer material that has passed through the transfer unit, and is disposed on the back surface side of the transfer material. A neutralization device that extends long in a direction substantially perpendicular to the surface of the image carrier, applies a voltage having the same polarity as the toner of the toner image formed on the surface of the image carrier, and neutralizes the transfer material, and a holder that holds the neutralization device. And an image forming apparatus having the same.
[0002]
[Prior art]
An image forming apparatus of the above type configured as an electronic copying machine, a printer, a facsimile, or a multifunction machine having at least two of these functions has been conventionally known.
[0003]
In this type of image forming apparatus, a voltage having a polarity opposite to that of the toner of the toner image formed on the surface of the image carrier is applied to the transfer device, thereby forming an electric field between the surface of the image carrier and the transfer device, The toner image on the image carrier is electrostatically transferred to the surface of the transfer material to transfer the toner image. Further, a charge having the same polarity as that of the toner is applied to the transfer material after the transfer of the toner image by the charge removing device, so that the separation property of the transfer material from the surface of the image carrier is enhanced.
[0004]
Conventionally, as such a static eliminator, a static elimination needle member having a plurality of needle-like projections arranged in the longitudinal direction is used, and discharge from the apex of the needle-like projection toward the back surface of the transfer material causes the transfer material to be removed. Charge of the same polarity as the toner. As a result, the adhesion of the transfer material to the surface of the image carrier is eliminated, or the adhesion is weakened, and the transfer material is reliably separated from the surface of the image carrier.
[0005]
By the way, in the transfer section for transferring the toner image from the surface of the image carrier to the transfer material, as described above, a charge having a polarity opposite to the charge polarity of the toner is applied to the transfer material. An electric field is formed between the toner image carried on the surface of the transfer material immediately after the separation and the surrounding surface of the transfer material, that is, the background portion, so that a part of the toner forming the toner image becomes close to the toner image. May be electrostatically transferred to the background. Such a phenomenon is generally called “toner scattering”. However, when such a phenomenon occurs, the toner image transferred onto the transfer material becomes unclear, and the image quality is deteriorated.
[0006]
In order to eliminate the above-mentioned drawbacks, a method is conceivable in which the tip of the needle-like projection of the static eliminator is brought closer to the transfer device, and the transfer material is neutralized at a portion closer to the transfer portion. With this configuration, since the transfer material immediately after passing through the transfer portion can be neutralized, the above-described toner scattering phenomenon can be prevented. However, according to this configuration, since the tip of the needle-like protrusion of the static eliminator approaches the transfer device, a current leaks due to, for example, a discharge between the two, thereby lowering the potential of the transfer device, and causing a decrease in the potential of the image carrier. The transfer efficiency of the toner image to the transfer material is reduced.
[0007]
Therefore, it is conceivable to increase the value of the voltage applied to the transfer device to compensate for the decrease in transfer efficiency. However, the value of the leak current flowing between the static eliminator and the transfer device depends on the surrounding environment such as humidity. Since the value greatly depends on the conditions, if the value of the voltage applied to the transfer device is uniformly increased, for example, when the humidity is low, the voltage value becomes excessive. On the other hand, charges having a polarity opposite to the original polarity may be injected, and the charge polarity of the toner may be reversed. In this case, the toner having the inverted polarity is reattached to the surface of the image carrier, so that the transfer efficiency of the toner image to the transfer material is reduced, and the image quality of the toner image transferred to the transfer material is deteriorated. I can not escape.
[0008]
On the other hand, it is desirable that the separation property when separating the transfer material from the image carrier is as high as possible. In order to improve the separability of the transfer material, the voltage applied to the static eliminator may be increased. However, since the polarity of the voltage applied to the static eliminator is the same as the polarity of the toner transferred to the transfer material surface, when a high voltage is applied to the static eliminator, the toner on the transfer material surface is transferred to the image carrier surface. It is inevitable that the toner image is transferred electrostatically and adheres again, and the image quality of the toner image on the surface of the transfer material is deteriorated.
[0009]
[Problems to be solved by the invention]
The present invention has been made based on the above-described novel recognition, and an object of the present invention is to prevent the above-described toner scattering phenomenon from occurring and to prevent a current leak between a charge removing device and a transfer device. An object of the present invention is to provide an image forming apparatus of the type described at the beginning, which can prevent a decrease in transfer efficiency based on the transfer rate and can enhance the separability of the transfer material from the surface of the image carrier without any trouble.
[0010]
[Means for Solving the Problems]
In order to achieve the above object, the present invention is directed to an image forming apparatus of the type described at the beginning, wherein the static eliminator is tapered toward a back surface of the transfer material downstream of the transfer unit in the moving direction of the transfer material. And a plurality of first needle-shaped projections arranged in the longitudinal direction of the static eliminator, and formed to be tapered toward the transfer material back surface portion closer to the transfer portion than the first needle-shaped projections, and A plurality of second needle-shaped protrusions arranged in a longitudinal direction of the static eliminator; the holder is made of an insulator; and the first needle-shaped protrusion and the second needle-shaped protrusion are provided in a space inside the holder. An image forming apparatus is proposed, wherein needle-like projections are arranged, and the width of the space in the moving direction of the transfer material increases as approaching the back surface of the transfer material.
[0011]
Similarly, in order to achieve the above object, the present invention provides an image forming apparatus of the type described at the beginning, wherein the static eliminator is tapered toward a back surface of the transfer material downstream of the transfer unit in the direction of movement of the transfer material. And a plurality of first needle-like projections arranged in the longitudinal direction of the static eliminator, and a taper formed from the first needle-like projection toward the transfer material rear surface portion closer to the transfer portion than the first needle-like protrusion. And a plurality of second needle-shaped projections arranged in the longitudinal direction of the static eliminator, and an angle formed between the first needle-shaped projection and the second needle-shaped projection, wherein the first needle An image forming apparatus is characterized in that the angle measured from the projection to the upstream side in the moving direction of the transfer material is set to 10 ° to 40 ° (claim 2).
[0012]
Further, according to the present invention, in order to achieve the above object, in the image forming apparatus of the type described at the beginning, the static eliminator is tapered toward a back surface portion of the transfer material downstream of the transfer section in the moving direction of the transfer material. And a plurality of first needle-like projections arranged in the longitudinal direction of the static eliminator, and a taper formed from the first needle-like projection toward the transfer material rear surface portion closer to the transfer portion than the first needle-like protrusion. And a plurality of second needle-like projections arranged in the longitudinal direction of the charge removing device, wherein the distance between the tip of the first needle-like projection and the back surface of the transfer material is larger than that of the second needle-like projection. An image forming apparatus is proposed in which the distance from the tip of the transfer material to the back surface of the transfer material is set large.
[0013]
Further, in the image forming apparatus according to any one of claims 1 to 3, the static eliminator has a single static elimination needle member, and the static elimination needle member has the first needle-like protrusion and the second static elimination needle member. Advantageously, the needle-like projections are formed together (claim 4).
[0014]
Further, in the image forming apparatus according to any one of claims 1 to 3, the static eliminator has at least two first and second static elimination needle members, and the first static elimination needle member includes the first static elimination needle member. Advantageously, one needle-like projection is formed, and the second needle-like projection is formed on a second static elimination needle member.
[0018]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings, and the above-mentioned conventional disadvantages will be more specifically clarified with reference to the drawings.
[0019]
FIG. 1 is a schematic cross-sectional view showing the inside of an image forming apparatus according to an embodiment of the present invention from the front side. An image forming unit 2 is detachably mounted on an image forming apparatus main body 1. The transfer unit 3 is incorporated. The image forming apparatus shown here is configured as a copying machine, and the copying machine may have functions such as a printer and a facsimile. The image forming unit 2 is attached to and detached from the image forming apparatus main body from the near side of the image forming apparatus main body 1. The front side or the front side of the image forming apparatus is a side where the operator normally operates the image forming apparatus, and the opposite side is the back side of the image forming apparatus.
[0020]
FIG. 2 is an enlarged sectional view when the image forming unit 2 and the transfer unit 3 are viewed from the front side. As shown in FIGS. 1 and 2, the image forming unit 2 has a unit case 4, and inside the case 4 is a drum-shaped photosensitive member 5 as an example of an image carrier and an example of a charging device. Each of the charging rollers 6 is rotatably mounted.
[0021]
During the image forming operation, the photoconductor 5 is driven to rotate clockwise in FIG. 2 by a driving device (not shown), and at this time, the surface of the photoconductor is neutralized by the neutralizing light L1 to the reference potential. The charging roller 6 is driven to rotate while being in pressure contact with the surface of the photoreceptor 5, and uniformly charges the surface of the photoreceptor to a predetermined polarity, in this example, a negative polarity. The surface of the photoconductor 5 charged in this way is irradiated with a light image from a document or a light-modulated laser L2, whereby a predetermined electrostatic latent image is formed on the photoconductor 5. The surface potential of the photoreceptor surface portion irradiated with light decreases, and this forms an electrostatic latent image. The potential of the photoreceptor surface portion not exposed to light does not substantially decrease, and this forms a background portion.
[0022]
On the other hand, the developing roller 8 of the developing device 7 is rotatably supported on the unit case 4 as shown in FIG. 2, and a bias voltage having the same polarity as the charging polarity of the photoconductor is applied to the developing roller 8 in this embodiment. Is done. A developing case 9 constituted by a part of the unit case 4 contains a powdery developer D, and the developer D is carried on a developing roller 8 which is driven to rotate counterclockwise. Conveyed. When the transported developer reaches between the photoconductor 5 and the developing roller 8, the toner in the developer is electrostatically transferred to the electrostatic latent image formed on the photoconductor 5, and the latent image is transferred to the toner. It is visualized as an image. In this example, the toner is charged to a negative polarity having the same polarity as the charging polarity of the photoconductor 5, and the toner is electrostatically attached to the surface of the photoconductor to which light is applied, that is, the electrostatic latent image. The so-called reversal phenomenon occurs.
[0023]
The transfer unit 3 includes, as shown in FIGS. 3 and 4, a transfer roller 11, which is an example of a transfer device, a static eliminator 14, a holder 15 made of an insulator that holds the static eliminator 14, And the transfer roller 11 and the static eliminator 14 extend in parallel with the photoconductor 5. The transfer roller 11 of this embodiment has a central shaft 38 made of a conductive material, for example, metal, and an elastic body 39 fixed around the elastic body 39 and having a medium resistivity. , For example, 10 ⁶ To 10 ⁹ It is about Ωcm. In the state shown in FIG. 2, the transfer roller 11 is rotated counterclockwise by a driving device (not shown) while being pressed against the surface of the photoconductor 5. The transfer roller 11 is rotatably driven in a direction in which the surface of the transfer roller moves in the same direction as the moving direction of the surface of the photoconductor 5 at the contact portion with the photoconductor 5.
[0024]
On the other hand, a transfer sheet P, which is an example of a transfer material, is transferred from a selected one of the plurality of sheet feeders 16, 17, 18, and 19 shown in FIG. The sheet is conveyed to the transfer section 20 as indicated by an arrow A. Then, when the transfer paper P passes through the transfer unit 20, the toner image formed on the surface of the photoconductor 5 is transferred onto the transfer paper P by the action of the transfer voltage applied to the transfer roller 11. The transfer paper P is sent in the same direction as the moving direction of the surface of the photoreceptor 5 at the contact portion while abutting on the surface of the photoreceptor 5, and at this time, as shown in FIG. A voltage having a polarity opposite to the charged polarity of the toner of the toner image formed on the surface of the photoreceptor, that is, a positive polarity in this example, is applied to the central shaft 38 by the power supply 10. As a result, an electric field is formed in the transfer section 20 between the transfer roller 11 and the photoconductor 5 in a direction in which the toner on the photoconductor 5 moves to the surface of the transfer paper P, and the toner image is formed on the surface of the transfer paper P. Transcribed.
[0025]
On the other hand, as is clear from FIG. 5, the charge removing device 14 is located downstream of the transfer unit 20 in the moving direction of the transfer paper P from the transfer unit 20 that transfers the toner image on the photosensitive member surface to the surface of the transfer paper P. In a state separated from the back surface of the transfer paper P passing through 20, the transfer paper P is disposed on the back surface side, and extends in a direction substantially perpendicular to the moving direction A of the transfer paper P, that is, in the axial direction of the photoconductor 5. ing. The static eliminator 14 includes a static elimination needle member 28 made of a conductive material, for example, a thin metal plate. As shown in FIG. A voltage having the same polarity as the charged polarity of the toner of the toner image and the charged polarity on the surface of the photoreceptor, in this example, a negative polarity is applied. The configuration of the charge removing device 14 will be described later in detail.
[0026]
In this way, the transfer paper P that has passed through the transfer unit 20 is separated from the photoconductor 5 while receiving the discharging action of the negative charge from the charge removing device 14. The charge removing device 14 removes the charge of the transfer material charged by the transfer device, that is, the positive polarity charge in this example, or reduces the amount of the charge, thereby improving the separability of the transfer material from the image bearing member. . As shown in FIG. 1, the transfer paper P leaving the photoreceptor 5 passes between the fixing roller 21A and the pressure roller 21B of the fixing device 21. At this time, the toner image on the transfer paper is transferred by the action of heat and pressure. It is fixed on paper. Next, the transfer paper P is discharged outside the main body of the image forming apparatus as a copy paper on which a recording image formed of a toner image is formed, and is stacked on a discharge tray 22.
[0027]
In the transport direction of the transfer paper P, a conductive neutralizing member including, for example, a static elimination brush 50 is provided at a portion on the upstream side of the fixing device 21, and the static elimination brush 50 transfers the transfer paper before entering the fixing device 21. It is in contact with the back surface of P and is grounded as shown in FIG.
[0028]
The toner remaining on the photoconductor 5 after the transfer of the toner image is removed from the surface of the photoconductor by the cleaning member 24 of the cleaning device 23 and falls into the cleaning case 25 formed by a part of the unit case 4.
[0029]
FIG. 3 is a perspective view of the transfer unit 3, and FIG. 4 is an exploded perspective view of the transfer unit 3. As shown in these drawings and FIG. 2, a holding body 13 that holds a transfer roller 11, which is an example of a transfer device, , A first holding member 26 and a second holding member 27. The first holding member 26 has its base end side supported by the side plates 30 and 31 of the image forming apparatus main body 1. It is supported by the attached support member 49 and maintains the posture shown in FIG. The first and second holding members 26 and 27 are made of, for example, a hard synthetic resin, and are connected to each other. These holding members 26 and 27 may be integrally formed.
[0030]
As shown in FIGS. 2 and 4, the transfer roller 11 is rotatably supported by bearings 40 and 41 on the front and rear sides of the center shaft 38, respectively. Compression springs 44 and 45 are press-fitted between the bearings 40 and 41 and the second holding member 27, respectively, and are held by bearing holding portions 42 and 43 formed integrally with the member 27, respectively.
[0031]
As shown in FIG. 4, a gear 46 is fitted in front of the center axis of the transfer roller 11 such that the gear 46 cannot rotate relative to the center axis 38. , 48 are fitted rotatably. A drive gear (not shown) meshes with the gear 46, and the transfer roller 11 is rotationally driven by the drive device via these gears. At this time, the abutment rollers 47 and 48 abut against the surface of the photoconductor 5, and the transfer roller 11 is positioned with respect to the photoconductor 5. As shown in FIG. 4, the holder 15 of the static eliminator 14 is detachably attached to the static eliminator mounting portion 57 of the second holding member 27.
[0032]
As described above, the illustrated image forming apparatus has an image carrier configured as the photoreceptor 5 on which a toner image is formed on the surface while being driven to rotate. A transfer roller 11 for electrostatically transferring the toner image formed on the surface of the image carrier to the surface of a transfer material composed of transfer paper P sent in substantially the same direction as the moving direction of the surface of the image carrier. And a transfer unit that transfers the toner image on the surface of the image carrier onto the surface of the transfer material by the transfer device, and is located on the downstream side in the moving direction of the transfer material, and passes through the transfer unit 20. The toner of the toner image formed on the surface of the image bearing member is arranged on the back side of the transfer material in a state where the toner image is formed on the surface of the image bearing member while being separated from the back surface of the transfer material. Voltage of the same polarity as A charge removing device 14 for neutralizing the transfer material, and a holder 15 for holding the charge removing device 14. Here, it is clear from the above description that, for convenience, the surface of the transfer material on which the toner image is transferred from the image carrier is referred to as the front surface, and the surface on the opposite side is referred to as the back surface.
[0033]
The configuration described above does not differ from the conventional image forming apparatus. At this time, in this type of conventional image forming apparatus, the static eliminator 14 extends in a direction substantially perpendicular to the moving direction A of the transfer paper P as shown in FIGS. It was constituted by a conductive static elimination needle member 28a on which a large number of needle-like projections 29a were formed. As described above, a voltage having the same polarity as the charge polarity of the toner is applied to the charge eliminating needle member 28a, and a charge is applied to the transfer material P by discharging a negative charge from the tip of each needle-like protrusion 29a.
[0034]
At this time, as shown schematically in FIG. 14 and as described above, a positive voltage having a polarity opposite to that of the toner T on the photoconductor 5 is applied to the transfer roller 11, whereby a negative voltage on the photoconductor surface is generated. The polar toner T is electrostatically transferred to the front surface of the transfer paper P. At this time, the back surface of the transfer paper P contacting the transfer roller 11 is positively charged by the action of the voltage applied to the transfer roller 11. It is charged to polarity. A negative charge is applied to the back surface of the transfer paper P by the discharge from the needle-shaped protrusion 29a of the charge removing device 14 on the back surface of the transfer paper P, thereby removing the positive charge of the transfer paper P. Or decrease. In this manner, the adhesion of the transfer paper P to the surface of the photoconductor 5 is removed or reduced, and the transfer paper P is prevented from remaining on the surface of the photoconductor 5. It is separated from the curved surface of the photoconductor 5.
[0035]
However, as shown in FIG. 14, the toner of negative polarity is carried on the surface of the transfer paper P immediately after being separated from the photoreceptor 5, and the back surface is charged to the positive polarity. An electric field indicated by an arrow E in FIG. 14 is formed between the toner T of the carried toner image and the surface of the transfer paper around the toner T, that is, the background. As a result, part of the toner in the toner image is electrostatically transferred to the surface of the transfer paper near the toner image. This is the "toner scattering" phenomenon, and this phenomenon is likely to occur in the front area and the rear area of the toner image in the moving direction A of the transfer paper P. When the toner scattering phenomenon occurs, the toner image transferred to the transfer paper P becomes unclear, and the image quality deteriorates.
[0036]
As a method for removing the above-mentioned disadvantage, as shown in FIG. 16, the tip of the needle-like projection 29a of the static eliminator 14 is brought close to the transfer section 20, and the negative charge from the needle-like projection 29a discharges the surface of the transfer paper. It is conceivable that the transfer paper P is neutralized before the toner scatters on the background. In this way, the transfer paper P immediately after passing through the transfer unit 20 can be neutralized, and thus the positive charge on the back surface of the transfer paper P immediately after separation from the photoreceptor surface can be eliminated or the amount of the charge can be reduced. The formation of the electric field E shown in FIG. 14 can be prevented, and the occurrence of toner scattering can be prevented.
[0037]
However, when the static eliminator 14 and the transfer roller 11 are moved closer to each other as shown in FIG. 16, since high voltages having opposite polarities are applied to them, a current leak occurs between the two by, for example, discharge. In particular, in an environment with high humidity, a leak phenomenon is likely to occur. When such a current leakage phenomenon occurs, the potential of the transfer roller 11 decreases, and thereby the transfer efficiency of the toner image from the photoconductor 5 to the transfer paper P decreases.
[0038]
Therefore, if a higher voltage is applied to the transfer roller 11 to compensate for the above-described decrease in transfer efficiency, the value of the leak current flowing between the transfer roller 11 and the charge removing device 14 varies depending on environmental conditions. Therefore, for example, when the humidity is low, the applied voltage value to the transfer roller 11 becomes excessive, so that a positive charge is injected into the toner on the transfer paper existing in the transfer unit 20, and the polarity is inverted to the positive. Inevitably reattach to the surface.
[0039]
As described above with reference to FIG. 2, the grounding neutralization brush 50 is brought into contact with the back surface of the transfer paper P before being sent to the fixing device 21. Even when the back surface of the transfer sheet P is negatively charged by the discharge, the back surface of the transfer sheet P is discharged, and when the transfer sheet P is sandwiched between the fixing roller 21A and the pressure roller 21B, the transfer sheet P This is a measure for preventing the toner on the surface of the fixing roller 21A from electrostatically adhering to the surface of the fixing roller 21A.
[0040]
When such a configuration is employed, as shown in FIG. 16, when the tip of the needle-like projection of the charge removing device 14 is brought closer to the transfer unit 20 and the distance between the charge removing device 14 and the photoconductor 5 is reduced, the charge removing device 14 is removed. , The back surface of the transfer paper P is strongly negatively charged. As shown in FIG. 16, the negative charge is removed by the charge removing brush 50. If the charge amount is large at this time, when the charge flows to the charge removing brush 50, the toner carried on the surface of the transfer paper P It has an electrostatic effect on the toner in the image, which causes some of the toner to scatter to the surrounding background. This phenomenon is called "character scattering" because toner scatters around a toner image such as a character. However, if such a phenomenon occurs, the image quality of the toner image deteriorates.
[0041]
Further, in the conventional configuration shown in FIG. 14, in order to efficiently separate the transfer paper P from the photoconductor 5, it is necessary to increase the value of the voltage applied to the charge removing device 14. However, in this case, the polarity of the applied voltage and the charging polarity of the toner T carried on the surface of the transfer paper P immediately after being separated from the photoreceptor 5 are the same. There is a possibility that the toner image may be electrically separated from the surface of the transfer paper P and may adhere to the surface of the photoconductor 5 again, thereby deteriorating the image quality of the toner image. When the voltage applied to the charge removing device 14 is increased, the amount of negative charge on the back surface of the transfer paper P increases. Therefore, when the charge is removed by the charge removing brush 50, the above-described character scattering phenomenon easily occurs.
[0042]
In FIGS. 14 and 16, the symbols “+” and “−” attached to the back side of the transfer paper P indicate the charging polarity, and in these figures, the toner particles are schematically illustrated. Although shown in an enlarged manner, the sign “−” attached to each toner T also indicates the charging polarity. This is the same in FIGS. 5 and 7.
[0043]
In order to eliminate the above-mentioned various defects, in the image forming apparatus of the present embodiment, as shown in FIGS. 5 and 6, a plurality of first needle-like projections arranged in the longitudinal direction thereof are used as the static eliminator 14 described above. 29 and a plurality of second needle-like projections 32 similarly arranged in the longitudinal direction of the static eliminator 14. In the example shown here, the static eliminator 14 has one static elimination needle member 28 made of a conductive material such as a metal plate. The second needle-like projections 32 are formed together.
[0044]
Each first needle-like projection 29 is formed so as to be tapered toward the back surface of the transfer material downstream of the transfer unit 20 in the moving direction of the transfer material made of the transfer paper P, and each second needle-like protrusion 32 is formed. The first needle-like protrusion 29 is formed to be tapered toward the transfer material rear surface portion closer to the transfer portion 20 than the first needle-like protrusion 29. The first needle-like projections 29 and the second needle-like projections 32 are alternately arranged in the extending direction of the static elimination needle member 28, and they are directed toward the photoconductor 5 at an angle larger than 0 °. It protrudes. FIG. 6 shows the first and second needle-like projections 29 and 32 in an enlarged manner. The width W of the base of each of the needle-like projections 29 and 32 in the longitudinal direction of the static eliminator is, for example, about 2 mm. Is set to
[0045]
As described above, a negative voltage having the same polarity as that of the toner is applied to the thus-formed discharging device 14 by the power supply 12 as described above. At this time, the discharging device 14 is moved in the moving direction A of the transfer paper P. A first needle-like projection 29 facing the downstream side thereof and a second needle-like projection 32 facing the upstream side thereof. A negative charge is applied to the back surface. The second needle-like projection 32 is located in the vicinity of the transfer unit 20, and the first needle-like projection 29 faces a portion downstream of the transfer unit 20 in the transfer paper transport direction. The projection 29 projects in a direction perpendicular to the back surface of the transfer sheet P.
[0046]
With the above configuration, the transfer sheet P is subjected to the discharging action of the negative charges over a wide range S (FIG. 5) in the feeding direction A. The transfer paper P is subjected to a discharging action by the discharge for a longer time than in the prior art. For this reason, the voltage value applied to the static eliminator 14 can be greatly reduced as compared with the related art. Although the absolute value of the voltage value applied to the static eliminator is lower than in the related art, since the transfer paper P is removed over a long period of time, the static elimination effect does not decrease. Since the tip of the second needle-like projection 32 is located near the transfer unit 20 and very close to the transfer roller 11, as described above with reference to FIG. Since the occurrence of the phenomenon can be prevented and the voltage value applied to the charge removing device 14 is suppressed to a low value, the occurrence of a leak current between the charge removing device 14 and the transfer roller 11 can be prevented, and the voltage applied to the transfer roller 11 can be reduced. Even if the value is not particularly increased, a decrease in the toner image transfer efficiency can be prevented, and the re-adhesion of the toner to the photoconductor 5 can be prevented.
[0047]
Further, even if the voltage value applied to the static eliminator 14 is reduced as described above, the transfer paper P is neutralized over a long period of time, so that the static elimination effect can be enhanced. Even if the back surface is charged to a negative polarity, the charge amount can be reduced. This can prevent the toner on the transfer paper P from re-adhering to the photoreceptor 5, and can prevent the occurrence of the character scattering phenomenon after the static elimination brush 50 eliminates the static electricity. In this manner, the transfer paper P can be efficiently separated from the photoconductor 5, and a high-quality toner image can be formed on the transfer paper P. Even if the back surface of the transfer paper P is negatively charged by the discharge of the charge removing device 14, the charge polarity is the same as the charge polarity of the photoconductor surface. Does not decrease, but rather increases the separation.
[0048]
The holder 15 holding the static eliminator 14 is made of an insulator. As shown in FIG. 5, the base end 14A of the static eliminator 14 is sandwiched between the pair of wall portions 15A and 15B of the holder 15. The static eliminator 14 is held by the holder 15. Further, both the wall portions 15A and 15B of the holder 15 are separated from each other as approaching the transfer paper P side, and a space G is formed here. In the space G inside the holder 15, the first needle-like projection 29 and the second needle-like projection 32 of the static eliminator 14 are arranged. If the needle-like projections 29, 32 project outside from the space G of the holder 15, the transfer paper P may come into contact with the needle-like projections 29, 32. It was put in. Even if the transfer paper P comes into light contact with the end of the wall of the holder 15, the holder 15 is an insulator and does not cause any trouble.
[0049]
When the holder 15 is configured as described above, it is necessary to gradually increase the width of the space G of the holder 15 toward the transfer paper P. The holder 15 is configured such that the width of the space G in the moving direction A of the transfer material formed of the transfer paper P increases as approaching the back surface of the transfer material. With this configuration, the first needle-like projection 29 and the second needle-like projection 32 can guarantee the above-described operation of providing the transfer sheet P with a charge removing effect over a wide range S.
[0050]
In the example shown in FIGS. 5 and 6, the static eliminator 14 has one static elimination needle member 28, and the first and second needle-like projections 29 and 32 are formed thereon. It is possible to prevent the number of 14 components from increasing. This provides an advantage that the structure of the static elimination device can be simplified. However, on the other hand, it is difficult to alternately form the first needle-like projections 29 and the second needle-like projections 32 at an angle on one sheet of the static elimination needle member 28. Manufacturing costs may increase.
[0051]
On the other hand, in the example shown in FIGS. 7 and 8, the static eliminator 14 has at least two first and second conductive static elimination needle members 128 and 228, and the first static elimination needle member 128. The first needle-like projection 29 described above is formed on the second static elimination needle member 228, and the second needle-like projection 32 is formed on the second static elimination needle member 228. In FIG. 7, the first static elimination needle member 128 and the second static elimination needle member 228 are spaced apart from each other with a slight space therebetween, but they may be overlapped with each other or both may be bonded together. . As shown in FIG. 7, when the static elimination needle members 128 and 228 are separated from each other, it is necessary to apply a predetermined voltage to both of them by the power supply 12. Other configurations of the example shown in FIGS. 7 and 8 are not different from the configurations shown in FIGS.
[0052]
If the static elimination device is constituted by a plurality of static elimination needle members, and the first needle-like projection 29 and the second needle-like projection 32 are formed on each of them, the manufacture of each of the static elimination needle members is simplified, and the total cost is reduced. Can be reduced.
[0053]
9A shows the angle θ between the first needle-like projection 29 and the second needle-like projection 32 of the static eliminator 14, and the angle θ between the first needle-like projection 29 and the transfer paper P FIG. 5 is an explanatory diagram showing an angle θ measured toward an upstream side in a movement direction A. In the example shown here, the first needle-like projection 29 projects in a direction perpendicular to the transfer paper P after passing through the transfer section.
[0054]
On the other hand, FIG. 9B is a view for explaining the static elimination needle member 28a of the conventional static eliminator 14 and the inclined state of the needle-like projection 29a, and the base end portion of the static elimination needle member 28a is transferred. The angle formed by the needle-like projection 29a with respect to the line B extending toward the paper P is defined as θ.
[0055]
FIG. 10 is a graph showing how the toner scattering and the character scattering appear when the angle θ shown in FIGS. 9A and 9B is changed. The straight line Q2 similarly shows the occurrence state of the character scattering by the conventional configuration. In this graph, "good" indicates that the occurrence of scattering of characters and toner is small, and "defective" indicates that the occurrence of scattering is remarkable.
[0056]
As can be seen from the figure, according to the conventional configuration, toner scattering becomes more pronounced as the angle θ becomes smaller, and character scattering becomes more pronounced as the angle θ becomes larger.
[0057]
On the other hand, a straight line Q3 indicates the state of occurrence of toner scattering and character scattering by the image forming apparatus shown in FIGS. As can be seen from this, when the angle θ takes any value of 10 ° to 40 °, the occurrence of both toner scattering and character scattering is suppressed.
[0058]
Further, the angle θ formed by the first needle-like projection 29 and the second needle-like projection 32 can be set to an appropriate angle larger than zero, but as can be seen from FIG. Advantageously, it is 40 °. That is, the angle θ between the first needle-like projection 29 and the second needle-like projection 32 and measured from the first needle-like projection 29 toward the upstream side in the transfer material moving direction is 10 degrees. When the angle is set to 40 ° to 40 °, the occurrence of toner scattering and character scattering can be effectively suppressed.
[0059]
By the way, the distances X1 and X2 from the tips of the first and second needle-like projections 29 and 32 of the static eliminator 14 shown in FIGS. 5 and 7 to the transfer paper P can be set as appropriate. If the distance X2 from the tip of the needle-like projection 32 to the transfer paper P is set too small, the influence of the discharge from the tip to the transfer unit 20 may decrease the transfer efficiency of the toner image onto the transfer paper P. There is. Therefore, the distance X2 needs to be set relatively large so that the above-described problem does not occur. However, in this case, the charge removing function for the transfer paper P is reduced.
[0060]
On the other hand, since the first needle-like projection 29 is originally relatively far away from the transfer unit 20, even if the distance X1 from the tip to the transfer paper P is set to be small, the influence of the discharge will not affect the transfer unit 20. It does not extend to.
[0061]
In the examples shown in FIGS. 5 and 7, focusing on the above-described points, the second needle-like projection is smaller than the distance X1 from the tip of the first needle-like projection 29 to the back surface of the transfer material made of the transfer paper P. The distance X2 from the pointed end of P.32 to the back surface of the transfer material is set large. With such a configuration, it is possible to prevent the influence of the discharge from the second needle-like projections 32 from reaching the transfer unit 20, prevent the transfer efficiency of the toner image from lowering, and reduce the point of the first needle-like projections 29. By bringing the transfer paper P closer to the transfer paper, it is possible to prevent a decrease in the charge removal function for the transfer paper P.
[0062]
In this type of image forming apparatus, various types of transfer paper P are used, from a transfer paper having a relatively large thickness to a transfer paper having a relatively small thickness. Here, for the transfer paper having a large paper thickness, the reference sign P in FIG. ₁ , And the symbol P ₂ Is attached. The transfer paper having a large thickness is referred to as thick paper, and the transfer paper having a small thickness is referred to as thin paper. ₁ Is thin paper P ₂ Stiffer than cardboard P ₁ Is easily separated from the photoconductor 5 as shown in FIG. On the other hand, thin paper P ₂ Is difficult to separate from the photoconductor 5 as shown by a broken line in FIG.
[0063]
Therefore, as the transfer paper P, the thin paper P ₂ Is used, the tip of the first needle-like projection 29 is brought close to the surface of the photoreceptor 5 as shown in FIG. ₂ To improve the static elimination efficiency for ₂ It is desirable to surely separate the photoconductor 5 from the photoconductor 5. However, when the first needle-like projections 29 are configured in this manner, the transfer paper P is made of thick paper P ₁ Is used, the cardboard P ₁ Is originally easily separated from the photoreceptor 5, and as shown in FIG. ₁ May hit the first needle-like projection 29 or the holder 15, and transfer paper transfer trouble may occur.
[0064]
Therefore, in the image forming apparatus of the example shown in FIGS. 12 and 13, in order to adjust the distance from the tip of the first needle-like projection 29 to the surface of the image carrier composed of the photoconductor 5, the charge removing device 14 is used. A drive device 33 for adjusting movement is provided. More specifically, the distal end of one wall 15B of the holder 15 is pivotally supported on the image forming apparatus main body via a pin 34, and a solenoid at the base end of the holder 15 The plunger 35 is connected via a flexible member 36, one end of a tension spring 37 is locked on the other side, and the other end of the spring 37 is locked on the image forming apparatus main body side. Other configurations of the image forming apparatus shown in FIGS. 12 and 13 are the same as those described above.
[0065]
Cardboard P as transfer paper ₁ When is used, as shown in FIG. 12, the solenoid 35 is turned off, and the tip of the first needle-like projection 29 occupies a position relatively far away from the surface of the photoconductor 5. Therefore, the thick paper P after the transfer of the toner image ₁ When the photoconductor 5 is separated from the photoreceptor 5, it does not hit the first needle-like projection 29 or the holder 15, so that no transport trouble occurs. Although the first needle-like projection 29 is relatively far away from the surface of the photoconductor 5, the thick paper P ₁ Is easily separated from the photoreceptor 5 from the beginning. ₁ There is no decrease in the separability from the photoreceptor 5 due to insufficient charge removal.
[0066]
On the other hand, thin paper P ₂ Is used, as shown in FIG. 13, the solenoid 35 is turned on by an instruction from a control device (not shown), and the plunger is pulled. Thereby, the holder 15 rotates around the pin 34, and the point of the first needle-like projection 29 approaches the surface of the photoconductor 5. For this reason, the thin paper P ₂ The static elimination function is improved for thin paper P ₂ Can be reliably separated from the photoreceptor 5. At this time, the thin paper P ₂ Since it is originally difficult to separate from the photoreceptor 5, it moves through a path that is far away from the tip of the first needle-like projection 29. As a result, even when the first needle-like projection 29 approaches the photosensitive member surface, the thin paper P ₂ Does not come into contact with the first needle-like projection 29 or hit the holder 15 to cause a transport trouble.
[0067]
With the configuration described above, the transfer paper is ₁ Is also the thin paper P ₂ Also, the transfer paper can be efficiently separated from the surface of the photoreceptor 5 without causing a transport trouble.
[0068]
In the examples shown in FIGS. 12 and 13, the driving device 33 that adjusts and moves the static eliminator 14 is configured as a driving device that swings the holder 15 that holds the static eliminator 14. The configuration of the driving device can be simplified, and the distance from the tip of the second needle-like projection 32 to the photoconductor 5 or the transfer unit 20 does not change at all or hardly changes when the holder 15 takes any posture. Thus, it is possible to prevent the transfer section 20 from being adversely affected by the discharge.
[0069]
In the embodiment described above, the static eliminator is provided with the first and second two rows of needle-like projections 29, 32, but the number may be three or more. Further, the present invention can be applied to various types of image forming apparatuses other than the illustrated type. For example, the present invention can be widely applied to an image forming apparatus using a corona discharger, a transfer brush or a transfer blade, and the like, and an image forming apparatus using a belt-shaped photoconductor as a transfer device. Further, there is also known an image forming apparatus in which a toner image formed on the surface of a photoreceptor is primarily transferred to an intermediate transfer member such as a belt or a drum, and then the toner image is secondarily transferred to a final transfer material such as transfer paper. However, the present invention can be applied to a configuration in which a toner image formed on an image carrier formed of the intermediate transfer body is transferred to a final transfer material without any trouble.
[0070]
【The invention's effect】
According to the configuration of the first aspect, it is possible to prevent the toner scattering phenomenon from occurring, to prevent the toner image transfer efficiency from being lowered due to the current leak between the charge removing device and the transfer device, and to prevent the toner from being transferred from the image carrier. Of the transfer material can be improved, and the transfer material can be prevented from contacting the static eliminator.
[0072]
According to the second aspect of the present invention, it is possible to prevent the toner scattering phenomenon from occurring, and to prevent the toner image transfer efficiency from being lowered due to the current leak between the charge removing device and the transfer device. Of the transfer material can be improved.
[0073]
According to the configuration of the third aspect, it is possible to prevent the toner scattering phenomenon from occurring, to prevent the toner image transfer efficiency from being lowered due to the current leak between the charge removing device and the transfer device, and to prevent the toner from being transferred from the image carrier. In addition, it is possible to prevent the transfer efficiency from deteriorating, to enhance the static elimination effect on the transfer material, and to further enhance the separability of the transfer material from the image carrier.
[0074]
According to the configuration described in claim 4, an increase in the number of components of the static elimination device can be prevented, and the configuration can be simplified.
[0075]
According to the configuration of the fifth aspect, the manufacture of the static elimination device is facilitated, and the cost can be reduced.
[Brief description of the drawings]
FIG. 1 is a schematic cross-sectional view illustrating an entire configuration of an image forming apparatus.
FIG. 2 is a sectional view of an image forming unit and a transfer unit.
FIG. 3 is a perspective view of a transfer unit.
FIG. 4 is an exploded perspective view of the transfer unit.
FIG. 5 is an explanatory diagram illustrating relative positions of a photoconductor, a transfer roller, and a charge removing device.
FIG. 6 is a partial perspective view of the static eliminator.
FIG. 7 is an explanatory view similar to FIG. 5, showing an example in which the static eliminator is composed of two static elimination needle members.
FIG. 8 is a partial perspective view of the static elimination needle member shown in FIG. 7;
FIG. 9 is an explanatory diagram showing angles of needle-like projections of the static eliminator.
FIG. 10 is a graph showing a difference in functions between the static eliminator of the embodiment of the present invention and a conventional static eliminator;
FIG. 11 is a view for explaining a difference in the separating property of a thick paper and a thin paper from a photoconductor.
FIG. 12 is an explanatory view similar to FIG. 5, showing an example in which a driving device for adjusting and moving the static eliminator is provided.
FIG. 13 is an explanatory view similar to FIG. 12, showing a state where the holder shown in FIG. 12 is tilted.
FIG. 14 is an explanatory diagram similar to FIG. 5, illustrating an example of a conventional static eliminator.
FIG. 15 is a perspective view of a conventional static eliminator.
FIG. 16 is an explanatory diagram similar to FIG. 5, showing another example of the related art.
[Explanation of symbols]
14 Static eliminator
15 Holder
20 transcription unit
28 Static elimination needle member
29 1st needle-shaped protrusion
32 Second needle-shaped protrusion
33 Drive
128 Static elimination needle member
228 Static elimination needle member
A Moving direction
G space
X1 distance
X2 distance
θ angle

Claims

An image carrier on which a toner image is formed on the surface thereof while being driven to rotate; and a transfer material fed in substantially the same direction as the moving direction of the surface of the image carrier at the contact portion while being in contact with the surface of the image carrier A transfer device that electrostatically transfers the toner image formed on the surface of the image carrier onto the surface of the image carrier to transfer the toner image, and a transfer unit that transfers the toner image on the surface of the image carrier onto the surface of the transfer material by the transfer device Is also located downstream of the transfer material in the direction of movement of the transfer material, and is disposed on the side of the back surface of the transfer material that has passed through the transfer unit and is separated from the back surface of the transfer material. An image extending in a direction perpendicular to the image carrier, comprising: a static eliminator configured to apply a voltage having the same polarity as that of the toner of the toner image formed on the surface of the image bearing member to neutralize a transfer material; and a holder configured to hold the static eliminator. In the forming device,
A plurality of first needle-shaped protrusions, wherein the static eliminator is formed to be tapered toward a transfer material back surface portion downstream of the transfer unit in the moving direction of the transfer material, and is arranged in a longitudinal direction of the static eliminator; A plurality of second needle-like projections which are formed to be tapered toward the transfer material back surface portion closer to the transfer portion than the first needle-like projections and are arranged in the longitudinal direction of the static eliminator; The holder is made of an insulator, and the first needle-like projection and the second needle-like projection are arranged in a space inside the holder, and the width of the space in the moving direction of the transfer material is An image forming apparatus, wherein the image is enlarged as approaching a rear surface.

An image carrier on which a toner image is formed on the surface thereof while being driven to rotate; and a transfer material fed in substantially the same direction as the moving direction of the surface of the image carrier at the contact portion while being in contact with the surface of the image carrier A transfer device that electrostatically transfers the toner image formed on the surface of the image carrier onto the surface of the image carrier to transfer the toner image, and a transfer unit that transfers the toner image on the surface of the image carrier onto the surface of the transfer material by the transfer device Is also located downstream of the transfer material in the direction of movement of the transfer material, and is disposed on the side of the back surface of the transfer material that has passed through the transfer unit and is separated from the back surface of the transfer material. An image extending in a direction perpendicular to the image carrier, comprising: a static eliminator configured to apply a voltage having the same polarity as that of the toner of the toner image formed on the surface of the image bearing member to neutralize a transfer material; and a holder configured to hold the static eliminator. In the forming device,
A plurality of first needle-shaped protrusions, wherein the static eliminator is formed to be tapered toward a transfer material back surface portion downstream of the transfer unit in the moving direction of the transfer material, and is arranged in a longitudinal direction of the static eliminator; A plurality of second needle-like projections which are formed to be tapered toward the transfer material back surface portion closer to the transfer portion than the first needle-like projections and are arranged in the longitudinal direction of the static eliminator; The angle between the first needle-like projection and the second needle-like projection, and the angle measured from the first needle-like projection toward the upstream side in the transfer material moving direction is 10 ° to 40 °. An image forming apparatus characterized by being set.

An image carrier on which a toner image is formed on the surface thereof while being driven to rotate; and a transfer material fed in substantially the same direction as the moving direction of the surface of the image carrier at the contact portion while being in contact with the surface of the image carrier A transfer device that electrostatically transfers the toner image formed on the surface of the image carrier onto the surface of the image carrier to transfer the toner image, and a transfer unit that transfers the toner image on the surface of the image carrier onto the surface of the transfer material by the transfer device Is also located downstream of the transfer material in the direction of movement of the transfer material, and is disposed on the side of the back surface of the transfer material that has passed through the transfer unit and is separated from the back surface of the transfer material. An image extending in a direction perpendicular to the image carrier, comprising: a static eliminator configured to apply a voltage having the same polarity as that of the toner of the toner image formed on the surface of the image bearing member to neutralize a transfer material; and a holder configured to hold the static eliminator. In the forming device,
A plurality of first needle-shaped protrusions, wherein the static eliminator is formed to be tapered toward a transfer material back surface portion downstream of the transfer unit in the moving direction of the transfer material, and is arranged in a longitudinal direction of the static eliminator; A plurality of second needle-like projections which are formed to be tapered toward the transfer material back surface portion closer to the transfer portion than the first needle-like projections and are arranged in the longitudinal direction of the static eliminator; An image forming apparatus, wherein the distance from the tip of the second needle-like projection to the back surface of the transfer material is set larger than the distance from the tip of the first needle-like projection to the back surface of the transfer material. .

4. The static elimination device has one static elimination needle member, and the first needle projection and the second needle projection are both formed on the static elimination needle member. Image forming apparatus.

The static eliminator has first and second at least two static elimination needle members, wherein the first static elimination needle member has the first needle-like protrusion, and the second static elimination needle member has the second static elimination needle member. The image forming apparatus according to claim 1, wherein the needle-shaped protrusion is formed.