JP3766960B2 - Electrostatic latent image liquid developing apparatus and liquid developing method - Google Patents

Description

【００２８】
プリウェット液回収装置５１は、現像ローラ５１０に当接するように設けられたプリウェット液回収ローラ５１２と、プリウェット液回収ローラ５１２に当接するように設けられた掻き取りブレード５２０と、回収タンク５２２と、を備えている。プリウェット液回収ローラ５１２は現像ローラ５１０の回転方向と同方向に回転する。また、プリウェット液回収ローラ５１２は、図２に示すように、電源装置５１７によりバイアス電圧が印加されている。このバイアス電圧は、プリウェット液回収ローラ５１２と現像ローラ５１０との間に生じる電界により、プラスに帯電したトナーがプリウェット液回収ローラ５１２に対して斥力を受けるように設定されている。これは、トナーの現像ローラ５１０への付着力をプリウェット液回収ローラ５１２への付着力よりも強くすることにより、液体現像剤５０８がプリウェット液回収ローラ５１２に付着するのを防止するためである。これにより、プリウェット液２２０のみをプリウェット液回収ローラ５１２に付着させることができる。尚、本実施例では、現像バイアス電圧を−１５０Ｖに設定したときに、プリウェット液回収ローラ５１２に印加するバイアス電圧を−１００〜−５０Ｖに設定した。
【００２９】
現像剤回収装置５２は、現像ローラ５１０に当接するように設けられた現像剤回収ローラ５１４と、回収された液体現像剤５０８を貯蔵する回収タンク５２４と、タンク５０２に貯蔵された液体現像剤５０８よりも更にトナー濃度の高い液体現像剤５０９が貯蔵されたタンク５２６と、濃度測定装置５２８と、濃度調整装置５３０と、を備えている。現像剤回収ローラ５１４は現像ローラ５１０の回転方向と反対方向に回転する。また、現像剤回収ローラ５１４は、図２に示すように、電源装置５１９によりバイアス電圧が印加されている。このバイアス電圧は、現像剤回収ローラ５１４と現像ローラ５１０との間に生じる電界により、プラスに帯電したトナーが現像剤回収ローラ５１４に対して引力を受けるように設定されている。これは、トナーの現像剤回収ローラ５１４への付着力を現像ローラ５１０への付着力より強くすることにより、液体現像剤５０８を現像剤回収ローラ５１４の表面に付着させるためである。尚、本実施例では、現像バイアス電圧を−１５０Ｖに設定したときに、現像剤回収ローラ５１４に印加するバイアス電圧を−２５０〜−２００Ｖに設定した。
【００３０】
現像剤回収ローラ５１４に付着した液体現像剤５０８は、図２に示すように、回収タンク５２６に回収された後、濃度測定装置５２８によりトナー濃度が測定される。濃度測定装置５２８は、液体現像剤５０８の光透過率を測定し、この光透過率に基づきトナー濃度を算出する。濃度調整装置５３０は、濃度測定装置５２８で算出されたトナー濃度に基づき、回収された液体現像剤５０８にタンク５２６に貯蔵された液体現像剤５０９を混合してトナー濃度を調整する。濃度調整装置５３０によりトナー濃度が調整された液体現像剤５０８は、タンク５０２に搬送されて再利用される。
【００３１】
本実施例の転写装置６０は、図１に示すように、中間転写体である中間転写ドラム６０２と、中間転写ドラム６０２に離接可能に設けられた二次転写体である二次転写ローラ６０４と、中間転写ドラム６０２に残留するトナーを除去する除去ローラ６０６と、を備えている。
【００３２】
中間転写ドラム６０２は、感光体１０と当接するように設置されており、感光体１０の回転方向と反対方向に回転する。また、中間転写ドラム６０２は、転写時に、図１に示すような電源装置６０８によりトナーと反対の極性を有する電荷で帯電される。これにより、すなわち静電気力によって感光体１０上のトナー像を中間転写ドラム６０２上に一次転写する。
【００３３】
中間転写ドラム６０２は、ステンレス等の剛体で形成された芯金と、芯金の周囲に形成された弾性層と、弾性層の表面に形成された表面層とを有する。このため、感光体１０上に形成されたトナー像と中間転写ドラム６０２とが接触する際の接触圧力を分散させることができるので、感光体１０上のトナー像が乱れるのを防止することができる。尚、中間転写ドラム６０２の硬度は、５〜５０度ＪＩＳ−Ａ、できれば１５〜４０度ＪＩＳ−Ａであることが望ましい。硬度が５度ＪＩＳ−Ａ以下であると、柔らかすぎるため一定形状を保つことが困難になる。一方、硬度が５０度ＪＩＳ−Ａ以上であると、固すぎるため、感光体１０上に形成されたトナー像と中間転写ドラム６０２とを接触させた際に、感光体１０上のトナー像を押しつぶすおそれがある。
【００３４】
中間転写ドラム６０２の弾性層を形成する部材としては、ポリスチレン、ポリエチレン、ポリウレタン、ポリ塩化ビニル、ＮＢＲ（ニトリル・ブチレン・ラバー）等の発泡体、あるいは、シリコンゴム、ウレタンゴム等の低硬度のゴム部材がある。但し、ゴム部材は、一般に弾性変形させた状態で長年使用すると、永久変形して本来の形状、すなわち円柱状に戻らなくなることがある。このため、弾性層を形成する部材には、できれば発泡体を用いることが好ましい。尚、芯金の周囲にゴム部材で弾性層を形成し、更にその表面に発泡体で弾性層を形成してもよい。
【００３５】
中間転写ドラム６０２の表面層は液体現像剤５０８のキャリア液であるシリコンオイルに膨潤しない部材で形成されている。表面層を形成する方法としては、例えば、弾性層の表面に合成ゴム系結合体をコーティングする方法、弾性層の表面をチューブで被覆する方法等がある。これ等のチューブは、つなぎ目のない所謂エンドレスチューブである樹脂チューブ、例えばポリイミド、ＰＥＴ等で形成されたチューブであることが望ましい。尚、弾性層がウレタンゴム、フロロシリコンゴム等のシリコンオイルに膨潤しないゴム部材で形成されている場合は中間転写ドラムの側面を表面層で覆う必要はないが、発泡体等のシリコンオイルに膨潤するもので形成されている場合は中間転写ドラムの側面を表面層で覆う必要がある。
【００３６】
中間転写ドラム６０２の電気抵抗値は１０⁴ 〜１０¹¹Ωｃｍ、できれば１０⁶ 〜１０⁹ Ωｃｍあることが望ましい。電気抵抗値が１０⁴ Ωｃｍ以下であると、中間転写ドラム６０２を帯電した際に、中間転写ドラム６０２から感光体１０に急激に放電し、感光体１０を損傷し、転写不良が発生する。一方、電気抵抗値が１０¹¹Ωｃｍ以上であると、中間転写ドラム６０２の帯電が十分でなくなり、中間転写ドラム６０２と感光体１０上に形成されたトナー像との間の静電気力が弱まりトナーの移動が十分に行われなくなる。中間転写ドラム６０２を上記のような電気抵抗値にするためには、中間転写ドラム６０２の表面を導電加工するか、あるいは、表面層を形成する部材に導電性微粒子を添加するなどして、電気抵抗値を下げる必要がある。
【００３７】
中間転写ドラム６０２の表面は、離型性を有する光沢面であることが望ましい。これは、トナーとの離型性をよくすることにより、中間転写ドラム６０２に付着したトナーの除去を容易にするためである。したがって、中間転写ドラム６０２の表面層を形成する部材として、ラテックス、コーティングされたゴム部材、フッ素コーティング等の離型コートが施されたポリイミド等の樹脂チューブ、または、表面に離型効果を有するＰＦＡ、ＰＴＦＥ、ＥＴＦＥ、ＦＥＰ等の樹脂チューブを用いることが望ましい。
【００３８】
二次転写ローラ６０４は、中間転写ドラム６０２の回転方向と反対方向に回転することにより、記録媒体である紙を中間転写ドラム６０２と二次転写ローラ６０４との間に送り込む。この際、二次転写ローラ６０４は紙を介して中間転写ドラム６０２に押圧される。また、二次転写ローラ６０４は、図１に示すように、電源装置６１２によりトナーと反対の極性を有する電荷で帯電されている。このため、中間転写ドラム６０２の弾性層と二次転写ローラ６０４の静電気力とにより中間転写体と記録媒体との密着性を向上させることができるので、記録媒体の表面の凹凸に関係なく良好に転写することができる。
【００３９】
二次転写ローラ６０４の表面には、フッ素コーティングが施されている。これは、トナーとの離型性をよくすることにより、二次転写ローラ６０４に付着したトナーの除去を容易にして二次転写ローラ６０４が汚れるのを防止するためである。
【００４０】
除去ローラ６０６は、中間転写ドラム６０２に離接可能に、且つクリーニング時に当接するように設置されており、中間転写ドラム６０２の回転方向と反対方向に回転する。また、除去ローラ６０６は、図１に示すように、電源装置６１４によりトナーと反対の極性を有する電荷で帯電されている。これにより、二次転写工程終了後に中間転写ドラム６０２に残留するトナーを除去ローラ６０６の表面に付着させ、中間転写ドラム６０２から除去する。
【００４１】
本実施例のクリーニング装置７０は、除去ローラ７０２と、除去ローラ７０２に接続された電源装置７０４とを備えている。除去ローラ７０２は、感光体１０に当接するように設けられており、感光体１０の回転方向と反対方向に回転する。電源装置７０４は、除去ローラ７０２をトナーと反対の極性を有する電荷で帯電するように除去ローラ７０２に電圧を印加する。これにより、感光体１０上に残留するトナーを除去する。
【００４２】
次に、本実施例に用いた画像形成用資材について説明する。本実施例に用いた液体現像剤は、エポキシ等のバインダーとなるレジン、トナーに所定の電荷、本実施例ではプラスの電荷を与える荷電制御剤、着色顔料、トナーを均一に分散させる分散剤等からなるトナーと、キャリア液とからなる。トナーの構成は、従来の液体現像剤に用いられてきたものと基本的には同様であるが、帯電特性及び分散性の調整のためそれらの処方はシリコンオイルに適合するよう変更してある。トナーの平均粒径は、小さい程、解像度がよくなるが、粒径が小さいと物理的接着力が大きくなり転写する際に、はがし難くなる。このため、本実施例ではトナーの平均粒径は、転写性の向上を目的として２〜４μｍあたりに中心が来るように調整してある。
【００４３】
液体現像剤の粘性は、用いるキャリア液、レジン、着色顔料、荷電制御剤などおよびそれらの濃度により決まる。本実施例では、粘度を５０〜６０００ｍＰａ・ｓ、トナー濃度を５〜４０％の範囲で変化させて実験した。
【００４４】
キャリア液は、高電気抵抗を示すジメチルポリシロキサンオイル、環状ポリジメチルシロキサンオイル等を用いる。尚、現像ローラ５１０上の液体現像剤層中に含まれるキャリア液はきわめて少量であるので、感光体１０の潜像面に供給される液体現像剤中に含まれるキャリア液もきわめて少量である。したがって、転写時に紙等に吸収されるキャリア液はきわめて少量となるので、粘度が１０００ｍＰａ・ｓ以下であれば定着後に残留するキャリア液は、ほとんど見られない。本発明者等の実験によれば、キャリア液に粘度が２．５ｍＰａ・ｓである米国ダウコーニング社のＤＣ３４４及び粘度が６．５ｍＰａ・ｓである米国ダウコーニング社のＤＣ３４５を用いて出画実験を行ったときは、いずれも定着後に紙上に残留するキャリア液は見られなかった。しかし、揮発性が高いため、現像装置を密閉構造にする必要が生じた。また、キャリア液に粘度が２０ｍＰａ・ｓである信越シリコン社のＫＦ−９６−２０を用いて出画実験を行ったときは、定着後に紙上に残留するキャリア液は見られなかった。また、揮発性がそれほど高くないので、現像装置を密閉構造にする必要は生じなかった。ＤＣ３４４，ＤＣ３４５及びＫＦ−９６−２０は、一般的に化粧品に用いられるもので毒性等の安全性は高い。キャリア液については、信越シリコン社のＫＦ９９３７等他に多くの種類があり、電気抵抗、蒸発特性、表面張力、安全性等が満たされていればいずれを選択してもよい。
【００４５】
また、発明者等が行った実験では、表面張力が大きい場合にはかぶりやトナーの塊が付着することがあり、実験的には表面張力が２１ｄｙｎ／ｃｍ以上では画質に問題が起こりやすいことが分かった。
【００４６】
電気抵抗値としては、トナーの帯電安定性の問題があり、１０¹⁴Ωｃｍ以上が望ましい。最低限１０¹²Ωｃｍ以上は必要である。本実施例の説明では、これらの実験結果に鑑み、価格が低く入手の容易なＤＣ３４５を用いた例を示す。
【００４７】
プリウェット液は、画像支持体上に形成された静電潜像を乱すことなく、定着時に容易に蒸発し、かぶりやトナーの塊が付着しないものであることが要求される。例としては、米国ダウコーニング社のＤＣ３４４，ＤＣ２００−０．６５，−１．０，−２．０、信越シリコン社のＫＦ９６Ｌ−１，ＫＦ９９３７などが挙げられる。一般的に蒸発性の高いシリコンオイルを選択することが好ましい。
【００４８】
発明者等の行った実験では、液粘度が０．５〜３ｍＰａ・ｓの範囲で問題なく現像、転写、定着による液の乾燥が行われたが、５ｍＰａ・ｓから６ｍＰａ・ｓ程度ではやや定着時の液の乾燥に時間と温度が必要になる傾向が見られた。１０ｍＰａ・ｓでは乾燥に要するエネルギーが大きくなり過ぎ一般的ではない。また、０．５ｍＰａ・ｓ以下であると揮発性が高くなるので、危険物として法規制の対象となり適当でない。また、紙への加熱の影響もあり、沸点は、２５０℃以下のものであることが好ましい。
【００４９】
表面張力は、現像剤と画像支持体との付着力をなくし、離型性をよくして画像の汚れを防ぎ、画質の解像力を向上させるため、できるだけ低いものがよい。本発明者等の実験によれば、２０〜２１ｄｙｎ／ｃｍ程度が限界でこれより低いものを選択する必要がある。
【００５０】
電気抵抗は、低い場合、潜像電荷をリークして像をぼかしてしまう。従って、できるだけ高いものを使用する必要がある。実験的には１０¹⁴Ωｃｍ程度以上が望ましい。最低限１０¹²Ωｃｍは必要である。
【００５１】
次に、本実施例の画像形成装置１の動作について説明する。
先ず、図４（Ａ）に示すように、帯電装置３０により感光体１０の表面をトナーと反対の極性を有する電荷、本実施例の場合はマイナスの電荷で帯電する。一般に帯電装置３０には、コロナ放電器が用いられる。次に、露光装置４０により帯電した感光体１０上に反転像を露光する。例えば、レーザースキャナーにより反転像を露光して感光体１０の表面に静電潜像を形成する。図４（Ｂ）に示すようにレーザースキャナーの光が当たった部分は、導電化するので電荷が消失し、光の当たらなかった部分は電荷の像である静電潜像として残る。
【００５２】
次に、図４（Ｃ）に示すように、プリウェット装置２０により感光体１０上にプリウェット液２２０を塗布する。タンク２０２に貯蔵されたプリウェット液２２０は、供給ローラ２０２ａにより汲み上げられて搬送ローラ２０４に供給される。搬送ローラ２０４に供給されたプリウェット液２２０は塗布ローラ２０６に搬送された後、感光体１０上に塗布される。このように、ローラを介してプリウェット２２０を塗布することにより、感光体１０上に薄層のプリウェット液層を形成する。
【００５３】
次に、現像装置５０により静電潜像を顕像化する。タンク５０２に貯蔵された液体現像剤５０８は、供給ローラ５０２ａにより搬送ローラ５０４に供給される。搬送ローラ５０４に供給された液体現像剤５０８は、塗布ローラ５０６ａ，５０６ｂに搬送された後、現像ローラ５１０に塗布される。このように、複数のローラを介して液体現像剤５０８を塗布することにより、現像ローラ５１０上に均一で薄層の液体現像剤層を形成する。また、供給ローラ５０２ａ、搬送ローラ５０４及び塗布ローラ５０６ａ，５０６ｂは、それぞれ電源装置５１３、電源装置５１１及び電源装置５３１によりバイアス電圧が印加される。これにより、液体現像剤５０８の現像ローラ５１０への供給量を調節している。次に、図４（Ｄ）に示すように、現像ローラ５１０上の液体現像剤層を、感光体１０上のプリウェット液層とソフトコンタクトさせることにより感光体１０の表面に形成された静電潜像に近接させて、静電気力により、帯電したトナーを感光体１０上に移動させ、感光体１０上にトナー像を形成する。尚、現像時に感光体１０から現像ローラ５１０に移動したプリウェット液２２０はプリウェット液回収装置５１により、また現像後に現像ローラ５１０上に残留する液体現像剤５０８は現像剤回収装置５２によりそれぞれ回収される。
【００５４】
次に、転写装置６０により感光体１０上に形成されたトナー像を記録媒体である紙に転写する。先ず、図４（Ｅ）に示すように、感光体１０上に形成されたトナー像を、トナーと電源装置６０８によりトナーと反対の極性を有する電荷で帯電された中間転写ドラム６０２との間に生じる静電気力により、中間転写ドラム６０２上に一次転写する。次に、図４（Ｆ）に示すように、中間転写ドラム６０２上に一次転写されたトナー像を、二次転写ローラ６０４の中間転写ドラム６０２への押圧力及び二次転写ローラ６０４に印加された二次転写バイアスによって生じる静電気力により、中間転写ドラム６０２と二次転写ローラ６０４との間に送り込まれた紙に二次転写する。一方、感光体１０は、クリーニング装置７０により感光体１０上に残留した液体現像剤５０８が除去され、その後、除電装置８０により除電される。
【００５５】
次に、図４（Ｇ）に示すように、図１には図示されていない定着装置６２０により、紙上に二次転写されたトナー像を定着する。定着装置６２０の定着ローラ６２２内に設けられた定着ヒータ６２４は、トナーを熱的に溶融させる。これにより、紙上にトナー像を定着する。
【００５６】
図５乃至図９は、本実施例の現像過程について詳細に説明するための図であり、図５は現像過程の全体を説明するための図、図６は接近過程のようすを示す図、図７はトナー移動過程のようすを示す図、図８は非画像部の分離過程を示す図、図９は画像部の分離過程を示す図である。従来の現像過程と異なり本実施例の現像過程は、図５に示すように、現像ローラが感光体に接近して液体現像剤層がプリウェット液層に接近する接近過程と、液体現像剤層とプリウェット液層とがソフトコンタクトしてトナーが移動するトナー移動過程と、現像ローラが感光体から離れて現像ローラに付着するトナーと感光体上に付着するトナーとに分離される分離過程との３つの過程から成り立っていると考えられる。
【００５７】
接近過程では、図６に示すように、現像ローラ５１０に弾性を有する円柱状に形成されたものを用いたことにより、現像ローラ５１０の感光体１０への押圧力調節して現像ローラ５１０上の液体現像剤層と感光体１０上のプリウェット液層とが接触する際の接触圧力を分散させると、キャリア液とトナーからなる高粘度の液体現像剤層とプリウェット液層とはソフトコンタクトされる。この際、液体現像剤層及びプリウェット液層を介して現像ローラ５１０と感光体１０との間に微小ギャップ即ち間隔ｄが形成される。尚、粘度の低いプリウェット液は前後に若干押し出されてプリウェット液の液溜りが生ずる。
【００５８】
トナー移動過程においては、図７に示すように画像部では、トナーが感光体１０上の電荷と現像ローラ５１０との間に形成される電界によって主にクーロン力によりプリウェット液層を通過して潜像面に移動する。一方、非画像部のトナーは、基本的には感光体１０の表面と液体現像剤層とがプリウェット液層により分離されているので、不要なトナーの感光体１０の表面への付着は起こらない。
【００５９】
分離過程においては、非画像部では、図８に示すように基本的に液体現像剤層は現像ローラ５１０に残留する。プリウェット液層と液体現像剤層との界面では２つの層が分離する際に、粘度の低いプリウェット液層の一部が液体現像剤層に転移して分離する。したがって、２つの層の分離点は、プリウェット液層の内部にあると考えられる。一方、画像部では、図９に示すように感光体１０の表面に移動したトナーがプリウェット液層を押しのけるため、プリウェット液層はトナー層の上に位置し、その層内で分離する。現像ローラ５１０上には、トナーが移動した後に残るキャリア液の一部とプリウェット液の一部が層を形成する。感光体１０上に残ったプリウェット液は、後の転写工程において、トナーの静電気力による移動を容易にする。
【００６０】
図１０は液体現像剤層を薄層化したことの意義を説明するための図である。現像ローラ５１０上に塗布された液体現像剤層が厚すぎると、液体現像剤５０８の粘度が高いので、静電気力で現像ローラ５１０から感光体１０の表面に移動しようとするトナー群が、その周りに位置するトナーに対して粘性を断ち切れずにクラスターを形成して、感光体１０の表面に移動するため、トナーの過剰付着が起こり、画像ノイズが発生する。このクラスターの発生を抑えるために、液体現像剤層の層厚を現像が十分にできる最小限の値に抑える必要がある。
【００６１】
図１１は金属等の剛体で形成された現像ローラと感光体とをハードコンタクトさせたようすを示す図であり、図１２は本実施例のソフトコンタクトを説明するための図である。上記で説明したように、本実施例の現像過程では、プリウェット液層の画像形成への機能は重要である。したがって、現像過程における重要な要件はプリウェット液層と液体現像剤層の２層の状態を維持することである。図１１に示すように、剛体で形成された現像ローラと感光体とをハードコンタクトさせると２層の状態を維持することができない。本実施例では、図１２に示すように、弾性を有する現像ローラ５１０を用い、現像ローラ５１０の感光体１０への押圧力を調節して現像ローラ５１０上に形成された液体現像剤層と感光体１０上に形成されたプリウェット液層とが接触する際の接触圧力を分散させることにより、液体現像剤層とプリウェット液層とを２層状態を維持しつつ接触させている。尚、この際、液体現像剤層及びプリウェット液層を介して現像ローラ５１０と感光体１０との間にあたかも微小ギャップ、すなわち間隔ｄが形成されたようになる。
【００６２】
次に、液体現像剤層の層厚、プリウェット液層の層厚及び現像ギャップ即ち間隔の最適化について説明する。液体現像剤層の層厚は、液体現像剤の粘性が５０〜１００ｍＰａ・ｓ以上のものについては、特に５００ｍＰａ・ｓ以上のものについては、薄くする必要がある。理想的には、現像時に要求されるトナー現像量（すなわち、ソリッド部の濃度）を満たす層厚より若干厚目が良い。これは、粘度の高い液体現像剤を用いた場合、現像時に、静電気的に選択されたトナーが液の粘性により余計なトナーを引き連れて感光体上に移動してしまうために、トナーの異常付着を生じてしまい画像汚れを引き起こすからである。発明者等の実験では、トナー濃度の高い液体現像剤については、５μｍからトナー濃度の低いものは４０μｍ程度の層厚で良好な画像が得られた。また、トナー濃度２０〜３０％の液体現像剤を用いた場合、液体現像剤の層厚が８〜２０μｍ程度で良好な画質が得られた。
【００６３】
プリウェット液層の層厚は、選択されたプリウェット液の粘度、表面張力により最適値が存在する。薄過ぎる場合には、高粘度の液体現像剤が感光体上に不規則に付着して画像汚れを生じる。プリウェット液の量を増やしていくに従って、画像汚れは改善されて、最適値が確認される。更に量を増やしていくと、潜像の電荷が流れ鮮鋭度、解像力の低下が起こる。また、現像時にトナー流れを生じやはり画像がぼける傾向を示す。ＤＣ３４４を用いた実験では、３０μｍ以下、特に２０μｍ以下の厚みで良好な結果を得られた。これより粘性の低いものについては、この結果より薄めでも、厚目でも良い結果を得られる。しかしながら、高粘度のものに関しては、最適値は範囲が狭くなる傾向にある。
【００６４】
感光体と現像ローラのギャップ、すなわち間隔は、狭いほうが画質において解像力、ソリッド部の濃度の均一性が良くなるのは、従来の現像法と同じである。本実施例に用いた高粘性の液体現像剤では、トナー間の凝集力が強いため、粉体現像剤のように、現像剤支持体あるいはキャリア粒子から機械的衝撃、静電気力により遊離したトナーが現像に使われるような現象が起きない。すなわち、液体現像剤層と感光体との間に空気層を介在させては現像がなされない。それゆえ、現像ローラ５１０と液体現像剤層、液体現像剤層とプリウェット液層、プリウェット液層と感光体１０がそれぞれ接触している関係になることが必須である。したがって、微小ギャップ即ち間隔ｄは、液体現像剤層、プリウェット液層の厚み以下でそれぞれの層を乱さない程度の寸法でなければならない。本実施例では、現像ローラ５１０の感光体１０への押圧力を調節して、液体現像剤の粘度、トナー濃度の違いに応じ、感光体１０上のプリウェット液層と現像ローラ５１０上の液体現像剤層とを接触させたときに間隔ｄが８μｍから５０μｍの間になるようにした。
【００６５】
上述の条件下で画出し実験をおこなった結果を表２に示す。これらの結果から本実施例の現像法に最適な現像剤及びプリウェット液の粘性に関する範囲は、現像剤が１００ｍＰａ・ｓから６０００ｍＰａ・ｓ、プリウェット液が０．５ｍＰａ・ｓから５ｍＰａ・ｓの間であることが分かった。また、画質に関しては、現像ベルト上の液体現像剤層の厚み、プリウェット液層の厚み、現像ギャップ即ち間隔等の影響により変化するが、現像諸条件の最適化をしても概ね表２に示すような傾向にあり、液体現像剤の最適な領域は表２に示した範囲に入ることを確認した。尚、プリウェット液のシリコンオイルにはダウコーニング製のＤＣ２００シリーズを用い、また現像液のキャリア液には同社製のＤＣ３４５を用いた。
【００６６】
【表２】

【００６７】
本発明の第一実施例によれば、供給ローラ５０２ａ、搬送ローラ５０４及び塗布ローラ５０６ａ，５０６ｂを介して現像ローラ５１０上に液体現像剤５０８を塗布することにより、各ローラ上の液体現像剤の層厚は隣合うローラとの当接部で薄く均一に規制されるので、現像ローラ５１０上に高濃度高粘性の液体現像剤５０８を薄く均一に塗布することができる。
【００６８】
また、本発明の第一実施例によれば、供給ローラ５０２ａにバイアス電圧を印加する電源装置５１３を設けると共に、アースに接続されたバックプレート５０３を現像タンク５０２に内設したことにより、供給ローラ５０２ａとバックプレート５０３との間に電界を生じさせて、トナーに働く静電気力によって液体現像剤５０８の汲み上げ量を調節することができる。また、現像タンク５０２内の液体現像剤５０８を静電気力によって汲み上げるので、現像タンク５０２の設置位置に制限がなく、したがって、画像形成装置の設計の自由度を向上させることができる。さらに、搬送ローラ５０４にバイアス電圧を印加する電源装置５１１と塗布ローラ５０６ａ，５０６ｂに電圧を印加する電源装置５３１とを設けたことにより、トナーと搬送ローラ５０４との間に働く静電気力及びトナーと塗布ローラ５０６ａ，５０６ｂとの間に働く静電気力によって液体現像剤５０８の現像ローラ５１０への塗布量、すなわち現像ローラ５１０上の液体現像剤の層厚を調節することができる。
【００６９】
また、本発明の第一実施例によれば、現像ローラ５１０上の液体現像剤層の光反射率を測定し、この光反射率に基づき層厚を算出する層厚測定装置５３と、層厚測定装置５３で算出された層厚に基づき、電源装置５１１及び電源装置５１３の電圧値を調整する制御装置５４とを設けたことにより、常に適量の液体現像剤５０８を現像ローラ５１０に供給することができる。
【００７０】
さらに、本発明の第一実施例によれば、現像ローラ５１０上に液体現像剤５０８を塗布する２つの塗布ローラ５０６ａ，５０６ｂを設けたことにより、液体現像剤５０８の粘性とトナーの分散性との影響により発生する塗布ムラ（波立ち）を密にして、より均一な液体現像剤層を現像ローラ５１０上に形成することができる。
【００７１】
また、本発明の第一実施例によれば、液体現像剤のキャリア液としてシリコンオイルを用いたことにより、従来のものに比べて以下に述べる利点を有する。
【００７２】
従来の液体現像剤は、一般にキャリア液としてIsoparG （登録商標：Exxon 社製）を用いている。このIsoparは、シリコンオイルほど抵抗値が高くないので、トナー濃度を濃くすると、即ち粒子間距離が小さくなると、トナーの帯電性が悪くなる。したがって、Isoparの場合は、トナー濃度に限界がある。これに対して、本実施例で用いたシリコンオイルは、抵抗値が十分に大きいので、トナー濃度を濃くすることができる。また、一般にIsoparの場合、トナーの分散状態が良く、したがって、トナー濃度が１〜２％でも、トナー同士が反発しあうので、均一にトナーが分散している。これに対して、シリコンオイルは、トナー濃度が１〜２％の場合、分散性が良くなく、じきに沈殿してしまう。しかし、トナー濃度を５〜４０％にすると、密に詰まった状態となり、安定して分散する。このため、本実施例では、トナーが高密度に分散された高粘度の液体現像剤を使用している。これにより、従来の低濃度の液体現像剤に比べて、現像液の液量を大幅に低減することができ、現像装置の小型化を図ることができる。更に、本実施例の液体現像剤は高粘度の液体であるので、保管や取り扱いの点でも、従来の低粘度の液体現像剤や粉体現像剤に比べて容易になる。
【００７３】
従来の液体現像剤で用いていたIsoparは、前述のように、揮発性が高く、しかも悪臭を放つので、作業環境を悪化させるだけでなく、公害を起こすという問題があった。これに対して本実施例で用いているシリコンオイルは、化粧品用として用いられていることからも明らかなように、安全な液体であり、また無臭であるので、本実施例によれば、作業環境を改善することができ、また公害の問題も発生しない。
【００７４】
また、本発明の第一実施例によれば、感光体１０上に離型性を有し化学的に不活性な誘電性液であるプリウェット液２２０塗布するプリウェット装置２０を設けたことにより、感光体１０の非画像部にトナーが付着するのを防止することができる。
【００７５】
次に、本発明の第二実施例について図１３乃至図１６を参照して説明する。
図１３は本発明の第二実施例である画像形成装置の概略構成図、図１４は図１３に示す画像形成装置に用いられるプリウェット装置の概略斜視図、図１５は図１４に示すプリウェット装置の動作を説明するための図、図１６はプリウェット液供給体を感光体１０に当接させたときのプリウェット液の流れを表した図である。尚、第二実施例において第一実施例と同じ機能を有するものについては、同一の符号又は対応する符号を付すことによりその詳細な説明を省略する。
【００７６】
本発明の第二実施例である画像形成装置は、第一実施例の画像形成装置と同様に、いわゆる正規現像を用いたものである。本実施例の画像形成装置２は、図１３に示すように、画像支持体である感光体１０と、感光体１０上にプリウェット液を塗布するプリウェット装置２５と、感光体１０を帯電する帯電装置３０と、感光体１０上に像を露光する露光装置４０と、感光体１０の静電潜像が形成された部分にトナーを供給することにより静電潜像を顕像化する現像装置５５と、感光体１０上に形成されたトナー像を所定の紙に転写する転写装置６０と、感光体１０上に残留したトナーを除去するクリーニング装置７０と、帯電された感光体１０を除電する除電装置８０と、図示されていないが紙に転写されたトナーを定着させる定着装置と、を備えている。
【００７７】
図１３に示す画像形成装置２が図１に示す第一実施例の画像形成装置１と異なる点は、プリウェット装置２０に代えてプリウェット装置２５を用いたこと、および現像装置５０に代えて現像装置５５を用いたことである。したがって、本実施例では、プリウェット装置２５及び現像装置５５について説明し、その他の装置の詳細な説明を省略する。
【００７８】
本実施例のプリウェット装置２５は、図１４に示すように、感光体１０上に描かれる画像幅と略同じ長さを有する板状のプリウェット液供給体２５２と、プリウェット液供給体２５２を収納するケース２５４と、プリウェット液２２０を貯蔵するタンク２５６と、タンク２５６に貯蔵されたプリウェット液２２０を汲み上げるポンプ２５８と、チューブ２６０ａ，２６０ｂと、変位装置２６２と、を備えている。
【００７９】
プリウェット液供給体２５２には、気孔が連続した立体網目構造を有する連続多孔質体、例えばベルイータ（登録商標：カネボウ（株））が用いられる。ベルイータは、気孔の容積分だけプリウェット液２２０を保持することができ、また気孔の容積を越えるプリウェット液２２０が供給されたときには、プリウェット液２２０の流れ方向に対し垂直な方向においてプリウェット液２２０を均一に放出することができる。ケース２５４の感光体１０と対向する面には、図１５に示すように、プリウェット液供給体２５２の底面を感光体１０に当接させることができるように開口部２５４ａが設けられている。チューブ２６０ａは、ポンプ２５８により汲み上げられたプリウェット液２２０をプリウェット液供給体２５２の供給側２５２ａに搬送する。尚、プリウェット液供給体２５２の供給側２５２ａとケース２５４との間には空間部２５４ｂが形成されており、プリウェット液２２０はこの空間部２５４ｂに蓄えられた後、供給側２５２ａから供給される。チューブ２６０ｂは、プリウェット液供給体２５２の放出側２５２ｂから放出されたプリウェット液２２０をタンク２５６に搬送する。変位装置２６２は、外部からの信号が入力されていないときは、図１５（Ａ）に示すように、プリウェット液供給体２５２を感光体１０から離れた位置に保持し、外部からの信号が入力されているときは、図１５（Ｂ）に示すように、プリウェット液供給体２５２を感光体１０に当接する。
【００８０】
本実施例の現像装置５５は、現像剤支持体である現像ベルト５６０と、現像ベルト５６０を回転駆動すると共に現像ベルト５６０の一部を感光体１０に当接するように保持する駆動ローラ５６２ａ，５６２ｂと、現像ベルト５６０の表面に液体現像剤５０８を塗布する現像剤供給装置５７と、電源装置５１１，５１３，５３１と、現像ベルト５６０上の液体現像剤５０８の層厚を測定する層厚測定装置５３と、層厚測定装置５３の結果に基づき電源装置５１１，５１３，５３１を制御する制御装置５４と、現像時に感光体１０から現像ベルト５６０に移動したプリウェット液２２０を回収するプリウェット液回収装置５１と、現像後に現像ベルト５６０上に残留する液体現像剤５０８を回収する現像剤回収装置５８と、を備えている。尚、電源装置５１１，５１３，５３１、制御装置５４及びプリウェット液回収装置５１は、第一実施例のものと同様である。
【００８１】
現像ベルト５６０は、駆動ローラ５６２ａ，５６２ｂによって感光体１０の回転方向と反対方向に回転することにより、感光体１０の表面に現像剤供給装置５７によって供給された液体現像剤５０８を供給する。現像ベルト５６０には、シームレスのニッケルベルトのような金属ベルト、ポリイミドフィルムベルトのような樹脂ベルト等の可撓性を有する部材が用いられる。これにより、現像ベルト５６０のテンションを調節して現像ベルト５６０上に形成された液体現像剤層と感光体１０上に形成されたプリウェット液層とが接触する際の接触圧力を分散させると、液体現像剤層及びプリウェット液層を介して感光体１０と現像ベルト５６０との間にあたかも間隔が形成されたようになる。このため、現像過程において、現像ベルト５６０上に形成された液体現像剤層と感光体１０上に形成されたプリウェット液層とを層同士を区別できるような２層状態を維持しつつ接触させることができる。尚、現像ベルト５６０は、電気的な現像バイアスが印加できるようにするために、電気抵抗値が１０³ Ωｃｍ程度であることが望ましい。したがって、樹脂ベルトを用いる場合には、ベルトの表面を導電加工するか、ベルトの材質に導電性微粒子を添加するなどして電気抵抗値を下げる必要がある。ベルト自体が導電性を有する場合、駆動ローラ５６２ａ，５６２ｂには、現像バイアスを印加できるように導電性微粒子が添加された電気抵抗値の低いゴムローラが用いられる。ベルトの表面に導電加工を施した場合はベルトの表面に接触する導体を配設し、この導体に現像バイアスを印加する。
【００８２】
現像剤供給装置５７は、四つの現像カートリッジ５７ａ，５７ｂ，５７ｃ，５７ｄ（以下、単に現像カートリッジともいう）と、図示されていない離接装置と、を備えている。各現像カートリッジは、現像ベルト５６０の表面に液体現像剤５０８を塗布する塗布ローラ５０６ａ，５０６ｂと、液体現像剤５０８を貯蔵するタンク５５２と、タンク５５２内に貯蔵された液体現像剤５０８を汲み上げる供給ローラ５０２ａと、供給ローラ５０２ａによって供給された液体現像剤５０８を塗布ローラ５０６ａ，５０６ｂに搬送する搬送ローラ５０４と、導電性部材で形成されたバックプレート５０３と、を備えている。尚、供給ローラ５０２ａ、搬送ローラ５０４、塗布ローラ５０６ａ，５０６ｂ及びバックプレート５０３は、第一実施例のものと同様であるのでその詳細な説明を省略する。
【００８３】
現像カートリッジ５７ａのタンク５５２にはイエローのトナーを含む液体現像剤５０８ａが、現像カートリッジ５７ｂのタンク５５２にはマゼンタのトナーを含む液体現像剤５０８ｂが、現像カートリッジ５７ｃのタンク５５２にはシアンのトナーを含む液体現像剤５０８ｃが、そして、現像カートリッジ５７ｄのタンク５５２にはブラックのトナーを含む液体現像剤５０８ｄがそれぞれ貯蔵されている（以下、液体現像剤５０８ａ，５０８ｂ，５０８ｃ，５０８ｄを単に液体現像剤５０８ともいう）。図示されていない離接装置は、各現像カートリッジの塗布ローラ５５６ａ，５５６ｂを現像ベルト５６０に当接させる。
【００８４】
上記構成の現像剤供給装置５７は、図示されていない離接装置によって、いずれかの現像カートリッジの塗布ローラ５０６ａ，５０６ｂを現像ベルト５６０に当接させることにより、現像ベルト５６０の表面に所望の色のトナーを含む液体現像剤５０８を塗布する。
【００８５】
現像剤回収装置５８は、四つの現像剤回収ローラ５８０ａ，５８０ｂ，５８０ｃ，５８０ｄ（以下、単に現像剤回収ローラともいう）が回転軸５８２に取り付けられて構成されている。回転軸５８２は、図示されていない駆動装置により、現像ベルト５６０上にイエローのトナーを含む液体現像剤５０８ａが塗布されているときは現像剤回収ローラ５８０ａを、マゼンタのトナーを含む液体現像剤５０８ｂが塗布されているときは現像剤回収ローラ５８０ｂを、シアンのトナーを含む液体現像剤５０８ｃが塗布されているときは現像剤回収ローラ５８０ｃを、そして、ブラックのトナーを含む液体現像剤５０８ｄが塗布されているときは現像剤回収ローラ５８０ｄを、それぞれ当接するように回転駆動される。
【００８６】
各現像剤回収ローラは現像ベルト５６０の回転方向と反対方向に回転する。また、各現像剤回収ローラは、図１３に示すように、電源装置５８３により回転軸５８２を介してバイアス電圧が印加されている。このバイアス電圧は、現像ベルト５６０と現像ベルト５６０に当接する現像剤回収ローラとの間に生じる電界により、トナーが現像剤回収ローラに対して引力を受けるように設定されている。
【００８７】
上記構成の現像剤回収装置５８は、現像ベルト５６０に塗布されている液体現像剤の色に応じて当接する現像剤回収ローラを切換え、現像後に現像ベルト５６０上に残留する液体現像剤を回収する。
【００８８】
次に、本実施例の画像形成装置２の動作について説明する。
先ず、帯電装置３０によって感光体１０の表面を帯電し、その後、露光装置４０により帯電した感光体１０上に反転像を露光する。
【００８９】
次に、プリウェット装置２５により感光体１０上にプリウェット液２２０を塗布する。プリウェット装置２５は、外部からの信号が入力されるとプリウェット液供給体２５２を感光体１０に当接する。プリウェット液供給体２５２の内部には、ポンプ２５８によりプリウェット液２２０が常時循環しており、プリウェット液供給体２５２であるベルイータの気孔の容積を越えるプリウェット液２２０は、図１６に示すように、プリウェット液供給体２５２の放出側２５２ｂから放出されると共にプリウェット液供給体２５２の底面から放出され、感光体１０に傷を付けることなく感光体１０上に均一に塗布される。
【００９０】
次に、現像装置５５により静電潜像を顕像化する。タンク５５２に貯蔵された液体現像剤５０８は、供給ローラ５０２ａにより搬送ローラ５０４に供給される。搬送ローラ５０４に供給された液体現像剤５０８は、塗布ローラ５０６ａ，５０６ｂに搬送された後、現像ベルト５６０に塗布される。このように、複数のローラを介して液体現像剤５０８を塗布することにより、現像ベルト５６０上に均一で薄層の液体現像剤層を形成する。また、供給ローラ５０２ａ、搬送ローラ５０４及び塗布ローラ５０６ａ，５０６ｂは、それぞれ電源装置５１３、電源装置５１１及び電源装置５３１によりバイアス電圧が印加される。これにより、液体現像剤５０８の現像ベルト５６０への供給量を調節している。尚、図示されていない離接装置により、現像ベルト５６０にいずれかの現像カートリッジの塗布ローラ５０６ａ，５０６ｂを当接させることにより、イエロー、マゼンダ、シアン及びブラックのいずれかのトナーを含む液体現像剤５０８を現像ベルト５６０に塗布することができる。
【００９１】
次に、このようにして現像ベルト５６０上に形成された液体現像剤層を感光体１０の表面に形成された静電潜像に近接させて、静電気力により、帯電したトナーを感光体１０上に移動させ、トナー像を形成する。尚、現像時に感光体１０から現像ベルト５６０に移動したプリウェット液２２０はプリウェット液回収装置５１により回収される。また、現像後に現像ベルト５６０上に残留する液体現像剤５０８は現像剤回収装置５８により各色毎に回収される。
【００９２】
次に、転写装置６０により感光体１０上に形成されたトナー像を中間転写ドラム６０２上に一次転写する。感光体１０上に形成されたトナー像は、感光体１０上に形成されたトナー像と電源装置６０８によりトナーと反対の極性を有する電荷で帯電した中間転写ドラム６０２との間に生じる静電気力により、中間転写ドラム６０２上に移動し一次転写される。一方、感光体１０は、クリーニング装置７０により感光体１０上に残留した液体現像剤５０８が除去され、その後、除電装置８０により除電される。そして、図示されていない離接装置により、現像ベルト５６０に当接する塗布ローラ５０６ａ，５０６ｂが切り換えられ、再び上記の帯電から除電までのサイクルを繰り返すことにより、中間転写ドラム６０２上にイエロー、マゼンダ、シアン及びブラックのトナー像を次々と重ねて一次転写する。これにより、中間転写ドラム６０２上にカラー化に対応したトナー像を形成する。
【００９３】
次に、転写装置６０により中間転写ドラム６０２上に形成されたカラー化に対応したトナー像を記録媒体である紙に二次転写する。中間転写ドラム６０２上に形成されたカラー化に対応したトナー像は、二次転写ローラ６０４の中間転写ドラム６０２への押圧力及び二次転写ローラ６０４に印加された二次転写バイアスによって生じる静電気力により、中間転写ドラム６０２と二次転写ローラ６０４との間に送り込まれた紙に二次転写される。そして、図示されていない定着装置により、紙上に定着する。これにより、紙上にカラー画像を形成することができる。
【００９４】
本発明の第二実施例によれば、感光体１０上に形成されたトナー像を中間転写ドラム６０２上に一次転写するという工程をイエロー、マゼンダ、シアン及びブラックの各色毎に順次行うことにより中間転写ドラム６０２上にカラー化に対応したトナー像を形成し、その後、中間転写ドラム６０２上に形成されたカラー化に対応したトナー像を記録媒体に二次転写するので、感光体上に形成されたトナー像を直接紙に順次転写する場合に比べて、紙のずれ等を考慮する必要がなく、したがって、紙に転写されるカラー画像のレジストレーションを合わせるのが容易になる。その他の効果は第一実施例のものと同様である。
【００９５】
尚、上記の第一実施例及び第二実施例では、画像支持体をトナーと反対の極性を有する電荷で帯電し、その後、画像支持体に光を当てて反転像を露光し、光が当たらなかった部分、即ち導電化していない部分に可視像化すべき静電潜像を形成する、いわゆる正規現像を用いたものについて説明したが、本発明はこれに限定されるものではなく、画像支持体をトナーと同じの極性を有する電荷で帯電し、その後、画像支持体に光を当てて正規像を露光し、画像支持体の光が当たった部分に可視像化すべき潜像を形成する、いわゆる反転現像を用いたものでもよい。本発明者等は、反転現像を適用した装置において、プラスに帯電したトナーを用い、現像バイアス電圧を５００Ｖに設定したところ、各ローラに印加するバイアス電圧と液体現像剤のコーティング量との間に表３に示す関係があることを確認した。ここで、Ｖ₁ は塗布ローラ５０６ａ，５０６ｂに印加するバイアス電圧を、Ｖ₂ は搬送ローラ５０４に印加するバイアス電圧を、Ｖ₃ は供給ローラ５０２ａに印加するバイアス電圧を、Ｖ_P はバックプレート５０３の電圧を表している。
【００９６】
【表３】

【００９７】
次に、本発明の第三実施例について図１７及び図１８を参照して説明する。
図１７は本発明の第三実施例である画像形成装置の概略構成図、図１８は現像バイアス電圧の印加と塗布ローラの離接のタイミングを表した図である。尚、第三実施例において第二実施例と同じ機能を有するものについては、同一の符号又は対応する符号を付すことによりその詳細な説明を省略する。
【００９８】
本発明の第三実施例である画像形成装置は、画像支持体をトナーと同じ極性を有する電荷で帯電し、その後、画像支持体に光を当てて正規像を露光し、画像支持体の光が当たった部分に可視像化すべき像を形成する、いわゆる反転現像を用いたものである。本実施例の画像形成装置３が図１３に示す第二実施例の画像形成装置２と異なる点は、感光体１０をトナーと反対の極性を有する電荷で帯電する帯電装置３０に代えて感光体１０をトナーと同じ極性を有する電荷で帯電する帯電装置３０ａを用いたこと及び現像装置５５に代えて現像装置５５ａを用いたことである。その他の構成は第二実施例のものと同様であるのでその詳細な説明を省略する。
【００９９】
本実施例の現像装置５５ａが第二実施例の現像装置５５と異なる点は、図１７に示すように、現像ベルト５６０の感光体１０との接触点Ｐから現像カートリッジ５７ｄの塗布ローラ５０６ａとの接触点Ｑまでの長さＬを感光体１０に形成され得る潜像の長さの最大値より長くしたこと、および現像時にのみ現像バイアス電圧を現像ベルト５６０に印加するようにしたことである。本実施例では、液体現像剤にプラスに帯電したトナーを用い、現像バイアス電圧を５００Ｖに設定した。
【０１００】
上記構成の現像装置５５ａにおける現像バイアス電圧の印加及び塗布ローラ５０６ａ，５０６ｂの離接のタイミングについて図１８を参照して説明する。ここで、Ｖ_B は現像バイアス電圧、Ｒ₁ は現像カートリッジ５７ａの塗布ローラ５０６ａ，５０６ｂ、Ｒ₂ は現像カートリッジ５７ｂの塗布ローラ５０６ａ，５０６ｂ、Ｒ₃ は現像カートリッジ５７ｃの塗布ローラ５０６ａ，５０６ｂ、そして、Ｒ₄ は現像カートリッジ５７ｄの塗布ローラ５０６ａ，５０６ｂを表している。また、Ｒ₁ 〜Ｒ₄ において、ハイは現像ベルト５６０に当接している状態を、ローは現像ベルト５６０から離れている状態を表している。本実施例の現像装置５５ａは、図１８に示すように、現像時にのみ現像バイアス電圧（５００Ｖ）を印加するようにすると共に、塗布ローラ５０６ａ，５０６ｂによる液体現像剤５０８の現像ベルト５６０への供給は、現像工程に先立って、即ち現像ベルト５６０に現像バイアス電圧が印加されていないときに行うようにしている。これは、液体現像剤５０８の現像ベルト５６０への塗布が現像ベルト５６０に印加されたトナーと同じ極性を有する現像バイアス電圧によって妨害されるのを防止するためである。尚、本実施例の現像装置５５ａでは、上述したように、現像ベルト５６０の感光体１０との接触点Ｐから現像カートリッジ５７ｄの塗布ローラ５０６ａとの接触点Ｑまでの長さＬを感光体１０に形成され得る潜像の長さの最大値より長くしてあるので、現像バイアス電圧の印加及び塗布ローラ５０６ａ，５０６ｂの離接のタイミングを図１８に示すようにしても、感光体１０の潜像面に必要な量の液体現像剤５０８を供給することができる。
【０１０１】
本実施例の画像形成装置３の動作は、第二実施例の画像形成装置２が正規現像を用いているのに対し、本実施例の画像形成装置３が反転現像を用いている点を除いては、基本的に第二実施例の画像形成装置２と同様である。したがって、本実施例の画像形成装置３の動作の詳細な説明を省略する。
【０１０２】
本発明の第三実施例によれば、現像ベルト５６０の感光体１０との接触点Ｐから現像カートリッジ５７ｄの塗布ローラ５０６ａとの接触点Ｑまでの長さＬを感光体１０に形成され得る潜像の長さの最大値より長くすると共に、現像時にのみ現像バイアス電圧を印加するようにしたことにより、液体現像剤５０８の現像ベルト５６０への塗布が現像ベルト５６０に印加されたトナーと同じ極性を有する現像バイアス電圧によって妨害されるのを防止することができる。これにより、塗布ローラ５０６ａ，５０６ｂ、搬送ローラ５０４及び供給ローラ５０２ａに印加するバイアス電圧の絶対値を小さくすることができるので、簡易な構成によって液体現像剤５０８の現像ベルト５６０への供給量を調節することができる。その他の効果は第二実施例のものと同様である。
【０１０３】
尚、上記の第一実施例乃至第三実施例では、供給ローラ５０２ａ，搬送ローラ５０４及び塗布ローラ５０６ａ，５０６ｂにバイアス電圧を印加して液体現像剤５０８の現像剤支持体への供給量を調節するものについて説明したが、本発明はこれに限定されるものではない。これ等のローラのうち少なくとも１つにバイアス電圧を印加することにより、液体現像剤５０８の現像剤支持体への供給量を調節するものであればよい。たとえば、供給ローラ５０２ａにのみバイアス電圧を印加するものであってもよい。
【０１０４】
次に、本発明の第四実施例について図１９を参照して説明する。
図１９は本発明の第四実施例である画像形成装置の概略構成図である。尚、第四実施例において第二実施例と同じ機能を有するものについては、同一の符号又は対応する符号を付すことによりその詳細な説明を省略する。
【０１０５】
本発明の第四実施例である画像形成装置は、第三実施例の画像形成装置と同様に、いわゆる反転現像を用いたものである。本実施例の画像形成装置４が図１３に示す第二実施例の画像形成装置２と異なる点は、感光体１０をトナーと反対の極性を有する電荷で帯電する帯電装置３０に代えて感光体１０をトナーと同じ極性を有する電荷で帯電する帯電装置３０ａを用いたこと及び現像装置５５に代えて現像装置５５ｂを用いたことである。その他の構成は第二実施例のものと同様であるのでその詳細な説明を省略する。
【０１０６】
本実施例の現像装置５５ｂが第二実施例の現像装置５５と異なる点は、図１９に示すように、塗布ローラ５０６ａ，５０６ｂ、搬送ローラ５０４、バックプレート５０３、タンク５５２及び供給ローラ５０２ａにバイアス電圧を印加する電源装置５１３のアース端子を現像ベルト５６０と等電位にしたことである。これは、液体現像剤５０８の現像ベルト５６０への塗布が現像ベルト５６０に印加されたトナーと同じ極性を有する現像バイアス電圧によって妨害されるのを防止するためである。尚、本実施例では、第三実施例装置と同様に液体現像剤にプラスに帯電したトナーを用い、現像バイアス電圧を５００Ｖに設定した。
【０１０７】
本実施例の画像形成装置４の動作は、第二実施例の画像形成装置２が正規現像を用いているのに対し、本実施例の画像形成装置４が反転現像を用いている点を除いては、基本的に第二実施例の画像形成装置２と同様である。したがって、本実施例の画像形成装置４の動作の詳細な説明を省略する。
【０１０８】
本発明の第四実施例によれば、塗布ローラ５０６ａ，５０６ｂと搬送ローラ５０４とを現像ベルト５６０と等電位にしたことにより、液体現像剤５０８の現像ベルト５６０への塗布が現像ベルト５６０に印加されたトナーと同じ極性を有する現像バイアス電圧によって妨害されるのを防止することができる。その他の効果は第二実施例のものと同様である。
【０１０９】
尚、上記の第四実施例では、塗布ローラ５０６ａ，５０６ｂと搬送ローラ５０４とを現像ベルト５６０と等電位にしたものについて説明したが、本発明はこれに限定されるものではなく、バイアス電圧が印加されていないローラを現像ベルト５６０と等電位にしたものであればよい。たとえば、搬送ローラ５０４にバイアス電圧を印加するときは、塗布ローラ５０６ａ，５０６ｂと供給ローラ５０２ａとを現像ベルト５６０と等電位にしたものであればよい。
【０１１０】
また、上記の第二実施例乃至第四実施例では、現像剤供給装置として、現像ベルト５６０上にイエローのトナーを含む液体現像剤５０８ａを塗布する現像カートリッジ５７ａと、マゼンダのトナーを含む液体現像剤５０８ｂを塗布する現像カートリッジ５７ｂと、シアンのトナーを含む液体現像剤５０８ｃを塗布する現像カートリッジ５７ｃと、ブラックのトナーを含む液体現像剤５０８ｄを塗布する現像カートリッジ５７ｄと、を設けたものについて説明したが、本発明はこれに限定されるものではない。現像剤供給装置は、現像剤支持体に所望の色のトナーを含む液体現像剤を塗布する現像カートリッジを必要に応じて二個又は三個設けたものであってもよい。この場合、現像剤回収装置が備える現像剤回収ローラの数も、現像カートリッジの数に応じたものとすればよい。
【０１１１】
本発明は、上記の各実施例に限定されるものではなく、その要旨の範囲内で数々の変形が可能である。たとえば、上記の各実施例では、画像支持体として有機感光体を用いた場合について説明したが、本発明はこれに限定されるものではなく、画像支持体は、カールソン法で用いる各種感光体あるいはイオノグラフィ等の静電潜像を直接形成する導体上に絶縁体層を形成したもの、静電プロッタで用いるような静電記録紙でもよい。
【０１１２】
また、上記の各実施例では、露光装置により画像支持体上に像を露光し、その後、プリウェット装置により画像支持体上にプリウェット液を塗布するものについて説明したが、本発明はこれに限定されるものではなく、プリウェット液の塗布は、現像工程に先立って行われるものであればよい。たとえば、プリウェット装置により画像支持体上にプリウェット液を塗布し、その後、露光装置により画像支持体上に像を露光するものであってもよい。また、プリウェット装置は、上記の各実施例で用いたものに限定されるものではなく、一定の量のプリウェット液を感光体の表面に均一に塗布することができるものであればよい。たとえば、軸方向に並んだ複数のノズルからプリウェット液を吐出させることにより塗布するもの、スポンジローラ等により塗布するもの等でもよい。また、プリウェット液の粘度が０．５〜５ｍＰａ・ｓ、電気抵抗が１０¹²Ωｃｍ以上、沸点が１００〜２５０℃、表面張力が２１ｄｙｎ／ｃｍ以下であれば、プリウェット液はシリコンを主成分とするものでなくてもよい。さらに、画像支持体の表面に離型性を有する材料をコーティングした場合、特にプリウェット装置を必要とするものではない。
【０１１３】
また、上記の各実施例では、現像装置における液体現像剤の現像剤支持体への供給として、供給ローラ、搬送ローラ及び塗布ローラを介して現像剤支持体上に液体現像剤を塗布するものについて説明したが、本発明はこれに限定されるものではなく、現像装置は少なくとも２つのローラを介して現像剤支持体上に液体現像剤を塗布するものであればよい。たとえば、供給ローラと塗布ローラとの間に２個以上の搬送ローラを設けてもよいし、また、搬送ローラを設けることなく供給ローラによって汲み上げられた液体現像剤を直接塗布ローラに供給するものであってもよい。また、液体現像剤を貯蔵するタンクに必ずしもバックプレートを内設する必要はない。さらに、現像剤支持体は、上記の各実施例で用いたものに限定されるものではなく、金属等の導電性を有する剛体で形成されたものでもよい。但し、剛体で形成された現像ローラを用いる場合、現像ローラ上に形成された液体現像剤層と感光体上に形成されたプリウェット液層とを２層状態を維持しつつ接触させるため、感光体に可撓性を有するベルト状部材で形成されたものを用いるか、または、現像ローラと感光体ドラムとの間に微小なギャップ即ち間隔ｄを形成するようにして現像ローラを設置する必要がある。
【０１１４】
さらに、上記の各実施例では、転写装置における一次転写として、電源装置６０８によって中間転写ドラム６０２をトナーと反対の極性を有する電荷で帯電することにより、感光体１０上に形成されたトナー像を中間転写ドラム６０２上に一次転写するものについて説明したが、本発明はこれに限定されるものではない。転写装置は、たとえば、コロナ放電器により中間転写体をトナーと反対の極性を有する電荷で帯電するようにしたものであってもよい。また、上記の各実施例では、転写装置における二次転写として、二次転写ローラ６０４の中間転写ドラム６０２への押圧力及び二次転写ローラ６０４に印加されたバイアス電圧によって生じる静電気力により、中間転写ドラム６０２上のトナー像を紙に二次転写するものについて説明したが、本発明はこれに限定されるものではない。転写装置は、中間転写体上のトナー像を紙に二次転写することができるものであればよい。たとえば、二次転写体の内部に定着ヒータを設け、中間転写体上のトナーを加熱した場合、中間転写体上のトナー像を紙に二次転写すると同時に定着することができる。
【０１１５】
また、上記の各実施例では、クリーニング装置として、トナーと反対の極性を有する電荷で帯電された除去ローラ７０２を用いたものについて説明したが、本発明はこれに限定されない。クリーニング装置は、感光体上に残留するトナーを除去することができるものであればよく、例えば、感光体上に残留するトナーをブレード等を用いて掻き取るものでもよい。
【０１１６】
また、本発明は上記の各実施例に限定されるものではなく、液体現像剤の層厚が５〜４０μｍであれば、高粘性現像剤の粘度は１００００ｍＰａ・ｓであっても良い。現状では、６０００ｍＰａ・ｓ以上の高粘度の現像剤は、キャリア液とトナーとの攪拌が難しくなるので、コスト的にあわなくなると考えるが、安価に入手できるようになれば、６０００ｍＰａ・ｓ以上でもよい。粘度が１００００ｍＰａ・ｓを越えるものは、現実的でなくなる。また、液体現像剤のキャリア液はシリコンオイルに限定されない。
【０１１７】
【発明の効果】
以上説明したように本発明の静電潜像の液体現像装置によれば、複数のローラを介して現像剤支持体上に高濃度高粘性の液体現像剤を塗布する塗布手段を設けたことにより、各ローラ上の液体現像剤の層厚は隣合うローラとの当接部で薄く均一に規制されるので、現像剤支持体上に高濃度高粘性の液体現像剤を薄く均一に塗布することができ、また複数のローラのうち少なくとも一つのローラに電圧を印加する電圧印加手段を設けたことにより、帯電したトナーと電圧が印加されたローラとの間に働く静電気力によって液体現像剤の現像剤支持体への搬送量を調節することができ、したがって、これ等により所望の液量を液体現像剤を画像支持体の潜像面に均一に供給することができ、また、トナーが高濃度に分散された液体現像剤を薄層にして現像することにより、高解像度で且つ小型化が容易で、しかも低公害化が可能な静電潜像の液体現像装置を提供することができる。
【０１１８】
本発明の他の静電潜像の液体現像装置によれば、高濃度高粘性の液体現像剤を現像剤支持体に当接して現像剤支持体上に塗布する複数のローラを設けたことにより、液体現像剤の粘性とトナーの分散性との影響により現像剤支持体上の液体現像剤層に濃淡のムラができるのを防止することができ、これにより、現像剤支持体上に高濃度高粘性の液体現像剤を薄く均一に塗布することができ、したがって、画像支持体の潜像面に液体現像剤を均一に供給することができ、また、トナーが高濃度に分散された液体現像剤を薄層にして現像することにより、高解像度で且つ小型化が容易で、しかも低公害化が可能な静電潜像の液体現像装置を提供することができる。
【図面の簡単な説明】
【図１】本発明の第一実施例である画像形成装置の概略構成図である。
【図２】図１に示す画像形成装置に用いられる現像装置の概略構成図である。
【図３】図２に示す現像装置の動作を説明するための図である。
【図４】図１に示す画像形成装置の動作を説明するための図である。
【図５】現像過程の全体を説明するための図である。
【図６】接近過程のようすを示す図である。
【図７】トナー移動過程のようすを示す図である。
【図８】非画像部の分離過程を示す図である。
【図９】画像部の分離過程を示す図である。
【図１０】液体現像剤を薄層化したことの意義を説明するための図である。
【図１１】現像ローラと感光体とをハードコンタクトさせたようすを示す図である。
【図１２】本発明のソフトコンタクトを説明するための図である。
【図１３】本発明の第二実施例である画像形成装置の概略構成図である。
【図１４】図１３に示す画像形成装置に用いられるプリウェット装置の概略斜視図である。
【図１５】図１４に示すプリウェット装置の動作を説明するための図である。
【図１６】プリウェット液供給体を感光体に当接させたときのプリウェット液の流れを表した図である。
【図１７】本発明の第三実施例である画像形成装置の概略構成図である。
【図１８】現像バイアス電圧の印加と塗布ローラの離接のタイミングを表した図である。
【図１９】本発明の第四実施例である画像形成装置の概略構成図である。
【符号の説明】
１，２，３，４ 画像形成装置
１０ 感光体
２０，２５ プリウェット装置
３０，３０ａ 帯電装置
４０ 露光装置
５０，５５，５５ａ，５５ｂ 現像装置
５１ プリウェット液回収装置
５２，５８ 現像剤回収装置
５３ 層厚測定装置
５４ 制御装置
５７ 現像剤供給装置
５７ａ，５７ｂ，５７ｃ，５７ｄ 現像カートリッジ
６０ 転写装置
７０ クリーニング装置
８０ 除電装置
２０２，２５６，５０２，５５２ タンク
２０２ａ，５０２ａ 供給ローラ
２０４，５０４ 搬送ローラ
２０６，５０６ａ，５０６ｂ 塗布ローラ
２２０ プリウェット液
２５２ プリウェット液供給体
２５４ ケース
２５８ ポンプ
２６０ａ，２６０ｂ チューブ
２６２ 変位装置
３０２ 遮光板
５０３ バックプレート
５０８，５０８ａ，５０８ｂ，５０８ｃ，５０８ｄ，５０９ 液体現像剤
５１０ 現像ローラ
５１２ プリウェット液回収ローラ
５１１，５１３，５１５，５１７，５１９，５３１，５８３，６０８，６１２，６１４，７０４ 電源装置
５１４，５８０ａ，５８０ｂ，５８０ｃ，５８０ｄ 現像剤回収ローラ
５２０ 掻き取りブレード
５２２，５２４ 回収タンク
５２８ 濃度測定装置
５３０ 濃度調整装置
５６０ 現像ベルト
５６２ａ，５６２ｂ 駆動ローラ
５８２ 回転軸
６０２ 中間転写ドラム
６０４ 二次転写ローラ
６０６，７０２ 除去ローラ
６２０ 定着装置
６２２ 定着ローラ
６２４ 定着ヒータ[0001]
[Industrial application fields]
The present invention relates to an electrostatic latent image liquid developing apparatus and a liquid developing method for visualizing an electrostatic latent image formed by a method such as electrophotography, electrostatic recording, or ionography using a liquid developer. Is.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, in an electrostatic latent image liquid developing apparatus that develops an electrostatic latent image formed on an image support with toner, which is a charged visualization particle, a liquid developer is formed on the latent image surface on the image support. Are provided on the surface of the developing roller, which is a developer support, and a liquid developer is held in the recess and supplied to the image support. A sponge roller is used as the developer support. A method of supplying the liquid developer absorbed by the sponge roller to the image support by pressing the image support on the image support, or a developer by immersing the image support in a developer tank in which the liquid developer is stored A method of supplying a liquid developer directly to an image support without using a support is used.
[0003]
[Problems to be solved by the invention]
By the way, a conventional electrostatic recording apparatus or the like generally uses a low-viscosity liquid developer obtained by mixing toner in an organic solvent IsoparG (registered trademark: manufactured by Exxon) at a ratio of about 1 to 2%. However, in order to suppress the generation of solvent vapor and realize a safer and more compact liquid developing apparatus, it is necessary to use a highly viscous liquid developer having a higher concentration than the liquid developer used in the conventional apparatus. Although desirable, no such device has been found in the past. Therefore, when such a high-concentration and high-viscosity liquid developer is used, it is not clear what method is suitable as a method for supplying the liquid developer to the latent image surface of the image support.
[0004]
【the purpose】
The present invention has been made based on the above circumstances, and provides a liquid developing apparatus and a liquid developing method for an electrostatic latent image that can uniformly supply a liquid developer to the latent image surface of an image support. It is the purpose.
[0005]
[Means for Solving the Problems]
In order to achieve the above object, an electrostatic latent image liquid developing apparatus according to the present invention develops an electrostatic latent image developed with toner, which is a visualized particle charged with an electrostatic latent image formed on an image support. A liquid developing apparatus, comprising: a developer support; a liquid developer having a high viscosity of 100 to 10,000 mPa · s in which a toner is dispersed in a high concentration in an insulating liquid on the developer support; and a plurality of rollers. And applying means for applying a voltage to at least one of the plurality of rollers, and applying the liquid developer applied on the developer support to the image support. Development means for supplying to the latent image surface The developing means further includes a layer thickness measuring means for measuring a layer thickness of the liquid developer applied on the developer support, and the voltage based on the layer thickness measured by the layer thickness measuring means. Comprising control means for controlling the application means; It is characterized by that.
[0007]
[Action]
The electrostatic latent image liquid developing device of the present invention is provided with a coating means for applying a high-concentration and high-viscosity liquid developer on a developer support through a plurality of rollers, thereby developing liquid on each roller. Since the layer thickness of the agent is thinly and uniformly regulated at the contact portion with the adjacent roller, the high-concentration and high-viscosity liquid developer can be applied thinly and uniformly on the developer support. Further, by providing a voltage applying means for applying a voltage to at least one of the plurality of rollers, the developer support of the liquid developer is supported by an electrostatic force acting between the charged toner and the voltage-applied roller. The conveyance amount to the body, that is, the layer thickness of the liquid developer on the developer support can be adjusted. Furthermore, the electrostatic latent image liquid developing device of the present invention develops a liquid developer in which toner is dispersed at a high concentration in a thin layer, so that the amount of liquid is smaller than that of a conventional low concentration liquid developer. Can be much less. When the viscosity of the liquid developer is 10,000 mPa · s or more, it becomes difficult to stir the insulating liquid and the toner, and how to make the liquid developer becomes a problem. Therefore, a liquid developer of 10,000 mPa · s or more is not cost-effective and is not realistic. On the other hand, at 100 mPa · s or less, the toner density is lowered and the dispersibility of the toner is deteriorated, so that it is impossible to develop the developer in a thin layer. The layer thickness of the liquid developer layer on the developer support needs to be thin when the toner concentration is high and thick when it is low. Also, the higher the viscosity, the thinner it is necessary. However, if the layer thickness is greater than 40 μm, excessive adhesion of toner occurs and image noise occurs. On the other hand, if the layer thickness is less than 5 μm, unevenness occurs when a solid black image is output.
[0008]
Further, another electrostatic latent image liquid developing apparatus of the present invention is provided with a plurality of rollers for applying a high density and high viscosity liquid developer to the developer support in contact with the developer support. Further, it is possible to form a more uniform liquid developer layer on the developing belt by densely applying unevenness (ripple) caused by the viscosity of the liquid developer and the dispersibility of the toner. Further, by developing a thin layer of a liquid developer in which toner is dispersed at a high concentration, the amount of liquid is similar to that of a conventional low-concentration liquid developer, similar to the electrostatic latent image liquid developing device of the present invention. It can be much less than that.
[0009]
In the above-described electrostatic latent image liquid developing apparatus, the insulating liquid has a viscosity of 0.5 to 1000 mPa · s and an electric resistance of 10 ¹² When a liquid developer having an Ωcm or higher, a surface tension of 21 dyn / cm or lower, and a boiling point of 100 ° C. or higher is used, a high viscosity liquid developer can be obtained. Since the liquid developer formed on the developer support is formed in a thin layer, the amount of the insulating liquid contained in the liquid developer adhering to the latent image surface of the image support is very small. Accordingly, the amount of insulating liquid absorbed by the paper or the like at the time of transfer is extremely small, so that the problem of adhesion of the insulating liquid to the paper or the like does not particularly occur if the viscosity is 1000 mPa · s or less. However, if the viscosity is 0.5 mPa · s or less, the volatility becomes high, and it is not suitable because it is handled as a dangerous substance. If the boiling point of the insulating liquid is 100 ° C. or less, the amount of evaporation increases, so there is a problem in the storage method of the developer, the entire apparatus must be sealed, and it is difficult to improve the working environment. . Electrical resistance is 10 ¹² If it is less than Ωcm, the insulating properties are deteriorated, and the toner has a problem of electrical conductivity and cannot be used as a developer. Therefore, it is desirable that the electric resistance is as high as possible. When the surface tension is 21 dyn / cm or more, the wettability is deteriorated. Therefore, the surface tension is desirably as low as possible.
[0010]
Further, when the liquid developer contains toner having an average particle diameter of 0.1 to 5 μm at a concentration of 5 to 40%, a liquid developer in which the toner is dispersed at a high concentration in an insulating liquid can be obtained. it can. Further, the resolution is improved substantially in inverse proportion to the particle size of the toner. Usually, the toner is present in a mass of about 5 to 10 on the printed paper, and therefore, when the average particle size of the toner is 5 μm or more, the resolution is deteriorated. On the other hand, when the average particle size of the toner is 0.1 μm or less, the physical adhesive force increases, and it becomes difficult to remove the toner during transfer.
[0011]
【Example】
The first embodiment of the present invention will be described below with reference to FIGS.
1 is a schematic configuration diagram of an image forming apparatus according to a first embodiment of the present invention, FIG. 2 is a schematic configuration diagram of a developing device used in the image forming apparatus shown in FIG. 1, and FIG. 3 is a schematic diagram of the developing device shown in FIG. FIG. 4 is a diagram for explaining the operation, and FIG. 4 is a diagram for explaining the operation of the image forming apparatus shown in FIG.
[0012]
In the image forming apparatus according to the first embodiment of the present invention, the image support is charged with a charge having a polarity opposite to that of the toner, and then the image support is exposed to light to expose the reverse image. In other words, a so-called regular development is used in which an electrostatic latent image to be visualized is formed on a portion that is not electrically conductive. As shown in FIG. 1, an image forming apparatus 1 according to the present embodiment includes a photosensitive drum (hereinafter also referred to as a photosensitive member) 10 that is an image support, and a prewetting apparatus that applies a prewetting liquid onto the photosensitive member 10. 20, a charging device 30 for charging the photoconductor 10, an exposure device 40 for exposing an image on the photoconductor 10, and electrostatically supplying toner to a portion of the photoconductor 10 where an electrostatic latent image is formed. A developing device 50 that visualizes a latent image, a transfer device 60 that transfers a toner image formed on the photoconductor 10 to a predetermined paper, a cleaning device 70 that removes toner remaining on the photoconductor 10, A neutralizing device 80 for neutralizing the charged photoreceptor 10 and a fixing device (not shown) for fixing the toner image transferred to the paper are provided. In order to prevent the charging device 30 from being affected by the static eliminator 80, a light shielding plate 302 is attached to the side surface on the side where the static eliminator 80 is installed.
[0013]
For the photoconductor 10, the charging device 30, the exposure device 40, the static eliminator 80, and the fixing device, the prior art used in the conventional electronic printer can be used in most cases. Therefore, the description of each of the above devices is omitted, and the pre-wet device 20, the developing device 50, the transfer device 60, and the cleaning device 70, which are main parts of the present embodiment, will be described below.
[0014]
As shown in FIG. 1, the pre-wet apparatus 20 of the present embodiment is provided with a tank 202 for storing a pre-wet liquid 220 to be described later, and a supply partly immersed in the pre-wet liquid 220 in the tank 202. A roller 202a, a conveyance roller 204 provided so as to be in contact with the supply roller 202a, and an application roller 206 provided so as to be in contact with the conveyance roller 204 and the photosensitive member 10 are provided.
[0015]
The supply roller 202 a rotates in the direction opposite to the rotation direction of the transport roller 204 to supply the pre-wet liquid 220 stored in the tank 202 to the transport roller 204. The conveyance roller 204 conveys the pre-wet liquid 220 supplied by the supply roller 202 a to the application roller 206 by rotating in the direction opposite to the rotation direction of the application roller 206. The application roller 206 applies the pre-wet liquid 220 to the surface of the photoconductor 10 by rotating in the direction opposite to the rotation direction of the photoconductor 10. Thereby, a thin pre-wet liquid layer is formed on the photoreceptor 10. The roller was used for supplying the pre-wet liquid 220 to the photoconductor 10 even when the photoconductor 10 was rotated at a higher speed than before, by increasing the rotation speed of the roller, a desired amount of the pre-wet liquid 220 was supplied. This is because the toner can be supplied to the surface of the photoreceptor 10. Thereby, it can respond to a high-speed image output. The number of transport rollers 204 provided between the supply roller 202a and the application roller 206 is not limited to one, and a plurality of transport rollers 204 may be provided. Further, when the pre-wet liquid 220 can be applied thinly and uniformly on the surface of the photoconductor 10, the transport roller 204 may not be provided separately.
[0016]
In order to apply the pre-wet liquid 220 thinly and uniformly on the surface of the photoconductor 10, it is desirable to use a material having good lipophilicity for the supply roller 202a, the conveyance roller 204, and the application roller 206. Examples of highly oleophilic rollers include ceramic rollers (manufactured by Nippon Steel Co., Ltd.) with special surface treatment applied to ceramics mainly composed of alumina and titania, and BEET (manufactured by Miyagawa Roller) made of synthetic resin. is there.
[0017]
As shown in FIG. 2, the developing device 50 of the present embodiment includes a developing roller 510 that is a developer support, application rollers 506 a and 506 b that apply a liquid developer 508 to be described later on the surface of the developing roller 510, and a liquid A tank 502 that stores the developer 508, a supply roller 502a that pumps up the liquid developer 508 stored in the tank 502, and a transport roller that transports the liquid developer 508 supplied by the supply roller 502a to the coating rollers 506a and 506b. 504, a back plate 503 formed of a conductive member, a power supply device 513 that applies a voltage to the supply roller 502a, a power supply device 511 that applies a voltage to the transport roller 504, and a voltage to the coating rollers 506a and 506b And a layer for measuring the layer thickness of the liquid developer 508 on the developing roller 510 The control device 54 that controls the power supply devices 511, 513, and 531 based on the results of the measurement device 53, the layer thickness measurement device 53, and the pre-wet liquid that collects the pre-wet liquid 220 that has moved from the photoconductor 10 to the developing roller 510 during development. A liquid recovery device 51 and a developer recovery device 52 that recovers the liquid developer 508 remaining on the developing roller 510 after development are provided.
[0018]
The developing roller 510 is installed in contact with the photosensitive member 10, and is applied to the latent image surface of the photosensitive member 10 by the application rollers 506 a and 506 b by rotating in the direction opposite to the rotating direction of the photosensitive member 10. A liquid developer 508 is supplied. The developing roller 510 includes a cored bar formed of a rigid body such as stainless steel, an elastic layer formed around the cored bar, and a surface layer formed on the surface of the elastic layer. Therefore, the contact when the liquid developer layer formed on the developing roller 510 comes into contact with the pre-wet liquid layer formed on the photosensitive member 10 by adjusting the pressing force of the developing roller 510 to the photosensitive member 10. When the pressure is dispersed, an interval is formed between the photosensitive member 10 and the developing roller 510 via the liquid developer layer and the pre-wet liquid layer. Thereby, the liquid developer layer formed on the developing roller 510 and the pre-wet liquid layer formed on the photoreceptor 10 can be brought into contact with each other while maintaining a two-layer state in which the layers can be distinguished from each other. The hardness of the developing roller 510 is desirably 5 to 60 degrees JIS-A. When the hardness is 5 degrees JIS-A or lower, it is too soft to maintain a certain shape. On the other hand, if the hardness is 60 degrees JIS-A or higher, it is too hard, so that the liquid developer layer on the developing roller 510 and the pre-wet liquid layer on the photoreceptor 10 are brought into contact with each other while maintaining the two-layer state. Therefore, it is necessary to install the developing roller 510 so that a gap is formed between the developing roller 510 and the photoreceptor 10 through the liquid developer layer and the pre-wet liquid layer.
[0019]
As a member for forming the elastic layer of the developing roller 510, a foamed material such as polystyrene, polyethylene, polyurethane, polyvinyl chloride, NBR (nitrile / butylene / rubber), or a low-hardness rubber member such as silicon rubber or urethane rubber. There is. However, if the rubber member is used for many years in a generally elastically deformed state, it may be permanently deformed and may not return to its original shape, that is, a roller shape. For this reason, it is preferable to use a foam for the member which forms an elastic layer if possible. In addition, an elastic layer may be formed of a foam around the core metal, and an elastic layer may be formed of a rubber member on the surface thereof. The surface layer of the developing roller 510 is formed of a conductive member that does not swell in silicon oil that is a carrier liquid of the liquid developer 508. As shown in FIG. 2, the electric resistance value of the conductive member is 10 so that an electric developing bias can be applied to the developing roller 510 by the power supply device 515. ^Three It is desirable to be about Ωcm. As a method for forming the surface layer, for example, a method of coating a synthetic rubber-based composite in which conductive particles such as carbon black are dispersed on the surface of the elastic layer, the elastic layer is covered with a heat-shrinkable tube having conductivity, There is a method in which heat is applied to cause heat shrinkage. Or you may make it inject | pour an elastic material into the inside of a tube which has electroconductivity, or make the injected elastic material foam, and may form an elastic layer in the inside of a surface layer. As the tube having conductivity, a resin tube such as polyimide, polycarbonate, nylon, or a metal tube such as nickel is used. Moreover, as a heat-shrinkable tube having conductivity, a resin tube such as PFA or PTFE is used. These tubes are preferably so-called endless tubes without joints. When the elastic layer is formed of an elastic member that does not swell in silicon oil such as urethane rubber, it is not necessary to form a surface layer on the surface of the elastic layer. However, in order to make it possible to apply an electrical developing bias to the developing roller 510, the surface of the elastic layer is subjected to conductive processing, or conductive fine particles are added to the member forming the elastic layer, etc. Is the desired value, ie 10 ^Three It needs to be about Ωcm. The developing bias voltage is an electrostatic force (attractive force) acting between the toner and the developing roller 510, and an electrostatic force (attractive force) acting between the toner and the portion of the photoreceptor 10 where the electrostatic latent image is formed. It must be set to be weaker and stronger than the electrostatic force (attractive force) acting between the toner and the portion of the photoreceptor 10 where the electrostatic latent image is not formed. In this embodiment, positively charged toner is used as the liquid developer, and the developing bias voltage is set to -150V.
[0020]
As shown in FIG. 3, a part of the supply roller 502 a is installed so as to be immersed in the liquid developer 508 in the tank 502, and the tank 502 is rotated by rotating in the direction opposite to the rotation direction of the transport roller 504. The liquid developer 508 stored therein is pumped up and supplied to the conveying roller 504. The power supply device 513 applies a predetermined bias voltage to the supply roller 502a based on a signal from the control means 54. The back plate 503 is provided so as to cover a part of the supply roller 502a, and is grounded. As a result, an electric field is generated between the supply roller 502a and the back plate 503, and the pumping amount of the liquid developer 508 from the tank 502 is adjusted by the electrostatic force acting on the toner. Note that the bias voltage need not always be applied. When applying the liquid developer 508 to the developing roller 510, it may be performed in advance so that the liquid developer 508 having a desired liquid amount is already supplied to the applying rollers 506a and 506b.
[0021]
As shown in FIG. 3, the transport roller 504 is provided so as to contact the supply roller 502a, and the liquid supplied by the supply roller 502a by rotating in the direction opposite to the rotation direction of the application rollers 506a and 506b. The developer 508 is conveyed to the application rollers 506a and 506b. The power supply device 511 applies a predetermined bias voltage to the transport roller 504 based on a signal from the control unit 54. Thus, an electric field is generated between the transport roller 504 and the supply roller 502a, and the transport amount of the liquid developer 508 from the supply roller 502a to the transport roller 504 is adjusted by the electrostatic force acting on the toner.
[0022]
As shown in FIG. 3, the application rollers 506 a and 506 b are provided so as to come into contact with the transport roller 504 and the development roller 510, and rotate in the direction opposite to the rotation direction of the development roller 510. The liquid developer 508 conveyed by the conveyance roller 504 is applied to the surface. The power supply device 531 applies a predetermined bias voltage to the application rollers 506a and 506b based on a signal from the control unit 54. As a result, an electric field is generated between the application rollers 506a and 506b and the conveyance roller 504, and the conveyance amount of the liquid developer 508 from the conveyance roller 504 to the application rollers 506a and 506b is adjusted by the electrostatic force acting on the toner. At the same time, an electric field is generated between the applying rollers 506a and 506b and the developing roller 510 to adjust the amount of the liquid developer 508 applied to the developing roller 510.
[0023]
The supply roller 502a, the transport roller 504, and the application rollers 506a and 506b are used for supplying the liquid developer 508 to the developing roller 510. In this embodiment, as described later, the toner is dispersed in a high concentration and has a high viscosity. This is because since the liquid developer 508 is used, it is necessary to apply a small amount of the liquid developer thinly and uniformly on the developing roller 510. By applying the liquid developer on the developer support via a plurality of rollers, the layer thickness of the liquid developer on each roller is regulated thinly and uniformly at the contact portion with the adjacent roller. A high-concentration and high-viscosity liquid developer can be applied thinly and uniformly on the agent support. Also, the two application rollers 506a and 506b are used to form a more uniform liquid developer layer by densely applying unevenness (ripple) caused by the viscosity of the liquid developer 508 and the dispersibility of the toner. This is because it is formed on the developing roller. The number of application rollers is not limited to two, and one or three or more may be provided. That is, it is desirable to determine the number of application rollers according to required accuracy such as image quality unevenness.
[0024]
The supply roller 502a, the conveyance roller 504, and the application rollers 506a and 506b must have high electrical resistance values. Electrical resistance value is 10 ⁸ -10 ¹³ It is desirable to be Ωcm. Electric resistance value is 10 ⁸ If it is Ωcm or less, when a bias voltage is applied, the adjacent roller is suddenly discharged, and the pumping amount and transport amount of the liquid developer 508 cannot be adjusted sufficiently. In particular, since the application rollers 506a and 506b are in contact with the developing roller 510, it is necessary to increase the electric resistance value of the developing roller 510 sufficiently. On the other hand, the electrical resistance value is 10 ¹³ If it is Ωcm or more, charging becomes insufficient when a bias voltage is applied, and it is impossible to sufficiently adjust the pumping amount and transport amount of the liquid developer 508.
[0025]
When hard rollers having a hardness of 60 ° (JIS A) or higher are used for the supply roller 502a and the coating rollers 506a and 506b, it is desirable to use a soft roller having a hardness of 60 ° (JIS A) or lower for the transport roller 504. Thus, by arranging the hard roller and the soft roller in contact with each other alternately, the soft roller is elastically deformed by the pressing force to the hard roller, and a nip is formed at the contact portion with the hard roller. The nip makes it possible to make the liquid developer layer on each roller uniform. In order to elastically deform the soft roller, the harder the better. The hardness of the hard roller is desirably 90 ° (JIS-A) or higher. Further, when the pressing force of the soft roller to the hard roller is strong, a high torque is required to rotate each roller. For this reason, it is preferable that the soft roller be elastically deformed with a weak pressing force. The hardness of the soft roller is preferably 40 ° (JIS-A) or less. However, when the hardness is 15 ° (JIS-A) or less, it is difficult to maintain a certain shape, and it becomes difficult to form a nip at the contact portion with the hard roller.
[0026]
The layer thickness measuring device 53 measures the light reflectance of the liquid developer 508 applied on the developing roller 510 and calculates the layer thickness based on this light reflectance. The control device 54 adjusts the voltage values of the power supply device 511, the power supply device 513, and the power supply device 531 based on the layer thickness calculated by the layer thickness measurement device 53. As a result, an appropriate amount of liquid developer 508 is supplied to the developing roller 510. It is desirable that the voltage values of the power supply devices 511, 513 and 531 can be controlled manually. According to the experiments by the present inventors, when a positively charged toner is used as the liquid developer and the developing bias voltage applied to the developing roller 510 is set to −150 V, the bias voltage applied to each roller and the liquid developer are set. It was confirmed that there is a relationship shown in Table 1 between the coating amount and the coating amount. Where V ₁ Indicates the bias voltage applied to the application rollers 506a and 506b, V ₂ Is the bias voltage applied to the transport roller 504, V _Three Is the bias voltage applied to the supply roller 502a, V _p Represents the voltage of the back plate 503.
[0027]
[Table 1]

[0028]
The pre-wet liquid recovery device 51 includes a pre-wet liquid recovery roller 512 provided so as to contact the developing roller 510, a scraping blade 520 provided so as to contact the pre-wet liquid recovery roller 512, and a recovery tank 522. And. The pre-wet liquid recovery roller 512 rotates in the same direction as the rotation direction of the developing roller 510. Further, as shown in FIG. 2, a bias voltage is applied to the pre-wet liquid recovery roller 512 by a power supply device 517. This bias voltage is set so that the positively charged toner receives a repulsive force on the pre-wet liquid recovery roller 512 by an electric field generated between the pre-wet liquid recovery roller 512 and the developing roller 510. This is to prevent the liquid developer 508 from adhering to the pre-wet liquid collection roller 512 by making the adhesion force of the toner to the development roller 510 stronger than the adhesion force to the pre-wet liquid collection roller 512. is there. Thereby, only the pre-wet liquid 220 can be attached to the pre-wet liquid recovery roller 512. In this embodiment, when the developing bias voltage is set to −150V, the bias voltage applied to the pre-wet liquid recovery roller 512 is set to −100 to −50V.
[0029]
The developer recovery device 52 includes a developer recovery roller 514 provided so as to contact the developing roller 510, a recovery tank 524 that stores the recovered liquid developer 508, and a liquid developer 508 stored in the tank 502. Furthermore, a tank 526 in which a liquid developer 509 having a higher toner density is stored, a density measuring device 528, and a density adjusting device 530 are provided. The developer recovery roller 514 rotates in the direction opposite to the rotation direction of the developing roller 510. Further, as shown in FIG. 2, a bias voltage is applied to the developer recovery roller 514 by a power supply device 519. This bias voltage is set so that the positively charged toner receives an attractive force with respect to the developer recovery roller 514 by an electric field generated between the developer recovery roller 514 and the development roller 510. This is because the liquid developer 508 adheres to the surface of the developer collection roller 514 by making the adhesion force of the toner to the developer collection roller 514 stronger than the adhesion force to the development roller 510. In this embodiment, when the developing bias voltage is set to −150V, the bias voltage applied to the developer recovery roller 514 is set to −250 to −200V.
[0030]
As shown in FIG. 2, the liquid developer 508 adhering to the developer recovery roller 514 is recovered in the recovery tank 526, and then the toner density is measured by the density measuring device 528. The density measuring device 528 measures the light transmittance of the liquid developer 508 and calculates the toner concentration based on this light transmittance. The density adjusting device 530 adjusts the toner concentration by mixing the collected liquid developer 508 with the liquid developer 509 stored in the tank 526 based on the toner concentration calculated by the density measuring device 528. The liquid developer 508 having the toner density adjusted by the density adjusting device 530 is transported to the tank 502 and reused.
[0031]
As shown in FIG. 1, the transfer device 60 of this embodiment includes an intermediate transfer drum 602 that is an intermediate transfer member, and a secondary transfer roller 604 that is a secondary transfer member that is detachably attached to the intermediate transfer drum 602. And a removing roller 606 for removing toner remaining on the intermediate transfer drum 602.
[0032]
The intermediate transfer drum 602 is installed so as to contact the photoconductor 10 and rotates in the direction opposite to the rotation direction of the photoconductor 10. The intermediate transfer drum 602 is charged with a charge having a polarity opposite to that of the toner by a power supply device 608 as shown in FIG. 1 at the time of transfer. Thus, the toner image on the photoconductor 10 is primarily transferred onto the intermediate transfer drum 602 by electrostatic force.
[0033]
The intermediate transfer drum 602 includes a cored bar formed of a rigid body such as stainless steel, an elastic layer formed around the cored bar, and a surface layer formed on the surface of the elastic layer. For this reason, the contact pressure when the toner image formed on the photoconductor 10 and the intermediate transfer drum 602 come into contact can be dispersed, so that the toner image on the photoconductor 10 can be prevented from being disturbed. . The intermediate transfer drum 602 preferably has a hardness of 5 to 50 degrees JIS-A, preferably 15 to 40 degrees JIS-A. When the hardness is 5 degrees JIS-A or lower, it is too soft to maintain a certain shape. On the other hand, if the hardness is 50 degrees JIS-A or higher, the toner image on the photoconductor 10 is crushed when the toner image formed on the photoconductor 10 and the intermediate transfer drum 602 are brought into contact with each other. There is a fear.
[0034]
As a member for forming the elastic layer of the intermediate transfer drum 602, foams such as polystyrene, polyethylene, polyurethane, polyvinyl chloride, NBR (nitrile / butylene / rubber), or low-hardness rubbers such as silicon rubber and urethane rubber are used. There are parts. However, when a rubber member is used for many years in a generally elastically deformed state, it may be permanently deformed and may not return to its original shape, that is, a cylindrical shape. For this reason, it is preferable to use a foam for the member which forms an elastic layer if possible. Note that an elastic layer may be formed of a rubber member around the metal core, and an elastic layer may be formed of a foam on the surface thereof.
[0035]
The surface layer of the intermediate transfer drum 602 is formed of a member that does not swell in silicon oil that is a carrier liquid of the liquid developer 508. Examples of the method for forming the surface layer include a method of coating the surface of the elastic layer with a synthetic rubber-based conjugate, a method of covering the surface of the elastic layer with a tube, and the like. These tubes are preferably resin tubes, which are so-called endless tubes, such as polyimide and PET. When the elastic layer is formed of a rubber member that does not swell in silicone oil such as urethane rubber or fluorosilicone rubber, it is not necessary to cover the side surface of the intermediate transfer drum with a surface layer, but it swells in silicone oil such as foam. In the case where the intermediate transfer drum is formed, the side surface of the intermediate transfer drum needs to be covered with a surface layer.
[0036]
The electric resistance value of the intermediate transfer drum 602 is 10 ^Four -10 ¹¹ Ωcm, preferably 10 ⁶ -10 ⁹ It is desirable that it be Ωcm. Electric resistance value is 10 ^Four If it is Ωcm or less, when the intermediate transfer drum 602 is charged, it is suddenly discharged from the intermediate transfer drum 602 to the photoconductor 10 to damage the photoconductor 10 and transfer failure occurs. On the other hand, the electrical resistance value is 10 ¹¹ If it is Ωcm or more, the intermediate transfer drum 602 is not sufficiently charged, the electrostatic force between the intermediate transfer drum 602 and the toner image formed on the photoreceptor 10 is weakened, and the toner does not move sufficiently. In order to set the intermediate transfer drum 602 to the above-described electric resistance value, the surface of the intermediate transfer drum 602 is subjected to conductive processing, or conductive fine particles are added to a member forming the surface layer. The resistance value needs to be lowered.
[0037]
The surface of the intermediate transfer drum 602 is desirably a glossy surface having releasability. This is because the toner attached to the intermediate transfer drum 602 can be easily removed by improving the releasability from the toner. Accordingly, as a member for forming the surface layer of the intermediate transfer drum 602, latex, a coated rubber member, a resin tube such as polyimide coated with a release coating such as a fluorine coating, or a PFA having a release effect on the surface It is desirable to use resin tubes such as PTFE, ETFE, and FEP.
[0038]
The secondary transfer roller 604 rotates in a direction opposite to the rotation direction of the intermediate transfer drum 602, thereby feeding paper as a recording medium between the intermediate transfer drum 602 and the secondary transfer roller 604. At this time, the secondary transfer roller 604 is pressed against the intermediate transfer drum 602 through the paper. Further, as shown in FIG. 1, the secondary transfer roller 604 is charged with a charge having a polarity opposite to that of the toner by the power supply device 612. Therefore, the adhesion between the intermediate transfer member and the recording medium can be improved by the elastic layer of the intermediate transfer drum 602 and the electrostatic force of the secondary transfer roller 604. Can be transferred.
[0039]
The surface of the secondary transfer roller 604 is coated with fluorine. This is to improve the releasability from the toner, thereby facilitating the removal of the toner adhering to the secondary transfer roller 604 and preventing the secondary transfer roller 604 from becoming dirty.
[0040]
The removal roller 606 is disposed so as to be able to be separated from and contacted to the intermediate transfer drum 602 and to be in contact with the cleaning, and rotates in a direction opposite to the rotation direction of the intermediate transfer drum 602. Further, as shown in FIG. 1, the removal roller 606 is charged with a charge having a polarity opposite to that of the toner by the power supply device 614. As a result, the toner remaining on the intermediate transfer drum 602 after the completion of the secondary transfer process is adhered to the surface of the removal roller 606 and removed from the intermediate transfer drum 602.
[0041]
The cleaning device 70 of this embodiment includes a removal roller 702 and a power supply device 704 connected to the removal roller 702. The removal roller 702 is provided so as to contact the photoconductor 10 and rotates in the direction opposite to the rotation direction of the photoconductor 10. The power supply device 704 applies a voltage to the removal roller 702 so that the removal roller 702 is charged with an electric charge having a polarity opposite to that of the toner. Thereby, the toner remaining on the photoconductor 10 is removed.
[0042]
Next, the image forming material used in this embodiment will be described. The liquid developer used in this embodiment is a resin that serves as a binder such as epoxy, a charge control agent that gives a predetermined charge to the toner, and a positive charge in this embodiment, a coloring pigment, a dispersant that uniformly disperses the toner, and the like. And a carrier liquid. The construction of the toner is basically the same as that used in conventional liquid developers, but their formulation has been changed to be compatible with silicone oil to adjust charging characteristics and dispersibility. The smaller the average particle diameter of the toner, the better the resolution. However, when the particle diameter is small, the physical adhesive force increases and it becomes difficult to peel off when transferring. For this reason, in this embodiment, the average particle diameter of the toner is adjusted so as to be centered around 2 to 4 μm for the purpose of improving transferability.
[0043]
The viscosity of the liquid developer is determined by the carrier liquid used, the resin, the color pigment, the charge control agent, etc., and their concentrations. In this embodiment, the experiment was performed by changing the viscosity in the range of 50 to 6000 mPa · s and the toner concentration in the range of 5 to 40%.
[0044]
As the carrier liquid, dimethylpolysiloxane oil, cyclic polydimethylsiloxane oil or the like exhibiting high electrical resistance is used. Note that since the amount of carrier liquid contained in the liquid developer layer on the developing roller 510 is very small, the amount of carrier liquid contained in the liquid developer supplied to the latent image surface of the photoreceptor 10 is also very small. Accordingly, the amount of the carrier liquid absorbed by the paper or the like at the time of transfer is extremely small, so that the carrier liquid remaining after fixing is hardly seen if the viscosity is 1000 mPa · s or less. According to the experiments by the present inventors, a drawing experiment using DC344 of US Dow Corning with a viscosity of 2.5 mPa · s and DC345 of US Dow Corning with a viscosity of 6.5 mPa · s was used as the carrier liquid. In any case, no carrier liquid remained on the paper after fixing. However, since the volatility is high, the developing device has to be sealed. Further, when an image forming experiment was performed using KF-96-20 manufactured by Shin-Etsu Silicon Co., Ltd. having a viscosity of 20 mPa · s, the carrier liquid remaining on the paper after fixing was not observed. Further, since the volatility is not so high, it is not necessary to make the developing device in a sealed structure. DC344, DC345 and KF-96-20 are generally used in cosmetics and have high safety such as toxicity. There are many types of carrier liquids such as KF9937 manufactured by Shin-Etsu Silicon Co., Ltd., and any of them may be selected as long as electrical resistance, evaporation characteristics, surface tension, safety and the like are satisfied.
[0045]
Also, in experiments conducted by the inventors, fogging and toner lumps may adhere when the surface tension is high, and experimentally, problems may occur in image quality when the surface tension is 21 dyn / cm or more. I understood.
[0046]
The electrical resistance value has a problem of toner charging stability. ¹⁴ Ωcm or more is desirable. 10 at a minimum ¹² Ωcm or more is necessary. In the description of this embodiment, in view of these experimental results, an example is shown in which a DC 345 that is inexpensive and easily available is used.
[0047]
The pre-wet liquid is required to evaporate easily at the time of fixing without disturbing the electrostatic latent image formed on the image support, and to prevent fog or toner lump from adhering. Examples include DC344, DC200-0.65, -1.0, -2.0 of Dow Corning, USA, KF96L-1, KF9937 of Shin-Etsu Silicon. In general, it is preferable to select silicon oil having high evaporability.
[0048]
In the experiment conducted by the inventors, the liquid was dried by development, transfer, and fixing without any problem in the range of the liquid viscosity of 0.5 to 3 mPa · s, but it was slightly fixed at about 5 mPa · s to 6 mPa · s. There was a tendency for time and temperature to be required to dry the liquid. At 10 mPa · s, the energy required for drying becomes too large, which is not general. Moreover, since volatility becomes high as it is 0.5 mPa * s or less, it becomes the object of a legal regulation as a dangerous substance, and is not suitable. Also, due to the effect of heating the paper, the boiling point is preferably 250 ° C. or less.
[0049]
The surface tension should be as low as possible in order to eliminate the adhesive force between the developer and the image support, improve the releasability, prevent image smearing, and improve the resolution of image quality. According to the experiments by the present inventors, it is necessary to select a lower limit of about 20 to 21 dyn / cm.
[0050]
When the electrical resistance is low, the latent image charge leaks and the image is blurred. Therefore, it is necessary to use as high as possible. 10 experimentally ¹⁴ About Ωcm or more is desirable. 10 at a minimum ¹² Ωcm is required.
[0051]
Next, the operation of the image forming apparatus 1 of this embodiment will be described.
First, as shown in FIG. 4A, the charging device 30 charges the surface of the photoconductor 10 with a charge having a polarity opposite to that of the toner, in this embodiment, a negative charge. Generally, a corona discharger is used for the charging device 30. Next, a reverse image is exposed on the photosensitive member 10 charged by the exposure device 40. For example, the reverse image is exposed by a laser scanner to form an electrostatic latent image on the surface of the photoreceptor 10. As shown in FIG. 4B, the portion exposed to the light of the laser scanner becomes conductive, so that the charge disappears, and the portion not exposed to the light remains as an electrostatic latent image that is an image of the charge.
[0052]
Next, as shown in FIG. 4C, a prewetting liquid 220 is applied onto the photoreceptor 10 by the prewetting apparatus 20. The pre-wet liquid 220 stored in the tank 202 is pumped up by the supply roller 202 a and supplied to the transport roller 204. The pre-wet liquid 220 supplied to the transport roller 204 is transported to the application roller 206 and then applied onto the photoreceptor 10. In this way, a thin pre-wet liquid layer is formed on the photoreceptor 10 by applying the pre-wet 220 through the roller.
[0053]
Next, the electrostatic latent image is visualized by the developing device 50. The liquid developer 508 stored in the tank 502 is supplied to the transport roller 504 by the supply roller 502a. The liquid developer 508 supplied to the transport roller 504 is transported to the application rollers 506a and 506b and then applied to the development roller 510. In this manner, the liquid developer 508 is applied through a plurality of rollers, thereby forming a uniform and thin liquid developer layer on the developing roller 510. In addition, bias voltages are applied to the supply roller 502a, the transport roller 504, and the application rollers 506a and 506b by the power supply device 513, the power supply device 511, and the power supply device 531 respectively. Thereby, the supply amount of the liquid developer 508 to the developing roller 510 is adjusted. Next, as shown in FIG. 4D, the liquid developer layer on the developing roller 510 is softly contacted with the pre-wet liquid layer on the photoconductor 10 to form an electrostatic formed on the surface of the photoconductor 10. The charged toner is moved onto the photoconductor 10 by electrostatic force in the vicinity of the latent image, and a toner image is formed on the photoconductor 10. The pre-wet liquid 220 that has moved from the photoreceptor 10 to the developing roller 510 during development is collected by the pre-wet liquid collecting device 51, and the liquid developer 508 remaining on the developing roller 510 after development is collected by the developer collecting device 52. Is done.
[0054]
Next, the toner image formed on the photoconductor 10 is transferred to paper as a recording medium by the transfer device 60. First, as shown in FIG. 4E, a toner image formed on the photoreceptor 10 is transferred between the toner and the intermediate transfer drum 602 charged with a charge having a polarity opposite to that of the toner by the power supply device 608. Primary transfer is performed on the intermediate transfer drum 602 by the generated electrostatic force. Next, as shown in FIG. 4F, the toner image primarily transferred onto the intermediate transfer drum 602 is applied to the pressing force of the secondary transfer roller 604 to the intermediate transfer drum 602 and the secondary transfer roller 604. Secondary transfer is performed on the paper fed between the intermediate transfer drum 602 and the secondary transfer roller 604 by the electrostatic force generated by the secondary transfer bias. On the other hand, the liquid developer 508 remaining on the photoconductor 10 is removed from the photoconductor 10 by the cleaning device 70, and thereafter, the photoconductor 10 is discharged by the charge removal device 80.
[0055]
Next, as shown in FIG. 4G, the toner image secondarily transferred onto the paper is fixed by a fixing device 620 not shown in FIG. A fixing heater 624 provided in the fixing roller 622 of the fixing device 620 thermally melts the toner. As a result, the toner image is fixed on the paper.
[0056]
FIG. 5 to FIG. 9 are diagrams for explaining in detail the development process of the present embodiment, FIG. 5 is a diagram for explaining the whole development process, and FIG. 6 is a diagram showing the approach process. 7 is a diagram showing the toner movement process, FIG. 8 is a diagram showing a non-image portion separation process, and FIG. 9 is a diagram showing an image portion separation process. Unlike the conventional development process, the development process of this embodiment includes an approach process in which the developing roller approaches the photosensitive member and the liquid developer layer approaches the pre-wet liquid layer, as shown in FIG. And the pre-wet liquid layer in soft contact with each other to move the toner, and the separation process in which the developing roller is separated from the toner that adheres to the developing roller away from the photosensitive member and the toner that adheres to the photosensitive member. It is thought that it consists of these three processes.
[0057]
In the approaching process, as shown in FIG. 6, the developing roller 510 is formed in a cylindrical shape having elasticity, so that the pressing force of the developing roller 510 against the photosensitive member 10 is adjusted and the developing roller 510 is adjusted. When the contact pressure when the liquid developer layer and the pre-wet liquid layer on the photoreceptor 10 are in contact with each other is dispersed, the high-viscosity liquid developer layer composed of the carrier liquid and the toner and the pre-wet liquid layer are in soft contact. The At this time, a minute gap, that is, a distance d is formed between the developing roller 510 and the photoreceptor 10 through the liquid developer layer and the pre-wet liquid layer. Note that the pre-wet liquid having a low viscosity is slightly pushed back and forth to cause a pool of the pre-wet liquid.
[0058]
In the toner movement process, as shown in FIG. 7, in the image portion, the toner passes through the pre-wet liquid layer mainly by the Coulomb force due to the electric field formed between the charge on the photoconductor 10 and the developing roller 510. Move to the latent image plane. On the other hand, in the toner in the non-image area, the surface of the photoreceptor 10 and the liquid developer layer are basically separated by the pre-wet liquid layer, so that unnecessary toner does not adhere to the surface of the photoreceptor 10. Absent.
[0059]
In the separation process, the liquid developer layer basically remains on the developing roller 510 in the non-image area as shown in FIG. When the two layers are separated at the interface between the pre-wet liquid layer and the liquid developer layer, a part of the pre-wet liquid layer having a low viscosity is transferred to the liquid developer layer and separated. Therefore, the separation point of the two layers is considered to be inside the pre-wet liquid layer. On the other hand, in the image portion, as shown in FIG. 9, the toner moved to the surface of the photoreceptor 10 pushes the pre-wet liquid layer, so that the pre-wet liquid layer is located on the toner layer and separated in the layer. A part of the carrier liquid remaining after the toner moves and a part of the pre-wet liquid form a layer on the developing roller 510. The pre-wet liquid remaining on the photoconductor 10 facilitates movement of the toner due to electrostatic force in a later transfer process.
[0060]
FIG. 10 is a diagram for explaining the significance of thinning the liquid developer layer. If the liquid developer layer applied on the developing roller 510 is too thick, the viscosity of the liquid developer 508 is high, so that a group of toners trying to move from the developing roller 510 to the surface of the photoconductor 10 by electrostatic force is around it. As a result, the toner is moved to the surface of the photoconductor 10 without breaking the viscosity with respect to the toner positioned at the position of the toner, so that the toner is excessively adhered and image noise is generated. In order to suppress the occurrence of this cluster, it is necessary to suppress the layer thickness of the liquid developer layer to a minimum value at which development can be sufficiently performed.
[0061]
FIG. 11 is a view showing a state where the developing roller formed of a rigid body such as metal and the photosensitive member are in hard contact, and FIG. 12 is a view for explaining the soft contact of this embodiment. As described above, in the development process of this embodiment, the function of the pre-wet liquid layer for image formation is important. Therefore, an important requirement in the development process is to maintain the two-layer state of the pre-wet liquid layer and the liquid developer layer. As shown in FIG. 11, if the developing roller formed of a rigid body and the photoconductor are in hard contact, the two-layer state cannot be maintained. In the present embodiment, as shown in FIG. 12, a developing roller 510 having elasticity is used, and the pressing force of the developing roller 510 to the photosensitive member 10 is adjusted so that the liquid developer layer formed on the developing roller 510 and the photosensitive roller are photosensitive. By dispersing the contact pressure when the pre-wet liquid layer formed on the body 10 contacts, the liquid developer layer and the pre-wet liquid layer are brought into contact with each other while maintaining the two-layer state. At this time, a minute gap, that is, a distance d is formed between the developing roller 510 and the photoconductor 10 through the liquid developer layer and the pre-wet liquid layer.
[0062]
Next, optimization of the layer thickness of the liquid developer layer, the layer thickness of the pre-wet liquid layer, and the development gap, that is, the interval will be described. The layer thickness of the liquid developer layer needs to be reduced when the viscosity of the liquid developer is 50 to 100 mPa · s or more, particularly when the viscosity is 500 mPa · s or more. Ideally, the thickness is slightly larger than the layer thickness that satisfies the toner development amount (that is, the density of the solid portion) required during development. This is because when a high-viscosity liquid developer is used, the toner selected electrostatically at the time of development moves to the photosensitive member due to the viscosity of the liquid, and the toner adheres abnormally. This is because the image is smudged and causes image contamination. In the experiments by the inventors, a good image was obtained with a layer thickness from about 5 μm to about 40 μm for a liquid developer having a high toner concentration and a toner having a low toner concentration. In addition, when a liquid developer having a toner concentration of 20 to 30% was used, good image quality was obtained when the layer thickness of the liquid developer was about 8 to 20 μm.
[0063]
The thickness of the pre-wet liquid layer has an optimum value depending on the viscosity and surface tension of the selected pre-wet liquid. If it is too thin, the high-viscosity liquid developer adheres irregularly on the photoreceptor and causes image smearing. As the amount of the pre-wet liquid is increased, the image contamination is improved and the optimum value is confirmed. As the amount is further increased, the latent image charges and the sharpness and resolution are lowered. In addition, toner flows at the time of development and the image tends to be blurred. In the experiment using DC344, good results were obtained with a thickness of 30 μm or less, particularly 20 μm or less. For those having a lower viscosity than this, a thinner or thicker result can be obtained. However, for high viscosity ones, the optimum value tends to narrow.
[0064]
The narrower the gap between the photoconductor and the developing roller, that is, the interval, the better the resolution and the uniformity of the density of the solid portion in the image quality, as in the conventional developing method. In the high-viscosity liquid developer used in this example, the cohesive force between the toners is strong. Therefore, like a powder developer, the toner released from the developer support or carrier particles by mechanical impact and electrostatic force is not generated. The phenomenon used for development does not occur. That is, development is not performed if an air layer is interposed between the liquid developer layer and the photoreceptor. Therefore, it is essential that the developing roller 510 and the liquid developer layer, the liquid developer layer and the pre-wet liquid layer, and the pre-wet liquid layer and the photoconductor 10 are in contact with each other. Therefore, the minute gap, that is, the distance d must be a dimension that is less than the thickness of the liquid developer layer and the pre-wet liquid layer and does not disturb the respective layers. In this embodiment, the pressing force of the developing roller 510 to the photoconductor 10 is adjusted so that the pre-wet liquid layer on the photoconductor 10 and the liquid on the developing roller 510 are adjusted according to the difference in the viscosity and toner concentration of the liquid developer. The distance d was between 8 μm and 50 μm when contacting the developer layer.
[0065]
Table 2 shows the results of the image output experiment under the above conditions. From these results, the range of the viscosity of the developer and the pre-wet liquid optimum for the developing method of the present embodiment is 100 mPa · s to 6000 mPa · s for the developer and 0.5 mPa · s to 5 mPa · s for the pre-wet liquid. It turns out that it is between. Further, the image quality varies depending on the influence of the thickness of the liquid developer layer on the developing belt, the thickness of the pre-wet liquid layer, the developing gap, that is, the interval, etc. It was confirmed that the optimum region of the liquid developer was within the range shown in Table 2. In addition, DC200 series made by Dow Corning was used for the silicon oil of the prewetting liquid, and DC345 made by the same company was used for the carrier liquid of the developer.
[0066]
[Table 2]

[0067]
According to the first embodiment of the present invention, the liquid developer 508 is applied on the developing roller 510 via the supply roller 502a, the conveying roller 504, and the applying rollers 506a and 506b, thereby forming the liquid developer on each roller. Since the layer thickness is thinly and uniformly regulated at the contact portion with the adjacent roller, the high-concentration and high-viscosity liquid developer 508 can be thinly and uniformly applied onto the developing roller 510.
[0068]
Further, according to the first embodiment of the present invention, the power supply device 513 for applying a bias voltage to the supply roller 502a is provided, and the back plate 503 connected to the ground is provided in the developing tank 502, whereby the supply roller An electric field is generated between 502a and the back plate 503, and the pumping amount of the liquid developer 508 can be adjusted by the electrostatic force acting on the toner. Further, since the liquid developer 508 in the developing tank 502 is pumped up by electrostatic force, there is no restriction on the installation position of the developing tank 502, and therefore the degree of freedom in designing the image forming apparatus can be improved. Further, by providing a power supply device 511 for applying a bias voltage to the conveying roller 504 and a power supply device 531 for applying a voltage to the application rollers 506a and 506b, the electrostatic force acting between the toner and the conveying roller 504 and the toner The application amount of the liquid developer 508 to the developing roller 510, that is, the layer thickness of the liquid developer on the developing roller 510 can be adjusted by electrostatic force acting between the applying rollers 506a and 506b.
[0069]
Further, according to the first embodiment of the present invention, the layer thickness measuring device 53 that measures the light reflectance of the liquid developer layer on the developing roller 510 and calculates the layer thickness based on the light reflectance, the layer thickness By providing the power supply device 511 and the control device 54 that adjusts the voltage value of the power supply device 513 based on the layer thickness calculated by the measuring device 53, an appropriate amount of liquid developer 508 is always supplied to the developing roller 510. Can do.
[0070]
Further, according to the first embodiment of the present invention, by providing the two application rollers 506a and 506b for applying the liquid developer 508 on the developing roller 510, the viscosity of the liquid developer 508, the dispersibility of the toner, and the like. The coating unevenness (ripple) generated by the influence of the above can be made dense, and a more uniform liquid developer layer can be formed on the developing roller 510.
[0071]
Further, according to the first embodiment of the present invention, the use of silicon oil as the carrier liquid of the liquid developer has the following advantages over the conventional one.
[0072]
Conventional liquid developers generally use IsoparG (registered trademark: manufactured by Exxon) as a carrier liquid. Since Isopar has a resistance value that is not as high as that of silicone oil, when the toner concentration is increased, that is, when the interparticle distance is decreased, the chargeability of the toner is deteriorated. Therefore, in the case of Isopar, there is a limit to the toner density. On the other hand, since the silicone oil used in this embodiment has a sufficiently large resistance value, the toner density can be increased. In general, in the case of Isopar, the dispersion state of the toner is good. Therefore, even when the toner concentration is 1 to 2%, the toners repel each other, so that the toner is uniformly dispersed. On the other hand, when the toner concentration is 1 to 2%, silicone oil does not have good dispersibility and soon precipitates. However, when the toner concentration is 5 to 40%, the toner is densely packed and stably dispersed. For this reason, in this embodiment, a high-viscosity liquid developer in which toner is dispersed at high density is used. Thereby, compared with the conventional low concentration liquid developer, the amount of the developer can be greatly reduced, and the developing device can be downsized. Furthermore, since the liquid developer of the present embodiment is a high-viscosity liquid, it is easier in terms of storage and handling than conventional low-viscosity liquid developers and powder developers.
[0073]
As described above, Isopar used in a conventional liquid developer has high volatility and emits a foul odor, which causes a problem that it not only deteriorates the working environment but also causes pollution. On the other hand, the silicone oil used in this example is a safe liquid and odorless, as is clear from the fact that it is used for cosmetics. The environment can be improved and pollution problems do not occur.
[0074]
Further, according to the first embodiment of the present invention, the prewetting device 20 for applying the prewetting liquid 220 which is a dielectric liquid having releasability and being chemically inert is provided on the photoconductor 10. Further, it is possible to prevent the toner from adhering to the non-image portion of the photoreceptor 10.
[0075]
Next, a second embodiment of the present invention will be described with reference to FIGS.
13 is a schematic configuration diagram of an image forming apparatus according to a second embodiment of the present invention, FIG. 14 is a schematic perspective view of a pre-wet apparatus used in the image forming apparatus shown in FIG. 13, and FIG. 15 is a pre-wet shown in FIG. FIG. 16 is a diagram for explaining the operation of the apparatus, and FIG. 16 is a diagram showing the flow of the pre-wet liquid when the pre-wet liquid supply body is brought into contact with the photosensitive member 10. In addition, about the thing which has the same function as 1st Example in 2nd Example, the detailed description is abbreviate | omitted by attaching | subjecting the same code | symbol or corresponding code | symbol.
[0076]
The image forming apparatus according to the second embodiment of the present invention uses so-called regular development, like the image forming apparatus according to the first embodiment. As shown in FIG. 13, the image forming apparatus 2 according to the present exemplary embodiment charges the photoconductor 10 that is an image support, a prewet device 25 that applies a prewetting liquid onto the photoconductor 10, and the photoconductor 10. A charging device 30, an exposure device 40 that exposes an image on the photoreceptor 10, and a developing device that visualizes the electrostatic latent image by supplying toner to a portion of the photoreceptor 10 where the electrostatic latent image is formed. 55, a transfer device 60 for transferring the toner image formed on the photoconductor 10 to a predetermined paper, a cleaning device 70 for removing the toner remaining on the photoconductor 10, and the charged photoconductor 10 are neutralized. The neutralization device 80 and a fixing device (not shown) for fixing the toner transferred to the paper are provided.
[0077]
The image forming apparatus 2 shown in FIG. 13 is different from the image forming apparatus 1 of the first embodiment shown in FIG. 1 in that the prewetting device 25 is used instead of the prewetting device 20 and the developing device 50 is used. This is because the developing device 55 is used. Therefore, in this embodiment, the prewetting device 25 and the developing device 55 will be described, and detailed descriptions of other devices will be omitted.
[0078]
As shown in FIG. 14, the pre-wet apparatus 25 of the present embodiment includes a plate-like pre-wet liquid supply body 252 and a pre-wet liquid supply body 252 having substantially the same length as the image width drawn on the photoconductor 10. , A tank 256 for storing the pre-wet liquid 220, a pump 258 for pumping the pre-wet liquid 220 stored in the tank 256, tubes 260a and 260b, and a displacement device 262.
[0079]
For the pre-wet liquid supply body 252, a continuous porous body having a three-dimensional network structure in which pores are continuous, for example, Berita (registered trademark: Kanebo Co., Ltd.) is used. The bell eta can hold the pre-wet liquid 220 by the volume of the pores. When the pre-wet liquid 220 exceeding the pore volume is supplied, the pre-wet liquid 220 is pre-wet in the direction perpendicular to the flow direction of the pre-wet liquid 220. The liquid 220 can be discharged uniformly. As shown in FIG. 15, an opening 254 a is provided on the surface of the case 254 facing the photoconductor 10 so that the bottom surface of the pre-wet liquid supply body 252 can be brought into contact with the photoconductor 10. The tube 260 a conveys the pre-wet liquid 220 pumped up by the pump 258 to the supply side 252 a of the pre-wet liquid supply body 252. A space 254b is formed between the supply side 252a of the pre-wet liquid supply body 252 and the case 254, and the pre-wet liquid 220 is stored in the space 254b and then supplied from the supply side 252a. The The tube 260 b conveys the pre-wet liquid 220 discharged from the discharge side 252 b of the pre-wet liquid supply body 252 to the tank 256. When no external signal is input, the displacement device 262 holds the pre-wet liquid supply body 252 at a position away from the photoconductor 10 as shown in FIG. When it is input, the pre-wet liquid supply body 252 is brought into contact with the photoconductor 10 as shown in FIG.
[0080]
The developing device 55 of this embodiment includes a developing belt 560 that is a developer support, and driving rollers 562a and 562b that rotationally drive the developing belt 560 and hold a part of the developing belt 560 in contact with the photoconductor 10. A developer supplying device 57 for applying the liquid developer 508 to the surface of the developing belt 560, a power supply device 511, 513, 531 and a layer thickness measuring device for measuring the layer thickness of the liquid developer 508 on the developing belt 560. 53, a control device 54 that controls the power supply devices 511, 513, and 531 based on the results of the layer thickness measuring device 53, and a prewet liquid recovery that recovers the prewet liquid 220 that has moved from the photoconductor 10 to the developing belt 560 during development. A device 51 and a developer recovery device 58 that recovers the liquid developer 508 remaining on the development belt 560 after development are provided. The power supply devices 511, 513, 531, the control device 54, and the pre-wet liquid recovery device 51 are the same as those in the first embodiment.
[0081]
The developing belt 560 supplies the liquid developer 508 supplied by the developer supply device 57 to the surface of the photoconductor 10 by rotating in the direction opposite to the rotation direction of the photoconductor 10 by the driving rollers 562a and 562b. For the developing belt 560, a flexible member such as a metal belt such as a seamless nickel belt or a resin belt such as a polyimide film belt is used. Accordingly, when the tension of the developing belt 560 is adjusted to disperse the contact pressure when the liquid developer layer formed on the developing belt 560 and the pre-wet liquid layer formed on the photoreceptor 10 are in contact with each other, An interval is formed between the photoconductor 10 and the developing belt 560 through the liquid developer layer and the pre-wet liquid layer. Therefore, in the development process, the liquid developer layer formed on the developing belt 560 and the pre-wet liquid layer formed on the photoreceptor 10 are brought into contact with each other while maintaining a two-layer state in which the layers can be distinguished from each other. be able to. The developing belt 560 has an electric resistance value of 10 so that an electric developing bias can be applied. ^Three It is desirable to be about Ωcm. Therefore, when a resin belt is used, it is necessary to reduce the electric resistance value by conducting conductive processing on the surface of the belt or adding conductive fine particles to the belt material. When the belt itself has conductivity, rubber rollers having a low electrical resistance value to which conductive fine particles are added so that a developing bias can be applied are used as the driving rollers 562a and 562b. When conductive processing is performed on the surface of the belt, a conductor that contacts the surface of the belt is provided, and a developing bias is applied to the conductor.
[0082]
The developer supply device 57 includes four developing cartridges 57a, 57b, 57c, and 57d (hereinafter also simply referred to as developing cartridges) and a separating / connecting device (not shown). Each developing cartridge applies coating rollers 506a and 506b for applying the liquid developer 508 to the surface of the developing belt 560, a tank 552 for storing the liquid developer 508, and a pump for pumping up the liquid developer 508 stored in the tank 552. A roller 502a, a transport roller 504 that transports the liquid developer 508 supplied by the supply roller 502a to the coating rollers 506a and 506b, and a back plate 503 formed of a conductive member. Since the supply roller 502a, the transport roller 504, the application rollers 506a and 506b, and the back plate 503 are the same as those in the first embodiment, detailed description thereof is omitted.
[0083]
The liquid developer 508a containing yellow toner is contained in the tank 552 of the developing cartridge 57a, the liquid developer 508b containing magenta toner is contained in the tank 552 of the developing cartridge 57b, and the cyan toner is contained in tank 552 of the developing cartridge 57c. And the liquid developer 508d containing black toner is stored in the tank 552 of the developing cartridge 57d (hereinafter, the liquid developers 508a, 508b, 508c, and 508d are simply referred to as the liquid developer). 508). A separation / contact device (not shown) causes the application rollers 556a and 556b of each development cartridge to contact the development belt 560.
[0084]
The developer supply device 57 having the above-described configuration causes a desired color on the surface of the developing belt 560 by bringing the application rollers 506a and 506b of any of the developing cartridges into contact with the developing belt 560 by a separation / contact device (not shown). The liquid developer 508 containing the toner is applied.
[0085]
The developer collecting device 58 is configured by attaching four developer collecting rollers 580 a, 580 b, 580 c, and 580 d (hereinafter also simply referred to as developer collecting rollers) to a rotating shaft 582. When the liquid developer 508a containing yellow toner is applied on the developing belt 560 by a driving device (not shown), the rotating shaft 582 causes the developer collecting roller 580a to be replaced with the liquid developer 508b containing magenta toner. Is applied, developer recovery roller 580b is applied, liquid developer 508c containing cyan toner is applied, developer recovery roller 580c is applied, and liquid developer 508d containing black toner is applied. When this is done, the developer recovery roller 580d is rotationally driven so as to abut each other.
[0086]
Each developer recovery roller rotates in a direction opposite to the rotation direction of the developing belt 560. Further, as shown in FIG. 13, a bias voltage is applied to each developer recovery roller via a rotating shaft 582 by a power supply device 583. This bias voltage is set so that the toner is attracted to the developer recovery roller by an electric field generated between the development belt 560 and the developer recovery roller in contact with the development belt 560.
[0087]
The developer recovery device 58 configured as described above switches the developer recovery roller that abuts in accordance with the color of the liquid developer applied to the development belt 560, and recovers the liquid developer remaining on the development belt 560 after development. .
[0088]
Next, the operation of the image forming apparatus 2 of this embodiment will be described.
First, the surface of the photoconductor 10 is charged by the charging device 30, and then the reverse image is exposed on the photoconductor 10 charged by the exposure device 40.
[0089]
Next, a prewetting liquid 220 is applied onto the photoreceptor 10 by the prewetting device 25. The pre-wet device 25 abuts the pre-wet liquid supply body 252 against the photoconductor 10 when an external signal is input. In the pre-wet liquid supply body 252, the pre-wet liquid 220 is constantly circulated by a pump 258, and the pre-wet liquid 220 exceeding the pore volume of the bell eta as the pre-wet liquid supply body 252 is shown in FIG. As described above, the light is discharged from the discharge side 252b of the pre-wet liquid supply body 252 and is also discharged from the bottom surface of the pre-wet liquid supply body 252, and is uniformly applied onto the photoconductor 10 without scratching the photoconductor 10.
[0090]
Next, the electrostatic latent image is visualized by the developing device 55. The liquid developer 508 stored in the tank 552 is supplied to the transport roller 504 by the supply roller 502a. The liquid developer 508 supplied to the transport roller 504 is transported to the application rollers 506a and 506b and then applied to the developing belt 560. Thus, the liquid developer 508 is applied via a plurality of rollers, thereby forming a uniform and thin liquid developer layer on the developing belt 560. In addition, bias voltages are applied to the supply roller 502a, the transport roller 504, and the application rollers 506a and 506b by the power supply device 513, the power supply device 511, and the power supply device 531 respectively. Thereby, the supply amount of the liquid developer 508 to the developing belt 560 is adjusted. Note that a liquid developer containing any one of yellow, magenta, cyan, and black toner is obtained by bringing the application rollers 506a and 506b of any of the developing cartridges into contact with the developing belt 560 by a separation / contact device (not shown). 508 can be applied to the developing belt 560.
[0091]
Next, the liquid developer layer thus formed on the developing belt 560 is brought close to the electrostatic latent image formed on the surface of the photosensitive member 10, and the charged toner is electrostatically applied on the photosensitive member 10. To form a toner image. The pre-wet liquid 220 that has moved from the photoreceptor 10 to the developing belt 560 during development is collected by the pre-wet liquid collection device 51. Further, the liquid developer 508 remaining on the developing belt 560 after development is collected for each color by the developer collecting device 58.
[0092]
Next, the toner image formed on the photoconductor 10 by the transfer device 60 is primarily transferred onto the intermediate transfer drum 602. The toner image formed on the photoconductor 10 is generated by an electrostatic force generated between the toner image formed on the photoconductor 10 and the intermediate transfer drum 602 charged with a charge having a polarity opposite to that of the toner by the power supply device 608. Then, it moves onto the intermediate transfer drum 602 and is primarily transferred. On the other hand, the liquid developer 508 remaining on the photoconductor 10 is removed from the photoconductor 10 by the cleaning device 70, and thereafter, the photoconductor 10 is discharged by the charge removal device 80. Then, the application rollers 506a and 506b that contact the developing belt 560 are switched by a separation / contact device (not shown), and the above-described cycle from charging to charge removal is repeated, whereby yellow, magenta, Cyan and black toner images are overlaid one after another for primary transfer. As a result, a toner image corresponding to colorization is formed on the intermediate transfer drum 602.
[0093]
Next, the toner image corresponding to the coloration formed on the intermediate transfer drum 602 is secondarily transferred to paper as a recording medium by the transfer device 60. The toner image corresponding to colorization formed on the intermediate transfer drum 602 is an electrostatic force generated by the pressing force of the secondary transfer roller 604 to the intermediate transfer drum 602 and the secondary transfer bias applied to the secondary transfer roller 604. As a result, the image is secondarily transferred to the paper fed between the intermediate transfer drum 602 and the secondary transfer roller 604. Then, the image is fixed on paper by a fixing device (not shown). Thereby, a color image can be formed on paper.
[0094]
According to the second embodiment of the present invention, the step of primarily transferring the toner image formed on the photoconductor 10 onto the intermediate transfer drum 602 is performed sequentially for each color of yellow, magenta, cyan, and black. A toner image corresponding to colorization is formed on the transfer drum 602, and then the toner image corresponding to colorization formed on the intermediate transfer drum 602 is secondarily transferred to a recording medium, so that it is formed on the photoreceptor. It is not necessary to consider paper misalignment or the like as compared with the case of sequentially transferring the toner images directly onto the paper, and therefore it becomes easy to match the registration of the color image transferred onto the paper. Other effects are the same as those of the first embodiment.
[0095]
In the first and second embodiments described above, the image support is charged with a charge having a polarity opposite to that of the toner, and then the reverse image is exposed by irradiating the image support with light. Although a description has been given of what uses so-called regular development that forms an electrostatic latent image to be visualized in a portion that has not been made conductive, that is, a portion that has not been made conductive, the present invention is not limited to this, and image support The body is charged with a charge having the same polarity as the toner, and then the image support is exposed to light to expose the normal image, and a latent image to be visualized is formed on the exposed portion of the image support. Alternatively, what uses so-called reversal development may be used. The inventors of the present invention applied positively charged toner in an apparatus to which reversal development was applied and set the development bias voltage to 500 V. As a result, between the bias voltage applied to each roller and the coating amount of the liquid developer. It was confirmed that there is a relationship shown in Table 3. Where V ₁ Indicates the bias voltage applied to the application rollers 506a and 506b, V ₂ Is the bias voltage applied to the transport roller 504, V _Three Is the bias voltage applied to the supply roller 502a, V _P Represents the voltage of the back plate 503.
[0096]
[Table 3]

[0097]
Next, a third embodiment of the present invention will be described with reference to FIGS.
FIG. 17 is a schematic configuration diagram of an image forming apparatus according to the third embodiment of the present invention, and FIG. 18 is a diagram showing the timing of application of a developing bias voltage and separation / contact of the application roller. In addition, about the thing which has the same function as 2nd Example in 3rd Example, the detailed description is abbreviate | omitted by attaching | subjecting the same code | symbol or corresponding code | symbol.
[0098]
The image forming apparatus according to the third embodiment of the present invention charges an image support with an electric charge having the same polarity as that of toner, and then irradiates the image support with light to expose a normal image. In this case, so-called reversal development is used, in which an image to be visualized is formed on the portion hit by. The image forming apparatus 3 of the present embodiment is different from the image forming apparatus 2 of the second embodiment shown in FIG. 13 in that the photoconductor 10 is replaced with a charging device 30 that charges with a charge having a polarity opposite to that of the toner. That is, the charging device 30a that charges 10 with the same polarity as the toner is used, and the developing device 55a is used instead of the developing device 55. Since the other configuration is the same as that of the second embodiment, its detailed description is omitted.
[0099]
The difference between the developing device 55a of the present embodiment and the developing device 55 of the second embodiment is that, as shown in FIG. 17, from the contact point P of the developing belt 560 with the photosensitive member 10 to the application roller 506a of the developing cartridge 57d. That is, the length L up to the contact point Q is made longer than the maximum value of the length of the latent image that can be formed on the photosensitive member 10 and the developing bias voltage is applied to the developing belt 560 only at the time of development. In this embodiment, positively charged toner is used as the liquid developer, and the developing bias voltage is set to 500V.
[0100]
The timing of application of the developing bias voltage and separation / contact of the coating rollers 506a and 506b in the developing device 55a having the above configuration will be described with reference to FIG. Where V _B Is the development bias voltage, R ₁ Are the application rollers 506a and 506b of the developing cartridge 57a, R ₂ Are the application rollers 506a and 506b of the developing cartridge 57b, R _Three Are the application rollers 506a and 506b of the developing cartridge 57c, and R _Four Represents the application rollers 506a and 506b of the developing cartridge 57d. R ₁ ~ R _Four In FIG. 6, “High” indicates a state where the belt is in contact with the developing belt 560, and “Low” indicates a state where the belt is separated from the developing belt 560. As shown in FIG. 18, the developing device 55a of this embodiment applies a developing bias voltage (500 V) only during development, and supplies the liquid developer 508 to the developing belt 560 by the application rollers 506a and 506b. Is performed prior to the developing process, that is, when the developing bias voltage is not applied to the developing belt 560. This is to prevent the application of the liquid developer 508 to the developing belt 560 from being disturbed by the developing bias voltage having the same polarity as the toner applied to the developing belt 560. In the developing device 55a of this embodiment, as described above, the length L from the contact point P of the developing belt 560 with the photosensitive member 10 to the contact point Q of the developing cartridge 57d with the coating roller 506a is set to the photosensitive member 10. 18 is longer than the maximum value of the length of the latent image that can be formed on the photosensitive member 10, so that the development bias voltage application and the application roller 506a, 506b contact timing shown in FIG. A required amount of liquid developer 508 can be supplied to the image plane.
[0101]
The operation of the image forming apparatus 3 of this embodiment is that the image forming apparatus 2 of the second embodiment uses regular development, whereas the image forming apparatus 3 of the present embodiment uses reversal development. This is basically the same as the image forming apparatus 2 of the second embodiment. Therefore, detailed description of the operation of the image forming apparatus 3 of the present embodiment is omitted.
[0102]
According to the third embodiment of the present invention, the length L from the contact point P of the developing belt 560 with the photoreceptor 10 to the contact point Q with the application roller 506a of the developing cartridge 57d can be formed on the photoreceptor 10. By making the image length longer than the maximum value of the image and applying the developing bias voltage only during development, the liquid developer 508 is applied to the developing belt 560 with the same polarity as the toner applied to the developing belt 560. Can be prevented from being disturbed by a developing bias voltage having As a result, the absolute value of the bias voltage applied to the application rollers 506a and 506b, the transport roller 504, and the supply roller 502a can be reduced, so that the supply amount of the liquid developer 508 to the development belt 560 can be adjusted with a simple configuration. can do. Other effects are the same as those of the second embodiment.
[0103]
In the first to third embodiments, a supply voltage of the liquid developer 508 to the developer support is adjusted by applying a bias voltage to the supply roller 502a, the transport roller 504, and the application rollers 506a and 506b. Although what has been described has been described, the present invention is not limited to this. What is necessary is just to adjust the supply amount of the liquid developer 508 to the developer support by applying a bias voltage to at least one of these rollers. For example, a bias voltage may be applied only to the supply roller 502a.
[0104]
Next, a fourth embodiment of the present invention will be described with reference to FIG.
FIG. 19 is a schematic configuration diagram of an image forming apparatus according to the fourth embodiment of the present invention. In addition, about the thing which has the same function as 2nd Example in 4th Example, the detailed description is abbreviate | omitted by attaching | subjecting the same code | symbol or corresponding code | symbol.
[0105]
The image forming apparatus according to the fourth embodiment of the present invention uses so-called reversal development, like the image forming apparatus according to the third embodiment. The image forming apparatus 4 of this embodiment is different from the image forming apparatus 2 of the second embodiment shown in FIG. 13 in that the photoconductor 10 is replaced with a charging device 30 for charging with a charge having a polarity opposite to that of the toner. That is, the charging device 30a that charges 10 with the same polarity as the toner is used, and the developing device 55b is used instead of the developing device 55. Since the other configuration is the same as that of the second embodiment, its detailed description is omitted.
[0106]
The developing device 55b of this embodiment is different from the developing device 55 of the second embodiment in that the application rollers 506a and 506b, the transport roller 504, the back plate 503, the tank 552, and the supply roller 502a are biased as shown in FIG. That is, the ground terminal of the power supply device 513 to which the voltage is applied is made equipotential with the developing belt 560. This is to prevent the application of the liquid developer 508 to the developing belt 560 from being disturbed by the developing bias voltage having the same polarity as the toner applied to the developing belt 560. In this embodiment, as in the third embodiment, a positively charged toner is used for the liquid developer, and the developing bias voltage is set to 500V.
[0107]
The operation of the image forming apparatus 4 of the present embodiment is that the image forming apparatus 2 of the second embodiment uses regular development, whereas the image forming apparatus 4 of the present embodiment uses reversal development. This is basically the same as the image forming apparatus 2 of the second embodiment. Therefore, detailed description of the operation of the image forming apparatus 4 of this embodiment is omitted.
[0108]
According to the fourth embodiment of the present invention, the application rollers 506a and 506b and the conveying roller 504 are equipotential with the developing belt 560, so that the application of the liquid developer 508 to the developing belt 560 is applied to the developing belt 560. Can be prevented from being disturbed by a developing bias voltage having the same polarity as the toner used. Other effects are the same as those of the second embodiment.
[0109]
In the fourth embodiment, the application rollers 506a and 506b and the conveying roller 504 are set to the same potential as the developing belt 560. However, the present invention is not limited to this, and the bias voltage is not limited to this. What is necessary is just to make the roller which is not applied equipotential with the developing belt 560. For example, when a bias voltage is applied to the conveying roller 504, the application rollers 506a and 506b and the supply roller 502a may have the same potential as the developing belt 560.
[0110]
In the second to fourth embodiments, the developer supply device includes a developing cartridge 57a for applying a liquid developer 508a containing yellow toner on the developing belt 560, and a liquid developer containing magenta toner. A description will be given of a developing cartridge 57b for applying a developer 508b, a developing cartridge 57c for applying a liquid developer 508c containing cyan toner, and a developing cartridge 57d for applying a liquid developer 508d containing black toner. However, the present invention is not limited to this. The developer supply device may be provided with two or three developing cartridges for applying a liquid developer containing a toner of a desired color on the developer support as required. In this case, the number of developer collecting rollers provided in the developer collecting device may be set according to the number of developing cartridges.
[0111]
The present invention is not limited to the above embodiments, and various modifications are possible within the scope of the gist. For example, in each of the above embodiments, the case where an organic photoconductor is used as the image support has been described. However, the present invention is not limited to this, and the image support may be various photoconductors used in the Carlson method or An electrostatic recording paper such as that used in an electrostatic plotter may be used in which an insulator layer is formed on a conductor that directly forms an electrostatic latent image such as ionography.
[0112]
In each of the above embodiments, the exposure apparatus exposes an image on the image support, and then the pre-wet apparatus applies the pre-wet liquid onto the image support. The application of the pre-wet liquid is not limited as long as it is performed prior to the development step. For example, a pre-wet liquid may be applied on the image support by a pre-wet apparatus, and then the image may be exposed on the image support by an exposure apparatus. Further, the pre-wetting apparatus is not limited to those used in each of the above embodiments, and any pre-wetting apparatus may be used as long as it can uniformly apply a predetermined amount of the pre-wetting liquid to the surface of the photoreceptor. For example, it may be applied by discharging pre-wet liquid from a plurality of nozzles arranged in the axial direction, or applied by a sponge roller or the like. Further, the viscosity of the pre-wet liquid is 0.5 to 5 mPa · s, and the electric resistance is 10 ¹² The pre-wet liquid may not be mainly composed of silicon as long as it is Ωcm or more, the boiling point is 100 to 250 ° C., and the surface tension is 21 dyn / cm or less. Further, when the surface of the image support is coated with a material having releasability, a prewetting device is not particularly required.
[0113]
In each of the above embodiments, the liquid developer is applied to the developer support via the supply roller, the transport roller and the application roller as the supply of the liquid developer to the developer support in the developing device. As described above, the present invention is not limited to this, and the developing device only needs to apply the liquid developer onto the developer support via at least two rollers. For example, two or more conveyance rollers may be provided between the supply roller and the application roller, or the liquid developer pumped up by the supply roller is directly supplied to the application roller without providing the conveyance roller. There may be. Further, it is not always necessary to provide a back plate in the tank for storing the liquid developer. Further, the developer support is not limited to that used in each of the above embodiments, and may be formed of a rigid body having conductivity such as metal. However, in the case of using a developing roller formed of a rigid body, the liquid developer layer formed on the developing roller and the pre-wet liquid layer formed on the photosensitive member are brought into contact with each other while maintaining a two-layer state. It is necessary to use a member formed of a belt-like member having flexibility in the body, or to install the developing roller so as to form a minute gap, that is, a distance d between the developing roller and the photosensitive drum. is there.
[0114]
Further, in each of the above-described embodiments, as the primary transfer in the transfer device, the power transfer device 608 charges the intermediate transfer drum 602 with a charge having a polarity opposite to that of the toner, whereby the toner image formed on the photoconductor 10 is obtained. Although the primary transfer on the intermediate transfer drum 602 has been described, the present invention is not limited to this. The transfer device may be, for example, a device in which the intermediate transfer member is charged with a charge having a polarity opposite to that of the toner by a corona discharger. In each of the above embodiments, as the secondary transfer in the transfer device, an intermediate force is generated by the pressing force of the secondary transfer roller 604 to the intermediate transfer drum 602 and the electrostatic force generated by the bias voltage applied to the secondary transfer roller 604. Although the toner image on the transfer drum 602 is secondarily transferred to paper, the present invention is not limited to this. The transfer device may be any device that can secondarily transfer the toner image on the intermediate transfer member onto paper. For example, when a fixing heater is provided inside the secondary transfer member and the toner on the intermediate transfer member is heated, the toner image on the intermediate transfer member can be fixed on the paper at the same time as the secondary transfer.
[0115]
In each of the above embodiments, the cleaning device using the removing roller 702 charged with the charge having the opposite polarity to that of the toner has been described. However, the present invention is not limited to this. The cleaning device may be any device as long as it can remove the toner remaining on the photoconductor, and for example, may be a device that scrapes off the toner remaining on the photoconductor using a blade or the like.
[0116]
Further, the present invention is not limited to the above-described embodiments, and the viscosity of the high-viscosity developer may be 10,000 mPa · s as long as the layer thickness of the liquid developer is 5 to 40 μm. At present, it is considered that a developer having a high viscosity of 6000 mPa · s or higher is difficult to stir between the carrier liquid and the toner, so that it is not cost effective. Good. Those having a viscosity exceeding 10,000 mPa · s are not realistic. Further, the carrier liquid of the liquid developer is not limited to silicon oil.
[0117]
【The invention's effect】
As described above, according to the electrostatic latent image liquid developing apparatus of the present invention, the application means for applying the high-concentration and high-viscosity liquid developer onto the developer support via the plurality of rollers is provided. Since the layer thickness of the liquid developer on each roller is regulated thinly and uniformly at the contact portion with the adjacent roller, a high-concentration and high-viscosity liquid developer should be applied thinly and uniformly on the developer support. In addition, by providing a voltage applying means for applying a voltage to at least one of the plurality of rollers, the liquid developer is developed by an electrostatic force acting between the charged toner and the voltage-applied roller. The amount of conveyance to the agent support can be adjusted, and accordingly, a desired amount of liquid can be supplied uniformly to the latent image surface of the image support, and the toner has a high concentration. Liquid developer dispersed in a thin layer By developing Te, easy and compact with high resolution, yet it is possible to provide a liquid developing device for electrostatic latent image capable of decreasing emissions.
[0118]
According to another electrostatic latent image liquid developing apparatus of the present invention, by providing a plurality of rollers for applying a liquid developer of high concentration and high viscosity to the developer support in contact with the developer support. The liquid developer layer on the developer support can be prevented from being uneven due to the influence of the viscosity of the liquid developer and the dispersibility of the toner, and thereby the high density on the developer support can be prevented. A highly viscous liquid developer can be applied thinly and uniformly, so that the liquid developer can be uniformly supplied to the latent image surface of the image support, and a liquid developer in which toner is dispersed at a high concentration By developing the agent in a thin layer, it is possible to provide a liquid developing device for an electrostatic latent image that has high resolution, can be easily miniaturized, and can reduce pollution.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram of an image forming apparatus according to a first embodiment of the present invention.
FIG. 2 is a schematic configuration diagram of a developing device used in the image forming apparatus shown in FIG.
FIG. 3 is a diagram for explaining the operation of the developing device shown in FIG. 2;
4 is a diagram for explaining the operation of the image forming apparatus shown in FIG. 1; FIG.
FIG. 5 is a diagram for explaining the entire development process;
FIG. 6 is a diagram showing how an approaching process is performed.
FIG. 7 is a diagram illustrating a toner moving process.
FIG. 8 is a diagram illustrating a separation process of a non-image portion.
FIG. 9 is a diagram illustrating a separation process of an image portion.
FIG. 10 is a diagram for explaining the significance of thinning the liquid developer.
FIG. 11 is a diagram illustrating a state where the developing roller and the photoconductor are in hard contact.
FIG. 12 is a diagram for explaining a soft contact of the present invention.
FIG. 13 is a schematic configuration diagram of an image forming apparatus according to a second embodiment of the present invention.
14 is a schematic perspective view of a pre-wet apparatus used in the image forming apparatus shown in FIG.
15 is a diagram for explaining the operation of the pre-wet apparatus shown in FIG. 14;
FIG. 16 is a diagram illustrating the flow of the pre-wet liquid when the pre-wet liquid supply body is brought into contact with the photosensitive member.
FIG. 17 is a schematic configuration diagram of an image forming apparatus according to a third embodiment of the present invention.
FIG. 18 is a diagram illustrating the timing of application of a developing bias voltage and separation / contact of a coating roller.
FIG. 19 is a schematic configuration diagram of an image forming apparatus according to a fourth embodiment of the present invention.
[Explanation of symbols]
1, 2, 3, 4 Image forming apparatus
10 photoconductor
20, 25 Pre-wet device
30, 30a charging device
40 Exposure equipment
50, 55, 55a, 55b Developing device
51 Pre-wet liquid recovery device
52, 58 Developer recovery device
53 Layer thickness measuring device
54 Control device
57 Developer supply device
57a, 57b, 57c, 57d Developing cartridge
60 Transfer device
70 Cleaning device
80 Static eliminator
202, 256, 502, 552 tanks
202a, 502a supply roller
204,504 Transport roller
206, 506a, 506b Application roller
220 Pre-wet liquid
252 Pre-wet liquid supplier
254 cases
258 pump
260a, 260b tube
262 Displacement device
302 Shading plate
503 Back plate
508, 508a, 508b, 508c, 508d, 509 Liquid developer
510 Development roller
512 Pre-wet liquid recovery roller
511, 513, 515, 517, 519, 531, 583, 608, 612, 614, 704
514, 580a, 580b, 580c, 580d Developer recovery roller
520 scraping blade
522,524 Recovery tank
528 Concentration measuring device
530 Density adjustment device
560 Development belt
562a, 562b Driving roller
582 axis of rotation
602 Intermediate transfer drum
604 Secondary transfer roller
606,702 removal roller
620 Fixing device
622 Fixing roller
624 Fixing heater

Claims (11)

An electrostatic latent image liquid developing device for developing an electrostatic latent image formed on an image support with toner, which is a charged visualization particle, comprising: a developer support; and a developer support on the developer support. Application means for applying a high-viscosity liquid developer of 100 to 10000 mPa · s in which toner is dispersed at a high concentration in an insulating liquid through a plurality of rollers, and voltage applied to at least one of the plurality of rollers And a voltage applying means for applying, and a developing means for supplying the liquid developer coated on the developer support to the latent image surface of the image support,
The developing means further includes a layer thickness measuring means for measuring the layer thickness of the liquid developer applied on the developer support, and the voltage application based on the layer thickness measured by the layer thickness measuring means. An electrostatic latent image liquid developing apparatus comprising a control means for controlling the means. The application unit includes a developer tank that stores the liquid developer, and a conductive plate provided in the developer tank, and a part of the rollers of the first stage among the plurality of rollers is the developer. It is arranged so as to be immersed in the liquid developer stored in a tank, and the voltage applying means applies a voltage between the first stage roller and the conductive plate. The liquid developing device for electrostatic latent images according to claim 1. The length from the contact position between the last roller of the plurality of rollers and the developer support to the contact position between the developer support and the image support can be formed on the image support. A development bias is applied to the developer support only when the liquid developer applied on the developer support is supplied to the latent image surface of the image support while being longer than the maximum length of the electrostatic latent image. 3. The electrostatic latent image liquid developing apparatus according to claim 1, wherein a voltage is applied. All of the plurality of rollers, except for the roller to which a voltage is applied by the voltage applying unit, is maintained at substantially the same potential as the developing bias voltage applied to the developer support. 4. The liquid developing device for electrostatic latent images according to claim 1, 2, or 3. On the image support, claim, characterized in that it comprises a pre-wet means for applying a pre-wet liquid is a chemically inert dielectric liquid has a releasing property 1, 2, 3 or 4. A liquid developing apparatus for electrostatic latent images according to 4 . The pre-wet liquid has a viscosity 0.5 to 5 · s, electric resistance 10 ¹² [Omega] cm or more, a boiling point of 100 to 250 ° C., a surface tension of claim 5, wherein the at most 21dyn / cm A liquid developing device for electrostatic latent images. 7. The electrostatic latent image liquid developing apparatus according to claim 6 , wherein the prewetting liquid is mainly composed of silicon oil. The liquid developer has an insulating liquid viscosity of 0.5 to 1000 mPa · s, an electric resistance of 10 ¹² Ωcm or more, a surface tension of 21 dyn / cm or less, and a boiling point of 100 ° C or more. The liquid developing device for electrostatic latent images according to 1, 2, 3, 4, 5, 6 or 7 . 9. The electrostatic latent image liquid developing apparatus according to claim 8, wherein the liquid developer uses silicon oil as an insulating liquid. The liquid developer is characterized in that it is intended to include a toner having an average particle size of 0.1~5μm at a concentration of 5-40% claims 1,2,3,4,5,6,7,8 or 9 The electrostatic latent image liquid developing apparatus. An electrostatic latent image liquid developing method for developing an electrostatic latent image formed on an image support with toner, which is a charged visualization particle, which is applied onto a developer support via a plurality of rollers. A developing step of supplying a liquid developer having a high viscosity of 100 to 10,000 mPa · s, in which toner is dispersed at a high concentration in an insulating liquid, to the latent image surface of the image support; A voltage is applied to at least one of the rollers, and a layer thickness of the liquid developer applied on the developer support is obtained, and a voltage applied to the roller is adjusted based on the obtained layer thickness. And adjusting the amount of the liquid developer transported to the developer support.

Images