JP4155089B2

JP4155089B2 - Developing device and image forming apparatus

Info

Publication number: JP4155089B2
Application number: JP2003124175A
Authority: JP
Inventors: 邦男重田; 宏秋田; 板垣　　整子
Original assignee: Konica Minolta Business Technologies Inc
Current assignee: Konica Minolta Business Technologies Inc
Priority date: 2003-04-28
Filing date: 2003-04-28
Publication date: 2008-09-24
Anticipated expiration: 2023-04-28
Also published as: JP2004326033A

Description

【０００１】
【発明の属する技術分野】
本発明は、現像装置およびこの現像装置を備えた画像形成装置に関する。
【０００２】
【従来の技術】
現在、電子写真方式を利用したある種の画像形成装置においては、例えばトナーとキャリアとからなる二成分現像剤を用い、適宜の撹拌手段によって摩擦帯電されたトナーを現像領域に搬送し、トナーを潜像担持体上に形成された静電潜像に付着させることによりトナー像を形成する現像方法が利用されており、このような二成分現像剤を用いた現像方法においては、現像剤におけるトナー濃度を一定に維持するために、トナー消費量に応じて新たなトナーを補給することが行われている。
【０００３】
このような画像形成装置においては、画像の高画質化が求められており、このような要請に対して、例えば粒子径が小さいトナーが用いられるようになってきており、また、トナーの小粒径化に伴ってキャリアの小粒径化が図れている。
【０００４】
而して、粒子径が小さいトナーおよび粒子径が小さいキャリアを用いることにより画質の高い画像を形成することができる反面、現像剤それ自体の流動性が低下して現像剤を十分に撹拌することが困難となり、その結果、新たに補給されたトナーは、所定の帯電量を有する状態とならないまま、現像領域に供給されることとなり、かぶりやトナー飛散が発生しやすくなる、という問題がある。
そして、このような問題は、例えばカラー画像を形成する場合など印字率が高い画像を連続して出力する場合に、顕著に生ずる。
【０００５】
一方、近年においては、環境保全に関する社会的な意識の高まりなどに伴って、例えばトナーをリサイクルするなどして省資源化が図られるようになってきている。
しかしながら、一旦現像に供された後に回収されたトナー（リサイクルトナー）は、その帯電特性が未使用のトナーに比して劣るものであるので、トナーの帯電量不足によるかぶりやトナー飛散が発生しやすくなる、という問題がある。
【０００６】
このような問題に対して、従来より、現像剤の撹拌効率を向上させる技術が多数提案されており、例えば補助撹拌部材として機能する部材を設けることにより撹拌手段を高い現像剤撹拌能力を有する構成のものとしたりすることが行われている（例えば特許文献１、特許文献２、特許文献３等参照。）。
【０００７】
【特許文献１】
特開平０７−０１３４２０号公報
【特許文献２】
特開平０９−１６６９１８号公報
【特許文献３】
特開平０９−２８８４１２号公報
【０００８】
【発明が解決しようとする課題】
しかしながら、上記のような技術においては、いずれのものも、現像剤の撹拌効率が向上する反面、現像装置内における現像剤の循環搬送速度が低下することとなり、その結果、現像剤担持体に供給される現像剤の、現像剤担持体の回転軸方向に対するトナー濃度が不均一となり、特に、印字率が高い画像を連続して出力する場合には、画像濃度むらが顕著に生じやすく、高い画質の画像を確実に形成することが困難である、という問題がある。
【０００９】
以上のように、補給された新トナーを十分な帯電量を有する状態とするために、現像剤の撹拌性能を向上させることによりかぶりやトナー飛散の発生を防止しようとした場合には、現像剤の搬送性能が低下することによる画像濃度むらが発生しやすくなるという問題があり、結局、かぶりやトナー飛散の発生、および画像濃度ムラの発生、といういわば相反する２つの問題を同時に解決することが困難である、というのが実状である。
【００１０】
本発明は、以上のような事情に基づいてなされたものであって、その目的は、現像剤の搬送速度を低下させることなしに、トナーを所定の大きさの帯電量を有する状態に混合撹拌することができ、従って、画質の高い画像を確実に形成することができる新規な構成の現像装置および画像形成装置を提供することにある。
【００１１】
【課題を解決するための手段】
本発明の現像装置は、互いに連通してトナーとキャリアとからなる二成分現像剤の循環搬送路を形成する現像剤供給回収部および現像剤撹拌部が前後方向に並んで形成されたハウジングと、前記現像剤供給回収部の前方側部分において潜像担持体と現像領域を介して対向するように設けられた現像剤担持体と、前記現像剤供給回収部の後方側部分において現像剤担持体と対向して当該現像剤担持体の回転軸方向に沿って延びるように設けられた、回転されて現像剤を回転軸方向に搬送する現像剤供給回収手段と、前記現像剤撹拌部において、各々、互いに対向して現像剤供給回収手段の回転軸方向に沿って延びるよう前後方向に並んで設けられた２つの現像剤撹拌手段とを備えてなり、
ハウジングには、現像剤撹拌部における２つの現像剤撹拌手段が対向する部分の上方であって、現像剤撹拌部における現像剤の搬送方向の上流側に位置される個所に、トナー供給用開口が形成されており、
現像剤撹拌部における２つの現像剤撹拌手段は、当該２つの現像剤撹拌手段が、互いに対向する部分において、各々の周面が上方から下方に向かって互いに順方向に移動されるよう回転されて、いずれも、現像剤を現像剤供給回収手段と互いに逆方向に搬送するものであって、各々の現像剤撹拌手段による現像剤の搬送量の総和が現像剤供給回収手段による現像剤搬送量と同等となる現像剤搬送能力を有するものであることを特徴とする。
【００１２】
本発明の現像装置においては、現像剤撹拌部における一方の現像剤撹拌手段は、回転軸方向に対する現像剤搬送能力が他方の現像剤撹拌手段と同等または他方の現像剤撹拌手段より低いものであり、現像剤供給回収部に対して後方側に設けられていることが好ましい。
【００１３】
本発明の現像装置は、互いに連通してトナーとキャリアとからなる二成分現像剤の循環搬送路を形成する現像剤供給回収部および現像剤撹拌部が前後方向に並んで形成されたハウジングと、前記現像剤供給回収部の前方側部分において潜像担持体と現像領域を介して対向するように設けられた現像剤担持体と、前記現像剤供給回収部の後方側部分において現像剤担持体と対向して当該現像剤担持体の回転軸方向に沿って延びるように設けられた、軸部材の外周面の全周にわたって回転軸方向に螺旋状に延びる撹拌部材を有する現像剤供給回収手段と、前記現像剤撹拌部において、各々、互いに対向して現像剤供給回収手段の回転軸方向に沿って延びるよう前後方向に並んで設けられた、第１の現像剤撹拌手段および第２の現像剤撹拌手段とを備えてなり、
ハウジングには、現像剤撹拌部における２つの現像剤撹拌手段が対向する部分の上方であって、現像剤撹拌部における現像剤の搬送方向の上流側に位置される個所に、トナー供給用開口が形成されており、
現像剤撹拌部における２つの現像剤撹拌手段は、当該２つの現像剤撹拌手段が、互いに対向する部分において、各々の周面が上方から下方に向かって互いに順方向に移動されるよう回転されて、いずれも、現像剤を現像剤供給回収手段と互いに逆方向に搬送するものであって、各々の現像剤撹拌手段による現像剤の搬送量の総和が現像剤供給回収手段による現像剤搬送量と同等となる現像剤搬送能力を有するものであり、
第２の現像剤撹拌手段は、軸部材の外周面に、当該軸部材に垂直な平面に対して互いに異なる方向に傾斜する第１の撹拌部材配置用レベル平面および第２の撹拌部材配置用レベル平面の各々に沿って設けられた複数の半楕円状の第１の撹拌部材群および第２の撹拌部材群を有するものであることを特徴とする。
【００１４】
本発明の現像装置においては、現像剤撹拌部における第２の現像剤撹拌手段は、回転軸方向に対する現像剤搬送能力が第１の現像剤撹拌手段と同等または第１の現像剤撹拌手段より低いものであり、現像剤供給回収部に対して後方側に設けられていることが好ましい。
【００１５】
本発明の現像装置は、互いに連通してトナーとキャリアとからなる二成分現像剤の循環搬送路を形成する現像剤供給回収部および現像剤撹拌部が前後方向に並んで形成されたハウジングと、前記現像剤供給回収部の前方側部分において潜像担持体と現像領域を介して対向するように設けられた現像剤担持体と、前記現像剤供給回収部の後方側部分において現像剤担持体と対向して当該現像剤担持体の回転軸方向に沿って延びるように設けられた、軸部材の外周面の全周にわたって回転軸方向に螺旋状に延びる撹拌部材を有する現像剤供給回収手段と、前記現像剤撹拌部において、各々、互いに対向して現像剤供給回収手段の回転軸方向に沿って延びるよう前後方向に並んで設けられた、第１の現像剤撹拌手段および第２の現像剤撹拌手段とを備えてなり、
ハウジングには、現像剤撹拌部における２つの現像剤撹拌手段が対向する部分の上方であって、現像剤撹拌部における現像剤の搬送方向の上流側に位置される個所に、トナー供給用開口が形成されており、
現像剤撹拌部における２つの現像剤撹拌手段は、当該２つの現像剤撹拌手段が、互いに対向する部分において、各々の周面が上方から下方に向かって互いに順方向に移動されるよう回転されて、現像剤を現像剤供給回収手段と互いに逆方向に搬送するものであって、各々の現像剤撹拌手段による現像剤の搬送量の総和が現像剤供給回収手段による現像剤搬送量と同等となる現像剤搬送能力を有するものであり、
第２の現像剤撹拌手段は、軸部材の外周面に、または軸部材と互いに径方向に離間した位置において、回転軸方向に沿って延びるように設けられたリブよりなる撹拌部材を有してなることを特徴とする。
【００１６】
本発明の現像装置においては、現像剤撹拌部における第２の現像剤撹拌手段は、回転軸方向に対する現像剤搬送能力が第１の現像剤撹拌手段と同等または第１の現像剤撹拌手段より低いものであり、現像剤供給回収部に対して後方側に設けられていることが好ましい。
【００１７】
また、本発明の現像装置においては、現像剤供給回収部においては、現像剤担持体および現像剤供給回収手段の両者の周面が、現像剤担持体と現像剤供給回収手段とが対向する部分において、互いに逆方向に移動されるよう動作制御されることが好ましい。
さらに、本発明の現像装置においては、体積平均粒径が３〜５μｍであるトナーと、トナーの体積平均粒径をＤｔ〔μｍ〕とするとき、体積平均粒径が５×Ｄｔ〜１０×Ｄｔであるキャリアとからなる二成分現像剤が用いられることが好ましい。
【００１８】
本発明の画像形成装置は、潜像担持体と、当該潜像担持体上に形成される静電潜像を現像してトナー像を形成するトナー像形成手段とを有するものにおいて、
トナー像形成手段は、上記のいずれかに記載の現像装置よりなり、
潜像担持体の移動速度をＶ［ｍｍ／ｓｅｃ］、潜像担持体上に形成されるトナー像の単位面積当たりの最大付着量をＭ［ｍｇ／ｃｍ²］、潜像担持体上に形成されるトナー像の当該潜像担持体の移動方向に直交する方向における最大幅をＬ［ｍｍ］、現像剤供給回収手段による回転軸方向に対する現像剤移動量をＷ［ｇ／ｓｅｃ］、現像剤供給回収手段の回転数をＲ［ｒｐｍ］とするとき、下記条件（イ）および条件（ロ）を満足することを特徴とする。
【００１９】
（条件イ）Ｗ ≧ Ｍ×Ｖ×Ｌ／１０００
（条件ロ）Ｒ ≦ ６００
【００２０】
本発明の画像形成装置は、潜像担持体と、当該潜像担持体上に形成される静電潜像を現像してトナー像を形成するトナー像形成手段と、潜像担持体上のトナー像を転写材または中間転写体に転写する転写手段と、潜像担持体上に残留するトナーを除去するクリーニング手段と、潜像担持体より除去されたトナーをトナー像形成手段に回収して再利用するトナーリサイクル手段とを有するものにおいて、
トナー像形成手段は、上記のいずれかに記載の現像装置よりなり、
現像装置を構成するハウジングには、２つの現像剤撹拌手段が互いに対向する部分の上方であって、現像剤撹拌部における現像剤の搬送方向に対してトナー供給用開口より上流側に位置される個所に、トナーリサイクル手段によって回収されたトナーを現像剤撹拌部に混入するためのリサイクルトナー混入用開口が形成されていることを特徴とする。
【００２１】
【作用】
上記構成の現像装置によれば、現像剤撹拌部における２つの現像剤撹拌手段と現像剤供給回収手段とによって現像剤を循環搬送することにより現像剤搬送速度のバランスをとり、２つの現像剤撹拌手段によって現像剤を回転軸方向に搬送しながら周方向に撹拌することによりトナーの帯電を立ち上げる構成とされていることにより、現像剤が回転軸方向に搬送される過程において、現像剤の搬送速度を低下させることなしに現像剤撹拌部において十分な混合撹拌時間が確保される結果、現像剤撹拌部における現像剤の混合撹拌動作によりトナーが所期の電荷（帯電量）を有する状態にまで帯電された状態において、現像剤供給回収手段によって軸方向に対して均一なトナー濃度で現像剤担持体に供給され、これにより、トナーの帯電不良によるかぶりやトナー飛散の発生が確実に防止されると共に、得られる可視画像における画像濃度むらの発生が確実に防止される。
しかも、２つの現像剤撹拌手段を当該２つの現像剤撹拌手段が対向する部分において各々の周面が上方から下方に向かって互いに順方向に移動するよう回転させると共に、当該２つの現像剤撹拌手段の対向部分の上方からトナーを補給する（自由落下させる）構造とされていることにより、トナー補給位置での現像剤中への補給トナーの沈み込みが加速されるので、補給トナーが現像剤中に均一に分散され、これにより、現像剤撹拌部においてトナーを十分に混合撹拌することができる。
【００２２】
上記構成の画像形成装置によれば、上記のような現像装置を備えてなり、特定の動作設定条件を満足する状態で現像プロセスが行われることにより、現像剤の十分な混合、撹拌が行われてトナーが所期の帯電量を有する状態に帯電された現像剤が回転軸方向に対して均一なトナー濃度で現像剤担持体に供給されて、潜像担持体上の潜像が現像されるので、例えば印字率が高い画像を連続して出力することにより大量のトナー消費およびトナー補給が繰り返して行われた現像剤が用いられる場合や、未使用のトナーに比して帯電性能が劣るリサイクルトナーを含む現像剤が用いられる場合であっても、トナー飛散、かぶり、画像濃度ムラ等の問題が生じることが確実に防止され、画質の高い画像が確実に得られる。
【００２３】
【発明の実施の形態】
以下、本発明について図面を参照して詳細に説明する。
＜第１実施形態＞
図１は、本発明の画像形成装置の一例における構成の概略を示す説明図、図２は、本発明の現像装置の一例における構成の概略を示す部分断面図、図３は、図２に示す現像装置におけるＡ−Ａ断面の縦断断面図、図４は、図２に示す現像装置におけるＢ−Ｂ断面の縦断断面図である。
【００２４】
この画像形成装置は、複数の支持ローラ１１、１２、１３、１４群によって張架された状態で配設された、無端ベルト状の中間転写体（以下、「中間転写ベルト」という。）１０を備えており、この中間転写ベルト１０の外周面に沿って、互いに異なる色のトナー像を形成する４つのトナー像形成ユニット２０Ｙ、２０Ｍ、２０Ｃ、２０Ｋが、中間転写ベルト１０が各色トナー像に係るトナー像形成ユニットにおける潜像担持体２１、２１、２１、２１の各々に対接されながら循環移動されるよう、離間して並ぶよう設けられていると共に、中間転写ベルト１０の移動方向におけるトナー像形成ユニット配置領域より下流側の位置に二次転写機構２６が設けられて、構成されている。
【００２５】
イエロートナー像に係るトナー像形成ユニット２０Ｙは、回転されるドラム状の潜像担持体２１と、この潜像担持体２１の外周面に沿って、各々、潜像担持体２１の回転方向に対して動作順に並ぶよう配設された、帯電手段２２、露光手段２３、トナー像形成手段３０、一次転写機構２４、および潜像担持体クリーニング手段２５とにより構成されている。
また、マゼンタトナー像、シアントナー像およびブラックトナー像に係るトナー像形成ユニット２０Ｍ、２０Ｃおよび２０Ｋも、各々、イエロートナー像に係るトナー像形成ユニット２０Ｙと同様の構成を有するものとされている。
【００２６】
各々のトナー像形成ユニットにおける潜像担持体２１、２１、２１、２１は、いずれも、例えば、有機光導電体を含有させた例えばポリカーボネイトなどの樹脂よりなる感光層がドラム状の金属基体の外周面に形成されてなる有機感光体により構成されている。
【００２７】
各々のトナー像形成ユニットにおけるトナー像形成手段３０、３０、３０、３０は、例えば図２乃至図４に示される構成を有する現像装置により構成されている。以下、この現像装置について具体的に説明するが、本明細書においては、図２における左右方向を「前後方向」、図２における上下方向を「軸方向」、図３および図４における上下方向を「上下方向」というものとする。
【００２８】
この現像装置は、軸方向の両端部において互いに連通してトナーとキャリアとからなる二成分現像剤の循環搬送路を形成する現像剤供給回収部３２および現像剤撹拌部３３が前後方向に並んで形成されたハウジング３１を備えている。
【００２９】
現像剤供給回収部３２には、潜像担持体２１を臨む前方側部分において、回転されて現像剤を担持しながら周方向に搬送する現像剤担持体３４が、潜像担持体２１と現像領域を介して対向して軸方向に延びるよう、回転可能に軸支されて設けられていると共に、現像剤撹拌部３３に近接する後方側部分において、回転されて現像剤を撹拌しながら軸方向（図２において上方から下方に向かう方向）に搬送すると共に現像剤を現像剤担持体３４の軸方向の全域にわたって供給する現像剤供給回収手段３５が、現像剤担持体３４と対向して軸方向に延びるよう回転可能に軸支されて設けられている。
【００３０】
現像剤撹拌部３３には、２つの現像剤撹拌手段４０、４１が、前後方向に並んだ位置において互いに対向して軸方向に延びるよう、回転可能に軸支されて設けられている。
【００３１】
ハウジング３１は、現像剤担持体３４の一端側の端部より軸方向外方に突出して延びる突出部分３１Ａを有し、この突出部分３１Ａにおける天面板３１Ｂの、２つの現像剤撹拌手段４０、４１が互いに対向する部分の上方に位置される個所には、図示しないトナー補給機構よりの未使用のトナー（以下においては、「新トナー」という。）を現像剤撹拌部３３に供給するためのトナー供給用開口３１Ｃが形成されている。
トナー補給機構は、現像により消費したトナー量に応じて新トナーを補給する機能を有し、これにより、現像剤におけるトナー濃度が一定となる状態に維持される。
【００３２】
現像剤担持体３４は、例えば、回転可能に設けられた例えばアルミニウムなどの非磁性材料からなる現像スリーブと、この現像スリーブの内部に固定して設けられた、例えば複数の磁極を有する柱状の複数の磁石体からなる現像マグネットとにより構成されている。
【００３３】
現像剤供給回収手段３５は、例えば、図５に示されているように、軸部材３６の外周面の全周にわたって軸方向に均一な大きさのピッチｐで螺旋状に延びるよう形成された螺旋状羽根部材よりなる撹拌部材３７を有するスクリュー状の回転部材３８により構成されており、現像剤の搬送方向における下流側の端部部分（図２における下端側部分）が板状の羽根部材（図示せず）が軸部材３６の外周面に設けられてなるパドル状のものとされている。
現像剤供給回収手段３５は、現像剤担持体３４および現像剤供給回収手段３５の両者が対向する部分において現像剤担持体３４と互いに逆方向に移動されるよう、回転されることが好ましい。これにより、現像剤供給回収手段３５から現像剤担持体３４に供給される現像剤と、現像剤担持体３４上でトナーが消費され、現像剤供給回収手段３５に回収される現像剤との入れ替えを確実に行うことができ、従って、現像剤担持体３４上の現像剤のトナー濃度は均一となり、画像濃度ムラの発生を確実に防止することができる。
【００３４】
現像剤撹拌部３３における２つの現像剤撹拌手段４０、４１は、いずれも、現像剤を現像剤供給回収手段３５と互いに逆方向に搬送するものであって、各々の現像剤撹拌手段４０、４１による現像剤搬送量の総和が現像剤供給回収手段３５による現像剤搬送量と同等となる現像剤搬送能力を有するものとされる。
【００３５】
一方の現像剤撹拌手段（以下、「第１の現像剤撹拌手段」という。）４０は、軸方向に対する現像剤の搬送能力が現像剤移動量が現像剤供給回収手段３５より低いものとされる。
具体的には、第１の現像剤撹拌手段４０は、例えば基本的な構成が現像剤供給回収手段３５と同様のもの（図５参照。）とされ、軸部材３６の外周面の全周にわたって軸方向に所定の大きさのピッチｐ１で螺旋状に延びるよう形成された螺旋状羽根部材よりなる撹拌部材３７を有するスクリュー状の回転部材３８により構成されており、現像剤の搬送方向における下流側の端部部分（図２における上端側部分）が軸部材３６の外周面に複数の板状の羽根部材（図示せず）が径方向外方に延びるよう設けられたパドル状のものにより構成されている。この場合には、スクリューピッチの大きさｐ１が現像剤供給回収手段３５を構成する場合のスクリューピッチｐより小さく設定され、これにより、軸方向に対する現像剤の搬送能力が現像剤供給回収手段３５より低い状態とされる。
【００３６】
現像剤撹拌部３３に設けられる他方の現像剤撹拌手段（以下、「第２の現像剤撹拌手段」という。）４１は、軸方向に対する現像剤搬送能力が第１の現像剤撹拌手段と同等または第１の現像剤撹拌手段より低いものにより構成されることが好ましい。
具体的には、第２の現像剤撹拌手段４１は、図６に示されているように、軸部材４３の外周面に、この軸部材４３に垂直な平面に対して互いに異なる方向に傾斜する第１および第２の撹拌部材配置用レベル平面の各々に沿って設けられた複数の半楕円板よりなる第１の撹拌部材４４Ａ群および第２の撹拌部材４４Ｂ群を有する回転部材４５により構成されており、第１の撹拌部材４４Ａおよび第２の撹拌部材４４Ｂは、いずれも、所定の大きさの配置ピッチｐで軸方向に互いに離間した状態とされている。
第１の撹拌部材４４Ａ群の軸部材４３に対する取付角α１および第２の撹拌部材４４Ｂ群の軸部材４３に対する取付角α２は、互いに同等の大きさであっても、異なる大きさであってもよく、取付角α１、α２の大きさは目的に応じて適宜に設定することができる。
【００３７】
この現像装置においては、現像剤の軸方向に対する搬送能力が低い第２の現像剤撹拌手段４１が現像剤供給回収部３２に対して後方側に設けられることが好ましい。
【００３８】
現像剤撹拌部３３においては、第１の現像剤撹拌手段４０および第２の現像剤撹拌手段４１の各々の周面が、２つの現像剤撹拌手段４０、４１が互いに対向する部分において、上方から下方に向かって互いに順方向に移動されるよう、第１の現像剤撹拌手段４０および第２の現像剤撹拌手段４１が適宜の駆動機構により回転されることが好ましい。
図示されている現像装置においては、第１の現像剤撹拌手段４０および第２の現像剤撹拌手段４１が互いに連動して駆動される構成とされている。
【００３９】
この現像装置においては、トナーとキャリアとからなる二成分現像剤が用いられる。
二成分現像剤を構成するトナーは、体積平均粒径が３〜５μｍであるものであることが好ましい。体積平均粒径が３〜５μｍである小粒径トナーを使用することにより、高解像性と優れた細線再現性を有するトナー画像を確実に形成することができ、また、ソリッド部においては画像濃度の安定したトナー画像を確実に形成することができる。
キャリアは、トナーの体積平均粒径をＤｔ〔μｍ〕とするとき、体積平均粒径が５×Ｄｔ〜１０×Ｄｔ〔μｍ〕であるものであることが好ましい。体積平均粒径がトナーの体積平均粒径の５倍〜１０倍の大きさであるキャリアを使用することにより、小粒径トナーを用いた場合でもキャリア表面の帯電付与性能を向上させることができ、これにより、かぶりやトナー飛散の発生を確実に防止することができ、しかも、キャリア付着の発生を確実に防止することができ、従って、均一な画像濃度を有すると共にきめの細かい画質の高い画像を確実に得ることができる。
【００４０】
以上の画像形成装置においては、トナー像形成手段３０による現像処理が、下記条件（イ）および条件（ロ）を満足する動作設定条件に調整された状態において、行われる。
条件（イ）；Ｗ ≧ Ｍ×Ｖ×Ｌ／１０００
条件（ロ）；Ｒ ≦ ６００
【００４１】
上記条件（イ）および条件（ロ）において、Ｖは、潜像担持体２１の周速度［ｍｍ／ｓｅｃ］、Ｍは、潜像担持体２１上に形成されるトナー像の単位面積当たりの最大付着量［ｍｇ／ｃｍ²］、Ｌは、潜像担持体２１上に形成されるトナー像の、潜像担持体２１の移動方向に直交する方向（軸方向）の最大幅［ｍｍ］、Ｗは、現像剤供給回収部３２における現像剤供給回収手段３５による軸方向に対する現像剤移動量［ｇ／ｓｅｃ］、Ｒは、現像剤供給回収手段３５の回転数を、それぞれ示す。
【００４２】
現像剤供給回収手段３５による軸方向に対する現像剤移動量Ｗが過小である場合には、現像剤供給回収手段３５による現像剤の搬送方向における下流側の現像剤供給領域において、現像剤中のトナー濃度が低下して十分な量のトナーを現像領域に供給することが困難となり、画像濃度ムラが発生しやすくなる。
現像剤供給回収手段３５の回転数Ｒが過大である場合には、軸部が加熱されることによって現像剤が劣化しやすくなり、画質の高い画像を確実に形成することが困難である。
【００４３】
上記の画像形成装置においては、次のようにして画像形成動作が行われる。
すなわち、先ず、トナー像形成ユニット２０Ｙ、２０Ｍ、２０Ｃ、２０Ｋの各々において、帯電手段２２による帯電処理および露光手段２３による露光処理が行われて潜像担持体２１上に原稿画像に対応した静電潜像が形成され、トナー像形成手段３０による現像処理が行われて潜像担持体２１の各々に各色トナー像が形成される。
具体的には、トナー像形成手段３０による静電潜像の現像処理が行われるに際しては、現像剤撹拌部３３において、現像剤が軸方向に搬送される過程において、第１の現像剤撹拌手段４０および第２の現像剤撹拌手段４１によって周方向に撹拌され、これにより、トナーが所定の大きさの帯電量を有する状態に摩擦帯電された状態で現像剤供給回収部３２に導入され、現像剤供給回収部３２において、現像剤供給回収手段３５によって周方向に撹拌されながら軸方向に搬送されて現像剤担持体３４の表面に軸方向の全域にわたって供給されて、現像剤担持体３４上に磁気ブラシが形成された状態で担持され、そして、現像剤規制部材３９によって磁気ブラシが穂切りされて適正な量に規制された状態において現像領域に搬送され、現像領域において、磁気ブラシが潜像担持体２１の表面に接触されることにより潜像担持体２１上に形成された静電潜像に従ってトナーが付着して現像が行われ、これによりトナー像が形成される。
現像剤担持体３４に供給され、現像領域においてトナーが消費された現像剤は、現像剤担持体３４に供給されずに現像剤供給回収部３２に残留している現像剤とともに現像剤供給回収手段３５によって現像剤撹拌部３３に向かって搬送され、例えば、現像剤供給回収部３２の下流側に設けられたトナー濃度センサにより現像剤の透磁率を検知することにより検出されるトナー濃度に基づいて、トナーの消費量に応じた新トナーがトナー補給機構により現像剤撹拌部３３に補給される。
【００４４】
そして、一次転写機構２４により各色トナー像が中間転写ベルト１０上に順次に一次転写されて重ね合わせられることにより中間転写ベルト１０上にカラートナー像が形成され、このカラートナー像は中間転写ベルト１０に担持されたままの状態で二次転写領域に搬送され、二次転写領域において、二次転写機構２６により搬送されてきた転写材Ｐ上に二次転写され、その後、図示しない定着手段による定着処理が行われ、これにより、可視画像が形成される。
【００４５】
而して、上記構成の画像形成装置によれば、トナー像形成手段３０が、第１の現像剤撹拌手段４０および第２の現像剤撹拌手段４１と、現像剤供給回収手段３５とによって現像剤を循環搬送すること（前２者と後者とが互いに同等の現像剤搬送能力を有するものであること）により現像剤搬送速度のバランスをとり、第１の現像剤撹拌手段４０および第２の現像剤撹拌手段４１の両者によって現像剤を周方向に撹拌することによりトナーの帯電を立ち上げる構成とされていることにより、現像剤が軸方向に搬送される過程において、現像剤の搬送速度を低下させることなしに現像剤撹拌部３３において十分な混合撹拌時間が確保される結果、現像剤撹拌部３３における現像剤の混合撹拌動作によりトナーが所期の電荷（帯電量）を有する状態にまで帯電された状態において、現像剤供給回収手段３５によって軸方向に対して均一なトナー濃度で現像剤担持体３４に供給される。
具体的には、現像剤供給回収手段による軸方向に対する現像剤搬送量を、第１の現像剤撹拌手段４０および第２の現像剤撹拌手段４１の両者で分担して現像剤の搬送速度のバランスを確保しているので、第１の現像剤撹拌手段４０および第２の現像剤撹拌手段４１の個々の搬送速度を、一の現像剤撹拌手段により搬送速度のバランスを確保する構成のものに比して、小さくすることができ、これにより、現像装置全体の現像剤搬送速度を低下させることなしに十分な混合撹拌時間が確保され、現像剤撹拌部３３から現像剤供給回収部３２に導入される現像剤は、トナーが所期の帯電量を有する状態にまで帯電された状態のものとなる。
従って、所期の帯電状態とされた現像剤が現像剤担持体３４に軸方向に対して均一なトナー濃度で供給された状態で、潜像担持体２１上の潜像が現像されるので、トナーの帯電不良によるかぶりやトナー飛散の発生が確実に防止されると共に、得られる可視画像における画像濃度むらの発生が確実に防止され、画像濃度やカラーバランスの整った画質の高い画像が確実に得られる。
そして、第２の現像剤撹拌手段４１を現像剤撹拌能力が第１の現像剤撹拌手段４０より高いものにより構成することにより、上記の効果が確実に得られる。
【００４６】
また、現像剤の撹拌性能が高い回転部材を単に現像剤撹拌手段として用いた構成とするだけでは、トナーを速やかに所期の帯電状態とすること（トナーの帯電立ち上がり特性を急峻なものとすること）は困難であるが、上記構成の現像装置によれば、第１の現像剤撹拌手段４０および第２の現像剤撹拌手段４１をこれら２つの現像剤撹拌手段４０、４１が対向する部分において各々の周面が上方から下方に向かって互いに順方向に移動するよう回転させると共に、２つの現像剤撹拌手段４０、４１が対向する部分の上方からトナーを補給する（トナーを自由落下させる）構造とされていることにより、トナー補給位置での現像剤中への補給トナーの沈み込みが加速されるので、補給トナーが現像剤中に均一に分散され、これにより、現像剤撹拌部においてトナーを確実に所期の帯電量を有する状態に帯電させることができる。
【００４７】
また、特定の条件（イ）および条件（ロ）を満足する状態で現像プロセスが行われることにより、現像剤を、軸方向に対するトナー濃度むらがない、換言すれば軸方向のトナー濃度差が極めて小さい状態で、現像領域に供給することができ、画像濃度むらのない均一な画像濃度を有する画像を得ることができる。また、現像剤供給回収手段３５の回転数Ｒが６００ｒｐｍ以下に設定されること（条件（ロ））により現像剤供給回収手段３５を高速に回転させた場合に軸部が加熱されることによって現像剤が劣化することを確実に防止することができる。
【００４８】
以上のように、上記構成の画像形成装置によれば、印字率が高い画像を連続して出力することにより大量のトナー消費とトナー補給が繰り返し行われた現像剤を用いる場合であっても、トナーとキャリアとが十分に混合撹拌されて、十分なトナーの帯電立ち上がり特性が得られ、しかも、現像剤が軸方向に対して均一なトナー濃度で現像領域に供給されるため、高速、例えば１分間当たりのプリント枚数が５０枚以上となるようなプロセス速度で画像形成動作が行われる場合であっても、かぶりやトナー飛散が生ずることがなく、しかも画像濃度むらのない均一な画像濃度の画像を確実に形成することができる。
【００４９】
さらに、現像剤の軸方向に対する搬送能力が低い第２の現像剤撹拌手段４１が現像剤供給回収部３２に対して後方側に設けられていることにより、現像剤供給回収部３２と現像剤撹拌部３３との連通部の近傍において発生しやすい現像剤の滞留が生ずることが確実に防止されて現像剤の循環搬送が円滑に行われ、これにより、現像剤を軸方向に対して均一なトナー濃度で現像剤担持体３４に供給することができ、画像濃度むらのない画質の高い画像を形成することができる。
【００５０】
以上、本発明の好適な一実施形態について説明したが、本発明の現像装置においては、現像剤撹拌部３３に設けられる第１の現像剤撹拌手段４０および第２の現像剤撹拌手段４１は、いずれも、上記構成のものに限定されるものではなく、現像剤供給回収手段との関係において設定される軸方向に対する現像剤搬送能力を有し、両者の間において、現像剤搬送能力および現像剤撹拌能力が所定の関係を満足する構成のものであれば、実用上十分な効果を得ることができる。
【００５１】
例えば、第１の現像剤撹拌手段４０および第２の現像剤撹拌手段４１は、図７〜図９に示される構成のものであってもよい。
図７〜図９に示されている回転部材は、いずれも、基本的な構成は、図５に示されている螺旋状スクリューよりなる回転部材と同様のものであるが、現像剤撹拌能力が図５に示されているものに比して高いものとされている。
【００５２】
図７に示されている回転部材５０Ａは、軸部材５１の外周面の全周にわたって軸方向に所定の大きさのピッチｐで螺旋状に延びる螺旋状羽根部材よりなる主撹拌部材５２が形成されていると共に、軸部材５１の外周面に径方向外方に向かって延びる棒状または板状の垂直羽根部材よりなる補助撹拌部材５３がスクリューピッチＰ間毎に一つずつ設けられてなるものである。補助撹拌部材５３は、主撹拌部材５２のスクリューピッチ間の軸方向における中央位置に配設されている。
【００５３】
図８に示されている回転部材５０Ｂは、軸部材５４の外周面の全周にわたって軸方向に所定の大きさ大きさのピッチｐで螺旋状に延びる螺旋状羽根部材よりなる主撹拌部材５５が形成されていると共に、主撹拌部材５５のスクリューピッチＰ間において、軸部材５４の外周面に径方向外方に向かって延びる棒状または板状の垂直羽根部材よりなる補助撹拌部材５６の複数（例えば４つ）が、周方向に互いに等間隔毎に離間した位置において設けられてなるものである。
【００５４】
図９に示されている回転部材５０Ｃは、軸部材５７の外周面の全周にわたって軸方向に所定の大きさのピッチｐで螺旋状に伸びよう形成された螺旋状羽根部材よりなる撹拌部材５８を有してなり、撹拌部材５８の外周縁部に軸方向に貫通して延びる切欠部５９が形成されてなるものである。この例においては、切欠部５９は、例えば１スクリューピッチ当たりに４箇所ずつ、周方向に等間隔毎に離間した位置に形成されている。
【００５５】
本発明においては、第１の現像剤撹拌手段４０および第２の現像剤撹拌手段４１は、十分なトナーの帯電立ち上がり特性が確実に得られるという観点から、現像剤撹拌能力が高いものである程、好ましい。
【００５６】
図１０および図１１は、本発明の現像装置において第１の現像剤撹拌手段４０および第２の現像剤撹拌手段４１として用いられる回転部材の一層好適な構成例を示す斜視図である。
【００５７】
図１０に示されている回転部材６０は、軸部材６１の外周面の全周にわたって軸方向に所定の大きさのピッチｐで螺旋状に延びるよう形成された主撹拌部材６２を有すると共に、軸部材６１と径方向に離間した位置、具体的には、主撹拌手段６２の外周縁部において、軸方向に延びるよう設けられた板状のリブ部材よりなる補助撹拌手段６３を有してなるものである。
この回転部材６０においては、４つの補助撹拌手段６３が周方向に等間隔毎に離間した位置に設けられている。
【００５８】
図１１に示されている回転部材７０は、基本的な構成は図６に示される回転部材４５と同様のものとされており、半楕円板状の第１の撹拌部材７２Ａおよび第２の撹拌部材７２Ｂの外周縁部に軸部材７１に沿って軸方向に延びるよう設けられた板状のリブ部材よりなる補助撹拌部材７３を有してなるものである。
この回転部材７０においては、４つの補助撹拌手段７３が周方向に等間隔毎に離間した位置に設けられている。
【００５９】
これらの回転部材６０、７０は、軸部材６１、７１を中心に回転されることにより、現像剤撹拌部３３における現像剤が軸方向に搬送される過程において、主撹拌部材により周方向に撹拌されると共に補助撹拌部材としてのリブ部材６３、７３により周方向に撹拌される。
【００６０】
上記のような補助撹拌部材６３、７３を有する回転部材６０、７０により現像剤撹拌手段が構成されてなる現像装置によれば、上述したような作用、効果が一層確実に得られ、トナーの帯電不良によるかぶりやトナー飛散が生ずることが確実に防止されると共に、現像剤担持体３４に供給される現像剤の軸方向に対するトナー濃度の不均一性による画像濃度ムラが生ずることが確実に防止される。
従って、このような現像装置を備えてなる画像形成装置によれば、十分な撹拌が行われてトナーが所期の帯電量を有する状態に帯電された現像剤が現像剤担持体３４に軸方向に対して均一なトナー濃度で供給され、潜像担持体２１上の潜像が現像されるので、トナー飛散、かぶり、画像濃度ムラ等の問題が生じることが確実に防止され、画質の高い画像が確実に得られる。
【００６１】
以上においては、本発明を複数のトナー像形成ユニットを備えてなるカラー画像形成用の画像形成装置に適用した場合について説明したが、このような構成の画像形成装置に限定されるものではなく、種々の構成のものに有効に適用することができ、例えばモノクロ画像形成用の画像形成装置に適用した場合であっても、上記のような作用、効果が減じられるものではない。
【００６２】
＜第２実施形態＞
本発明の第２実施形態に係る画像形成装置は、潜像担持体クリーニング手段により除去されたトナーをトナー像形成手段に回収して再利用するトナーリサイクル手段を有するものとされている。
図１２は、本発明の画像形成装置における構成の概略を示す説明図である。
この画像形成装置は、回転されるドラム状の潜像担持体１１０を備えてなり、この潜像担持体１１０の外周面に沿って、帯電手段１１１、露光手段１１２、トナー像形成手段１２０、転写手段１１３、分離手段１１４、および潜像担持体クリーニング手段１１５が、各々、潜像担持体１１０の回転方向に対して動作順に並んで配置されて構成されており、潜像担持体クリーニング手段１１５によって潜像担持体１１０より除去されたトナーをトナー像形成手段１２０に回収する回収搬送手段１３１を有するトナーリサイクル手段１３０が設けられている。図１２における１３２は、潜像担持体クリーニング手段１１５によって潜像担持体１１０上より掻き取られたトナーを潜像担持体１１０の軸方向に搬送する搬送手段である。
この画像形成装置におけるトナー像形成手段１２０は、例えば図１３に示されているように、基本的な構成は、上記第１実施形態におけるトナー像形成手段（図２乃至図４）３０と同様のものとされており、ハウジング３１の突出部分３１Ａの天面板３１Ｂにおける、第１の現像剤撹拌手段４０および第２の現像剤撹拌手段４１が互いに対向する部分の上方位置であって、第１の現像剤撹拌手段４０による現像剤の搬送方向におけるトナー供給用開口３１Ｃより上流側の位置に、トナーリサイクル手段１３０によって回収されたトナー（以下、「リサイクルトナー」という。）を現像剤撹拌部３３に混入するためのリサイクルトナー混入用開口１３３が形成されている。
【００６３】
リサイクルトナー混入用開口１３３が形成される位置は、現像剤撹拌部３３における現像剤の搬送方向に対してトナー補給機構による新トナーのトナー供給用開口３１Ｃの形成位置と所定の順序を満足する状態で形成されてさえいれば、特に制限されないが、現像剤撹拌部３３における現像剤の搬送方向に対してトナー供給用開口３１Ｃの形成位置より５〜３０ｍｍ上流側の位置に形成されていることが実用上好ましい。
【００６４】
リサイクルトナーは、現像剤におけるリサイクルトナーの新トナーに対する比率（リサイクルトナー比率）が５０質量％以下である状態が維持されるよう、その供給量が調整された状態において現像剤撹拌部３３に混入される。
【００６５】
上記構成の現像装置によれば、基本的には、上述したように、現像剤撹拌部３３において、現像剤が軸方向に搬送される過程において、現像剤の搬送速度を低下させることなしに十分な混合撹拌時間が確保されるので、現像剤撹拌部３３における現像剤の混合撹拌動作によりトナーが所期の電荷（帯電量）を有する状態にまで帯電された状態で、現像剤を現像剤供給回収手段３５によって軸方向に対して均一なトナー濃度で現像剤担持体３４に供給することができ、しかも、リサイクルトナー混入用開口１３３が現像剤撹拌部３３における現像剤の搬送方向におけるトナー供給用開口３１Ｃより上流側に形成されていることにより、新トナーに比して流動性が悪く帯電性が低い（帯電しにくい、帯電立ち上がりが悪い）リサイクルトナーの混合撹拌時間を長く確保することができるので、リサイクルトナーについても十分な帯電立ち上がり特性を得ることができ、従って、トナーの帯電不良によるかぶりやトナー飛散の発生を確実に防止することができると共に、得られる可視画像における画像濃度むらの発生を確実に防止することができる。
従って、このような現像装置を備えてなる画像形成装置によれば、例えば、印字率が高い画像を連続して出力することにより大量のトナー消費とリサイクルトナーを含むトナー補給が繰り返し行われた現像剤が用いられる場合であっても、トナーとキャリアとが十分に混合撹拌されて、十分なトナーの帯電立ち上がり特性が得られ、しかも、現像剤が軸方向に対して均一なトナー濃度で現像領域に供給されるため、高速、例えば１分間当たりのプリント枚数が５０枚以上となるようなプロセス速度で画像形成動作が行われる場合であっても、かぶりやトナー飛散が生ずることがなく、しかも画像濃度むらのない均一な画像濃度を有する画質の高い画像を確実に形成することができる。
【００６６】
以上、本発明の実施形態について説明したが、本発明は上記の態様に限定されるものではなく、種々の変更を加えることができる。
例えば、現像剤供給回収手段、第１の現像剤撹拌手段および第２の現像剤撹拌手段を構成する回転部材の具体的な構成、例えば、螺旋状羽根部材のピッチの大きさ、補助撹拌部材の形状および大きさ、回転部材の回転数（現像剤の軸方向に対する搬送速度）およびその他の構成は目的に応じて適宜設定することができる。
また、第１の現像剤撹拌手段および第２の現像剤撹拌手段は、互いに独立した駆動機構により回転される構成であってもよい。
【００６７】
以下に、本発明の効果を確認するために行った実験例について説明する。
【００６８】
〔回転部材の作製〕
現像剤供給回収手段、第１の現像剤撹拌手段および第２の現像剤撹拌手段として用いられる回転部材（回転部材Ａ〜Ｒ）を作製した。
【００６９】
（回転部材Ａ）
図５に示される構成に従って、螺旋状羽根部材（撹拌部材）を右上方に巻き上がるように（左巻き）軸部材の外周面に形成して螺旋状スクリューを作製すると共に、この螺旋状羽根部材による現像剤の搬送方向下流側の長さ３０ｍｍにわたる端部領域を４つの平板状羽根部材よりなる撹拌部材が軸部材の外周面に径方向外方に延びる状態で設けられてなるパドル形状とした回転部材Ａを作製した。そして、この回転部材Ａの両端部に、外径寸法が２４ｍｍである円板状のフランジ部材を軸部材を挿通させた状態で設けた。この回転部材Ａの具体的な諸元は、以下に示す通りである。
最大外径（ｄ）：２４ｍｍ、軸部を除く回転軸方向長さ（螺旋状羽根部材および板状羽根部材が設けられた領域の大きさ）：４４０ｍｍ、軸部材の外径：６ｍｍ、螺旋状羽根部材のスクリューピッチ（ｐ）：３０ｍｍ、螺旋状羽根部材の厚み：１ｍｍ
【００７０】
（回転部材Ｂ）
回転部材Ａにおいて、螺旋状羽根部材を左上方に巻き上がるように（右巻き）軸部材の外周面に形成したことの他は回転部材Ａと同様の構成を有する回転部材Ｂを作製した。
【００７１】
（回転部材Ｃ）
図９に示される構成に従って、螺旋状羽根部材（撹拌部材）を右上方に巻き上がるように（左巻き）軸部材の外周面に形成すると共に、この螺旋状羽根部材の外周縁部に切欠部を形成してなる螺旋状スクリューを作製すると共に、この螺旋状羽根部材による現像剤の搬送方向下流側の長さ３０ｍｍにわたる端部領域を４つの平板状の撹拌部材が軸部材の外周面に径方向外方に延びる状態で設けられてなるパドル形状とした回転部材Ｃを作製した。そして、この回転部材Ｃの両端部に、外径寸法が２４ｍｍである円板状のフランジ部材を軸部材を挿通させた状態で設けた。この回転部材Ｃの具体的な諸元は、以下に示す通りである。
最大外径（ｄ）：２４ｍｍ、軸部を除く回転軸方向長さ（螺旋状羽根部材が設けられた領域の大きさ）：４４０ｍｍ、軸部材の外径：６ｍｍ、螺旋状羽根部材のスクリューピッチ（ｐ）：３０ｍｍ、螺旋状羽根部材の厚み：１ｍｍ、切欠部の径方向長さ（ｔ）：５ｍｍ、切欠部の周方向長さ（ｗ）：２ｍｍ、切欠部の形成箇所：１ピッチ当たり４箇所ずつ周方向に対して等間隔毎に形成
【００７２】
（回転部材Ｄ）
回転部材Ｃにおいて、螺旋状羽根部材のスクリューピッチを２０ｍｍとしたことの他は回転部材Ｃと同様の構成を有する回転部材Ｄを作製した。
【００７３】
（回転部材Ｅ）
図７に示される構成に従って、右上方に巻き上がるように（左巻き）軸部材の外周面に形成された螺旋状羽根部材（主撹拌部材）を有すると共に、径方向外方に延びる複数の板状の垂直羽根部材（補助撹拌部材）を有する螺旋状スクリューを作製すると共に、この螺旋状羽根部材による現像剤の搬送方向下流側の長さ３０ｍｍにわたる端部領域を４つの平板状の撹拌部材が軸部材の外周面に径方向外方に延びる状態で設けられてなるパドル形状とした回転部材Ｅを作製した。そして、この回転部材Ｅの両端部に、外径寸法が２４ｍｍである円板状のフランジ部材を軸部材を挿通させた状態で設けた。この回転部材Ｅの具体的な諸元は、以下に示す通りである。
最大外径（ｄ）：２４ｍｍ、軸部を除く回転軸方向長さ（螺旋状羽根部材が設けられた領域の大きさ）：４４０ｍｍ、軸部材の外径：６ｍｍ、螺旋状羽根部材のスクリューピッチ（ｐ）：３０ｍｍ、螺旋状羽根部材の厚み：１ｍｍ、垂直羽根部材の配置位置：１ピッチ当たりに１つずつ、螺旋状羽根部材のピッチ間の中央位置に配置、垂直羽根部材の回転軸方向長さ（ｗ）：３ｍｍ、垂直羽根部材の径方向長さ（ｈ）：８ｍｍ
【００７４】
（回転部材Ｆ）
回転部材Ｅにおいて、螺旋状羽根部材のスクリューピッチを２０ｍｍとしたことの他は回転部材Ｅと同様の構成を有する回転部材Ｆを作製した。
【００７５】
（回転部材Ｇ）
図８に示される構成に従って、右上方に巻き上がるように（左巻き）軸部材の外周面に形成された螺旋状羽根部材（主撹拌部材）を有すると共に、径方向外方に延びる複数の板状の垂直羽根部材（補助撹拌部材）を有する螺旋状スクリューを作製すると共に、この螺旋状羽根部材による現像剤の搬送方向下流側の長さ３０ｍｍにわたる端部領域を４つの平板状の撹拌部材が軸部材の外周面に径方向外方に延びる状態で設けられてなるパドル形状とした回転部材Ｇを作製した。そして、この回転部材Ｇの両端部に、外径寸法が２４ｍｍである円板状のフランジ部材を軸部材を挿通させた状態で設けた。この回転部材Ｇの具体的な諸元は、以下に示す通りである。
最大外径（ｄ）：２４ｍｍ、軸部を除く回転軸方向長さ（螺旋状羽根部材が設けられた領域の大きさ）：４４０ｍｍ、軸部材の外径：６ｍｍ、螺旋状羽根部材のスクリューピッチ（ｐ）：３０ｍｍ、螺旋状羽根部材の厚み：１ｍｍ、垂直羽根部材の配置位置：１ピッチ当たりに４つずつ、周方向に対して等間隔毎に、螺旋状羽根部材のピッチ間の中央位置に配置、垂直羽根部材の回転軸方向長さ（ｗ）：３ｍｍ、垂直羽根部材の径方向長さ（ｈ）：８ｍｍ
【００７６】
（回転部材Ｈ）
回転部材Ｇにおいて、垂直羽根部材の回転軸方向長さ（ｗ）を２０ｍｍとしたことの他は回転部材Ｇと同様の構成を有する回転部材Ｈを作製した。
【００７７】
（回転部材Ｉ）
図１０に示される構成に従って、右上方に巻き上がるように（左巻き）軸部材の外周面に形成された螺旋状羽根部材（主撹拌部材）を有すると共に、螺旋状羽根部材の外周縁における軸部材を挟んで対向した位置に形成された、各々、回転軸方向に延びる２つの平板状のリブ部材（補助撹拌部材）を有する螺旋状スクリューを作製すると共に、この螺旋状羽根部材による現像剤の搬送方向下流側の長さ３０ｍｍにわたる端部領域を４つの平板状の撹拌部材が軸部材の外周面に径方向外方に延びる状態で設けられてなるパドル形状とした回転部材Ｉを作製した。そして、この回転部材Ｉの両端部に、外径寸法が２４ｍｍである円板状のフランジ部材を軸部材を挿通させた状態で設けた。この回転部材Ｉの具体的な諸元は、以下に示す通りである。
最大外径：２４ｍｍ、軸部を除く回転軸方向長さ（螺旋状羽根部材および板状羽根部材が設けられた領域の大きさ）：４４０ｍｍ、軸部材の外径：６ｍｍ、螺旋状羽根部材のスクリューピッチ（ｐ）：３０ｍｍ、螺旋状羽根部材の厚み：１ｍｍ、リブ部材の径方向長さ（ｔ）：３ｍｍ
【００７８】
（回転部材Ｊ）
回転部材Ｉにおいて、リブ部材の径方向長さ（ｔ）を５ｍｍとしたことの他は回転部材Ｉと同様の構成を有する回転部材Ｊを作製した。
【００７９】
（回転部材Ｋ）
回転部材Ｉにおいて、４つのリブ部材を、螺旋状羽根部材の外周縁における、周方向に対して等間隔毎に離間した位置に、設けたことの他は回転部材Ｉと同様の構成を有する回転部材Ｋを作製した。
【００８０】
（回転部材Ｌ）
回転部材Ｉにおいて、螺旋状羽根部材（撹拌部材）を左上方に巻き上がるように（右巻き）軸部材の外周面に形成すると共に、螺旋状羽根部材のスクリューピッチ（ｐ）を２０ｍｍとしたことの他は回転部材Ｉと同様の構成を有する回転部材Ｌを作製した。
【００８１】
（回転部材Ｍ）
回転部材Ｉにおいて、螺旋状羽根部材（撹拌部材）を左上方に巻き上がるように（右巻き）軸部材の外周面に形成すると共に、リブ部材の径方向長さ（ｔ）を５ｍｍとしたことの他は回転部材Ｉと同様の構成を有する回転部材Ｍを作製した。
【００８２】
（回転部材Ｎ）
回転部材Ｉにおいて、螺旋状羽根部材（撹拌部材）を左上方に巻き上がるように（右巻き）軸部材の外周面に形成すると共に、４つのリブ部材を、螺旋状羽根部材の外周縁における、周方向に対して等間隔毎に離間した位置に設けたことの他は回転部材Ｉと同様の構成を有する回転部材Ｎを作製した。
【００８３】
（回転部材Ｏ）
図６に示される構成に従って、軸部材に垂直な平面に対して互いに異なる方向に傾斜する第１および第２の撹拌部材配置用レベル平面の各々に沿って設けられた複数の半楕円板よりなる第１の撹拌部材群および第２の撹拌部材群を有する回転部材Ｏを作製した。そして、この回転部材Ｏの両端部に、外径寸法が２４ｍｍである円板状のフランジ部材を軸部材を挿通させた状態で設けた。この回転部材Ｏの具体的な諸元は、以下に示す通りである。
最大外径（ｄ）：２４ｍｍ、軸部を除く回転軸方向長さ（撹拌部材が設けられた領域の大きさ）：４４０ｍｍ、軸部材の外径：６ｍｍ、第１の撹拌部材群の軸部材に対する取付角度（α１）：−４５°、第２の撹拌部材群の軸部材に対する取付角度（α２）：＋４５°（第１の撹拌部材群と互いに逆方向に傾斜）、撹拌部材の配置ピッチ（ｐ）：２５ｍｍ
【００８４】
（回転部材Ｐ）
回転部材Ｏにおいて、第１の撹拌部材群の軸部材に対する取付角度（α１）および第２の撹拌部材群の軸部材に対する取付角度（α２）を、それぞれ、軸部材に対して回転部材Ｏと逆方向に傾斜する状態（α１＝＋４５゜、α２＝−４５゜）としたことの他は回転部材Ｏと同様の構成を有する回転部材Ｐを作製した。
【００８５】
（回転部材Ｑ）
図１１に示される構成に従って、軸部材に垂直な平面に対して互いに異なる方向に傾斜する第１および第２の撹拌部材配置用レベル平面の各々に沿って設けられた複数の半楕円板よりなる第１の撹拌部材群および第２の撹拌部材群を有すると共に、第１の撹拌部材群および第２の撹拌部材群の外周縁部における、周方向に対して等間隔毎に離間した位置において、軸方向に延びる４つの板状の補助撹拌部材を有する回転部材Ｑを作製した。そして、この回転部材Ｑの両端部に、外径寸法が２４ｍｍである円板状のフランジ部材を軸部材を挿通させた状態で設けた。この回転部材Ｑの具体的な諸元は、以下に示す通りである。
最大外径（ｄ）：２４ｍｍ、軸部を除く回転軸方向長さ（撹拌部材が設けられた領域の大きさ）：４４０ｍｍ、軸部材の外径：６ｍｍ、第１の撹拌部材群の軸部材に対する取付角度（α１）：−４５°、第２の撹拌部材群の軸部材に対する取付角度（α２）：＋４５°（第１の撹拌部材群と互いに逆方向に傾斜）、撹拌部材の配置ピッチ（ｐ）：２５ｍｍ、補助撹拌部材の径方向長さ（ｔ）：３ｍｍ
【００８６】
（回転部材Ｒ）
回転部材Ｑにおいて、第１の撹拌部材群の軸部材に対する取付角度（α１）および第２の撹拌部材群の軸部材に対する取付角度（α２）を、それぞれ、軸部材に対して回転部材Ｑと逆方向に傾斜する状態（α１＝＋４５゜、α２＝−４５゜）としたことの他は回転部材Ｑと同様の構成を有する回転部材Ｒを作製した。
【００８７】
＜実験例１＞
〔現像装置の作製〕
図２乃至図４に示される構成に従って、現像剤供給回収手段、第１の現像剤撹拌手段および第２の現像剤撹拌手段が下記表１に従って選ばれた回転部材により構成された本発明に係る現像装置１〜８を作製した。
また、下記表１に従って選ばれた第１の現像剤撹拌手段および第２の現像剤撹拌手段を、互いに対向する部分において各々の周面が下方から上方に向かって順方向に移動するよう回転させるよう設定した比較用の現像装置９を作製した。
さらに、図１４に示されるように、第２の現像剤撹拌手段を有さないことの他は図２に示されるものと同様の構成を有し、現像剤供給回収手段および第１の撹拌搬送手段が下記表１に示す組み合わせに従って選ばれた回転部材により構成された比較用の現像装置１０〜１９を作製した。
【００８８】
現像剤担持体を構成する現像スリーブは、外径が３０ｍｍ、軸方向長さが３３０ｍｍであるものである。
本発明に係る現像装置１〜８および比較用の現像装置９の各々におけるトナー供給用開口の形成位置は、第１の現像剤撹拌手段と第２の現像剤撹拌手段とが互いに対向する部分の上方位置であって、現像剤撹拌部における現像剤の搬送方向に対して上流側の端縁から１５ｍｍ下流側の位置である。
比較用の現像装置１０〜１９の各々におけるトナー供給用開口の形成位置は、第１の現像剤撹拌手段の後方側の端縁部分の上方位置であって、第１の現像剤撹拌手段による現像剤の搬送方向における上流側の端縁から１５ｍｍ下流側の位置である。
【００８９】
現像剤としては、イエロートナー、マゼンタトナー、シアントナーおよびブラックトナーの各々に係る現像剤のいずれのものも、トナー濃度が７質量％である二成分現像剤を用い、本発明に係る現像装置１〜８および比較用の現像装置９には１１００ｇ、比較用の現像装置１０〜１９には７５０ｇの現像剤をそれぞれ充填した。
トナーは、イエロートナー、マゼンタトナー、シアントナーおよびブラックトナーのいずれのものも、体積平均粒径が４．５±０．１５μｍ、粒径分布の標準偏差（ａ）と平均粒径（ｂ）とにより示されるＣＶ値〔ａ／ｂ×１００％〕が１８±２％である各色の重合トナーに、大粒径シリカ０．８質量％、小粒径シリカ０．２質量％、大粒径チタニア０．２質量％、小粒径チタニア０．４質量％、ステアリン酸カルシウム０．０５質量％を外添処理したものを用いた。
キャリアは、イエロートナー、マゼンタトナー、シアントナーおよびブラックトナーの各々に係る現像剤のいずれのものも、体積平均粒径が２５μｍ、飽和磁化６０ｅｍｕ／ｇのフェライト粒子の表面に、アクリル系樹脂をフェライト粒子に対する被覆量が３質量％となる状態でコーティングしたものを用いた。
【００９０】
本発明に係る現像装置１〜８および比較用の現像装置９〜１９の各々を適宜の単体駆動機に装着し、現像剤供給回収手段、第１の現像剤撹拌手段および第２の現像剤撹拌手段のそれぞれの回転速度を下記表１に従って設定し、現像剤供給回収部における現像剤移動量を測定した。結果を下記表１に示す。現像剤移動量の測定は、現像スリーブは駆動せずに、現像剤供給回収手段、第１の現像剤撹拌手段および第２の現像剤撹拌手段のみを駆動し、現像剤供給回収手段下流側の現像器ハウジングの底面に現像剤排出口を設け、この現像剤排出口から単位時間当たりに排出される現像剤の重量を測定することにより行った。
【００９１】
【表１】

【００９２】
〔画像形成装置〕
図１に示される構成に従って、上記の本発明に係る現像装置１〜８および比較用の現像装置９〜１９の各々が搭載されたカラー画像形成用の画像形成装置１〜１９を製造し、画像出力テストを以下の画像形成条件にて行った。画像形成条件は、各色トナー像に係るトナー像形成ユニットのいずれのものも同じに設定した。
【００９３】
＜画像形成条件＞
・プロセス速度（Ｖ）：２２０ｍｍ／ｓｅｃ（１分間当たりの画像出力枚数が５０枚）
・現像スリーブ回転数：２１０〜２８０ｒｐｍの範囲内で調整して、潜像担持体上の単位面積当たりのトナー付着量（Ｍ）が０．４ｍｇ／ｃｍ²となる状態とした。
・感光体と現像スリーブとの最近接距離（現像ギャップ）：０．３ｍｍ
・現像バイアス：交流バイアス（ＡＣ）成分を直流バイアス成分（ＤＣ）に重畳したもの、
交流バイアス成分；Ｖａｃ＝１ｋＶｐｐ、ｆａｃ＝５ｋＨｚ、波形＝正弦波
直流バイアス成分；感光体における最大露光部の表面電位ＶＬの検知結果に応じてＶｄｃ＝ＶＬ−５００Ｖとなる状態に制御した。
・現像スリーブによる現像剤搬送量：２５±２ｍｇ／ｃｍ²
・現像スリーブの軸方向における磁気ブラシの形成幅：３２０ｍｍ
・トナー補給制御：供給スクリューによる現像剤の搬送方向下流側の端縁からから８０ｍｍ上流側の位置にトナー濃度センサ（透磁率センサ）を設けてその検知結果に応じてトナー補給モータを制御した。
トナー補給速度：最大３０ｇ／ｍｉｎ
・感光体表面電位：
最大露光部電位（ＶＬ）：−５０Ｖ〜−１００Ｖ
帯電電位（未露光部電位）（ＶＨ）：現像バイアスにおける直流バイアス成分の設定値に応じてＶＨ＝Ｖｄｃ−１５０Ｖとなる状態に制御
【００９４】
画像出力テストは、下記（１）〜（６）の画像出力を４回繰り返して行い（トータルＡ４×２０００枚）、文字／ラインパターンのかぶりの発生有無、文字散りの発生有無、ソリッドパターンの濃度むらの発生有無の評価を下記評価基準に基づいて行った。結果を下記表２に示す。
（１）シアン（Ｃ）単色の文字／ライン＋中間調（１０段）パターン（印字率３０％）を連続して５０枚出力する手順。
（２）シアン（Ｃ）のソリッドパターン（印字率８０％）連続１５０枚出力する手順。
（３）Ｃ単色の文字／ラインパターン（印字率７％）を連続して５０枚出力する手順。
（４）赤（マゼンタ（Ｍ）＋シアン（Ｃ））単色の文字／ライン＋中間調（１０段）パターン（Ｍ、Ｃとも印字率３０％）を連続して５０枚出力する手順。
（５）赤単色のソリッドパターン（マゼンタ（Ｍ）、シアン（Ｃ）とも印字率８０％）を連続して１５０枚出力する手順。
（６）赤（マゼンタ（Ｍ）＋シアン（Ｃ））単色の文字／ラインパターン（印字率７％）を連続して５０枚出力する手順。
【００９５】
＜評価基準＞
（イ）画像のかぶり：
画像のかぶりは、未使用の用紙の反射濃度を０としたときの、文字／ラインパターン白地部の相対反射濃度を測定し、相対反射濃度が０．００４以下である場合を「○」、相対反射濃度が０．００４を超え、０．００６以下である場合を「△」、相対反射濃度が０．００６を超える場合を「×」として評価した。
【００９６】
（ロ）文字散り：
文字散りは、４ポイントの「鐘」という文字を拡大して観察したときの、文字輪郭のシャープさおよび文字の滲み度合の状態を評価した。
そして、「鐘」の文字の空間部がすっきりと抜けていて文字の輪郭が明瞭であり、文字周辺部のトナー散りも極めて少ない場合を「○」、「鐘」の文字の空間部がややつぶれいる（トナー散りでやや埋まっている）が、文字周辺部のトナー散りは少ない場合を「△」、「鐘」の文字の空間部がつぶれており（トナー散りで埋まっている）、しかも、文字周辺部のトナー散りが多く、文字の輪郭が滲んでいる場合を「×」とした。
【００９７】
（ハ）画像濃度むら：
画像濃度むらは、シアン単色のソリッドパターンまたは赤単色のソリッドパターンのページ内における任意の９箇所の色差（Ｌ＊ａ＊ｂ＊空間での距離）により評価した。シアン単色のソリッドパターンについての９箇所の色差が３以下であり、かつ、赤単色のソリッドパターンについての９箇所の色差が７以下である場合を「○」、シアン単色のソリッドパターンについての９箇所の色差が３を超え、５以下であり、かつ、赤単色のソリッドパターンについての９箇所の色差が７以下である場合、または、シアン単色のソリッドパターンについての９箇所の色差が３以下であり、かつ、赤単色のソリッドパターンについての９箇所の色差が７を超え、９以下である場合を「△」、シアン単色のソリッドパターンについての９箇所の色差が３を超え、かつ、赤単色のソリッドパターンについての９箇所の色差が９を超える場合を「×」とした。
【００９８】
（ニ）機内汚れ：
機内汚れは、画像出力テスト終了後に現像装置を取り外し、現像装置装着部近傍の汚れの状態を目視にて観察して評価した。
そして、機内汚れが認められない場合、または現像装置装着部のみに極軽微な汚れがみられる場合を「○」、現像装置装着部の近傍（例えば両端部等）にわずかな汚れがみられる場合を「△」、現像装置装着部の汚れが周辺部（例えば帯電装置等）にまで拡大している場合を「×」とした。
【００９９】
【表２】

【０１００】
＜実験例２＞
〔現像装置の作製〕
実験例１で用いた現像装置１〜５および比較用の現像装置１０〜１９の各々において、現像剤撹拌部における現像剤の搬送方向に対してトナー供給口より８ｍｍ上流側の位置にリサイクルトナー混入用開口を形成したことの他は現像装置１〜５と同様の構成を有する、本発明に係る現像装置２０〜２４、および比較用の現像装置１０〜１９と同様の構成を有する比較用の現像装置２５〜３４を作製した。
【０１０１】
図１２に示される構成に従って、上記の本発明に係る現像装置２０〜２４および比較用の現像装置２５〜３４の各々が搭載された、トナーリサイクル手段を有するモノクロ画像形成用の画像形成装置２０〜３４を製造した。トナーリサイクル手段は、リサイクルトナーを現像装置に搬送するための搬送手段が、単位時間当たりのトナー搬送量が最大で３０ｇ／ｍｉｎであるものにより構成されてなるものである。
そして、画像形成装置２５〜３４の各々について、プロセス速度を３２０ｍｍ／ｓｅｃ（１分間当たりの画像出力枚数が６５枚）に設定すると共に、現像剤供給回収手段、第１の現像剤撹拌手段および第２の現像剤撹拌手段の各々の回転速度を下記表３に示す条件に従って設定したことの他は、実験例１のブラックトナー像に係るトナー像形成ユニットと同様の画像形成条件で、下記（７）〜（９）の画像出力を８回繰り返して行う（トータルＡ４×２０００枚）画像出力テストを行うことにより、文字／ラインパターンのかぶりの発生有無、文字散りの発生有無、および機内汚れの発生有無の評価を上記評価基準に基づいて行うと共に、ソリッドパターンの画像濃度むらの発生有無の評価を下記評価基準に基づいて行った。結果を下記表４に示す。
【０１０２】
（７）黒（ＢＫ）単色の文字／ライン＋中間調（１０段）パターン（印字率３０％）を連続して５０枚出力する手順。
（８）黒（ＢＫ）単色のソリッドパターン（印字率８０％）を連続して１５０枚出力する手順。
（９）黒（ＢＫ）単色の文字／ラインパターン（印字率７％）を連続して５０枚出力する手順。
【０１０３】
＜評価基準＞
画像濃度むらは、ブラックソリッドパターンのページ内における任意の９箇所の相対反射濃度を測定し、ブラックソリッドパターンについての９箇所の相対反射濃度がいずれも１．３以上であり、かつ、最大値と最小値との差が０．１以下である場合を「○」、相対反射濃度の最小値が１．２以上１．３未満であり、かつ、最大値と最小値との差が０．１以下である場合を「△」、相対反射濃度の最小値が１．２未満、または最大値と最小値との差が０．１５を超える場合を「×」として評価した。
【０１０４】
【表３】

【０１０５】
【表４】

【０１０６】
以上の結果から明らかなように、本発明に係る画像形成装置によれば、印字率が高い画像を連続して出力することにより大量のトナー消費とリサイクルトナーを含むトナー補給が繰り返し行われた現像剤が用いられる場合であっても、現像剤について十分な帯電立ち上がり特性が得られると共に現像剤を軸方向に対して均一なトナー濃度で現像剤担持体に供給することができ、かぶり、文字散りおよび画像濃度ムラ等の画像欠陥の発生が確実に防止されると共に、トナー飛散による機内汚れの発生が確実に防止され、画質の高い画像を確実に形成することができることが確認された。
これに対して、比較用の画像形成装置においては、画像かぶり、文字散り、画像濃度むらおよび機内汚れの少なくとも一つ以上の問題が発生しており、画質の高い画像を確実に得ることができないことが確認された。特に、トナーリサイクル機構を備えたモノクロ画像形成装置（実験例２）において、回転部材の回転速度を高くして十分な現像剤の移動速度を得、これにより、軸方向に対する画像濃度むらの発生を防止する構成とされた場合には、撹拌トルクが大幅に増加したため、画像出力テストを中止せざるをえず、出力画像を得ることができなかった。この理由について調査したところ、軸部に現像剤が融着し始めていることが確認された。
【０１０７】
【発明の効果】
本発明の現像装置によれば、現像剤撹拌部において、現像剤が回転軸方向に搬送される過程において、現像剤の搬送速度を低下させることなしに十分な混合撹拌時間を確保することができるので、現像剤撹拌部における現像剤の混合撹拌動作によりトナーが所期の帯電量を有する状態にまで帯電された状態において、現像剤が現像剤供給回収手段によって軸方向に対して均一なトナー濃度で現像剤担持体に供給され、従って、トナーの帯電不良によるかぶりやトナー飛散の発生を確実に防止することができると共に、得られる可視画像における画像濃度むらの発生を確実に防止することができる。
しかも、２つの現像剤撹拌手段を当該２つの現像剤撹拌手段が対向する部分において各々の周面が上方から下方に向かって互いに順方向に移動するよう回転駆動させると共に、当該２つの現像剤撹拌手段の対向部分の上方からトナーを補給する構造とされていることにより、トナー補給位置での現像剤中への補給トナーの沈み込みが加速されるので、補給トナーが現像剤中に均一に分散され、これにより、補給トナーについて十分な帯電立ち上がり特性が得られる。
【０１０８】
また、回転軸方向に対する現像剤の搬送能力が実質的に零である現像剤撹拌手段が現像剤供給回収部に対して後方側に配置されていることにより、現像剤供給回収部と現像剤撹拌部との連通部の近傍において発生しやすい現像剤の滞留が生ずることが確実に防止されて現像剤の循環搬送が円滑に行われ、これにより、現像剤を軸方向に対して均一なトナー濃度で現像剤担持体に供給することができ、画像濃度むらのない均一な画像を一層確実に形成することができる。
【０１０９】
本発明の画像形成装置によれば、上記のような現像装置を備えてなり、特定の動作設定条件を満足する状態で現像プロセスが行われることにより、十分な撹拌が行われてトナーが所期の帯電量を有する状態まで帯電された現像剤が現像剤担持体に回転軸方向に対して均一なトナー濃度で供給されて、潜像担持体上の潜像が現像されるので、印字率が高い画像を連続して出力することにより大量のトナー消費とリサイクルトナーを含むトナー補給が繰り返し行われた現像剤が用いられる場合であっても、トナーとキャリアとが十分に混合撹拌されて、十分なトナーの帯電立ち上がり特性が得られ、しかも、軸方向に対して均一なトナー濃度で現像領域に供給されるため、かぶりやトナー飛散が生ずることがなく、しかも画像濃度むらのない均一な画像濃度を有する画質の高い画像を確実に形成することができる。
【図面の簡単な説明】
【図１】本発明の画像形成装置の一例における構成の概略を示す説明図である。
【図２】本発明の現像装置の一例における構成の概略を示す部分断面図である。
【図３】図２に示す現像装置におけるＡ−Ａ断面の縦断断面図である。
【図４】図２に示す現像装置におけるＢ−Ｂ断面の縦断断面図である。
【図５】現像剤供給回収手段および第１の現像剤撹拌手段を構成する回転部材の一構成例を示す平面図である。
【図６】第２の現像剤撹拌手段を構成する回転部材の一構成例を示す斜視図である。
【図７】第１の現像剤撹拌手段および第２の現像剤撹拌手段を構成する回転部材の他の構成例を示す斜視図である。
【図８】第１の現像剤撹拌手段および第２の現像剤撹拌手段を構成する回転部材の更に他の構成例を示す平面図である。
【図９】第１の現像剤撹拌手段および第２の現像剤撹拌手段を構成する回転部材の更に他の構成例を示す平面図である。
【図１０】第１の現像剤撹拌手段および第２の現像剤撹拌手段を構成する回転部材の他の構成例を示す斜視図である。
【図１１】第１の現像剤撹拌手段および第２の現像剤撹拌手段を構成する回転部材の更に他の構成例を示す斜視図である。
【図１２】本発明の画像形成装置の他の例における構成の概略を示す説明図である。
【図１３】本発明の現像装置の他の例における構成の概略を示す部分断面図である。
【図１４】実験例において用いた比較用の現像装置の構成の概略を示す説明図であり、（イ）は部分断面図、（ロ）は（イ）におけるａ−ａ断面の縦断断面図、（ハ）は（イ）におけるｂ−ｂ断面の縦断断面図である。
【符号の説明】
１０中間転写体（中間転写ベルト）
１１、１２、１３、１４支持ローラ
２０Ｙ、２０Ｍ、２０Ｃ、２０Ｋトナー像形成ユニット
２１潜像担持体
２２帯電手段
２３露光手段
２４一次転写機構
２５潜像担持体クリーニング手段
２６二次転写機構
３０トナー像形成手段
３１ハウジング
３１Ａ突出部分
３１Ｂ天面板
３１Ｃトナー供給用開口
３２現像剤供給回収部
３３現像剤撹拌部
３４現像剤担持体
３５現像剤供給回収手段
３６軸部材
３７撹拌部材
３８回転部材
３９現像剤規制部材
４０第１の現像剤撹拌手段
４１第２の現像剤撹拌手段
４３軸部材
４４Ａ第１の撹拌部材
４４Ｂ第２の撹拌部材
４５回転部材
Ｐ転写材
５０Ａ、５０Ｂ、５０Ｃ回転部材
５１、５４、５７軸部材
５２、５５主撹拌部材
５３、５６補助撹拌部材
５８撹拌部材
５９切欠部
６０、７０回転部材
６１、７１軸部材
６２主撹拌部材
６３、７３補助撹拌手段
７２Ａ第１の撹拌部材
７２Ｂ第２の撹拌部材
１１０潜像担持体
１１１帯電手段
１１２露光手段
１１３転写手段
１１４分離手段
１１５潜像担持体クリーニング手段
１２０トナー像形成手段
１３０トナーリサイクル手段
１３１回収搬送手段
１３２搬送手段
１３３リサイクルトナー混入用開口[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a developing device and an image forming apparatus including the developing device.
[0002]
[Prior art]
At present, in a certain type of image forming apparatus using an electrophotographic system, for example, a two-component developer composed of a toner and a carrier is used. A developing method for forming a toner image by attaching to an electrostatic latent image formed on a latent image carrier is used. In the developing method using such a two-component developer, the toner in the developer is used. In order to keep the density constant, new toner is replenished according to the amount of toner consumption.
[0003]
In such an image forming apparatus, there is a demand for higher image quality, and in response to such a demand, for example, toner having a small particle diameter has been used. As the diameter is reduced, the carrier has a smaller particle diameter.
[0004]
Thus, by using a toner having a small particle size and a carrier having a small particle size, a high-quality image can be formed, but the flowability of the developer itself is lowered and the developer is sufficiently stirred. As a result, the newly replenished toner is supplied to the development area without having a predetermined charge amount, and there is a problem that fogging and toner scattering are likely to occur.
Such a problem is conspicuous when an image having a high printing rate is continuously output, for example, when a color image is formed.
[0005]
On the other hand, in recent years, with increasing social awareness regarding environmental protection, resources are being saved by recycling toner, for example.
However, since toner collected after being subjected to development (recycled toner) is inferior to unused toner in its charging characteristics, fog and toner scattering due to insufficient charge amount of the toner occurs. There is a problem that it becomes easy.
[0006]
Many techniques for improving the developer stirring efficiency have been proposed for such problems. For example, by providing a member that functions as an auxiliary stirring member, the stirring means has a high developer stirring ability. (For example, refer to Patent Document 1, Patent Document 2, Patent Document 3, etc.).
[0007]
[Patent Document 1]
Japanese Unexamined Patent Publication No. 07-013420
[Patent Document 2]
JP 09-166918 A
[Patent Document 3]
JP 09-288212 A
[0008]
[Problems to be solved by the invention]
However, in any of the techniques described above, the developer agitation efficiency is improved, but the developer circulation speed in the developing device is reduced, and as a result, the developer is supplied to the developer carrier. The toner density of the developer to be developed in the direction of the rotation axis of the developer carrier becomes non-uniform, and particularly when images with a high printing rate are output continuously, uneven image density is likely to occur, resulting in high image quality. There is a problem that it is difficult to reliably form the image.
[0009]
As described above, in order to prevent the occurrence of fog and toner scattering by improving the stirring performance of the developer in order to bring the replenished new toner into a state having a sufficient charge amount, the developer Image density unevenness is likely to occur due to a decrease in the conveyance performance of the toner. Eventually, two conflicting problems of fogging, toner scattering, and image density unevenness can be solved simultaneously. The reality is that it is difficult.
[0010]
The present invention has been made based on the above circumstances, and its purpose is to mix and agitate the toner in a state having a predetermined charge amount without reducing the developer conveyance speed. Accordingly, an object of the present invention is to provide a developing device and an image forming apparatus having a novel configuration capable of reliably forming an image with high image quality.
[0011]
[Means for Solving the Problems]
The developing device of the present invention includes a housing in which a developer supply / recovery unit and a developer agitation unit that are in communication with each other and form a circulation conveyance path of a two-component developer composed of toner and a carrier are arranged side by side in the front-rear direction, A developer carrier provided to face a latent image carrier through a development region in a front side portion of the developer supply and recovery unit; and a developer carrier in a rear side portion of the developer supply and recovery unit; In the developer supply and recovery means, which is provided so as to face and extend along the rotation axis direction of the developer carrying member, and which rotates and conveys the developer in the rotation axis direction, and the developer stirring unit, Two developer agitating means provided side by side in the front-rear direction so as to extend along the rotation axis direction of the developer supply and recovery means facing each other,
The housing is provided with a toner supply opening at a position above the portion where the two developer agitating units in the developer agitating portion are opposed to each other and upstream of the developer agitating direction in the developer agitating portion. Formed,
The two developer agitating means in the developer agitating section are rotated so that the two developer agitating means are moved in the forward direction from the upper side to the lower side in the portions facing each other. In both cases, the developer is transported in the opposite direction to the developer supply / recovery means, and the total transport amount of the developer by each developer stirring means is the developer transport amount by the developer supply / recovery means. It has the same developer transport capability.
[0012]
In the developing device of the present invention, one developer agitation unit in the developer agitation unit has a developer conveyance capability in the rotation axis direction that is equivalent to or lower than that of the other developer agitation unit. The developer supply / recovery unit is preferably provided on the rear side.
[0013]
The developing device of the present invention includes a housing in which a developer supply / recovery unit and a developer agitation unit that are in communication with each other and form a circulation conveyance path of a two-component developer composed of toner and a carrier are arranged side by side in the front-rear direction, A developer carrier provided to face a latent image carrier through a development region in a front side portion of the developer supply and recovery unit; and a developer carrier in a rear side portion of the developer supply and recovery unit; A developer supply / recovery unit having a stirring member that spirally extends in the rotation axis direction over the entire circumference of the outer peripheral surface of the shaft member, which is provided so as to extend along the rotation axis direction of the developer carrying member; In the developer agitation unit, a first developer agitation unit and a second developer agitation unit are provided side by side in the front-rear direction so as to extend along the rotation axis direction of the developer supply / recovery unit, facing each other. Means Ete will,
The housing is provided with a toner supply opening at a position above the portion where the two developer agitating units in the developer agitating portion are opposed to each other and upstream of the developer agitating direction in the developer agitating portion. Formed,
The two developer agitating means in the developer agitating section are rotated so that the two developer agitating means are moved in the forward direction from the upper side to the lower side in the portions facing each other. In both cases, the developer is transported in the opposite direction to the developer supply / recovery means, and the total transport amount of the developer by each developer stirring means is the developer transport amount by the developer supply / recovery means. Has the same developer transport capability,
The second developer agitation means includes a first agitation member disposition level plane and a second agitation member disposition level that are inclined in different directions with respect to a plane perpendicular to the shaft member on the outer peripheral surface of the shaft member. It has a plurality of semi-elliptical first stirring member groups and second stirring member groups provided along each of the planes.
[0014]
In the developing device of the present invention, the second developer agitation unit in the developer agitation unit has the same or lower developer conveying capability in the rotation axis direction than the first developer agitation unit. It is preferable that it is provided on the rear side with respect to the developer supply / recovery unit.
[0015]
The developing device of the present invention includes a housing in which a developer supply / recovery unit and a developer agitation unit that are in communication with each other and form a circulation conveyance path of a two-component developer composed of toner and a carrier are arranged side by side in the front-rear direction, A developer carrier provided to face a latent image carrier through a development region in a front side portion of the developer supply and recovery unit; and a developer carrier in a rear side portion of the developer supply and recovery unit; A developer supply / recovery unit having a stirring member that spirally extends in the rotation axis direction over the entire circumference of the outer peripheral surface of the shaft member, which is provided so as to extend along the rotation axis direction of the developer carrying member; In the developer agitation unit, a first developer agitation unit and a second developer agitation unit are provided side by side in the front-rear direction so as to extend along the rotation axis direction of the developer supply / recovery unit, facing each other. Means Ete will,
The housing is provided with a toner supply opening at a position above the portion where the two developer agitating units in the developer agitating portion are opposed to each other and upstream of the developer agitating direction in the developer agitating portion. Formed,
The two developer agitating means in the developer agitating section are rotated so that the two developer agitating means are moved in the forward direction from the upper side to the lower side in the portions facing each other. The developer is transported in the opposite direction to the developer supply / recovery means, and the total transport amount of the developer by each developer stirring means is equal to the developer transport amount by the developer supply / recovery means. It has developer transport capability,
The second developer agitating means has an agitating member made of a rib provided so as to extend along the rotation axis direction on the outer peripheral surface of the shaft member or at a position radially separated from the shaft member. It is characterized by becoming.
[0016]
In the developing device of the present invention, the second developer agitation unit in the developer agitation unit has the same or lower developer conveying capability in the rotation axis direction than the first developer agitation unit. It is preferable that it is provided on the rear side with respect to the developer supply / recovery unit.
[0017]
In the developing device of the present invention, in the developer supply / recovery section, the peripheral surfaces of both the developer carrier and the developer supply / recovery means are portions where the developer carrier and the developer supply / recovery means face each other. In this case, it is preferable that the operation is controlled so as to be moved in opposite directions.
Further, in the developing device of the present invention, when the volume average particle diameter of the toner is 3 to 5 μm and the volume average particle diameter of the toner is Dt [μm], the volume average particle diameter is 5 × Dt to 10 × Dt. It is preferable to use a two-component developer composed of a carrier.
[0018]
The image forming apparatus of the present invention includes a latent image carrier and a toner image forming unit that develops an electrostatic latent image formed on the latent image carrier to form a toner image.
The toner image forming unit comprises any of the developing devices described above,
The moving speed of the latent image carrier is V [mm / sec], and the maximum adhesion amount per unit area of the toner image formed on the latent image carrier is M [mg / cm.²] The maximum width of the toner image formed on the latent image carrier in the direction orthogonal to the moving direction of the latent image carrier is L [mm], and the developer movement amount with respect to the rotation axis direction by the developer supply and recovery means When W [g / sec] and the rotation speed of the developer supply / recovery means are R [rpm], the following conditions (A) and (B) are satisfied.
[0019]
(Condition A) W ≧ M × V × L / 1000
(Condition B) R ≦ 600
[0020]
The image forming apparatus of the present invention includes a latent image carrier, a toner image forming unit that develops an electrostatic latent image formed on the latent image carrier to form a toner image, and a toner on the latent image carrier. Transfer means for transferring the image to the transfer material or intermediate transfer member, cleaning means for removing the toner remaining on the latent image carrier, and toner removed from the latent image carrier are collected in the toner image forming means and recycled. With toner recycling means to use,
The toner image forming unit comprises any of the developing devices described above,
In the housing constituting the developing device, the two developer agitating units are located above the portions facing each other and upstream of the toner supply opening in the developer conveying direction in the developer agitating unit. A recycle toner mixing opening for mixing the toner collected by the toner recycling means into the developer stirring unit is formed at a location.
[0021]
[Action]
According to the developing device configured as described above, the developer transport speed is balanced by circulating and transporting the developer by the two developer agitating units and the developer supply and recovery unit in the developer agitating unit, so that the two developer agitating units are balanced. The developer is transported in the direction of the rotation axis while being stirred in the circumferential direction by means of the means to raise the charge of the toner, so that the developer is conveyed in the process of being conveyed in the direction of the rotation axis. As a result of ensuring sufficient mixing and stirring time in the developer stirring section without reducing the speed, the developer mixing and stirring operation in the developer stirring section results in the toner having a desired charge (charge amount). In a charged state, the developer is supplied to the developer carrier with a uniform toner concentration in the axial direction by the developer supply / recovery means. The occurrence of fog and toner scattering can be reliably prevented, occurrence of uneven image density in the resulting visible image is reliably prevented.
In addition, the two developer agitating means are rotated so that the respective peripheral surfaces move in the forward direction from the upper side to the lower side at the portions where the two developer agitating means face each other, and the two developer agitating means Since the toner is replenished (freely dropped) from above the opposite portion of the toner, sinking of the replenished toner into the developer at the toner replenishing position is accelerated, so that the replenished toner is contained in the developer. Thus, the toner can be sufficiently mixed and stirred in the developer stirring section.
[0022]
According to the image forming apparatus having the above configuration, the developing device as described above is provided, and the developing process is performed in a state satisfying specific operation setting conditions, whereby the developer is sufficiently mixed and stirred. The developer charged in a state where the toner has a desired charge amount is supplied to the developer carrier with a uniform toner concentration in the rotation axis direction, and the latent image on the latent image carrier is developed. So, for example, when a developer with a large amount of toner consumption and toner replenishment is used by continuously outputting images with a high printing rate, or when the charging performance is inferior to that of unused toner Even when a developer containing toner is used, problems such as toner scattering, fogging, and image density unevenness are surely prevented, and an image with high image quality can be reliably obtained.
[0023]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in detail with reference to the drawings.
<First Embodiment>
FIG. 1 is an explanatory diagram showing an outline of the configuration of an example of the image forming apparatus of the present invention, FIG. 2 is a partial cross-sectional view showing an outline of the configuration of an example of the developing apparatus of the present invention, and FIG. 3 is shown in FIG. FIG. 4 is a vertical cross-sectional view of the developing device shown in FIG. 2, and FIG. 4 is a vertical cross-sectional view of the developing device shown in FIG.
[0024]
In this image forming apparatus, an endless belt-like intermediate transfer body (hereinafter referred to as “intermediate transfer belt”) 10 disposed in a stretched state by a plurality of

support rollers

11, 12, 13, and 14 groups. And four toner

image forming units

20Y, 20M, 20C, and 20K that form toner images of different colors along the outer peripheral surface of the intermediate transfer belt 10, and the intermediate transfer belt 10 relates to each color toner image. Toner images in the moving direction of the intermediate transfer belt 10 are provided so as to be circulated and moved in contact with each of the

latent image carriers

21, 21, 21, 21 in the toner image forming unit. A secondary transfer mechanism 26 is provided at a position downstream of the forming unit arrangement region.
[0025]
The toner image forming unit 20Y related to the yellow toner image includes a rotating drum-shaped latent image carrier 21 and an outer peripheral surface of the latent image carrier 21 with respect to the rotation direction of the latent image carrier 21. The charging unit 22, the exposure unit 23, the toner image forming unit 30, the primary transfer mechanism 24, and the latent image carrier cleaning unit 25 are arranged so as to be arranged in the order of operation.
Further, the toner

image forming units

20M, 20C, and 20K related to the magenta toner image, the cyan toner image, and the black toner image each have the same configuration as the toner image forming unit 20Y related to the yellow toner image.
[0026]
Each of the

latent image carriers

21, 21, 21, and 21 in each toner image forming unit includes, for example, a photosensitive layer made of a resin such as polycarbonate containing an organic photoconductor. It is composed of an organic photoreceptor formed on the surface.
[0027]
The toner

image forming means

30, 30, 30, 30 in each toner image forming unit is configured by a developing device having the configuration shown in FIGS. 2 to 4, for example. Hereinafter, the developing device will be described in detail. In this specification, the horizontal direction in FIG. 2 is the “front-rear direction”, the vertical direction in FIG. 2 is the “axial direction”, and the vertical direction in FIGS. It shall be called “vertical direction”.
[0028]
In this developing device, a developer supply / recovery unit 32 and a developer agitation unit 33 are arranged in the front-rear direction so as to communicate with each other at both ends in the axial direction to form a two-component developer circulation conveyance path composed of toner and carrier. A formed housing 31 is provided.
[0029]
In the developer supply / recovery unit 32, a developer carrier 34 that rotates and conveys the developer in the circumferential direction at the front portion facing the latent image carrier 21, and the latent image carrier 21 and the development region. And is rotatably supported so as to extend in the axial direction so as to oppose each other, and in the rear side portion adjacent to the developer stirring portion 33, the developer is rotated and stirred in the axial direction ( A developer supply / recovery means 35 that transports the developer in the whole axial direction of the developer carrier 34 and conveys the developer in the axial direction in FIG. It is pivotally supported so as to extend.
[0030]
The developer agitating section 33 is provided with two developer agitating means 40 and 41 that are rotatably supported so as to extend in the axial direction so as to face each other at positions aligned in the front-rear direction.
[0031]
The housing 31 has a protruding portion 31A that protrudes outward in the axial direction from the end on one end side of the developer carrier 34, and the two developer stirring means 40, 41 of the top plate 31B in the protruding portion 31A. Is a toner for supplying unused toner (hereinafter referred to as “new toner”) from a toner replenishing mechanism (not shown) to the developer agitating unit 33 at a position positioned above the portions facing each other. A supply opening 31C is formed.
The toner replenishing mechanism has a function of replenishing new toner in accordance with the amount of toner consumed by development, and thereby maintains a constant toner concentration in the developer.
[0032]
The developer carrier 34 is, for example, a developing sleeve made of a nonmagnetic material such as aluminum that is rotatably provided, and a plurality of columnar poles having a plurality of magnetic poles that are fixedly provided inside the developing sleeve. And a developing magnet made of a magnet body.
[0033]
For example, as shown in FIG. 5, the developer supply / recovery means 35 is a spiral formed so as to extend spirally at a pitch p of a uniform size in the axial direction over the entire outer periphery of the shaft member 36. 2 is configured by a screw-like rotating member 38 having an agitating member 37 made of a blade member, and a downstream end portion (lower end portion in FIG. 2) in the developer transport direction is a plate-like blade member (see FIG. 2). (Not shown) has a paddle shape provided on the outer peripheral surface of the shaft member 36.
The developer supply / recovery means 35 is preferably rotated so that the developer carrier 34 and the developer supply / recovery means 35 are moved in opposite directions to the developer carrier 34 at a portion where the developer carrier 34 and the developer supply / recovery means 35 face each other. As a result, the developer supplied from the developer supply / recovery means 35 to the developer carrier 34 and the developer consumed on the developer carrier 34 and the developer recovered by the developer supply / recovery means 35 are replaced. Therefore, the toner density of the developer on the developer carrying member 34 becomes uniform, and the occurrence of uneven image density can be reliably prevented.
[0034]
The two developer agitating means 40 and 41 in the developer agitating unit 33 both convey the developer in the opposite direction to the developer supply / recovery means 35, and each developer agitating means 40 and 41. It is assumed that the total developer transport amount due to the developer transport ability is equivalent to the developer transport amount by the developer supply and recovery means 35.
[0035]
One developer agitating means (hereinafter referred to as “first developer agitating means”) 40 has a developer conveyance capacity in the axial direction lower than the developer supply / recovery means 35. .
Specifically, the first developer agitation unit 40 has a basic configuration similar to that of the developer supply / recovery unit 35 (see FIG. 5), for example, and extends over the entire circumference of the outer peripheral surface of the shaft member 36. It is constituted by a screw-like rotating member 38 having a stirring member 37 made of a spiral blade member formed so as to extend spirally at a pitch p1 of a predetermined size in the axial direction, and is downstream in the developer conveying direction. 2 (upper end portion in FIG. 2) is composed of a paddle-like member provided on the outer peripheral surface of the shaft member 36 so that a plurality of plate-like blade members (not shown) extend radially outward. ing. In this case, the size p1 of the screw pitch is set to be smaller than the screw pitch p in the case where the developer supply / recovery unit 35 is configured, so that the developer transport capability in the axial direction is greater than that of the developer supply / recovery unit 35. It is assumed to be low.
[0036]
The other developer agitating means (hereinafter referred to as “second developer agitating means”) 41 provided in the developer agitating section 33 has a developer conveying capability in the axial direction equivalent to that of the first developer agitating means or It is preferable that the first developer agitation means is used.
Specifically, as shown in FIG. 6, the second developer stirring means 41 is inclined on the outer peripheral surface of the shaft member 43 in different directions with respect to a plane perpendicular to the shaft member 43. The rotating member 45 includes a first stirring member 44A group and a second stirring member 44B group made of a plurality of semi-elliptical plates provided along each of the first and second stirring member arrangement level planes. The first stirring member 44A and the second stirring member 44B are both in a state of being spaced apart from each other in the axial direction at a predetermined arrangement pitch p.
The mounting angle α1 with respect to the shaft member 43 of the first stirring member 44A group and the mounting angle α2 with respect to the shaft member 43 of the second stirring member 44B group may be the same size or different sizes. The magnitudes of the mounting angles α1 and α2 can be appropriately set according to the purpose.
[0037]
In the developing device, it is preferable that the second developer agitation means 41 having a low ability to convey the developer in the axial direction is provided on the rear side with respect to the developer supply / recovery unit 32.
[0038]
In the developer agitating unit 33, the peripheral surfaces of the first developer agitating means 40 and the second developer agitating means 41 are arranged from above at the part where the two developer agitating means 40, 41 face each other. It is preferable that the first developer agitating means 40 and the second developer agitating means 41 are rotated by an appropriate driving mechanism so as to be moved in the forward direction toward each other.
In the illustrated developing device, the first developer agitating means 40 and the second developer agitating means 41 are driven in conjunction with each other.
[0039]
In this developing device, a two-component developer composed of toner and carrier is used.
The toner constituting the two-component developer is preferably one having a volume average particle diameter of 3 to 5 μm. By using a small particle diameter toner having a volume average particle diameter of 3 to 5 μm, a toner image having high resolution and excellent fine line reproducibility can be reliably formed. A toner image having a stable density can be reliably formed.
The carrier preferably has a volume average particle diameter of 5 × Dt to 10 × Dt [μm], where Dt [μm] is the volume average particle diameter of the toner. By using a carrier having a volume average particle size of 5 to 10 times the volume average particle size of the toner, the charge imparting performance of the carrier surface can be improved even when a small particle size toner is used. As a result, it is possible to reliably prevent the occurrence of fogging and toner scattering, and also to reliably prevent the occurrence of carrier adhesion. Therefore, an image having a uniform image density and a fine image quality. Can be definitely obtained.
[0040]
In the image forming apparatus described above, the developing process by the toner image forming unit 30 is performed in a state adjusted to operation setting conditions that satisfy the following conditions (A) and (B).
Condition (A); W ≧ M × V × L / 1000
Condition (b); R ≦ 600
[0041]
In the above conditions (a) and (b), V is the peripheral speed [mm / sec] of the latent image carrier 21, and M is the maximum per unit area of the toner image formed on the latent image carrier 21. Adhesion amount [mg / cm²], L is the maximum width [mm] of the toner image formed on the latent image carrier 21 in the direction (axial direction) orthogonal to the moving direction of the latent image carrier 21, and W is the developer supply / recovery unit The developer movement amount [g / sec] with respect to the axial direction by the developer supply / recovery means 35 at 32 and R indicates the number of rotations of the developer supply / recovery means 35, respectively.
[0042]
When the developer movement amount W in the axial direction by the developer supply / recovery means 35 is excessively small, the toner in the developer in the developer supply area on the downstream side in the developer transport direction by the developer supply / recovery means 35. The density decreases and it becomes difficult to supply a sufficient amount of toner to the development region, and image density unevenness tends to occur.
When the rotation speed R of the developer supply / recovery means 35 is excessive, the shaft is heated, so that the developer is likely to deteriorate, and it is difficult to reliably form an image with high image quality.
[0043]
In the above image forming apparatus, an image forming operation is performed as follows.
That is, first, in each of the toner

image forming units

20Y, 20M, 20C, and 20K, the charging process by the charging unit 22 and the exposure process by the exposure unit 23 are performed, and the electrostatic image corresponding to the document image is formed on the latent image carrier 21. A latent image is formed, and development processing is performed by the toner image forming unit 30 to form each color toner image on each latent image carrier 21.
Specifically, when the developing process of the electrostatic latent image by the toner image forming unit 30 is performed, the developer agitating unit 33 performs the first developer agitating unit in the process of transporting the developer in the axial direction. 40 and the second developer agitating means 41 are agitated in the circumferential direction, whereby the toner is introduced into the developer supply / recovery unit 32 in a state of being triboelectrically charged so as to have a predetermined charge amount. In the developer supply / recovery unit 32, the developer is supplied and collected in the axial direction while being circumferentially agitated by the developer supply / recovery means 35, supplied to the entire surface of the developer carrier 34 in the axial direction, and then on the developer carrier 34. The magnetic brush is carried in a formed state, and the magnetic brush is cut off by the developer regulating member 39 and conveyed to the developing area in a state where the magnetic brush is regulated to an appropriate amount. Then, when the magnetic brush is brought into contact with the surface of the latent image carrier 21, the toner adheres in accordance with the electrostatic latent image formed on the latent image carrier 21, and development is performed, whereby a toner image is formed. The
The developer that has been supplied to the developer carrier 34 and has consumed the toner in the developing region is not supplied to the developer carrier 34 and remains in the developer supply / recovery unit 32, together with the developer supply / recovery means. 35, for example, based on the toner concentration detected by detecting the magnetic permeability of the developer by a toner concentration sensor provided downstream of the developer supply / recovery unit 32. Then, new toner corresponding to the amount of toner consumption is supplied to the developer agitating unit 33 by the toner supply mechanism.
[0044]
Each color toner image is sequentially primary transferred and superimposed on the intermediate transfer belt 10 by the primary transfer mechanism 24 to form a color toner image on the intermediate transfer belt 10, and the color toner image is formed on the intermediate transfer belt 10. In the secondary transfer area, the secondary transfer area is secondarily transferred onto the transfer material P conveyed by the secondary transfer mechanism 26, and then fixed by a fixing means (not shown). Processing is performed, whereby a visible image is formed.
[0045]
Thus, according to the image forming apparatus having the above-described configuration, the toner image forming unit 30 includes the developer by the first developer stirring unit 40, the second developer stirring unit 41, and the developer supply / recovery unit 35. The first developer agitating means 40 and the second development are balanced by circulating and conveying the developer (the former two and the latter have the same developer conveying ability). The developer agitating means 41 both agitates the developer in the circumferential direction to raise the toner charge, so that the developer conveyance speed is reduced during the process of conveying the developer in the axial direction. As a result of securing a sufficient mixing and stirring time in the developer stirring unit 33 without causing the toner to stir, the toner has a desired charge (charge amount) due to the developer stirring and mixing operation in the developer stirring unit 33. In a state of being charged to be supplied to the developer carrying member 34 with a uniform toner density with respect to the axial direction by the developer supplying and collecting means 35.
Specifically, the developer transport amount in the axial direction by the developer supply / recovery means is shared by both the first developer stirring means 40 and the second developer stirring means 41 to balance the developer transport speed. Therefore, the individual conveying speeds of the first developer agitating means 40 and the second developer agitating means 41 are compared with those having a structure in which the balance of the conveying speed is ensured by one developer agitating means. As a result, a sufficient mixing and stirring time is ensured without reducing the developer transport speed of the entire developing device, and the developer is fed from the developer stirring unit 33 to the developer supply and recovery unit 32. The developer is in a state where the toner is charged to a state where the toner has a desired charge amount.
Accordingly, the latent image on the latent image carrier 21 is developed in a state in which the developer charged in the desired state is supplied to the developer carrier 34 with a uniform toner density in the axial direction. Occurrence of fogging and toner scattering due to poor charging of toner is reliably prevented, and occurrence of uneven image density in the obtained visible image is reliably prevented, and a high-quality image with a well-balanced image density and color balance is ensured. can get.
The second developer agitation means 41 is configured with a developer agitation ability higher than that of the first developer agitation means 40, so that the above effect can be obtained with certainty.
[0046]
Further, by simply using a rotating member having a high developer stirring performance as a developer stirring means, the toner can be quickly charged to the desired state (the toner charge rising characteristic is steep). However, according to the developing device having the above-described configuration, the first developer agitating means 40 and the second developer agitating means 41 are arranged at a portion where the two developer agitating means 40 and 41 are opposed to each other. A structure in which each peripheral surface is rotated so as to move in the forward direction from the upper side to the lower side, and the toner is replenished from above the portion where the two

developer agitating units

40 and 41 are opposed (the toner is freely dropped). As a result, the sinking of the replenishment toner into the developer at the toner replenishment position is accelerated, so that the replenishment toner is uniformly dispersed in the developer. The toner can be reliably charged in a state having a desired charge amount in parts.
[0047]
In addition, since the development process is performed in a state where the specific condition (a) and the condition (b) are satisfied, the developer has no toner density unevenness in the axial direction, in other words, the toner density difference in the axial direction is extremely high. In a small state, the image can be supplied to the development area, and an image having a uniform image density without uneven image density can be obtained. Further, when the rotation speed R of the developer supply / recovery means 35 is set to 600 rpm or less (condition (b)), when the developer supply / recovery means 35 is rotated at a high speed, the shaft portion is heated and developed. It is possible to reliably prevent the agent from deteriorating.
[0048]
As described above, according to the image forming apparatus having the above configuration, even when a developer in which a large amount of toner is consumed and toner is replenished by continuously outputting an image with a high printing rate is used, The toner and the carrier are sufficiently mixed and agitated to obtain a sufficient charge rising characteristic of the toner, and the developer is supplied to the development region with a uniform toner concentration in the axial direction. Even when the image forming operation is performed at a process speed such that the number of printed sheets per minute is 50 sheets or more, an image having a uniform image density with no fogging and toner scattering and no uneven image density. Can be reliably formed.
[0049]
Further, since the second developer agitation means 41 having a low conveying ability in the axial direction of the developer is provided on the rear side with respect to the developer supply / recovery unit 32, the developer supply / recovery unit 32 and the developer agitation The stagnation of the developer that is likely to occur in the vicinity of the communicating portion with the portion 33 is reliably prevented, and the developer is circulated and conveyed smoothly, whereby the developer is uniformly distributed in the axial direction. The image can be supplied to the developer carrier 34 with a density, and an image with high image quality without uneven image density can be formed.
[0050]
The preferred embodiment of the present invention has been described above. In the developing device of the present invention, the first developer agitating means 40 and the second developer agitating means 41 provided in the developer agitating unit 33 are: None of them is limited to the above-mentioned configuration, and has a developer conveying capability in the axial direction set in relation to the developer supply and recovery means, and between the developer conveying capability and the developer. If the stirring ability satisfies the predetermined relationship, a practically sufficient effect can be obtained.
[0051]
For example, the first developer agitation unit 40 and the second developer agitation unit 41 may be configured as shown in FIGS.
Each of the rotating members shown in FIGS. 7 to 9 has the same basic configuration as the rotating member made of a helical screw shown in FIG. It is higher than that shown in FIG.
[0052]
The rotating member 50A shown in FIG. 7 has a main stirring member 52 formed of a spiral blade member that spirally extends at a pitch p having a predetermined size in the axial direction over the entire outer periphery of the shaft member 51. In addition, one auxiliary stirring member 53 made of a rod-like or plate-like vertical blade member extending radially outward is provided on the outer peripheral surface of the shaft member 51 for each screw pitch P. . The auxiliary stirring member 53 is disposed at a central position in the axial direction between the screw pitches of the main stirring member 52.
[0053]
The rotating member 50B shown in FIG. 8 includes a main agitating member 55 made of a spiral blade member that spirally extends at a pitch p having a predetermined size in the axial direction over the entire circumference of the outer peripheral surface of the shaft member 54. A plurality of auxiliary stirring members 56 (for example, rod-like or plate-like vertical blade members extending outward in the radial direction on the outer peripheral surface of the shaft member 54 between the screw pitches P of the main stirring member 55 (for example, 4) are provided at positions spaced apart from each other at equal intervals in the circumferential direction.
[0054]
The rotating member 50 </ b> C shown in FIG. 9 is a stirring member 58 composed of a spiral blade member formed so as to extend spirally at a pitch p having a predetermined size in the axial direction over the entire outer periphery of the shaft member 57. And a notch 59 extending in the axial direction is formed in the outer peripheral edge of the stirring member 58. In this example, the notches 59 are formed, for example, at four positions per screw pitch, at positions spaced apart at equal intervals in the circumferential direction.
[0055]
In the present invention, the first developer agitating means 40 and the second developer agitating means 41 have a higher developer agitating ability from the viewpoint that a sufficient toner charge rising characteristic can be obtained with certainty. ,preferable.
[0056]
FIG. 10 and FIG. 11 are perspective views showing a more preferable configuration example of the rotating member used as the first developer stirring means 40 and the second developer stirring means 41 in the developing device of the present invention.
[0057]
The rotating member 60 shown in FIG. 10 has a main stirring member 62 formed so as to extend spirally at a pitch p having a predetermined size in the axial direction over the entire circumference of the outer peripheral surface of the shaft member 61. Auxiliary stirring means 63 made of a plate-like rib member provided so as to extend in the axial direction at a position separated from the member 61 in the radial direction, specifically, at the outer peripheral edge of the main stirring means 62 It is.
In this rotating member 60, four auxiliary stirring means 63 are provided at positions spaced apart at equal intervals in the circumferential direction.
[0058]
The rotating member 70 shown in FIG. 11 has a basic configuration similar to that of the rotating member 45 shown in FIG. 6, and includes a semi-elliptical plate-like first stirring member 72A and a second stirring member. The auxiliary stirring member 73 which consists of a plate-shaped rib member provided so that it may extend in the axial direction along the shaft member 71 in the outer periphery part of the member 72B is formed.
In this rotating member 70, four auxiliary stirring means 73 are provided at positions spaced apart at equal intervals in the circumferential direction.
[0059]
These rotating members 60 and 70 are rotated around the

shaft members

61 and 71, and thus are stirred in the circumferential direction by the main stirring member in the process in which the developer in the developer stirring unit 33 is conveyed in the axial direction. And is stirred in the circumferential direction by

rib members

63 and 73 as auxiliary stirring members.
[0060]
According to the developing device in which the developer agitating means is constituted by the rotating members 60 and 70 having the auxiliary agitating

members

63 and 73 as described above, the operation and effect as described above can be obtained more reliably, and toner charging can be performed. The occurrence of fog and toner scattering due to defects is reliably prevented, and image density unevenness due to non-uniformity of the toner density in the axial direction of the developer supplied to the developer carrier 34 is reliably prevented. The
Therefore, according to the image forming apparatus provided with such a developing device, the developer charged in a state where the toner is sufficiently stirred and the toner has a predetermined charge amount is axially applied to the developer carrier 34. Since the latent image on the latent image carrier 21 is developed with a uniform toner density, problems such as toner scattering, fogging, and uneven image density are surely prevented, and high-quality images can be obtained. Is definitely obtained.
[0061]
In the above, the case where the present invention is applied to an image forming apparatus for forming a color image including a plurality of toner image forming units has been described. However, the present invention is not limited to the image forming apparatus having such a configuration. The present invention can be effectively applied to various configurations. For example, even when the present invention is applied to an image forming apparatus for forming a monochrome image, the above operations and effects are not reduced.
[0062]
Second Embodiment
The image forming apparatus according to the second embodiment of the present invention includes a toner recycling unit that collects and reuses the toner removed by the latent image carrier cleaning unit in the toner image forming unit.
FIG. 12 is an explanatory diagram showing an outline of the configuration of the image forming apparatus of the present invention.
The image forming apparatus includes a rotating drum-shaped latent image carrier 110, and along the outer peripheral surface of the latent image carrier 110, a charging unit 111, an exposure unit 112, a toner image forming unit 120, a transfer unit. The means 113, the separating means 114, and the latent image carrier cleaning means 115 are each arranged side by side in the operation order with respect to the rotation direction of the latent image carrier 110. A toner recycling unit 130 having a collecting and conveying unit 131 for collecting the toner removed from the latent image carrier 110 to the toner image forming unit 120 is provided. In FIG. 12, reference numeral 132 denotes a conveyance unit that conveys the toner scraped off from the latent image carrier 110 by the latent image carrier cleaning unit 115 in the axial direction of the latent image carrier 110.
For example, as shown in FIG. 13, the toner image forming means 120 in this image forming apparatus has the same basic configuration as the toner image forming means (FIGS. 2 to 4) 30 in the first embodiment. In the top plate 31B of the protruding portion 31A of the housing 31, the first developer agitating means 40 and the second developer agitating means 41 are positioned above the portions facing each other, and The toner collected by the toner recycling means 130 (hereinafter referred to as “recycled toner”) is placed in the developer stirring section 33 at a position upstream of the toner supply opening 31 </ b> C in the developer transport direction by the developer stirring means 40. A recycled toner mixing opening 133 for mixing is formed.
[0063]
The position where the recycled toner mixing opening 133 is formed satisfies the predetermined order with the position of the toner supply opening 31C for new toner by the toner replenishment mechanism in the developer transport direction in the developer agitating unit 33. Although it is not particularly limited, it may be formed at a position 5 to 30 mm upstream from the formation position of the toner supply opening 31 </ b> C with respect to the developer transport direction in the developer stirring unit 33. Practically preferred.
[0064]
The recycled toner is mixed into the developer agitation unit 33 in a state where the supply amount is adjusted so that the ratio of the recycled toner to the new toner in the developer (recycled toner ratio) is maintained at 50% by mass or less. The
[0065]
According to the developing device having the above configuration, basically, as described above, in the developer agitating unit 33, the developer is transported in the axial direction. Since a proper mixing and stirring time is ensured, the developer is supplied to the developer in a state where the toner is charged to a state having a predetermined charge (charge amount) by the developer mixing and stirring operation in the developer stirring unit 33. The collecting means 35 can supply the developer carrier 34 with a uniform toner density in the axial direction, and the recycled toner mixing opening 133 is for supplying toner in the developer transport direction in the developer agitating portion 33. Since it is formed on the upstream side of the opening 31C, it has poor fluidity and low chargeability compared to the new toner (it is difficult to be charged and charge rise is poor). Since a long stirring time can be secured, sufficient charge rising characteristics can be obtained even with recycled toner, and therefore, fogging and toner scattering due to poor charging of the toner can be surely prevented and obtained. It is possible to reliably prevent the occurrence of image density unevenness in the visible image.
Therefore, according to the image forming apparatus provided with such a developing device, for example, development in which a large amount of toner consumption and toner supply including recycled toner are repeatedly performed by continuously outputting images with a high printing rate. Even when the agent is used, the toner and the carrier are sufficiently mixed and agitated to obtain sufficient charge rising characteristics of the toner, and the developer can be developed at a uniform toner concentration in the axial direction. Therefore, even when the image forming operation is performed at a high speed, for example, at a process speed such that the number of printed sheets per minute is 50 sheets or more, fog or toner scattering does not occur, and the image It is possible to reliably form a high-quality image having a uniform image density without density unevenness.
[0066]
As mentioned above, although embodiment of this invention was described, this invention is not limited to said aspect, A various change can be added.
For example, the specific configuration of the rotating member constituting the developer supply / recovery means, the first developer stirring means, and the second developer stirring means, for example, the pitch of the spiral blade member, the auxiliary stirring member The shape and size, the number of rotations of the rotating member (conveying speed with respect to the axial direction of the developer), and other configurations can be appropriately set according to the purpose.
Further, the first developer agitation unit and the second developer agitation unit may be configured to be rotated by mutually independent drive mechanisms.
[0067]
Below, the experiment example performed in order to confirm the effect of this invention is demonstrated.
[0068]
(Production of rotating member)
Rotating members (rotating members A to R) used as a developer supply / recovery unit, a first developer agitation unit, and a second developer agitation unit were produced.
[0069]
(Rotating member A)
According to the configuration shown in FIG. 5, a spiral blade member (stirring member) is formed on the outer peripheral surface of the shaft member so as to roll up rightward (left-handed) to produce a spiral screw. A paddle-shaped rotation in which an agitating member made of four flat blade members is provided on the outer peripheral surface of the shaft member in a state of extending radially outward in an end region extending 30 mm in length on the downstream side in the developer conveyance direction Member A was produced. And the disk-shaped flange member whose outer diameter dimension is 24 mm was provided in the both ends of this rotation member A in the state which penetrated the shaft member. Specific specifications of the rotating member A are as follows.
Maximum outer diameter (d): 24 mm, length in the rotation axis direction excluding the shaft (size of the region where the spiral blade member and the plate blade member are provided): 440 mm, outer diameter of the shaft member: 6 mm, spiral Screw pitch (p) of blade member: 30 mm, thickness of spiral blade member: 1 mm
[0070]
(Rotating member B)
In the rotating member A, a rotating member B having the same configuration as that of the rotating member A was produced except that the spiral blade member was formed on the outer peripheral surface of the shaft member so as to wind up in the upper left direction (right winding).
[0071]
(Rotating member C)
In accordance with the configuration shown in FIG. 9, the spiral blade member (stirring member) is formed on the outer peripheral surface of the shaft member so as to wind upward (left-handed), and a notch is formed on the outer peripheral edge of the spiral blade member. A spiral screw is formed, and at the end region extending 30 mm downstream in the developer transport direction by the spiral blade member, four flat stirring members are radially arranged on the outer peripheral surface of the shaft member. A paddle-shaped rotating member C provided so as to extend outward was produced. And the disc-shaped flange member whose outer diameter dimension is 24 mm was provided in the both ends of this rotation member C in the state which penetrated the shaft member. Specific specifications of the rotating member C are as follows.
Maximum outer diameter (d): 24 mm, length in the rotation axis direction excluding the shaft (size of the region where the spiral blade member is provided): 440 mm, outer diameter of the shaft member: 6 mm, screw pitch of the spiral blade member (P): 30 mm, thickness of the spiral blade member: 1 mm, radial length of the notch (t): 5 mm, circumferential length of the notch (w): 2 mm, formation location of the notch: per pitch 4 points are formed at equal intervals in the circumferential direction
[0072]
(Rotating member D)
In the rotating member C, a rotating member D having the same configuration as that of the rotating member C was prepared except that the screw pitch of the spiral blade member was 20 mm.
[0073]
(Rotating member E)
In accordance with the configuration shown in FIG. 7, a plurality of plate-like members having a spiral blade member (main stirring member) formed on the outer peripheral surface of the shaft member so as to wind up to the upper right (left-handed) and extending radially outward A spiral screw having a vertical blade member (auxiliary stirring member) is prepared, and four plate-like stirring members are pivoted on an end region extending 30 mm in length on the downstream side in the developer transport direction by the spiral blade member. A rotating member E having a paddle shape formed on the outer peripheral surface of the member so as to extend radially outward was produced. And the disc-shaped flange member whose outer diameter dimension is 24 mm was provided in the both ends of this rotation member E in the state which penetrated the shaft member. Specific specifications of the rotating member E are as follows.
Maximum outer diameter (d): 24 mm, length in the rotation axis direction excluding the shaft (size of the region where the spiral blade member is provided): 440 mm, outer diameter of the shaft member: 6 mm, screw pitch of the spiral blade member (P): 30 mm, thickness of the spiral blade member: 1 mm, arrangement position of the vertical blade member: one arranged per pitch, at the center position between the pitches of the helical blade member, direction of the rotation axis of the vertical blade member Length (w): 3 mm, radial length of vertical blade member (h): 8 mm
[0074]
(Rotating member F)
In the rotating member E, a rotating member F having the same configuration as the rotating member E was produced except that the screw pitch of the spiral blade member was set to 20 mm.
[0075]
(Rotating member G)
In accordance with the configuration shown in FIG. 8, a plurality of plate-like members having a spiral blade member (main stirring member) formed on the outer peripheral surface of the shaft member so as to wind up to the upper right (left-handed) and extending radially outward A spiral screw having a vertical blade member (auxiliary stirring member) is prepared, and four plate-like stirring members are pivoted on an end region extending 30 mm in length on the downstream side in the developer transport direction by the spiral blade member. A rotating member G having a paddle shape provided on the outer peripheral surface of the member so as to extend radially outward was produced. And the disk-shaped flange member whose outer diameter dimension is 24 mm was provided in the both ends of this rotation member G in the state which made the shaft member penetrate. Specific specifications of the rotating member G are as follows.
Maximum outer diameter (d): 24 mm, length in the rotation axis direction excluding the shaft (size of the region where the spiral blade member is provided): 440 mm, outer diameter of the shaft member: 6 mm, screw pitch of the spiral blade member (P): 30 mm, thickness of the spiral blade member: 1 mm, arrangement position of the vertical blade member: four positions per pitch, the center position between the pitches of the spiral blade member at equal intervals in the circumferential direction , The vertical blade member rotational axis length (w): 3 mm, the vertical blade member radial length (h): 8 mm
[0076]
(Rotating member H)
In the rotating member G, a rotating member H having the same configuration as that of the rotating member G was manufactured except that the length (w) of the vertical blade member in the rotation axis direction was 20 mm.
[0077]
(Rotating member I)
In accordance with the configuration shown in FIG. 10, it has a spiral blade member (main stirring member) formed on the outer peripheral surface of the shaft member so as to wind up to the upper right (left-handed), and a shaft member at the outer peripheral edge of the spiral blade member A spiral screw having two flat rib members (auxiliary stirring members) each formed in a position opposed to each other and extending in the rotation axis direction is manufactured, and developer is conveyed by the spiral blade member A rotating member I having a paddle shape in which four flat stirring members are provided on the outer peripheral surface of the shaft member in a radially outward direction in an end region extending 30 mm in length on the downstream side in the direction was produced. And the disk-shaped flange member whose outer diameter dimension is 24 mm was provided in the both ends of this rotation member I in the state which made the shaft member penetrate. Specific specifications of the rotating member I are as follows.
Maximum outer diameter: 24 mm, length in the rotation axis direction excluding the shaft (size of the region where the spiral blade member and the plate blade member are provided): 440 mm, the outer diameter of the shaft member: 6 mm, the spiral blade member Screw pitch (p): 30 mm, thickness of spiral blade member: 1 mm, radial length of rib member (t): 3 mm
[0078]
(Rotating member J)
In the rotating member I, a rotating member J having the same configuration as the rotating member I was prepared except that the radial length (t) of the rib member was 5 mm.
[0079]
(Rotating member K)
Rotating member I has a configuration similar to that of rotating member I except that four rib members are provided at equal intervals in the circumferential direction on the outer peripheral edge of the spiral blade member. Member K was produced.
[0080]
(Rotating member L)
In the rotating member I, the spiral blade member (stirring member) was formed on the outer peripheral surface of the shaft member so as to wind up in the upper left (right-handed), and the screw pitch (p) of the spiral blade member was 20 mm. A rotating member L having the same configuration as that of the rotating member I was prepared.
[0081]
(Rotating member M)
In the rotating member I, the spiral blade member (stirring member) is formed on the outer peripheral surface of the shaft member so as to wind up to the upper left (right-handed), and the radial length (t) of the rib member is 5 mm. A rotating member M having the same configuration as that of the rotating member I was prepared.
[0082]
(Rotating member N)
In the rotating member I, the spiral blade member (stirring member) is formed on the outer peripheral surface of the shaft member so as to roll up to the upper left (right-handed), and four rib members are formed on the outer peripheral edge of the spiral blade member. A rotating member N having the same configuration as that of the rotating member I was manufactured except that the rotating member I was provided at positions spaced at equal intervals in the circumferential direction.
[0083]
(Rotating member O)
According to the configuration shown in FIG. 6, a plurality of semi-elliptical plates provided along each of the first and second stirring member disposition level planes inclined in different directions with respect to the plane perpendicular to the shaft member A rotating member O having a first stirring member group and a second stirring member group was produced. And the disk-shaped flange member whose outer diameter dimension is 24 mm was provided in the both ends of this rotation member O in the state which penetrated the shaft member. Specific specifications of the rotating member O are as follows.
Maximum outer diameter (d): 24 mm, length in the rotation axis direction excluding the shaft portion (size of region where the stirring member is provided): 440 mm, outer diameter of the shaft member: 6 mm, shaft member of the first stirring member group Mounting angle (α1): −45 °, mounting angle (α2) of the second stirring member group with respect to the shaft member: + 45 ° (inclined in the opposite direction to the first stirring member group), pitch of the stirring members ( p): 25 mm
[0084]
(Rotating member P)
In the rotating member O, the mounting angle (α1) of the first stirring member group with respect to the shaft member and the mounting angle (α2) of the second stirring member group with respect to the shaft member are respectively opposite to those of the rotating member O with respect to the shaft member. A rotating member P having the same configuration as that of the rotating member O was manufactured except that the state was inclined in the direction (α1 = + 45 °, α2 = −45 °).
[0085]
(Rotating member Q)
According to the configuration shown in FIG. 11, a plurality of semi-elliptical plates provided along each of the first and second stirring member arrangement level planes inclined in different directions with respect to the plane perpendicular to the shaft member While having the first stirring member group and the second stirring member group, in the outer peripheral edge portion of the first stirring member group and the second stirring member group, at positions spaced apart at equal intervals in the circumferential direction, A rotating member Q having four plate-like auxiliary stirring members extending in the axial direction was produced. And the disk-shaped flange member whose outer diameter dimension is 24 mm was provided in the both ends of this rotation member Q in the state which penetrated the shaft member. Specific specifications of the rotating member Q are as follows.
Maximum outer diameter (d): 24 mm, length in the rotation axis direction excluding the shaft portion (size of region where the stirring member is provided): 440 mm, outer diameter of the shaft member: 6 mm, shaft member of the first stirring member group Mounting angle (α1): −45 °, mounting angle (α2) of the second stirring member group with respect to the shaft member: + 45 ° (inclined in the opposite direction to the first stirring member group), pitch of the stirring members ( p): 25 mm, length of auxiliary stirring member in radial direction (t): 3 mm
[0086]
(Rotating member R)
In the rotating member Q, the mounting angle (α1) of the first stirring member group with respect to the shaft member and the mounting angle (α2) of the second stirring member group with respect to the shaft member are respectively opposite to the rotating member Q with respect to the shaft member. A rotating member R having the same configuration as that of the rotating member Q was manufactured except that the state was inclined in the direction (α1 = + 45 °, α2 = −45 °).
[0087]
<Experimental example 1>
[Production of development device]
According to the configuration shown in FIGS. 2 to 4, according to the present invention, the developer supply / recovery means, the first developer stirring means, and the second developer stirring means are constituted by rotating members selected according to Table 1 below. Developing devices 1 to 8 were produced.
Further, the first developer agitation means and the second developer agitation means selected according to the following Table 1 are rotated so that the respective peripheral surfaces move in the forward direction from the lower side to the upper side at the portions facing each other. A comparative developing device 9 set as described above was produced.
Further, as shown in FIG. 14, it has the same configuration as that shown in FIG. 2 except that it does not have the second developer stirring means, and the developer supply / recovery means and the first stirring and conveying means. Comparative developing devices 10 to 19 each having a rotating member selected according to the combination shown in Table 1 were prepared.
[0088]
The developing sleeve constituting the developer carrying member has an outer diameter of 30 mm and an axial length of 330 mm.
In each of the developing devices 1 to 8 and the comparative developing device 9 according to the present invention, the toner supply opening is formed at a position where the first developer agitating means and the second developer agitating means face each other. The upper position is a position 15 mm downstream from the upstream edge with respect to the developer transport direction in the developer stirring section.
In each of the developing devices 10 to 19 for comparison, the toner supply opening is formed at a position above the edge portion on the rear side of the first developer agitating means and developed by the first developer agitating means. The position is 15 mm downstream from the upstream edge in the agent transport direction.
[0089]
As the developer, any one of the developers related to yellow toner, magenta toner, cyan toner and black toner uses a two-component developer having a toner concentration of 7% by mass, and the developing device 1 according to the present invention is used. -8 and comparative developing device 9 were filled with 1100 g of developer, and comparative developing devices 10-19 were filled with 750 g of developer.
As for the toner, any of yellow toner, magenta toner, cyan toner and black toner has a volume average particle size of 4.5 ± 0.15 μm, a standard deviation (a) of particle size distribution and an average particle size (b). In each color polymerized toner having a CV value [a / b × 100%] of 18 ± 2%, a large particle size silica 0.8 mass%, a small particle size silica 0.2 mass%, a large particle size titania 0.2% by mass, 0.4% by mass of small particle size titania, and 0.05% by mass of calcium stearate were externally added.
As for the carrier, any of the developers related to yellow toner, magenta toner, cyan toner and black toner has a volume average particle diameter of 25 μm and a saturation magnetization of 60 emu / g. What was coated so that the coating amount with respect to the particles was 3% by mass was used.
[0090]
Each of the developing devices 1 to 8 and the comparative developing devices 9 to 19 according to the present invention is mounted on an appropriate single driving machine, and a developer supply and recovery unit, a first developer stirring unit, and a second developer stirring unit are mounted. The rotational speed of each of the means was set according to Table 1 below, and the amount of developer movement in the developer supply / recovery unit was measured. The results are shown in Table 1 below. The developer moving amount is measured by driving only the developer supply / recovery means, the first developer stirring means, and the second developer stirring means without driving the developing sleeve, and the developer supply / recovery means downstream. A developer discharge port was provided on the bottom surface of the developing device housing, and the weight of the developer discharged per unit time from the developer discharge port was measured.
[0091]
[Table 1]

[0092]
[Image forming apparatus]
In accordance with the configuration shown in FIG. 1, image forming apparatuses 1 to 19 for forming a color image on which each of the developing apparatuses 1 to 8 according to the present invention and the developing apparatuses 9 to 19 for comparison are mounted are manufactured. The output test was performed under the following image forming conditions. The image forming conditions were set to be the same for all of the toner image forming units related to the respective color toner images.
[0093]
<Image forming conditions>
-Process speed (V): 220 mm / sec (50 images output per minute)
・ Developing sleeve rotation speed: Adjusted within the range of 210 to 280 rpm, the toner adhesion amount (M) per unit area on the latent image carrier is 0.4 mg / cm²It became the state which becomes.
-The closest distance between the photosensitive member and the developing sleeve (developing gap): 0.3 mm
・ Development bias: an AC bias (AC) component superimposed on a DC bias component (DC),
AC bias component; Vac = 1 kVpp, fac = 5 kHz, waveform = sine wave
DC bias component: Control was performed so that Vdc = VL−500 V in accordance with the detection result of the surface potential VL of the maximum exposed portion of the photoreceptor.
・ Developer transport amount by developing sleeve: 25 ± 2 mg / cm²
-Magnetic brush formation width in the axial direction of the developing sleeve: 320 mm
Toner replenishment control: A toner concentration sensor (permeability sensor) is provided at a position 80 mm upstream from the edge on the downstream side of the developer conveyance direction by the supply screw, and the toner replenishment motor is controlled according to the detection result.
Toner replenishment speed: Max. 30 g / min
-Photoconductor surface potential:
Maximum exposure area potential (VL): -50V to -100V
Charging potential (unexposed portion potential) (VH): Control is performed so that VH = Vdc−150 V in accordance with the set value of the DC bias component in the developing bias.
[0094]
The image output test is performed by repeating the image output of the following (1) to (6) four times (total A4 × 2000), whether character / line pattern fogging occurs, character scattering occurrence, solid pattern density Evaluation of the occurrence of unevenness was performed based on the following evaluation criteria. The results are shown in Table 2 below.
(1) A procedure of outputting 50 sheets of cyan (C) single color characters / line + halftone (10 steps) pattern (printing rate 30%) continuously.
(2) A procedure for outputting 150 continuous patterns of cyan (C) (printing rate 80%).
(3) A procedure for continuously outputting 50 C single-color characters / line patterns (printing rate: 7%).
(4) A procedure in which 50 sheets of red (magenta (M) + cyan (C)) monochromatic character / line + halftone (10 steps) pattern (printing rate of 30% for both M and C) are output continuously.
(5) A procedure for continuously outputting 150 solid red solid patterns (printing rate of 80% for both magenta (M) and cyan (C)).
(6) A procedure for continuously outputting 50 red / magenta (M) + cyan (C)) single color characters / line patterns (printing rate: 7%).
[0095]
<Evaluation criteria>
(B) Image cover:
For image fogging, the relative reflection density of the white portion of the character / line pattern when the reflection density of unused paper is 0 is measured. If the relative reflection density is 0.004 or less, “○” is given. The case where the reflection density exceeded 0.004 and was 0.006 or less was evaluated as “Δ”, and the case where the relative reflection density exceeded 0.006 was evaluated as “x”.
[0096]
(B) Letter scattering:
For character scattering, the sharpness of the character outline and the degree of blurring of the character when the four-point “bell” character was observed in an enlarged manner were evaluated.
When the space of the “bell” character is clearly removed and the outline of the character is clear and the toner scattering around the character is extremely small, the space portion of the “bell” character is slightly crushed. If there is little toner splatter around the character ("Slightly scattered"), "△", "bell" character space is crushed (filled with toner scatter), and characters The case where there was a lot of toner scattering in the peripheral area and the outline of the character was blurred was designated as “X”.
[0097]
(C) Image density unevenness:
The image density unevenness was evaluated by the color difference (distance in L * a * b * space) at any nine positions in the page of the solid pattern of cyan monochrome or solid pattern of red. “○” indicates that the color difference at 9 locations for the cyan solid pattern is 3 or less and the color difference at 9 locations for the red solid pattern is 7 or less, 9 locations for the cyan solid pattern The color difference of 3 is more than 3 and 5 or less, and the color difference of 9 places for the solid solid pattern of red is 7 or less, or the color difference of 9 places for the solid pattern of cyan single color is 3 or less In addition, the color difference of 9 points for the solid pattern of red single color exceeds 7 and 9 or less is “△”, the color difference of 9 points for the solid pattern of cyan single color exceeds 3 and the color difference of red single color A case where the color difference at 9 locations of the solid pattern exceeded 9 was defined as “x”.
[0098]
(D) In-flight dirt:
In-machine contamination was evaluated by removing the developing device after completion of the image output test and visually observing the state of the contamination near the developing device mounting portion.
If no in-machine contamination is observed, or if only slight contamination is seen only on the developing device mounting part, “○”, and if there is slight contamination near the developing device mounting part (for example, both ends). “△”, and “x” when the stain on the developing device mounting portion extends to the peripheral portion (for example, the charging device).
[0099]
[Table 2]

[0100]
<Experimental example 2>
[Production of development device]
In each of the developing devices 1 to 5 and the comparative developing devices 10 to 19 used in Experimental Example 1, the recycled toner is mixed at a position 8 mm upstream from the toner supply port with respect to the developer transport direction in the developer stirring unit. Comparative development having the same configuration as the developing devices 20 to 24 according to the present invention and the developing devices 10 to 19 for comparison, having the same configuration as the developing devices 1 to 5 except that the opening for forming is formed Devices 25-34 were made.
[0101]
In accordance with the configuration shown in FIG. 12, each of the developing devices 20 to 24 according to the present invention and the developing devices 25 to 34 for comparison is mounted, and the image forming devices 20 to 20 for forming a monochrome image having toner recycling means are mounted. 34 was produced. The toner recycling means is configured such that the conveying means for conveying the recycled toner to the developing device has a maximum toner conveyance amount per unit time of 30 g / min.
For each of the image forming apparatuses 25 to 34, the process speed is set to 320 mm / sec (the number of image output sheets per minute is 65), and the developer supply and recovery means, the first developer agitation means, and the first 2 except that the rotation speeds of the developer agitating units 2 were set in accordance with the conditions shown in Table 3 below, under the same image forming conditions as those of the toner image forming unit relating to the black toner image of Experimental Example 1 (7 ) To (9) are repeated eight times (total A4 × 2000). By performing an image output test, the presence / absence of fogging of characters / line patterns, the presence / absence of character scattering, and the occurrence of internal dirt The presence / absence was evaluated based on the above evaluation criteria, and the presence / absence of occurrence of solid pattern image density unevenness was evaluated based on the following evaluation criteria. The results are shown in Table 4 below.
[0102]
(7) A procedure of outputting 50 black (BK) single-color characters / lines + halftone (10 steps) pattern (print rate 30%) continuously.
(8) A procedure for continuously outputting 150 black (BK) solid patterns (printing rate 80%).
(9) A procedure of outputting 50 black (BK) single color characters / line patterns (printing rate: 7%) continuously.
[0103]
<Evaluation criteria>
The image density unevenness is measured by measuring the relative reflection density at any nine locations in the page of the black solid pattern, and the relative reflection density at each of the nine locations for the black solid pattern is 1.3 or more, and the maximum value is The case where the difference from the minimum value is 0.1 or less is “◯”, the minimum value of the relative reflection density is 1.2 or more and less than 1.3, and the difference between the maximum value and the minimum value is 0.1. The case where it was below was evaluated as “Δ”, and the case where the minimum value of the relative reflection density was less than 1.2, or the difference between the maximum value and the minimum value exceeded 0.15 was evaluated as “x”.
[0104]
[Table 3]

[0105]
[Table 4]

[0106]
As is apparent from the above results, according to the image forming apparatus of the present invention, the development in which a large amount of toner consumption and toner replenishment including recycled toner are repeatedly performed by continuously outputting images with a high printing rate. Even when a developer is used, sufficient charge rising characteristics can be obtained with respect to the developer, and the developer can be supplied to the developer carrier with a uniform toner concentration in the axial direction. In addition, it was confirmed that image defects such as image density unevenness can be surely prevented, and the occurrence of in-machine contamination due to toner scattering can be reliably prevented, so that an image with high image quality can be reliably formed.
On the other hand, in the comparative image forming apparatus, at least one problem of image fogging, character scattering, image density unevenness, and in-machine contamination occurs, and a high-quality image cannot be obtained reliably. It was confirmed. In particular, in a monochrome image forming apparatus (Experimental Example 2) equipped with a toner recycling mechanism, the rotational speed of the rotating member is increased to obtain a sufficient developer moving speed, thereby causing uneven image density in the axial direction. In the case of the configuration to prevent, since the agitation torque has increased significantly, the image output test has to be stopped and an output image cannot be obtained. When this reason was investigated, it was confirmed that the developer started to be fused to the shaft portion.
[0107]
【The invention's effect】
According to the developing device of the present invention, a sufficient mixing and stirring time can be ensured in the developer agitating unit without reducing the developer conveying speed in the process of conveying the developer in the rotation axis direction. Therefore, in a state where the toner is charged to a state where the toner has a predetermined charge amount by the mixing and stirring operation of the developer in the developer stirring unit, the developer is uniformly concentrated in the axial direction by the developer supply and recovery means. Therefore, it is possible to reliably prevent the occurrence of fogging and toner scattering due to poor charging of the toner, and also reliably prevent the occurrence of image density unevenness in the obtained visible image. .
In addition, the two developer agitating means are driven to rotate so that their peripheral surfaces move in the forward direction from the upper side to the lower side at the portions where the two developer agitating means are opposed to each other, and the two developer agitating means are used. Since the toner is replenished from above the opposite portion of the means, the replenishment toner sinks into the developer at the toner replenishment position, so that the replenishment toner is uniformly dispersed in the developer. Thus, sufficient charge rising characteristics can be obtained for the replenishment toner.
[0108]
In addition, since the developer agitating means having substantially zero developer carrying capability in the rotation axis direction is arranged on the rear side with respect to the developer supply and recovery unit, the developer supply and recovery unit and the developer agitation unit are arranged. The developer is prevented from staying in the vicinity of the communication portion and the developer is circulated and transported smoothly, so that the developer is uniformly distributed in the axial direction. Can be supplied to the developer carrying member, and a uniform image without unevenness in image density can be formed more reliably.
[0109]
According to the image forming apparatus of the present invention, the developing device as described above is provided, and the developing process is performed in a state satisfying specific operation setting conditions, whereby sufficient agitation is performed and the toner is obtained. The developer charged to a state having a charge amount of 1 is supplied to the developer carrier with a uniform toner concentration in the rotation axis direction, and the latent image on the latent image carrier is developed. Even when a developer is used in which a large amount of toner is continuously output and toner replenishment including recycle toner is repeatedly used, the toner and the carrier are sufficiently mixed and agitated. In addition, the toner has excellent charge rise characteristics and is supplied to the development area with a uniform toner concentration in the axial direction, so that fog and toner scattering do not occur and the image density is uniform. An image of high quality having an image density can be reliably formed.
[Brief description of the drawings]
FIG. 1 is an explanatory diagram showing an outline of a configuration in an example of an image forming apparatus of the present invention.
FIG. 2 is a partial cross-sectional view illustrating an outline of a configuration in an example of a developing device of the present invention.
FIG. 3 is a longitudinal sectional view taken along the line AA in the developing device shown in FIG. 2;
4 is a vertical cross-sectional view of a BB cross section in the developing device shown in FIG. 2. FIG.
FIG. 5 is a plan view showing a configuration example of a rotating member constituting the developer supply / recovery means and the first developer agitation means.
FIG. 6 is a perspective view illustrating a configuration example of a rotating member that constitutes a second developer stirring unit.
FIG. 7 is a perspective view showing another configuration example of the rotating member constituting the first developer agitating unit and the second developer agitating unit.
FIG. 8 is a plan view showing still another configuration example of the rotating member constituting the first developer agitating unit and the second developer agitating unit.
FIG. 9 is a plan view showing still another configuration example of a rotating member constituting the first developer stirring unit and the second developer stirring unit.
FIG. 10 is a perspective view showing another configuration example of a rotating member constituting the first developer agitating unit and the second developer agitating unit.
FIG. 11 is a perspective view showing still another configuration example of the rotating member constituting the first developer agitating unit and the second developer agitating unit.
FIG. 12 is an explanatory diagram showing an outline of a configuration in another example of the image forming apparatus of the present invention.
FIG. 13 is a partial cross-sectional view schematically showing the configuration of another example of the developing device of the present invention.
14A and 14B are explanatory views showing an outline of a configuration of a comparative developing device used in an experimental example. FIG. 14A is a partial cross-sectional view, and FIG. 14B is a vertical cross-sectional view taken along the line aa in FIG. (C) is a longitudinal sectional view of the bb cross section in (A).
[Explanation of symbols]
10 Intermediate transfer member (intermediate transfer belt)
11, 12, 13, 14 Support roller
20Y, 20M, 20C, 20K toner image forming unit
21 Latent image carrier
22 Charging means
23 Exposure means
24 Primary transfer mechanism
25 Latent image carrier cleaning means
26 Secondary transfer mechanism
30 Toner image forming means
31 Housing
31A Protruding part
31B Top panel
31C Toner supply opening
32 Developer supply / recovery unit
33 Developer stirrer
34 Developer carrier
35 Developer supply / recovery means
36 Shaft member
37 Stirring member
38 Rotating member
39 Developer regulating member
40 First developer stirring means
41 Second developer stirring means
43 Shaft member
44A First stirring member
44B Second stirring member
45 Rotating member
P transfer material
50A, 50B, 50C Rotating member
51, 54, 57 Shaft member
52, 55 Main stirring member
53, 56 Auxiliary stirring member
58 Stirring member
59 Notch
60, 70 Rotating member
61, 71 Shaft member
62 Main stirring member
63, 73 Auxiliary stirring means
72A First stirring member
72B second stirring member
110 Latent image carrier
111 Charging means
112 Exposure means
113 Transfer means
114 Separation means
115 Latent image carrier cleaning means
120 Toner image forming means
130 Toner recycling means
131 Collecting and conveying means
132 Conveying means
133 Recycled toner mixing opening

Claims

A housing in which a developer supply and recovery unit and a developer agitation unit that are in communication with each other and form a circulation conveyance path for the two-component developer composed of toner and carrier are formed side by side in the front-rear direction, and the developer supply and recovery unit A developer carrier provided so as to face the latent image carrier through the developing region in the front portion, and the developer carrier facing the developer carrier in the rear portion of the developer supply / recovery unit. A developer supply / recovery means that is provided so as to extend along the rotation axis direction of the body, and that rotates and conveys the developer in the rotation axis direction; Two developer stirring means provided side by side in the front-rear direction so as to extend along the rotation axis direction of the collecting means,
The housing is provided with a toner supply opening at a position above the portion where the two developer agitating units in the developer agitating portion are opposed to each other and upstream of the developer agitating direction in the developer agitating portion. Formed,
The two developer agitating means in the developer agitating section are rotated so that the two developer agitating means are moved in the forward direction from the upper side to the lower side in the portions facing each other. In both cases, the developer is transported in the opposite direction to the developer supply / recovery means, and the total transport amount of the developer by each developer stirring means is the developer transport amount by the developer supply / recovery means. A developing device having an equivalent developer transport capability.

One developer agitation unit in the developer agitation unit has a developer conveying capability in the rotation axis direction that is equal to or lower than that of the other developer agitation unit, and is smaller than that of the other developer agitation unit. The developing device according to claim 1, wherein the developing device is provided on a rear side.

A housing in which a developer supply and recovery unit and a developer agitation unit that are in communication with each other and form a circulation conveyance path for the two-component developer composed of toner and carrier are formed side by side in the front-rear direction, and the developer supply and recovery unit A developer carrier provided so as to face the latent image carrier through the developing region in the front portion, and the developer carrier facing the developer carrier in the rear portion of the developer supply / recovery unit. In the developer supply / recovery means having a stirring member that is provided so as to extend along the rotation axis direction of the body and that extends in a spiral manner in the rotation axis direction over the entire circumference of the outer peripheral surface of the shaft member, Each provided with a first developer agitation means and a second developer agitation means, which are arranged in the front-rear direction so as to extend along the rotation axis direction of the developer supply and recovery means, facing each other,
The housing is provided with a toner supply opening at a position above the portion where the two developer agitating units in the developer agitating portion are opposed to each other and upstream of the developer agitating direction in the developer agitating portion. Formed,
The two developer agitating means in the developer agitating section are rotated so that the two developer agitating means are moved in the forward direction from the upper side to the lower side in the portions facing each other. In both cases, the developer is transported in the opposite direction to the developer supply / recovery means, and the total transport amount of the developer by each developer stirring means is the developer transport amount by the developer supply / recovery means. Has the same developer transport capability,
The second developer agitation means includes a first agitation member disposition level plane and a second agitation member disposition level that are inclined in different directions with respect to a plane perpendicular to the shaft member on the outer peripheral surface of the shaft member. A developing device comprising a plurality of semi-elliptical first stirring member groups and second stirring member groups provided along each of the planes.

The second developer agitation unit in the developer agitation unit has a developer conveyance capability in the rotation axis direction that is equal to or lower than that of the first developer agitation unit, and is supplied and recovered by the developer. The developing device according to claim 3, wherein the developing device is provided on a rear side with respect to the portion.

A housing in which a developer supply and recovery unit and a developer agitation unit that are in communication with each other and form a circulation conveyance path for the two-component developer composed of toner and carrier are formed side by side in the front-rear direction, and the developer supply and recovery unit A developer carrier provided so as to face the latent image carrier through the developing region in the front portion, and the developer carrier facing the developer carrier in the rear portion of the developer supply / recovery unit. In the developer supply / recovery means having a stirring member that is provided so as to extend along the rotation axis direction of the body and that extends in a spiral manner in the rotation axis direction over the entire circumference of the outer peripheral surface of the shaft member, Each provided with a first developer agitation means and a second developer agitation means, which are arranged in the front-rear direction so as to extend along the rotation axis direction of the developer supply and recovery means, facing each other,
The housing is provided with a toner supply opening at a position above the portion where the two developer agitating units in the developer agitating portion are opposed to each other and upstream of the developer agitating direction in the developer agitating portion. Formed,
The two developer agitating means in the developer agitating section are rotated so that the two developer agitating means are moved in the forward direction from the upper side to the lower side in the portions facing each other. The developer is transported in the opposite direction to the developer supply / recovery means, and the total transport amount of the developer by each developer stirring means is equal to the developer transport amount by the developer supply / recovery means. It has developer transport capability,
The second developer agitating means has an agitating member made of a rib provided so as to extend along the rotation axis direction on the outer peripheral surface of the shaft member or at a position radially separated from the shaft member. A developing device.

The second developer agitation unit in the developer agitation unit has a developer conveyance capability in the rotation axis direction that is equal to or lower than that of the first developer agitation unit, and is supplied and recovered by the developer. The developing device according to claim 5, wherein the developing device is provided on a rear side with respect to the portion.

In the developer supply / recovery unit, the peripheral surfaces of both the developer carrier and the developer supply / recovery means are moved in opposite directions at a portion where the developer carrier and the developer supply / recovery means face each other. The developing device according to claim 1, wherein:

A two-component developer comprising a toner having a volume average particle diameter of 3 to 5 μm and a carrier having a volume average particle diameter of 5 × Dt to 10 × Dt where the volume average particle diameter of the toner is Dt [μm]. The developing device according to claim 1, wherein the developing device is used.

In an image forming apparatus comprising: a latent image carrier; and a toner image forming unit that develops an electrostatic latent image formed on the latent image carrier to form a toner image.
The toner image forming unit includes the developing device according to any one of claims 1 to 8.
The moving speed of the latent image carrier is V [mm / sec], the maximum adhesion amount per unit area of the toner image formed on the latent image carrier is M [mg / cm ² ], and the latent image carrier is formed on the latent image carrier. The maximum width of the toner image in the direction orthogonal to the moving direction of the latent image carrier is L [mm], the developer movement amount with respect to the rotation axis direction by the developer supply and recovery means is W [g / sec], and the developer. An image forming apparatus characterized by satisfying the following condition (A) and condition (B) when the rotation speed of the supply and recovery means is R [rpm].
(Condition A) W ≧ M × V × L / 1000
(Condition B) R ≦ 600

A latent image carrier, toner image forming means for developing an electrostatic latent image formed on the latent image carrier to form a toner image, and a toner image on the latent image carrier as a transfer material or intermediate transfer member Transfer means for transferring to the toner, cleaning means for removing the toner remaining on the latent image carrier, and toner recycling means for collecting and reusing the toner removed from the latent image carrier to the toner image forming means. In the image forming apparatus,
The toner image forming unit includes the developing device according to any one of claims 1 to 8.
In the housing constituting the developing device, the two developer agitating units are located above the portions facing each other and upstream of the toner supply opening in the developer conveying direction in the developer agitating unit. An image forming apparatus, wherein an opening for mixing recycled toner for mixing toner collected by toner recycling means into a developer stirring unit is formed at a location.