JP2004341193A - Image recording apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image recording apparatus using a toner recycling system featuring that: sequence control to inject a residual toner in specified timing is carried out, the residual toner remaining on an image carrying body after transferred and held in a nip part between the image carrying body and a contact electrifying member, so that the toner is accurately injected to between the image carrying body and an image recording medium and that image defects can be prevented; and the exposure light quantity is increased as the number of continuously passing sheets increases so as to respond the amount of the residual toner which increases with the number of passing sheets. <P>SOLUTION: The image recording apparatus is equipped with: a means to electrify the image carrying body by contact electrification and to produce an electrostatic latent image on the electrified face of the image carrying body; a means to visualize the electrostatic latent image with the toner; and a means to transfer the visualized toner image onto the image recording medium. In this apparatus, a pre-exposure apparatus 7 is installed between the transfer part and the contact withstand electrifying part, and the image carrying body is exposed to increase the potential contrast with respect to the contact withstand electrifying member. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

【０１２３】
評価のポイントとしてはベタ黒画像中の白ポチ、ベタ白画像中の黒ポチ、および画像ムラ等である。それぞれ遮光、かぶり、帯電不良に起因する。１００枚目の画像を目で確認し、評価した。表中の評価記号について以下説明する。これらは画像状態の程度を表しており、白ポチ、黒ポチ、画像ムラのすべてに共通して使用している。
【０１２４】
◎：非常に良好な画像状態。全く画像に乱れが観察されない。
【０１２５】
○：ほとんど白ポチ、黒ポチ、画像ムラが観察されない。
【０１２６】
△：若干白ポチ、黒ポチ、画像ムラが画像に現れている。
【０１２７】
×：白ポチ、黒ポチ、画像ムラをよく観察することができる。
【０１２８】
実施例１−１では電位コントラストΔＶの上昇レートを画像記録媒体毎に１Ｖ、実施例１−２では電位コントラストΔＶの上昇レートを画像記録媒体毎に４ Ｖに制御して評価を行った。比較例１−３では、１５０ Ｖの電位コントラストΔＶを与えたが、その後は電位コントラストΔＶを変化させなかった。比較例１−４では、前露光装置７による露光を行わなかった。
【０１２９】
実施例１−１ではベタ黒画像中の白ポチおよび、ベタ白画像中の黒ポチが若干観察され、画像状態は△であった。また、帯電不良に起因する画像ムラはほとんど観察されなかった。
【０１３０】
一枚目の電位コントラストΔＶが１５０ Ｖで、電位コントラスト上昇レートが画像記録媒体毎に１ Ｖであるので１００枚目の画像形成時には２４９ Ｖまで電位コントラストΔＶが上昇していることになる。この上昇レートでは連続通紙に伴う転写残トナーの増加に対応することができず、通紙枚数が増加するに従い、画像記録媒体間部分に吐き出すタイミング以外で帯電ローラ２へと混入する転写残トナー量が増加する。このため、遮光とかぶりを原因とする画像欠陥が現れた。
【０１３１】
１００枚通紙された時点での感光ドラム１の電位は−３５１ Ｖであり、この電位では帯電ローラ２で十分に帯電しうる電位である。したがって帯電特性は良好であった。
【０１３２】
実施例１−２ではベタ黒画像中の白ポチおよび、ベタ白画像中の黒ポチほとんど観察されず、画像状態は○であった。また、帯電不良に起因すると考えられる画像ムラもほとんど観察されなかった。
【０１３３】
一枚目の電位コントラストΔＶが１５０ Ｖで、電位コントラスト上昇レートが画像記録媒体毎に４ Ｖであるので１００枚目の画像形成時には５４６Ｖまで電位コントラストΔＶが上昇している。この上昇レートは連続通紙に伴う転写残トナー量の増加に応じたものであり、画像記録媒体間部分以外に漏れ出る転写残トナーはほとんどない。画像記録媒体間部分に吐き出されるタイミングで帯電ローラ２に混入される転写残トナーは、画像記録媒体間部分に吐き出されるタイミングでローラ清掃モードの電圧が印加されることにより、感光ドラム１と帯電ローラ２のニップ下流部において効率よく感光ドラム１上の画像記録媒体間部分に吐き出される。結果として遮光、かぶり、帯電不良の原因となる転写残トナーはほとんどなく、良好な画像を得ることができた。
【０１３４】
１００枚通紙の時点で感光ドラム１の電位は−５４ Ｖまで高まっているが、帯電ローラ２で帯電しうる電位であった。
【０１３５】
実施例との比較を行うため、初期電位コントラストとして各実施例と同様の１５０ Ｖを与えたが、その後電位コントラストを変化させなかった比較例１−３と、前露光装置７による露光除電を行わなかった比較例１−４を行った。
【０１３６】
比較例１−３ではベタ黒画像中の白ポチおよび、ベタ白画像中の黒ポチがよく観察され、画像状態は×であった。画像ムラはほとんど観察されなかった。
【０１３７】
１００枚通紙後の電位コントラストΔＶが１５０ Ｖのままであるので連続通紙中の転写残トナーの増加に対して感光ドラム１への転写残トナーの保持力が及ばなくなり、感光ドラム１上の画像記録媒体間部分に吐き出すタイミング以外で転写残トナーが帯電ローラ２へと混入してしまう。この転写残トナーは感光ドラム１と帯電ローラ２のニップ下流部で感光ドラム１に付着する。感光ドラム１に付着した転写残トナーは遮光、およびかぶりの原因となり、画像欠陥の原因となる。
【０１３８】
比較例１−４では前露光装置７による露光を行わなかった。そのため、感光ドラム１と帯電ローラ２のニップ上流部で転写残トナーを保持する力がなく、転写残トナーが感光ドラム１から帯電ローラ２の付着・混入が起こる。比較例１−３と同様のメカニズムにより、画像欠陥の原因となる。
【０１３９】
以上の実施例１より、電位コントラストΔＶの上昇レートが４ Ｖの実施例１−２において良好な画像形成が行われていたことがわかった。実施例１−１との比較により、電位コントラストを画像記録媒体間毎に上昇させていくことにより、増加していく転写残トナーを感光ドラム１と帯電ローラ２のニップ部に正確に保持することができ、良好な画像形成が行えることが確認できた。
【０１４０】
（実施例２）
実施例１では感光ドラム１と帯電ローラ２のニップ部における電位コントラスト増大手段として、前露光装置７を転写ローラ５と帯電ローラ２の間に配設して、感光ドラム１の除電を行い、電位コントラストを増大させた。
【０１４１】
前露光装置７からの露光量を制御することにより電位コントラストの上昇レートを制御したが、光を用いているために実際には数Ｖ単位での制御は困難である。
【０１４２】
そこで本実施例２では露光による除電ではなく、帯電により感光ドラム１と帯電ローラ２のニップ部における電位コントラストを増大させた。電位コントラスト増大手段として光を用いない帯電によれば、より精密な電位コントラストの制御が可能である。本実施例２の装置構成として、前露光装置７の代わりに前帯電装置８を前露光装置７と同じ位置に配設した例を図４に示す。
【０１４３】
帯電装置８はコロナ放電を利用した帯電装置である。転写ローラ５と帯電ローラ２の間において、高圧を印加することにより、生じる放電電流に感光ドラム帯電面をさらすことで感光ドラム帯電面を所定に帯電させるものである。
【０１４４】
この時のシーケンス制御図を図５に示す。前帯電装置８の制御は前露光装置７の制御と同様である。
【０１４５】
以上の装置構成、およびシーケンスを用いて、本実施例２を実施した。詳細は実施例１と同様であるのでここでは述べない。
【０１４６】
本実施例２において、電位コントラストの上昇レートを変化させた実施例２−１および２−２を行い、それぞれ画像欠陥の評価と帯電特性の評価を行った。また、実施例との比較を行うため、比較例２−３、２−４も行った。
【０１４７】
《評価》
表２に本評価の結果を示す。表に基づく考察を以下、詳述する。
【０１４８】
前帯電装置８による帯電で感光ドラム１の表面に電荷を与え、電位を−４５０ Ｖとするように設定した。この時の電位コントラストΔＶは帯電ローラ２の電位が−６００ Ｖであるので１５０Ｖとなる。電位コントラストΔＶは前帯電装置８による帯電量によって変化し、帯電量の増大に伴って増加する。
一枚目の電位コントラストΔＶが１５０Ｖとなる状態から通紙を行い、連続通紙に伴い、電位コントラストを種々の上昇レートで増加させていった。連続通紙を１００枚行い、１００枚目の画像評価を行った。
ベタ黒およびベタ白画像をそれぞれ１００枚連続でプリントし、ベタ黒、ベタ白画像のそれぞれ１００枚目を評価した。
【０１４９】
【表２】

【０１５０】
評価のポイントおよび表中の記号は実施例１と同じであるのでここでは述べない。
【０１５１】
実施例２−１から２−４で電位コントラストΔＶの上昇レートを画像記録媒体毎に１ Ｖから４ Ｖに変化させた。比較例として実施例２−５および実施例２−６を行った。実施例２−１としては、１５０Ｖの電位コントラストΔＶを与えたが、その後は電位コントラストΔＶを変化させなかった。実施例２−６では、前帯電装置８による露光を行わなかった。
【０１５２】
実施例２−１においてはベタ黒画像中の白ポチおよび、ベタ白画像中の黒ポチが若干観察され、画像状態は△であった。また、帯電不良に起因する画像ムラはほとんど観察されなかった。
【０１５３】
条件は実施例１−１と同じであり、同様のメカニズムに基づいた画像形成が進む。この電位コントラスト上昇レートでは連続通紙に伴う転写残トナーの増加に対応することができず、画像記録媒体間部分に吐き出すタイミング以外で帯電ローラ２へと混入する転写残トナー量が増加する。結果として遮光、かぶりによる画像欠陥が生じる。
【０１５４】
実施例２−２においてはベタ黒画像中の白ポチはほとんど観察されず、ベタ白画像中の黒ポチは若干観察された。画像状態はベタ黒画像中の白ポチが○、ベタ白画像中の黒ポチが△であった。また、帯電不良に起因すると考えられる画像ムラはほとんど観察されなかった。
【０１５５】
一枚目の電位コントラストΔＶが１５０ Ｖで、電位コントラスト上昇レートが画像記録媒体毎に２ Ｖであるので１００枚目の画像形成時には３４８ Ｖまで電位コントラストΔＶが上昇している。この上昇レートでも通紙枚数が増えるに従い増加する転写残トナー量に完全に対応することができていないが、感光ドラム１と帯電ローラ２のニップ部に保持できる転写残トナー量が増えたため、画像記録媒体間部分以外に漏れ出る転写残トナー量が減少し、画像状態が改善された。
【０１５６】
実施例２−３においてはベタ黒画像中の白ポチはほとんど観察されず、ベタ白画像中の黒ポチはが若干観察された。画像状態はベタ黒画像中の白ポチが○、ベタ白画像中の黒ポチが△であった。また、帯電不良に起因する画像ムラはほとんど観察されなかった。
【０１５７】
一枚目の電位コントラストΔＶが１５０ Ｖで電位コントラスト上昇レートが画像記録媒体毎に３ Ｖであるので１００枚目の画像形成時には４４７ Ｖまで電位コントラストΔＶが上昇していることになる。まだ若干連続通紙に伴う転写残トナー量の増加に対応できていないが、実施例２−１と２−２に比べて帯電ローラ２と感光ドラム１のニップ部に保持できる転写残トナー量は増加しており、遮光、かぶり、帯電不良の影響は軽減されている。
【０１５８】
実施例２−４ではベタ黒画像中の白ポチおよび、ベタ白画像中の黒ポチはほとんど観察されず、画像状態は○であった。実施例２−２および２−３で観察されたベタ黒画像中の白ポチとベタ白画像中の黒ポチのレベルの差はほとんど観察されなかった。また、画像ムラもほとんど観察されなかった。
【０１５９】
一枚目の電位コントラストΔＶが１５０ Ｖで電位コントラスト上昇レートが画像記録媒体毎に４Ｖであるので１００枚目の画像形成時には５４６ Ｖまで電位コントラストΔＶが上昇していることになる。この上昇レートは連続通紙に伴う転写残トナー量の増加に応じたものであり、画像記録媒体間部分以外に漏れでる転写残トナーはほとんどない。したがって良好な画像形成が行われた。
【０１６０】
実施例との比較を行うため、初期電位コントラストとして各実施例と同様の１５０ Ｖを与えたが、その後電位コントラストを変化させなかった比較例２−５と、前帯電装置８による帯電を行わなかった比較例２−６を行った。
【０１６１】
これらの比較例は比較例１−３、１−４と同様の条件であるのでここで詳細は述べない。
【０１６２】
比較例２−５、２−６で、ベタ黒画像中の白ポチおよび、ベタ白画像中の黒ポチがよく観察され、画像状態は×であった。画像ムラはほとんど観察されなかった。
【０１６３】
以上の実施例２より、電位コントラストの増大手段として帯電を用いれば、ボルトオーダーでの電位コントラスト上昇レート制御が行えることがわかった。電位コントラスト上昇レートの変化に伴い、画像欠陥にも変化が観察され、電位コントラスト上昇レートが画像欠陥に与える影響も観察することができた。
【０１６４】
（実施例３）
実施例１および実施例２では感光ドラム１上の画像記録媒体間部分においてに露光、もしくは帯電をおこない、感光ドラム１と帯電ローラ２の間の電位コントラストを増大させた。また、その露光量、および帯電量は一回の露光、および帯電の間は一定であった。
【０１６５】
しかしながら実際には露光中、もしくは帯電中にも感光ドラム１と帯電ローラ２のニップ部ｎに持ち運ばれてくる転写残トナー量は増えつづける。そのため、露光量、もしくは帯電量もそれに応じて増加させればより安定に転写残トナーを感光ドラム１と帯電ローラ２のニップ部に保持することができるようになる。
【０１６６】
この時のシーケンス制御図を図６および図７に示す。図６に示すのは前露光装置７を用いた場合のシーケンス制御図である。これまで一回の露光においては一定であった前露光量を一回毎の露光において連続的に上昇させた。図７に示すのは前帯電装置８を用いた場合のシーケンス制御図であるが、こちらの図においてもこれまで一回の帯電において一定であった前帯電量を一回毎に連続的に増加させた。本実施例３においては、露光中、および帯電中の、露光量、および帯電量は、それぞれ上昇レートと同じ上昇速度で増加させた。
【０１６７】
本体装置構成については実施例１および実施例２に記載したものと同じであるのでここにおいても詳述しない。
【０１６８】
《評価》
前露光装置７用いた実施例３−１、３−２および比較例３−３、３−４、前帯電装置８を用いた実施例４−１〜４−４および比較例４−５、４−６において、それぞれ画像欠陥の評価と帯電特性の評価を行った。その結果をそれぞれ表３および表４に示す。評価方法は実施例１および実施例２に記載済みであるのでここでは述べない。表３を表１と、表４を表２と比較し、考察を詳述する。
【０１６９】
表３においては、表１と比較して、電位コントラスト上昇レートが画像記録媒体間毎に４ Ｖである実施例３−２のみ画像評価結果が上がった。ほかの実施例３−１および比較例３−３、３−４はそれぞれ実施例１−１および比較例１−３および１−４と比較して変化しなかった。
【０１７０】
露光中、もしくは帯電中に露光量、ないしは帯電量を増大させるシーケンスは、実施例１において画像評価が○の場合のみ、画像レベルをあげることができた。このシーケンスは電位コントラストΔＶがちょうど転写残トナーを感光ドラム１上に保持できるくらいの大きさの場合に効果がある。露光中に漏れ出るわずかな転写残トナーを残らず保持することにより、若干画像レベルが向上した。
【０１７１】
表４においては、表２と比較して、電位コントラスト上昇レートが画像記録媒体間毎に４Ｖである実施例４−４において画像評価結果が上がっている。ほかの実施例４−１〜４−３および比較例４−５、４−６はそれぞれ実施変化していない。表３の場合と同様、このシーケンスは電位コントラストΔＶがちょうど転写残トナーを感光ドラム１上に保持できるくらいの大きさの場合に効果があった。
【０１７２】
以上、実施例３をまとめると、実施例３で用いられたシーケンスを用いれば、画像状態を改善できることが確認できた。また、その効果は電位コントラストの上昇レートがちょうど転写残トナーの増加に対応している場合によくあらわれる。
【０１７３】
【表３】

【０１７４】
【表４】

【０１７５】
【発明の効果】
以上のように本発明によれば、像担持体上の画像記録媒体間部分のタイミングで接触帯電部材と像担持体の間の電位コントラストを像担持体上の画像記録媒体部分に比べて大きくする、より具体的には帯電直前の像担持体に露光もしくは帯電を行うことにより像担持体および接触帯電部材との間の電位コントラストを大きくして、転写残トナーを接触帯電部材と像担持体の帯電ニップ部に保持するシーケンス制御において、画像記録媒体間部分毎に露光および帯電を強めていくことで画像記録媒体間部分毎に増加する転写残トナーを安定して帯電ニップ部に保持することができ、遮光や、かぶり等の問題を防ぐことができるようになる。
【０１７６】
また、毎回の露光中、もしくは帯電中に露光量、もしくは帯電量を増加させることにより、より状態のよい画像形成が行える。
【図面の簡単な説明】
【図１】実施例１の画像形成装置の概略構成図
【図２】帯電ローラ２と感光ドラム１のニップ部における転写残トナー保持電界の概念図
【図３】実施例１のシーケンス制御図
【図４】実施例２の画像形成装置の概略構成図
【図５】実施例２のシーケンス制御図
【図６】実施例３のシーケンス制御図（前露光装置７を用いた場合）
【図７】実施例３のシーケンス制御図（前帯電装置８を用いた場合）
【符号の説明】
１ 感光ドラム（像担持体、被帯電体）
２ 帯電ローラ（接触帯電部材）
３ レーザービームスキャナ（露光装置）
４ 現像装置
４ａ 現像スリーブ
ｔ 現像剤（トナー）
ｍ 帯電促進粒子
５ 転写ローラ
６ 定着装置
Ｐ 転写材
Ａ 電界
Ｂ 電界による転写残トナー保持力
ｔ１ 転写残トナー[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an image forming apparatus such as a copying machine and a printer.
[0002]
More specifically, the present invention relates to an image forming apparatus of a toner recycling (cleanerless) system.
[0003]
[Prior art]
2. Description of the Related Art In a transfer type image forming apparatus using an electrophotographic technique, transfer residual toner remaining on a photoconductor (image carrier) after transfer has been collected from the photoconductor surface by a cleaner (cleaning device) and discarded as waste toner.
[0004]
It is desirable that this waste toner is not emitted from the viewpoint of environmental protection.
[0005]
Toner recycle (cleanerless) system that eliminates the cleaner and removes the transfer residual toner on the photoreceptor after transfer from the photoreceptor by "simultaneous development cleaning" by the developing device and collects and reuses it in the developing device. Image forming apparatuses have appeared.
[0006]
Simultaneous development and cleaning means that the toner remaining on the photoreceptor after the transfer is developed at the next and subsequent steps, that is, the photoreceptor is subsequently charged and exposed to form a latent image. Fogging potential difference V, which is the potential difference between the DC voltage applied to the developing device and the surface potential of the photoconductor. _back ). According to this method, since the transfer residual toner is collected in the developing device and reused after the next process, waste toner can be eliminated, and troublesome maintenance can be reduced. In addition, the cleaner-less system has a great advantage in terms of space, and can greatly reduce the size of the image recording apparatus.
[0007]
In the toner recycling system, the transfer residual toner is not removed from the surface of the photoconductor by a dedicated cleaner as described above, but is transferred to a developing device via a contact charging member and used again in the developing process.
[0008]
An apparatus using a toner recycling system is known, for example, from Japanese Patent Application Laid-Open No. H11-163,837.
[0009]
[Patent Document 1]
JP-A-9-96947
[0010]
[Problems to be solved by the invention]
In the image forming apparatus of the toner recycling system, when a contact charging member is employed as a charging unit for the image carrier, a dedicated cleaner for removing residual transfer residual toner remaining on the surface of the image carrier after transfer is not used. The transfer residual toner remaining on the image carrier surface is carried as it is by rotation of the image carrier surface to a charging portion which is a contact portion between the image carrier and the contact charging member, and the contact charging member is contaminated with toner. The following problems occur.
[0011]
{Circle around (1)} When the transfer residual toner accumulated in the contact charging member such as the charging roller is discharged to the image carrier during the image forming process using the image exposure, if the discharged toner amount is large, the exposure is blocked and the white image is formed on the image. Pochi occurs. This phenomenon is hereinafter referred to as light shielding. Further, when the discharged toner cannot be collected by development, it is generated in the image as a black spot on a white background. This phenomenon is hereinafter referred to as fogging.
[0012]
{Circle around (2)} When the toner is excessively accumulated on the contact charging member, the toner impairs the charging property of the contact charging member, so that good charging properties cannot be obtained.
[0013]
It is necessary to adjust the amount of toner discharged from the charging member and the amount of toner to be held so as not to cause (1) and (2). Since the amount of remaining toner also increases, it is necessary to adjust the toner accordingly.
[0014]
It is known that the toner attached to the charging member is discharged to the photoconductor by changing the potential contrast between the surface potential of the photoconductor and the DC bias applied to the charging member (see, for example, Patent Document 1). .).
[0015]
Therefore, the present invention relates to an image recording apparatus of a contact charging system, a transfer system, and a toner recycling system, in which a simple member such as a charging roller or a fur brush is used as a contact charging member. By cleaning efficiently without deteriorating the quality, the ozone-less direct charging (injection charging) and toner recycling system can be performed without problems at a low applied voltage, and high-quality image formation is maintained for a long time. The purpose is to do so.
[0016]
[Means for Solving the Problems]
The present invention is an image forming apparatus having the following configuration.
[0017]
(1) an image carrier, a charging device for charging the image carrier, a unit for writing information by creating an electrostatic latent image on a charged surface of the image carrier, and a method for writing the electrostatic latent image with toner Developing means for visualizing, and means for transferring the visualized toner image onto the image recording medium, the developing means remaining on the image carrier after transferring the toner image onto the image recording medium In an image forming apparatus having a function of collecting toner, the image forming apparatus further includes a unit configured to change a potential contrast between the image carrier and the charging member, and the amount of change in the potential contrast is determined during continuous paper feeding. An image forming apparatus, wherein the size is increased for each of the upper image recording media.
[0018]
(2) The potential contrast between the image carrier and the charging member is made larger between the image recording media on the image carrier than on the image recording medium on the image carrier. An image forming apparatus according to claim 1.
[0019]
(3) The device according to any one of claims 1 to 2, wherein the potential contrast increasing means between the image carrier and the charging member between the image recording media on the image carrier is a static elimination means by exposure. The image forming apparatus as described in the above.
[0020]
(4) The means for increasing the potential contrast between the image carrier and the charging member between image recording media on the image carrier is a means for charging the image carrier by a pre-charging device. Item 3. The image forming apparatus according to any one of Items 1 to 2.
[0021]
(5) The image forming apparatus according to any one of claims 1, 2 and 4, wherein the pre-charging charging device is a charging device using a non-contact charging member.
[0022]
(6) The charging device contacts the charging member to which the voltage has been applied to the image carrier, forms a nip with the image carrier, and applies a voltage to the charging member to thereby form the image. The image forming apparatus according to claim 1, wherein the image forming apparatus is a contact charging device that charges a surface of a carrier.
[0023]
(7) The developing agent of the developing means includes toner and charge-promoting particles, and adheres to the image carrier in a developing section and remains on the image carrier after transfer of the toner image to paper serving as an image recording medium. 7. The charge promotion particles according to claim 1, wherein the charge promotion particles in the developer are carried to supply the charge promotion particles to a nip portion between the charging member and the image carrier. Image forming apparatus.
[0024]
(8) The image forming apparatus according to any one of claims 1 to 7, wherein the contact charging member is rotated while maintaining a speed difference in a direction opposite to a rotation direction of the image carrier.
[0025]
(9) The charge promoting particles have a volume resistance of 10 ¹² The image forming apparatus according to any one of claims 1 to 5, wherein the resistance is equal to or less than Ω · cm.
[0026]
(10) The volume resistivity of the charge-promoting particles is 10 ¹⁰ The image forming apparatus according to any one of claims 1 to 5, wherein the resistance is equal to or less than Ω · cm.
[0027]
(Action)
The untransferred toner remaining on the surface of the image carrier without being transferred to the image recording medium at the transfer portion is carried to the nip portion between the contact charging member and the image carrier as the surface of the image carrier moves.
[0028]
Then, in the present invention, the image carrier surface is scanned and exposed by a pre-exposure device disposed between the transfer device and the charging device to eliminate the charge on the image carrier surface, or between the transfer device and the charging device. An electric charge is applied to the image carrier by an arranged pre-charging device, thereby increasing a potential contrast in a nip portion between the contact charging member and the image carrier, and holding the transfer residual toner on the image carrier. An electric field that causes the transfer residual toner to be held in the nip portion between the contact charging member and the image carrier, to adhere to and mix with the contact charging member, and further, an image recording medium on the image carrier. Prevents discharge of transfer residual toner to the part.
[0029]
The retained transfer residual toner is discharged onto the image carrier again from the nip between the contact charging member and the image carrier at a certain timing. It is exhaled through the following steps (1) and (2).
[0030]
{Circle around (1)} The transfer residual toner held in the nip between the contact charging member and the image carrier is attached to and mixed into the contact charging member by weakening the potential contrast between the contact charging member and the image carrier.
[0031]
(2) A cleaning voltage is applied to the contact charging member in accordance with the adhesion and mixing of the transfer residual toner to the contact charging member, and the transfer residual toner is discharged onto the image carrier again.
[0032]
(1) and (2) are not discharged to the image recording medium portion on the image bearing band, but are controlled by timing of discharging to the non-image recording medium portion via the contact charging member which is driven to rotate in the opposite direction to the image carrier. By doing so, it is possible to prevent the transfer residual toner from being discharged onto the image recording medium portion on the image carrier, and to eliminate the causes of light blocking and fogging.
[0033]
Further, as the image formation continues, the amount of the transfer residual toner carried to the nip between the contact charging member and the image carrier also increases with each image recording medium.
[0034]
To cope with this, the potential contrast between the contact charging member and the image carrier is increased for each image recording medium during continuous paper feeding. As a result, the amount of transfer residual toner that can be held in the nip between the contact charging member and the image carrier for each image recording medium increases, so that the amount of transfer residual toner carried to the nip can be increased. Can be.
[0035]
In addition to the above-mentioned method, a method is conceivable in which the nip portion between the contact charging member and the image carrier has a large potential contrast from the first image recording medium portion, assuming an increase in transfer residual toner. According to the method, it is necessary to set so as to hold a larger amount of toner for durability, and there is a problem that the chargeability of the image carrier by the contact charging member is low.
[0036]
According to the method of increasing the potential contrast for each image recording medium, it is possible to prevent a state in which an unnecessary potential contrast is generated between the image bearing member and the contact charging member, and the problem of chargeability is also improved. .
[0037]
Thus, according to the present invention, it is possible to accurately control the discharge of the transfer residual toner to the portion between the image recording media on the image carrier, and to maintain high-quality image formation for a long time. Become like Further, even after an image having a high image ratio is output, high-quality image formation can be maintained for a long period of time.
[0038]
BEST MODE FOR CARRYING OUT THE INVENTION
(Example 1)
FIG. 1 is a schematic structural diagram of an example of an image recording apparatus according to the present invention.
[0039]
《Configuration of main unit》
The image forming apparatus of this embodiment is a laser beam printer using a transfer type electrophotographic process, a contact charging method, and a toner recycling (cleanerless) system.
[0040]
Reference numeral 1 denotes an image carrier. In this embodiment, a rotating drum type negative OPC photosensitive member (negative photosensitive member, hereinafter referred to as a photosensitive drum) having a diameter of 24 mm is used. The photosensitive drum 1 is driven to rotate at a predetermined peripheral speed in a clockwise direction indicated by an arrow.
[0041]
Reference numeral 2 denotes a conductive elastic roller as a contact charging member disposed in contact with the photosensitive drum 1 with a predetermined pressing force (hereinafter, referred to as a charging roller). n is a charging nip between the photosensitive drum 1 and the charging roller 2. This charging roller holds conductive charge-promoting particles m (conductive particles for the purpose of charge promotion) on the outer peripheral surface thereof, and a nip portion n between the photosensitive drum 1 and the charging roller 2 has a charge-promoting particle m. m is interposed.
[0042]
The charging roller 2 is rotationally driven in a direction (counter) opposite to the rotation direction of the photosensitive drum 1 at the nip n, and contacts the surface of the photosensitive drum 1 with a speed difference. M is a drive source for the charging roller 2. Further, at the time of image recording by the printer, a predetermined charging bias is applied to the charging roller 2 from a charging bias applying power source S1. As a result, the peripheral surface of the rotary photosensitive drum 1 is uniformly contact-charged to a predetermined polarity and potential by the direct charging (injection charging) method.
[0043]
In this embodiment, the switch SW of the charging bias application power supply S1 is controlled to switch to the A contact side during image recording of the printer, and a DC voltage of −600 V of the DC power supply SDC is applied to the core metal 2a of the charging roller 2 to rotate the printer. The surface of the photosensitive drum 1 is directly charged to a voltage of approximately -600 V substantially equal to the applied DC voltage (A mode).
[0044]
The charging roller 2, the charge accelerating particles m, and the direct charging will be described in detail in another section.
[0045]
Reference numeral 3 denotes a laser beam scanner (exposure device) including a laser diode, a polygon mirror, and the like. The laser beam scanner 3 outputs a laser beam whose intensity is modulated in accordance with a time-series electric digital pixel signal of target image information, and scans and exposes the uniformly charged surface of the rotary photosensitive drum 1 with the laser beam. . By this scanning exposure L, an electrostatic latent image corresponding to the target image information is formed on the surface of the rotating photosensitive drum 1.
[0046]
Reference numeral 4 denotes a developing device. The charge accelerating particles m are added to the developer t. The developing device 4 reversely develops the electrostatic latent image on the surface of the rotating photosensitive drum 1 as a toner image at a developing site a. The developing device 4 will be described in detail in another section.
[0047]
Reference numeral 5 denotes a medium-resistance transfer roller as a contact transfer unit, which is brought into pressure contact with the photosensitive drum 1 at a predetermined pressure to form a transfer nip portion b. A transfer material P as a recording medium is supplied to the transfer nip b from a paper supply unit (not shown) at a predetermined timing, and a predetermined transfer bias voltage is applied to the transfer roller 5 from a transfer bias application power source S3. The toner image on the photosensitive drum 1 side is sequentially transferred to the surface of the transfer material P fed to the transfer nip portion b.
[0048]
The transfer roller 5 used in the present embodiment has a medium resistance foam layer formed on a metal core, and has a roller resistance value of 5 × 10 ⁸ The transfer was performed by applying a voltage of +2.0 kV to the metal core. The transfer material P introduced into the transfer nip portion b is conveyed by nipping the transfer nip portion b, and the toner image formed and carried on the surface of the rotary photosensitive drum 1 on its surface side is sequentially reduced by electrostatic force and pressing force. Is transcribed.
[0049]
Reference numeral 6 denotes a fixing device such as a heat fixing method. The transfer agent P fed to the transfer nip portion b and receiving the transfer of the toner image on the photosensitive drum 1 is separated from the surface of the rotary photosensitive drum 1 and introduced into the fixing device 6, where the toner image is fixed. It is discharged out of the apparatus as an image formed product (print, copy).
[0050]
The printer of this embodiment is cleaner-less, and the transfer residual toner remaining on the surface of the rotating photosensitive drum 1 after the transfer of the toner image to the transfer material p is not removed by the dedicated cleaner (cleaning device). With the rotation, the toner reaches the developing site a via the charging nip n, and is collected and reused by the simultaneous cleaning in the developing device 4.
[0051]
<< Charging roller 2 >>
The charging roller 2 as a contact charging member in this embodiment is manufactured by forming a medium resistance layer 2b of rubber or foam on a cored bar 2a.
[0052]
The medium resistance layer 2b is formulated with a resin (eg, urethane), conductive particles (eg, carbon black), a sulfide agent, a foaming agent, and the like, and is formed in a roller shape on the cored bar 2a. Thereafter, the surface was polished as needed to form a charging roller 2 as a conductive elastic roller having a diameter of 12 mm and a length of 200 mm.
[0053]
When the resistance of the charging roller 2 of this embodiment was measured, it was 100 kΩ. As for the roller resistance, 100 V is applied between the core metal 2a and the aluminum drum while the charging roller 2 is pressed against an aluminum drum of φ30 mm so that a total pressure of 1 kg is applied to the core metal 2a of the charging roller 2. And measured.
[0054]
Here, it is important that the charging roller 2 serving as a contact charging member functions as an electrode. That is, it is necessary to obtain sufficient contact with the member to be charged by providing elasticity, and at the same time, it is necessary to have a resistance low enough to charge the moving member to be charged. On the other hand, it is necessary to prevent voltage leakage when a low withstand voltage defect site such as a pinhole exists in the charged body. When a photoreceptor for electrophotography is used as a member to be charged, 10 to obtain sufficient chargeability and leakage resistance. ⁴ -10 ⁷ A resistance of Ω is desirable.
[0055]
It is desirable that the surface of the charging roller 2 has micro unevenness that can hold the charging promoting particles m.
[0056]
If the hardness of the charging roller 2 is too low, the contact with the member to be charged is deteriorated because the shape is not stable. If the hardness is too high, the charging nip n cannot be secured between the charging roller 2 and The preferred range is 25 to 50 degrees in Asker C hardness because the microscopic contact with the surface of the member to be charged is deteriorated.
[0057]
The material of the charging roller 2 is not limited to the elastic foam, but may be EPDM, urethane, NBR, silicone rubber, or IR black or the like for adjusting the resistance. A rubber material in which a conductive substance is dispersed, and a foamed material thereof can be used. In addition, it is also possible to adjust the resistance by using an ionic conductive material without dispersing the conductive substance.
[0058]
The charging roller 2 is provided by being pressed against a photosensitive drum 1 as a member to be charged with a predetermined pressing force against elasticity, and in this embodiment, a charging nip portion n having a width of several mm is formed. .
[0059]
In the present embodiment, the charging roller 2 is rotated clockwise at approximately 80 rpm at approximately 80 rpm so that the surface of the charging roller and the surface of the photoreceptor move at the same speed in opposite directions in the charging nip n. That is, the surface of the charging roller 2 as a contact charging member has a speed difference with respect to the surface of the photosensitive drum 1 as a member to be charged.
[0060]
<< Developing device 4 >>
The developing device 4 of the present embodiment is a reversal developing device using a one-component magnetic toner (negative toner) as the developer t. The charge accelerating particles m are added to the developer t.
[0061]
Reference numeral 4a denotes a non-magnetic rotation phenomenon sleeve as a developer carrying conveyance member in which a magnet roll 4b is included, and the developer t + m in the developing device is transported on the rotation phenomenon sleeve 4a by a regulating blade 4c. Regulated and charged.
[0062]
The developer coated on the rotation phenomenon sleeve 4a is conveyed to the development site (development area) a, which is the opposing portion of the photosensitive drum 1 and the sleeve 4a, by the rotation of the rotation development sleeve 4a. A developing bias is applied to the sleeve 4a from a developing bias applying power source S2.
[0063]
In this embodiment, the developing bias voltage is
DC voltage: -450V
AC voltage: peak-to-peak voltage 1600 V, frequency 1.8 kHz,
Superimposed voltage.
[0064]
Thus, the electrostatic latent image on the photosensitive drum 1 is reversely developed with the toner t.
[0065]
a) Toner t: A one-component magnetic toner t, which is a developer, is prepared by mixing a binder resin, magnetic particles, and a charge control agent, and performing kneading, pulverizing, and classifying processes. It is produced by adding a fluidizing agent or the like as an external additive. The weight average particle diameter (D4) of the toner was 7 μm.
[0066]
b) Charge-promoting particles m: In this embodiment, the charge-promoting particles m have a specific resistance of 10 ⁶ Alumina powder having Ω · cm and an average particle size of 3 μm was used. Then, 1 part by weight of the alumina powder as the charge accelerating particles m was added to 100 parts by weight of the classified toner t, uniformly dispersed by a mixer, and stored in the developing device 4.
[0067]
As the material of the charge accelerating particles m, various kinds of conductive particles such as a mixture with other conductive inorganic particles such as metal oxides and organic substances, or a surface-treated mixture thereof can be used.
[0068]
The particle resistance is a specific resistance of 10 due to the transfer of electric charges via the particles. ¹² Ω · cm or less, preferably 10 ¹⁰ Ω · cm or less is desirable.
[0069]
The resistance was measured by the tablet method and normalized. That is, the bottom area is 2.26 cm. ² A powder sample of about 0.5 g was placed in the cylinder, and a pressure of 15 kg was applied to the upper and lower electrodes. At the same time, a voltage of 100 V was applied, the resistance was measured, and then the resistivity was normalized to calculate the specific resistance.
[0070]
The particle size is desirably 50 μm or less in order to obtain good charging uniformity. In the present invention, the particle size when the particles constitute an aggregate is defined as the average particle size of the aggregate. For the measurement of the particle size, 100 or more samples were extracted from observation by an optical or electron microscope, the volume particle size distribution was calculated using the maximum chord length in the horizontal direction, and the 50% average particle size was determined.
[0071]
It does not matter at all that the charge promotion particles exist not only in the state of primary particles but also in the state of aggregation of secondary particles. Regardless of the state of aggregation, the form is not important as long as the function as the charge accelerating particles can be realized as an aggregate.
[0072]
The charge-promoting particles are preferably white or nearly transparent so that they do not hinder the exposure of the latent image, particularly when used to charge the photoreceptor, and are therefore preferably non-magnetic. Further, considering that the charge accelerating particles are partially transferred from the photoreceptor to the recording material P, color recording is preferably colorless or white. Also, in order to prevent light scattering by particles during image exposure, the lower limit of the particle size is considered to be 10 nm as a limit so that particles can be stably obtained.
[0073]
《Direct charging》
a) When the developing device 4 develops the toner of the electrostatic latent image on the photosensitive drum 1 side by the developing device 4, an appropriate amount of the charge promotion particles m added to the developer t of the developing device 4 moves to the photosensitive drum 1 side together with the toner at the developing site a. I do.
[0074]
The toner image on the photosensitive drum 1 is attracted to the transfer material P side by the influence of the transfer bias in the transfer nip portion b and is positively transferred, but the charge promoting particles m on the photosensitive drum 1 are transferred by being conductive. It does not positively transfer to the material P side, and remains substantially adhered and held on the photosensitive drum 1. Further, the effect of improving the transfer efficiency of the toner image from the photosensitive drum 1 side to the transfer material P side can be obtained by the presence of the charge promoting particles m substantially adhered and held on the surface of the photosensitive drum 1.
[0075]
In a cleanerless printer, the transfer residual toner remaining on the surface of the photosensitive drum 1 after the transfer and the above-described residual charge accelerating particles m are transferred to the charging nip n between the photosensitive drum 1 and the charging roller 2 by rotation of the photosensitive drum 1. The carrier is carried as it is, and the supply of the charge accelerating particles m to the charge nip portion n and the attachment and mixing to the charge roller 2 occur.
[0076]
Therefore, contact charging of the photosensitive drum 1 is performed in a state where the charge promoting particles m are present in the charging nip portion n between the photosensitive drum 1 and the charging roller 2.
[0077]
b) The presence of the charge-promoting particles m in the charging nip portion n between the photosensitive drum 1 and the charging roller 2 has a large frictional resistance due to the lubricant effect of the charge-promoting particles m. It is possible to easily and effectively bring a charge roller into contact with the surface of the photosensitive drum 1 with a speed difference even if it is difficult to make contact with the charge roller. At the same time, the charging roller 2 comes into close contact with the surface of the photosensitive drum 1 via the particles m and comes into contact with the surface of the photosensitive drum 1 more frequently.
[0078]
By providing a speed difference between the charging roller 2 and the photosensitive drum 1, the chance that the charge promoting particles m contact the photosensitive drum 1 in the nip portion between the charging roller 2 and the photosensitive drum 1 is significantly increased, and high contact property is obtained. And the charge-promoting particles m present in the nip portion between the charging roller 2 and the photosensitive drum 1 rub the surface of the photosensitive drum 1 without gaps, so that the charge can be directly injected into the photosensitive drum 1. 2, the direct charging (injection charging) is dominant due to the interposition of the charge promoting particles m.
[0079]
As a configuration for providing a speed difference, the charging roller 2 is rotationally driven to provide a speed difference from the photosensitive drum 1. Preferably, it is carried to the charging nip portion n. Preferably, the charging roller 2 is driven to rotate in order to temporarily collect and level the transfer residual toner on the photosensitive drum 1 carried to the charging nip portion n by the charging roller 2. It is desirable to configure so as to rotate in a direction opposite to the moving direction of the surface. That is, it is possible to predominantly perform direct charging by temporarily separating the transfer residual toner on the photosensitive drum 1 by reverse rotation and performing charging.
[0080]
Therefore, high charging efficiency, which cannot be obtained by conventional roller charging, can be obtained, and a charging potential substantially equal to the voltage applied to the charging roller 2 can be applied to the photosensitive drum 1. Thus, even when the charging roller 2 is used as the contact charging member, the applied bias required for charging the charging roller 2 is a voltage equivalent to the charging potential required for the photosensitive drum 1 and is stable and safe without using a discharge phenomenon. A simple contact charging system or device can be realized.
[0081]
Further, since the charging roller 2 is in contact with the photosensitive drum 1 with a speed difference, the pattern of the transfer residual toner from the transfer nip portion b to the charging nip portion n is disturbed and broken, and in the halftone image, The previous image pattern portion does not appear as a ghost.
[0082]
c) With the endurance, even if the charge accelerating particles m fall off from the charging nip portion n or the charging roller 2, the printer is operated, and thus the charging contained in the developer t of the developing device 4 as described above. Since the accelerating particles m move to the surface of the photosensitive drum 1 at the developing site a and continue to be sequentially supplied to the transfer nip n by the movement of the surface of the photosensitive drum 1, a favorable condition due to the presence of the electrifying particles m in the charging nip n is obtained. The chargeability is stably maintained over a long period.
[0083]
The charge-promoting particles that have fallen off from the charging nip n or the charging roller 2 are collected by the developing device 4 at the developing site a, mixed with the developer t, and circulated.
[0084]
By pre-loading the charge accelerating particles m on the surface of the charging roller 2, the above-described direct charging performance can be exhibited without any trouble from the very beginning of use of the printer.
[0085]
d) Since the printer is cleaner-less, the untransferred toner remaining on the surface of the photosensitive drum 1 after the transfer is carried to the charging nip portion n of the photosensitive drum 1 and the charging roller 2 by the movement of the photosensitive drum 1 as it is. Adheres and mixes into charging roller 2.
[0086]
Since the conventional toner is an insulator, the adhesion or mixing of the transfer residual toner to the charging roller 2 is also a factor that causes a charging failure in charging the photosensitive drum.
[0087]
However, even in this case, since the charge accelerating particles m are interposed in the charging nip portion n between the photosensitive drum 1 and the charging roller 2, it is possible to maintain close contact and contact resistance of the charging roller 2 with the photosensitive drum 1. Despite contamination of the charging roller 2 by transfer residual toner, ozone-less direct charging can be stably maintained at a low applied voltage for a long time, and uniform charging properties can be provided.
[0088]
e) The transfer residual toner adhering to and entering the charging roller 2 is gradually discharged from the charging roller 2 onto the photosensitive drum 1 and reaches the developing site a with the movement of the photosensitive drum 1 surface. ) (Toner recycling). As described above, in the simultaneous cleaning with development, the toner remaining on the photosensitive drum 1 after the transfer is developed in the subsequent image forming process, that is, the photosensitive member is charged and exposed to form a latent image, and the latent image is formed. During development, the fogging bias of the developing device, that is, the fogging potential difference V, which is the potential difference between the DC voltage applied to the developing device and the surface potential of the photosensitive member. _back Is to be recovered. In the case of the reversal phenomenon as in the printer according to the present embodiment, the simultaneous cleaning of development involves applying an electric field for collecting the toner from the dark portion potential of the photoconductor to the developing sleeve and attaching the toner from the developing sleeve to the bright portion potential of the photoconductor. This is done by the action of an electric field.
[0089]
f) If the intervening amount of the charge-promoting particles in the charging nip n between the photosensitive drum 1 as the image carrier and the charging roller 2 as the contact charging member is too small, the lubricating effect by the charge-promoting particles cannot be sufficiently obtained. In addition, the friction between the charging roller 2 and the photosensitive drum 1 is large, and it is difficult to drive the charging roller 2 to rotate the photosensitive drum 1 with a speed difference. That is, the driving torque becomes excessively large, and the surface of the charging roller 2 and the photosensitive drum 1 is shaved if the forcible rotation is performed. Further, the effect of increasing the contact chance by the charge-promoting particles may not be obtained, so that sufficient charging performance cannot be obtained. On the other hand, if the amount is too large, the particles of the charge-promoting particles falling off the charging roller 2 are significantly increased, which adversely affects image formation. According to experiments, the intervening amount was 10 ³ Pieces / mm ² More than one is desirable. 10 ³ Pieces / mm ² If it is lower, sufficient lubricating effect and effect of increasing the chance of contact cannot be obtained, resulting in a decrease in charging performance.
[0090]
More preferably 10 ³ ~ 5 × 10 ⁵ Pieces / mm ² Is preferred. 5 × 10 ⁵ Pieces / mm ² When the ratio exceeds the above range, the particles of the charge accelerating particles dropping onto the photosensitive drum 1 increase remarkably, and the exposure amount to the photosensitive drum 1 becomes insufficient irrespective of the light transmittance of the particles themselves. 5 × 10 ⁵ Pieces / mm ² In the following, the amount of particles falling off is also suppressed low, and the adverse effect can be improved. When the abundance of the particles dropped on the photosensitive drum 1 is measured in the intervening amount range, 10 ² -10 ⁵ Pieces / mm ² Therefore, as the abundance which has no adverse effect on image formation, ⁵ Pieces / mm ² The following is desired. A method of measuring the intervening amount and the abundance amount on the photosensitive drum 1 will be described. It is desirable that the intervening amount is measured directly at the charging nip n between the charging roller 2 and the photosensitive drum 1, but most of the particles existing on the photosensitive drum 1 before coming into contact with the charging roller 2 contact while moving in the opposite direction. In the present invention, the amount of particles on the surface of the charging roller 2 immediately before reaching the charging nip n is defined as the intervening amount. Specifically, the rotation of the photosensitive drum 1 and the charging roller 2 is stopped without applying a charging bias, and the surfaces of the photosensitive drum 1 and the charging roller 2 are illuminated with a video microscope (OVM1000N manufactured by OLYMPUS) and a digital still recorder (made by DELTAS). SR-3100). The charging roller 2 is brought into contact with the slide glass under the same conditions as the charging roller 2 is brought into contact with the photosensitive drum 1, and the contact surface is photographed from a rear surface of the slide glass with a video microscope at ten or more locations using a 1000 × objective lens. did. In order to separate individual particles from the obtained digital image, binarization processing was performed with a certain threshold value, and the number of regions where particles were present was measured using desired image processing software. The amount of the abundance on the photosensitive drum 1 was measured by photographing the photosensitive drum 1 with the same video microscope and performing the same processing. The adjustment of the intervening amount was performed by setting the blending amount of the charge accelerating particles m in the developer t of the developing device 4. Generally, the charge-promoting particles are contained in an amount of 0.01 to 20 parts by weight based on 100 parts by weight of the developer (toner).
[0091]
<< About control between image recording media >>
In the present embodiment, the image recording medium is provided with a roller cleaning mode (contact charging member cleaning mode) for efficiently removing transfer residual toner adhering to and mixing into the charging roller 2 serving as a contact charging member from the charging roller 2. During the non-image formation period, the transfer residual toner is discharged onto the image carrier. As a result, the level of contamination of the charging roller 2 due to the transfer residual toner is always kept low, so that good chargeability can be obtained. Further, the transfer residual toner is discharged during non-image formation between image recording media. Records can be stably maintained over a long period of time.
[0092]
That is, as a voltage application mode to the charging roller 2 as a contact charging member, an A mode (non-roller cleaning mode) in which a DC voltage is applied during image formation to uniformly charge the photosensitive drum 1 as an image carrier, There is a B mode (roller cleaning mode) for applying a voltage obtained by superimposing a DC voltage and an AC voltage (cleaning bias) during non-image formation, and the frequency of the AC voltage in the B mode is approximately 5 to 500 Hz.
[0093]
a) A mode
In the present embodiment, the switch SW of the charging bias application power supply S1 is controlled to be switched to the A contact side by a sequence control circuit (not shown) at the time of image recording by the printer, and the charging roller 2 is connected to the core 2a by the DC power supply S1. _DC Is applied, the surface of the rotating photosensitive drum 1 is directly charged to a voltage of about -600 V substantially equal to the applied DC voltage, and image recording is performed.
[0094]
b) B mode
In the present embodiment, the switch SW of the charging bias application power supply S1 is controlled to switch to the B contact side by a sequence control circuit (not shown) at the time of image recording by the printer, and the DC power supply S _DC AC power supply S _AC Are connected in series, so that the core metal 2a of the charging roller 2
DC voltage: -600V
AC voltage: peak-to-peak voltage 200 V, frequency, for example, 50 Hz,
Is applied.
[0095]
Further, in this B mode, the developing sleeve 4a of the developing device 4 is provided with the same
DC voltage: -450V
AC voltage: peak-to-peak voltage 1600 V, frequency 1.8 kHz,
Was applied.
[0096]
By maintaining these bias relationships, the toner negatively charged on the charging roller 2 is developed on the photosensitive drum 1 (the toner on the charging roller 2 is discharged to the photosensitive drum 1), and the toner is further discharged. Is collected with the back contrast of the developing device 4.
[0097]
In this case, by supplying the charge accelerating particles m to the charging roller 2, the releasability of the toner from the charging roller 2 is improved, that is, the releasability is increased, and The discharge of the toner to the photosensitive drum 1 side is promoted, the charging roller 2 contaminated by the toner is efficiently cleaned, and the ozone-less direct charging and the toner recycling system can be performed without a problem at a low applied voltage, thereby achieving a high quality image. It is possible to maintain the formation for a long period of time, and to maintain the high-quality image formation for a long period even after outputting an image having a high image ratio.
[0098]
In the B mode, it is desirable that the cleaning bias applied to the charging roller 2 is set so that the difference between the photosensitive drum potential and the charging roller potential downstream of the charging nip n in the photosensitive drum moving direction is large. Setting is more appropriate.
[0099]
<< Pre-exposure device 7 >>
Reference numeral 7 denotes a pre-exposure device for exposing and discharging the photosensitive drum charged surface between the transfer roller 5 and the charging roller 2.
[0100]
In the exposed photosensitive drum 1, the potential contrast with the charging roller 2 increases.
[0101]
The transfer residual toner remaining on the photosensitive drum 1 without being transferred onto the transfer material P by the transfer device of No. 5 is transferred to the charging nip portion by the potential contrast between the image bearing member subjected to the charge removal by the exposure device and the charging roller 2. At n, it receives the force held by the photosensitive drum.
[0102]
Accordingly, it is possible to prevent the transfer residual toner from adhering to and mixing with the charging roller, and to keep the charging roller 2 in a clean state.
[0103]
In addition, by controlling the exposure amount and combining with the roller cleaning mode described above, it is possible to form a sequence for accurately discharging the untransferred toner to the portion between the image recording media on the photosensitive drum 1.
[0104]
Example 1 was performed using the above-described apparatus configuration.
[0105]
In the case where the above-described sequence is formed, the exposure amount is changed between a portion between image recording media on the photosensitive drum 1 and an image recording medium portion. First, when the exposure is turned off in the portion between the image recording media on the photosensitive drum 1, there is no potential contrast between the charging roller 2 and the photosensitive drum 1, and no electric field for holding the transfer residual toner on the photosensitive drum 1 is generated. Adhesion and mixing of the transfer residual toner to the charging roller 2 occurs.
[0106]
When the photosensitive drum 1 is neutralized by exposure, the photosensitive drum 1 that has been charged to the negative polarity by the charging roller loses its charge, the negative polarity is weakened, and an electric field is generated from the photosensitive drum 1 toward the charging roller 2. Since the toner is negatively charged, the electric field receives a force pressed against the photosensitive drum 1.
[0107]
FIG. 2 is a conceptual diagram of an electric field A generated between the charging roller 2 and the photosensitive drum 1 and a holding force B of the transfer residual toner t1. Since the potential of the photosensitive drum 1 is higher than that of the charging roller 2 due to exposure and charging, the direction of the electric field A is from the photosensitive drum 1 to the charging roller 2. At this time, the force B for holding the transfer residual toner t1 on the photosensitive drum 1 acts in the opposite direction to the electric field A because the toner has a negative polarity.
[0108]
The photosensitive drum 1 is charged to -600 V by a charging roller. When the potential of the photosensitive drum 1 becomes −450 V due to static elimination by exposure, the potential contrast ΔV between the charging roller 2 and the photosensitive drum 1 becomes 150 V, and an electric field for holding the transfer residual toner on the photosensitive drum 1 is generated.
[0109]
An electric field is generated in the image recording medium portion on the photosensitive drum 1 as described above, and the toner is held at the nip between the photosensitive drum 1 and the charging roller 2 so that the transfer residual toner is not discharged.
[0110]
As described above, the potential contrast is strengthened in the image recording medium portion on the photosensitive drum 1 so that the transfer residual toner is held in the nip portion n of the charging roller 2 and the photosensitive drum 1, and in the portion between the image recording media on the photosensitive drum 1. The transfer residual toner is transferred to the charging roller 2 by weakening or making the potential contrast zero. The transfer residual toner transferred to the charging roller 2 receives the voltage in the B mode of the roller cleaning mode, and is discharged onto the photosensitive drum 1 again. These are all controlled so as to discharge the transfer residual toner between the image recording media.
[0111]
All of the untransferred toner does not adhere to or mix with the charging roller 2 when the exposure is OFF, but a certain amount remains on the photosensitive drum 1. In the case of continuous paper passing, the transfer residual toner amount increases as the number of passed paper sheets increases.
[0112]
To cope with this, the exposure amount is increased for each image recording medium on the photosensitive drum 1.
[0113]
FIG. 3 shows a sequence control diagram for discharging the transfer residual toner at this time.
[0114]
The pre-exposure is controlled at the timing of exposing the image recording medium on the photosensitive drum 1 and turning off the exposure between the image recording media. Specifically, the pre-exposure is turned off at a timing shifted from the portion between the image recording media on the photosensitive drum 1 by one rotation of the charging roller 2. At this time, the transfer residual toner held in the nip between the photosensitive drum 1 and the charging roller 2 and the transfer residual toner that reaches the nip during the exposure OFF are mixed on the charging roller 2. The pre-exposure is turned on again at the timing when the portion between the image recording media on the photosensitive drum 1 reaches the nip portion, and the transfer residual toner of the next image recording medium portion is held in the nip portion. A roller cleaning AC bias of the charging roller 2 is applied in synchronization with the ON timing of the pre-exposure, and the transfer residual toner mixed into the charging roller 2 is discharged onto the photosensitive drum 1. By controlling the pre-exposure and the roller cleaning AC bias at this timing, it is possible to discharge the transfer residual toner to the portion between the image recording media on the photosensitive drum 1. When the next image recording medium portion on the photosensitive drum 1 reaches the nip between the charging roller 2 and the photosensitive drum 1, the roller cleaning AC bias is turned off.
[0115]
The pre-exposure amount is constant during one exposure. By increasing the pre-exposure amount for each portion between the image recording media, the potential contrast between the charging roller 2 and the photosensitive drum 1 is increased for each portion between the image recording media so that the transfer residue that can be held on the photosensitive drum 1 is increased. The toner amount is increased in accordance with the increase in the amount of the transfer residual toner remaining on the photosensitive drum 1. Assuming that the rate of increase in potential contrast is aV for each image recording medium, the a (n-1) V potential contrast will increase in the nth image formation.
[0116]
This potential contrast increase rate is desirably set to an appropriate value according to the increase amount of the transfer residual toner. If the potential contrast increase rate cannot keep up with the increase in the transfer residual toner, the influence of light shielding and fogging can be gradually observed in continuous paper feeding. Conversely, if the potential contrast increase rate is faster than the increase in the transfer residual toner, problems such as an increase in power consumption and poor charging of the photosensitive drum 1 by the charging roller 2 occur.
[0117]
In Example 1, Examples 1-1 and 1-2 in which the rate of increase in potential contrast was changed were performed, and evaluation of image defects and evaluation of charging characteristics were performed, respectively. Further, Comparative Examples 1-3 and 1-4 were also performed for comparison with the examples.
[0118]
《Evaluation》
Table 1 shows the results of the evaluation. The evaluation method and consideration based on the table will be described in detail below.
[0119]
The surface of the photosensitive drum 1 was neutralized by exposure by the pre-exposure device 7, and the potential was set to -450V. At this time, the potential contrast ΔV is 150 V because the potential of the charging roller 2 is −600 V. The potential contrast ΔV changes depending on the amount of exposure by the pre-charging device 7, and increases as the amount of exposure increases.
[0120]
The sheet is passed from the state where the potential contrast ΔV of the first sheet is 150 V, and the potential contrast is changed to various ascending rates by increasing the amount of exposure by the pre-exposure device 7 in accordance with the continuous sheet passing. I went. 100 sheets were continuously fed, and the 100th image was evaluated.
[0121]
Solid black and solid white images were continuously printed on 100 sheets each, and the 100th solid black and solid white image were evaluated.
[0122]
[Table 1]

[0123]
The points of evaluation are white spots in a solid black image, black spots in a solid white image, and image unevenness. These are caused by shading, fogging and poor charging, respectively. The 100th image was visually checked and evaluated. The evaluation symbols in the table are described below. These indicate the degree of the image state, and are commonly used for all white spots, black spots, and image unevenness.
[0124]
A: Very good image state. No disturbance is observed in the image.
[0125]
：: Almost no white spots, no black spots, and no image unevenness were observed.
[0126]
Δ: White spots, black spots, and image unevenness appear slightly in the image.
[0127]
X: White spots, black spots, and image unevenness can be well observed.
[0128]
In Example 1-1, the rate of increase of the potential contrast ΔV was controlled at 1 V for each image recording medium, and in Example 1-2, the rate of increase of the potential contrast ΔV was controlled at 4 V for each image recording medium, and evaluation was performed. In Comparative Example 1-3, a potential contrast ΔV of 150 V was applied, but thereafter, the potential contrast ΔV was not changed. In Comparative Example 1-4, the exposure by the pre-exposure device 7 was not performed.
[0129]
In Example 1-1, white spots in the solid black image and black spots in the solid white image were slightly observed, and the image state was Δ. Also, almost no image unevenness due to poor charging was observed.
[0130]
Since the potential contrast ΔV of the first sheet is 150 V and the potential contrast increasing rate is 1 V for each image recording medium, the potential contrast ΔV has increased to 249 V at the time of forming the 100th image. At this rising rate, it is not possible to cope with the increase of the transfer residual toner due to continuous paper passing, and as the number of paper passing increases, the transfer residual toner mixed into the charging roller 2 at a timing other than discharge to the portion between the image recording media. The amount increases. For this reason, image defects due to light shielding and fogging appeared.
[0131]
The potential of the photosensitive drum 1 at the time when 100 sheets have passed is -351 V, and this potential is a potential that can be sufficiently charged by the charging roller 2. Therefore, the charging characteristics were good.
[0132]
In Example 1-2, white spots in a solid black image and black spots in a solid white image were hardly observed, and the image state was ○. Further, almost no image unevenness considered to be caused by poor charging was observed.
[0133]
Since the potential contrast ΔV of the first sheet is 150 V and the potential contrast increasing rate is 4 V for each image recording medium, the potential contrast ΔV increases to 546 V at the time of forming the 100th image. This increase rate corresponds to an increase in the amount of transfer residual toner due to continuous paper passing, and almost no transfer residual toner leaks to portions other than the portion between image recording media. The transfer residual toner mixed into the charging roller 2 at the timing of being discharged to the portion between the image recording media is applied to the photosensitive drum 1 and the charging roller by applying the voltage of the roller cleaning mode at the timing of being discharged to the portion between the image recording media. In the downstream portion of the nip 2, the toner is efficiently discharged to the portion between the image recording media on the photosensitive drum 1. As a result, there was almost no transfer residual toner causing light blocking, fogging, and charging failure, and a good image could be obtained.
[0134]
At the time of passing 100 sheets, the potential of the photosensitive drum 1 was increased to −54 V, but was a potential that could be charged by the charging roller 2.
[0135]
In order to make a comparison with the example, 150 V was applied as the initial potential contrast as in each example, but after that, exposure neutralization was performed by the pre-exposure device 7 and the comparative example 1-3 in which the potential contrast was not changed. Comparative Examples 1-4 which did not exist were performed.
[0136]
In Comparative Example 1-3, white spots in a solid black image and black spots in a solid white image were often observed, and the image state was x. Almost no image unevenness was observed.
[0137]
Since the potential contrast ΔV after passing 100 sheets remains at 150 V, the holding force of the transfer residual toner on the photosensitive drum 1 does not reach the increase of the transfer residual toner during continuous paper passing, and The transfer residual toner is mixed into the charging roller 2 at a timing other than the timing of discharging to the portion between the image recording media. This transfer residual toner adheres to the photosensitive drum 1 at a downstream portion of the nip between the photosensitive drum 1 and the charging roller 2. The transfer residual toner attached to the photosensitive drum 1 causes light shielding and fogging, and causes image defects.
[0138]
In Comparative Example 1-4, the exposure by the pre-exposure device 7 was not performed. For this reason, there is no force for holding the transfer residual toner in the upstream portion of the nip between the photosensitive drum 1 and the charging roller 2, and the transfer residual toner adheres to and mixes with the charging roller 2 from the photosensitive drum 1. The same mechanism as in Comparative Example 1-3 causes image defects.
[0139]
From Example 1 described above, it was found that good image formation was performed in Example 1-2 in which the rate of increase in the potential contrast ΔV was 4 V. By increasing the potential contrast for each image recording medium by comparison with Example 1-1, the increasing transfer residual toner is accurately held at the nip between the photosensitive drum 1 and the charging roller 2. It was confirmed that good image formation was possible.
[0140]
(Example 2)
In the first embodiment, a pre-exposure device 7 is disposed between the transfer roller 5 and the charging roller 2 as a means for increasing the potential contrast in the nip portion between the photosensitive drum 1 and the charging roller 2. Increased contrast.
[0141]
Although the rate of increase in the potential contrast is controlled by controlling the amount of exposure from the pre-exposure device 7, it is actually difficult to control in units of several volts because light is used.
[0142]
Therefore, in the second embodiment, the potential contrast in the nip portion between the photosensitive drum 1 and the charging roller 2 is increased by charging, not by static elimination by exposure. According to the charging without using light as the potential contrast increasing means, more precise control of the potential contrast is possible. FIG. 4 shows an example in which the pre-charging device 8 is disposed at the same position as the pre-exposure device 7 instead of the pre-exposure device 7 as the device configuration of the second embodiment.
[0143]
The charging device 8 is a charging device using corona discharge. By applying a high voltage between the transfer roller 5 and the charging roller 2, the charged surface of the photosensitive drum is charged to a predetermined level by exposing the charged surface of the photosensitive drum to a discharge current generated.
[0144]
FIG. 5 shows a sequence control diagram at this time. The control of the pre-charging device 8 is the same as the control of the pre-exposure device 7.
[0145]
Example 2 was implemented using the above-described apparatus configuration and sequence. Details are the same as in the first embodiment, and will not be described here.
[0146]
In Example 2, Examples 2-1 and 2-2 in which the rate of increase in potential contrast was changed were performed, and evaluation of image defects and evaluation of charging characteristics were performed, respectively. Further, Comparative Examples 2-3 and 2-4 were also performed for comparison with the examples.
[0147]
《Evaluation》
Table 2 shows the results of this evaluation. The discussion based on the table is described in detail below.
[0148]
An electric charge was applied to the surface of the photosensitive drum 1 by charging by the pre-charging device 8, and the potential was set to -450V. At this time, the potential contrast ΔV is 150 V because the potential of the charging roller 2 is −600 V. The potential contrast ΔV changes depending on the amount of charge by the pre-charging device 8, and increases as the amount of charge increases.
The paper was passed from the state where the potential contrast ΔV of the first sheet became 150 V, and the potential contrast was increased at various rising rates with continuous paper passing. 100 sheets were continuously fed, and the 100th image was evaluated.
Solid black and solid white images were continuously printed on 100 sheets each, and the 100th solid black and solid white image were evaluated.
[0149]
[Table 2]

[0150]
The evaluation points and the symbols in the table are the same as in the first embodiment, and will not be described here.
[0151]
In Examples 2-1 to 2-4, the rate of increase of the potential contrast ΔV was changed from 1 V to 4 V for each image recording medium. Examples 2-5 and 2-6 were performed as comparative examples. In Example 2-1, a potential contrast ΔV of 150 V was applied, but thereafter, the potential contrast ΔV was not changed. In Example 2-6, the exposure by the pre-charging device 8 was not performed.
[0152]
In Example 2-1, white spots in the solid black image and black spots in the solid white image were slightly observed, and the image state was Δ. Also, almost no image unevenness due to poor charging was observed.
[0153]
The conditions are the same as in Example 1-1, and the image formation proceeds based on the same mechanism. This potential contrast increase rate cannot cope with an increase in transfer residual toner due to continuous paper passing, and the amount of transfer residual toner mixed into the charging roller 2 increases at a timing other than discharge to the portion between image recording media. As a result, image defects due to shading and fogging occur.
[0154]
In Example 2-2, white spots in the solid black image were hardly observed, and black spots in the solid white image were slightly observed. In the image state, the white dots in the solid black image were 、, and the black dots in the solid white image were △. Further, almost no image unevenness possibly caused by poor charging was observed.
[0155]
Since the potential contrast ΔV of the first sheet is 150 V and the potential contrast increasing rate is 2 V for each image recording medium, the potential contrast ΔV is increased to 348 V at the time of forming the 100th image. Even at this rising rate, it is not possible to completely cope with the amount of transfer residual toner that increases as the number of sheets passed increases, but the amount of transfer residual toner that can be held in the nip portion between the photosensitive drum 1 and the charging roller 2 increases, so that the image The amount of transfer residual toner leaking to portions other than the portion between the recording media was reduced, and the image state was improved.
[0156]
In Example 2-3, white spots in the solid black image were hardly observed, and black spots in the solid white image were slightly observed. In the image state, the white dots in the solid black image were 、, and the black dots in the solid white image were △. Also, almost no image unevenness due to poor charging was observed.
[0157]
Since the potential contrast ΔV of the first sheet is 150 V and the potential contrast increasing rate is 3 V for each image recording medium, the potential contrast ΔV has increased to 447 V at the time of forming the 100th image. Although it has not yet been able to cope with the increase in the amount of transfer residual toner due to the continuous paper passing, the amount of transfer residual toner that can be held in the nip portion between the charging roller 2 and the photosensitive drum 1 is smaller than in Examples 2-1 and 2-2. The influence of light blocking, fogging and poor charging has been reduced.
[0158]
In Example 2-4, white spots in the solid black image and black spots in the solid white image were hardly observed, and the image state was ○. Almost no difference in the level between the white spots in the solid black image and the black spots in the solid white image observed in Examples 2-2 and 2-3 was observed. Also, almost no image unevenness was observed.
[0159]
Since the potential contrast ΔV of the first sheet is 150 V and the potential contrast increasing rate is 4 V for each image recording medium, the potential contrast ΔV has increased to 546 V at the time of forming the 100th image. This increase rate corresponds to an increase in the amount of transfer residual toner accompanying continuous paper passing, and almost no transfer residual toner leaks to portions other than the portion between image recording media. Therefore, good image formation was performed.
[0160]
In order to make a comparison with the embodiment, 150 V was applied as the initial potential contrast as in each embodiment. However, after that, the comparative example 2-5 in which the potential contrast was not changed, and the charging by the pre-charging device 8 was not performed. Comparative Example 2-6 was performed.
[0161]
Since these comparative examples have the same conditions as those of comparative examples 1-3 and 1-4, the details will not be described here.
[0162]
In Comparative Examples 2-5 and 2-6, white spots in a solid black image and black spots in a solid white image were often observed, and the image state was x. Almost no image unevenness was observed.
[0163]
From the above Example 2, it was found that if charging is used as the means for increasing the potential contrast, the potential contrast increase rate control on the order of volts can be performed. With the change in the potential contrast increase rate, a change was also observed in the image defect, and the effect of the potential contrast increase rate on the image defect could be observed.
[0164]
(Example 3)
In the first and second embodiments, exposure or charging is performed in the portion between the image recording media on the photosensitive drum 1 to increase the potential contrast between the photosensitive drum 1 and the charging roller 2. Further, the exposure amount and the charging amount were constant during one exposure and charging.
[0165]
However, in actuality, the amount of transfer residual toner carried to the nip n between the photosensitive drum 1 and the charging roller 2 during the exposure or the charging continues to increase. Therefore, if the exposure amount or the charge amount is increased accordingly, the transfer residual toner can be more stably held in the nip portion between the photosensitive drum 1 and the charging roller 2.
[0166]
FIGS. 6 and 7 show sequence control diagrams at this time. FIG. 6 is a sequence control diagram when the pre-exposure device 7 is used. The pre-exposure amount, which was constant in a single exposure, is continuously increased in each exposure. FIG. 7 is a sequence control diagram in the case where the pre-charging device 8 is used. In this figure as well, the pre-charge amount, which has been constant in one charging operation, is continuously increased each time. I let it. In Example 3, the exposure amount and the charging amount during the exposure and during the charging were respectively increased at the same increasing rate as the increasing rate.
[0167]
The configuration of the main body device is the same as that described in the first and second embodiments, and will not be described in detail here.
[0168]
《Evaluation》
Examples 3-1 and 3-2 and Comparative Examples 3-3 and 3-4 using the pre-exposure device 7, Examples 4-1 to 4-4 and Comparative Examples 4-5 and 4 using the pre-charging device 8. At -6, image defects and charging characteristics were evaluated. The results are shown in Tables 3 and 4, respectively. The evaluation method has already been described in Example 1 and Example 2 and will not be described here. Table 3 is compared with Table 1 and Table 4 is compared with Table 2, and the consideration is described in detail.
[0169]
In Table 3, as compared with Table 1, the image evaluation result increased only in Example 3-2 in which the potential contrast increase rate was 4 V for each image recording medium. Other Examples 3-1 and Comparative Examples 3-3 and 3-4 did not change as compared with Example 1-1 and Comparative Examples 1-3 and 1-4, respectively.
[0170]
In the sequence for increasing the exposure amount or the charging amount during the exposure or the charging, the image level could be increased only when the image evaluation was ○ in Example 1. This sequence is effective when the potential contrast ΔV is just large enough to hold the transfer residual toner on the photosensitive drum 1. The image level was slightly improved by keeping all the transfer residual toner leaking during the exposure.
[0171]
In Table 4, as compared with Table 2, the image evaluation result is higher in Example 4-4 where the potential contrast increase rate is 4 V for each image recording medium. The other Examples 4-1 to 4-3 and Comparative Examples 4-5 and 4-6 have not been changed. As in the case of Table 3, this sequence was effective when the potential contrast ΔV was just large enough to hold the untransferred toner on the photosensitive drum 1.
[0172]
As described above, by summarizing the third embodiment, it was confirmed that the image state can be improved by using the sequence used in the third embodiment. The effect often appears when the rate of increase in the potential contrast just corresponds to the increase in the transfer residual toner.
[0173]
[Table 3]

[0174]
[Table 4]

[0175]
【The invention's effect】
As described above, according to the present invention, the potential contrast between the contact charging member and the image carrier is increased at the timing of the portion between the image recording media on the image carrier as compared with the image recording medium portion on the image carrier. More specifically, the potential contrast between the image bearing member and the contact charging member is increased by exposing or charging the image bearing member immediately before charging, and the transfer residual toner is transferred between the contact charging member and the image bearing member. In the sequence control of holding in the charging nip portion, by increasing exposure and charging in each portion between image recording media, it is possible to stably hold the transfer residual toner that increases in each portion between image recording media in the charging nip portion. Thus, problems such as shading and fogging can be prevented.
[0176]
In addition, by increasing the exposure amount or the charging amount during each exposure or charging, a better image can be formed.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram of an image forming apparatus according to a first embodiment.
FIG. 2 is a conceptual diagram of a transfer residual toner holding electric field in a nip portion between a charging roller 2 and a photosensitive drum 1.
FIG. 3 is a sequence control diagram according to the first embodiment.
FIG. 4 is a schematic configuration diagram of an image forming apparatus according to a second embodiment.
FIG. 5 is a sequence control diagram according to the second embodiment.
FIG. 6 is a sequence control diagram according to a third embodiment (when the pre-exposure device 7 is used).
FIG. 7 is a sequence control diagram according to the third embodiment (when the pre-charging device 8 is used).
[Explanation of symbols]
1. Photosensitive drum (image carrier, charged object)
2 Charging roller (contact charging member)
3 laser beam scanner (exposure device)
4 Developing device
4a Developing sleeve
t Developer (toner)
m Charge promotion particles
5 Transfer roller
6 Fixing device
P transfer material
A Electric field
B Transfer toner retention force by electric field
t1 Transfer residual toner

Claims (10)

An image carrier, a charging device that charges the image carrier, a unit that writes information by creating an electrostatic latent image on a charged surface of the image carrier, and a development that visualizes the electrostatic latent image with toner Means for transferring the visualized toner image onto the image recording medium, and recovering the toner remaining on the image carrier after the developing means transfers the toner image onto the image recording medium. An image forming apparatus which also has a function of changing a potential contrast between the image carrier and the charging member, wherein the amount of change in the potential contrast is determined by an image on the image carrier during continuous paper feeding. An image forming apparatus characterized in that the size is increased for each recording medium. 2. The image forming apparatus according to claim 1, wherein a potential contrast between the image carrier and the charging member is larger between image recording media on the image carrier than on an image recording medium on the image carrier. 3. Image forming device. 3. The image according to claim 1, wherein the potential contrast increasing means between the image carrier and the charging member between the image recording media on the image carrier is a static elimination means by exposure. Forming equipment. 3. The image carrier according to claim 1, wherein the potential contrast increasing means between the image carrier and the charging member between the image recording media on the image carrier is a means for charging the image carrier by a pre-charging device. The image forming apparatus according to any one of the above. 5. The image forming apparatus according to 4, wherein the pre-charging charging device is a charging device using a non-contact charging member. The charging device contacts a charging member to which a voltage is applied with the image carrier, forms a nip portion with the image carrier, and then applies a voltage to the charging member, thereby causing the image carrier surface to move. The image forming apparatus according to claim 1, wherein the image forming apparatus is a contact charging device for charging. The developer of the developing unit contains toner and charge-promoting particles, and adheres to the image carrier in a developing section and remains on the image carrier after transfer of the toner image to paper as an image recording medium. 7. The image forming apparatus according to claim 1, wherein the charge promotion particles are supplied to a nip portion between the charging member and the image carrier by carrying the charge promotion particles. apparatus. The image forming apparatus according to claim 1, wherein the contact charging member is rotated while maintaining a speed difference in a direction opposite to a rotation direction of the image carrier. The image forming apparatus according to any one of claims 1 or 5-8, characterized in that the volume resistivity of the charging performance enhancement particles is less than 10 ¹² Ω · cm. The image forming apparatus according to any one of claims 1 or 5-8, characterized in that the volume resistivity of the charging performance enhancement particles is less than ¹⁰ 10 Ω · cm.

Images