JP3582271B2 - Developing device - Google Patents

Description

上記例の着色粒子の比重は１．０、酸化チタン微粒子の比重は４．５である。
【００３５】
一般に、トナー粒子の粒径は画質に大きな影響を与え、粒径が大きくなるほど画像は粗くなる。平均粒径が２０μｍ程度のトナーでも実用上の問題はないが、細線の解像力を高くするためには、平均粒径が１０μｍ以下のトナーを用いるのが望ましい。しかしながら、トナー径が小さくなるとトナーとキャリアの間に作用する物理的付着力が支配的となり現像性が低下する。また、トナー径が小さくなるとトナーの凝集もおこりやすく取扱いの問題が生じる。このような観点から本願発明で用いるトナーは、平均粒径５μｍ以上、１０μｍ以下のものが望ましい。
【００３６】
トナー用の主バインダ樹脂としては、上記例で使用されているポリエステル樹脂の他に、以下のものを使用することができる。例えば、ポリスチレン、スチレン−プロピレン共重合体、スチレン−ブタヂエン共重合体、スチレン−塩化ビニル共重合体、スチレン−酢酸ビニル共重合体、スチレン−アクリル酸エステル共重合体、スチレン−メタクリル酸エステル共重合体、ポリウレタン樹脂等があり、これらを単体で、または必要に応じて複数のバインダ樹脂を混合して用いられる。
ヒートロール定着時にロールとの離型性を高めトナーオフセットを防止する意味から、エチレン、プロピレン等のオレフィン系単独または共重合体、カルナバワックス等のワックス成分を加えてもよい。この際、ワックス成分の添加量としてはトナーに対して０．５ｗｔ％以上、１０ｗｔ％以下が望ましい。添加量がこれより少ないとワックス成分の効果が出ない。また、添加量がこれより多いと熱によりトナーが変形しやすくなり現像剤の帯電性が変化して安定した画像濃度が得られなくなる。
【００３７】
また、トナーの力学的強度を強くしたり、ヒートロール定着時にトナーの凝集力を高めトナーオフセットを防止する意味から、重量平均分子量が１００，０００以上の高分子量ポリマや、架橋ポリマを含有させてもよい。これら、高分子量ポリマや、架橋ポリマの含有量については、トナーに対して６０ｗｔ％以下が望ましい。含有量がこれより多いと定着時にトナーが良好に溶融定着せず定着不良が問題となるからである。
【００３８】
トナーの着色剤については、黒色系としてはカーボンブラック、ニグロシン、黒鉛等が用いられる。
有彩色系としては、次のようなものを用いることができる。
（イエロー、または、オレンジ顔料）
Ｃ．Ｉ．ピグメントオレンジ３１、Ｃ．Ｉ．ピグメントオレンジ４３、Ｃ．Ｉ．ピグメントイエロー１２、Ｃ．Ｉ．ピグメントイエロー１４、Ｃ．Ｉ．ピグメントイエロー１７、Ｃ．Ｉ．ピグメントイエロー９３、Ｃ．Ｉ．ピグメントイエロー９４、Ｃ．Ｉ．ピグメントイエロー１３８、Ｃ．Ｉ．ピグメントイエロー１７４
（マジェンタ、または、レッド顔料）
Ｃ．Ｉ．ピグメントレッド５、Ｃ．Ｉ．ピグメントレッド４８：１、Ｃ．Ｉ．ピグメントレッド５３：１、Ｃ．Ｉ．ピグメントレッド５７：１、Ｃ．Ｉ．ピグメントレッド１２２、Ｃ．Ｉ．ピグメントレッド１２３、Ｃ．Ｉ．ピグメントレッド１３９、Ｃ．Ｉ．ピグメントレッド１４４、Ｃ．Ｉ．ピグメントレッド１４９、Ｃ．Ｉ．ピグメントレッド１６６、Ｃ．Ｉ．ピグメントレッド１７７、Ｃ．Ｉ．ピグメントレッド１７８、Ｃ．Ｉ．ピグメントレッド２２２
（サイアン、または、グリーン顔料）
Ｃ．Ｉ．ピグメントグリーン７、Ｃ．Ｉ．ピグメントブルー１５、Ｃ．Ｉ．ピグメントブルー１５：２、Ｃ．Ｉ．ピグメントブルー１５：３、Ｃ．Ｉ．ピグメントブルー６０
また、これらトナー着色剤の含有量は、トナーに対し０．５ｗｔ％以上、２０重量％以下であることが望ましい。０．５ｗｔ％未満では、発色性が十分でなく鮮明な画質が得られなくなり、２０ｗｔ％を越えるとトナー中での着色剤の分散不良による画質の濃度むらが生じるからである。
さらに、トナーに磁性を持たせるために磁性体微粉末を含ませてもよい。
【００３９】
また、トナーとしては、上記材料を混練、粉砕、分級してなる混練粉砕型トナーの他に、ビニル基を有する反応性モノマーを用いて懸濁重合や乳化重合によって得られる重合トナーや、あるいは、上記バインダー樹脂と着色剤を有機溶剤中に溶解させ、それを水中に分散させて造粒する溶解懸濁トナーを用いることができる。転写性から見てこれらトナーの形状は球形である方がより優れた転写性が期待でき、その意味では重合トナーや溶解懸濁トナー、あるいは、混練粉砕型トナーを熱風処理してなる球形化トナーが望ましい。
【００４０】
また、このように作製したトナーの帯電性や粉体特性を制御するために、下記の微粒子をトナーに外添することもできる。
このような微粒子はトナー像に付着、もしくはトナー像に混ざり込みトナー像とともに転写されることがあることからトナー像を乱したり、定着後のトナー画像の色ムラや抜け等を起こさないことが重要である。そのようなことからも本発明では、少なくともトナー粒径以下の粒径の微粒子が使用される。また細線や網点の再現性を考慮すると微粒子の粒径はより小さい方が好ましく、５μｍ以下の粒径の微粒子を使用することが望まれる。
【００４１】
さらに、像担持体に微粒子を付着させた状態で潜像形成を行うことから、これら微粒子が遮光効果を有することは望ましくない。微粒子の遮光効果については、要求される画質をもとに、その付着量、付着状態から決まるものではあるが、微粒子そのものができるだけ遮光効果の低いものが好ましく、色合いとしては透明、あるいは薄色であり、粒径はトナー粒径以下、望ましくは１００ｎｍ以下の粒径の微粒子が使用される。
【００４２】
微粒子の材料としては、具体的には、酸化チタン、アルミナ、シリカ、チタン酸バリウム、チタン酸カルシウム、チタン酸ストロンチウム、酸化亜鉛、酸化マグネシウム、酸化ジルコニウム、硫酸バリウム、炭酸バリウム、炭酸カルシウム、炭化ケイ素、窒化ケイ素、酸化クロム、ベンガラ等の無機微粉末や、ポリアクリレート、ポリメタクリレート、ポリメチルメタクリレート、ポリエチレン、ポリプロピレン、ポリフッ化ビニリデン、ポリテトラフルオロエチレン等の有機微粉末が挙げられる。環境安定性を考慮するとこれら微粒子は吸湿性が少ないことが望ましく、特に、酸化チタン、アルミナ、シリカ等の吸湿性を有する無機微粉末の場合は、疎水化処理を施したものが用いられる。これら無機微粉末の疎水化処理は、例えば、ジアルキルジハロゲン化シラン、トリアルキルハロゲン化シラン、アルキルトリハロゲン化シラン等のシランカップリング剤やジメチルシリコンオイル等の疎水化処理剤と上記微粉末とを高温度下で反応させて行うことができる。
【００４３】
〈キャリア〉
上記現像装置で用いられるキャリアは、例えば次のようなものである。
スチレン−アクリル共重合体（数平均分子量：２３，０００、重量平均分子量：９８，０００、Ｔｇ＝７８°Ｃ）３０ｗｔ％、カーボンブラック（塩基性カーボンブラック：ｐＨ＝８．５）３ｗｔ％、粒状マグネタイト（最大磁化８０ｅｍｕ／ｇ、粒径０．５μｍ ）６７ｗｔ％を混練、粉砕、分級して平均粒径を４５μｍとしたものである。このキャリアの帯電極性は正極性で、電気抵抗値は１０^１２Ωｃｍであり、比重は２．２である。なお、平均粒径はマイクロトラック（日機装社製）で測定した値である。
【００４４】
上記キャリアは磁性体微粉末をポリマーに混合してなる、いわゆるポリマーキャリアであるが、鉄・フェライト・マグネタイト等の金属粒子よりなる磁性体粒子キャリアを用いることもできる。ポリマーキャリアは磁性体粒子キャリアに比べて一般に磁化が低いために、柔らかく密度の高い磁気ブラシを形成することができ高画質画像を得ることができる。また、像担持体上に付着した場合に、像担持体表面を傷つけるおそれも少ないという利点がある。さらに、比重も小さいためにキャリアの質量も小さく、現像装置内で現像剤がミキシングされる際にトナーに対するストレスが小さくなり、寿命の長い現像剤を提供できるという長所がある。一方、磁性体粒子キャリアはキャリアの比重が大きいためにキャリアの質量も大きく、現像装置内で現像剤がミキシングされる際にトナーに対するストレスが大きくなるが、現像剤の帯電の立ち上がりが早いという利点があり、要求される性能によってキャリアを使い分ければよい。
【００４５】
キャリアの粒子径については、粒子径が小さいほど磁気ブラシは密になる。平均粒径が６０μｍ以下になるとその効果が現れ始める。しかし、平均粒径が３５μｍ未満となるような粒子径が小さいキャリアになると、キャリアの磁気的拘束力が弱まるために像担持体上へのキャリア付着が発生する。これらのことから、キャリア粒子径は平均粒径が３５μｍ以上、６０μｍ以下が望ましい。
【００４６】
〈現像剤〉
上記トナーとキャリアとを混合した現像剤としては、例えば、トナー濃度（ＴＣ：Ｔｏｎｅｒ Ｃｏｎｃｅｎｔｒａｔｉｏｎ）を１０ｗｔ％としたものを用いることができる。ここでＴＣは次式で示される。
【数２】

【００４７】
上記トナーとキャリアとを混合して現像剤としたときのトナーの電荷量は、高すぎるとトナーのキャリアに対する付着力が強くなりすぎて、トナーが現像されないといった現象が発生する。一方、電荷量が低すぎるとトナーのキャリアに対する付着力が弱くなり遊離トナーによるトナークラウドが発生し、プリントにおけるカブリが問題となる。トナーを転移して良好な現像を行なうという観点からは、現像剤中のトナーの電荷量が絶対値で５〜５０μＣ／ｇ、好ましくは、１０〜４０μＣ／ｇの範囲にあることが望ましい。
本実施形態において、前述のように調整した現像剤３ｇを、底面積３ｃｍ^２ 、高さ３．５ｃｍの円筒状のガラス瓶に入れ、振幅３０ｃｍ、一分間に３０往復のペースで３分間ミキシングしてそのときのトナーの帯電量をブローオフ法で測定した。その結果、電荷量は−１５μＣ／ｇとなった。
【００４８】
次に上記のような現像装置の動作について説明する。
搬送ロール３の磁界発生部材１４は固定支持されており、現像剤搬送部材１３が図示しない駆動手段により図中に示す矢印Ｂ方向に周回移動する。現像剤搬送部材１３上の現像剤には磁界発生部材１４の磁力が作用し、現像剤搬送部材１３上に磁性キャリアが穂状に連なった磁気ブラシが形成される。この磁気ブラシは現像剤搬送部材１３で磁界の変動にともなって転動し、これにより現像剤が撹拌されてトナーの摩擦帯電が行われる。そして、磁気ブラシは現像剤搬送部材１３の移動に伴って現像ロール２との対向位置に搬送される。これらの対向位置では、現像剤搬送部材１３上の磁気ブラシが現像ロール２に接触し、マグネットロール１１の磁力により現像剤が現像ロール２へ受け渡される。現像ロール２に供給された現像剤は、マグネットロール１１の磁力によって現像スリーブ１２上で磁気ブラシを形成し、この磁気ブラシが現像スリーブ１２の周回移動により現像領域に搬送される。現像領域では像担持体１と現像ロール２との間に現像電界が作用しており、この電界内で磁気ブラシ中のトナーが像担持体１上の潜像に転移され、現像が行われる。
【００４９】
その後、現像領域を通過した現像剤は、現像スリーブ１２の周回移動により搬送ロール３との対向位置に搬送され、搬送ロール３上の磁気ブラシとの接触により回収される。搬送ロール３上に回収された現像剤は現像剤搬送部材１３上で磁気ブラシを形成し、現像剤搬送部材１３の周回移動によってトナーホッパー４と対向するトナー補給領域Ａに搬送される。
【００５０】
このトナー補給領域Ａでは、磁界発生部材１４の磁極Ｎ_２ がその両側の磁極Ｓ_１ ，Ｓ_２ よりも弱く着磁されており、現像剤搬送部材１３の周面上の磁束密度がその両側部分より小さくなっている。このため、現像剤搬送部材１３上の現像剤の磁気的拘束力が弱まり、磁気ブラシの形状が崩れて現像剤が自由に動けるようになる。このような状態でトナーホッパー４から新たなトナーが供給されると、現像剤は比較的自由度の高い状態でトナーと接触することになり、現像剤の混合性が飛躍的に向上される。また、磁気ブラシの形状が崩れることにより、現像剤の充填密度が高まり、現像剤中に取り込まれるトナーの量を常に安定化することができる。すなわち、従来のように磁気ブラシが形成された状態で新たなトナーが供給されると、磁気ブラシ間に間隙があることから過剰のトナーを取り込んでしまうことになるが、本実施形態のように磁気ブラシが崩れた状態で新たなトナーが供給されると、現像剤の充填密度が高まることにより過剰のトナーが現像剤中に取り込まれるのを防止できる。こうして適量のトナーを均一に取り込んだ現像剤がトナー補給領域Ａから搬出されると、再び現像剤搬送部材１３上で現像剤の搬送に必要な磁界が働き、磁気ブラシの形状となり搬送される。
【００５１】
そして、現像剤搬送部材１３上の現像剤は現像ロール２との対向位置で現像ロール２上に受け渡され、現像スリーブ１２の周回移動により現像領域に搬送される。これにより、現像領域に搬送される現像剤を、安定したトナー濃度に維持することができ、トナーの帯電不良を防止できると共に、濃度の安定した画像が得られる。
【００５２】
＜帯電テスト１＞
次に、上記のような現像装置の効果を確認するため、トナー補給領域Ａでの磁界強度を変化させて、現像剤の帯電性を調べた結果について説明する。
この実験では、表１に示すように、磁界発生部材の磁極Ｎ_２ の磁力を１５ｍＴ〜５５ｍＴまでの５段階に設定し、その両側の磁極Ｓ_１ ，Ｓ_２ の磁力を４０ｍＴに設定した。なお、磁力発生部材の磁極の磁力については、表１ではトナー補給領域Ａの磁極についてのみ表記しており、トナー補給領域以外の磁極の磁力はすべて４５ｍＴに設定した。
実験では、現像装置にφ１００ｍｍのアルミパイプを、現像ロールと０．５ｍｍの間隔を開けて対向させ、現像ロールに−５００Ｖの電圧を印加するとともに、アルミパイプを接地して、アルミパイプにトナーを現像させて消費させながらトナーを補給するというテストを行った。アルミパイプの周速は１００ｍｍ／ｓ、現像ロールの周速は１５０ｍｍ／ｓ、現像剤搬送部材上の現像剤の移動速度は１５０ｍｍ／ｓに設定した。
【００５３】
この状態で、１時間現像を行い、その間、５分後、１０分後、２０分後、６０分後にアルミパイプをとり外した状態で現像装置だけを１分間駆動させて現像ロールからのトナーのクラウドの発生状態を目視で調べた。また、そのときの現像剤中のトナー濃度（ＴＣ）をブローオフ法で調べた。ちなみにＴＣのふれの実用上問題のないレベルは３ｗｔ％以内である。
（以下余白）
【表１】

【００５４】
結果は表１に示すように、トナー補給領域の磁極の磁力を下げたものではクラウドの発生もなく、また、ＴＣも安定した値を示すことが確認された。しかしながら、１−ａの条件では、クラウドの発生やＴＣの安定性については問題はなかったが、現像剤の搬送に使用上特に問題はないレベルの若干のムラが目視で観察された。これは、トナー補給領域の磁極の磁力を下げすぎたために、現像剤の流れにムラが生じたためと考えられる。
【００５５】
このように上記現像装置では、現像剤搬送部材上の現像剤と新たに補給されるトナーとの混合性を向上することができ、トナーの電荷量を安定化することができると共に、クラウド等の画質劣化のない画像を得ることができる。
【００５６】
図３は、請求項１又は請求項３に記載の発明の一実施形態である現像装置のトナー補給領域を示す部分構成図である。
この現像装置は、トナーホッパー２４が設けられたトナー補給領域Ａにおける磁界発生部材３４と現像剤搬送部材３３との間に、板状の磁性部材２５が介挿されているものである。また、この板状の磁性部材２５が設けられた位置と対向する磁界発生部材３４の磁極Ｓ_１ ，Ｎ_２ ，Ｓ_２ は、現像剤を搬送するために設けられた他の磁極と同じ強さで着磁されている。
【００５７】
上記現像剤搬送部材３３は、ＳＵＳからなる外径φ２０ｍｍのスリーブであり、図示しない駆動手段により周回可能に支持されている。また、磁界発生部材３４は、現像剤搬送部材３３と同軸で回転可能に支持された磁極数２６の対称マグネットロールであり、外径φ１６ｍｍで、磁極ピッチが約２．４ｍｍに設定されている。
また、板状の磁性部材２５は、厚さ０．３ｍｍの鋼板からなり、周回可能に支持された現像剤搬送部材３３と磁界発生部材３４との間で固定支持されている。この磁性部材２５と対向する現像剤搬送部材３３の周面上では、磁束密度は約２５ｍＴとなっており、その両側の磁極と対向する現像剤搬送領域では磁束密度は約４５ｍＴとなっている。
なお、この現像装置の他の構成は図１に示す現像装置と同じである。
【００５８】
このような現像装置では、板状の磁性部材２５によって現像剤搬送部材３３の表面付近の磁界強度が低減され、現像剤に磁界発生部材３４の磁力が作用しにくくなる。このため、トナー補給領域Ａでは現像剤に磁気的拘束力が及ばず、現像剤が比較的自由に動けるようになり、新たに補給されるトナーと現像剤との混合性が良くなる。また、磁気ブラシが崩れて磁性キャリアは分離した状態となるため、現像剤の充填密度が高まり、現像剤中に取り込まれるトナーの量を常に安定化させることができる。
【００５９】
＜帯電テスト２＞
上記現像装置の効果を確認するため、板状の磁性部材の厚さを変えてトナー濃度、およびクラウドの発生状況を調べる実験を行った。
この実験では、現像剤搬送部材と磁界発生部材との間に、厚さ０．２ｍｍ、０．３ｍｍ、０．５ｍｍの板状の磁性部材を設け、トナー補給領域Ａで現像剤搬送部材上の現像剤に作用する磁力が段階的に弱くなるようにした。
【００６０】
このような条件で、テスト１と同様のテストを行った結果を表２に示す。
【表２】

ここで、２−ａは０．５ｍｍ、２−ｂは０．３ｍｍ、２−ｃは０．２ｍｍの磁性部材を磁力発生部材と現像剤搬送部材との間に設けたものである。２−ｄは磁性部材を設けないものである。また、表２に示す磁力は、各磁極と対向する現像剤搬送部材の周面上の磁束密度を示すものである。
【００６１】
その結果、表２に示すように、磁性部材によってトナー補給領域の磁力を低減したものではクラウドの発生もなく、トナー濃度も安定した値を示すことが確認された。
【００６２】
図４は、請求項４に記載の発明の一実施形態である現像装置のトナー補給領域を示す部分構成図である。
この現像装置は、トナーホッパー４４が設けられたトナー補給領域Ａと対向する磁界発生部材５４に隣り合う二つの磁極を配設し、この二つの磁極が同極性となるようにしたものである。この二つの磁極はＳ極であり、現像剤搬送部材５３の周面上における半径方向の最大磁束密度は４５ｍＴに設定されている。また、この磁界発生部材５４は周回移動する現像剤搬送部材５３内に固定支持されている。
なお、この現像装置の他の構成は図１に示す現像装置と同じである。
【００６３】
この現像装置では、トナー補給領域Ａで同極性の二つの磁極が隣接しており、現像剤搬送部材５３上の現像剤に反発磁界が作用する。このような反発磁界が形成されている場合、現像剤に働く磁力は磁極と対向する周面上では強いが、隣接する磁極間と対向する周面上では弱いものとなる。このため、磁極と対向する位置に現像剤が集中的に付着し、磁極間都対向する位置では現像剤が付着しにくくなり、この磁力の弱い部分で現像剤は比較的自由に動ける状態となる。
従って、新たに補給されるトナーと現像剤との混合性が良くなり、現像剤中へのトナーの過剰の取り込みを防止でき、トナーの帯電性を安定化することができる。さらに、反発磁界においては、磁極と対向する周面上に現像剤の溜りが生じ、それが現像剤を搬送するときの壁となって作用し、搬送された現像剤が現像剤の溜りに衝突することで不要なトナーを振り落とす効果が得られる。このため、より安定したトナー濃度を維持することができる。
【００６４】
＜帯電テスト３＞
上記現像装置における反発磁界の効果を確認するため、磁界発生部材の隣接する同極性の磁極の強さを変えて、トナー濃度およびクラウドの発生状況を調べる実験を行った。
この実験では、隣接する磁極及びその両側の磁極の強さは表３に示す条件で行った。なお、表記以外の磁力発生部材の磁極の磁力はすべて４５ｍＴである。その結果を表３に示す。
（以下余白）
【表３】

【００６５】
表３に示すように、クラウドの発生についても、トナー濃度ＴＣのふれについてもテスト１及びテスト２よりも良好な結果を得た。これは、おそらく現像剤が搬送される時に反発磁極と対向する周面上に形成された現像剤溜まりに衝突することによって、過剰のトナーを振り落とす作用が加わったためと推定される。
【００６６】
図５は、請求項５に記載の発明の一実施形態である現像装置のトナー補給領域を示す部分構成図である。
この現像装置は、現像剤搬送部材７３の移動方向におけるトナーホッパー６４の上流側と下流側の壁面に、該現像剤搬送部材７３と間隙をおいて対向するように磁性部材６５が支持されている。また、磁性部材６５と対向する磁界発生部材７４の位置には磁極が配置されている。
上記磁性部材６５は鋼板からなるものであるが、他の磁性材料も適宜に設定可能である。
なお、この現像装置の他の構成は図１に示す現像装置と同じである。
【００６７】
このような現像装置では、トナーホッパー６４の上流側と下流側、すなわち現像剤搬送部材７３上の現像剤の搬入口と搬出口付近で、磁界発生部材７４と磁性部材６５との間に磁気力が働き、磁性キャリアが集中的に連なった現像剤の磁気カーテンが形成される。これにより、トナーがトナーホッパー６４との対向するトナー補給領域Ａからハウジング７０内の現像剤搬送領域へ漏れ出すのが防止され、現像剤が過剰のトナーを取り込むのを回避できる。
【００６８】
＜帯電テスト４＞
上記現像装置の効果を確認するため、トナーホッパーの壁面に磁性部材を設ける場合と設けない場合とで、それぞれ現像装置を連続１２時間駆動させてトナークラウドの発生状況を調べる実験を行った。
この実験において磁界発生部材７４の磁極の配置および強さは、表１と同じ条件で行った。
【００６９】
その結果、磁性部材を設けない場合、２時間迄は１−ａ、１−ｂ、１−ｃの条件で、現像剤の磁気カーテンがなくともトナークラウドは発生しなかったが、３時間を過ぎるころから、徐々に僅かではあるがクラウドが発生し始めた。このクラウドの程度は画質上には問題はない。一方、磁性部材を設けた場合には、現像剤の磁気カーテンの効果により、１−ａ、１−ｂ、１−ｃの条件で、１２時間を経てもトナークラウドは発生しなかった。これは、磁性部材を設けない場合には、トナーがトナー補給領域から漏れ出し、トナーの帯電性が低下し、キャリアとの付着が弱くなるためと考えられる。
【００７０】
なお、上述の実施形態ではロールタイプの現像装置を用いて説明したが、本願発明はそのような構成にとらわれるものではなく、ベルトタイプの現像装置でも同様の効果が得られることは明白である。
【００７１】
【発明の効果】
以上説明したように、本願の発明に係る現像装置では、トナー補給手段との対向位置で、磁界発生部材により形成される磁界を低減若しくは反発磁界を形成して、現像剤搬送手段上の現像剤に新たなトナーを補給するので、トナーと現像剤との混合性を向上することができ、現像剤中に取り込まれるトナー量を常に安定化させることができる。このため、簡単な構成で、現像領域に搬送される現像剤のトナー濃度、及びトナーの電荷量をほぼ一定に維持することができ、濃度ムラやクラウドのない画像を長期にわたり安定して維持することができる。また、従来のような複雑なトナー濃度制御手段が不要となり、低コスト化および装置の小型化が可能となる。また、トナー補給手段が設けられた位置の下流側に現像剤の磁気カーテンを形成することにより、トナー補給領域からのトナー漏れを防止して現像剤中のトナー濃度をより安定化することができる。
【図面の簡単な説明】
【図１】請求項１又は請求項２に記載の発明の一実施形態である現像装置を示す概略構成図である。
【図２】上記現像装置のトナー補給領域付近の構成を示す部分拡大図である。
【図３】請求項１又は請求項３に記載の発明の一実施形態である現像装置のトナー補給領域付近の構成を示す部分拡大図である。
【図４】請求項４に記載の発明の一実施形態である現像装置のトナー補給領域付近の構成を示す部分拡大図である。
【図５】請求項５に記載の発明の一実施形態である現像装置のトナー補給領域付近の構成を示す部分拡大図である。
【符号の説明】
１ 像担持体
２ 現像ロール
３，２３，４３，６３ 搬送ロール
４，２４，４４，６４ トナーホッパー
９ 現像用開口
１０，３０，５０，７０ ハウジング
１１ マグネットロール
１２ 現像スリーブ
１３，３３，５３，７３ 現像剤搬送部材
１４，３４，５４，７４ 磁界発生部材
２５ 板状磁性部材
６５ 磁性部材[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention uses a two-component developer containing a magnetic carrier and a toner that is electrically adsorbed on the magnetic carrier, and forms a toner in the two-component developer on a latent image formed on an image carrier such as a photoconductor. And a developing device for selectively transferring and visualizing.
[0002]
[Prior art]
In the electrophotographic method, a developing method using a two-component developer containing a toner and a magnetic carrier has features that the toner is easily charged and aggregation of the toner particles hardly occurs. For this reason, although it is necessary to control the amount of toner contained in the two-component developer, that is, the toner concentration, it has been widely used conventionally.
In a developing device using such a two-component developer, it is important how the toner density and the charge amount of the toner can be controlled with high accuracy. For example, if the toner density is too low, the density of the printed image will be insufficient, and if the toner density is too high, a toner cloud will easily occur, leading to problems such as background contamination of the print image and contamination inside the apparatus.
[0003]
The appropriate range of the toner density at this time depends on the charge amount of the toner. For example, when the toner density is the same, the print image density is lower when the toner charge amount is high, when the toner charge amount is high and when the toner charge amount is low. This is because when the charge amount of the toner is high, the electrostatic adhesion of the toner to the carrier is increased, thereby deteriorating the developability, and the number of toners required for saturated development of the electrostatic latent image is reduced. It can be done for some reason. Also, when the toner density is the same, the toner cloud is more likely to occur when the toner charge amount is low between the case where the toner charge amount is high and the case where the toner charge amount is low. This is because when the charge amount of the toner is low, the electrostatic adhesion of the toner to the carrier is low.
[0004]
Therefore, when controlling the toner concentration, it is important to grasp the chargeability of the developer. It is meaningless to control the toner concentration to a constant value when the chargeability of the developer greatly changes due to the environment and aging. For example, as a toner density control method, a fixed amount replenishing method in which toner is replenished in accordance with a print amount, or a method in which toner is replenished by detecting the amount of toner in a developer is used. There is a method of replenishing the developer, but when the chargeability of the developer changes, even if the toner concentration is controlled to a predetermined value, the charge amount of the toner does not always reach the predetermined value, and the toner concentration is accurately adjusted. Even if controlled, the expected effect cannot be obtained.
[0005]
To solve such a problem, for example, there is a method of actually detecting the amount of developed toner on the image carrier and replenishing the toner. This method controls the toner concentration in the developer by directly detecting the amount of the developing toner, that is, the developing concentration, and is more effective than the above-described method of replenishing the developer with an amount of toner corresponding to the used amount. Is big.
[0006]
However, detecting the amount of toner in the developer or controlling the toner concentration by detecting the amount of developed toner on the image carrier as described above leads to an increase in the cost of the apparatus. In addition, since the toner concentration control method merely replenishes the toner, the toner concentration cannot be reduced other than forcibly discarding the toner when the toner concentration becomes higher than a predetermined value.
[0007]
As a countermeasure against such a problem, for example, as disclosed in Japanese Patent Publication No. 5-59427 and Japanese Patent Application Laid-Open No. H7-84456, a technique has been proposed in which the toner density is controlled with a simpler configuration. I have.
The technique disclosed in Japanese Patent Publication No. 59594/1993 stabilizes the amount of toner attached to a magnetic carrier by rubbing the spikes of a magnetic brush on a sleeve with toner in a toner hopper through a mesh screen. And the toner density is controlled to be substantially constant.
[0008]
Further, the technology disclosed in Japanese Patent Application Laid-Open No. 7-84456 discloses a technique in which the space around the developing roller is made a narrow space, and the amount of the carrier in this space is made substantially constant by making the amount of the carrier in this space almost constant. Is adjusted to control the toner density.
[0009]
[Problems to be solved by the invention]
However, such a developing device has the following problems.
In the developing device described in Japanese Patent Publication No. 5-59427, since the developer is rubbed against the mesh screen, stress is applied to the developer, and the life of the developer is greatly reduced. Further, since the fluidity of the toner or the chargeability of the toner, that is, the adhesive force between the toner and the carrier greatly contributes to the control of the toner concentration, when the fluidity of the toner or the chargeability of the toner changes due to the environment or aging. Has a problem that the toner density control range deviates from the initially set range and the print image quality differs from the initial one.
[0010]
Also, there is a large difference in the amount of toner to be replenished between a case where a solid image having a gradation such as a photograph, a painting, and a map is mainly printed and a case where a line image is mainly printed. In the screen method, since the contact area between the carrier and the toner is limited, it is difficult to keep the toner concentration constant when the amount of toner to be replenished fluctuates greatly.
[0011]
On the other hand, in the developing device described in JP-A-7-84456, when a magnetic toner is used, it is necessary to incorporate the magnetic powder into the toner. However, there is a problem that color toner cannot be used. In addition, if the toner is made non-magnetic with an emphasis on coloring, the disclosed technology cannot function as a developing device. That is, when the non-magnetic toner is used in the developing device, the non-magnetic toner and the magnetic carrier are accommodated in the narrow space without being stirred, so that the toner is insufficiently charged. Since this toner does not have the effect of preventing scattering due to magnetic force, it tends to form a cloud, and a large amount of toner cloud appears as fog on an image, and a print with good image quality cannot be obtained.
[0012]
Further, the developing devices disclosed in Japanese Patent Publication No. 5-59427 and Japanese Patent Application Laid-Open No. H7-84456 each have a structure in which the carrier is always magnetically attracted to the surface of the developing roll. Form a magnetic brush in which carriers are spike-shaped. Therefore, when new toner is replenished, the developer is in a magnetically agglomerated state, and the replenished toner is difficult to uniformly mix in the developer, resulting in uneven density in the visualized image. Cheap. Further, when the magnetic carrier is magnetically aggregated, the effective charging area of the carrier is reduced, and poorly charged toner is easily generated. Further, since there is a gap between the magnetic brushes in which the carriers are connected in a spike shape, excessive toner is taken into the gap. For this reason, charging of the toner becomes insufficient, which leads to image quality deterioration such as clouding and fogging.
[0013]
The invention according to the present application has been made in view of the above problems, and an object of the invention is to make it possible to control the toner concentration and the toner charge amount in a two-component developer with a simple configuration. An object of the present invention is to provide a developing device that can obtain a good image without deterioration in image quality even when a magnetic toner is used.
[0014]
[Means for Solving the Problems]
In order to solve the above-mentioned problem, the invention according to claim 1 includes: a toner particle that transfers to an electrostatic latent image on an image carrier to visualize the electrostatic latent image; A developing device using a two-component developer containing magnetic carrier particles to be charged, comprising: a magnetic field generating member provided with a plurality of magnetic poles on an endless peripheral surface; An endless developer transporting means supported so as to be able to move around, and magnetically attracted onto the peripheral surface of the developer transporting means at a position along the peripheral surface of the developer transporting means. A toner replenishing means for replenishing the developer with new toner, wherein a magnetic flux density on the peripheral surface of the developer conveying means at a position where the toner replenishing means is provided is smaller than both side portions thereof And
[0015]
In the above invention, the magnetic pole material forming the magnetic field generating member may be any material that is usually used as a permanent magnet. For example, ferrite, magnetite, a metal-based magnet magnetized on a metal material such as iron, magnetite on a polymer Magnetic carriers such as plastic magnets magnetized on powder or ferrite powder dispersion, and sheet magnets magnetized on polymer or rubber with magnetite powder or ferrite powder dispersed into a sheet are attracted Any material that generates a magnetic field can be used.
[0016]
The developer conveying means is made of a non-magnetic material, and when it is necessary to apply a voltage such as a developing bias, a material that at least makes the surface potential uniform is used. As such a material, a metal is suitable because of its excellent workability. Among them, a material such as aluminum, stainless steel, and phosphor bronze is used.
[0017]
As the two-component developer, known ones can be appropriately used, and the toner may be either magnetic or non-magnetic. As the carrier, a known carrier such as metal fine particles such as ferrite, magnetite, and iron, a metal particle carrier obtained by coating the surface of the metal fine particles with a polymer, or a polymer carrier obtained by adding a magnetic powder to a polymer may be used. it can.
[0018]
The developing device as described above includes a magnetic field generating member having a plurality of magnetic poles along the peripheral surface, and a developer conveying means rotatably supported outside the magnetic field generating member. A magnetic brush in which a magnetic carrier having toner adhered thereto due to the magnetic force is formed in a spike shape on the peripheral surface of the developer conveying means, and is conveyed by the orbital movement of the developer conveying means. A toner replenishing unit for replenishing the developer carried by the developer transporting unit with new toner is disposed at a position facing the developer transporting unit, and a magnetic flux density on the developer transporting unit is provided in the toner replenishment area. Is reduced from both sides thereof, so that in the toner replenishing area, the magnetic binding force of the developer conveyed on the developer conveying means is weakened, and the shape of the magnetic brush collapses, so that the developer can move freely. .
[0019]
When new toner is supplied to the developer in such a state, the developer comes into contact with the toner in a relatively high degree of freedom, and the mixing property of the developer is dramatically improved. In addition, the collapse of the shape of the magnetic brush increases the packing density of the developer, so that the amount of toner taken into the developer can be constantly stabilized. That is, if new toner is supplied in a state where the magnetic brush is formed as in the related art, excessive toner is taken in due to the gap between the magnetic brushes. When new toner is supplied with the brush broken, the filling density of the developer increases, and it is possible to prevent excess toner from being taken into the developer. When the developer in which an appropriate amount of toner has been uniformly taken out is carried out of the toner replenishing area, the magnetic force necessary for carrying the developer acts again on the peripheral surface of the developer carrying means, and is carried in the form of a magnetic brush. Therefore, replenishment of new toner is smoothly performed, and the problem of image quality deterioration such as density unevenness at the time of development and cloud and fog due to poorly charged toner is solved.
[0020]
As means for reducing the magnetic flux density on the developer conveying means in the toner replenishing area, the magnetic field generating member fixed and supported is opposed to the toner replenishing area. At least one of the magnetic poles is magnetized to be weaker than other magnetic poles magnetized to attract and transport the developer onto the developer transport unit. At this time, the magnetic force of the magnetic field generating member can be appropriately set as long as the transport of the developer is not abnormal, that is, the flow of the developer is not uneven.
[0021]
Further, a plate-like magnetic member may be interposed between the magnetic field generating member and the developer conveying means in the toner supply area. This plate-shaped magnetic member reduces the magnetic field intensity near the surface of the developer conveying means, so that the magnetic restraining force is less likely to act on the developer, and the developer is compared on the peripheral surface of the developer conveying means. You can move freely. For this reason, the magnetic carrier in the developer is separated in the toner supply area, and the new toner and the developer are sufficiently mixed, the filling density of the developer is increased, and the amount of the toner taken into the developer is increased. Can always be stabilized.
[0022]
According to a fourth aspect of the present invention, there is provided an image forming apparatus comprising: a toner particle that transfers to an electrostatic latent image on an image carrier to visualize the electrostatic latent image; and a magnetic carrier particle that contacts and frictionally charges the toner particle. A magnetic field generating member having a plurality of magnetic poles provided on an endless peripheral surface; and a revolving movement outside the peripheral surface of the magnetic field generating member. Having a supported endless developer conveying means, On the developer conveying means, a magnetic brush in which the magnetic carriers are spliced by a magnetic field formed by the magnetic field generating member is formed, A toner replenishing unit is provided at a position along the peripheral surface of the developer transporting unit to supply new toner to the developer magnetically attracted on the peripheral surface of the developer transporting unit. It is assumed that two adjacent magnetic poles of the magnetic field generating member, which are magnetized at the position where is provided, have the same polarity.
[0023]
As described above, by adopting a configuration in which magnetic poles of the same polarity are adjacent to each other in a region facing the toner replenishing unit, a repelling magnetic field acts on the developer conveyed to the toner replenishment region. When such a repulsive magnetic field is formed, a magnetic attraction force acting on the developer is strong on the magnetic poles, but there is a region where no action occurs between adjacent magnetic poles. This is obvious when observing the state of adhesion of the developer under the repulsive magnetic field. The developer is intensively attached near the magnetic poles, and the developer is hard to adhere between the magnetic poles. When the developer is continuously fed into a region where such a repelling magnetic field acts, the developer is conveyed so as to jump over the repelling magnetic field. Accordingly, by providing such a repulsive magnetic field, the mixing property between the replenished toner and the developer can be improved, and the excessive charging of the toner into the developer can be prevented, thereby improving the chargeability. Further, before and after the repulsive magnetic field, a pool of the developer is generated on the magnetic pole, which acts as a wall for transporting the developer, and the developer transported beyond the repulsive magnetic field causes the pool of the developer to accumulate. By colliding with the toner, an effect of shaking off unnecessary toner can be obtained. Therefore, a more stable toner concentration of the developer can be maintained.
[0024]
According to a fifth aspect of the present invention, there is provided a magnetic member supported downstream of the position where the toner replenishing means is provided so as to face the developer conveying means with a gap therebetween.
As a result, a magnetic force acts between the developer transporting means and the magnetic member near the downstream side of the toner replenishing means, and a magnetic curtain in which magnetic carriers are intensively connected is formed. This prevents the toner from leaking from the area facing the toner replenishing means to the developer transport area, and prevents the developer from taking in excessive toner in the developer transport area.
[0025]
The method of transporting the developer in the developer transport area can be set as appropriate. For example, a magnetic force generating member is included in a non-magnetic developer transport unit, and the developer transport unit is moved while the magnetic field generating member is fixed. Then, there is a method in which the developer is transported while tumbling, or a method in which the magnetic force generating member and the developer transport means are moved in the same direction or the opposite direction to transport the developer while tumbling. Also, when rotating the magnetic force generating member and the developer transporting means, the speed difference between the magnetic field generating member and the developer transporting means is reduced so that the developer on the developer transporting means is in accordance with the pitch of the magnetic poles of the magnetic force generating member. There is also a method in which the developer is transported in a state where the magnetic brush shape is shown, and the developer is transported without tumbling. However, the method of rotating the magnetic field generating member as described above cannot be applied in the invention described in claim 2.
[0026]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a schematic configuration diagram showing a developing device according to an embodiment of the present invention.
In this developing device, a developing opening 9 is provided in a portion of the housing 10 in which the developer is accommodated, facing the image carrier 1. The developing roll 2 is provided at a position where the developing opening 9 is provided, and is closely opposed to the image carrier 1. A plurality of magnetic poles are magnetized at a small pitch on the peripheral surface of the developing roll 2. The developing roll attracts the developer to form a developer layer, and transports the developer to a developing area facing the image carrier 1. . Further, on the opposite side of the position facing the image carrier 1, a transport roll 3 facing the developing roll 2 with a predetermined gap is provided. The transport roll 3 includes a rotatable hollow cylindrical non-magnetic developer transport member 13 and a cylindrical magnetic field generating member 14 located inside the developer transport member 13. It is magnetically attracted to form a magnetic brush in which carriers are spike-shaped. A toner hopper 4 for storing toner is provided above the transport roll 3, and new toner is supplied from the toner hopper 4 to the developer on the transport roll 3.
[0027]
The magnetic field generating member 14 of the transport roll 3 has magnetic poles of different polarities alternately arranged over the entire circumference, and is fixedly supported coaxially with the developer transport member 13 that moves around the outside. The magnetic field generating member 14 forms a magnetic brush on the surface of the developer conveying member 13 by a magnetic field formed between adjacent magnetic poles. The magnetic brush is conveyed while being stirred by the developer conveying member 13 moving around.
[0028]
The magnetic field generating member 14 is a magnet roll in which N poles and S poles are alternately symmetrically magnetized along the peripheral surface, and has a diameter of 18 mm, 26 magnetic poles, and a magnetic pole pitch of about 2.4 mm. As shown in FIG. 2, the magnetic field generating member 14 has one of the magnetic poles N in a region (toner replenishment region) facing the toner hopper 4. ₂ But the magnetic poles S on both sides ₁ , S ₂ Are weaker than other magnetic poles. In the present embodiment, the magnetic force of the magnetic field generating member 14 is the magnetic pole N ₂ 25 mT on the peripheral surface of the developer transport member 13 facing the magnetic pole S ₁ , S ₂ It is 40 mT on the peripheral surface facing the magnetic pole, and 45 mT in the region facing the other magnetic poles, that is, the region for transporting the developer of the developer transporting member 13.
[0029]
As shown in FIG. 2, the magnetic pole of the magnetic field generating member 14 in the toner supply area A is located near the boundary of the toner supply area A, that is, near the wall surface of the toner hopper 4. At the position of the magnetic pole, the spikes of the developer come into contact with the inner wall of the toner hopper 4, thereby preventing the toner from leaking from the toner supply area A into the housing 10.
[0030]
The developer transporting member 13 is made of a non-magnetic and conductive endless film, and is driven to rotate around the magnetic field generating member 14 by driving means (not shown). The developer conveying member 3 is formed of a sleeve formed of SUS and having an outer diameter of 20 mm.
[0031]
The developing roll 2 includes a hollow cylindrical non-magnetic conductive developing sleeve 12 rotatably supported, and a magnet roll 11 fixedly supported in the developing sleeve coaxially with the developing sleeve. The magnet roll 11 has magnetic poles of different polarities alternately magnetized along the entire circumference, and a magnetic brush of a two-component developer is applied to the surface of the developing sleeve 12 by a magnetic field formed between adjacent magnetic poles. Is formed. Then, as the developing sleeve 12 rotates, the magnetic brush is transported to the developing area.
[0032]
The magnet roll 11 has a diameter of 18 mm, 30 magnetic poles are magnetized at a pitch of about 2.1 mm, and the maximum magnetic flux density (polar magnetic force) of each magnetic pole on the developing sleeve 12 is 30 mT. The developing sleeve 12 has an outer diameter of 20 mm and is formed of SUS. A developing bias voltage is applied to the developing sleeve 11 from a developing bias power supply (not shown), and a developing electric field is formed between the developing sleeve 11 and the image carrier 1. Is transferred to an electrostatic latent image on the image carrier.
[0033]
Next, the two-component developer used in the developing device will be described.
<toner>
As the toner, for example, toner prepared as follows can be used.
94 wt% of polyester (number average molecular weight: 4,300, weight average molecular weight: 9,800, Tg = 58 ° C.) and 6 wt% of cyanine blue 4938 (Dainichi Seika) are kneaded and pulverized to obtain colored particles having an average particle diameter of 7 μm. . Titanium oxide fine particles having an average particle diameter of 40 nm are externally added to the colored particles at a coverage of 30% of the surface area of the colored particles to obtain a cyan toner. The charge polarity of this toner is negative, and the average particle diameter is a value measured by a Coulter counter (manufactured by Coulter Inc.).
[0034]
The coverage f (%) is such that the average particle diameter of the colored particles is dt (m), the average particle diameter of the titanium oxide fine particles is da (m), the specific gravity of the colored particles is ρt, and the specific gravity of the titanium oxide fine particles is ρa, Assuming that the weight of the titanium oxide fine particles is Wa (kg) and the weight of the colored particles is Wt (kg), the weight is given by the following equation.
(Equation 1)

The specific gravity of the colored particles in the above example is 1.0, and the specific gravity of the titanium oxide fine particles is 4.5.
[0035]
Generally, the particle size of toner particles has a large effect on image quality, and the larger the particle size, the coarser the image. Although there is no practical problem with toner having an average particle diameter of about 20 μm, it is desirable to use a toner having an average particle diameter of 10 μm or less in order to increase the resolution of fine lines. However, as the toner diameter decreases, the physical adhesive force acting between the toner and the carrier becomes dominant and the developability decreases. Further, when the toner diameter is small, aggregation of the toner is liable to occur, causing a problem in handling. From such a viewpoint, the toner used in the present invention preferably has an average particle diameter of 5 μm or more and 10 μm or less.
[0036]
As the main binder resin for the toner, the following can be used in addition to the polyester resin used in the above example. For example, polystyrene, styrene-propylene copolymer, styrene-butadiene copolymer, styrene-vinyl chloride copolymer, styrene-vinyl acetate copolymer, styrene-acrylate copolymer, styrene-methacrylate copolymer There are a coalescence, a polyurethane resin and the like, and these are used alone or, if necessary, by mixing a plurality of binder resins.
An olefin homopolymer or copolymer such as ethylene and propylene, or a wax component such as carnauba wax may be added from the viewpoint of enhancing the releasability from the roll and preventing toner offset during heat roll fixing. At this time, the amount of the wax component added is preferably 0.5 wt% or more and 10 wt% or less based on the toner. If the amount is less than this, the effect of the wax component is not obtained. On the other hand, if the addition amount is larger than this, the toner is likely to be deformed by heat, and the chargeability of the developer changes, so that a stable image density cannot be obtained.
[0037]
Further, from the viewpoint of increasing the mechanical strength of the toner or increasing the cohesive strength of the toner during heat roll fixing and preventing toner offset, a high molecular weight polymer having a weight average molecular weight of 100,000 or more or a crosslinked polymer is contained. Is also good. The content of the high molecular weight polymer or the crosslinked polymer is desirably 60 wt% or less based on the toner. If the content is larger than this, the toner does not melt and fix well at the time of fixing, and a fixing defect becomes a problem.
[0038]
As for the colorant of the toner, carbon black, nigrosine, graphite and the like are used as the black type.
The following can be used as the chromatic color system.
(Yellow or orange pigment)
C. I. Pigment Orange 31, C.I. I. Pigment Orange 43, C.I. I. Pigment Yellow 12, C.I. I. Pigment Yellow 14, C.I. I. Pigment Yellow 17, C.I. I. Pigment Yellow 93, C.I. I. Pigment Yellow 94, C.I. I. Pigment yellow 138, C.I. I. Pigment Yellow 174
(Magenta or red pigment)
C. I. Pigment Red 5, C.I. I. Pigment Red 48: 1, C.I. I. Pigment Red 53: 1, C.I. I. Pigment Red 57: 1, C.I. I. Pigment Red 122, C.I. I. Pigment Red 123, C.I. I. Pigment Red 139, C.I. I. Pigment Red 144, C.I. I. Pigment Red 149, C.I. I. Pigment Red 166, C.I. I. Pigment Red 177, C.I. I. Pigment Red 178, C.I. I. Pigment Red 222
(Sian or green pigment)
C. I. Pigment Green 7, C.I. I. Pigment Blue 15, C.I. I. Pigment Blue 15: 2, C.I. I. Pigment Blue 15: 3, C.I. I. Pigment Blue 60
Further, the content of the toner colorant is preferably 0.5 wt% or more and 20 wt% or less based on the toner. If the amount is less than 0.5% by weight, the color developability is not sufficient and a clear image cannot be obtained. If the amount exceeds 20% by weight, unevenness in image quality due to poor dispersion of the colorant in the toner occurs.
Further, a magnetic fine powder may be included in order to impart magnetism to the toner.
[0039]
Further, as the toner, kneading, pulverizing the above materials, in addition to kneading and pulverizing type toner obtained by classification, a polymerized toner obtained by suspension polymerization or emulsion polymerization using a reactive monomer having a vinyl group, or A dissolved suspension toner in which the binder resin and the colorant are dissolved in an organic solvent and dispersed in water to form granules can be used. In terms of transferability, spherical toners can be expected to have better transferability if they are spherical. In that sense, spherical toners obtained by hot-air treatment of polymerized toners, dissolved suspension toners, or kneaded and crushed toners Is desirable.
[0040]
Further, in order to control the chargeability and powder characteristics of the toner thus produced, the following fine particles can be externally added to the toner.
Such fine particles adhere to the toner image or are mixed with the toner image and may be transferred together with the toner image.Therefore, the fine particles do not disturb the toner image and do not cause color unevenness or omission of the toner image after fixing. is important. For this reason, in the present invention, fine particles having a particle diameter of at least the toner particle diameter are used. In consideration of the reproducibility of fine lines and halftone dots, the particle size of the fine particles is preferably smaller, and it is desired to use fine particles having a particle size of 5 μm or less.
[0041]
Further, since the latent image is formed with the fine particles adhered to the image carrier, it is not desirable that these fine particles have a light shielding effect. The light-shielding effect of the fine particles is determined based on the required image quality based on the amount of the particles attached and the state of adhesion, but it is preferable that the fine particles themselves have a light-shielding effect that is as low as possible. Fine particles having a particle size equal to or less than the toner particle size, preferably 100 nm or less are used.
[0042]
Specific examples of the material of the fine particles include titanium oxide, alumina, silica, barium titanate, calcium titanate, strontium titanate, zinc oxide, magnesium oxide, zirconium oxide, barium sulfate, barium carbonate, calcium carbonate, and silicon carbide. And inorganic fine powders such as silicon nitride, chromium oxide, and red iron oxide; and organic fine powders such as polyacrylate, polymethacrylate, polymethyl methacrylate, polyethylene, polypropylene, polyvinylidene fluoride, and polytetrafluoroethylene. In consideration of environmental stability, it is desirable that these fine particles have low hygroscopicity. In particular, in the case of inorganic fine powder having hygroscopicity such as titanium oxide, alumina, silica, etc., those subjected to a hydrophobic treatment are used. Hydrophobic treatment of these inorganic fine powders, for example, dialkyl dihalogenated silane, trialkyl halogenated silane, silane coupling agent such as alkyl trihalogenated silane or hydrophobic treatment agent such as dimethyl silicone oil and the fine powder and The reaction can be performed at a high temperature.
[0043]
<Career>
The carrier used in the developing device is, for example, as follows.
Styrene-acrylic copolymer (number average molecular weight: 23,000, weight average molecular weight: 98,000, Tg = 78 ° C.) 30 wt%, carbon black (basic carbon black: pH = 8.5) 3 wt%, granular 67 wt% of magnetite (maximum magnetization: 80 emu / g, particle size: 0.5 μm) was kneaded, pulverized, and classified to have an average particle size of 45 μm. The charge polarity of this carrier is positive and the electric resistance value is 10 ¹² Ωcm, and the specific gravity is 2.2. The average particle size is a value measured with a Microtrac (manufactured by Nikkiso Co., Ltd.).
[0044]
The carrier is a so-called polymer carrier obtained by mixing magnetic fine powder with a polymer, but a magnetic particle carrier made of metal particles such as iron, ferrite and magnetite can also be used. Since the polymer carrier generally has lower magnetization than the magnetic particle carrier, a soft and high-density magnetic brush can be formed and a high-quality image can be obtained. In addition, there is an advantage that the possibility of damaging the surface of the image carrier when adhered to the image carrier is reduced. Further, since the specific gravity is small, the mass of the carrier is also small, and the stress on the toner when the developer is mixed in the developing device is reduced, so that there is an advantage that a developer having a long life can be provided. On the other hand, the magnetic particle carrier has a large carrier mass due to the large specific gravity of the carrier, and the stress on the toner increases when the developer is mixed in the developing device, but the charge of the developer rises quickly. Therefore, the carrier may be properly used depending on the required performance.
[0045]
Regarding the particle size of the carrier, the smaller the particle size, the denser the magnetic brush. When the average particle size becomes 60 μm or less, the effect starts to appear. However, when the carrier has a small particle diameter such that the average particle diameter is less than 35 μm, the magnetic binding force of the carrier is weakened, and the carrier adheres to the image carrier. From these facts, the average particle diameter of the carrier is desirably 35 μm or more and 60 μm or less.
[0046]
<Developer>
As the developer in which the toner and the carrier are mixed, for example, a developer having a toner concentration (TC: Toner Concentration) of 10 wt% can be used. Here, TC is expressed by the following equation.
(Equation 2)

[0047]
If the charge amount of the toner when the toner and the carrier are mixed to form a developer is too high, a phenomenon that the toner is not developed because the adhesion of the toner to the carrier becomes too strong. On the other hand, if the charge amount is too low, the adhesion of the toner to the carrier is weakened, and a toner cloud due to free toner is generated, which causes fogging in printing. From the viewpoint of transferring toner and performing good development, it is desirable that the charge amount of the toner in the developer is in the range of 5 to 50 μC / g, preferably 10 to 40 μC / g in absolute value.
In the present embodiment, 3 g of the developer adjusted as described above is applied to a bottom area of 3 cm. ² The sample was placed in a cylindrical glass bottle having a height of 3.5 cm, mixed at an amplitude of 30 cm at a pace of 30 reciprocations per minute for 3 minutes, and the charge amount of the toner at that time was measured by a blow-off method. As a result, the charge amount was −15 μC / g.
[0048]
Next, the operation of the above-described developing device will be described.
The magnetic field generating member 14 of the transport roll 3 is fixed and supported, and the developer transport member 13 is circulated in a direction indicated by an arrow B in FIG. The magnetic force of the magnetic field generating member 14 acts on the developer on the developer transport member 13, and a magnetic brush in which magnetic carriers are connected in a spike shape is formed on the developer transport member 13. The magnetic brush rolls with the fluctuation of the magnetic field in the developer conveying member 13, whereby the developer is agitated and the toner is triboelectrically charged. Then, the magnetic brush is transported to a position facing the developing roll 2 as the developer transporting member 13 moves. At these opposing positions, the magnetic brush on the developer conveying member 13 contacts the developing roll 2, and the developer is transferred to the developing roll 2 by the magnetic force of the magnet roll 11. The developer supplied to the developing roll 2 forms a magnetic brush on the developing sleeve 12 by the magnetic force of the magnet roll 11, and the magnetic brush is conveyed to the developing area by the orbital movement of the developing sleeve 12. In the developing area, a developing electric field acts between the image carrier 1 and the developing roll 2, and in this electric field, the toner in the magnetic brush is transferred to a latent image on the image carrier 1 and development is performed.
[0049]
Thereafter, the developer that has passed through the developing region is transported to a position facing the transport roll 3 by the circumferential movement of the developing sleeve 12, and is collected by contact with the magnetic brush on the transport roll 3. The developer collected on the transport roll 3 forms a magnetic brush on the developer transport member 13, and is transported to the toner replenishment area A facing the toner hopper 4 by the circumferential movement of the developer transport member 13.
[0050]
In the toner supply area A, the magnetic pole N of the magnetic field generating member 14 ₂ Are the magnetic poles S on both sides ₁ , S ₂ The magnetic flux density on the peripheral surface of the developer conveying member 13 is smaller than that on both sides thereof. For this reason, the magnetic binding force of the developer on the developer conveying member 13 is weakened, and the shape of the magnetic brush is broken, so that the developer can move freely. When new toner is supplied from the toner hopper 4 in such a state, the developer comes into contact with the toner with a relatively high degree of freedom, and the mixing property of the developer is greatly improved. In addition, the collapse of the shape of the magnetic brush increases the packing density of the developer, so that the amount of toner taken into the developer can be constantly stabilized. That is, if new toner is supplied in a state where the magnetic brush is formed as in the related art, excess toner is taken in due to the gap between the magnetic brushes. When new toner is supplied in a state where the magnetic brush is collapsed, excess toner can be prevented from being taken into the developer by increasing the filling density of the developer. When the developer in which an appropriate amount of toner has been uniformly taken out is carried out from the toner replenishing area A, a magnetic field necessary for carrying the developer acts on the developer carrying member 13 again, and is carried in the form of a magnetic brush.
[0051]
Then, the developer on the developer conveying member 13 is transferred to the developing roll 2 at a position facing the developing roll 2, and is conveyed to the developing area by the circumferential movement of the developing sleeve 12. As a result, the developer conveyed to the developing area can be maintained at a stable toner concentration, and it is possible to prevent poor charging of the toner and obtain an image having a stable concentration.
[0052]
<Charging test 1>
Next, in order to confirm the effect of the developing device as described above, a result of examining the chargeability of the developer by changing the magnetic field intensity in the toner supply area A will be described.
In this experiment, as shown in Table 1, the magnetic pole N ₂ Are set in five steps from 15 mT to 55 mT, and the magnetic poles S on both sides thereof are set. ₁ , S ₂ Was set to 40 mT. The magnetic force of the magnetic poles of the magnetic force generating member is shown in Table 1 only for the magnetic poles in the toner supply area A, and the magnetic forces of the magnetic poles other than the toner supply area are all set to 45 mT.
In the experiment, a φ100 mm aluminum pipe was opposed to the development roll with a 0.5 mm interval between the development roll and a voltage of −500 V was applied to the development roll, the aluminum pipe was grounded, and toner was applied to the aluminum pipe. A test was conducted to supply toner while developing and consuming. The peripheral speed of the aluminum pipe was set to 100 mm / s, the peripheral speed of the developing roll was set to 150 mm / s, and the moving speed of the developer on the developer conveying member was set to 150 mm / s.
[0053]
In this state, development was performed for 1 hour. During this time, after 5 minutes, 10 minutes, 20 minutes, and 60 minutes, the aluminum pipe was removed, and only the development device was driven for 1 minute to remove toner from the development roll. The state of cloud generation was visually inspected. Further, the toner concentration (TC) in the developer at that time was examined by a blow-off method. Incidentally, the level at which there is no practical problem of the TC run-out is within 3 wt%.
(Below)
[Table 1]

[0054]
As shown in Table 1, it was confirmed that when the magnetic force of the magnetic pole in the toner replenishment area was reduced, no cloud was generated, and TC also showed a stable value. However, under the condition 1-a, although there was no problem with respect to generation of cloud and stability of TC, slight unevenness was visually observed at a level at which there was no particular problem in transporting the developer. This is probably because the magnetic force of the magnetic pole in the toner replenishment area was too low, causing uneven flow of the developer.
[0055]
As described above, in the developing device, the mixing property between the developer on the developer conveying member and the newly supplied toner can be improved, and the charge amount of the toner can be stabilized, and the developer such as a cloud can be used. An image without image quality deterioration can be obtained.
[0056]
FIG. 3 is a partial configuration diagram showing a toner supply area of the developing device according to one embodiment of the present invention.
In this developing device, a plate-shaped magnetic member 25 is interposed between a magnetic field generating member 34 and a developer conveying member 33 in a toner replenishing area A in which a toner hopper 24 is provided. The magnetic pole S of the magnetic field generating member 34 facing the position where the plate-shaped magnetic member 25 is provided. ₁ , N ₂ , S ₂ Are magnetized with the same strength as the other magnetic poles provided for transporting the developer.
[0057]
The developer transporting member 33 is a sleeve made of SUS and having an outer diameter of 20 mm, and is supported by a driving unit (not shown) so as to be able to rotate. The magnetic field generating member 34 is a symmetrical magnet roll having 26 magnetic poles rotatably supported coaxially with the developer conveying member 33, and has an outer diameter of 16 mm and a magnetic pole pitch of about 2.4 mm.
The plate-shaped magnetic member 25 is made of a steel plate having a thickness of 0.3 mm, and is fixed and supported between a developer conveying member 33 and a magnetic field generating member 34 which are supported so as to be able to rotate. The magnetic flux density is approximately 25 mT on the peripheral surface of the developer transport member 33 facing the magnetic member 25, and the magnetic flux density is approximately 45 mT in the developer transport region facing the magnetic poles on both sides thereof.
The other structure of the developing device is the same as that of the developing device shown in FIG.
[0058]
In such a developing device, the magnetic strength of the magnetic field near the surface of the developer conveying member 33 is reduced by the plate-shaped magnetic member 25, and the magnetic force of the magnetic field generating member 34 hardly acts on the developer. For this reason, in the toner replenishment area A, the developer does not exert a magnetic binding force, the developer can relatively freely move, and the mixing property between the newly replenished toner and the developer is improved. Further, since the magnetic brush is broken and the magnetic carrier is separated, the packing density of the developer is increased, and the amount of toner taken into the developer can be always stabilized.
[0059]
<Charging test 2>
In order to confirm the effect of the developing device, an experiment was conducted in which the thickness of the plate-shaped magnetic member was changed to check the toner concentration and the state of generation of cloud.
In this experiment, a plate-like magnetic member having a thickness of 0.2 mm, 0.3 mm, and 0.5 mm was provided between the developer conveying member and the magnetic field generating member. The magnetic force acting on the developer was gradually reduced.
[0060]
Table 2 shows the results of the same test as Test 1 under such conditions.
[Table 2]

Here, 2-a has a magnetic member of 0.5 mm, 2-b has a thickness of 0.3 mm, and 2-c has a magnetic member of 0.2 mm provided between the magnetic force generating member and the developer conveying member. 2-d does not have a magnetic member. The magnetic force shown in Table 2 indicates the magnetic flux density on the peripheral surface of the developer conveying member facing each magnetic pole.
[0061]
As a result, as shown in Table 2, it was confirmed that when the magnetic force in the toner replenishment area was reduced by the magnetic member, no cloud was generated, and the toner concentration showed a stable value.
[0062]
FIG. 4 is a partial configuration diagram showing a toner supply area of the developing device according to the embodiment of the present invention.
In this developing device, two magnetic poles are arranged adjacent to a magnetic field generating member 54 facing a toner replenishing area A provided with a toner hopper 44, and these two magnetic poles have the same polarity. These two magnetic poles are S poles, and the maximum magnetic flux density in the radial direction on the peripheral surface of the developer conveying member 53 is set to 45 mT. Further, the magnetic field generating member 54 is fixed and supported in the developer conveying member 53 that moves around.
The other structure of the developing device is the same as that of the developing device shown in FIG.
[0063]
In this developing device, two magnetic poles of the same polarity are adjacent to each other in the toner supply area A, and a repelling magnetic field acts on the developer on the developer transport member 53. When such a repulsive magnetic field is formed, the magnetic force acting on the developer is strong on the peripheral surface facing the magnetic poles, but weak on the peripheral surface facing between adjacent magnetic poles. For this reason, the developer is intensively attached to the position facing the magnetic pole, and it is difficult for the developer to adhere to the position opposite to the magnetic pole, and the developer is relatively free to move at the portion where the magnetic force is weak. .
Therefore, the mixing property between the newly replenished toner and the developer is improved, so that excessive incorporation of the toner into the developer can be prevented, and the chargeability of the toner can be stabilized. Further, in the repulsive magnetic field, a pool of developer is generated on the peripheral surface facing the magnetic pole, which acts as a wall for transporting the developer, and the transported developer collides with the pool of developer. By doing so, an effect of shaking off unnecessary toner can be obtained. Therefore, a more stable toner concentration can be maintained.
[0064]
<Charging test 3>
In order to confirm the effect of the repulsive magnetic field in the developing device, an experiment was conducted in which the strength of the magnetic pole of the same polarity adjacent to the magnetic field generating member was changed to check the toner density and the generation state of the cloud.
In this experiment, the strengths of the adjacent magnetic poles and the magnetic poles on both sides thereof were measured under the conditions shown in Table 3. The magnetic force of the magnetic poles of the magnetic force generating member other than the notation is all 45 mT. Table 3 shows the results.
(Below)
[Table 3]

[0065]
As shown in Table 3, good results were obtained as compared to Test 1 and Test 2 with respect to generation of cloud and fluctuation of toner concentration TC. This is presumed to be due to the effect of oscillating excess toner being added, possibly by colliding with the developer pool formed on the peripheral surface facing the repulsive magnetic pole when the developer is transported.
[0066]
FIG. 5 is a partial configuration diagram showing a toner supply area of the developing device according to an embodiment of the present invention.
In this developing device, a magnetic member 65 is supported on the upstream and downstream wall surfaces of the toner hopper 64 in the movement direction of the developer conveying member 73 so as to face the developer conveying member 73 with a gap therebetween. . A magnetic pole is disposed at a position of the magnetic field generating member 74 facing the magnetic member 65.
The magnetic member 65 is made of a steel plate, but other magnetic materials can be appropriately set.
The other structure of the developing device is the same as that of the developing device shown in FIG.
[0067]
In such a developing device, the magnetic force is applied between the magnetic field generating member 74 and the magnetic member 65 on the upstream side and the downstream side of the toner hopper 64, that is, near the entrance and exit of the developer on the developer conveying member 73. Works to form a magnetic curtain of the developer in which the magnetic carriers are concentratedly connected. This prevents the toner from leaking from the toner replenishment area A facing the toner hopper 64 to the developer transport area in the housing 70, and can prevent the developer from taking in excessive toner.
[0068]
<Charging test 4>
In order to confirm the effect of the developing device, an experiment was conducted in which the developing device was driven continuously for 12 hours to check the generation state of the toner cloud when the magnetic member was provided on the wall surface of the toner hopper and when the magnetic member was not provided.
In this experiment, the arrangement and strength of the magnetic poles of the magnetic field generating member 74 were performed under the same conditions as in Table 1.
[0069]
As a result, when the magnetic member was not provided, no toner cloud was generated without the magnetic curtain of the developer under the conditions of 1-a, 1-b, and 1-c up to 2 hours, but after 3 hours. From then on, the cloud began to emerge, albeit slightly. The degree of this cloud is not a problem in image quality. On the other hand, when the magnetic member was provided, no toner cloud was generated even after 12 hours under the conditions of 1-a, 1-b and 1-c due to the effect of the magnetic curtain of the developer. This is considered to be because the toner leaks from the toner replenishing area when the magnetic member is not provided, the chargeability of the toner is reduced, and the adhesion to the carrier is weakened.
[0070]
Although the above embodiment has been described using a roll-type developing device, the present invention is not limited to such a configuration, and it is apparent that a similar effect can be obtained with a belt-type developing device.
[0071]
【The invention's effect】
As described above, in the developing device according to the present invention, the magnetic field generated by the magnetic field generating member is reduced or the repulsive magnetic field is formed at the position facing the toner replenishing unit, so that the developer on the developer conveying unit is Since new toner is supplied to the toner, the mixing property between the toner and the developer can be improved, and the amount of toner taken into the developer can be constantly stabilized. Therefore, with a simple configuration, the toner density of the developer conveyed to the developing area and the charge amount of the toner can be maintained almost constant, and an image without density unevenness or cloud can be stably maintained for a long period of time. be able to. Further, complicated toner density control means as in the related art is not required, and cost reduction and downsizing of the apparatus can be achieved. Further, by forming a magnetic curtain of the developer downstream of the position where the toner replenishing means is provided, it is possible to prevent toner leakage from the toner replenishment area and to further stabilize the toner concentration in the developer. .
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram showing a developing device according to an embodiment of the invention described in claim 1 or 2;
FIG. 2 is a partially enlarged view showing a configuration near a toner supply area of the developing device.
FIG. 3 is a partially enlarged view showing a configuration in the vicinity of a toner supply region of the developing device according to the embodiment of the present invention.
FIG. 4 is a partially enlarged view showing a configuration in the vicinity of a toner supply area of a developing device according to an embodiment of the present invention.
FIG. 5 is a partially enlarged view showing a configuration in the vicinity of a toner supply area of a developing device according to an embodiment of the present invention.
[Explanation of symbols]
1 Image carrier
2 Development roll
3,23,43,63 Transport roll
4,24,44,64 Toner hopper
9 Opening for development
10,30,50,70 Housing
11 Magnet roll
12 Developing sleeve
13, 33, 53, 73 Developer transport member
14,34,54,74 Magnetic field generating member
25 Plate-shaped magnetic member
65 Magnetic material

Claims (5)

A developing device using a two-component developer including toner particles that transfer to an electrostatic latent image on an image carrier to visualize the electrostatic latent image, and magnetic carrier particles that contact and frictionally charge the toner particles. So,
A magnetic field generating member provided with a plurality of magnetic poles on an endless peripheral surface,
Outside the peripheral surface of the magnetic field generating member, having an endless developer conveying means supported so as to be able to move around,
A toner replenishing unit is provided at a position along the peripheral surface of the developer transport unit to supply new toner to the developer magnetically attracted on the peripheral surface of the developer transport unit,
A developing device, wherein a magnetic flux density on the peripheral surface of the developer conveying means at a position where the toner replenishing means is provided is smaller than both sides thereof. The developing device according to claim 1,
The magnetic field generating member is fixedly supported,
At least one of the magnetic poles facing the position where the toner replenishing unit is provided is magnetized weaker than the other magnetic poles magnetized to attract and transport the developer onto the developer transporting unit. A developing device characterized by the above-mentioned. The developing device according to claim 1,
A developing device, wherein a plate-shaped magnetic member is inserted between the magnetic field generating member at the position where the toner replenishing unit is provided and the developer conveying unit. A developing device using a two-component developer including toner particles that transfer to an electrostatic latent image on an image carrier to visualize the electrostatic latent image, and magnetic carrier particles that contact and frictionally charge the toner particles. So,
A magnetic field generating member provided with a plurality of magnetic poles on an endless peripheral surface,
Outside the peripheral surface of the magnetic field generating member, having an endless developer conveying means supported so as to be able to move around,
On the developer conveying means, a magnetic brush in which the magnetic carriers are spliced by a magnetic field formed by the magnetic field generating member is formed,
A toner replenishing unit is provided at a position along the peripheral surface of the developer transport unit to supply new toner to the developer magnetically attracted on the peripheral surface of the developer transport unit,
A developing device characterized in that two adjacent magnetic poles of the magnetic field generating member, which are magnetized at a position where the toner replenishing unit is provided, have the same polarity. The developing device according to claim 1, claim 2, claim 3, or claim 4,
A developing device, further comprising a magnetic member supported on the downstream side of the position where the toner replenishing unit is provided so as to face the developer conveying unit with a gap therebetween.

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