JP4418570B2 - Development device - Google Patents

Description

【００２８】
第二現像スリーブ３０である現像剤担持体（現像スリーブ）は、非磁性部材であるφ３０のアルミＡ２０１７に膜を形成したものを用いる。その内部には、図３、及び、下記の表２に示す６極の磁場パターンよりなるマグネットを有する。かかる現像スリーブ２０には＋４００ＶのＤＣバイアスと、図４に示すようなＶ_ppの値が１５００Ｖ、周波数２．７ｋＨｚの矩形波とを印加する。かかる条件は、前述した第一現像スリーブと同一で共通である。従って、第一及び第二の現像スリーブに対して電源が１つで足りるので、コストダウンに繋がり、且つ、電源のスペースが少なくて済むといったメリットもある。現像スリーブは対ドラムに対して１２０％の速度で回転する。
【００２９】
【表２】

【００３０】
各現像スリーブ表面の現像剤の層厚を規制するためのブレードは、第一の現像スリーブ２０に対しては、厚さ１．０ｍｍの板状磁性ブレードを用い、第二の現像スリーブ３０上の現像剤の層厚の規制は、上流側の現像スリーブ２０によって行う。従って、第一現像スリーブ２０と第二現像スリーブ３０との間の距離は５００μｍにした。これは、第一と第二の現像スリーブでのトナー供給量が等しくなるようにするための値である。
【００３１】
このようにすることで、第一と第二の現像スリーブ上におけるトナーコート量（Ｍ／Ｓ）を約１．０ｍｇ／ｃｍ²に揃えた。第二現像スリーブの（Ｓ−Ｄ)_gapは２５０μｍである。単位時間あたりのトナー供給量（Ｍ／Ｓ）を揃えることは、複数の現像スリーブの現像特性を一致させ、階調性を安定させる制御を可能にする上で最も重要である。
その上、近年のデジタル画像やグラフィック化に対応した画像の階調性並びに階調安定性の要求に応えるためには、第一と第二の現像スリーブにおける現像特性を一致させることが重要な課題となる。上述のように、単位時問あたりのトナー供給量は等しい。又、第一現像スリーブの現像極はＮ２、第二現像スリーブの現像極はＮ２であり、磁力、半値幅も同じである。しかし、１０ｋ枚耐久後の現像特性は、図９に示したように異なる（上が第二現像、下が第一現像）。以下、このことについて説明する。
【００３２】
これは、先に述べたように、第一現像スリーブ２０では、磁性ブレードによってトナー層厚規制がされるのに対して、第二現像スリーブ３０は、第一現像スリーブ２０による規制で、且つ、第一現像スリーブ２０は、トナー層厚規制部において、トナーの進行方向と逆方向に回転する。そのため、第二現像スリーブと第一現像スリーブとの間でトナーは強く擦られ、トナーの摩擦帯電能力が、通常の磁性ブレード規制の場合に比べて高くなる。つまり、第一現像スリーブ２０に比べて第二現像スリーブ３０は、トリボ（Ｑ／Ｍ）が大きくなる。一般に、現像特性はトリボ（Ｑ／Ｍ）に依存するために、図９に示したように、Ｑ／Ｍの差が現像特性の差としてＶ−Ｄカーブに現れてくる。この傾向は、プロセススピード４００ｍｍ／ｓ以上の高速機のような、現像時間が十分にとれず、現像スリーブ回転速度が速くて、トナー層厚規制部材部におけるトナーヘの摩擦力が大きい場合に顕著になる。又、この差が図９の現像特性（１０ｋ枚時）の違いを生じさせる（図９は、横軸がコントラスト電位で、縦軸が濃度（Ｄ）を示すＶ−Ｄ特性と呼ばれる）。
【００３３】
次に、第二の問題点である現像スリーブの寿命について、説明する。
本実施例の現像装置で使用する現像方式は、現像スリーブ間に部材がないために、よりコンパクトな構成になっている。この方式では、第一現像スリーブは磁性ブレートによってトナーの層厚が規制された後、第二現像スリーブのトナーの層厚を規制する。即ち、第一現像スリーブ２０は、１回転の間に２回トナーとのシェアを受ける。それに対して、第二現像スリーブ３０は、規制部で１回シェアを受ける。つまり、画像形成耐久において、第一現像スリーブ表面は、第二現像スリーブに比べて約２倍程のシェアを受けることになるため、第一現像スリーブヘの耐久によるトナーの固着の頻度が増えることになる。尚、これは、正極性トナーに特有の現象である。
【００３４】
スリーブ寿命はトナー固着でほぼ決まるため、このことが、第一現像スリーブと第二現像スリーブのコート寿命（スリーブ寿命）を異なるものとしている。このため、一方の現像スリーブの寿命はまだあるのに、先に別の現像スリーブを交換しなければならなず、更に、その後に別の現像スリーブを交換するといったことが起こる。このため、頻繁にメンテナンスすることが必要となり、メンテナンスにかかるコストがかさむことが生じる。従って、複数の現像スリーブを使用する装置の場合には、現像スリーブの寿命の共通化が望まれる。
【００３５】
本実施例の現像装置は、以上のことに鑑みて構成されたものである。本実施例の現像装置で用いる現像スリーブは、その表面をコーティング部材で被覆したものを使用した。膜の処方としては、アルミニウム製スリーブ表面に、フェノール樹脂中に結晶性グラファイト及びカーボンが含有された樹脂組成物を、形成された膜厚が１０μｍとなるように１５０℃の環境で硬化させて樹脂膜を形成した。膜の厚さは、安定、且つ、均一な膜を形成するために１０μｍ程度とした。又、樹脂膜の組成のＰ／Ｂ比は、１／２．５とした。ここで、Ｂは樹脂の重量、Ｐは樹脂以外のものの重量（結晶性グラファイト＋カーボン）を表す。
【００３６】
この際、従来の膜の組成では正極性トナーに対しての帯電特性が悪いために、本実施例では、フェノール樹脂に、４級アンモニウム塩を７０重量部有するものを用いた。又、耐久によって生じるトナーの搬送量（Ｍ／Ｓ）の低下を防ぐために、炭素化又は黒鉛化した球状粒子を含有させたコーティング材料を用いた。これらの効果の差は表３に示すように、前者は帯電量アップ、後者はコート安定性、コート量アップに効いていることが分かる。これらについて説明する。
【表３】

【００３７】
上記で用いた第４級アンモニウム塩化合物は、添加されるとフェノール樹脂中に均一に分散され、更に、加熱硬化して被膜を形成した際にフェノール樹脂の構造中に取り込まれ、その結果、上記化合物を有するフェノール樹脂組成物自身が負帯電性を有する物質へと変化する。従って、このような材料を用いて形成された被覆層を有する現像剤担持体（スリーブ）を用いれば、現像剤を好適に正極性に帯電させることが可能となる。本発明において好適に使用できる上記した機能を有する第４級アンモニウム塩化合物としては、例えば、下記一般式で表わされる化合物が挙げられる。
【００３８】

（式中のＲ₁、Ｒ₂、Ｒ₃、Ｒ₄は、夫々置換基を有してもよいアルキル基、置換基を有してもよいアリール基、アルアルキル基を表わし、Ｒ₁〜Ｒ₄は夫々同一でも或いは異なっていてもよい。Ｘ^-は、酸の陰イオンを表わす。）
【００３９】
上記の一般式において、Ｘ^-の酸イオンの具体例としては、例えば、有機硫酸イオン、有機スルホン酸イオン、有機リン酸イオン、モリブデン酸イオン、タングステン酸イオン、モリブデン原子或いはタングステン原子を含むヘテロポリ酸等が挙げられる。
【００４０】

【００４１】
本実施例では、フェノール樹脂に、上記（１）に示したような特定の第４級アンモニウム塩化合物を添加した樹脂組成物を使用して被覆層を形成した。このようにすると、先に述べたように、結着樹脂であるフェノール樹脂を加熱硬化させて被覆層を形成させた際に、第４級アンモニウム塩化合物がフェノール樹脂の構造中に取り込まれる。このため、前記したネガ性シリカ粒子或いはネガ性テフロン粒子等のような粒子添加系の場合と異なり、部分的にではなく、被覆層全体として正帯電性現像剤に対する正摩擦帯電付与性を向上させることができる。更に、上記の粒子添加系の被膜と異なり、加工性が損なわれたり、被覆層の強度低下を生じることもない。
【００４２】
次に、本実施例で使用した炭素化又は黒鉛化させた球状粒子について説明する。日本カーボン社のカーボンマイクロビーズ（ＰＣ）で粒径５μｍで、図７に示したような測定装置で測定した場合の抵抗が、１０^-1〜１０^-2Ωｃｍのものである。
膜の処方は、フェノール樹脂１００重量部に対して、結晶性グラファイト９０重量部、カーボン１０重量部、４級アンモニウム７０重量部、球状粒子７５重量部とした。ちなみに、グラファイトとカーボンの比はカーボンの分散性より９：１が好ましい。膜は吹き付け法によりスリーブ上に塗付した後、１５０℃で３０分間乾燥させる。次に、本発明を特徴づける結晶性グラファイトの露出について説明する。
【００４３】
本発明者らは、正極性トナーに対しては、現像スリーブのコート表面におけるグラフィトの露出量によって、帯電量、画像濃度、画質が変化することを見いだし、これを複数現像スリーブ系に応用した。図８−１は、コートしたスリーブの表面のグラファイト面積（Ｇｒ露出度）と帯電量（Ｑ／Ｍ）の関係を示したものである。ここで、グラファイトの露出量（％）は、図１４に示したように、コート表面の顕微鏡観察により光沢のあるグラファイト部分の全面積をＣＣＤ読み込みによる画像処理でよりだして、それを観察視野の面積で除したものである。図８−１からグラファイトの面積が増えると正帯電量が増え、その結果、図８−２に示したように画像濃度が上がることがわかった。
【００４４】
本発明では、上記のことを利用し、現像スリーブのコート表面におけるグラファイト露出量を適宜に制御することによって、上記したように第一と第二との間で生じていた現像スリーブの現像性の違いを、同じコート処方にもかかわらず同じくすることを可能とする。この具体的な方法について説明する。これらの特性を応用して、本実施例では、第一と第二の現像スリーブのコート条件を、下記の表４に示したようにした。その処方は、上述した同じ条件で行なったが、その後の磨き処理を施すことで、表４に示したように、グラファイトの露出度を、６０％と４５％に変えることができた。磨きは、ラッピングテープ（＃３０００）を用い、１．５ｋｇの圧力で現像スリーブ表面に３ｃｍのテープをあて、その磨き回数を変えることによって行なった。具体的には、第一現像スリーブは２４回で、第二現像スリーブは８回の磨き処理を施し、これらの現像スリーブを使用した結果、表４に示したように、帯電量（Ｑ／Ｍ）をほぼ同じにすることができた。
【００４５】
【表４】

【００４６】
比較のために、上記コート処理をしない場合について検討したところ、第一現像スリーブの帯電量は６．８μＣ／ｇであり、第二現像スリーブの帯電量は９．０μＣ／ｇであり、第一及び第二の現像スリーブ間で差が生じていた。これは、第二現像スリーブでは、第一現像スリーブによる層厚規制に加え、第一現像スリーブはトナー規制部でトナーの進行方向と逆方向に回転するために生じると考えられる。
【００４７】
このようにすることで、各現像スリーブにおいて、現像特性の指標であるＱ／Ｍ（トリボ）の値をほぼ同等にすることができ、その結果として、図９のように、第一と第二の現像スリーブ現像特性であるＶ−Ｄカーブ（１０ｋ枚時）に差があったものが、図１２に示したようにほぼ同一曲線にすることができた。
又、図８−３に示したように、グラファイトの露出量を大きくするとスリーブ上へのトナー付着を減らすことができることがわかった。これは、グラファイトが表面に出ることで、先述したように帯電性を向上させることができるだけではなく、表面の潤滑性が向上する結果、トナーのスリーブ上の固着を低減することができたものと考えられる。更に、このことで、画像の階調性並びに階調安定性の制御が可能になり、且つ、複数の現像スリーブの耐久寿命の共通化を図ることが可能となる。
【００４８】
以上の構成にすることで、高速機対応の小型現像システムであると共に、第一の目的である複数の現像スリーブを有する現像装置において、現像スリーブ毎で現像性が異なるのを防ぐことにより、近年のデジタル画像やグラフィック化に対応した画像に対する階調性並びに階調安定性の要求を満たすことができる。又、第二の目的である複数の現像スリーブを有する現像装置において、現像スリーブの寿命を共通化することが達成されるため、サービスマンのメンテナンスにかかる手間が省け、サービスコストを低減することもできる。更に、第三の目的であるスリーブゴースト画像がなく、高い濃度の画像が安定して得られる現像装置を提供することができる。
【００４９】
＜実施例２＞
本実施例にかかる画像形成装置は、実施例１で使用したと同様である。
本実施例の特徴は、上流側の現像スリーブの帯電性を上げる方法として、夫々の現像スリーブに使用するコート材中の結晶性グラファイトの粒径を、上流側だけ小さくし、それ以外は、同じ形成条件で各現像スリーブにコートすることで、コート表面に露出するグラファイトの量を多くしたものである。これは、グラファイトの粒径を小径化すると、その表面積が増えることによる。かかる方法によれば、現像スリーブの小径化が図られ、省スペース化が達成される。又、本実施例では、グラファイトの露出量を製造段階で管理する方法として、現像スリーブ表面の光沢度を測定し、これによってグラファイト露出量を測定することによって行なった。
【００５０】
次に、本実施例で用いた現像装置２について詳しく説明する。現像剤は、正極性の一成分磁性トナーを用いた。図１（１）に示すように現像スリーブは２本よりなり、第一の現像剤担持体（現像スリーブ）２０は非磁性部材であるφ２０のアルミＡ２０１７の上にＦＧＢ＃６００でブラスト処理をした後、コーティングを行なったものである。第二のスリーブも同様で、現像剤担持体（現像スリーブ）３０は非磁性部材であるφ２０のアルミＡ２０１７の上にＦＧＢ＃６００でブラスト処理し、コーテイングを行なった。このコーティングは、スリーブ周期で発生するスリーブゴースト画像を防止すると共に、スリーブ表面の耐久性を高めるために行なわれる。
【００５１】
第一の現像スリーブは、対ドラムに対して１２０％の速度で回転する。トナーは磁気ブレードで層厚を規制し、（Ｓ−Ｂ)_gapは２５０μｍとした。第一現像スリーブと感光ドラムとの距離（Ｓ−Ｄ)_gapは２５０μｍとし、第一の現像スリーブには＋４００ＶのＤＣバイアスと、図４に示したように、Ｖ_pp１５００Ｖ、周波数２．７ｋＨｚの矩形波をＡＣバイアスとして印加し、磁性一成分非接触現像を行った。従って、現像コントラストは飛翔方向に３００Ｖ、かぶりとりコントラストが１００Ｖとなる。第二の現像スリーブ３０は、非磁性部材であるφ２０のアルミＡ２０１７に膜を形成したものを用いた。現像スリーブには、＋４００ＶのＤＣバイアスと図４に示すようにＶ_pp１５００Ｖ、周波数２．７ｋＨｚの矩形波を印加する。第一現像スリーブと同一なので共通であり、電源は１つでよいのでコストダウンに繋がり、且つ、電源のスペースが少なくて済むメリットがある。現像スリーブは対ドラムに対して１２０％の速度で回転する。ブレードは、実施例１と同様である。次に、本実施例の特徴を述べる。
【００５２】
本実施例では、上流側の現像スリーブのコート材としては、下記のものを用いた。樹脂（Ｂ）として、４級アンモニウム塩７０部を有するフェノール樹脂１００部（全体で１７０部）を用い、ピグメント（Ｐ）として、カーボンと平均粒径３μｍの小径のグラファイトを用いた。この膜は、実施例１で用いた膜よりも、グラファイトの粒径が小さい分、同じ重量を添加することで、表面での露出面積を大きくすることができ、その点で、帯電性、トナー固着防止に更に効果がある。この材料を用いた際の処方を以下に示した。
【００５３】
膜の処方は、アルミニウム製の現像スリーブ表面に、４級アンモニウム塩を有するフェノール樹脂と結晶性の小径グラファイト及びカーボンを１７０：３６：４の重量比割合で混合した塗工液を、乾燥膜厚が１０μｍとなるようにコートし、その後、１５０℃環境下で硬化させることによって樹脂膜を得た。膜の厚さは、安定して、且つ、均一な膜を形成するためは、厚さを１０μｍ程度とすることが好ましい。本処方により、第一スリーブのグラファイト露出量を７２％と更に上げることができ、帯電量も、更に１０．８μＣ／ｇと上げることができた。第二スリーブのコートを５０％とした。又、光沢度の測定は東京電色ＧＬＯＳＳＭＥＴＥＲ ＴＣ−１０８ＤＰ／Ａを用いた。
【００５４】
本発明者らの検討によれば、図１１に示すように、グラファイトの露出量と現像スリーブ表面の光沢度との間には相関関係があることがわかった。本実施例では、これをスリーブ表面コートの管理方法として採用した。このようにすることで、現像特性の指標であるＱ／Ｍ（トリボ）の値を、各現像スリーブ間でほぼ同等にすることができ、その結果として、現像特性であるＶ−Ｄカーブをほぼ同一曲線にすることができた。このことで、画像の階調性並びに階調安定性の制御が可能になり、且つ、耐久寿命の共通化が図れ、又、光沢度によるグラファイトの露出管理により簡易に製造し、品質の安定性を向上すさせることができた。
【００５５】
以上の構成にすることで、本実施例では、高速機対応の現像システムでありながら、第一の目的である、複数の現像スリーブを有する小型現像装置において、各現像スリーブ毎で現像性が異なるのを有効に防ぐことが可能となり、近年のデジタル画像やグラフィック化に対応した画像の階調性並びに階調安定性の要求を満たす現像装置が得られる。又、第二の目的である、複数の現像スリーブを有する現像装置において、各現像スリーブの寿命を共通化することで、サービスマンのメンテナンスにかかる手間を省き、サービスコストを低減することができ、高濃度の画像が安定して得られる現像装置を提供することができる。更に、第三の目的である高速化に対して、画像濃度が高濃度で且つ安定しており、省スペース化すると共に、１００万枚までの寿命の現像装置を提供できた。
【００５６】
＜実施例３＞
本実施例の特徴は、リユース画像形成装置に本発明の現像装置を適用したことである。リユース系トナーは、基本的には転写されずに残りクリーニングで回収された廃トナーであるために、トナーの劣化により、Ｎｅｗトナーと比較してトリボが極端に小さいため、現像性が落ち、且つ、廃トナーの凝集度が高くなり、（Ｓ−Ｂ)_gapでのシェアが高まり、膜の削れも多くなる。これを示したのが、図１３−１である。これはリユース径の現像特性である。Ｎｅｗトナーを使用する場合（図９参照）と比較して、全体的に濃度が低く、更に現像スリーブ間の差が大きくなっていることがわかる。
【００５７】
本実施例はこれらのことを鑑みて実施したものである。本実施例では図１０に示したリユース系の画像形成システムで、感光体としてａ−Ｓｉドラムを用いたデジタル復写機について説明する。プロセススピードは６００ｍｍ／ｓの１２０枚／分である。この感光ドラム２０１の表面を、一次帯電器２０３により＋５００Ｖに一様帯電する。次いで、波長６８０μｍの半導体レーザーで６００ｄｐｉでＰＷＭによる露光２１２を行って、感光ドラム２０１上に静電潜像を形成する。次に、現像器２０２により反転現像し、トナー像として可視化する。現像剤には磁性一成分ポジトナーを用い、ジャンピング現像をする。トナー粒径は６．０μｍである。
【００５８】
従来の２成分現像剤では、キヤリアの交換を１０万枚毎にサービスマンが行わねばならずメンテナンスフリーでないため、リユースの利点があまり反映できなかった。本実施例では、耐久性が無限でノーメンテナンスで済む乾式磁性一成分トナーを用いた。現像バイアスは、第一、第二の現像スリーブ共に２４００Ｈｚ、１５００Ｖ_pp、Ｄｕｔｙ５０％の交流電圧に＋４００Ｖの直充電圧を重畳したバイアス電圧を印加する。（Ｓ−Ｂ)_gapは第一が２５０μｍで、（Ｓ−Ｄ)_gapは共に２５０μｍとした。その後、ポスト帯電器で総電流＋２００μＡ流してトナー像を帯電させた後、矢印方向に進む転写材に転写帯電器２０４により転写し、定着器７に送ってトナー像を定着する。一方、感光ドラム１上の転写残りのトナーをクリーニング装置２０６により除去、回収して搬送パイプ２０８を通して廃トナー（リユーストナー）を現像ホッパー２０９Ｂに戻す。搬送パイプにはスクリュー状の搬送部材が内部にあり、回転することでリユーストナーを運ぶ。
【００５９】
更に詳細を述べると、図１０に示したように、運ばれたリユーストナーは現像ホッパー２０９Ｂに入れられ再利用される。又、別に、Ｎｅｗトナーはホッパー２０９Ａに入れられ、マグローラ２１Ａ及び２１Ｂにより、磁力で夫々のトナーは引きつけられ、マグローラ２１Ａ及び２１Ｂが回転することにより現像器内にトナーは運ばれる。
【００６０】
本実施例の現像装置では、リユーストナーとＮｅｗトナーを現像器内で混ぜる方法を採用したが、ホッパー内に混合するスペースを設けて、ここで混ぜる構成としても構わない。現像器内で混ぜられたトナーは再び現像スリーブに送られ、感光体上の静電潜像の現像に用いられる。マグローラ２１Ａの通常の回転速度は２回転／分であり、マグローラ２１Ｂの回転速度を適宜に変化させる。即ち、マグローラ２１Ｂの回転の信号は、現像器内のピエゾセンサー（ＴＤＫ製）にトナーの自重がかからなくなり、振動すると、トナー供給信号が発せられる。通常は、マグローラ２１Ｂは、マグローラ２１Ａに対して１０／９０（マグローラ２１Ａ：マグローラ２１Ｂ＝９：１）にする。本実施例の現像器の構成は、実施例２で用いた場合と同様であり、フェノール樹脂と結晶性グラファイト、カーボンを用いた膜で、現像スリーブの径は共にφ２０である。
【００６１】
上記したように、本実施例の現像装置をリユース系に適用することによって、通常のＮｅｗトナーを用いた場合よりも現像性が低くなるため、図１３−１に示したように、Ｎｅｗトナーを用いた場合と比べて更に現像特性に差があったものが、図１３−２に示したように、全体の濃度は若千低いものの、第一現像スリーブのトリボ（Ｑ／Ｍ）を第二現像スリーブと同程度にすることができた。ちなみに第一が８．９μＣ／ｇ、第二が９．４μＣ／ｇであった。このようにすることで、全体的に帯電性の低いリユース系においても、現像特性の指標であるＱ／Ｍ（トリボ）の値をほぼ同等にすることができ、その結果として、現像特性であるＶ−Ｄカーブをほぼ同一曲線にすることができた（図１３−２参照）。又、このことで、画像の階調性並びに階調安定性の制御が可能になり、且つ、複数の現像スリーブにおいて耐久寿命の共通化が図れたリユース系とすることができることがわかった。
【００６２】
以上のような構成により、リユース対応の現像システムであると共に、第一の目的である複数の現像スリーブを有する小型現像装置において、現像スリーブ毎で現像性が異なるのを防ぐことにより、近年のデジタル画像やグラフィック化に対応した画像の階調性並びに階調安定性の要求を満たすことができ、又、第二の目的である複数の現像スリーブを有する現像装置において、現像スリーブの寿命を共通化することであり、サービスマンのメンテナンスにかかる手間を省くことでサービスコストも低減することができ、高濃度の画像が安定して得られる現像装置を提供することができた。又、第三の目的である高速化に対して、濃度が高濃度で且つ安定し、省スペース化すると共に、リユースで環境性に優れた現像装置を提供できた。
【００６３】
【発明の効果】
以上説明したように、本発明によれば、本発明の第一の目的である複数の現像スリーブを有する現像装置において、現像スリーブ毎で現像性が異なるのを有効に防止することが可能となり、近年の、デジタル画像やグラフィック化に対応した画像の階調性並びに階調安定性の要求を充分に満たすことのできる現像装置が提供される。
又、本発明によれば、本発明の第二の目的である複数の現像スリーブを有する小型現像装置において、現象スリーブの寿命を共通化することが可能で、これにより、サービスマンのメンテナンスにかかる手間を省くことでサービスコストを低減でき、本発明の第三の目的である高速化に対して、高濃度の画像が安定して得られる現像装置が提供される。
本発明によれば、更には、以上の第一〜第三の目的を同時に実現することが可能となる。
【図面の簡単な説明】
【図１】図１−Ａは実施例１の現像装置を簡単に説明するための図であり、図１−Ｂは実施例２の現像スリーブを説明するための図である。
【図２】図２は実施例１及び実施例２で用いる画像形成装置を説明するための図である。
【図３】図３は実施例１で用いる現像スリーブの磁極配置を説明するための図である。
【図４】図４は実施例１で用いる現像バイアスを説明するための図である。
【図５】図５は本実施例の複数スリーブとシールの関係を説明するための図である。
【図６】図６は、本実施例の複数スリーブとシールの長手方向の関係を説明するための図である。
【図７】図７は、粉体の抵抗を測定する方法を説明するための図である。
【図８】図８−１、８−２、８−３はグラファイトの露出量と帯電量、濃度、汚染を説明するための図である。
【図９】図９は、従来例における現像特性を説明するための図である。
【図１０】図１０は、実施例３のリユース画像形成装置を説明するための図である。
【図１１】図１１は、従来のリユース画像形成装置の現像特性を説明するための図である。
【図１２】図１２は実施例１で改良された現像特性を説明するための図である。
【図１３】図１３一１は、従来のリユース系の現像特性を説明するための図であり、図１３−２は実施例３のリユース系の現像特性を説明するための図である。。
【図１４】図１４は、磨き回数とグラファイトの露出量の関係を説明するための図である。
【図１５】図１５は従来の画像形成装置を説明するための図である。
【符号の説明】
１：ドラム感光体
２：現像器
３：一次帯電器
４：転写帯電器
５：分離帯電器
６：クリー二ング装置
７：定着装置
９：現像器ホッパー
１０：ポスト帯電器
１２：画像露光
２０：第一の現像スリーブ
３０：第二の現像スリーブ[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a developing device used for a copying machine, a laser beam printer, a facsimile, a printing apparatus, and the like using an electrophotographic system.
[0002]
[Prior art]
Conventionally, after an electrostatic latent image carrier is uniformly charged and then subjected to analog exposure or image exposure with a semiconductor laser or LED to form an electrostatic latent image on the electrostatic latent image carrier. Then, this is visualized as a developer image by a developing device, and after the visible image is transferred to a transfer material, the transfer material is separated from the electrostatic latent image carrier, fixed by a fixing device, and output as an image. An image forming apparatus is known. Hereinafter, the process will be described with reference to FIG.
[0003]
The image forming apparatus includes, for example, a photosensitive drum 1 as an electrostatic latent image carrier. The photosensitive drum 1 includes a photoconductive layer such as OPC or a-Si on its surface and rotates in the direction of arrow A. Is done. For image formation, first, the surface of the photosensitive drum 1 is uniformly charged to, for example, −700 V by the primary charger 3. Next, image exposure 12 based on image signal information is performed, the surface potential of the exposed portion on the photosensitive drum 1 is attenuated to, for example, −200 V, and an electrostatic latent image corresponding to the image signal of the image is formed on the photosensitive drum 1. Form. At this time, for example, a semiconductor laser or an LED array is used for the image exposure 12. Next, the formed latent image is developed by the developing device 2 which is a one-component developing device, and visualized as a toner image. A developing device using a dry one-component developer is simple and does not require replacement of a carrier or the like, and thus has high durability and long life. Examples of such a device include a jumping developing device using a magnetic one-component toner.
[0004]
The developing device 2 uses negatively charged black toner. At the time of development, a DC bias of about −500 V is applied to the developer carrying member as a developing bias to reversely develop the latent image. Thereafter, pre-transfer treatment is performed using a charger 10 as necessary (usually, corona is applied by DC or AC, or light neutralization is combined), and the transfer material supplied to the photosensitive drum 1 is applied. Is transferred by the transfer charger 4. Thereafter, the transfer material is sent to the fixing device 7 to fix the toner image and obtain a fixed image. On the other hand, the transfer residual toner remaining on the photosensitive drum 1 is removed by the cleaning device 6 to prepare for the next image formation.
[0005]
In order to increase the speed of the image forming apparatus, as described in Japanese Patent Laid-Open No. 03-204084, the developing device includes a plurality of developing rollers of a developing device using a two-component magnetic brush. In addition, as described in Japanese Patent Laid-Open No. 02-188778, the distance between the sleeve and the photosensitive member is made closer to the sleeve on the downstream side, so that the toner replenishment amount from the sleeve is made uniform. is doing. Further, as a developing device having a plurality of development sleeves that have been downsized, a developing device as disclosed in Japanese Patent Publication No. 3-5579 has been proposed.
[0006]
On the other hand, Japanese Patent Application Laid-Open No. 1-112253, Japanese Patent Application Laid-Open No. 2-284158, and the like propose to use a toner having a small particle diameter in order to achieve high image quality and high definition. With such a negatively chargeable toner having such a small particle size, the surface charge per unit weight tends to increase because the surface area per unit weight increases. For this reason, the toner adheres to the developer carrier due to a so-called charge-up phenomenon, and as a result, the developer newly supplied onto the developer carrier becomes difficult to be charged, and the charge amount of the developer becomes non-uniform. easy. For this reason, a sleeve ghost is likely to occur on the image, and a nonuniform image such as a streak-like image or a haze-like image tends to appear in the obtained image, particularly in a solid image or a halftone image. On the other hand, in JP-A-1-277256, JP-A-3-36570, etc., the generation of such an excessively charged developer and the strong adhesion of the developer to the developer carrier are described. In order to prevent this, a method has been proposed in which a film made of a resin composition in which a conductive material such as carbon or graphite or a solid lubricant is dispersed in a resin is formed on a developer carrier.
[0007]
[Problems to be solved by the invention]
However, a developing device having a plurality of developer carriers (developing sleeves) is excellent in terms of maintaining the density, and in particular, a structure having no toner layer thickness regulating member between the developing sleeves is compact. In this development system, the following are listed. ~ 3. There was a problem like this.
[0008]
1. In the developing method in which the toner layer thickness regulation of the downstream developing sleeve (hereinafter simply referred to as the downstream developing sleeve) is performed by the upstream developing sleeve (hereinafter simply referred to as the upstream developing sleeve), The method of regulating the layer thickness of the downstream developing sleeve is different. In the downstream developing sleeve, the toner is rubbed vigorously to counter-rotate with the rotating upstream developing sleeve and perform layer thickness regulation. In the developing sleeve, the toner tribo was different. That is, since the tribo of the downstream developing sleeve is higher than that of the upstream developing sleeve, the developability differs between the upstream developing sleeve and the downstream developing sleeve. On the other hand, a common development bias is often used to save space and reduce costs. In this case, however, density control is difficult because the developability differs for each development sleeve, and digital images in recent years have become difficult to control. In contrast, there is a contradiction to the demand for gradation and gradation stability of an image corresponding to graphics. The above phenomenon was particularly severe when a positive toner having a small toner charge amount and low developability was used.
[0009]
2. In the developing device having a plurality of developing sleeves, a magnetic blade or the like is used for the toner layer thickness regulation of the upstream developing sleeve, whereas the toner layer thickness regulation is performed by the upstream developing sleeve for the downstream developing sleeve. . Therefore, in addition to the normal layer thickness regulation for the upstream developing sleeve, the toner layer thickness regulation is performed once again at the lower part, so that the number of times of passing through the toner layer thickness regulating member is increased compared to the downstream developing sleeve. In addition, the degree of friction that the sleeve surface receives from the toner increases. As a result, since the probability of toner adhesion to each developing sleeve in durability increases on the upstream developing sleeve side compared to the downstream side, the life differs between the downstream side and the upstream side. This phenomenon of sticking was particularly severe when positive toner was used. As described above, when the life of each developing sleeve is different, the replacement maintenance interval of the developing sleeve is also different for each developing sleeve, and it becomes necessary for the service person to visit the user frequently, leading to a waste of service cost.
[0010]
3. The high-speed machine has a high development speed, so the development time is short and the development time is not sufficient. As a result, the developability is unstable and the image density fluctuates greatly. This is particularly severe when a positive polarity toner having a small size and low developability is used.
[0011]
It is difficult to solve the above problems at the same time and to make a developing device satisfying all of them, and it has not been realized at present. Accordingly, the first object of the present invention is to cope with recent digital images and graphic images by effectively preventing the phenomenon that developability differs for each developing sleeve in a small developing device having a plurality of developing sleeves. The object is to achieve gradation and gradation stability that can be achieved. A second object of the present invention is to eliminate the need for frequent maintenance by service personnel by sharing the life of each developing sleeve in a developing device having a plurality of developing sleeves. The purpose is to reduce this. A third object of the present invention is to provide a developing device that can stably obtain a high-density image even when the image forming speed is increased. Furthermore, particularly in a developing device using a positive toner, the above first to third objects are achieved.
[0012]
[Means for Solving the Problems]
The above object is achieved by the present invention described below. That is, the present invention is a developing device that visualizes an electrostatic latent image formed on an electrostatic latent image carrier with a positively chargeable developer carried on the surface of the developer carrier, Common development bias is used A developer carrier on the upstream side having a plurality of developer carriers and restricting the developer layer thickness on the developer carrier located downstream with respect to the rotation direction of the electrostatic latent image carrier By line Present In the image device, each of the plurality of developer carriers has a magnetic member therein, and each surface is coated with a coating member having crystalline graphite, and the plurality of developers The arrangement of the carrier is such that each surface state coated with the coating member is a developer carrier upstream of the developer carrier positioned downstream with respect to the rotation direction of the electrostatic latent image carrier. The developing device is characterized in that the exposed amount of the crystalline graphite is larger.
[0013]
As a specific aspect of the developing device of the present invention, the surface state of the coating member on the surface of the developer carrying member is set to be higher than that of the developer carrying member positioned downstream with respect to the rotation direction of the electrostatic latent image carrying member. In order to increase the exposure amount of the crystalline graphite on the surface of the developer carrying member on the upstream side, the surface of the coating member is appropriately polished.
[0014]
In another aspect, the surface of the coating member on the surface of the developer carrier is developer carrier upstream of the developer carrier positioned downstream relative to the rotation direction of the electrostatic latent image carrier. In order to increase the exposed amount of crystalline graphite on the surface of the body, the glossiness of the surface of the developer carrier disposed upstream is larger than the glossiness of the surface of the developer carrier disposed downstream. The thing which was done is mentioned.
[0015]
As another aspect, among the plurality of developer carriers, the coating member coated on the surface of the developer carrier disposed on the upstream side is the surface of the developer carrier disposed on the downstream side. One having a particle size of crystalline graphite smaller than that of the coating member coated on the surface is mentioned.
[0016]
Moreover, as another aspect, the coating member has what has resin formed with the resin composition containing a phenol resin and a quaternary ammonium salt compound at least.
[0017]
Another embodiment includes a coating member having spherical particles that are carbonized or graphitized.
[0018]
The above-described developing device of the present invention prevents development characteristics from being different for each developing sleeve that has occurred in the developing device having a plurality of developing sleeves, which is the first object of the present invention. To meet the demands of gradation and stability of the image corresponding to the development, and to make the life of the developing sleeve common in a small developing device having a plurality of developing sleeves, which is the second object of the present invention. By doing so, it is possible to reduce the number of maintenances by service personnel and to reduce the service cost. Furthermore, the third object of the present invention is to stably form high-density images for higher speed. A developing device is provided. As a result, it is possible to achieve all of the above first to third objects at the same time.
[0019]
【Example】
Next, the present invention will be described in more detail with reference to examples.
<Example 1>
FIG. 2 shows an outline of an image forming apparatus having a developing device of this embodiment as a part thereof. The image forming apparatus is a digital copying machine that uses an a-Si drum photoreceptor of φ108 as the photoreceptor 1, has a process speed of 500 mm / sec, and can form 102 black and white images per minute. The photoconductor used in the developing device of this embodiment is made of a-Si, but has a feature that it is more durable than an organic photoconductor, has a life of 3 million sheets or more, and is suitable for a high-speed machine. Hereinafter, a procedure until an image is formed by the image forming apparatus shown in FIG. 2 will be described.
[0020]
First, the photosensitive drum 1 is uniformly charged to, for example, +500 V by the charger 3, and then image exposure 12 is performed on the photosensitive drum 1 at 600 dpi. The image exposure 12 is a laser beam modulated by a first image signal using a semiconductor laser as a light source, and the laser beam is polarized by a polygon mirror that rotates at a constant rotation speed by a motor, passes through an imaging lens, After being reflected by the folding mirror (not shown), the photosensitive member 1 is raster scanned, and the surface potential of the exposed portion is attenuated to, for example, +100 V to form an image-like electrostatic latent image. The wavelength of the beam is 680 nm. Thereafter, the latent image is developed with the developer in the developing container 2. Further, the toner is positively charged by the post charger 10 and the adsorption force between the photosensitive member and the toner is weakened so that subsequent transfer and separation are easy. Then, the transfer charger 4 transfers the toner image onto the transfer material proceeding in the direction of the arrow in the drawing, and further sends it to the fixing device 7 to fix the toner image.
[0021]
The developing device of this embodiment is simple and does not require maintenance for a developing sleeve life of up to 2,000 k sheets, and uses a developing system that uses a highly durable black magnetic one-component developer. Regular development using the body (developing sleeve) is performed. In the toner replenishment operation, when the toner near 2B in FIG. 1 (1) runs out, a signal to rotate the mag roll 24 is output by the signal of the piezoelectric element 22, and the rotation of the mag roll 24 causes the hopper 9B to rotate. The toner is replenished into the developing device.
[0022]
Next, the developing device 2 used in this embodiment will be described in more detail.
First, as the developer, a one-component magnetic toner of positive polarity that is simple and does not require maintenance, and has high durability, high reliability, and high productivity is used. The toner has a weight average particle diameter of 7.8 μm and SiO 2 as an external additive. ₂ Is applied to the surface of the toner particles at a ratio of 0.8% by weight.
[0023]
In the developing device 2 used in this embodiment, as shown in FIG. 1A, the developing sleeve is composed of two rollers 20 and 30, and the first developer carrier (developing sleeve) 20 is non- After blasting with FGB # 300 on φ30 aluminum A2017, which is a magnetic member, as shown in FIG. 1 (2), a coated material was used. The same applies to the second developing sleeve 30. The developer carrying member (developing sleeve) 30 is blasted with FGB # 300 on φ30 aluminum A2017, which is a nonmagnetic member, as shown in FIG. In this way, a coating was used. The above-described coating treatment on the surface of the developing sleeve is for preventing the occurrence of a sleeve ghost image that occurs in the developing sleeve cycle, which is a problem in Japanese Patent Laid-Open No. 3-36570, for example, and improving the durability of the sleeve surface. Yes (a film that protects the aluminum surface).
[0024]
Next, the magnetic seal member will be described. As shown in FIG. 5, in this embodiment, the first developing sleeve 20 and the second developing sleeve 30 configured as described above are each provided with six magnetic poles. Then, along the outer periphery of these developing sleeves, a Moldalloy (KN plating, magnetic permeability of 10) whose main component is iron for two developing sleeves having a shape as shown in FIG. ^-6 The magnetic seal member prepared in (1) was provided near both ends of the developing sleeve. At this time, the gap between each surface of the developing sleeve and the magnetic seal member was set to 420 μm ± 100 μm over the entire circumference.
[0025]
The magnet length of the magnetic roller of the magnetic pole arranged in the first developing sleeve 20 was L1 = 305 mm, and the magnetic length of the magnetic roller of the magnetic pole arranged in the second developing sleeve 30 was also L2 = 305 mm. As for the attachment position of the magnetic seal, it is most preferable to match the position of the outer end of the appropriate magnetic seal with respect to the magnet roller and the end of the magnet roller. This is because when the magnet comes out of the outside of the magnetic seal, a magnetic force is also present on the outside in the longitudinal direction, so that the toner is carried out by the magnetic force and causes toner leakage. is there. On the other hand, if the end of the magnet enters too much with respect to the outer end of the magnetic seal, a magnetic brush is originally formed between the magnetic seal and the magnet roller to eliminate toner leakage. However, in order to form a magnetic brush with the width of the magnetic seal on the developing sleeve even though there is no magnetic force at the outer end of the magnetic seal, the outer toner leaks to the end and at the same time the toner layer Thickness also increases, and there are cases where it falls off. In addition, since there is a backlash in the longitudinal direction due to the relationship between the developing sleeve and the magnet, the end of the magnetic seal is located 1 mm inside from the end of the magnet roller, as shown in FIG. Was to be located.
[0026]
The first developing sleeve 20 includes a fixed magnet roller having a six-pole magnetic field pattern shown in FIGS. 3 and 5 and Table 1 below. The developing sleeve rotates with respect to the photosensitive drum 1 at a speed of 120%. In this embodiment, the toner carried on the surface of the developing sleeve has a layer thickness regulated by the magnetic blade, but the distance (SB) between the developing sleeve (S) and the magnetic blade (B). _gap Was 250 μm. Also, the distance (SD) between the first developing sleeve and the photosensitive drum (D) _gap Was 250 μm. Further, the developing sleeve 20 has a DC bias of +400 V and, as shown in FIG. _pp A rectangular wave having a value of 1500 V and a frequency of 2.7 kHz was superimposed and applied as an AC bias to perform magnetic one-component non-contact development. Accordingly, the development contrast is 300V in the flight direction, and the fog removal contrast is 100V.
[0027]
[Table 1]

[0028]
The developer carrying member (developing sleeve) that is the second developing sleeve 30 is a non-magnetic member of φ30 aluminum A2017 formed with a film. Inside, there is a magnet having a six-pole magnetic field pattern shown in FIG. 3 and Table 2 below. The developing sleeve 20 has a DC bias of +400 V and a V as shown in FIG. _pp A rectangular wave having a value of 1500 V and a frequency of 2.7 kHz is applied. Such conditions are the same as and common to the first developing sleeve described above. Therefore, since only one power source is sufficient for the first and second developing sleeves, there is an advantage that the cost can be reduced and the space for the power source can be reduced. The developing sleeve rotates at a speed of 120% with respect to the counter drum.
[0029]
[Table 2]

[0030]
As the blade for regulating the developer layer thickness on the surface of each developing sleeve, a plate-like magnetic blade having a thickness of 1.0 mm is used for the first developing sleeve 20, and the blade on the second developing sleeve 30 is used. The developer layer thickness is regulated by the upstream developing sleeve 20. Therefore, the distance between the first developing sleeve 20 and the second developing sleeve 30 is set to 500 μm. This is a value for making the toner supply amounts in the first and second developing sleeves equal.
[0031]
In this way, the toner coat amount (M / S) on the first and second developing sleeves is about 1.0 mg / cm. ² Aligned. (SD) of the second developing sleeve _gap Is 250 μm. The uniform supply amount of toner (M / S) per unit time is the most important in making it possible to control the development characteristics of a plurality of development sleeves to be consistent and to stabilize the gradation.
In addition, in order to meet the demands for gradation and gradation stability of digital images and graphics corresponding to recent digital images, it is important to match the development characteristics of the first and second developing sleeves. It becomes. As described above, the toner supply amount per unit time is equal. Further, the developing pole of the first developing sleeve is N2, the developing pole of the second developing sleeve is N2, and the magnetic force and the half width are the same. However, the development characteristics after the endurance of 10k sheets are different as shown in FIG. 9 (upper is the second development, and lower is the first development). This will be described below.
[0032]
As described above, in the first developing sleeve 20, the toner layer thickness is regulated by the magnetic blade, whereas the second developing sleeve 30 is regulated by the first developing sleeve 20, and The first developing sleeve 20 rotates in the direction opposite to the toner traveling direction in the toner layer thickness regulating portion. Therefore, the toner is rubbed strongly between the second developing sleeve and the first developing sleeve, and the triboelectric charging ability of the toner becomes higher than that in the case of normal magnetic blade regulation. That is, the tribo (Q / M) of the second developing sleeve 30 is larger than that of the first developing sleeve 20. In general, since the development characteristics depend on the tribo (Q / M), as shown in FIG. 9, the difference in Q / M appears in the VD curve as the difference in development characteristics. This tendency is conspicuous when the development time is not sufficient, the developing sleeve rotation speed is high, and the frictional force on the toner in the toner layer thickness regulating member is large, as in a high-speed machine with a process speed of 400 mm / s or more. Become. This difference also causes a difference in development characteristics (at 10k sheets) in FIG. 9 (referred to as VD characteristics in FIG. 9 where the horizontal axis indicates contrast potential and the vertical axis indicates density (D)).
[0033]
Next, the life of the developing sleeve, which is the second problem, will be described.
The developing system used in the developing device of this embodiment has a more compact configuration because there is no member between the developing sleeves. In this system, the toner layer thickness of the first developing sleeve is regulated by the magnetic blade, and then the toner layer thickness of the second developing sleeve is regulated. That is, the first developing sleeve 20 receives a share with the toner twice during one rotation. On the other hand, the second developing sleeve 30 receives a share once at the restricting portion. In other words, in the image forming durability, the surface of the first developing sleeve receives about twice as much share as the second developing sleeve, so that the frequency of toner fixing due to the durability to the first developing sleeve increases. Become. This is a phenomenon peculiar to the positive toner.
[0034]
Since the sleeve life is almost determined by toner adhesion, this makes the coat life (sleeve life) of the first developing sleeve and the second developing sleeve different. For this reason, although one developing sleeve still has a life, another developing sleeve must be replaced first, and then another developing sleeve is replaced. For this reason, frequent maintenance is required, which increases the cost of maintenance. Therefore, in the case of an apparatus using a plurality of developing sleeves, it is desired to make the life of the developing sleeves common.
[0035]
The developing device of the present embodiment is configured in view of the above. The developing sleeve used in the developing device of this example was that whose surface was coated with a coating member. As a film formulation, a resin composition containing crystalline graphite and carbon in a phenol resin is cured on an aluminum sleeve surface in an environment of 150 ° C. so that the formed film thickness becomes 10 μm. A film was formed. The thickness of the film was about 10 μm in order to form a stable and uniform film. Further, the P / B ratio of the composition of the resin film was set to 1 / 2.5. Here, B represents the weight of the resin, and P represents the weight of the material other than the resin (crystalline graphite + carbon).
[0036]
At this time, since the conventional film composition has poor charging characteristics with respect to the positive toner, in this example, a phenol resin having 70 parts by weight of a quaternary ammonium salt was used. Also, a coating material containing carbonized or graphitized spherical particles was used in order to prevent a decrease in toner conveyance amount (M / S) caused by durability. As shown in Table 3, it can be seen that the former is effective in increasing the charge amount, and the latter is effective in increasing the coating stability and the coat amount. These will be described.
[Table 3]

[0037]
When added, the quaternary ammonium salt compound used above is uniformly dispersed in the phenolic resin, and is further taken into the structure of the phenolic resin when it is heated and cured to form a film. The phenol resin composition itself having a compound changes to a substance having negative chargeability. Therefore, if a developer carrier (sleeve) having a coating layer formed using such a material is used, the developer can be suitably charged to a positive polarity. Examples of the quaternary ammonium salt compound having the functions described above that can be suitably used in the present invention include compounds represented by the following general formula.
[0038]

(R in the formula ₁ , R ₂ , R _Three , R _Four Represents an alkyl group which may have a substituent, an aryl group which may have a substituent, and an aralkyl group, respectively. ₁ ~ R _Four May be the same or different. X ^- Represents the anion of the acid. )
[0039]
In the above general formula, X ^- Specific examples of the acid ions include organic sulfate ions, organic sulfonate ions, organic phosphate ions, molybdate ions, tungstate ions, heteropolyacids containing molybdenum atoms or tungsten atoms.
[0040]

[0041]
In this example, a coating layer was formed using a resin composition in which a specific quaternary ammonium salt compound as shown in (1) above was added to a phenol resin. In this case, as described above, when the phenol resin as the binder resin is heat-cured to form the coating layer, the quaternary ammonium salt compound is taken into the structure of the phenol resin. For this reason, unlike the case of the particle addition system such as the negative silica particles or the negative Teflon particles described above, the positive triboelectric charge imparting property to the positively chargeable developer as a whole is improved rather than partially. be able to. Further, unlike the above-described particle-added coating, the workability is not impaired and the strength of the coating layer is not reduced.
[0042]
Next, the carbonized or graphitized spherical particles used in this example will be described. When the carbon microbeads (PC) manufactured by Nippon Carbon Co., Ltd. have a particle diameter of 5 μm and measured with a measuring apparatus as shown in FIG. ^-1 -10 ^-2 Ωcm.
The formulation of the film was 90 parts by weight of crystalline graphite, 10 parts by weight of carbon, 70 parts by weight of quaternary ammonium, and 75 parts by weight of spherical particles with respect to 100 parts by weight of phenol resin. Incidentally, the ratio of graphite to carbon is preferably 9: 1 from the dispersibility of carbon. The film is applied onto the sleeve by a spraying method and then dried at 150 ° C. for 30 minutes. Next, the exposure of crystalline graphite that characterizes the present invention will be described.
[0043]
The present inventors have found that the charge amount, the image density, and the image quality change depending on the exposure amount of the graphite on the coating surface of the developing sleeve for the positive toner, and applied this to the multiple developing sleeve system. FIG. 8A shows the relationship between the graphite area (Gr exposure) on the surface of the coated sleeve and the charge amount (Q / M). Here, as shown in FIG. 14, the exposure amount (%) of graphite is obtained by observing the entire surface of the glossy graphite portion by microscopic observation of the coat surface by image processing by CCD reading, Divide by area. As can be seen from FIG. 8A, as the area of graphite increases, the amount of positive charge increases, and as a result, the image density increases as shown in FIG.
[0044]
In the present invention, by utilizing the above-described facts and appropriately controlling the graphite exposure amount on the coating surface of the developing sleeve, the developing property of the developing sleeve that has occurred between the first and the second as described above can be improved. Allows the difference to be the same despite the same coat formulation. This specific method will be described. By applying these characteristics, in this embodiment, the coating conditions of the first and second developing sleeves are as shown in Table 4 below. The formulation was performed under the same conditions as described above. However, by performing the subsequent polishing treatment, as shown in Table 4, the exposure degree of graphite could be changed between 60% and 45%. Polishing was performed by using a wrapping tape (# 3000), applying a 3 cm tape to the surface of the developing sleeve at a pressure of 1.5 kg, and changing the number of times of polishing. Specifically, the first developing sleeve was polished 24 times and the second developing sleeve was polished 8 times. As a result of using these developing sleeves, as shown in Table 4, the charge amount (Q / M ) Was almost the same.
[0045]
[Table 4]

[0046]
For comparison, the case where the coating treatment was not performed was examined. The charge amount of the first developing sleeve was 6.8 μC / g, and the charge amount of the second developing sleeve was 9.0 μC / g. And there was a difference between the second developing sleeve. This is considered to occur because in the second developing sleeve, in addition to the layer thickness regulation by the first developing sleeve, the first developing sleeve rotates in the direction opposite to the toner traveling direction at the toner regulating portion.
[0047]
In this way, in each developing sleeve, the Q / M (tribo) value that is an index of the developing characteristics can be made substantially equal. As a result, as shown in FIG. As shown in FIG. 12, the V-D curve (at the time of 10k sheets), which is the developing characteristic of the developing sleeve, has a difference.
Further, as shown in FIG. 8-3, it was found that the toner adhesion on the sleeve can be reduced by increasing the exposure amount of graphite. This is because not only can the chargeability be improved by the appearance of graphite on the surface as described above, but also the lubricity of the surface is improved, and as a result, the adhesion of the toner on the sleeve could be reduced. Conceivable. In addition, this makes it possible to control the gradation and gradation stability of the image, and to share the durability life of the plurality of developing sleeves.
[0048]
With the above configuration, in a developing device having a plurality of developing sleeves, which is a first purpose, a small-sized developing system compatible with a high-speed machine, it has recently been possible to prevent development performance from being different for each developing sleeve. Therefore, it is possible to satisfy the requirements of gradation and gradation stability for digital images and images corresponding to graphics. In addition, in the developing device having a plurality of developing sleeves, which is the second object, it is possible to make the life of the developing sleeves common, so that it is possible to reduce the service cost by eliminating the labor for maintenance by service personnel. it can. Furthermore, it is possible to provide a developing device that can stably obtain a high-density image without a sleeve ghost image as a third object.
[0049]
<Example 2>
The image forming apparatus according to the present embodiment is the same as that used in the first embodiment.
The feature of this embodiment is that the particle size of the crystalline graphite in the coating material used for each developing sleeve is reduced only on the upstream side as a method for increasing the charging property of the upstream developing sleeve, and the rest is the same By coating each developing sleeve under the formation conditions, the amount of graphite exposed on the coating surface is increased. This is because the surface area of the graphite increases as the particle size of the graphite is reduced. According to this method, the diameter of the developing sleeve can be reduced and space saving can be achieved. Further, in this embodiment, as a method of managing the exposure amount of graphite at the manufacturing stage, the glossiness of the surface of the developing sleeve is measured, thereby measuring the graphite exposure amount.
[0050]
Next, the developing device 2 used in this embodiment will be described in detail. As the developer, a positive-polarity one-component magnetic toner was used. As shown in FIG. 1 (1), there are two developing sleeves, and the first developer carrier (developing sleeve) 20 is blasted with FGB # 600 on a non-magnetic member φ20 aluminum A2017. Thereafter, coating was performed. The same applies to the second sleeve, and the developer carrier (developing sleeve) 30 was blasted with FGB # 600 on φ20 aluminum A2017, which is a nonmagnetic member, and coated. This coating is performed in order to prevent sleeve ghost images that occur in the sleeve cycle and to increase the durability of the sleeve surface.
[0051]
The first developing sleeve rotates at a speed of 120% with respect to the drum. The toner regulates the layer thickness with a magnetic blade, and (SB) _gap Was 250 μm. Distance between first developing sleeve and photosensitive drum (SD) _gap Is 250 μm, the first developing sleeve has a DC bias of +400 V, and, as shown in FIG. _pp A rectangular wave having a frequency of 1500 V and a frequency of 2.7 kHz was applied as an AC bias to perform magnetic one-component non-contact development. Accordingly, the development contrast is 300V in the flight direction, and the fog removal contrast is 100V. As the second developing sleeve 30, a non-magnetic member of φ20 aluminum A2017 formed with a film was used. The developing sleeve has a DC bias of + 400V and V as shown in FIG. _pp A rectangular wave with 1500 V and a frequency of 2.7 kHz is applied. Since it is the same as the first developing sleeve, it is common and only one power source is required, which leads to a cost reduction and a small power source space. The developing sleeve rotates at a speed of 120% with respect to the counter drum. The blade is the same as in Example 1. Next, features of the present embodiment will be described.
[0052]
In this embodiment, the following materials were used as the coating material for the upstream developing sleeve. As the resin (B), 100 parts of phenolic resin (70 parts in total) having 70 parts of a quaternary ammonium salt was used, and carbon and graphite having an average particle diameter of 3 μm were used as the pigment (P). In this film, the exposed area on the surface can be increased by adding the same weight as the graphite having a smaller particle diameter than the film used in Example 1. In this respect, the charging property, toner More effective in preventing sticking. The formulation when using this material is shown below.
[0053]
The film is formulated by coating a coating liquid prepared by mixing a phenolic resin having a quaternary ammonium salt with crystalline small-diameter graphite and carbon at a weight ratio of 170: 36: 4 on the surface of an aluminum developing sleeve. Was coated to a thickness of 10 μm, and then cured at 150 ° C. to obtain a resin film. The thickness of the film is preferably about 10 μm in order to form a stable and uniform film. With this formulation, the graphite exposure amount of the first sleeve could be further increased to 72%, and the charge amount could be further increased to 10.8 μC / g. The second sleeve coat was 50%. Moreover, the measurement of glossiness used Tokyo Denshoku GLOSSMETER TC-108DP / A.
[0054]
According to the study by the present inventors, it has been found that there is a correlation between the exposed amount of graphite and the glossiness of the surface of the developing sleeve, as shown in FIG. In this example, this was adopted as a method for managing the sleeve surface coat. In this way, the value of Q / M (tribo), which is an index of development characteristics, can be made substantially equal between the development sleeves. As a result, the VD curve, which is development characteristics, is almost equal. It was possible to make the same curve. This makes it possible to control the gradation and gradation stability of the image, to share the durability life, and to easily manufacture and control the quality of the graphite by controlling the exposure of graphite based on the glossiness. Was able to improve.
[0055]
With the above-described configuration, in this embodiment, although the development system is compatible with a high-speed machine, in the small development device having a plurality of development sleeves, which is the first object, developability differs for each development sleeve. Therefore, it is possible to obtain a developing device that satisfies the requirements of gradation and gradation stability of digital images and images corresponding to recent graphics. In addition, in the developing device having a plurality of developing sleeves, which is the second purpose, by sharing the life of each developing sleeve, it is possible to save the labor for maintenance of the serviceman and reduce the service cost, A developing device capable of stably obtaining a high-density image can be provided. In addition, the image density is high and stable with respect to the high speed, which is the third object, and it is possible to provide a developing device that saves space and has a lifetime of up to 1 million sheets.
[0056]
<Example 3>
A feature of this embodiment is that the developing device of the present invention is applied to a reuse image forming apparatus. Reusable toner is basically waste toner that has not been transferred and has been collected by cleaning. Therefore, due to toner deterioration, the tribo is extremely small compared to New toner, resulting in poor developability and , The agglomeration degree of the waste toner is increased, and (SB) _gap The market share will increase, and the film will also be scraped. This is shown in FIG. This is a development characteristic of a reuse diameter. It can be seen that the overall density is lower and the difference between the developing sleeves is larger than when using New toner (see FIG. 9).
[0057]
The present embodiment was implemented in view of these matters. In the present embodiment, a digital copying machine using an a-Si drum as a photoreceptor in the reuse-type image forming system shown in FIG. 10 will be described. The process speed is 120 mm / min at 600 mm / s. The surface of the photosensitive drum 201 is uniformly charged to +500 V by the primary charger 203. Next, PWM exposure 212 is performed at 600 dpi with a semiconductor laser having a wavelength of 680 μm to form an electrostatic latent image on the photosensitive drum 201. Next, reversal development is performed by the developing device 202 to visualize the toner image. A magnetic one-component positive toner is used as a developer, and jumping development is performed. The toner particle size is 6.0 μm.
[0058]
In the conventional two-component developer, the replacement of the carrier has to be performed every 100,000 sheets, and it is not maintenance-free, so the advantage of reuse cannot be reflected so much. In this embodiment, a dry magnetic one-component toner having infinite durability and no maintenance is used. The development bias is 2400 Hz and 1500 V for both the first and second development sleeves. _pp A bias voltage obtained by superimposing a direct charge pressure of +400 V on an AC voltage of Duty 50% is applied. (SB) _gap The first is 250 μm, (SD) _gap Both were 250 μm. Thereafter, the toner image is charged by flowing a total current +200 μA in the post charger, and then transferred to a transfer material proceeding in the direction of the arrow by the transfer charger 204 and sent to the fixing device 7 to fix the toner image. On the other hand, the transfer residual toner on the photosensitive drum 1 is removed and collected by the cleaning device 206, and the waste toner (reused toner) is returned to the developing hopper 209B through the transport pipe 208. The conveyance pipe has a screw-shaped conveyance member inside, and carries reuse toner by rotating.
[0059]
More specifically, as shown in FIG. 10, the transported reuse toner is put into the developing hopper 209B and reused. Separately, New toner is put into the hopper 209A, and the respective toners are attracted by the magnetic force by the mag rollers 21A and 21B, and the toner is carried into the developing device by rotating the mag rollers 21A and 21B.
[0060]
In the developing device of the present embodiment, a method of mixing reuse toner and New toner in the developing unit is adopted, but a space for mixing in the hopper may be provided and mixed here. The toner mixed in the developing device is sent again to the developing sleeve and used for developing the electrostatic latent image on the photoreceptor. The normal rotation speed of the mag roller 21A is 2 rotations / minute, and the rotation speed of the mag roller 21B is appropriately changed. That is, the rotation signal of the mag roller 21B does not apply the weight of the toner to the piezo sensor (made by TDK) in the developing device, and when it vibrates, a toner supply signal is generated. Normally, the mag roller 21B is 10/90 (mag roller 21A: mag roller 21B = 9: 1) with respect to the mag roller 21A. The configuration of the developing device of this example is the same as that used in Example 2, and is a film using phenol resin, crystalline graphite, and carbon, and the diameter of the developing sleeve is φ20.
[0061]
As described above, when the developing device of this embodiment is applied to the reuse system, the developability becomes lower than that in the case of using the normal New toner. Therefore, as shown in FIG. As shown in FIG. 13-2, although the development characteristics were further different from those used, the overall density is a little lower, but the tribo (Q / M) of the first developing sleeve is set to the second. It was possible to make it the same level as the developing sleeve. Incidentally, the first was 8.9 μC / g and the second was 9.4 μC / g. In this way, even in a reuse system having a low overall chargeability, the value of Q / M (tribo), which is an index of development characteristics, can be made substantially equal, and as a result, development characteristics are obtained. The VD curve could be made substantially the same curve (see FIG. 13-2). In addition, it has been found that this makes it possible to control the gradation and gradation stability of an image, and to achieve a reuse system in which a plurality of developing sleeves can share a durable life.
[0062]
With the above-described configuration, the development system is compatible with reuse, and in the small development device having a plurality of development sleeves, which is the first purpose, by preventing development performance from being different for each development sleeve, It can meet the requirements of gradation and gradation stability of images corresponding to images and graphics, and the development tool with multiple developing sleeves, which is the second purpose, shares the life of developing sleeves. Therefore, the service cost can be reduced by eliminating the labor for maintenance by a serviceman, and a developing device capable of stably obtaining a high density image can be provided. In addition, for the third purpose of speeding up, it was possible to provide a developing device that is highly concentrated and stable, saves space, and is reusable and excellent in environmental performance.
[0063]
【The invention's effect】
As described above, according to the present invention, in the developing device having a plurality of developing sleeves, which is the first object of the present invention, it is possible to effectively prevent the developing property from being different for each developing sleeve, In recent years, a developing device that can sufficiently satisfy the demands of gradation and gradation stability of a digital image and an image corresponding to graphicization is provided.
In addition, according to the present invention, in the small developing device having a plurality of developing sleeves, which is the second object of the present invention, it is possible to make the life of the phenomenon sleeve common, and this leads to maintenance of the serviceman. There is provided a developing device capable of reducing the service cost by omitting the trouble and stably obtaining a high-density image for the high speed which is the third object of the present invention.
According to the present invention, the above first to third objects can be realized at the same time.
[Brief description of the drawings]
FIG. 1A is a diagram for simply explaining a developing device of Example 1, and FIG. 1B is a diagram for explaining a developing sleeve of Example 2. FIG.
FIG. 2 is a diagram for explaining an image forming apparatus used in the first and second embodiments.
FIG. 3 is a diagram for explaining a magnetic pole arrangement of a developing sleeve used in the first embodiment.
FIG. 4 is a diagram for explaining a developing bias used in the first embodiment.
FIG. 5 is a diagram for explaining the relationship between a plurality of sleeves and a seal according to the present embodiment.
FIG. 6 is a diagram for explaining a relationship in the longitudinal direction between a plurality of sleeves and a seal according to the present embodiment.
FIG. 7 is a diagram for explaining a method of measuring the resistance of powder.
8A, 8B, and 8C are diagrams for explaining the graphite exposure amount, charge amount, concentration, and contamination. FIG.
FIG. 9 is a diagram for explaining development characteristics in a conventional example.
FIG. 10 is a diagram for explaining a reuse image forming apparatus according to a third embodiment.
FIG. 11 is a diagram for explaining development characteristics of a conventional reuse image forming apparatus.
FIG. 12 is a diagram for explaining development characteristics improved in Example 1. FIG.
13 is a diagram for explaining the development characteristics of a conventional reuse system, and FIG. 13-2 is a diagram for explaining the development characteristics of a reuse system of Example 3. FIG. .
FIG. 14 is a diagram for explaining the relationship between the number of times of polishing and the exposure amount of graphite.
FIG. 15 is a diagram for explaining a conventional image forming apparatus.
[Explanation of symbols]
1: drum photoreceptor
2: Developer
3: Primary charger
4: Transfer charger
5: Separating charger
6: Cleaning device
7: Fixing device
9: Developer hopper
10: Post charger
12: Image exposure
20: First developing sleeve
30: Second developing sleeve

Claims (6)

A developing device that visualizes an electrostatic latent image formed on an electrostatic latent image carrier with a positively chargeable developer carried on the surface of the developer carrier, wherein a plurality of common developing biases are used. The developer layer thickness regulation of the developer on the developer carrier positioned downstream with respect to the rotation direction of the electrostatic latent image carrier is controlled by the upstream developer carrier. in line cormorant current image device, each of the plurality of the developer carrying member, which incorporates a magnetic member, and the surface of each is covered with a coating member having a crystalline graphite, and, these multiple The developer is disposed on the upstream side of the developer carrier positioned on the downstream side with respect to the rotation direction of the electrostatic latent image carrier. The exposed amount of crystalline graphite is larger in the carrier Developing apparatus is characterized in that it is configured so that. The surface of the coating member on the surface of the developer carrier is exposed to crystalline graphite on the surface of the developer carrier upstream of the developer carrier positioned downstream with respect to the rotation direction of the electrostatic latent image carrier. The developing device according to claim 1, wherein the surface of the coating member is polished to increase the amount.   The surface of the coating member on the surface of the developer carrier is exposed to crystalline graphite on the surface of the developer carrier upstream of the developer carrier positioned downstream with respect to the rotation direction of the electrostatic latent image carrier. The glossiness of the surface of the developer carrying member arranged on the upstream side is made larger than the glossiness of the surface of the developer carrying member arranged on the downstream side in order to increase the amount. Development device.   In order to increase the exposure amount of the crystalline graphite on the upstream side of the developer carrying body positioned on the downstream side with respect to the rotation direction of the electrostatic latent image carrying body, The particle size of the crystalline graphite in the coating member coated on the surface of the developer carrier disposed in the surface is the particle size of the crystalline graphite in the coating member coated on the surface of the developer carrier disposed on the downstream side. The developing device according to any one of claims 1 to 3, wherein the developing device is made smaller.   The developing device according to claim 1, wherein the coating member is formed of a resin composition containing at least a phenol resin and a quaternary ammonium salt compound.   The developing device according to claim 1, wherein the coating member has carbonized or graphitized spherical particles.

Images