JP4065480B2 - Developing device and image forming apparatus - Google Patents

Description

表１によれば、第一磁極と第二磁極を異極性にした場合、上流現像剤担持体上の現像剤コートは安定する。
【００４５】
又、上流現像剤担持体の下流現像剤担持体側に０〜１０ｍＴの磁力の領域があると、この領域では現像剤の搬送力が無いため、現像剤が現像剤担持体上で滞留してしまい、図５（ａ）に示すようなコート不良の状態となってしまう。特に、この現象は、高速回転する現像剤担持体を用いる場合、現像剤の搬送速度が追いつかなくなり顕著となる。又、第一磁極と第二磁極が同極性である場合、なおさら０〜１０ｍＴの磁力の領域を増やすこととなるため、上述の現像剤の滞留は顕著となる。
【００４６】
従って、第一磁極と第二磁極とは異極性であることが必要となる。
【００４７】
次に、第一磁極と第三磁極の関係について説明する。
【００４８】
第一磁極は、現像に寄与する磁極であり、表２に示すように、通常、画像かぶりを防止するため、磁力を８０ｍＴ以上にする必要がある。
【００４９】
【表２】

第一磁極と第三磁極の磁力が等しい場合には、上流現像剤担持体上で０〜１０ｍＴの磁力の領域が第一磁極と上流現像剤担持体及び下流現像剤担持体の対向部に存在するため、第三磁極の磁力を小さくし第一磁極及び第三磁極によって形成される０〜１０ｍＴの磁力の位置を第二磁極に近づけることが望ましい。更に、この間での現像剤の搬送力を高めるため、第二磁極は第三磁極より磁力を強くすることで第三磁極の磁力の影響を低減することができる。又、第一磁極の磁力と第二磁極の磁力との関係については、これらが異極性で、一方の磁力が大きいことが現像剤搬送力を増すのに好ましいため、上述の、第一磁極の磁力≧８０ｍＴの条件より第一磁極の磁力を大きくすることがよい。そのため、第一磁極の磁力＞第二磁極の磁力となるのである。
【００５０】
よって、第一磁極、第二磁極、第三磁極によって上流現像剤担持体上に形成される１０ｍＴ以下の磁力の領域を低減するためのこれらの磁力の関係は、上記▲１▼、▲２▼となる。尚、上述したように、二成分系の現像剤と用いた場合とは異なり、第二磁極と第三磁極の位置については、検討の結果、上流現像剤担持体の回転中心と下流現像剤担持体の回転中心とを結ぶ線よりも第二磁極及び第三磁極を潜像担持体側（現像装置の外側）に出すと下流現像剤担持体での現像剤帯電を安定しづらくなるため、第二磁極及び第三磁極を上記線よりも現像装置内部側（潜像担持体の遠方側）に配置することがより望ましい。
【００５１】
ここで、第一磁極、第二磁極、第三磁極に関して、上流現像剤担持体上に現像剤が滞留しないための検討した結果について説明する。ここでは、第三磁極の磁力を４０ｍＴから徐々に１０ｍＴずつ変化させ、このときの第一磁極、第三磁極の組み合わせにおける上流現像剤担持体上のコート状態について○又は×で評価した。ここでの評価については、図５（ａ）に示すような状態が×であり、図５（ｂ）に示すような状態が○である。尚、この評価基準については、かぶり（○：２％未満、×：２％以上）、コート安定性（×：ハーフトーン画像（反射濃度Ｄ：０．５）にむらあり、そのむら濃度差が０．１以上）とする。
【００５２】
この結果、表３に示すような結果となった。
【００５３】
【表３】

表３における各表は、第三磁極の磁力を４０ｍＴから１００ｍＴまで変化させた際の上流現像剤担持体上の現像剤コート性を示している。これは実機で１０ｋ枚耐久した際のコート性である。
【００５４】
表３により、
（１）第一磁極と第三磁極は同極性であり、第二磁極は第一磁極及び第三磁極と異極性であり、
（２）｜磁極Ａの磁力｜＞｜磁極Ｂの磁力｜＞｜磁極Ｃの磁力｜であると、
上流現像剤担持体上の現像剤コート性が安定することがわかる。
【００５５】
尚、図３（ａ）に示す角度θは５°とした。又、この角度θを０〜２０°で上記と同様の検討を行なったが、定性的にこれらの関係は同じであった。
【００５６】
本実施形態では、上流現像スリーブ２０は表４に示すような磁極構成とし、下流現像スリーブ３０は表５に示すような磁極構成とした。
【００５７】
【表４】

【００５８】
【表５】

上流現像スリーブ２０は、非磁性部材であるφ２０のＳＵＳ３０５の上にＦＧＢ＃６００でブラスト処理をした後、図６に示すようにコーティングをおこなったものである。
【００５９】
上流現像スリーブ２０の内部には、図３（ａ）及び表４に示すような磁場パターンを有する磁性部材たるマグネット２０Ｂが固定配置されている。上流現像スリーブ２０は、感光ドラム１の周速度に対して１５０％の周速度で回転するようになっている。
【００６０】
上流現像スリーブ２０上のトナーは、磁気ブレード２０Ａによって層厚が規制される。本実施形態では、上流現像スリーブ２０と磁気ブレード２０Ａとの距離Ｓ−Ｂｇａｐが２５０μｍに設定されている。
【００６１】
上流現像スリーブ２０と感光ドラム１との距離Ｓ−Ｄｇａｐは２００μｍとなっている。本実施形態では、バイアス印加手段（図示せず）によって、＋３００ＶのＤＣバイアス電圧と図７に示すような波形でＶｐｐ１２００Ｖ、周波数２．５ｋＨｚの矩形波のＡＣバイアス電圧とを重畳して上流現像スリーブ２０に印加して磁性一成分非接触現像を行う。従って、現像コントラストは飛翔方向に２００Ｖ、かぶりとりコントラストが１５０Ｖとなる。
【００６２】
下流現像スリーブ３０も上流現像スリーブ２０と同様に、非磁性部材であるφ２０のＳＵＳ３０５の上にＦＧＢ＃６００でブラスト処理して表面粗さをＲｚ３μｍとしている。尚、このＲｚの測定には、接触式表面粗さ計（サーフコーダーＳＥ−３３００（株）小坂研究所）を用いた。又、この測定条件としては、カットオフ値が０．８ｍｍであり、測定長さが２．５ｍｍであり、送りスピードが０．１ｍｍ／ｓｅｃであり、倍率が５０００倍である。
【００６３】
下流現像スリーブ３０の内部には、図３（ａ）及び表５に示す４極の磁場パターンよりなる磁性部材たるマグネット３０Ｂが固定配置されている。
【００６４】
下流現像スリーブ３０には、＋３００ＶのＤＣバイアス電圧と図７に示すような波形でＶｐｐ１２００Ｖ、周波数２．５ｋＨｚの矩形波とを重畳して印加可能になっている。本実施形態では、下流現像スリーブ３０に印加される現像バイアス電圧は上流現像スリーブ２０に印加される現像バイアス電圧と同一なので、上記バイアス印加手段のための電源を共用して一つにしてコストダウンを図ることができ、又、電源のためのスペースが少なくて済むので省スペース化を図ることができる。
【００６５】
下流現像スリーブ３０は、感光ドラム１の周速度に対して１５０％の周速度で回転するようになっている。
【００６６】
下流現像スリーブ３０上のトナーは、上流現像スリーブ２０によって層厚が規制される。本実施形態では、下流現像スリーブ３０と感光ドラム１とのＳ−Ｄｇａｐは２５０μｍとなっている。
【００６７】
本実施形態では、図８（ａ）に示すように、上流現像スリーブ２０は内部に４極の磁極をもつマグネット２０Ｂを有し、下流現像スリーブ３０は４極の磁極をもつマグネット３０Ｂを有しており、上流現像スリーブ２０及び下流現像スリーブ３０の外周に沿って形成され主に鉄よりなるモルダロイ（ＫＮメッキ、透磁率１０−６）で作製された磁性シール部材２Ｄが図８（ｂ）に示すように上流現像スリーブ２０及び下流現像スリーブ３０の軸線方向の両端部近傍に設けられている。上流現像スリーブ２０及び下流現像スリーブ３０の表面と磁性シール部材２Ｄとのギャップは４００μｍ±１００μｍになっている。
【００６８】
本実施形態では、上流現像スリーブ２０及び下流現像スリーブ３０の軸線方向における、マグネット２０Ｂの長さはＬｌ＝３０５ｍｍであり、マグネット３０Ｂの長さはＬ２＝３０５ｍｍである。
【００６９】
マグネット２０Ｂ，３０Ｂに対する磁性シール部材２Ｄの適切な取り付け位置については、上流現像スリーブ２０及び下流現像スリーブ３０の軸線方向における、磁性シール部材２Ｄの外側の端部の位置とマグネット２０Ｂ，３０Ｂの端部の位置とを一致させるのが一番好ましい。これは、磁性シール部材２Ｄの上記軸線方向の外側端部の位置よりマグネット２０Ｂ，３０Ｂが外側に出ると長手方向（上記軸線方向）の外にも磁力が存在することとなるために、その磁力でトナーが外に運ばれてしまい、トナー漏れを引き起こすためである。又、本来、磁性シール部材２Ｄは磁性シール部材２Ｄとマグネット２０Ｂ，３０Ｂとの間で磁気ブラシを形成してトナー漏れを無くすためものであるが、逆に磁性シール部材２Ｄの上記軸線方向の外側端部の位置に対してマグネット２０Ｂ，３０Ｂの端部の位置が中側に入り過ぎると、磁性シール部材２Ｄの上記外側端部では磁性シール部材２Ｄによる磁力が存在しないのにもかかわらず、上流現像スリーブ２０及び下流現像スリーブ３０上には磁性シール部材２Ｄの幅で磁気ブラシを形成するために、上記外側端部に位置するトナーは端部から漏れると同時に、上流現像スリーブ２０及び下流現像スリーブ３０上のトナー層厚も大きくなり、ボタ落ちする場合も有るからである。本実施形態では、上記長手方向には、上流現像スリーブ２０及び下流現像スリーブ３０とマグネット２０Ｂ，３０Ｂとの関係等でガタがあるために、それらを考慮して図８（ｂ）に示すようにマグネット２０Ｂ，３０Ｂの端部位置から１ｍｍ内側に入ったところに磁性シール部材２Ｄの上記外側端部が位置するようにした。
【００７０】
次に、本実施形態における画像処理について説明する。
【００７１】
本実施形態においては、図９に示す画像信号制御部がディザ法による２値化にて次のように画像処理を行なう。
【００７２】
画像処理部２０１は、図９に示すように、入力される画像信号に対して、解像度変換等、操作者の所望する画像処理を施す。
【００７３】
γ補正部２０２は、画像信号に対して、ＬＵＴ算出部２０５によるルックアップテーブル（ＬＵＴ）を参照してγ補正を行う。
【００７４】
そして、２値処理部２０３は、それぞれγ補正後の画像信号に基づいて、レーザーの駆動信号を発生する。
【００７５】
２値処理部２０３から出力される駆動信号に基づきレーザー部２０４が駆動され、上述したように画像に対応する画像露光１２がなされる。本実施形態では、現像コントラストに対して、γ補正部２０２内のＬＵＴがＬＵＴ算出部２０５によって現在の動作環境において適切となるように設定されている。
【００７６】
本実施形態では、上述したように、適切な現像コントラストに加え、適切な階調補正（例えばγ補正等）を施す。そして、得られた階調特性が理想的な濃度再現曲線（ＴＲＣ；ｔｏｎｅ ｒｅｐｒｏｄｕｃｔｉｏｎ ｃｕｒｖｅ）になるように、ＬＵＴ算出部２０５においてγ補正部２０２のＬＵＴを更新する。
【００７７】
尚、本実施形態の効果は、負極性の感光ドラム、正極性のトナーを用いた正規現像を行う場合においても同様である。
【００７８】
又、本実施形態では、交流成分の現像バイアス電圧を現像剤担持体に印加しているため、上流現像スリーブ２０で余分に現像した部分を下流現像スリーブ３０で再び現像装置２内に戻すことができるためトナー消費量を減らすことができる。トナー消費量に関して画像比率６％原稿で測定したところ、従来の磁性一成分系の現像剤を用いた現像装置で５０〜６０ｍｇ／枚であるところ、本実施形態では４１ｍｇ／枚となった。
【００７９】
よって、本実施形態によれば、磁性一成分系のトナーを用いたメンテナンスフリーな小型現像装置において、上流現像剤担持体上の現像剤の均一で安定したコーティングを実現し、高画質で安定した濃度を維持しつつトナー消費量の少ない現像装置を提供すること、及び高速機において省スペース化したコンパクトな現像装置にすることで分散型の小型のプリントオンデマンドに適した高速機を提供することができる。
【００８０】
（第二の実施形態）
次に、本発明の第二の実施形態について説明する。尚、第一の実施形態と同様の構成に関しては、その説明を省略する。
【００８１】
一般に現像スリーブ表面がＳＵＳ、Ａｌ素管では現像剤のトリボの制御がしずらいが、本実施形態では、それを鑑みて、上流現像剤担持体たる上流現像スリーブと下流現像剤担持体たる下流現像スリーブとによるトナーのトリボを制御するために上流現像スリーブ及び下流現像スリーブに各々最適なコート処方を採用し、負極帯電性の磁性一成分トナーを用いている。
【００８２】
又、上流現像スリーブの磁極は、トナーの搬送性を鑑みて５極構成にして、上流現像スリーブの現像装置内で反発極を形成させてトナーを一度現像スリーブから大きな固まりを離してトナーの現像スリーブへの連れまわりを低減化が図られている。現像スリーブの表面のコーティングについては、特開平３−３６５７０等で問題となってる現像スリーブ周期で発生するスリーブゴースト画像を防止するとともに現像スリーブ表面の耐久性を高めるためである（Ａｌ表面を保護する膜である）。尚、本実施形態での現像スリーブ間距離ｄは６００μｍとした。
【００８３】
かかる画像形成装置は、潜像担持体としてφ１０８のａ−Ｓｉドラム感光体を用いており、第一の実施形態と同様、プロセススピードが４７０ｍｍ／ｓｅｃで毎分９０枚の白黒デジタル複写機である。本実施形態の現像剤は、重量平均粒径７．５μｍのネガ帯電トナーであり、外添剤として１．０％（重量％）のＳｉＯ₂が塗されている。
【００８４】
本実施形態では、現像スリーブのコート膜の処方はＡｌ現像スリーブ表面にフェノール樹脂と結晶性グラファイト及びカーボンを混合して、膜厚１０μｍで１５０℃環境で硬化させた膜を用いた。膜の厚さは安定かつ均一な膜を形成するための厚さは２０μｍ程度である。この場合Ｐ／Ｂ比は１／２．５である。ここで、Ｂは樹脂の重量、Ｐは樹脂以外のものの重量（結晶性グラファイト＋カーボン）を表す。
【００８５】
本構成のように上流現像スリーブで下流現像スリーブのとトナーコート量を規制する場合に、負極性トナーに対しての帯電特性が高すぎるために下流現像スリーブのみに４級アンモニウム塩を７０重量部有するフェノール樹脂を用いた。
【００８６】
第４級アンモニウム塩化合物は、添加されるとフェノール樹脂中に均一に分散され、更に、加熱硬化して被膜を形成する際にフェノール樹脂の構造中に取り込まれ、その結果、上記化合物を有するフェノール樹脂組成物自身が負帯電性を有する物質へと変化する。従って、このような材料を用いて形成された被覆層を有する現像剤担持体を用いれば、現像剤を好適に正極性に帯電させることが可能となる。
【００８７】
本発明において好適に使用される、上記した機能を有する第４級アンモニウム塩化合物としては、例えば、下記一般式で表わされる化合物が挙げられる。
【００８８】
【化１】

化１に示す式中のＲｌ、Ｒ２、Ｒ３、Ｒ４は、夫々置換基を有してもよいアルキル基、置換基を有してもよいアリール基、アルアルキル基を表わし、Ｒｌ−Ｒ４は夫々同一でも或いは異なっていてもよい。Ｘ−は、酸の陰イオンを表わす。
【００８９】
上記の化１に示す一般式において、Ｘ−の酸イオンの具体例としては、有機硫酸イオン、有機スルホン酸イオン、有機リン酸イオン、モリブデン酸イオン、タングステン酸イオン、モリブデン原子或いはタングステン原子を含むヘテロポリ酸等が挙げられる。
【００９０】
【化２】

化２に示すようにフェノール樹脂に、本発明で用いる特定の第４級アンモニウム塩化合物を添加した樹脂組成物を使用して被覆層を形成すると、先に述べたように、結着樹脂であるフェノール樹脂を加熱硬化させて被覆層を形成した場合に、該第４級アンモニウム塩化合物がフェノール樹脂の構造中に取り込まれる。このため、上記したネガ性シリカ粒子或いはネガ性テフロン粒子等のような粒子添加系の場合と異なり、部分的にではなく、被覆層全体として正帯電性現像剤に対する正摩擦帯電付与性が向上する。更に、粒子添加系の被膜と異なり、加工性が損なわれたり、被覆層の強度低下を生じることもない。
【００９１】
本発明に好適に用いられる、第４級アンモニウム塩化合物としては、具体的には、次のようなものが挙げられるが、勿論、本発明は、これらに限定されるものではない。
【００９２】
【化３】

【００９３】
【化４】

【００９４】
【化５】

【００９５】
【化６】

【００９６】
【化７】

【００９７】
【化８】

【００９８】
【化９】

【００９９】
【化１０】

本発明において使用する結着樹脂を構成するフェノール樹脂として、その製造工程において、触媒として含窒素化合物を用いて製造されたものを用いると、特に、加熱硬化時に第４級アンモニウム塩化合物がフェノール樹脂の構造中に取り込まれ易く、トナーのチャージアップ防止に好ましいことがわかった。従って、本発明においては、このような作用を有する、その製造工程において触媒として含窒素化合物を用いて製造されたフェノール樹脂を現像剤担持体上の被覆層を構成する材料の１つとして用いれば、トナーのチャージアップを防止する現像装置の実現が可能となる。
【０１００】
本発明で好適に使用し得る、フェノール樹脂の製造工程において触媒として用いられる含窒素化合物としては、例えば、酸性触媒としては、硫酸アンモニウム、燐酸アンモニウム、スルファミド酸アンモニウム、炭酸アンモニウム、酢酸アンモニウム、マレイン酸アンモニウムといったアンモニウム塩又はアミン塩類が挙げられ、塩基性触媒としては、アンモニア、或は、ジメチルアミン、ジエチルアミン、ジイソプロピルアミン、ジイソブチルアミン、ジアミルアミン、トリメチルアミン、トリエチルアミン、トリｎ−ブチルアミン、トリアミルアミン、ジメチルベンジルアミン、ジエチルベンジルアミン、ジメチルアニリン、ジエチルアニリン、Ｎ，Ｎ−ジｎ−ブチルアニリン、Ｎ，Ｎ−ジアミルアニリン、Ｎ，Ｎ−ジｔ一アミルアニリン、Ｎ−メチルエタノールアミン、Ｎ−エチルエタノールアミン、ジエタノールアミン、トリエタノールアミン、ジメチルエタノールアミン、ジエチルエタノールアミン、エチルジエタノールアミン、ｎ−ブチルジエタノールアミン、ジｎ−ブチルエタノールアミン、トリイソプロパノールアミン、エチレンジアミン、ヘキサメチレンテトラミン等のアミノ化合物、ピリジン、α−ピコリン、β−ピコリン、γ一ピコリン、２，４−ルチジン、２，６−ルチジン等のピリジン及びその誘導体、キノリン化合物、イミダゾール、２一メチルイミダゾール、２，４−ジメチルイミダゾール、２−エチル−４−メチルイミダゾール、２−フェニルイミダゾール、２−フェニル−４−メチルイミダゾール、２一ヘプタデシルイミダゾール等のイミダゾール及びその誘導体等の含窒素複素環式化合物等が挙げられる。
【０１０１】
本発明において、被覆層の抵抗値を、上記の値に調整するためには、下記に挙げる導電性物質を被覆層中に含有させることが好ましい。この際に使用される導電性物質としては、例えば、アルミニウム、銅、ニッケル、銀等の金属粉体、酸化アンチモン、酸化インジウム、酸化スズ等の金属酸化物、カーボンファイバー、カーボンブラック、グラファイト等の炭素物等が挙げられる。本発明においては、これらのうち、カーボンブラック、とりわけ導電性のアモルファスカーボンは、特に電気伝導性に優れ、高分子材料に充填して導電性を付与したり、その添加量をコントロールするだけで、ある程度任意の導竜度を得ることができるため好適に用いられる。
【０１０２】
最終的な膜の処方はフェノール樹脂２５０重量部に対して平均粒径７．５μｍのグラファイト９０重量部、カーボン１０重量部、４級アンモニウム７０部である。ちなみに、グラファイトとカーボンの比は膜全体の抵抗の安定化のため、グラファイトをカーボンの３倍以上にすることが好ましい。膜は吹き付け法により現像スリーブに塗付後、１５０度で３０分間乾燥させる。
【０１０３】
このコートの最適化をおこなうことで通常は下流現像スリーブ側のトリボ（帯電量）が大きいのに対して、本実施形態では上流現像スリーブ上９μＣ／ｇ、下流現像スリーブ上９．２μＣ／ｇとほぼ同等な値に制御することができた。このことにより、高温高湿、常温低湿等の環境の変化に対しても両現像スリーブで最適化されているため現像特性が安定になる。
【０１０４】
上流現像スリーブ２０の内部には、図１０及び表６に示すように、５極の磁場パターンを有するマグネットが固定配置されている。
【０１０５】
【表６】

【０１０６】
下流現像スリーブ３０は、非磁性部材であるφ２０のアルミＡ２０１７に膜を形成したものを用いる。下流現像スリーブ３０の内部には、図１０及び表７に示す４極の磁場パターンよりなるマグネットを有する。
【０１０７】
【表７】

下流現像スリーブ３０には−５５０ＶのＤＣバイアス電圧と図７に示すような波形でＶｐｐ１５００Ｖ、周波数２．７ｋＨｚの矩形波を印加する。下流現像スリーブ３０に印加されるＡＣバイアス電圧及びＤＣバイアス電圧は、上流現像スリーブ２０に印加されるＡＣバイアス電圧及びＤＣバイアス電圧と同一なので、電源を共用して１つにすることによりコストダウンを図ることができると共に、電源のためのスペースが少なくて済むメリットがある。下流現像スリーブ３０は、感光ドラム１の周速度に対して１２５％の周速度で回転するようになっている。
【０１０８】
下流現像スリーブ３０上のトナーは、上流現像スリーブ２０によって層厚規制がなされる。上流現像スリーブ２０と下流現像スリーブ３０との間の距離ｄは６００μｍとなっている。
【０１０９】
上流現像スリーブ２０、下流現像スリーブ３０の磁極構成は、表６及び表７に示す通り、それぞれ５極、４極である。上流現像スリーブ２０の磁極が５極である理由については、上述の通りである。
【０１１０】
よって、本実施形態によれば、磁性一成分トナーを用いたメンテナンスフリーな小型現像装置において、上流現像剤担持体上の現像剤の均一で安定したコーティングを実現し、高画質で安定した濃度を維持しつつトナー消費量の少ない現像装置を提供すること、及び高速機において省スペース化したコンパクトな現像装置にすることで分散型の小型のプリントオンデマンドに適した高速機を提供することができる。更には、上流現像剤担持体上でのトナーのつれ回りを低減してトナー劣化を低減し、又、これらのトナーの帯電特性に最適なコート処方を用いることで帯電制御もすることができる。
【０１１１】
（第三の実施形態）
次に、本発明の第三の実施形態について説明する。尚、第一の実施形態又は第二の実施形態と同様の構成に関しては、その説明を省略する。
【０１１２】
本実施形態にかかる現像装置は第二の実施形態と同様である。
【０１１３】
本実施形態の特徴は、リユース画像形成装置に本発明の現像装置を適用したことである。
【０１１４】
リユース系トナーは基本的には転写されずに残りクリーニングで回収された廃トナーであるために、劣化で新たなトナーと比較して、トリボが極端に小さいために反転成分トナー量が多いため、飛散が更に悪くなる。本実施形態はこれらのことを鑑みて実施したものである。
【０１１５】
本実施形態における上流現像スリーブ、下流現像スリーブの磁極、コート材の処方については、第二の実施形態と同様である。
【０１１６】
本実施形態にかかる画像形成装置は、図１１に示す画像形成システムでプロセススピードが５００ｍｍ／ｓの１１０枚／分のデジタル複写機であって、感光体としてａ−Ｓｉドラムを用いてた潜像担持体たる感光ドラム１を備えている。
【０１１７】
かかる画像形成装置にあっては、この感光ドラム１の表面が、一次帯電器３により−７００Ｖに一様帯電される。
【０１１８】
次いで、一様に帯電された感光ドラム１の表面が波長６８０μｍの半導体レーザーで６００ｄｐｉにてＰＷＭによる画像露光１２がなされ、感光ドラム１上に静電潜像が形成される。
【０１１９】
次に、上記静電潜像が現像装置２により正規現像されトナー像として可視化される。本実施形態の現像装置は、現像剤としてトナー粒径８．０μｍの磁性一成分ネガトナーを用いたジャンピング現像法を採用している。これは、従来の２成分現像剤ではキャリアの交換を１０万枚ごとにサービスマンが行わねばならずメンテナンスフリーでないためリユースの利点があまり繁栄できない。それに対して、本実施形態では、耐久性が無限でノーメンテナンスで済む乾式磁性一成分トナーを用いている。現像バイアス電圧は、上流現像スリーブ２０及び下流現像スリーブ３０共に２４００Ｈｚ、１５００Ｖｐｐ、Ｄｕｔｙ５０％の交流バイアス電圧に＋２００Ｖの直流バイアス電圧を重畳した現像バイアス電圧を印加する。本実施形態では、上流現像スリーブ２０と磁気ブレード２０Ａとの距離Ｓ−Ｂｇａｐは２５０μｍとなっており、上流現像スリーブ２０及び下流現像スリーブ３０と感光ドラム１との距離Ｓ−Ｄｇａｐは共に２５０μｍとなっている。
【０１２０】
その後、上記トナー像は、帯電手段たるポスト帯電器１０によって総電流−２００μＡが流されて帯電された後、矢印方向に進む記録材たる転写材に転写手段たる転写帯電器４により転写される。
【０１２１】
上記トナー像の転写を受けた上記転写材は、分離帯電器２０５によって感光ドラム１から分離された後、定着装置７に搬送され、定着装置７にて上記トナー像が定着される。
【０１２２】
一方、感光ドラム１上の転写残りのトナーは、除去手段たるクリーニング装置６により感光ドラム１上から除去されて回収され搬送パイプ８を通して廃トナー（リユースートナー）として現像ホッパー９Ｂに戻される。
【０１２３】
搬送パイプ８には、スクリュー状の搬送部材が内部に配設され、該搬送部材が回転することによりリユーストナーが現像ホッパー９Ｂに向けて運ばれる。こうして、図１１に示すように、搬送パイプ８の搬送部材によって運ばれたリユーストナーは現像ホッパー９Ｂに入れられ再利用される。又、リユーストナーとは別に新たなトナーが、ホッパー９Ａに入れられ、マグローラ２４Ａ，２４Ｂにより磁力でそれぞれのトナーは引きつけられ、マグローラ２４Ａ，２４Ｂが回転することにより現像装置２内にそれぞれのトナーが運ばれる。尚、本実施形態では、リユーストナーと新たなトナーを現像装置内で混ぜる方法を採用したが、ホッパー内に混合するスペースを設け、そのスペース内で混ぜても構わない。
【０１２４】
現像装置２内で混ぜられたトナーは再び上流現像スリーブ２０及び下流現像スリーブ３０に送られ、感光ドラム１上の静電潜像の現像に供される。本実施形態では、マグローラ２４Ａの通常の回転速度は２回転／分であり、マグローラ２４Ｂの回転速度はマグローラ２４Ａの回転速度に対する所定の比率で変化させる。本実施形態では、現像装置２内に設けられたピエゾセンサー（ＴＤＫ製）にトナーの自重がかからなくなり、該ピエゾセンサからの信号が振動すると、マグローラ２４Ａ，２４Ｂを回転させるため、トナー供給信号が発せられる。通常はマグローラ２４Ｂはマグローラ２４Ａの回転速度に対して１０／９０（マグローラ２４Ａの回転速度：マグローラ２４Ｂの回転速度＝９：１）の比率の回転速度にて回転するようになっている。
【０１２５】
本実施形態では、距離ｄ＝８００μｍである。又、上流現像スリーブ２０のマグネット２０Ｂ内に配置されるＮ２（磁極Ａ）の磁力は８０ｍＴであり、下流現像スリーブ３０のマグネット３０Ｂ内に配置されるＳ１（磁極Ｂ）の磁力は７５ｍＴである。更に、磁極Ａと、マグネット３０Ｂ内の感光ドラム１との近接部若しくはその近傍部に配置されるＮ１（磁極Ｃ）とは同極性であり、磁極Ｂは磁極Ａ及び磁極Ｃと異極性である。
【０１２６】
又、磁極Ａ及び磁極Ｂは、上流現像スリーブ２０の回転中心と下流現像スリーブ３０の回転中心とを結ぶ線に対して現像装置２内部側（感光ドラム１の遠方側）に位置している。更に、図３（ａ）に示す角度θが１０°である。
【０１２７】
そして、本実施形態では、磁極Ａの磁力［ｍＴ］と磁極Ｂの磁力［ｍＴ］と、距離ｄ［μｍ］との関係が、
０．５≧（８０＋７５）／８００≧０．２
を満たすため、下流現像スリーブ３０上のトナーコート性の安定化が図られている。
【０１２８】
よって、本実施形態によれば、磁性一成分トナーを用いたメンテナンスフリーなトナーリユース小型現像装置において、上流現像剤担持体上の現像剤の均一で安定したコーティングを実現し、高画質で安定した濃度を維持しつつトナー消費量の少ない現像装置を提供すること、及び高速機において省スペース化したコンパクトな現像装置にすることで分散型の小型のプリントオンデマンドに適した高速機を提供することができる。
【０１２９】
【発明の効果】
以上説明したように、本出願にかかる第一の発明によれば、第一磁極、第二磁極、第三磁極の極性及び磁力の適正化が図られているので、複数の現像担持体を備え一成分系の現像剤を採用する現像装置において、隣り合う二つの現像剤担持体のうち潜像担持体の回転方向における上流側の上流現像剤担持体上に磁性一成分系の現像剤を均一に安定してコートすることができる。
【０１３０】
又、本出願にかかる第二の発明によれば、第一磁極、第二磁極、第三磁極の極性及び磁力と、上流現像材担持体と下流現像剤担持体との間の距離との適正化が図られているので、複数の現像担持体を備え一成分系の現像剤を採用する現像装置において、隣り合う二つの現像剤担持体のうち潜像担持体の回転方向における上流側の上流現像剤担持体上に磁性一成分系の現像剤を均一に安定してコートすることができる。
【０１３１】
更に、本出願にかかる第三の発明によれば、第一磁極、第二磁極、第三磁極の極性及び磁力の適正化が図られているので、複数の現像担持体を備え一成分系の現像剤を採用する現像装置において、隣り合う二つの現像剤担持体のうち潜像担持体の回転方向における上流側の上流現像剤担持体上に磁性一成分系の現像剤を均一に安定してコートすることができる。
【０１３２】
又、本出願にかかる第四の発明によれば、第一磁極、第二磁極、第三磁極の極性及び磁力の適正化が図られているので、複数の現像担持体を備え一成分系の現像剤を採用する現像装置において、隣り合う二つの現像剤担持体のうち潜像担持体の回転方向における上流側の上流現像剤担持体上に磁性一成分系の現像剤を均一に安定してコートすることができる。
【０１３３】
更に、本出願にかかる第五の発明によれば、第一磁極、第二磁極、第三磁極の極性及び磁力の適正化が図られているので、複数の現像担持体を備え一成分系の現像剤を採用する現像装置において、隣り合う二つの現像剤担持体のうち潜像担持体の回転方向における上流側の上流現像剤担持体上に磁性一成分系の現像剤を均一に安定してコートすることができる。
【０１３４】
又、本出願にかかる第六の発明によれば、第一磁極、第二磁極、第三磁極の極性及び磁力の適正化が図られていると共に、現像剤担持体の表面の保護が図られているので、複数の現像担持体を備え一成分系の現像剤を採用する現像装置において、隣り合う二つの現像剤担持体のうち潜像担持体の回転方向における上流側の上流現像剤担持体上に磁性一成分系の現像剤を均一に安定してコートすることができる。
【０１３５】
更に、本出願にかかる第七の発明によれば、第一磁極、第二磁極、第三磁極の極性及び磁力の適正化が図られているので、複数の現像担持体を備え一成分系の現像剤を採用する現像装置において、隣り合う二つの現像剤担持体のうち潜像担持体の回転方向における上流側の上流現像剤担持体上に磁性一成分系の現像剤を均一に安定してコートすることができる。
【図面の簡単な説明】
【図１】本発明の第一の実施形態にかかる画像形成装置の概略構成を示す模式的断面図である。
【図２】図１の画像形成装置に備えられた現像装置の概略構成を示す模式的断面図である。
【図３】図２の現像装置の現像剤担持体の内部に設けられた磁性部材の磁極配置を説明するための図である。
【図４】（ａ）は、一成分系の現像剤を用いる場合の現像剤担持体上の現像剤の動きを説明するための図であり、（ｂ）は、二成分系の現像剤を用いる場合の現像剤担持体上の現像剤の動きを説明するための図である。
【図５】現像剤担持体の磁性部材の磁極の位置、極性と上流現像剤担持体上の現像剤コート性との関係を説明するための図である。
【図６】図２の現像装置に備えられた現像剤担持体のコーティング部材を説明するための図である。
【図７】本発明の第一の実施形態における現像剤担持体に印加されるバイアス電圧の交流成分の波形を説明するための図である。
【図８】本発明の第一の実施形態における現像剤担持体の磁性部材の配置と該現像剤担持体の軸線方向の端部におけるシールとを説明するための図である。
【図９】本発明の第一の実施形態における画像処理を説明するための図である。
【図１０】本発明の第二の実施形態における現像装置の現像剤担持体の内部に設けられた磁性部材の磁極配置を説明するための図である。
【図１１】本発明の第三の実施形態にかかる画像形成装置の概略構成を示す模式的断面図である。
【図１２】従来の画像形成装置の概略構成を示す模式的断面図である。
【図１３】図１２の画像形成装置に備えられた現像装置の概略構成を示す模式的断面図である。
【図１４】図１３の現像装置の現像剤担持体の内部に設けられた磁性部材の磁極配置を説明するための図である。
【符号の説明】
１ 感光ドラム（潜像担持体）
２ 現像装置
４ 転写帯電器（転写手段）
６ クリーニング装置（クリーニング手段）
２０Ｂ，３０Ｂ マグネット（磁性部材）
２０ 上流現像スリーブ（現像剤担持体，上流現像剤担持体）
３０ 下流現像スリーブ（現像剤担持体，下流現像剤担持体）[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a developing device and an image forming apparatus used for a copying machine, a laser beam printer, a facsimile, a printing apparatus, and the like that employ an electrophotographic system.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, in an image forming apparatus that employs an electrophotographic method or the like, after a latent image carrier is uniformly charged, analog exposure or image exposure with a semiconductor laser or LED is performed to An electrostatic latent image is formed on the surface, the developing device visualizes the electrostatic latent image as a developer image, the developer image is transferred to a transfer material as a recording material, and the transfer material is transferred to the latent image carrier. There is known an image forming apparatus that outputs a fixed image by separating it from the image and performing a fixing process by a fixing device.
[0003]
First, an example of the operation of the conventional image forming apparatus will be described with reference to FIG.
[0004]
The image forming apparatus includes a photosensitive drum 101 that is a latent image carrier that includes a photoconductive layer such as OPC or a-Si and rotates in the direction of arrow A.
[0005]
In such an image forming apparatus, first, the surface of the photosensitive drum 101 is uniformly charged to, for example, +500 V by the primary charger 103.
[0006]
Next, the image exposure 112 corresponding to the image signal information attenuates the surface potential of the exposed portion on the photosensitive drum 101 to −200 V, for example, and a latent image corresponding to the image signal of the image is formed on the photosensitive drum 101. For the image exposure 112, for example, a semiconductor laser or an LED array is used.
[0007]
Next, the latent image is developed and visualized as a toner image by the developing device 102 as a developing device shown in FIG. 13 using a one-component developer. A developing device using a one-component developer is simple and does not require replacement of a carrier or the like, and has a high durability and a long life. For example, there is a jumping development using a magnetic one-component toner. The developing device 102 includes an upstream developing sleeve 20 as a developer carrying member in which a magnetic pole arrangement and a magnet with a magnetic force as shown in FIG. 14 are fixedly arranged. The developing device 102 uses negatively charged black toner. Further, during development, a DC bias voltage of about −500 V is applied to the upstream developing sleeve 20 provided in the developing device 102 as a developing bias voltage, and the latent image on the photosensitive drum 101 is reversely developed.
[0008]
Since a photosensitive drum 101 having a long durability life such as a high-speed machine has a large outer diameter of the photosensitive drum and cannot separate the curvature of the transfer material from the photosensitive drum, the photosensitive drum 101 carrying the toner image can be charged as necessary. The post-charger 110 performs pre-transfer processing (usually applying corona by DC or AC, or combining light neutralization).
[0009]
Thereafter, the toner image on the photosensitive drum 101 is transferred by the transfer charger 104 onto a transfer material supplied between the photosensitive drum 101 and the transfer charger 104.
[0010]
The transfer material that has received the transfer of the toner image by the transfer charger 104 is separated from the photosensitive drum 101 by the separation charger 105 and then conveyed to the fixing device 107, where the toner image is transferred onto the transfer material by the fixing device 107. To be a fixed image.
[0011]
On the other hand, the photosensitive drum 101 after the transfer process is not subjected to development, and the residual transfer toner remaining on the photosensitive drum 101 is removed by the cleaning device 106 to prepare for the next image formation.
[0012]
By the way, in order to increase the speed of the image forming apparatus, in the conventional developing apparatus, as described in JP-A-03-204084, a developing sleeve as a developer carrier is added to a developing apparatus using a two-component magnetic brush. A plurality of developing sleeves as developer carriers are provided as described in JP-A-02-188778, and the distance between each developing sleeve and the photosensitive member as a latent image carrier is photosensitive. 2. Description of the Related Art There is known a developing device in which the toner supply amount from the developing sleeve to the photosensitive member is made uniform by approaching the developing sleeve closer to the downstream side in the rotation direction of the body.
[0013]
Conventionally, in a developing device having a plurality of developing sleeves, there is a developing device in which the developing sleeve is downsized as disclosed in Japanese Patent Publication No. 3-5579 in order to reduce the size of the image forming apparatus. Are known.
[0014]
Furthermore, regarding the magnetic force of a plurality of developing sleeves by such two-component development, JP-A-9-80919 and Japanese Patent No. 3017514 have been proposed.
[0015]
[Problems to be solved by the invention]
However, conventionally, in a developing device having a plurality of developing sleeves as described above, the upstream upstream developer carrier in the rotational direction of the latent image carrier among the two adjacent developer carriers is downstream. Is disposed close to the downstream developer carrier to such an extent that the amount of developer on the downstream developer carrier is regulated to a predetermined amount, so that space can be saved. When a one-component developer is used, it is difficult to uniformly coat the developer on the developer carrier as in the case of using a two-component developer using a carrier. For this reason, there has been no product that has been commercialized or presented at a conference as a developer using a magnetic one-component developer in a developing device having a plurality of developing sleeves as described above.
[0016]
In particular, a replenishing system developing device that replenishes developer as needed and a developing system that uses a plurality of developer carriers are suitable for high-speed machines, but not as a so-called cartridge system. Since durability and stability are required, it was further difficult to realize.
[0017]
Therefore, the present invention provides an upstream developer upstream of a latent image carrier in the rotation direction of two adjacent developer carriers in a developing device including a plurality of developer carriers and employing a one-component developer. It is an object of the present invention to provide a developing device and an image forming apparatus that can uniformly and stably coat a magnetic one-component developer on a carrier.
[0018]
[Means for Solving the Problems]
According to the present application, the object is a developing device that visualizes the latent image as a developer image by applying a magnetic one-component developer to the rotating latent image carrier that carries the latent image on the surface. A plurality of developer carriers that are arranged in close proximity to the latent image carrier and that carry and rotate the developer on the surface, and the plurality of developer carriers rotate in the same direction and are adjacent to each other. Of the two developer carriers, the downstream developer is so developed that the upstream upstream developer carrier in the rotational direction of the latent image carrier regulates the amount of developer on the downstream downstream developer carrier to a predetermined amount. In the developing device disposed close to the developer carrier, each developer carrier has a magnetic member therein, and each magnetic member is connected to the latent image carrier of the upstream developer carrier. A first magnetic pole disposed in the proximity portion or the vicinity thereof, and an upstream developer carrier A second magnetic pole disposed adjacent to or in the vicinity of the downstream developer carrier and adjacent to the downstream side in the rotation direction of the upstream developer carrier relative to the first magnetic pole, and the downstream developer carrier A third magnetic pole disposed in the vicinity of the upstream developer carrier or in the vicinity thereof; The downstream developer carrier is opposed to the latent image carrier and is located adjacent to the downstream side of the downstream developer carrier in the rotation direction with respect to the third magnetic pole and has a polarity different from that of the third magnetic pole. A fourth magnetic pole, The first magnetic pole and the third magnetic pole have the same polarity, the second magnetic pole is different from the first magnetic pole and the third magnetic pole, and the second magnetic pole and the third magnetic pole are Positioned on the far side of the latent image carrier with respect to a line connecting the rotation center of the upstream developer carrier and the rotation center of the downstream developer carrier, the magnetic force of the first magnetic pole is A, and the second magnetic pole This is achieved by the invention that satisfies the relationship of | A |> | B |> | C | where B is the magnetic force of the third magnetic pole and C is the magnetic force of the third magnetic pole.
[0025]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.
[0026]
(First embodiment)
First, a first embodiment of the present invention will be described.
[0027]
FIG. 1 shows a schematic configuration of an image forming apparatus according to the present embodiment.
[0028]
The image forming apparatus according to the present embodiment is a black-and-white digital copying machine with a process speed of 470 mm / sec and 90 sheets per minute, and includes a photosensitive drum 1 as a latent image carrier that is a φ-Si a-photosensitive drum. ing.
[0029]
In such an image forming apparatus, as shown in FIG. 1, after the photosensitive drum 1 as a latent image carrier is uniformly charged to, for example, +450 V by the primary charger 3, image exposure 12 is performed at 600 dpi. The image exposure 12 is a laser beam modulated by an image signal using a semiconductor laser as a light source. This laser beam is polarized by a polygon mirror (not shown) that is rotated at a constant rotational speed by a motor (not shown). After being reflected by a folding mirror (not shown) through an image lens (not shown), the photosensitive drum 1 is raster scanned and the surface potential of the exposed portion is attenuated to, for example, +50 V to form an image-like latent image. Form. The wavelength of the laser beam in this embodiment is 680 mm.
[0030]
Thereafter, the latent image is developed as a toner image by the developing device 2. In the present embodiment, development is performed using a black magnetic one-component developer as a highly durable development method that is simple and does not require maintenance up to a life of 2000 k of the developing sleeve, and the upstream developing sleeve 20 that is an upstream developer carrier and the downstream side. Reversal development is performed using two developer carriers with the downstream developing sleeve 30 as a developer carrier. In this embodiment, when the toner as the developer near the stirring bar 2B shown in FIG. 2 runs out, the piezoelectric element 22 detects this and rotates the mag roller 24 so that the toner in the hopper 9B is transferred to the developing device 2. To be replenished.
[0031]
After the electrostatic latent image on the photosensitive drum 1 is visualized as a toner image by the developing device 2, the toner image is charged with a differential current +100 μA (AC + DC) by a post charger 10 as a charging unit, and is transferred and separated. After the suction force with respect to the photosensitive drum 1 is weakened to facilitate the transfer, the image is transferred to a transfer material as a recording material that advances in the direction of the arrow by the transfer charger 4 as a transfer means.
[0032]
The transfer material that has received the transfer of the toner image is separated from the photosensitive drum 1 by the separation charger 5 and then sent to the fixing device 7, and the toner image is fixed by the fixing device 7.
[0033]
Next, the developing device 2 of this embodiment will be described in detail.
[0034]
In the developing device 2 of the present embodiment, the upstream developing sleeve 20 and the downstream developing sleeve 30 are disposed close to each other as shown in FIG. 3A, and are in the same direction (arrow direction in the figure). Rotate to.
[0035]
First, the points of the present invention will be described.
[0036]
Conventionally, when a two-component developer having a toner and a carrier is used, the flow of the developer on the developer carrier is shown in FIG. 4B, as shown in FIG. The developer is transferred from the upstream developer carrier to the downstream developer carrier in the vicinity. That is, the developer is conveyed on the developing sleeve on the side facing the latent image carrier. This is because when a two-component developer is used, the toner is mainly charged by the carrier, so that the developer only needs to be conveyed from the developer carrier to the latent image carrier.
[0037]
However, when a magnetic one-component developer is used, in which the developer carrier mainly contributes to charging of the developer, it is necessary to coat the developer in a thin layer on the developer carrier and sufficiently charge it. Therefore, the flow of the developer on the downstream developer carrier is as shown in FIG. 4A, which is clearly different from the case of using a two-component developer, and the latent image from the developer carrier. In addition to the developer conveyance to the carrier, the developer coat on the developer carrier must be made uniform and charged.
[0038]
Therefore, in this embodiment, as shown in FIG. 3B, the magnetic pole A as the first magnetic pole disposed in the vicinity of the photosensitive drum 1 in the upstream developing sleeve 20 or in the vicinity thereof, and the upstream developing sleeve 20. A magnetic pole B, which is a second magnetic pole disposed in the vicinity of the downstream developing sleeve 30 or in the vicinity thereof, and a third portion disposed in the vicinity of the upstream developing sleeve 20 in the downstream developing sleeve 30 or in the vicinity thereof. And a magnetic pole C as a magnetic pole.
[0039]
The relationship between these magnetic poles is
(1) The magnetic pole A and the magnetic pole C have the same polarity, and the magnetic pole B has a different polarity from the magnetic pole A and the magnetic pole C.
{Circle around (2)} | Magnetic force of magnetic pole A |> | Magnetic force of magnetic pole B |> | Magnetic force of magnetic pole C |
[0040]
Thus, in this embodiment, the toner coat on the upstream developing sleeve 20 is stabilized.
[0041]
Here, the relationship between the magnetic force and polarity of the first magnetic pole, the second magnetic pole, and the third magnetic pole will be described.
[0042]
First, the second magnetic pole and the third magnetic pole will be described. Here, in the same manner as the arrangement of the second magnetic pole and the third magnetic pole shown in FIG. 4B, the state of the developer coat on the upstream developer carrying member was examined by changing the polarity of the second magnetic pole and the third magnetic pole. . The magnetic force of each magnetic pole of the second magnetic pole and the third magnetic pole is 70 mT.
[0043]
Table 1 shows the results regarding the polarities of the second magnetic pole and the third magnetic pole and the state of the developer coat on the upstream developer carrier.
[0044]
[Table 1]

According to Table 1, when the first magnetic pole and the second magnetic pole have different polarities, the developer coat on the upstream developer carrier is stable.
[0045]
Further, if there is a magnetic force region of 0 to 10 mT on the downstream developer carrier side of the upstream developer carrier, the developer stays on the developer carrier because there is no developer conveying force in this region. As shown in FIG. 5A, the coat is in a defective state. In particular, this phenomenon becomes significant when the developer carrying member that rotates at a high speed is used and the transport speed of the developer cannot catch up. Further, when the first magnetic pole and the second magnetic pole have the same polarity, the area of magnetic force of 0 to 10 mT is further increased, so that the above-mentioned retention of the developer becomes remarkable.
[0046]
Therefore, the first magnetic pole and the second magnetic pole need to have different polarities.
[0047]
Next, the relationship between the first magnetic pole and the third magnetic pole will be described.
[0048]
The first magnetic pole is a magnetic pole that contributes to development. As shown in Table 2, normally, in order to prevent image fogging, the magnetic force needs to be 80 mT or more.
[0049]
[Table 2]

When the magnetic forces of the first magnetic pole and the third magnetic pole are equal, a region of magnetic force of 0 to 10 mT is present on the upstream developer carrier at the opposing portion of the first magnetic pole, the upstream developer carrier, and the downstream developer carrier. Therefore, it is desirable to reduce the magnetic force of the third magnetic pole and bring the position of the magnetic force of 0 to 10 mT formed by the first magnetic pole and the third magnetic pole closer to the second magnetic pole. Furthermore, in order to increase the developer conveying force during this period, the magnetic force of the second magnetic pole can be made stronger than that of the third magnetic pole, thereby reducing the influence of the magnetic force of the third magnetic pole. In addition, regarding the relationship between the magnetic force of the first magnetic pole and the magnetic force of the second magnetic pole, these are different polarities, and it is preferable to increase one of the magnetic forces in order to increase the developer conveying force. It is better to increase the magnetic force of the first magnetic pole than the condition of magnetic force ≧ 80 mT. Therefore, the magnetic force of the first magnetic pole is greater than the magnetic force of the second magnetic pole.
[0050]
Therefore, the relationship of these magnetic forces for reducing the region of magnetic force of 10 mT or less formed on the upstream developer carrier by the first magnetic pole, the second magnetic pole, and the third magnetic pole is the above-mentioned (1), (2). It becomes. As described above, unlike the case of using a two-component developer, the positions of the second magnetic pole and the third magnetic pole have been studied, and as a result of investigation, the rotation center of the upstream developer carrier and the downstream developer carry If the second magnetic pole and the third magnetic pole are projected to the latent image carrier side (outside the developing device) from the line connecting the rotation center of the body, the developer charge on the downstream developer carrier becomes difficult to stabilize. More preferably, the magnetic pole and the third magnetic pole are arranged on the inner side of the developing device (on the far side of the latent image carrier) than the above line.
[0051]
Here, a description will be given of a result of examination for preventing the developer from staying on the upstream developer carrier with respect to the first magnetic pole, the second magnetic pole, and the third magnetic pole. Here, the magnetic force of the third magnetic pole was gradually changed from 40 mT by 10 mT, and the coating state on the upstream developer carrying member in the combination of the first magnetic pole and the third magnetic pole at this time was evaluated by ○ or ×. Regarding the evaluation here, the state as shown in FIG. 5A is x, and the state as shown in FIG. As for this evaluation standard, there is unevenness in fog (◯: less than 2%, ×: 2% or more), coat stability (×: halftone image (reflection density D: 0.5), and the uneven density difference is 0.1 or more).
[0052]
As a result, the results shown in Table 3 were obtained.
[0053]
[Table 3]

Each table in Table 3 shows the developer coatability on the upstream developer carrying member when the magnetic force of the third magnetic pole is changed from 40 mT to 100 mT. This is the coatability when 10k pieces are endured with an actual machine.
[0054]
According to Table 3,
(1) The first magnetic pole and the first three The magnetic pole is the same polarity, the second magnetic pole is different from the first magnetic pole and the third magnetic pole,
(2) | Magnetic force of magnetic pole A |> | Magnetic force of magnetic pole B |> | Magnetic force of magnetic pole C |
It can be seen that the developer coatability on the upstream developer carrier is stable.
[0055]
The angle θ shown in FIG. 3A is 5 °. Further, the same examination as described above was performed with the angle θ being 0 to 20 °, but these relationships were qualitatively the same.
[0056]
In this embodiment, the upstream developing sleeve 20 has a magnetic pole configuration as shown in Table 4, and the downstream developing sleeve 30 has a magnetic pole configuration as shown in Table 5.
[0057]
[Table 4]

[0058]
[Table 5]

The upstream developing sleeve 20 is obtained by performing blasting with FGB # 600 on SUS305 of φ20 which is a non-magnetic member, and then coating as shown in FIG.
[0059]
Inside the upstream developing sleeve 20, a magnet 20B, which is a magnetic member having a magnetic field pattern as shown in FIG. The upstream developing sleeve 20 rotates at a peripheral speed of 150% with respect to the peripheral speed of the photosensitive drum 1.
[0060]
The layer thickness of the toner on the upstream developing sleeve 20 is regulated by the magnetic blade 20A. In this embodiment, the distance S-Bgap between the upstream developing sleeve 20 and the magnetic blade 20A is set to 250 μm.
[0061]
The distance S-Dgap between the upstream developing sleeve 20 and the photosensitive drum 1 is 200 μm. In this embodiment, a bias applying means (not shown) superimposes a DC bias voltage of +300 V and a rectangular wave AC bias voltage of Vpp 1200 V and a frequency of 2.5 kHz with a waveform as shown in FIG. 20 to perform magnetic one-component non-contact development. Accordingly, the development contrast is 200V in the flight direction, and the fog removal contrast is 150V.
[0062]
Similarly to the upstream developing sleeve 20, the downstream developing sleeve 30 is blasted with FGB # 600 on SUS 305 having a diameter of 20 which is a nonmagnetic member, and the surface roughness is set to Rz 3 μm. In addition, the contact-type surface roughness meter (Surf coder SE-3300 Kosaka Laboratory) was used for this Rz measurement. As measurement conditions, the cutoff value is 0.8 mm, the measurement length is 2.5 mm, the feed speed is 0.1 mm / sec, and the magnification is 5000 times.
[0063]
Inside the downstream developing sleeve 30, a magnet 30B which is a magnetic member having a four-pole magnetic field pattern shown in FIG.
[0064]
A DC bias voltage of +300 V and a rectangular wave with a Vpp of 1200 V and a frequency of 2.5 kHz can be applied to the downstream developing sleeve 30 in a superimposed manner as shown in FIG. In the present embodiment, since the developing bias voltage applied to the downstream developing sleeve 30 is the same as the developing bias voltage applied to the upstream developing sleeve 20, the power supply for the bias applying means is shared to reduce the cost. In addition, it is possible to save space because the space for the power source is small.
[0065]
The downstream developing sleeve 30 rotates at a peripheral speed of 150% with respect to the peripheral speed of the photosensitive drum 1.
[0066]
The layer thickness of the toner on the downstream developing sleeve 30 is regulated by the upstream developing sleeve 20. In this embodiment, the S-Dgap between the downstream developing sleeve 30 and the photosensitive drum 1 is 250 μm.
[0067]
In this embodiment, as shown in FIG. 8A, the upstream developing sleeve 20 has a magnet 20B having a four-pole magnetic pole inside, and the downstream developing sleeve 30 has a magnet 30B having a four-pole magnetic pole. FIG. 8B shows a magnetic seal member 2D formed along the outer circumference of the upstream developing sleeve 20 and the downstream developing sleeve 30 and made of a mold alloy (KN plating, permeability 10-6) mainly made of iron. As shown, the upstream developing sleeve 20 and the downstream developing sleeve 30 are provided near both ends in the axial direction. The gap between the surfaces of the upstream developing sleeve 20 and the downstream developing sleeve 30 and the magnetic seal member 2D is 400 μm ± 100 μm.
[0068]
In the present embodiment, the length of the magnet 20B in the axial direction of the upstream developing sleeve 20 and the downstream developing sleeve 30 is Ll = 305 mm, and the length of the magnet 30B is L2 = 305 mm.
[0069]
As for the proper mounting position of the magnetic seal member 2D with respect to the magnets 20B and 30B, the position of the outer end of the magnetic seal member 2D and the end of the magnets 20B and 30B in the axial direction of the upstream developing sleeve 20 and the downstream developing sleeve 30 It is most preferable to match the position of. This is because when the magnets 20B and 30B come out from the position of the outer end portion in the axial direction of the magnetic seal member 2D, a magnetic force exists outside the longitudinal direction (the axial direction). This is because the toner is carried outside and causes toner leakage. Further, the magnetic seal member 2D is originally intended to form a magnetic brush between the magnetic seal member 2D and the magnets 20B and 30B to eliminate toner leakage, but conversely, the magnetic seal member 2D has an outer side in the axial direction. If the positions of the end portions of the magnets 20B and 30B are too much inward relative to the position of the end portion, the magnetic seal member 2D has no magnetic force at the outer end portion of the magnetic seal member 2D. In order to form a magnetic brush with the width of the magnetic seal member 2D on the developing sleeve 20 and the downstream developing sleeve 30, the toner positioned at the outer end leaks from the end, and at the same time, the upstream developing sleeve 20 and the downstream developing sleeve. This is because the thickness of the toner layer on the surface 30 is also increased, and there is a case where the toner drops. In this embodiment, since there is a backlash in the longitudinal direction due to the relationship between the upstream developing sleeve 20 and the downstream developing sleeve 30 and the magnets 20B and 30B, as shown in FIG. The outer end of the magnetic seal member 2D is positioned at a position 1 mm inside from the end of the magnets 20B and 30B.
[0070]
Next, image processing in this embodiment will be described.
[0071]
In the present embodiment, the image signal control unit shown in FIG. 9 performs image processing as follows by binarization by the dither method.
[0072]
As shown in FIG. 9, the image processing unit 201 performs image processing desired by the operator, such as resolution conversion, on the input image signal.
[0073]
The γ correction unit 202 performs γ correction on the image signal with reference to a lookup table (LUT) by the LUT calculation unit 205.
[0074]
The binary processing unit 203 generates a laser drive signal based on the image signal after γ correction.
[0075]
The laser unit 204 is driven based on the drive signal output from the binary processing unit 203, and the image exposure 12 corresponding to the image is performed as described above. In the present embodiment, the LUT in the γ correction unit 202 is set to be appropriate for the development contrast by the LUT calculation unit 205 in the current operating environment.
[0076]
In the present embodiment, as described above, appropriate gradation correction (for example, γ correction) is performed in addition to appropriate development contrast. Then, the LUT of the γ correction unit 202 is updated in the LUT calculation unit 205 so that the obtained gradation characteristics become an ideal density reproduction curve (TRC).
[0077]
The effect of this embodiment is the same in the case of performing regular development using a negative photosensitive drum and positive toner.
[0078]
In the present embodiment, since the developing bias voltage of the AC component is applied to the developer carrying member, the portion developed excessively by the upstream developing sleeve 20 can be returned to the developing device 2 again by the downstream developing sleeve 30. Therefore, the toner consumption can be reduced. The toner consumption was measured with an image ratio of 6% original, and it was 50 to 60 mg / sheet in a conventional developing device using a magnetic one-component developer, but 41 mg / sheet in this embodiment.
[0079]
Therefore, according to this embodiment, a uniform and stable coating of the developer on the upstream developer carrier is realized in the maintenance-free small developing device using the magnetic one-component toner, and the image quality is stable. To provide a developing device that consumes less toner while maintaining the density, and to provide a high-speed device suitable for distributed small print-on-demand by making a compact developing device that saves space in the high-speed device. Can do.
[0080]
(Second embodiment)
Next, a second embodiment of the present invention will be described. In addition, the description is abbreviate | omitted regarding the structure similar to 1st embodiment.
[0081]
In general, it is difficult to control the developer tribo when the surface of the developing sleeve is SUS or Al, but in this embodiment, in view of this, the upstream developing sleeve as the upstream developer carrier and the downstream as the downstream developer carrier. In order to control the toner tribo with the developing sleeve, an optimum coating formulation is adopted for each of the upstream developing sleeve and the downstream developing sleeve, and negatively charged magnetic one-component toner is used.
[0082]
In addition, the magnetic pole of the upstream developing sleeve has a five-pole configuration in consideration of toner transportability, and a repulsive pole is formed in the developing device of the upstream developing sleeve so that the toner is once separated from the developing sleeve to develop the toner. Reduction of the accompanying to the sleeve is reduced. The coating on the surface of the developing sleeve is to prevent the sleeve ghost image generated in the developing sleeve cycle, which is a problem in JP-A-3-36570, and to improve the durability of the developing sleeve surface (protect the Al surface). Is a membrane). In the present embodiment, the distance d between the developing sleeves is 600 μm.
[0083]
Such an image forming apparatus uses a φ-Si a-photosensitive drum of φ108 as a latent image carrier, and is a black and white digital copying machine of 90 sheets per minute at a process speed of 470 mm / sec, as in the first embodiment. . The developer of this embodiment is a negatively charged toner having a weight average particle diameter of 7.5 μm, and 1.0% (wt%) of SiO as an external additive. ₂ Is painted.
[0084]
In this embodiment, the coating film for the developing sleeve was formulated by mixing a phenol resin, crystalline graphite, and carbon on the surface of the Al developing sleeve and curing the film in a 150 ° C. environment with a film thickness of 10 μm. The thickness of the film is about 20 μm for forming a stable and uniform film. In this case, the P / B ratio is 1 / 2.5. Here, B represents the weight of the resin, and P represents the weight of the material other than the resin (crystalline graphite + carbon).
[0085]
When the toner coating amount of the downstream developing sleeve is regulated by the upstream developing sleeve as in this configuration, the charging characteristic for the negative polarity toner is too high, so that 70 parts by weight of quaternary ammonium salt is added only to the downstream developing sleeve. The phenol resin which has is used.
[0086]
When added, the quaternary ammonium salt compound is uniformly dispersed in the phenolic resin, and further taken into the structure of the phenolic resin when it is cured by heating to form a film. The resin composition itself changes to a material having negative chargeability. Therefore, if a developer carrier having a coating layer formed using such a material is used, the developer can be suitably charged positively.
[0087]
Examples of the quaternary ammonium salt compound having the functions described above that are preferably used in the present invention include compounds represented by the following general formula.
[0088]
[Chemical 1]

Rl, R2, R3, and R4 in the formula shown in Chemical Formula 1 represent an alkyl group that may have a substituent, an aryl group that may have a substituent, and an aralkyl group, respectively, and Rl-R4 each represents They may be the same or different. X- represents an anion of an acid.
[0089]
In the general formula shown in Chemical Formula 1 above, specific examples of the X-acid ion include organic sulfate ion, organic sulfonate ion, organic phosphate ion, molybdate ion, tungstate ion, molybdenum atom or tungsten atom. Heteropoly acid and the like can be mentioned.
[0090]
[Chemical 2]

As shown in Chemical Formula 2, when a coating layer is formed using a resin composition obtained by adding a specific quaternary ammonium salt compound used in the present invention to a phenol resin, as described above, it is a binder resin. When the phenol resin is cured by heating to form a coating layer, the quaternary ammonium salt compound is incorporated into the structure of the phenol resin. For this reason, unlike the case of the particle addition system such as the negative silica particles or the negative Teflon particles described above, the positive triboelectric charge imparting property to the positively chargeable developer as a whole is improved, not partially. . Further, unlike the particle-added coating, the processability is not impaired and the strength of the coating layer is not reduced.
[0091]
Specific examples of the quaternary ammonium salt compound suitably used in the present invention include the following, but the present invention is of course not limited thereto.
[0092]
[Chemical 3]

[0093]
[Formula 4]

[0094]
[Chemical formula 5]

[0095]
[Chemical 6]

[0096]
[Chemical 7]

[0097]
[Chemical 8]

[0098]
[Chemical 9]

[0099]
[Chemical Formula 10]

As the phenol resin constituting the binder resin used in the present invention, a quaternary ammonium salt compound is used in the production process, particularly when a quaternary ammonium salt compound is used during the heat curing. It was found that it was easy to be incorporated into the structure of the toner and preferable for preventing charge-up of the toner. Therefore, in the present invention, if a phenol resin having such an action and produced using a nitrogen-containing compound as a catalyst in the production process is used as one of the materials constituting the coating layer on the developer carrier. Therefore, it is possible to realize a developing device that prevents the toner from being charged up.
[0100]
Examples of the nitrogen-containing compound used as a catalyst in a phenol resin production process that can be suitably used in the present invention include, for example, ammonium sulfate, ammonium phosphate, ammonium sulfamate, ammonium carbonate, ammonium acetate, and ammonium maleate. Examples of the basic catalyst include ammonia, dimethylamine, diethylamine, diisopropylamine, diisobutylamine, diamylamine, trimethylamine, triethylamine, tri-n-butylamine, triamylamine, dimethylbenzylamine. , Diethylbenzylamine, dimethylaniline, diethylaniline, N, N-di-n-butylaniline, N, N-diamilaniline, N, N-di-t-amylaniline N-methylethanolamine, N-ethylethanolamine, diethanolamine, triethanolamine, dimethylethanolamine, diethylethanolamine, ethyldiethanolamine, n-butyldiethanolamine, di-n-butylethanolamine, triisopropanolamine, ethylenediamine, hexamethylene Amino compounds such as tetramine, pyridine, α-picoline, β-picoline, γ-picoline, pyridine and derivatives thereof such as 2,4-lutidine, 2,6-lutidine, quinoline compounds, imidazole, 2-methylmethylimidazole, 2, Imidazo such as 4-dimethylimidazole, 2-ethyl-4-methylimidazole, 2-phenylimidazole, 2-phenyl-4-methylimidazole, 2-heptadecylimidazole, etc. And nitrogen-containing heterocyclic compounds such as derivatives.
[0101]
In this invention, in order to adjust the resistance value of a coating layer to said value, it is preferable to contain the electroconductive substance mentioned below in a coating layer. Examples of the conductive material used at this time include metal powders such as aluminum, copper, nickel, and silver, metal oxides such as antimony oxide, indium oxide, and tin oxide, carbon fiber, carbon black, and graphite. Examples include carbon materials. In the present invention, among these, carbon black, in particular conductive amorphous carbon, is particularly excellent in electrical conductivity, and it can be filled with a polymer material to impart conductivity, or only by controlling the amount of addition. It is preferably used because an arbitrary degree of dragon resistance can be obtained to some extent.
[0102]
The final film formulation is 90 parts by weight of graphite having an average particle size of 7.5 μm, 10 parts by weight of carbon and 70 parts by weight of quaternary ammonium with respect to 250 parts by weight of phenol resin. Incidentally, the ratio of graphite to carbon is preferably at least 3 times that of carbon in order to stabilize the resistance of the entire film. The film is applied to the developing sleeve by spraying and then dried at 150 degrees for 30 minutes.
[0103]
By optimizing the coating, the tribo (charge amount) on the downstream developing sleeve side is usually large, whereas in this embodiment, 9 μC / g on the upstream developing sleeve and 9.2 μC / g on the downstream developing sleeve are used. It was possible to control to almost the same value. As a result, the development characteristics are stabilized because both development sleeves are optimized against changes in the environment such as high temperature and high humidity and room temperature and low humidity.
[0104]
As shown in FIG. 10 and Table 6, a magnet having a 5-pole magnetic field pattern is fixedly arranged inside the upstream developing sleeve 20.
[0105]
[Table 6]

[0106]
As the downstream developing sleeve 30, a non-magnetic member of φ20 aluminum A2017 formed with a film is used. Inside the downstream developing sleeve 30, a magnet having a four-pole magnetic field pattern shown in FIG.
[0107]
[Table 7]

A DC bias voltage of −550 V and a rectangular wave of Vpp 1500 V and frequency 2.7 kHz are applied to the downstream developing sleeve 30 with a waveform as shown in FIG. Since the AC bias voltage and the DC bias voltage applied to the downstream developing sleeve 30 are the same as the AC bias voltage and the DC bias voltage applied to the upstream developing sleeve 20, the cost can be reduced by using one power source. In addition to being able to plan, there is an advantage that the space for the power source can be reduced. The downstream developing sleeve 30 rotates at a peripheral speed of 125% with respect to the peripheral speed of the photosensitive drum 1.
[0108]
The layer thickness of the toner on the downstream developing sleeve 30 is regulated by the upstream developing sleeve 20. A distance d between the upstream developing sleeve 20 and the downstream developing sleeve 30 is 600 μm.
[0109]
As shown in Tables 6 and 7, the magnetic pole configurations of the upstream developing sleeve 20 and the downstream developing sleeve 30 are 5 poles and 4 poles, respectively. The reason why the upstream developing sleeve 20 has five magnetic poles is as described above.
[0110]
Therefore, according to the present embodiment, a uniform and stable coating of the developer on the upstream developer carrying member is realized in a maintenance-free small-sized developing device using a magnetic one-component toner, and a stable density is achieved with high image quality. It is possible to provide a high-speed machine suitable for distributed small print-on-demand by providing a developing apparatus that consumes less toner while maintaining a compact developing apparatus that saves space in a high-speed machine. . Furthermore, toner deterioration on the upstream developer carrier can be reduced to reduce toner deterioration, and charge control can be performed by using a coat formulation optimum for the charging characteristics of these toners.
[0111]
(Third embodiment)
Next, a third embodiment of the present invention will be described. In addition, the description is abbreviate | omitted regarding the structure similar to 1st embodiment or 2nd embodiment.
[0112]
The developing device according to this embodiment is the same as that of the second embodiment.
[0113]
A feature of this embodiment is that the developing device of the present invention is applied to a reuse image forming apparatus.
[0114]
Since the reuse toner is basically waste toner that is not transferred and collected by cleaning, the amount of reversal component toner is large because the tribo is extremely small compared to new toner due to deterioration. Scattering is even worse. This embodiment is implemented in view of these points.
[0115]
The prescription of the upstream developing sleeve, the magnetic pole of the downstream developing sleeve, and the coating material in this embodiment is the same as in the second embodiment.
[0116]
The image forming apparatus according to the present embodiment is a digital copier having a process speed of 500 mm / s and 110 sheets / min in the image forming system shown in FIG. 11, and a latent image using an a-Si drum as a photoconductor. A photosensitive drum 1 as a carrier is provided.
[0117]
In such an image forming apparatus, the surface of the photosensitive drum 1 is uniformly charged to −700 V by the primary charger 3.
[0118]
Next, the uniformly charged surface of the photosensitive drum 1 is subjected to image exposure 12 by PWM with a semiconductor laser having a wavelength of 680 μm at 600 dpi, and an electrostatic latent image is formed on the photosensitive drum 1.
[0119]
Next, the electrostatic latent image is normally developed by the developing device 2 and visualized as a toner image. The developing device of the present embodiment employs a jumping development method using a magnetic one-component negative toner having a toner particle size of 8.0 μm as a developer. This is because a conventional two-component developer has to be replaced every 100,000 sheets by a service person and is not maintenance-free, so the advantage of reuse cannot be prosperous. On the other hand, in the present embodiment, a dry magnetic one-component toner that is infinitely durable and requires no maintenance is used. As the developing bias voltage, a developing bias voltage obtained by superimposing a DC bias voltage of +200 V on an AC bias voltage of 2400 Hz, 1500 Vpp, Duty 50% is applied to both the upstream developing sleeve 20 and the downstream developing sleeve 30. In this embodiment, the distance S-Bgap between the upstream developing sleeve 20 and the magnetic blade 20A is 250 μm, and the distances S-Dgap between the upstream developing sleeve 20 and the downstream developing sleeve 30 and the photosensitive drum 1 are both 250 μm. ing.
[0120]
Thereafter, the toner image is charged with a total current of −200 μA flowing through the post charger 10 serving as a charging unit, and then transferred to a transfer material serving as a recording material moving in the direction of the arrow by the transfer charger 4 serving as a transfer unit.
[0121]
The transfer material that has received the transfer of the toner image is separated from the photosensitive drum 1 by the separation charger 205 and then conveyed to the fixing device 7 where the toner image is fixed.
[0122]
On the other hand, the transfer residual toner on the photosensitive drum 1 is removed from the photosensitive drum 1 by the cleaning device 6 serving as a removing unit, collected, and returned to the developing hopper 9B through the transport pipe 8 as waste toner (reused toner).
[0123]
A screw-shaped conveyance member is disposed inside the conveyance pipe 8, and the reuse toner is conveyed toward the developing hopper 9 </ b> B as the conveyance member rotates. Thus, as shown in FIG. 11, the reuse toner carried by the conveyance member of the conveyance pipe 8 is put into the developing hopper 9B and reused. In addition to the reuse toner, new toner is put into the hopper 9A, and each toner is attracted by the magnetic force by the mag rollers 24A and 24B. Carried. In this embodiment, the method of mixing the reuse toner and new toner in the developing device is adopted. However, a space for mixing in the hopper may be provided and mixed in the space.
[0124]
The toner mixed in the developing device 2 is sent again to the upstream developing sleeve 20 and the downstream developing sleeve 30 to be used for developing the electrostatic latent image on the photosensitive drum 1. In the present embodiment, the normal rotation speed of the mag roller 24A is 2 rotations / minute, and the rotation speed of the mag roller 24B is changed at a predetermined ratio with respect to the rotation speed of the mag roller 24A. In the present embodiment, when the weight of the toner is not applied to the piezo sensor (manufactured by TDK) provided in the developing device 2 and the signal from the piezo sensor vibrates, the mag rollers 24A and 24B are rotated. Be emitted. Normally, the mag roller 24B rotates at a rotation speed ratio of 10/90 (the rotation speed of the mag roller 24A: the rotation speed of the mag roller 24B = 9: 1) with respect to the rotation speed of the mag roller 24A.
[0125]
In the present embodiment, the distance d = 800 μm. The magnetic force of N2 (magnetic pole A) disposed in the magnet 20B of the upstream developing sleeve 20 is 80 mT, and the magnetic force of S1 (magnetic pole B) disposed in the magnet 30B of the downstream developing sleeve 30 is 75 mT. Further, the magnetic pole A and N1 (magnetic pole C) arranged in the vicinity of the photosensitive drum 1 in the magnet 30B or in the vicinity thereof have the same polarity, and the magnetic pole B is different in polarity from the magnetic pole A and the magnetic pole C. .
[0126]
Further, the magnetic pole A and the magnetic pole B are located on the inner side of the developing device 2 (the far side of the photosensitive drum 1) with respect to a line connecting the rotation center of the upstream developing sleeve 20 and the rotation center of the downstream developing sleeve 30. Further, the angle θ shown in FIG. 3A is 10 °.
[0127]
In this embodiment, the relationship between the magnetic force [mT] of the magnetic pole A, the magnetic force [mT] of the magnetic pole B, and the distance d [μm] is
0.5 ≧ (80 + 75) /800≧0.2
In order to satisfy this condition, the toner coat property on the downstream developing sleeve 30 is stabilized.
[0128]
Therefore, according to the present embodiment, in a maintenance-free toner-reusing small-sized developing device using a magnetic one-component toner, a uniform and stable coating of the developer on the upstream developer carrier is realized, and the image quality is stable. To provide a developing device that consumes less toner while maintaining the density, and to provide a high-speed device suitable for distributed small print-on-demand by making a compact developing device that saves space in the high-speed device. Can do.
[0129]
【The invention's effect】
As described above, according to the first invention of the present application, the polarities and magnetic forces of the first magnetic pole, the second magnetic pole, and the third magnetic pole are optimized, so that a plurality of development carriers are provided. In a developing device that employs a one-component developer, a magnetic one-component developer is uniformly distributed on an upstream developer carrier on the upstream side in the rotation direction of the latent image carrier among two adjacent developer carriers. Can be stably coated.
[0130]
According to the second invention of the present application, the appropriateness of the polarities and magnetic forces of the first magnetic pole, the second magnetic pole, and the third magnetic pole, and the distance between the upstream developer carrier and the downstream developer carrier. Therefore, in a developing device that includes a plurality of developer carriers and employs a one-component developer, upstream of the two adjacent developer carriers in the rotation direction of the latent image carrier. A magnetic one-component developer can be uniformly and stably coated on the developer carrying member.
[0131]
Further, according to the third invention of the present application, since the polarities and magnetic forces of the first magnetic pole, the second magnetic pole, and the third magnetic pole are optimized, a single component system including a plurality of development carriers is provided. In a developing device employing a developer, a magnetic one-component developer is uniformly and stably distributed on an upstream developer carrier on the upstream side in the rotation direction of the latent image carrier among two adjacent developer carriers. Can be coated.
[0132]
Further, according to the fourth invention of the present application, since the polarities and magnetic forces of the first magnetic pole, the second magnetic pole, and the third magnetic pole are optimized, a single-component system including a plurality of development carriers is provided. In a developing device employing a developer, a magnetic one-component developer is uniformly and stably distributed on an upstream developer carrier on the upstream side in the rotation direction of the latent image carrier among two adjacent developer carriers. Can be coated.
[0133]
Further, according to the fifth invention of the present application, since the polarities and magnetic forces of the first magnetic pole, the second magnetic pole, and the third magnetic pole are optimized, a plurality of development carriers are provided and a one-component system is provided. In a developing device employing a developer, a magnetic one-component developer is uniformly and stably distributed on an upstream developer carrier on the upstream side in the rotation direction of the latent image carrier among two adjacent developer carriers. Can be coated.
[0134]
According to the sixth aspect of the present invention, the polarities and magnetic forces of the first magnetic pole, the second magnetic pole, and the third magnetic pole are optimized, and the surface of the developer carrier is protected. Therefore, in a developing device that includes a plurality of developer carriers and employs a one-component developer, an upstream developer carrier on the upstream side in the rotation direction of the latent image carrier among two adjacent developer carriers. A magnetic one-component developer can be uniformly and stably coated thereon.
[0135]
Further, according to the seventh invention of the present application, since the polarities and magnetic forces of the first magnetic pole, the second magnetic pole, and the third magnetic pole are optimized, a single-component system including a plurality of development carriers is provided. In a developing device employing a developer, a magnetic one-component developer is uniformly and stably distributed on an upstream developer carrier on the upstream side in the rotation direction of the latent image carrier among two adjacent developer carriers. Can be coated.
[Brief description of the drawings]
FIG. 1 is a schematic cross-sectional view showing a schematic configuration of an image forming apparatus according to a first embodiment of the present invention.
2 is a schematic cross-sectional view showing a schematic configuration of a developing device provided in the image forming apparatus of FIG.
3 is a diagram for explaining a magnetic pole arrangement of a magnetic member provided inside a developer carrying member of the developing device of FIG. 2;
FIG. 4A is a diagram for explaining the movement of a developer on a developer carrier when a one-component developer is used, and FIG. 4B is a diagram illustrating a two-component developer. FIG. 10 is a diagram for explaining the movement of the developer on the developer carrier when used.
FIG. 5 is a diagram for explaining the relationship between the position and polarity of a magnetic pole of a magnetic member of a developer carrier and developer coatability on an upstream developer carrier.
6 is a view for explaining a coating member of a developer carrying member provided in the developing device of FIG. 2;
FIG. 7 is a diagram for explaining a waveform of an AC component of a bias voltage applied to a developer carrier in the first embodiment of the present invention.
FIG. 8 is a view for explaining the arrangement of the magnetic member of the developer carrier and the seal at the end in the axial direction of the developer carrier in the first embodiment of the present invention.
FIG. 9 is a diagram for explaining image processing in the first embodiment of the present invention;
FIG. 10 is a diagram for explaining a magnetic pole arrangement of a magnetic member provided inside a developer carrier of a developing device according to a second embodiment of the present invention.
FIG. 11 is a schematic cross-sectional view showing a schematic configuration of an image forming apparatus according to a third embodiment of the present invention.
FIG. 12 is a schematic cross-sectional view showing a schematic configuration of a conventional image forming apparatus.
13 is a schematic cross-sectional view showing a schematic configuration of a developing device provided in the image forming apparatus of FIG.
14 is a view for explaining a magnetic pole arrangement of a magnetic member provided inside a developer carrying member of the developing device of FIG. 13;
[Explanation of symbols]
1 Photosensitive drum (latent image carrier)
2 Development device
4 Transfer charger (transfer means)
6 Cleaning device (cleaning means)
20B, 30B Magnet (magnetic member)
20 Upstream developing sleeve (developer carrier, upstream developer carrier)
30 downstream development sleeve (developer carrier, downstream developer carrier)

Claims (6)

A developing device that visualizes the latent image as a developer image by applying a magnetic one-component developer to a rotating latent image carrier that carries a latent image on the surface, and is in close proximity to the latent image carrier And a plurality of developer carriers that rotate and carry a developer on the surface, the plurality of developer carriers rotate in the same direction, and the latent An upstream developer carrier on the upstream side in the rotation direction of the image carrier is disposed close to the downstream developer carrier to such an extent that the amount of developer on the downstream developer carrier is regulated to a predetermined amount. Developing device,
Each developer carrier has a magnetic member therein, and each magnetic member has a first magnetic pole disposed in the vicinity of or near the latent image carrier of the upstream developer carrier, and upstream. A second magnetic pole disposed adjacent to or downstream from the first magnetic pole in the vicinity of the downstream side of the developer carrier and the downstream side of the developer carrier. The third magnetic pole disposed in the vicinity of or near the upstream developer carrier of the developer carrier and the opposite portion of the downstream developer carrier to the latent image carrier and the third magnetic pole A fourth magnetic pole disposed adjacent to the downstream side of the developer carrier rotating direction downstream of the magnetic pole and having a different polarity from the third magnetic pole, wherein the first magnetic pole and the third magnetic pole have the same polarity And the second magnetic pole is different in polarity from the first magnetic pole and the third magnetic pole,
The second magnetic pole and the third magnetic pole are located on the far side of the latent image carrier with respect to a line connecting the rotation center of the upstream developer carrier and the rotation center of the downstream developer carrier,
When the magnetic force of the first magnetic pole is A, the magnetic force of the second magnetic pole is B, and the magnetic force of the third magnetic pole is C, the relationship | A |> | B |> | C | is satisfied. A developing device.   The developing device according to claim 1, wherein the magnetic force A of the first magnetic pole is 80 mT or more, and the magnetic force B of the second magnetic pole and the magnetic force C of the third magnetic pole are 50 mT or more, respectively.   3. The developing device according to claim 1, wherein each developer carrying member is configured to be applied with a bias voltage composed of an alternating current component and a direct current component during development.   4. The developing device according to claim 1, wherein each developer carrying member is configured such that a surface thereof is covered with a coating member having crystalline graphite and a phenol resin. 5.   An image forming apparatus for recording an image formed by a series of image forming processes on a recording material, comprising a latent image carrier and the developing device according to any one of claims 1 to 4. An image forming apparatus.   Transfer means for transferring the developer image on the latent image carrier to the recording material, and the developer remaining on the latent image carrier after the transfer of the developer image to the recording material by the transfer means is removed. The image forming apparatus according to claim 5, further comprising: a cleaning unit, wherein the developing device is configured to collect and reuse the developer removed from the latent image carrier by the cleaning unit. apparatus.

Images