【０００１】
【発明の属する技術分野】
本発明は、感光体ドラム等の像担持体上に形成された潜像に現像剤を付着させて可視像化する現像装置、及び該現像装置が備えられた、電子写真方式や静電記録方式を用いた複写機又はレーザービームプリンタ等の画像形成装置に関するものである。
【０００２】
【従来の技術】
従来より、現像剤担持体の表面に顕画剤としての乾式現像剤を担持し、その現像剤を静電潜像が担持されている像担持体の表面近傍に搬送供給させて、そして、像担持体と現像剤担持体との間に交互電界を印加しながら静電潜像を現像することにより、静電潜像を顕像化する方法がよく知られている。
【０００３】
尚、上記現像剤担持体には、一般に現像スリーブが用いられる場合が多いので、以下の説明では「現像スリーブ」と称し、又、像担持体は、一般に感光体ドラムが用いられる場合が多いので、以下の説明では「感光体ドラム」と称すこととする。
【０００４】
上記の現像方法としては、例えば、キャリア粒子とトナー粒子とを含む二成分現像剤により、内部に磁界発生手段であるマグネットローラが配置されている現像スリーブの表面に磁気ブラシを形成させ、微小な現像間隔を保持して対向させた感光体ドラムに、この磁気ブラシを摺擦又は近接させ、更に現像スリーブ側から感光体ドラム側への転移及び逆転移を繰り返し行わせて、感光体ドラム上の静電潜像の現像を行う所謂磁気ブラシ現像法が知られいてる。
【０００５】
又、簡易なカラー現像や多重現像を目的とした、二成分現像剤を用いた非接触方式の交互電界現像法も知られている。これらの現像方法によって感光体ドラム上に形成されたトナー像は、必要に応じて紙等の被転写材上に転写された後、熱、圧力或いは溶剤蒸気等により定着されて複写画像が得られる。
【０００６】
又、現像装置における現像極構成において、層厚規制部材即ち穂立ち規制部材で現像剤の磁気ブラシによる穂立ちを規制して現像スリーブ上の現像剤量を規制する、穂立ち規制部材と対向した磁極である層厚規制極（カット極）と、現像容器内にあり、隣り合わせた同極性の磁極により反発極構成をとることにより、現像剤を現像スリーブより剥離する機能と、現像剤担持体に現像剤をくみ上げる機能をもたせたときの、くみ上げ極とは、別々に独立して備えられることが通常だった。
【０００７】
このような構成の場合、汲み上げ極とカット極と穂立ち規制部材との間で現像剤が滞留し、現像剤が劣化しやすいという問題点があった。そこで、カット極と汲み上げ極と同極性にして隣り合わせて、つまり、カット極と汲み上げ極をひとつの極で行うように、カット極を穂立ち規制部材に対向させること、つまり、軽負荷現像方式をとることにより、その現像剤劣化を軽減することが可能となった。
【０００８】
ところで、近年、一層の高画質化が要求されており、特に低濃度部でのがさつきの低下が課題であった。これに対して、二成分現像剤に、従来のフェライトキャリアよりも磁化量をさげた磁性キャリアを用いることで、更なる高画質化を達成することが可能となった。
【０００９】
しかし、感光体ドラムへの現像剤供給方向を順方向にした、つまり現像スリーブの回転方向が感光体ドラムに対して順方向である、順方向現像方式を用いた場合、従来の磁化量が高いフェライトキャリアを用いた場合に比べて、低濃度と高濃度の画像が進行方向に向かってこの順にあるとき、その濃度段差の低濃度側の下流側に、白抜けと呼ばれる異常画像が発生しやすくなった。又、高濃度部に低濃度部が連続する場合に、高濃度部の後端が更に濃くなる、所謂ハキヨセ現象の問題も発生しやすかった。
【００１０】
これらの画像不良に対しては、感光体ドラムへの現像剤供給方向を逆方向（カウンター方向）、つまり現像スリーブの回転方向を感光体ドラムとの対向部にて表面が感光体ドラムと逆方向に移動する方向、つまりカウンター方向にすることによって、解決できることが確認されており、低磁化キャリアを用いた場合、カウンター現像方式が用いられることが多い。
【００１１】
ここで、カット極と汲み上げ極をひとつにして規制部材に対向させる軽負荷構造であり、低磁化キャリアを含む現像剤を用いた、現像部において現像スリーブの表面移動方向が感光体ドラムと逆方向であるカウンター現像装置である、従来の現像装置の例１’を図６に示す。
【００１２】
現像装置１’は、現像容器１０を備え、その内部は隔壁１６によって現像室Ｒ１と攪拌室Ｒ２とに区画され、攪拌室Ｒ２の上方にはトナー貯蔵室Ｒ３がある。
【００１３】
トナー貯蔵室Ｒ３の中には補給用のトナーＴ１が収容されている。トナー貯蔵室Ｒ３下部にある補給口２０から、現像で消費されたトナーに見合った量のトナーＴ１が攪拌室Ｒ２内に落下補給される。
【００１４】
一方、現像室Ｒ１、及び攪拌室Ｒ２内には、トナー粒子と磁性キャリアとが混合された二成分現像剤Ｔが収容されている。現像室Ｒ１内には現像剤搬送スクリュー１１が収容されており、回転駆動によって現像剤Ｔを現像スリーブ１３の長手方向に沿って搬送する。又、攪拌室Ｒ２内に収容されている搬送スクリュー１２による現像剤搬送方向は、スクリュー１１の搬送方向とは反対方向である。
【００１５】
現像室Ｒ１と攪拌室Ｒ２との間に設けられた隔壁１６には、手前側と奥側に連通部（不図示）となる開口が設けられており、スクリュー１１で搬送された現像剤Ｔはこの一方の連通部からスクリュー１２に受け渡され、又、スクリュー１２で搬送された現像剤Ｔは他方の連通部からスクリュー１１に受け渡され、現像室Ｒ１と攪拌室Ｒ２とで循環している。
【００１６】
又、現像容器１０の感光体ドラム４に近接する部位には開口部が設けられている。開口部には、アルミニウムや非磁性ステンレス鋼等の非磁性材質であり、且つその表面に適度な凹凸が設けられている非磁性現像スリーブ１３が設けられ、感光体ドラム４と対向している。
【００１７】
現像スリーブ１３は、その表面が、現像部４１となる感光体ドラム４との対向部において感光体ドラム４と逆方向に移動するように、矢印ｂの方向、つまり感光体ドラム４と同方向に回転する。更に、現像スリーブ１３は、表面に、現像容器１０下端にある層厚規制ブレード１７によって適正な層厚に規制された現像剤Ｔを担持した後、現像剤Ｔを現像部４１へと搬送する。
【００１８】
現像スリーブ１３によって担持された現像剤Ｔで形成される磁気ブラシが、現像部４１で矢印ａ方向に回転する感光体ドラム４に接触することによって、感光体ドラム４上に形成されている静電潜像が、この現像部４１で現像される。現像スリーブ１３内にはローラ状の磁界発生手段であるマグネットローラ１５が固定配置され、現像部４１には現像磁極Ｓ１が位置している。
【００１９】
このマグネットローラ１５は、本例では、現像部４１に対向する現像磁極として、磁極Ｓ１を有している。現像磁極Ｓ１が、現像部４１に形成する現像磁界により、現像スリーブ１３上に現像剤にて磁気ブラシが形成され、この磁気ブラシが感光体ドラム４に接触して静電潜像を現像する。その際、現像剤のうち磁気ブラシに付着しているトナーと共に、スリーブ１３表面に付着しているトナーも静電潜像の画像領域に転移して現像に供される。
【００２０】
図６では、マグネットローラ１５は、現像部４１の位置の現像磁極Ｓ１の他に、Ｎ１、Ｎ２、Ｎ３及びＳ２極を有している。斯かる構成により、現像スリーブ１３の現像容器１０開口付近で内部側の位置のＮ１にて、現像スリーブ１３上に塗布された現像剤は、現像スリーブ１３が回転することによって、現像容器１０開口部に位置する層厚規制部材である穂立ち規制部材１７を通過して適正な現像剤層厚に規制されて現像容器１０外部に移動し、現像部４１に位置する現像磁極Ｓ１に至り、その磁界中で穂立ちした現像剤が感光体ドラム４上の静電潜像を現像する。
【００２１】
その後、現像スリーブ１３の回転により現像剤Ｔが現像部４１から現像容器１０内部に戻るまでの位置に配置されたＮ３及び現像容器１０内部側の、Ｓ２、Ｎ２により搬送されて現像容器１０内に入り、更には現像極Ｓ１と対極に位置するＮ２極とその隣の層厚規制極であるＮ１極間の反発磁界により、現像スリーブ１３上の現像剤Ｔは現像室Ｒ１内へ落下する。現像室Ｒ１内に落下した現像剤Ｔは、スクリュー１１に搬送され攪拌室Ｒ２にて、現像によりトナーが消耗されている場合は新たなトナー補給を受けてスクリュー１２により攪拌搬送され、再び現像室Ｒ１に搬送され現像に供される。
【００２２】
【発明が解決しようとする課題】
しかし、前述のように、上流側に隣り合った磁極と反発極構成をとり、穂立ち規制部材１７に対向した層厚規制極（図６ではＮ１）により現像室Ｒ１内の現像剤Ｔを汲み上げ、且つ、現像剤Ｔの層厚規制を同時に行う軽負荷構造であり、現像スリーブ１３の回転方向が感光体ドラム４に対してカウンター方向であるカウンター現像装置では、例えば、高デューティーの画像がくると、現像スリーブ１３上の現像剤のキャリアとトナーの比であるＴ／Ｄ比（現像剤中のトナー重量／現像剤（トナーとキャリア）の総重量）が低くなり、その状態の剤が攪拌室Ｒ１に落下する。そして、このＴ／Ｄ比の低下した状態の剤と、現像に供されていない通常のＴ／Ｄ比状態の現像剤との攪拌が不十分なまま、次の画像形成を行うことになり、攪拌不良を原因とするスクリュー跡（Ｔ／Ｄムラ）という問題が発生しやすかった。
【００２３】
これは、軽負荷現像を用いない場合は、現像剤の層厚規制を行う極と現像剤を汲み上げる極が別になっており、現像剤を汲み上げてから層厚規制を受けるまでの間で圧縮をうけ、十分に攪拌されていたため、この攪拌不良によるＴ／Ｄムラが発生しにくかった。
【００２４】
従って、本発明の目的は、磁化量を下げたキャリアを用いた現像を行い、該キャリアとトナーとを含む現像剤を担持する現像剤担持体の現像部における表面移動方向像担持体と逆方向になるように回転し、現像剤担持体内の磁界発生手段において、層厚規制部材に対向した層厚規制極が上流側に隣り合った磁極と反発極性をとり、現像室内の現像剤を汲み上げ且つ層厚規制を同時に行う現像装置において、現像剤の劣化、がさつき、白抜け等の画像不良を防ぎ、更に、Ｔ／Ｄムラを防いで高画質な画像を形成できる現像装置及び画像形成装置を提供することである。
【００２５】
【課題を解決するための手段】
上記目的は本発明に係る現像装置及び画像形成装置にて達成される。要約すれば、第１の本発明は、トナーと磁性キャリアを含む現像剤を担持し、回転して像担持体と対向した現像部に搬送する現像剤担持体と、該現像剤担持体内に非回転に配置された磁界発生手段と、現像剤を前記現像剤担持体から回収し、補給された新たな現像剤と混合攪拌する攪拌室と、該攪拌室にて混合攪拌された現像剤を前記現像剤担持体上に供給する現像室と、該現像室にて前記現像剤担持体上に担持された現像剤に対して層厚規制する層厚規制部材と、を有する現像装置において、
前記磁界発生手段は、前記層厚規制部材と対向した層厚規制極が、前記現像室内において前記現像剤担持体回転方向上流側に隣り合わせた極と反発極構成であり、該反発極構成によって、前記現像剤担持体に対して、現像剤の剥離、汲み上げを行い、前記層厚規制極が前記現像室内の現像剤をくみ上げ及び現像剤の層厚規制を同時に行う構成であり、前記磁性キャリアは、７．９５７７５ｋＡ／ｍの磁界中における磁化量Ｍ［Ａｍ2／ｋｇ］が８〜５５［Ａｍ2／ｋｇ］の範囲内であり、
前記現像室と前記攪拌室は、どちらかを上にして鉛直方向上下に構成され、前記現像剤担持体は、担持する現像剤が、前記現像室にて前記層厚規制部材による層厚規制を受け、次に前記現像部を通過して、次に前記攪拌室に取り込まれる方向で且つ前記像担持体との対向部での表面移動方向が前記像担持体と逆方向となる方向に回転することを特徴とする現像装置を提供する。
【００２６】
第２の本発明は、像担持体上に潜像を形成する潜像形成手段と、前記潜像を現像する第１の本発明の現像装置と、を備えることを特徴とする画像形成装置を提供する。
【００２７】
【発明の実施の形態】
以下、本発明に係る現像装置及び画像形成装置を、図面に則して更に詳しく説明する。尚、現像装置は、例えば以下に述べるような画像形成装置の中で使用されるが、必ずしもこの形態に限られるものではない。
【００２８】
実施例１
図３は本発明の実施例１に係る現像装置１を備える画像形成装置の概略断面図である。
【００２９】
本画像形成装置は、複数の画像形成ステーションを有する４ステーションのレーザビームプリンタであり、これには感光体ドラム４の周囲に画像形成手段を有して構成される画像形成ステーションがマゼンタｍ、シアンｃ、イエローｙ及びブラックｋの４色に対応して設けられ、各ステーションＰｍ、Ｐｃ、Ｐｙ、Ｐｋにて形成された感光体ドラム４ｍ、４ｃ、４ｙ、４ｋに対向して移動する転写ベルト９ａによって搬送される転写材上に転写される。
【００３０】
即ち、マゼンタ、シアン、イエロー及びブラックの画像形成ステーションＰｍ、Ｐｃ、Ｐｙ、Ｐｋにそれぞれ感光体ドラム４ｍ、４ｃ、４ｙ、４ｋが配接され、これらの感光体ドラム体４ｍ、４ｃ、４ｙ、４ｋは図３の矢印方向（図３では時計方向）に回転される。そして、各感光体ドラム４ｍ、４ｃ、４ｙ、４ｋの周囲には、コロナ帯電器６ｍ、６ｃ、６ｙ、６ｋと、潜像形成手段である光走査手段としての走査光学装置７ｍ、７ｃ、７ｙ、７ｋと、現像装置１ｍ、１ｃ、１ｙ、１ｋ及びクリーニング器８ｍ、８ｃ、８ｙ、８ｋが配接されている。
【００３１】
更に、画像形成手段の一部を構成する転写部は、各画像形成ステーションＰｍ〜Ｐｋに共通して用いられる転写ベルト９ａ及び各感光体ドラム４ｍ〜４ｋ用の転写帯電器９ｍ、９ｃ、９ｙ、９ｋを有し、フルカラー画像形成は、転写ベルト９ａ上に担持された転写材上に感光体ドラム４ｍ〜４ｋ上に形成されたトナー像を順次転写することによって実現される。
【００３２】
一方、転写材は、給紙カセット５から転写ベルト９ａ上に供給され、転写工程が終了すると転写ベルト９ａから分離され、定着器２を経てトレイ３に排出される。
【００３３】
又、前記走査光学装置７ｍ、７ｃ、７ｙ、７ｋは、不図示のレーザ光源と、このレーザ光源からのレーザ光を走査する回転ポリゴンミラーと、走査ビームを感光体ドラム４ｍ〜４ｋ表面の母線上に集光するｆθレンズと、その光束を偏向する反射ミラーと、走査ビームの特定位置を検出するビーム検出装置とで構成されている。
【００３４】
ここで、現像装置１ｍ〜１ｋの詳細を、図１及び図２に基づいて説明する。尚、現像装置１ｍ〜１ｋ及び感光体ドラム４ｍ〜４ｋは、現像装置１ｍ〜１ｋ内部の現像剤の色以外は同様の構成であり、以下の説明においては、「現像装置１」「感光体ドラム４」と総称する。図１は、現像装置１の概略断面図、図２は同現像装置１の現像容器１０部分の長手方向の断面図でである。
【００３５】
本発明では、現像剤として非磁性トナーと磁性キャリアを含む二成分現像剤が用いられており、磁性キャリアとしては、７．９５７７５ｋＡ／ｍ、即ち、１ｋＯｅ（１キロエールステッド）の磁界中における磁化量Ｍ［Ａｍ2／ｋｇ］が８〜５５［Ａｍ2／ｋｇ］の範囲内、比較的低磁化のものを用いていることを特徴とする。尚、本明細書にては、１ｋＯｅ＝約７．９５７７５Ａｍ2／ｋｇとする。
【００３６】
磁性キャリアとして低磁化のものを用いると、キャリア同士に働く磁気的な拘束力が弱まるために、キャリアにより形成される磁気ブラシの穂が柔らかくなり、現像部４１において感光体ドラム４と摺擦する力が弱くなる。すると、感光体ドラム４上に現像されたトナー像を磁気ブラシの穂の摺擦力によって乱す力が弱くなるので、画像のがさつき感が少なくなり、高画質な画像を得ることが可能となる。
【００３７】
上記磁気特性のキャリアとして、本実施例では、磁性金属酸化物及び非磁性金属酸化物である磁性体をバインダー樹脂中に分散した状態の出発原料から重合法により生成された、所謂、樹脂磁性キャリア（磁性体分散型樹脂磁性キャリア）を用いているが、磁気特性が上記した範囲のものであれば、他の製法により製造したものを用いてもよい。
【００３８】
磁性キャリアの磁化が上記した範囲以下のものを用いると、現像剤を感光体ドラム４へと担持搬送する現像剤担持体である現像スリーブ１３との磁気的拘束力が弱過ぎるために、磁性キャリアが感光体ドラム４に付着してしまう現象が顕著になった。又、磁化が上記した範囲以上のものを用いると、磁気ブラシの穂が硬過ぎてしまい、所望の高画質な画像を得ることができなかったため、磁性キャリアの磁化を上記の範囲に限定した。
【００３９】
磁性キャリアの磁気特性については以下の方法を用いた。即ち、理研電子（株）製の振動磁場型磁気特性自動記録装置ＢＨＶ−３０を用いて測定した。７．９５７７５ｋＡ／ｍの外部磁場を作り、そのときの磁性キャリアの磁化の強さを求める。キャリアは円筒状のプラスチック容器に十分密になるようにパッキングする。この状態で磁気モーメントを測定し、キャリアを入れた状態の実際の重量を測定し、磁化の強さ（Ａｍ2／ｋｇ）を求める。ついで、磁性キャリア粒子の真比重を乾式自動密度系アキュピック１３３０（島津製作所（株）製）により求め、磁化の強さに真比重を掛け合わせることにより、単位面積あたりの磁化の強さ（Ａｍ2／ｋｇ）を求めた。
【００４０】
本実施例に係る現像装置１は、非磁性トナーと上記に説明した低磁化の磁性キャリアを含む二成分現像剤が収容された現像容器１０内に、感光体ドラム４に対向した開口部に設けられた現像剤担持体としての現像スリーブ１３と、現像スリーブ１３上に担持された現像剤の穂を規制する穂立ち規制部材である層厚規制部材１７を有している。そして、現像容器１０内の略中央部は、図面に垂直方向に延在する隔壁１６によって現像室Ｒ１と攪拌室Ｒ２とに区画されており、現像剤は現像室Ｒ１及び攪拌室Ｒ２に収容されている。
【００４１】
上記現像室Ｒ１及び攪拌室Ｒ２には、現像剤攪拌、搬送手段として第１及び第２の搬送スクリュー１１、１２がそれぞれ配接されている。第１の搬送スクリュー１１は現像室Ｒ１内の現像剤を搬送し、また、第２の搬送スクリュー１２は現像剤濃度制御装置の制御の下でトナー補給口２０（図２）から攪拌室Ｒ２内の第２の搬送スクリュー１２の上流側に供給されるトナーと攪拌室Ｒ２内に既にある現像剤とを攪拌しながら搬送し、現像剤のトナー濃度を均一化する。
【００４２】
又、隔壁１６の両端部には、現像室Ｒ１と攪拌室Ｒ２とを連通させる連通部１８、１９が形成されており、現像室Ｒ１と攪拌室Ｒ２間の現像剤の受け渡しを行っている。
【００４３】
更に、現像室Ｒ１の感光体ドラム４に対向した現像部４１に相当する位置には現像容器１０の開口部が開口しており、この開口部に現像スリーブ１３が感光体ドラム４方向に一部露出するようにして回転可能に配接されている。尚、この現像スリーブ１３は非磁性材で構成され、その内部には磁界発生手段であるマグネットローラ１５が非回転状態で設置されており、このマグネットローラ１５は本実施例の現像極Ｓ１と現像剤を搬送する磁極Ｓ２、Ｓ３、Ｎ１、Ｎ２を有している。
【００４４】
しかして、現像スリーブ１３は現像時に図１の、現像部４１にて感光体ドラム４と表面が逆方向に移動する方向、つまり感光体ドラム４の回転に対してカウンター方向である矢印ｂ方向に回転し、穂立ち規制部材１７による磁気ブラシの穂切りによって層厚を規制された二成分現像剤を担持してこれを感光体ドラム４と対向した現像部４１へ搬送し、感光体ドラム４上に形成された潜像に現像剤を供給して潜像を現像する。このとき、現像効率（つまり、潜像へのトナーの付与率）を向上させるために、現像スリーブ１３には電源２１から直流電圧と交互電圧である交流電圧とを重畳した現像バイアス電圧が印加される。
【００４５】
層厚規制部材である穂立ち規制部材１７は、アルミニウム等の非磁性部材若しくは、非磁性部材に磁性部材を取り付けた又は磁性部材のみで構成され、感光体ドラム４と対向した現像部４１よりも現像スリーブ１３の回転方向上流側に配設されている。そして、この穂立ち規制部材１７の先端部と現像スリーブ１３との間を現像剤の非磁性トナーと磁性キャリアの両方が通過して現像部４１へと送られる。
【００４６】
尚、穂立ち規制部材１７の現像スリーブ１３の表面との間隙を調整することによって、現像スリーブ１３上に担持した現像剤磁気ブラシの穂切り量が規制されて現像部４１へ搬送される現像剤量が調節される。
【００４７】
ところで、第１の搬送スクリュー１１は、図２に示すように、現像室Ｒ１内の底部に現像スリーブ１３の軸方向（現像幅方向）に沿ってほぼ平行に配置されており、非磁性もしくは磁性の回転軸の周りに非磁性材料から構成される羽根部材をスパイラル状に設けたスクリュー構造とされ、回転して現像室Ｒ１内の現像剤を現像室Ｒ１の底部にて現像スリーブ１３の軸線方向に沿って一方向に搬送する。
【００４８】
又、第２の搬送スクリュー１２も第１の搬送スクリュー１１と同様に回転軸の周りに羽根部材を第１の搬送スクリュー１１とは逆向きにしてスパイラル状に設けたスクリュー構造とされ、攪拌室Ｒ２内の底部に第１の搬送スクリュー１１と同方向に回転して攪拌室Ｒ２内の現像剤を第１の搬送スクリュー１１と反対方向に搬送する。このようにして、第１及び第２搬送スクリュー１１、１２の回転による搬送によって、現像剤が隔壁１６の両端の連通部１８、１９を通って現像室Ｒ１と攪拌室Ｒ２との間で循環される。
【００４９】
尚、現像スリーブ１３上に担持されて現像部４１に搬送され，現像に供された後、現像部４１において現像に供されないで残った現像剤は、現像スリーブ１３の回転に伴って再び攪拌室Ｒ２内へ戻され、マグネットローラ１５の現像容器１０内部側に位置する反発極構成をとる隣り合った磁極Ｓ２、Ｓ３により現像スリーブ１３上から掻き落とされ、攪拌室Ｒ２内へ回収される。
【００５０】
一方、第１の搬送スクリュー１１の回転により搬送された現像剤は、反発極構成磁極の一方で、現像スリーブ１３回転方向下流側の磁極であり、穂立ち規制部材１７に対向した層厚規制極でもあるＳ２により、その磁束密度の絶対値に比例した量で現像スリーブ１３上に汲み上げられ、同時に層厚規制を受け、再び現像スリーブ１３の回転によって、現像極Ｓ１に対向する現像部４１に搬送される。
【００５１】
尚、現像剤の汲み上げ量は、磁極Ｓ２からの磁界で形成される現像スリーブ１３の中心方向へ作用する磁気拘束力と現像スリーブ１３の回転方向に作用する搬送力と、層厚規制部材（穂きり部材）１７と現像スリーブ１３の表面との間隙を調整することによって、現像スリーブ１３上に担持した現像剤磁気ブラシの穂き量が規制されて現像領域４１へ搬送される現像剤量が調節され、決定される。
【００５２】
そして、こうした本実施例の現像装置１の構成として、図１及び図２に示すように、従来例１’に比べて現像容器１０内の現像剤の循環が次のようになっている。
【００５３】
本発明の特徴部分としては、現像室Ｒ１と現像室Ｒ２を鉛直方向下と上に配置させる。本実施例では、攪拌室Ｒ２を現像室Ｒ１より鉛直方向上方に配置しているため、攪拌室Ｒ２から現像室Ｒ１への現像剤の受け渡しは隔壁１６の片方の端部１８において上から下へと重力方向に沿ってなされる。
【００５４】
その後、現像剤は現像に供されるか搬送スクリュー１１で攪拌搬送され、隔壁１６のもう片方の端部の連通部１９において搬送力と圧力によって下から上へと送られ、上方の攪拌室Ｒ２内で現像室Ｒ１から搬送された現像剤と、現像に供された後のＴ／Ｄ比の低下した剤と、補給したトナーとを攪拌搬送し、再度隔壁１６の片方の端部の連通部１８において上から下へと重力方向に沿って現像室Ｒ１へと搬送される。
【００５５】
つまり、現像に供された現像剤は、現像スリーブ１３から現像に供されることのない攪拌室Ｒ２側に落とされ、そこで、現像に供した後のＴ／Ｄ比が低下した現像剤と通常のＴ／Ｄ比の現像剤及び現像容器１０に補給されたトナーが攪拌搬送される。その後、十分攪拌搬送された後に、現像室Ｒ１側に現像剤は送られ、現像に供されることになる。従って、課題となっていたスクリュー跡即ちＴ／Ｄムラを防止することができる。
【００５６】
又、本実施例では、攪拌室Ｒ２が現像室Ｒ１より上下方向で上に配置されているが、これは感光体ドラム４が現像部４１で上から下に向かって移動しているため、それとカウンター方向に、スリーブ１３を現像部４１で下から上に移動させるためである。つまり、現像スリーブ１３を感光体ドラム４を現像部にて表面移動方向がと逆方向となるように回転させるためである。従って、現像部４１で感光体ドラム４が下から上に向かって移動する場合、スリーブ１３を現像部４１で上から下に移動させるため、攪拌室Ｒ２を現像室Ｒ１より上下方向で下に配置することとなる。つまり、攪拌室Ｒ２と現像室Ｒ１が鉛直方向でどちらかを上にして構成されていれば、方向は適宜選択すればよい。
【００５７】
こうして、高画質をふまえて磁化量を下げたキャリアを含む現像剤を用いた場合に、層厚規制部材に対向した極により現像室内の現像剤の汲み上げ、及び、現像剤の層厚規制を同時に行う、現像スリーブと感光体ドラムの対向部における表面移動方向が逆方向であるカウンター現像装置において、以上説明したように、現像室と攪拌室を、どちらかを上にして鉛直方向上下に配置させ、現像スリーブに担持された現像剤が現像室にて層厚規制部材による層厚規制を受け、次に現像部を通過して、次に攪拌室に取り込まれる方向に回転することで、現像剤劣化、白抜けやがさつき等の画像不良を防ぎ、更に、磁化量の高いフェライトキャリアを用いた場合の画質と同等以上にスクリュー跡等のＴ／Ｄムラの画像不良を防ぎ、高画質画像が提供できる。
【００５８】
実施例２
本発明の実施例２を図４、図５に基づいて説明する。実施例１では、図２に示すように、現像室Ｒ１と現像室Ｒ２間の現像剤の受け渡しを隔壁１６の両端の連通部１８、１９で行っていた。しかし、隔壁１６の両端で行おうとすると、現像剤を下から上へと受け渡す連通部１９側で、Ｔ／Ｄ比が低下した剤が反発極で落とされたものが、この連通部１９の部分で連れまわるという弊害が生じやすい。そのため、そこで画像ムラが生じるので、連通部１９の部分を画像域外にもっていく必要が生じ、現像容器１０の搬送スクリュー１１、１２の軸方向を長くする必要が生じる。
【００５９】
そこで、本実施例では、図４（ａ）に示すように、現像室Ｒ１と攪拌室Ｒ２とを区画する隔壁１６に設けられた、現像剤を下から上へと受け渡す図２に示す連通部１９をなくし、現像スリーブ１３を主に利用して現像剤の現像室Ｒ１から攪拌室Ｒ２への受け渡しを行う。
【００６０】
ここで、図４及び図５を用いて現像剤の循環を示す。まず、図４（ａ）に示すように攪拌室Ｒ１から現像室Ｒ２への現像剤の受け渡しは、隔壁１６の片方の端部１８において上から下へと重力方向にそって行う。その後、現像スリーブ１３の回転により現像剤が現像スリーブ１３上を穂立ち規制部材１７により穂切りされ、感光体ドラム４と対向した現像部４１へと搬送され、そして、現像に供された後に攪拌室Ｒ２に取り込まれることによって下側の現像室Ｒ１から上側の攪拌室Ｒ２に現像剤の受け渡しを行う。
【００６１】
しかし、現像剤の搬送速度によっては、現像室Ｒ１の第１搬送スクリュー１１の現像剤搬送方向最下流部分である、隔壁１６の連通部１８が設けられていない方の端部において、現像室Ｒ１に現像剤がたまりやすい場合がある。そのために、現像剤があふれる等の弊害が生じる。
【００６２】
その対策として、図５に示すように、第１の搬送スクリュー１１と平行に、且つ水平方向に隣り合う第３のスクリュー２２を設ける。第１搬送スクリュー１１と第３のスクリューとの間にはそれらと平行に隔壁２３を設ける。よって、第３スクリュー２２が、現像室Ｒ１に対して隔壁２３によって、水平方向に隣り合わせに区画された現像剤送り室２４に配置されたことになる。
【００６３】
現像容器１０の水平方向の断面図である図４（ｂ）を用いて、現像室Ｒ１と現像剤送り室２４との関係を説明する。
【００６４】
現像室側Ｒ１の現像剤が多くなったときに隔壁２３の上部に設けられた連通部２５より、現像剤送り室２４へと搬送される。本実施例においては、隔壁２３の連通部２５は、現像室Ｒ１と攪拌室Ｒ２を区切る隔壁１６の連通部１８の反対側に設けられている。又、現像室Ｒ１より連通部２５を通して搬送されてきた現像剤を、第３のスクリュー２２は現像室Ｒ１内のスクリュー１１と逆方向に現像剤を搬送する。第３のスクリュー２２の現像剤搬送方向最下流の位置で、隔壁２３の端部には、連通部２６が設けられ、ここで、現像剤送り室２４から現像室Ｒ１へと送られ、現像に供されることになる。ここで、壁２３に設けられた、現像剤送り室２４から現像室Ｒ１への連通部２６は、隔壁１６の連通部１８と同じ側にある。
【００６５】
つまり、本実施例においては、現像室Ｒ１内の現像剤が過剰となった場合は、過剰となった分を、現像室Ｒ１に対して攪拌室Ｒ２と別の方向に設けられた現像剤送り室２４を使用して循環させ、現像剤があふれ出すのを回避している。
【００６６】
尚、本実施例においても、現像剤として、７．９５７７５ｋＡ／ｍ（１キロエールステッド）の磁界中における磁化量Ｍ［Ａｍ2／ｋｇ］が８〜５５［Ａｍ2／ｋｇ］の範囲内である磁性キャリアと非磁性トナーを含む二成分現像剤が用いられ、実施例１のように、軽付加構造をとるカウンター現像装置であり、現像室Ｒ１と攪拌室Ｒ２が鉛直方向上下に配置されている。
【００６７】
又、本実施例では、攪拌室Ｒ２が現像室Ｒ１より上下方向で上に配置されているが、感光体ドラム４の回転方向により、攪拌室Ｒ２を現像室Ｒ１より上下方向で下に配置してもよい。
【００６８】
こうすることにより、軽圧縮現像装置の性能を維持したまま、磁化量をさげたキャリアを用いた場合に、大型化にすることなく、Ｔ／Ｄムラ等の画像不良を防ぎ、更に、現像後のＴ／Ｄの低い現像剤の連れ周りも回避でき、磁化量の高いフェライトキャリアを用いた場合の画質と同等以上の高画質画像が提供できる。
【００６９】
実施例３
本発明の実施例は、実施例２において、攪拌室Ｒ２から現像室Ｒ１への現像剤の送り量を適正にし、第３スクリュー２２を必要としない場合である。つまり現像装置１としては、概観図を、現像剤送り室２４を設けない実施例１の図１の形状とし、現像剤の送りは、図４（ａ）に示された、第１搬送スクリュー１１現像剤搬送方向下流側の攪拌室Ｒ２との連通部１９を設けない実施例２の構成とする。
【００７０】
現像剤の送り量の調整は、図４（ａ）の攪拌室Ｒ２から現像室Ｒ１への連通部１８の現像剤通路の窓の大きさにより調整し、設定しておくこととする。この方法によって、現像室Ｒ１には、常に所定の量の現像剤が収納されているので、現像剤が過剰となり、あふれることもない。
【００７１】
又、本実施例では、攪拌室Ｒ２が現像室Ｒ１より上下方向で上に配置されているが、感光体ドラム４の回転方向により、攪拌室Ｒ２を上下方向で下に配置してもよい。
【００７２】
本実施例のように、現像剤を常に適当な量に調整する手段を設ければ、実施例２に説明した現像剤送り室を設けることによる現像容器の大型化が回避でき、更なる小型化が可能となり、軽圧縮現像装置の性能を維持したまま、磁化量をさげたキャリアを用いた場合に、Ｔ／Ｄムラ、スクリュー跡等の画像不良を防ぎ、磁化量の高いフェライトキャリアを用いた場合の画質と同等以上の画像が提供できる。
【００７３】
【発明の効果】
以上説明したように、本発明によれば、トナーと磁性キャリアを含む現像剤を担持し、現像剤を現像剤担持体から回収し、補給された新たな現像剤と混合攪拌する攪拌室と、攪拌室にて混合攪拌された現像剤を現像剤担持体上に供給する現像室と、を有する現像装置において、磁界発生手段は、層厚規制部材と対向した層厚規制極が、現像室内において現像剤担持体回転方向上流側に隣り合わせた極と反発極構成であり、反発極構成によって、現像剤担持体に対して、現像剤の剥離、汲み上げを行い、層厚規制極が現像室内の現像剤をくみ上げ及び現像剤の層厚規制を同時に行う構成であり、磁性キャリアは、７．９５７７５ｋＡ／ｍの磁界中における磁化量Ｍ［Ａｍ2／ｋｇ］が８〜５５［Ａｍ2／ｋｇ］の範囲内であり、現像室と攪拌室は、どちらかを上にして鉛直方向上下に構成され、現像剤担持体は、担持する現像剤が、現像室にて層厚規制部材による層厚規制を受け、次に現像部を通過して、次に攪拌室に取り込まれる方向で且つ像担持体との対向部で像担持体と表面移動方向が逆方向になるように回転するので、がさつきや白抜け等の画像不良、現像剤の劣化等を防ぎ、更に形成画像のＴ／Ｄムラを防ぎ、高画質な画像を提供することができる。
【図面の簡単な説明】
【図１】本発明に係る現像装置の一実施例を示す概略構成図である。
【図２】本発明に係る現像装置の一実施例を示す長手方向の横断面図である。
【図３】本発明に係る画像形成装置の一実施例を示す概略構成図である。
【図４】本発明に係る現像装置の他の実施例を示す長手方向の横断面図（図４（ａ））と縦断面図（図４（ｂ））である。
【図５】本発明に係る現像装置の他の実施例を示す概略構成図である。
【図６】従来の現像装置の一例を示す概略構成図である。
【符号の説明】
１ 現像装置
４ 感光体ドラム（像担持体）
１０ 現像容器
１１ 第１搬送スクリュー
１２ 第２搬送スクリュー
１３ 現像スリーブ（現像剤担持体）
１５ マグネットローラ（磁界発生手段）
１６ 現像室と攪拌室の隔壁
１７ 穂立ち規制部材（層厚規制部材）
１８、１９ 現像室と攪拌室の連通部
２０ トナー補給口
２１ 現像バイアス電源
２２ 第３搬送スクリュー
２３ 現像室と現像剤送り室との隔壁
２４ 現像剤送り室
２５、２６ 現像室と現像剤送り室の連通部
４１ 現像部
Ｒ１ 現像室
Ｒ２ 攪拌室[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a developing device for attaching a developer to a latent image formed on an image carrier such as a photoreceptor drum to form a visible image, and an electrophotographic or electrostatic recording device provided with the developing device. The present invention relates to an image forming apparatus such as a copying machine or a laser beam printer using a method.
[0002]
[Prior art]
Conventionally, a dry developer as a developer is carried on the surface of a developer carrier, and the developer is transported and supplied to the vicinity of the surface of the image carrier on which an electrostatic latent image is carried. It is well known that the electrostatic latent image is developed by applying an alternating electric field between the carrier and the developer carrier to develop the electrostatic latent image.
[0003]
Note that, in general, a developing sleeve is generally used for the developer carrying member. Therefore, in the following description, the developing carrier is referred to as a “developing sleeve”. In the following description, it will be referred to as “photosensitive drum”.
[0004]
As the above-mentioned developing method, for example, a two-component developer containing carrier particles and toner particles is used to form a magnetic brush on the surface of a developing sleeve in which a magnet roller serving as a magnetic field generating means is disposed, and a minute brush is formed. This magnetic brush is rubbed or brought close to the photoconductor drum opposed to the photoconductor drum while maintaining the development interval, and the transfer and the reverse transfer from the development sleeve side to the photoconductor drum side are repeatedly performed. A so-called magnetic brush developing method for developing an electrostatic latent image is known.
[0005]
Also, a non-contact type alternating electric field development method using a two-component developer for the purpose of simple color development or multiple development is known. The toner image formed on the photosensitive drum by these developing methods is transferred onto a transfer material such as paper as necessary, and then fixed by heat, pressure, solvent vapor, or the like to obtain a copied image. .
[0006]
Further, in the developing electrode configuration in the developing device, the layer thickness regulating member, ie, the rising regulating member, regulates the rising of the developer by the magnetic brush to regulate the amount of the developer on the developing sleeve. The layer thickness regulation pole (cut pole), which is a magnetic pole, and the repulsion pole configuration in the developer container, which are adjacent to each other and have the same polarity, allow the developer to be separated from the developing sleeve, and the developer carrier When the function of pumping up the developer is provided, it is usual that the pumping pole is provided separately and independently.
[0007]
In the case of such a configuration, there is a problem that the developer stays between the pumping pole, the cut pole, and the spike regulating member, and the developer is easily deteriorated. Therefore, the cut pole and the pumping pole have the same polarity and are adjacent to each other, that is, the cut pole is opposed to the spike regulating member so that the cut pole and the pumping pole are performed by one pole. As a result, the deterioration of the developer can be reduced.
[0008]
By the way, in recent years, higher image quality has been demanded, and there has been a problem that the roughness is lowered particularly in a low density portion. On the other hand, by using a magnetic carrier having a smaller amount of magnetization than a conventional ferrite carrier for a two-component developer, it has become possible to achieve higher image quality.
[0009]
However, when the developer is supplied to the photosensitive drum in the forward direction, that is, the rotation direction of the developing sleeve is the forward direction with respect to the photosensitive drum, the conventional developing method has a high magnetization amount. Compared to the case of using a ferrite carrier, when low- and high-density images are in this order in the traveling direction, an abnormal image called white spots is more likely to occur downstream of the low-density side of the density step. became. In addition, when a low-density part is continuous with a high-density part, the problem of the so-called Hakiyose phenomenon, which is the case where the rear end of the high-density part further darkens, tends to occur.
[0010]
For these image defects, the direction in which the developer is supplied to the photosensitive drum is reversed (counter direction), that is, the rotation direction of the developing sleeve is opposite to the photosensitive drum and the surface is in the opposite direction to the photosensitive drum. It has been confirmed that the above problem can be solved by setting the direction of movement in the direction of movement, that is, the counter direction. When a low magnetization carrier is used, a counter development method is often used.
[0011]
Here, it is a light-load structure in which the cut pole and the pumping pole are combined into one to oppose the regulating member. FIG. 6 shows an example 1 'of a conventional developing device which is a counter developing device.
[0012]
The developing device 1 ′ includes a developing container 10. The inside of the developing device 1 ′ is partitioned by a partition 16 into a developing chamber R 1 and a stirring chamber R 2, and a toner storage chamber R 3 is provided above the stirring chamber R 2.
[0013]
Supply toner T1 is stored in the toner storage chamber R3. An amount of toner T1 corresponding to the toner consumed in the development is dropped and replenished into the stirring chamber R2 from the replenishing port 20 at the lower part of the toner storage chamber R3.
[0014]
On the other hand, a two-component developer T in which toner particles and a magnetic carrier are mixed is contained in the developing chamber R1 and the stirring chamber R2. A developer transport screw 11 is accommodated in the developing chamber R1 and transports the developer T along the longitudinal direction of the developing sleeve 13 by rotational driving. The direction in which the developer is transported by the transport screw 12 housed in the stirring chamber R2 is opposite to the direction in which the screw 11 is transported.
[0015]
The partition 16 provided between the developing chamber R1 and the stirring chamber R2 is provided with an opening serving as a communication portion (not shown) on the front side and the back side, and the developer T conveyed by the screw 11 is The developer T transferred from one of the communicating portions to the screw 12 and conveyed by the screw 12 is transferred to the screw 11 from the other communicating portion and circulates between the developing chamber R1 and the stirring chamber R2. .
[0016]
Further, an opening is provided in a portion of the developing container 10 close to the photosensitive drum 4. The opening is provided with a non-magnetic developing sleeve 13 made of a non-magnetic material such as aluminum or non-magnetic stainless steel and having appropriate irregularities on its surface, and faces the photosensitive drum 4.
[0017]
The developing sleeve 13 is moved in a direction indicated by an arrow b, that is, in the same direction as the photosensitive drum 4 so that the surface thereof moves in a direction opposite to the photosensitive drum 4 at a portion facing the photosensitive drum 4 serving as the developing unit 41. Rotate. Further, the developing sleeve 13 carries the developer T whose surface is regulated to an appropriate layer thickness by the layer thickness regulating blade 17 at the lower end of the developing container 10, and then conveys the developer T to the developing unit 41.
[0018]
When the magnetic brush formed of the developer T carried by the developing sleeve 13 comes into contact with the photosensitive drum 4 rotating in the direction of arrow a in the developing unit 41, the electrostatic brush formed on the photosensitive drum 4 is formed. The latent image is developed by the developing unit 41. A magnet roller 15 serving as a roller-shaped magnetic field generating means is fixedly arranged in the developing sleeve 13, and a developing magnetic pole S 1 is located in the developing unit 41.
[0019]
In this embodiment, the magnet roller 15 has a magnetic pole S1 as a developing magnetic pole facing the developing unit 41. The developing magnetic pole S1 forms a magnetic brush with a developer on the developing sleeve 13 by a developing magnetic field formed in the developing unit 41, and the magnetic brush contacts the photosensitive drum 4 to develop an electrostatic latent image. At this time, of the developer, the toner attached to the surface of the sleeve 13 together with the toner attached to the magnetic brush is transferred to the image area of the electrostatic latent image and used for development.
[0020]
In FIG. 6, the magnet roller 15 has N1, N2, N3 and S2 poles in addition to the developing magnetic pole S1 at the position of the developing section 41. With such a configuration, the developer applied on the developing sleeve 13 at the position N1 on the inner side near the opening of the developing container 10 of the developing sleeve 13 causes the opening of the developing container 10 to be opened by the rotation of the developing sleeve 13. Is moved to the outside of the developing container 10 after being regulated to an appropriate developer layer thickness by passing through the spike regulating member 17 which is a layer thickness regulating member located at the developing section 41, reaches the developing magnetic pole S1 located at the developing section 41, and its magnetic field. The developer rising inside develops the electrostatic latent image on the photosensitive drum 4.
[0021]
Thereafter, the developer T is conveyed by the rotation of the developing sleeve 13 to the developer container N3, which is disposed at a position until the developer T returns from the developing unit 41 to the inside of the developer container 10, and S2 and N2 inside the developer container 10, and into the developer container 10. The developer T on the developing sleeve 13 falls into the developing chamber R1 due to the repelling magnetic field between the developing pole S1 and the N2 pole located opposite to the developing pole S1 and the N1 pole which is the layer thickness regulating pole adjacent thereto. The developer T that has fallen into the developing chamber R1 is conveyed to the screw 11 and, in the stirring chamber R2, when the toner has been consumed by the development, receives a new toner supply and is stirred and conveyed by the screw 12, and again the developing chamber It is transported to R1 and used for development.
[0022]
[Problems to be solved by the invention]
However, as described above, the magnetic pole adjacent to the upstream side has a repelling pole configuration, and the developer T in the developing chamber R1 is pumped up by the layer thickness regulating electrode (N1 in FIG. 6) opposed to the spike regulating member 17. In a counter developing device in which the layer thickness of the developer T is simultaneously controlled and the rotation direction of the developing sleeve 13 is the counter direction with respect to the photosensitive drum 4, a high-duty image comes, for example. And the T / D ratio (toner weight in the developer / total weight of the developer (toner and carrier)), which is the ratio of the carrier and the toner of the developer on the developing sleeve 13, is reduced, and the agent in that state is stirred. It falls into the room R1. Then, the next image formation is carried out with insufficient stirring of the developer in the state where the T / D ratio is lowered and the developer in the normal T / D ratio state that is not subjected to the development. The problem of screw marks (T / D unevenness) due to poor stirring was likely to occur.
[0023]
This is because when light load development is not used, the pole for regulating the layer thickness of the developer and the pole for pumping the developer are separate, and the compression is performed between the time when the developer is pumped and the time when the layer thickness is regulated. As a result, T / D unevenness due to poor stirring was not easily generated.
[0024]
Accordingly, an object of the present invention is to perform development using a carrier having a reduced amount of magnetization, and to move the surface in the developing section of the developer carrier that carries the developer containing the carrier and the toner in the direction opposite to the image carrier. In the magnetic field generating means in the developer carrier, the layer thickness regulating pole facing the layer thickness regulating member takes a repulsion polarity with the magnetic pole adjacent to the upstream side, and pumps up the developer in the developing chamber and In a developing device that simultaneously regulates a layer thickness, a developing device and an image forming apparatus that can prevent image defects such as deterioration, roughness, and white spots of a developer, and that can form a high-quality image while preventing T / D unevenness are provided. To provide.
[0025]
[Means for Solving the Problems]
The above object is achieved by a developing device and an image forming apparatus according to the present invention. In summary, a first aspect of the present invention provides a developer carrier that carries a developer containing a toner and a magnetic carrier, and that rotates and transports the developer to a developing unit facing the image carrier. A magnetic field generating means arranged in rotation, a developer chamber for recovering the developer from the developer carrier, mixing and stirring the replenished new developer, and a developer mixed and stirred in the stirring chamber; A developing chamber that supplies the developer on the developer carrier, and a layer thickness regulating member that regulates the layer thickness of the developer carried on the developer carrier in the developing chamber;
The magnetic field generating means has a layer thickness regulating member facing the layer thickness regulating member, a pole and a repelling pole configuration adjacent to the developer carrier rotating direction upstream side in the developing chamber, and by the repulsing pole configuration, For the developer carrier, the developer is separated and pumped up, and the layer thickness regulation electrode is configured to simultaneously pump up the developer in the developing chamber and regulate the layer thickness of the developer, wherein the magnetic carrier is , 7.95775 kA / m in a magnetic field M [Am Two / Kg] is 8 to 55 [Am Two / Kg], and
The developing chamber and the stirring chamber are vertically arranged with one of them up, and the developer carrying member is configured such that the developer to be carried thereon is regulated by the layer thickness regulating member by the layer thickness regulating member in the developing chamber. Receiving, then passing through the developing unit, and then rotating in a direction in which it is taken into the stirring chamber and in which a surface movement direction in a portion facing the image carrier is opposite to the image carrier. A developing device is provided.
[0026]
According to a second aspect of the present invention, there is provided an image forming apparatus comprising: a latent image forming unit that forms a latent image on an image carrier; and a developing device according to the first aspect of the present invention that develops the latent image. provide.
[0027]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, the developing device and the image forming apparatus according to the present invention will be described in more detail with reference to the drawings. The developing device is used in, for example, an image forming apparatus described below, but is not necessarily limited to this embodiment.
[0028]
Example 1
FIG. 3 is a schematic sectional view of an image forming apparatus including the developing device 1 according to the first embodiment of the present invention.
[0029]
The image forming apparatus is a four-station laser beam printer having a plurality of image forming stations, and includes an image forming station having image forming means around a photosensitive drum 4 including magenta m and cyan. The transfer belt 9a is provided corresponding to four colors of c, yellow y and black k, and moves in opposition to the photosensitive drums 4m, 4c, 4y, and 4k formed by the stations Pm, Pc, Py, and Pk. Is transferred onto the transfer material conveyed by.
[0030]
That is, the photosensitive drums 4m, 4c, 4y, and 4k are connected to the magenta, cyan, yellow, and black image forming stations Pm, Pc, Py, and Pk, respectively. Is rotated in the direction of the arrow in FIG. 3 (clockwise in FIG. 3). Around the photoconductor drums 4m, 4c, 4y, and 4k, corona chargers 6m, 6c, 6y, and 6k, and scanning optical devices 7m, 7c, and 7y as optical scanning units that are latent image forming units. 7k, developing devices 1m, 1c, 1y, 1k and cleaning devices 8m, 8c, 8y, 8k are connected.
[0031]
Further, a transfer unit constituting a part of the image forming means includes a transfer belt 9a commonly used in each of the image forming stations Pm to Pk and transfer chargers 9m, 9c, 9y for the photosensitive drums 4m to 4k. 9k, and full-color image formation is realized by sequentially transferring the toner images formed on the photosensitive drums 4m to 4k onto a transfer material carried on the transfer belt 9a.
[0032]
On the other hand, the transfer material is supplied onto the transfer belt 9 a from the paper feed cassette 5, is separated from the transfer belt 9 a when the transfer process is completed, and is discharged to the tray 3 via the fixing device 2.
[0033]
The scanning optical devices 7m, 7c, 7y, and 7k include a laser light source (not shown), a rotating polygon mirror that scans the laser light from the laser light source, and a scanning beam on a generating line on the surfaces of the photosensitive drums 4m to 4k. Lens, a reflecting mirror that deflects the light beam, and a beam detector that detects a specific position of the scanning beam.
[0034]
Here, details of the developing devices 1m to 1k will be described with reference to FIGS. The developing devices 1m to 1k and the photosensitive drums 4m to 4k have the same configuration except for the color of the developer inside the developing devices 1m to 1k. In the following description, the "developing device 1", "photosensitive drum" 4 ". FIG. 1 is a schematic sectional view of the developing device 1, and FIG. 2 is a longitudinal sectional view of a developing container 10 portion of the developing device 1.
[0035]
In the present invention, a two-component developer containing a non-magnetic toner and a magnetic carrier is used as a developer, and the magnetic carrier has a magnetization of 7.95775 kA / m, that is, a magnetization in a magnetic field of 1 kOe (1 kOe). Quantity M [Am Two / Kg] is 8 to 55 [Am Two / Kg], which has a relatively low magnetization. In this specification, 1 kOe = about 7.95775 Am Two / Kg.
[0036]
When a magnetic carrier having a low magnetization is used, the magnetic binding force acting between the carriers is weakened, so that the magnetic brush ears formed by the carrier are softened and rub against the photosensitive drum 4 in the developing unit 41. The power becomes weak. Then, since the force of disturbing the toner image developed on the photosensitive drum 4 by the sliding force of the magnetic brush ears is weakened, the sense of roughness of the image is reduced, and a high quality image can be obtained. .
[0037]
In the present embodiment, as a carrier having the above-mentioned magnetic characteristics, a so-called resin magnetic carrier produced by a polymerization method from a starting material in a state where a magnetic material which is a magnetic metal oxide and a non-magnetic metal oxide is dispersed in a binder resin is used. (Magnetic material-dispersed resin magnetic carrier) is used, but a magnetic material manufactured by another manufacturing method may be used as long as the magnetic characteristics are in the above-mentioned range.
[0038]
When the magnetization of the magnetic carrier is less than the above range, the magnetic binding force with the developing sleeve 13 which is a developer carrier for carrying and transporting the developer to the photosensitive drum 4 is too weak. The phenomenon that the particles adhere to the photosensitive drum 4 became remarkable. Further, if the magnetization of the magnetic brush is more than the above range, the spike of the magnetic brush is too hard to obtain a desired high-quality image, so the magnetization of the magnetic carrier is limited to the above range.
[0039]
The following method was used for the magnetic characteristics of the magnetic carrier. That is, the measurement was performed using an oscillating magnetic field type automatic magnetic property recording apparatus BHV-30 manufactured by Riken Denshi Co., Ltd. An external magnetic field of 7.95775 kA / m is created, and the magnetization strength of the magnetic carrier at that time is determined. The carrier is packed tightly in a cylindrical plastic container. In this state, the magnetic moment is measured, the actual weight of the state with the carrier inserted is measured, and the magnetization intensity (Am Two / Kg). Next, the true specific gravity of the magnetic carrier particles is obtained by a dry automatic density system Acupic 1330 (manufactured by Shimadzu Corporation), and the magnetic strength is multiplied by the true specific gravity to obtain the magnetization intensity per unit area (Am). Two / Kg).
[0040]
The developing device 1 according to the present embodiment is provided at an opening facing the photosensitive drum 4 in a developing container 10 containing a two-component developer containing a non-magnetic toner and a low-magnetic magnetic carrier described above. And a layer thickness regulating member 17 which is a spike regulating member that regulates the spikes of the developer carried on the developing sleeve 13. A substantially central portion of the developing container 10 is divided into a developing chamber R1 and a stirring chamber R2 by a partition 16 extending in a direction perpendicular to the drawing, and the developer is stored in the developing chamber R1 and the stirring chamber R2. ing.
[0041]
First and second transport screws 11 and 12 are connected to the developing chamber R1 and the agitating chamber R2, respectively, as developer agitating and transporting means. The first conveying screw 11 conveys the developer in the developing chamber R1, and the second conveying screw 12 moves from the toner replenishing port 20 (FIG. 2) into the stirring chamber R2 under the control of the developer concentration control device. The toner supplied to the upstream side of the second conveying screw 12 and the developer already in the stirring chamber R2 are conveyed while being stirred, and the toner concentration of the developer is made uniform.
[0042]
In addition, communicating portions 18 and 19 are formed at both ends of the partition 16 to communicate the developing chamber R1 and the stirring chamber R2, and transfer the developer between the developing chamber R1 and the stirring chamber R2.
[0043]
Further, an opening of the developing container 10 is opened at a position corresponding to the developing unit 41 facing the photosensitive drum 4 in the developing chamber R1, and a developing sleeve 13 is partially formed in the opening in the direction of the photosensitive drum 4. It is rotatably connected so as to be exposed. The developing sleeve 13 is made of a non-magnetic material, and a magnet roller 15 as a magnetic field generating means is installed in a non-rotating state inside the developing sleeve 13. The magnet roller 15 is connected to the developing pole S1 of the present embodiment. It has magnetic poles S2, S3, N1, N2 for transporting the agent.
[0044]
Thus, the developing sleeve 13 moves in the direction in which the surface of the photosensitive drum 4 moves in the opposite direction to the surface of the photosensitive drum 4 in the developing unit 41 during development, that is, in the direction of arrow b which is a counter direction to the rotation of the photosensitive drum 4 during development. The two-component developer is rotated and the thickness of the two-component developer is regulated by the cutting of the magnetic brush by the rising control member 17, and is transported to the developing unit 41 facing the photosensitive drum 4. The developer is supplied to the latent image formed in the step (a) to develop the latent image. At this time, in order to improve the development efficiency (that is, the rate at which toner is applied to the latent image), a developing bias voltage in which a DC voltage and an AC voltage that is an alternating voltage are superimposed is applied to the developing sleeve 13 from the power supply 21. You.
[0045]
The spike regulating member 17, which is a layer thickness regulating member, is made of a non-magnetic member such as aluminum, or a magnetic member attached to a non-magnetic member, or is composed of only a magnetic member. The developing sleeve 13 is disposed on the upstream side in the rotation direction. Then, both the non-magnetic toner of the developer and the magnetic carrier pass between the front end of the spike regulating member 17 and the developing sleeve 13 and are sent to the developing unit 41.
[0046]
By adjusting the gap between the spike regulating member 17 and the surface of the developing sleeve 13, the amount of spikes of the developer magnetic brush carried on the developing sleeve 13 is regulated and the developer conveyed to the developing unit 41. The amount is adjusted.
[0047]
As shown in FIG. 2, the first transport screw 11 is disposed substantially parallel to the bottom of the developing chamber R1 along the axial direction (developing width direction) of the developing sleeve 13 and is non-magnetic or magnetic. Is a screw structure in which a blade member made of a non-magnetic material is spirally provided around a rotation axis of the developing chamber R1 so that the developer in the developing chamber R1 is rotated at the bottom of the developing chamber R1 in the axial direction of the developing sleeve 13. Along one direction.
[0048]
Similarly to the first transport screw 11, the second transport screw 12 has a screw structure in which the blade member is provided in a spiral shape around the rotation axis in a direction opposite to that of the first transport screw 11. The developer in the agitating chamber R2 is conveyed in the opposite direction to the first conveying screw 11 by rotating in the same direction as the first conveying screw 11 to the bottom in R2. In this way, the developer is circulated between the developing chamber R1 and the stirring chamber R2 through the communicating portions 18 and 19 at both ends of the partition 16 by the transport by the rotation of the first and second transport screws 11 and 12. You.
[0049]
After being carried on the developing sleeve 13 and conveyed to the developing unit 41 and subjected to the development, the remaining developer which is not subjected to the development in the developing unit 41 remains again with the rotation of the developing sleeve 13 in the stirring chamber. It is returned into R2, is scraped off from the developing sleeve 13 by the adjacent magnetic poles S2 and S3 having a repulsive pole structure located inside the developing container 10 of the magnet roller 15, and is collected into the stirring chamber R2.
[0050]
On the other hand, the developer conveyed by the rotation of the first conveying screw 11 is one of the repulsion pole constituent magnetic poles, the magnetic pole on the downstream side in the rotation direction of the developing sleeve 13, and the layer thickness regulating pole facing the spike regulating member 17. In step S2, the magnetic flux density is pumped onto the developing sleeve 13 in an amount proportional to the absolute value of the magnetic flux density. Is done.
[0051]
The amount of the developer pumped is determined by the magnetic restraining force acting in the direction of the center of the developing sleeve 13 formed by the magnetic field from the magnetic pole S2, the conveying force acting in the rotating direction of the developing sleeve 13, and the layer thickness regulating member (spike). By adjusting the gap between the cutting member 17 and the surface of the developing sleeve 13, the amount of the brush of the developer magnetic brush carried on the developing sleeve 13 is regulated, and the amount of the developer conveyed to the developing area 41 is adjusted. Is determined.
[0052]
As shown in FIGS. 1 and 2, the configuration of the developing device 1 of the present embodiment is such that the developer circulates in the developing container 10 as compared with the conventional example 1 'as follows.
[0053]
As a characteristic part of the present invention, the developing chamber R1 and the developing chamber R2 are arranged vertically below and above. In this embodiment, since the stirring chamber R2 is disposed vertically above the developing chamber R1, the transfer of the developer from the stirring chamber R2 to the developing chamber R1 is performed from above to below at one end 18 of the partition wall 16. And along the direction of gravity.
[0054]
Thereafter, the developer is supplied for development or is agitated and transported by the transport screw 11, and is transported upward from the bottom by the transport force and pressure at the communication portion 19 at the other end of the partition 16, and the upper agitating chamber R2 The developer conveyed from the developing chamber R1, the agent having a reduced T / D ratio after being subjected to the development, and the replenished toner are agitated and conveyed, and the communicating portion at one end of the partition 16 again. At 18, the developer is conveyed from the top to the bottom along the direction of gravity to the developing chamber R1.
[0055]
That is, the developer subjected to the development is dropped from the developing sleeve 13 to the side of the stirring chamber R2 which is not subjected to the development, and the developer having the reduced T / D ratio after the development is subjected to the normal operation. Of the T / D ratio and the toner supplied to the developing container 10 are agitated and conveyed. Thereafter, after being sufficiently stirred and conveyed, the developer is sent to the developing chamber R1 side, and is subjected to development. Therefore, it is possible to prevent the problem of a screw mark, that is, T / D unevenness, which has been a problem.
[0056]
In the present embodiment, the stirring chamber R2 is disposed above the developing chamber R1 in the up-down direction. However, this is because the photosensitive drum 4 is moving downward from above in the developing unit 41. This is because the developing unit 41 moves the sleeve 13 upward from the bottom in the counter direction. In other words, this is because the developing sleeve 13 is rotated so that the surface movement direction of the photosensitive drum 4 is opposite to that of the photosensitive drum 4 in the developing section. Accordingly, when the photosensitive drum 4 moves upward from below in the developing section 41, the stirring chamber R2 is arranged below the developing chamber R1 in the vertical direction in order to move the sleeve 13 from above to below in the developing section 41. Will be done. That is, as long as the stirring chamber R2 and the developing chamber R1 are configured with one of them facing upward in the vertical direction, the direction may be appropriately selected.
[0057]
In this way, when using a developer containing a carrier with a reduced amount of magnetization for high image quality, pumping of the developer in the developing chamber and regulation of the layer thickness of the developer by the pole facing the layer thickness regulating member at the same time. As described above, in the counter developing device in which the surface movement direction in the opposing portion of the developing sleeve and the photoconductor drum is opposite, as described above, the developing chamber and the stirring chamber are arranged vertically one above the other. The developer carried on the developing sleeve is subjected to layer thickness regulation by the layer thickness regulating member in the developing chamber, and then passes through the developing section, and then rotates in a direction in which the developer is taken into the stirring chamber. Prevents image defects such as deterioration, white spots, and roughness, and prevents image defects such as T / D unevenness such as screw marks, which are equal to or higher than the image quality when using a ferrite carrier with a high magnetization amount. In offer That.
[0058]
Example 2
Second Embodiment A second embodiment of the present invention will be described with reference to FIGS. In the first embodiment, as shown in FIG. 2, the transfer of the developer between the developing chamber R1 and the developing chamber R2 is performed by the communicating portions 18 and 19 at both ends of the partition wall 16. However, if it is attempted to carry out at both ends of the partition wall 16, the agent whose T / D ratio has been reduced by the repulsion poles on the side of the communication portion 19 which transfers the developer from the bottom to the top is changed to the communication portion 19. It is easy to cause the ill effect of being taken by the part. For this reason, image unevenness occurs, so that it is necessary to move the communication portion 19 out of the image area, and it is necessary to lengthen the conveying screws 11 and 12 of the developing container 10 in the axial direction.
[0059]
Therefore, in the present embodiment, as shown in FIG. 4A, the communication shown in FIG. 2 for transferring the developer from the bottom to the top provided on the partition wall 16 that partitions the developing chamber R1 and the stirring chamber R2. The transfer of the developer from the developing chamber R1 to the stirring chamber R2 is performed mainly by using the developing sleeve 13 without the portion 19.
[0060]
Here, the circulation of the developer will be described with reference to FIGS. 4 and 5. First, as shown in FIG. 4A, the transfer of the developer from the stirring chamber R1 to the developing chamber R2 is performed along one end 18 of the partition 16 from top to bottom in the direction of gravity. Thereafter, the developer is cut off by the spike regulating member 17 on the developing sleeve 13 by the rotation of the developing sleeve 13, conveyed to the developing section 41 facing the photosensitive drum 4, and stirred after being subjected to development. The developer is transferred from the lower developing chamber R1 to the upper stirring chamber R2 by being taken into the chamber R2.
[0061]
However, depending on the developer transport speed, the developing chamber R1 may be located at the most downstream end of the first transport screw 11 of the developing chamber R1 in the developer transport direction, where the communicating portion 18 of the partition 16 is not provided. In some cases, the developer is easily accumulated. As a result, adverse effects such as overflow of the developer occur.
[0062]
As a countermeasure, as shown in FIG. 5, a third screw 22 is provided parallel to the first transport screw 11 and adjacent to the first transport screw 11 in the horizontal direction. A partition 23 is provided between the first transport screw 11 and the third screw in parallel with them. Therefore, the third screw 22 is disposed in the developer feeding chamber 24 which is horizontally divided by the partition wall 23 with respect to the developing chamber R1.
[0063]
The relationship between the developing chamber R1 and the developer feeding chamber 24 will be described with reference to FIG. 4B, which is a horizontal sectional view of the developing container 10.
[0064]
When the amount of the developer on the developing chamber side R <b> 1 increases, the developer is conveyed to the developer feeding chamber 24 from the communication part 25 provided above the partition wall 23. In the present embodiment, the communication part 25 of the partition 23 is provided on the opposite side of the communication part 18 of the partition 16 separating the developing chamber R1 and the stirring chamber R2. The third screw 22 conveys the developer conveyed from the developing chamber R1 through the communication portion 25 in a direction opposite to the direction of the screw 11 in the developing chamber R1. At the most downstream position of the third screw 22 in the developer conveyance direction, a communication portion 26 is provided at an end of the partition wall 23, where the communication portion 26 is sent from the developer feeding chamber 24 to the developing chamber R1, and is used for development. Will be offered. Here, a communication part 26 provided on the wall 23 from the developer feeding chamber 24 to the developing chamber R1 is on the same side as the communication part 18 of the partition 16.
[0065]
That is, in the present embodiment, when the amount of the developer in the developing chamber R1 becomes excessive, the excess amount is transferred to the developer feeding chamber provided in a direction different from that of the stirring chamber R2 with respect to the developing chamber R1. The chamber 24 is circulated to prevent the developer from overflowing.
[0066]
In the present embodiment, the amount of magnetization M [Am in a magnetic field of 7.95775 kA / m (1 kOe) is also used as the developer. Two / Kg] is 8 to 55 [Am Two / Kg], a two-component developer containing a magnetic carrier and a non-magnetic toner is used, and the counter developing device has a light addition structure as in Example 1. The developing chamber R1 and the stirring chamber R2 are They are arranged vertically above and below.
[0067]
In this embodiment, the stirring chamber R2 is disposed above the developing chamber R1 in the vertical direction. However, the stirring chamber R2 is disposed below the developing chamber R1 in the vertical direction depending on the rotation direction of the photosensitive drum 4. You may.
[0068]
In this way, when a carrier having a reduced amount of magnetization is used while maintaining the performance of the light compression developing device, image defects such as T / D unevenness can be prevented without increasing the size, and after development. Can also avoid the entrainment of the developer having a low T / D, and provide a high-quality image equal to or higher than the image quality when a ferrite carrier having a high magnetization amount is used.
[0069]
Example 3
The embodiment of the present invention is a case where the amount of the developer fed from the stirring chamber R2 to the developing chamber R1 is made appropriate and the third screw 22 is not required in the second embodiment. That is, as the developing device 1, the general view has the shape shown in FIG. 1 of the first embodiment in which the developer feed chamber 24 is not provided, and the feed of the developer is performed by the first transport screw 11 shown in FIG. The configuration of the second embodiment does not include the communication portion 19 with the stirring chamber R2 on the downstream side in the developer transport direction.
[0070]
The amount of the developer to be fed is adjusted and set according to the size of the window of the developer passage of the communicating portion 18 from the stirring chamber R2 to the developing chamber R1 in FIG. According to this method, a predetermined amount of the developer is always stored in the developing chamber R1, so that the developer becomes excessive and does not overflow.
[0071]
Further, in this embodiment, the stirring chamber R2 is disposed vertically above the developing chamber R1, but the stirring chamber R2 may be disposed vertically below depending on the rotation direction of the photosensitive drum 4.
[0072]
If a means for constantly adjusting the amount of the developer is provided as in the present embodiment, it is possible to avoid an increase in the size of the developing container due to the provision of the developer feeding chamber described in the second embodiment, and to further reduce the size. When a carrier having a reduced amount of magnetization is used while maintaining the performance of the light compression developing device, image defects such as T / D unevenness and screw marks are prevented, and a ferrite carrier having a high amount of magnetization is used. An image equal to or higher than the image quality of the case can be provided.
[0073]
【The invention's effect】
As described above, according to the present invention, a stirring chamber that carries a developer containing a toner and a magnetic carrier, collects the developer from the developer carrier, and mixes and agitates with the replenished new developer; A developing chamber for supplying the developer mixed and stirred in the stirring chamber onto the developer carrying member, the magnetic field generating means includes a layer thickness regulating pole facing the layer thickness regulating member, and It has a pole and a repelling pole configuration adjacent to the upstream side in the rotation direction of the developer carrier.The repelling pole configuration allows the developer to be peeled off and pumped up from the developer carrier, and the layer thickness regulating pole is used for developing in the developing chamber. In this configuration, the developer is pumped up and the layer thickness of the developer is regulated at the same time. The magnetic carrier has a magnetization amount M [Am in a magnetic field of 7.95775 kA / m. Two / Kg] is 8 to 55 [Am Two / Kg], the developing chamber and the agitating chamber are vertically arranged with one of them up, and the developer carrying member is configured such that the developer to be carried thereon is controlled by a layer thickness regulating member in the developing chamber. Because it is rotated in the direction in which it is regulated by the layer thickness, then passes through the developing section, and is then taken into the stirring chamber, and the surface moving direction is opposite to that of the image carrier at the portion facing the image carrier. In addition, it is possible to prevent image defects such as roughness and white spots, deterioration of the developer, and the like, and to prevent T / D unevenness of a formed image, thereby providing a high-quality image.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram showing one embodiment of a developing device according to the present invention.
FIG. 2 is a longitudinal cross-sectional view showing one embodiment of a developing device according to the present invention.
FIG. 3 is a schematic configuration diagram illustrating an embodiment of an image forming apparatus according to the present invention.
FIG. 4 is a longitudinal cross-sectional view (FIG. 4 (a)) and a longitudinal cross-sectional view (FIG. 4 (b)) showing another embodiment of the developing device according to the present invention.
FIG. 5 is a schematic configuration diagram showing another embodiment of the developing device according to the present invention.
FIG. 6 is a schematic configuration diagram illustrating an example of a conventional developing device.
[Explanation of symbols]
1 Developing device
4 Photoconductor drum (image carrier)
10 Developing container
11 First transport screw
12 Second transport screw
13 Developing sleeve (developer carrier)
15 Magnet roller (magnetic field generating means)
16 Partition walls of developing chamber and stirring chamber
17 Hot standing regulating member (layer thickness regulating member)
18, 19 Communication section between developing chamber and stirring chamber
20 Toner supply port
21 Development bias power supply
22 Third transport screw
23 Partition wall between developing chamber and developer feeding chamber
24 Developer feed chamber
25, 26 Communication section between developer chamber and developer feed chamber
41 Developing unit
R1 development room
R2 stir chamber
