JP3952952B2 - Image forming apparatus - Google Patents

Description

【０１８２】
上記の表で、×は回収ブラシ装置を通過した後もトナーが感光体ドラム上および印字後に回収不良ゴーストが目視で確認できるレベルを示す。△は回収ブラシ装置を通過した後にトナーが感光体ドラム上および印字後に回収不良ゴーストが目視で確認できるが、印字後に回収不良ゴーストが目視で確認できないレベルを示す。○は、回収ブラシ装置を通過した後、トナーが感光体ドラム上に目視で確認できない、印字後にも回収不良ゴーストが目視で確認できないレベルを示す。さらに、Ｅは回収ブラシ装置と感光体ドラムとの間で異常放電が発生した場合を示す。
【０１８３】
なお、交流電圧に重畳する直流電圧を−８００〜＋８００Ｖの間で変化させても、回収能力に有意差は認められなかった。
【０１８４】
また、交流電圧に矩形波を用いると回収能力が低下、三角波を用いると正弦波と同等の回収能力であった。
【０１８５】
また、前段の転写装置で転写させたトナーを次段の転写装置に１ｋＶかけて逆転写させたトナーの回収能力も（表１）と同様な傾向となった。
【０１８６】
また、転写ローラに印加する電圧を５００Ｖに落とし、転写効率を約７３％にして負極の転写残トナーを増やしたもの（正極のトナーも存在している）、未帯電トナー、−１３、−４７μＣ／ｇ帯電量トナーを回収ブラシ装置に供給しても、（表１）に示す比べて多少回収可能領域は狭まるが、ほぼ同等の交流電圧設定範囲に設定することで、回収ブラシ装置に回収できることも確認できた。強いて述べると−１０〜−５０Ｃ／ｇの帯電量の範囲で極力シャープな帯電量分布にする方が好ましい。
【０１８７】
また、１００Ｈｚ程度の周波数で１０００Ｖ以上のピーク間電圧を印加すると、目視でブラシ繊維が振動し、回収ブラシ装置と感光体ドラムとの接触領域からトナーミストが発生することが確認された。さらに周波数をあげると、目視ではブラシ繊維の振動は不明であるが、トナーミスト量が増加した。周波数が大きいため、目視では確認できないレベルでブラシ繊維が微小振動しているものと考えられる。
【０１８８】
以上の結果から、特定の交流電圧と周波数を設定範囲に設定することで回収ブラシ装置に転写残留トナーを回収できることが判明した。強いて述べると、−１０〜−５０Ｃ／ｇの帯電量の範囲で極力シャープな帯電量分布にする方がより好ましい。
【０１８９】
（実施例２）
次に、種々の形状係数１．２５、１．６０のトナーを感光体ドラムに付着させ、上記と同様の実験を行った。その結果を（表２）に示す。
【０１９０】
【表２】

【０１９１】
なお、球形度１．２５のトナーについては、（表１）に示す場合と回収能力に有意差は認められなかった。
【０１９２】
以上の結果から、球形度１．２５では（表１）と同様な結果になり、球形度を１．６０にすると、（表１）に示す場合比べて回収可能領域は狭まるが、特定の交流電圧設定範囲に設定することで、回収ブラシ装置に回収できることが判明した。強いて述べると、トナーの形状係数は１．５０以下が好ましい。
【０１９３】
（実施例３）
次に、形状係数１．４３のトナーを用いて、回収ブラシ装置に印加する電圧に交流重畳をやめ、直流電圧のみを変えて、種々の転写効率にて、回収ブラシ装置の通過前後での感光体ドラム表面上のトナー付着量と印字後に回収ブラシ装置のトナー回収不良によるゴーストを目視で観察した。その結果を（表３）に示す。
【０１９４】
【表３】

【０１９５】
なお、−６００Ｖ以下、＋６００Ｖ以上にすると回収能力が若干悪くなる傾向にあった。
【０１９６】
また、前段の転写装置で転写させたトナーを次段の転写装置に１ｋＶかけて逆転写させたトナーの回収能力については、十分ではないものの−３００〜−６００Ｖの設定範囲でトナーの回収性能が見られた。なお、印加電圧−３００、−６００Ｖの方が＋３００、＋６００Ｖより若干回収性能が良いのは、転写残トナーの量の差と思われる。
【０１９７】
また、印加電圧が−３００Ｖより−６００Ｖ、＋３００Ｖより＋６００Ｖの方が若干良い回収性が良いと。
【０１９８】
感光体ドラムの表面電位の絶対値４００Ｖより大きい直流電圧を印加する方が回収性能が良いことがわかった。また、トナーの形状係数の差については、実施例２と同様な結果で、形状係数が１．６０以下でより回収能力があることが判明した。
【０１９９】
また、−１３μＣ／ｇ帯電量トナーを回収ブラシ装置に供給すると、−２５μＣ／ｇトナーに比べて回収性能が多少低下した。
【０２００】
また、回収ブラシ装置に印加するバイアスが交流の場合は、ブラシローラの内部までトナーが入り込んでおり、直流のみの印加ではブラシ先端にのみ（ブラシローラ表面）回収していると、交流印加の回収バッファ量（約３００ｍｇ）が多くなることが確認できた。
【０２０１】
以上の結果から、直流電圧のみの場合では、転写効率９７％未満では＋３００〜６００Ｖ、転写効率９７％以上と逆転写トナーでは−３００〜−６００Ｖの設定範囲で、十分ではないもののトナーの回収性能が認められた。また、感光体ドラムの表面電位より絶対値で大きい直流電圧を印加する方がより良いトナーの回収性能が認められた。また、トナーの形状係数は１．５０以下が好ましい。
【０２０２】
また、トナーの帯電量は−１０〜−５０μＣ／ｇ、より好ましくは−１５〜−４５μＣ／ｇの範囲に設定した方が良い。
【０２０３】
また、回収バッファ量に関しては、交流印加の方が有利であることが判明した。
【０２０４】
（実施例４）
次に、形状係数１．４３のトナーを用いて、回収ブラシ装置にトナーが蓄積された状態で、周波数を３ｋＨｚに固定して、ピーク間電圧と重畳する直流電圧とを変化させ、かつ回収ブラシ装置に印加する直流電圧の極性を反転して、回収ブラシ装置からのトナーの吐き出し効果を評価した。その結果を（表４）に示す。
【０２０５】
【表４】

【０２０６】
上記の表で×は、回収ブラシ装置に上記電圧を印加したときに、回転する感光体ドラムへのトナーの付着が目視で認められないケース、すなわち、回収ブラシ装置からトナーが吐き出されていないケースを示す。また△は、回収ブラシ装置に上記電圧を印加したときに、回転する感光体ドラムへのトナーの付着が認められ、かつ回収ブラシ装置にトナーが残留しているケースを示す。
【０２０７】
なお、交流印加で回収したトナー（ブラシローラ内部までトナーが入り込んだ状態）での吐き出し性能は（表４）に示す結果であるが、直流印加で回収したトナー（ブラシローラのブラシ先端のみで回収した状態）での吐き出し性能は、トナーがブラシローラ内部に無い分で、回収ブラシ装置にトナーが残留していなかった。つまり、直流印加で回収したトナーは完全に吐き出すことが可能である。
【０２０８】
以上の結果から、形状係数１．４３のトナーの場合、ピーク間電圧が低い場合、または直流電圧のみの場合では、トナーの十分ではないもののトナーの吐き出し性能が認められた。また、直流印加で回収したトナーは完全に吐き出すことが可能であることが判明した。
【０２０９】
（実施例５）
次に、形状係数１．２５のトナーを用いて、（表４）と同様の評価を行った。その結果を（表５）に示す。
【０２１０】
【表５】

【０２１１】
上記の表で○は、回収ブラシ装置に印加する直流電圧の極性を反転したときに、回転する感光体ドラムへのトナーの付着が目視で認められるケースを示す。
【０２１２】
以上の結果から、ピーク間電圧が低い場合、または直流電圧のみの場合では、トナーの形状を球形にすることで、さらなるトナーの吐き出し性能が認められた。
【０２１３】
（実施例６）
次に、形状係数１．４３のトナーを用いて、種々のトナーの帯電量に対して、回収ブラシ装置にトナーが蓄積された状態で、回収ブラシ装置に印可する直流電圧を変化させてかつ回収ブラシ装置に印加する直流電圧の極性を反転して、回収ブラシ装置からのトナーの吐き出し効果を評価した。その結果を（表６）に示す。
【０２１４】
【表６】

【０２１５】
以上の結果から、トナーを−１０〜−５０Ｃ／ｇの帯電量の範囲で極力シャープな帯電量分布にする方がより吐き出し性能が良いことが判明した。
【０２１６】
（実施例７）
次に、回収ブラシ装置のブラシ抵抗による回収・吐き出し性能とその他の影響について簡単に評価した。
【０２１７】
実施例１〜６で使用したブラシ抵抗はＥ４であったが、抵抗が若干低いため、ブラシに印加するバイアスが±４、５００Ｖと低くても、ＯＰＣドラムを帯電してしまい、表面電位がばらつく傾向にあった。その結果、画像ムラが発生した。
【０２１８】
ブラシ抵抗が約Ｅ１０の場合は、回収バイアス−４００Ｖ、吐き出しバイアス±４００Ｖ極性切替えの場合、抵抗がＥ４に比較して、回収・吐き出し性能が良好で、表面電位への影響も少なかった。
【０２１９】
以上の結果から下記の通り、本発明の作用効果を考察する。
【０２２０】
実施例１、２から分かる通り、交流電圧のピーク間電圧を放電開始電圧の２倍〜２ｋＶｐｐ、周波数１〜７ｋＨｚに設定すると、トナーは帯電極性に関わらず回収ブラシ装置に回収される。よって、トナーを直接回収ブラシ装置に吸引する力は、静電気力以外の力と考えられる。また、実施例１でブラシ繊維が機械的に振動していると考えられることから、ブラシ繊維の機械的な力が作用しているものと考えられる。
【０２２１】
すなわち、ブラシ繊維が振動することで、トナーとブラシ繊維との間に機械的付着力が生じる。さらに振動を継続することでブラシ内にトナーが潜り込み、ブラシ繊維でトナーが抱え込まれる。この結果トナーの帯電極性に関わらず、回収ブラシ装置側にトナーが回収されるものと考えられる。
【０２２２】
また、放電開始電圧の二倍以上のピーク間電圧は、ブラシ繊維を振動させる効果があるものと考えられる。
【０２２３】
すなわち、負極性の電圧ピーク時では、ブラシ繊維先端からマイナス電荷が感光体ドラム表面に放出される。この結果ブラシ繊維先端に近接した感光体ドラム表面には、マイナス電荷を帯びた領域Ａが形成される。放電後ブラシ先端にマイナス電荷が充電されると、感光体ドラムの帯電極性と同極性のため、ブラシ繊維と感光体ドラム表面とは静電的に反発する。ブラシ先端周囲に未帯電またはプラス電荷を帯びた領域Ｂが感光体ドラム表面に存在すると、ブラシ先端は領域Ｂに吸引される。この結果ブラシ先端には感光体ドラム表面上の領域Ａから領域Ｂに移動する力が作用する。
【０２２４】
次に、負極性の電圧ピーク時では、上記とは逆の力が作用する。この結果、ブラシ繊維が振動するものと考えられる。また、領域Ａと領域Ｂとの間隔は、交流電圧の周波数と回収ブラシ装置と感光体ドラムとの相対速度、およびブラシ繊維密度によって決定される。ブラシ繊維が振動しやすい領域ＡＢ間の間隔があるため、実施例１、２のような周波数依存性が見られたものと考えられる。
【０２２５】
また、ブラシ繊維密度については、ブラシ繊維が振動しやすい領域ＡＢ間の間隔を決める要素でもあるが、感光体ドラム１上のトナーの接触機会を多くするためにブラシ繊維密度を上げた方がいいし、回収されたブラシ中に入り込んだトナーの吐き出し性能を確保するにはブラシ繊維密度を小さくした方が良い。このような考え方から、また、実施例でのブラシ繊維密度が３６０Ｆ／ｍｍ² で、吐き出し性能が若干悪いことから、ブラシ繊維密度は５０〜４００Ｆ／ｍｍ² であることが好ましい。
【０２２６】
また、トナーの形状係数が１．００〜１．５０である方が回収性能は良好である。これはトナーが球形である方が感光体ドラム１との離型性が高いため、静電気力および機械的な力で感光体ドラム１上のトナーを回収しやすいと考えられる。
【０２２７】
また、実施例３から回収バイアスが直流電圧のみの場合では、転写効率９７％未満では＋３００〜６００Ｖ、転写効率９７％以上と逆転写トナーでは−３００〜−６００Ｖの設定範囲で、十分ではないもののトナーの回収性能が認められ、また、感光体ドラムの表面電位より絶対値で大きい直流電圧を印加することでさらに高いトナーの回収性能が認められた。
【０２２８】
これらの結果は、感光体ドラムの表面電位とブラシ繊維の間に電界が生じる電位差が確保されることによって感光体ドラム表面上のトナーに静電誘引力が有効に働く電位差と考えられる。つまり、感光体ドラム表面電位の絶対値より大きい直流電圧をブラシに印加することが望ましいことを示唆している。しかし、放電開始電圧以上の電圧を印加するのは、感光体ドラム上のトナーの極性を変化させるので、あまり望ましくない。
【０２２９】
また、トナーの形状係数は１．５０以下が好ましい。これは転写効率９７％未満になると負極トナーの転写残が多くなっており、転写効率９７％以上と逆転写トナーの場合は、正極トナーの転写残が多くなっていることを示しているが、直流電圧のみを回収バイアスに用いる場合は両極性トナーを一度に取ることが困難なので、できるだけトナーを球形にする転写条件最適化等の転写効率向上を図り、正極性の逆転写トナーを回収するシステムが理想的と考えられる。
【０２３０】
また、トナーの帯電量は−１０〜−５０μＣ／ｇ、より好ましくは−１５〜−４５μＣ／ｇの範囲に設定した方が良いことから、帯電量はある程度高くシャープにすることにより、トナーにかかる静電気力を確保でき、転写性が向上できる範囲となっていると考えられる。
【０２３１】
また、実施例４では逆にピーク間電圧が放電開始電圧以下でないとトナーが回収ブラシ装置から吐き出されない。これは、ブラシ繊維が振動していると、トナーはブラシ内部に移動してしまうためと考えられる。よって、トナーを吐き出す際にはブラシ繊維が振動しない状態が好ましいと考えられる。実施例４ではピーク間電圧が５００Ｖ以下の場合に相当する。このとき重畳された直流電圧の極性と同極性のトナーがブラシから離脱して感光体ドラムに移動したものと考えられる。
【０２３２】
また、感光体ドラムの表面電位より絶対値で大きい直流電圧を印加することでさらに高いトナーの吐き出し性能が認められた。これらの結果は、感光体ドラムの表面電位とブラシ繊維の間に電界が生じる電位差が確保されることによって感光体ドラム表面上のトナーに静電誘引力が有効に働く電位差と考えられる。つまり感光体ドラム表面電位の絶対値より大きい直流電圧をブラシに印加することが好ましいことを示唆している。但し、放電開始電圧以上は前述したように感光体ドラム上のトナーの極性を変化させるのであまり好ましくない。
【０２３３】
実施例５では、トナーの形状を球形にすることで、ブラシ繊維とトナーの離型性があがり、実施例４より吐き出し性能が向上したものと考えられる。
【０２３４】
なお、トナーを回収ブラシ装置から吐き出す際に直流電圧成分の極性を反転させたが、本方式では未帯電トナーが回収ブラシ装置に蓄積されてしまう。よって、回収ブラシ繊維の材料として、トナーを正負どちらかの極性に帯電させやすいものが好ましい。本試験では帯電系列上、自身がプラスに帯電しやすいナイロン系繊維を用いた。このような材料を用いることで、ブラシ繊維が振動する際、ブラシに取りこまれたトナーが次第に特定の極性に帯電するので、トナーを静電気的に吐き出すことが可能になる。
【０２３５】
実施例６では、トナーを−１０〜−５０Ｃ／ｇの帯電量の範囲で極力シャープな帯電量分布にする方がより吐き出し性能が良いことが判明した。これは、トナーの帯電量が低過ぎると、トナーにかかる静電誘引力が小さくなるので吐き出し性能が低下、逆に高過ぎるとトナー電荷に見合う転写電界が不足して転写残トナーが極端に増加して回収性能が低下したと考えられる。
【０２３６】
【発明の効果】
以上のように、本発明によれば、回収ブラシ装置およびトナー除去装置を用いて感光体上に残留するトナーを正負帯電極性に関わらず効率よく回収することができるので、装置の小型化および低価格化、感光体の長寿命化が可能で、かつ転写残留トナーの極性に依存しないトナー除去装置を具備した画像形成装置となるという有効な効果が得られる。
【図面の簡単な説明】
【図１】本発明の一実施の形態であるブラシ振動手段を有する画像形成装置を示す説明図
【図２】本発明の他の実施の形態である画像形成装置を示す説明図
【図３】本発明のさらに他の実施の形態であるカラー画像を形成する画像形成装置を示す説明図
【図４】図１の画像形成装置に係る電圧印加タイミングチャート
【図５】図２の画像形成装置に係る電圧印加タイミングチャート
【図６】図３の画像形成装置に係る一例としての電圧印加タイミングチャート
【図７】図３の画像形成装置に係る他の一例としての電圧印加タイミングチャート
【図８】従来のブラシ方式によるクリーニング装置の概略を示す説明図
【符号の説明】
１ 感光体ドラム（像担持体）
２ レジストローラ
３ 転写装置（転写手段）
４ 定着装置
５ 受像紙
６ 帯電装置
７ 露光源
８ 現像装置（現像手段）
１０ 上流側案内手段
１１ 下流側案内手段
１２ 回収ブラシ装置（第一の回収手段）
１３ トナー除去装置
１４ ベルト支持ローラ
１５ 紙搬送ベルト
１６ 紙吸着装置
１７ａ 回収ブラシ部材用電源（第一の電圧印加手段）
１７ｂ 回収ブラシ部材用電源（第二の電圧印加手段）
１０１ 感光体ドラム
１０２ ブラシローラ
１０３ 中間ローラ
１０４ 掻き取り部材[0001]
BACKGROUND OF THE INVENTION
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus and an image forming method applied to a copying machine, a facsimile, a printer, and the like, and in particular, an image forming apparatus that forms an image by transferring a developer image formed on an image carrier onto image receiving paper. And an image forming method.
[0002]
[Prior art]
In general, in an image forming apparatus using an electrophotographic method, after a toner image formed on an image carrier is transferred onto image receiving paper, residual toner remaining on the image carrier is collected by a cleaning device, and this collection is performed. Toner is temporarily accumulated in a collection container and discarded when the amount of collected toner reaches a certain amount.
[0003]
In the full-color image forming apparatus, image data is received from a host device such as a personal computer or a workstation, and color separation is performed into four colors of yellow, magenta, cyan, and black based on the image data. A toner image of each color is formed on the image carrier based on the image information, and the toner images of each color are superimposed on an intermediate transfer member such as an intermediate transfer roll or an intermediate transfer belt, and then transferred onto the image receiving paper all at once. Have gained. In this case as well, the residual toner remaining on the image carrier or intermediate transfer member is collected by a cleaning device, and the collected toner is temporarily accumulated in a collection container, so that the amount of collected toner is kept constant. When it reaches, it is discarded.
[0004]
In such an image forming apparatus, the cleaning process for removing the residual toner remaining on the image bearing member or the intermediate transfer member is performed by using the residual toner as it is as a result of contamination such as ghosting or fogging in the recorded image or color mixing due to color mixing. This is an extremely important process because the cause of unevenness is eliminated.
[0005]
In recent years, as the problem of environmental protection has been closed up, it is required to reduce the collected amount of residual toner collected and discarded in this way as much as possible. There is a demand for utilization.
[0006]
Further, the problem of reducing the amount of waste for environmental protection and the reuse of waste is not limited to the residual toner collected from the image carrier or the intermediate transfer member. Components are also required. However, when a cleaning device is attached to the image carrier or intermediate transfer member, the cleaning blade or the like of the cleaning device is brought into sliding contact with the surface of the image carrier or intermediate transfer member, and this is worn (film reduction of the image carrier, etc.). This is an obstacle to extending the life of the image carrier and intermediate transfer member.
[0007]
From this point of view, conventionally, as one of techniques for cleaning the surface of an image carrier in an image forming apparatus using an electrophotographic method, Japanese Patent Application Laid-Open No. 9-90840, Japanese Patent No. 3137962, and the like. A brush method has been proposed.
[0008]
FIG. 8 shows a schematic configuration of a conventional cleaning apparatus using a brush system. In FIG. 8, reference numeral 101 denotes a photoconductor, and reference numeral 102 denotes a brush roller that rotates in contact with the photoconductor 101. Reference numeral 103 denotes an intermediate roller in contact with the brush roller 102, and reference numeral 104 denotes a scraping member that scrapes off the toner on the intermediate roller. After the transfer, the toner remaining on the photosensitive member 101 is mechanically or electrostatically collected on the brush roller side. Further, the collected toner is electrostatically transferred to the intermediate roller and then removed from the intermediate roller by the scraping member. The removed toner is transported and stored in a waste toner container by a toner transport means (not shown).
[0009]
Further, Japanese Patent No. 3137962 proposes a technique for applying a voltage between a peak-to-peak voltage of 400 to 700 V, a frequency of 100 to 2,000 Hz, and a DC bias of 100 to 300 V to the brush roller.
[0010]
[Patent Document 1]
Japanese Patent Laid-Open No. 9-90840
[Patent Document 2]
Japanese Patent No. 3137962
[0011]
[Problems to be solved by the invention]
However, the configuration as described above has the following problems.
[0012]
First, at least three brush rolls, intermediate rolls, and scraping members are required as components of the cleaning device, and a plurality of bias power sources are required to move the toner to the intermediate rolls by electrostatic force. There is a point. For this reason, it is very difficult to reduce the size and cost of the cleaning device. For example, a method has been proposed in which the toner adhering directly to the brush fiber is flickered without using an intermediate roller. However, if the flicker and the brush roller are left in contact with each other for a long time, the brush fiber is deformed. However, there is a problem that the cleaning performance of the brush roller is locally lowered.
[0013]
Second, the charge distribution of the toner conveyed to the cleaning device changes broader than that in the developing device, and toners having both positive and negative charge polarities are mixed. For this reason, there is a problem that even if the toner is collected on the brush roller side by electrostatic force, only the toner having a polarity opposite to the bias voltage can be collected.
[0014]
Also, to solve the problem of toners with both positive and negative charge polarity, try to collect as much reverse transfer toner (mainly positively charged) as possible on the brush roller side by increasing the transfer efficiency by using spherical toner. Attempts have been made, but the clear toner shape (toner adhesion), the charge amount and the conditions for collecting and discharging the remaining toner on the brush roller are not clearly regulated. The electrostatic attraction force acts on the toner sufficiently because the physical adhesion force to the surface of the image carrier becomes larger than the electrostatic attraction force acting, the toner charge amount is too low or too high. In many cases, it is difficult to remove the residual toner from the surface of the image carrier simply by electrostatic attraction.
[0015]
In addition, since the brush resistance value of the brush roller is not clearly regulated, the electrostatic attraction force acting on the toner from the brush roller cannot be sufficiently secured, and the toner collection / discharge performance is deteriorated. There is a problem that the carrier is charged and image unevenness occurs.
[0016]
In addition, since the pile density of the brush fibers of the brush roller is not clearly regulated, there are too few opportunities for the brush fibers of the brush roller to contact the toner on the image carrier, and it is difficult for the toner to enter the static brush fibers. In addition, there is a problem that even if the toner in the brush fiber exerts an electrostatic attraction force, it is difficult to discharge the toner. In addition, there is a problem that the toner in the brush fiber comes out without applying an electrostatic attraction force, and an image defect occurs.
[0017]
Furthermore, in such a toner collection / discharge method (cleaning device), although the residual toner can be easily removed from the toner having a relatively large particle diameter, the average particle diameter has been increasing in use in recent years. For toner having a small particle size of about 5 to 7 μm, the physical attractive force on the surface of the image carrier is larger than the electrostatic attractive force acting on the toner from the conductive brush roller. Therefore, it is difficult to remove the residual toner from the surface of the image carrier.
[0018]
Japanese Patent No. 3137962 proposes a method in which a DC voltage is superimposed on an AC voltage on a brush roller. However, although positive and negative polarity toner vibrates between the brush roller and the photosensitive drum. It is considered extremely difficult to collect all the bipolar toner in the brush. This is because the alternating electric field strength between the brush roller and the photosensitive member gradually weakens as the brush roller and the photosensitive member are gradually separated, and the toner cannot reciprocate between the two. As a result, although the toner having the opposite polarity to the voltage applied to the brush roller is attracted to the brush roller, it is considered that the toner having the same polarity repels and moves to the photoreceptor.
[0019]
Accordingly, the present invention provides an image forming apparatus and an image forming method including a cleaning device that can reduce the size and cost of the device, extend the life of the image carrier, and does not depend on the polarity of the transfer residual toner. For the purpose.
[0020]
[Means for Solving the Problems]
  In order to solve this problem, an image forming apparatus according to the present invention includes:Photoconductor, charging device for charging the photoconductor, transfer device for transferring toner conveyed on the photoconductor, recovery brush device for primary recovery of toner remaining on the photoconductor, and transfer device A toner removing device for secondary recovery of the toner on the top, applying a voltage of the same polarity as the positively charged toner to the recovery brush device and the charging device, and applying a reverse polarity voltage of the positively charged toner to the transfer device. Applying a positive polarity toner and a reverse polarity voltage to the recovery brush device; applying a same polarity voltage to the positive charge toner to the charging device; and applying a positive polarity toner and a reverse polarity voltage to the transfer device. Residual toner primarily collected by the collecting brush device is secondarily collected by a toner removing device in two steps.The configuration.
[0021]
  ThisRecovery brush deviceandToner removal deviceUsingPhotoconductorSince the toner remaining on the top can be efficiently collected regardless of the positive and negative charge polarity, the size and cost of the apparatus can be reduced.PhotoconductorThe service life can be extended and does not depend on the polarity of the residual toner.Toner removal deviceIs obtained.
[0064]
DETAILED DESCRIPTION OF THE INVENTION
  Hereinafter, embodiments of the present invention will be described with reference to FIGS. In these drawings, the same members are denoted by the same reference numerals, and redundant description is omitted.
[0065]
The configuration and operation of the image forming apparatus according to the embodiment of the present invention will be described below with reference to FIGS.
[0066]
FIG. 1 is an explanatory view showing an image forming apparatus having brush vibration means according to an embodiment of the present invention, and FIG. 2 is an explanatory view showing an image forming apparatus according to another embodiment of the present invention.
[0067]
1 and 2, reference numeral 1 denotes a photosensitive drum (image carrier) corresponding to an electrostatic latent image holding member, in which a photosensitive layer is provided on a metal drum. In the photosensitive drum 1, an OPC layer, an a-SiH layer, a selenium layer, or the like is used as the photosensitive layer. Further, a conductive undercoat layer may be provided between the aluminum base tube and the CGL so that scratches and dirt on the base tube do not affect the charging characteristics of the photosensitive drum 1.
[0068]
Reference numeral 6 denotes a charging device that is arranged with a predetermined gap from the surface of the photosensitive drum 1 and charges the photosensitive drum 1. 1 and 2 show a scorotron charging device, but a non-contact charging device such as a corotron charging device or a solid charging element may also be used, and the surface of the photosensitive drum 1 may be contacted. A contact charging device such as a charging roller or a charging brush may be used. In this embodiment, a case where a scorotron charging device is used will be described.
[0069]
Reference numeral 7 denotes an exposure source that irradiates the surface of the charged photosensitive drum 1 with light to form an electrostatic latent image. Laser light, LED light, CRT light, EL light, or the like may be used as an exposure source as long as the photosensitive drum 1 emits light having a high absorption spectrum.
[0070]
Reference numeral 8 denotes a developing device as developing means for developing the electrostatic latent image on the photosensitive drum 1. The developing device 8 may be either a two-component developing device or a one-component developing device, but in this embodiment, a two-component developing device is used. In the case of a two-component developing device, a two-component developer in which carrier particles and toner particles are mixed is used. The carrier particles are composed of magnetic particles such as ferrite, magnetite, and iron powder.
[0071]
Also, a coat carrier that coats the surface of the magnetic core particles with a coating material may be used. Examples of the coating material include amino resins such as urea-formaldehyde resins, melamine resins, benzoguanamine resins, urea resins, polyamide resins, and epoxy resins, and also polyvinyl and polyvinylidene resins, acrylic resins, and polymethyl methacrylate. Examples thereof include cellulose resins such as resins, polyacrylonitrile resins, polyvinyl acetate resins, polyvinyl acetate resins, polyvinyl alcohol resins, polyvinyl butyral resins, ethyl cellulose resins, silicone resins, fluorine resins, and the like, and the above mixtures may also be used.
[0072]
The carrier particles are preferably spherical. In the case of a flake shape or a flat plate shape, the ability to collect the transfer residual toner in the developing device 8 increases, but on the other hand, brush-like image noise tends to occur.
[0073]
The average particle size of the carrier particles is preferably 30 μm to 70 μm, and more preferably 35 μm to 55 μm. Below the above range, the coercive force of the magnetic brush is reduced and easily separated from the developing sleeve, so that carrier adhesion to the photosensitive drum 1 increases. On the other hand, when the above range is exceeded, the carrier surface area per unit weight becomes small, and the charging of the toner (visual image particles) becomes unstable. In the case of the so-called cleaner-less system in which waste toner is not generated, the surface area of the magnetic brush that comes into contact with the transfer residual toner is reduced, so that the contact opportunity between the transfer residual toner and the magnetic brush is reduced. The recovery ability from 1 will be reduced. Furthermore, since the toner is conveyed by carrier particles larger than the electrostatic latent image, it becomes impossible to develop a fine electrostatic latent image.
[0074]
Regardless of the two-component developing device or the one-component developing device, the toner particles are composed of a binder resin in which a colorant is dispersed. The binder resin material is polystyrene, styrene-alkyl acrylate copolymer, styrene-alkyl methacrylate copolymer, styrene-acrylonitrile copolymer, styrene-butadiene copolymer, styrene-maleic anhydride copolymer. , Polyethylene, polypropylene and the like. Furthermore, polyester, polyurethane, epoxy resin, silicone resin, polyamide, modified rosin, paraffin wax and the like are used. In addition, as colorants, carbon black, nigrosine, aniline blue, calcoil blue, chrome yellow, ultramarine blue, DuPont oil red, quinoline yellow, methylene blue chloride, phthalocyanine blue, malachite green oxalate, lamp black, rose bengal, C. I. Pigment red 48: 1, C.I. I. Pigment red 122, C.I. I. Pigment red 57: 1, C.I. I. Pigment yellow 97, C.I. I. Pigment Yellow 180 can be listed. In addition to the above components, the toner of the present invention can contain a charge control agent, wax, and the like as necessary. Furthermore, external additives such as inorganic oxides such as silica, titanium oxide, and zinc oxide, and organic fine particles can be added as necessary.
[0075]
The toner preferably has a spherical shape. In the present invention, as will be described in detail later, when the projected area S and the circumferential length L of the toner particles are used, the sphericity, that is, the shape factor C (C = L² / 4πS) is preferably 1.0 to 1.5. More preferably, the shape factor C is 1.0 to 1.3. More preferably, it is 1.1-1.3.
[0076]
As described above, in this specification, the shape factor (sphericity) is (perimeter length).² / (4π * projected area).
[0077]
When the shape factor exceeds the above range, not only the toner releasability is lowered and the transfer efficiency is lowered, but also the maximum transfer efficiency of the halftone image and the solid black image can be realized with the same transfer voltage. It becomes difficult. Therefore, the transfer residual toner increases, which is not preferable. On the other hand, below the above range, the releasability of the toner is too high and the toner is easily separated from the image receiving paper and the photosensitive drum 1, and toner scattering on the image receiving paper after transfer and toner contamination of the charging device 6 are likely to occur. .
[0078]
The range of the shape factor is a range in which the toner particles are easily detached from the photosensitive drum 1 with a small electrostatic force and are easily separated from the brush fibers of the collection brush device 12 with a small electrostatic force, as will be described later. . In order to realize the above shape factor, it is preferable to use a toner prepared by a suspension polymerization method or an emulsion polymerization method. In addition, the toner base produced by the mechanical pulverization method may be dropped into a hot air stream and subjected to spheronization treatment, or spheronization treatment may be performed by other methods.
[0079]
The charge amount of the toner will be described in detail later, but in the present invention, it is preferably −10 to −50 μC / g for negative charge (10 to 50 μC / g for positive charge). More preferably, it is −15 to −45 μC / g (15 to 45 μC / g in the case of positive charging).
[0080]
If the charge amount exceeds the above range, the charge amount of the toner is too large and the development amount is extremely reduced, the transfer electric field corresponding to the toner charge is insufficient, the transfer residual toner is extremely increased, Repel each other and cause splattering in transcription. On the other hand, below the above range, the toner tends to be charged to a reverse polarity due to excessive transfer electric field in the transfer process, Paschen discharge before and after the transfer nip or charge injection in the transfer nip, and the transfer residual toner becomes extremely large. Increase or cause reverse transcription.
[0081]
In addition, as described later, the range of the charge amount is such that the toner particles are easily detached and attached from the photosensitive drum 1 with a small electrostatic force, and are detached from and attached to the brush fibers of the recovery brush device 12 with a small electrostatic force. Easy range.
[0082]
The volume median diameter of the toner is preferably 5.0 to 7.5 μm. If it is less than the above range, the mechanical adhesion between the toner particles and the photosensitive drum 1 is increased, and the transfer efficiency is lowered. On the other hand, if it exceeds the above range, it becomes difficult to faithfully develop a fine electrostatic latent image.
[0083]
In order to achieve a sufficient image density, the concealment rate for concealing the image receiving paper with toner when a solid black image is printed is reduced to 0.55 mg / cm 2.² It is necessary to develop with the above toner amount. However, when the amount of the developing toner increases, it becomes difficult to transfer to the image receiving paper up to the lowest toner layer on the photosensitive drum 1. Even when a high transfer bias is applied to transfer a solid black image on the photosensitive drum 1, an excessive voltage is supplied to the halftone image, and as a result, the polarity of the toner is reduced during the transfer process. The halftone image transfer efficiency is reduced due to inversion. Therefore, in the present invention, a toner having a volume median diameter in the above range is used, and a developing toner amount on the photosensitive drum 1 is 0.55 mg / cm.² The following is preferable.
[0084]
Further, it is preferable that the particle size distribution variation coefficient of the toner is 30% or less, and no particles of 3 μm or less and 16 μm or more exist. As a result, the toner particle size distribution can be made very narrow and uniform with uniform particle size, so that the toner charge amount distribution can be made stable, uniform and sharp, and the remaining toner on the photosensitive drum 1 after development transfer. Can be greatly reduced, and the simultaneous cleaning with development can be improved. That is, waste toner can be greatly reduced, which is advantageous to running costs and is environmentally friendly. Further, as described later, the above range is a range in which the toner particles are easily detached from the photosensitive drum 1 with a small electrostatic force, and are easily separated from the brush fibers of the collection brush device 12 with a small electrostatic force.
[0085]
A predetermined developing voltage is applied to the developing sleeve 8c by a power source (not shown). In the case of a two-component developing device, the developing voltage is preferably a voltage obtained by superimposing an AC voltage on a DC voltage. Further, since the toner is easily detached from the carrier particles by using the spherical toner as described above, the development can be performed even if the DC voltage level is low.
[0086]
In the case where the photosensitive drum 1 and the developing sleeve 8c are not in contact with each other even in a one-component developing device, a voltage obtained by superimposing an AC voltage on a DC voltage is preferable. As a result, the toner particles can be easily detached from the developing sleeve, so that development is possible even when the DC voltage level is low.
[0087]
Any of an AC voltage waveform, a sine wave, a rectangular wave, a triangular wave, and a sawtooth wave may be used, or an AC wave with a modulated duty ratio may be applied. The peak-to-peak voltage of the AC voltage is preferably 500V to 2,000V. Below the above range, the toner is less likely to vibrate and the AC voltage effect is reduced. On the other hand, when the above range is exceeded, carrier adhesion to the photosensitive drum 1 occurs. If the carrier particle conductivity is high, a discharge occurs between the magnetic brush on the developing sleeve and the photosensitive drum 1, disturbing the toner on the photosensitive drum 1. When a higher peak-to-peak voltage is applied, discharge traces are formed on the photosensitive drum 1 and the developing sleeve due to the discharge.
[0088]
The frequency of the AC voltage is preferably 1 kHz to 8 kHz. Outside the above range, the toner development amount decreases. This is considered that there exists a natural frequency at which the toner is easily detached from the magnetic brush.
[0089]
Further, when the toner discharged from the collecting brush device 12 described later is collected by the developing device 8, it is preferable to further set the frequency to 4 kHz to 7 kHz and the peak-to-peak voltage to 1 to 2 kVpp. Outside the above range, the recovery efficiency of the toner on the photosensitive drum 1 is lowered. This is considered to be due to the existence of a natural frequency at which the toner is detached from the photosensitive drum 1 and easily taken into the magnetic brush of the developing device 8. If the voltage effect is reduced and the above range is exceeded, carrier adhesion to the photosensitive drum 1 occurs.
[0090]
In the case where the toner discharged from the collection brush device 12 is not collected by the developing device 8, the frequency may be set outside the above range or only the DC voltage may be applied.
[0091]
Reference numeral 3 denotes a transfer device as transfer means. As the transfer device 3, a transfer roller in which a conductive urethane, EPDM, silicon or other sponge layer is wound around a metal core, a transfer brush made of conductive fibers such as nylon or rayon, a conductive rubber plate or a conductive film sheet A transfer blade or transfer film in contact with the tip, a conductive belt in which a conductive material is dispersed in a resin material such as PTFE, PFA, TEP, polyimide, or polycarbonate are used. As will be described later, when the toner discharged from the collection brush device 12 by the transfer device 3 is collected by the scraping member, it is preferable that the toner particles are easily separated from the transfer device 3 mechanically. Therefore, among the transfer devices described above, it is preferable to use a transfer device such as a transfer roller or a transfer belt having a film layer such as PFA or PTFE on the surface.
[0092]
A registration roller 2 conveys the image receiving paper at a predetermined speed. Reference numeral 5 denotes image receiving paper such as plain paper, postcard paper, and OHP sheet. Reference numeral 10 denotes upstream guide means for guiding the conveyance direction of the image receiving paper 5 from the registration roller 2 to the photosensitive drum 1. A fixing device 4 fixes the toner image transferred onto the image receiving paper 5. Reference numeral 11 denotes a downstream guide unit that guides the conveyance direction of the image receiving paper 5 from the transfer region to the fixing device 4.
[0093]
In the high humidity environment, the image receiving paper 5 has a low resistance, and a current leaks from the flexible member 3 b to the guiding means 10 and 11 through the image receiving paper 5. For this reason, sufficient electric charge is not supplied to the back surface of the image receiving paper 5 and a transfer defect occurs. In order to solve this problem, it is preferable that the guide means 10 and 11 are made of an insulating member or a voltage having the same polarity as the transfer voltage is applied. A self-biasing element such as a resistance element or a Zener diode element may be connected between the guiding means 10 and 11 and the ground.
[0094]
A fixing device 4 includes a heating unit 4a and a pressing unit 4b. 1 and 2, the heating means 4a and the pressurizing means 4b show roller shapes, but the present invention is not limited to this, and a film-like or belt-like heating means, pressurizing means, etc. are used. May be.
[0095]
A recovery brush device (first recovery means) 12 is disposed between the transfer device 3 and the charging device 6 in the rotation direction of the photosensitive drum 1. The collection brush device 12 is disposed so that the brush fibers are substantially perpendicular to the surface of the photosensitive drum 1 and are in contact with the surface of the photosensitive drum 1.
[0096]
1 and 2, the fixed brush member is illustrated, but a roll brush member may be used. Further, the roll-shaped brush member may rotate, and the rotation direction may be either the forward direction or the reverse direction with respect to the surface of the photosensitive drum 1.
[0097]
The collection brush device 12 uses a material in which fibers (pile) in which a conductive material is dispersed in yarns such as nylon, rayon, cellulose, and polyester are woven or planted. The resistance of the collection brush device 12 is E4-13 Ω · cm² More preferably, it is E6-12 Ω · cm. Pile length is 0.5-7mm, pile thickness is 2-10 denier, pile density is 50-400F / mm² It is preferable that
[0098]
As will be described in detail later, when the resistance of the collection brush device 12 falls below the above range, the photosensitive drum 1 is charged by the brush roller, and image unevenness occurs. On the other hand, if it exceeds the above range, the electrostatic attraction force acting on the toner from the collection brush device 12 cannot be sufficiently ensured, and the toner collection / discharge performance deteriorates.
[0099]
If the pile thickness is less than the above range, the hardness of the brush fiber becomes too soft, and the remaining toner and the reverse transfer toner on the photosensitive drum 1 are mechanically rubbed and scraped off. Toner recovery power is reduced. When the above range is exceeded, the surface area of the brush fibers is reduced, the amount of toner recovery buffer is reduced, and the hardness of the brush fibers is increased, so that the photosensitive drum 1 is damaged and the life is shortened.
[0100]
If the pile density range is not reached, the chance of the brush fibers coming into contact with the toner on the photosensitive drum 1 is extremely reduced, so that the toner recovery capability is lowered. On the other hand, if the above range is exceeded, it is difficult for toner to enter the brush fibers, and instead the amount of toner collection buffer is reduced, or the toner once entering the brush fibers becomes difficult to be discharged by electrostatic attraction.
[0101]
Reference numeral 17 denotes a power supply for the collection brush device as voltage application means connected to the collection brush device 12. The recovery brush device power source (first voltage application means) 17a shown in FIG. 1 is controlled so as to be applied to the recovery brush device 12 by switching between an AC voltage, a positive DC voltage, and a negative DC voltage. Further, the recovery brush device power source (second voltage applying means) 17b shown in FIG. 2 is controlled so that the positive DC voltage and the negative DC voltage are switched and applied to the recovery brush device 12.
[0102]
Reference numeral 13 denotes a toner removing device as a visible image particle removing unit that mechanically scrapes off toner adhering to the surface of the transfer device 3 with a scraping member. The toner removing device 13 may use a rubber blade, a brush, a web, or the like other than those shown in FIGS.
[0103]
In the present embodiment, it is assumed that the toner once collected by the collecting brush device 12 is discharged to the photosensitive drum 1 and then collected again by the transfer device 3 and removed by the toner removing device 13. In addition to this, the developing device 8 may collect the toner. When the developing device 8 collects toner, the toner removing device 13 is not necessary, and it is suitable for downsizing and cost reduction of the image forming apparatus. However, in the case of a color image forming apparatus, when the toner is collected in the developing device 8, a so-called color mixing problem in which the toner of a color different from the original color is mixed and the hue of the print image is changed easily occurs.
[0104]
Next, the operation of the image forming apparatus of the present invention will be described with reference to FIGS. 1 and 2 and the timing charts of FIGS.
[0105]
First, the image forming apparatus receives an image signal transmitted from the outside such as a computer, and starts a preparatory process before image formation. First, the fixing device 4 is heated, and after reaching a predetermined temperature, the rotation driving of the fixing device 4 is started. Further, the rotational driving of the photosensitive drum 1 is also started. At this time, a predetermined voltage is applied to the charging device 6, and the photosensitive drum 1 is charged to a predetermined surface potential. Further, the rotational driving of the developing device 8 is also started. At this time, a voltage obtained by superimposing a DC voltage on an AC voltage is applied to the developing sleeve. In addition, an AC voltage is applied to the recovery brush device 12. In addition, the image receiving paper 5 stored in a paper feeding cassette (not shown in FIG. 1) is fed to the registration rollers 2 and is held between the registration rollers 2.
[0106]
After the above preparation process is completed, the image forming process is started while the operation of each member is continued.
[0107]
First, when the charged surface of the photosensitive drum 1 is transported to a position facing the exposure source 7, light corresponding to the received image signal is irradiated onto the surface of the photosensitive drum 1. As a result, the charged potential of the surface of the photosensitive drum 1 in the region irradiated with light decreases. As a result, an electrostatic latent image is formed on the surface of the photosensitive drum 1.
[0108]
Next, when the electrostatic latent image on the surface of the photosensitive drum 1 is conveyed to a position facing the developing device 8, the toner on the developing sleeve to which a predetermined voltage is applied becomes the electrostatic latent image and the developing sleeve. Moves on the photosensitive drum 1 in accordance with the potential difference of. As a result, toner adheres to the electrostatic latent image on the photosensitive drum 1, and a toner image is formed on the photosensitive drum 1.
[0109]
The toner image formed on the surface of the photosensitive drum 1 is conveyed to a transfer area where the transfer device 3 and the photosensitive drum 1 are in contact with each other. At this time, a voltage having a polarity opposite to that of the toner particles is applied to the transfer device 3.
[0110]
On the other hand, the rotation of the registration roller 2 is started, and the conveyance of the image receiving paper 5 sandwiched between the registration rollers 2 is started in synchronization with the conveyance of the toner image to the transfer area.
[0111]
The image receiving paper 5 conveyed along the upstream guide means 10 enters the transfer area. While passing through the transfer region, an electric field E is formed between the image receiving paper 5 and the photosensitive drum 1 by the electric charge accumulated on the back surface of the image receiving paper 5 from the transfer device 3. As a result, the toner charge q and the Coulomb force F = qE by the electric field E act, and the toner on the photosensitive drum 1 is transferred to the image receiving paper 5 side. Toner that is not charged with a normal polarity or toner with excessive mechanical adhesion is not attracted to the image receiving paper 5 by the Coulomb force F, and remains on the surface of the photosensitive drum 1 as transfer residual toner.
[0112]
The transfer residual toner is transported to the photosensitive drum 1 and transported to the recovery brush device 12 to which an AC voltage is applied by the recovery brush device power source 17a (FIG. 1). When the AC voltage is applied, the brush fibers vibrate and suck the transferred residual toner. As a result, the transfer residual toner is collected by the collection brush device 12, and the surface of the photosensitive drum 1 is cleaned.
[0113]
Alternatively, the transfer residual toner is conveyed by the recovery brush device power source 17b (FIG. 2) to the recovery brush device 12 to which a direct charge voltage having the same polarity as the normal charging polarity of the toner for printing is applied. (Hereinafter, such toner is referred to as “regular toner”). By applying a DC voltage having the same polarity as that of the regular toner, the electrostatic attracting force is applied to the toner having the opposite polarity to that of the regular toner (at the time of excessive transfer), and is attracted to the brush fiber. Thereby, the transfer residual toner at the time of excessive transfer is collected by the collection brush device 12, and the surface of the photosensitive drum 1 is cleaned.
[0114]
In addition, when a DC voltage having the same polarity as the charging polarity of the regular toner is applied to the collection brush device 12, the power supply is simplified and damage to the photosensitive drum 1 is reduced as compared with the case where an AC voltage is applied. Although there is a merit, it is necessary to leave the toner having the same polarity as that of the regular toner as much as possible in the residual toner after transfer. This is to increase the transfer efficiency as much as possible. It is better to make the toner spherical as much as possible, the charge amount distribution is sharp and uniform charge, and as described above, the sphericity (projection area, (perimeter length))² / (4π * projected area)) is 1.00 to 1.50, preferably 1.0 to 1.3, and the charge amount is −10 to −50 μC / g (10 to 50 μC / g in the case of positive charge), preferably It is preferable to use a toner in which particles of −15 to −45 μC / g (15 to 45 μC / g in the case of positive charging), particle size distribution variation coefficient of 30% or less, 3 μm or less, and 16 μm or more do not exist. Of course, when applying the AC bias to the recovery brush device 12, it is more preferable to use the toner described above because the reliability increases.
[0115]
On the other hand, the image receiving paper 5 that has passed through the transfer area is conveyed to the fixing device 4 along the downstream guide means 11. While passing through the fixing device 4, the toner image on the image receiving paper 5 is heated and fixed. After passing through the fixing device 4, the image receiving paper 5 is discharged out of the image forming apparatus, and the output of the fixed print image is completed.
[0116]
Next, after the image forming process is completed, the first discharging process is started.
[0117]
In the first discharging process, a DC voltage having the same polarity as the charging polarity of the regular toner is applied to the collection brush device 12. As a result, among the toner collected by the collection brush device 12, toner having a normal charging polarity is discharged from the collection brush device 12 to the surface of the photosensitive drum 1. The voltage application to the charging device 6 continues from the image forming process.
[0118]
Further, the voltage applied to the developing device 8 is switched to only a DC voltage. Further, the voltage applied to the transfer device 3 is switched to a DC voltage having a polarity opposite to the charging polarity of the regular toner.
[0119]
The toner discharged on the surface of the photosensitive drum 1 is carried and conveyed as the photosensitive drum 1 rotates and passes through the charging device 6. Since ions having the same polarity as the regular toner are poured from the charging device 6 onto the surface of the photosensitive drum 1, the charge amount of the toner on the photosensitive drum 1 is increased.
[0120]
Next, the toner on the photosensitive drum 1 passes through the developing device 8. At this time, since only a DC voltage is applied to the developing device 8, no alternating electric field is formed between the photosensitive drum 1 and the developing device 8. Therefore, since the toner particles do not vibrate, the toner collecting ability from the photosensitive drum 1 to the developing device 8 is extremely lowered. Thus, the toner on the photosensitive drum 1 is carried and conveyed to the transfer device 3 without being collected by the developing device 8. Since a voltage having a polarity opposite to the charging polarity of the normal toner is applied to the transfer device 3, the toner on the photosensitive drum 1 is attracted to the transfer device 3 side by a Coulomb force. The toner transferred to the transfer device 3 side is removed from the surface of the transfer device 3 by the scraping member of the toner removing device 13.
[0121]
After the first toner discharging step is performed at least during one rotation of the photosensitive drum 1, the second discharging step is started.
[0122]
In the second discharge step, the polarity of the voltage applied to the recovery brush device 12 is reversed. As a result, the toner charged in the opposite polarity to the regular toner remaining in the collection brush device 12 is discharged to the surface of the photosensitive drum 1. The voltage application to the other devices continues from the previous toner discharging step.
[0123]
The reverse polarity toner discharged to the surface of the photosensitive drum 1 is carried and conveyed as the photosensitive drum 1 rotates, and passes through the charging device 6. Since ions having the same polarity as the regular toner are poured from the charging device 6 onto the surface of the photosensitive drum 1, the toner on the photosensitive drum 1 is inverted to the regular charged polarity.
[0124]
Next, the toner on the photosensitive drum 1 passes through the developing device 8. At this time, since only a DC voltage is applied to the developing device 8, no alternating electric field is formed between the photosensitive drum 1 and the developing device 8. Therefore, since the toner particles do not vibrate, the toner collecting ability from the photosensitive drum 1 to the developing device 8 is extremely lowered. Thus, the toner on the photosensitive drum 1 is carried and conveyed to the transfer device 3 without being collected by the developing device 8.
[0125]
Since a voltage having a polarity opposite to the charging polarity of the normal toner is applied to the transfer device 3, the toner on the photosensitive drum 1 is attracted to the transfer device 3 side by a Coulomb force. The toner transferred to the transfer device 3 side is removed from the surface of the transfer device 3 by the scraping member of the toner removing device 13.
[0126]
Therefore, the photosensitive drum 1 and the transfer device 3 that execute the first discharge process and the second discharge process constitute a second recovery unit.
[0127]
At least while the photosensitive drum 1 makes one revolution, the second toner discharging step is performed, and then the rotation of the photosensitive drum 1 is stopped. Furthermore, the voltage application to each device is also stopped, and all operations are completed.
[0128]
In the above configuration, the scorotron charging device has been described. However, as described above, a contact-type charging device such as a charging roller or a charging brush that contacts the photosensitive drum 1 and the charging device may be used. However, in the case of the contact charging device, it is desirable that the voltage polarity of the charging device and the recovery brush device 12 be the same in the first discharging process and the second discharging process. Otherwise, the toner discharged from the collection brush device 12 adheres to the charging device, and a process or member for cleaning the charging device is required.
[0129]
Further, it is difficult to normally reverse the charging polarity of the toner discharged from the collection brush device 12 in the second discharging step. For this reason, if the toner of reverse polarity is to be collected by electrostatic force, the toner on the developing sleeve moves to the photosensitive drum 1, so that it is extremely difficult to collect it to the developing device 8. Therefore, when using a contact-type charging device, it is preferable to collect toner in the developing device 8 with a force other than electrostatic force, or to provide a separate collecting means as described above. In this case, the second recovery means is the photosensitive drum 1 and the developing device 8.
[0130]
In the present embodiment, a color image forming apparatus using a plurality of colors of toner may be used. The form of the color image forming apparatus will be described below.
[0131]
FIG. 3 is an explanatory view showing an image forming apparatus for forming a color image according to still another embodiment of the present invention.
[0132]
In FIG. 3, reference numerals 1K, 1C, 1M, and 1Y denote photosensitive drums corresponding to the toners of the respective colors. 6K, 6C, 6M, and 6Y are charging devices that charge the surface of each photosensitive drum 1. Although the roller-shaped charging device 6 is illustrated in FIG. 3, a non-contact charging device such as a corotron charging device or a solid charging element may be used, and a charging brush or the like that contacts the surface of the photosensitive drum may be used. A contact charging device may be used.
[0133]
Reference numerals 7K, 7C, 7M, and 7Y denote exposure sources that form an electrostatic latent image by irradiating light onto the surface of the charged photosensitive drum 1 of each color. Laser light, LED light, CRT light, EL light, or the like may be used as an exposure source as long as the photosensitive drum 1 emits light having a high absorption spectrum.
[0134]
8K, 8C, 8M, and 8Y are developing devices that develop the electrostatic latent image on the photosensitive drum 1 of each color with toner of each color. The developing device 8 may be either a two-component developing device or a one-component developing device, but in the present embodiment, a two-component developing device is used as described above.
[0135]
Reference numerals 12K, 12C, 12M, and 12Y denote collection brush devices (first collection means). The collection brush device 12 is disposed so that the brush fibers are substantially perpendicular to the surface of the photosensitive drum 1 and are in contact with the surface of the photosensitive drum 1. In addition, although the roll-shaped brush member was illustrated in FIG. 3, a fixed-type brush member may be sufficient. Further, the roll-shaped brush member may rotate, and the rotation direction may be either the forward direction or the reverse direction with respect to the surface of the photosensitive drum 1.
[0136]
The collection brush device 12 uses a material in which fibers (pile) in which a conductive material is dispersed in yarns such as nylon, rayon, cellulose, and polyester are woven or planted. The resistance value of the brush fiber is E4-13Ω · cm² More preferably, it is E6-12 Ω · cm. Pile length is 0.5-7mm, pile thickness is 2-10 denier, pile density is 50-400F / mm² It is preferable that Each recovery brush device 12 is connected to a power supply (not shown) for the recovery brush device as shown in FIGS. 1 and 2.
[0137]
Reference numeral 15 denotes a transfer belt for carrying and receiving the image receiving paper 5. The transfer belt 15 uses a resin material such as PTFE, PFA, TEP, polyimide, or polycarbonate as a base material. Further, a conductive material may be dispersed in order to adjust the electric resistance of the transfer belt 15.
[0138]
Reference numerals 18K, 18C, 18M, and 18Y denote bias supply units that come into contact with the respective photosensitive drums 1 via the transfer belt 15. The bias supply unit 18 may use a brush shape, a roller shape, a blade shape, a film shape, or the like as long as it can supply a predetermined charge to the back surface of the transfer belt 15. Further, a non-contact corona discharger or a solid charging element may be used on the back surface of the transfer belt 15.
[0139]
A belt support roller 14 stretches the transfer belt 15. Reference numeral 16 denotes a paper adsorbing device for applying a bias voltage to the image receiving paper 5 conveyed on the transfer belt 15 and sucking and fixing the image receiving paper 5 to the transfer belt 15 by Coulomb force. Reference numeral 19 denotes a charge eliminating needle for discharging the image receiving paper 5 to separate the image receiving paper 5 from the transfer belt 15.
[0140]
Reference numeral 13 denotes a toner removing device that removes toner adhering to the transfer belt 15, a brush roller that contacts and rotates with the transfer belt 15, and an intermediate roller 13 b that electrostatically collects toner adhering to the brush roller 13 a. And a scraping member that mechanically scrapes off the toner adhering to the intermediate roller 13b. In addition to this, the toner removing device 13 may use a rubber blade, a metal scraper, a web, or the like.
[0141]
Next, the operation of the color image forming apparatus of the present invention will be described with reference to FIG. 3 and the timing charts of FIGS.
[0142]
First, the color image forming apparatus receives an image signal transmitted from the outside such as a computer, and starts a preparatory process before image formation. First, the fixing device 4 (not shown) is heated, and after reaching a predetermined temperature, rotational driving of the fixing device 4 is started. Further, the rotational driving of the transfer belt 15 and the photosensitive drum 1 is also started. At this time, a predetermined voltage is applied to the charging device 6 for each color, and the photosensitive drum 1 is charged to a predetermined surface potential. Further, the rotational driving of the developing device 8 for each color is also started. At this time, a voltage obtained by superimposing a DC voltage on an AC voltage is applied to the developing sleeve. In addition, an AC voltage or a DC voltage having the same polarity as the regular toner charging polarity is applied to the recovery brush device 12. Further, the image receiving paper 5 stored in a paper feeding cassette (not shown in FIG. 3) is fed to a registration roller 2 (not shown) and is held between the registration rollers 2.
[0143]
After the above preparation process is completed, the image forming process is started while the operation of each member is continued.
[0144]
First, when the charged surface of the photosensitive drum 1 is transported to a position facing the exposure source 7, light corresponding to the received image signal is irradiated onto the surface of the photosensitive drum 1. As a result, the charged potential of the surface of the photosensitive drum 1 in the region irradiated with light decreases. As a result, an electrostatic latent image is formed on the surface of the photosensitive drum 1.
[0145]
Next, when the electrostatic latent image on the surface of the photosensitive drum 1 is conveyed to a position facing the developing device 8, the toner on the developing sleeve to which a predetermined voltage is applied becomes the electrostatic latent image and the developing sleeve. Moves on the photosensitive drum 1 in accordance with the potential difference of. As a result, toner adheres to the electrostatic latent image on the photosensitive drum 1, and a toner image is formed on the photosensitive drum 1.
[0146]
The toner image formed on the surface of the photosensitive drum 1 is conveyed to a transfer area where the transfer belt 15 and the photosensitive drum 1 are in contact with each other. At this time, a voltage having a polarity opposite to that of the toner particles is applied to the bias supply means.
[0147]
On the other hand, the rotation of the registration roller 2 is started, and the conveyance of the image receiving paper 5 held between the registration rollers 2 is started and conveyed to the transfer belt 15.
[0148]
By passing between the transfer belt 15 and the paper suction device 16, the image receiving paper 5 is attracted to the transfer belt 15 by the Coulomb force, is carried and conveyed by the transfer belt 15, and enters the transfer area of each color. While passing through the transfer region, an electric field E is formed between the image receiving paper 5 and the photosensitive drum 1 by the electric charge accumulated on the back surface of the image receiving paper 5 from the transfer device 3. As a result, the toner charge q and the Coulomb force F = qE by the electric field E act, and the toner on the photosensitive drum 1 is transferred to the image receiving paper 5 side. Toner that is not charged with a normal polarity or toner with excessive mechanical adhesion is not attracted to the image receiving paper 5 by the Coulomb force F, and remains on the surface of the photosensitive drum 1 as transfer residual toner.
[0149]
The transfer residual toner is transported to the photosensitive drum 1 and transported to the recovery brush device 12 to which an AC voltage is applied.
[0150]
When the AC voltage is applied, the brush fibers vibrate and suck the transferred residual toner. As a result, the transfer residual toner is collected by the collection brush device 12, and the surface of the photosensitive drum 1 is cleaned. Alternatively, the toner is conveyed to the collection brush device 12 to which a DC voltage having the same polarity as the charging polarity of the regular toner is applied. By applying a DC voltage having the same polarity as the regular toner charging polarity, the electrostatic attracting force is applied to the toner having the opposite polarity to that of the regular toner conveyed from the brush fiber (at the time of excessive transfer), and the brush fiber. To suck. Thereby, the transfer residual toner at the time of excessive transfer is collected by the collection brush device 12, and the surface of the photosensitive drum 1 is cleaned.
[0151]
When a DC voltage having the same polarity as the charging polarity of the regular toner is applied to the collection brush device 12, there are advantages such as a simple power supply and less damage to the photosensitive drum 1 than when an AC voltage is applied. As much as possible, it is necessary to leave the toner having the same polarity as that of the regular toner as the transfer residual toner. This is to increase the transfer efficiency as much as possible. It is better to make the toner spherical as much as possible, the charge amount distribution is sharp and uniform charge, and as described above, the sphericity (projection area, (perimeter length))² / (4π * projected area)) is 1.00 to 1.50, preferably 1.0 to 1.3, and the charge amount is −10 to −50 μC / g (10 to 50 μC / g in the case of positive charge), preferably It is preferable to use a toner in which particles of −15 to −45 μC / g (15 to 45 μC / g in the case of positive charging), a particle size distribution variation coefficient of 30% or less, 3 μm or less, and 16 μm or more are not present. Of course, when applying the AC bias to the recovery brush device 12, it is more preferable to use the toner described above because the reliability increases.
[0152]
On the other hand, the image receiving paper 5 that has sequentially passed through the transfer regions of the respective colors is conveyed to the vicinity of the static elimination needle in a state where a plurality of color toner images are formed. In the vicinity of the static elimination needle, the transfer belt 15 and the image receiving paper 5 are separated by the curvature of the support roller and the static elimination on the back surface of the image receiving paper 5 by the static elimination needle. The image receiving paper 5 separated from the transfer belt 15 is conveyed to the fixing device 4.
[0153]
Further, when the color toner is sequentially transferred, the toner transferred to the image receiving paper 5 on the upstream side is often reversely transferred on the downstream transfer. As described above, the reversely transferred toner is also conveyed to the collecting brush device 12 to which an AC voltage is applied. When the AC voltage is applied, the brush fibers vibrate and suck the transferred residual toner.
[0154]
As a result, the transfer residual toner is collected by the collection brush device 12, and the surface of the photosensitive drum 1 is cleaned. Alternatively, the toner is conveyed to the collection brush device 12 to which a DC voltage having the same polarity as the charging polarity of the regular toner is applied. By applying a DC voltage having the same polarity as the charging polarity of the normal toner, an electrostatic attracting force is applied to the toner (reverse transfer toner) having the opposite polarity to the charging polarity of the normal toner conveyed from the brush fiber, and the brush fiber. To suck. Thereby, the transfer residual toner at the time of excessive transfer is collected by the collection brush device 12, and the surface of the photosensitive drum 1 is cleaned.
[0155]
While passing through the fixing device 4, the toner image on the image receiving paper 5 is heated and fixed. After passing through the fixing device 4, the image receiving paper 5 is discharged out of the image forming apparatus, and the output of the fixed print image is completed. On the other hand, the transfer belt 15 from which the image receiving paper 5 has been separated passes through the toner removing device 13 and removes toner and paper dust adhering to the transfer belt 15.
[0156]
Next, after the image forming process is completed, the first discharging process is started.
[0157]
In the first discharging process, a DC voltage having the same polarity as the charging polarity of the regular toner is applied to the collection brush device 12. As a result, among the toner collected by the collection brush device 12, toner having a normal charging polarity is discharged from the collection brush device 12 to the surface of the photosensitive drum 1.
[0158]
Further, the voltage applied to the charging device 6 is also the same voltage as that of the recovery brush device 12. In addition, the voltage applied to the developing device 8 is switched to only a DC voltage. Further, the voltage applied to the transfer bias supply means is switched to a DC voltage having a polarity opposite to the charging polarity of the normal toner.
[0159]
The toner discharged on the surface of the photosensitive drum 1 is carried and conveyed as the photosensitive drum 1 rotates and passes through the charging device 6. Since the voltage having the same polarity as the charging polarity of the toner is applied to the charging device 6, the toner on the photosensitive drum 1 passes through without being attached to the charging device 6.
[0160]
Next, the toner on the photosensitive drum 1 passes through the developing device 8. At this time, since only a DC voltage is applied to the developing device 8, no alternating electric field is formed between the photosensitive drum 1 and the developing device 8. Therefore, since the toner particles do not vibrate, the toner collecting ability from the photosensitive drum 1 to the developing device 8 is extremely lowered. As a result, the toner on the photosensitive drum 1 is carried and conveyed to the transfer region without being collected by the developing device 8.
[0161]
Since a voltage having a polarity opposite to the charging polarity of the normal toner is applied to the transfer bias supply means, the toner on the photosensitive drum 1 is attracted to the transfer belt 15 side by a Coulomb force. The toner transferred to the transfer belt 15 side is transferred to the toner removing device 13 after passing through the transfer area of each color. In the toner removing device 13, the toner is mechanically peeled off from the transfer belt 15 by the rotation of the brush roller. The toner adhering to the brush roller is transferred to the intermediate roller by Coulomb force and removed by the scraping member.
[0162]
At least the photosensitive drum 1 makes one round and the toner is transported from the most upstream transfer region to the most downstream transfer region, and then the first toner discharging step is performed, and then the second discharging step is started.
[0163]
In the second discharge step, the polarity of the voltage applied to the recovery brush device 12 is reversed. As a result, the toner charged in the opposite polarity to the regular toner remaining in the collection brush device 12 is discharged to the surface of the photosensitive drum 1. Further, a voltage equivalent to that of the recovery brush device 12 is applied to the charging device 6. The transfer bias supply means is applied with a voltage having the same polarity as the regular toner charging polarity.
[0164]
The reverse polarity toner discharged to the surface of the photosensitive drum 1 is carried and conveyed as the photosensitive drum 1 rotates, and passes through the charging device 6. Since a voltage having the same polarity as the charged polarity of the discharged toner is applied to the charging device 6, the toner passes through the charging device 6 without adhering.
[0165]
Next, the toner on the photosensitive drum 1 passes through the developing device 8. At this time, since only a DC voltage is applied to the developing device 8, no alternating electric field is formed between the photosensitive drum 1 and the developing device 8. Therefore, since the toner particles do not vibrate, the toner collecting ability from the photosensitive drum 1 to the developing device 8 is extremely lowered. Thus, the toner on the photosensitive drum 1 is carried and conveyed to the transfer region without being collected by the developing device 8.
[0166]
Since the transfer bias supply means is applied with a voltage having a polarity opposite to the charged polarity of the toner discharged from the collection brush device 12, the toner on the photosensitive drum 1 is attracted to the transfer belt 15 side by the Coulomb force. . The toner that has passed through the transfer regions of the respective colors and has transferred to the transfer belt 15 side is removed from the transfer belt surface by the toner removing device 13 in the same manner as in the first discharging step.
[0167]
At least the photosensitive drum 1 makes one turn and the second toner discharging step is performed while the toner is conveyed from the most upstream transfer region to the most downstream transfer region, and then the transfer belt 15 and the photosensitive drum 1 are connected. Stop rotation. Furthermore, the voltage application to each device is also stopped, and all operations are completed.
[0168]
In the above description, the transfer belt 15 is shown as a component for supporting the image receiving paper 5, but a drum shape or a roller shape may be used in addition to the belt. Alternatively, an intermediate transfer belt may be used in which a four-color toner image is formed on the belt without being directly carried and conveyed, and then secondarily transferred to the image receiving paper 5.
[0169]
In the above configuration, a contact charging method such as a charging roller is used, and the toner discharged from the recovery brush device 12 is not recovered by the developing device 8. In the case of the contact charging method, it is desirable that the voltage polarity of the charging device 6 and the recovery brush device 12 be the same in the first discharging process and the second discharging process. Otherwise, the toner discharged from the collection brush device 12 adheres to the charging device 6 and a process or member for cleaning the charging device 6 is required.
[0170]
Further, it is difficult to normally reverse the charging polarity of the toner discharged from the collection brush device 12 in the second discharging step. For this reason, if the toner of reverse polarity is to be collected by electrostatic force, the toner on the developing sleeve moves to the photosensitive drum 1, so that it is extremely difficult to collect it to the developing device 8. Therefore, when using a contact-type charging device, it is preferable to collect toner in the developing device 8 with a force other than electrostatic force, or to provide a separate collecting means as described above.
[0171]
In the case of a color image forming apparatus, upstream toner is mixed in the collecting brush device 12 that is in contact with the downstream photosensitive drum 1. Therefore, when the toner stored in the collecting brush device 12 is collected by the developing device 8, a different color toner is mixed into the developing device 8, and a so-called color mixing problem that the color reproduction range is narrowed occurs. Therefore, in order to avoid the problem of color mixing, it is preferable to collect and remove the toner discharged on the photosensitive drum 1 by a device other than the developing device 8.
[0172]
Up to now, the toner discharging process from the collecting brush device 12 has been described only by the polarity of the voltage applied to the collecting brush device 12, the charging device 6, the developing device 8, and the transfer device 3. You may move by the potential difference between members. In that case, for example, it may be a DC voltage having an absolute value larger than the surface potential of the photosensitive drum 1, and the potential difference is preferably 200 to 600V. When this potential difference range is exceeded, discharge starts and the toner charging polarity is changed to deteriorate the performance of toner movement such as recovery from the recovery brush device 12, discharge, and transfer recovery. If the potential difference is below this range, the electrostatic attraction due to the electric field applied to the toner is small, and the toner cannot be moved sufficiently.
[0173]
Next, specific embodiments of the recovery brush device according to the present invention and the toner used therein will be described.
[0174]
Example 1
A woven rotary brush having the following specifications was attached to the image forming apparatus as a collection brush apparatus, and the collection ability of transfer residual toner was evaluated.
[0175]
Rotating brush outer diameter: 7.5mm
Brush fiber material: Nylon conductive yarn
Brush thickness: 2 denier
Brush density: 360F / mm²
Pile length: 1.75mm
Brush fiber resistance: about E4Ω · cm
Amount of biting into the photosensitive drum: about 0.45 mm
As the photosensitive drum, an OPC drum having a film thickness of about 20 μm and φ16, in which CGL and CTL are sequentially laminated on an aluminum base tube, was used. The toner used was a non-magnetic toner having a 50% volume diameter of about 6 μm and a shape factor of about 1.43. The surface potential of the photosensitive drum was about −400V. About 0.5 mg / cm of developing toner on the surface of the photosensitive drum² It was. At this time, the charge amount of the toner developed on the surface of the photosensitive drum was about −25 μC / g.
[0176]
As a transfer device, an electrical resistance of about 10^TenAn intermediate transfer belt of Ω and thickness of 120 μm was used, and a transfer roller was used on the back side of the intermediate transfer belt at the transfer portion. The transfer roller has an electric resistance of about 10 with carbon black dispersed in EPDM.^Four An Ω sponge layer was used. Further, the transfer roller was in contact with the photosensitive drum so that the contact width (transfer area) was about 2 mm.
[0177]
The photosensitive drum was rotated at a speed of about 125 mm / s, and a voltage of about 700 V was applied to the transfer roller. The transfer efficiency under these transfer conditions was 98%.
[0178]
Further, as a result of measuring the surface potential of the photosensitive drum by applying a DC voltage to the recovery brush device, the discharge start voltage between the recovery brush device and the surface of the photosensitive drum was about 520V.
[0179]
Under the above conditions, the amount of toner adhered on the surface of the photosensitive drum before and after passing through the collection brush device and after printing are changed by changing the peak-to-peak voltage Vpp of the sinusoidal AC voltage applied to the collection brush device and the frequency f. Ghosts due to poor toner recovery of the recovery brush device were visually observed.
[0180]
The results are shown in (Table 1).
[0181]
[Table 1]

[0182]
In the above table, “X” indicates a level at which the uncollected ghost can be visually confirmed after the toner passes on the photosensitive drum and after printing even after passing through the collecting brush device. Δ indicates a level at which the recovery failure ghost can be visually confirmed after passing through the recovery brush device, but the recovery failure ghost cannot be visually confirmed after printing. ○ indicates a level at which the toner cannot be visually confirmed on the photosensitive drum after passing through the recovery brush device, and the recovery failure ghost cannot be visually confirmed even after printing. Further, E indicates a case where an abnormal discharge has occurred between the recovery brush device and the photosensitive drum.
[0183]
Even when the direct current voltage superimposed on the alternating current voltage was changed between −800 and +800 V, no significant difference was found in the recovery ability.
[0184]
Further, when a rectangular wave was used for the AC voltage, the recovery capability was lowered, and when a triangular wave was used, the recovery capability was equivalent to a sine wave.
[0185]
Further, the recovery ability of the toner obtained by reversely transferring the toner transferred by the transfer device of the previous stage to the transfer device of the next stage by applying 1 kV has the same tendency as in Table 1.
[0186]
Also, the voltage applied to the transfer roller is reduced to 500 V, the transfer efficiency is about 73%, and the negative transfer residual toner is increased (positive toner is also present), uncharged toner, −13, −47 μC Even when toner / g charge amount toner is supplied to the recovery brush device, the recoverable region is somewhat narrower than shown in Table 1, but it can be recovered to the recovery brush device by setting the AC voltage setting range to be almost equivalent. Was also confirmed. In short, it is preferable to make the charge amount distribution as sharp as possible within the range of the charge amount of −10 to −50 C / g.
[0187]
Further, it was confirmed that when a peak-to-peak voltage of 1000 V or higher was applied at a frequency of about 100 Hz, the brush fibers vibrated visually, and toner mist was generated from the contact area between the recovery brush device and the photosensitive drum. When the frequency was further increased, the vibration of the brush fibers was not visually confirmed, but the amount of toner mist increased. Since the frequency is large, it is considered that the brush fibers are slightly vibrating at a level that cannot be visually confirmed.
[0188]
From the above results, it has been found that the transfer residual toner can be collected in the collection brush device by setting the specific AC voltage and frequency within the set range. In short, it is more preferable to make the charge amount distribution as sharp as possible within a charge amount range of −10 to −50 C / g.
[0189]
(Example 2)
Next, toners having various shape factors of 1.25 and 1.60 were adhered to the photosensitive drum, and the same experiment as described above was performed. The results are shown in (Table 2).
[0190]
[Table 2]

[0191]
For the toner having a sphericity of 1.25, no significant difference was found in the recovery ability from the case shown in (Table 1).
[0192]
From the above results, the sphericity of 1.25 is similar to that of (Table 1). When the sphericity is set to 1.60, the recoverable area is narrower than that shown in (Table 1), but a specific AC It turned out that it can collect | recover in a collection | recovery brush apparatus by setting to a voltage setting range. In short, the shape factor of the toner is preferably 1.50 or less.
[0193]
(Example 3)
Next, using toner having a shape factor of 1.43, AC superposition is stopped on the voltage applied to the recovery brush device, and only the DC voltage is changed, so that the photosensitivity before and after passing through the recovery brush device is changed with various transfer efficiencies. The amount of toner adhering to the surface of the body drum and the ghost due to poor toner recovery of the recovery brush device were visually observed after printing. The results are shown in (Table 3).
[0194]
[Table 3]

[0195]
In addition, when it was set to -600V or less and + 600V or more, there existed a tendency for collection | recovery capability to deteriorate a little.
[0196]
In addition, although the toner collecting ability in which the toner transferred by the preceding transfer device is reversely transferred to the succeeding transfer device by 1 kV is not sufficient, the toner collecting performance is within a setting range of −300 to −600V. It was seen. Note that the slightly better recovery performance at the applied voltages of −300 and −600 V than at +300 and +600 V seems to be due to the difference in the amount of residual toner.
[0197]
Further, it is said that the recoverability is slightly better when the applied voltage is -600 V than -300 V and +600 V than +300 V.
[0198]
It has been found that the recovery performance is better when a DC voltage larger than the absolute value 400V of the surface potential of the photosensitive drum is applied. Further, regarding the difference in the shape factor of the toner, it was found that the shape factor was 1.60 or less and the recovery capability was higher with the same result as in Example 2.
[0199]
Further, when -13 μC / g charge amount toner was supplied to the recovery brush device, the recovery performance was somewhat deteriorated as compared with -25 μC / g toner.
[0200]
When the bias applied to the recovery brush device is alternating current, the toner enters the brush roller, and when only the direct current is applied, the toner is recovered only at the brush tip (brush roller surface). It was confirmed that the buffer amount (about 300 mg) was increased.
[0201]
From the above results, in the case of only the DC voltage, the toner recovery performance is not sufficient in the setting range of +300 to 600 V when the transfer efficiency is less than 97%, and the transfer efficiency of 97% or more and the reverse transfer toner is −300 to −600 V. Was recognized. In addition, better toner recovery performance was observed when a DC voltage having an absolute value larger than the surface potential of the photosensitive drum was applied. The shape factor of the toner is preferably 1.50 or less.
[0202]
Further, the charge amount of the toner should be set in the range of −10 to −50 μC / g, more preferably −15 to −45 μC / g.
[0203]
Further, it has been found that application of alternating current is more advantageous with respect to the recovery buffer amount.
[0204]
(Example 4)
Next, using a toner having a shape factor of 1.43, with the toner accumulated in the recovery brush device, the frequency is fixed to 3 kHz, the peak-to-peak voltage and the DC voltage to be superimposed are changed, and the recovery brush The polarity of the DC voltage applied to the apparatus was reversed, and the toner discharge effect from the recovery brush apparatus was evaluated. The results are shown in (Table 4).
[0205]
[Table 4]

[0206]
In the above table, “X” indicates a case in which toner adhesion to the rotating photosensitive drum is not visually recognized when the voltage is applied to the recovery brush device, that is, a case where toner is not discharged from the recovery brush device. Indicates. Further, Δ indicates a case where adhesion of toner to the rotating photosensitive drum is recognized and the toner remains in the collection brush device when the voltage is applied to the collection brush device.
[0207]
The discharge performance of the toner collected by applying AC (the state where the toner enters the brush roller) is the result shown in (Table 4), but the toner collected by applying DC (collected only by the brush tip of the brush roller). In the discharged state, the toner was not left inside the brush roller, and no toner remained in the collecting brush device. That is, it is possible to completely discharge the toner collected by applying DC.
[0208]
From the above results, in the case of the toner having a shape factor of 1.43, when the voltage between peaks is low or only the DC voltage is used, the toner discharge performance is recognized although the toner is not sufficient. It has also been found that the toner recovered by direct current application can be completely discharged.
[0209]
(Example 5)
Next, the same evaluation as in (Table 4) was performed using a toner having a shape factor of 1.25. The results are shown in (Table 5).
[0210]
[Table 5]

[0211]
In the table above, ◯ indicates a case where adhesion of toner to the rotating photosensitive drum is visually recognized when the polarity of the DC voltage applied to the recovery brush device is reversed.
[0212]
From the above results, when the peak-to-peak voltage is low, or when only the DC voltage is used, further toner discharge performance is recognized by making the toner shape spherical.
[0213]
(Example 6)
Next, using a toner having a shape factor of 1.43, the DC voltage applied to the recovery brush device is changed and recovered while the toner is accumulated in the recovery brush device for various toner charge amounts. The polarity of the DC voltage applied to the brush device was reversed, and the toner discharge effect from the recovery brush device was evaluated. The results are shown in (Table 6).
[0214]
[Table 6]

[0215]
From the above results, it was found that the discharge performance is better when the toner has a sharp charge amount distribution within a charge amount range of −10 to −50 C / g.
[0216]
(Example 7)
Next, the recovery / discharge performance and other effects due to the brush resistance of the recovery brush device were briefly evaluated.
[0217]
The brush resistance used in Examples 1 to 6 was E4. However, since the resistance is slightly low, even if the bias applied to the brush is as low as ± 4,500 V, the OPC drum is charged and the surface potential varies. There was a trend. As a result, image unevenness occurred.
[0218]
When the brush resistance is about E10, when the recovery bias is -400 V and the discharge bias ± 400 V polarity is switched, the resistance is excellent in the recovery and discharge performance and the influence on the surface potential is less than that of E4.
[0219]
From the above results, the effects of the present invention will be considered as follows.
[0220]
As can be seen from Examples 1 and 2, when the peak-to-peak voltage of the AC voltage is set to 2 to 2 kVpp of the discharge start voltage and the frequency of 1 to 7 kHz, the toner is recovered by the recovery brush device regardless of the charging polarity. Therefore, the force for directly attracting the toner to the collecting brush device is considered to be a force other than the electrostatic force. Moreover, since it is thought that the brush fiber is vibrating mechanically in Example 1, it is thought that the mechanical force of the brush fiber is acting.
[0221]
That is, when the brush fiber vibrates, a mechanical adhesion force is generated between the toner and the brush fiber. Furthermore, by continuing the vibration, the toner sinks into the brush, and the toner is held by the brush fiber. As a result, it is considered that the toner is collected on the collecting brush device side regardless of the charging polarity of the toner.
[0222]
Further, it is considered that a peak-to-peak voltage that is twice or more the discharge start voltage has an effect of vibrating the brush fibers.
[0223]
That is, at the time of a negative voltage peak, negative charges are released from the tip of the brush fiber to the surface of the photosensitive drum. As a result, a negatively charged region A is formed on the surface of the photosensitive drum close to the tip of the brush fiber. When a negative charge is charged at the tip of the brush after discharging, the brush fiber and the surface of the photosensitive drum are electrostatically repelled because of the same polarity as the charging polarity of the photosensitive drum. If a region B that is uncharged or has a positive charge around the tip of the brush exists on the surface of the photosensitive drum, the tip of the brush is attracted to the region B. As a result, a force that moves from region A to region B on the surface of the photosensitive drum acts on the brush tip.
[0224]
Next, at the negative voltage peak, a force opposite to the above acts. As a result, it is considered that the brush fibers vibrate. The interval between the region A and the region B is determined by the frequency of the AC voltage, the relative speed between the recovery brush device and the photosensitive drum, and the brush fiber density. Since there is an interval between the regions AB where the brush fibers are likely to vibrate, it is considered that the frequency dependence as in Examples 1 and 2 was observed.
[0225]
The brush fiber density is also an element that determines the interval between the areas AB where the brush fibers are likely to vibrate. However, it is better to increase the brush fiber density in order to increase the chance of contact of the toner on the photosensitive drum 1. In order to secure the discharge performance of the toner that has entered the collected brush, it is better to reduce the brush fiber density. From such an idea, the brush fiber density in the example is 360 F / mm.² Since the discharge performance is slightly poor, the brush fiber density is 50 to 400 F / mm.² It is preferable that
[0226]
Further, the recovery performance is better when the shape factor of the toner is 1.00 to 1.50. This is because the toner having a spherical shape has higher releasability from the photosensitive drum 1, and it is considered that the toner on the photosensitive drum 1 can be easily collected by electrostatic force and mechanical force.
[0227]
In addition, when the recovery bias is only a DC voltage from Example 3, the setting range of +300 to 600 V is not sufficient when the transfer efficiency is less than 97%, and the transfer efficiency is 97% or more and the reverse transfer toner is −300 to −600 V. Toner recovery performance was observed, and higher toner recovery performance was observed by applying a DC voltage that was larger in absolute value than the surface potential of the photosensitive drum.
[0228]
These results are considered to be a potential difference in which an electrostatic attraction force effectively acts on the toner on the surface of the photosensitive drum by securing a potential difference in which an electric field is generated between the surface potential of the photosensitive drum and the brush fiber. That is, it is suggested that it is desirable to apply a DC voltage larger than the absolute value of the photosensitive drum surface potential to the brush. However, applying a voltage higher than the discharge start voltage changes the polarity of the toner on the photosensitive drum, which is not very desirable.
[0229]
The shape factor of the toner is preferably 1.50 or less. This shows that when the transfer efficiency is less than 97%, the transfer residual of the negative electrode toner increases, and in the case of the transfer efficiency of 97% or more and the reverse transfer toner, the transfer residual of the positive electrode toner increases. When only DC voltage is used for the recovery bias, it is difficult to take bipolar toner at a time, so a system that recovers positive reverse transfer toner by improving transfer efficiency such as optimizing transfer conditions to make the toner spherical as much as possible Is considered ideal.
[0230]
Further, since it is better to set the charge amount of the toner in the range of −10 to −50 μC / g, more preferably in the range of −15 to −45 μC / g. It is considered that the electrostatic force can be secured and the transferability can be improved.
[0231]
On the other hand, in Example 4, toner is not discharged from the recovery brush device unless the peak-to-peak voltage is equal to or lower than the discharge start voltage. This is considered because the toner moves into the brush when the brush fiber vibrates. Therefore, it is considered preferable that the brush fibers do not vibrate when the toner is discharged. Example 4 corresponds to the case where the peak-to-peak voltage is 500 V or less. At this time, it is considered that the toner having the same polarity as that of the superimposed DC voltage is detached from the brush and moved to the photosensitive drum.
[0232]
Further, by applying a DC voltage having an absolute value larger than the surface potential of the photosensitive drum, higher toner discharging performance was recognized. These results are considered to be a potential difference in which an electrostatic attraction force effectively acts on the toner on the surface of the photosensitive drum by securing a potential difference in which an electric field is generated between the surface potential of the photosensitive drum and the brush fiber. That is, it is suggested that a DC voltage larger than the absolute value of the photosensitive drum surface potential is preferably applied to the brush. However, the discharge start voltage or higher is not so preferable because the polarity of the toner on the photosensitive drum is changed as described above.
[0233]
In Example 5, it is considered that the release property of the brush fiber and the toner is improved by making the shape of the toner spherical, and the discharge performance is improved compared to Example 4.
[0234]
Although the polarity of the DC voltage component is reversed when the toner is discharged from the collection brush device, uncharged toner is accumulated in the collection brush device in this method. Therefore, the material of the collected brush fiber is preferably a material that can easily charge the toner to either positive or negative polarity. In this test, nylon fibers that are easily charged positively in the charging series were used. By using such a material, when the brush fiber vibrates, the toner taken in by the brush is gradually charged to a specific polarity, so that the toner can be discharged electrostatically.
[0235]
In Example 6, it was found that the discharge performance is better when the toner has a sharp charge amount distribution as much as possible within a charge amount range of −10 to −50 C / g. This is because if the charge amount of the toner is too low, the electrostatic attraction force applied to the toner will be reduced, so the discharge performance will be reduced, and conversely if it is too high, the transfer electric field corresponding to the toner charge will be insufficient and the residual toner will be extremely increased. Therefore, it is considered that the recovery performance has deteriorated.
[0236]
【The invention's effect】
  As described above, according to the present invention,Recovery brush deviceandToner removal deviceUsingPhotoconductorSince the toner remaining on the top can be efficiently collected regardless of the positive and negative charge polarity, the size and cost of the apparatus can be reduced.PhotoconductorThe service life can be extended and does not depend on the polarity of the residual toner.Toner removal deviceAn effective effect of obtaining an image forming apparatus having the above is obtained.
[Brief description of the drawings]
FIG. 1 is an explanatory view showing an image forming apparatus having brush vibration means according to an embodiment of the invention.
FIG. 2 is an explanatory view showing an image forming apparatus according to another embodiment of the present invention.
FIG. 3 is an explanatory view showing an image forming apparatus for forming a color image according to still another embodiment of the present invention.
4 is a voltage application timing chart according to the image forming apparatus of FIG.
5 is a voltage application timing chart according to the image forming apparatus of FIG.
6 is a voltage application timing chart as an example of the image forming apparatus of FIG.
7 is a voltage application timing chart as another example of the image forming apparatus of FIG.
FIG. 8 is an explanatory view showing an outline of a conventional brush type cleaning device.
[Explanation of symbols]
1 Photosensitive drum (image carrier)
2 Registration roller
3 Transfer device (transfer means)
4 Fixing device
5 Receiving paper
6 Charging device
7 Exposure source
8 Developing device (Developing means)
10 Upstream guide means
11 Downstream guide means
12 Collection brush device (first collection means)
13 Toner removal device
14 Belt support roller
15 Paper transport belt
16 Paper adsorption device
17a Power supply for recovery brush member (first voltage applying means)
17b Power supply for recovery brush member (second voltage applying means)
101 Photosensitive drum
102 Brush roller
103 Intermediate roller
104 Scraping member

Claims (1)

A photoreceptor,
A charging device for charging the photoreceptor;
A transfer device for transferring toner conveyed on the photoconductor;
A collection brush device that primarily collects toner remaining on the photoreceptor;
A toner removing device for secondary recovery of toner on the transfer device;
A first step of applying the same polarity voltage as the positively charged toner to the recovery brush device and the charging device, and applying a reverse polarity voltage of the positively charged toner to the transfer device; and a reverse polarity of the positively charged toner to the recovery brush device In the second step of applying a voltage, applying the same polarity voltage as the positively charged toner to the charging device, and applying a reverse polarity voltage to the positively charged toner to the transfer device, the residual toner primarily recovered by the recovery brush device is removed. An image forming apparatus for secondary collection in a toner removing device .

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