JP3883240B2

JP3883240B2 - Development device

Info

Publication number: JP3883240B2
Application number: JP27952796A
Authority: JP
Inventors: 誠二岡; 康秋葉; 清典津田; 一小山
Original assignee: Ricoh Co Ltd
Current assignee: Ricoh Co Ltd
Priority date: 1995-11-14
Filing date: 1996-10-22
Publication date: 2007-02-21
Anticipated expiration: 2016-10-22
Also published as: JPH09197833A

Description

【０００１】
【発明の属する技術分野】
本発明は、画像形成装置における２成分現像剤を用いる現像装置に関する。
【０００２】
【従来の技術】
従来、トナー濃度検知手段を必要とせず、現像剤の動きによってトナーを取り込む現像装置が知られている。しかし、この現像装置では、現像剤の動きが活発な箇所とそうでない箇所、あるいは現像剤の多い箇所と少ない箇所においてトナーの取り込み量が異なり、部分的にトナー濃度が不安定となって画像濃度ムラやかぶりが発生し易い。そこで、トナーホッパー内に２つのトナー供給部材を配設し、各トナー供給部材で形成される経路に現像剤を通過させることにより、装置長手方向における濃度ムラやかぶりを解決する技術が特開昭６３−４２８２号公報に開示されている。
【０００３】
【発明が解決しようとする課題】
しかし、上記公報に開示された技術では、トナー供給部材を２つ使用するため、現像ユニットが大型化してしまうと共にコストアップしてしまうという問題点がある。
【０００４】
本発明は上記問題点を解決し、部品点数を低減させ、機能の集約化を行うことにより、小型化及び低コスト化を図りつつ品質の安定化を行うことができる現像装置の提供を目的とする。
【０００５】
【課題を解決するための手段】
請求項１記載の発明は、内部に磁界発生手段を有し、トナーと磁性キャリアとを含む２成分現像剤を担持して搬送する現像剤担持体と、前記現像剤担持体に担持されて搬送される前記現像剤の層厚を規制する第１の規制部材と、第１の規制部材よりも前記現像剤担持体上の現像剤の搬送方向上流側に配設された第２の規制部材と、第１の規制部材と第２の規制部材との間に位置する現像剤収容部と、第２の規制部材よりも前記現像剤担持体上の現像剤の搬送方向上流側に、前記現像剤担持体にトナーを供給する開口部を有するトナー収容部と、第２の規制部材によって規制された前記現像剤によって前記現像剤担持体上に循環移動する第一循環現像剤層が形成される空間と、前記現像剤収容部内には前記現像剤担持体上に形成された第一循環現像剤層とは異なる循環移動する第二循環現像剤層が形成される空間とを備える共に、第２の規制部材は前記二つの空間を仕切る仕切り部材として機能し、前記現像剤収容部に侵入した前記現像剤担持体上の現像剤のトナー濃度の変化により、第２の規制部材により規制される現像剤量を変化させて、前記現像剤担持体上の現像剤のトナー取り込み状態を変化させることを特徴とする。
【０００６】
請求項２記載の発明は、請求項１記載の現像装置において、さらに、前記現像剤収容部内に侵入した前記現像剤担持体上の現像剤のトナー濃度が所定のトナー濃度となった際に、第２の規制部材により通過を規制された現像剤が前記現像剤担持体上の現像剤と前記トナーとの接触部に溜まり、該現像剤が前記接触部を塞ぐことにより前記現像剤担持体上の現像剤のトナー取り込み状態を停止させることを特徴とする。
【０００７】
請求項３記載の発明は、トナーと磁性キャリアとを含む２成分現像剤を貯留する現像剤収容部と、潜像担持体と対向配置され、内部に磁界発生手段を備えた回動自在の現像剤担持体と、前記現像剤担持体上に担持された前記現像剤の層厚を規制する第１の規制部材と、トナー収容部とを具備し、前記現像剤収容部内における前記現像剤の移動により、前記現像剤と接触すべく前記トナー収容部内に貯留されたトナーを前記現像剤収容部内に取り込む現像装置において、第１の規制部材よりも前記現像剤担持体上の現像剤の搬送方向上流側に配設された第２の規制部材と、第２の規制部材によって規制された前記現像剤によって前記現像剤担持体上に循環移動する第一循環現像剤層が形成される空間と、前記現像剤収容部内には前記現像剤担持体上に形成された第一循環現像剤層とは異なる循環移動する第二循環現像剤層が形成される空間とを有し、前記現像剤収容部の内壁から前記現像剤担持体表面までの最大距離よりも、第２の規制部材の前記現像剤担持体表面に最も近い部分から前記現像剤担持体表面までの距離を小さくすると共に、第２の規制部材は前記二つの空間を仕切る仕切り部材として機能し、前記現像剤収容部に侵入した前記現像剤担持体上の現像剤のトナー濃度の変化により、第２の規制部材により規制される現像剤量を変化させて前記現像剤担持体上の現像剤のトナー取り込み状態を変化させることを特徴とする。
【０００８】
請求項４記載の発明は、トナーと磁性キャリアとからなる２成分現像剤を貯留する現像剤収容部と、潜像担持体と対向配置され、内部に磁界発生手段を備えた回動自在の現像剤担持体と、前記現像剤担持体上に担持された前記現像剤の層厚を規制する第１の規制部材と、トナー収容部と、第２の規制部材によって規制された前記現像剤によって前記現像剤担持体上に循環移動する第一循環現像剤層が形成される空間と、前記現像剤収容部内には前記現像剤担持体上に形成された第一循環現像剤層とは異なる循環移動する第二循環現像剤層が形成される空間とを具備し、前記現像剤収容部内における前記現像剤の移動により、前記現像剤と接触すべく前記トナー収容部内に貯留されたトナーを前記現像剤収容部内に取り込む現像装置において、前記現像剤担持体表面までの距離が最大となる前記現像剤収容部の内壁面の部位よりも前記現像剤担持体の回転方向上流側の位置に、前記現像剤担持体表面と対向すべく、前記現像剤収容部内に入り込む前記トナーの量を規制する第２の規制部材を配設し、前記現像剤収容部の内壁から前記現像剤担持体表面までの最大距離よりも、第２の規制部材の前記現像剤担持体表面に最も近い部分から前記現像剤担持体表面までの距離を小さくすると共に、第２の規制部材は前記二つの空間を仕切る仕切り部材として機能し、前記現像剤収容部に侵入した前記現像剤担持体上の現像剤のトナー濃度の変化により、第２の規制部材により規制される現像剤量を変化させて、前記現像剤担持体上の現像剤のトナー取り込み状態を変化させることを特徴とする。
【００２１】
【実施例】
図１は、本発明の第１の実施例を採用した画像形成装置の現像装置要部の概略構成図である。
潜像担持体である感光体ドラム１の側方に配設された現像装置１３は、支持ケース１４、現像剤担持体としての現像スリーブ１５、現像剤収容部材１６、現像剤規制部材としての第１ドクターブレード１７等から主に構成されている。
【００２２】
感光体ドラム１側に開口を有する支持ケース１４は、内部にトナー１８を収容するトナー収容部としてのトナーホッパー１９を形成している。トナーホッパー１９の感光体ドラム１側寄りには、トナー１８と磁性粒子であるキャリアとからなる現像剤２２を収容する現像剤収容部１６ａを形成する現像剤収容部材１６が、支持ケース１４と一体的に設けられている。また、現像剤収容部材１６の下方に位置する支持ケース１４には、対向面１４ｂを有する突出部１４ａが形成されており、現像剤収容部材１６の下部と対向面１４ｂとの間の空間によって、トナー１８を供給するためのトナー供給開口部２０が形成されている。
【００２３】
トナーホッパー１９の内部には、図示しない駆動手段によって回動されるトナー供給手段としてのトナーアジテータ２１が配設されている。トナーアジテータ２１は、トナーホッパー１９内のトナー１８をトナー供給開口部２０に向けて撹拌しながら送り出す。また、トナーホッパー１９の、感光体ドラム１と対向する側には、トナーホッパー１９内のトナー１８の量が少なくなったときにこれを検知するトナーエンド検知手段１４ｃが配設されている。
【００２４】
感光体ドラム１とトナーホッパー１９との間の空間には、現像スリーブ１５が配設されている。図示しない駆動手段で図の矢印方向に回転駆動される現像スリーブ１５は、その内部に、現像装置１３に対して相対位置不変に配設された、磁界発生手段としての図示しない磁石を有している。
【００２５】
現像剤収容部材１６の、支持ケース１４に取り付けられた側と対向する側には、第１ドクターブレード１７が一体的に取り付けられている。第１ドクターブレード１７は、その先端と現像スリーブ１５の外周面との間に一定の隙間を保った状態で配設されている。
【００２６】
現像剤収容部材１６の、トナー供給開口部２０の近傍に位置する部位には、規制部材としての第２ドクターブレード２３が配設されている。第２ドクターブレード２３は、その自由端が現像スリーブ１５の外周面に対して一定の隙間を保つべく、現像スリーブ１５の表面に形成される現像剤２２の層の流れを妨げる方向、すなわち、自由端を現像スリーブ１５の中心に向けて、基端を現像剤収容部材１６に一体的に取り付けられている。
【００２７】
現像剤収容部１６ａは、現像スリーブ１５の磁力が及ぶ範囲で、現像剤２２を循環移動させるに十分な空間を有するように構成されている。
【００２８】
なお、対向面１４ｂは、トナーホッパー１９側から現像スリーブ１５側に向けて下向きに傾斜するよう、所定の長さにわたって形成されている。これにより、振動、現像スリーブ１５の内部に設けられた図示しない磁石の磁力分布のむら、現像剤２２中の部分的なトナー濃度の上昇等が発生した際に、第２ドクターブレード２３と現像スリーブ１５の周面との間から現像剤収容部１６ａ内のキャリアが落下しても、落下したキャリアは対向面１４ｂで受けられて現像スリーブ１５側に移動し、磁力で現像スリーブ１５に磁着されて再び現像剤収容部１６ａ内に供給される。これにより現像剤収容部１６ａ内のキャリア量の減少を防止することができ、画像形成時における、現像スリーブ１５の軸方向での画像濃度むらの発生を防止することができる。対向面１４ｂの傾斜角度αとしては５゜程度が、また、所定の長さｌとしては、好ましくは２〜２０ｍｍ、さらに好ましくは３〜１０ｍｍ程度が望ましい。
【００２９】
上記構成により、トナーホッパー１９の内部からトナーアジテータ２１によって送り出されたトナー１８は、トナー供給開口部２０を通って現像スリーブ１５に担持された現像剤２２に供給され、現像剤収容部１６ａへ運ばれる。そして、現像剤収容部１６ａ内の現像剤２２は、現像スリーブ１５に担持されて感光体ドラム１の外周面と対向する位置まで搬送され、トナー１８のみが感光体ドラム１上に形成された静電潜像と静電的に結合することにより、感光体ドラム１上にトナー像が形成される。
【００３０】
ここで、上記トナー像形成時における現像剤２２の挙動を説明する。
現像装置１３に磁性キャリア２２ａのみからなるスタート剤をセットすると、図２に示すように、磁性キャリア２２ａは現像スリーブ１５の表面に磁着されるものと現像剤収容部１６ａ内に収容されるものとに分かれる。現像剤収容部１６ａ内に収容された磁性キャリア２２ａは、現像スリーブ１５の矢印ａ方向への回転に伴い、現像スリーブ１５内からの磁力によって矢印ｂ方向へ、１ｍｍ／ｓ以上の移動速度で循環移動する。そして、現像スリーブ１５の表面に磁着された磁性キャリア２２ａの表面と現像剤収容部１６ａ内で移動する磁性キャリア２２ａの表面との境界部において界面Ｘが形成される。
【００３１】
次に、トナーホッパー１９にトナー１８がセットされると、トナー供給開口部２０より現像スリーブ１５に担持された磁性キャリア２２ａにトナー１８が供給される。従って、現像スリーブ１５は、トナー１８と磁性キャリア２２ａとの混合物である現像剤２２を担持することとなる。
【００３２】
現像剤収容部１６ａ内では、収容されている現像剤２２の存在により、現像スリーブ１５によって搬送される現像剤２２に対して、その搬送を停止させようとする力が働いている。そして、現像スリーブ１５に担持された現像剤２２の表面に存在するトナー１８が界面Ｘへ搬送されると、界面Ｘ近傍における現像剤２２間の摩擦力が低下して界面Ｘ近傍の現像剤２２の搬送力が低下し、これにより界面Ｘ近傍での現像剤２２の搬送量が減少する。
【００３３】
一方、合流点Ｙより現像スリーブ１５の回転方向上流側の現像剤２２には、上述の現像剤収容部１６ａ内のような、現像スリーブ１５によって搬送される現像剤２２に対して、その搬送を停止させるような力は作用しないので、合流点Ｙへ搬送されてきた現像剤２２と界面Ｘを搬送される現像剤２２との搬送量のバランスが崩れて現像剤２２の玉突状態が発生し、合流点Ｙの位置が上昇して界面Ｘを含む現像剤２２の層厚が増加する。また、第１ドクターブレード１７を通過した現像剤２２の層厚も徐々に増加し、この増加した現像剤２２が第２ドクターブレード２３によって掻き落とされる。
【００３４】
そして、第１ドクターブレード１７を通過した現像剤２２が所定のトナー濃度に達すると、図４に示すように、第２ドクターブレード２３に掻き落とされて層状となった増加分の現像剤２２がトナー供給開口部２０を塞ぎ、この状態でトナー１８の取り込みが終了する。このとき、現像剤収容部１６ａ内ではトナー濃度が高くなることにより現像剤２２の嵩が大きくなり、これにより現像剤収容部１６ａ内の空間が狭くなることによって、現像剤２２が図の矢印ｂ方向に循環移動する移動速度も低下する。
【００３５】
このトナー供給開口部２０を塞ぐように形成された現像剤２２の層において、第２ドクターブレード２３に掻き落とされた現像剤２２は、図４に矢印ｃで示すように、速度１ｍｍ／ｓ以上の移動速度で移動して対向面１４ｂで受けられるが、対向面１４ｂが現像スリーブ１５側に向けて角度αで下方に傾斜し、かつ、所定長さｌを有しているため、現像剤２２の層の移動による、トナーホッパー１９への現像剤２２の落下を防止することができ、現像剤２２の量を常に一定に保つことができるので、トナー供給を常時一定に自己制御することが可能となる。
【００３６】
このときの所定のトナー濃度としては、数々の実験、研究等の結果、下式１で示される、磁性キャリア２２ａの粒径等を考慮したキャリア被覆率の計算式を用い、キャリア被覆率が１００％となるトナー濃度を上限トナー濃度としたときに、地汚れやベタ部の白抜け等のない良好な画像が得られることが判明した。
被覆率（Ｔｎ）＝（ｎ個のトナーが占有する面積の和／キャリアの表面積）×１００…（式１）
ここで、トナー１個が占有する面積は２（√３）ｒ² 、キャリア１個の表面積は４π（Ｒ＋ｒ）² であるので、キャリア被覆率（Ｔｎ）は下式２のように表される。
【００３７】
【数１】

【００３８】
また、トナー濃度の値（ｗｔ％）はトナーの重さ／（トナーの重さ＋キャリアの重さ）×１００で表される。ここでは普遍性を持たせるため、図５（ａ），（ｂ）に示すように、キャリア及びトナーをそれぞれ球形とみなし、キャリア表面をトナーが隙間なく最密状態の斜方配置で覆ったときのトナー濃度を考え、すなわち、キャリア１個の表面をｎ個のトナーが１層の状態で完全に覆った状態を被覆率１００％とする。このときの１個のキャリア表面を隙間なく覆うトナー数を限界トナー数とする。このキャリア被覆率の計算には、従来、平面的近似と球面的近似とが提案されているが、本実施例では、実用的なトナー及びキャリアの半径比の実用的な範囲において、平面的近似によって計算する。
【００３９】
この平面的近似による計算は、図５（ａ）に示すように、トナー１８及び磁性キャリア２２ａの半径をそれぞれｒ，Ｒとし、図５（ｂ）に示すように、半径（ｒ＋Ｒ）の球の表面を１個の実質的占有面積である平行四辺形ＤＥＦＧの面積で除して限界トナー数Ｎを求めると、Ｎは下式３で示される。なお、この近似方法では、磁性キャリア２２ａの表面がトナー１８からみて平面とみなせる条件；Ｒ》ｒが必要である。
【００４０】
【数２】

【００４１】
また、現像剤２２のトナー濃度Ｃ（ｗｔ％）をキャリア表面上のトナー数ｎを用いて表すと、キャリア１個の重さ；４πＲ³ ρ_c ／３、トナー１個の重さ；４πｒ³ ρ_t ／３であるので、下式４のようになる。ここで、ｒはトナー粒径の半径（μｍ）、Ｒはキャリア粒径の半径（μｍ）、ρ_t はトナーの真比重（ｇ／ｃｍ³ ）、ρ_c はキャリアの真比重（ｇ／ｃｍ³ ）である。
【００４２】
【数３】

【００４３】
上記式２及び式４からｎを消去して整理すると、下式５を得る。
【００４４】
【数４】

【００４５】
図６（ａ）は、キャリア被覆率が１００％のときのトナー濃度におけるトナー１８の付着状態をスケッチした図である。同図に示すように、キャリア被覆率１００％のときには、磁性キャリア２２ａの粒子表面にトナー１８が隙間なく１層で付着している。一方、図６（ｂ）は、キャリア被覆率が１６９％のときのトナー濃度におけるトナー１８の付着状態をスケッチしたものである。同図に示すように、キャリア被覆率１６９％のときには、磁性キャリア２２ａの粒子表面をトナー１８が幾重にも重なって覆っている。このようにキャリア被覆率が１００％を超えると、キャリア２２ａの表面をトナー１８が完全に覆ってしまうことが確認された。
【００４６】
ところで、キャリア被覆率が１００％を超えた状態で現像剤収容部１６ａに入った現像剤２２は、互いに摩擦を繰り返すこととなる。トナー１８は磁性キャリア２２ａとの摩擦によって帯電するが、キャリア被覆率が１００％を超える場合にはキャリア表面が露出しないため、既に磁性キャリア２２ａを覆っているトナー１８をさらにトナー１８が覆うこととなる。従って、トナー１８同士が擦れ合うことによって、正に帯電するトナーと負に帯電するトナーとが発生し、帯電状態が不均一となってしまう。ここで、例えば、キャリア２２ａとトナー１８との摩擦によってトナー１８が負に帯電されたとすると、トナー１８同士の摩擦によって正に帯電されたトナー１８は静電潜像への付着が正常に行われなくなり、地汚れ等の不具合を生じてしまう。
【００４７】
このように、式５に示す式を用いてキャリア被覆率が１００％を超えないようなトナー濃度を上限トナー濃度として決定し、この上限トナー濃度を実現できるキャリア量の現像剤を現像剤収容部１６ａにセットすることで、地汚れ等の不具合を発生させることなく、良好なトナー像を得ることができる。
【００４８】
現像領域でトナー１８が消費されると、界面Ｘ上のトナー濃度が減少することにより、界面Ｘでのトナー搬送力が増加する。この搬送力の増加に伴い、厚くなった現像剤２２の層を引き戻そうとする力が作用して、現像剤２２の状態が図４に示す状態から図３に示す状態へと変化する。図３に示す状態となると、トナー１８の取り込みが再び開始され、これが所定のトナー濃度となるまで行われる。
【００４９】
上述のように、現像剤収容部１６ａが、現像スリーブ１５の磁力が及ぶ範囲で現像剤２２を移動させるに十分な空間を有することにより、現像剤収容部１６ａ内の現像剤２２がトナー濃度の如何に拘らず１ｍｍ／ｓ以上の速度で常時循環が可能であり、第１ドクターブレード１７あるいは現像領域を通過した現像剤２２と現像剤収容部１６ａ内の現像剤２２との入れ替えが徐々に行われ、現像剤収容部１６ａ内にセットした現像剤２２を全て使用することができる。これにより、現像剤２２にかかるストレスを分散させることができ、磁性キャリアの膜削れの防止、あるいはトナースペント化の進行を遅らせることができる。すなわち現像剤２２の寿命を延ばすことができるため、小型でありながら画像形成枚数の多い高速域までもカバーすることが可能な現像装置を実現することができる。
【００５０】
第１の実施例において、図７に示すように、突出部１４ａと現像スリーブ１５との間隙δ１を第２ドクターブレード２３の先端と現像スリーブ１５との間隙δ２以上と構成することにより、現像スリーブ１５の表面上に形成された現像剤２２の層を薄層化した状態でトナー１８の供給を制御することができるため、画像面積の多い画像を形成した場合にも消費されたトナー１８を迅速に現像剤２２に供給することができ、何枚も連続で画像形成を行うことができる。
【００５１】
第１の実施例の変形例として、図８に示すように、現像剤収容部材１６に代えて現像剤収容部材２４を用いてもよい。この現像剤収容部材２４は、第１ドクターブレード１７と対向する側の側壁２４ｂが現像スリーブ１５側に傾いて設けられている。この現像剤収容部材２４を用いることにより、第２ドクターブレード２３を設けることなく側壁２４ｂで現像剤２２の層圧を規制することができる。なお、現像剤収容部材２４内の現像剤収容部２４ａは、現像スリーブ１５の磁力が及ぶ範囲で、現像剤２２を循環移動させるに十分な空間を有するように構成されている。
【００５２】
図９は、本発明の第２の実施例を採用した画像形成装置の現像装置要部の概略構成図である。
感光体ドラム１の側方に配設された現像装置２は、支持ケース３、現像剤担持体としての現像スリーブ４、現像剤収容部材５、規制部材としての第１ドクターブレード６等から主に構成されている。
【００５３】
感光体ドラム１側に開口を有する支持ケース３は、内部にトナー７を収容するトナーホッパー８を形成している。トナーホッパー８の感光体ドラム１側寄りには、トナー７と磁性粒子であるキャリアとからなる現像剤１１を収容する現像剤収容部５ａを形成する現像剤収容部材５が、支持ケース３と一体的に設けられている。また、現像剤収容部材５の下方には、部材３ａが支持ケース３と一体的に設けられており、現像剤収容部材５の下部と部材３ａの上部との空間によって、トナー７を供給するためのトナー供給開口部９が形成されている。
【００５４】
トナーホッパー８の内部には、図示しない駆動手段によって回動されるトナー供給手段としてのトナーアジテータ１０が配設されている。トナーアジテータ１０は、トナーホッパー８の内部のトナー７をトナー供給開口部９に向けて撹拌しながら送り出す。
【００５５】
感光体ドラム１とトナーホッパー８との間の空間には、現像スリーブ４が配設されている。図示しない駆動手段で図の矢印方向に回転駆動される現像スリーブ４は、その内部に、現像装置２に対して相対位置不変に配設された、Ｐ１極、Ｐ２極、Ｐ３極、Ｐ４極の４極の磁石を有している。Ｐ１極は感光体ドラム１の外周面に、Ｐ２極、Ｐ３極は支持ケース３と現像スリーブ４との間の現像剤通路に、また、Ｐ４極は現像剤収容部５ａにそれぞれ対応する位置に配設されている。
【００５６】
現像剤収容部材５の、支持ケース３に取り付けられた側と対向する側には、第１ドクターブレード６が一体的に取り付けられている。第１ドクターブレード６は、その先端と現像スリーブ４の外周面との間に一定の隙間を保った状態で配設されている。また、現像剤収容部材５の、トナー供給開口部９の近傍に位置する部位には、規制部材としての第２ドクターブレード１２が配設されている。第２ドクターブレード１２は、その自由端が現像スリーブ４の外周面に対して一定の隙間を保つべく、基端を現像剤収容部材５に一体的に取り付けられている。
【００５７】
上記構成により、トナーホッパー８の内部からトナーアジテータ１０によって送り出されたトナー７は、トナー供給開口部９を通って現像スリーブ４に担持された現像剤１１に供給され、現像剤収容部５ａ内へ運ばれる。そして、現像剤収容部５ａ内の現像剤１１は、現像スリーブ４に担持されて感光体ドラム１の外周面と対向する位置まで搬送され、トナー７のみが感光体ドラム１上に形成された静電潜像と静電的に結合することにより、感光体ドラム１上にトナー像が形成される。
【００５８】
上記動作中、現像剤収容部５ａ内における現像剤１１は、図１０に示す矢印の方向に回転しており、第２ドクターブレード１２の先端と現像スリーブ４の外周面との間からトナー７を現像剤収容部５ａ内に取り込んでいるが、現像剤収容部５ａ内の現像剤１１の抗力（重力、嵩の増加）の影響により、トナー７の取り込みが左右される。そこで、現像剤収容部５ａの内壁面５ｂから現像スリーブ４の外周面までの最大距離Ｓを変化させ、そのときのトナー濃度を測定した結果、最大距離Ｓを現像スリーブ４の半径ｒ１よりも小さくすると、狙いのトナー濃度に達する前に現像剤収容部５ａ内の現像剤１１の嵩及び重力が増加し、抗力が増加するためにトナーの取り込み時間が少なくなり、狙いのトナー濃度に達する前に上限トナー濃度となってしまうため、最適領域のトナー濃度で使用できないことが判明した。
【００５９】
また、収容スペースを狭くした分、現像剤収容部５ａ内にセットする現像剤１１の量を少なくすると、Ｐ４極の磁力を弱めないと現像剤１１が動かなくなり、現像剤１１が動くまでＰ４極の磁力を弱めると、製造上、Ｐ１極の磁力もそれに付随して弱くなってしまい、キャリアが感光体ドラム１に付着してしまう等の問題が発生し、たとえＰ１極の磁力を維持できたとしても、第１ドクターブレード６を通過する現像剤１１の量が不安定となり、現像スリーブ軸方向でのムラのある画像となってしまうということが判明した。
【００６０】
また、現像剤収容部５ａ内へのトナー７の取り込み量は、図１１に示すように、第２ドクターブレード１２の先端と現像スリーブ４の外周面との間の隙間によって左右される。そこで、この隙間を変化させ、そのときのトナー濃度を測定した結果、この隙間を第１ドクターブレード６の先端と現像スリーブ４の外周面との間の隙間ＤＧの２倍以下とすると、第２ドクターブレード１２に塞き止められてかなりの量の現像剤１１が溢れ出し、トナー７も現像剤収容部５ａ内へ入りにくくなってトナー濃度が低下してしまうということが判明した。
【００６１】
また、第２ドクターブレード１２の先端と現像スリーブ４の外周面との間の隙間を隙間ＤＧの６倍以上とすると、現像剤収容部５ａ内へ取り込まれたときに現像スリーブ軸方向に現像剤１１の量ムラが発生し、部分的にトナー７を取り込み易い箇所と取り込みにくい箇所ができてしまい、画像ムラが発生してしまうということが判明した。
【００６２】
さらに、現像剤収容部５ａ内へのトナー７の取り込み量は、図１２に示すように、第２ドクターブレード１２の高さ方向の突き出し位置Ｘ１によっても左右される。この突き出し位置Ｘ１が現像スリーブ４の中心Ｏよりも下方に位置すると、トナー７の取り込み位置が下方寄りとなり、重力の影響によりトナー７を取り込みにくくなってしまう。
【００６３】
現像剤収容部５ａ内での現像剤１１の動きは、図１３に示すように、現像スリーブ４内の磁石の磁力によっても左右される。そこで、Ｐ２極、Ｐ３極、Ｐ４極の磁力を一定とし、Ｐ１極の磁力を変化させて実験を行った結果、Ｐ１極の磁力をＰ４極の磁力の１．２倍以上（例えばＰ４極の磁力が６０．０ミリテスラであれば、Ｐ１極の磁力は７２．０ミリテスラ以上）とすることにより、現像剤収容部５ａ内での現像剤１１の動きが活発化し、第１ドクターブレード６を通過する現像剤１１の量が安定化することが判明した。
【００６４】
図１４は、本発明に用いられる現像剤１１のキャリア量とトナー７の上限濃度との関係を示している。現像剤収容部５ａ内にセットされるキャリアの量が多いほど現像剤収容部５ａ内にトナー７を取り込む時間が減少してトナー濃度が低くなり、キャリアの量が少ないほどトナー濃度は高くなる。また、隙間ＤＧを広げると、上限トナー濃度を高く設定することができる。
【００６５】
【発明の効果】
請求項１記載の発明によれば、第２の規制部材が増加した現像剤の通過を規制し、規制された現像剤がトナーの取り込みを制御することにより、トナー供給を常時一定に自己制御することができるので、簡易な構成でトナー濃度の調整を容易に行うことができる。
【００６６】
請求項５記載の発明によれば、キャリア被覆率が１００％のときに適正トナー濃度とすることにより、キャリア表面を完全にトナーが覆うことにより、キャリアの膜削れを防止することができ、現像剤の寿命を延ばすことができる。
【００６７】
請求項７記載の発明によれば、トナー供給開口部において、トナー濃度に応じた層厚の現像剤層を形成することができるので、トナーの取り込みを自己制御することができ、小型で低コストの現像装置を提供することができる。
【００６８】
請求項８記載の発明によれば、トナー供給開口部に現像剤の層を形成する際の現像剤の循環移動速度を１ｍｍ／ｓ以上としたので、トナー取り込み部で常に現像剤の撹拌を行うことができ、トナーの帯電量の低下を防止して異常画像の発生を防止することができる。
【００６９】
請求項１２記載の発明によれば、現像剤収容室が現像剤の循環に十分なスペースを有するので、トナー濃度センサーを用いることなく、現像剤収容室内のトナー濃度を一定範囲内に維持することができる。
【００７０】
請求項１３記載の発明によれば、トナーの取り込み部に存在する現像剤を、第２の規制部材が現像剤担持体の軸方向において均一化させるので、トナーを均一に取り込むことにより画像ムラを防止することができる。
【００７１】
請求項１４記載の発明によれば、トナーの取り込み部に存在する現像剤を、第２の規制部材が現像剤担持体の軸方向において均一化させつつ、適量を現像剤収容室内に取り込むので、トナーを均一に取り込むことにより画像ムラを防止すると共に、適正なトナー濃度とすることができる。
【００７２】
請求項１５記載の発明によれば、第２の規制部材の先端位置を現像剤担持体の中心位置よりも上方に設けることにより、現像剤の自重による、取り込み部での現像剤の動きの制限を緩和し、磁力で保持できる現像剤の量によりトナー濃度をコントロールすることができる。
【００７３】
請求項１６記載の発明によれば、現像剤収容室内での現像剤の動きを活発化させつつ、キャリア付着しないように第１極の磁力を高くすることにより、現像剤担持体の軸方向においてムラのない良好な画像を得ることができる。
【図面の簡単な説明】
【図１】本発明の第１の実施例を採用した画像形成装置の現像装置要部の概略構成図である。
【図２】本発明の第１の実施例における現像剤の挙動を説明する部分側断面図である。
【図３】本発明の第１の実施例における現像剤の挙動を説明する部分側断面図である。
【図４】本発明の第１の実施例における現像剤の挙動を説明する部分側断面図である。
【図５】本発明の第１の実施例におけるキャリア被覆率を説明する模式図である。
【図６】本発明の第１の実施例における（ａ）キャリア被覆率１００％時のキャリアへのトナーの付着状態を示す図、（ｂ）キャリア被覆率１６９％時のキャリアへのトナーの付着状態を示す図である。
【図７】本発明の第１の実施例の変形例を説明する部分側断面図である。
【図８】本発明の第１の実施例の他の変形例を説明する部分側断面図である。
【図９】本発明の第２の実施例を採用した画像形成装置の現像装置要部の概略構成図である。
【図１０】本発明の第２の実施例を説明する現像装置要部の部分側断面図である。
【図１１】本発明の第２の実施例を説明する現像装置要部の部分側断面図である。
【図１２】本発明の第２の実施例を説明する現像装置要部の部分側断面図である。
【図１３】本発明の第２の実施例を説明する現像装置要部の部分側断面図である。
【図１４】本発明の第２の実施例に用いられる現像剤のキャリア量とトナー上限濃度との関係を示す線図である。
【符号の説明】
１潜像担持体（感光体ドラム）
２，１３現像装置
４，１５現像剤担持体（現像スリーブ）
５ａ，１６ａ，２４ａ現像剤収容部
５ｂ内壁面
６，１７第１の規制部材（第１ドクターブレード）
７，１８トナー
８，１９トナー収容部（トナーホッパー）
９，２０トナー供給開口部
１０，２１トナー供給手段（トナーアジテータ）
１１，２２現像剤
１２，２３第２の規制部材（第２ドクターブレード）
２２ａ磁性キャリア
ｒ１現像剤担持体の半径
Ｓ最大距離
Ｘ界面部（界面）
Ｘ１第２の規制部材の先端位置[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a developing device using a two-component developer in an image forming apparatus.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, developing devices that do not require toner density detecting means and take in toner by the movement of a developer are known. However, in this developing device, the amount of toner taken in is different between a portion where the developer moves actively and a portion where the developer is not active, or a portion where the developer is high and a portion where the developer is low, and the toner density partially becomes unstable, resulting in an image density. Unevenness and fog are likely to occur. Therefore, a technique for solving density unevenness and fogging in the longitudinal direction of the apparatus by disposing two toner supply members in the toner hopper and allowing the developer to pass through a path formed by each toner supply member. This is disclosed in Japanese Patent No. 63-4282.
[0003]
[Problems to be solved by the invention]
However, in the technique disclosed in the above publication, since two toner supply members are used, there is a problem that the developing unit becomes large and the cost increases.
[0004]
SUMMARY OF THE INVENTION An object of the present invention is to provide a developing device capable of solving the above-mentioned problems, reducing the number of parts, and consolidating functions, thereby stabilizing the quality while reducing the size and cost. To do.
[0005]
[Means for Solving the Problems]
According to the first aspect of the present invention, there is provided a developer carrier having a magnetic field generating means therein and carrying and transporting a two-component developer containing toner and a magnetic carrier, and carried and carried by the developer carrier. A first regulating member that regulates the layer thickness of the developer that is applied, and a second regulating member that is disposed on the upstream side in the transport direction of the developer on the developer carrier relative to the first regulating member; A developer accommodating portion positioned between the first restricting member and the second restricting member, and an upstream side in the transport direction of the developer on the developer carrier relative to the second restricting member. Before A toner container having an opening for supplying toner to the developer carrying member and a first circulating developer layer that circulates on the developer carrying member by the developer regulated by the second regulating member are formed. And a space in which a second circulating developer layer that circulates differently from the first circulating developer layer formed on the developer carrier is formed in the developer accommodating portion, The second restricting member functions as a partition member that partitions the two spaces, and is provided in the developer accommodating portion. Invaded By changing the toner density of the developer on the developer carrier, the amount of developer regulated by the second regulating member is changed to change the toner intake state of the developer on the developer carrier. It is characterized by.
[0006]
The invention described in claim 2 is the developing device according to claim 1, further comprising: When the toner density of the developer on the developer carrier that has entered the developer container reaches a predetermined toner density, the developer that is restricted from passing by the second regulating member is the developer carrier. The developer stays in the contact portion between the developer and the toner, and the developer closes the contact portion, thereby stopping the toner intake state of the developer on the developer carrier. It is characterized by that.
[0007]
According to a third aspect of the present invention, there is provided a developer containing portion for storing a two-component developer containing toner and a magnetic carrier, and a rotatable developing device disposed opposite to the latent image carrier and provided with a magnetic field generating means inside. A developer carrying member, a first regulating member for regulating a layer thickness of the developer carried on the developer carrying member, and a toner containing unit, and the movement of the developer in the developer containing unit Accordingly, in the developing device that takes in the toner stored in the toner accommodating portion into the developer accommodating portion so as to come into contact with the developer, the developer on the developer carrying member is upstream of the first regulating member in the conveying direction. A second regulating member disposed on the side, a space in which a first circulating developer layer that circulates on the developer carrying member is formed by the developer regulated by the second regulating member, The developer is carried in the developer container. A space in which a second circulating developer layer that circulates differently from the first circulating developer layer formed thereon is formed, and is the maximum from the inner wall of the developer accommodating portion to the surface of the developer carrier. The distance from the portion of the second restricting member closest to the surface of the developer carrying member to the surface of the developer carrying member is made smaller than the distance, and the second restricting member serves as a partition member that partitions the two spaces. Function in the developer container Invaded By changing the toner density of the developer on the developer carrier, the amount of developer regulated by the second regulating member is changed to change the toner intake state of the developer on the developer carrier. Features.
[0008]
According to a fourth aspect of the present invention, there is provided a developer containing portion for storing a two-component developer composed of toner and a magnetic carrier, and a rotatable developing device disposed opposite to the latent image carrier and provided with a magnetic field generating means inside. The developer carrying member, the first regulating member regulating the layer thickness of the developer carried on the developer carrying member, the toner containing portion, and the developer regulated by the second regulating member. A space in which a first circulating developer layer that circulates on the developer carrying member is formed, and a circulatory movement different from the first circulating developer layer formed on the developer carrying member in the developer accommodating portion. And a space in which a second circulating developer layer is formed, and the developer stored in the toner storage portion to come into contact with the developer by the movement of the developer in the developer storage portion. In the developing device to be taken into the container, In order to face the developer carrier surface at a position on the upstream side in the rotation direction of the developer carrier relative to the portion of the inner wall surface of the developer container where the distance to the developer carrier surface is maximum, A second restricting member for restricting the amount of the toner entering the developer accommodating portion is provided, and the second restricting member is larger than the maximum distance from the inner wall of the developer accommodating portion to the surface of the developer carrying member. The distance from the portion closest to the surface of the developer carrying member to the surface of the developer carrying member is reduced, and the second regulating member functions as a partition member that partitions the two spaces. Invaded By changing the toner density of the developer on the developer carrier, the amount of developer regulated by the second regulating member is changed to change the toner intake state of the developer on the developer carrier. It is characterized by.
[0021]
【Example】
FIG. 1 is a schematic configuration diagram of a main part of a developing device of an image forming apparatus employing a first embodiment of the present invention.
The developing device 13 disposed on the side of the photosensitive drum 1 serving as a latent image carrier has a support case 14, a developing sleeve 15 as a developer carrier, a developer accommodating member 16, and a first member as a developer regulating member. It is mainly composed of one doctor blade 17 or the like.
[0022]
A support case 14 having an opening on the side of the photosensitive drum 1 forms a toner hopper 19 as a toner storage portion that stores toner 18 therein. Near the photosensitive drum 1 side of the toner hopper 19, a developer accommodating member 16 that forms a developer accommodating portion 16 a that accommodates a developer 22 composed of toner 18 and a carrier that is magnetic particles is integrated with the support case 14. Provided. The support case 14 positioned below the developer accommodating member 16 is formed with a protruding portion 14a having a facing surface 14b. The space between the lower portion of the developer accommodating member 16 and the facing surface 14b A toner supply opening 20 for supplying the toner 18 is formed.
[0023]
Inside the toner hopper 19, a toner agitator 21 is disposed as toner supply means that is rotated by a drive means (not shown). The toner agitator 21 sends out the toner 18 in the toner hopper 19 toward the toner supply opening 20 while stirring. Further, on the side of the toner hopper 19 that faces the photosensitive drum 1, a toner end detection unit 14 c that detects when the amount of toner 18 in the toner hopper 19 decreases is disposed.
[0024]
A developing sleeve 15 is disposed in a space between the photosensitive drum 1 and the toner hopper 19. The developing sleeve 15 that is rotationally driven in the direction of the arrow in the figure by a driving means (not shown) has a magnet (not shown) as a magnetic field generating means disposed in its relative position with respect to the developing device 13. Yes.
[0025]
A first doctor blade 17 is integrally attached to the side of the developer accommodating member 16 that faces the side attached to the support case 14. The first doctor blade 17 is disposed in a state where a certain gap is maintained between the tip of the first doctor blade 17 and the outer peripheral surface of the developing sleeve 15.
[0026]
A second doctor blade 23 as a restricting member is disposed in a portion of the developer accommodating member 16 located in the vicinity of the toner supply opening 20. The second doctor blade 23 has a free end that prevents a flow of the developer 22 layer formed on the surface of the developing sleeve 15 in order to keep a certain gap with respect to the outer peripheral surface of the developing sleeve 15, that is, free The base end is integrally attached to the developer accommodating member 16 with the end facing the center of the developing sleeve 15.
[0027]
The developer accommodating portion 16a is configured to have a space sufficient for circulating and moving the developer 22 within a range that the magnetic force of the developing sleeve 15 reaches.
[0028]
The facing surface 14b is formed over a predetermined length so as to incline downward from the toner hopper 19 side toward the developing sleeve 15 side. As a result, when vibration, uneven magnetic distribution of a magnet (not shown) provided in the developing sleeve 15 or a partial increase in toner concentration in the developer 22 occurs, the second doctor blade 23 and the developing sleeve 15 are generated. Even if the carrier in the developer accommodating portion 16a falls from between the peripheral surface of the toner and the peripheral surface, the dropped carrier is received by the facing surface 14b and moves toward the developing sleeve 15 and is magnetically attached to the developing sleeve 15 by magnetic force. The toner is again supplied into the developer accommodating portion 16a. As a result, it is possible to prevent a decrease in the amount of carrier in the developer accommodating portion 16a, and it is possible to prevent occurrence of uneven image density in the axial direction of the developing sleeve 15 during image formation. The inclination angle α of the facing surface 14b is about 5 °, and the predetermined length l is preferably 2 to 20 mm, more preferably about 3 to 10 mm.
[0029]
With the above configuration, the toner 18 delivered from the inside of the toner hopper 19 by the toner agitator 21 is supplied to the developer 22 carried on the developing sleeve 15 through the toner supply opening 20, and is carried to the developer accommodating portion 16a. It is. The developer 22 in the developer accommodating portion 16a is carried on the developing sleeve 15 and conveyed to a position facing the outer peripheral surface of the photosensitive drum 1, and only the toner 18 is formed on the photosensitive drum 1. A toner image is formed on the photosensitive drum 1 by electrostatic coupling with the electrostatic latent image.
[0030]
Here, the behavior of the developer 22 during the toner image formation will be described.
When a starting agent consisting only of a magnetic carrier 22a is set in the developing device 13, as shown in FIG. 2, the magnetic carrier 22a is magnetized on the surface of the developing sleeve 15 and is accommodated in the developer accommodating portion 16a. And divided. The magnetic carrier 22a accommodated in the developer accommodating portion 16a circulates at a moving speed of 1 mm / s or more in the arrow b direction by the magnetic force from the inside of the developing sleeve 15 as the developing sleeve 15 rotates in the arrow a direction. Moving. An interface X is formed at the boundary between the surface of the magnetic carrier 22a magnetically attached to the surface of the developing sleeve 15 and the surface of the magnetic carrier 22a moving in the developer accommodating portion 16a.
[0031]
Next, when the toner 18 is set in the toner hopper 19, the toner 18 is supplied from the toner supply opening 20 to the magnetic carrier 22 a carried on the developing sleeve 15. Therefore, the developing sleeve 15 carries the developer 22 that is a mixture of the toner 18 and the magnetic carrier 22a.
[0032]
In the developer accommodating portion 16a, due to the presence of the accommodated developer 22, a force is applied to the developer 22 conveyed by the developing sleeve 15 to stop the conveyance. Then, when the toner 18 existing on the surface of the developer 22 carried on the developing sleeve 15 is conveyed to the interface X, the frictional force between the developers 22 in the vicinity of the interface X is reduced and the developer 22 in the vicinity of the interface X is reduced. This reduces the transport force of the developer 22, thereby reducing the transport amount of the developer 22 in the vicinity of the interface X.
[0033]
On the other hand, the developer 22 on the upstream side in the rotation direction of the developing sleeve 15 with respect to the junction Y is transported with respect to the developer 22 transported by the developing sleeve 15 as in the developer accommodating portion 16a described above. Since the force for stopping does not act, the balance of the transport amount of the developer 22 transported to the junction Y and the developer 22 transported through the interface X is lost, and the crushing state of the developer 22 occurs. As a result, the position of the confluence point Y rises and the layer thickness of the developer 22 including the interface X increases. Further, the layer thickness of the developer 22 that has passed through the first doctor blade 17 also gradually increases, and the increased developer 22 is scraped off by the second doctor blade 23.
[0034]
When the developer 22 that has passed through the first doctor blade 17 reaches a predetermined toner concentration, as shown in FIG. 4, the increased amount of developer 22 that has been scraped off by the second doctor blade 23 and layered is formed. The toner supply opening 20 is closed, and in this state, the toner 18 is completely taken in. At this time, the volume of the developer 22 is increased by increasing the toner concentration in the developer accommodating portion 16a, and the space in the developer accommodating portion 16a is thereby narrowed. The moving speed that circulates in the direction also decreases.
[0035]
In the developer 22 layer formed so as to close the toner supply opening 20, the developer 22 scraped off by the second doctor blade 23 has a speed of 1 mm / s or more as shown by an arrow c in FIG. However, since the opposing surface 14b is inclined downward at an angle α toward the developing sleeve 15 side and has a predetermined length l, the developer 22 is moved. The developer 22 can be prevented from dropping into the toner hopper 19 due to the movement of the toner layer, and the amount of the developer 22 can be kept constant at all times, so that the toner supply can be always self-controlled to be constant. It becomes.
[0036]
As the predetermined toner concentration at this time, the carrier coverage is 100 using the calculation formula of the carrier coverage in consideration of the particle diameter of the magnetic carrier 22a shown by the following formula 1 as a result of numerous experiments and researches. It has been found that when the toner concentration of% is set to the upper limit toner concentration, a good image with no background stains or solid white spots can be obtained.
Coverage ratio (Tn) = (sum of areas occupied by n toners / surface area of carrier) × 100 (Equation 1)
Here, the area occupied by one toner is 2 (√3) r. ² The surface area of one carrier is 4π (R + r) ² Therefore, the carrier coverage (Tn) is expressed by the following formula 2.
[0037]
[Expression 1]

[0038]
Further, the toner density value (wt%) is expressed as toner weight / (toner weight + carrier weight) × 100. Here, in order to give universality, when the carrier and the toner are regarded as spheres as shown in FIGS. 5A and 5B, and the carrier surface is covered with an oblique arrangement in which the toner is in a close-packed state without any gaps. That is, a state in which the surface of one carrier is completely covered with n toners in a single layer is defined as a coverage of 100%. At this time, the number of toners covering one carrier surface without any gap is defined as the limit toner number. Conventionally, a planar approximation and a spherical approximation have been proposed for the calculation of the carrier coverage, but in this embodiment, a planar approximation is applied within a practical range of a practical toner and carrier radius ratio. Calculate by
[0039]
As shown in FIG. 5A, the calculation based on this planar approximation is such that the radii of the toner 18 and the magnetic carrier 22a are r and R, respectively, and a sphere having a radius (r + R) as shown in FIG. 5B. When the surface is divided by the area of one parallelogram DEFG, which is a substantial occupation area, the limit number of toners N is obtained. In this approximation method, the condition that the surface of the magnetic carrier 22a can be regarded as a plane when viewed from the toner 18; R >> r is necessary.
[0040]
[Expression 2]

[0041]
Further, when the toner concentration C (wt%) of the developer 22 is expressed using the number of toners n on the carrier surface, the weight of one carrier; 4πR ^Three ρ _c / 3, weight of one toner; 4πr ^Three ρ _t Therefore, the following formula 4 is obtained. Here, r is the radius (μm) of the toner particle size, R is the radius (μm) of the carrier particle size, and ρ _t Is the true specific gravity of the toner (g / cm ^Three ), Ρ _c Is the true specific gravity of the carrier (g / cm ^Three ).
[0042]
[Equation 3]

[0043]
When n is deleted from the

above formulas

2 and 4 and rearranged, the following formula 5 is obtained.
[0044]
[Expression 4]

[0045]
FIG. 6A is a sketch of the toner 18 adhesion state at a toner concentration when the carrier coverage is 100%. As shown in the figure, when the carrier coverage is 100%, the toner 18 adheres to the particle surface of the magnetic carrier 22a in one layer without any gap. On the other hand, FIG. 6B is a sketch of the adhesion state of the toner 18 at the toner concentration when the carrier coverage is 169%. As shown in the figure, when the carrier coverage is 169%, the toner 18 covers the particle surface of the magnetic carrier 22a in layers. Thus, it was confirmed that when the carrier coverage exceeds 100%, the toner 18 completely covers the surface of the carrier 22a.
[0046]
By the way, the developer 22 that has entered the developer accommodating portion 16a with the carrier coverage exceeding 100% repeats friction with each other. The toner 18 is charged by friction with the magnetic carrier 22a, but when the carrier coverage exceeds 100%, the carrier surface is not exposed, so that the toner 18 already covers the toner 18 already covering the magnetic carrier 22a. Become. Therefore, when the toners 18 rub against each other, a positively charged toner and a negatively charged toner are generated, and the charged state becomes uneven. Here, for example, if the toner 18 is negatively charged due to friction between the carrier 22a and the toner 18, the toner 18 positively charged due to friction between the toners 18 is normally attached to the electrostatic latent image. It will disappear, causing problems such as dirt.
[0047]
Thus, using the equation shown in Equation 5, a toner concentration that does not exceed 100% as the carrier coverage is determined as the upper limit toner concentration, and a developer having a carrier amount that can realize this upper limit toner concentration is used as the developer accommodating portion. By setting it to 16a, a good toner image can be obtained without causing problems such as background contamination.
[0048]
When the toner 18 is consumed in the development area, the toner density on the interface X decreases, and the toner conveyance force at the interface X increases. As the transport force increases, a force for pulling back the thickened developer layer 22 acts to change the state of the developer 22 from the state shown in FIG. 4 to the state shown in FIG. In the state shown in FIG. 3, the toner 18 starts to be taken in again until the toner density reaches a predetermined level.
[0049]
As described above, since the developer accommodating portion 16a has a sufficient space to move the developer 22 within the range where the magnetic force of the developing sleeve 15 reaches, the developer 22 in the developer accommodating portion 16a has a toner concentration. Regardless of the case, it is possible to constantly circulate at a speed of 1 mm / s or more, and the developer 22 that has passed through the first doctor blade 17 or the developing area and the developer 22 in the developer accommodating portion 16a are gradually replaced. In other words, all of the developer 22 set in the developer accommodating portion 16a can be used. As a result, the stress applied to the developer 22 can be dispersed, and the film removal of the magnetic carrier can be prevented or the progress of toner spent can be delayed. In other words, since the life of the developer 22 can be extended, it is possible to realize a developing device that can cover a high-speed range in which the number of image formations is large while being small.
[0050]
In the first embodiment, as shown in FIG. 7, the developing sleeve is configured such that the gap δ1 between the protrusion 14a and the developing sleeve 15 is equal to or larger than the gap δ2 between the tip of the second doctor blade 23 and the developing sleeve 15. Since the supply of the toner 18 can be controlled in a state where the developer 22 layer formed on the surface 15 is thinned, the consumed toner 18 can be quickly removed even when an image having a large image area is formed. Can be supplied to the developer 22 and image formation can be performed continuously for many sheets.
[0051]
As a modification of the first embodiment, as shown in FIG. 8, a developer accommodating member 24 may be used instead of the developer accommodating member 16. The developer accommodating member 24 is provided such that a side wall 24b facing the first doctor blade 17 is inclined toward the developing sleeve 15 side. By using the developer accommodating member 24, the layer pressure of the developer 22 can be regulated by the side wall 24b without providing the second doctor blade 23. Note that the developer accommodating portion 24a in the developer accommodating member 24 is configured to have a sufficient space for circulating the developer 22 within the range where the magnetic force of the developing sleeve 15 reaches.
[0052]
FIG. 9 is a schematic configuration diagram of a main part of the developing device of the image forming apparatus adopting the second embodiment of the present invention.
The developing device 2 disposed on the side of the photosensitive drum 1 mainly includes a support case 3, a developing sleeve 4 as a developer carrying member, a developer containing member 5, a first doctor blade 6 as a regulating member, and the like. It is configured.
[0053]
A support case 3 having an opening on the side of the photosensitive drum 1 forms a toner hopper 8 that accommodates toner 7 therein. Near the photosensitive drum 1 side of the toner hopper 8, a developer accommodating member 5 that forms a developer accommodating portion 5 a that accommodates a developer 11 composed of toner 7 and a carrier that is magnetic particles is integrated with the support case 3. Provided. In addition, a member 3a is provided integrally with the support case 3 below the developer containing member 5, and the toner 7 is supplied by the space between the lower part of the developer containing member 5 and the upper part of the member 3a. The toner supply opening 9 is formed.
[0054]
Inside the toner hopper 8, a toner agitator 10 is disposed as toner supply means that is rotated by a drive means (not shown). The toner agitator 10 sends out the toner 7 inside the toner hopper 8 toward the toner supply opening 9 while stirring.
[0055]
A developing sleeve 4 is disposed in the space between the photosensitive drum 1 and the toner hopper 8. The developing sleeve 4 that is rotationally driven in the direction of the arrow in the figure by a driving means (not shown) has P1, P2, P3, and P4 poles disposed therein in a relative position unchanged with respect to the developing device 2. It has a 4-pole magnet. The P1 pole is at the outer peripheral surface of the photosensitive drum 1, the P2 pole and the P3 pole are at the developer passage between the support case 3 and the developing sleeve 4, and the P4 pole is at a position corresponding to the developer accommodating portion 5a. It is arranged.
[0056]
A first doctor blade 6 is integrally attached to the side of the developer containing member 5 that faces the side attached to the support case 3. The first doctor blade 6 is disposed in a state where a certain gap is maintained between the tip thereof and the outer peripheral surface of the developing sleeve 4. Further, a second doctor blade 12 as a regulating member is disposed in a portion of the developer containing member 5 that is located in the vicinity of the toner supply opening 9. The second doctor blade 12 is integrally attached to the developer containing member 5 at the base end so that the free end thereof maintains a constant gap with respect to the outer peripheral surface of the developing sleeve 4.
[0057]
With the above configuration, the toner 7 sent out from the inside of the toner hopper 8 by the toner agitator 10 is supplied to the developer 11 carried on the developing sleeve 4 through the toner supply opening 9, and into the developer accommodating portion 5a. Carried. The developer 11 in the developer accommodating portion 5a is carried by the developing sleeve 4 and conveyed to a position facing the outer peripheral surface of the photosensitive drum 1, and only the toner 7 is formed on the photosensitive drum 1. A toner image is formed on the photosensitive drum 1 by electrostatic coupling with the electrostatic latent image.
[0058]
During the above operation, the developer 11 in the developer accommodating portion 5a is rotated in the direction of the arrow shown in FIG. 10, and the toner 7 is removed from between the tip of the second doctor blade 12 and the outer peripheral surface of the developing sleeve 4. The toner 7 is taken into the developer container 5a, but the toner 7 is influenced by the influence of the drag (gravity and bulk increase) of the developer 11 in the developer container 5a. Therefore, as a result of changing the maximum distance S from the inner wall surface 5b of the developer accommodating portion 5a to the outer peripheral surface of the developing sleeve 4 and measuring the toner density at that time, the maximum distance S is smaller than the radius r1 of the developing sleeve 4. Then, before reaching the target toner concentration, the bulk and gravity of the developer 11 in the developer containing portion 5a increase, and the drag increases, so that the toner intake time is reduced, and before the target toner concentration is reached. Since the upper limit toner density is reached, it has been found that the toner density in the optimum region cannot be used.
[0059]
Further, if the amount of the developer 11 set in the developer accommodating portion 5a is reduced by the amount corresponding to the narrowed accommodation space, the developer 11 does not move unless the magnetic force of the P4 pole is weakened, and the P4 pole until the developer 11 moves. When the magnetic force of P1 is weakened, the magnetic force of the P1 pole is also weakened in the manufacturing process, causing a problem that the carrier adheres to the photosensitive drum 1, and the magnetic force of the P1 pole can be maintained. However, it has been found that the amount of the developer 11 passing through the first doctor blade 6 becomes unstable, resulting in an image having unevenness in the axial direction of the developing sleeve.
[0060]
Further, the amount of toner 7 taken into the developer accommodating portion 5a depends on the gap between the tip of the second doctor blade 12 and the outer peripheral surface of the developing sleeve 4, as shown in FIG. Therefore, as a result of changing this gap and measuring the toner density at that time, if this gap is less than twice the gap DG between the tip of the first doctor blade 6 and the outer peripheral surface of the developing sleeve 4, the second It has been found that a considerable amount of the developer 11 overflows due to being blocked by the doctor blade 12, and the toner 7 is also difficult to enter the developer accommodating portion 5a, resulting in a decrease in toner density.
[0061]
Further, if the gap between the tip of the second doctor blade 12 and the outer peripheral surface of the developing sleeve 4 is 6 times or more of the gap DG, the developer in the axial direction of the developing sleeve when taken into the developer containing portion 5a. It was found that 11 unevenness occurred, and a portion where the toner 7 was easily captured and a portion where it was difficult to capture were partially formed, resulting in image unevenness.
[0062]
Furthermore, as shown in FIG. 12, the amount of toner 7 taken into the developer accommodating portion 5a also depends on the protruding position X1 of the second doctor blade 12 in the height direction. When the protruding position X1 is located below the center O of the developing sleeve 4, the toner 7 taking-in position is closer to the lower side, and it becomes difficult to take in the toner 7 due to the influence of gravity.
[0063]
The movement of the developer 11 in the developer accommodating portion 5a depends on the magnetic force of the magnet in the developing sleeve 4 as shown in FIG. Therefore, as a result of performing experiments by changing the magnetic force of the P1 pole, the magnetic force of the P1 pole to 1.2 times or more of the magnetic force of the P4 pole (for example, the P4 pole) If the magnetic force is 60.0 millitesla, the magnetic force of the P1 pole is 72.0 millitesla or more), and the movement of the developer 11 in the developer accommodating portion 5a is activated and passes through the first doctor blade 6. It was found that the amount of developer 11 to be stabilized.
[0064]
FIG. 14 shows the relationship between the carrier amount of the developer 11 used in the present invention and the upper limit density of the toner 7. As the amount of carrier set in the developer accommodating portion 5a increases, the time for taking the toner 7 into the developer accommodating portion 5a decreases and the toner concentration decreases, and as the amount of carrier decreases, the toner concentration increases. Further, when the gap DG is widened, the upper limit toner density can be set high.
[0065]
【The invention's effect】
According to the first aspect of the present invention, the second regulating member regulates the passage of the increased developer, and the regulated developer controls the toner uptake, so that the toner supply is always self-controlled to be constant. Therefore, the toner density can be easily adjusted with a simple configuration.
[0066]
According to the fifth aspect of the present invention, by setting the proper toner concentration when the carrier coverage is 100%, the carrier surface can be completely covered with the toner, so that the carrier film can be prevented from being scraped. The life of the agent can be extended.
[0067]
According to the seventh aspect of the present invention, since a developer layer having a layer thickness corresponding to the toner concentration can be formed at the toner supply opening, toner uptake can be self-controlled, and the size and cost can be reduced. The developing device can be provided.
[0068]
According to the eighth aspect of the present invention, the developer circulation speed when the developer layer is formed in the toner supply opening is set to 1 mm / s or more, so the developer is always stirred in the toner intake portion. In addition, it is possible to prevent the occurrence of abnormal images by preventing the toner charge amount from decreasing.
[0069]
According to the twelfth aspect of the present invention, since the developer storage chamber has a sufficient space for the circulation of the developer, the toner concentration in the developer storage chamber is maintained within a certain range without using the toner concentration sensor. Can do.
[0070]
According to the thirteenth aspect of the present invention, since the second regulating member makes the developer present in the toner take-in portion uniform in the axial direction of the developer carrying member, unevenness of the image is obtained by taking in the toner uniformly. Can be prevented.
[0071]
According to the fourteenth aspect of the present invention, the developer present in the toner take-in portion is taken into the developer accommodating chamber while the second regulating member makes the developer carrying member uniform in the axial direction, so that By uniformly taking in the toner, image unevenness can be prevented and an appropriate toner density can be obtained.
[0072]
According to the fifteenth aspect of the present invention, by providing the tip position of the second restricting member above the center position of the developer carrier, the movement of the developer in the take-in portion due to the weight of the developer is limited. The toner density can be controlled by the amount of the developer that can be held by magnetic force.
[0073]
According to the sixteenth aspect of the present invention, in the axial direction of the developer carrying member, the magnetic force of the first pole is increased so as to prevent the carrier from adhering while activating the movement of the developer in the developer containing chamber. A good image without unevenness can be obtained.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram of a main part of a developing device of an image forming apparatus employing a first embodiment of the present invention.
FIG. 2 is a partial cross-sectional view for explaining the behavior of the developer in the first embodiment of the present invention.
FIG. 3 is a partial side sectional view for explaining the behavior of the developer in the first embodiment of the present invention.
FIG. 4 is a partial side sectional view for explaining the behavior of the developer in the first embodiment of the present invention.
FIG. 5 is a schematic diagram for explaining carrier coverage in the first embodiment of the present invention.
FIGS. 6A and 6B are diagrams showing (a) the state of toner adhesion to the carrier when the carrier coverage is 100%, and (b) toner adhesion to the carrier when the carrier coverage is 169% in the first embodiment of the present invention. It is a figure which shows a state.
FIG. 7 is a partial side sectional view for explaining a modification of the first embodiment of the present invention.
FIG. 8 is a partial side sectional view for explaining another modification of the first embodiment of the present invention.
FIG. 9 is a schematic configuration diagram of a main part of a developing device of an image forming apparatus adopting a second embodiment of the present invention.
FIG. 10 is a partial sectional side view of a main part of a developing device for explaining a second embodiment of the present invention.
FIG. 11 is a partial sectional side view of a main part of a developing device for explaining a second embodiment of the present invention.
FIG. 12 is a partial sectional side view of a main part of a developing device for explaining a second embodiment of the present invention.
FIG. 13 is a partial sectional side view of a main part of a developing device for explaining a second embodiment of the present invention.
FIG. 14 is a graph showing the relationship between the carrier amount of the developer used in the second embodiment of the present invention and the toner upper limit density.
[Explanation of symbols]
1 Latent image carrier (photosensitive drum)
2,13 Development device
4,15 Developer carrier (Development sleeve)
5a, 16a, 24a Developer container
5b inner wall
6, 17 First restriction member (first doctor blade)
7,18 Toner
8,19 Toner container (toner hopper)
9,20 Toner supply opening
10, 21 Toner supply means (toner agitator)
11, 22 Developer
12, 23 Second regulating member (second doctor blade)
22a Magnetic carrier
r1 Radius of developer carrier
S Maximum distance
X interface (interface)
X1 Tip position of the second regulating member

Claims

A developer carrier having a magnetic field generating means therein and carrying and transporting a two-component developer containing toner and a magnetic carrier;
A first regulating member that regulates a layer thickness of the developer carried and conveyed by the developer carrying member;
A second restricting member disposed on the upstream side in the transport direction of the developer on the developer carrying member relative to the first restricting member;
A developer accommodating portion located between the first restriction member and the second restriction member;
The conveyance direction upstream side of the developer on said developer carrying member than the second regulating member, a toner accommodating portion having an opening for supplying toner to the prior SL developer carrying member,
A space in which a first circulating developer layer that circulates on the developer carrying member by the developer regulated by a second regulating member is formed;
In the developer accommodating portion, a space for forming a second circulating developer layer that circulates differently from the first circulating developer layer formed on the developer carrier is formed.
The second restricting member functions as a partition member that partitions the two spaces, and is regulated by the second restricting member due to a change in the toner concentration of the developer on the developer carrying member that has entered the developer containing portion. A developing device, wherein the amount of developer taken in is changed to change the toner intake state of the developer on the developer carrying member.

When the toner density of the developer on the developer carrying member that has entered the developer containing portion reaches a predetermined toner concentration, the developer that is restricted from passing by the second regulating member is the developer carrying body. 2. The toner collecting state of the developer on the developer carrying member is stopped by accumulating at a contact portion between the developer and the toner on the upper surface and closing the contact portion with the developer. Development device.

A developer container for storing a two-component developer containing toner and a magnetic carrier;
A rotatable developer carrier disposed opposite to the latent image carrier and having a magnetic field generating means therein;
A first regulating member that regulates a layer thickness of the developer carried on the developer carrying body;
A toner container,
In the developing device that takes in the toner stored in the toner storage portion into the developer storage portion to come into contact with the developer by the movement of the developer in the developer storage portion,
A second restricting member disposed on the upstream side in the transport direction of the developer on the developer carrying member relative to the first restricting member;
A space in which a first circulating developer layer that circulates on the developer carrying member by the developer regulated by a second regulating member is formed;
A space in which a second circulating developer layer that circulates differently from the first circulating developer layer formed on the developer carrier is formed in the developer accommodating portion;
The distance from the portion closest to the developer carrier surface of the second regulating member to the developer carrier surface is made smaller than the maximum distance from the inner wall of the developer container to the developer carrier surface. The second restricting member functions as a partition member for partitioning the two spaces, and the second restricting member causes a change in the toner concentration of the developer on the developer carrying member that has entered the developer containing portion. A developing device characterized in that the toner intake state of the developer on the developer carrying member is changed by changing the regulated developer amount.

A developer container for storing a two-component developer comprising toner and a magnetic carrier;
A rotatable developer carrier disposed opposite to the latent image carrier and having a magnetic field generating means therein;
A first regulating member that regulates a layer thickness of the developer carried on the developer carrying body;
A toner container;
A space in which a first circulating developer layer that circulates on the developer carrying member by the developer regulated by a second regulating member is formed;
In the developer accommodating portion, a space in which a second circulating developer layer that circulates differently from the first circulating developer layer formed on the developer carrier is formed, and
In the developing device that takes in the toner stored in the toner storage portion into the developer storage portion to come into contact with the developer by the movement of the developer in the developer storage portion,
In order to face the developer carrier surface at a position on the upstream side in the rotation direction of the developer carrier from the site of the inner wall surface of the developer container where the distance to the developer carrier surface is maximum, A second restricting member for restricting the amount of the toner entering the developer accommodating portion is provided, and the second restricting member is larger than the maximum distance from the inner wall of the developer accommodating portion to the surface of the developer carrying member. The distance from the portion closest to the surface of the developer carrying member to the surface of the developer carrying member is reduced, and the second regulating member functions as a partition member that partitions the two spaces. Due to the change in the toner density of the developer on the developer carrier that has entered , the amount of developer regulated by the second regulating member is changed, and the toner intake state of the developer on the developer carrier is changed. It is characterized by letting The developing device.