JP3576756B2 - Image forming device - Google Patents

Description

（ＡＲＥＡ：トナー投影面積、ＭＸＬＮＧ：絶対最大長、ＰＥＲＩ：周長）
【００３５】
トナーの形状係数ＳＦ１は球形度合を示し、１４０より大きいと球形から徐々に不定形となる。ＳＦ２は凸凹度合を示し、１２０より大きいとトナー表面の凸凹が顕著となる。
【００３６】
トナー表面を外添剤により、被覆することにより、トナー同士若しくは感光体間に微小な間隙を設けることで、さらに重合トナーの流動性を向上したり、転写効率を１００％近くにまで向上することが可能である。その意味で、トナー表面における第１の外添剤被覆率が、５〜９９％、さらに好ましくは１０〜９９％であることが好ましい。トナー表面の外添剤被覆率は、日立製作所製ＦＥ−ＳＥＭ（Ｓ−８００）を用いトナー像を１００個無作為にサンプリングし、その画像情報はインターフェースを介してニコレ社製画像解析装置（Ｌｕｚｅｘ３）に導入し解析を行い算出した。
【００３７】
また使用される第１の外添剤もしくは第２の外添剤としては、トナーに添加した時の耐久性の点から、トナー粒子の重量平均径の１／３以下の粒径であることが好ましい。この添加剤の粒径とは、電子顕微鏡におけるトナー粒子の表面観察により求めたその平均粒径を意味する。外添剤としては、たとえば、以下のようなものが用いられる。
【００３８】
金属酸化物（酸化アルミニウム，酸化チタン，チタン酸ストロンチウム，酸化セリウム，酸化マグネシウム，酸化クロム，酸化錫，酸化亜鉛など）・窒化物（窒化ケイ素など）・炭化物（炭化ケイ素など）・金属塩（硫酸カルシウム，硫酸バリウム，炭酸カルシウムなど）・脂肪酸金属塩（ステアリン酸亜鉛，ステアリン酸カルシウムなど）・カーボンブラック・シリカなど。
【００３９】
これら外添剤は、トナー粒子１００重量部に対し、０．０１〜１０重量部が用いられ、好ましくは、０．０５〜５重量部が用いられる。これら外添剤は、単独で用いても、また、複数併用しても良い。それぞれ、疎水化処理を行ったものが、より好ましい。
【００４０】
図８は、トナーのトリボ電荷量を測定する装置の説明図である。まず、底に５００メッシュのスクリーン４３のある金属製の測定容器４２に、摩擦帯電量を測定しようとする二成分現像剤を５０〜１００ｍｌ容量のポリエチレン製のビンに入れ、約１０〜４０秒間手で振とうし、該現像剤を約０．５〜１．５ｇ入れて金属製の蓋４４をする。この時の測定容器４２全体の重量を量りＷ１（ｋｇ）とする。次に、吸引機４１（測定容器４２と接する部分は少なくとも絶縁体）において、吸引口４７から吸引し風量調節弁４６を調節して真空計４５の圧力を２５０ｍｍＡｑとする。この状態で充分、好ましくは２分間吸引を行い樹脂を吸引除去する。この時の電位計４９の電位をＶ（ボルト）とする。ここで４８はコンデンサーであり容量をＣ（Ｆ）とする。また吸引後の測定容器４２全体の重量を量りＷ２（ｋｇ）とする。このトナーの摩擦帯電量は下式のごとく計算される。
【００４１】
【数２】

【００４２】
（実施例１）
本発明における第一の実施例を図１に示す。
【００４３】
本実施例は一成分現像剤として、粉砕法により製造されたトナーを球形化処理して得られた球形化トナーＴ１に、２種類の外添剤を外添したものを用いている。なお、定着手段・転写材等の記述は省略してある。
【００４４】
像担持体である感光ドラム１０は図中矢印方向に周速１００ｍｍ／ｓｅｃで回転し、帯電ローラ１３により−７００Ｖという表面電位に設定される。ここで帯電ローラ１３は外径４ｍｍの心棒に、カーボンブラックを分散したウレタンゴムを形成し外径１０ｍｍ、電気抵抗１０^６Ωである弾性ローラとしたものである。ここで帯電ローラの材質としてはシリコーンゴム・ＥＰＤＭ等の各種弾性体も用いることが出来るが、感光体を所定電位まで十分に帯電するためには１０^７Ω以下、リークの発生を防止するためには１０^５Ω以上の電気抵抗に設定することが好ましい。帯電ローラ１３には帯電電源１７より−７００Ｖの直流電圧に５００Ｈｚ・２ｋＶｐｐの交流電圧を重畳している。
【００４５】
露光手段１４は画像に応じた露光を感光ドラム１０に行い、静電潜像を形成する。ここで画像部である明部電位は−１５０Ｖ、非画像部である暗部電位は−７００Ｖである。
【００４６】
現像装置４０は現像スリーブ３を有し、現像スリーブ３は感光ドラム１０と２５０μｍの間隙を持って位置しており、現像スリーブ３上のトナーを電界により飛翔せしめ、感光ドラム１０上の静電潜像をトナー像化する。
【００４７】
感光ドラム上のトナー像は転写ローラ１１により転写紙上に転写され、定着手段により加熱・押圧され転写紙上に固定される。転写ローラ１１はＥＰＤＭのスポンジに金属酸化物を分散させることで電気抵抗１０^８Ωに設定された弾性ローラであり、通紙時には転写紙・ドラム側に８μＡの定電流を流すように制御され、転写紙裏面に充分なポジ電荷を付与している。
【００４８】
転写紙に転写されず感光ドラム１０上に残留したトナーは、クリーニング装置１２中に設置されたクリーニングブレード１８により、感光ドラムから剥がされ、除去される。但しトナーＴ１から分離された外添剤については、粒径が小さいため完全にはクリーニングブレード１８で除去されずにスリ抜けて帯電ローラ１３上に付着する。
【００４９】
次に現像装置４０について詳細に説明する。
【００５０】
現像装置４０中には、球形トナーであるトナーＴ１が存在する。トナーＴ１は負帯電性非磁性一成分トナーであり、粉砕トナーを後述する方法で球形化したものに、ネガ帯電性の外添剤と強ポジ帯電性の外添剤の２種類が外添されたものである。
【００５１】
現像装置４０中のトナー撹拌部材６は、図中矢印の方向に回転しており、球形トナーＴ１を現像スリーブ３ならびに現像剤供給ローラ５に向けて搬送している。
【００５２】
また現像装置４０はアルミニウムからなる直径１６φの導電性円柱スリーブ３を有し、図示されていない間隙規制部材により、対向する感光ドラム１０と２５０μｍの間隔を保って配置されている。
【００５３】
現像スリーブ３にはウレタンスポンジ製の現像剤供給ローラ５が当接されている。現像剤供給ローラ５は直径８ｍｍであり、現像スリーブ３に侵入量１ｍｍで当接されており、図示されていないギアにより現像スリーブ３とカウンタ方向に周速５０ｍｍ／ｓｅｃで駆動されている。現像剤供給ローラ５は現像スリーブ３とカウンタ当接方向に回転することで現像スリーブ３上のトナー履歴（いわゆるゴースト）を除去すると同時にトナーＴを現像スリーブ３上に供給する。現像剤供給ローラ５は連泡のスポンジから出来ており、アスカーＣ硬度で２０°の低硬度品である。ここで現像剤供給ローラ５は柔らかいほどトナー供給・除去時のトナー劣化を抑制できる。
【００５４】
現像スリーブ３にはトナー量規制部材として現像剤規制部材１が当接されており、現像スリーブ３上のトナーを規制して球形トナーＴ１を摩擦帯電し、現像に適した電荷をトナーに与えると同時に、トナー薄層７を形成し現像領域（ドラム対向位置）に搬送されるトナー量を規定している。
【００５５】
現像領域に搬送されたトナーは、現像時、現像スリーブ３に感光ドラムとの間に印加した現像電源４による現像電界により、現像スリーブ３から感光ドラム１００上に飛翔し、感光ドラム１００上の潜像に付着し、潜像をトナー像として可視化する。
【００５６】
次に、本実施例における球形トナーＴ１について説明する。
【００５７】
球形化トナーを製造する方法としては、スチレン−アクリル共重合体を主成分とする結着樹脂，低軟化点物質である離型剤，カーボンブラックを着色剤，モノアゾ染料の金属錯体塩を荷電制御剤として加圧ニーダーやエクストルーダー又はメディア分散機を用い均一に分散せしめた後、機械的又はジェット気流下でターゲットに衝突させ、所望のトナー粒径に微粉砕化せしめた後、塑性球形化処理を行う。更に分級工程を経て粒度分布をシャープ化せしめトナー化する。
【００５８】
塑性球形化処理を行う具体的装置としては、奈良機械（株）「ハイブリダイゼーション・システム」、ターボエ業（株）「ターボミル」などがあり、例えば、ハイブリダイゼーション・システムは回転板にブレードが装着されており、回転板が高速回転をする事により、循環気流中のトナーが高速回転するブレードに激突する。この際、トナーの凸部分が衝撃エネルギーにより塑性変形をうけて滑面化されトナー全体としては、球形方向への形状変化が起こる。
【００５９】
その他、球形化する手段としてはトナーの表面をスプレードライヤーを用いて熱風により溶融して球形化したり、トナーを熱気流中に分散してその表面を溶融して球形化する方法などが提案されており、このような製造方法により作成された球形化トナーを本実施例に用いてもよい。
【００６０】
本実施例において球形トナーＴ１は上記製造方法により平均粒径８μｍで、トナーの形状係数ＳＦ１＝１１５、ＳＦ２＝１１０の球形トナーが得られた。本球形トナーＴ１の前述したトリボ測定法による摩擦帯電量は−３８μＣ／ｇであった。
【００６１】
ここで摩擦帯電量の測定時には、粒径５０μｍのフェライトキャリア９．７ｇ中に外添剤を０．３ｇ混入し、ポリエチレン容器中で３００回振とうした後に測定を行った。
【００６２】
本実施例において球形トナーＴ１の表面は、図２（ａ）に示したように球形トナーＴ１が１００重量部に対して、トナーと同極性であるネガ帯電性の外添剤１．０重量部に加えて、トナーと逆極性であるポジ帯電性の外添剤０．８重量部を各トナー粒子表面に付着せしめて、非球形化してある。上記２種類の外添剤を外添した後の球形トナーＴ１のトナー形状係数はＳＦ１＝１５０、ＳＦ２＝１３５であった。
【００６３】
ここでネガ帯電性の外添剤として用いたのは、ＢＥＴ法による比表面積が３００ｍ^２／ｇ、一次粒径が８ｎｍである疎水性シリカであり、摩擦帯電量は−１１０μＣ／ｇであった。トナーと同極性であるネガ帯電性外添剤の効果としては、トナー帯電性の向上、トナー流動性の向上等の従来の外添剤の効果をトナーに付与することである。
【００６４】
一方、ポジ帯電性の外添剤としては、一次粒径０．５μｍである無色のＰＭＭＡ粒子を添加してある。本実施例におけるポジ帯電性外添剤の摩擦帯電量は＋４０μＣ／ｇであった。トナーと逆極性であるポジ帯電性外添剤の効果としては、一次粒径０．５μｍの粒子を球形トナーに付着させることで、トナー形状を適度に非球形化し、トナーの滑り性の制御が可能となる。したがってトナーが現像ブレードをスリ抜けず、良好なトナー帯電と均一なトナー薄層を得ることが出来る。またトナーが現像剤供給ローラをすり抜けないことでスリーブ上トナーのチャージアップを防ぎ、画像再現性を向上する。
【００６５】
ここで本発明においては、トナー表面におけるネガ帯電性外添剤とポジ帯電性外添剤は図２（ａ）のように存在している。ポジ帯電性外添剤の被覆率αを５０％以下とすることで、外添剤を含めたトナー全体のトリボを安定してネガに帯電する事が出来るため、カブリの少ない良好な画像を得ることが出来る。前述した測定方法によると本実施例における球形トナーＴ１表面における外添剤被覆率は強ネガ帯電性外添剤が８０％、ポジ帯電性外添剤が２２％であった。
【００６６】
またポジ帯電性外添剤の効果を高めるためには、ポジ帯電性外添剤個々の粒子についてネガ帯電性外添剤が付着してもポジであることが好ましい。具体的にはネガ帯電性外添剤の摩擦帯電量の絶対値Ｑ１、外添量をＭ１、ポジ帯電性外添剤の摩擦帯電量の絶対値Ｑ２、外添量Ｍ２、ポジ帯電性外添剤のトナーＴ１表面に占める面積被覆率αとしたときに
Ｑ２×Ｍ２＞Ｑ１×Ｍ１×α
なる条件にすることで、ポジ帯電性外添剤を安定してポジ極性に帯電し、現像／転写時におけるポジ外添剤の分離を容易にし、本発明における効果を安定して得ることが可能となる。
【００６７】
さらにポジ帯電性外添剤としては球形ではなく不定形であり、粒径が大きな粒子を用いることで、少ない外添量でもトナーの滑り性の制御を可能にしている。ポジ外添剤の一次粒径は０．１〜２μｍとすることでトナー形状係数ＳＦ１を増加させるとともに、現像／転写時にポジ外添剤を分離しやすく出来る。ネガ帯電性外添剤については０．１μｍ〜１ｎｍとすることで良好な転写特性が得られた。
【００６８】
なお本発明においては、ポジ帯電性外添剤によりトナーの形状係数ＳＦ１を増加させることで現像時における良好なトナーコート性を得ると同時に、ジャンピング現像法を適正化することで、図２（ｂ）に示したようにドラム上トナーからポジ帯電性外添剤をトナーから分離し、転写時におけるトナー形状係数ＳＦ１を低下して、転写効率・転写中抜けを向上している。
【００６９】
本実施例においては、現像電源４より現像バイアスとして現像スリーブ３には１．５ｋＶｐｐ、周波数２ｋＨｚの交流電圧と−５００Ｖの直流電圧が印加されており、２５０μｍの間隙をもって対向する感光ドラム上の静電潜像にトナーを飛翔せしめ、トナー像を形成している。
【００７０】
本実施例で用いたジャンピング現像法によれば、交番電界により現像剤担持体と感光ドラム上の画像部ＶＬ、非画像部Ｖｄ間においてトナーの転移・逆転移を発生させることで、ポジ帯電性の外添剤を効果的にネガ帯電性であるトナーから分離し、現像スリーブもしくは非画像部に回収する。これは適切な交番電界により１度感光ドラムの画像部に付着したトナーに対しても再度現像スリーブ側に飛翔させることで、ポジ帯電性外添剤の分離機会を増大させるためである。またジャンピング現像に依れば正規に帯電した−極性のトナーは、画像部に適度なエッジ効果を生じ、鮮明なエッジシャープネスと非画像部に近い潜像である中間調の再現性を向上し、かつ＋極性のトナーに関しては現像スリーブに回収することが可能であるため、後述するＤＣ現像法に比べて非画像部におけるカブリを削減できる。
【００７１】
交流を印加しないＤＣ現像方法においてはトナーを強い電界により往復動作させることがないため、１度ドラム上に付着したトナーからはポジ帯電性外添剤を充分に除去できない。また逆極性に帯電した＋極性のトナーは非画像部に付着し、いわゆる画像カブリを形成しやすく、画像品位を落としてしまう。
【００７２】
ここで現像電界として用いた交番電界の振幅と現像剤のＳＦ１ならびに転写効率の関係について説明する。現像電界振幅Ａは現像電源のピークトゥピーク交流電圧Ｖｐｐ、現像スリーブと感光ドラム間距離ＳＤとすると
Ａ＝Ｖｐｐ／２ＳＤ
で表せる。図５に示したように現像電界振幅Ａ＝０であるＤＣ現像方法では、現像後転写前のドラム上トナーの形状係数ＳＦ１＝１５０であり、現像装置中のトナーとほぼ同じでであった。その結果、転写効率は７７％しかなかった。一方、現像間隙に交番電界を形成し、且つ現像電界振幅を２ｋＶ／ｍｍ以上とすることでポジ帯電性外添剤をトナー表面から分離し、転写前のトナー形状係数ＳＦ１を１３０以下まで低下させた。その結果、トナーが球形化された後に転写されるため転写効率は９５％まで向上した。現像電界振幅を５ｋＶ／ｍｍ以上とすると潜像条件によってはリークが発生するため、現像電界振幅としては２ｋＶ／ｍｍ以上５ｋＶ／ｍｍ以下が望ましい。
【００７３】
ここで球形トナーとしては、外添する以前の形状係数ＳＦ−１が１００〜１３０、ＳＦ−２が１００〜１２０であり、且つ第１の外添剤と第２の外添剤を外添した後の形状係数ＳＦ−１が１３０〜１７０、ＳＦ−２が１２０〜１６０の範囲である球形トナーを用いたときに、上記現像電界振幅にて現像時におけるトナーコートと転写効率が両立された。
【００７４】
さらに本実施例では帯電ローラ上にポジ帯電性外添剤が蓄積するのを防止するために、非画像形成時において、帯電ローラからポジ帯電性外添剤を除去する電界を印加している。帯電電圧の直流成分Ｃｈ（ＤＣ）、交流成分Ｃｈ（ＡＣ）、現像電圧の直流成分Ｄｅｖ（ＤＣ）・交流成分Ｄｅｖ（ＡＣ）、転写電圧Ｔｒとしてタイミングチャートを図３に示すと、先ず画像形成終了と共に転写電圧が２．０ｋＶから−１．２ｋＶ印加に変化し、感光ドラム１０の表面電位を−５００Ｖにせしめる。次に帯電電源がＤＣ−７００Ｖから−３５０Ｖに切り替わり、同時に帯電電源の交流電圧は切られる。現像電圧の交流成分１．５ｋＶｐｐは画像形成終了と共に切られるが、現像電圧の直流印加電圧−５００Ｖは変化しない。
【００７５】
上記タイミングチャートに基づく画像形成時の感光ドラム上の各部分における表面電位について図４（ａ）に示すと、帯電ローラの電位（一点鎖線で記した）は−７００Ｖであり、感光ドラム電位（点線で記した）は帯電・露光後の非画像部Ｖｄ＝−７００Ｖ、画像部Ｖ１＝−１５０Ｖ、転写後はＴｒ＝＋５０Ｖである。現像スリーブ電位（実線で記した）は−５００Ｖであるから、ネガ帯電性であるトナーは感光ドラム上の画像部Ｖ１に付着し、転写紙上に転写される。一方、トナーから分離された感光ドラム上のポジ帯電性外添剤は、ポジであるため感光ドラムから転写紙に転写されず、且つ一次粒径が０．５μｍであり通常のクリーニング装置では完全に除去するのは困難であるため、一部スリ抜けてしまう。クリーニング装置をスリ抜けたポジ帯電性外添剤は、帯電ローラ対向部において感光ドラム間に形成される電界により帯電ローラに付着する。
【００７６】
前記帯電ローラに付着したポジ帯電性外添剤は樹脂粒子で電気抵抗が高いため、多量に蓄積すると帯電ローラの電気抵抗を部分的に上昇させ、ハーフトーンムラ等の画像不良を発生させるので、本発明では電界により帯電ローラから除去する。
【００７７】
図４（ｂ）に非画像形成時における各部材の電位を記す。転写ローラにより−５００Ｖに帯電された感光ドラムに対して、帯電ローラ電位は−３５０Ｖであるため、帯電ローラ上のポジ帯電性外添剤は感光ドラム上に電界により移行する。このとき感光ドラム上と現像スリーブ間は略同一の電位で、且つ現像電圧の交流成分が切れているため、外添剤、トナーの移行は共に存在しない。一方、転写ローラ電位（二点鎖線で記した）は−１．２ｋＶであるため、転写ローラ対向部において感光ドラム間で形成される電界により、ポジ帯電性外添剤は転写ローラに一時的に移行し、次の画像形成時に転写紙間の電界により転写紙裏面に移行し、機外に排出される。ポジ帯電性外添剤は無色の樹脂粒子であるため、転写紙裏面に定着されても汚れとして認識されない。
【００７８】
また、非画像形成時に転写ローラにトナーと同極性の電圧を印加することは、例えば小サイズ紙の通紙時に非通紙部に存在するドラム上のトナー（いわゆるドラム上のカブリ）が転写ローラを汚染した際には、転写ローラ上に付着したネガ帯電性のトナーを転写ローラから除去する役割も同時に果たしている。
【００７９】
すなわち本実施例における発明を用いることで、画像形成装置における現像手段内ではトナー形状係数ＳＦ１が大きな非球形化トナーとする。したがってトナーの摩擦・摺擦を容易にすることで、現像ブレードにおいてトナー薄層形成並びにトリボ付与を向上し、トナー供給部材における現像スリーブ上の残留トナーの確実な剥ぎ取りを可能にする。
【００８０】
且つ転写時にはトナー形状係数ＳＦ１を小さくすることで、トナーを球形化し、転写効率、転写中抜け抑制を向上することが可能となった。
【００８１】
さらに非画像形成時にはポジ帯電性外添剤を帯電ローラから感光ドラムに移行させる電界を生じることにより、クリーニング装置をスリ抜けたポジ帯電性外添剤を帯電ローラから除去し、一時的に転写ローラに付着せしめた後、画像形成時に転写紙裏面に転写して排出するため、トナーから分離されたポジ帯電性外添剤が帯電ローラ、転写ローラに蓄積して電気抵抗ムラを生じることなく、長期にわたり安定した接触帯電が実現された。
【００８２】
また本実施例では、非画像形成時として感光ドラム上に画像が形成されない非通紙時には毎回帯電ローラからポジ帯電性外添剤を除去しているが、一定のインターバル毎に実施したり、装置起動時（前回転時）や装置終了時（後回転時）にのみ実施することも可能である。
【００８３】
（実施例２）
実施例２は本発明における画像形成装置としてクリーナレス画像形成装置、帯電手段として帯電ブラシ、一成分現像剤としてコア／シェル構造を有する重合トナーを適用したものである。
【００８４】
以下図６により説明する。本実施例の構成は基本的に実施例１と類似であるが、転写後の感光ドラム上残留トナーを回収するクリーニング装置が存在せず、残留トナーは帯電ブラシによりネガに帯電された後、現像装置により回収されるクリーナレスシステムである。したがってクリーナレスシステムは画像形成装置の小型化、トナーの有効活用が可能となるというメリットを有する。
【００８５】
しかしながらクリーナレスシステムにおいては、感光ドラム上に残留したトナーが多量に存在すると次の画像形成プロセス時において、感光ドラムの帯電不良、露光不良によって画像不良を発生してしまう。
【００８６】
そこで安定したクリーナレスシステムを得るには転写効率を１００％近くまで高めることが望まれている。
【００８７】
本実施例では、前述したように高い転写効率が得られる球形トナーを簡易に得る手段として懸濁重合法を用いることで、トナーの小粒径化が容易になると同時にトナーの粒径分布をシャープにし、画像の高精細化を達成し、さらに懸濁重合法によりトナーにコア／シエル構造を持たせることで、定着性の向上と耐ブロッキング性の両立、ならびにコア部に離型剤を用いることによる定着部オイル塗布部材の簡素化を可能にした。
【００８８】
以下に本実施例に用いられた重合トナーＴ２について説明する。
【００８９】
本実施例におけるトナーは前述した重合法により製造されたトナーであり、イオン交換水７１０ｇに、０．ｌＭ−Ｎａ_３ＰＯ_４水溶液４５０ｇを投入し、６０℃に加温した後、ＴＫ式ホモミキサー（特殊機化工業製）を用いて、１２０００ｒｐｍにて撹拌した。これに１．０Ｍ−ＣａＣｌ_２水溶液６８ｇを徐々に添加し、Ｃａ_３（ＰＯ_４）_２を含む水系媒体を得た。
（モノマー）スチレン １６５ｇ
ｎ−ブチルアクリレート １５ｇ
（荷電制御剤）サリチル酸金属化合物 ３ｇ
（極性レジン）飽和ポリエステル １０ｇ
（酸価１４，ピーク分子量８０００）
（離型剤）エステルワックス（融点７０℃） １５ｇ
【００９０】
上記処方を６０℃に加温し、ＴＫ式ホモミキサー（特殊機化工業製）を用いて、１２０００ｒｐｍにて均一に溶解、分散した。これに、重合開始剤２，２’−アゾビス（２，４−ジメチルバレロニトリル）１０ｇを溶解し、重合性単量体組成物を調製した。
【００９１】
前記水系媒体中に上記重合性単量体組成物を投入し、６０℃，Ｎ_２雰囲気下において、ＴＫ式ホモミキサーにて１００００ｒｐｍで１０分間撹拌し、重合性単量体組成物を造粒した。その後、パドル撹拌翼で撹拌しつつ、８０℃に昇温し、１０時間反応させた。重合反応終了後、減圧下で残存モノマーを留去し、冷却後、塩酸を加えリン酸カルシウムを溶解させた後、ろ過、水洗、乾燥をして、重量平均径約７．５μｍのシャープな着色懸濁粒子を得た。
【００９２】
本実施例において重合トナーＴ２は上記製造方法により、トナーの形状係数ＳＦ１＝１１０、ＳＦ２＝１０９の重合トナーが得られた。本重合トナーＴ２の摩擦帯電量は−３０μＣ／ｇであった。
【００９３】
ここで、トナー表面のかかる部分を重合法により形成されたトナーについては、分散媒中にプレトナー（モノマー組成物）粒子として存在させ必要な部分を重合反応により生成するため、表面性については、かなり平滑化されており、トナーの滑り性が非常に高い。したがって現像ブレードにより均一に規制するのが難しい。さらに重合トナーにコア／シェル構造を持たせることで前述したようなメリットが得られるものの、トナー中の低軟化物質はトナー自体の強度を低下させるため、現像ブレードならびに現像剤供給ローラは低い当接圧で現像スリーブに当接する必要があり、現像スリーブ上での規制・剥ぎ取り、またブレードによるクリーニングがさらに難しくなっていた。
【００９４】
そこで本実施例において重合トナーＴ２は、重合トナーＴ２が１００重量部に対して、トナーと同極性であるネガ帯電性の外添剤１．８重量部に加えて、トナーと逆極性であるポジ帯電性の外添剤０．８重量部を各トナー粒子表面に付着せしめてある。
【００９５】
ここでネガ帯電性の外添剤として用いたのはＢＥＴ法による比表面積が３００ｍ^２／ｇ、一次粒径が８ｎｍである疎水性シリカであり、ブローオフ法による摩擦帯電量は−１１０μＣ／ｇであった。トナーと同極性であるネガ帯電性外添剤の効果としては、トナー帯電性の向上、トナー流動性の向上等の従来の外添剤の効果をトナーに付与することである。
【００９６】
一方、ポジ帯電性の外添剤としては、平均粒径１μｍである無色のメラミン−ホルムアルデヒド樹脂粒子を添加している。本実施例におけるポジ帯電性外添剤の摩擦帯電量は＋５５μＣ／ｇであった。トナーと逆極性であるポジ帯電性外添剤の効果としては、実施例１と同様でトナーの滑り性の制御であり、現像装置内ではトナー形状係数ＳＦ１を大きくすることで現像ブレードにおけるトナーの規制・帯電の安定化と、現像剤供給ローラにおける現像スリーブ上の残留トナーの剥ぎ取りを容易にする。かつ所定の交番電界下にて感光ドラム上に現像することで感光ドラム上のトナーＴ２からはポジ帯電性外添剤を除去し、球形化することで良好な転写特性を得る。
【００９７】
本実施例ではポジ帯電性外添剤の粒径を大きくし、且つ摩擦帯電量を大きくすることで、ＳＦ１・ＳＦ２ともに１００に近い重合トナーＴ２でも実施例１の球形トナーＴｌ同様に滑り性を制御することが可能となった。
【００９８】
また、本発明におけるトナー表面におけるポジ帯電性外添剤の面積被覆率α＝１４％であるため、ポジに帯電した反転トナーは微量であり、長期耐久においても安定したトナートリボが得られた。
【００９９】
さらにネガ帯電性外添剤の摩擦帯電量の絶対値Ｑ１、外添量をＭ１、ポジ帯電性外添剤の摩擦帯電量の絶対値Ｑ２、外添量Ｍ２、ポジ帯電性外添剤のトナーＴ２表面に占める面積被覆率αとしたときに
Ｑ２×Ｍ２＞Ｑ１×Ｍ１×α
なる条件を満たすため、ポジ帯電性外添剤を安定してポジ極性に帯電し、現像／転写時におけるポジ外添剤の分離を容易にし、転写時にはトナー形状係数を低下し、球形化して転写効率を向上している。
【０１００】
なお本実施例においても実施例１同様の現像条件（現像間隙距離２５０μｍ、交流電圧１．５ｋＶｐｐ・２ｋＨｚ）により、トナーには適切な交番電界が印加されているため、感光ドラム上の潜像を充分に現像すると共に、感光ドラム上のトナーからポジ帯電性外添剤を除去している。現像装置中の重合トナーＴ２の形状係数ＳＦ１＝１１０であるのに対し、現像後転写前の感光ドラム画像部上の重合トナーＴ２の形状係数ＳＦ１＝１１３であり、転写効率は９８％であった。また微量に存在する逆極性に帯電した反転トナーは、実施例１同様に、交番電界により現像スリーブ側に戻して画像カブリを防止することが可能である。
【０１０１】
また、本実施例では帯電手段として接触帯電部材である帯電ブラシを用いている。帯電ブラシ１５はカーボンブラックを分散することにより電気抵抗１０^６Ωに設定された太さ６デニール，長さ２ｍｍのナイロン繊維から形成され、−７００Ｖの直流電圧に１．４ｋＶｐｐの交流電圧を重畳している。したがって転写後に感光ドラム上に残留したポジ帯電性外添剤は、実施例１同様に帯電手段である帯電ブラシ１５に付着する。
【０１０２】
本実施例における帯電ブラシは強ポジ帯電性であるナイロン繊維より形成されるため、ブラシにより摺擦することで、ポジ帯電性である外添剤の一部をネガに摩擦帯電し、画像形成時でも電界により帯電ブラシから除去することが可能である。また転写残トナーの内でポジに帯電しているトナーについてはブラシと摩擦帯電することにより殆どネガトナーに反転して、外添剤・トナーの帯電ブラシヘの蓄積を防止する。これにより帯電ブラシの汚染を改善することが可能である。
【０１０３】
なお画像形成時に極性をネガに反転された外添剤、クリーナレスに起因する転写残トナーが帯電部材から除去されると、外添剤・転写残トナーは感光ドラム上で露光部を通過することになるが、十分に少量かつ均一であるため、露光を遮ることに依る画像不良は発生しなかった。またトナー、外添剤はネガに帯電しているため現像領域において電界により現像装置に回収される（もしくは感光ドラム上で画像を形成する）。
【０１０４】
さらに非画像形成時には実施例１同様に図３に示したタイミングチャートに基づき、帯電ブラシ中のポジ帯電したままの外添剤は電界により感光ドラム上に移動し、転写ローラに一時的に回収された後、次の画像形成時に転写紙裏面に転写されて機外に排出される。ポジ帯電性外添剤は無色の樹脂粒子であるため、転写紙裏面に定着されても画像として認識されない。したがって本実施例における画像形成装置を用いることで、簡易な構成である接触帯電・転写装置と一成分現像装置を用いても、接触帯電・転写手段の抵抗変動を抑制し重合トナーを安定して現像スリーブ上にコートし、且つ転写時には転写効率の向上したため、クリーナレスシステムにおける現像部でのトナー回収が容易になり、長期にわたり画像不良のない安定したクリーナレスシステムを提供することが可能となった。
【０１０５】
【発明の効果】
以上のよう説明したように、本発明によれば、一成分現像剤と同極性である第１の外添剤によりトナーの帯電性・流動性を向上すると共に、一成分現像剤と逆極性である第２の外添剤を現像時ならびに転写時に印加する電界により一成分現像剤から分離することで、転写時における一成分現像剤の形状を現像手段内における一成分現像剤の形状から変化させ、一成分現像剤の表面形状を変化させることが可能となる。現像手段内ではトナー形状係数ＳＦ１を大きくすることでトナーを非球形化し、トナーの摩擦・摺擦を容易にすることで、現像ブレードにおけるトナー薄層形成、並びにトリボ付与を向上できる。且つ転写時にはトナー形状係数ＳＦ１を小さくすることで、トナーを球形化し、転写効率、転写中抜け抑制を向上できる。
【０１０６】
さらにクリーニングされずに像担持体上に残留した第２の外添剤が接触帯電手段に付着しても、非画像形成時に接触帯電手段から除去し現像器において回収するため、接触帯電手段上に第２の外添剤が蓄積することがなく、長期にわたり像担持体の均一な帯電が達成され、良好な画像出力が得られるようになった。
【図面の簡単な説明】
【図１】実施例１の概略構成図である。
【図２】本発明に用いられる現像剤の（ａ）現像前と（ｂ）現像後の概念図である。
【図３】本発明の帯電電圧・現像電圧・転写電圧のタイミングチャートである。
【図４】感光ドラム電位・帯電ローラ電位・現像スリーブ電位・転写ローラ電位の関係図である。
【図５】現像電界振幅と現像剤形状、転写効率の関係図である。
【図６】実施例２の概略構成図である。
【図７】従来の電子写真装置の概略構成図である。
【図８】摩擦帯電量測定装置の概略構成図である。
【符号の説明】
Ｔ１ 球形化トナー
Ｔ２ 重合トナー
１ 現像剤規制部材
２ 金属薄板
３ 現像スリーブ
４ 現像電源
５ 現像剤供給ローラ
６ 現像剤撹拌器
７ トナーコート層
１０ 感光ドラム（像担持体）[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an image forming apparatus that forms a latent image on an image carrier such as an electrophotographic photosensitive member or an electrostatic recording dielectric, visualizes the latent image, and then transfers the latent image to a recording medium to form an image. It is about.
[0002]
[Prior art]
As an output unit of an external device such as a computer or a copying machine, an image forming apparatus using an electrophotographic method as shown in FIG. 7 has been conventionally proposed. An electrophotographic photoreceptor 10 having a drum shape as a latent image carrier is uniformly charged by a charging roller 13. Next, the exposure device 14 irradiates the photoreceptor 10 with light in accordance with image information input from an external device to form a latent image. The electrostatic latent image on the photosensitive drum 10 is reversely developed in the developing device 40 by the developer T having the same polarity as that of the primary charger 117 to be a visible image, that is, a toner image (reversal development). The toner image is transferred to the transfer material P by the transfer roller 11. The transfer material P is separated from the photoreceptor 10 and is subsequently conveyed to a fixing device 126, where it becomes a permanent image after fixing. On the other hand, the developer T on the photosensitive drum 10 remaining without being transferred by the transfer roller 11 is removed by the cleaning device 12, and the photosensitive drum 10 is subjected to the next image forming process.
[0003]
Here, the developing device 40 in FIG. 7 will be described in detail. In recent years, a non-magnetic one-component developing method has been put to practical use as a simple color developing method. The developing device has a developing container 40a containing a toner T which is an insulating one-component developer. In the present embodiment, the toner T is a negatively chargeable non-magnetic toner containing a pigment of any of yellow, magenta, cyan, and black colors.
[0004]
In the developing device 40, a toner agitating member 6 rotates in a direction indicated by an arrow in the drawing, and conveys the toner T toward the developing sleeve 3 and the developer supply roller 5.
[0005]
The developing device 40 has a conductive cylindrical sleeve 3 having an outer diameter of 16 mm made of a metal such as aluminum or stainless steel, and is arranged at a constant distance from the opposing photosensitive drum 10 by a gap regulating member (not shown). .
[0006]
A developer supply roller 5 made of urethane sponge is in contact with the developing sleeve 3. The developer supply roller 5 removes the toner history (so-called ghost) on the developing sleeve 3 by rotating in the opposite direction to the developing sleeve 3 and supplies the toner T onto the developing sleeve 3 at the same time.
[0007]
A developing blade 1 is in contact with the developing sleeve 3 as a toner amount regulating member. The developing blade 1 regulates the toner on the developing sleeve 3 to form a thin toner layer 7 and is transported to a developing area (a drum facing position). Specifies the amount. The amount of toner conveyed to the developing area is determined by the contact pressure and contact length of the developing blade 1 that comes into contact with the developing sleeve 3. The developing blade 1 is bonded or welded to a thin metal plate 2 of phosphor bronze or stainless steel having a thickness of several hundred μm, and the elasticity of the thin metal plate 2 causes the developing blade 1 to uniformly contact the developing sleeve 3. It is a blade. At this time, the contact condition of the developing blade 1 is determined by the material, thickness, penetration amount, and set angle of the all-thin thin plate 2, and the amount of the transported toner is 0.3 to 1.0 mg / unit unit surface area of the developing sleeve 3. cm²Stipulated.
[0008]
At the time of development, the toner conveyed to the developing area flies from the developing sleeve 3 onto the photosensitive drum 10 rotating in the direction of the arrow due to a developing electric field generated by a developing power supply applied between the developing sleeve 3 and the photosensitive drum 10. The latent image adheres to the latent image on the drum 10 and is visualized as a toner image.
[0009]
Here, the toner T will be described. Conventionally, toner has been produced by uniformly dispersing a resin, a release agent composed of a low softening point substance, a colorant, a charge control agent, and the like using a pressure kneader, an extruder, or a media disperser. In addition to the method of producing a toner by a so-called pulverization method in which a target is collided with a target under a jet stream, finely pulverized to a desired toner particle size, and further subjected to a classification process to sharpen the particle size distribution to form a toner, JP-B-56-13945 discloses a method of atomizing a molten mixture into air using a disk or a multi-fluid nozzle to obtain a spherical toner, and JP-B-36-10231, JP-A-59-53856, A method in which a toner is directly produced by using a suspension polymerization method described in JP-A-59-61842, or an aqueous system in which a monomer is soluble and a polymer obtained is insoluble. The toner can be manufactured using a dispersion polymerization method in which a toner is directly produced using an organic solvent or an emulsion polymerization method typified by a soap-free polymerization method in which a toner is produced by directly polymerizing in the presence of a water-soluble polar polymerization initiator. It is.
[0010]
In recent years, it has been found that by using a spherical toner, the fluidity of the toner and the transfer efficiency during toner transfer can be improved.
[0011]
There are two main methods for producing spherical toner.
1. A conventional pulverized toner surface is subjected to a plastic spheroidizing treatment by thermal and mechanical stress. 2. It is manufactured by a polymerization method.
[0012]
Regarding the function and effect of the toner shape, it is possible to greatly improve the transfer efficiency of the toner by making it spherical. In the case of irregular-shaped toner such as pulverized toner, if the transfer roller pressure is high during roller transfer, the toner is mechanically pressed against the photoreceptor, resulting in poor transfer, and so-called “missing characters” tend to occur. With a spherical toner, "missing of a character" hardly occurs.
[0013]
As the polymerized toner, a suspension polymerization method under normal pressure or under pressure, which can obtain a fine particle toner having a spherical particle size distribution of 4 to 8 μm with a sharp particle size distribution, is particularly preferable.
[0014]
In recent years, as a part of improving the image quality of electrophotography, the toner particle size has been reduced. However, the energy required to pulverize the particles is proportional to the square of the toner particle size. It is difficult to reduce the diameter. However, since the polymerization method generates toner particles using a chemical reaction, it is easy to reduce the particle size of the toner, and it is easy to obtain a sharp particle size distribution. Therefore, the polymerization method is a spherical high-quality image. Also suitable for forming.
[0015]
Also, according to the suspension polymerization method, it is possible to encapsulate a low softening point substance, and as a specific method, the polarity of the material in an aqueous medium is made smaller for the low softening point substance than for the main monomer. By setting and further adding a small amount of a highly polar resin or monomer, a toner having a so-called core / shell structure in which a low softening point substance is coated with an outer shell resin can be obtained.
[0016]
In a polymerized toner having such a core / shell structure, by using a material having a low softening point as a core material, it is possible to perform heat fixing with a smaller amount of heat than before.
[0017]
Further, by using a highly releasable substance as the core substance, it is possible to prevent the toner from being welded to the fixing roller. This eliminates the need to apply a release agent such as silicone oil to the fixing device, so that the configuration of the fixing device is simplified, and the cost and maintenance of the fixing device can be reduced.
[0018]
[Problems to be solved by the invention]
As mentioned earlier, the use of spherical toner
(1) Improving transfer efficiency
(2) Improvement of omission during transfer
There is such a merit.
[0019]
Further, by manufacturing the spherical toner by a polymerization method,
(3) Easy reduction of toner particle size
(4) Sharp toner particle size distribution (sharp tribo distribution)
By giving the toner a core / shell structure by a suspension polymerization method as the polymerization method,
(5) Improving fixability and blocking resistance
(6) Simplification of the oil applying member in the fixing section by using a release agent for the core section
Is achieved, and high image quality and low cost of the entire image forming apparatus are achieved.
[0020]
Here, in the conventional one-component developing device, in order to obtain good developing characteristics (image density, toner adhesion (fogging) to non-image areas, toner scattering, etc.), the toner on the developing sleeve is uniformly slid by the regulating member. It is necessary to form a stable toner thin layer that is rubbed, triboelectrically charged, and rubbed.
[0021]
Further, in the above-described conventional non-magnetic one-component developing device, the toner on the developing sleeve 3 is scraped off once by the non-magnetic developer supply member 5, and the past toner history is removed, and then a new toner layer is formed on the developing sleeve. Need to supply. If the toner on the developing sleeve 3 cannot be scraped, charge-up of the toner or image unevenness in halftone occurs, and the image quality is significantly reduced.
[0022]
Therefore, when the spherical toner such as the polymerized toner is used as a one-component developer, particularly a non-magnetic one-component developer to achieve the above object, the following problems occur.
[0023]
First, since the spherical toner / polymerized toner has a spherical shape, the friction is small and slippery as compared with a pulverized toner having an irregular shape and a lot of irregularities, so that the toner slips off the surface of the developer regulating member 1. . Therefore, a uniform thin toner layer (toner application amount of 0.3 to 1.0 mg / cm) is formed on the developer carrier 3.²) Is difficult to form. The toner that has slipped out of the developer regulating member 1 without being triboelectrically charged with the developing sleeve cannot adhere to the developing sleeve with a mirror image force, and scatters from the developing sleeve to contaminate the image forming apparatus or output image. Was degraded.
[0024]
Secondly, since the spherical toner / polymerized toner is spherical, the friction is small and slippery as compared with a pulverized toner having an irregular shape and many irregularities. Therefore, since the surface of the developer supply member 1 slips out, it is difficult to mechanically scrape the developer supply member 5 from the developing sleeve 3. Therefore, a residual toner layer is formed on the developing sleeve 3 and the supply of new toner by the developer supply member 5 is hindered. And other various image degradations.
[0025]
Third, since the spherical toner and the polymerized toner are slippery, there is a problem that the triboelectric charge is reduced. In particular, in a non-magnetic one-component developing device, unless sufficient tribo is given to the spherical toner, the toner coating amount on the developing sleeve is reduced or becomes non-uniform, resulting in a decrease in image density and a halftone image. As a result, the quality of the output image is significantly reduced as image unevenness.
[0026]
The polymerized toner having a core / shell structure has the above-mentioned merits, and the low softening point substance in the toner lowers the fixing temperature of the toner but lowers the strength of the toner itself. The supply roller needs to contact the developing sleeve with a low contact pressure, and it has become more difficult to regulate and peel off the developer.
[0027]
That is, although making the toner spherical has the above advantages at the time of transfer, the above problem also occurs at the time of development, and it has been difficult to optimize the entire image forming apparatus.
[0028]
On the other hand, for the spherical toner, a first external additive having the same polarity as the toner (negative external additive) and a second external additive having the opposite polarity to the toner (positive external additive) By externally adding at least two kinds of particles of the above, in the developing device, irregularities are formed on the toner surface by a positively chargeable external additive to control the toner slipperiness, and an electric field formed at the time of development causes the positively chargeable external additive to be formed. By separating the additive from the toner, the toner can be made spherical at the time of transfer. However, although the above method can achieve both the merits of transfer with spherical toner and the stability of toner coat at the time of development, the method is used in an image forming apparatus that charges a photosensitive drum by a contact charging unit such as a roller or a brush. In this case, the positively chargeable external additive that has slipped out of the cleaning device adheres and accumulates on the contact charging means, causing the electric resistance of the contact charging means to become non-uniform. Had occurred. Therefore, in order to achieve both high transfer efficiency and toner coat stability by the above-described method, a complicated and expensive cleaning device that does not allow even an external additive having a small particle diameter to slip off is required, or a relatively high voltage is required and the cost is high. It was necessary to charge the image carrier by non-contact charging means.
[0029]
Means and Action for Solving the Problems
The present invention provides an image carrier, a charging unit that contacts the image carrier and charges the surface of the image carrier to a predetermined potential, and a developing unit that visualizes an electrostatic latent image on the image carrier with a one-component developer. In an image forming apparatus including a transfer unit that transfers a visualized toner image on an image carrier to a transfer material,
The one-component developer has at least two kinds of external additive particles, a first external additive having the same polarity as the one-component developer, and a second external additive having the opposite polarity to the one-component developer. And an electric field in which the second external additive moves from the charging unit to the image carrier during non-image formation.And
The transfer unit is a contact transfer unit, and applies an electric field in which the second external additive moves from the image carrier to the transfer unit during non-image formation.To an image forming apparatus.
[0030]
A first external additive having the same polarity as the one-component developer improves the chargeability and fluidity of the toner, and a second external additive having a polarity opposite to that of the one-component developer is applied during development and transfer. By separating from the one-component developer by the electric field generated, the shape of the one-component developer at the time of transfer can be changed from the shape of the one-component developer in the developing means, and the surface shape of the one-component developer can be changed It becomes.
[0031]
Further, in the developing means, the toner is made non-spherical by increasing the toner shape factor SF1, and the friction and rubbing of the toner are facilitated, whereby the formation of a thin toner layer on the developing blade and the application of tribo are improved. At the time of transfer, the toner is made spherical by reducing the toner shape factor SF1 to improve transfer efficiency and suppression of transfer omission.
[0032]
Further, even if the second external additive remaining on the image carrier without being cleaned adheres to the contact charging means, the second external additive is removed from the contact charging means during non-image formation. The agent is not accumulated, the image carrier is uniformly charged over a long period of time, and a good image output is obtained.
[0033]
BEST MODE FOR CARRYING OUT THE INVENTION
SF1 and SF2 indicating the shape factor used in the present invention are obtained by randomly sampling 100 toner images using FE-SEM (S-800) manufactured by Hitachi, Ltd., and the image information is manufactured by Nicole Corporation via an interface. It was introduced into an image analyzer (Luzex3) and analyzed, and the values calculated by the following equation were defined as shape factors SF1 and SF2 in the present invention.
[0034]
(Equation 1)

(AREA: toner projection area, MXLNG: absolute maximum length, PERI: circumference)
[0035]
The shape factor SF1 of the toner indicates a degree of spherical shape. When the shape factor SF1 is larger than 140, the shape gradually becomes irregular from a spherical shape. SF2 indicates the degree of unevenness, and if it is larger than 120, the unevenness of the toner surface becomes remarkable.
[0036]
By coating the toner surface with an external additive, a minute gap is provided between the toners or between the photoconductors, thereby further improving the fluidity of the polymerized toner and improving the transfer efficiency to nearly 100%. Is possible. In that sense, the first external additive coverage on the toner surface is preferably 5 to 99%, more preferably 10 to 99%. The coverage of the external additive on the toner surface was determined by randomly sampling 100 toner images using FE-SEM (S-800) manufactured by Hitachi, Ltd., and the image information was obtained via an interface using an image analyzer (Luzex3 manufactured by Nicole). ) And analyzed.
[0037]
The first external additive or the second external additive used may have a particle diameter of 1/3 or less of the weight average diameter of the toner particles from the viewpoint of durability when added to the toner. preferable. The particle diameter of the additive means an average particle diameter thereof obtained by observing the surface of the toner particles with an electron microscope. As the external additive, for example, the following are used.
[0038]
Metal oxides (aluminum oxide, titanium oxide, strontium titanate, cerium oxide, magnesium oxide, chromium oxide, tin oxide, zinc oxide, etc.), nitrides (silicon nitride, etc.), carbides (silicon carbide, etc.), metal salts (sulfuric acid, etc.) Calcium, barium sulfate, calcium carbonate, etc., fatty acid metal salts (zinc stearate, calcium stearate, etc.), carbon black, silica, etc.
[0039]
These external additives are used in an amount of 0.01 to 10 parts by weight, preferably 0.05 to 5 parts by weight, based on 100 parts by weight of the toner particles. These external additives may be used alone or in combination of two or more. Those subjected to a hydrophobic treatment are more preferable.
[0040]
FIG. 8 is an explanatory diagram of an apparatus for measuring a triboelectric charge amount of a toner. First, in a metal measuring container 42 having a 500-mesh screen 43 at the bottom, a two-component developer whose triboelectric charge is to be measured is put into a polyethylene bottle having a capacity of 50 to 100 ml, and is manually placed for about 10 to 40 seconds. Then, about 0.5 to 1.5 g of the developer is put, and a metal lid 44 is closed. At this time, the entire weight of the measuring container 42 is weighed to be W1 (kg). Next, in the suction device 41 (at least a portion in contact with the measurement container 42 is at least an insulator), the air is suctioned from the suction port 47 and the air volume control valve 46 is adjusted to adjust the pressure of the vacuum gauge 45 to 250 mmAq. In this state, suction is sufficiently performed, preferably for 2 minutes, to remove the resin by suction. The potential of the electrometer 49 at this time is set to V (volt). Here, 48 is a capacitor, and its capacity is C (F). In addition, the whole measurement container 42 after suction is weighed and defined as W2 (kg). The triboelectric charge of the toner is calculated by the following equation.
[0041]
(Equation 2)

[0042]
(Example 1)
FIG. 1 shows a first embodiment of the present invention.
[0043]
In this embodiment, as a one-component developer, a toner obtained by subjecting a toner manufactured by a pulverizing method to a spheroidizing process and externally adding two kinds of external additives to a spheroidized toner T1 is used. Note that the description of the fixing means and the transfer material is omitted.
[0044]
The photosensitive drum 10, which is an image carrier, rotates at a peripheral speed of 100 mm / sec in the direction of the arrow in the figure, and is set to a surface potential of -700 V by the charging roller 13. Here, the charging roller 13 is formed by forming urethane rubber in which carbon black is dispersed on a mandrel having an outer diameter of 4 mm, and has an outer diameter of 10 mm and an electric resistance of 10 mm.⁶It is an elastic roller of Ω. Here, various types of elastic materials such as silicone rubber and EPDM can be used as the material of the charging roller.⁷Ω or less, and 10 to prevent leakage⁵It is preferable to set the electric resistance to Ω or more. On the charging roller 13, an AC voltage of 500 Hz and 2 kVpp is superimposed on a DC voltage of −700 V from the charging power supply 17.
[0045]
The exposure unit 14 performs exposure corresponding to the image on the photosensitive drum 10 to form an electrostatic latent image. Here, the bright portion potential as the image portion is -150V, and the dark portion potential as the non-image portion is -700V.
[0046]
The developing device 40 has a developing sleeve 3. The developing sleeve 3 is located at a distance of 250 μm from the photosensitive drum 10, and causes the toner on the developing sleeve 3 to fly by an electric field, and the electrostatic latent on the photosensitive drum 10. The image is converted into a toner image.
[0047]
The toner image on the photosensitive drum is transferred onto a transfer sheet by a transfer roller 11, and is heated and pressed by a fixing unit and fixed on the transfer sheet. The transfer roller 11 has an electric resistance 10 by dispersing a metal oxide in an EPDM sponge.⁸This is an elastic roller set to Ω, and is controlled so that a constant current of 8 μA flows to the transfer paper / drum side when the paper is passed, and a sufficient positive charge is applied to the back surface of the transfer paper.
[0048]
The toner remaining on the photosensitive drum 10 without being transferred to the transfer paper is peeled off and removed from the photosensitive drum by a cleaning blade 18 installed in the cleaning device 12. However, the external additive separated from the toner T <b> 1 has a small particle size and is not completely removed by the cleaning blade 18 but slips off and adheres to the charging roller 13.
[0049]
Next, the developing device 40 will be described in detail.
[0050]
In the developing device 40, there is a toner T1 which is a spherical toner. The toner T1 is a negatively-chargeable non-magnetic one-component toner, and two types of a negatively chargeable external additive and a strongly positively chargeable external additive are externally added to a pulverized toner formed into a spherical shape by a method described later. It is a thing.
[0051]
The toner stirring member 6 in the developing device 40 rotates in the direction of the arrow in the figure, and conveys the spherical toner T1 toward the developing sleeve 3 and the developer supply roller 5.
[0052]
The developing device 40 has a conductive cylindrical sleeve 3 made of aluminum and having a diameter of 16φ, and is arranged at a distance of 250 μm from the opposing photosensitive drum 10 by a gap regulating member (not shown).
[0053]
A developer supply roller 5 made of urethane sponge is in contact with the developing sleeve 3. The developer supply roller 5 has a diameter of 8 mm, is in contact with the developing sleeve 3 at an intrusion amount of 1 mm, and is driven by the gear (not shown) in the counter direction at a peripheral speed of 50 mm / sec. The developer supply roller 5 rotates in the counter contact direction with the developing sleeve 3 to remove the toner history (so-called ghost) on the developing sleeve 3 and supply the toner T onto the developing sleeve 3 at the same time. The developer supply roller 5 is made of open-cell sponge, and is a low hardness product having an Asker C hardness of 20 °. Here, as the developer supply roller 5 is softer, the deterioration of the toner at the time of supplying and removing the toner can be suppressed.
[0054]
A developer regulating member 1 is in contact with the developing sleeve 3 as a toner amount regulating member. The toner regulating member 1 regulates the toner on the developing sleeve 3 to frictionally charge the spherical toner T1 and to apply a charge suitable for development to the toner. At the same time, the thin toner layer 7 is formed and the amount of toner to be transported to the developing area (drum facing position) is defined.
[0055]
At the time of development, the toner conveyed to the developing area flies from the developing sleeve 3 onto the photosensitive drum 100 by a developing electric field generated by the developing power supply 4 applied between the developing sleeve 3 and the photosensitive drum, and the latent image on the photosensitive drum 100 Attach to the image and visualize the latent image as a toner image.
[0056]
Next, the spherical toner T1 in this embodiment will be described.
[0057]
Methods for producing the spherical toner include a binder resin containing a styrene-acrylic copolymer as a main component, a release agent having a low softening point, a coloring agent for carbon black, and a charge control for a metal complex salt of a monoazo dye. After uniformly dispersing using a pressure kneader, extruder or media disperser as an agent, it is made to impinge on the target mechanically or under a jet stream, finely pulverized to a desired toner particle size, and then subjected to plastic sphering treatment. I do. Further, through a classification step, the particle size distribution is sharpened to form a toner.
[0058]
Specific devices for performing the plastic sphering process include Nara Machinery Co., Ltd. “Hybridization System” and Turbo Eg Co., Ltd. “Turbo Mill”. When the rotating plate rotates at a high speed, the toner in the circulating airflow collides with the blade rotating at a high speed. At this time, the convex portion of the toner undergoes plastic deformation due to impact energy and is smoothed, and the toner as a whole undergoes a shape change in a spherical direction.
[0059]
In addition, as a means for spheroidizing, a method has been proposed in which the surface of the toner is melted and spheroidized by hot air using a spray drier, or the toner is dispersed in a hot air stream to melt the surface and spheroidize. The spheroidized toner produced by such a manufacturing method may be used in the present embodiment.
[0060]
In the present embodiment, a spherical toner having an average particle diameter of 8 μm and a shape factor of SF1 = 115 and SF2 = 110 was obtained by the above-described manufacturing method. The triboelectricity of the spherical toner T1 measured by the above-described tribometric method was −38 μC / g.
[0061]
Here, when measuring the triboelectric charge amount, 0.3 g of an external additive was mixed into 9.7 g of a ferrite carrier having a particle size of 50 μm, and the measurement was performed after shaking 300 times in a polyethylene container.
[0062]
In this embodiment, as shown in FIG. 2A, the surface of the spherical toner T1 is 1.0 part by weight of the negatively chargeable external additive having the same polarity as the toner with respect to 100 parts by weight of the spherical toner T1. In addition, 0.8 parts by weight of a positively chargeable external additive having a polarity opposite to that of the toner is adhered to the surface of each toner particle to make it non-spherical. The toner shape factors of the spherical toner T1 after externally adding the above two types of external additives were SF1 = 150 and SF2 = 135.
[0063]
Here, the reason why the specific surface area measured by the BET method was 300 m²/ G, a hydrophobic silica having a primary particle size of 8 nm, and a triboelectric charge of -110 μC / g. The effect of the negatively chargeable external additive having the same polarity as that of the toner is to impart the effect of the conventional external additive such as improvement in toner chargeability and toner fluidity to the toner.
[0064]
On the other hand, as a positively chargeable external additive, colorless PMMA particles having a primary particle size of 0.5 μm are added. The triboelectric charge of the positively chargeable external additive in this example was +40 μC / g. The effect of the positively chargeable external additive having the opposite polarity to that of the toner is that particles having a primary particle size of 0.5 μm adhere to the spherical toner, thereby making the toner shape appropriately non-spherical and controlling the slipperiness of the toner. It becomes possible. Therefore, the toner does not slip out of the developing blade, and a good toner charge and a uniform thin toner layer can be obtained. In addition, since the toner does not slip through the developer supply roller, charge-up of the toner on the sleeve is prevented, and image reproducibility is improved.
[0065]
Here, in the present invention, the negatively chargeable external additive and the positively chargeable external additive on the toner surface are present as shown in FIG. By setting the coverage α of the positively chargeable external additive to 50% or less, the tribo of the entire toner including the external additive can be negatively charged stably, and a good image with less fog can be obtained. I can do it. According to the measurement method described above, the coverage of the external additive on the surface of the spherical toner T1 in this example was 80% for the strongly negatively charged external additive and 22% for the positively charged external additive.
[0066]
In order to enhance the effect of the positively chargeable external additive, it is preferable that the positively chargeable external additive is positive even if the negatively chargeable external additive adheres to each particle. More specifically, the absolute value Q1 of the triboelectric charge amount of the negatively chargeable external additive, the external addition amount M1, the absolute value Q2 of the triboelectric charge amount of the positively chargeable external additive, the external addition amount M2, the positively chargeable external additive When the area coverage α of the agent on the surface of the toner T1
Q2 × M2> Q1 × M1 × α
Under these conditions, it is possible to stably charge the positively chargeable external additive to a positive polarity, facilitate separation of the positive external additive during development / transfer, and stably obtain the effects of the present invention. It becomes.
[0067]
Further, the positively chargeable external additive is not spherical but amorphous, and by using particles having a large particle size, it is possible to control the slipperiness of the toner even with a small external addition amount. By setting the primary particle size of the positive external additive to 0.1 to 2 μm, the toner shape factor SF1 can be increased, and the positive external additive can be easily separated during development / transfer. Good transfer characteristics were obtained by setting the negatively chargeable external additive to 0.1 μm to 1 nm.
[0068]
In the present invention, by increasing the shape factor SF1 of the toner with a positively chargeable external additive, good toner coatability at the time of development can be obtained, and at the same time, by optimizing the jumping development method, FIG. As shown in (2), the positively chargeable external additive is separated from the toner on the drum from the toner, and the toner shape factor SF1 at the time of transfer is reduced to improve transfer efficiency and omission during transfer.
[0069]
In the present embodiment, an AC voltage of 1.5 kVpp, a frequency of 2 kHz, and a DC voltage of -500 V are applied to the developing sleeve 3 as a developing bias from the developing power source 4, and a static voltage on the opposing photosensitive drum with a gap of 250 μm is applied. The toner is made to fly on the latent image to form a toner image.
[0070]
According to the jumping development method used in the present embodiment, the transfer / reverse transfer of the toner is caused between the developer carrier and the image portion VL and the non-image portion Vd on the photosensitive drum by the alternating electric field, so that the positive charging property is improved. Is effectively separated from the negatively chargeable toner and collected in a developing sleeve or a non-image portion. This is to increase the chance of separating the positively chargeable external additive by causing the toner once attached to the image portion of the photosensitive drum to fly again to the developing sleeve side by an appropriate alternating electric field. Also, depending on the jumping development, the normally charged negative polarity toner produces an appropriate edge effect in the image area, improves sharp edge sharpness and reproducibility of halftone which is a latent image close to the non-image area, Further, since the positive polarity toner can be collected in the developing sleeve, fog in the non-image area can be reduced as compared with the DC developing method described later.
[0071]
In the DC developing method in which an alternating current is not applied, the toner is not reciprocated by a strong electric field, so that the positively chargeable external additive cannot be sufficiently removed from the toner once adhered on the drum. In addition, the toner of the positive polarity charged to the opposite polarity adheres to the non-image portion, easily forms so-called image fog, and deteriorates image quality.
[0072]
Here, the relationship between the amplitude of the alternating electric field used as the developing electric field, the SF1 of the developer, and the transfer efficiency will be described. Assuming that a developing electric field amplitude A is a peak-to-peak AC voltage Vpp of a developing power source and a distance SD between the developing sleeve and the photosensitive drum,
A = Vpp / 2SD
Can be represented by As shown in FIG. 5, in the DC developing method in which the developing electric field amplitude A = 0, the shape factor SF1 of the toner on the drum after development and before transfer was 150, which was almost the same as the toner in the developing device. As a result, the transfer efficiency was only 77%. On the other hand, by forming an alternating electric field in the developing gap and setting the developing electric field amplitude to 2 kV / mm or more, the positively chargeable external additive is separated from the toner surface, and the toner shape factor SF1 before transfer is reduced to 130 or less. Was. As a result, the transfer efficiency was improved to 95% because the toner was transferred after being formed into a sphere. If the developing electric field amplitude is 5 kV / mm or more, a leak may occur depending on the latent image condition. Therefore, the developing electric field amplitude is preferably 2 kV / mm or more and 5 kV / mm or less.
[0073]
Here, as the spherical toner, the shape factor SF-1 before external addition is 100 to 130, SF-2 is 100 to 120, and the first external additive and the second external additive are externally added. When a spherical toner having a shape factor SF-1 in the range of 130 to 170 and SF-2 in the range of 120 to 160 was used, the toner coating and the transfer efficiency at the time of development were compatible with the development electric field amplitude.
[0074]
Further, in this embodiment, in order to prevent accumulation of the positively chargeable external additive on the charging roller, an electric field for removing the positively chargeable external additive from the charging roller is applied during non-image formation. FIG. 3 is a timing chart showing the DC component Ch (DC) and the AC component Ch (AC) of the charging voltage, the DC component Dev (DC) and the AC component Dev (AC) of the developing voltage, and the transfer voltage Tr. Upon completion, the transfer voltage changes from 2.0 kV to -1.2 kV, and the surface potential of the photosensitive drum 10 is reduced to -500 V. Next, the charging power source is switched from DC-700V to -350V, and at the same time, the AC voltage of the charging power source is turned off. The AC component of the development voltage of 1.5 kVpp is cut off when the image formation is completed, but the DC application voltage of the development voltage of -500 V does not change.
[0075]
FIG. 4A shows the surface potential of each part on the photosensitive drum at the time of image formation based on the timing chart, and the potential of the charging roller (indicated by a dashed line) is -700 V, and the potential of the photosensitive drum (dotted line) Is non-image portion Vd = -700 V after charging / exposure, image portion V1 = -150 V, and Tr = + 50 V after transfer. Since the developing sleeve potential (shown by the solid line) is -500 V, the negatively charged toner adheres to the image portion V1 on the photosensitive drum and is transferred onto the transfer paper. On the other hand, the positively chargeable external additive on the photosensitive drum separated from the toner is not transferred from the photosensitive drum to the transfer paper because it is positive, and has a primary particle size of 0.5 μm. Since it is difficult to remove, a part of the file will slip off. The positively chargeable external additive that has slipped out of the cleaning device adheres to the charging roller by an electric field formed between the photosensitive drums at the charging roller facing portion.
[0076]
Since the positively chargeable external additive attached to the charging roller is a resin particle having a high electric resistance, when accumulated in a large amount, the electric resistance of the charging roller partially increases, and image defects such as halftone unevenness are generated. In the present invention, the toner is removed from the charging roller by an electric field.
[0077]
FIG. 4B shows the potential of each member during non-image formation. Since the potential of the charging roller is -350 V with respect to the photosensitive drum charged to -500 V by the transfer roller, the positively chargeable external additive on the charging roller moves onto the photosensitive drum by an electric field. At this time, since the potential on the photosensitive drum and that between the developing sleeve are substantially the same and the AC component of the developing voltage is cut off, there is no transfer of the external additive and the toner. On the other hand, since the transfer roller potential (indicated by the two-dot chain line) is -1.2 kV, the positively chargeable external additive is temporarily applied to the transfer roller by the electric field formed between the photosensitive drums at the transfer roller facing portion. Then, at the time of the next image formation, the image is transferred to the back surface of the transfer sheet by the electric field between the transfer sheets, and is discharged outside the apparatus. Since the positively chargeable external additive is a colorless resin particle, it is not recognized as a stain even if it is fixed on the back surface of the transfer paper.
[0078]
Applying a voltage having the same polarity as that of the toner to the transfer roller during non-image formation means that, for example, toner on the drum (so-called fog on the drum) existing in the non-sheet-passing portion when small-size paper passes is transferred to the transfer roller. When the toner is contaminated, the toner also plays a role of removing the negatively charged toner attached to the transfer roller from the transfer roller.
[0079]
That is, by using the invention of the present embodiment, a non-spherical toner having a large toner shape factor SF1 in the developing unit of the image forming apparatus is obtained. Therefore, by facilitating the friction and rubbing of the toner, the formation of a thin toner layer and the provision of a tribo in the developing blade are improved, and the toner remaining on the developing sleeve in the toner supply member can be reliably peeled off.
[0080]
At the time of transfer, the toner is made spherical by reducing the toner shape factor SF1 to improve the transfer efficiency and the suppression of missing during transfer.
[0081]
Further, during non-image formation, an electric field is generated to transfer the positively chargeable external additive from the charging roller to the photosensitive drum, thereby removing the positively chargeable external additive that has slipped out of the cleaning device from the charging roller, and temporarily transferring the transfer roller. After being adhered to the toner, the toner is transferred to the back side of the transfer paper during image formation and discharged, so that the positively chargeable external additive separated from the toner does not accumulate on the charging roller and the transfer roller, resulting in non-uniform electrical resistance. Over a long period of time, stable contact charging was realized.
[0082]
Further, in the present embodiment, the positively chargeable external additive is removed from the charging roller every time when the image is not formed on the photosensitive drum when the image is not formed on the photosensitive drum at the time of non-image formation. It is also possible to carry out only at the time of startup (during pre-rotation) or at the time of ending the apparatus (during post-rotation).
[0083]
(Example 2)
In the second embodiment, a cleanerless image forming apparatus is used as an image forming apparatus, a charging brush is used as a charging unit, and a polymer toner having a core / shell structure is used as a one-component developer.
[0084]
This will be described below with reference to FIG. The configuration of this embodiment is basically similar to that of the first embodiment. However, there is no cleaning device for collecting the residual toner on the photosensitive drum after the transfer, and the residual toner is charged negatively by a charging brush and then developed. It is a cleanerless system collected by the device. Therefore, the cleanerless system has the advantages that the size of the image forming apparatus can be reduced and the toner can be effectively used.
[0085]
However, in a cleaner-less system, if a large amount of toner remains on the photosensitive drum, an image failure occurs due to poor charging and exposure of the photosensitive drum during the next image forming process.
[0086]
Therefore, in order to obtain a stable cleanerless system, it is desired to increase the transfer efficiency to nearly 100%.
[0087]
In this embodiment, as described above, by using the suspension polymerization method as a means for easily obtaining a spherical toner capable of obtaining a high transfer efficiency, it is easy to reduce the particle size of the toner, and at the same time, the particle size distribution of the toner is sharpened. The use of a release agent in the core to achieve both high fixability and blocking resistance by providing a toner with a core / shell structure by the suspension polymerization method. Simplifies the oil applying member in the fixing section.
[0088]
Hereinafter, the polymerized toner T2 used in this embodiment will be described.
[0089]
The toner according to the present embodiment is a toner manufactured by the above-described polymerization method. 1M-Na₃PO₄After 450 g of the aqueous solution was charged and heated to 60 ° C., the mixture was stirred at 12000 rpm using a TK homomixer (manufactured by Tokushu Kika Kogyo). 1.0M-CaCl₂68 g of an aqueous solution is gradually added, and Ca₃(PO₄)₂Was obtained.
(Monomer) Styrene 165g
15 g of n-butyl acrylate
(Charge control agent) salicylic acid metal compound 3g
(Polar resin) saturated polyester 10g
(Acid value 14, peak molecular weight 8000)
(Release agent) 15 g of ester wax (melting point 70 ° C)
[0090]
The above formulation was heated to 60 ° C., and uniformly dissolved and dispersed at 12000 rpm using a TK homomixer (manufactured by Tokushu Kika Kogyo). Into this, 10 g of a polymerization initiator 2,2'-azobis (2,4-dimethylvaleronitrile) was dissolved to prepare a polymerizable monomer composition.
[0091]
The polymerizable monomer composition is charged into the aqueous medium,₂Under an atmosphere, the mixture was stirred with a TK homomixer at 10,000 rpm for 10 minutes to granulate a polymerizable monomer composition. Thereafter, while stirring with a paddle stirring blade, the temperature was raised to 80 ° C., and the reaction was performed for 10 hours. After the completion of the polymerization reaction, the remaining monomer is distilled off under reduced pressure, and after cooling, hydrochloric acid is added to dissolve the calcium phosphate, followed by filtration, washing with water and drying to give a sharp colored suspension having a weight average diameter of about 7.5 μm. Particles were obtained.
[0092]
In the present embodiment, as the polymerized toner T2, a polymerized toner having the shape factors SF1 = 110 and SF2 = 109 was obtained by the above manufacturing method. The triboelectric charge amount of the main polymerization toner T2 was −30 μC / g.
[0093]
Here, for a toner in which such a portion of the toner surface is formed by a polymerization method, a necessary portion is generated by a polymerization reaction by allowing the toner to exist as a pre-toner (monomer composition) particle in a dispersion medium. It is smooth and has very high slipperiness of the toner. Therefore, it is difficult to control the developing blade uniformly. Although the above-mentioned advantages can be obtained by giving the polymerized toner a core / shell structure, since the low softening substance in the toner lowers the strength of the toner itself, the developing blade and the developer supply roller have low contact. It is necessary to make contact with the developing sleeve with pressure, so that regulation and stripping on the developing sleeve and cleaning with a blade have become more difficult.
[0094]
Therefore, in this embodiment, the polymerized toner T2 is prepared by adding 1.8 parts by weight of a negatively chargeable external additive having the same polarity as the toner to 100 parts by weight of the polymerized toner T2, and adding a positive polarity having the opposite polarity to the toner. 0.8 parts by weight of a chargeable external additive is adhered to the surface of each toner particle.
[0095]
Here, the specific surface area measured by the BET method was 300 m²/ G, a hydrophobic silica having a primary particle size of 8 nm, and a triboelectric charge by a blow-off method of -110 µC / g. The effect of the negatively chargeable external additive having the same polarity as that of the toner is to impart the effect of the conventional external additive such as improvement in toner chargeability and toner fluidity to the toner.
[0096]
On the other hand, as a positively chargeable external additive, colorless melamine-formaldehyde resin particles having an average particle size of 1 μm are added. The triboelectric charge of the positively chargeable external additive in this example was +55 μC / g. The effect of the positively chargeable external additive having the opposite polarity to that of the toner is the control of the slipperiness of the toner in the same manner as in the first embodiment. In the developing device, the toner shape factor SF1 is increased to increase the toner Regulation and stabilization of charging, and easy removal of residual toner on the developing sleeve in the developer supply roller. In addition, by developing on the photosensitive drum under a predetermined alternating electric field, the positively chargeable external additive is removed from the toner T2 on the photosensitive drum, and good transfer characteristics are obtained by making the toner T2 spherical.
[0097]
In this embodiment, by increasing the particle size of the positively chargeable external additive and increasing the amount of triboelectricity, even in the case of the polymerization toner T2 close to 100 in both SF1 and SF2, the slip property is improved as in the case of the spherical toner Tl in Example 1. It became possible to control.
[0098]
Further, since the area coverage α of the positively chargeable external additive on the toner surface in the present invention was 14%, the amount of the positively charged reversal toner was very small, and a stable toner tribo was obtained even in long-term durability.
[0099]
Furthermore, the absolute value Q1 of the triboelectric charge amount of the negatively chargeable external additive, the external addition amount M1, the absolute value Q2 of the triboelectric charge amount of the positively chargeable external additive, the external addition amount M2, the toner of the positively chargeable external additive When the area coverage ratio α occupying the T2 surface is
Q2 × M2> Q1 × M1 × α
In order to satisfy the following conditions, the positively chargeable external additive is stably charged to a positive polarity to facilitate separation of the positive external additive at the time of development / transfer, and at the time of transfer, the toner shape factor is reduced, and the toner is transferred into a spherical shape. Improve efficiency.
[0100]
In this embodiment, a suitable alternating electric field is applied to the toner under the same developing conditions as in Embodiment 1 (developing gap distance 250 μm, AC voltage 1.5 kVpp · 2 kHz). In addition to sufficient development, the positively chargeable external additive is removed from the toner on the photosensitive drum. While the shape factor SF1 of the polymerized toner T2 in the developing device was 110, the shape factor SF1 of the polymerized toner T2 on the photosensitive drum image portion after development and before transfer was 113, and the transfer efficiency was 98%. . Further, as in the first embodiment, the reverse toner charged in a small amount and having the opposite polarity can be returned to the developing sleeve side by the alternating electric field to prevent image fog.
[0101]
In this embodiment, a charging brush, which is a contact charging member, is used as a charging unit. The charging brush 15 has an electric resistance of 10 by dispersing carbon black.⁶It is formed from nylon fiber having a thickness of 6 denier and a length of 2 mm set to Ω, and an AC voltage of 1.4 kVpp is superimposed on a DC voltage of -700 V. Therefore, the positively chargeable external additive remaining on the photosensitive drum after the transfer adheres to the charging brush 15 serving as a charging unit as in the first embodiment.
[0102]
In the present embodiment, the charging brush is formed of a strongly positively chargeable nylon fiber, so that a part of the positively chargeable external additive is frictionally charged to the negative by rubbing with a brush, and the image is formed during image formation. However, it can be removed from the charging brush by an electric field. Of the transfer residual toner, the positively charged toner is frictionally charged with the brush and almost inverted to the negative toner, thereby preventing external additives and toner from being accumulated on the charged brush. This makes it possible to improve the contamination of the charging brush.
[0103]
When the external additive whose polarity has been reversed to negative and the transfer residual toner due to cleanerlessness are removed from the charging member during image formation, the external additive and the transfer residual toner pass through the exposed portion on the photosensitive drum. However, since it was sufficiently small and uniform, no image defect due to blocking the exposure occurred. Further, since the toner and the external additive are negatively charged, the toner and the external additive are collected in the developing device by the electric field in the developing area (or an image is formed on the photosensitive drum).
[0104]
Further, at the time of non-image formation, the externally charged positive additive in the charging brush moves to the photosensitive drum by the electric field and is temporarily collected by the transfer roller based on the timing chart shown in FIG. Then, at the time of the next image formation, the image is transferred to the back surface of the transfer paper and discharged outside the apparatus. Since the positively chargeable external additive is a colorless resin particle, it is not recognized as an image even when fixed on the back surface of the transfer paper. Therefore, by using the image forming apparatus in the present embodiment, even if the contact charging / transferring device and the one-component developing device having a simple configuration are used, the resistance fluctuation of the contact charging / transferring unit is suppressed, and the polymerization toner is stabilized. Coating on the developing sleeve and improved transfer efficiency during transfer facilitates toner recovery in the developing section of the cleanerless system, making it possible to provide a stable cleanerless system without image defects for a long time. Was.
[0105]
【The invention's effect】
As described above, according to the present invention, the first external additive having the same polarity as the one-component developer improves the chargeability and fluidity of the toner, and has the opposite polarity to the one-component developer. The shape of the one-component developer at the time of transfer is changed from the shape of the one-component developer in the developing means by separating a certain second external additive from the one-component developer by an electric field applied during development and transfer. The surface shape of the one-component developer can be changed. In the developing means, the toner is made non-spherical by increasing the toner shape factor SF1, and the friction and rubbing of the toner are facilitated, so that the formation of a thin toner layer on the developing blade and the application of tribo can be improved. At the time of transfer, the toner is made spherical by reducing the toner shape factor SF1 to improve transfer efficiency and suppression of missing during transfer.
[0106]
Further, even if the second external additive remaining on the image carrier without being cleaned adheres to the contact charging unit, it is removed from the contact charging unit during non-image formation and collected in the developing device. The second external additive did not accumulate, the image carrier was uniformly charged over a long period of time, and a good image output was obtained.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram of a first embodiment.
FIG. 2 is a conceptual diagram of a developer used in the present invention (a) before development and (b) after development.
FIG. 3 is a timing chart of a charging voltage, a developing voltage, and a transfer voltage according to the present invention.
FIG. 4 is a diagram illustrating a relationship among a photosensitive drum potential, a charging roller potential, a developing sleeve potential, and a transfer roller potential.
FIG. 5 is a diagram illustrating a relationship between a developing electric field amplitude, a developer shape, and a transfer efficiency.
FIG. 6 is a schematic configuration diagram of a second embodiment.
FIG. 7 is a schematic configuration diagram of a conventional electrophotographic apparatus.
FIG. 8 is a schematic configuration diagram of a triboelectric charge amount measuring device.
[Explanation of symbols]
T1 Spherical toner
T2 polymerized toner
1 Developer regulating member
2 Metal sheet
3 Developing sleeve
4 Development power supply
5 Developer supply roller
6 Developer stirrer
7 Toner coat layer
10 Photosensitive drum (image carrier)

Claims (11)

An image carrier; a charging unit that contacts the image carrier and charges the surface of the image carrier to a predetermined potential; a developing unit that visualizes an electrostatic latent image on the image carrier with a one-component developer; An image forming apparatus including a transfer unit that transfers a toner image on an image carrier to a transfer material,
The one-component developer has at least two kinds of external additive particles, a first external additive having the same polarity as the one-component developer, and a second external additive having the opposite polarity to the one-component developer. And applying an electric field in which the second external additive moves from the charging means to the image carrier during non-image formation ,
The image forming apparatus according to claim 1, wherein the transfer unit is a contact transfer unit, and applies an electric field in which the second external additive moves from the image carrier to the transfer unit during non-image formation . 2. The image forming apparatus according to claim 1, wherein the area coverage α of the second external additive on the surface of the one-component developer is 50% or less. 3. The weight mixing ratio M1 of the first external additive to the developer, the weight mixing ratio M2 of the second external additive to the developer, the absolute value Q1 of the triboelectric charge amount of the first external additive, the second The relationship between the absolute value Q2 of the triboelectric charge amount of the external additive and the area coverage α occupied by the second external additive on the surface of the one-component developer is represented by Q1 × M1 × α <Q2 × M2.
The image forming apparatus according to claim 1 or 2, characterized in that a. It said first primary particle size of the external additive particles 1 nm~100 nm, in any one of claims 1 to 3 primary particle diameter of the second external additive is characterized in that it is a 0.1~2μm The image forming apparatus according to any one of the preceding claims. The one-component developer has a shape factor SF-1 before external addition of 100 to 130, SF-2 of 100 to 120, and a shape after externally adding a first external additive and a second external additive. factor SF-1 is 130 to 170, SF-2 is an image forming apparatus according to any one of claims 1 to 4, characterized in that in the range of 120 to 160. The image forming apparatus according to any one of claims 1 to 5, characterized in that part or all of the one-component developing agent is formed by a polymerization method. Wherein part or all of the one-component developer is a low softening point substance, image formation according to any one of claims 1 to 6, characterized in that the melting point of the low-softening substance is 40 to 90 ° C. apparatus. The developing unit includes a case containing a non-magnetic one-component developer, and a developer carrier that supplies a one-component developer to an electrostatic latent image formed on the image carrier by rotating in a certain direction to visualize the electrostatic latent image. A developer supply member disposed opposite to the developer carrier to apply a non-magnetic one-component developer onto the developer carrier, and a developer supply member downstream of the developer supply member in the rotation direction of the developer carrier. present in pressure contact with the developer carrying member to regulate the amount of the developer carrying member of a developing agent, and uniformly, characterized in that it comprises a coating allowed to developer regulating member according to claim 1 to 7 An image forming apparatus according to any one of the above. The developer carrier is disposed to face the image carrier with a constant development gap, and forms an alternating electric field in the development gap to allow the non-magnetic one-component developer to move between the developer carrier and the image carrier. the image forming apparatus according to any one of claims 1 to 8, wherein the reciprocating between. The image forming apparatus according to claim 9 , wherein the amplitude of the alternating electric field applied to the developer carrier and the image carrier is 2 kV / mm to 5 kV / mm. The image forming apparatus according to any one of claims 1 to 10 and recovering the developing means a one component developer remaining on an image bearing member after the transferring unit.

Images