JP2004021095A

JP2004021095A - Method and device for development, and method and apparatus for image formation

Info

Publication number: JP2004021095A
Application number: JP2002178610A
Authority: JP
Inventors: Hajime Koyama; 小山　一
Original assignee: Ricoh Co Ltd
Current assignee: Ricoh Co Ltd
Priority date: 2002-06-19
Filing date: 2002-06-19
Publication date: 2004-01-22

Abstract

PROBLEM TO BE SOLVED: To provide a developing method by which an image of high quality having high image density at a solid part, no image damage (transfer omission, a fixation defect, etc.) due to carrier sticking, and good solid filling can be obtained by making large an area where a latent image is developed with toner by making the whole developer carrier contribute to development as a development area. SOLUTION: In the developing method characterized in that a developer carrier 111 having magnets inside is arranged opposite an image carrier 100 and the developer carrier 111 carries a two-component developer containing a toner T and a magnetic carrier MC and conveys the developer to development areas A to C formed with the image carrier and a magnetic brush is formed of a nap of the aggregated magnetic carrier having the toner on the surface in the development areas to develop the latent image formed on the image carrier with the toner of the magnetic brush, the latent image on the image carrier is developed in the development areas with a suspended toner separated from the magnetic carrier MC which has the toner on the surface and has residual magnetism (σ<SB>r</SB>) ≥10 emu/cm<SP>3</SP>. COPYRIGHT: (C)2004,JPO

Description

【０００１】
【発明の属する技術分野】
本発明は、電子写真方式の画像形成プロセスに用いられる現像方法、及びその現像方法を用いた現像装置、及びその現像装置を用いた画像形成方法、及び前記現像装置を備えた複写機、プリンタ、プロッタ、ファクシミリ等の画像形成装置に関する。
【０００２】
【従来の技術】
現在、複写機、プリンタ、プロッタ、ファクシミリ等の画像形成装置では、光導電性を有する感光層を表面に設けた像担持体（以下、「感光体」と記す）上に静電潜像を形成し、この静電潜像を、現像剤を収納した現像装置によって現像して可視像化し、この可視像をシート状の記録媒体に転写し定着して最終画像を得ている。
現像装置に収納される現像剤は、主にトナーと磁性キャリアによって構成される二成分現像剤（以下、単に「現像剤」と記す）が、カラー化が容易なことから広く用いられている。現像剤は、現像装置内の攪拌・混合により摩擦帯電され、この摩擦帯電された静電電荷によってトナーを磁性キャリア表面に静電的に付着させている。このトナーを付着させた磁性キャリアは、内部に磁石を配置した現像剤担持体（以下、「現像スリーブ」と記す）表面に磁力で引きつけられて担持され、回転する現像スリーブ上を現像領域に向けて搬送される。
【０００３】
現像スリーブの感光体に最近接する位置には、現像のための磁石（以下、「現像主磁石」と記す）が現像スリーブ内部に配置されている。搬送される現像剤が、この現像主磁石に近づくにつれて、現像主磁石の磁力線に沿って、現像剤中の多数の磁性キャリアが集合して穂またはチェーンを形成する。この多数の穂が、まるでブラシのように見えることから磁気ブラシと一般に呼称され、この磁気ブラシの状態を利用する現像方式が磁気ブラシ現像と呼称されている。この磁気ブラシ現像では、誘電体である磁性キャリアが、感光体と現像スリーブ間の電界強度を高めることで、磁気ブラシの穂の先端部を構成している磁性キャリアの表面からトナーが感光体表面へと移ることで静電潜像が現像されると考えられている。したがって、これまでは、この磁性キャリアが集合した穂によって形成される磁気ブラシがない部分は、トナーの現像に利用されていなかった。そのために、トナーが現像できる部位は限られた領域であったために、現像されるトナーを多くすることは、他の条件を調整する下では非常に困難であった。
【０００４】
しかしながら、この限られた領域の中で、高濃度の画像を得る現像方法が提案されている。例えば、特許第２６６８７８１号公報には、二成分現像剤を用いて、磁性粒子の穂に担持されたトナー粒子と現像剤担持体上に担持されたトナー粒子とを交番電界により現像する現像方法が提案されている。
また、特開２０００−２１４６３０号公報には、４０μｍ以下の小粒径で且つ磁化率も５０ｅｍｕ／ｇ以下と余り高くない磁性キャリアを用い、きめこまかいソフトタッチの磁気ブラシで高濃度でざらつき感の少ない高画質画像を得ることを狙った現像方法が開示されている。
【０００５】
【発明が解決しようとする課題】
しかし、上記従来技術の現像方法のうち、前者の現像方法では、現像領域は磁性粒子が摺擦している領域であり、この領域にある磁性粒子の穂に保持されたトナー粒子と現像剤担持体上のトナー粒子だけでは十分な高濃度の画像を得ることが困難である。また、磁性粒子の穂が少ないため電極効果によりソリッド部のベタ埋まりの良い滑らかな高品位の画像を得るのは困難である。また、後者の現像方法では、磁性キャリアが感光体に付着するというキャリア付着の問題がある。
【０００６】
本発明は上記事情に鑑みなされたものであり、現像剤担持体全体を現像領域として現像に寄与させることでトナーにより潜像が現像される領域を多くし、ソリッド部における画像濃度が高く、キャリア付着による画像ダメージ（例えば転写抜けや定着不良）がなく、かつ、ベタ埋まりの良い高品位の画像を得ることができる現像方法及び現像装置を提供することを課題とし、さらには、その現像装置を用い、高品位の画像を得ることができる画像形成方法及び画像形成装置を提供することを課題とする。
【０００７】
【課題を解決するための手段】
前記課題を解決するための手段として、請求項１に係る発明は、内部に磁石を有する現像剤担持体を像担持体に対向して配置し、この現像剤担持体でトナーと磁性キャリアとを含む二成分現像剤を担持して前記像担持体との間に形成される現像領域に搬送し、該現像領域内で、表面にトナーを有する磁性キャリアが集合した穂からなる磁気ブラシを形成し、該磁気ブラシの磁性キャリア表面から離脱した遊離トナーで前記像担持体上に形成された潜像を現像する現像方法において、前記磁性キャリアは、粒径が５〜１００μｍであり、磁性体含有量が３０重量％であり、磁気特性は、磁場１０００エルステッドにおける磁化の強さ（σ_１０００）が３０乃至１０００ｅｍｕ／ｃｍ^３であり、現像部の磁場を通過後、キャリアを消磁又は減磁する前の磁場０エルステッドにおける残留磁化（σ_ｒ）が１０ｅｍｕ／ｃｍ^３以上であることを特徴としており、残留磁化の大きな磁性キャリアを用いることにより、像担持体へのキャリア付着を防止すると同時に、トナーの帯電の立上げを改善することが可能となる。
【０００８】
請求項２に係る発明は、トナーを担持するトナー担持体を像担持体に対向して配置すると共に、内部に磁石を有する現像剤担持体を前記トナー担持体に対向して配置し、その現像剤担持体でトナーと磁性キャリアとを含む二成分現像剤を担持して前記トナー担持体との間に形成されるトナー供給及びトナー薄層形成領域に搬送し、トナー担持体との間に形成されるトナー供給電界の作用領域で、表面にトナーを有する磁性キャリアが集合した穂からなる磁気ブラシを形成し、該磁気ブラシの磁性キャリア表面から離脱した遊離トナーを前記トナー担持体に付着させ、該トナー担持体でトナーを担持して前記像担持体との間に形成される現像領域に搬送し、像担持体上に形成された潜像をトナーで現像する現像方法において、前記磁性キャリアは、粒径が５〜１００μｍであり、磁性体含有量が３０重量％であり、磁気特性は、磁場１０００エルステッドにおける磁化の強さ（σ_１０ _００）が３０乃至１０００ｅｍｕ／ｃｍ^３であり、現像部の磁場を通過後、キャリアを消磁又は減磁する前の磁場０エルステッドにおける残留磁化（σ_ｒ）が１０ｅｍｕ／ｃｍ^３以上であることを特徴としており、残留磁化の大きな磁性キャリアを用いることにより、トナー担持体へのキャリア付着を防止すると同時に、トナーの帯電の立上げを改善することが可能となる。
【０００９】
請求項３に係る発明は、請求項１記載の現像方法において、前記現像領域内で、磁性キャリアの集合した穂が立ち上がり、そして穂が寝る間にトナーを離脱させて、この離脱させた遊離トナーを現像に用いることを特徴としており、遊離トナーを現像に有効に用いることが可能となる。
【００１０】
請求項４に係る発明は、請求項１記載の現像方法において、前記現像領域内に、少なくとも像担持体と現像剤担持体との最近接位置に配置される現像主磁極と、像担持体回転方向に対して前記主磁極の上流側に隣接または近接して配置される主磁極と逆極性の磁極とを備えることを特徴としており、現像領域内での磁界変化を大きくしてキャリアの動きの変化を促進し、キャリアからトナーが遊離し易くすることが可能となる。
【００１１】
請求項５に係る発明は、請求項１記載の現像方法において、前記現像領域内で現像主磁極により作用する磁場は、像担持体表面における最大磁束密度が５０〜１５０ｍＴであることを特徴としており、像担持体表面における最大磁束密度を５０〜１５０ｍＴと適正範囲にすることにより、磁気ブラシの硬さ、きめこまかさ、現像剤担持体のキャリア保持能力等を好適に保つことが可能となる。
【００１２】
請求項６に係る発明は、請求項１記載の現像方法において、現像剤に、トナーと独立または一緒にキャリアを補給する機構を備えたことを特徴としており、現像剤循環部には一定量以上に現像剤が増加したらオーバーフローする様にしておくことによって、キャリアを順次新しいキャリアと交換する構成にでき、現像剤の定期的な一斉交換をする保守が不要となる。
【００１３】
請求項７に係る発明は、請求項１記載の現像方法において、前記磁性キャリアの体積平均粒径が５０μｍ以下であることを特徴としており、高トナー濃度の現像剤でキャリア付着や地汚れがなく、ざらつき感もなく高濃度で高画質な画像を得ることが可能となる。また、磁性キャリアの体積平均粒径をトナー粒径以下にすると、キャリア付着しても画像に及ぼすダメージ（画像欠陥）は非常に少なくなり、高画質な画像を得ることが可能となる。
【００１４】
請求項８に係る発明は、請求項１記載の現像方法において、前記磁性キャリアの体積平均粒径が、像担持体上の光書込み画像（潜像）の最小画素径以下であることを特徴としており、ざらつき感がなく、高精細な画像を得ることが可能となる。
【００１５】
請求項９に係る発明は、請求項１記載の現像方法において、前記磁性キャリアのダイナミック（動的）電気抵抗値（下記の測定方法▲１▼で測定した電気抵抗値）が１０^５〜１０^１０Ωであることを特徴としている。
測定方法▲１▼：ダイナミック電気抵抗値の測定方法。
磁石を内包したローラ（直径φ２０ｍｍ、回転数６００ｒｐｍ）で磁性キャリアを坦持して、幅６５ｍｍ、長さ１ｍｍの面積の電極をギャップ０．９ｍｍで当接させ、２００Ｖ（または２００Ｖ未満の耐圧上限レベル。鉄粉キャリアでは数Ｖ）の印加電圧を印加した時の測定値をダイナミック電気抵抗値とする。
【００１６】
尚、直流（ＤＣ）バイアス現像で好ましいキャリアのダイナミック電気抵抗値は１０^６〜１０^８Ωの範囲であり、現像剤担持体の像担持体に対する線速比は２乃至５倍がＤＣバイアス現像に好適である。
また、現像剤のドクター部通過量は現像部で磁気ブラシが像担持体に接触する程度の量が必要で、現像剤担持体と像担持体の間隙が０．４ｍｍ程度では２０〜６０ｍｇ／ｃｍ^２（現像剤の見かけの嵩密度が１．５〜２．０ｍｇ／ｃｍ^２の場合）が好適である。
さらに、交流（ＡＣ）バイアス現像ではＤＣバイアス現像より該してキャリアのダイナミック電気抵抗値は高めが良く１０^８〜１０^１０Ωの範囲が好ましい。一方、現像剤担持体の像担持体に対する線速比はＤＣバイアス現像より低目に設定でき１．２乃至３倍程度で十分な画像濃度の画像を得ることができる。
【００１７】
請求項１０に係る発明は、請求項１記載の現像方法において、前記トナーとして磁性トナーを用いることを特徴としており、非磁性トナーを用いる場合よりも地汚れやキャリア付着防止をより低減することが可能となる。
尚、カラートナーに磁性トナーを使用する場合は、特にイエローの様に明度の高いトナーでは、磁性体量を他色の明度の低いトナーより少なくしたり、該明度の高いトナーは非磁性トナーや、表面色が明るい磁性粉使用の磁性トナーにする等が色の濁り防止の点から有効である。
【００１８】
請求項１１に係る発明は、請求項１記載の現像方法において、前記磁性キャリアの表層がカーボンを含有しない皮膜で被覆されていることを特徴としており、磁性キャリアの表層をカーボンを含有しない皮膜で被覆することにより、磁性キャリアの表層膜が削れてもカラートナーの色の濁りの原因にならない。
【００１９】
請求項１２に係る発明は、請求項１記載の現像方法において、前記現像剤担持体の表面の回動軸方向の凹凸の平均間隔Ｓｍが、像担持体上の光書込み画像（潜像）の最小画素径の２倍以下で、十点平均粗さＲｚが磁性キャリアの体積平均粒径の１／２以下であることを特徴としており、現像剤担持体の表面をこのように構成することにより、磁気ブラシがきめこまかく安定し、均一でざらつき感のない且つ、高精細画像を形成できる。
【００２０】
請求項１３に係る発明は、請求項１記載の現像方法において、現像用磁気ブラシを形成する現像剤の現像直前における磁性キャリア表面に対するトナーの被覆率（下記の測定方法▲２▼で測定した被覆率）が２０〜１００％であることを特徴としており、低帯電や逆極性帯電の遊離トナーが発生し難く且つ、トナー不足もないので画像濃度が十分で地汚れやトナー飛散が極めて少ない現像方法を提供できる。
【００２１】
測定方法▲２▼：被覆率の算出。
ここで、本発明で定義する被覆率について詳記する。一般に、被覆率とはトナー、キャリアの平均粒径のみを用いて算出されることが多い。しかし、トナーとキャリアの平均粒径のみを用いて算出した被覆率では、トナー、キャリアの粒径分布に関わらず平均粒径が同値であれさえすれば、同じ被覆率となるため、粒径分布を考慮した実粒径の充填状態は計算しきれず正確性に欠ける。そこで、本発明における被覆率の計算は、トナーとキャリアの各粒径分布を考慮した計算法を用いている。すなわち、トナーとキャリアの粒径を所定の領域に細分化して、それらの各領域で算出した（トナーの全投影面積）／（キャリアの全表面積）に対して、その総和である（トナーの全実投影面積）／（キャリアの全実表面積）の比率を算出するものである。この算出法によると、より観察状態に近い充填状態が定量化され、トナーとキャリアの実粒径による被覆率を制御するとみなすことができる。
【００２２】
以下、その算出法を説明する。基本的には、
被覆率＝（トナーの全投影面積）／（キャリアの全表面積）×１００
であるので、まずはトナーの全投影面積、キャリアの全表面積を個々に求める。まず、トナーの全投影面積であるが、トナーの粒径をコールターカウンター等の粒度分布測定器を用いて測定し、小刻みなトナー粒径分布に区切ったヒストグラムデータに集約する。それを各チャンネルとして、各チャンネル毎のトナー代表径Ｒｔ（チャンネルの上下端の粒径の平均値）と、そのチャンネル領域に含まれるトナーの個数ｎｔを用いて、代表粒径の球の投影面積×個数を求め、その値を全チャンネルの総和ｓ１とする。この総和ｓ１は、
ｓ１＝Σ（π（Ｒｔ／２）２×ｎｔ）
となる。
次に各チャンネルの代表粒径の粒子質量×個数を求め、総和をｗ１とすると、
ｗ１＝Σ（４／３π（Ｒｔ／２）３×σｔ×ｎｔ）
となる。ここでσｔはトナーの密度を表す。
以上よりｓ１とｗ１を用いて、
（トナー１ｇ当たりの全投影面積）＝ｓ１×（１ｇ／ｗ１）　・・・（１）
が導かれる。
【００２３】
同様にキャリアの全表面積も、キャリアの粒径をコールターカウンター等の粒度分布測定器を用いて測定し、小刻みなキャリア粒径分布に区切ったヒストグラムデータに集約する。それを各チャンネルとして、各チャンネル毎のキャリア代表径Ｒｃ（チャンネルの上下端の粒径の平均値）とそのチャンネル領域に含まれるキャリアの個数ｎｃを用いて、代表粒径の球の表面積×個数を求め、その値を全チャンネルの総和ｓ２とする。この総和ｓ２は、
ｓ２＝Σ（４π（Ｒｃ／２）２×ｎｃ）×ｎｃ
となる。
次に各チャンネルの代表粒径の粒子質量×個数を求め、総和をｗ２とすると、
ｗ２＝Σ（４／３π（Ｒｃ／２）３×σｃ×ｎｃ）
となる。ここでσｃはキャリアの密度を表す。
以上よりｓ２とｗ２を用いて、
（キャリア１ｇ当たりの全表面積）＝ｓ２×（１ｇ／ｗ２）　・・・（２）
が導かれる。
【００２４】
最終的に、被覆率Ｔｎは、トナーの全質量をＭｔ、キャリアの全質量をＭｃとして、
Ｔｎ＝（トナー１ｇ当たりの全投影面積）×Ｍｔ／（キャリア１ｇ当たりの全投影面積）×Ｍｃ
で表されるため、トナー濃度をＣ（％）とした時、上記（１）、（２）式を用いて、次に示す式（３）が得られる（Ｃ＝Ｍｔ／（Ｍｔ＋Ｍｃ）から、Ｍｔ／Ｍｃ＝Ｃ／１−Ｃであるため）。
被覆率：Ｔｎ＝Ｃ・Ｓｔ／（１−Ｃ）・Ｓｃ×１００　　・・・（３）
但し、Ｓｔ＝トナー１ｇ当たりの全投影面積
Ｓｃ＝キャリア１ｇ当たりの全投影面積
Ｃ＝トナー濃度
【００２５】
請求項１４に係る発明は、請求項１記載の現像方法において、前記現像剤担持体に磁力で担持されている現像剤を、現像領域の磁場通過後、消磁または減磁する手段を備えることを特徴としており、現像領域の磁場通過後に現像剤を消磁または減磁することにより、トナーを補給し現像剤と混合・攪拌する際に、現像剤の磁気凝集力による現像剤流動性及び分散性低下を防止できるので、現像剤の攪拌能力、トナー帯電立上げ能力の良い現像方法を提供できる。
【００２６】
請求項１５に係る発明は、請求項１記載の現像方法において、前記現像領域を通過した後で転写領域に至る前に、像担持体表面に対向して磁気的にキャリアを捕集するキャリアキャッチャを備えることを特徴としており、像担持体へのキャリア付着が起きても、キャリアキャッチャで磁気的にキャリアを捕集することができるので、後工程である、転写、クリーニング、定着等へのダメージを防止できる。また、捕集したキャリアを現像部に戻して再使用することも可能である。
【００２７】
請求項１６に係る発明は、請求項１記載の現像方法において、前記現像剤担持体上の二成分現像剤量を規制する規制部材（例えばドクターブレード）を備え、該規制部材を通過した後で現像領域に至る前に、現像剤担持体表面に対向し磁気ブラシに近接または接触する態様のキャリア飛散防止用現像剤ガイド板を備えることを特徴としており、キャリアが一旦磁気ブラシから離れても下流の磁極の磁力が強く働く領域に設けたキャリア飛散防止用現像剤ガイド板によりガイドされるので、キャリア飛散問題を防止できる。
【００２８】
請求項１７に係る発明は、請求項１記載の現像方法において、平均残留磁化の異なる２種以上の磁性キャリアを混合したキャリアを用いることを特徴としており、キャリアの残留磁化を適宜制御することが可能となる。
【００２９】
請求項１８に係る発明は、請求項１乃至１７のいずれか一つに記載の現像方法において、二成分現像剤を担持する現像剤担持体上で磁性キャリアが集合した穂が立ち上がり、そして穂が寝る間に、磁性キャリアからトナーを離脱させると共に、磁性キャリアから離脱させた遊離トナーを、対向配置された回動部材（像担持体またはトナー担持体）側へ移動させる電界を形成して該回動部材に付着させることを特徴としており、帯電トナーが電界パターンに応じて移動するので、地汚れのない且つ濃度が十分な画像を形成することが可能となる。
【００３０】
請求項１９に係る発明は、請求項１乃至１８のいずれか一つに記載の現像方法において、磁性キャリアの粉体特性及び磁気特性と、現像領域内またはトナー供給領域内の磁石の磁気特性及び形態特性とを、現像剤担持体上で磁性キャリアが集合した穂が立ち上がり、そして穂が寝る間に、磁性キャリアからトナーを離脱させるように設定することを特徴としており、現像領域内で、表面にトナーを有する磁性キャリアから、トナーを像担持体に散布して現像することが可能となる。
【００３１】
請求項２０に係る発明は、請求項１乃至１９のいずれか一つに記載の現像方法において、二成分現像剤を担持する現像剤担持体の形態特性及び電気特性と、対向配置された回動部材（像担持体またはトナー担持体）の形態特性及び電気特性を、磁性キャリアから離脱させたトナーを対向配置された回動部材側へ移動させる電界を形成するように設定することを特徴としており、表面にトナーを有する磁性キャリアから、トナーを対向する回動部材（像担持体またはトナー担持体）に散布して付着させることが可能となる。
【００３２】
請求項２１に係る発明は、請求項１乃至２０のいずれか一つに記載の現像方法において、二成分現像剤を担持する現像剤担持体上で磁性キャリアが集合した穂が立ち上がるときに、トナーを付着させる態様で対向配置された回動部材（像担持体またはトナー担持体）との対向領域内の磁石により、磁気ブラシの先端が二成分現像剤担持体上の磁性キャリアの集合した現像剤層から分離した状態であることを特徴としている。
【００３３】
請求項２２に係る発明は、請求項１乃至２１のいずれか一つに記載の現像方法において、二成分現像剤を担持する現像剤担持体上で磁性キャリアが集合した穂が寝るときに、トナーを付着させる態様で対向配置された回動部材（像担持体またはトナー担持体）との対向領域内の磁石により、磁気ブラシの先端が現像剤担持体上の磁性キャリアの集合した現像剤層と一緒になった状態であることを特徴としている。
【００３４】
請求項２３に係る発明は、内部に磁石を有する現像剤担持体を像担持体に対向して配置し、この現像剤担持体でトナーと磁性キャリアとを含む二成分現像剤を担持して前記像担持体との間に形成される現像領域に搬送し、該現像領域内で、表面にトナーを有する磁性キャリアが集合した穂からなる磁気ブラシを形成し、該磁気ブラシのトナーで前記像担持体上に形成された潜像を現像する現像方法において、前記現像領域内で、表面にトナーを有する残留磁化（σ_ｒ）が１０ｅｍｕ／ｃｍ^３以上の磁性キャリアから、トナーを像担持体に散布して現像することを特徴としている。
また、請求項２４に係る発明は、請求項２３記載の現像方法において、前記現像領域内で形成される磁気ブラシを像担持体に接触させて、磁性キャリア表面からトナーを離脱させ、この離脱させた遊離トナーを像担持体へ散布させ、現像することを特徴としている。
さらに請求項２５に係る発明は、請求項２３または２４記載の現像方法において、前記現像領域内で形成される磁気ブラシを像担持体に接触させて、既に現像されているトナーを像担持体から離脱させることを特徴としている。
【００３５】
請求項２６に係る発明は、内部に磁石を有する現像剤担持体を像担持体に対向して配置し、この現像剤担持体でトナーと磁性キャリアとを含む二成分現像剤を担持して前記像担持体との間に形成される現像領域に搬送し、該現像領域内で、表面にトナーを有する磁性キャリアが集合した穂からなる磁気ブラシを形成し、該磁気ブラシのトナーで前記像担持体上に形成された潜像を現像する現像方法において、前記現像領域内で、トナーを表面に有する残留磁化（σ_ｒ）が１０ｅｍｕ／ｃｍ^３以上の磁性キャリアにより形成される磁気ブラシを像担持体に摺擦または近接させて、トナーで現像させることを特徴としている。
また、請求項２７に係る発明は、請求項２６記載の現像方法において、前記現像領域内で、磁気ブラシを像担持体に摺擦または近接させて、既に現像されたトナーを像担持体から離脱させることを特徴としている。
【００３６】
請求項２８に係る発明は、内部に磁石を有する現像剤担持体を像担持体に対向して配置し、この現像剤担持体でトナーと磁性キャリアとを含む二成分現像剤を担持して前記像担持体との間に形成される現像領域に搬送し、前記像担持体上に形成された潜像をトナーで現像する現像方法において、前記現像領域内で、表面にトナーを有する残留磁化（σ_ｒ）が１０ｅｍｕ／ｃｍ^３以上の磁性キャリアが集合した穂と、磁性キャリア表面から離脱させる遊離トナーとを含む磁気ブラシを形成し、磁性キャリアの集合した穂が立ち上がり、そして穂が寝る間にトナーを離脱させて現像し、かつ、磁気ブラシを像担持体に接触させて離脱させる遊離トナーを像担持体へ散布して現像し、かつ、磁気ブラシを像担持体に摺擦または近接させて現像することを特徴としている。
【００３７】
請求項２９に係る発明は、請求項２８記載の現像方法において、前記現像領域内で形成される磁気ブラシを像担持体に接触させて像担持体からトナーを離脱させ、かつ、磁気ブラシを像担持体に摺擦または近接させて、既に現像されたトナーを像担持体から離脱させることを特徴としている。
また、請求項３０に係る発明は、請求項２８または２９記載の現像方法において、前記現像剤担持体の内部に有する磁石の中心は、現像領域内で、現像剤搬送方向の下流側に傾けることを特徴としている。
さらに請求項３１に係る発明は、請求項２８，２９または３０記載の現像方法において、前記現像剤担持体の線速（Ｖｓ）と前記像担持体の線速（Ｖｐ）との線速比（Ｖｓ／Ｖｐ）を、
０．９＜Ｖｓ／Ｖｐ＜４
の範囲に設定して現像することを特徴としている。
【００３８】
請求項３２に係る発明は、請求項２８乃至３１のいずれか一つに記載の現像方法において、前記現像領域内で磁性キャリア表面から離脱させる遊離トナーを、像担持体と現像剤担持体との間に印加する電界により像担持体側に転移させ現像することを特徴としている。
また、請求項３３に係る発明は、請求項３２記載の現像方法において、像担持体と現像剤担持体との間に印加する電界が、交番電界であることを特徴としている。
【００３９】
請求項３４に係る発明は、内部に磁石を有する現像剤担持体を像担持体に対向して配置し、この現像剤担持体でトナーと磁性キャリアとを含む二成分現像剤を担持して前記像担持体との間に形成される現像領域に搬送し、前記像担持体上に形成された潜像をトナーで現像する現像方法において、前記現像領域内で、表面にトナーを有する磁性キャリアが集合した穂と、磁性キャリア表面から離脱させる遊離トナーとを含む磁気ブラシを形成し、磁性キャリアの集合した穂が立ち上がり、さらに寝る間にトナーを離脱させて像担持体上の潜像を現像し、かつ、磁気ブラシを像担持体に近接させて現像することを特徴としている。
【００４０】
請求項３５に係る発明は、請求項３４記載の現像方法において、前記現像剤担持体上に形成される磁気ブラシが、像担持体に非接触状態で現像することを特徴としている。
また、請求項３６に係る発明は、請求項３４または３５記載の現像方法において、前記現像領域内で、磁性キャリア表面から離脱させる遊離トナーを、像担持体と現像剤担持体との間に印加する電界により像担持体側に転移させ現像することを特徴としている。
さらに請求項３７に係る発明は、請求項３４，３５または３６記載の現像方法において、前記像担持体と現像剤担持体との間に印加する電界が、交番電界であることを特徴としている。
【００４１】
請求項３８に係る発明は、像担持体に対向して配置され、該像担持体上に形成された潜像を現像して可視像化する現像装置において、請求項１乃至３７のいずれか一つに記載の現像方法により現像することを特徴としている。
【００４２】
請求項３９に係る発明は、像担持体上に潜像を形成し、該像担持体上の潜像を現像手段で現像して可視像化した後、その可視像を直接または中間転写体を介して記録媒体に転写し、定着して画像を形成する画像形成方法において、前記現像手段として、請求項３８記載の現像装置を用いたことを特徴としている。
【００４３】
請求項４０に係る発明は、光導電性を有する像担持体と、該像担持体を帯電する帯電手段と、帯電された像担持体に光を照射して潜像を形成する手段と、像担持体上の潜像を現像して可視像化する現像手段と、像担持体上の可視像を直接または中間転写体を介して記録媒体に転写する手段と、記録媒体に転写された可視像を定着する手段とを備えた画像形成装置において、前記現像手段として、請求項３８記載の現像装置を備えたことを特徴としている。
【００４４】
【発明の実施の形態】
以下、本発明の実施の形態を図面に基づいて詳細に説明する。
図１は本発明の現像方法の説明図であり、本発明の現像方法は、図１（ａ）に示すように、内部に磁石体を有する現像剤担持体（例えば、円筒状の現像スリーブ１１１Ｓとその内部に配置された磁石ローラ１１１Ｍからなる現像ローラ）１１１を像担持体（例えば、光導電性の感光体）１００に対向して配置し、この現像剤担持体１１１でトナーと磁性キャリアとを含む二成分現像剤を担持して前記像担持体１００との間に形成される現像領域に搬送し、該現像領域内で、表面にトナーを有する磁性キャリアが集合した穂からなる磁気ブラシを形成し、該磁気ブラシの磁性キャリア表面から離脱した遊離トナーで像担持体１００上に形成された潜像Ｌを現像する現像方法である。尚、図中の符号１１４は現像剤担持体１１１に担持された現像剤の搬送量や層厚を規制する規制部材（ドクターブレード等）であり、Ｖｐは現像バイアス印加用の電源である。また、図１（ｂ）は、本発明の現像方法における現像領域内での二成分現像剤の状態を模式的に表した概略図である。ここで、現像領域とは、磁性キャリアＭＣが集合する穂が磁気ブラシを形成しているか、または現像スリーブ１１１Ｓ上に薄い現像剤層を形成しているかの状態に係わらず、現像剤中のトナーＴが感光体１００に向かって現像される領域を言う。
【００４５】
図２は図１に示す現像剤担持体（現像ローラ）１１１の現像スリーブ１１１Ｓの内部に配置された磁石ローラ１１１Ｍによる磁力分布とその大きさ程度を示す図である。図２に示すように、現像スリーブ１１１Ｓ内には複数の磁石ＭＧ１ａ，ＭＧ１ｂ，ＭＧ１ｃ，ＭＧ２，ＭＧ３，ＭＧ４，ＭＧ５，ＭＧ６を有する磁石ローラ（複数の磁極が着磁された磁石ローラでも良い）１１１Ｍが設けられており、複数の磁石ＭＧ１ａ，ＭＧ１ｂ，ＭＧ１ｃ，ＭＧ２，ＭＧ３，ＭＧ４，ＭＧ５，ＭＧ６による磁力分布がそれぞれＰ１ａ，Ｐ１ｂ，Ｐ１ｃ，Ｐ２，Ｐ３，Ｐ４，Ｐ５，Ｐ６である。具体的には、感光体１００と現像スリーブ１１１Ｓが対向するほぼ中央に二成分現像剤の磁気ブラシを形成するための現像主磁石ＭＧ１ｂ、当該現像主磁石ＭＧ１ｂの磁力形成を補助する主磁石磁力形成補助磁石ＭＧ１ａ，ＭＧ１ｃ、現像スリーブ上に現像剤を汲み上げるための磁石ＭＧ４、汲み上げられた現像剤を現像領域まで搬送する磁石ＭＧ５，ＭＧ６、現像後の領域で現像剤を搬送する磁石ＭＧ２，ＭＧ３を備えている。これら各磁石ＭＧ１ｂ，ＭＧ１ａ，ＭＧ１ｃ，ＭＧ４，ＭＧ５，ＭＧ２，ＭＧ３は現像スリーブ１１１Ｓの半径方向に向けて配置されている。本例では磁石ローラ１１１Ｍを８極の磁石によって構成しているが、現像剤の汲み上げ性や、黒ベタ画像追従性等を向上させるために、磁石ＭＧ３からドクターブレード（図示せず）の間に磁石（磁極）を増やして１０極や１２極で構成しても良い。
【００４６】
現像主磁石群ＭＧ１を成す磁石ＭＧ１ａ，ＭＧ１ｂ，ＭＧ１ｃは、この順で上流側から並ぶ横断面の小さな磁石から構成されており、これら磁石は希土類金属合金により作製されている。具体的にはサマリウム合金磁石、特にサマリウムコバルト合金磁石などを用いることもできる。希土類金属合金磁石のうち代表的な鉄ネオジウムボロン合金磁石では最大エネルギー積が３５８ｋＪ／ｍ^３であり、鉄ネオジウムボロン合金ボンド磁石では最大エネルギー積が８０ｋＪ／ｍ^３前後である。このような磁石によって従来の磁石と異なり、相当に小サイズ化しても必要な現像ローラ表面磁力を確保できる。或る程度スリーブ径を大きくすることが許容される場合には、従来のフェライト磁石やフェライトボンド磁石を用い、スリーブ側に向いた磁石先端を細く形成することで半値幅を狭くすることが可能である。
【００４７】
本例では、現像主磁石ＭＧ１ｂ（磁力分布Ｐ１ｂ）と、現像スリーブ上に現像剤を汲み上げるための磁石ＭＧ４（磁力分布Ｐ４）と、汲み上げられた現像剤を現像領域まで搬送する磁石ＭＧ６（磁力分布Ｐ６）と、現像後の領域で現像剤を搬送する磁石ＭＧ２，ＭＧ３（磁力分布Ｐ２，Ｐ３）がＮ極をなし、主磁石磁力形成補助磁石ＭＧ１ａ，ＭＧ１ｃ（磁力分布Ｐ１ａ，Ｐ１ｃ）と、汲み上げられた現像剤を搬送する磁石ＭＧ５（磁力分布Ｐ５）がＳ極をなしている。ここで、現像領域内で現像主磁石ＭＧ１ｂ（磁力分布Ｐ１ｂ）により作用する磁場は、感光体表面における最大磁束密度が５０〜１５０ｍＴであることが好ましく、主磁石ＭＧ１ｂ（磁力分布Ｐ１ｂ）としては、現像スリーブ１１１Ｓ上で８５ｍＴ以上の法線方向磁力を有する磁石が用いられる。これは、例えば６０ｍＴ以上の磁力を有すれば、キャリア付着などの異常画像の発生が無いことが確認されているからである。しかし、これよりも小さい磁力の場合にはキャリア付着が発生したので好ましくない。また、磁石ＭＧ１ａ，ＭＧ１ｂ，ＭＧ１ｃの磁石幅は２ｍｍであり、この時の現像主磁石ＭＧ１ｂ（磁力分布Ｐ１ｂ）の半値幅は１６°であった。さらに磁石の幅を狭くすることで、半値幅は更に細くなることが確認された。また、１．６ｍｍ幅を用いた際の主磁石（磁力分布Ｐ１ｂ）の半値幅は１２°であった。
【００４８】
主磁石ＭＧ１ｂ（磁力分布Ｐ１ｂ）と主磁石磁力形成補助磁石ＭＧ１ａ，ＭＧ１ｃ（磁力分布Ｐ１ａ，Ｐ１ｃ）の位置関係を図３に示す。主磁石磁力形成補助磁石ＭＧ１ａ，ＭＧ１ｃ（磁力分布Ｐ１ａ，Ｐ１ｃ）の半値幅は３５°以下に形成する。この部分での半値幅は外側に位置する磁石ＭＧ２やＭＧ６（磁力分布Ｐ２，Ｐ６）の半値幅が大きいために主磁石でのように半値幅を相対的に狭く設定することができない。主磁石ＭＧ１ｂ（磁力分布Ｐ１ｂ）と主磁石磁力形成補助磁石ＭＧ１ａやＭＧ１ｃ（磁力分布Ｐ１ａ，Ｐ１ｃ）の位置関係については、主磁石ＭＧ１ｂ（磁力分布Ｐ１ｂ）の両側にある主磁石磁力形成補助磁石ＭＧ１ａ，ＭＧ１ｃ（磁力分布Ｐ１ａ，Ｐ１ｃ）による挟角を３０°以下に形成する。上記の例では、主磁石ＭＧ１ｂ（磁力分布Ｐ１ｂ）での半値幅を１６°に設定するために当該挟角は２２°とした。さらに主磁石磁力形成補助磁石ＭＧ１ａ，ＭＧ１ｃ（磁力分布Ｐ１ａ，Ｐ１ｃ）と当該補助磁石の外側にある磁石ＭＧ２，ＭＧ６（磁力分布Ｐ２，Ｐ６）とによる変極点（０ｍＴ：磁力がＮ極からＳ極、Ｓ極からＮ極に変わる点）の挟角を１２０°以下にする。
【００４９】
ここで、現像領域前域部とは、図１中のＡ_０に示すように、図２に示した主磁石磁力形成補助磁石ＭＧ１ａ（磁力分布Ｐ１ａ）によって、現像剤中の磁性キャリアＭＣが表面にトナーＴを有しながら、複数の磁性キャリアＭＣが集合して穂を形成し、さらに、その磁力線に沿って磁性キャリアＭＣの穂が立ち上がり、そして現像スリーブ１１１Ｓ側に寝るまでの領域と、Ａ_１に示すように、現像主磁石ＭＧ１ｂ（磁力分布Ｐ１ｂ）の近傍に近づいた現像剤中の磁性キャリアＭＣが、表面にトナーＴを有しながら、複数の磁性キャリアＭＣが集合して穂を形成し、さらに、その磁力線に沿って磁性キャリアＭＣの穂が立ち上がり始める領域をいう。
【００５０】
図４（ａ）は、本発明の現像方法における現像領域前域部Ａ_０での磁性キャリアＭＣの穂の立ち上がりから穂が寝るまでの状況を模式的に示す図である。この磁石の配置されている位置では、磁石の極性に係わらず磁気ブラシを形成し、磁石の間では薄い層になっている。図４（ａ）に示すように、それまで磁性キャリアＭＣの集団の現像剤層中に閉じこめられている磁性キャリアＭＣは、互いに磁力を有しているために、磁石間では法線方向の磁力線は小さいが、互いに隣接する磁石は逆極になっているために周方向の磁力線は大きいため、これが磁石間では磁石上のものと比較して薄い磁性キャリアＭＣの集団である現像剤層を形成する力になっていて、磁性キャリアＭＣは現像剤層の集団の中に留めておかれる。
【００５１】
この現像剤層が主磁石磁力形成補助磁石ＭＧ１ａ（磁力分布Ｐ１ａ）の位置にくると、いくつかの磁性キャリアＭＣが集合して穂を形成して立ち上がる。この穂を形成するために集合する磁性キャリアＭＣの個数は、一般に現像剤規制部材（ドクターブレード等）１１４を通過する現像剤の量で決定されるが、それ以外にも磁性キャリアＭＣの磁気的性質、磁石の有する磁力の大きさ、磁石の形状、配置の仕方による磁力線の大きさ及び傾きによって決定される。また、主磁石磁力形成補助磁石ＭＧ１ａ（磁力分布Ｐ１ａ）は固定されているが、現像スリーブ１１１Ｓは図中の矢印１１１Ｒ方向に回転しているために立ち上がり始めた穂の位置における磁力線の角度、大きさも変わっていく。このとき、磁性キャリアＭＣの磁気応答性に遅れがあるため、磁力線に沿った形状に磁気ブラシがすぐに揃わない、さらに、多数の磁性キャリアＭＣが集合した穂は、集団からの拘束力から抜け出して立ち上がるが、磁石の大きな磁場が作用し、全ての磁性キャリアＭＣの磁気的な極性は同一方向を向いており、互いに反発力が作用している。これらのために、磁性キャリアＭＣの現像剤層が突然に割れて、磁性キャリアＭＣの穂が磁気ブラシとして立ち上がる。
【００５２】
したがって、磁性キャリアＭＣが穂を形成して立ち上がることで、トナーＴが磁性キャリアＭＣの集団の中に閉じ込められていたのが空間に解放され、さらに、磁性キャリアＭＣの表面に吸着しているトナーＴに大きな遠心力が作用することで、トナーＴは磁性キャリアＭＣ表面から離脱して現像空間に解放され遊離トナーＴとなる。さらに、穂は磁場の変化のため一定の速度で立ち上がったり、寝たりせず、加速度を持つ。このため、トナーＴには慣性力が働き、磁性キャリアＭＣ表面から離脱して現像空間に解放され遊離トナーＴとなる。また、磁性キャリアＭＣの表面から離脱させた遊離トナーＴは、磁性キャリアＭＣとの静電的付着力、物理的付着力が作用していないために、現像電界等によって容易に移動させることができる。尚、図４（ａ）と同様に、本発明の現像方法における現像領域前域部Ａ_１での磁性キャリアＭＣの穂の立ち上がりの様子を図４（ｂ）に模式的に示す。
【００５３】
本発明の現像方法は、磁性キャリアＭＣの粒径等の粉体特性、飽和磁化の強さ等の磁気特性と現像主磁石の飽和磁化の強さ等の磁気特性、幅及び形状等の形態特性により磁性キャリアＭＣ表面のトナーＴに作用する力を制御し、遊離トナーＴを発生させることができる。さらに本発明の現像方法では、この遊離トナーＴを有する磁気ブラシを形成することで、感光体１００上の潜像Ｌに対するトナーＴの付着量を大きくすることができ、いわゆる現像性の高い現像方法を得ることができる。また、本発明の現像方法は、現像領域の最初の前域部Ａ（Ａ_０及びＡ_１）で、低い電界でも現像できる遊離トナーＴを生じさせることで、いわゆる現像性の高い現像方法を得ることができる。
【００５４】
尚、以上で説明したような現像領域前域部Ａ_０及びＡ_１における磁性キャリアＭＣとトナーＴの挙動は、本発明者らが、実体顕微鏡（オリンパス社製：ＳＺＨ１０）とハイスピードカメラ（フォトロン社製：ＦＡＳＴＣＡＭ−Ｕｌｔｉｍａ−Ｉ^２）とを用いて、９０００〜４０５００コマ／秒の撮影速度で撮影した映像により確認されている。また、以下に説明する現像領域中域部Ｂと後域部Ｃについても、同じように確認されている。
【００５５】
本発明の現像方法は、図１（ｂ）中のＢに示すように、現像領域中域部内で、表面にトナーＴを有する磁性キャリアＭＣから、トナーＴを感光体１００に散布して現像するものである。この感光体１００へのトナーＴの散布は磁気ブラシの穂が感光体１００に強く接触することにより生ずる。図５は、本発明の現像方法における現像領域中域部Ｂでの磁性キャリアＭＣの穂が感光体１００に強く接触する状況を模式的に示す図である。現像スリーブ１１１Ｓ上で、現像領域中域部Ｂにおける磁性キャリアＭＣが集合して形成される穂の大きさ、特にその高さは、上述したように、磁性キャリアＭＣの粒径等の粉体特性、飽和磁化の強さ等の磁気特性と現像主磁石の飽和磁化の強さ等の磁気特性、幅及び形状等の形態的特性により決定される。そのために、現像領域中域部Ｂでは、現像スリーブ１１１Ｓ上にある磁性キャリアＭＣの穂は、現像スリーブ１１１Ｓ上で滑る場合を除いて、ほぼ現像スリーブ１１１Ｓと同じ速度で移動している。そのために、磁性キャリアＭＣの穂の高さが現像スリーブ１１１と感光体１００との距離よりも高くなる場合は、現像主磁石の磁力線に沿って立ち上がる速度と現像スリーブ１１１Ｓの周速の両方の速度を持って感光体１００に強く接触する。
【００５６】
また、感光体１００に強く接触する前に、磁性キャリアＭＣの穂が完全に立ち上がっていたとしても、現像スリーブ１１１Ｓと感光体１００の現像領域の中心部が最もその間の距離が狭くなっており、したがって、磁性キャリアＭＣの穂は、次第に狭くなっていく方向に移動して行くため、磁性キャリアＭＣの穂の高さが、現像スリーブ１１１Ｓと感光体１００との間の最近接部よりも大きい場合は、磁性キャリアＭＣの穂は、現像スリーブ１１１Ｓの周速から感光体１００の周速を相殺した速度で感光体１００に強く接触する。このときに、磁性キャリアＭＣ上に静電的に付着しているトナーＴが、衝撃によって磁性キャリアＭＣ表面から離脱し、遠心力Ｆによる運動の慣性力、感光体１００表面の潜像Ｌによる電界と現像スリーブ１１１Ｓと感光体１００間に印加されている電界によって、感光体１００上に付着し潜像Ｌが現像される。
【００５７】
本発明の現像方法は、図１（ｂ）中のＣに示す現像領域後域部内で、磁気ブラシを感光体１００に摺擦または近接させて、磁性キャリアＭＣからトナーＴが現像される現像方法である。ここで、現像領域後域部Ｃは、磁性キャリアＭＣの磁気ブラシが、感光体１００に摺擦または近接したまま現像スリーブ１１１Ｓ上を搬送される領域である。図６は、本発明の現像方法における現像領域後域部Ｃで、トナーＴが現像される状況を模式的に示す図である。現像スリーブ１１１Ｓと感光体１００との間には、通常図１（ａ）に示す現像バイアス印加用の電源Ｖｐにより、トナーＴを現像するための電界が印加されている。
ここで、図７は反転現像方式における直流電界を印加している状態を模式的に示す図である。有機顔料をキャリア生成材料に用いる有機感光体１００では、一般に負極性（−）の電荷を乗せることが多い。現像方式の中で、感光体１００に乗せる帯電電荷の極性は大きな問題ではない。さらに、レーザ光で潜像を書き込む場合、書込量を少なくするために文字部（画像部）を露光するため、この部分の帯電電荷がキャリア生成材料から生成される正孔により中和されて、図７に示すように、文字部（画像部）の電位が低下する。この文字部（画像部）に、現像スリーブ１１１に負極性の電界を印加して、負極性のトナーＴを現像させる。この現像領域後域部Ｃでは、感光体１００側に開かれた空間を有する磁性キャリアＭＣ上のトナーＴは、感光体１００と現像スリーブ１１１Ｓとの間の電界及び感光体１００と磁性キャリアＭＣとの間に生ずる電界により感光体１００の静電潜像Ｌに現像される。
【００５８】
一方、トナーＴが現像領域前域部Ａまたは現像領域中域部Ｂで現像されたために表面に存在するトナーＴが少なくなって、帯電量が過多になった磁性キャリアＭＣは、感光体１００を摺擦しながら移動するために、先に現像したトナーＴに追いつき、強く接触することで、その衝撃力と、互いに逆極性に帯電していることから生ずる静電的なクーロン力とによって、磁性キャリアＭＣ表面に吸着させて、感光体１００から離脱させる。この場合、主に感光体１００上の非画像部では、帯電装置による静電荷が少ないために、トナーＴを感光体１００に吸着しておく電界が小さいことから、非画像部のトナーＴを離脱させることが多い。このために、非画像部における地汚れを防止して高品位の画像を得ることができる。
【００５９】
また、本発明の現像方法は、感光体１００に対向して配置され、内部に磁石を有する現像スリーブ１１１Ｓが、トナーＴとトナーＴを保持する磁性キャリアＭＣとを含む二成分現像剤を表面に担持し、感光体１００との間に形成される現像領域に搬送し、現像スリーブ１１１Ｓ表面上に形成される潜像ＬをトナーＴで現像する現像方法において、現像スリーブ１１１Ｓは、現像領域で、表面にトナーＴを有する磁性キャリアＭＣが集合した穂と、磁性キャリアＭＣ表面から離脱させる遊離トナーＴとを含む磁気ブラシを形成し、磁性キャリアＭＣの集合した穂が立ち上がり、そして穂が寝る間にトナーＴを離脱させて現像し、かつ現像領域内で形成される磁気ブラシを感光体１００に強く接触させて、感光体１００へのトナーＴの散布を生じさせ現像し、かつ現像領域内の磁性キャリアＭＣを感光体１００に摺擦または近接させて現像する現像方法である。
【００６０】
現像領域内の前域部Ａ_０及びＡ_１では、磁性キャリアＭＣが集合して穂になり、立ち上がりから穂が寝るまでの間にトナーＴを磁性キャリアＭＣから離脱させる。これに、現像のための電界を印加することで、そのまま感光体１００に向かわせて現像することができる。さらに、現像領域内の中域部Ｂでは、磁性キャリアＭＣの穂がさらに感光体１００に接触し、磁性キャリアＭＣ上のトナーＴを感光体１００上に散布して、感光体１００の潜像Ｌを現像する。さらに、この接触により、先に現像されている感光体１００上のトナーＴを吸着し、再び磁性キャリアＭＣ上に回収する。これにより、前域部Ａ_０及びＡ_１、中域部Ｂにおける現像で、非画像部または低電位の画像部に現像されたトナーＴが引き戻されるので高品位の画像を得ることができる。さらに、後域部Ｃでは、磁気ブラシ先端の磁性キャリアＭＣが感光体１００に摺擦または近接して、印加される電界によりトナーＴで感光体１００上の潜像Ｌを現像する。また、この摺擦または近接により、先に現像されている感光体１００上からトナーＴを離脱させ、再び磁性キャリアＭＣ上に付着させる。これにより、後域部Ｃにおける現像では非画像部または低電位の画像部に現像されたトナーＴが引き戻されるので高品位の画像を得ることができる。従って、本発明の現像方法では、現像スリーブ１１１の感光体１００に向いている面全体を現像領域とすることができる。その中で、磁性キャリアＭＣの運動態様が特徴的な３領域（前域部Ａ，中域部Ｂ，後域部Ｃ）に注目して磁性キャリアＭＣの運動態様を制御することで、感光体１００上のトナー量を多くして高品位の画像を得ることができる。
【００６１】
本発明の現像方法では、現像スリーブ１１１Ｓの内部に配置された磁石の中心は、現像領域内で、現像剤搬送方向の下流側に傾ける現像方法とすることが好ましい。これにより、現像領域前域部Ａ_０，Ａ_１を広くすることができ、磁性キャリアＭＣの穂が立ち上がるときに離脱して現像されるトナーＴを増やすことができる。
さらに、本発明の現像方法では、現像スリーブ１１１Ｓの線速（Ｖｓ）と感光体１００の線速（Ｖｐ）との線速比（Ｖｓ／Ｖｐ）は、
０．９＜Ｖｓ／Ｖｐ＜４
の範囲にある現像方法とする。
現像スリーブ１１１Ｓと感光体１００は、対向している部分では図中の矢印１１１Ｒ，１００Ｒで示すように同方向に回転している。現像スリーブ１１１Ｓの線速が感光体１００の線速より小さくとも、つまり線速比（Ｖｓ／Ｖｐ）が１以下でも磁性キャリアＭＣ表面から離脱させるトナーＴが十分にあるため、現像されるトナー付着量を多く維持することが可能になる。例えば線速比（Ｖｓ／Ｖｐ）を０．９より大きな線速比とすれば、現像スリーブ１１１Ｓの回転により現像されるトナーＴを多くして、画像濃度の高い画像を得ることができる。尚、遊離トナーＴの量によっては、さらに線速比を下げられる可能性が残っている。また、線速比（Ｖｓ／Ｖｐ）を大きくすると、現像領域中域部Ｂでの感光体１００に接触する衝撃が大きくなるために、散布して現像されるトナー付着量は増加するが、衝撃により感光体１００から離脱されるトナーＴが増加する。さらに、現像領域後域部Ｃでは磁気ブラシが感光体１００に摺擦または近接すると、磁性キャリアＭＣの穂に接触する回数が多くなるために感光体１００から離脱させるトナー量が増加する。特に、線速比（Ｖｓ／Ｖｐ）が４以上では、ハーフトーン部の後端白抜けや横細線画像のカスレが多くなるため、線速比（Ｖｓ／Ｖｐ）は４未満であることが好ましい。
【００６２】
現像バイアス印加用電源Ｖｐにより現像スリーブ１１１Ｓと感光体１００との間に印加する電界は、特に、直流と交流を重畳させて発生させる交番電界が好ましい。図８は反転現像方式における直流と交流の交番電界を印加している状態を模式的に示す図である。上述した直流電界と同じように、例えば、負極性トナーＴは、現像スリーブ１１１Ｓと感光体１００との間に印加された電界により現像される。この場合も、現像スリーブ１１１Ｓ上の磁性キャリアＭＣが誘電体であるために、感光体１００と磁性キャリアＭＣが集合した穂では、さらに電界が強調された電界が生ずることにより、磁性キャリアＭＣ上に付着しているトナーＴが、感光体１００の静電潜像Ｌに現像される。さらに、交番電界が印加されていることにより、現像されて感光体１００上にあるトナーＴが振動するように運動し、次第に潜像Ｌに忠実に揃えられ高品位の画像を得ることができる。また、ここでも、感光体１００に磁気ブラシの穂が近接していると磁性キャリアＭＣによって強調された電界が生ずるために、この部分でトナーＴが振動するようにより激しく運動し、さらに、潜像Ｌに忠実に揃えられ高品位の画像を得ることができる。
【００６３】
また、本発明の現像方法は、現像スリーブ１１１Ｓ上の磁気ブラシの穂が感光体１００に接触することのない非接触状態にしても良く、この場合は、現像スリーブ１１１Ｓが、現像領域で、表面にトナーＴを有する磁性キャリアＭＣが集合した穂と、磁性キャリアＭＣ表面から離脱させる遊離トナーＴとを含む磁気ブラシを形成し、磁性キャリアＭＣの集合した穂が立ち上がり、そして穂が寝る間にトナーＴを離脱させて現像し、かつ現像領域内で、磁性キャリアＭＣを感光体１００に近接させて現像する現像方法となる。
【００６４】
現像スリーブ１１１Ｓ上の磁気ブラシの穂が感光体１００に接触することのない非接触状態に保つことで、現像領域の前域部Ａ_０及びＡ_１で、磁性キャリアＭＣ表面から離脱させる遊離トナーＴとを含む磁気ブラシを形成し、磁性キャリアＭＣの集合した穂が立ち上がり、そして、あるいは穂が寝る間にトナーＴを離脱させて現像する。その後、磁気ブラシが現像スリーブ１１１Ｓにより搬送される間は、磁気ブラシの先端を感光体１００に近接させて、磁性キャリアＭＣ上のトナーＴにより現像する。また、磁気ブラシが現像スリーブ１１１Ｓにより搬送される間は、磁気ブラシの先端を感光体１００に近接させても、感光体１００に接触して現像されたトナーＴを離脱させることがないために、トナー付着量を低下させることがなく、画像品位を低下させることがない。
【００６５】
尚、本発明の現像方法で用いる磁性キャリアは、例えば、粒径が５〜１００μｍであり、磁性体含有量が３０重量％であり、磁気特性は、磁場１０００エルステッドにおける磁化の強さ（σ_１０００）が３０乃至１０００ｅｍｕ／ｃｍ^３であり、現像部の磁場を通過後、キャリアを消磁又は減磁する前の磁場０エルステッドにおける残留磁化（σ_ｒ）が１０ｅｍｕ／ｃｍ^３以上であることが好ましい。このように残留磁化（σ_ｒ）の大きな磁性キャリアを用いることにより、感光体１００へのキャリア付着を防止すると同時に、トナーの帯電の立上げを改善することが可能となる。
また、平均残留磁化の異なる２種以上の磁性キャリアを混合したキャリアを用いてもよく、この場合には、磁性キャリアの残留磁化を適宜制御することが可能となる。
また、本発明の現像方法を後述する現像装置に適用する場合に、二成分現像剤に、トナーと独立または一緒に磁性キャリアを補給する機構を設けても良く、現像剤循環部には一定量以上に現像剤が増加したらオーバーフローする様にしておくことによって、キャリアを順次新しいキャリアと交換する構成にでき、現像剤の定期的な一斉交換をする保守が不要となる。
【００６６】
さらに本発明の現像方法においては、前記磁性キャリアの体積平均粒径が５０μｍ以下であることが好ましく、高トナー濃度の現像剤でキャリア付着や地汚れがなく、ざらつき感もなく高濃度で高画質な画像を得ることが可能となる。また、磁性キャリアの体積平均粒径をトナー粒径以下にすると、キャリア付着しても画像に及ぼすダメージ（画像欠陥）は非常に少なくなり、高画質な画像を得ることが可能となる。
また、磁性キャリアの体積平均粒径が、感光体１００上の光書込み画像（潜像）の最小画素径以下である場合には、ざらつき感がなく、高精細な画像を得ることが可能となる。
【００６７】
さらに本発明の現像方法においては、磁性キャリアのダイナミック（動的）電気抵抗値（前述の測定方法▲１▼で測定した電気抵抗値）が１０^５〜１０^１０Ωであることが好ましい。
尚、直流（ＤＣ）バイアス現像で好ましいキャリアのダイナミック電気抵抗値は１０^６〜１０^８Ωの範囲であり、現像剤担持体１１１（現像スリーブ１１１Ｓ）の感光体１００に対する線速比は２乃至５倍がＤＣバイアス現像に好適である。また、現像剤のドクター部通過量は現像部で磁気ブラシが感光体１００に接触する程度の量が必要で、現像スリーブ１１１Ｓと感光体１００の間隙（現像ギャップ）が０．４ｍｍ程度では２０〜６０ｍｇ／ｃｍ^２（現像剤の見かけの嵩密度が１．５〜２．０ｍｇ／ｃｍ^２の場合）が好適である。
さらに、交流（ＡＣ）バイアス現像ではＤＣバイアス現像より該してキャリアのダイナミック電気抵抗値は高めが良く１０^８〜１０^１０Ωの範囲が好ましい。一方、現像スリーブ１１１Ｓの感光体１００に対する線速比はＤＣバイアス現像より低目に設定でき１．２乃至３倍程度で十分な画像濃度の画像を得ることができる。
【００６８】
さらに本発明の現像方法においては、トナーＴとして磁性トナーを用いてもよく、この場合には、非磁性トナーを用いる場合よりも地汚れやキャリア付着防止をより低減することが可能となる。
尚、カラートナーに磁性トナーを使用する場合は、特にイエローの様に明度の高いトナーでは、磁性体量を他色の明度の低いトナーより少なくしたり、該明度の高いトナーは非磁性トナーや、表面色が明るい磁性粉使用の磁性トナーにする等が色の濁り防止の点から有効である。
また、磁性キャリアＭＣの表層がカーボンを含有しない皮膜で被覆されている構成としてもよい。磁性キャリアの表層をカーボンを含有しない皮膜で被覆することにより、磁性キャリアの表層膜が削れてもカラートナーの色の濁りの原因にならない。
【００６９】
さらに本発明の現像方法においては、現像スリーブ１１１Ｓの表面の回動軸方向の凹凸の平均間隔Ｓｍが、感光体１００上の光書込み画像（潜像）の最小画素径の２倍以下で、十点平均粗さＲｚが磁性キャリアの体積平均粒径の１／２以下であることが好ましく、現像スリーブ１１１Ｓの表面をこのように構成することにより、磁気ブラシがきめこまかく安定し、均一でざらつき感のない、高精細画像を形成できる。
また、本発明の現像方法においては、現像用磁気ブラシを形成する現像剤の現像直前における磁性キャリア表面に対するトナーの被覆率（前述の測定方法▲２▼で測定した被覆率）が２０〜１００％であることが好ましく、このようにすることにより、低帯電や逆極性帯電の遊離トナーが発生し難く、且つトナー不足もないので、画像濃度が十分で地汚れやトナー飛散が極めて少ない現像方法を実現できる。
【００７０】
さらに本発明の現像方法においては、現像スリーブ１１１Ｓに磁力で担持されている現像剤を、現像領域の磁場通過後、消磁または減磁する手段を設けてもよく、現像領域の磁場通過後に現像剤を消磁または減磁することにより、トナーを補給し現像剤と混合・攪拌する際に、現像剤の磁気凝集力による現像剤流動性及び分散性低下を防止できるので、現像剤の攪拌能力、トナー帯電立上げ能力の良い現像方法を実現できる。
また、感光体１００が現像領域を通過した後で転写領域に至る前に、感光体表面に対向して磁気的にキャリアを捕集するキャリアキャッチャを設けるとよく、感光体へのキャリア付着が起きても、キャリアキャッチャで磁気的にキャリアを捕集することができるので、後工程である、転写、クリーニング、定着等へのダメージを防止できる。また、捕集したキャリアを現像部に戻して再使用することも可能となる。
【００７１】
さらに本発明の現像方法においては、現像スリーブ１１１Ｓ上の二成分現像剤量を規制する規制部材（例えばドクターブレード）１１４を備えているが、この規制部材１１４を通過した後で現像領域に至る前に、現像スリーブ表面に対向し磁気ブラシに近接または接触する態様のキャリア飛散防止用現像剤ガイド板を設けるとよく、磁性キャリアが一旦磁気ブラシから離れても、下流の磁極の磁力が強く働く領域に設けたキャリア飛散防止用現像剤ガイド板によりキャリアがガイドされるので、キャリア飛散問題を防止できる。
【００７２】
以上、本発明の現像方法について説明したが、本発明は、現像剤担持体（現像ローラ）に担持された二成分現像剤のトナーで像担持体上の潜像を現像する現像方法の他、現像剤担持体に担持された二成分現像剤のトナーを一旦トナー担持体に付着させ、そのトナー担持体で担持搬送するトナーで像担持体上の潜像を現像する現像方法にも適用することができる。すなわち、本発明は、トナーを担持するトナー担持体（一成分現像ローラ）を感光体に対向して配置すると共に、内部に磁石を有する現像剤担持体（円筒状のスリーブとその内部に配置された磁石ローラからなるトナー供給ローラ）をトナー担持体（一成分現像ローラ）に対向して配置し、その現像剤担持体（トナー供給ローラ）でトナーと磁性キャリアとを含む二成分現像剤を担持してトナー担持体（一成分現像ローラ）との間に形成されるトナー供給及びトナー薄層形成領域に搬送し、トナー担持体（一成分現像ローラ）との間に形成されるトナー供給電界の作用領域で、表面にトナーを有する磁性キャリアが集合した穂からなる磁気ブラシを形成し、該磁気ブラシの磁性キャリア表面から離脱した遊離トナーをトナー担持体（一成分現像ローラ）に付着させ、該トナー担持体（一成分現像ローラ）でトナーを担持して感光体との間に形成される現像領域に搬送し、感光体上に形成された潜像をトナーで現像する現像方法としてもよい。尚、この場合には、前述の図１〜８において感光体１００をトナー担持体（一成分現像ローラ）に置き換えれば、遊離トナーをトナー担持体に付着させる原理を同様に説明することができる。また、この場合にも、二成分現像剤に用いる磁性キャリアは、粒径が５〜１００μｍであり、磁性体含有量が３０重量％であり、磁気特性は、磁場１０００エルステッドにおける磁化の強さ（σ_１０００）が３０乃至１０００ｅｍｕ／ｃｍ^３であり、現像部の磁場を通過後、キャリアを消磁又は減磁する前の磁場０エルステッドにおける残留磁化（σ_ｒ）が１０ｅｍｕ／ｃｍ^３以上である。また、現像剤担持体に担持された二成分現像剤のトナーを一旦トナー担持体に付着させた後、トナー担持体（一成分現像ローラ）で担持搬送したトナーにより感光体上に形成された潜像を現像する方法は、通常の一成分トナーを用いた現像方式と同様であるので、ここでは説明を省略する。
【００７３】
（第１の実施形態）
次に、本発明の現像方法を適用した現像装置及び画像形成装置の実施形態について説明する。
図９は、本発明の現像方法を適用する現像装置を備えた画像形成装置の一実施形態を示す概略要部構成図である。
図９において、感光層を表面に設け筒状をした感光体１００の周囲には、感光体１００の表面を帯電するための帯電装置１０１が設けられている。感光体１００は図９において矢印１００Ｒで示す反時計回りの向きに回転される。この感光体１００に対向し、所定の現像ギャップＧＰを有するようにして、現像装置１１０の現像ローラ（図１（ａ）及び図２と同様に、筒状の現像スリーブ１１１Ｓと、その内部に配置された複数の磁石を有する磁石ローラ１１１Ｍからなる現像ローラ）１１１が配置されている。
【００７４】
現像ローラ１１１は、現像ケーシング１１５内に収納され、その現像ケーシング１１５の開口部（現像開口部）１１５ａの位置で感光体１００と対向しているが、現像ケーシング１１５の開口部（現像開口部）１１５ａの上下の部分は、現像スリーブ１１１Ｓの表面に対向し磁気ブラシに近接または接触する態様のキャリア飛散防止用現像剤ガイド板を兼ねた構成となっている。
また、現像装置１１０の現像ケーシング１１５内には現像剤（前記したようにトナーＴと磁性キャリアＭＣからなる二成分現像剤）が収容されていて、撹拌スクリュー１１２，１１３の回転により撹拌・搬送されて現像ローラ１１１の現像スリーブ１１１に供給される。
現像ケーシング１１５の上部にはトナー供給手段としての構成部分があり、トナー収納部１１６が設けられていて、消費されたトナーに見合う適量分が現像ケーシング１１５内に補給されるようになっている。尚、この供給手段の部分は、トナーとともにキャリアを補給するような機構とすることも可能である。
【００７５】
感光体１００において、帯電装置１０１よりもこの感光体１００の回転方向１００Ｒの下流部位には、予め帯電装置１０１により一様に帯電された帯電処理面に静電潜像を形成するためのレーザー光線Ｌｂが照射される位置があり、この位置でのレーザー光線の照射により静電潜像Ｌが形成される。静電潜像Ｌが形成された感光体１００は、現像ローラ１１１の現像スリーブ１１１Ｓと対向した現像領域に至り、この現像領域で該静電潜像Ｌに帯電したトナーが付着してトナー像が形成される。
尚、感光体１００の周囲には、帯電装置１０１や現像装置１１０の他に、感光体１００上にレーザー光線Ｌｂを露光して静電潜像を形成する光書込装置や、感光体１００上のトナー像を記録紙へ転写するための転写装置、感光体１００上の残留トナーを除去するためのクリーニング装置、感光体１００上の残留電位を除去するための除電装置等が配設されているが、これらの図示は省略してある。
【００７６】
このような構成において、帯電装置（例えばスコロトロン帯電器）１０１によって表面を一様に帯電された感光体１００は、不図示の光書込装置からのレーザー光Ｌｂの露光によって静電潜像Ｌを形成され、現像装置１１０の現像ローラ１１１によってトナー像を形成される。当該トナー像は、不図示の転写ベルトなどでなる転写装置によって、感光体１００表面から、不図示の給紙トレイから搬送された記録紙へ転写される。この転写の際に感光体１００に静電的に付着した記録紙は、分離爪によって感光体１００から分離される。そして未定着の記録紙上のトナー像は不図示の定着装置によって記録紙に定着される。一方、転写されずに感光体１００上に残留したトナーＴは、不図示のクリーニング装置によって除去され回収される。残留トナーＴを除去された感光体１００は不図示の除電ランプで初期化され、次回の画像形成プロセスに供される。
【００７７】
前述したように、現像装置１１０内には、現像ローラ１１１が感光体１００に近接するように配置されていて、双方の対向部分に現像領域が形成されている。現像ローラ１１１を構成する現像スリーブ１１１Ｓ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り、不図示の回転駆動機構によって図中の矢印１１１Ｒで示す時計回り方向に回転されるようになっている。また、図２に示したように、現像スリーブ１１１Ｓ内には複数の磁石ＭＧ１ａ，ＭＧ１ｂ，ＭＧ１ｃ，ＭＧ２，ＭＧ３，ＭＧ４，ＭＧ５，ＭＧ６を有する磁石ローラ（複数の磁極が着磁された磁石ローラでも良い）１１１Ｍが設けられており、複数の磁石ＭＧ１ａ，ＭＧ１ｂ，ＭＧ１ｃ，ＭＧ２，ＭＧ３，ＭＧ４，ＭＧ５，ＭＧ６による磁力分布がそれぞれＰ１ａ，Ｐ１ｂ，Ｐ１ｃ，Ｐ２，Ｐ３，Ｐ４，Ｐ５，Ｐ６である。
【００７８】
本実施形態では、感光体１００の感光体径が９０ｍｍで、感光体１００の線速が２４５ｍｍ／秒に設定され、現像スリーブ１１１Ｓのスリーブ径が３０ｍｍで、現像スリーブ１１１Ｓの線速が３８５ｍｍ／秒に設定されている。したがって、感光体線速Ｖｐに対するスリーブ線速Ｖｓの比（Ｖｓ／Ｖｐ）は１．５７である。尚、本実施形態では、現像スリーブ１１１Ｓの線速の感光体１００の線速に対する比（Ｖｓ／Ｖｐ）は最低０．９にまで下げても必要な画像濃度を得ることができる。
【００７９】
感光体１００と現像スリーブ１１１Ｓとの間隔である現像ギャップＧＰは例えば０．４ｍｍに設定されている。この現像ギャップＧＰは、従来では磁性キャリアＭＣの粒径が５０μｍであれば０．６５ｍｍ以下、言い換えれば、磁性キャリアＭＣの粒径の１３倍以下に設定することが望ましい。現像ギャップＧＰがあまり狭くなると、磁気ブラシが感光体１００に広範囲で接触するようになるために、横線細りや後端白抜け等の方向依存性が起こりやすくなる。逆に、現像ギャップＧＰが広くなると、十分な電界強度が得られず、孤立ドットやソリッド部でムラ等の画像欠陥を生ずる。電界強度を維持するために、印加する電圧を大きくすることも可能であるが、放電によるいわゆる白ポチと呼ばれるソリッド部の白く抜けた画像等の異常画像が発生しやすくなる。
【００８０】
現像剤の搬送方向（図９において矢印１１１Ｒで示す時計回り方向）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、すなわち、現像スリーブ１１１上の現像剤層の厚みを規制する層厚規制部材としてのドクターブレード１１４が設けられている。このドクターブレード１１４と現像スリーブ１１１Ｓとの間隔であるドクターギャップは０．８７ｍｍに設定されている。従来、ドクターブレードとしては非磁性材料のみからなる板状のものが使用されていたが、本実施形態におけるドクターブレード１１４は、磁性材料からなる板を従来の非磁性の板に接合した構成を有している。このように磁性材料を用いることで、後述するように、穂高の揃った磁気穂が形成されやすくなる。現像スリーブ１１１Ｓの感光体１００とは反対側の領域には、現像ケーシング１１５内の現像剤を攪拌しながら現像スリーブ１１１Ｓへ汲み上げるための攪拌スクリュー１１２，１１３が設けられている。現像ケーシング１１５内の現像剤は、トナーＴと磁性キャリアＭＣからなる現像剤であり、現像剤は図示しない駆動手段により回転する攪拌スクリュー１１２，１１３で混合・攪拌され、トナーＴが摩擦帯電される。このときのトナーの帯電量（ｑ／ｍ）は、−５〜−６０μＣ／ｇ、好ましくは、−１０〜−３０μＣ／ｇがよい。
【００８１】
また、磁性キャリアＭＣとしては、鉄、ニッケル、コバルト等の金属又はこれらと他の金属による合金、マグネタイト、γ−ヘマタイト、二酸化クロム、銅亜鉛フェライト、マンガン亜鉛フェライト等の酸化物、マンガン−銅−アルミニウム等のホイスラー合金等、種々の強磁性体の粒子を用いることができる。さらに、この強磁性体の粒子をスチレン−アクリル系、シリコーン系、フッ素系等の樹脂で被覆してもよい。これらは、トナーＴとの帯電性を考慮して適宜選択することができる。また、磁性体粒子を被覆する樹脂には、荷電制御剤、導電性物質等を添加してもよい。また、スチレン−アクリル系、ポリエステル系等の樹脂中にこれらの磁性体粒子を分散させたものであってもよい。この強磁性体の飽和磁化の強さは、４５〜８５ｅｍｕ／ｇが好ましい。４５ｅｍｕ／ｇ未満では、飽和磁化の強さが低いために搬送性が低下し、また、感光体１００へのキャリア付着が多くなる。８５ｅｍｕ／ｇを越えると、飽和磁化の強さが高いために、磁気ブラシが強くなり、スキャベンジ効果が強く、ハーフトーン部にスキャベンジ跡が生じ、画像品質を低下させる。
【００８２】
トナーＴとしては、少なくとも熱可塑性の樹脂とカーボンブラック、銅フタロシアニン系、キナクリドン系、ビスアゾ系の顔料を有するものを用いる。樹脂としては、スチレン−アクリル系、ポリエステル系の樹脂が好ましい。この他に、定着助剤としてポリプロピレン等のワックス、トナー帯電量を制御するための含合金染料を内添することができる。さらに、表面処理したシリカ、アルミナ、酸化チタン等の酸化物、窒化物、炭化物等を外添してもよい。さらに、脂肪酸金属塩、樹脂微粒子等を併せて外添してもよい。
【００８３】
ここで、本実施形態では図１０に示すように、現像主磁石ＭＧ１ｂ（磁力分布Ｐ１ｂ）の現像スリーブ１１１Ｓ上における法線方向の磁気力のピーク位置Ｍ１が、感光体１００と現像スリーブ１１１Ｓとの最近接位置Ｍ０から感光体１００の移動方向１００Ｒ（反時計回り方向）における下流側になるように、磁石ローラ１１１Ｍの各磁石が配置されている。換言すれば、最近接位置Ｍ０に対して磁気力のピーク位置Ｍ１がθ＝０〜３０°の角度だけずれるようにしている。これは、磁気ブラシが形成される初期段階における遊離トナーＴの発生部位が、遊離トナーＴが感光体１００の潜像Ｌとしての画像部へ移動できる領域にできるだけ多く位置するようにしたものであり、望ましくは、図１（ｂ）に示した現像領域前域部Ａ（Ａ_０，Ａ_１）における遊離トナーＴの発生部位を、最近接位置Ｍ０に対向させるものである。主磁石ＭＧ１ｂ（磁力分布Ｐ１ｂ）と磁石ＭＧ６（磁力分布Ｐ６）との極角度は６０度であり、両磁石の中間で磁力が０になる点が３０度である。さらに換言すれば、磁気ブラシが最近接位置Ｍ０又はその近傍で立ち上がるようにし、あるいは、感光体１００の移動方向上流側における現像主磁石ＭＧ１ｂ（磁力分布Ｐ１ｂ）の磁力線の裾野部分が、最近接位置Ｍ０又はその近傍に位置するようにしたものである。
【００８４】
かかる構成により、磁気ブラシが形成される現像領域前域部Ａ_０及びＡ_１で発生するクラウド状ないしスモーク状の遊離トナーＴは、その大部分が現像電界によって感光体１００の画像部へ移動し易くなる。この現像状況を図１１に基づいて段階的に説明する。図１１は、本発明の第１の実施形態における現像方法の説明図であり、現像領域で遊離トナー及び磁気ブラシのトナーにより感光体の潜像を現像する状況を模式的に示す図である。
【００８５】
まず、図示していない磁気ブラシが形成される現像領域前域部Ａ_０、及び図１１（ａ）に示すように磁気ブラシが形成される現像領域前域部Ａ_１、すなわち磁気ブラシが現像スリーブ１１１に押し付けられた状態から起き上がる位置で、衝撃力、遠心力等によりトナーＴが動き得る空間が形成され、磁性キャリアＭＣ上のトナーＴ及び磁性キャリアＭＣが集合する穂と穂との間に挟まれたトナーＴを離脱させる。また現像領域前域部Ａ_０においては、穂が起き上がった位置あるいは再び磁気ブラシが現像スリーブ１１１Ｓに押し付けられるまでの間にも衝撃力、遠心力等によりトナーＴが動き得る空間が形成され、磁性キャリアＭＣ上のトナーＴ及び磁性キャリアＭＣが集合する穂と穂との間に挟まれたトナーＴを離脱させる。これによって、多数の遊離トナーＴがクラウド状ないしスモーク状に発生する。
【００８６】
この遊離トナーＴ群は、図１１（ｂ）に示すように、現像電界により感光体１００の潜像（画像部）Ｌに引き付けられ、現像される。非画像部では、電界は現像スリーブ１１１Ｓ側へ向いており、遊離トナーＴは磁性キャリアＭＣに戻るか現像スリーブ１１１Ｓ上に移動する。これにより、トナーＴの使用効率を向上させることができるとともに、トナー飛散による装置内の汚れを防止することができる。また、本実施形態では、感光体１００と現像スリーブ１１１Ｓが対向する部位において、図示しない交番電界印加手段（図１（ａ）に示す現像バイアス印加用電源Ｖｐ）により交番電界が印加される。さらに、本実施形態では、図１（ｂ）に示した現像領域中域部Ｂ及び後域部Ｃで磁気ブラシが感光体１００に接触しているため、磁気ブラシ先端の磁性キャリアＭＣ（感光体１００に近い磁性キャリア）と感光体１００との間に電極効果が働き、より画像部のトナー層を均一化し、非画像部の地汚れトナーＴを効率良くスキャベンジすることができる。この効果は、直流バイアス印加時にも有効である。また、従来の二成分接触現像方式に批べ、磁気ブラシが感光体１００と接触している時間が短いため、横線細りや後端白抜け等の方向依存性も起こらない。
【００８７】
このように、交番電界及び二成分接触現像により、図１１（ｃ）に示すように、磁気ブラシの先端の磁性キャリアＭＣと感光体１００との間でトナーＴが往復運動（振動）をする。このトナーＴの往復運動は、画像部Ｌではトナー層の均一化を助長してドット再現性のよい高画質化をもたらし、非画像部では地汚れトナーＴに対してスキャべンジ効果をもたらす。
【００８８】
尚、本実施形態で用いた磁性キャリアＭＣの平均粒径は３５μｍ、磁化の強さは８５ｅｍｕ／ｇ、トナーＴの平均粒径７μｍ、トナー濃度７ｗｔ％、トナー帯電量−２２．５μＣ／ｇであった。現像条件は、帯竜電位−７００Ｖ、画像部電位−１００Ｖ、非画像部電位−６５０Ｖ、現像電界：直流成分−５００Ｖに交流成分としてＶｐ−ｐ：８００Ｖ、周波数：４．５ｋＨの矩形波を重畳した交番電界を使用した。
これにより、ハーフトーン部でのザラツキがなく、ソリッド部でのベタ濃度も高く、ラインや文字の鮮鋭度も優れた高画質が得られることがわかった。
【００８９】
（第２の実施形態）
図１２は、本発明の第２の実施形態における現像方法の説明図であり、現像領域で磁気ブラシの非接触状態を保ちながら遊離トナーＴにより感光体の潜像Ｌを現像する状況を模式的に示す図である。
ここでは、現像装置と画像形成装置は第１の実施形態と同じ構成のものを用いた。但し、磁気ブラシの非接触状態を保つために、現像条件のうち、現像ギャップＧＰを第１の実施形態よりも広い０．７ｍｍとし、現像電界の中の直流成分を−８００Ｖに設定した。また、感光体１００の帯電電位は−９５０Ｖ、画像部電位は−５０Ｖ、非画像部電位は−９００Ｖとし、他は第１の実施形態と同様に行った。図１２（ａ）〜（ｃ）に示すように、本実施形態では、磁気ブラシの非接触状態を保ちながら遊離トナーＴにより感光体１００の潜像Ｌを現像することにより、ハーフトーン部でのザラツキがなく、ソリッド部でのベタ濃度も高く、横細線や文字の鮮鋭度も優れた高画質が得られることがわかった。
【００９０】
（第３の実施形態）
次に、第３の実施形態として、実施形態１で説明したような本発明に係る現像方法を行う現像装置を色数分備えたカラー画像形成装置の構成例について説明する。
図１９は、画像形成装置の一実施形態としてのカラー複写機の概略構成を示している。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）１、カラー画像記録装置（以下、カラープリンタという）２、給紙バンク３、図示省略の制御部等で構成されている。
上記カラースキャナ１は、コンタクトガラス４上の原稿５の画像を照明ランプ６、ミラー群７ａ、７ｂ及びレンズ８を介してカラーセンサ９に結像して、原稿５のカラー画像情報を、例えばレッド（Ｒｅｄ）、グリーン（Ｇｒｅｅｎ）、ブルー（Ｂｌｕｅ）（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。
カラーセンサ９は、本例ではＲ，Ｇ，Ｂの色分解手段とＣＣＤ（ｃｈａｒｇｅ　ｃｏｕｐｌｅｄ　ｄｅｖｉｃｅ）のような光電変換素子で構成され、原稿５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１で得たＲ，Ｇ，Ｂの色分解画像信号強度レベルをもとにして図示しない画像処理部で色変換処理を行い、ブラック（Ｂｌａｃｋ：以下、Ｂｋという）、シアン（Ｃｙａｎ：以下、Ｃという）、マゼンタ（Ｍａｇｅｎｔａ：以下、Ｍという）、イエロー（Ｙｅｌｌｏｗ：以下、Ｙという）のカラー画像データを得る。
【００９１】
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１の動作は次のとおりである。後述のカラープリンタ２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６及びミラー群７ａ，７ｂ等からなる光学系が矢印左方向へ原稿５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２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。
【００９２】
上記カラープリンタ２は、像担持体としての筒状をした感光体１００、書き込み光学ユニット１０、現像手段としてのリボルバー現像ユニット（回転型現像装置）１１、中間転写装置１２、定着装置１３等で構成されている。
感光体１００は矢印の反時計方向に回転し、その周りには、感光体クリ−ニング装置１４、除電ランプ１５、帯電器１０１、帯電電位検出手段としての電位センサ１６、リボルバー現像ユニット１１の選択された現像器１１０Ｋ（例えば実施形態１の図９で説明した構成の現像装置１１０に相当する）、現像濃度パターン検知器１７、中間転写装置１２の中間転写ベルト１８などが配置されている。
【００９３】
また、上記書き込み光学ユニット１０は、カラースキャナ１からのカラー画像データを光信号に変換して、原稿５の画像に対応した光書き込みを行い、感光体１００に静電潜像を形成するものであり、例えば、この書き込み光学ユニット１０は、光源としての半導体レーザー１９、図示しないレーザー発光駆動制御部、ポリゴンミラー２０とその回転用モータ２１、ｆ／θレンズ２２、反射ミラー２３などで構成されている。
【００９４】
上記リボルバー現像ユニット１１は、Ｂｋ現像器１１０Ｋ、Ｃ現像器１１０Ｃ、Ｍ現像器１１０Ｍ、Ｙ現像器１１０Ｙ、及び各現像器を矢印の反時計方向に回転させる不図示のリボルバー回転駆動部などで構成されている。
各現像器は、感光体１００に対向して配置された現像剤担持体（図１（ａ）、図２及び図９に示すように、筒状の現像スリーブ１１１Ｓとその内部に配置された複数の磁石を有する磁石ローラ１１１Ｍとからなる現像ローラ）１１１と、現像剤を撹拌・搬送するために回転する攪拌部材（図９に示す攪拌スクリュー１１２，１１３等）などを備え、現像ローラ１１１の現像スリーブ１１１ＳがトナーＴとトナーを保持する磁性キャリアＭＣとを含む二成分現像剤を表面に担持して、この担持した二成分現像剤を感光体１００との間の対向領域である現像領域に搬送し、現像ローラ１１１と感光体１００との間に電界を印加し、感光体１００の表面上に形成されている潜像をトナーで現像する。
各現像器１１０（Ｋ，Ｃ，Ｍ，Ｙ）内のトナーは磁性キャリアであるフェライトキャリアとの撹拌によって負極性に帯電され、また、各現像ローラ１１１の現像スリーブ１１１Ｓには図示しない現像バイアス用の電源Ｖｐ（図１（ａ）参照）によって負の直流電圧Ｖ_ＤＣに交流電圧Ｖ_ＡＣが重畳された現像バイアスが印加され、現像スリーブ１１１Ｓが感光体１００の導電性支持体（金属基体層等）に対して所定電位にバイアスされている。
【００９５】
複写機本体の待機状態では、リボルバー現像ユニット１１はＢｋ現像器１１０Ｋ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１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を開始し、このカラー画像データに基づき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静電潜像という（Ｃ、Ｍ、Ｙについても同様））。このＢｋ静電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現像ローラ１１１（現像スリーブ１１１Ｓ）を回転開始して、Ｂｋ静電潜像をＢｋトナーで現像する。そして、以後Ｂｋ静電潜像領域の現像動作を続けるが、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が現像位置に来るまで、リボルバー現像ユニット１１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させる。
【００９６】
上記中間転写装置１２は、中間転写ベルト１８、ベルトクリーニング装置２５、搬送ベルト３８、紙転写コロナ放電器（以下、紙転写器という）２６などで構成されている。中間転写ベルト１８は駆動ローラ１８ａ、転写対向ロ−ラ１８ｂ、クリーニング対向ローラ１８ｃ及び従動ローラ群に張架されており、図示しない駆動モータにより駆動制御される。
この中間転写ベルト１８の材質は、ＥＴＦＥ（エチレンテトラフロロエチレン）であり、その電気抵抗は表面抵抗で１０^８〜１０^１０Ω／ｃｍ^２程度である。またベルトクリーニング装置２５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１８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ブレード接離機構によって中間転写ベルト１８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２６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１８上の重ねトナー像を記録媒体（例えば記録紙）２７に一括転写する。
【００９７】
カラープリンタ２内の記録紙カセット２８及び給紙バンク３内の記録紙カセット２９ａ，２９ｂ，２９ｃには、各種サイズの記録紙２７が収納されており、指定されたサイズの記録紙２７のカセットから、給紙コロ３０，３１ａ，３１ｂ，３１ｃによってレジストローラ対３２方向に給紙、搬送される。また、ＯＨＰ用紙や厚紙などの手差し給紙用にプリンタ２の右側面に手差しトレイ３３がある。
【００９８】
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１００は矢印の反時計方向に、中間転写ベルト１８は矢印の時計回りに図示しない駆動モータによって回転される。そして、中間転写ベルト１８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１８上に重ねてトナー像が形成される。
【００９９】
ここでより詳しく述べると、上記Ｂｋトナー像形成は次のように行われる。帯電器１０１はコロナ放電によって感光体１００を負電荷で一様帯電する。そして、半導体レーザー１９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１００の露光された部分は、露光光量に比例する電荷が消失し、Ｂｋ静電潜像が形成される。
このＢｋ静電潜像に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１００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トナーが吸着し、静電潜像と相似なＢｋトナー像が形成される。
感光体１００上に形成されたＢｋトナー像は、感光体１００と接触状態で等速駆動している中間転写ベルト１８の表面に、ベルト転写器３４によって転写される（以下、感光体１００から中間転写ベルト１８へのトナー像転写をベルト転写という）。
【０１００】
ベルト転写後の感光体１００上の若干の未転写残留トナーは、感光体１００の再使用に備えて感光体クリーニング装置１４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図示しない排トナータンクに蓄えられる。
また、感光体１００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１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静電潜像形成を行う。そして、先のＢｋ静電潜像の後端部が通過した後で、且つＣ静電潜像の先端部が到達する前にリボルバー現像ユニット１１の回転動作が行われ、Ｃ現像器１１０Ｃが現像位置にセットされてＣ静電潜像がＣトナーで現像される。
以後、Ｃ静電潜像領域の現像を続けるが、Ｃ静電潜像の後端部が通過した時点で、先のＢｋ現像器１１０Ｋの場合と同様にリボルバー現像ユニット１１の回転動作を行い、次のＭ現像器１１０Ｍを現像位置に移動させる。これもやはり次のＭ静電潜像の先端部が現像位置に到達する前に完了させる。尚、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は省略する。
【０１０１】
上記中間転写ベルト１８には、感光体１００に順次形成する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色のトナー像が紙転写ベルト３８で搬送される記録紙２７に紙転写器２６により一括転写される。
上記画像形成動作を開始する時期に、記録紙２７は記録紙カセット２８，２９ａ，２９ｂ，２９ｃまたは手差しトレイ３３のいずれかから給送され、レジストローラ対３２のニップで待機している。紙転写器２６に中間転写ベルト１８上のトナー像先端が差し掛かるときに、丁度、記録紙２７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３２が駆動され、紙転写ベルト３８の助けで記録紙２７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２７が中間転写ベルト１８上のトナー像と重ねられて正電位の紙転写器２６の上を通過する。このとき、コロナ放電電流で記録紙２７が正電荷で荷電され、トナー画像のほとんどが記録紙２７上に転写される。続いて紙転写器２６の左側に配置した図示しない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２７は除電され、中間転写ベルト１８から剥離され、さらに紙転写ベルト３８から剥離されて紙搬送ベルト３５に移る。
【０１０２】
中間転写ベルト１８面から４色重ねトナー像を一括転写された記録紙２７は、紙搬送ベルト３５で定着装置３６に搬送され、所定温度に制御された定着ローラ３６ａと加圧ローラ３６ｂのニップ部でトナー像が溶融定着され、排出ローラ対３７で装置本体外に送り出され、図示しない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。
一方、ベルト転写後の感光体１００の表面は、感光体クリーニング装置１４（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１５で均一に除電される。また、記録紙２７にトナー像を転写した後の中間転写ベルト１８の表面は、ベルトクリーニング装置２５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。
【０１０３】
ここで、リピートコピーのときは、カラースキャナ１の動作及び感光体１００への画像形成は、１枚目の４色目（Ｙ）の画像形成工程に引き続き、所定のタイミングで２枚目の１色目（Ｂｋ）の画像形成工程に進む。また、中間転写ベルト１８の方は、１枚目の４色重ねトナー像の記録紙２７への一括転写工程に引き続き、表面のベルトクリーニング装置２５でクリーニングされた領域に、２枚目のＢｋトナー像がベルト転写されるようにする。その後は、１枚目と同様の動作になる。
【０１０４】
以上は、４色フルカラーコピーを得るコピーモードであったが、３色コピーモード、２色コピーモードの場合は、指定された色と回数の分について、上記と同様の動作を行うことになる。
また、単色コピーモードの場合は、所定枚数が終了するまでの間、リボルバー現像ユニット１１の所定色の現像器のみを現像作動状態にして、ベルトクリーニング装置２５のブレードを中間転写ベルト１８に押圧状態のまま連続してコピー動作を行う。
【０１０５】
また、Ａ３サイズのフルカラーコピーモードの場合には、中間転写ベルト１８が１周するごとに１色のトナー像を形成し、４回転で４色のトナー像を形成していくのが望ましいが、装置全体を小さく、つまり中間転写ベルト１８の周長を抑え、小サイズの場合のコピースピードを確保し、かつ最大サイズのコピースピードも落さないようにするためには、中間転写ベルト１８が２周する間に１色のトナー像を形成するのが好ましい。この場合には、Ｂｋトナー像を中間転写ベルト１８に転写した後、次の中間転写ベルト１８の１周では、カラープリンタ２における現像及び転写が行われずに空回転し、その次の１周で次色のＣトナーによる現像を行い、そのＣトナー像を中間転写ベルト１８に転写するように順次行っていく。このとき現像器切り換えのためのリボルバー現像ユニット１１の回転動作は、上記空回転時に行う。
【０１０６】
【発明の効果】
以上説明したように、本発明では、従来の現像領域よりも広い範囲で現像領域を設定することにより、現像領域におけるトナーの現像される量を多くして、ソリッド部のベタ濃度の高い画像を得る現像方法を実現することができる。さらに本発明では、磁気ブラシと感光体を接触させることにより、感光体上に現像されたトナーを磁気ブラシ先端の磁性キャリアで離脱させることで、ソリッド部のベタ埋まりが良く滑らかで、非画像部のかぶりも少なく、かつ横細線や文字の鮮鋭度も優れた高品位の画像を得ることができる現像方法を実現することができる。また、磁気ブラシと感光体を非接触にすることで、ハーフトーン部でのザラツキがなく、横細線や文字の鮮鋭度も優れた画像を得る現像方法を実現することができる。
【０１０７】
本発明では、上記現像方法を用い、従来の現像領域よりも広い範囲で現像領域を設定することにより、現像スリーブの回転数を高くしなくとも、現像されるトナーの供給量を多くすることができ、ソリッド部のベタ濃度の高い画像を得ることができる現像装置を実現することができる。また、本発明では、磁気ブラシと感光体を接触させることにより、感光体上に現像されたトナーを磁気ブラシ先端の磁性キャリアで離脱させることで、ソリッド部のベタ埋まりが良く滑らかで、非画像部のかぶりも少なく、かつ横細線や文字の鮮鋭度も優れた高品位の画像を得ることができる現像装置を実現することができる。
【０１０８】
さらに本発明では、上記現像装置を用い、広い範囲で現像領域を設定することにより、現像されるトナーの供給量を多くすることで、機械を設計する際の現像ギャップ、現像スリーブの回転数等の許容範囲を広くすることでき、また、ソリッド部のベタ埋まりが良く滑らかで、非画像部のかぶりも少なく、かつ横細線や文字の鮮鋭度も優れた高品位の画像を得ることができる画像形成方法及び画像形成装置を実現でき、特に、カラー画像を形成する場合には、ハーフトーン部の再現性の優れた画像を得ることができる画像形成方法及び画像形成装置を実現することができる。
【図面の簡単な説明】
【図１】本発明の現像方法の説明図であり、（ａ）は現像部の概略構成例を示す図、（ｂ）は本発明の現像方法における現像領域内での二成分現像剤の状態を模式的に表した概略図である。
【図２】図１に示す現像剤担持体（現像ローラ）の現像スリーブ内に配置された磁石ローラ（複数の磁石）による磁力分布とその大きさ程度を示す図である。
【図３】図２に示す磁石ローラ（複数の磁石）の主磁石と主磁石磁力形成補助磁石の位置関係を示す図である。
【図４】本発明の現像方法における現像領域前域部で、磁性キャリアの穂の立ち上がる状況を模式的に示す図である。
【図５】本発明の現像方法における現像領域中域部で、磁性キャリアの穂が感光体に強く接触する状況を模式的に示す図である。
【図６】本発明の現像方法における現像領域後域部で、トナーが現像される状況を模式的に示す図である。
【図７】反転現像方式における直流電界を印加している状態を模式的に示す図である。
【図８】反転現像方式における直流と交流の交番電界を印加している状態を模式的に示す図である。
【図９】本発明の現像方法を適用する現像装置を備えた画像形成装置の一実施形態を示す概略要部構成図である。
【図１０】本発明の現像方法における現像スリーブ内の主磁石の配置を概略的に示す図である。
【図１１】本発明の第１の実施形態における現像方法の説明図であり、現像領域で遊離トナー及び磁気ブラシのトナーにより感光体の潜像を現像する状況を模式的に示す図である。
【図１２】本発明の第２の実施形態における現像方法の説明図であり、現像領域で磁気ブラシの非接触状態を保ちながら遊離トナーにより感光体の潜像Ｌを現像する状況を模式的に示す図である。
【図１３】本発明の第３の実施形態における画像形成装置の一例としてのカラー複写機の概略構成図である。
【符号の説明】
１０：書き込み光学ユニット
１１：リボルバー現像ユニット（回転型現像装置）
１２：中間転写装置
１３：定着装置
１４：感光体クリーニング装置
１５：除電ランプ
１８：中間転写ベルト
２６：紙転写器
２７：紙転写ベルト
１００：感光体（像担持体）
１０１：帯電装置
１１０：現像装置
１１０Ｋ：ブラック（Ｂｋ）現像器
１１０Ｃ：シアン（Ｃ）現像器
１１０Ｍ：マゼンタ（Ｍ）現像器
１１０Ｙ：イエロー（Ｙ）現像器
１１１：現像ローラ（現像剤担持体）
１１１Ｓ：現像スリーブ
１１１Ｍ：磁石ローラ
１１２，１１３：攪拌スクリュー
１１４：ドクターブレード（規制部材）
１１５：現像ケーシング
１１６：トナー収納部
Ａ（Ａ_０，Ａ_１）：現像領域前域部
Ｂ：現像領域中域部
Ｃ：現像領域後域部
Ｌ：潜像
ＭＧ１ａ，ＭＧ１ｂ，ＭＧ１ｃ，ＭＧ２，ＭＧ３，ＭＧ４，ＭＧ５，ＭＧ６：磁石
ＭＣ：磁性キャリア
Ｔ：トナー[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a developing method used in an electrophotographic image forming process, a developing device using the developing method, an image forming method using the developing device, a copier including the developing device, a printer, The present invention relates to an image forming apparatus such as a plotter and a facsimile.
[0002]
[Prior art]
At present, in image forming apparatuses such as copiers, printers, plotters, and facsimile machines, an electrostatic latent image is formed on an image carrier (hereinafter, referred to as a "photoconductor") provided with a photoconductive photosensitive layer on the surface. Then, the electrostatic latent image is developed into a visible image by a developing device containing a developer, and the visible image is transferred to a sheet-shaped recording medium and fixed to obtain a final image.
As a developer housed in the developing device, a two-component developer mainly composed of a toner and a magnetic carrier (hereinafter simply referred to as “developer”) is widely used because it is easy to colorize. The developer is frictionally charged by stirring and mixing in the developing device, and the toner is electrostatically adhered to the surface of the magnetic carrier by the frictionally charged electrostatic charge. The magnetic carrier with the toner attached thereto is carried by being attracted by a magnetic force to the surface of a developer carrying member (hereinafter, referred to as a “developing sleeve”) in which a magnet is disposed, and is directed toward the developing area on the rotating developing sleeve. Transported.
[0003]
A magnet for development (hereinafter, referred to as “developing main magnet”) is arranged inside the development sleeve at a position of the development sleeve closest to the photoconductor. As the developer conveyed approaches the developing main magnet, a large number of magnetic carriers in the developing agent gather along the lines of magnetic force of the developing main magnet to form ears or chains. These many ears are generally called a magnetic brush because they look like a brush, and a developing method using the state of the magnetic brush is called a magnetic brush development. In this magnetic brush development, the magnetic carrier, which is a dielectric, increases the electric field strength between the photoconductor and the developing sleeve, so that toner is transferred from the surface of the magnetic carrier constituting the tip of the magnetic brush to the photoconductor surface. Is considered to develop the electrostatic latent image. Therefore, heretofore, a portion where there is no magnetic brush formed by ears in which the magnetic carriers are gathered has not been used for developing toner. Therefore, since the portion where the toner can be developed is limited, it is very difficult to increase the amount of the toner to be developed under other conditions.
[0004]
However, a developing method for obtaining a high-density image in this limited area has been proposed. For example, Japanese Patent No. 2,668,781 discloses a developing method in which toner particles carried on magnetic particles and toner particles carried on a developer carrying member are developed by an alternating electric field using a two-component developer. Proposed.
Japanese Patent Application Laid-Open No. 2000-214630 discloses that a magnetic brush having a small particle size of 40 μm or less and a magnetic susceptibility of 50 emu / g or less is used. A developing method aiming at obtaining a high quality image is disclosed.
[0005]
[Problems to be solved by the invention]
However, in the former developing method of the prior art, the developing region is a region where the magnetic particles are rubbing, and the toner particles held in the ears of the magnetic particles in this region and the developer carrying It is difficult to obtain a sufficiently high density image only with toner particles on the body. In addition, since there are few ears of the magnetic particles, it is difficult to obtain a smooth high-quality image with good solid filling of the solid portion due to the electrode effect. Further, in the latter developing method, there is a problem of carrier adhesion, in which the magnetic carrier adheres to the photoreceptor.
[0006]
The present invention has been made in view of the above circumstances, and increases the area where a latent image is developed by toner by contributing to development by using the entire developer carrier as a development area. An object of the present invention is to provide a developing method and a developing device capable of obtaining a high-quality image which is free from image damage (for example, transfer omission or fixing defect) due to adhesion and has good solid filling. It is an object of the present invention to provide an image forming method and an image forming apparatus that can be used to obtain a high-quality image.
[0007]
[Means for Solving the Problems]
As a means for solving the above-mentioned problems, the invention according to claim 1 includes disposing a developer carrying member having a magnet inside in opposition to an image carrier, and using the developer carrying member to separate a toner and a magnetic carrier. The two-component developer containing the developer is transported to a development area formed between the image carrier and the magnetic carrier, and a magnetic brush is formed in the development area. A developing method for developing a latent image formed on the image carrier with free toner detached from the surface of the magnetic carrier of the magnetic brush, wherein the magnetic carrier has a particle size of 5 to 100 μm, Is 30% by weight, and the magnetic characteristics are as follows.₁₀₀₀) Is 30 to 1000 emu / cm³After passing through the magnetic field of the developing unit, the residual magnetization (σ in the magnetic field 0 Oe before the carrier is demagnetized or demagnetized._r) Is 10 emu / cm³As described above, by using a magnetic carrier having a large residual magnetization, it is possible to prevent the carrier from adhering to the image carrier and to improve the rise of the toner charge.
[0008]
According to a second aspect of the present invention, a toner carrier for carrying a toner is disposed facing the image carrier, and a developer carrier having a magnet therein is disposed facing the toner carrier. A two-component developer containing a toner and a magnetic carrier is carried on a toner carrier, and is supplied to the toner carrier formed between the toner carrier and the toner thin layer forming area, and is formed between the toner carrier and the toner carrier. In the working area of the toner supply electric field to be formed, to form a magnetic brush consisting of ears in which magnetic carriers having toner on the surface gather, free toner separated from the magnetic carrier surface of the magnetic brush is attached to the toner carrier, The developing method of carrying a toner on the toner carrier and transporting the toner to a development area formed between the image carrier and the latent image formed on the image carrier with toner, , The particle size is 5 to 100 [mu] m, the magnetic substance content is 30 wt%, magnetic properties, intensity of magnetization in a magnetic field 1000 Oe (sigma₁₀ ₀₀) Is 30 to 1000 emu / cm³After passing through the magnetic field of the developing unit, the residual magnetization (σ in the magnetic field 0 Oe before the carrier is demagnetized or demagnetized._r) Is 10 emu / cm³As described above, by using a magnetic carrier having a large residual magnetization, it is possible to prevent the carrier from adhering to the toner carrier and to improve the rise of the toner charge.
[0009]
According to a third aspect of the present invention, in the developing method according to the first aspect, in the developing area, the spikes of the magnetic carriers gather, and the toner is released while the spikes lie down. Is used for development, and the free toner can be effectively used for development.
[0010]
According to a fourth aspect of the present invention, in the developing method according to the first aspect, a developing main magnetic pole arranged at least in a closest position between the image carrier and the developer carrier in the developing area; It is characterized by having a main pole arranged adjacent or close to the upstream side of the main pole with respect to the direction and a magnetic pole of the opposite polarity, and increasing the change in the magnetic field in the developing region to increase the movement of the carrier. The change can be promoted, and the toner can be easily released from the carrier.
[0011]
According to a fifth aspect of the present invention, in the developing method of the first aspect, a magnetic field applied by the developing main magnetic pole in the developing area has a maximum magnetic flux density of 50 to 150 mT on the surface of the image carrier. By setting the maximum magnetic flux density on the surface of the image carrier to an appropriate range of 50 to 150 mT, the hardness, fineness of the magnetic brush, the carrier holding ability of the developer carrier, and the like can be suitably maintained.
[0012]
According to a sixth aspect of the present invention, in the developing method according to the first aspect, a mechanism is provided for supplying a carrier to the developer independently or together with the toner. By making the overflow occur when the amount of the developer increases, the carrier can be sequentially replaced with a new carrier, so that the maintenance for performing the simultaneous simultaneous replacement of the developer becomes unnecessary.
[0013]
According to a seventh aspect of the present invention, in the developing method of the first aspect, the volume average particle diameter of the magnetic carrier is 50 μm or less. It is possible to obtain a high-density and high-quality image without a feeling of roughness. Further, when the volume average particle diameter of the magnetic carrier is equal to or smaller than the toner particle diameter, damage (image defect) on the image even when the carrier adheres is extremely reduced, and a high quality image can be obtained.
[0014]
The invention according to claim 8 is the developing method according to claim 1, wherein the volume average particle diameter of the magnetic carrier is equal to or less than the minimum pixel diameter of an optically written image (latent image) on an image carrier. Therefore, it is possible to obtain a high-definition image without a feeling of roughness.
[0015]
According to a ninth aspect of the present invention, in the developing method according to the first aspect, the magnetic carrier has a dynamic electric resistance value (electric resistance value measured by the following measuring method (1)).⁵-10¹⁰Ω.
Measurement method (1): A method for measuring the dynamic electric resistance value.
A magnetic carrier is carried by a roller (diameter φ20 mm, rotation speed 600 rpm) containing a magnet, and an electrode having an area of 65 mm in width and 1 mm in length is brought into contact with a gap of 0.9 mm, and a withstand voltage upper limit of 200 V (or less than 200 V). Level: A value measured when an applied voltage of several V for an iron powder carrier is applied is defined as a dynamic electric resistance value.
[0016]
Note that the carrier preferably has a dynamic electric resistance of 10 in direct current (DC) bias development.⁶-10⁸And a linear velocity ratio of the developer carrier to the image carrier of 2 to 5 times is suitable for DC bias development.
Further, the amount of developer passing through the doctor portion needs to be such that the magnetic brush comes into contact with the image carrier in the developing portion, and when the gap between the developer carrier and the image carrier is about 0.4 mm, 20 to 60 mg / cm.²(The apparent bulk density of the developer is 1.5 to 2.0 mg / cm²Is preferable.
Further, in the alternating current (AC) bias development, the dynamic electric resistance value of the carrier is higher than that of the DC bias development, which is better.⁸-10¹⁰The range of Ω is preferred. On the other hand, the linear velocity ratio of the developer carrier to the image carrier can be set lower than that of DC bias development, and an image having a sufficient image density can be obtained at about 1.2 to 3 times.
[0017]
According to a tenth aspect of the present invention, in the developing method of the first aspect, a magnetic toner is used as the toner, and it is possible to further reduce background contamination and carrier adhesion prevention as compared with a case where a non-magnetic toner is used. It becomes possible.
When a magnetic toner is used as the color toner, the amount of the magnetic material may be smaller than that of the low-brightness toner of another color, particularly for a high-brightness toner such as yellow, or the high-brightness toner may be a non-magnetic toner or the like. The use of a magnetic toner using a magnetic powder having a bright surface color is effective from the viewpoint of preventing color turbidity.
[0018]
The invention according to claim 11 is the developing method according to claim 1, wherein the surface layer of the magnetic carrier is coated with a film containing no carbon, and the surface layer of the magnetic carrier is coated with a film containing no carbon. By coating, even if the surface layer film of the magnetic carrier is scraped, the color toner does not become cloudy.
[0019]
According to a twelfth aspect of the present invention, in the developing method according to the first aspect, the average interval Sm of the unevenness of the surface of the developer carrier in the direction of the rotation axis is equal to the optically written image (latent image) on the image carrier. It is characterized in that the ten-point average roughness Rz is equal to or less than 1/2 of the volume average particle diameter of the magnetic carrier at twice or less the minimum pixel diameter, and by configuring the surface of the developer carrier in this way. In addition, the magnetic brush is finely and stably formed, and a high-definition image can be formed without any roughness.
[0020]
According to a thirteenth aspect of the present invention, in the developing method according to the first aspect, a coverage of the toner on the surface of the magnetic carrier immediately before the development of the developer for forming the magnetic brush for development (the coverage measured by the following measurement method (2)) The developing method is characterized in that free toner of low charge or reverse polarity is hardly generated, and there is no shortage of toner, so that the image density is sufficient and background contamination and toner scattering are extremely small. Can be provided.
[0021]
Measurement method (2): Calculation of coverage.
Here, the coverage defined in the present invention will be described in detail. In general, the coverage is often calculated using only the average particle size of the toner and the carrier. However, the coverage calculated using only the average particle size of the toner and the carrier is the same as long as the average particle size is the same regardless of the particle size distribution of the toner and the carrier. The filling state of the actual particle size in consideration of the above cannot be calculated completely and lacks accuracy. Therefore, the calculation of the coverage in the present invention uses a calculation method in consideration of the respective particle size distributions of the toner and the carrier. In other words, the particle diameters of the toner and the carrier are subdivided into predetermined regions, and the sum of (the total projected area of the toner) / (the total surface area of the carrier) calculated in each of these regions is the total (the total amount of the toner). The ratio of (actual projected area) / (total actual surface area of the carrier) is calculated. According to this calculation method, the filling state closer to the observation state is quantified, and it can be considered that the covering ratio based on the actual particle diameters of the toner and the carrier is controlled.
[0022]
Hereinafter, the calculation method will be described. Basically,
Coverage = (total projected area of toner) / (total surface area of carrier) × 100
Therefore, first, the total projected area of the toner and the total surface area of the carrier are individually obtained. First, regarding the total projected area of the toner, the particle size of the toner is measured by using a particle size distribution measuring device such as a Coulter counter, and is aggregated into histogram data divided into small particle size distributions. Using these as the channels, the projected area of a sphere having the representative particle diameter is calculated using the toner representative diameter Rt (the average value of the particle diameter at the upper and lower ends of the channel) for each channel and the number nt of the toner included in the channel area. X The number is obtained, and the value is set as the sum s1 of all the channels. This sum s1 is
s1 = Σ (π (Rt / 2) 2 × nt)
It becomes.
Next, the particle mass of the representative particle size of each channel × the number is obtained, and the total sum is defined as w1.
w1 = Σ (4 / 3π (Rt / 2) 3 × σt × nt)
It becomes. Here, σt represents the density of the toner.
From the above, using s1 and w1,
(Total projected area per g of toner) = s1 × (1g / w1) (1)
Is led.
[0023]
Similarly, for the total surface area of the carrier, the particle size of the carrier is measured by using a particle size distribution measuring device such as a Coulter counter, and is aggregated into histogram data divided into small carrier particle size distributions. Using the carrier representative diameter Rc (the average value of the particle diameter at the upper and lower ends of the channel) and the number nc of the carriers included in the channel region as the channels, the surface area of the sphere having the representative particle diameter × the number is used. Is obtained, and its value is set as the sum s2 of all the channels. This sum s2 is
s2 = Σ (4π (Rc / 2) 2 × nc) × nc
It becomes.
Next, the particle mass of the representative particle diameter of each channel × the number is obtained, and the sum is w2,
w2 = Σ (4 / 3π (Rc / 2) 3 × σc × nc)
It becomes. Here, σc represents the carrier density.
From the above, using s2 and w2,
(Total surface area per gram of carrier) = s2 × (1g / w2) (2)
Is led.
[0024]
Finally, the coverage Tn is defined as Mt being the total mass of the toner and Mc being the total mass of the carrier.
Tn = (total projected area per gram of toner) × Mt / (total projected area per gram of carrier) × Mc
When the toner density is C (%), the following equation (3) is obtained using the above equations (1) and (2) (from C = Mt / (Mt + Mc), Mt / Mc = C / 1−C).
Coverage: Tn = C · St / (1-C) · Sc × 100} (3)
Where St = total projection area per g of toner
Sc = total projected area per gram of carrier
C = toner density
[0025]
According to a fourteenth aspect of the present invention, in the developing method according to the first aspect, there is provided a means for demagnetizing or demagnetizing the developer carried on the developer carrier by magnetic force after passing through a magnetic field in a development area. By demagnetizing or demagnetizing the developer after passing the magnetic field in the development area, when replenishing the toner and mixing / stirring with the developer, the developer fluidity and dispersibility decrease due to the magnetic cohesion of the developer. Therefore, it is possible to provide a developing method having a good stirring ability of the developer and a good ability to start up the charging of the toner.
[0026]
According to a fifteenth aspect of the present invention, in the developing method according to the first aspect, a carrier catcher which magnetically collects the carrier facing the surface of the image carrier after passing through the developing area and before reaching the transfer area. Even if the carrier adheres to the image carrier, the carrier can be magnetically collected by the carrier catcher, so that the subsequent processes such as transfer, cleaning, and fixing are damaged. Can be prevented. It is also possible to return the collected carrier to the developing section and reuse it.
[0027]
The invention according to claim 16 is the developing method according to claim 1, further comprising a regulating member (for example, a doctor blade) for regulating the amount of the two-component developer on the developer carrier, and after passing through the regulating member. Before reaching the developing area, a carrier scattering prevention developer guide plate is provided, which faces the developer carrier and is close to or in contact with the magnetic brush. Since the carrier is guided by the carrier scattering prevention developer guide plate provided in the region where the magnetic force of the magnetic pole strongly acts, the carrier scattering problem can be prevented.
[0028]
According to a seventeenth aspect of the present invention, in the developing method of the first aspect, a carrier obtained by mixing two or more kinds of magnetic carriers having different average residual magnetizations is used, and the residual magnetization of the carrier can be appropriately controlled. It becomes possible.
[0029]
An invention according to claim 18 is the developing method according to any one of claims 1 to 17, wherein the spikes in which the magnetic carriers are gathered rise on the developer carrier that carries the two-component developer, and the spikes are formed. While sleeping, the toner is released from the magnetic carrier, and an electric field is formed to move the free toner released from the magnetic carrier to the side of the rotating member (image carrier or toner carrier) disposed opposite to the toner. It is characterized in that it is attached to a moving member, and since the charged toner moves in accordance with the electric field pattern, it is possible to form an image free from background contamination and having a sufficient density.
[0030]
The invention according to claim 19 is the developing method according to any one of claims 1 to 18, wherein the powder characteristics and the magnetic characteristics of the magnetic carrier, and the magnetic characteristics and the magnetic characteristics of the magnet in the development region or the toner supply region. The morphological characteristics are characterized in that the magnetic carrier is set on the developer carrier so that the spike rises and the toner is detached from the magnetic carrier while the spike is sleeping. The toner can be spread on the image carrier from the magnetic carrier having the toner and developed.
[0031]
According to a twentieth aspect of the present invention, in the developing method according to any one of the first to nineteenth aspects, the morphological characteristics and the electrical characteristics of the developer carrying member for carrying the two-component developer and the rotation of the developer carrying member facing the two-component developer. It is characterized in that the morphological and electrical characteristics of the member (image carrier or toner carrier) are set so as to form an electric field for moving the toner separated from the magnetic carrier to the side of the rotating member opposed to the magnetic carrier. In addition, it becomes possible to scatter and attach the toner from the magnetic carrier having the toner on the surface to the opposing rotating member (image carrier or toner carrier).
[0032]
According to a twenty-first aspect of the present invention, in the developing method according to any one of the first to twentieth aspects, when the ears on which the magnetic carriers are gathered rise on the developer carrier that carries the two-component developer, A magnet in a region facing a rotating member (image carrier or toner carrier) which is disposed so as to adhere to the magnetic brush so that the tip of the magnetic brush is a collection of magnetic carriers on a two-component developer carrier; It is characterized by being separated from the layer.
[0033]
According to a twenty-second aspect of the present invention, in the developing method according to any one of the first to twenty-first aspects, when the ears on which the magnetic carriers are aggregated fall on the developer carrying member that carries the two-component developer, the toner The tip of the magnetic brush is brought into contact with the developer layer in which the magnetic carriers on the developer carrier are gathered by the magnet in the region facing the rotating member (image carrier or toner carrier) disposed so as to adhere to the developer layer. It is characterized by being together.
[0034]
The invention according to claim 23 is that a developer carrying member having a magnet therein is disposed to face the image carrier, and the developer carrying member carries a two-component developer containing a toner and a magnetic carrier. The magnetic brush is conveyed to a developing area formed between the image bearing member and a magnetic brush formed of spikes in which magnetic carriers having toner on the surface are gathered in the developing area. In a developing method for developing a latent image formed on a body, a residual magnetization (σ) having a toner on a surface in the developing area._r) Is 10 emu / cm³It is characterized in that toner is sprayed from the magnetic carrier to the image carrier for development.
According to a twenty-fourth aspect of the present invention, in the developing method according to the twenty-third aspect, the magnetic brush formed in the developing area is brought into contact with the image carrier to release the toner from the surface of the magnetic carrier. It is characterized in that the free toner is spread on the image carrier and developed.
According to a twenty-fifth aspect of the present invention, in the developing method according to the twenty-third or twenty-fourth aspect, the magnetic brush formed in the developing area is brought into contact with the image carrier to remove already developed toner from the image carrier. It is characterized by being detached.
[0035]
The invention according to claim 26 is characterized in that a developer carrying member having a magnet therein is disposed to face the image carrier, and the developer carrying member carries a two-component developer containing a toner and a magnetic carrier. The magnetic brush is conveyed to a developing area formed between the image bearing member and a magnetic brush formed of spikes in which magnetic carriers having toner on the surface are gathered in the developing area. In a developing method for developing a latent image formed on a body, a residual magnetization (σ) having a toner on a surface in the developing area._r) Is 10 emu / cm³The magnetic brush formed by the above magnetic carrier is rubbed or brought close to the image carrier, and is developed with toner.
According to a twenty-seventh aspect of the present invention, in the developing method according to the twenty-sixth aspect, a magnetic brush is rubbed or brought close to the image carrier in the developing area to separate the already developed toner from the image carrier. It is characterized by having
[0036]
The invention according to claim 28, wherein a developer carrier having a magnet inside is arranged to face the image carrier, and the developer carrier carries a two-component developer containing a toner and a magnetic carrier. In a developing method of transporting the latent image formed on the image carrier with toner to a developing area formed between the image carrier and the toner, the residual magnetization (toner having toner on the surface in the developing area) may be used. σ_r) Is 10 emu / cm³Forming a magnetic brush including the magnetic carrier gathering ears and free toner to be separated from the magnetic carrier surface, the magnetic carrier gathering ears rising, and releasing the toner while the ears lie down to develop, Further, the toner is characterized in that free toner which is released by bringing the magnetic brush into contact with the image carrier is sprayed and developed on the image carrier, and the magnetic brush is rubbed or brought close to the image carrier for development.
[0037]
According to a twenty-ninth aspect of the present invention, in the developing method according to the twenty-eighth aspect, the magnetic brush formed in the developing area is brought into contact with the image carrier to release toner from the image carrier, and the magnetic brush is moved to the image bearing member. It is characterized in that the already developed toner is separated from the image carrier by rubbing or approaching the carrier.
According to a thirtieth aspect of the present invention, in the developing method according to the thirty-eighth or twenty-ninth aspect, the center of the magnet inside the developer carrier is inclined downstream in the developer transport direction within the developing area. It is characterized by.
The invention according to claim 31 is the developing method according to claim 28, 29 or 30, wherein a linear velocity ratio (Vs) between the linear velocity (Vs) of the developer carrier and the linear velocity (Vp) of the image carrier. Vs / Vp)
0.9 <Vs / Vp <4
And developing.
[0038]
According to a thirty-second aspect of the present invention, in the developing method according to any one of the twenty-eighth to thirty-first aspects, the free toner released from the surface of the magnetic carrier in the developing area is formed between the image carrier and the developer carrier. It is characterized in that it is transferred to the image carrier side by an electric field applied therebetween and developed.
The invention according to claim 33 is the developing method according to claim 32, wherein the electric field applied between the image carrier and the developer carrier is an alternating electric field.
[0039]
The invention according to claim 34, wherein a developer carrying member having a magnet therein is disposed to face the image carrying member, and the developer carrying member carries a two-component developer containing a toner and a magnetic carrier. In a developing method of transporting a latent image formed on the image carrier with toner to a developing area formed between the image carrier and the magnetic carrier having toner on the surface in the developing area, A magnetic brush containing the collected spikes and the free toner detached from the surface of the magnetic carrier is formed. The spikes of the magnetic carrier rise, and the toner is detached while sleeping to develop the latent image on the image carrier. In addition, the magnetic brush is developed close to the image carrier.
[0040]
According to a thirty-fifth aspect of the present invention, in the developing method according to the thirty-fourth aspect, the magnetic brush formed on the developer carrier develops the image carrier in a non-contact state.
According to a thirty-sixth aspect of the present invention, in the developing method according to the thirty-fourth or thirty-fifth aspect, in the developing area, free toner to be detached from the surface of the magnetic carrier is applied between the image carrier and the developer carrier. It is characterized in that it is transferred to the image carrier side by the electric field and developed.
According to a thirty-seventh aspect, in the developing method according to the thirty-fourth, thirty-fifth or thirty-sixth aspect, the electric field applied between the image carrier and the developer carrier is an alternating electric field.
[0041]
The invention according to claim 38 is a developing device which is arranged to face an image carrier and develops a latent image formed on the image carrier to make it a visible image. It is characterized by being developed by the developing method described in one of the above.
[0042]
The invention according to claim 39 is a method for forming a latent image on an image carrier, developing the latent image on the image carrier by a developing means to visualize the latent image, and then directly or intermediately transferring the visible image. An image forming method in which an image is transferred to a recording medium via a body and fixed to form an image, wherein the developing device according to claim 38 is used as the developing unit.
[0043]
The invention according to claim 40 is an image carrier having photoconductivity, charging means for charging the image carrier, means for irradiating the charged image carrier with light to form a latent image, Developing means for developing the latent image on the carrier to make it a visible image; means for transferring the visible image on the image carrier directly or via an intermediate transfer body to a recording medium; An image forming apparatus provided with a means for fixing a visible image, wherein the developing device according to claim 38 is provided as the developing means.
[0044]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 1 is an explanatory view of the developing method of the present invention. As shown in FIG. 1A, the developing method of the present invention employs a developer carrying member having a magnet body therein (for example, a cylindrical developing sleeve 111S). And a developing roller composed of a magnet roller 111 M disposed inside the image bearing member (for example, a photoconductive photoconductor) 100, and the toner carrier and the magnetic carrier are separated by the developer carrier 111. Is transported to a developing area formed between the image carrier 100 and a two-component developer containing the same, and in the developing area, a magnetic brush made of ears in which magnetic carriers having toner on the surface are gathered is used. This is a developing method of developing the latent image L formed on the image carrier 100 with the free toner formed and detached from the magnetic carrier surface of the magnetic brush. Reference numeral 114 in the drawing denotes a regulating member (eg, doctor blade) that regulates the transport amount and layer thickness of the developer carried on the developer carrying member 111, and Vp denotes a power supply for applying a developing bias. FIG. 1B is a schematic view schematically showing the state of the two-component developer in the developing area in the developing method of the present invention. Here, the development area refers to the toner in the developer regardless of whether the ears on which the magnetic carriers MC gather form a magnetic brush or a thin developer layer on the development sleeve 111S. T indicates a region where the toner is developed toward the photoconductor 100.
[0045]
FIG. 2 is a diagram showing a magnetic force distribution by a magnet roller 111M arranged inside a developing sleeve 111S of the developer carrier (developing roller) 111 shown in FIG. 1 and its magnitude. As shown in FIG. 2, a magnet roller (or a magnet roller having a plurality of magnetized magnetic poles) 111M having a plurality of magnets MG1a, MG1b, MG1c, MG2, MG3, MG4, MG5, and MG6 is provided in the developing sleeve 111S. The magnetic force distributions of the plurality of magnets MG1a, MG1b, MG1c, MG2, MG3, MG4, MG5, and MG6 are P1a, P1b, P1c, P2, P3, P4, P5, and P6, respectively. Specifically, a developing main magnet MG1b for forming a magnetic brush of a two-component developer is formed substantially at the center where the photoconductor 100 and the developing sleeve 111S face each other, and a main magnet magnetic force forming assisting the forming of the magnetic force of the developing main magnet MG1b. The auxiliary magnets MG1a and MG1c, the magnet MG4 for pumping the developer onto the developing sleeve, the magnets MG5 and MG6 for transporting the pumped developer to the development area, and the magnets MG2 and MG3 for transporting the developer in the area after development. Have. These magnets MG1b, MG1a, MG1c, MG4, MG5, MG2, MG3 are arranged in the radial direction of the developing sleeve 111S. In this example, the magnet roller 111M is formed of an eight-pole magnet, but between the magnet MG3 and the doctor blade (not shown), in order to improve the developer pumping property and the black solid image follow-up property. The number of magnets (magnetic poles) may be increased, and the number of poles may be 10 or 12.
[0046]
The magnets MG1a, MG1b, MG1c forming the developing main magnet group MG1 are composed of magnets having small cross sections arranged in this order from the upstream side, and these magnets are made of a rare earth metal alloy. Specifically, a samarium alloy magnet, in particular, a samarium cobalt alloy magnet can be used. Among the rare earth metal alloy magnets, a typical iron neodymium boron alloy magnet has a maximum energy product of 358 kJ / m.³And the maximum energy product of the iron-neodymium boron alloy bonded magnet is 80 kJ / m³Before and after. With such a magnet, unlike a conventional magnet, a necessary magnetic force on the surface of the developing roller can be secured even if the size is considerably reduced. If it is permissible to increase the sleeve diameter to a certain extent, it is possible to narrow the half-width by using a conventional ferrite magnet or ferrite bonded magnet and forming the magnet tip that faces the sleeve narrow. is there.
[0047]
In this example, the developing main magnet MG1b (magnetic force distribution P1b), a magnet MG4 (magnetic force distribution P4) for pumping the developer onto the developing sleeve, and a magnet MG6 (magnetic force distribution) for transporting the pumped developer to the developing area. P6) and the magnets MG2 and MG3 (magnetic force distributions P2 and P3) that transport the developer in the area after development form N poles, and are pumped up with the main magnet magnetic force forming auxiliary magnets MG1a and MG1c (magnetic force distributions P1a and P1c). The magnet MG5 (magnetic force distribution P5) that conveys the supplied developer forms an S pole. Here, the magnetic field applied by the developing main magnet MG1b (magnetic force distribution P1b) in the developing region preferably has a maximum magnetic flux density of 50 to 150 mT on the surface of the photoconductor, and the main magnet MG1b (magnetic force distribution P1b) A magnet having a normal magnetic force of 85 mT or more on the developing sleeve 111S is used. This is because it has been confirmed that no abnormal image such as carrier adhesion occurs when the magnetic force is, for example, 60 mT or more. However, a magnetic force smaller than this is not preferable because carrier adhesion occurs. The magnet width of the magnets MG1a, MG1b, MG1c was 2 mm, and the half-width of the developing main magnet MG1b (magnetic force distribution P1b) at this time was 16 °. Further, it was confirmed that the half width was further reduced by reducing the width of the magnet. The half width of the main magnet (magnetic force distribution P1b) when using a 1.6 mm width was 12 °.
[0048]
FIG. 3 shows the positional relationship between the main magnet MG1b (magnetic force distribution P1b) and the main magnet magnetic force forming auxiliary magnets MG1a, MG1c (magnetic force distributions P1a, P1c). The half value width of the main magnet magnetic force forming auxiliary magnets MG1a, MG1c (magnetic force distributions P1a, P1c) is set to 35 ° or less. Since the half width of the magnets MG2 and MG6 (magnetic force distributions P2 and P6) located on the outside is large in this portion, the half width cannot be set relatively narrow as in the case of the main magnet. Regarding the positional relationship between the main magnet MG1b (magnetic force distribution P1b) and the main magnet magnetic force forming auxiliary magnets MG1a and MG1c (magnetic force distributions P1a, P1c), the main magnet MG1a on both sides of the main magnet MG1b (magnetic force distribution P1b). , MG1c (magnetic force distributions P1a, P1c) are formed at an angle of 30 ° or less. In the above example, the included angle was set to 22 ° in order to set the half width in the main magnet MG1b (magnetic force distribution P1b) to 16 °. Further, the inflection point (0 mT: magnetic force is from N pole to S pole) due to the main magnet magnetic force forming auxiliary magnets MG1a, MG1c (magnetic force distributions P1a, P1c) and magnets MG2, MG6 (magnetic force distributions P2, P6) outside the auxiliary magnet , The point at which the S pole changes to the N pole) is set to 120 ° or less.
[0049]
Here, the front area of the development area is A in FIG.₀As shown in FIG. 2, a plurality of magnetic carriers MC are aggregated while the magnetic carrier MC in the developer has the toner T on the surface by the main magnet magnetic force forming auxiliary magnet MG1a (magnetic force distribution P1a) shown in FIG. A region where a spike is formed, the spike of the magnetic carrier MC rises along the line of magnetic force, and then lies on the developing sleeve 111S side;₁As shown in the figure, the magnetic carriers MC in the developer approaching the vicinity of the developing main magnet MG1b (magnetic force distribution P1b) have a plurality of magnetic carriers MC gathering to form ears while having the toner T on the surface. Further, it refers to a region where the ears of the magnetic carrier MC start to rise along the line of magnetic force.
[0050]
FIG. 4A shows a development area front area A in the development method of the present invention.₀FIG. 5 is a diagram schematically showing a state from the rising of the ears of the magnetic carrier MC to the falling of the ears in FIG. At the position where the magnet is arranged, a magnetic brush is formed regardless of the polarity of the magnet, and a thin layer is formed between the magnets. As shown in FIG. 4A, the magnetic carriers MC confined in the developer layer of the group of the magnetic carriers MC have a magnetic force with each other. Is small, but the magnets adjacent to each other have opposite poles, so the circumferential magnetic lines of force are large, so this forms a developer layer that is a group of magnetic carriers MC that is thinner between the magnets than on the magnets. The magnetic carrier MC is kept in the group of the developer layer.
[0051]
When this developer layer comes to the position of the main magnet magnetic force forming auxiliary magnet MG1a (magnetic force distribution P1a), some magnetic carriers MC gather to form ears and stand up. The number of magnetic carriers MC gathered to form the ears is generally determined by the amount of developer passing through a developer regulating member (such as a doctor blade) 114. It is determined by the properties and the magnitude of the magnetic force of the magnet, the size and inclination of the magnetic field lines depending on the shape and arrangement of the magnet. Further, although the main magnet magnetic force forming auxiliary magnet MG1a (magnetic force distribution P1a) is fixed, the angle and size of the magnetic force line at the position of the ear at which the developing sleeve 111S starts rising because the developing sleeve 111S is rotating in the direction of the arrow 111R in the figure. It also changes. At this time, since the magnetic responsiveness of the magnetic carrier MC has a delay, the magnetic brushes are not immediately aligned in the shape along the lines of magnetic force, and the ears in which a large number of magnetic carriers MC are gathered out of the restraining force from the group. However, the large magnetic field of the magnet acts, the magnetic polarities of all the magnetic carriers MC are oriented in the same direction, and repulsive forces act on each other. As a result, the developer layer of the magnetic carrier MC is suddenly broken, and the ears of the magnetic carrier MC rise as a magnetic brush.
[0052]
Therefore, when the magnetic carrier MC forms ears and rises, the toner T is trapped in the group of the magnetic carriers MC, but is released into the space, and further, the toner T adsorbed on the surface of the magnetic carrier MC When a large centrifugal force acts on T, the toner T separates from the surface of the magnetic carrier MC and is released into the developing space to become free toner T. In addition, the ears do not rise or sleep at a constant speed due to a change in the magnetic field, but have acceleration. For this reason, an inertial force acts on the toner T, so that the toner T is separated from the surface of the magnetic carrier MC and released into the developing space, and becomes the free toner T. Further, the free toner T detached from the surface of the magnetic carrier MC can be easily moved by a developing electric field or the like because no electrostatic or physical adhesive force acts on the magnetic carrier MC. . In addition, similarly to FIG. 4A, the development area front area A in the development method of the present invention.₁FIG. 4 (b) schematically shows how the ears of the magnetic carrier MC rise in the above.
[0053]
The developing method of the present invention includes powder characteristics such as the particle size of the magnetic carrier MC, magnetic characteristics such as the intensity of saturation magnetization, magnetic characteristics such as the intensity of saturation magnetization of the developing main magnet, and morphological characteristics such as width and shape. Thus, the force acting on the toner T on the surface of the magnetic carrier MC can be controlled, and the free toner T can be generated. Further, in the developing method of the present invention, by forming the magnetic brush having the free toner T, the amount of the toner T attached to the latent image L on the photoreceptor 100 can be increased. Can be obtained. Further, in the developing method of the present invention, the first front region A (A₀And A₁By generating the free toner T that can be developed even in a low electric field, a so-called developing method having high developability can be obtained.
[0054]
The development area front area A as described above₀And A₁The behavior of the magnetic carrier MC and the toner T in the above was determined by the present inventors using a stereo microscope (Olympus: SZH10) and a high-speed camera (Photron: FASTCAM-Ultima-I).²) Is confirmed by an image photographed at a photographing speed of 9000 to 40500 frames / sec. Further, the same is confirmed in the developing region middle region B and the rear region C described below.
[0055]
In the developing method of the present invention, as shown by B in FIG. 1B, toner T is dispersed on the photoreceptor 100 from the magnetic carrier MC having the toner T on the surface and developed in the middle region of the developing area. Things. The dispersion of the toner T on the photoconductor 100 is caused by the fact that the ears of the magnetic brush strongly contact the photoconductor 100. FIG. 5 is a diagram schematically illustrating a situation in which the ears of the magnetic carrier MC strongly contact the photoconductor 100 in the middle area B of the developing area in the developing method of the present invention. On the developing sleeve 111S, the size of the spikes formed by the aggregation of the magnetic carriers MC in the middle region B of the developing region, particularly the height thereof, depends on the powder characteristics such as the particle size of the magnetic carriers MC as described above. And the magnetic characteristics such as the intensity of the saturation magnetization, the magnetic characteristics such as the intensity of the saturation magnetization of the developing main magnet, and the morphological characteristics such as width and shape. For this reason, in the middle region B of the developing region, the ears of the magnetic carrier MC on the developing sleeve 111S are moving at substantially the same speed as the developing sleeve 111S, except that the magnetic carrier MC slides on the developing sleeve 111S. Therefore, when the height of the magnetic carrier MC is higher than the distance between the developing sleeve 111 and the photosensitive member 100, both the speed of rising along the magnetic line of magnetic force of the developing main magnet and the peripheral speed of the developing sleeve 111S are used. And makes strong contact with the photoconductor 100.
[0056]
Also, even if the ears of the magnetic carrier MC are completely raised before strongly contacting the photoconductor 100, the distance between the developing sleeve 111S and the center of the development area of the photoconductor 100 is the shortest, Accordingly, since the ears of the magnetic carrier MC move in the direction of gradually narrowing, the height of the ears of the magnetic carrier MC is larger than the closest part between the developing sleeve 111S and the photoconductor 100. In other words, the ears of the magnetic carrier MC make strong contact with the photoconductor 100 at a speed obtained by offsetting the peripheral speed of the photoconductor 100 from the peripheral speed of the developing sleeve 111S. At this time, the toner T electrostatically adhering to the magnetic carrier MC is separated from the surface of the magnetic carrier MC by impact, and the inertial force of the movement due to the centrifugal force F and the electric field due to the latent image L on the surface of the photoconductor 100. The latent image L is developed on the photoconductor 100 by the electric field applied between the photoconductor 100 and the developing sleeve 111S.
[0057]
In the developing method of the present invention, a magnetic brush is rubbed or brought into contact with the photoreceptor 100 in the rear area of the developing area shown by C in FIG. It is. Here, the rear area C of the development area is an area where the magnetic brush of the magnetic carrier MC is conveyed on the development sleeve 111S while rubbing or approaching the photoconductor 100. FIG. 6 is a view schematically showing a situation where the toner T is developed in the rear area C of the development area in the development method of the present invention. An electric field for developing the toner T is applied between the developing sleeve 111S and the photoreceptor 100 by a power supply Vp for applying a developing bias shown in FIG.
Here, FIG. 7 is a diagram schematically showing a state in which a DC electric field is applied in the reversal development system. In the organic photoreceptor 100 using an organic pigment as a carrier generation material, generally, a negative (−) charge is often applied. In the developing method, the polarity of the charged electric charge put on the photoconductor 100 is not a big problem. Furthermore, when writing a latent image with a laser beam, the character portion (image portion) is exposed to reduce the amount of writing, so that the charged charges in this portion are neutralized by holes generated from the carrier generation material. As shown in FIG. 7, the potential of the character portion (image portion) decreases. A negative electric field is applied to the developing sleeve 111 to the character portion (image portion) to develop the negative toner T. In the rear area C of the developing area, the toner T on the magnetic carrier MC having a space opened to the photoconductor 100 side receives the electric field between the photoconductor 100 and the developing sleeve 111S and the toner T on the magnetic carrier MC. The electrostatic latent image L on the photoreceptor 100 is developed by the electric field generated during the period.
[0058]
On the other hand, since the toner T is developed in the development area front area A or the development area middle area B, the amount of the toner T existing on the surface decreases and the magnetic carrier MC having an excessive charge amount causes the photoconductor 100 to lose its charge. In order to move while rubbing, it catches up with the previously developed toner T and makes strong contact with it, so that the impact force and the electrostatic Coulomb force generated by being charged to opposite polarities cause magnetic force. It is adsorbed on the surface of the carrier MC and is separated from the photoconductor 100. In this case, mainly in the non-image area on the photoreceptor 100, the electric field for adsorbing the toner T to the photoreceptor 100 is small because the electrostatic charge by the charging device is small. Often. For this reason, a high-quality image can be obtained by preventing background contamination in the non-image portion.
[0059]
Further, in the developing method of the present invention, the developing sleeve 111 S disposed opposite to the photoreceptor 100 and having a magnet inside includes a two-component developer including the toner T and the magnetic carrier MC holding the toner T on the surface. In the developing method of carrying and transporting the latent image L formed on the surface of the developing sleeve 111S with the toner T, the developing sleeve 111S includes: A magnetic brush including the spikes on which the magnetic carrier MC having the toner T on the surface gathers and the free toner T detached from the surface of the magnetic carrier MC is formed. The toner T is released and developed, and the magnetic brush formed in the development area is brought into strong contact with the photoconductor 100 to cause the toner T to be spread on the photoconductor 100. It was developed, and a developing process for developing magnetic carrier MC within the development area rubs or proximity to the photosensitive member 100.
[0060]
Front area A in the development area₀And A₁Then, the magnetic carriers MC gather to form ears, and the toner T is separated from the magnetic carriers MC from the rising to the time when the ears fall. By applying an electric field for development to this, development can be performed directly on the photoconductor 100. Further, in the middle area B in the developing area, the spikes of the magnetic carrier MC further contact the photoconductor 100, and the toner T on the magnetic carrier MC is scattered on the photoconductor 100, so that the latent image L of the photoconductor 100 Develop. Further, by this contact, the toner T on the photoreceptor 100 that has been developed previously is adsorbed and collected on the magnetic carrier MC again. As a result, the front area A₀And A₁In the development in the middle region B, the toner T developed in the non-image portion or the low-potential image portion is pulled back, so that a high-quality image can be obtained. Further, in the rear region C, the magnetic carrier MC at the tip of the magnetic brush rubs or approaches the photoconductor 100, and the latent image L on the photoconductor 100 is developed with the toner T by the applied electric field. Further, due to the rubbing or approach, the toner T is detached from the photoreceptor 100 that has been previously developed, and adheres to the magnetic carrier MC again. Accordingly, in the development in the rear area C, the toner T developed in the non-image area or the low-potential image area is pulled back, so that a high-quality image can be obtained. Therefore, in the developing method of the present invention, the entire surface of the developing sleeve 111 facing the photoconductor 100 can be set as the developing area. By controlling the movement mode of the magnetic carrier MC by focusing on three regions (the front region A, the middle region B, and the rear region C) in which the movement mode of the magnetic carrier MC is characteristic, A high-quality image can be obtained by increasing the amount of toner above 100.
[0061]
In the developing method of the present invention, it is preferable that the center of the magnet disposed inside the developing sleeve 111S be inclined in the developing region to the downstream side in the developer conveying direction. As a result, the development area front area A₀, A₁Can be increased, and the amount of toner T that is detached and developed when the ears of the magnetic carrier MC rise can be increased.
Further, in the developing method of the present invention, the linear velocity ratio (Vs / Vp) between the linear velocity (Vs) of the developing sleeve 111S and the linear velocity (Vp) of the photoconductor 100 is:
0.9 <Vs / Vp <4
The developing method falls within the range.
The developing sleeve 111S and the photoreceptor 100 rotate in the same direction at the opposing portions as indicated by arrows 111R and 100R in the figure. Even if the linear velocity of the developing sleeve 111S is lower than the linear velocity of the photoconductor 100, that is, even if the linear velocity ratio (Vs / Vp) is 1 or less, there is enough toner T to be detached from the surface of the magnetic carrier MC. It is possible to maintain a large amount. For example, if the linear speed ratio (Vs / Vp) is set to a linear speed ratio larger than 0.9, the toner T developed by the rotation of the developing sleeve 111S is increased, and an image with high image density can be obtained. Note that there is a possibility that the linear velocity ratio can be further reduced depending on the amount of the free toner T. Further, when the linear velocity ratio (Vs / Vp) is increased, the impact of contacting the photoconductor 100 in the middle area B of the developing area increases, so that the amount of adhered toner that is scattered and developed increases. As a result, the toner T detached from the photoconductor 100 increases. Further, when the magnetic brush rubs or approaches the photoconductor 100 in the rear area C of the development area, the number of times of contact with the ears of the magnetic carrier MC increases, so that the amount of toner detached from the photoconductor 100 increases. In particular, when the linear velocity ratio (Vs / Vp) is 4 or more, the trailing edge white spots in the halftone portion and blurring of the horizontal fine line image increase, so that the linear velocity ratio (Vs / Vp) is preferably less than 4. .
[0062]
The electric field applied between the developing sleeve 111S and the photoconductor 100 by the developing bias application power supply Vp is particularly preferably an alternating electric field generated by superimposing DC and AC. FIG. 8 is a diagram schematically showing a state in which a DC and AC alternating electric field is applied in the reversal development system. Similarly to the DC electric field described above, for example, the negative toner T is developed by the electric field applied between the developing sleeve 111S and the photoconductor 100. Also in this case, since the magnetic carrier MC on the developing sleeve 111S is a dielectric, the electric field in which the photoconductor 100 and the magnetic carrier MC are gathered is further enhanced in the ear where the photoconductor 100 and the magnetic carrier MC are gathered. The attached toner T is developed into the electrostatic latent image L on the photoconductor 100. Further, by the application of the alternating electric field, the toner T on the photoconductor 100 is developed and moves so as to vibrate, and the latent image L is gradually aligned with the latent image L, so that a high-quality image can be obtained. Also in this case, if the ears of the magnetic brush are close to the photoreceptor 100, an electric field emphasized by the magnetic carrier MC is generated, so that the toner T vibrates more vigorously in this portion, and further, the latent image L and a high-quality image can be obtained.
[0063]
Further, in the developing method of the present invention, the magnetic brush on the developing sleeve 111S may be in a non-contact state in which the spike does not contact the photoconductor 100. In this case, the developing sleeve 111S is Forming a magnetic brush including the spikes on which the magnetic carrier MC having the toner T is gathered and the free toner T detached from the surface of the magnetic carrier MC. This is a development method in which T is released for development, and the magnetic carrier MC is developed in the vicinity of the photoconductor 100 in the development area.
[0064]
By maintaining the magnetic brush ears on the developing sleeve 111S in a non-contact state where the ears do not come into contact with the photoconductor 100, the front area A of the developing area is maintained.₀And A₁Thus, a magnetic brush including the free toner T to be detached from the surface of the magnetic carrier MC is formed, and the spikes of the magnetic carrier MC rise, and the toner T is detached and developed while the spikes are sleeping. Thereafter, while the magnetic brush is being conveyed by the developing sleeve 111S, the magnetic brush is developed with the toner T on the magnetic carrier MC while the tip of the magnetic brush is brought close to the photoconductor 100. Also, while the magnetic brush is being conveyed by the developing sleeve 111S, even if the tip of the magnetic brush is brought close to the photoconductor 100, the developed toner T does not come off in contact with the photoconductor 100. There is no reduction in the amount of adhered toner and no deterioration in image quality.
[0065]
The magnetic carrier used in the developing method of the present invention has, for example, a particle size of 5 to 100 μm, a magnetic substance content of 30% by weight, and a magnetic property of the magnetic carrier (σ) at a magnetic field of 1000 Oe.₁₀₀₀) Is 30 to 1000 emu / cm³After passing through the magnetic field of the developing unit, the residual magnetization (σ in the magnetic field 0 Oe before the carrier is demagnetized or demagnetized._r) Is 10 emu / cm³It is preferable that it is above. Thus, the residual magnetization (σ_rThe use of a magnetic carrier having a large size can prevent the carrier from adhering to the photoreceptor 100 and can improve the rise of toner charge at the same time.
Further, a carrier obtained by mixing two or more types of magnetic carriers having different average residual magnetizations may be used. In this case, it is possible to appropriately control the residual magnetization of the magnetic carriers.
Further, when the developing method of the present invention is applied to a developing device described later, a mechanism for replenishing the magnetic carrier to the two-component developer independently or together with the toner may be provided. By overflowing when the amount of the developer increases as described above, the carrier can be sequentially replaced with a new carrier, and maintenance for periodically performing the simultaneous replacement of the developer becomes unnecessary.
[0066]
Further, in the developing method of the present invention, the volume average particle diameter of the magnetic carrier is preferably 50 μm or less, and there is no carrier adhesion or background smear with a developer having a high toner concentration, and high density and high image quality without roughness. It is possible to obtain a perfect image. Further, when the volume average particle diameter of the magnetic carrier is equal to or smaller than the toner particle diameter, damage (image defect) on the image even when the carrier adheres is extremely reduced, and a high quality image can be obtained.
When the volume average particle diameter of the magnetic carrier is equal to or smaller than the minimum pixel diameter of the optically written image (latent image) on the photoconductor 100, it is possible to obtain a high-definition image without roughness. .
[0067]
Further, in the developing method of the present invention, the magnetic carrier has a dynamic electric resistance (electric resistance measured by the above-mentioned measuring method (1)) of 10%.⁵-10¹⁰It is preferably Ω.
Note that the carrier preferably has a dynamic electric resistance of 10 in direct current (DC) bias development.⁶-10⁸The linear velocity ratio of the developer carrier 111 (developing sleeve 111S) to the photoconductor 100 is 2 to 5 times, which is suitable for DC bias development. Further, the amount of the developer passing through the doctor portion needs to be such that the magnetic brush contacts the photosensitive member 100 in the developing portion. If the gap (developing gap) between the developing sleeve 111S and the photosensitive member 100 is about 0.4 mm, the amount of developer is 20 to 60mg / cm²(The apparent bulk density of the developer is 1.5 to 2.0 mg / cm²Is preferable.
Further, in the alternating current (AC) bias development, the dynamic electric resistance value of the carrier is higher than that of the DC bias development, which is better.⁸-10¹⁰The range of Ω is preferred. On the other hand, the linear velocity ratio of the developing sleeve 111S to the photoreceptor 100 can be set lower than that of the DC bias development, and an image having a sufficient image density can be obtained at about 1.2 to 3 times.
[0068]
Further, in the developing method of the present invention, a magnetic toner may be used as the toner T. In this case, it is possible to further reduce background contamination and prevention of carrier adhesion as compared with the case of using a non-magnetic toner.
When a magnetic toner is used as the color toner, the amount of the magnetic material may be smaller than that of the low-brightness toner of another color, particularly for a high-brightness toner such as yellow, or the high-brightness toner may be a non-magnetic toner or the like. The use of a magnetic toner using a magnetic powder having a bright surface color is effective from the viewpoint of preventing color turbidity.
Further, the configuration may be such that the surface layer of the magnetic carrier MC is covered with a film containing no carbon. By coating the surface layer of the magnetic carrier with a film containing no carbon, even if the surface layer film of the magnetic carrier is scraped, the color of the color toner does not become cloudy.
[0069]
Further, in the developing method of the present invention, the average interval Sm of the unevenness of the surface of the developing sleeve 111S in the rotation axis direction is less than twice the minimum pixel diameter of the optically written image (latent image) on the photoconductor 100, and The point average roughness Rz is preferably equal to or less than １／ of the volume average particle diameter of the magnetic carrier, and by arranging the surface of the developing sleeve 111S in this manner, the magnetic brush is finely stable and has a uniform and rough feeling. No, high definition images can be formed.
In the developing method of the present invention, the coverage of the toner on the surface of the magnetic carrier (coverage measured by the above-mentioned measuring method (2)) is 20 to 100% immediately before the development of the developer forming the magnetic brush for development. In this manner, low-charge or reverse-polarity free toner is less likely to be generated, and there is no toner shortage. realizable.
[0070]
Further, in the developing method of the present invention, means for demagnetizing or demagnetizing the developer carried on the developing sleeve 111S by magnetic force after passing through the magnetic field of the developing area may be provided. Demagnetizing or demagnetizing the toner, when the toner is replenished and mixed / stirred with the developer, it is possible to prevent a decrease in the fluidity and dispersibility of the developer due to the magnetic cohesion of the developer. It is possible to realize a developing method having a good charge starting ability.
Further, it is preferable to provide a carrier catcher that magnetically collects the carrier in opposition to the photoconductor surface after the photoconductor 100 passes through the development area and before the photoconductor 100 reaches the transfer area. However, since the carrier can be magnetically collected by the carrier catcher, damage to transfer, cleaning, fixing, and the like, which are subsequent steps, can be prevented. Further, the collected carrier can be returned to the developing section and reused.
[0071]
Further, in the developing method of the present invention, a regulating member (for example, a doctor blade) 114 for regulating the amount of the two-component developer on the developing sleeve 111S is provided. Further, a carrier scattering prevention developer guide plate may be provided in such a manner as to face the developing sleeve surface and approach or come into contact with the magnetic brush, and even if the magnetic carrier is once separated from the magnetic brush, a region where the magnetic force of the downstream magnetic pole strongly acts. Since the carrier is guided by the carrier scattering prevention developer guide plate provided in the above, the carrier scattering problem can be prevented.
[0072]
Although the developing method of the present invention has been described above, the present invention provides a developing method of developing a latent image on an image carrier with a two-component developer toner carried on a developer carrier (developing roller). The present invention is also applicable to a developing method in which a toner of a two-component developer carried on a developer carrier is once adhered to the toner carrier, and a latent image on the image carrier is developed with the toner carried and carried by the toner carrier. Can be. That is, according to the present invention, a toner carrier (one-component developing roller) for carrying a toner is arranged to face a photoconductor, and a developer carrier having a magnet inside (a cylindrical sleeve and an inside thereof is arranged). A toner supply roller composed of a magnet roller is disposed opposite to a toner carrier (one-component developing roller), and the developer carrier (toner supply roller) carries a two-component developer containing toner and a magnetic carrier. The toner supply between the toner carrier (one-component developing roller) and the toner supply layer formed between the toner carrier and the toner carrier (one-component developing roller) In the working area, a magnetic brush composed of spikes in which magnetic carriers having toner on the surface are gathered is formed, and the free toner detached from the magnetic carrier surface of the magnetic brush is transferred to the toner carrier (one-component developer). Roller, and carries the toner on the toner carrier (one-component developing roller), transports the toner to a development area formed between the photoconductor, and develops the latent image formed on the photoconductor with the toner. Developing method. In this case, if the photosensitive member 100 is replaced with a toner carrier (one-component developing roller) in FIGS. 1 to 8 described above, the principle of attaching free toner to the toner carrier can be similarly explained. Also in this case, the magnetic carrier used in the two-component developer has a particle size of 5 to 100 μm, a magnetic substance content of 30% by weight, and a magnetic characteristic indicating the intensity of magnetization at a magnetic field of 1,000 Oersted ( σ₁₀₀₀) Is 30 to 1000 emu / cm³After passing through the magnetic field of the developing unit, the residual magnetization (σ in the magnetic field 0 Oe before the carrier is demagnetized or demagnetized._r) Is 10 emu / cm³That is all. Further, after the toner of the two-component developer carried on the developer carrying member is once adhered to the toner carrying member, the latent image formed on the photoreceptor by the toner carried and carried by the toner carrying member (one-component developing roller). The method of developing an image is the same as that of a normal developing method using one-component toner, and a description thereof will not be repeated.
[0073]
(1st Embodiment)
Next, an embodiment of a developing device and an image forming apparatus to which the developing method of the present invention is applied will be described.
FIG. 9 is a schematic configuration diagram showing a main part of an embodiment of an image forming apparatus provided with a developing device to which the developing method of the present invention is applied.
In FIG. 9, a charging device 101 for charging the surface of the photoconductor 100 is provided around the cylindrical photoconductor 100 provided with a photosensitive layer on the surface. The photoconductor 100 is rotated in a counterclockwise direction indicated by an arrow 100R in FIG. The developing roller of the developing device 110 (as in FIGS. 1A and 2, a cylindrical developing sleeve 111 S and a developing sleeve 111 S are disposed inside the developing roller 110) so as to face the photosensitive member 100 and have a predetermined developing gap GP. (Developing roller) 111 composed of a magnet roller 111M having a plurality of magnets.
[0074]
The developing roller 111 is housed in the developing casing 115 and faces the photoconductor 100 at the position of the opening (developing opening) 115a of the developing casing 115. However, the opening (developing opening) of the developing casing 115 is provided. The upper and lower portions of 115a also serve as a carrier scattering prevention developer guide plate that faces the magnetic brush and faces the surface of the developing sleeve 111S.
A developer (a two-component developer composed of the toner T and the magnetic carrier MC as described above) is contained in the developing casing 115 of the developing device 110, and is stirred and conveyed by rotation of the stirring screws 112 and 113. To the developing sleeve 111 of the developing roller 111.
A component serving as a toner supply unit is provided at the upper part of the developing casing 115, and a toner storage unit 116 is provided. An appropriate amount corresponding to consumed toner is supplied into the developing casing 115. It should be noted that the supply unit may be configured to supply a carrier together with the toner.
[0075]
In the photoconductor 100, a laser beam Lb for forming an electrostatic latent image on a charging processing surface uniformly charged in advance by the charging device 101 is provided downstream of the charging device 101 in the rotation direction 100 R of the photoconductor 100. Is irradiated, and the irradiation of the laser beam at this position forms an electrostatic latent image L. The photoreceptor 100 on which the electrostatic latent image L is formed reaches a developing area opposed to the developing sleeve 111S of the developing roller 111. In this developing area, the charged toner adheres to the electrostatic latent image L to form a toner image. It is formed.
Around the photoconductor 100, in addition to the charging device 101 and the developing device 110, an optical writing device that forms an electrostatic latent image by exposing the photoconductor 100 with a laser beam Lb, A transfer device for transferring the toner image to the recording paper, a cleaning device for removing the residual toner on the photoconductor 100, and a static eliminator for removing the residual potential on the photoconductor 100 are provided. Are not shown.
[0076]
In such a configuration, the photoconductor 100 whose surface is uniformly charged by the charging device (for example, a scorotron charger) 101 forms an electrostatic latent image L by exposure to laser light Lb from an optical writing device (not shown). The toner image is formed by the developing roller 111 of the developing device 110. The toner image is transferred from the surface of the photoconductor 100 to recording paper conveyed from a paper feed tray (not shown) by a transfer device including a transfer belt (not shown). The recording paper electrostatically attached to the photoconductor 100 at the time of this transfer is separated from the photoconductor 100 by the separation claw. The unfixed toner image on the recording paper is fixed on the recording paper by a fixing device (not shown). On the other hand, the toner T remaining on the photoconductor 100 without being transferred is removed and collected by a cleaning device (not shown). The photoconductor 100 from which the residual toner T has been removed is initialized by an unillustrated static elimination lamp, and used for the next image forming process.
[0077]
As described above, in the developing device 110, the developing roller 111 is disposed so as to be close to the photoconductor 100, and a developing region is formed on both opposing portions. The developing sleeve 111S constituting the developing roller 111 is formed of a non-magnetic material such as aluminum, brass, stainless steel, or conductive resin in a cylindrical shape, and is rotated clockwise as indicated by an arrow 111R in the figure by a rotation driving mechanism (not shown). It is to be rotated in the direction. Further, as shown in FIG. 2, a magnet roller having a plurality of magnets MG1a, MG1b, MG1c, MG2, MG3, MG4, MG5, and MG6 (a magnet roller having a plurality of magnetized magnetic poles) is provided in the developing sleeve 111S. (Good) 111M, and the magnetic force distribution by the plurality of magnets MG1a, MG1b, MG1c, MG2, MG3, MG4, MG5, and MG6 is P1a, P1b, P1c, P2, P3, P4, P5, and P6, respectively.
[0078]
In the present embodiment, the photoconductor diameter of the photoconductor 100 is set to 90 mm, the linear speed of the photoconductor 100 is set to 245 mm / sec, the sleeve diameter of the developing sleeve 111S is set to 30 mm, and the linear speed of the developing sleeve 111S is set to 385 mm / sec. Is set to Therefore, the ratio (Vs / Vp) of the sleeve linear velocity Vs to the photoconductor linear velocity Vp is 1.57. In this embodiment, the required image density can be obtained even if the ratio (Vs / Vp) of the linear speed of the developing sleeve 111S to the linear speed of the photoconductor 100 is reduced to at least 0.9.
[0079]
The developing gap GP, which is the distance between the photoconductor 100 and the developing sleeve 111S, is set to, for example, 0.4 mm. Conventionally, if the particle size of the magnetic carrier MC is 50 μm, the development gap GP is preferably set to 0.65 mm or less, in other words, 13 times or less the particle size of the magnetic carrier MC. If the developing gap GP is too narrow, the magnetic brush comes into contact with the photoconductor 100 in a wide range, and thus the direction dependency such as the thinning of the horizontal line and the trailing edge whiteout tends to occur. Conversely, if the developing gap GP is widened, a sufficient electric field strength cannot be obtained, and image defects such as unevenness in isolated dots and solid portions occur. In order to maintain the electric field strength, it is possible to increase the applied voltage. However, an abnormal image such as a so-called white spot image, which is a white portion of a solid portion due to electric discharge, is likely to occur.
[0080]
At the upstream side of the developing area in the developer transport direction (clockwise direction indicated by arrow 111R in FIG. 9), the height of the developer chain, that is, the thickness of the developer layer on the developing sleeve 111 is regulated. A doctor blade 114 is provided as a layer thickness regulating member. The doctor gap, which is the distance between the doctor blade 114 and the developing sleeve 111S, is set to 0.87 mm. Conventionally, a plate-shaped doctor blade made of only a non-magnetic material has been used. However, the doctor blade 114 in this embodiment has a configuration in which a plate made of a magnetic material is joined to a conventional non-magnetic plate. are doing. By using a magnetic material in this way, as described later, magnetic spikes with uniform spike heights are easily formed. In the region of the developing sleeve 111S opposite to the photoconductor 100, stirring screws 112 and 113 for pumping the developer in the developing casing 115 to the developing sleeve 111S while stirring are provided. The developer in the developing casing 115 is a developer composed of the toner T and the magnetic carrier MC. The developer is mixed and stirred by the stirring screws 112 and 113 that are rotated by a driving unit (not shown), and the toner T is frictionally charged. . The charge amount (q / m) of the toner at this time is -5 to -60 C / g, and preferably -10 to -30 C / g.
[0081]
Further, as the magnetic carrier MC, metals such as iron, nickel, and cobalt or alloys of these and other metals, oxides such as magnetite, γ-hematite, chromium dioxide, copper zinc ferrite, manganese zinc ferrite, manganese-copper- Various ferromagnetic particles such as a Heusler alloy such as aluminum can be used. Further, the ferromagnetic particles may be coated with a styrene-acrylic, silicone, fluorine-based resin, or the like. These can be appropriately selected in consideration of the chargeability with the toner T. In addition, a charge control agent, a conductive substance, and the like may be added to the resin that coats the magnetic particles. Further, the magnetic particles may be dispersed in a styrene-acrylic or polyester resin. The saturation magnetization of the ferromagnetic material is preferably 45 to 85 emu / g. If it is less than 45 emu / g, the transportability is reduced due to the low intensity of the saturation magnetization, and the carrier adhesion to the photoconductor 100 is increased. If it exceeds 85 emu / g, the intensity of the saturation magnetization is high, so that the magnetic brush becomes strong, the scavenging effect is strong, and a scavenge mark is generated in the halftone portion, thereby deteriorating the image quality.
[0082]
As the toner T, a toner having at least a thermoplastic resin and pigments of carbon black, copper phthalocyanine, quinacridone, and bisazo is used. As the resin, a styrene-acrylic or polyester resin is preferable. In addition, a wax such as polypropylene and an alloy-containing dye for controlling the charge amount of the toner can be internally added as a fixing aid. Furthermore, oxides, nitrides, carbides and the like of surface-treated silica, alumina, titanium oxide and the like may be externally added. Further, a fatty acid metal salt, resin fine particles and the like may be externally added together.
[0083]
Here, in the present embodiment, as shown in FIG. 10, the peak position M1 of the magnetic force of the developing main magnet MG1b (magnetic force distribution P1b) on the developing sleeve 111S in the normal direction is the position between the photosensitive member 100 and the developing sleeve 111S. Each magnet of the magnet roller 111M is arranged so as to be downstream from the closest position M0 in the moving direction 100R (counterclockwise direction) of the photoconductor 100. In other words, the peak position M1 of the magnetic force is shifted from the closest position M0 by an angle of θ = 0 to 30 °. This is such that the generation site of the free toner T in the initial stage of the formation of the magnetic brush is located as much as possible in an area where the free toner T can move to the image portion as the latent image L of the photoconductor 100. Desirably, the front area A (A) of the development area shown in FIG.₀, A₁), The portion where the free toner T is generated is opposed to the closest position M0. The pole angle between the main magnet MG1b (magnetic force distribution P1b) and the magnet MG6 (magnetic force distribution P6) is 60 degrees, and the point at which the magnetic force becomes 0 between the two magnets is 30 degrees. In other words, the magnetic brush rises at or near the closest position M0, or the bottom portion of the magnetic force line of the developing main magnet MG1b (magnetic force distribution P1b) on the upstream side in the moving direction of the photoconductor 100 is positioned at the closest position. It is located at or near M0.
[0084]
With such a configuration, the development area front area A where the magnetic brush is formed₀And A₁Most of the cloud-like or smoke-like free toner T generated in step (1) easily moves to the image area of the photoconductor 100 due to the developing electric field. This developing situation will be described step by step with reference to FIG. FIG. 11 is an explanatory diagram of the developing method according to the first embodiment of the present invention, and is a diagram schematically illustrating a situation in which a latent image on a photoconductor is developed with free toner and toner of a magnetic brush in a developing area.
[0085]
First, a development area front area A where a magnetic brush (not shown) is formed₀, And a front area A of a developing area where a magnetic brush is formed as shown in FIG.₁That is, at a position where the magnetic brush is raised from a state in which the magnetic brush is pressed against the developing sleeve 111, a space in which the toner T can move due to impact force, centrifugal force or the like is formed, and the toner T and the magnetic carrier MC on the magnetic carrier MC gather. And the toner T sandwiched between the spikes and the ears. Also, the development area front area A₀In this case, a space in which the toner T can move due to impact force, centrifugal force or the like is formed even at the position where the ears are raised or before the magnetic brush is pressed against the developing sleeve 111S again. The toner T sandwiched between the ears where the carrier MC gathers is released. As a result, a large number of free toners T are generated in the form of cloud or smoke.
[0086]
The loose toner group T is attracted to the latent image (image portion) L of the photoconductor 100 by the developing electric field and is developed, as shown in FIG. In the non-image area, the electric field is directed toward the developing sleeve 111S, and the loose toner T returns to the magnetic carrier MC or moves onto the developing sleeve 111S. Thereby, the use efficiency of the toner T can be improved, and the inside of the apparatus due to toner scattering can be prevented. Further, in the present embodiment, an alternating electric field is applied by a not-shown alternating electric field applying means (developing bias application power supply Vp shown in FIG. 1A) to a portion where the photoconductor 100 and the developing sleeve 111S face each other. Further, in the present embodiment, since the magnetic brush is in contact with the photoconductor 100 in the middle area B and the rear area C of the developing area shown in FIG. An electrode effect works between the magnetic carrier (close to 100) and the photoconductor 100, so that the toner layer in the image area can be made more uniform, and the background toner T in the non-image area can be efficiently scavenged. This effect is also effective when a DC bias is applied. Also, unlike the conventional two-component contact developing method, the time during which the magnetic brush is in contact with the photoreceptor 100 is short, so that there is no direction dependency such as thinning of a horizontal line or white void at the rear end.
[0087]
As shown in FIG. 11C, the toner T reciprocates (oscillates) between the magnetic carrier MC at the tip of the magnetic brush and the photoconductor 100 due to the alternating electric field and the two-component contact development. The reciprocating motion of the toner T promotes the uniformity of the toner layer in the image portion L to bring about high image quality with good dot reproducibility, and brings the scavenging effect to the background toner T in the non-image portion.
[0088]
The average particle size of the magnetic carrier MC used in the present embodiment is 35 μm, the magnetization strength is 85 emu / g, the average particle size of the toner T is 7 μm, the toner concentration is 7 wt%, and the toner charge amount is −22.5 μC / g. there were. The developing conditions were as follows: a rectangular wave of Vp-p: 800 V and a frequency: 4.5 kHz as an AC component on a DC component of -500 V; The used alternating electric field was used.
As a result, it was found that there was no roughness in the halftone portion, the solid density was high in the solid portion, and high image quality with excellent line and character sharpness was obtained.
[0089]
(Second embodiment)
FIG. 12 is an explanatory diagram of a developing method according to the second embodiment of the present invention, and schematically illustrates a situation in which a latent image L of a photoconductor is developed with free toner T while maintaining a non-contact state of a magnetic brush in a developing area. FIG.
Here, the developing device and the image forming device have the same configuration as in the first embodiment. However, in order to maintain the non-contact state of the magnetic brush, of the developing conditions, the developing gap GP was set to 0.7 mm, which was wider than in the first embodiment, and the DC component in the developing electric field was set to -800 V. The charging potential of the photoconductor 100 was -950 V, the potential of the image portion was -50 V, and the potential of the non-image portion was -900 V, and the other steps were the same as in the first embodiment. As shown in FIGS. 12A to 12C, in the present embodiment, the latent image L of the photoconductor 100 is developed with the free toner T while keeping the magnetic brush in a non-contact state, so that the halftone portion is formed. It was found that high image quality with no roughness, high solid density in the solid part, and excellent sharpness of horizontal thin lines and characters was obtained.
[0090]
(Third embodiment)
Next, as a third embodiment, a configuration example of a color image forming apparatus including developing devices for performing the developing method according to the present invention as described in the first embodiment for the number of colors will be described.
FIG. 19 shows a schematic configuration of a color copying machine as an embodiment of the image forming apparatus. The color copying machine includes a color image reading device (hereinafter, referred to as a color scanner) 1, a color image recording device (hereinafter, referred to as a color printer) 2, a paper feed bank 3, a control unit (not shown), and the like.
The color scanner 1 forms an image of an original 5 on a contact glass 4 on a color sensor 9 via an illumination lamp 6, mirror groups 7a and 7b, and a lens 8, and converts color image information of the original 5 into, for example, red. (Red), green (Green), and blue (Blue) (hereinafter, referred to as R, G, and B, respectively) are read for each color separation light and converted into electrical image signals.
In this example, the color sensor 9 is composed of R, G, B color separation means and a photoelectric conversion element such as a CCD (charge coupled device), and simultaneously reads three color images obtained by performing color separation on the image of the original 5. ing. Then, based on the R, G, and B color separation image signal intensity levels obtained by the color scanner 1, color conversion processing is performed by an image processing unit (not shown), and black (Black: hereinafter, referred to as Bk) and cyan ( Color image data of cyan (hereinafter, referred to as C), magenta (hereinafter, referred to as M), and yellow (hereinafter, referred to as Y) are obtained.
[0091]
The operation of the color scanner 1 for obtaining the color image data of Bk, C, M, and Y is as follows. Upon receiving a scanner start signal that is timed with the operation of the color printer 2 to be described later, an optical system including the illumination lamp 6 and the mirror groups 7a and 7b scans the original 5 in the left direction of the arrow. One color image data is obtained. By repeating this operation four times in total, color image data of four colors is sequentially obtained. Then, each time the color printer 2 sequentially visualizes the images and superimposes them to form a final four-color full-color image.
[0092]
The color printer 2 includes a cylindrical photoreceptor 100 as an image carrier, a writing optical unit 10, a revolver developing unit (rotary developing device) 11 as a developing unit, an intermediate transfer device 12, a fixing device 13, and the like. Have been.
The photoreceptor 100 rotates in the counterclockwise direction indicated by an arrow, and around the photoreceptor cleaning device 14, a neutralizing lamp 15, a charger 101, a potential sensor 16 as a charging potential detecting means, and a revolver developing unit 11 are selected. A developing device 110K (e.g., corresponding to the developing device 110 having the configuration described in FIG. 9 of the first embodiment), a development density pattern detector 17, an intermediate transfer belt 18 of the intermediate transfer device 12, and the like are arranged.
[0093]
The writing optical unit 10 converts color image data from the color scanner 1 into an optical signal, performs optical writing corresponding to the image of the original 5, and forms an electrostatic latent image on the photoconductor 100. For example, the writing optical unit 10 includes a semiconductor laser 19 as a light source, a laser emission drive control unit (not shown), a polygon mirror 20 and a rotation motor 21, an f / θ lens 22, a reflection mirror 23, and the like. I have.
[0094]
The revolver developing unit 11 includes a Bk developing unit 110K, a C developing unit 110C, an M developing unit 110M, a Y developing unit 110Y, and a revolver rotation driving unit (not shown) for rotating each developing unit in a counterclockwise direction indicated by an arrow. Have been.
Each of the developing devices includes a developer carrier (see FIG. 1A, FIGS. 2 and 9) and a plurality of cylindrical developing sleeves 111S disposed inside the photoconductor 100. And a stirring member (such as stirring screws 112 and 113 shown in FIG. 9) that rotates to stir and transport the developer. The sleeve 111S carries a two-component developer containing the toner T and the magnetic carrier MC holding the toner on the surface, and conveys the carried two-component developer to a development area which is an area facing the photoconductor 100. Then, an electric field is applied between the developing roller 111 and the photoconductor 100 to develop the latent image formed on the surface of the photoconductor 100 with the toner.
The toner in each of the developing devices 110 (K, C, M, and Y) is charged to a negative polarity by stirring with a ferrite carrier as a magnetic carrier, and a developing bias (not shown) is applied to a developing sleeve 111S of each developing roller 111. The negative DC voltage V is supplied by the power supply Vp (see FIG. 1A)._DCAC voltage V_ACIs applied, and the developing sleeve 111S is biased to a predetermined potential with respect to the conductive support (metal base layer or the like) of the photoconductor 100.
[0095]
In the standby state of the copying machine main body, the Bk developing unit 110K of the revolver developing unit 11 is set at the developing position, and when the copying operation is started, the color scanner 1 starts reading the 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 begin (hereinafter, an electrostatic latent image based on Bk image data is referred to as a Bk electrostatic latent image (the same applies to C, M, and Y)). . Before the front end of the electrostatic latent image reaches the Bk development position so that development can be performed from the front end of the Bk electrostatic latent image, the Bk developing roller 111 (developing sleeve 111S) starts rotating, and the Bk electrostatic latent image is started. The image is developed with Bk toner. After that, the developing operation of the Bk electrostatic latent image area is continued. When the trailing end of the electrostatic latent image passes the Bk developing position, the revolver development is performed until the developing device of the next color comes to the developing position. The unit 11 rotates. This is completed at least before the leading end of the electrostatic latent image based on the next image data arrives.
[0096]
The intermediate transfer device 12 includes an intermediate transfer belt 18, a belt cleaning device 25, a transport belt 38, a paper transfer corona discharger (hereinafter, referred to as a paper transfer device) 26, and the like. The intermediate transfer belt 18 is stretched around a driving roller 18a, a transfer opposing roller 18b, a cleaning opposing roller 18c, and a driven roller group, and is driven and controlled by a driving motor (not shown).
The material of the intermediate transfer belt 18 is ETFE (ethylene tetrafluoroethylene), and its electrical resistance is 10⁸-10¹⁰Ω / cm²It is about. Further, the belt cleaning device 25 includes an entrance seal, a rubber blade, a discharge coil, an entrance seal, and a mechanism for contacting / separating the rubber blade, and the like. During the belt transfer of the fourth color image, the entrance seal and the blade are separated from the surface of the intermediate transfer belt 18 by the blade contact / separation mechanism. The paper transfer unit 26 applies an AC voltage + DC voltage or a DC voltage by a corona discharge method, and collectively transfers the superimposed toner image on the intermediate transfer belt 18 to a recording medium (for example, recording paper) 27.
[0097]
Recording papers 27 of various sizes are stored in the recording paper cassette 28 in the color printer 2 and the recording paper cassettes 29a, 29b, 29c in the paper supply bank 3, and the cassettes of the recording paper 27 of the designated size are removed. The paper is fed and conveyed in the direction of the registration roller pair 32 by the paper feed rollers 30, 31a, 31b and 31c. A manual tray 33 is provided on the right side of the printer 2 for manually feeding OHP paper or thick paper.
[0098]
In the color copying machine having the above-described configuration, when the image forming cycle is started, first, the photoconductor 100 is rotated counterclockwise by an arrow, and the intermediate transfer belt 18 is rotated clockwise by an arrow by a drive motor (not shown). Then, with the rotation of the intermediate transfer belt 18, the Bk toner image formation, the C toner image formation, the M toner image formation, and the Y toner image formation are performed, and finally, the intermediate transfer belt 18 is formed in the order of Bk, C, M, and Y. A toner image is formed on top of the toner image.
[0099]
More specifically, the formation of the Bk toner image is performed as follows. The charger 101 uniformly charges the photosensitive member 100 with negative charges by corona discharge. Then, the semiconductor laser 19 performs raster exposure based on the Bk color image signal. When this raster image is exposed, in the exposed portion of the photoreceptor 100 that is initially uniformly charged, the charge proportional to the amount of exposure light disappears, and a Bk electrostatic latent image is formed.
When the negatively charged Bk toner on the Bk developing sleeve comes into contact with the Bk electrostatic latent image, no toner adheres to the portion where the charge of the photoconductor 100 remains, 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 photoconductor 100 is transferred to the surface of the intermediate transfer belt 18 that is driven at a constant speed in a state of contact with the photoconductor 100 by a belt transfer device 34 (hereinafter, the intermediate image is transferred from the photoconductor 100 to the intermediate (Transfer of the toner image to the transfer belt 18 is referred to as belt transfer.)
[0100]
Some untransferred residual toner on the photoconductor 100 after the belt transfer is cleaned by the photoconductor cleaning device 14 in preparation for reuse of the photoconductor 100. The collected toner is stored in a waste toner tank (not shown) via a collection pipe.
Further, on the photoconductor 100 side, the process proceeds to the C image forming process after the Bk image forming process. At a predetermined timing, reading of C image data by the color scanner 1 is started. An image is formed. Then, after the rear end of the previous Bk electrostatic latent image has passed and before the front end of the C electrostatic latent image has reached, the rotating operation of the revolver developing unit 11 is performed, and the C developing device 110C The C electrostatic latent image is set at the position and is developed with C toner.
Thereafter, the development of the C electrostatic latent image area is continued, but when the rear end of the C electrostatic latent image passes, the revolver developing unit 11 is rotated as in the case of the Bk developing device 110K described above, The next M developing device 110M is moved to the developing position. This is also completed before the leading end of the next M electrostatic latent image reaches the developing position. In the M and Y image forming processes, the operations of reading the color image data, forming the electrostatic latent image, and developing are the same as those in the above-described processes of BK and C, and thus the description is omitted.
[0101]
The Bk, C, M, and Y toner images sequentially formed on the photoreceptor 100 are sequentially aligned on the same surface on the intermediate transfer belt 18 to form a four-color superimposed toner image. , The four color toner images are collectively transferred by the paper transfer device 26 to the recording paper 27 conveyed by the paper transfer belt 38.
At the time when the image forming operation is started, the recording paper 27 is fed from one of the recording paper cassettes 28, 29 a, 29 b, 29 c or the manual feed tray 33, and stands by at the nip of the registration roller pair 32. When the leading end of the toner image on the intermediate transfer belt 18 approaches the paper transfer unit 26, the registration roller pair 32 is driven so that the leading end of the recording paper 27 coincides with the leading end of the toner image, and the paper transfer belt 38 The registration of the recording paper 27 with the toner image is performed with the aid of the above. Then, the recording paper 27 is superimposed on the toner image on the intermediate transfer belt 18 and passes over the positive potential paper transfer unit 26. At this time, the recording paper 27 is charged with a positive charge by the corona discharge current, and most of the toner image is transferred onto the recording paper 27. Subsequently, the recording paper 27 is neutralized when passing through a portion opposite to a separation static eliminator by an AC + DC corona (not shown) arranged on the left side of the paper transfer unit 26, is separated from the intermediate transfer belt 18, and is further separated from the paper transfer belt 38. Then, the sheet moves to the paper transport belt 35.
[0102]
The recording paper 27 on which the four-color superimposed toner image is collectively transferred from the surface of the intermediate transfer belt 18 is conveyed to a fixing device 36 by a paper conveyance belt 35, and a nip portion between a fixing roller 36a and a pressure roller 36b controlled to a predetermined temperature. , The toner image is fused and fixed, is sent out of the apparatus main body by the discharge roller pair 37, and is stacked face up on a copy tray (not shown) to obtain a full color copy.
On the other hand, the surface of the photoconductor 100 after the transfer of the belt is cleaned by the photoconductor cleaning device 14 (brush roller, rubber blade), and is uniformly discharged by the discharge lamp 15. The surface of the intermediate transfer belt 18 after the transfer of the toner image onto the recording paper 27 is cleaned by pressing the blade of the belt cleaning device 25 again by the blade contact / separation mechanism.
[0103]
Here, in the case of the repeat copy, the operation of the color scanner 1 and the image formation on the photosensitive member 100 are performed at a predetermined timing following the image formation process of the fourth color (Y) of the first sheet. Proceed to the image forming step (Bk). The intermediate transfer belt 18 transfers the second sheet of Bk toner to the area cleaned by the belt cleaning device 25 on the front surface following the batch transfer step of the first sheet of the four-color superimposed toner image onto the recording paper 27. Allow the image to be belt transferred. After that, the operation is the same as that of the first sheet.
[0104]
The above is the copy mode for obtaining the four-color full-color copy. However, in the case of the three-color copy mode and the two-color copy mode, the same operation as described above is performed for the designated color and the number of times.
In the case of the single-color copying mode, only the developing device of the predetermined color of the revolver developing unit 11 is in the developing operation state until the predetermined number of sheets is completed, and the blade of the belt cleaning device 25 is pressed against the intermediate transfer belt 18. The copy operation is performed continuously with the operation as it is.
[0105]
In the case of the full-color copy mode of A3 size, it is desirable to form a one-color toner image each time the intermediate transfer belt 18 makes one rotation, and to form a four-color toner image by four rotations. In order to reduce the size of the entire apparatus, that is, to reduce the peripheral length of the intermediate transfer belt 18, secure the copy speed in the case of a small size, and not to reduce the copy speed of the maximum size, the intermediate transfer belt 18 must be 2 It is preferable to form a one-color toner image during the rotation. In this case, after the Bk toner image is transferred to the intermediate transfer belt 18, in the next rotation of the intermediate transfer belt 18, the color printer 2 idles without performing development and transfer, and in the next rotation, Development is performed with the C toner of the next color, and the C toner image is sequentially transferred to the intermediate transfer belt 18. At this time, the rotating operation of the revolver developing unit 11 for switching the developing device is performed during the idle rotation.
[0106]
【The invention's effect】
As described above, in the present invention, by setting the development area in a wider range than the conventional development area, the amount of toner to be developed in the development area is increased, and an image having a high solid density in a solid portion is obtained. The resulting developing method can be realized. Furthermore, in the present invention, the toner developed on the photoreceptor is separated by the magnetic carrier at the tip of the magnetic brush by contacting the magnetic brush with the photoreceptor, so that the solid portion is well filled with solids and the non-image portion is smooth. It is possible to realize a developing method capable of obtaining a high-quality image with less fogging and excellent horizontal fine lines and sharpness of characters. Further, by making the magnetic brush and the photoconductor non-contact, it is possible to realize a developing method for obtaining an image with no roughness in the halftone portion and excellent sharpness of horizontal thin lines and characters.
[0107]
In the present invention, the supply amount of the toner to be developed can be increased without increasing the rotation speed of the development sleeve by setting the development region in a wider range than the conventional development region using the above-described development method. Thus, it is possible to realize a developing device capable of obtaining an image having a high solid density in a solid portion. Further, in the present invention, by contacting the magnetic brush with the photoreceptor, the toner developed on the photoreceptor is separated by the magnetic carrier at the tip of the magnetic brush, so that the solid portion of the solid portion is well-filled, smooth and non-image. It is possible to realize a developing device capable of obtaining a high-quality image with less fogging of the portion and excellent horizontal fine lines and sharpness of characters.
[0108]
Further, in the present invention, by using the above-described developing device and setting the developing area in a wide range, the supply amount of the toner to be developed is increased, so that the developing gap, the rotational speed of the developing sleeve, etc. Image that can obtain a high-quality image with good solid filling in solid areas, smooth fog in non-image areas, and excellent sharpness of horizontal thin lines and characters. A forming method and an image forming apparatus can be realized. In particular, when a color image is formed, an image forming method and an image forming apparatus capable of obtaining an image with excellent reproducibility of a halftone portion can be realized.
[Brief description of the drawings]
FIGS. 1A and 1B are explanatory diagrams of a developing method of the present invention, in which FIG. 1A shows a schematic configuration example of a developing unit, and FIG. 1B shows a state of a two-component developer in a developing area in the developing method of the present invention. It is the schematic diagram which represented typically.
FIG. 2 is a diagram showing a magnetic force distribution by a magnet roller (a plurality of magnets) arranged in a developing sleeve of a developer carrier (developing roller) shown in FIG. 1 and its magnitude.
3 is a diagram showing a positional relationship between a main magnet of a magnet roller (a plurality of magnets) shown in FIG. 2 and a main magnet magnetic force forming auxiliary magnet.
FIG. 4 is a diagram schematically showing a situation in which ears of a magnetic carrier rise in a development area front region in a development method of the present invention.
FIG. 5 is a view schematically showing a situation in which the ears of a magnetic carrier are in strong contact with a photoreceptor in a middle region of a developing region in the developing method of the present invention.
FIG. 6 is a view schematically showing a state in which toner is developed in a rear area of a development area in the development method of the present invention.
FIG. 7 is a diagram schematically showing a state in which a DC electric field is applied in a reversal development system.
FIG. 8 is a diagram schematically showing a state in which a DC and AC alternating electric field is applied in a reversal development system.
FIG. 9 is a schematic configuration diagram illustrating a main part of an embodiment of an image forming apparatus including a developing device to which the developing method of the present invention is applied.
FIG. 10 is a diagram schematically showing an arrangement of main magnets in a developing sleeve in the developing method of the present invention.
FIG. 11 is an explanatory diagram of a developing method according to the first embodiment of the present invention, schematically illustrating a situation in which a latent image on a photoconductor is developed with free toner and toner of a magnetic brush in a developing area.
FIG. 12 is an explanatory diagram of a developing method according to a second embodiment of the present invention, schematically showing a situation in which a latent image L on a photoconductor is developed with free toner while maintaining a non-contact state of a magnetic brush in a developing area. FIG.
FIG. 13 is a schematic configuration diagram of a color copying machine as an example of an image forming apparatus according to a third embodiment of the present invention.
[Explanation of symbols]
10: Writing optical unit
11: Revolver developing unit (rotary developing device)
12: Intermediate transfer device
13: Fixing device
14: Photoconductor cleaning device
15: Static elimination lamp
18: Intermediate transfer belt
26: Paper transfer unit
27: Paper transfer belt
100: photoreceptor (image carrier)
101: Charging device
110: Developing device
110K: Black (Bk) developing device
110C: cyan (C) developing device
110M: Magenta (M) developing device
110Y: Yellow (Y) developing device
111: developing roller (developer carrier)
111S: developing sleeve
111M: Magnet roller
112, 113: stirring screw
114: Doctor blade (regulation member)
115: developing casing
116: toner storage section
A (A₀, A₁): Area in front of development area
B: middle part of development area
C: Area behind the development area
L: latent image
MG1a, MG1b, MG1c, MG2, MG3, MG4, MG5, MG6: Magnet
MC: Magnetic carrier
T: Toner

Claims

A developer carrying member having a magnet therein is disposed to face the image carrier, and a two-component developer including a toner and a magnetic carrier is carried by the developer carrying member and formed between the image carrying member and the developer carrying member. The magnetic carrier having a magnetic brush having toner on its surface is formed in the developing area, and a magnetic brush composed of spikes is formed in the developing area. In a developing method for developing the latent image formed thereon,
The magnetic carrier has a particle size of 5 to 100 μm, a magnetic substance content of 30% by weight, and a magnetic property of which the magnetization intensity (σ ₁₀₀₀ ) at a magnetic field of 1000 Oe is 30 to ₁₀₀₀ emu / cm ³ . And a remanent magnetization (σ _r ) of 10 emu / cm ³ or more in a magnetic field of 0 Oe before the carrier is demagnetized or demagnetized after passing through the magnetic field of the developing unit.

A toner carrier for carrying toner is arranged opposite to the image carrier, and a developer carrier having a magnet inside is arranged opposite to the toner carrier, and the toner carrier and the magnetic carrier are held by the developer carrier. And a toner-supplying electric field formed between the two-component developer and the toner-carrying member, the toner-supplying member formed between the developer-carrying member and the toner-carrying member. Forming a magnetic brush composed of ears on which magnetic carriers having toner on the surface are gathered, and attaching free toner detached from the magnetic carrier surface of the magnetic brush to the toner carrier, and carrying the toner on the toner carrier. Transporting to a development area formed between the image carrier and the latent image formed on the image carrier is developed with toner,
The magnetic carrier has a particle size of 5 to 100 μm, a magnetic substance content of 30% by weight, and a magnetic property of which the magnetization intensity (σ ₁₀₀₀ ) at a magnetic field of 1000 Oe is 30 to ₁₀₀₀ emu / cm ³ . And a remanent magnetization (σ _r ) of 10 emu / cm ³ or more in a magnetic field of 0 Oe before the carrier is demagnetized or demagnetized after passing through the magnetic field of the developing unit.

The developing method according to claim 1,
A developing method, wherein spikes in which magnetic carriers are gathered rise in the developing area, and the toner is released while the spikes are sleeping, and the released free toner is used for development.

The developing method according to claim 1,
In the developing area, a developing main magnetic pole arranged at least at the closest position between the image carrier and the developer carrier, and an adjoining or adjacent upstream side of the main magnetic pole with respect to the rotating direction of the image carrier. And a magnetic pole of opposite polarity.

The developing method according to claim 1,
A magnetic field applied by the developing main magnetic pole in the developing area has a maximum magnetic flux density of 50 to 150 mT on the surface of the image carrier.

The developing method according to claim 1,
A developing method comprising a mechanism for replenishing a carrier to a developer independently or together with a toner.

The developing method according to claim 1,
A developing method, wherein the volume average particle diameter of the magnetic carrier is 50 μm or less.

The developing method according to claim 1,
A developing method, wherein the volume average particle diameter of the magnetic carrier is equal to or less than the minimum pixel diameter of an optically written image (latent image) on an image carrier.

The developing method according to claim 1,
A developing method, wherein the magnetic carrier has a dynamic electric resistance of 10 ⁵ to 10 ¹⁰ Ω.

The developing method according to claim 1,
A developing method, wherein a magnetic toner is used as the toner.

The developing method according to claim 1,
A developing method, wherein a surface layer of the magnetic carrier is coated with a film containing no carbon.

The developing method according to claim 1,
The average spacing Sm of the irregularities in the direction of the rotation axis on the surface of the developer carrier is not more than twice the minimum pixel diameter of the optically written image (latent image) on the image carrier, and the ten-point average roughness Rz is magnetic. A developing method, wherein the volume average particle diameter of the carrier is 1/2 or less.

The developing method according to claim 1,
A developing method, wherein the coverage of the toner on the surface of the magnetic carrier immediately before the development of the developer forming the magnetic brush for development is 20 to 100%.

The developing method according to claim 1,
A developing method, comprising: means for demagnetizing or demagnetizing the developer carried on the developer carrier by magnetic force after passing through a magnetic field in a development area.

The developing method according to claim 1,
A developing method comprising: a carrier catcher that magnetically collects a carrier in opposition to the surface of the image carrier after passing through the developing area and before reaching the transfer area.

The developing method according to claim 1,
A regulating member for regulating the amount of the two-component developer on the developer carrying member, and after passing through the regulating member and before reaching the developing region, is opposed to the surface of the developer carrying member and is close to or in contact with the magnetic brush. A developing method comprising the carrier scattering prevention developer guide plate according to the aspect.

The developing method according to claim 1,
A developing method using a carrier obtained by mixing two or more magnetic carriers having different average residual magnetizations.

The developing method according to any one of claims 1 to 17,
On the developer carrier that carries the two-component developer, the spikes on which the magnetic carriers are gathered rise, and while the spikes lie down, the toner is released from the magnetic carrier, and the free toner that is released from the magnetic carrier is arranged in opposition. An electric field for moving to the side of the rotating member (image carrier or toner carrier), and attaching the electric field to the rotating member.

The developing method according to any one of claims 1 to 18,
The powder characteristics and magnetic characteristics of the magnetic carrier, and the magnetic characteristics and morphological characteristics of the magnet in the developing area or the toner supply area are determined by comparing the magnetic carrier gathering on the developer carrier with the spikes of the magnetic carrier rising and then falling down. A developing method wherein the toner is separated from the magnetic carrier.

The developing method according to any one of claims 1 to 19,
A toner in which the morphological and electrical characteristics of a developer carrier for carrying a two-component developer and the morphological and electrical characteristics of a rotating member (image carrier or toner carrier) disposed opposite to the magnetic carrier are removed. A developing method for setting an electric field for moving the liquid crystal to the side of the rotating member arranged oppositely.

The developing method according to any one of claims 1 to 20,
When the spikes on which the magnetic carriers are gathered rise on the developer carrier that carries the two-component developer, an area opposed to a rotating member (image carrier or toner carrier) that is arranged to face the toner so as to adhere the toner. A developing method wherein the tip of the magnetic brush is separated from the developer layer on which the magnetic carriers on the two-component developer carrier are gathered by the magnets inside.

The developing method according to any one of claims 1 to 21,
A region facing a rotating member (image carrier or toner carrier) that is opposed to the toner carrier when the ears on which the magnetic carriers are gathered fall down on the developer carrier carrying the two-component developer. A developing method, wherein a tip of a magnetic brush is brought into a state of being joined with a developer layer in which magnetic carriers on a developer carrying member are gathered by a magnet inside.

A developer carrying member having a magnet therein is disposed to face the image carrier, and a two-component developer including a toner and a magnetic carrier is carried by the developer carrying member and formed between the image carrying member and the developer carrying member. A magnetic brush formed of spikes in which magnetic carriers having toner on the surface are gathered, and a latent image formed on the image carrier with the toner of the magnetic brush in the developing area. In a developing method for developing
And developing the toner by spraying the toner onto the image carrier from a magnetic carrier having a residual magnetization (σ _r ) having a toner on the surface and having a residual magnetization (σ _r ) of 10 emu / cm ³ or more in the developing area.

The developing method according to claim 23,
Contacting the magnetic brush formed in the developing area with the image carrier to release the toner from the surface of the magnetic carrier, and spraying the released free toner to the image carrier for development; Method.

The developing method according to claim 23 or 24,
A developing method, wherein a magnetic brush formed in the developing area is brought into contact with an image carrier to release toner already developed from the image carrier.

A developer carrying member having a magnet therein is disposed to face the image carrier, and a two-component developer including a toner and a magnetic carrier is carried by the developer carrying member and formed between the image carrying member and the developer carrying member. A magnetic brush formed of spikes in which magnetic carriers having toner on the surface are gathered, and a latent image formed on the image carrier with the toner of the magnetic brush in the developing area. In a developing method for developing
In the developing area, a magnetic brush formed of a magnetic carrier having a residual magnetization (σ _r ) having a toner on its surface and having a residual magnetization of 10 emu / cm ³ or more is rubbed or brought close to the image carrier to develop with the toner. Characteristic developing method.

The developing method according to claim 26,
A developing method, wherein a magnetic brush is rubbed or brought close to the image carrier in the developing area to release the already developed toner from the image carrier.

A developer carrying member having a magnet therein is disposed to face the image carrier, and a two-component developer including a toner and a magnetic carrier is carried by the developer carrying member and formed between the image carrying member and the developer carrying member. Transporting the latent image formed on the image carrier with toner,
Forming a magnetic brush including, in the developing region, an ear in which magnetic carriers having a residual magnetization (σ _r ) having toner on the surface thereof of 10 emu / cm ³ or more and free toner to be detached from the magnetic carrier surface; The spikes of the carrier rise, and the toner is released and developed while the spikes sleep, and the free toner to be released by contacting the magnetic brush with the image carrier is sprayed and developed on the image carrier, and Developing by rubbing or approaching a magnetic brush to an image carrier.

The developing method according to claim 28,
The magnetic brush formed in the developing area is brought into contact with the image carrier to release the toner from the image carrier, and the magnetic brush is rubbed or brought close to the image carrier to remove the already developed toner from the image carrier. A developing method characterized by being detached from a carrier.

The developing method according to claim 28 or 29,
A developing method, wherein a center of a magnet provided inside the developer carrier is inclined downstream in a developer transport direction in a developing area.

31. The developing method according to claim 28, 29 or 30,
The linear velocity ratio (Vs / Vp) between the linear velocity (Vs) of the developer carrier and the linear velocity (Vp) of the image carrier is
0.9 <Vs / Vp <4
A developing method, wherein the development is performed in the range of:

The developing method according to any one of claims 28 to 31,
A developing method, wherein free toner released from the surface of the magnetic carrier in the developing area is transferred to the image carrier by an electric field applied between the image carrier and the developer carrier, and developed.

The developing method according to claim 32,
An electric field applied between the image carrier and the developer carrier is an alternating electric field.

A developer carrying member having a magnet therein is disposed to face the image carrier, and a two-component developer including a toner and a magnetic carrier is carried by the developer carrying member and formed between the image carrying member and the developer carrying member. Transporting the latent image formed on the image carrier with toner,
In the developing area, a magnetic brush including a magnetic carrier having a magnetic carrier having a toner on the surface thereof and a free toner to be detached from the magnetic carrier surface is formed. And developing the latent image on the image carrier by developing the magnetic brush close to the image carrier.

The developing method according to claim 34,
A developing method, wherein the magnetic brush formed on the developer carrier develops the image carrier in a non-contact state.

The developing method according to claim 34 or 35,
In the developing method, the free toner detached from the surface of the magnetic carrier is transferred to the image carrier by an electric field applied between the image carrier and the developer carrier, and developed.

The developing method according to claim 34, 35 or 36,
A developing method, wherein the electric field applied between the image carrier and the developer carrier is an alternating electric field.

In a developing device that is arranged to face the image carrier and develops a latent image formed on the image carrier to visualize the latent image,
A developing device for performing development by the developing method according to claim 1.

A latent image is formed on an image carrier, and the latent image on the image carrier is developed into a visible image by developing means, and then the visible image is transferred to a recording medium directly or via an intermediate transfer body. And an image forming method for forming an image by fixing.
39. An image forming method using the developing device according to claim 38 as the developing unit.

An image carrier having photoconductivity, charging means for charging the image carrier, means for irradiating the charged image carrier with light to form a latent image, and developing the latent image on the image carrier Developing means for visualizing the image, means for transferring the visible image on the image carrier directly or via an intermediate transfer member to a recording medium, and means for fixing the visible image transferred to the recording medium. In the image forming apparatus provided with
An image forming apparatus comprising the developing device according to claim 38 as the developing unit.