JP3989169B2 - Developing roller, developing device, and image forming apparatus - Google Patents

Description

【００２３】
表１に示すように、マグローラ５１のみによる現像極部の磁束密度は５０ｍｔで半値幅は３７度である。希土類マグネットブロック５４による磁束密度は６０ｍｔで半値幅は１７度である。そして、磁石ローラ体５０の現像極部の磁束密度は１１０ｍｔで半値幅は２５度である。この結果から、磁石ローラ体５０の現像極部の磁束密度は、マグローラ５１＋マグネットブロック５４、の関係になっていることが分かった。したがって、本発明のように磁石ローラ体の高磁力化を達成するには、フェライトマグローラの現像極と希土類マグネットブロックの極性を同一にし、夫々の磁力を高めることで所望の磁束密度を得ることができる。
【００２４】
一方、半値幅は、希土類磁石であるマグネットブロック５４が急峻な波形を有していても、ベース（基体）となるフェライト磁石のマグローラ５１の影響を大きく受けるため、マグネットブロック５４単独の半値幅より大きくなってしまい、課題とする半値幅２０度以下を達成できないことが分かった。
【００２５】
そこで、本願発明者らは、ベースとなるフェライトマグローラの着磁条件を検討し、現像極部のピーク幅（ボトム部）の狭幅化を計った。すなわち、着磁工程で着磁ヨーク幅の変更や着磁ヨークの位置をずらすことにより、ピーク幅を狭くして、半値幅を小さくしようとするものである。なお、現像極部のピーク幅とは、図５に示すように、現像極部における磁気波形のボトム部の幅、すなわち磁束密度ピークの開き角度のことを言う。
【００２６】
次に、図６〜図８は、本願発明者らが試作した磁石ローラ体の磁気波形図を示すものである。各磁石ローラ体の構成は、図１〜４で説明したものと同じく、円筒形の基体ローラである溝付きフェライトマグローラ５１に希土類マグネットブロック５４を埋め込んだものである。図５〜図７の各磁石ローラ体は、希土類マグネットブロック５４は同じ物を用い、フェライトマグローラ５１の着磁条件（現像極部の着磁条件）が異なっている。
【００２７】
図６〜図８において、フェライトマグローラ５１の現像極部の磁気波形を升目を付して示してあるが、マグローラ５１の現像極部のピーク幅を狭幅化することにより、磁石ローラ体としての現像極の磁気波形（図に実線で示してある）のシャープネスが向上していることが分かる。
【００２８】
各磁石ローラ体における現像極部のフェライトマグローラ５１及びマグネットブロック５４のピーク幅と磁束密度ならびに磁石ローラ体としての現像極部の磁束密度と半値幅を次の表２に示す。
【００２９】
【表２】

【００３０】
表２において、フェライトマグローラ５１の現像極部の着磁条件は、Ａ，Ｂ，Ｃの３つの条件が、ピーク幅５０度で磁束密度４０ｍＴ、ピーク幅３０度で磁束密度２０ｍＴ、ピーク幅１０度で磁束密度４ｍＴとなっている。希土類マグネットブロック５４のピーク幅及び磁束密度は３条件とも同じ３０度、７２ｍＴである。
【００３１】
マグローラ５１の現像極部の着磁条件Ａ，Ｂ，Ｃにより、磁石ローラ体５０としての現像極の磁束密度及び半値幅は、それぞれ１１５ｍＴで２５度、９５ｍＴで２０度、７８ｍＴで１８度となった。この結果から、フェライトマグローラ５１の現像極部の着磁条件を変更し、マグローラ現像極部のピーク幅を小さくすることにより磁石ローラ体現像極の半値幅も小さくなること、目標とする半値幅２０度以下を達成するためには、フェライトマグローラ５１の現像極部のピーク幅が希土類マグネットブロック５４のピーク幅以下であることが必要と分かった。
【００３２】
なお、希土類マグネットブロック５４は全て同じ材料を使用し、幅２ｍｍ、高さ（法線方向）２．５ｍｍ、長さ３００ｍｍで、等方性のＮｄ−Ｆｅ−Ｂ系材料を使用した。また、測定プローブと磁石表面のギャップは１．０ｍｍで行った。
【００３３】
一方、表２から分かるように、磁石ローラ体としての現像極の磁束密度は、マグローラ５１の磁束密度が低くなると、小さくなる。その結果、着磁条件Ｃでは、磁石ローラ体としての現像極磁束密度が７８ｍＴで、目標の８０ｍＴが達成できていない（半値幅は１８度とクリアしている）。
【００３４】
したがって、マグローラ現像極部のピーク幅を小さくすることにより磁石ローラ体現像極の半値幅を２０度未満とする場合には、希土類マグネットブロックの磁力がさらに要求されることになる。
【００３５】
今回実験に使用した希土類磁石のＮｄ−Ｆｅ−Ｂ系材料は最大エネルギー積（ＢＨ）ｍａｘが６４ｋＪ／ｍ^３（８．０ＭＧＯｅ）の材料であるが、さらに高エネルギーの材料も等方性Ｎｄ−Ｆｅ−Ｂ系材料の中でも上市されている。しかし、それらの材料は磁石粉の含有率を高めて高磁力化を達成しているので、材料の柔軟性が乏しく、外部応力に弱く、非常に割れやすい脆い材料となっている。
【００３６】
現像ローラにおける磁石ローラ体のマグネットブロックとして使用する場合、幅１．０〜２ｍｍ、高さ２〜３ｍｍ、長さ３００〜３１０ｍｍの棒状になっており、より一層割れやすい形状となっている。従って、等方性Ｎｄ-Ｆｅ-Ｂ以外でさらに高磁力の材料が要求される。
【００３７】
より高磁力の材料を求めて、磁気特性、脆さ、成型性等を鋭意検討した結果、異方性のＮｄ−Ｆｅ−Ｂ系材料と異方性のＳｍ−Ｆｅ−Ｎ系材料の２種が等方性のＮｄ−Ｆｅ−Ｂ系以上であることがわかった。
【００３８】
異方性のＮｄ−Ｆｅ−Ｂ系材料は（ＢＨ）ｍａｘが約１２ＭＧＯｅあり、等方性Ｎｄ−Ｆｅ−Ｂ系の１．５倍の磁力である。磁粉の配合比が低くできるため、プラスティック材料の持つフレキシビリテイーが維持され、割れ難くなっている（バインダーはナイロン１２を使用）。
【００３９】
次に異方性のＳｍ−Ｆｅ−Ｎ系材料は（ＢＨ）ｍａｘが約９．５ＭＧＯｅあり、等方性Ｎｄ−Ｆｅ−Ｂ系の１．２倍の磁力である。磁粉の配合比が低くできるため、プラステイック材料の持つフレキシビリテイーが維持され、割れ難くなっている（バインダーはゴム系材料を使用）。
【００４０】
これら２種の材料を上記着磁条件Ｃの磁石ローラ体で評価した結果を次の表３に示す。
【００４１】
【表３】

【００４２】
ここで比較検討した希土類マグネットブロックは、全て幅２ｍｍ高さ２．５ｍｍ（着磁方向）、長さ３００ｍｍで、測定プローブと磁石表面のギャップは１．０ｍｍで測定した。
【００４３】
このように、異方性のＮｄ−Ｆｅ−Ｂ系材料と異方性のＳｍ−Ｆｅ−Ｎ系材料をマグネットブロック５４として用いることにより、半値幅を２０°以下に狭くしても、８０ｍＴ以上の磁束密度が得られるようになった。
【００４４】
なお、上記説明では、現像極部における希土類マグネットブロック５４は１極（１個）であったが、複数極（複数個）を設けても良い。その場合、フェライトマグローラ５１の現像極部のピーク幅が複数個の希土類マグネットブロック全体でのピーク幅以下であればよい。
【００４５】
次に、上述したような、磁石ローラ体を内蔵する現像ローラを備える現像装置について説明する。
図１２は、本発明に係る現像ローラを備える現像装置の断面構成図である。この図に示すように、現像装置４内には、現像剤担持体である現像ローラ４１が画像形成装置の感光体ドラム２０に近接するように配置されていて、双方の対向部分には、感光体ドラムと磁気ブラシが接触する現像領域が形成されている。現像ローラ４１は、アルミニウム、真鍮、ステンレス、導電性樹脂などの非磁性体を円筒形に形成してなる現像スリーブ４３が不図示の回転駆動機構によって図中時計回りに回転されるようになっている。本実施形態においては、感光体ドラム２０と現像スリーブ４３との間隔である現像ギャップは０．４ｍｍに設定されている。現像ギャップは、従来では０．６５ｍｍから０．８ｍｍ程度に設定されていた。
【００４６】
現像剤の搬送方向（図で見て時計回り方向）における現像領域の上流側部分には、現像剤チェーン穂の穂高さ、即ち、現像スリーブ上の現像剤量を規制するドクタブレード４５が設置されている。このドクタブレード４５と現像スリーブ４３との間隔であるドクタギャップは０．４ｍｍに設定されている。更に現像ローラの感光体ドラムとは反対側領域には、現像装置ケーシング４６内の現像剤を攪拌しながら現像ローラ４１へ汲み上げるためのスクリュー４７が設置されている。
【００４７】
現像ローラのスリーブ４３内には、当該現像スリーブ４３の周表面に現像剤の穂立ちを生じるように磁界を形成する磁石ローラ体（磁石ローラ）５０が固定状態で備えられる。この磁石ローラ体５０は、上述したようにフェライトマグローラに希土類マグネットブロックを埋め込んだものである。マグネットブロックとしては、異方性のＮｄ−Ｆｅ−Ｂ系材料または異方性のＳｍ−Ｆｅ−Ｎ系材料のものを使用することで、半値幅２０°以下で８０ｍＴ以上の磁束密度が得られるものである。この磁石ローラ体から発せられる法線方向磁力線に沿うように、現像剤のキャリアが現像スリーブ４３上にチェーン状に穂立ちを起こし、このチェーン状に穂立ちを生じたキャリアに帯電トナーが付着されて、磁気ブラシが構成される。当該磁気ブラシは現像スリーブ４３の回転によって現像スリーブ４３と同方向（図で見て時計回り方向）に移送されることとなる。
【００４８】
磁石ローラ体５０は複数の磁極を有している。上記希土類マグネットブロック５４によって現像領域部分に現像剤の穂立ちを生じさせる現像極と、スクリュー４７に対向してスリーブ４３上に現像剤を汲み上げるための汲み上げ極と、汲み上げられた現像剤を現像領域まで搬送するための搬送極と、現像後の領域で現像剤を搬送する磁極である。
【００４９】
画像濃度の低い感光体上のトナー像（付着量の少ないトナー像）を現像する際に、本実施例の磁気ブラシを使用した場合には、現像ニップ幅が小さいため、感光体上を摺擦する磁気ブラシの接触量（時間）が少なくなり、磁気ブラシ先端部に発生するカウンターチャージの発生量が低下する。結果として、カウンターチャージをもったキャリアがトナー像を引き付けることによる画像後端部が白く抜ける現象を抑えることが可能となる。したがって、画像濃度の低い感光体上のトナー像（付着量の少ないトナー像）の再現性を向上することが可能となった。
【００５０】
また画像濃度が高くなる理由として、現像極の磁気ブラシの長さが小さくなり、現像ニップ幅を小さくすることが可能となり、したがって、現像スリーブが回転移動し、現像極を通過する際の短くなった磁気ブラシが立ち始め現像ニップ間を通過する時間が早くなり（対感光体線速比がこの部分だけ早くなる現象が起こっている）、感光体に摺擦する現像剤の量が増加するために画像濃度が高くなる。更に現像ニップ幅が小さいので現像ニップ領域前の現像剤滞留部の現像剤量が少なく、カウンターチャージの発生を抑えることが可能となったために画像濃度の低下を抑えることができ、結果として、後端白抜けの無い画像能力の向上した現像装置を提供することができる。
【００５１】
本実施形態の現像装置における現像領域のイメージを図１３に示し、従来例のものを図１４に示す。
最後に、本発明の適用を電子写真式カラー複写装置（以下、カラー複写機という）に広げて説明する。図１５を用いて、本カラー複写機の概略構成及び動作について説明する。このカラー複写機は、カラー画像読取装置（以下、カラースキャナという）１１、カラー画像記録装置（以下、カラープリンタという）１２、給紙バンク１３等で構成されている。
【００５２】
上記カラースキャナ１１は、コンタクトガラス１０１上の原稿１０の画像を照明ランプ１０２、ミラー群１０３ａ，１０３ｂ，１０３ｃ及びレンズ１０４を介してカラーセンサ１０５に結像して、原稿１０のカラー画像情報を、例えば赤、緑、青（以下、それぞれＲ，Ｇ，Ｂという）の色分解光毎に読み取り、電気的な画像信号に変換する。ここで、カラーセンサ１０５は、本例ではＲ，Ｇ，Ｂの色分解手段とＣＣＤのような光電変換素子で構成され、原稿１０の画像を色分解した３色のカラー画像を同時に読み取っている。そして、このカラースキャナ１１で得たＲ，Ｇ，Ｂの色分解画像信号強度レベルを基にして、不図示の画像処理部で色変換処理を行い、黒（以下、Ｂｋという）、シアン（以下、Ｃという）、マゼンタ（以下、Ｍという）、イエロー（以下、Ｙという）のカラー画像データを得る。
【００５３】
上記Ｂｋ、Ｃ、Ｍ、Ｙのカラー画像データを得るためのカラースキャナ１１の動作は次の通りである。後述のカラープリンタ１２の動作とタイミングを取ったスキャナスタート信号を受けて、照明ランプ１０２及びミラー群１０３ａ，１０３ｂ，１０３ｃ等からなる光学系が矢印左方向へ原稿１０を走査し、１回の走査毎に１色のカラー画像データを得る。この動作を合計４回繰り返すことによって、順次４色のカラー画像データを得る。そして、その都度カラープリンタ１２で順次顕像化しつつ、これを重ね合わせて最終的な４色フルカラー画像を形成する。
【００５４】
上記カラープリンタ１２は、像担持体としての感光体ドラム２０、書き込み光学ユニット２２、リボルバ現像ユニット２３、中間転写装置２６、定着装置２７等で構成されている。 上記感光体ドラム２０は矢印の反時計方向に回転し、その周りには、感光体クリーニング装置２０１、除電ランプ２０２、帯電器２０３、電位センサ２０４、リボルバ現像ユニット２３の選択された現像器、現像濃度パターン検知器２０５、中間転写装置２６の中間転写ベルト２６１などが配置されている。
【００５５】
また、上記書き込み光学ユニット２２は、カラースキャナ１１からのカラー画像データを光信号に変換して、原稿１０の画像に対応した光書き込みを行い、感光体ドラム２０に静電潜像を形成する。この書き込み光学ユニット２２は、光源としての半導体レーザー２２１、不図示のレーザー発光駆動制御部、ポリゴンミラー２２２とその回転用モータ２２３、ｆ／θレンズ２２４、反射ミラー２２５などで構成されている。
【００５６】
また、上記リボルバ現像ユニット２３は、Ｂｋ現像器２３１Ｋ、Ｃ現像器２３１Ｃ、Ｍ現像器２３１Ｍ及びＹ現像器２３１Ｙと、各現像器を矢印の反時計方向に回転させる後述のリボルバ回転駆動部などで構成されている。各現像器は図１２の現像器４に相当するもので、静電潜像を現像するために現像剤の穂を感光体ドラム２０の表面に接触させて回転する現像スリーブと、現像剤を汲み上げて攪拌するために回転する現像剤パドルなどで構成されている。各現像器２３１内のトナーはフェライトキャリアとの攪拌によって負極性に帯電され、また、各現像スリーブには不図示の現像バイアス電源によって負の直流電圧Ｖｄｃに交流電圧Ｖａｃが重畳された現像バイアスが印加され、現像スリーブが感光体ドラム２０の金属基体層に対して所定電位にバイアスされている。複写機本体の待機状態では、リボルバ現像ユニット２３はＢｋ現像器２３１Ｋが現像位置にセットされており、コピー動作が開始されると、カラースキャナ１１で所定のタイミングからＢｋカラー画像データの読み取りが開始され、このカラー画像データに基づいてレーザー光による光書き込み、静電潜像形成が始まる（以下、Ｂｋ画像データによる静電潜像をＢｋ潜像という。Ｃ、Ｍ、Ｙについても同様）。このＢｋ潜像の先端部から現像可能とすべくＢｋ現像位置に静電潜像先端部が到達する前にＢｋ現像スリーブを回転開始しておいて、Ｂｋ潜像をＢＫトナーで現像する。Ｂｋ潜像領域の現像動作が続いて、静電潜像後端部がＢｋ現像位置を通過した時点で、速やかに次の色の現像器（本例では通常Ｃ現像器）が現像位置にくるまで、リボルバ現像ユニット２３が回転する。これは少なくとも、次の画像データによる静電潜像先端部が到達する前に完了する。
【００５７】
上記中間転写装置２６は、中間転写ベルト２６１、ベルトクリーニング装置２６２、紙転写コロナ放電器（以下、紙転写器という）２６３などで構成されている。中間転写ベルト２６１は駆動ローラ２６４ａ、転写対向ローラ２６４ｂ、クリーニング対向ローラ２６４ｃ及び従動ローラ群に張架されており、不図示の駆動モータにより、駆動制御される。またベルトクリーニング装置２６２は、入口シール、ゴムブレード、排出コイル、入口シール及びゴムブレードの接離機構等で構成されており、１色目のＢｋ画像を中間転写ベルト２６１に転写した後の２、３、４色目の画像をベルト転写している間は接離機構によって中間転写ベルト２６１の表面から入口シール、ブレードを離間させておく。また紙転写器２６３は、コロナ放電方式にてＡＣ電圧＋ＤＣ電圧、又はＤＣ電圧を印加して、中間転写ベルト２６１上の重ねトナー像を記録紙に一括転写する。
【００５８】
また、カラープリンタ１２内の記録紙カセット２０７及び給紙バンク１３内の記録紙カセット３０ａ，３０ｂ，３０ｃには、各種サイズの記録紙が収納されており、指定されたサイズの記録紙のカセットから、給紙コロ２８，３１ａ，３１ｂ，３１ｃによってレジストローラ対２９方向に給紙、搬送される。また、プリンタ１２の図で見て右側面には、ＯＨＰ用紙や厚紙などの手差し給紙用の手差しトレイ２１が設けられている。
【００５９】
上記構成のカラー複写機において、画像形成サイクルが開始されると、まず感光体ドラム２０は矢印の反時計方向に、中間転写ベルト２６１は矢印の時計回りに不図示の駆動モータによって回転される。中間転写ベルト２６１の回転に伴ってＢｋトナー像形成、Ｃトナー像形成、Ｍトナー像形成、Ｙトナー像形成が行われ、最終的にＢｋ、Ｃ、Ｍ、Ｙの順に中間転写ベルト２６１上に重ねてトナ−像が形成される。
【００６０】
上記Ｂｋトナー像形成は次のように行なわれる。帯電器２０３はコロナ放電によって感光体ドラム２０を負電荷で約−７００Ｖに一様帯電する。そして、半導体レーザー２２１はＢｋカラー画像信号に基づいてラスタ露光を行う。このラスタ像が露光されたとき、当初一様荷電された感光体ドラム２０の露光部分は、露光光量に比例する電荷が消失し、Ｂｋ潜像が形成される。そして、このＢｋ潜像にＢｋ現像スリーブ上の負帯電のＢｋトナーが接触することにより、感光体ドラム２０の電荷が残っている部分にはトナーが付着せず、電荷の無い部分、つまり露光された部分にはＢｋトナーが吸着され、静電潜像と相似なＢｋトナー像が形成される。そして、感光体ドラム２０上に形成されたＢｋトナー像は、感光体ドラム２０と接触状態で等速駆動している中間転写ベルト２６１の表面に、ベルト転写器２６５によって転写される（以下、感光体ドラム２０から中間転写ベルト２６１へのトナー像転写をベルト転写という）。
【００６１】
感光体ドラム２０上の若干の未転写残留トナーは、感光体ドラム２０の再使用に備えて感光体クリーニング装置２０１で清掃される。ここで回収されたトナーは回収パイプを経由して不図示の排トナータンクに蓄えられる。
【００６２】
感光体ドラム２０側ではＢｋ画像形成工程の次にＣ画像形成工程に進み、所定のタイミングでカラースキャナ１１によるＣ画像データ読み取りが始まり、そのＣ画像データによるレーザー光書き込みで、Ｃ潜像形成が行われる。そして、先のＢｋ潜像の後端部が通過した後で、かつＣ潜像の先端部が到達する前にリボルバー現像ユニット２３の回転動作が行なわれ、Ｃ現像器２３１Ｃが現像位置にセットされてＣ潜像がＣトナーで現像される。Ｃ潜像領域の現像が続いて、Ｃ潜像の後端部が現像位置を通過した時点で、先のＢｋ現像器２３１Ｂの場合と同様にリボルバー現像ユニット２３の回転動作がなされ、次のＭ現像器２３１Ｍを現像位置に移動させる。これもやはり次のＭ潜像の先端部が現像位置に到達する前に完了させる。
【００６３】
なお、Ｍ及びＹの画像形成工程については、それぞれのカラー画像データ読み取り、静電潜像形成、現像の動作が上述のＢｋ、Ｃの工程と同様であるので説明を省略する。
【００６４】
上記中間転写ベルト２６１には、感光体ドラム２０に順次形成されるＢｋ、Ｃ、Ｍ、Ｙのトナー像を、同一面に順次位置合わせして、４色重ねのトナー像が形成され、次の転写工程において、この４色のトナー像が記録紙に紙転写器２６３により一括転写される。
【００６５】
上記画像形成動作が開始される時期に、記録紙は上記記録紙カセット又は手差しトレイのいずれかから給送され、レジストローラ対２９のニップで待機している。そして、紙転写器２６３に中間転写ベルト２６１上のトナー像先端がさしかかるときに、ちょうど記録紙の先端がこのトナー像の先端に一致するようにレジストローラ対２９が、駆動され、記録紙とトナー像とのレジスト合わせが行われる。そして、記録紙が中間転写ベルト２６１上のトナー像と重ねられて正電位の紙転写器２６３の上を通過する。このときコロナ放電電流で記録紙が正電荷で荷電され、トナー画像が記録紙上に転写される。続いて紙転写器２６３の図で見て左側に配置されるべき不図示のＡＣ＋ＤＣコロナによる分離除電器との対向部を通過するときに、記録紙は除電され、中間転写ベルト２６１から剥離して搬送ベルト２１１に移る。
【００６６】
そして、中間転写ベルト２６１面から４色重ねトナー像を一括転写された記録紙は、搬送ベルト２１１で定着装置２７に搬送され、所定温度に制御された定着ローラ２７１と加圧ローラ２７２のニップ部でトナー像が溶融定着され、排出ローラ対３２で装置本体外に送り出され、不図示のコピートレイに表向きにスタックされ、フルカラーコピーを得る。
【００６７】
一方、ベルト転写後の感光体ドラム２０の表面は、感光体クリーニング装置２０１（ブラシローラ、ゴムブレード）でクリーニングされ、除電ランプ２０２で均一に除電される。また、記録紙にトナー像を転写した後の中間転写ベルト２６１の表面は、ベルトクリーニング装置２６２のブレードを再びブレード接離機構で押圧することによってクリーニングされる。
【００６８】
以上、本発明を図示の実施形態により説明したが、本発明はこれに限定されるものではない。例えば、現像装置の現像ローラ以外の部分の構成は、適宜変更することができる。もちろん、現像装置が装着される画像形成装置の構成、例えば作像部の構成等は任意な構成とすることができる。
【００６９】
【発明の効果】
以上説明したように、本発明によれば、着磁された円筒状マグネットロールの現像極部分の磁気波形における磁束密度ピークの開き角度であるピーク幅が、高磁力マグネットブロックの磁気波形における磁束密度ピークの開き角度であるピーク幅以下であるので、現像極の磁気波形において半値幅の狭幅化が達成でき、現像ニップ幅を小さくすることが可能となり、したがって、高品質な画像を得るために必要な特性を持った現像ローラを簡単な構成で低コストに実現することができる。
【００７０】
請求項２の構成により、円筒状マグネットロールの現像極の極性とマグネットブロックの極性が同一であるので、現像極部における磁束密度が両者の和となり、大きな磁束密度を得ることができる。
【００７１】
請求項３の構成により、高磁力マグネットブロックが異方性のＮｄ−Ｆｅ−Ｂ系材料からなるので、半値幅を狭くした場合でも高い磁束密度を得ることができ、また、脆さ・成型性の面で改良されたマグネットブロックとすることができる。
【００７２】
請求項４の構成により、高磁力マグネットブロックが異方性のＳｍ−Ｆｅ−Ｎ系材料からなるので、半値幅を狭くした場合でも高い磁束密度を得ることができ、また、脆さ・成型性の面で改良されたマグネットブロックとすることができる。
【００７３】
請求項５の現像装置により、高品質な画像を得るために必要な特性を持った現像ローラを備えるので、全濃度域に渡って良質な画像を得ることのできる現像装置を低コストに提供することができる。
【００７４】
請求項６の画像形成装置により、高品質な画像を得るために必要な特性を持った現像ローラを備えた現像装置を有することにより、全濃度域にわたって良質な画像を得ることのできる画像形成装置を提供することができる。
【図面の簡単な説明】
【図１】溝付きマグローラの一例を示す斜視図である。
【図２】そのフェライトマグローラの磁気波形を示す模式図である。
【図３】そのマグローラに埋め込んだ希土類マグネットブロックによる磁気波形を示す模式図である。
【図４】フェライトマグローラと希土類マグネットブロックからなる磁石ローラ体の磁気波形を示す模式図である。
【図５】現像極部のピーク幅を説明するための模式図である。
【図６】磁石ローラ体の試作例における磁気波形を示す模式図である。
【図７】着磁条件を変えた他の試作例における磁気波形を示す模式図である。
【図８】着磁条件を変えた更に他の試作例における磁気波形を示す模式図である。
【図９】現像極の半値幅を説明するための模式図である。
【図１０】フェライトマグロールの一例を示す断面図である。
【図１１】フェライトマグロールの他の例を示す断面図である。
【図１２】本発明に係る現像ローラを備える現像装置の断面構成図である。
【図１３】その現像装置における現像領域での現像ギャップやニップの大きさを示す模式図である。
【図１４】従来の現像装置における現像領域での現像ギャップやニップの大きさを示す模式図である。
【図１５】本発明に係る画像形成装置の全体構成を示す断面図である。
【符号の説明】
４ 現像装置
２０ 感光体ドラム（潜像担持体）
４１ 現像ローラ
４５ 現像スリーブ(現像剤担持体)
５０ 磁石ローラ体
５１ フェライトマグロール（円筒状マグネットロール）
５４ 希土類マグネットブロック（高磁力のマグネットブロック）[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an image forming apparatus such as a copying machine, a printer, and a facsimile, a developing device, and a developing roller.
[0002]
[Prior art]
In electrophotographic and other image forming methods using powder toner, magnetic brush development using a two-component developer is well known and widely used in image forming apparatuses such as copying machines, printers and facsimiles.
[0003]
In magnetic brush development, the developer is transported to the surface of the developer carrier, the developer is held in a brush shape (magnetic brush) and brought into contact with the image carrier, and an image carrier on which an electrostatic latent image is formed The toner is selectively attached to the latent image surface by an electric field between the sleeve to which an electrical bias is applied and development is performed.
[0004]
The developer carrier is usually configured as a cylindrical sleeve (developing sleeve), and a magnet body (magnet roller) that forms a magnetic field so as to cause the developer to rise on the sleeve surface is provided inside the sleeve. ing. At the time of spike, the carrier is spiked on the sleeve so as to follow the lines of magnetic force generated by the magnet roller, and charged toner is attached to the carrier related to the spike. The magnet roller has a plurality of magnetic poles, and the magnets forming the respective magnetic poles are configured in a rod shape or the like, and includes a developing main magnetic pole (developing pole) that raises the developer particularly in the developing region portion of the sleeve surface. ing. When at least one of the sleeve and the magnet roller moves, the developer that has risen on the surface of the sleeve moves, and the developer conveyed to the development area follows the magnetic lines generated from the development pole. The developer chain spike comes into contact with the surface of the latent image carrier so as to bend, and the developer developer chain spike rubs against the electrostatic latent image based on the relative linear velocity difference from the latent image carrier. The toner is supplied while matching. The developing area is a range in which the magnetic brush rises on the developer carrier and is in contact with the latent image carrier.
[0005]
In the conventional magnetic brush developing device, the developing conditions for increasing the image density and the developing conditions for obtaining a low-contrast image are not compatible, and both the high density portion and the low density portion are improved at the same time. Is difficult. That is, the development conditions for increasing the image density include (i) narrowing the development gap, which is the distance between the latent image carrier and the development sleeve, or (ii) widening the development area width. It is done. On the other hand, development conditions for obtaining a low-contrast image favorably include (i ′) widening the development gap or (ii ′) narrowing the development region width. That is, both development conditions are opposite and are incompatible, and it is generally difficult to obtain a good image by satisfying both conditions over the entire density range.
[0006]
For example, when importance is attached to a low-contrast image, an abnormal image called so-called “rear end white spot” is likely to occur. In addition, a phenomenon has occurred in which a horizontal line of a grid image formed with the same width becomes thinner than a vertical line, or a small dot image such as one dot is not developed.
[0007]
To satisfy the development conditions for increasing the image density and the development conditions for obtaining a low-contrast image, which have been problems in the past, at high points in time, and to obtain a high-quality image over the entire density range The present applicant has previously proposed a developing method and a developing device (Japanese Patent Application No. 2000-29637).
[0008]
[Problems to be solved by the invention]
In the developing device previously proposed by the applicant of the present application, the developing pole portion of the developing roller has a narrower pole angle than the conventional developing roller (the half width of the developing pole in the conventional two-component development: about 50 degrees). Therefore, high magnetic properties are required for the magnet material. Further, the accuracy of the main pole portion is required to be higher than that of the conventional developing roller (± 1 degree compared to the conventional ± 2 degrees). As shown in FIG. 9, the half-value width is an angular width of a portion indicating a half value of the magnetic flux density Br in the normal direction of the developing roller.
[0009]
A ferrite magnet generally used in a conventional developing device cannot obtain a large magnetic flux density with a narrow half-value width. A magnet made of a rare earth element can obtain a large magnetic flux density, but is expensive. Therefore, as a practical magnet configuration of the developing roller, a rare earth magnet is used only for the main developing pole portion that requires high magnetic characteristics, and a ferrite magnet is used for the other poles.
[0010]
JP-A-2-222109 discloses an isotropic rare earth element R—Fe—B system for a magnet roll (ferrite mag roll) made of a ferrite material formed in a cylindrical shape as shown in FIGS. A magnet roll in which a magnet block formed of magnetic powder and a binding material is embedded is disclosed.
[0011]
However, in the magnet roll configured as described in the above publication, it is difficult to realize the condition that the development electrode has a half-value width of 20 degrees or less and the accuracy of the main electrode part ± 1 degree in order to obtain a high-quality image. There was a problem that there was.
[0012]
SUMMARY OF THE INVENTION It is an object of the present invention to solve the above-mentioned problems and to provide a developing roller having high magnetic properties and high accuracy of a main pole portion and a developing device capable of obtaining a high-quality image over the entire density range at low cost. And
[0013]
It is also an object of the present invention to provide an image forming apparatus that can obtain a high-quality image over the entire density range.
[0014]
[Means for Solving the Problems]
According to the present invention, there is provided a developing roller having a magnet roller body disposed inside a non-magnetic sleeve, wherein the magnet roller body is a cylindrical magnet roll formed by mixing magnetic powder and a polymer compound. , a cylindrical magnet roll development pole portions are magnetized, at least one pole or more high magnetic force magnet block disposed in a portion corresponding to the developing pole of the cylindrical magnet roll were the magnetized peak width is the opening angle of the magnetic flux density peak in the magnetic waveform of the development pole portion of the cylindrical magnet roll is solved by the at peak width less is the opening angle of the magnetic flux density peak in the magnetic waveform of a magnet block.
[0015]
In order to solve the above problems, the present invention proposes that the polarity of the developing pole of the cylindrical magnet roll is the same as the polarity of the magnet block.
[0016]
Moreover, in order to solve the said subject, this invention proposes that the said magnet block consists of anisotropic Nd-Fe-B type material.
Moreover, in order to solve the said subject, this invention proposes that the said magnet block consists of anisotropic Sm-Fe-N type material.
[0017]
Moreover, the said subject is solved by the developing apparatus provided with the developing roller of any one of Claims 1-4.
Further, the above problem is solved by an image forming apparatus provided with the developing device according to claim 5.
[0018]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
First, a magnet roller body having a configuration in which a rare earth magnet is used for the developing pole and a ferrite magnet is used for the other poles will be described.
[0019]
FIG. 1 is a perspective view showing a grooved magnet roller obtained by extrusion molding. A mag roller 51 shown in this figure is a magnet roll made of a ferrite-based material, and a groove 52 is formed in a portion corresponding to a developing pole. A rare earth magnet block, which will be described later, is embedded in the groove 52. Reference numeral 53 denotes a core bar of the mag roller 51.
[0020]
The magnet roller 51 is magnetized with a yoke to obtain a desired magnetic waveform (magnetic force distribution). An example of the obtained magnetic waveform is shown in FIG.
FIG. 3 shows a magnetic waveform by a rare earth magnet block embedded in the mag roller. A rod-shaped magnet block 54 made of a rare earth element is fitted in the groove 52 of the mag roller 51. In this figure, a magnetic waveform by only the magnet block 54 is shown. As can be seen from this magnetic waveform, the magnetic force distribution of the rare earth magnet is pointed and produces a large magnetic flux density with a narrow half-value width.
[0021]
FIG. 4 shows a magnetic waveform finally obtained by a magnet roller body 50 in which a rare earth magnet block 54 is embedded in a magnet roller 51 made of a ferrite material. In FIG. 4, the magnetic waveform of the developing pole portion of the magnet roller body 50 composed of the magnet roller 51 and the magnet block 54 is indicated by a solid line in the figure. The results of obtaining the magnetic flux density and the half width from these magnetic waveforms are shown in Table 1 below.
[0022]
[Table 1]

[0023]
As shown in Table 1, the magnetic flux density of the developing pole portion only by the mag roller 51 is 50 mt, and the half width is 37 degrees. The magnetic flux density by the rare earth magnet block 54 is 60 mt, and the half width is 17 degrees. The magnetic flux density at the developing pole portion of the magnet roller body 50 is 110 mt and the full width at half maximum is 25 degrees. From this result, it was found that the magnetic flux density at the developing pole portion of the magnet roller body 50 has a relationship of mag roller 51 + magnet block 54. Therefore, in order to achieve a high magnetic force of the magnet roller body as in the present invention, the polarity of the developing pole of the ferrite magnet roller and the polarity of the rare earth magnet block are made the same, and the desired magnetic flux density is obtained by increasing the magnetic force of each. Can do.
[0024]
On the other hand, even if the magnet block 54, which is a rare earth magnet, has a steep waveform, the half-value width is greatly influenced by the magnet roller 51 of the ferrite magnet serving as the base (base), and therefore the half-value width is larger than the half-value width of the magnet block 54 alone. It became large and it turned out that the half value width of 20 degrees or less made into a subject cannot be achieved.
[0025]
Therefore, the inventors of the present application have studied the magnetization conditions of the ferrite mag roller as a base, and attempted to narrow the peak width (bottom portion) of the developing pole portion. That is, by changing the magnetizing yoke width or shifting the position of the magnetizing yoke in the magnetizing process, the peak width is narrowed to reduce the half-value width. As shown in FIG. 5, the peak width of the developing pole portion means the width of the bottom portion of the magnetic waveform in the developing pole portion, that is, the opening angle of the magnetic flux density peak.
[0026]
Next, FIG. 6 to FIG. 8 show magnetic waveform diagrams of the magnet roller body made by the inventors of the present application as a prototype. The configuration of each magnet roller body is the same as that described with reference to FIGS. 1 to 4, in which a rare earth magnet block 54 is embedded in a grooved ferrite magnet roller 51 which is a cylindrical base roller. Each of the magnet roller bodies of FIGS. 5 to 7 uses the same rare earth magnet block 54, and the magnetizing conditions of the ferrite magnet roller 51 (magnetizing conditions of the developing pole portion) are different.
[0027]
6 to 8, the magnetic waveform of the development pole portion of the ferrite mag roller 51 is shown with a grid, but by reducing the peak width of the development pole portion of the mag roller 51, the magnetic roller body It can be seen that the sharpness of the magnetic waveform (shown by a solid line in the figure) of the developing pole is improved.
[0028]
The peak width and magnetic flux density of the ferrite magnet roller 51 and the magnet block 54 at the developing pole in each magnet roller body, and the magnetic flux density and the half-value width of the developing pole as the magnet roller body are shown in Table 2 below.
[0029]
[Table 2]

[0030]
In Table 2, the magnetization conditions of the developing pole portion of the ferrite mag roller 51 are three conditions of A, B, and C: a magnetic flux density of 40 mT at a peak width of 50 degrees, a magnetic flux density of 20 mT at a peak width of 30 degrees, and a peak width of 10 The magnetic flux density is 4 mT. The peak width and magnetic flux density of the rare earth magnet block 54 are the same 30 degrees and 72 mT in all three conditions.
[0031]
Due to the magnetizing conditions A, B, and C of the developing pole portion of the mag roller 51, the magnetic flux density and half-value width of the developing pole as the magnet roller body 50 are 25 degrees at 115 mT, 20 degrees at 95 mT, and 18 degrees at 78 mT, respectively. It was. From this result, by changing the magnetization condition of the developing pole portion of the ferrite mag roller 51 and reducing the peak width of the mag roller developing pole portion, the half width of the magnet roller body developing pole is also reduced, and the target half width is reached. It has been found that in order to achieve 20 degrees or less, the peak width of the developing pole portion of the ferrite mag roller 51 needs to be equal to or less than the peak width of the rare earth magnet block 54.
[0032]
The rare earth magnet blocks 54 are all made of the same material, and are made of an isotropic Nd—Fe—B-based material having a width of 2 mm, a height (normal direction) of 2.5 mm, and a length of 300 mm. The gap between the measurement probe and the magnet surface was 1.0 mm.
[0033]
On the other hand, as can be seen from Table 2, the magnetic flux density of the developing pole as the magnet roller body decreases as the magnetic flux density of the mag roller 51 decreases. As a result, under the magnetizing condition C, the developing pole magnetic flux density as the magnet roller body is 78 mT, and the target 80 mT cannot be achieved (the half width is cleared to 18 degrees).
[0034]
Therefore, the magnetic force of the rare earth magnet block is further required when the full width at half maximum of the magnet roller body development pole is less than 20 degrees by reducing the peak width of the mag roller development pole.
[0035]
The rare earth magnet Nd—Fe—B material used in this experiment is a material having a maximum energy product (BH) max of 64 kJ / m ³ (8.0 MGOe), but even higher energy materials are isotropic Nd— Among Fe-B materials, it is marketed. However, since these materials have increased the magnetic powder content to achieve high magnetic force, the materials have poor flexibility, are weak against external stress, and are brittle materials that are very fragile.
[0036]
When used as a magnet block of a magnet roller body in a developing roller, it has a rod shape with a width of 1.0 to 2 mm, a height of 2 to 3 mm, and a length of 300 to 310 mm, and is more easily broken. Therefore, a material having a higher magnetic force than isotropic Nd—Fe—B is required.
[0037]
As a result of earnest examination of magnetic properties, brittleness, moldability, etc. in search of materials with higher magnetic force, two types of materials, anisotropic Nd-Fe-B-based materials and anisotropic Sm-Fe-N-based materials Is more than isotropic Nd-Fe-B system.
[0038]
An anisotropic Nd—Fe—B-based material has (BH) max of about 12 MGOe, which is a magnetic force 1.5 times that of an isotropic Nd—Fe—B system. Since the blending ratio of the magnetic powder can be lowered, the flexibility of the plastic material is maintained and it is difficult to break (Nylon 12 is used as the binder).
[0039]
Next, the anisotropic Sm—Fe—N-based material has (BH) max of about 9.5 MGOe, which is 1.2 times the magnetic force of the isotropic Nd—Fe—B system. Since the blending ratio of the magnetic powder can be lowered, the flexibility of the plastic material is maintained and it is difficult to break (the rubber material is used as the binder).
[0040]
The results of evaluating these two types of materials with the magnet roller body under the above-mentioned magnetization condition C are shown in Table 3 below.
[0041]
[Table 3]

[0042]
The rare earth magnet blocks comparatively examined here were all measured with a width of 2 mm, a height of 2.5 mm (magnetization direction), a length of 300 mm, and a gap between the measurement probe and the magnet surface of 1.0 mm.
[0043]
Thus, by using an anisotropic Nd—Fe—B-based material and an anisotropic Sm—Fe—N-based material as the magnet block 54, even if the half-value width is narrowed to 20 ° or less, 80 mT or more. The magnetic flux density can be obtained.
[0044]
In the above description, the rare earth magnet block 54 in the developing pole portion is one pole (one piece), but a plurality of poles (a plurality) may be provided. In that case, the peak width of the developing pole portion of the ferrite mag roller 51 may be equal to or less than the peak width of the entire plurality of rare earth magnet blocks.
[0045]
Next, a developing device including the developing roller incorporating the magnet roller body as described above will be described.
FIG. 12 is a cross-sectional configuration diagram of a developing device including the developing roller according to the present invention. As shown in this figure, a developing roller 41, which is a developer carrying member, is disposed in the developing device 4 so as to be close to the photosensitive drum 20 of the image forming apparatus. A developing region where the body drum and the magnetic brush come into contact is formed. In the developing roller 41, a developing sleeve 43 formed of a nonmagnetic material such as aluminum, brass, stainless steel, or conductive resin in a cylindrical shape is rotated clockwise in the drawing by a rotation driving mechanism (not shown). Yes. In the present embodiment, the developing gap, which is the distance between the photosensitive drum 20 and the developing sleeve 43, is set to 0.4 mm. The development gap has conventionally been set to about 0.65 mm to 0.8 mm.
[0046]
A doctor blade 45 that regulates the height of the developer chain spike, that is, the amount of developer on the developing sleeve, is installed on the upstream side of the developing area in the developer transport direction (clockwise as viewed in the figure). ing. The doctor gap, which is the distance between the doctor blade 45 and the developing sleeve 43, is set to 0.4 mm. Further, a screw 47 for pumping up the developer in the developing device casing 46 to the developing roller 41 while stirring the developer is installed in a region opposite to the photosensitive drum of the developing roller.
[0047]
In the sleeve 43 of the developing roller, a magnet roller body (magnet roller) 50 that forms a magnetic field so as to cause the rising of the developer on the peripheral surface of the developing sleeve 43 is provided in a fixed state. The magnet roller body 50 is obtained by embedding a rare earth magnet block in a ferrite magnet roller as described above. As the magnet block, an anisotropic Nd—Fe—B-based material or an anisotropic Sm—Fe—N-based material is used, and a magnetic flux density of 80 mT or more can be obtained at a half-value width of 20 ° or less. Is. The developer carrier rises in a chain shape on the developing sleeve 43 so as to follow the normal direction magnetic line of force generated from the magnet roller body, and the charged toner adheres to the carrier that has the chain shape. Thus, a magnetic brush is configured. The magnetic brush is transferred in the same direction as the developing sleeve 43 (clockwise as viewed in the figure) by the rotation of the developing sleeve 43.
[0048]
The magnet roller body 50 has a plurality of magnetic poles. A developing pole for causing the developer to rise in the developing area by the rare earth magnet block 54, a pumping pole for pumping the developer onto the sleeve 43 opposite to the screw 47, and the developer thus pumped up to the developing area. And a magnetic pole for transporting the developer in the post-development region.
[0049]
When developing the toner image (toner image with a small amount of adhesion) on the photoconductor having a low image density, when the magnetic brush of this embodiment is used, the development nip width is small, so that the photoconductor is rubbed. The amount of contact (time) of the magnetic brush to be reduced decreases, and the amount of counter charge generated at the tip of the magnetic brush decreases. As a result, it is possible to suppress the phenomenon that the rear end portion of the image is whitened due to the carrier having the counter charge attracting the toner image. Therefore, it is possible to improve the reproducibility of the toner image (toner image with a small amount of adhesion) on the photoreceptor having a low image density.
[0050]
In addition, the image density is increased because the length of the magnetic brush of the developing pole is reduced, and the width of the developing nip can be reduced. Therefore, the developing sleeve is rotated and moved, and is shortened when passing through the developing pole. Since the magnetic brush starts standing and the time required to pass between the development nips is shortened (a phenomenon in which the linear velocity ratio to the photosensitive member is accelerated only in this portion), the amount of developer that rubs against the photosensitive member increases. The image density increases. Furthermore, since the developing nip width is small, the amount of developer in the developer retaining portion in front of the developing nip area is small, and it is possible to suppress the occurrence of counter charge, so that it is possible to suppress a decrease in image density. It is possible to provide a developing device with improved image capability without white spots.
[0051]
FIG. 13 shows an image of a developing area in the developing device of this embodiment, and FIG. 14 shows a conventional example.
Finally, the application of the present invention will be described by extending to an electrophotographic color copying apparatus (hereinafter referred to as a color copying machine). A schematic configuration and operation of the color copying machine will be described with reference to FIG. The color copying machine includes a color image reading device (hereinafter referred to as a color scanner) 11, a color image recording device (hereinafter referred to as a color printer) 12, a paper supply bank 13, and the like.
[0052]
The color scanner 11 forms an image of the document 10 on the contact glass 101 on the color sensor 105 via the illumination lamp 102, the mirror groups 103a, 103b, and 103c and the lens 104, and the color image information of the document 10 is obtained. For example, red, green, and blue (hereinafter referred to as R, G, and B) color separation lights are read and converted into electrical image signals. In this example, the color sensor 105 includes R, G, and B color separation means and a photoelectric conversion element such as a CCD, and simultaneously reads three color images obtained by color separation of the image of the document 10. . Then, based on the R, G, and B color separation image signal intensity levels obtained by the color scanner 11, color conversion processing is performed by an image processing unit (not shown) to obtain black (hereinafter referred to as Bk), cyan (hereinafter referred to as “Bk”). , C), magenta (hereinafter referred to as M), and yellow (hereinafter referred to as Y) color image data.
[0053]
The operation of the color scanner 11 for obtaining the Bk, C, M, and Y color image data is as follows. In response to a scanner start signal that takes the operation and timing of the color printer 12 to be described later, the optical system including the illumination lamp 102 and the mirror groups 103a, 103b, and 103c scans the document 10 in the left direction of the arrow, and scans once. One color image data is obtained every time. By repeating this operation a total of four times, color image data of four colors is sequentially obtained. Each time, the color printer 12 sequentially visualizes the images and superimposes them to form a final four-color full-color image.
[0054]
The color printer 12 includes a photosensitive drum 20 as an image carrier, a writing optical unit 22, a revolver developing unit 23, an intermediate transfer device 26, a fixing device 27, and the like. The photosensitive drum 20 rotates counterclockwise as indicated by an arrow, and around the photosensitive drum cleaning device 201, the charge eliminating lamp 202, the charger 203, the potential sensor 204, the selected developer of the revolver developing unit 23, and the development A density pattern detector 205, an intermediate transfer belt 261 of the intermediate transfer device 26, and the like are arranged.
[0055]
Further, the writing optical unit 22 converts the color image data from the color scanner 11 into an optical signal, performs optical writing corresponding to the image of the document 10, and forms an electrostatic latent image on the photosensitive drum 20. The writing optical unit 22 includes a semiconductor laser 221 as a light source, a laser light emission drive control unit (not shown), a polygon mirror 222 and its rotation motor 223, an f / θ lens 224, a reflection mirror 225, and the like.
[0056]
The revolver developing unit 23 includes a Bk developing unit 231K, a C developing unit 231C, an M developing unit 231M, and a Y developing unit 231Y, and a revolver rotation driving unit described below that rotates each developing unit counterclockwise as indicated by an arrow. It is configured. Each developing device corresponds to the developing device 4 in FIG. 12, and in order to develop an electrostatic latent image, a developing sleeve that rotates with the ears of the developer in contact with the surface of the photosensitive drum 20, and the developer is pumped up. And a developer paddle that rotates for stirring. The toner in each developing device 231 is negatively charged by stirring with a ferrite carrier, and each developing sleeve has a developing bias in which an AC voltage Vac is superimposed on a negative DC voltage Vdc by a developing bias power source (not shown). The developing sleeve is biased to a predetermined potential with respect to the metal base layer of the photosensitive drum 20 when applied. In the standby state of the copying machine main body, the revolver developing unit 23 has the Bk developing unit 231K set at the developing position, and when the copying operation is started, the color scanner 11 starts reading Bk color image data from a predetermined timing. Then, based on the color image data, optical writing with a laser beam and formation of an electrostatic latent image start (hereinafter, an electrostatic latent image based on Bk image data is referred to as a Bk latent image. The same applies to C, M, and Y). The Bk developing sleeve is started to rotate before the leading edge of the electrostatic latent image reaches the Bk developing position so that the leading edge of the Bk latent image can be developed, and the Bk latent image is developed with BK toner. When the developing operation of the Bk latent image area continues and the trailing edge of the electrostatic latent image passes the Bk developing position, the developing device for the next color (normally the C developing device in this example) immediately comes to the developing position. Until the revolver developing unit 23 rotates. This is completed at least before the leading edge of the electrostatic latent image by the next image data arrives.
[0057]
The intermediate transfer device 26 includes an intermediate transfer belt 261, a belt cleaning device 262, a paper transfer corona discharger (hereinafter referred to as a paper transfer device) 263, and the like. The intermediate transfer belt 261 is stretched around a drive roller 264a, a transfer counter roller 264b, a cleaning counter roller 264c, and a driven roller group, and is driven and controlled by a drive motor (not shown). The belt cleaning device 262 includes an inlet seal, a rubber blade, a discharge coil, an inlet seal, a rubber blade contact / separation mechanism, and the like. The belt cleaning device 262 is a few after the first color Bk image is transferred to the intermediate transfer belt 261. While the image of the fourth color is being transferred onto the belt, the entrance seal and the blade are separated from the surface of the intermediate transfer belt 261 by the contact / separation mechanism. The paper transfer unit 263 applies an AC voltage + DC voltage or a DC voltage by a corona discharge method, and collectively transfers the superimposed toner images on the intermediate transfer belt 261 onto the recording paper.
[0058]
The recording paper cassette 207 in the color printer 12 and the recording paper cassettes 30a, 30b, and 30c in the paper supply bank 13 store recording papers of various sizes. The paper is fed and conveyed in the direction of the registration roller pair 29 by the paper feed rollers 28, 31a, 31b, and 31c. Further, a manual feed tray 21 for manual paper feed such as OHP paper or thick paper is provided on the right side in the drawing of the printer 12.
[0059]
In the color copying machine having the above configuration, when an image forming cycle is started, first, the photosensitive drum 20 is rotated counterclockwise as indicated by an arrow, and the intermediate transfer belt 261 is rotated clockwise as indicated by an arrow by a drive motor (not shown). As the intermediate transfer belt 261 rotates, Bk toner image formation, C toner image formation, M toner image formation, and Y toner image formation are performed, and finally, on the intermediate transfer belt 261 in the order of Bk, C, M, and Y. Overlaid, a toner image is formed.
[0060]
The Bk toner image formation is performed as follows. The charger 203 uniformly charges the photosensitive drum 20 to about −700 V with a negative charge by corona discharge. The semiconductor laser 221 performs raster exposure based on the Bk color image signal. When this raster image is exposed, the charge proportional to the exposure light amount disappears in the exposed portion of the photosensitive drum 20 that is initially uniformly charged, and a Bk latent image is formed. When the negatively charged Bk toner on the Bk developing sleeve comes into contact with the Bk latent image, the toner does not adhere to the remaining portion of the photosensitive drum 20, and the portion without charge, that is, the exposed portion is exposed. The Bk toner is attracted to the portion, and a Bk toner image similar to the electrostatic latent image is formed. The Bk toner image formed on the photosensitive drum 20 is transferred by the belt transfer unit 265 to the surface of the intermediate transfer belt 261 that is driven at a constant speed in contact with the photosensitive drum 20 (hereinafter referred to as a photosensitive drum). Transfer of the toner image from the body drum 20 to the intermediate transfer belt 261 is referred to as belt transfer).
[0061]
Some untransferred residual toner on the photoconductor drum 20 is cleaned by the photoconductor cleaning device 201 in preparation for reuse of the photoconductor drum 20. The collected toner is stored in a waste toner tank (not shown) via a collection pipe.
[0062]
On the photosensitive drum 20 side, the process proceeds to the C image forming process after the Bk image forming process, and C image data reading by the color scanner 11 is started at a predetermined timing, and C latent image formation is performed by laser beam writing using the C image data. Done. Then, after the rear end portion of the previous Bk latent image passes and before the front end portion of the C latent image arrives, the revolver developing unit 23 is rotated, and the C developing unit 231C is set at the developing position. The C latent image is developed with C toner. When the development of the C latent image area is continued and the rear end of the C latent image passes the development position, the revolver developing unit 23 is rotated in the same manner as in the case of the previous Bk developing unit 231B, and the next M The developing device 231M is moved to the developing position. This is also completed before the leading edge of the next M latent image reaches the developing position.
[0063]
The description of the M and Y image forming steps will be omitted because the operations of reading color image data, forming an electrostatic latent image, and developing are the same as those in steps Bk and C described above.
[0064]
On the intermediate transfer belt 261, Bk, C, M, and Y toner images sequentially formed on the photosensitive drum 20 are sequentially aligned on the same surface to form a four-color superimposed toner image. In the transfer process, the four color toner images are collectively transferred to the recording paper by the paper transfer unit 263.
[0065]
At the time when the image forming operation is started, the recording paper is fed from either the recording paper cassette or the manual feed tray and is waiting at the nip of the registration roller pair 29. When the leading edge of the toner image on the intermediate transfer belt 261 approaches the paper transfer unit 263, the registration roller pair 29 is driven so that the leading edge of the recording paper coincides with the leading edge of the toner image, and the recording paper and toner Registration with the image is performed. Then, the recording paper is superimposed on the toner image on the intermediate transfer belt 261 and passes over the positive potential paper transfer device 263. At this time, the recording paper is charged with a positive charge by the corona discharge current, and the toner image is transferred onto the recording paper. Subsequently, the recording paper is neutralized and peeled off from the intermediate transfer belt 261 when passing through a portion facing a separation static eliminator by an AC + DC corona (not shown) that should be arranged on the left side in the drawing of the paper transfer unit 263. Move to conveyor belt 211.
[0066]
Then, the recording paper onto which the four-color superimposed toner images are collectively transferred from the surface of the intermediate transfer belt 261 is conveyed to the fixing device 27 by the conveying belt 211, and the nip portion between the fixing roller 271 and the pressure roller 272 controlled to a predetermined temperature. Then, the toner image is melted and fixed, sent out of the apparatus main body by the discharge roller pair 32, and stacked on the copy tray (not shown) so as to obtain a full color copy.
[0067]
On the other hand, the surface of the photosensitive drum 20 after the belt transfer is cleaned by the photosensitive member cleaning device 201 (brush roller, rubber blade), and is uniformly discharged by the discharging lamp 202. Further, the surface of the intermediate transfer belt 261 after the toner image is transferred to the recording paper is cleaned by pressing the blade of the belt cleaning device 262 again by the blade contact / separation mechanism.
[0068]
As mentioned above, although this invention was demonstrated by embodiment of illustration, this invention is not limited to this. For example, the configuration of parts other than the developing roller of the developing device can be changed as appropriate. Of course, the configuration of the image forming apparatus to which the developing device is mounted, for example, the configuration of the image forming unit, can be any configuration.
[0069]
【The invention's effect】
Magnetic flux density in the As described above, according to the present invention, magnetized peak width is the opening angle of the magnetic flux density peak in the magnetic waveform of the development pole portion of the cylindrical magnet roll, the magnetic waveform of the high magnetic force magnet block Since it is less than the peak width, which is the peak opening angle, it is possible to reduce the half-value width in the magnetic waveform of the development pole, and to reduce the development nip width, and thus to obtain a high-quality image. A developing roller having necessary characteristics can be realized at a low cost with a simple configuration.
[0070]
According to the second aspect of the present invention, since the polarity of the developing pole of the cylindrical magnet roll and the polarity of the magnet block are the same, the magnetic flux density in the developing pole portion is the sum of both, and a large magnetic flux density can be obtained.
[0071]
According to the configuration of claim 3, since the high magnetic force magnet block is made of an anisotropic Nd—Fe—B material, a high magnetic flux density can be obtained even when the half-value width is narrowed. The magnet block can be improved in terms of the above.
[0072]
According to the configuration of claim 4, since the high magnetic force magnet block is made of an anisotropic Sm—Fe—N-based material, a high magnetic flux density can be obtained even when the half-value width is narrowed, and brittleness and moldability are obtained. The magnet block can be improved in terms of the above.
[0073]
The developing device according to claim 5 is provided with a developing roller having characteristics necessary for obtaining a high-quality image. Thus, a developing device capable of obtaining a high-quality image over the entire density range is provided at low cost. be able to.
[0074]
7. An image forming apparatus capable of obtaining a high-quality image over the entire density range by including a developing device having a developing roller having characteristics necessary for obtaining a high-quality image by the image forming apparatus according to claim 6. Can be provided.
[Brief description of the drawings]
FIG. 1 is a perspective view showing an example of a grooved mag roller.
FIG. 2 is a schematic diagram showing a magnetic waveform of the ferrite mag roller.
FIG. 3 is a schematic diagram showing a magnetic waveform by a rare earth magnet block embedded in the mag roller.
FIG. 4 is a schematic diagram showing a magnetic waveform of a magnet roller body composed of a ferrite magnet roller and a rare earth magnet block.
FIG. 5 is a schematic diagram for explaining a peak width of a developing electrode portion.
FIG. 6 is a schematic diagram showing a magnetic waveform in a prototype of a magnet roller body.
FIG. 7 is a schematic diagram showing a magnetic waveform in another prototype with different magnetization conditions.
FIG. 8 is a schematic diagram showing a magnetic waveform in still another prototype with different magnetization conditions.
FIG. 9 is a schematic diagram for explaining a half width of a developing electrode.
FIG. 10 is a cross-sectional view showing an example of a ferrite mag roll.
FIG. 11 is a cross-sectional view showing another example of a ferrite mag roll.
FIG. 12 is a cross-sectional configuration diagram of a developing device including a developing roller according to the present invention.
FIG. 13 is a schematic diagram showing a development gap and a nip size in a development region in the developing device.
FIG. 14 is a schematic diagram showing the size of a development gap and a nip in a development region in a conventional development device.
FIG. 15 is a cross-sectional view showing an overall configuration of an image forming apparatus according to the present invention.
[Explanation of symbols]
4 Developing device 20 Photosensitive drum (latent image carrier)
41 Developing roller 45 Developing sleeve (developer carrier)
50 Magnet roller body 51 Ferrite mag roll (cylindrical magnet roll)
54 Rare earth magnet block (magnet block with high magnetic force)

Claims (6)

In the developing roller in which the magnet roller body is arranged inside the non-magnetic sleeve,
The magnet roller body is a cylindrical magnet roll formed by mixing magnetic powder and a polymer compound, and a cylindrical magnet roll having a developing pole portion magnetized, and a developing pole of the cylindrical magnet roll. Having a high magnetic force magnet block of at least one pole disposed in a corresponding part;
The peak width that is the opening angle of the magnetic flux density peak in the magnetic waveform of the developing pole portion of the magnetized cylindrical magnet roll is equal to or less than the peak width that is the opening angle of the magnetic flux density peak in the magnetic waveform of the magnet block. A developing roller characterized by.   The developing roller according to claim 1, wherein the polarity of the developing pole of the cylindrical magnet roll and the polarity of the magnet block are the same.   The developing roller according to claim 1, wherein the magnet block is made of an anisotropic Nd—Fe—B-based material.   The developing roller according to claim 1, wherein the magnet block is made of an anisotropic Sm—Fe—N-based material.   A developing device comprising the developing roller according to claim 1.   An image forming apparatus comprising the developing device according to claim 5.

Images