JP4427246B2

JP4427246B2 - Developing device, image forming apparatus, and process cartridge

Info

Publication number: JP4427246B2
Application number: JP2002362968A
Authority: JP
Inventors: 一小山; 信貴竹内; 高垣　　博光; 孝幸小池
Original assignee: Ricoh Co Ltd
Current assignee: Ricoh Co Ltd
Priority date: 2002-12-13
Filing date: 2002-12-13
Publication date: 2010-03-03
Anticipated expiration: 2022-12-13
Also published as: JP2004191882A

Description

【０００１】
【発明の属する技術分野】
本発明は、電子写真、静電記録、静電印刷等において、感光体表面に形成された静電荷像を顕像化するための現像装置、該現像装置を使用した画像形成装置、及びプロセスカートリッジに関するものである。
【０００２】
【従来の技術】
この種の発明として例えば特開平１０−６３０８１号公報記載の発明が公知である。この発明は、現像剤に過大な力を作用させずに、補給トナーを現像剤中に即時に分散させて適切な帯電量を付与することが可能であり、かつ現像剤収容部における現像剤のトナー濃度を均一化する能力の高い現像装置を提供するためになされたもので、トナーとキャリアとを混合した２成分現像剤を収容する現像剤収容部に、現像剤が循環移送される現像剤搬送路が設けられ、この現像剤搬送路内には送りねじ状の翼体を有する現像剤搬送部材が設けられており、この翼体間にメッシュ状のスクリーン部材が取り付けられている。この現像剤搬送部材が回転することによって、現像剤が搬送されるとともに、メッシュ状のスクリーン部材を複数回通過し、現像剤の攪拌が行なわれるとともに、トナーとキャリアとの摩擦によって適切な帯電が行なわれるように構成している。
【０００３】
また、特開２０００−１９８２３号公報に開示された発明も公知である。この発明は、現像装置の駆動開始時及び長時間連続攪拌時の現像剤劣化、現像剤の帯電量不足、画像濃度の低下、放置混色の増加等の問題を解消するためになされたもので、攪拌部の突起部材の最大投影面積Ｘが、
（Ｐ×Ｄ）／２００≦Ｘ≦（Ｐ×Ｄ）／７
０．０１５〔Ｄ×（Ｆ＋ｆ）〕≦Ｘ≦０．２〔Ｄ×（Ｆ＋ｆ）〕
の関係になるように設定している。なお、式中、Ｐは搬送部４５Ｂの螺旋状羽根部材のピッチ距離［ｍｍ］、Ｄは搬送部４５Ｂの螺旋状羽根部材の先端部の回転軌跡の直径［ｍｍ］、Ｘは突起部材の突設方向に対して垂直方向から投影したときの突起部材の最大投影面積［ｍｍ^２］、Ｆは搬送部４５Ｂの根元部における回転軸方向の幅寸法［ｍｍ］、ｆは搬送部４５Ｂの先端部における幅寸法［ｍｍ］である。
【０００４】
【特許文献１】
特開平１０−６３０８１号公報
【０００５】
【特許文献２】
特開２０００−１９８２３号公報
【０００６】
【発明が解決しようとする課題】
しかし、前者の発明では、スクリーン部材をパドル状に２ヶ所設けた場合は該部が最下方位置や現像ローラと最近接対向の際の動トルクが平均トルクより大幅に高まり、トルク変動が大きく、駆動モータトルク余裕を大きくとる必要があった。また該駆動モータトルクに余裕が少ないと現像系の回転ムラによって現像画像にピッチムラ、バンディング等の濃度ムラが発生し易い。一方、螺旋状スクリュー部分の一部又は全体をスクリーン部材で構成した場合は、スクリュー部材の開口個所に現像剤の横送り能力がないので、現像剤の横攪拌（現像ローラ軸方向の攪拌）の能力が低減する。
【０００７】
また、後者の発明では、螺旋状スクリューの回転軸部に突設された複数の突起部材は剤を遠心方向に抛出する機能があるが、空隙発生個所への現像剤の自重落下移動を利用する態様の現像剤の攪拌効果は殆ど得られない。流動する現像剤の分散混合、攪拌機能に関し改良の余地がある。
【０００８】
本発明はこのような従来技術の実情に鑑みてなされたもので、その目的は、トルクをあまり高めることなく、現像剤を効率よく、高速で剪断することが可能であって、補給トナーの現像剤への分散性・縦攪拌性（円周方向の攪拌性）を改良した現像装置及びこの現像装置を備えた画像形成装置並びにこの現像装置を使用した現像方法を提供することにある。
【０００９】
また、他の目的は、現像装置全体の駆動投入エネルギーに対しての現像剤の縦横攪拌（円周方向及び軸方向）、補給トナーの分散、及びトナー帯電立ち上げの効率の良い現像装置及び画像形成装置並びに前記現像装置を使用した現像方法を提供することにある。
【００１０】
【課題を解決するための手段】
前記目的を達成するため第１の手段は、体積平均粒径が１０μｍ以下のトナーと体積平均粒径が１００μｍ以下のキャリアとを含む２成分現像剤を収容する現像剤収容部と、表面に静電潜像が形成される像担持体と対向するように配置され、前記２成分現像剤の薄層を担持して、前記像担持体との近接位置に搬送する現像剤担持体と、前記現像剤担持体に平行して配置され前記２成分現像剤を攪拌して前記現像剤担持体に搬送する現像剤攪拌搬送部材と、を備え、前記現像剤担持体と前記像担持体との近接位置で前記現像剤担持体上の前記２成分現像剤からトナーを前記像担持体に転移させて、前記静電潜像を可視化する現像装置において、前記現像剤攪拌搬送部材が、駆動源から駆動力を得て回転駆動される回転軸と、該回転軸部の周囲に形成された螺旋状羽根部材により前記２成分現像剤を主として前記回転軸の軸方向に平行な方向に搬送する搬送部と、前記回転軸の軸方向に対して所定の角度をもって前記螺旋状羽根部材に固定された複数の線状部材からなり、前記２成分現像剤を主として剪断し、攪拌する攪拌部とから構成され、前記攪拌部の複数の線状部材の断面の前記回転軸の法線方向に占める長さの和Ｂ（＝Σｂ）の最大値ＢMAXが、キャリアの体積平均粒径をＲｃとしたときに、
Ｒｃ＜ＢMAX≦５０Ｒｃ
ＢMAX≦０．２（Ｄ−ｄ）
ただし、Ｄ：該攪拌搬送部材の螺旋状羽根部材の回転軌跡の直径［ｍｍ］
ｄ：該攪拌搬送部材の回転軸の外径［ｍｍ］
の関係に設定され、前記攪拌部の複数の線状部材の断面の形状が、前記回転軸の回転による前記線状部材の進行方向下流側に頂点を有する形状であり、前記螺旋状羽根部材と前記線状部材との固定位置とは異なる位置において前記複数の線状部材を互いに連結する連結部材を更に含み、前記複数の線状部材は、前記回転軸の回転方向に沿って並ぶように配設されており、前記線状部材は、複数の前記螺旋状羽根部材に対して前記回転軸の軸方向にわたって複数の点で固定されており、前記連結部材は、前記線状部材と前記螺旋状羽根部材との複数の固定点のうち隣接する二点間において前記複数の線状部材を互いに連結し、前記連結部材は、前記螺旋状羽根部材の螺旋形状に沿って螺旋状に配設された線状の部材であり、前記回転軸の軸方向にわたって複数の点で前記複数の線状部材を互いに連結することを特徴とする。
【００１１】
このように構成すると、二成分現像剤（以下、単に現像剤と称す）を高い効率で、かつ高速で剪断することが可能となり、補給トナーの現像剤への分散性・縦攪拌性をトルクを高めないで改良することができる。
また、このように構成すると、線状部材の変形防止による攪拌効率を高効率、高安定に維持することができる。
【００１２】
第２の手段は、第１の手段において、前記螺旋状羽根部材固定された複数の線状部材の５０％以上を、螺旋状羽根部材の先端部の回転軌跡上又は近傍に配置したことを特徴とする。
【００１３】
このように構成すると、現像剤の高効率、高速剪断を行い攪拌効率を向上させることができる。
【００１４】
第３の手段は、第１または第２の手段において、前記螺旋状羽根部材固定された複数の線状部材の６０％ないし９５％を、現像剤に埋没した状態で回転させることを特徴とする。
【００１５】
このように構成すると、トルク変動抑制により、駆動モータトルク抑制や、現像ローラ回転ムラ等によるピッチムラ、バンディング等の画像濃度ムラを防止することができる。
【００１６】
第４の手段は、第１ないし第３の手段において、前記螺旋状羽根部材に固定された複数の線状部材の軸方向断面であって、同一回転軌跡面に存在する該線状部材断面の占有率を７０％以下にすることを特徴とする。
【００１７】
このように構成すると、遊離トナーや現像剤の自重落下現象を利用して、攪拌搬送部材のトルクを上げずに現像剤の攪拌効率を向上させることができる。
【００１８】
第５の手段は、第１ないし第４の手段において、前記螺旋状羽根部材に固定された複数の線状部材が回転軌跡の異なる線状部材を含むこと、言い換えれば、一部の回転軌跡を互いに異なる回転軌跡になるように前記複数の線状部材を配置したことを特徴とする。
【００１９】
このように構成すると、最大トルクを上げないで剪断、分散機能を高め、攪拌効率を向上させることができる。
【００２０】
第６の手段は、第１の手段において、前記現像剤攪拌搬送部材の回転軸部の６０％以上を現像剤中に埋没させた状態で回転させることを特徴とする。
【００２１】
このように構成すると、攪拌効率の向上及び省スペース化を図ることができる。
【００２２】
第７の手段は、第１ないし第６の手段において、複数の線状部材を備えた現像剤攪拌搬送部材の少なくとも一対が現像剤搬送方向が異なるように設定されていることを特徴とする。
【００２３】
このように構成すると、現像剤の攪拌搬送部材の回転軸方向の偏りを防止することができる。
【００２４】
第８の手段は、第１ないし第７の手段において、前記螺旋状羽根部材に固定された複数の線状部材の一部の回転軌跡周速が、像担持体と対向する現像剤担持体の周速以下に設定されていることを特徴とする。
【００２５】
このように構成すると、駆動トルクの低減を図ることができる。
【００２８】
第９の手段は、第１ないし第８の手段において、前記線状部材の回転軸の法線方向に占める幅Ｗが前記２成分現像剤中のキャリアの体積平均粒径Ｒｃの２０倍以下になるように前記幅Ｗが設定されていることを特徴とする。
【００２９】
このように構成すると、現像剤の分散性向上と駆動トルク上昇防止の両立を図ることができる。
【００３０】
第１０の手段は、第１ないし第９の手段において、前記現像剤攪拌搬送部材の動トルク変動が＋２５％から−２５％の間に設定されていることを特徴とする。
【００３１】
このように構成すると、ピッチムラ、バンディング等の画像濃度ムラを防止することができる。
【００３２】
第１１の手段は、第１、第３及び第６の手段において、前記現像剤の流動度が４５ｓｅｃ／５０ｇ（ＪＩＳＺ−２５０２）以下であることを特徴とする。
【００３３】
このように構成すると、現像剤の分散性の向上と駆動トルクの低減を図ることができる。
【００３４】
第１２の手段は、第１の手段において、現像剤中のトナーの加速凝集度がパウダーテスタの計測値で２０％以下であることを特徴とする。ただし、加速凝集度測定篩のメッシュ径は７５μｍ、４５μｍ、２２μｍである。
【００３５】
このように構成すると、現像剤の分散性の向上と駆動トルクの低減を図ることができる。
【００４０】
第１３の手段は、第１の手段におけるトナーが、有機溶媒中に少なくとも、ウレア結合し得る変性されたポリエステル系樹脂と着色剤を含むトナー組成物を溶解または分散させ、該溶解または分散物を水系媒体中に分散し、重付加反応させ、この分散液の溶媒を除去、洗浄して得られたカラートナーであることを特徴とする。
【００４１】
このように構成すると、現像剤の分散性の向上と駆動トルクの低減を図ることができる。
【００４２】
第１４の手段は、第１または第１３の手段において、前記トナーは、重量平均粒径が４．０〜８．０μｍであり、粒径分布がＤｖ／Ｄｎ≦１．２５（Ｄｖ：重量平均粒径、Ｄｎ：個数平均粒径）であることを特徴とする。
【００４３】
このように構成すると、現像剤の分散性の向上と駆動トルクの低減を図ることができる。
【００４４】
第１５の手段は、第１、第１３及び第１４の手段において、前記トナーが、平均円形度０．９０〜０．９９のトナーであることを特徴とする。ただし、「円形度＝粒子の投影面積と同じ面積を有する円の周囲長／粒子投影像の周囲長」である。
【００４５】
このように構成すると、現像剤の分散性の向上と駆動トルク低減を図ることができる。
【００４６】
第１６の手段は、第１の手段において、現像剤担持体上トナーの感光体に対向した面におけるトナーの被覆率をＰ［％］、現像剤担持体線速ｖＤと感光体線速ｖＰの線速比をｖＤ／ｖＰとするとＰ・（ｖＤ／ｖＰ）が、
１／０．９８≦Ｐ・（ｖＤ／ｖＰ）／１００≦１．５／０．８
の範囲になるように制御することを特徴とする。
【００４７】
すなわち、
１０２≦Ｐ・（ｖＤ／ｖＰ）≦１８７．５
ただし、２成分現像剤における前記被覆率Ｐは、ｒ／Ｒ＜１の場合、次式で近似できる。
【００４８】
Ｐ＝１００×Ｃ×（√３）／｛２π（１００−Ｃ）（１＋ｒ／Ｒ）＾２（ｒ／Ｒ）（ρｔ／ρｃ）｝
Ｃ：トナー濃度（重量％）
ｒ：トナーの体積平均粒径
Ｒ：キャリアの体積平均粒径
ρｔ：トナーの真比重
ρｃ：キャリアの真比重
このように構成すると、濃度ムラ、ざらつき感の少ない高品質画像を得ることができる。
【００４９】
第１７の手段は、第１、第６、第７、第９、第１１及び第１２の手段において、現像剤が磁性キャリアとトナーからなる２成分現像剤であり、該磁性キャリアの体積平均粒径がトナーの体積平均粒径より大きく磁化が３０乃至１０００ｅｍｕ／ｃｍ＾３（１１ｋＯｅ磁場中）である事を特徴とする。なお、本明細書中で＾は冪乗を示し、ｃｍ＾３はｃｍの３乗、すなわち、立方センチメータを意味する。
【００５０】
このように構成すると、低ストレス現像とキャリア付着防止の両立を図ることができる。
【００５１】
第１８の手段は、第１の手段において、現像剤層の最大現像電位差印加時のダイナミック抵抗が１０＾７Ω・ｃｍ以下であることを特徴とする。
【００５２】
ただし、ダイナミック抵抗とは、磁石を内包したローラ（φ２０；６００ＲＰＭ）に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、耐圧上限レベル（高抵抗シリコンコートキャリアでは４００Ｖから鉄粉キャリアでは数Ｖ）未満の印加電圧を印加した時の抵抗値を示す。
【００５３】
このように構成すると、低ポテンシャル現像と地汚れ防止の両立を図ることができる。
【００５４】
第１９の手段は、像担持体を帯電させる帯電手段と、像担持体に潜像を形成するために光書き込みを行う露光装置と、前記露光装置によって形成された潜像を現像する請求項１ないし１８のいずれか１項に記載の現像装置と、前記現像装置によって現像された顕像を記録媒体に転写する転写装置と、前記転写手段によって転写された記録媒体上の顕像を定着する定着装置とを備えていることを特徴とする。
【００５５】
第２０の手段は、第１９記載の画像形成装置において、
０＜｜ＶＤ｜−｜ＶＢ｜＜｜ＶＤ−ＶＬ｜＜４００Ｖ
を満足していることを特徴とする。
【００５６】
このように構成すると、トナー消費量低減と定着エネルギー低減を図ることができる。
【００５７】
第２１の手段は、像担持体、帯電装置、現像装置、クリ−ニング装置より選ばれる少なくとも１つの手段を一体に支持し、画像形成装置本体に着脱自在であるプロセスカ−トリッジにおいて、前記現像装置が、請求項１ないし１８のいずれか１項に記載の現像装置からなることを特徴とする。
【００５８】
このおうに構成すると、プロセスカートリッジ現像剤へのハザード低減による長寿命化及び現像能力の向上を図ることができる。
【００５９】
第２２の手段は、第１ないし第９の手段に係る現像装置を使用して現像する現像方法において、動トルク変動が＋２５％から−２５％の間で前記現像剤攪拌搬送部材を回転させることを特徴とする。
【００６０】
このように構成すると、ピッチムラ、バンディング等の画像濃度ムラを防止することができる。
【００６１】
第２３の手段は、第１ないし第１５の手段に係る現像装置を使用して現像する現像方法において、前記現像剤担持体上のトナーの感光体に対向した面におけるトナーの被覆率をＰ［％］、現像剤担持体線速ｖＤと感光体線速ｖＰの線速比をｖＤ／ｖＰとすると、Ｐ・（ｖＤ／ｖＰ）が、
１／０．９８≦Ｐ・（ｖＤ／ｖＰ）／１００≦１．５／０．８
の範囲になるように制御することを特徴とする。
【００６２】
このように構成すると、濃度ムラ、ざらつき感の少ない高品質画像を得ることができる。
【００６３】
【発明の実施の形態】
以下、本発明の実施形態について図面を参照して説明する。なお、以下の説明において、前述の従来例と同等及び各実施形態で同等な各部には同一の参照符号を付し、重複する説明は適宜省略する。
【００６４】
図１は本発明の実施に係る画像形成システム装置全体の概略構成を示す図である。同図において、静電潜像担持体である感光体ドラム（以下、単に感光体と称す）１の周囲には、当該感光体１表面を帯電するための帯電装置２、一様帯電処理面に潜像を形成するためのレーザ光線で書き込む画像露光部３、感光体１表面の潜像に帯電トナーを付着させることによってトナー像を形成する現像装置４、感光体１表面に形成されたトナー像を記録紙へ転写するための転写装置５、感光体１上の残留トナーを除去するためのクリーニング装置６、感光体１上の残留電位を除去するための除電ランプ７が順に配設されている。このような構成において、帯電装置２の帯電ローラによって表面が一様に帯電された感光体１は、露光によって表面に静電潜像が形成され、トナーのみからなる１成分系現像剤又はトナーとキャリアを混合した２成分系現像剤を用いる現像装置４によってトナー像が形成される。このトナー像は、転写ベルトなどからなる転写装置５によって、不図示の給紙トレイから搬送されてくる記録紙へ感光体１表面から転写される。この転写の際に感光体１に静電的に付着した記録紙は、記録紙の重さ、剛性、記録紙と分離搬送手段との吸着力、分離爪等の効果で感光体１表面から分離される。そして、未定着の記録紙上のトナー像は加熱及び加圧する定着器８によって記録紙に定着される。一方、転写されずに感光体１上に残留したトナーは、クリーニング装置６によって除去され回収される。残留トナーが除去された感光体１は除電ランプ７で初期化され、次回の画像形成プロセスに供される。
【００６５】
図２は現像装置４の構成を示す図である。本実施形態に係る現像装置４は２成分現像剤を使用する現像装置である。現像装置４は現像容器４０と、現像容器４０の感光体１側の開口部４１に設けられた現像ローラ４２と、前記開口部４１の現像ローラ４２の表面に対向する位置に設けられたドクタブレード４３と、２段にわたって設けられ、現像剤４６を移送するとともに現像剤４６を攪拌する現像剤攪拌搬送部材４４，４５（以下、ダブルスクリューとも称す）とからなる。現像剤担持体である現像ローラ４１は感光体１に近接するように配置されていて、双方の対向部分には、感光体１と磁気ブラシが接触する現像領域が形成されている。現像ローラ４２は、アルミニウム、真鍮、ステンレス、導電性樹脂などの非磁性体を円筒形に形成してなる現像スリーブと、この現像スリーブを回転駆動する不図示の回転駆動機構からなり、この回転機構は前記現像スリーブを図２において時計回りに回転させる。以下、現像スリーブも含めて現像ローラと称す。なお、符号４６ａはスクリュー部現像剤だまりの現像剤４６の最上面を示し、符号４０ａはトナー補給孔を示す。
【００６６】
現像ローラ４１の表面はサンドブラストもしくは数十〜数百ｍｍの深さを有する複数の溝を形成する処理を行い１０〜２０μｍＲＺの範囲に入るように荒らしている。感光体１はアルミ等の素管に感光性を有する有機感光体を塗布し、感光層を形成したドラムタイプのものである。２成分現像剤はキャリア表面をトナー一層で最蜜に覆い尽くす程度の被覆率を１００％と見なした場合、非磁性トナーを用いたとき、高々７０％程度になるようにトナー補給を制御してトナー帯電不足によるトナー飛散や地汚れを防止している。なお、ＲＺは十点平均粗さを表す。
【００６７】
本実施形態においては、前記トナーのキャリアに対する被覆率を５０％中心に制御し、感光体１のドラム径が６０ｍｍで、ドラム線速が２４０ｍｍ／秒に設定され、現像スリーブのスリーブ径が２０ｍｍで、ローラ線速が６００ｍｍ／秒に設定されている。したがって、ドラム線速に対するスリーブ線速の比は２．５倍である。すると接触現像であれば、トナーと感光体１表面は現像ニップにおいて確実に１回ないし１．５回の割合でトナー粒径レベル範囲で接触することになり、現像電界が十分作用すれば、画像の欠落のないかつ画像濃度の十分な画像を得ることができる。
【００６８】
２成分現像剤における被覆率Ｐは、
ｒ／Ｒ≪１
の場合、
Ｐ＝１００×Ｃ×（√３）／｛２π（１００−Ｃ）（１＋ｒ／Ｒ）＾２（ｒ／Ｒ）（ρｔ／ρｃ）｝
Ｃ：トナー濃度（重量％）
ｒ：トナーの体積平均粒径
Ｒ：キャリアの体積平均粒径
ρｔ：トナーの真比重
ρｃ：キャリアの真比重
で近似できる。なお、現像バイアスが交番電界を生じる振動バイアスを用いると、現像剤担持体の潜像担持体に対する線速比を上記の２．５倍相当ではなく高々１．５倍程度にしても現像剤中のトナーを有効に現像に使用でき十分な現像を行なうことができる。図３に前記各要素とトナー飛散、地汚れの状態を比較して示す。
【００６９】
図４ないし図６に従来のダブルスクリューに使用している現像剤攪拌搬送部材の例を示す。
【００７０】
図４に示した現像剤攪拌搬送部材１０は回転軸１１の外周に螺旋状にスクリュー羽根１２を設けたもので、横方向の現像剤攪拌性については良いが、補給トナーの微分散については積極的な役割を示す構成になっていない。
【００７１】
図５に示した現像剤攪拌搬送部材１３は図４に示した現像剤攪拌搬送部材１０の軸方向にメッシュ部材１４を設け、スクリュー羽根１２と一体に回転させるようにしたもので、補給トナーの分散性が改善されるが、最大駆動トルクの上昇や横攪拌性能の低下等を招き、改良の余地が多々ある。なお、メッシュ部材は例えば、ＳＵＳ３０４世の平織り金網で、線径は０．２８ｍｍ、目開き１ｍｍ、開口率６１％である。
【００７２】
図６に示した現像剤攪拌搬送部材１５はスクリュー羽根１２が設けられた回転軸１１に棒状の部材１６を軸表面から円周方向に突出させ、撹拌機能を持たせたもので、このように構成すると分散性は改善されるが、駆動トルクを上昇させる割合に比べ該改善効果が少ない。
【００７３】
図７ないし図１１に本発明の実施形態に係るダブルスクリュー４４，４５に使用している現像剤攪拌搬送部材の例を示す。
【００７４】
図７は現像剤攪拌搬送部材１７を示すもので、同図（ａ）は正面図、同図（ｂ）は同図（ａ）のＡ−Ａ線断面図である。図７に示した現像剤攪拌搬送部材１７は、駆動源に接続して駆動回転される回転軸１１と、この回転軸１１の周囲に形成された螺旋状のスクリュー羽根１２と、前記スクリュー羽根１２に固定され、前記回転軸１１の軸方向に平行に配された複数本の線状部材１８とからなる。スクリュー羽根１２は現像剤４６を主に回転軸１１に平行に搬送する搬送部として機能し、線状部材１８は現像剤４６を主に剪断、攪拌する攪拌部として機能する。なお、この実施形態では、潜像部材１８は回転軸１１に平行に配置されているが、斜めに配置することもできる。
【００７５】
この現像剤攪拌搬送部材１７では、前記線状部材１８の断面の回転軸１１の法線方向に占める長さの和Ｂ（＝Σｂ）の最大値ＢMAXが、
Ｒｃ＜ＢMAX≦５０Ｒｃ・・・（１）
ＢMAX≦０．２（Ｄ−ｄ）・・・（２）
ただし、Ｒｃ：キャリアの体積平均粒径
Ｄ：現像剤攪拌搬送部材のスクリュー羽根の回転軌跡の直径［ｍｍ］
ｄ：現像剤攪拌搬送部材の回転軸の外径［ｍｍ］
に設定されている。
【００７６】
線状部材１８の１本当たりの断面の回転軸１１の法線方向に占める長さ（真円断面では直径に相当）についてはキャリア直径の２０倍以下が補給トナーの微分散の上から好適である。また、複数の線状部材１８の５０％以上（図７では１００％−断面比）を、スクリュー羽根１２の先端部の回転軌跡上又は近傍に配置し、角速度に対する線状部材１８の線速をなるべく大きくして攪拌性能の効率向上を図っている。
【００７７】
また、スクリュー羽根１２に固定された複数の線状部材１８は現像剤４６中に完全に埋没させずに６０％ないし９５％を、現像剤４６に埋没させた状態で回転させるようにしている。符号４６ｂは現像剤４６の上面４６ｂを示す。これによりトルク変動を抑え、かつ補給トナーを効率良く現像剤４６中に分散させることができる。なお、前記線状部材１８の断面は図８に示すように円（ａ）、楕円（ｂ）、正方形（ｃ）、三角形（ｄ）、菱形（ｅ）、長方形（ｆ）などの種々の形状を取り得るが、図示しているように進行（移動）方向下流側に面した表面が現像剤４６を抱え込み難いようキャリアの体積平均粒径を超える様な深さを有する凹部がなるべく存在しないように構成することが望ましい。なお、現像剤攪拌搬送部材１７の回転軸１１は特に攪拌能力がないので、回転軸１１の６０％〜１００％を現像剤に埋没させた状態で回転させることによって、殆ど攪拌効率を落とさずに省スペース化を図ることができる。
【００７８】
なお、図２のように複数本の現像剤攪拌搬送部材１７を使用する場合には、少なくとも一対の現像剤攪拌搬送部材１７の現像剤搬送方向が逆方向になるように配置すると、現像剤のバランスを良好に維持し易い。また、前記スクリュー羽根１２に固定された複数の線状部材１８の一部の回転時の周速が、感光体（像担持体）と対向する現像ローラ４２（現像剤担持体）の周速以下にし、トルクを下げても攪拌性能は良好に維持することができる。
【００７９】
図９は図７に示した現像剤攪拌搬送部材１７の第１変形例を示すもので、同図（ａ）は正面図、同図（ｂ）は同図（ａ）のＡ−Ａ線断面図である。この変形例に係る現像剤攪拌搬送部材１７ａは、図７の場合よりの多くの線状部材１８を設置したもので、分散機能を高めながら、最大駆動トルクが左程高まらないように、複数の線状部材１８の回転軌跡が異なるものを含むように線状部材１８の配置位置を設定したものである。この変形例においても図７に示したものの場合と同様に、複数の線状部材１８の軸方向断面であって、同一回転軌跡面に存在する該線状部材断面の占有率を７０％以下にし、攪拌効率向上に伴う最大トルク上昇を抑制している。
【００８０】
図１０は図７に示した現像剤攪拌搬送部材１７の第２変形例を示す正面図である。この第２の変形例に係る現像剤攪拌搬送部材１７ｂでは、横攪拌機能を示すスクリュー羽根１２を回転軸１１近傍で中抜きにしたリボン状のスクリュー羽根１２ａとし、現像ローラ４２との間で授受される現像剤以外にはなるべくストレスを与えず現像剤の寿命伸張と低トルク化を図ったものである。なお、複数の線状部材１８は図７の例の場合と同様に設けられている。
【００８１】
図１１は図７に示した現像剤攪拌搬送部材１７の第３変形例を示すもので、同図（ａ）は正面図、同図（ｂ）は同図（ａ）のＡ−Ａ線断面図、同図（ｃ）は同図（ａ）のＢ−Ｂ線断面図である。
【００８２】
この第３変形例に係る現像剤攪拌搬送部材１７ｃは、図７に示した現像剤攪拌搬送部材１７に対して複数の線状部材１８を連結する線状部材１９を螺旋状に配したもので、この変形例では、１本の線状部材１８を固定した隣接するスクリュー羽根１２の中間部で各線状部材１８と１本の前記線状部材１９が接合されている。これにより、線状部材１８の構造的な変形を抑制している。
【００８３】
このように本実施形態及び各変形例に係る現像剤攪拌搬送部材１７，１７ａ，１７ｂ，１７ｃは複雑な形状となっているが、少なくとも２つの分割部品構成にし、樹脂成型部品を合体した組み立て部品にすると、容易かつ安価に製造できる。
【００８４】
図１２ないし図１６は前述のように構成した本発明の実施形態の各特性を示す図である。
【００８５】
図１２は本実施形態に係る現像剤攪拌搬送部材の条件と地汚れとの関係を示す特性図で、キャリア粒径をパラメータにとったときのＢMAXと地汚れとの関係を示す。図１２から隣接する線状部材１８間の幅が広すぎても狭すぎても、補給トナーを現像剤４６中に分散させる機能が発揮できないことが分かる。また、隣接する線状部材１８間の最適幅はキャリア粒径により影響されることがこの図から分かる。
【００８６】
図１３は図１２で分かった特性からキャリア粒径の依存性を考慮し、平均粒径５０μｍキャリアの例を抜粋し、横軸は線状部材幅をキャリア粒径で割った値で示した。２５μｍ及び１００μｍのキャリア粒径の現像剤の場合も地汚れランク４以上を示す良好な線状部材幅の範囲もほぼ同様で、キャリア粒径より大きくかつ５０倍以下であった。
【００８７】
他の主な固定条件は、
現像ローラ径：３０ｍｍ
現像ローラの線速：３８０ｍｍ／ｓｅｃ
スクリュー羽根：最外径２４ｍｍ
螺旋ピッチ：２０ｍｍ
スクリュー羽根の線速：３７０ｍｍ／ｓｅｃ
現像ローラとスクリュー羽根との最外径部間隙：３ｍｍ
である。
【００８８】
図１４は動トルク特性を示す図で、現像ローラ４２とスクリュー羽根１２を通常通り同時回転させて剤循環がほぼ定常状態を示した状態で、現像ローラ４２を停止させて、スクリュー羽根１２のみを回転させた状態での動トルク（ＢMAXに対する最大トルク比）を示している。この例では、攪拌搬送、特に線状部材１８が現像剤４６中の最も剤密度が高まる鉛直下方にある場合や現像ローラ４２に最近接状態で対向した場合に最大トルクを示す例を示した。ＢMAX＝０を基準値１００として相対トルクでパラメータである［Ｄ−ｄ］が違う場合、１００を表すトルクは違う場合がある。なお、［Ｄ−ｄ］は前述のように、Ｄが現像剤攪拌搬送部材のスクリュー羽根の回転軌跡の直径［ｍｍ］を、ｄが現像剤攪拌搬送部材の回転軸の外径［ｍｍ］を表すことから、実際に現像剤の搬送と撹拌に寄与する半径方向の長さ寸法に対応する。
【００８９】
図１５は図１４の横軸を［Ｄ−ｄ］との比に置き換えて示したもので、Ｄ−ｄ＝１４ｍｍと７ｍｍはほぼ同じ線上にのっている。
【００９０】
他の主な固定条件は、
線状部材線径：１ｍｍ
現像ローラ径：３０ｍｍ
現像ローラの線速：３８０ｍｍ／ｓｅｃ
スクリュー羽根：最外径２４ｍｍ
螺旋ピッチ：２０ｍｍ
スクリュー羽根の線速：３７０ｍｍ／ｓｅｃ
現像ローラとスクリュー羽根との最外径部間隙：３ｍｍ
である。
【００９１】
このように各部が構成された本実施形態によれば、現像装置全体としても動トルク変動を低く抑えることができ、ピッチムラ、バンディング等の画像濃度ムラ防止と容易に両立させることができる。
【００９２】
図１６に混合率について、本実施形態に係るスクリュー羽根（現像剤攪拌搬送部材）を使用した場合と従来のスクリュー羽根の場合とを比較した例を示す。
【００９３】
混合率はスクリュー羽根１２の軸方向を現像剤中で５等分する位置でかつ現像ローラから最も遠い位置における５箇所の現像剤をサンプリングし、トナー濃度を測定してそのバラツキを経時的に追跡し、偏差として求めたものである。
【００９４】
初期剤の設定方法：スクリュー羽根の軸方向の剤循環・攪拌・搬送部の中央位置を境に前後にトナー濃度の異なる現像剤を所定量セットする。（例：前側トナー濃度８重量％、後側トナー濃度４重量％）
トナー濃度の標準偏差（ｎ分後）：σｎ
初期標準偏差：σ０…最も大きい
規格化標準偏差：σｎ’＝σｎ／σ０…初期は１になる
σｎ’＝ｅ＾−ｋαｔ
ｋ：定数（今回は０．４）
本実施形態に係るスクリュー羽根１２を使用し、混合率α＝１５の場合は、従来例の混合率α＝１０の場合に比べて同じ規格化標準偏差を示すまでに要する時間（但し初期は除く）は１／１．５で済む。しかも、トルク上昇分は図１４や図１５に示すように高々１０％に抑えることができる。
【００９５】
図１７は本発明の実施形態に係るトナーの構成を示す概念図である。本実施形態では、トナーの球形化、シャープ化、外添剤等で補給トナーが粒径オーダに微分散し易くしてある。
【００９６】
トナー２０は、樹脂２１中に、着色剤２２、離型剤２３、極性制御剤２４が分散し、表面に外部添加剤２５が点在した構成となっている。トナー２０中に分散された顔料系着色剤２２の分散粒径は個数平均径で０．５μｍ以下であり、かつその個数平均径が０．７μｍ以上の個数割合が５個数％以下で、着色剤２２が微分散されている。このように微分散させることにより、トナー粒径の微分側成分についても顔料系着色剤２２の成分比率のばらつきを少なくトナー表面の摩擦帯電性についても同様ばらつきを少なくすることができる。また、トナー２０同士の静電凝集を抑制でき、トナー凝集性を低く抑えることができる。なお、現像剤中のトナーの加速凝集度がパウダーテスタの計測値で２０％以下が好ましい。ただし、加速凝集度測定篩のメッシュ径は７５μｍ、４５μｍ、２２μｍである。
【００９７】
本実施形態に係るトナー２０は、有機溶媒中に少なくとも、イソシアネート基を含有するポリエステル系プレポリマーＡが溶解し、顔料系着色剤２２が分散し、離型剤２３が溶解ないし分散している油性分散液を水系媒体中に無機微粒子及び／又はポリマー微粒子の存在下で分散させるとともに、この分散液中で該プレポリマーＡをポリアミン及び／又は活性水素含有基を有するモノアミンＢと反応させてウレア基を有するウレア変性ポリエステル系樹脂Ｃを形成させ、このウレア変性ポリエステル系樹脂Ｃを含む分散液からそれに含まれる液状媒体を除去することにより得られるものである。ウレア変性ポリエステル系樹脂Ｃにおいて、そのＴｇは４０〜６５℃、好ましくは４５〜６０℃である。その数平均分子量Ｍｎは２５００〜５００００、好ましくは２５００〜３００００である。その重量平均分子量Ｍｗは１万〜５０万、好ましくは３万〜１０万である。
【００９８】
このトナー２０は、プレポリマーＡとアミンＢとの反応によって高分子量化されたウレア結合を有するウレア変性ポリエステル系樹脂Ｃをバインダー樹脂２１として含む。そして、そのバインダー樹脂中２１には着色剤２２が高分散している。このように構成したトナー２０は、トナー表面の摩擦帯電特性差が小さくトナー同士の静電凝集がし難く、補給トナーの分散が良い。
【００９９】
また、本実施形態に係るトナー２０では、顔料系着色剤２２の分散粒径及び形状は定着後でも殆ど変化せず、定着後の出力画像で、着色剤による光散乱、回折現象が粗分散の場合より顕著で、着色力が高く、かつ色調の鮮明な透過性の高い優れたカラートナーとなっている。このトナー２０では、少量トナー付着で十分な色調再現性が得られ、トナー消費量低減と定着エネルギー低減、及び高品質画像形成を両立させることができる。なお、染料系着色剤については分散粒径が分子オーダーに近いナノメータスケールになるので上記凝集性については有利である。
【０１００】
本実施形態に係るトナー２０は、磁性体を含有させた、磁性トナーでも使用することもできる。
【０１０１】
具体的な磁性体としては、マグネタイト、ヘマタイト、フェライト等の酸化鉄、コバルト、ニッケルのような金属あるいはこれら金属とアルミニウム、銅、鉛、マグネシウム、スズ、亜鉛、アンチモン、ベリリウム、ビスマス、カドミウム、カルシウム、マンガン、セレン、チタン、タングステン、バナジウムのような金属との合金及びその混合物等が挙げられる。
【０１０２】
これらの磁性体は平均粒径が０．１〜２μｍ程度のものが望ましく、このときの磁性体の含有量は、結着樹脂１００重量部に対して２０〜２００重量部、特に好ましくは結着樹脂１００重量部に対して４０〜１５０重量部である。
【０１０３】
用いられる添加剤としては、従来公知のものが使用できるが、具体的には、Ｓｉ，Ｔｉ，Ａｌ，Ｍｇ，Ｃａ，Ｓｒ，Ｂａ，Ｉｎ，Ｇａ，Ｎｉ，Ｍｎ，Ｗ，Ｆｅ，Ｃｏ，Ｚｎ，Ｃｒ，Ｍｏ，Ｃｕ，Ａｇ，Ｖ，Ｚｒ等の酸化物や複合酸化物等が挙げられ、特にＳｉ，Ｔｉ，Ａｌの酸化物であるシリカ、チタニア、アルミナが好適に用いられる。
【０１０４】
また、このときの添加剤の添加量は、母体粒子１００重量部に対して０．５〜１．８重量部であることが好ましく、特に好ましくは、０．７〜１．５重量部である。
【０１０５】
図１８は本発明の実施形態に係る現像剤の構成を示す図である。同図に示すように本実施形態に係る現像剤は、キャリア芯材２６の周りに帯電又は未帯電トナー２０がキャリア芯材２６の表面を完全に覆い尽くさないレベルに存在する。なお、キャリア芯材２６の外周面はキャリアコート層２７によりコーティングされている。
【０１０６】
図１９は本発明の実施形態に係る現像剤の流動度測定装置を示す図である。同図において、本実施形態に係る流動度測定装置３０は、支持台３１と、漏斗支持器３２と、漏斗支持器３２を支持台３１に対して所定の高さで取り付けるための支柱３３とからなり、支柱３３は支持台３１からほぼ垂直に立設されている。漏斗支持器３２は支柱３３から突出した板状部分に漏斗３４を支持する支持部３２ａが設けられ、この支持部３２ａに漏斗３４が上から挿入され、支持される。なお、漏斗３４の下方の支持台３１上にはコップなどの容器３５をおいて、漏斗３４から流れ出す現像剤４６を受けるようになっている。本発明では現像剤４６の重力による自己流動を分散、攪拌に利用するため、現像剤４６の流動度は４５ｓｅｃ／５０ｇ以下が好ましい。
【０１０７】
次に、トナー中の顔料系着色剤の分散粒径等のトナー物性の測定法について詳述する。
【０１０８】
トナー中の着色剤の分散粒径及び粒度分布を測定するには、トナー２０をエポキシ樹脂に包埋し、ミクロトームＭＴ６０００−ＸＬ（盟和商事製）にてトナーを約１００ｎｍに超薄切片化した測定サンプルを用意する。
【０１０９】
これを電子顕微鏡（日立製作所社製Ｈ−９０００ＮＡＲ）を用いて加速電圧１００ｋＶにしてＴＥＭ写真を１００００〜４００００倍にて複数個撮影し、その画像情報をＩＭＡＧＥＡＮＡＬＹＺＥＲの画像処理解析装置ＬＵＺＥＸ IIIにて画像データに変換する。対象顔料系着色剤粒子は粒径にして０．１μｍ以上の粒径を有する粒子について無作為にサンプリングが３００回を超えるまで測定を繰り返し、平均粒径と粒度（粒径）分布を求める。
【０１１０】
本実施形態に係るトナー２０の重量平均粒径（Ｄｖ）は４〜８μｍであり、その個数平均粒径（Ｄｎ）との比（Ｄｖ／Ｄｎ）は、
１．００≦Ｄｖ／Ｄｎ≦１．２５
である。Ｄｖ／Ｄｎをこのように規定することにより、高解像度、高画質のトナー２０を得ることが可能となる。また、より高品質の画像を得るには、着色剤２２の重量平均粒径（Ｄｖ）を４〜８μｍにし、個数平均粒径（Ｄｎ）との比（Ｄｖ／Ｄｎ）を、
１．００≦Ｄｖ／Ｄｎ≦１．２５
にし、かつ３μｍ以下の粒子を個数％で１〜１０個数％にするのがよい。より好ましくは、重量平均粒径を４〜６μｍにし、Ｄｖ／Ｄｎを、
１．００≦Ｄｖ／Ｄｎ≦１．１５
にするのがよい。このようなトナー２０は、放置で強固に凝集し難く、耐熱保存性、低温定着性、耐ホットオフセット性のいずれにも優れ、とりわけフルカラー複写機などに用いた場合に画像の光沢性に優れ、更に２成分現像剤においては、長期にわたるトナー２０の収支が行われても、現像剤４６中のトナー２０の粒子径の変動が少なくなり、現像装置における長期の攪拌においても、良好で安定したトナー帯電性、現像性が得られる。
【０１１１】
一般的には、トナー２０の粒子径は小さければ小さい程、高解像で高画質の画像を得るために有利であると言われているが、逆に、転写性やクリーニング性に対しては不利である。また、本発明で規定した範囲よりもトナー２０の体積平均粒子径が小さい場合、２成分現像剤４６では現像装置における長期の攪拌においてキャリア２８の表面（キャリヤコート層２７表面）にトナー２０が融着して、キャリア２８の帯電能力を低下させる。一方、一成分現像剤として用いた場合には、現像ローラ４２へのトナー２０のフィルミングや、トナー２０を薄層化するためのドクタブレード４３等の部材へのトナー２０の融着が発生しやすくなる。これらの現象は、トナー２０中の微粉の含有率が大きく関係し、特に３μｍ以下の粒子含有量が１０％を超えると、トナー２０のキャリア２８への付着が生じにくくなる上、高いレベルで帯電の安定性を図ることがむつかしくなる。
【０１１２】
逆に、トナーの粒子径が本発明で規定した範囲よりも大きい場合には、高解像で高画質の画像を得ることが難しくなると共に、現像剤４６中のトナー２０の収支が行われた場合にトナー２０の粒子径の変動が大きくなる場合が多い。また、重量平均粒子径／個数平均粒子径が１．２５よりも大きい場合も同様であることが明らかとなった。
【０１１３】
トナー２０の平均粒径及び粒度分布は、カーコールターカウンタ法により測定される。トナー粒子の粒度分布の測定装置としては、コールターカウンタＴＡ−IIやコールターマルチサイザII（いずれもコールター社製）があげられる。本実施形態においてはコールターカウンタＴＡ−II型を用い、個数分布、体積分布を出力するインターフェイス（日科技研社製）と、ＰＣ９８０１パーソナルコンピューター（ＮＥＣ製）とを接続し測定した。
【０１１４】
次に、トナーの個数分布及び体積分布の測定方法について述べる。
【０１１５】
まず、電解水溶液１００〜１５０ｍｌ中に分散剤として界面活性剤（好ましくはアルキルベンゼンスルフォン酸塩）を０．１〜５ｍｌ加える。ここで、電解液とは１級塩化ナトリウムを用いて形成した約１％ＮａＣｌ水溶液である。例えば、ＩＳＯＴＯＮ−II（コールター社製）が使用できる。ここで、更に測定試料を２〜２０ｍｇ加える。試料を懸濁した電解液は、超音波分散器で約１〜３分間分散処理を行ない、前記測定装置により、アパーチャとして１００μｍアパーチャを用いて、トナー粒子の体積、個数を測定して、体積分布と個数分布を算出する。
【０１１６】
チャンネルとしては、
２．００〜２．５２μｍ未満；
２．５２〜３．１７μｍ未満；
３．１７〜４．００μｍ未満；
４．００〜５．０４μｍ未満；
５．０４〜６．３５μｍ未満；
６．３５〜８．００μｍ未満；
８．００〜１０．０８μｍ未満
１０．０８〜１２．７０μｍ未満；
１２．７０〜１６．００μｍ未満；
１６．００〜２０．２０μｍ未満；
２０．２０〜２５．４０μｍ未満；
２５．４０〜３２．００μｍ未満；
３２．００〜４０．３０μｍ未満
の１３チャンネルを使用し、粒径２．００μｍ以上乃至４０．３０μｍ未満の粒子を対象とする。本実施形態のトナー２０に係わる体積分布から求めた体積基準の重量平均粒径（Ｄｖ）と、その個数分布から求めた個数平均粒径（Ｄｎ）により、その比Ｄｖ／Ｄｎを求めた。
【０１１７】
本実施形態に係るトナー２０の円形度は、フロー式粒子像分析装置ＦＰＩＡ−２０００（シスメックス（株）製）により計測される。前記トナー２０において、その平均円形度は０．９００〜０．９９０であり、特定の形状と形状の分布を有すことが重要である。平均円形度が０．９００未満ではトナーは不定形の形状を示し、満足した転写性やチリのない高画質画像を与えない。不定形のトナー粒子は感光体等への平滑性媒体への接触点が多く、また突起先端部に電荷が集中することから、ファンデルワールス力や鏡像力が比較的球形な粒子よりも高い。そのため静電的な転写工程においては、不定形粒子と球形の粒子の混在したトナーでは球形の粒子が選択的に移動し、文字部やライン部画像抜けが起る。また、残されたトナーは次の現像工程のために除去しなければならず、クリーナ装置が必要であったり、トナーイールド（画像形成に使用されるトナーの割合）が低かったりする不具合点が生じる。粉砕トナーの円形度は本装置で計測した場合、通常０．９１０〜０．９２０である。
【０１１８】
他の現像条件は以下のようになる。
【０１１９】
前述したが、現像剤４６の搬送方向（図２において反時計回り方向）における現像領域の上流側部分には、現像剤チェーン穂の穂高さ、即ち、現像スリーブ上の現像剤量を規制するドクタブレード４３が設置されている。このドクタブレード４３と現像スリーブ（現像ローラ）４２との間隔であるドクタギャップは０．３〜０．７ｍｍ程度に設定されている。現像部に搬送する現像剤量としては、２０〜１００ｍｇ／ｃｍ＾２が好適である。更に現像ローラ４２の感光体ドラム１とは反対側領域には、現像容器４０内の現像剤４６を攪拌しながら現像スリーブへ汲み上げるための攪拌・搬送手段（スクリュー、パドル等−図２ではスクリュー羽根４４，４５）が設置されている。また、感光体ドラム１と現像スリーブとの間隔である現像ギャップは０．３ｍｍに設定されている。現像ギャップは、キャリア粒径が５０μｍであれば１０倍程度（０．５５ｍｍ）以下に設定するのが良い。現像ギャップをこれより広くすると直流現像バイアス電圧印加条件下では、望ましいとされる画像濃度が出にくくなる。
【０１２０】
現像スリーブ４２（現像ローラに同じ）内には、当該現像スリーブの周表面に現像剤４６の穂立ちを生じるように磁界を形成する磁石ローラ体（磁石ローラ）が固定状態で備えられている。この磁石ローラ体から発せられる法線方向磁力線に沿うように、現像剤４６中のキャリア２８が現像スリーブ４２上にチェーン状に穂立ちを起こし、このチェーン状に穂立ちを生じたキャリアに帯電トナーが付着されて、磁気ブラシが構成される。当該磁気ブラシは現像スリーブ４２の回転によって現像スリーブ４２と同方向（図で見て反時計回り方向）に移送されることとなる。上記磁石ローラ体は、複数の磁極（磁石）を備えている。また現像主磁極上の現像スリーブ４２表面における現像領域の出口における好適な法線方向の磁束密度は６０ｍＴ以上である。汲み上げ性、黒ベタ画像追従性を向上させるために磁石（磁極）を更に増やして構成してもよい。該磁性キャリア２８の体積平均粒径がトナー２０の平均体積粒径より大きく磁化が３０〜１０００ｅｍｕ／ｃｍ＾３（１ｋＯｅ磁場中）にすると現像時に感光体１へのキャリア付着を抑制する効果と、前記現像剤４６からなる磁気ブラシの穂先端が感光体１に接触する場合の過剰接触圧防止によりざらつき感のない高品質画像を得ることができる。
【０１２１】
本実施形態では、最大現像電位差印加時のダイナミック抵抗が１０＾７Ω・ｃｍ以下の抵抗のキャリア２８を使用し、現像時間が短時間であっても現像電界に見合った十分なトナー２０を感光体１に付着させることができる。また前記キャリア２８の低抵抗化は現像剤層の誘電率を高め現像電界強度を強める役割も果たし、低電界現像ポテンシャルでも十分なトナー付着量の得られる現像ができた。
【０１２２】
ここで低電界ポテンシャル現像条件の一例について述べる。
【０１２３】
本実施形態では感光体１の帯電（露光前）電位Ｖ０を−３５０Ｖ、露光後電位ＶＬを−５０Ｖとして現像バイアス電圧ＶＢを−２５０Ｖすなわち現像ポテンシャル（ＶＬ−ＶＢ＝２００Ｖ）として現像工程が行われるものである。この時
０＜｜ＶＤ｜−｜ＶＢ｜＜｜ＶＤ−ＶＬ｜＜４００Ｖ
を満たす。上式で｜ＶＤ−ＶＬ｜＜４００Ｖは感光体１の露光された部分と露光されていない部分の放電を避けるためにパッシェンの放電則より設定したものである。本実施形態はネガポジのプロセスである。
【０１２４】
現像スリーブ４２上のトナーは感光体１上に形成された潜像に対して、現像スリーブ４２に印加された現像バイアスにより現像され、感光体１上で顕像化される。ちなみに本実施形態では感光体１の線速を２００ｍｍ／ｓ、現像スリーブ４２の線速を３００ｍｍ／ｓとしている。感光体１の直径を５０ｍｍ、供給部材の直径を１８ｍｍ、現像スリーブ４２の直径を１６ｍｍとして、現像行程が行われる。ここで現像スリーブ４２上のトナー帯電量は−１０〜−３０μＣ／ｇの範囲である。感光体１の厚みを２８μｍとし、光学系のビームスポット径を５０×６０μｍ、光量を０．２３ｍＷとしている。
【０１２５】
感光体１の帯電（露光前）電位Ｖ０を−３００Ｖ、露光後電位ＶＬを−１００Ｖとして現像バイアス電圧を−２５０Ｖすなわち現像ポテンシャル（ＶＬ−ＶＢ＝１５０Ｖ）として現像工程が行われるものである。
【０１２６】
感光体１上に形成されたトナーの顕像はその後、転写、定着工程を経て画像として完成される。転写は転写紙もしくは中間転写体の裏側に当接させたバイアス印加したローラもしくはチャージャー等が配設される。
【０１２７】
ここで前述の低電位現像の効果のひとつである低光量露光について説明する。
【０１２８】
光量を高密度としてビーム径を絞って露光する手法を用いて、２値プロセスが提案されてきた。ところが光量をアップする事による課題が存在する。１つは高密度の光量のビーム径を絞る事は光学設計の余裕度が低減し、部品精度の向上が不可欠でコストが上昇してしまうという点である。更にもう１つの点は光量が大きいために感光体１に対する帯電・露光における、通電電荷量アップによるいわゆる静電ハザードを受けて、寿命が短くなる要因の１つとなるという点である。そこで本実施形態では感光体１の初期帯電電位を低くし、露光量も同時に低減させることにより、汎用光学部品を使用して高精細な潜像を形成すると共に感光体１への静電ハザードを低減して長寿命化を可能にできる。
【０１２９】
低電位現像におけるγ曲線（現像電位差に対する現像量−図示せず）をみると、その傾きが大きく比較的低電位でも現像し易くすぐに飽和できる。これは現像ローラ４２上のトナー坦持量を一定にしてベタ画像で坦持体上の多くの割合のトナーを効率良く現像するのが比較的容易であることを示す。小径ドットを形成する場合も、本実施形態のように構成すると、帯電電位を低く抑えることができ、従来の約半分の光量でドット潜像を下げることが可能で、均一なドット画像を形成することができる。
【０１３０】
図１を基に本発明の本発明実施例のひとつである低電位プロセスによるプロセスカ−トリッジを有する画像形成装置の概略構成を示す。
【０１３１】
本実施形態においては、感光体１、帯電装置２、現像手装置４段及びクリ−ニング装置６等の構成要素のうち、複数のものをプロセスカ−トリッジとして一体に結合して構成し、このプロセスカ−トリッジを複写機やプリンタ等の画像形成装置本体に対して着脱可能に構成する。前述の現像装置４を有するプロセスカ−トリッジを有する画像形成装置は、感光体１が所定の周速度で回転駆動される。感光体１は回転過程において、帯電装置２によりその周面に正または負の所定電位の均一帯電を受け、次いで、スリット露光やレーザビ−ム走査露光等の露光装置から出射される画像露光光を受け、感光体１の周面に静電潜像が順次形成される。形成された静電潜像は、現像装置４によりトナー現像され、現像されたトナー像は、給紙部から感光体１と転写装置５との間に感光体１の回転と同期して給送された転写材に、前記転写装置５により順次転写されていく。像転写を受けた転写材は感光体１面から分離されて定着装置８へ導かれ、定着され、複写物（コピ−）として装置外へプリントアウトされる。像転写後の感光体１の表面は、クリーニング装置６によって転写残りトナーの除去を受けて清浄面化され、除電装置７でさらに除電された後、繰り返し画像形成に使用される。
【０１３２】
感光体ユニット、現像装置とも本発明で寿命は延びるが、それぞれの寿命が一致するとは限らないので、独立して取り付け、取り外しが可能なプロセスカートリッジを使用すると、その寿命に応じてそれぞれ別々に容易に交換することができる。また、独立して配設できるので簡単な機構を追加することにより、非現像時に現像ローラを感光体から退避させることも可能なので、現像ローラへのトナーフィルミングの促進が低減され、更に現像装置の寿命が延びる。
【０１３３】
図１に示した本実施例の現現像器において、現像時、現像スリーブには、電源により現像バイアスとして、直流電圧に交流電圧を重畳した振動バイアス電圧が印加される。背景部電位と画像部電位は、上記振動バイアス電位の最大値と最小値の間に位置している。これによって現像部に向きが交互に変化する交互電界が形成される。この交互電界中で現像剤のトナーとキャリアが激しく振動し、トナーが現像スリーブおよびキャリアへの静電的拘束力を振り切って感光体ドラムに飛翔し、感光体ドラムの潜像に対応して付着する。
【０１３４】
振動バイアス電圧の最大値と最小値の差（ピーク間電圧）は、０．５〜５ＫＶが好ましく、周波数は１〜１０ＫＨｚが好ましい。振動バイアス電圧の波形は、矩形波、サイン波、三角波等が使用できる。振動バイアスの直流電圧成分は、上記したように背景部電位と画像部電位の間の値であるが、画像部電位よりも背景部電位に近い値である方が、背景部電位領域へのかぶりトナーの付着を防止する上で好ましい。
【０１３５】
振動バイアス電圧の波形が矩形波の場合、デューティ比を５０％以下とすることが望ましい。ここでデューティ比とは、振動バイアスの１周期中でトナーが感光体に向かおうとする時間の割合である。このようにすることにより、トナーが感光体に向かおうとするピーク値とバイアスの時間平均値との差を大きくすることができるので、トナーの運動がさらに活発化し、トナーが潜像面の電位分布に忠実に付着してざらつき感を少なくし、解像力を向上させることができる。またトナーとは逆極性の電荷を有するキャリアが感光体に向かおうとするピーク値とバイアスの時間平均値との差を小さくすることができるので、キャリアの運動を沈静化し、潜像の背景部にキャリアが付着する確率を大幅に低減することができる。
【０１３６】
【発明の効果】
以上のように本発明によれば、トルクをあまり高めることなく、現像剤を効率よく、高速で剪断することが可能であって、補給トナーの現像剤への分散性・縦攪拌性に優れた現像装置及びこの現像装置を備えた画像形成装置並びにこの現像装置を使用した現像方法を提供することができる。
【０１３７】
また、本発明によれば、現像装置全体の駆動投入エネルギーに対しての現像剤の縦横攪拌、補給トナーの分散、及びトナー帯電立ち上げの効率の良い現像装置及び画像形成装置並びに前記現像装置を使用した現像方法を提供することができる。
【図面の簡単な説明】
【図１】本発明の実施に係る画像形成システム装置全体の概略構成を示す図である。
【図２】図１における現像装置の構成を示す図である。
【図３】キャリアの体積平均粒径Ｒ、トナーの体積平均粒径ｒ、キャリアの真比重ρｃ、トナーの真比重ρｔ、トナー濃度Ｃ、被覆率Ｐとトナー飛散、地汚れの状態を比較して示す図である。
【図４】従来から実施されている現像剤攪拌搬送部材の一例を示す図である。
【図５】従来から実施されている現像剤攪拌搬送部材の他の例を示す図である。
【図６】従来から実施されている現像剤攪拌搬送部材のさらに他の例を示す図である。
【図７】本発明の実施形態に係る現像剤攪拌搬送部材の一例を示す図である。
【図８】図７における現像剤攪拌搬送部材の線状部材の例を示す図である。
【図９】本発明の実施形態に係る現像剤攪拌搬送部材の他の例を示す図である。
【図１０】本発明の実施形態に係る現像剤攪拌搬送部材のさらに他の例を示す図である。
【図１１】本発明の実施形態に係る現像剤攪拌搬送部材のさらに他の例を示す図である。
【図１２】本発明の実施形態に係る現像装置の撹拌搬送部材条件と地汚れの関係を示す図である。
【図１３】本発明の実施形態に係る現像装置の撹拌搬送部材条件の地汚れの関係をパラメータを変えて示す図である。
【図１４】本発明の実施形態に係る現像装置の撹拌搬送部材条件と最大トルク比との関係を示す図である。
【図１５】本発明の実施形態に係る現像装置の撹拌搬送部材条件と再々トルク比との関係をパラメータを変えて示す図である。
【図１６】本発明の実施形態の係る現像装置の現像剤の混合率を比較して示す図である。
【図１７】本発明の実施形態に係るトナーの構成を示す図である。
【図１８】本発明の実施形態に係る現像剤の構成を示す図である。
【図１９】本実施形態における現像剤の流動度測定器を示す図である。
【符号の説明】
１感光体
２帯電装置
３画像露光装置
４現像装置
４０現像容器
４１現像ローラ
４２開口部
４３ドクタブレード
４４，４５現像剤攪拌搬送部材
５転写装置
６クリーニング装置
７除電送値
８定着装置
１１回転軸
１２，１２ａスクリュー羽根
１７，１７ａ，１７ｂ，１７ｃ現像剤攪拌搬送部材
１８線状部材
１９連結部材
２０トナー
２１樹脂
２２着色剤
２３離型剤
２４極性制御剤
２５外部添加剤
２６キャリア芯材
２７キャリアコート層
２８キャリア
３０流動度測定装置
３４漏斗[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a developing device for visualizing an electrostatic charge image formed on the surface of a photoreceptor in electrophotography, electrostatic recording, electrostatic printing, etc., an image forming apparatus using the developing device, and a process cartridge It is about.
[0002]
[Prior art]
As this kind of invention, for example, an invention described in JP-A-10-63081 is known. According to the present invention, it is possible to instantly disperse the replenishing toner in the developer without applying an excessive force to the developer, and to impart an appropriate charge amount, and the developer in the developer accommodating portion. A developer which is made to provide a developing device having a high ability to uniformize the toner density, and in which the developer is circulated and transferred to a developer containing portion containing a two-component developer in which toner and a carrier are mixed. A transport path is provided, and a developer transport member having a feed screw-like wing body is provided in the developer transport path, and a mesh-like screen member is attached between the wing bodies. By rotating the developer conveying member, the developer is conveyed, and the developer passes through the mesh-like screen member a plurality of times, and the developer is stirred. It is configured to be performed.
[0003]
The invention disclosed in Japanese Patent Laid-Open No. 2000-19823 is also known. This invention was made to solve problems such as developer deterioration at the start of driving of the developing device and at the time of continuous stirring for a long time, insufficient charge amount of the developer, a decrease in image density, and an increase in color mixing. The maximum projected area X of the protruding member of the stirring unit is
(P × D) / 200 ≦ X ≦ (P × D) / 7
0.015 [D × (F + f)] ≦ X ≦ 0.2 [D × (F + f)]
It is set to become a relationship. In the equation, P is the pitch distance [mm] of the spiral blade member of the transport unit 45B, D is the diameter [mm] of the rotation locus of the tip of the spiral blade member of the transport unit 45B, and X is the protrusion of the projection member. Maximum projected area of the projection member when projected from the direction perpendicular to the installation direction [mm²], F is the width dimension [mm] in the rotation axis direction at the root of the transport section 45B, and f is the width dimension [mm] at the tip of the transport section 45B.
[0004]
[Patent Document 1]
JP-A-10-63081
[0005]
[Patent Document 2]
JP 2000-19823 A
[0006]
[Problems to be solved by the invention]
However, in the former invention, when two screen members are provided in a paddle shape, the dynamic torque when the portion is closest to the lowermost position or the developing roller is significantly higher than the average torque, and the torque fluctuation is large. It was necessary to increase the drive motor torque margin. Further, if the drive motor torque has a small margin, uneven development such as pitch unevenness and banding tends to occur in the developed image due to uneven rotation of the developing system. On the other hand, when a part or the whole of the spiral screw portion is configured by a screen member, since there is no lateral feeding ability of the developer at the opening portion of the screw member, the lateral stirring of the developer (stirring in the developing roller axial direction) Ability is reduced.
[0007]
In the latter invention, the plurality of projecting members protruding from the rotating shaft portion of the helical screw have a function of squeezing out the agent in the centrifugal direction, but use the self-weight falling movement of the developer to the gap generation point. The developer stirring effect of the embodiment is hardly obtained. There is room for improvement with regard to the dispersion mixing and stirring function of the flowing developer.
[0008]
The present invention has been made in view of such a state of the art, and an object of the present invention is to develop a replenished toner that can efficiently shear a developer at high speed without significantly increasing torque. It is an object of the present invention to provide a developing device having improved dispersibility and longitudinal stirring property (circumferential stirring property) in an agent, an image forming apparatus provided with the developing device, and a developing method using the developing device.
[0009]
Another object of the present invention is to provide a developing device and an image that are efficient in the vertical and horizontal agitation of the developer (circumferential and axial directions) with respect to the drive input energy of the entire developing device, dispersion of replenishing toner, and toner charge start-up. Another object of the present invention is to provide a forming apparatus and a developing method using the developing apparatus.
[0010]
[Means for Solving the Problems]
  In order to achieve the above object, the first means includes a developer containing portion containing a two-component developer containing a toner having a volume average particle size of 10 μm or less and a carrier having a volume average particle size of 100 μm or less, A developer carrier disposed to face an image carrier on which an electrostatic latent image is formed, carrying a thin layer of the two-component developer, and transporting it to a position close to the image carrier; A developer agitating / conveying member that is arranged in parallel with the developer carrying member and stirs the two-component developer and conveys the developer to the developer carrying member, and a proximity position between the developer carrying member and the image carrier In the developing device for transferring the toner from the two-component developer on the developer carrier to the image carrier and visualizing the electrostatic latent image, the developer agitating and conveying member receives a driving force from a driving source. A rotary shaft that is driven to rotate, and a shape around the rotary shaft portion. A conveying unit configured to convey the two-component developer mainly in a direction parallel to the axial direction of the rotation shaft by the formed helical blade member; and the helical blade member having a predetermined angle with respect to the axial direction of the rotation shaft And a stirrer that mainly shears and stirs the two-component developer, and is a normal direction of the rotation axis of the cross section of the plurality of linear members of the stirrer When the maximum value BMAX of the sum B (= Σb) of the length occupying is Rc as the volume average particle diameter of the carrier,
Rc <BMAX ≦ 50Rc
BMAX ≦ 0.2 (D−d)
However, D: Diameter [mm] of the rotation locus | trajectory of the spiral blade member of this stirring conveyance member
d: Outer diameter [mm] of the rotating shaft of the stirring and conveying member
The cross-sectional shape of the plurality of linear members of the stirring unit is a shape having a vertex on the downstream side in the traveling direction of the linear member due to the rotation of the rotating shaft.And a connecting member that connects the plurality of linear members to each other at a position different from a fixed position of the spiral blade member and the linear member, and the plurality of linear members rotate the rotation shaft. The linear members are fixed at a plurality of points over the axial direction of the rotating shaft with respect to the plurality of spiral blade members, and the connecting members are arranged in a line along the direction. The plurality of linear members are connected to each other between two adjacent points among the plurality of fixed points of the linear member and the spiral blade member, and the connection member follows the spiral shape of the spiral blade member. The linear members are arranged in a spiral shape, and the linear members are connected to each other at a plurality of points along the axial direction of the rotating shaft.
[0011]
  With this configuration, the two-component developer (hereinafter simply referred to as developer) can be sheared at a high efficiency and at a high speed, and the dispersibility and longitudinal agitation of the replenishment toner to the developer can be increased. Can be improved without increasing.
Moreover, if comprised in this way, the stirring efficiency by prevention of a deformation | transformation of a linear member can be maintained highly efficient and highly stable.
[0012]
The second means is characterized in that, in the first means, 50% or more of the plurality of linear members fixed to the spiral blade member are arranged on or in the vicinity of the rotational locus of the tip of the spiral blade member. And
[0013]
If comprised in this way, the high efficiency of a developer and high-speed shearing can be performed, and stirring efficiency can be improved.
[0014]
The third means is characterized in that, in the first or second means, 60% to 95% of the plurality of linear members fixed to the spiral blade member are rotated while being buried in the developer. .
[0015]
With this configuration, it is possible to prevent drive motor torque suppression, pitch unevenness due to developing roller rotation unevenness, and image density unevenness such as banding due to torque fluctuation suppression.
[0016]
A fourth means is an axial cross section of a plurality of linear members fixed to the spiral blade member in the first to third means, and is a cross section of the linear member existing on the same rotation trajectory plane. The occupation ratio is 70% or less.
[0017]
If comprised in this way, the stirring efficiency of a developer can be improved, without raising the torque of a stirring conveyance member using the self-weight fall phenomenon of a free toner or a developer.
[0018]
The fifth means is that in the first to fourth means, the plurality of linear members fixed to the spiral blade member include linear members having different rotational trajectories, in other words, a part of the rotational trajectories. The plurality of linear members are arranged so as to have different rotation trajectories.
[0019]
If comprised in this way, a shearing and dispersion | distribution function can be improved without raising a maximum torque, and stirring efficiency can be improved.
[0020]
The sixth means is characterized in that, in the first means, 60% or more of the rotating shaft portion of the developer agitating / conveying member is rotated in a state where it is buried in the developer.
[0021]
If comprised in this way, improvement in stirring efficiency and space saving can be achieved.
[0022]
A seventh means is characterized in that, in the first to sixth means, at least a pair of the developer agitating / conveying members having a plurality of linear members are set so that the developer conveying directions are different.
[0023]
If comprised in this way, the bias | inclination of the rotating shaft direction of the stirring conveyance member of a developer can be prevented.
[0024]
According to an eighth means, in the first to seventh means, the circumferential speed of a part of the plurality of linear members fixed to the spiral blade member is such that the circumferential speed of the developer carrying member facing the image carrying member is It is characterized by being set below the peripheral speed.
[0025]
If comprised in this way, reduction of a drive torque can be aimed at.
[0028]
  First9Means of the first to the first8In this means, the width W is set so that the width W of the linear member in the normal direction of the rotation axis is not more than 20 times the volume average particle diameter Rc of the carrier in the two-component developer. It is characterized by that.
[0029]
If comprised in this way, coexistence with the dispersibility improvement of a developer and prevention of a drive torque raise can be aimed at.
[0030]
  First10Means of the first to the first9The dynamic torque fluctuation of the developer agitating / conveying member is set between + 25% and −25%.
[0031]
With this configuration, image density unevenness such as pitch unevenness and banding can be prevented.
[0032]
  First11In the first, third and sixth means, the developer has a fluidity of 45 sec / 50 g (JISZ-2502) or less.
[0033]
With this configuration, it is possible to improve the dispersibility of the developer and reduce the driving torque.
[0034]
  First12In the first means, the accelerated aggregation degree of the toner in the developer is 20% or less as measured by a powder tester. However, the mesh diameter of the accelerated aggregation degree measuring sieve is 75 μm, 45 μm, and 22 μm.
[0035]
With this configuration, it is possible to improve the dispersibility of the developer and reduce the driving torque.
[0040]
  First13In the first means, the toner composition in which the toner in the first means contains at least a modified polyester resin capable of urea bonding and a colorant is dissolved or dispersed in an organic solvent, and the dissolved or dispersed material is dissolved in an aqueous medium. It is a color toner obtained by dispersing in a polymer and allowing a polyaddition reaction to remove and wash the solvent of the dispersion.
[0041]
With this configuration, it is possible to improve the dispersibility of the developer and reduce the driving torque.
[0042]
  First14Means of the first or first13In this means, the toner has a weight average particle diameter of 4.0 to 8.0 μm and a particle diameter distribution of Dv / Dn ≦ 1.25 (Dv: weight average particle diameter, Dn: number average particle diameter). It is characterized by being.
[0043]
With this configuration, it is possible to improve the dispersibility of the developer and reduce the driving torque.
[0044]
  First15Means of the first, first13And the second14In this means, the toner is a toner having an average circularity of 0.90 to 0.99. However, “circularity = perimeter of a circle having the same area as the projected area of the particle / perimeter of the projected particle image”.
[0045]
With this configuration, it is possible to improve the dispersibility of the developer and reduce the driving torque.
[0046]
  First16In the first means, the toner coverage on the surface of the developer carrying member facing the photoreceptor is P [%], and the linear velocity of the developer carrying member linear velocity vD and the photosensitive member linear velocity vP. When the ratio is vD / vP, P · (vD / vP) is
1 / 0.98 ≦ P · (vD / vP) /100≦1.5/0.8
It is characterized by controlling to be in the range.
[0047]
That is,
102 ≦ P · (vD / vP) ≦ 187.5
However, the coverage P in the two-component developer can be approximated by the following equation when r / R <1.
[0048]
P = 100 × C × (√3) / {2π (100−C) (1 + r / R) ^ 2 (r / R) (ρt / ρc)}
C: Toner concentration (% by weight)
r: Volume average particle diameter of toner
R: Volume average particle diameter of carrier
ρt: true specific gravity of toner
ρc: True specific gravity of carrier
With this configuration, it is possible to obtain a high-quality image with little density unevenness and rough feeling.
[0049]
  First17Means of the first, sixth, seventh,9The second11And the second12The developer is a two-component developer composed of a magnetic carrier and a toner, and the magnetic carrier has a volume average particle size larger than that of the toner and a magnetization of 30 to 1000 emu / cm ^ 3 (in a 11 kOe magnetic field). ). In this specification, ^ indicates a power, and cm ^ 3 indicates the cube of cm, that is, cubic centimeter.
[0050]
With this configuration, it is possible to achieve both low stress development and carrier adhesion prevention.
[0051]
  First18This means is characterized in that, in the first means, the dynamic resistance of the developer layer when the maximum development potential difference is applied is 10 7 Ω · cm or less.
[0052]
However, the dynamic resistance means that a carrier is supported on a roller (φ20; 600 RPM) enclosing a magnet, an electrode having a width of 65 mm and a length of 1 mm is brought into contact with a gap of 0.9 mm, and a withstand voltage upper limit level (high The resistance value when an applied voltage of 400 V to less than a few V is applied to the iron powder carrier is shown for the resistance silicon coat carrier.
[0053]
With this configuration, it is possible to achieve both low potential development and prevention of background contamination.
[0054]
  First19The means comprises: a charging means for charging the image carrier; an exposure device for performing optical writing to form a latent image on the image carrier; and developing the latent image formed by the exposure device.18The developing device according to claim 1, a transfer device that transfers a developed image developed by the developing device to a recording medium, and a fixing device that fixes the developed image on the recording medium transferred by the transfer unit, It is characterized by having.
[0055]
  First20Means19In the described image forming apparatus,
0 <| VD | − | VB | <| VD−VL | <400V
It is characterized by satisfying.
[0056]
With this configuration, it is possible to reduce toner consumption and fixing energy.
[0057]
  First21In the process cartridge that integrally supports at least one means selected from an image carrier, a charging device, a developing device, and a cleaning device, and is detachable from the main body of the image forming apparatus, the developing device includes: Claims 1 to18It comprises the developing device described in any one of the above.
[0058]
With this configuration, it is possible to extend the life and improve the developing ability by reducing the hazard to the process cartridge developer.
[0059]
  First22Means of the first to the first9In the developing method for developing using the developing device according to the above means, the developer agitating and conveying member is rotated when the dynamic torque fluctuation is between + 25% and −25%.
[0060]
With this configuration, image density unevenness such as pitch unevenness and banding can be prevented.
[0061]
  First23Means of the first to the first15In the developing method of developing using the developing device according to the above means, the toner coverage on the surface of the developer carrying member facing the photoconductor is P [%], the developer carrying member linear velocity vD and If the linear velocity ratio of the photosensitive member linear velocity vP is vD / vP, P · (vD / vP) is
1 / 0.98 ≦ P · (vD / vP) /100≦1.5/0.8
It is characterized by controlling to be in the range.
[0062]
With this configuration, it is possible to obtain a high-quality image with little density unevenness and rough feeling.
[0063]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings. In the following description, the same reference numerals are assigned to the same parts as those in the above-described conventional example and the same in each embodiment, and duplicate descriptions are omitted as appropriate.
[0064]
FIG. 1 is a diagram showing a schematic configuration of an entire image forming system apparatus according to an embodiment of the present invention. In the figure, there is a charging device 2 for charging the surface of the photoconductor 1 around a photoconductor drum (hereinafter simply referred to as a photoconductor) 1 which is an electrostatic latent image carrier, and a uniformly charged surface. An image exposure unit 3 for writing with a laser beam for forming a latent image, a developing device 4 for forming a toner image by attaching a charged toner to the latent image on the surface of the photoreceptor 1, and a toner image formed on the surface of the photoreceptor 1 A transfer device 5 for transferring the toner onto the recording paper, a cleaning device 6 for removing the residual toner on the photoconductor 1, and a static elimination lamp 7 for removing the residual potential on the photoconductor 1 are arranged in this order. . In such a configuration, the photosensitive member 1 whose surface is uniformly charged by the charging roller of the charging device 2 has an electrostatic latent image formed on the surface by exposure, and a one-component developer or toner consisting only of toner. A toner image is formed by the developing device 4 using a two-component developer mixed with a carrier. This toner image is transferred from the surface of the photoreceptor 1 to a recording sheet conveyed from a paper feed tray (not shown) by a transfer device 5 including a transfer belt. The recording paper that electrostatically adheres to the photosensitive member 1 during the transfer is separated from the surface of the photosensitive member 1 by the effects of the weight and rigidity of the recording paper, the adsorption force between the recording paper and the separating and conveying means, and the separation claw. Is done. The toner image on the unfixed recording paper is fixed on the recording paper by a fixing device 8 that heats and pressurizes. On the other hand, toner remaining on the photoreceptor 1 without being transferred is removed and collected by the cleaning device 6. The photoreceptor 1 from which the residual toner has been removed is initialized by the charge eliminating lamp 7 and used for the next image forming process.
[0065]
FIG. 2 is a diagram showing a configuration of the developing device 4. The developing device 4 according to this embodiment is a developing device that uses a two-component developer. The developing device 4 includes a developing container 40, a developing roller 42 provided in the opening 41 on the photosensitive member 1 side of the developing container 40, and a doctor blade provided at a position facing the surface of the developing roller 42 in the opening 41. 43 and developer agitating / conveying members 44 and 45 (hereinafter also referred to as a double screw) that are provided in two stages and convey the developer 46 and agitate the developer 46. The developing roller 41, which is a developer carrying member, is disposed so as to be close to the photosensitive member 1, and a developing region where the photosensitive member 1 and the magnetic brush are in contact with each other is formed at the opposite portions. The developing roller 42 includes a developing sleeve formed of a non-magnetic material such as aluminum, brass, stainless steel, and conductive resin in a cylindrical shape, and a rotation driving mechanism (not shown) that rotationally drives the developing sleeve. Rotates the developing sleeve clockwise in FIG. Hereinafter, the developing sleeve is also referred to as a developing roller. Reference numeral 46a indicates the uppermost surface of the developer 46 in the screw portion developer pool, and reference numeral 40a indicates a toner supply hole.
[0066]
The surface of the developing roller 41 is roughened so as to fall within a range of 10 to 20 μm RZ by performing sandblasting or a process of forming a plurality of grooves having a depth of several tens to several hundreds of mm. The photosensitive member 1 is a drum type in which a photosensitive organic layer is applied to a base tube such as aluminum to form a photosensitive layer. The two-component developer controls toner replenishment so that it is at most 70% when non-magnetic toner is used, assuming that the coverage that covers the carrier surface with the toner layer is 100%. This prevents toner scattering and soiling due to insufficient toner charging. RZ represents ten-point average roughness.
[0067]
In this embodiment, the coverage of the toner with respect to the carrier is controlled to about 50%, the drum diameter of the photoreceptor 1 is set to 60 mm, the drum linear velocity is set to 240 mm / second, and the sleeve diameter of the developing sleeve is 20 mm. The roller linear velocity is set to 600 mm / second. Therefore, the ratio of the sleeve linear velocity to the drum linear velocity is 2.5 times. Then, in the case of contact development, the toner and the surface of the photoreceptor 1 are reliably in contact with each other in the development nip at a ratio of 1 to 1.5 times in the toner particle size level range. An image having a sufficient image density can be obtained.
[0068]
The coverage P in the two-component developer is
r / R << 1
in the case of,
P = 100 × C × (√3) / {2π (100−C) (1 + r / R) ^ 2 (r / R) (ρt / ρc)}
C: Toner concentration (% by weight)
r: Volume average particle diameter of toner
R: Volume average particle diameter of carrier
ρt: true specific gravity of toner
ρc: True specific gravity of carrier
Can be approximated by When a vibration bias that generates an alternating electric field is used as the developing bias, the linear velocity ratio of the developer carrying member to the latent image carrying member is not equivalent to 2.5 times the above but about 1.5 times as high as in the developer. This toner can be used effectively for development and sufficient development can be performed. FIG. 3 shows a comparison between the above-described elements and the state of toner scattering and soiling.
[0069]
4 to 6 show examples of the developer agitating and conveying member used in the conventional double screw.
[0070]
The developer agitating / conveying member 10 shown in FIG. 4 is provided with screw blades 12 spirally on the outer periphery of the rotating shaft 11 and is good for the developer agitating property in the lateral direction, but is positive for the fine dispersion of the replenishing toner. It is not configured to show a typical role.
[0071]
The developer agitating and conveying member 13 shown in FIG. 5 is provided with a mesh member 14 in the axial direction of the developer agitating and conveying member 10 shown in FIG. Although dispersibility is improved, there is a lot of room for improvement due to an increase in maximum driving torque and a decrease in lateral stirring performance. The mesh member is, for example, a plain woven wire mesh of SUS304 series, the wire diameter is 0.28 mm, the opening is 1 mm, and the opening ratio is 61%.
[0072]
The developer agitating / conveying member 15 shown in FIG. 6 has a rotating shaft 11 provided with screw blades 12 and a rod-like member 16 protruding in the circumferential direction from the shaft surface to have a stirring function. When configured, the dispersibility is improved, but the improvement effect is small compared to the ratio of increasing the driving torque.
[0073]
7 to 11 show examples of the developer stirring and conveying member used in the double screws 44 and 45 according to the embodiment of the present invention.
[0074]
7A and 7B show the developer agitating / conveying member 17. FIG. 7A is a front view, and FIG. 7B is a cross-sectional view taken along the line AA of FIG. The developer agitating / conveying member 17 shown in FIG. 7 is connected to a driving source to be rotated by a rotating shaft 11, a spiral screw blade 12 formed around the rotating shaft 11, and the screw blade 12. And a plurality of linear members 18 arranged parallel to the axial direction of the rotary shaft 11. The screw blades 12 function as a transport unit that transports the developer 46 mainly in parallel with the rotation shaft 11, and the linear member 18 functions as a stirring unit that mainly shears and stirs the developer 46. In this embodiment, the latent image member 18 is arranged in parallel to the rotation shaft 11, but can also be arranged obliquely.
[0075]
  In the developer agitating and conveying member 17, the maximum value BMAX of the sum B (= Σb) of the length of the cross section of the linear member 18 in the normal direction of the rotating shaft 11 is
  Rc <BMAX ≦ 50Rc (1)
BMAX≦ 0.2 (D−d) (2)
Where Rc: volume average particle diameter of the carrier
D: Diameter [mm] of the rotation trajectory of the screw blade of the developer stirring and conveying member
d: Outer diameter [mm] of the rotating shaft of the developer stirring and conveying member
Is set to
[0076]
The length of the cross section of each linear member 18 in the normal direction of the rotating shaft 11 (corresponding to the diameter in the case of a perfect circular section) is preferably 20 times or less the carrier diameter from the viewpoint of fine dispersion of the replenishment toner. is there. Further, 50% or more of the plurality of linear members 18 (100% in FIG. 7-cross-sectional ratio) is arranged on or near the rotation locus of the tip of the screw blade 12, and the linear velocity of the linear member 18 with respect to the angular velocity is set. The efficiency of stirring performance is improved by making it as large as possible.
[0077]
Further, the plurality of linear members 18 fixed to the screw blades 12 are not completely buried in the developer 46 but are rotated in a state where 60% to 95% are buried in the developer 46. Reference numeral 46 b indicates the upper surface 46 b of the developer 46. As a result, torque fluctuation can be suppressed and the replenishment toner can be efficiently dispersed in the developer 46. The cross section of the linear member 18 has various shapes such as a circle (a), an ellipse (b), a square (c), a triangle (d), a rhombus (e), and a rectangle (f) as shown in FIG. However, as shown in the figure, the surface facing the downstream side in the traveling (moving) direction is unlikely to have a concave portion having a depth exceeding the volume average particle diameter of the carrier so that the developer 46 is not easily held. It is desirable to configure. The rotating shaft 11 of the developer agitating / conveying member 17 has no particular stirring ability. Therefore, by rotating 60% to 100% of the rotating shaft 11 while being buried in the developer, the stirring efficiency is hardly lowered. Space can be saved.
[0078]
In the case of using a plurality of developer agitating / conveying members 17 as shown in FIG. 2, if the developer conveying directions of at least one pair of the developer agitating / conveying members 17 are arranged in opposite directions, It is easy to maintain a good balance. Further, the peripheral speed at the time of rotation of a part of the plurality of linear members 18 fixed to the screw blades 12 is equal to or lower than the peripheral speed of the developing roller 42 (developer carrier) facing the photoconductor (image carrier). Even if the torque is lowered, the stirring performance can be maintained well.
[0079]
FIG. 9 shows a first modification of the developer agitating / conveying member 17 shown in FIG. 7, wherein FIG. 9 (a) is a front view, and FIG. 9 (b) is a cross-sectional view taken along line AA of FIG. FIG. The developer agitating and conveying member 17a according to this modification is provided with a larger number of linear members 18 than in the case of FIG. 7, and a plurality of linear agitating members 17a are provided so that the maximum drive torque does not increase to the left while enhancing the dispersion function. The arrangement positions of the linear members 18 are set so as to include those in which the rotation trajectories of the linear members 18 are different. Also in this modified example, as in the case shown in FIG. 7, the occupation ratio of the cross-sections of the plurality of linear members 18 in the axial direction and existing in the same rotation locus plane is set to 70% or less. In addition, the maximum torque increase accompanying the improvement of the stirring efficiency is suppressed.
[0080]
FIG. 10 is a front view showing a second modification of the developer stirring and conveying member 17 shown in FIG. In the developer stirring / conveying member 17b according to the second modification, the screw blade 12 showing the lateral stirring function is changed to a ribbon-shaped screw blade 12a in which the screw shaft 12 is hollowed in the vicinity of the rotary shaft 11 and is exchanged with the developing roller 42. This is intended to extend the life of the developer and reduce the torque without applying stress as much as possible to the developer other than the developed developer. The plurality of linear members 18 are provided in the same manner as in the example of FIG.
[0081]
FIG. 11 shows a third modification of the developer agitating / conveying member 17 shown in FIG. 7. FIG. 11 (a) is a front view, and FIG. 11 (b) is a cross-sectional view taken along the line AA of FIG. The figure and the figure (c) are the BB sectional views of the figure (a).
[0082]
The developer agitating / conveying member 17c according to the third modification is a spirally arranged linear member 19 for connecting a plurality of linear members 18 to the developer agitating / conveying member 17 shown in FIG. In this modification, each linear member 18 and one linear member 19 are joined at an intermediate portion between adjacent screw blades 12 to which one linear member 18 is fixed. Thereby, structural deformation of the linear member 18 is suppressed.
[0083]
As described above, the developer agitating / conveying members 17, 17a, 17b, and 17c according to the present embodiment and the modified examples have complicated shapes, but are assembled parts in which at least two divided parts are configured and resin molded parts are combined. If it makes it, it can manufacture easily and cheaply.
[0084]
12 to 16 are diagrams showing the characteristics of the embodiment of the present invention configured as described above.
[0085]
FIG. 12 is a characteristic diagram showing the relationship between the condition of the developer agitating / conveying member according to this embodiment and the background stain, and shows the relationship between BMAX and the background stain when the carrier particle size is taken as a parameter. From FIG. 12, it can be seen that the function of dispersing the replenishment toner in the developer 46 cannot be exhibited even if the width between the adjacent linear members 18 is too wide or too narrow. It can also be seen from this figure that the optimum width between adjacent linear members 18 is affected by the carrier particle size.
[0086]
FIG. 13 shows an example of a carrier having an average particle diameter of 50 μm in consideration of the dependence of the carrier particle diameter on the basis of the characteristics found in FIG. 12, and the horizontal axis indicates the linear member width divided by the carrier particle diameter. In the case of the developer having a carrier particle size of 25 μm and 100 μm, the range of the excellent linear member width showing the soiling rank of 4 or more was almost the same, larger than the carrier particle size and 50 times or less.
[0087]
The other main fixed conditions are
Developing roller diameter: 30 mm
Linear speed of developing roller: 380 mm / sec
Screw blade: outer diameter 24mm
Spiral pitch: 20mm
Screw blade linear velocity: 370 mm / sec
Outermost diameter gap between developing roller and screw blade: 3 mm
It is.
[0088]
FIG. 14 is a diagram showing dynamic torque characteristics. In the state where the developing roller 42 and the screw blade 12 are simultaneously rotated as usual and the agent circulation is almost steady, the developing roller 42 is stopped and only the screw blade 12 is moved. The dynamic torque (maximum torque ratio with respect to BMAX) in the rotated state is shown. In this example, an example is shown in which the maximum torque is shown when stirring and conveying, particularly when the linear member 18 is located vertically below where the developer density in the developer 46 is the highest, or when facing the developing roller 42 in the closest state. When BMAX = 0 is the reference value 100 and the parameter [D−d] is different in relative torque, the torque representing 100 may be different. [D-d] is the diameter [mm] of the rotation trajectory of the screw blades of the developer stirring and conveying member, and d is the outer diameter [mm] of the rotating shaft of the developer stirring and conveying member, as described above. As a result, it corresponds to the length in the radial direction that actually contributes to the conveyance and stirring of the developer.
[0089]
FIG. 15 shows the horizontal axis of FIG. 14 replaced with the ratio of [D−d], and D−d = 14 mm and 7 mm are on substantially the same line.
[0090]
The other main fixed conditions are
Wire diameter: 1mm
Developing roller diameter: 30 mm
Linear speed of developing roller: 380 mm / sec
Screw blade: outer diameter 24mm
Spiral pitch: 20mm
Screw blade linear velocity: 370 mm / sec
Outermost diameter gap between developing roller and screw blade: 3 mm
It is.
[0091]
According to the present embodiment in which each part is configured as described above, the dynamic torque fluctuation can be suppressed to a low level as a whole developing device, and it is possible to easily achieve both image density unevenness prevention such as pitch unevenness and banding.
[0092]
FIG. 16 shows an example in which the mixing ratio is compared between the case where the screw blade (developer stirring and conveying member) according to this embodiment is used and the case of a conventional screw blade.
[0093]
The mixing ratio is determined by sampling the developer at five locations at the position where the axial direction of the screw blade 12 is equally divided into five in the developer and the farthest from the developing roller, measuring the toner concentration, and tracking the variation over time. And obtained as a deviation.
[0094]
Initial agent setting method: A predetermined amount of developer having different toner concentrations is set before and after the central position of the agent circulation / stirring / conveying portion in the axial direction of the screw blade. (Example: front toner concentration 8% by weight, rear toner concentration 4% by weight)
Standard deviation of toner density (after n minutes): σn
Initial standard deviation: σ0 ... largest
Standardized standard deviation: σn ′ = σn / σ0...
σn ′ = e ^ −kαt
k: Constant (this time 0.4)
When the screw blades 12 according to the present embodiment are used and the mixing rate α = 15, the time required to show the same standardized standard deviation compared to the case of the mixing rate α = 10 of the conventional example (excluding the initial period) ) Is 1 / 1.5. Moreover, the torque increase can be suppressed to at most 10% as shown in FIGS.
[0095]
FIG. 17 is a conceptual diagram showing the configuration of the toner according to the embodiment of the present invention. In the present embodiment, the replenished toner is easily finely dispersed in the particle size order by spheroidizing, sharpening, external additives, and the like.
[0096]
The toner 20 has a configuration in which a colorant 22, a release agent 23, and a polarity control agent 24 are dispersed in a resin 21, and an external additive 25 is scattered on the surface. The pigment-based colorant 22 dispersed in the toner 20 has a number average particle diameter of 0.5 μm or less, and a number ratio of the number average diameter of 0.7 μm or more is 5% by number or less. 22 is finely dispersed. By finely dispersing in this way, the variation in the component ratio of the pigment-based colorant 22 can be reduced with respect to the differential component of the toner particle diameter, and the variation in the triboelectric chargeability of the toner surface can be reduced as well. Further, electrostatic aggregation between the toners 20 can be suppressed, and toner aggregation can be suppressed low. The accelerated aggregation degree of the toner in the developer is preferably 20% or less as measured by a powder tester. However, the mesh diameter of the accelerated aggregation degree measuring sieve is 75 μm, 45 μm, and 22 μm.
[0097]
In the toner 20 according to the present embodiment, at least the polyester-based prepolymer A containing an isocyanate group is dissolved in the organic solvent, the pigment-based colorant 22 is dispersed, and the release agent 23 is dissolved or dispersed. The dispersion is dispersed in an aqueous medium in the presence of inorganic fine particles and / or fine polymer particles, and the prepolymer A is reacted with polyamine and / or monoamine B having an active hydrogen-containing group in the dispersion to cause urea groups. It is obtained by forming a urea-modified polyester-based resin C having the following, and removing the liquid medium contained therein from the dispersion containing the urea-modified polyester-based resin C. In the urea-modified polyester resin C, the Tg is 40 to 65 ° C, preferably 45 to 60 ° C. The number average molecular weight Mn is 2500 to 50000, preferably 2500 to 30000. The weight average molecular weight Mw is 10,000 to 500,000, preferably 30,000 to 100,000.
[0098]
The toner 20 includes, as a binder resin 21, a urea-modified polyester resin C having a urea bond that has been increased in molecular weight by the reaction between the prepolymer A and the amine B. In the binder resin 21, the colorant 22 is highly dispersed. The toner 20 configured as described above has a small difference in frictional charging characteristics on the toner surface, hardly causes electrostatic aggregation between the toners, and the replenishment toner is well dispersed.
[0099]
Further, in the toner 20 according to this embodiment, the dispersed particle diameter and shape of the pigment-based colorant 22 hardly change even after fixing, and light scattering and diffraction phenomena due to the colorant are roughly dispersed in the output image after fixing. This is an excellent color toner that is more noticeable, has a high tinting strength, and has a clear color tone and high transparency. With this toner 20, sufficient color tone reproducibility can be obtained with a small amount of toner attached, and both reduction in toner consumption, reduction in fixing energy, and high-quality image formation can be achieved. The dye-based colorant is advantageous with respect to the cohesiveness because the dispersed particle size is on the nanometer scale close to the molecular order.
[0100]
The toner 20 according to the present embodiment can also be used as a magnetic toner containing a magnetic material.
[0101]
Specific magnetic materials include iron oxides such as magnetite, hematite, and ferrite, metals such as cobalt and nickel, and these metals and aluminum, copper, lead, magnesium, tin, zinc, antimony, beryllium, bismuth, cadmium, and calcium. , Alloys with metals such as manganese, selenium, titanium, tungsten, vanadium, and mixtures thereof.
[0102]
These magnetic materials desirably have an average particle diameter of about 0.1 to 2 μm, and the content of the magnetic material at this time is 20 to 200 parts by weight, particularly preferably a binder, with respect to 100 parts by weight of the binder resin. It is 40-150 weight part with respect to 100 weight part of resin.
[0103]
As the additive used, conventionally known additives can be used. Specifically, Si, Ti, Al, Mg, Ca, Sr, Ba, In, Ga, Ni, Mn, W, Fe, Co, Zn , Cr, Mo, Cu, Ag, V, Zr, and the like, and composite oxides, and the like. In particular, silica, titania, and alumina that are oxides of Si, Ti, and Al are preferably used.
[0104]
Moreover, it is preferable that the addition amount of the additive at this time is 0.5-1.8 weight part with respect to 100 weight part of base particles, Most preferably, it is 0.7-1.5 weight part. .
[0105]
FIG. 18 is a diagram showing a configuration of a developer according to the embodiment of the present invention. As shown in the figure, the developer according to this embodiment is present at a level where the charged or uncharged toner 20 does not completely cover the surface of the carrier core material 26 around the carrier core material 26. The outer peripheral surface of the carrier core material 26 is coated with a carrier coat layer 27.
[0106]
FIG. 19 is a diagram showing a developer fluidity measuring apparatus according to an embodiment of the present invention. In the figure, a fluidity measuring device 30 according to this embodiment includes a support base 31, a funnel support 32, and a support 33 for attaching the funnel support 32 to the support base 31 at a predetermined height. The support 33 is erected substantially vertically from the support base 31. The funnel support 32 is provided with a support portion 32a for supporting the funnel 34 on a plate-like portion protruding from the support 33, and the funnel 34 is inserted into the support portion 32a from above and supported. A container 35 such as a cup is placed on the support base 31 below the funnel 34 to receive the developer 46 flowing out from the funnel 34. In the present invention, since the self-flow of the developer 46 due to gravity is used for dispersion and stirring, the fluidity of the developer 46 is preferably 45 sec / 50 g or less.
[0107]
Next, a method for measuring toner physical properties such as the dispersed particle diameter of the pigment-based colorant in the toner will be described in detail.
[0108]
In order to measure the dispersed particle size and particle size distribution of the colorant in the toner, the toner 20 was embedded in an epoxy resin, and the toner was ultrathinned to about 100 nm with a microtome MT6000-XL (manufactured by Kyowa Shoji). Prepare a measurement sample.
[0109]
Using an electron microscope (H-9000NAR manufactured by Hitachi, Ltd.), a plurality of TEM photographs were taken at an acceleration voltage of 100 kV at a magnification of 10,000 to 40000 times, and the image information was obtained with an image processing analyzer LUZEX III of IMAGE ANALYZER. Convert to image data. For the target pigment-based colorant particles, the measurement is repeated for particles having a particle size of 0.1 μm or more until sampling exceeds 300 times, and the average particle size and particle size (particle size) distribution are obtained.
[0110]
The toner 20 according to this embodiment has a weight average particle diameter (Dv) of 4 to 8 μm, and a ratio (Dv / Dn) to the number average particle diameter (Dn) is
1.00 ≦ Dv / Dn ≦ 1.25
It is. By defining Dv / Dn in this way, it is possible to obtain toner 20 with high resolution and high image quality. In order to obtain a higher quality image, the weight average particle diameter (Dv) of the colorant 22 is 4 to 8 μm, and the ratio (Dv / Dn) to the number average particle diameter (Dn) is
1.00 ≦ Dv / Dn ≦ 1.25
In addition, the number of particles of 3 μm or less is preferably 1 to 10% by number. More preferably, the weight average particle diameter is 4 to 6 μm, and Dv / Dn is
1.00 ≦ Dv / Dn ≦ 1.15
It is good to make it. Such a toner 20 is hard to agglomerate when left untreated, has excellent heat resistance, low-temperature fixability, and hot offset resistance, and is particularly excellent in image gloss when used in a full-color copying machine. Further, in the two-component developer, even if the balance of the toner 20 is performed for a long time, the fluctuation of the particle diameter of the toner 20 in the developer 46 is reduced, and the toner is good and stable even in the long-term stirring in the developing device. Chargeability and developability can be obtained.
[0111]
In general, it is said that the smaller the particle diameter of the toner 20 is, the more advantageous it is for obtaining a high-resolution and high-quality image. It is disadvantageous. In addition, when the volume average particle diameter of the toner 20 is smaller than the range defined in the present invention, the two-component developer 46 melts the toner 20 on the surface of the carrier 28 (the surface of the carrier coat layer 27) during long-term stirring in the developing device. The charging ability of the carrier 28 is lowered. On the other hand, when used as a one-component developer, filming of the toner 20 on the developing roller 42 and fusion of the toner 20 to a member such as a doctor blade 43 for thinning the toner 20 occur. It becomes easy. These phenomena are greatly related to the content of fine powder in the toner 20. Particularly, when the content of particles of 3 μm or less exceeds 10%, the toner 20 hardly adheres to the carrier 28 and is charged at a high level. It becomes difficult to aim for stability.
[0112]
On the contrary, when the toner particle diameter is larger than the range defined in the present invention, it becomes difficult to obtain a high-resolution and high-quality image, and the balance of the toner 20 in the developer 46 is performed. In many cases, the variation in the particle diameter of the toner 20 becomes large. It was also clarified that the same was true when the weight average particle diameter / number average particle diameter was larger than 1.25.
[0113]
The average particle size and the particle size distribution of the toner 20 are measured by a car Coulter counter method. Examples of the measurement device for the particle size distribution of toner particles include Coulter Counter TA-II and Coulter Multisizer II (both manufactured by Coulter). In this embodiment, a Coulter counter TA-II type was used, and measurement was performed by connecting an interface (manufactured by Nikka Giken Co., Ltd.) for outputting the number distribution and volume distribution to a PC 9801 personal computer (manufactured by NEC).
[0114]
Next, a method for measuring the toner number distribution and volume distribution will be described.
[0115]
First, 0.1 to 5 ml of a surfactant (preferably alkylbenzene sulfonate) is added as a dispersant to 100 to 150 ml of an aqueous electrolytic solution. Here, the electrolytic solution is an approximately 1% NaCl aqueous solution formed using primary sodium chloride. For example, ISOTON-II (manufactured by Coulter) can be used. Here, 2 to 20 mg of a measurement sample is further added. The electrolytic solution in which the sample is suspended is subjected to a dispersion process for about 1 to 3 minutes with an ultrasonic disperser, and the volume and the number of toner particles are measured with the measuring apparatus using a 100 μm aperture as the aperture, and the volume distribution is obtained. And calculate the number distribution.
[0116]
As a channel,
2.00 to less than 2.52 μm;
Less than 2.52 to 3.17 μm;
3.17 to less than 4.00 μm;
4.00 to less than 5.04 μm;
5.04 to less than 6.35 μm;
6.35 to less than 8.00 μm;
8.00 to less than 10.08 μm
10.08 to less than 12.70 μm;
12.70 to less than 16.00 μm;
16.00 to less than 20.20 μm;
Less than 20.20-25.40 μm;
25.40 to less than 32.00 μm;
32.00 to less than 40.30 μm
13 channels are used, and particles having a particle size of 2.00 μm to less than 40.30 μm are targeted. The ratio Dv / Dn was obtained from the volume-based weight average particle diameter (Dv) obtained from the volume distribution of the toner 20 of the present embodiment and the number average particle diameter (Dn) obtained from the number distribution.
[0117]
The circularity of the toner 20 according to this embodiment is measured by a flow type particle image analyzer FPIA-2000 (manufactured by Sysmex Corporation). The toner 20 has an average circularity of 0.900 to 0.990, and it is important to have a specific shape and shape distribution. When the average circularity is less than 0.900, the toner exhibits an irregular shape and does not give satisfactory transferability and high-quality images without dust. Since the irregularly shaped toner particles have many contact points with the smooth medium on the photosensitive member and the charge concentrates on the tip of the protrusion, the van der Waals force and the mirror image force are higher than those of the relatively spherical particles. Therefore, in the electrostatic transfer process, the spherical particles are selectively moved in the toner in which the amorphous particles and the spherical particles are mixed, and the character portion and the line portion image are lost. In addition, the remaining toner must be removed for the next development process, and there is a problem that a cleaner device is required or the toner yield (the ratio of toner used for image formation) is low. . The circularity of the pulverized toner is usually 0.910 to 0.920 when measured with this apparatus.
[0118]
Other development conditions are as follows.
[0119]
As described above, the upstream side of the developing region in the developer conveyance direction (counterclockwise direction in FIG. 2) is a doctor that regulates the height of the developer chain spike, that is, the amount of developer on the developing sleeve. A blade 43 is installed. The doctor gap, which is the distance between the doctor blade 43 and the developing sleeve (developing roller) 42, is set to about 0.3 to 0.7 mm. The amount of developer conveyed to the developing unit is preferably 20 to 100 mg / cm ^ 2. Further, in a region opposite to the photosensitive drum 1 of the developing roller 42, stirring / conveying means (screw, paddle, etc.—screw blade in FIG. 2) for pumping up the developer 46 in the developing container 40 to the developing sleeve while stirring. 44, 45) are installed. Further, the developing gap, which is the distance between the photosensitive drum 1 and the developing sleeve, is set to 0.3 mm. The development gap is preferably set to about 10 times (0.55 mm) or less if the carrier particle diameter is 50 μm. If the development gap is wider than this, it is difficult to obtain a desired image density under the condition of applying a DC development bias voltage.
[0120]
In the developing sleeve 42 (same as the developing roller), a magnet roller body (magnet roller) that forms a magnetic field is provided in a fixed state so that the developer 46 rises on the peripheral surface of the developing sleeve. The carrier 28 in the developer 46 rises in a chain shape on the developing sleeve 42 so as to follow the normal magnetic field lines emitted from the magnet roller body. Is attached to form a magnetic brush. The magnetic brush is transferred in the same direction as the developing sleeve 42 (counterclockwise direction in the drawing) by the rotation of the developing sleeve 42. The magnet roller body includes a plurality of magnetic poles (magnets). The preferred normal direction magnetic flux density at the exit of the developing region on the surface of the developing sleeve 42 on the developing main pole is 60 mT or more. In order to improve the pumping property and the black solid image following property, the number of magnets (magnetic poles) may be further increased. When the volume average particle size of the magnetic carrier 28 is larger than the average volume particle size of the toner 20 and the magnetization is 30 to 1000 emu / cm ^ 3 (in a 1 kOe magnetic field), the effect of suppressing carrier adhesion to the photosensitive member 1 during development; By preventing excessive contact pressure when the tip of the magnetic brush consisting of the developer 46 is in contact with the photoreceptor 1, a high-quality image without a feeling of roughness can be obtained.
[0121]
In this embodiment, the carrier 28 having a dynamic resistance of 10１０7 Ω · cm or less when a maximum development potential difference is applied is used, and sufficient toner 20 corresponding to the development electric field can be obtained even if the development time is short. 1 can be attached. The lower resistance of the carrier 28 also played a role of increasing the dielectric constant of the developer layer and increasing the strength of the developing electric field, so that development with a sufficient toner adhesion amount was achieved even at a low electric field developing potential.
[0122]
Here, an example of low electric field potential development conditions will be described.
[0123]
In this embodiment, the developing process is performed with the charging (pre-exposure) potential V0 of the photoreceptor 1 being −350V, the post-exposure potential VL being −50V, and the development bias voltage VB being −250V, that is, the development potential (VL−VB = 200V). Is. At this time
0 <| VD | − | VB | <| VD−VL | <400V
Meet. In the above equation, | VD−VL | <400 V is set according to Paschen's discharge law in order to avoid discharge of the exposed portion and the unexposed portion of the photoreceptor 1. This embodiment is a negative-positive process.
[0124]
The toner on the developing sleeve 42 is developed by the developing bias applied to the developing sleeve 42 with respect to the latent image formed on the photosensitive member 1, and is visualized on the photosensitive member 1. Incidentally, in this embodiment, the linear velocity of the photosensitive member 1 is 200 mm / s, and the linear velocity of the developing sleeve 42 is 300 mm / s. The developing process is performed with the photosensitive member 1 having a diameter of 50 mm, the supply member having a diameter of 18 mm, and the developing sleeve 42 having a diameter of 16 mm. Here, the toner charge amount on the developing sleeve 42 is in the range of −10 to −30 μC / g. The thickness of the photoreceptor 1 is 28 μm, the beam spot diameter of the optical system is 50 × 60 μm, and the light quantity is 0.23 mW.
[0125]
The developing process is performed with the charging (pre-exposure) potential V0 of the photoreceptor 1 being -300V, the post-exposure potential VL being -100V, and the development bias voltage being -250V, that is, the development potential (VL-VB = 150V).
[0126]
The visible image of the toner formed on the photoreceptor 1 is then completed as an image through a transfer and fixing process. For the transfer, a biased roller or charger that is in contact with the back side of the transfer paper or intermediate transfer member is disposed.
[0127]
Here, the low light exposure, which is one of the effects of the low potential development described above, will be described.
[0128]
A binary process has been proposed by using a technique in which exposure is performed by reducing the beam diameter with a high light intensity. However, there is a problem caused by increasing the amount of light. One is that reducing the beam diameter of the high-density light amount reduces the margin of optical design, and it is indispensable to improve the accuracy of parts, resulting in an increase in cost. Another point is that since the amount of light is large, it is one of the factors that shorten the service life due to a so-called electrostatic hazard due to an increase in the amount of energized charge in charging / exposure of the photosensitive member 1. Therefore, in this embodiment, by lowering the initial charging potential of the photoconductor 1 and simultaneously reducing the exposure amount, a general-purpose optical component is used to form a high-definition latent image and electrostatic hazard to the photoconductor 1 is reduced. It can be reduced and the life can be extended.
[0129]
Looking at the γ curve in low potential development (development amount with respect to development potential difference—not shown), the inclination is large and development is easy even at a relatively low potential and can be saturated immediately. This indicates that it is relatively easy to efficiently develop a large amount of toner on the carrier with a solid image while keeping the toner carrying amount on the developing roller 42 constant. Even in the case of forming a small-diameter dot, if configured as in the present embodiment, the charging potential can be kept low, the dot latent image can be lowered with about half the amount of light conventionally, and a uniform dot image is formed. be able to.
[0130]
FIG. 1 shows a schematic configuration of an image forming apparatus having a process cartridge by a low potential process, which is one of the embodiments of the present invention.
[0131]
In the present embodiment, a plurality of components such as the photosensitive member 1, the charging device 2, the developing hand device 4 stages, and the cleaning device 6 are integrally coupled as a process cartridge. The process cartridge is configured to be detachable from a main body of an image forming apparatus such as a copying machine or a printer. In the image forming apparatus having the process cartridge having the developing device 4 described above, the photosensitive member 1 is rotationally driven at a predetermined peripheral speed. In the rotating process, the photosensitive member 1 is uniformly charged with a predetermined positive or negative potential on the peripheral surface thereof by the charging device 2, and then receives image exposure light emitted from an exposure device such as slit exposure or laser beam scanning exposure. In response, electrostatic latent images are sequentially formed on the peripheral surface of the photoreceptor 1. The formed electrostatic latent image is developed with toner by the developing device 4, and the developed toner image is fed between the photosensitive member 1 and the transfer device 5 from the paper feeding unit in synchronization with the rotation of the photosensitive member 1. The transfer device 5 sequentially transfers the transferred material. The transfer material that has received the image transfer is separated from the surface of the photosensitive member 1, guided to the fixing device 8, fixed, and printed out as a copy (copy). The surface of the photoreceptor 1 after the image transfer is cleaned by removing the transfer residual toner by the cleaning device 6, further neutralized by the neutralization device 7, and then repeatedly used for image formation.
[0132]
The lifetime of the photosensitive unit and the developing device is extended by the present invention. However, the lifetimes of the photosensitive unit and the developing device are not necessarily the same, and therefore, when a process cartridge that can be independently attached and detached is used, it can be easily separated depending on the lifetime. Can be replaced. Further, since it can be arranged independently, it is possible to retract the developing roller from the photosensitive member at the time of non-development by adding a simple mechanism, so that the promotion of toner filming to the developing roller is reduced, and the developing device The lifespan of is extended.
[0133]
In the current developing device of this embodiment shown in FIG. 1, during development, a vibration bias voltage obtained by superimposing an AC voltage on a DC voltage is applied to the developing sleeve as a developing bias by a power source. The background portion potential and the image portion potential are located between the maximum value and the minimum value of the vibration bias potential. As a result, an alternating electric field whose direction changes alternately is formed in the developing portion. In this alternating electric field, the developer toner and carrier vibrate vigorously, and the toner flies off the electrostatic binding force on the developing sleeve and carrier and flies to the photosensitive drum, and adheres corresponding to the latent image on the photosensitive drum. To do.
[0134]
The difference (maximum peak voltage) between the maximum value and the minimum value of the vibration bias voltage is preferably 0.5 to 5 KV, and the frequency is preferably 1 to 10 KHz. As the waveform of the vibration bias voltage, a rectangular wave, a sine wave, a triangular wave, or the like can be used. As described above, the DC voltage component of the vibration bias is a value between the background part potential and the image part potential, but the value closer to the background part potential than the image part potential is more likely to cover the background part potential region. This is preferable for preventing toner adhesion.
[0135]
When the vibration bias voltage waveform is a rectangular wave, the duty ratio is preferably 50% or less. Here, the duty ratio is a ratio of time during which the toner is directed to the photosensitive member during one period of the vibration bias. By doing so, the difference between the peak value at which the toner is directed to the photoreceptor and the time average value of the bias can be increased, so that the movement of the toner is further activated and the potential of the latent image surface is increased. It adheres to the distribution faithfully, reduces the feeling of roughness, and improves the resolution. In addition, since the difference between the peak value of the carrier having a charge opposite to that of the toner and the time average value of the bias toward the photoconductor can be reduced, the movement of the carrier is calmed down, and the background portion of the latent image is reduced. The probability of carriers adhering to the substrate can be greatly reduced.
[0136]
【The invention's effect】
As described above, according to the present invention, the developer can be sheared efficiently and at high speed without significantly increasing torque, and the replenishment toner is excellent in dispersibility and longitudinal agitation in the developer. A developing device, an image forming apparatus including the developing device, and a developing method using the developing device can be provided.
[0137]
In addition, according to the present invention, a developing device and an image forming apparatus, and a developing device that are efficient in the vertical and horizontal stirring of the developer with respect to the drive input energy of the entire developing device, the dispersion of replenishment toner, and the start-up of toner charging. The used developing method can be provided.
[Brief description of the drawings]
FIG. 1 is a diagram showing a schematic configuration of an entire image forming system apparatus according to an embodiment of the present invention.
FIG. 2 is a diagram illustrating a configuration of the developing device in FIG. 1;
FIG. 3 compares the volume average particle diameter R of the carrier, the volume average particle diameter r of the toner, the true specific gravity ρc of the carrier, the true specific gravity ρt of the toner, the toner concentration C, the coverage P, the toner scattering, and the state of scumming. FIG.
FIG. 4 is a diagram illustrating an example of a developer stirring and conveying member that has been conventionally used.
FIG. 5 is a diagram illustrating another example of a developer stirring and conveying member that has been conventionally used.
FIG. 6 is a view showing still another example of a developer agitating / conveying member that has been conventionally used.
FIG. 7 is a diagram illustrating an example of a developer stirring and conveying member according to an embodiment of the present invention.
8 is a diagram illustrating an example of a linear member of the developer stirring and conveying member in FIG.
FIG. 9 is a view showing another example of the developer stirring and conveying member according to the embodiment of the present invention.
FIG. 10 is a view showing still another example of a developer stirring and conveying member according to an embodiment of the present invention.
FIG. 11 is a view showing still another example of a developer stirring and conveying member according to an embodiment of the present invention.
FIG. 12 is a diagram illustrating a relationship between stirring / conveying member conditions and background contamination of the developing device according to the exemplary embodiment of the present invention.
FIG. 13 is a diagram illustrating the relationship of background contamination of the agitating / conveying member condition of the developing device according to the embodiment of the present invention by changing parameters.
FIG. 14 is a diagram illustrating a relationship between the agitating / conveying member condition and the maximum torque ratio of the developing device according to the embodiment of the invention.
FIG. 15 is a diagram showing the relationship between the agitating / conveying member condition and the re-torque ratio in the developing device according to the embodiment of the present invention by changing parameters.
FIG. 16 is a diagram showing a comparison of developer mixing ratios in the developing device according to the embodiment of the present invention.
FIG. 17 is a diagram illustrating a configuration of a toner according to an exemplary embodiment of the present invention.
FIG. 18 is a diagram illustrating a configuration of a developer according to the embodiment of the invention.
FIG. 19 is a diagram showing a developer flow rate measuring device in the present embodiment.
[Explanation of symbols]
1 Photoconductor
2 Charging device
3 Image exposure equipment
4 Development device
40 Developer container
41 Developing roller
42 opening
43 Doctor blade
44, 45 Developer stirring and conveying member
5 Transfer device
6 Cleaning device
7 Charge removal value
8 Fixing device
11 Rotating shaft
12,12a Screw blade
17, 17a, 17b, 17c Developer stirring and conveying member
18 Linear members
19 Connecting member
20 Toner
21 resin
22 Colorant
23 Release agent
24 Polarity control agent
25 External additives
26 Carrier core
27 Carrier coat layer
28 Career
30 Fluidity measuring device
34 Funnel

Claims

A developer containing portion containing a two-component developer containing a toner having a volume average particle size of 10 μm or less and a carrier having a volume average particle size of 100 μm or less;
A developer carrier that is disposed so as to face an image carrier on which an electrostatic latent image is formed, carries a thin layer of the two-component developer, and conveys it to a position close to the image carrier; ,
A developer stirring and conveying member that is arranged in parallel with the developer carrying member and stirs the two-component developer and conveys it to the developer carrying member;
The electrostatic latent image is visualized by transferring toner from the two-component developer on the developer carrier to the image carrier at a position close to the developer carrier and the image carrier. In the developing device,
The developer stirring and conveying member
A rotating shaft that is driven to rotate by obtaining a driving force from a driving source;
A conveying unit that conveys the two-component developer mainly in a direction parallel to the axial direction of the rotating shaft by a spiral blade member formed around the rotating shaft;
Comprising a plurality of linear members fixed to the spiral blade member at a predetermined angle with respect to the axial direction of the rotating shaft, and comprising a stirring section for mainly shearing and stirring the two-component developer,
When the maximum value BMAX of the sum B (= Σb) of the length in the normal direction of the rotation axis of the cross section of the plurality of linear members of the stirring unit is Rc, the volume average particle diameter of the carrier is Rc.
Rc <BMAX ≦ 50Rc
BMAX ≦ 0.2 (D−d)
However, D: Diameter [mm] of the rotation locus of the spiral blade member of the stirring and conveying member
d: outer diameter [mm] of the rotating shaft of the stirring and conveying member
Is set to
The shape of the cross section of the plurality of linear members of the stirring section, Ri shape der having an apex in the traveling direction downstream side of the linear member by the rotation of the rotary shaft,
A connecting member that connects the plurality of linear members to each other at a position different from a fixed position of the spiral blade member and the linear member; and the plurality of linear members are arranged in a rotational direction of the rotating shaft. It is arranged to line up along,
The linear member is fixed to the plurality of spiral blade members at a plurality of points over the axial direction of the rotation shaft, and the connecting member includes a plurality of the linear member and the spiral blade member. Connecting the plurality of linear members to each other between two adjacent points among the fixed points,
The connecting member is a linear member arranged spirally along the spiral shape of the spiral blade member, and connects the plurality of linear members to each other at a plurality of points along the axial direction of the rotating shaft. A developing device.

The 50% or more of the plurality of linear members fixed to the spiral blade member is disposed in the vicinity of the rotation locus including the rotation locus of the tip portion of the spiral blade member. The developing device described.

The developer stirring and conveying member is arranged so that 60% to 95% of the plurality of linear members fixed to the spiral blade member rotate in a state of being buried in the two-component developer. The developing device according to claim 1 or 2.

It is an axial cross section of a plurality of linear members fixed to the spiral blade member, and the occupation ratio of the cross sections of the linear members existing on the same rotation locus plane is set to 70% or less. The developing device according to any one of claims 1 to 3.

5. The developing device according to claim 1, wherein the plurality of linear members fixed to the spiral blade member include linear members having different rotation trajectories.

2. The development according to claim 1, wherein the developer agitating member is arranged such that 60% or more of the rotation axis of the developer agitating and conveying member rotates in a state where it is buried in the two-component developer. apparatus.

7. The developing device according to claim 1, wherein at least a pair of the developer agitating and conveying members including the plurality of linear members are set to have different developer conveying directions. .

8. The peripheral speed of the rotation trajectory of some linear members of the plurality of linear members is set to be equal to or lower than the peripheral speed of the developer carrier. The developing device according to 1.

The width W is set so that the width W of the linear member in the normal direction of the rotation axis is not more than 20 times the volume average particle diameter Rc of the carrier in the two-component developer. The developing device according to any one of claims 1 to 8.

10. The developing device according to claim 1, wherein a dynamic torque fluctuation of the developer agitating / conveying member is set between + 25% and −25%.

The developing device according to claim 1, wherein the two-component developer has a fluidity of 45 sec / 50 g (JISZ-2502) or less.

2. The developing device according to claim 1, wherein the accelerated aggregation degree of the toner of the two-component developer is 20% or less.

The toner is dissolved or dispersed in a toner composition containing at least a modified polyester resin capable of urea bonding and a colorant in an organic solvent, and the dissolved or dispersed material is dispersed in an aqueous medium to perform a polyaddition reaction. The developing device according to claim 1, wherein the color toner is obtained by removing and washing the solvent of the dispersion.

The toner has a weight average particle size of 4.0 to 8.0 μm and a particle size distribution of Dv / Dn ≦ 1.25 (Dv: weight average particle size, Dn: number average particle size). The developing device according to claim 1 or 13.

The developing device according to claim 1, wherein the toner is a toner having an average circularity of 0.90 to 0.99.

When the toner coverage on the surface of the developer carrying member facing the photoreceptor is P [%], and the linear velocity ratio between the developer carrying member linear velocity vD and the photosensitive member linear velocity vP is vD / vP, P · (vD / vP) is
1 / 0.98 ≦ P · (vD / vP) /100≦1.5/0.8
2. The developing device according to claim 1, wherein the developing device is controlled so as to fall within the range.

The two-component developer comprises a magnetic carrier and a toner;
The volume average particle diameter of the magnetic carrier is larger than the volume average particle diameter of the toner, and the magnetization is 30 to 1000 emu / cm ^ 3 (in an 11 kOe magnetic field). And the developing device according to any one of 12 and 12.

A carrier is supported on the developer carrying body including a magnet when the maximum development potential difference is applied to the developer layer, and an electrode having a width of 65 mm and a length of 1 mm is brought into contact with a gap of 0.9 mm, and the pressure resistance is below the upper limit level. 2. The developing device according to claim 1, wherein the resistance value when the applied voltage is 10 <7> [Omega] .cm or less.

Charging means for charging the image carrier;
An exposure apparatus that performs optical writing to form a latent image on the image carrier;
The developing device according to any one of claims 1 to 18, which develops a latent image formed by the exposure device;
A transfer device for transferring the developed image developed by the developing device to a recording medium;
A fixing device for fixing a visible image on the recording medium transferred by the transfer unit;
An image forming apparatus comprising:

When the dark portion potential is VD, the post-exposure potential is VL, and the development bias voltage is VB.
0 <| VD | − | VB | <| VD−VL | <400V
The image forming apparatus according to claim 19, wherein:

In a process cartridge that integrally supports at least one means selected from an image carrier, a charging device, a developing device, and a cleaning device and is detachable from the image forming apparatus main body,
19. A process cartridge, wherein the developing device comprises the developing device according to any one of claims 1 to 18.

A developing method for developing using the developing device according to any one of claims 1 to 9,
A developing method, wherein the developer agitating / conveying member is rotated while a dynamic torque fluctuation is between + 25% and −25%.

16. A developing method in which development is performed using the developing device according to claim 1, wherein the toner coverage on the surface of the developer carrying member facing the photosensitive member is P [%]. When the linear velocity ratio between the developer carrying member linear velocity vD and the photosensitive member linear velocity vP is vD / vP,
P · (vD / vP) is
1 / 0.98 ≦ P · (vD / vP) /100≦1.5/0.8
The developing method is characterized in that it is controlled so as to be in the range.