JP2004145021A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of preventing toner scattering caused by exchanging charge between a guiding member and transfer paper. <P>SOLUTION: A conductive Mylar(R) 101 functioning as a conductive part is attached to the transfer paper opposed surface of an entrance guide 74, and further an insulating Mylar 102 functioning as a non-conductive sheet part is attached to the Mylar 101. Furthermore, constant voltage bias of +2[kV] is applied to the conductive Mylar from a power source 103 functioning as a means for applying bias to the conductive part. Thus, the toner scattering on all the surface of the transfer paper, which happens to arise because the transfer paper comes close to or comes into contact with the entrance guide, is prevented. <P>COPYRIGHT: (C)2004,JPO

Description

【００１８】
図４は、定着ユニット７の概略構成図である。定着ユニット７は、加熱ローラ７１および定着ローラ７２に掛け渡された定着ベルト７０、定着ベルト７０を介して定着ローラ７２に対向する位置に設けられた加圧ローラ７３を有している。定着ローラ７２と加圧ローラ７３とのニップ部が、加熱と共に加圧することによりトナー像を転写紙に定着させる定着ニップＮｔである。更に、第４のトナー像形成ユニット１Ｋを通過し合成トナー像が形成された転写紙を転写紙搬送ベルト６０から剥離し、定着ニップＮｔへ導くためのガイド部材として、入口ガイド７４が設けられている。入口ガイド７４は樹脂製であり、転写紙搬送ベルトから剥離された転写紙が入口ガイド７４に近接もしくは接触しながら定着ニップへと進入する。ここで、転写紙が近接もしくは接触しながら搬送されるのは、正常の動作であり、入口ガイド７４は転写紙上の未定着画像を安定して定着ニップＮｔへ受け渡すための役割も担っている。
【００１９】
ところで、入口ガイド７４に転写紙が摩擦接触等して入口ガイド７４が帯電し、帯電した入口ガイド７４と転写紙との間で電荷のやり取りが生じる場合がある。通常、転写紙上の未定着トナー像を構成しているトナーは、転写紙との間に静電気力、ファンデル＝ワールス力等によって付着している。この付着力は弱いため、入口ガイド７４と転写紙との間で電荷のやり取りが生じると未定着トナー像を形成しているトナーの転写紙への付着力が不安定となり、転写紙上で飛散してトナーチリを生じる場合がある。これは、未定着のトナー像を担持している転写紙が定着ニップ上流で入口ガイド７４に近接若しくは接触するために発生する。また、転写紙は紙種、乾燥状態、装置駆動時の湿度環境等によって抵抗が変化する。このため、入口ガイド７４と転写紙Ｐとの接触により発生するトナーチリ防止の目的で、フレームに用いられる樹脂の最適な体積抵抗を検討しても、多種多様な紙種及び環境下で使用する画像形成装置においては一意には決められない。
そこで、本実施形態においては、トナーチリを防止するための構成を有している。以下に、本発明の特徴について説明する。
【００２０】
〔実施例１〕
図１は、実施例１における定着ユニットの入口側概略構成図である。本実施形態においては、入口ガイド７４の転写紙対向面に導電性部としての導電性マイラ１０１を接着し、更にその上に非導電性シート部としての絶縁性マイラ１０２を接着している。また、絶縁性マイラ１０２はその厚みが０．１〜０．５〔ｍｍ〕のものを用いている。但し、この厚みの範囲は実用的な範囲であって、通常約１〔ｍｍ〕以下の厚みであれば使用可能である。更に、導電性マイラ１０１に導電性部バイアス印加手段として電源１０３からバイアスを印加している。また、導電性マイラ１０１としては体積抵抗が１０^６［Ωｃｍ］のもの、非導電性マイラとしては絶縁性のＰＥＴ（ポリエチレンテレフタレート）を用いた。導電性マイラ１０１に印加したバイアスは、＋２［ＫＶ］の定電圧バイアスである。
【００２１】
ここで、従来の定着ユニット構成について触れておく。
図６は従来用いられていた定着ユニット入口側概略構成図である。定着ベルト７０の転写ユニット側には本実施形態と同様に樹脂製の入口ガイド７４が具備されている。しかし、本実施形態と異なり、従来装置においては入口ガイド７４に導電性マイラ１０１及びその上に絶縁性マイラ１０２は接着されていなかった。
【００２２】
尚、図１と図６の定着ユニット７はずれも、入口ガイド下流に隣接して金属製の除電針１１０を設けている。これは、入口ガイドに沿って移動してくる転写紙の裏面に接触させて転写紙の帯電性を測定するためのものであり、あくまで実験的に測定を目的として具備したものである。よって、実際の装置には具備されてはいないものである。そして、本実施形態のプリンタと図６に示す従来型のプリンタとにおいて本発明の効果を調べるための比較を行った。次にその方法と結果を説明する。
【００２３】
従来型のプリンタと本実施形態のプリンタにおいて、作像を行った場合の転写紙の帯電量を、作像時に除電針１１０に流れる電流値で測定した。
従来型のプリンタにおいては、その電流値が−１．５〜＋５［μＡ］の範囲であった。この時の画像には、特に感光体ドラム１１Ｙ，１１Ｍ，１１Ｃ，１１Ｋと平行な方向の線画像が搬送方向後方に尾を引くように散乱するバンディング状のトナーチリが発生した。尚、従来型においては、第４のトナー像形成ユニット１Ｋでの転写電流値は３５［μＡ］である。
一方、本実施形態のプリンタにおいては、黒単色画像を作像した場合においてその電流値が＋２．５〜＋５．５［μＡ］の範囲であった。この時画像には、従来型のプリンタで発生したバンディング状のトナーチリは発生しなかった。
【００２４】
以上の結果から、次のことが分かる。従来型のプリンタにおいて、転写紙に流れる電流に−極性のものが発生した。通常、上記のように第４のトナー像形成ユニット１Ｋでの転写電流値は３５［μＡ］であるため、転写紙が帯電していない場合には除電針から流れる電流値は転写に用いられた＋極性のみとなるはずである。これに対して−極性の電流が発生したのは、転写紙が不安定に帯電しているからだということが言える。そして、トナーに対して反発する磁界を発生する−極性の電流が流れたことによって、バンディング状のトナーチリが発生したのである。
【００２５】
また、本実施形態のプリンタにおいては、黒単色画像を作像する際トナー像形成ユニット１Ｋでの転写電流値は３０［μＡ］であるのに対して、転写紙に流れる電流が＋２．５〜＋５．５［μＡ］と＋極性で安定した。これにより、転写紙に対する不均一な電荷の付与が防止されたことがわかる。
転写紙に流れる電流が＋極性で安定した理由は次のとおりである。入口ガイドの転写紙に対向する面に導電性マイラ１０１を設け、所定のバイアスを印加する。これによって、この入口ガイドに接触又は近接する転写紙が入口ガイドを構成する樹脂等の材料における帯電性の影響を受けずに済むように入口ガイド表面の地ならしをする。更に導電性マイラ１０１の表面を絶縁性マイラ１０２で覆い、絶縁性マイラ１０２を設けていない場合に生じる恐れのある転写紙に対する電流値の変化を生じないようにする。この転写紙に対する電流値の変化は、絶縁性マイラ１０２を設けていない場合、転写紙の挙動により導電性マイラ１０１と転写紙との距離が変化して生じることが考えられる。特に、導電性マイラ１０１に定電圧バイアスを印加した場合に生じやすいと考えられ、バンディング状のトナーチリが発生する恐れがある。よって、導電性マイラ単独での適用は推奨できない。本実施例１においては、導電性マイラ１０１表面に絶縁性マイラ１０２を設け、このような転写紙に対する電流値の変化を生じないようにすることができる。
【００２６】
また、本実施例１においては導電性マイラ１０１に＋２［ＫＶ］の定電圧バイアスを印加している。これは、転写バイアスＶｔと同極性のバイアスである。ここで、導電性マイラ１０１に本実施例１とは異なり転写バイアスＶｔと逆極性の−極性のバイアスを印加すると、転写紙からトナーを引き離そうとする電荷が転写紙に付与されることになる。実際、導電性マイラ１０１に−２［ＫＶ］のバイアスを印加したところ、実験的に具備した除電針から流れる電流値は−１．８〜−５．８［μＡ］であった。そしてこの場合、トナーが転写紙上全面でチリを生じてしまう。また、導電性マイラ１０１に印加するバイアスを−極性のままゼロに近づけると、実験的に具備した除電針から流れる電流値もゼロに近づいて行く。しかし、＋極性側に移行することはなく、この転写紙全面でのトナーチリの発生を防止することはできない。そこで、本実施例１においては、導電性マイラ１０１に転写バイアスＶｔと同極性である＋極性のバイアスを印加した。
【００２７】
更に、導電性マイラ１０１に印加するバイアス値の適正値を検討するために、導電性マイラ印加バイアス値（転写電流値）Ａ_ｍと転写バイアス値（転写電流値）Ａ_ｔとによって変化する転写画像の状態を調べた。その結果を図５に示す。但し、導電性マイラ１０１に印加するバイアスは転写バイアスＡ_ｔと同極性の場合のみについて調べた。これは、転写バイアスＡ_ｔと逆極性のバイアスを印加すると上記のようなトナーチリが生じることが分かっているためである。ここでバイアスの制御は、転写紙の抵抗値による影響を受けにくい定電流制御とした。
【００２８】
図５において、導電性マイラ印加バイアス値（転写電流値）Ａ_ｍと転写バイアス値（転写電流値）Ａ_ｔが５［μＡ］以上、５０［μＡ］の範囲について調べた。図５に示すように、この結果から、転写バイアス値（転写電流値）Ａ_ｔに対して導電性マイラ印加バイアス値（導電性マイラ電流値）Ａ_ｍが少ないと、トナーチリが発生した。逆に転写バイアス値（転写電流値）Ａ_ｔに対する導電性マイラ印加バイアス値（導電性マイラ電流値）Ａ_ｍが過多になると、副作用としてハーフトーン画像のムラが発生した。これは、導電性マイラ１０１に過剰に電流値が流れ、２ｂｙ２画像のようなハーフトーン画像に不均一なトナーの凝集が発生し、黒粒状のムラや異常放電跡が発生したためと考えられる。
【００２９】
以上のことから、導電性マイラ１０１に印加するバイアスを転写バイアスと同一にすれば、トナーチリも副作用であるハーフトーン画像のムラも発生しなくなり、より良好な転写画像を得ることができる。よって、本実施例１においては、導電性マイラ１０１に印加するバイアス値（転写電流値）Ａ_ｍを転写バイアス値（転写電流値）Ａ_ｔと同一にする。
例えば、転写材として厚紙やＯＨＰなどを用いる場合、作像線速を通常の転写紙より遅くし、転写バイアスもそれに応じて変える場合がある。このような場合でも、導電性マイラ１０１に印加するバイアスを転写バイアスと同一にすれば良好な転写画像を得ることができる。
【００３０】
尚、本実施例１において、印加する転写バイアス値（転写電流値）Ａ_ｔを４０［μＡ］より大きくすると、感光体に＋電荷が残り、感光体疲労や、それに伴う残像画像の発生を招く恐れがある。よって、ので、転写バイアス値（転写電流値）Ａ_ｔとしては４０［μＡ］以下とするのが望ましい。
【００３１】
〔実施例２〕
次に、実施例２について説明する。本実施例２は、実施例１と同じ図２に示すプリンタを用いている。装置の各構成及び設定について実施例１と同じ部分については説明を省略する。
本実施例２においては、実施例１のように黒単色画像を作像した場合と異なり、４色フルカラー画像を作像した場合について説明する。
【００３２】
先ず、導電性マイラ１０１に印加するバイアスの電源を４つの転写ローラ３１Ｙ、３１Ｍ、３１Ｃ、３１Ｋのうち最も下流にある黒画像の転写ローラ３１Ｋの電源と同一にした。よって、導電性マイラ１０１には、転写ローラ３１Ｋから印加されるバイアス値＋１５［μＡ］が印加される。
【００３３】
尚、本実施形態のプリンタにおいて、導電性マイラ１０１に印加するバイアスは、上記実施形態に記載した電圧に限定されるものではない。上記プリンタにおいては、例えば＋１〜２［ＫＶ］程度のバイアスを印加することが考えられる。
【００３４】
以上本実施形態においては、転写材として普通紙を使用しているが、これに限るものではない。例えば、厚紙、ＯＨＰ等を用いることもできる。その場合には、それに応じて転写バイアス、導電性マイラ１０１に印加するバイアス等を設定すればよい。これにより、転写材として種々の材質のものを使用しても、上記実施形態同様にトナーチリのない良好な転写画像を得ることができる。
【００３５】
実施例１及び２においては、導電性マイラ１０１に転写バイアスと同極性である＋極性のバイアスを印加している。これによって、導電性マイラ１０１に転写バイアスと逆極性のバイアスを印加する場合に入口ガイドに転写紙が近接もしくは接触することにより生じる恐れのある転写紙全面でのトナーチリの発生を防止することができる。
本実施例１及び２においては、導電性マイラ１０１に印加するバイアス値（転写電流値）Ａ_ｍを転写バイアス値（転写電流値）Ａ_ｔと同一にしている。これによって、トナーチリも副作用であるハーフトーン画像のムラも発生しなくなり、より良好な転写画像を得ることができる。また、導電性マイラ１０１に印加するバイアス値Ａ_ｍをある程度調整する必要があるときにも、そのバイアス値を転写バイアス値Ａ_ｔと同一に設定すればよいので、複雑な制御が必要なくなる。バイアス値Ａ_ｍをある程度調整する必要があるときとは、例えば、複数の作像線速を持ち、各線速での転写条件の最適値が異なる場合や、黒単色モード時には転写搬送部材がＹ、Ｍ、Ｃ感光体に対して離間するような制御を行う場合等がある。更に、転写材として厚紙やＯＨＰなど種々のものを用いる場合にも、導電性マイラ１０１に印加するバイアス値（転写電流値）Ａ_ｍを転写バイアス値（転写電流値）Ａ_ｔと同一に設定することで好な転写画像を得ることができる。
上記実施例２においては、導電性マイラ１０１に印加するバイアスの電源を転写手段の１つである黒画像の転写ローラ３１Ｋの電源と同一にし、導電性マイラ１０１には、転写ローラ３１Ｋと同一のバイアスを印加している。これによって、これによって、導電性マイラ１０１にバイアスを印加するために新たな電源を具備する必要がなくなるため、装置の大型化を防止できると共に、低コスト化を実現することができる。また、複数の作像線速を持ち、各線速での転写条件の最適値が異なる場合や、厚紙やＯＨＰなどの転写材の材質に応じて転写条件を適宜設定する場合にも、導電性マイラ１０１に印加するバイアスを独自に制御する必要がなくなる。よって、複雑な制御の必要がなくなるというメリットもある。
更に、実施例２においては、導電性マイラ１０１のバイアス印加を行う電源として装置に４つ設けている転写ローラ３１Ｙ，３１Ｍ，３１Ｃ，３１Ｋのうち最も下流にある黒画像の転写ローラ３１Ｋの電源を用いている。これによって、入口ガイド７４に最も近い位置に設けている転写ローラ３１Ｋの電源を共有することができ、他の転写ローラの電源を用いる場合に比して装置構成をより簡素化することができる。
また、上記実施例１及び２においては、入口ガイド７４として樹脂製のものを用いている。入口ガイド７４を金属製ではなく樹脂製とすることによって、軽量化、成型の容易さ、コストダウン等に有効である。また、複写機を多種多様な紙種及び環境下で使用する場合においては、樹脂の体積抵抗を一意的に決めることはできず、そのまま使用するとトナーチリが発生する恐れがある。しかし、本実施例１及び２においては、トナーチリを防止できる構成を設けているため、その恐れもない。
【００３６】
【発明の効果】
請求項１乃至４、及び７の画像形成装置によれば、案内部材を、転写材が対向する表面から順に非導電性シート部、導電性部バイアス印加手段による印加バイアスと同電位の導電性部を有するようにする。これにより、転写材が案内部材に接触又は近接しても転写材と案内部材との間で予期せぬ電荷移動が生じないようにし、未定着トナーの転写材表面に対する付着力が不安定化されないようにする。よって、案内部材と転写紙との間で電荷のやり取りが生じることにより発生するトナーチリを防止することができるという優れた効果がある。
請求項５及び６の画像形成装置によれば、案内部材を、転写材が対向する表面から順に非導電性シート部、導電性部バイアス印加手段による印加バイアスと同電位の導電性部を有するようにする。これにより、転写材が案内部材に接触又は近接しても転写材と案内部材との間で予期せぬ電荷移動が生じないようにし、未定着トナーの転写材表面に対する付着力が不安定化されないようにする。よって、案内部材と転写紙との間で電荷のやり取りが生じることにより発生するトナーチリを防止することができるという優れた効果がある。また、導電性部に印加するバイアスを、複数の転写手段のうちいずれかの転写手段における転写バイアスと同一極性、同一バイアス電圧としている。これによって、案内部材に接触又は近接する転写材上の画像の良好な転写条件を維持することができる。更に、導電性部に印加するバイアスを、複数の転写手段のうちいずれかの転写手段における転写バイアスと同一電源とすれば、新たな電源を設ける必要がなくなる。これによって、装置の大型化を防止することができる。
【図面の簡単な説明】
【図１】実施形態に係る画像形成装置の要部の説明図。
【図２】本実施形態に係るプリンタの概略構成図。
【図３】イエローのトナー像形成ユニットの概略構成を示す拡大図。
【図４】定着ユニットの概略構成図。
【図５】導電性マイラ印加バイアス値Ａ_ｍと転写バイアス値Ａ_ｔとによって変化する転写画像の状態を調べた結果を示す図。
【図６】従来型の画像形成装置における要部の説明図。
【符号の説明】
１Ｙ，１Ｍ，１Ｃ，１Ｋ　トナー像形成ユニット
２　　　光書込ユニット
３，４　給紙カセット
５　　　レジストローラ対
６　　　転写ユニット
７　　　ベルト定着方式の定着ユニット
８　　　排紙トレイ
１１Ｙ，１１Ｍ，１１Ｃ，１１Ｋ　感光体ドラム
２０Ｙ，２０Ｍ，２０Ｃ，２０Ｋ　現像ユニット
２２Ｙ，２２Ｍ，２２Ｃ，２２Ｋ　現像スリーブ
２５Ｙ　現像ドクタ
２８Ｙ　パワーパック
２９　　バイアス制御部
３１Ｙ、３１Ｍ、３１Ｃ、３１Ｋ　　　転写ローラ
６０　　転写紙搬送ベルト
７０　　定着ベルト
７１　　加熱ローラ
７２　　定着ローラ
７３　　加圧ローラ
７４　　入口ガイド
１００　転写紙
１０１　導電性マイラ
１０２　絶縁性マイラ
１０３　電源
１１０　除電針
Ｎｔ　　定着ニップ[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an image forming apparatus such as a copying machine, a facsimile, and a printer. More specifically, the present invention relates to an image forming apparatus having a transfer device that transfers a toner image onto a transfer material, a fixing device that fixes the toner image transferred onto the transfer material, and a guide member that guides the transfer material to a fixing position. It is.
[0002]
[Prior art]
Conventionally, as an image forming apparatus of this type, a latent image formed on a photoreceptor as an image carrier is developed by a developing device, and the developed toner image is transferred to a transfer paper as a transfer material by a transfer device. A fixing device using a fixing device is known. FIG. 6 is a schematic configuration diagram of a conventional image forming apparatus. The image forming apparatus shown in FIG. 1 includes a toner image forming unit 1K, a transfer paper transport belt 60 that carries and transports the transfer paper, a belt fixing type fixing unit 7 as a fixing device, and the like. In this apparatus, the transfer paper is carried on the transfer paper transport belt 60 by electrostatic attraction, and is transported so as to pass through a transfer position where the toner image formed by the toner image forming unit 1K is transferred. Then, the toner image is transferred onto the transfer paper passing through the transfer position. The transfer paper on which the toner image has been transferred is guided to the fixing nip Nt by a guide member 74 as a guide member provided between the toner image forming unit 1K and the fixing unit 7. At this time, the transfer paper enters the fixing nip Nt while approaching or contacting the guide member 74. The transfer paper that has entered the fixing nip Nt is heated and pressed between the fixing roller 72 and the pressure roller 73 in the fixing unit 7 so that the toner image carried on the surface is fixed. The transfer paper after the toner image is fixed is discharged from the fixing nip Nt.
[0003]
Incidentally, the guide member provided in the image forming apparatus is not limited to a member for guiding the transfer sheet to the fixing nip. For example, there is a device for guiding a transfer sheet to a transfer nip, which is described in an image forming apparatus of Patent Document 1.
[0004]
[Patent Document 1]
JP-A-6-118803
[0005]
[Problems to be solved by the invention]
In the image forming apparatus having the guide member 74 for guiding the transfer sheet to the fixing position as described above, toner dust may occur on the unfixed toner image on the transfer sheet. The possible causes are as follows.
When the transfer paper moves while contacting the guide member 74, the guide member 74 may be charged by friction. As the number of transfer sheets conveyed while contacting the surface of the guide member 74 increases, the charge amount of the guide member 74 gradually increases. Then, when the guide member 74 is frictionally charged to some extent, electric charges are exchanged between the transfer sheet and the guide member 74 that pass while contacting the surface thereof. In addition, there is transfer paper that passes over the guide member 74 in a close state without contacting the guide member. However, if the charge amount of the guide member 74 is high, the transfer paper between the guide member 74 and the transfer paper will be In some cases, exchange of charges may occur. Normally, the toner constituting the unfixed toner image on the transfer paper adheres to the transfer paper due to electrostatic force between the transfer paper and van der Waals force. Since the adhesive force is weak, if electric charges are exchanged between the guide member 74 and the transfer paper, the adhesive force of the toner forming the unfixed toner image to the transfer paper becomes unstable, and the toner scatters on the transfer paper. Toner dust.
[0006]
Here, in the image forming apparatus of Patent Document 1, the guide member is configured as follows in order to prevent omission during transfer and scattering of toner during transfer. In a direction substantially perpendicular to the transfer material moving direction, the guide member has a region where the guide member does not contact the transfer material usable in the apparatus, and at least a charge removing member corresponding to this region is provided. The static elimination member may be either grounded to a conductive sheet member provided upstream of the transfer nip, installed via a constant voltage element (varistor), or applied with a DC voltage having a polarity opposite to the transfer bias. It is what went.
However, this is to prevent toner scattering at the time of transfer. Therefore, it is not possible to prevent toner dust generated due to the exchange of charges between the guide member 74 and the transfer sheet before the transfer sheet carrying the unfixed image is transported to the fixing position.
[0007]
Further, in order to prevent toner dust generated due to the exchange of electric charges between the guide member 74 and the transfer paper, the following may be considered. That is, the volume resistance of the guide member 74 is examined and set according to the resistance value of the transfer sheet so that no charge exchange occurs between the guide member and the transfer sheet even when the guide member is charged. This is because, if the resistance value of the transfer paper to be used is known in advance, it is considered that the volume resistance of the guide member that does not cause the exchange of charges between the guide member and the transfer paper passing over the guide member can be derived. However, the transfer paper has a different resistance value depending on the paper type, and the resistance also changes depending on the degree of drying. For example, when the transfer paper is dry or when the apparatus is used in a low-humidity dry environment, the resistance of the transfer paper increases. For this reason, in an image forming apparatus used under various kinds of papers and environments, a desired volume resistance of the guide member 74 cannot be uniquely determined.
[0008]
The present invention has been made in view of the above background. It is an object of the present invention to provide an image forming apparatus capable of preventing toner dust caused by exchange of electric charge between a guide member and transfer paper.
[0009]
[Means for Solving the Problems]
In order to achieve the above object, an image forming apparatus according to claim 1 includes an image carrier that carries a toner image, a transfer unit that transfers the toner image on the image carrier to a transfer material, and a transfer device that transfers the toner image to the transfer material. An image forming apparatus comprising: a fixing unit for fixing the transferred toner image; and a guide member for guiding the transfer material carrying the unfixed toner image transferred by the transfer unit to a fixing position by the fixing unit. The member has a non-conductive sheet portion and a conductive portion in order from the surface facing the transfer material, and unexpected charge transfer does not occur between the transfer material and the guide member in the conductive portion. And a conductive portion bias applying means for applying a bias voltage for the purpose.
According to a second aspect of the present invention, in the image forming apparatus of the first aspect, the polarity of the bias applied to the conductive portion by the conductive portion bias applying means is to transfer a toner image to the transfer material. It has the same polarity as the transfer bias applied in the transfer means.
According to a third aspect of the present invention, in the image forming apparatus of the second aspect, a bias applied to the conductive portion by the conductive portion bias applying means is the same as the transfer bias. It is.
According to a fourth aspect of the present invention, in the image forming apparatus of the first, second, or third aspect, a power supply of a bias applied to the conductive portion by the conductive portion bias applying means is transferred by the transfer means. The power supply is the same as the bias.
The image forming apparatus according to claim 5, wherein a plurality of image carriers for carrying the toner images, a plurality of transfer means for sequentially superimposing and transferring the toner images on the plurality of image carriers onto a transfer material, and An image having a fixing unit for fixing the composite toner image transferred by superposition and a guide member for guiding the transfer material carrying the unfixed synthetic toner image transferred by the transfer unit to a fixing position by the fixing unit; In the forming apparatus, the guide member has a non-conductive sheet portion and a conductive portion in order from the surface facing the transfer material, and the conductive portion has an unexpected portion between the transfer material and the guide member. Providing a conductive part bias applying means for applying a bias voltage for preventing charge transfer from occurring, the polarity of a bias applied to the conductive part by the conductive part bias applying means, a bias voltage or a bias power supply, The same bias, the same bias voltage, or the same bias power supply as a transfer bias applied for transferring a toner image to the transfer material in any one of the plurality of transfer units. It is.
According to a sixth aspect of the present invention, in the image forming apparatus of the fifth aspect, a bias voltage or a bias power source applied to the conductive portion by the conductive portion bias applying unit is selected from among the plurality of transfer units. It is characterized in that it has the same polarity, the same bias voltage, or the same bias power as the transfer bias of the transfer means located most downstream.
In the image forming apparatus according to the first aspect, a guide member for guiding the transfer material from the transfer position to the fixing position is provided with a non-conductive sheet portion and a conductive portion in order from the surface facing the transfer material. In addition, a predetermined bias voltage is applied to the conductive portion by a conductive portion bias applying unit to prevent unexpected charge transfer between the transfer material and the guide member. As a result, the lower layer of the non-conductive sheet portion is set to a desired bias by the conductive portion to which the bias voltage is applied, so that a so-called leveling state is obtained. A non-conductive sheet portion is provided above the conductive portion to make it difficult for the bias applied to the conductive portion to be directly applied to the transfer material. As a result, even if the transfer material having passed the transfer position and carrying the unfixed toner image on the surface contacts or approaches the guide member, unexpected charge exchange occurs between the non-conductive sheet portion and the transfer paper. Will not be.
In the image forming apparatus according to the fifth aspect, the guide member for guiding the transfer material from the transfer position to the fixing position is provided with a non-conductive sheet portion and a conductive portion in order from the surface facing the transfer material. In addition, a predetermined bias voltage is applied to the conductive portion by a conductive portion bias applying unit to prevent unexpected charge transfer between the transfer material and the guide member. This bias voltage has the same polarity, the same bias voltage, or the same power supply as the transfer bias in any one of the plurality of transfer units. Thus, the conductive portion under the non-conductive sheet portion is leveled. A non-conductive sheet portion is provided above the conductive portion to make it difficult for the bias applied to the conductive portion to be directly applied to the transfer material. As a result, even if the transfer material having passed the transfer position and carrying the unfixed toner image on the surface contacts or approaches the guide member, unexpected charge exchange occurs between the non-conductive sheet portion and the transfer paper. Will not be. Further, the bias applied to the conductive portion has the same polarity or the same bias voltage as the transfer bias in any one of the plurality of transfer units. Thereby, it is possible to maintain favorable transfer conditions of the image on the transfer material that is in contact with or close to the guide member. In addition, if the bias applied to the conductive portion is the same power supply as the transfer bias in one of the plurality of transfer units, it is not necessary to provide a new power supply.
[0010]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, an embodiment in which the present invention is applied to an electrophotographic color laser printer as an image forming apparatus will be described.
FIG. 2 is a schematic configuration diagram of the printer according to the present embodiment. This printer has four toner image forming units 1Y, 1M, 1C and 1K for forming images of respective colors of yellow (Y), magenta (M), cyan (C) and black (K). In the following description, the suffixes Y, M, C, and K of the respective symbols indicate members for yellow, magenta, cyan, and black, respectively. The toner image forming units 1Y, 1M, 1C, and 1K are arranged in order from the upstream side in the moving direction (direction of arrow A in the figure) of a transfer sheet as a transfer material. Each of the toner image forming units 1Y, 1M, 1C, and 1K includes a photosensitive unit having photosensitive drums 11Y, 11M, 11C, and 11K as image carriers, and a developing unit. The toner image forming units 1Y, 1M, 1C, and 1K are arranged such that the rotation axes of the photosensitive drums in the respective photosensitive units are parallel to each other and at a predetermined pitch in the transfer paper moving direction. And so on.
[0011]
Further, the printer according to the present embodiment includes, in addition to the toner image forming units 1Y, 1M, 1C, and 1K, an optical writing unit 2, paper feed cassettes 3 and 4, and a registration roller pair 5. The printer also includes a transfer unit 6, a belt-fixing type fixing unit 7, a paper discharge tray 8, and the like. The transfer unit 6 has a transfer paper conveyance belt 60 as a transfer material conveyance member that carries the transfer paper and conveys it so as to pass through the transfer position of each toner image forming unit. The printer also includes a manual feed tray (not shown), a toner supply container, a waste toner bottle, a duplex / reversing unit, a power supply unit, and the like.
The optical writing unit 2 includes a light source, a polygon mirror, an f-θ lens, a reflection mirror, and the like, and applies a laser beam to the surface of each of the photosensitive drums 11Y, 11M, 11C, and 11K based on color-separated image data. Irradiate while scanning.
The transfer paper transport belt 60 is provided on a frame made of resin by a drive roller that is driven and rotated on one side and a transport roller that is a driven roller that is driven and rotated on the other side. The conveyance roller is driven to rotate in the direction of arrow A by rotation. The reason why the frame is made of resin instead of metal is that the unit is made lighter, easier to mold, and costs are reduced.
A dashed line in FIG. 2 indicates a transfer path of the transfer paper. The transfer paper at the uppermost position among the transfer papers P stored in the paper feed cassettes 3 and 4 is fed at the time of image formation, and is transported by transport rollers while being guided by a transport guide (not shown). The transfer paper conveyed in this manner is sent to a temporary stop position where the registration roller pair 5 is provided. The transfer paper sent out by the registration roller pair 5 at a predetermined timing is carried on the transfer paper transport belt 60 by electrostatic attraction, and passes through the transfer positions of the toner image forming units 1Y, 1M, 1C, and 1K. Conveyed. Transfer rollers 31Y, 31M, 31C, and 31K31 are provided on the transfer paper transport belt 60 near the nip between the transfer paper transport belt 60 and the photosensitive drum, and constitute transfer means. When the toner images of the respective colors are superimposedly transferred by the respective toner image forming units 1Y, 1M, 1C and 1K, a composite toner image is formed on the transfer paper. The synthesized toner image is fixed on transfer paper by a fixing unit 7 as a fixing unit, and then discharged onto a discharge tray 8.
[0012]
FIG. 3 is an enlarged view showing a schematic configuration of the yellow toner image forming unit 1Y among the toner image forming units 1Y, 1M, 1C, and 1K. The other toner image forming units 1M, 1C, and 1K also have the same configuration, and a description thereof will be omitted.
In FIG. 3, the toner image forming unit 1Y includes the photosensitive drum unit 10Y and the developing unit 20Y as described above. The photoconductor drum unit 10Y includes, in addition to the photoconductor drum 11Y, a brush roller 12Y for applying a lubricant to the surface of the photoconductor drum, and a swingable cleaning blade 13Y for cleaning the surface of the photoconductor drum. The photosensitive drum unit 10Y includes a non-contact type charging roller 15Y for uniformly charging the surface of the photosensitive drum after static elimination. In the present embodiment, the photosensitive drum of each photosensitive drum unit has an organic photosensitive drum (OPC) layer on the surface.
[0013]
In the photoconductor unit having the above configuration, first, the surface of the photoconductor drum 11Y is uniformly charged by the charging roller 15Y. The laser light L modulated and deflected by the optical writing unit 2 is irradiated on the surface while being scanned, so that an electrostatic latent image is formed on the surface of the photosensitive drum 11Y. The electrostatic latent image on the photoreceptor drum 11Y is developed by a later-described developing unit 20Y to become a yellow toner image. At the transfer position Pt where the transfer paper 100 on the transfer paper transport belt 60 passes, the toner image on the photosensitive drum 11Y is transferred to the transfer paper 100 by the transfer bias applied from the transfer roller 31Y. The surface of the photoconductor drum 11Y after the transfer of the toner image is cleaned by a cleaning blade 13Y after a predetermined amount of lubricant is applied by a brush roller 12Y. Thereafter, the charge is removed, and the preparation is made for the formation of the next electrostatic latent image.
[0014]
The developing unit 20Y uses a two-component developer containing a magnetic carrier and a negatively charged toner. The developing unit 20Y is provided with a developing sleeve 22Y so as to be partially exposed from an opening on the photosensitive drum side of the developing case 21Y. The developing sleeve 22Y is made of a non-magnetic material, and has a magnet roller as a fixedly disposed magnetic field generating means. The material of the developing sleeve 22Y is not particularly limited, and a non-magnetic material such as stainless steel, aluminum, or ceramics, or a material obtained by coating the non-magnetic material is used. The developing unit 20Y is also provided with conveying screws 23Y and 24Y, a developing doctor 25Y, a toner concentration sensor 26Y, a powder pump 27Y, and the like. The toner density sensor 26Y includes a magnetic permeability sensor (T sensor) that detects the magnetic permeability of the developer.
[0015]
The developer contained in the developing case 21Y is stirred and conveyed by the conveying screws 23Y and 24Y, so that the toner and the magnetic carrier are frictionally charged to opposite polarities. Then, a part of the developer is carried on the surface of the developing sleeve 22Y, and after the layer thickness is regulated by the developing doctor 25Y, the developer is conveyed to a developing position facing the photosensitive drum 11Y. At the developing position, the toner in the developer on the developing sleeve 22Y becomes an electrostatic latent image by a developing electric field formed by the electrostatic latent image on the photosensitive drum 11Y and the developing bias applied to the developing sleeve 22Y. Move towards. Thus, the electrostatic latent image on the photosensitive drum 11Y is developed. In the present embodiment, a negative latent image is formed on the negatively charged photosensitive drum 11Y, and a negative bias is applied as a developing bias to develop the negatively charged toner. Although the developing method is adopted, it is not limited to this method. For example, a so-called positive / positive developing method may be used, and the polarities of the toner and the surface of the photosensitive drum 11Y may be opposite to those described above.
[0016]
The toner concentration of the developer in the developing case 21Y is kept constant by toner replenishment by the powder pump 27Y according to the image area obtained from the image data and the detection result of the toner concentration sensor 26Y.
[0017]
The image forming conditions of the present embodiment are as follows.

[0018]
FIG. 4 is a schematic configuration diagram of the fixing unit 7. The fixing unit 7 includes a fixing belt 70 wrapped around the heating roller 71 and the fixing roller 72, and a pressure roller 73 provided at a position facing the fixing roller 72 via the fixing belt 70. The nip portion between the fixing roller 72 and the pressure roller 73 is a fixing nip Nt that fixes a toner image to transfer paper by applying pressure while heating. Further, an entrance guide 74 is provided as a guide member for separating the transfer paper on which the synthetic toner image has been formed after passing through the fourth toner image forming unit 1K from the transfer paper transport belt 60 and leading it to the fixing nip Nt. I have. The entrance guide 74 is made of resin, and the transfer paper separated from the transfer paper transport belt enters the fixing nip while approaching or contacting the entrance guide 74. Here, it is a normal operation that the transfer sheet is conveyed while approaching or in contact with the transfer sheet, and the entrance guide 74 also plays a role for stably transferring an unfixed image on the transfer sheet to the fixing nip Nt. .
[0019]
By the way, the transfer paper may come into contact with the entrance guide 74 due to friction or the like, and the entrance guide 74 may be charged, so that electric charges may be exchanged between the charged entrance guide 74 and the transfer paper. Normally, the toner constituting the unfixed toner image on the transfer paper adheres to the transfer paper by electrostatic force, Van der Waals force, or the like. Since the adhesive force is weak, if electric charges are exchanged between the entrance guide 74 and the transfer paper, the adhesive force of the toner forming the unfixed toner image to the transfer paper becomes unstable, and the toner scatters on the transfer paper. May cause toner dust. This occurs because the transfer paper carrying the unfixed toner image approaches or comes into contact with the entrance guide 74 upstream of the fixing nip. Further, the resistance of the transfer paper changes depending on the paper type, the dry state, the humidity environment when the apparatus is driven, and the like. For this reason, even if the optimal volume resistance of the resin used for the frame is examined for the purpose of preventing toner dust generated by the contact between the entrance guide 74 and the transfer paper P, even if the optimal volume resistance of the resin used for the frame is examined, the image used under a variety of paper types and environments is considered. It cannot be uniquely determined in the forming apparatus.
Therefore, the present embodiment has a configuration for preventing toner dust. Hereinafter, features of the present invention will be described.
[0020]
[Example 1]
FIG. 1 is a schematic configuration diagram of an inlet side of a fixing unit according to the first exemplary embodiment. In this embodiment, a conductive mylar 101 as a conductive part is adhered to the transfer paper facing surface of the entrance guide 74, and an insulating mylar 102 as a non-conductive sheet part is further adhered thereon. The insulating mylar 102 has a thickness of 0.1 to 0.5 [mm]. However, this thickness range is a practical range, and a thickness of about 1 [mm] or less can be used. Further, a bias is applied to the conductive mylar 101 from the power supply 103 as a conductive part bias applying unit. The volume resistance of the conductive Mylar 101 is 10%. ⁶ Insulated PET (polyethylene terephthalate) was used as a non-conductive mylar having a resistance of [Ωcm]. The bias applied to the conductive mylar 101 is a constant voltage bias of +2 [KV].
[0021]
Here, a conventional fixing unit configuration will be described.
FIG. 6 is a schematic configuration diagram of a fixing unit entrance side used conventionally. On the transfer unit side of the fixing belt 70, an entrance guide 74 made of resin is provided as in the present embodiment. However, unlike the present embodiment, the conductive mylar 101 and the insulating mylar 102 are not bonded to the entrance guide 74 in the conventional apparatus.
[0022]
In addition, even if the fixing unit 7 in FIGS. 1 and 6 is displaced, a metal discharging needle 110 is provided adjacent to the downstream of the entrance guide. This is for measuring the chargeability of the transfer paper by bringing it into contact with the back surface of the transfer paper moving along the entrance guide, and is provided for the purpose of measurement only experimentally. Therefore, it is not provided in an actual device. Then, comparison was made between the printer of the present embodiment and the conventional printer shown in FIG. 6 for examining the effects of the present invention. Next, the method and the result will be described.
[0023]
In the conventional printer and the printer of the present embodiment, the charge amount of the transfer paper when the image was formed was measured by the current value flowing through the static elimination needle 110 during the image formation.
In a conventional printer, the current value was in the range of -1.5 to +5 [μA]. At this time, banding-like toner dust was generated in which the line image parallel to the photoconductor drums 11Y, 11M, 11C, and 11K was scattered so as to trail behind in the transport direction. Incidentally, in the conventional type, the transfer current value in the fourth toner image forming unit 1K is 35 [μA].
On the other hand, in the printer of the present embodiment, when a black monochrome image is formed, the current value is in the range of +2.5 to +5.5 [μA]. At this time, no banding-like toner dust generated in the conventional printer occurred in the image.
[0024]
The following can be seen from the above results. In a conventional printer, a current having a negative polarity has occurred in a transfer paper. Usually, as described above, the transfer current value in the fourth toner image forming unit 1K is 35 [μA], and therefore, when the transfer paper is not charged, the current value flowing from the static elimination needle is used for transfer. It should be only + polarity. On the other hand, it can be said that the negative polarity current is generated because the transfer paper is unstablely charged. Then, a negative polarity current that generates a magnetic field repelling the toner caused banding-like toner dust to occur.
[0025]
Further, in the printer of the present embodiment, the transfer current value in the toner image forming unit 1K when forming a black monochromatic image is 30 [μA], whereas the current flowing through the transfer paper is +2.5 to It was stabilized at +5.5 [μA] and + polarity. This indicates that the application of non-uniform charges to the transfer paper was prevented.
The reason why the current flowing through the transfer paper is stable at the positive polarity is as follows. A conductive mylar 101 is provided on the surface of the entrance guide facing the transfer paper, and a predetermined bias is applied. As a result, the surface of the entrance guide is leveled so that the transfer paper in contact with or in proximity to the entrance guide does not need to be affected by the charging property of the material such as resin that constitutes the entrance guide. Further, the surface of the conductive mylar 101 is covered with an insulating mylar 102 so as to prevent a change in current value with respect to transfer paper that may occur when the insulating mylar 102 is not provided. It is considered that the change in the current value for the transfer sheet occurs when the distance between the conductive mylar 101 and the transfer sheet changes due to the behavior of the transfer sheet when the insulating mylar 102 is not provided. In particular, it is considered that this is likely to occur when a constant voltage bias is applied to the conductive mylar 101, and banding-like toner dust may occur. Therefore, application of the conductive mylar alone cannot be recommended. In the first embodiment, the insulating mylar 102 is provided on the surface of the conductive mylar 101 to prevent such a change in the current value for the transfer paper.
[0026]
In the first embodiment, a constant voltage bias of +2 [KV] is applied to the conductive mylar 101. This is a bias having the same polarity as the transfer bias Vt. Here, unlike the first embodiment, when a bias having a negative polarity opposite to the transfer bias Vt is applied to the conductive mylar 101, an electric charge for separating the toner from the transfer paper is applied to the transfer paper. Actually, when a bias of -2 [KV] was applied to the conductive Mylar 101, the current value flowing from the static elimination needle provided experimentally was -1.8 to -5.8 [μA]. In this case, the toner generates dust on the entire surface of the transfer paper. Further, when the bias applied to the conductive mylar 101 is approached to zero with the negative polarity, the value of the current flowing from the static elimination needle provided experimentally also approaches zero. However, the toner does not shift to the positive polarity side, and the generation of toner dust on the entire surface of the transfer paper cannot be prevented. Therefore, in the first embodiment, a bias of + polarity, which has the same polarity as the transfer bias Vt, is applied to the conductive mylar 101.
[0027]
Further, in order to examine an appropriate value of the bias value applied to the conductive mylar 101, a conductive mylar applied bias value (transfer current value) A _m And transfer bias value (transfer current value) A _t The state of the transferred image, which changes depending on the conditions, was examined. The result is shown in FIG. However, the bias applied to the conductive mylar 101 is a transfer bias A _t Only the case of the same polarity was examined. This is the transfer bias A _t It is known that when a bias having the opposite polarity is applied, toner dust as described above is generated. Here, the bias control is a constant current control that is hardly affected by the resistance value of the transfer paper.
[0028]
In FIG. 5, the conductive mylar applied bias value (transfer current value) A _m And transfer bias value (transfer current value) A _t Was examined in the range of 5 [μA] or more and 50 [μA]. As shown in FIG. 5, the transfer bias value (transfer current value) A _t To the conductive mylar applied bias value (conductive mylar current value) A _m If less, toner dust was generated. Conversely, transfer bias value (transfer current value) A _t Bias value (conductive Mylar current value) A _m Was excessive, halftone image unevenness occurred as a side effect. It is considered that this is because an excessive current value flowed through the conductive mylar 101, non-uniform toner aggregation occurred in a halftone image such as a 2-by-2 image, and black particle-like unevenness and abnormal discharge marks occurred.
[0029]
As described above, if the bias applied to the conductive mylar 101 is made the same as the transfer bias, the toner dust does not cause the halftone image unevenness which is a side effect, and a better transfer image can be obtained. Therefore, in the first embodiment, the bias value (transfer current value) A applied to the conductive mylar 101 _m Is the transfer bias value (transfer current value) A _t And the same as
For example, when thick paper, OHP, or the like is used as the transfer material, the image forming linear speed may be lower than that of normal transfer paper, and the transfer bias may be changed accordingly. Even in such a case, a good transfer image can be obtained if the bias applied to the conductive mylar 101 is the same as the transfer bias.
[0030]
In the first embodiment, the applied transfer bias value (transfer current value) A _t Is larger than 40 [μA], a positive charge remains on the photoconductor, which may cause fatigue of the photoconductor and generation of an afterimage. Therefore, the transfer bias value (transfer current value) A _t Is desirably 40 [μA] or less.
[0031]
[Example 2]
Next, a second embodiment will be described. The second embodiment uses the same printer shown in FIG. 2 as the first embodiment. A description of the same components and settings as those of the first embodiment will be omitted.
In the second embodiment, a case will be described in which a four-color full-color image is formed, unlike the case of forming a black single-color image as in the first embodiment.
[0032]
First, the power supply of the bias applied to the conductive mylar 101 was set to be the same as the power supply of the blackest image transfer roller 31K among the four transfer rollers 31Y, 31M, 31C, and 31K. Therefore, the bias value +15 [μA] applied from the transfer roller 31K is applied to the conductive mylar 101.
[0033]
In the printer according to the present embodiment, the bias applied to the conductive mylar 101 is not limited to the voltage described in the above embodiment. In the above printer, it is conceivable to apply a bias of, for example, about +1 to 2 [KV].
[0034]
As described above, in this embodiment, plain paper is used as the transfer material, but the present invention is not limited to this. For example, cardboard, OHP, or the like can be used. In that case, a transfer bias, a bias applied to the conductive mylar 101, and the like may be set accordingly. Thus, even if various materials are used as the transfer material, a good transfer image without toner dust can be obtained as in the above embodiment.
[0035]
In the first and second embodiments, a positive polarity bias having the same polarity as the transfer bias is applied to the conductive mylar 101. Accordingly, it is possible to prevent the generation of toner dust on the entire surface of the transfer paper, which may occur when the transfer paper approaches or comes into contact with the entrance guide when a bias having a polarity opposite to the transfer bias is applied to the conductive mylar 101. .
In the first and second embodiments, the bias value (transfer current value) A applied to the conductive mylar 101 _m Is the transfer bias value (transfer current value) A _t Is the same as As a result, unevenness of the halftone image, which is a side effect of toner dust, does not occur, and a better transfer image can be obtained. Also, a bias value A applied to the conductive mylar 101 _m When it is necessary to adjust the transfer bias value to some extent, the bias value is set to the transfer bias value A. _t Since it is sufficient to set the same as the above, complicated control is not required. Bias value A _m Is required to be adjusted to some extent, for example, when a plurality of image forming linear velocities are used, and the optimum value of the transfer condition at each linear speed is different, or when the black and single color mode is used, the transfer / conveyance member is Y, M, C photosensitive. There is a case where control to separate the body is performed. Furthermore, even when various materials such as cardboard and OHP are used as the transfer material, the bias value (transfer current value) A applied to the conductive mylar 101 _m Is the transfer bias value (transfer current value) A _t By setting the same as above, a good transfer image can be obtained.
In the second embodiment, the power supply of the bias applied to the conductive mylar 101 is the same as the power supply of the transfer roller 31K for the black image, which is one of the transfer means, and the conductive mylar 101 has the same power supply as the transfer roller 31K. Bias is applied. This eliminates the necessity of providing a new power supply for applying a bias to the conductive mylar 101, thereby preventing an increase in the size of the apparatus and realizing a reduction in cost. Also, the conductive mylar may be used when a plurality of image forming linear velocities are used and the optimum value of the transfer condition at each linear speed is different, or when the transfer condition is appropriately set according to the material of the transfer material such as cardboard or OHP. There is no need to independently control the bias applied to 101. Therefore, there is an advantage that complicated control is not required.
Further, in the second embodiment, as a power supply for applying a bias to the conductive mylar 101, the power supply of the black image transfer roller 31K, which is the most downstream among the four transfer rollers 31Y, 31M, 31C, and 31K, is provided. Used. As a result, the power supply of the transfer roller 31K provided at the position closest to the entrance guide 74 can be shared, and the apparatus configuration can be further simplified as compared with the case where the power supply of another transfer roller is used.
In the first and second embodiments, the entrance guide 74 is made of resin. By making the entrance guide 74 made of resin instead of metal, it is effective for weight reduction, ease of molding, cost reduction, and the like. Further, when the copying machine is used in various kinds of papers and environments, the volume resistance of the resin cannot be uniquely determined, and if used as it is, toner dust may be generated. However, in the first and second embodiments, there is provided a configuration capable of preventing toner dust, so there is no fear of such a situation.
[0036]
【The invention's effect】
According to the image forming apparatus of the present invention, the guide member is arranged in the order from the surface facing the transfer material to the non-conductive sheet portion and the conductive portion having the same potential as the bias applied by the conductive portion bias applying means. To have. This prevents unexpected charge transfer between the transfer material and the guide member even when the transfer material contacts or approaches the guide member, and does not destabilize the adhesion of unfixed toner to the transfer material surface. To do. Therefore, there is an excellent effect that it is possible to prevent toner dust caused by the exchange of charges between the guide member and the transfer paper.
According to the image forming apparatus of the present invention, the guide member has a non-conductive sheet portion and a conductive portion having the same potential as the bias applied by the conductive portion bias applying means in order from the surface facing the transfer material. To This prevents unexpected charge transfer between the transfer material and the guide member even when the transfer material contacts or approaches the guide member, and does not destabilize the adhesion of the unfixed toner to the transfer material surface. To do. Therefore, there is an excellent effect that it is possible to prevent toner dust caused by the exchange of charges between the guide member and the transfer paper. Further, the bias applied to the conductive portion has the same polarity and the same bias voltage as the transfer bias in any one of the plurality of transfer units. Thereby, favorable transfer conditions of the image on the transfer material that is in contact with or close to the guide member can be maintained. Furthermore, if the bias applied to the conductive portion is the same power supply as the transfer bias in one of the plurality of transfer units, it is not necessary to provide a new power supply. This can prevent the device from becoming larger.
[Brief description of the drawings]
FIG. 1 is an explanatory diagram of a main part of an image forming apparatus according to an embodiment.
FIG. 2 is a schematic configuration diagram of a printer according to the embodiment.
FIG. 3 is an enlarged view illustrating a schematic configuration of a yellow toner image forming unit.
FIG. 4 is a schematic configuration diagram of a fixing unit.
FIG. 5 shows a bias value A applied to a conductive mylar. _m And transfer bias value A _t FIG. 9 is a diagram illustrating a result of examining a state of a transferred image that changes according to the above.
FIG. 6 is an explanatory diagram of a main part in a conventional image forming apparatus.
[Explanation of symbols]
1Y, 1M, 1C, 1K Toner image forming unit
2 Optical writing unit
3,4 paper cassette
5 Registration roller pair
6 Transfer unit
7 Belt fixing type fixing unit
8 Output tray
11Y, 11M, 11C, 11K Photoconductor drum
20Y, 20M, 20C, 20K developing unit
22Y, 22M, 22C, 22K developing sleeve
25Y development doctor
28Y power pack
29 Bias control unit
31Y, 31M, 31C, 31K transfer roller
60 Transfer paper transport belt
70 Fixing belt
71 Heating roller
72 Fixing roller
73 Pressure roller
74 Entrance guide
100 transfer paper
101 Conductive Mylar
102 Insulating Mylar
103 power supply
110 Static elimination needle
Nt fixing nip

Claims (7)

An image carrier that carries the toner image; a transfer unit that transfers the toner image on the image carrier to a transfer material; a fixing unit that fixes the toner image transferred to the transfer material; A guide member for guiding the transfer material carrying the unfixed toner image to a fixing position by the fixing unit.
The guide member has a non-conductive sheet portion and a conductive portion in order from the surface facing the transfer material,
An image, wherein the conductive portion is provided with a conductive portion bias applying means for applying a bias voltage for preventing an unexpected charge transfer between the transfer material and the guide member. Forming equipment. The image forming apparatus according to claim 1,
The image forming apparatus according to claim 1, wherein a polarity of a bias applied to the conductive portion by the conductive portion bias applying unit is the same as a transfer bias applied in the transfer unit for transferring a toner image to the transfer material. apparatus. The image forming apparatus according to claim 2,
An image forming apparatus, wherein a bias applied to the conductive portion by the conductive portion bias applying means is the same as the transfer bias. The image forming apparatus according to claim 1, 2, or 3,
An image forming apparatus, wherein a power source of a bias applied to the conductive portion by the conductive portion bias applying unit is the same power source as a transfer bias applied by the transfer unit. A plurality of image carriers for carrying the toner images, a plurality of transfer means for sequentially superimposing and transferring the toner images on the plurality of image carriers to a transfer material, and a composite toner image superimposed and transferred to the transfer material. An image forming apparatus comprising: a fixing unit for fixing; and a guide member for guiding the transfer material carrying the unfixed synthetic toner image transferred by the transfer unit to a fixing position by the fixing unit.
The guide member has a non-conductive sheet portion and a conductive portion in order from the surface facing the transfer material,
A conductive part bias applying means for applying a bias voltage for preventing unexpected charge transfer between the transfer material and the guide member in the conductive part is provided,
The polarity, the bias voltage, or the bias power of the bias applied to the conductive portion by the conductive portion bias applying unit is used to transfer the toner image to the transfer material in any one of the plurality of transfer units. An image forming apparatus having the same polarity, the same bias voltage, or the same bias power as the transfer bias to be applied. The image forming apparatus according to claim 5,
The bias voltage or bias power applied to the conductive portion by the conductive portion bias applying unit is the same polarity, the same bias voltage, or the same bias as the transfer bias of the most downstream transfer unit of the plurality of transfer units. An image forming apparatus comprising a power supply. The image forming apparatus according to claim 1, 2, 3, 4, 5, or 6,
The above-mentioned guide member is provided on a resinous substrate by superposing two sheets of a conductive sheet as a conductive member and a non-conductive sheet on the surface of at least the region of the substrate facing the transfer material in order from the surface of the substrate. An image forming apparatus characterized by comprising:

Images