JP3931816B2

JP3931816B2 - Image forming method and image forming apparatus

Info

Publication number: JP3931816B2
Application number: JP2003033403A
Authority: JP
Inventors: 佐藤　　誠; 和利藤沢
Original assignee: Seiko Epson Corp
Current assignee: Seiko Epson Corp
Priority date: 2003-02-12
Filing date: 2003-02-12
Publication date: 2007-06-20
Anticipated expiration: 2023-02-12
Also published as: JP2004245926A

Description

【０００１】
【発明の属する技術分野】
本発明は、電子写真技術を用いて画像を形成するプリンター、ファクシミリ、複写機等の画像形成装置に適用する画像形成方法およびこの方法を用いた画像形成装置に関するものである。
【０００２】
【従来の技術】
一般に、電子写真技術を用いた画像形成装置は、外周面に感光層を有する感光体と、この感光体の外周面を一様に帯電させる帯電手段と、この帯電手段により一様に帯電させられた外周面を選択的に露光して静電潜像を形成する露光手段と、この露光手段により形成された静電潜像に現像剤であるトナーを付与して可視像（トナー像）とする現像手段と、この現像手段により現像されたトナー像を転写対象である用紙等のシート状記録媒体に転写させる転写手段と、この転写手段によりトナー像が転写された記録媒体上にそのトナー像を定着させる定着装置とを有している。
定着装置は、回転駆動される定着部材（例えば熱源を有する定着ローラや定着ベルト）と、この定着部材に圧接されて回転する加圧部材（例えば加圧ローラ）とを有しており、これら定着部材と加圧部材との圧接部に記録媒体を通しながら加熱することでトナー像を記録媒体上に溶融定着させるようになっている。
また、従来の画像形成装置として、シート状の記録媒体の片面または両面にトナー像を形成することができる画像形成装置が知られている（例えば、特許文献１参照）。
【０００３】
【特許文献１】
特開平１−１４５９７５号公報（第１頁下右欄、第６図）
【０００４】
【発明が解決しようとする課題】
記録媒体におけるトナー付着面およびトナー像の定着部材からの受熱時間の差はトナー付着面およびトナー像に温度ムラを生じさせ、トナー像にグロスムラ(画像の光沢ムラ)を生じさせる。
一方、片面または両面にトナー像を形成した記録媒体が定着部材と加圧部材との圧接部を通過する場合の記録媒体の挙動は、加熱されて溶融したトナーが粘着剤として作用するため次のようになる。
【０００５】
１．図３（ａ）に示すように、定着部材１と加圧部材２との圧接部Ｎを通過する記録媒体Ｐの定着部材１側Ｐ１にのみトナー像Ｔ１が形成されている場合は、定着部材１側に沿った挙動となる。
すなわち、記録媒体Ｐは、圧接部Ｎを通過することにより、そのトナー像Ｔ１が加熱溶融され、その粘着作用により定着部材１の表面１ａに沿って移動しようとするが、通常、定着部材１には、これに対向して剥離部材３が設けられているので、記録媒体Ｐはこの剥離部材３で定着部材１の表面１ａから剥離され、仮想線で示すように移動し、矢印ａで示すように所定の場所（例えば排紙トレイ）に向けて搬送される。
なお、図中Ｓは余白（記録媒体Ｐ上においてトナー像Ｔが形成されていない先端部分）である。
【０００６】
２．図３（ｂ）に示すように、圧接部Ｎを通過する記録媒体Ｐの加圧部材２側Ｐ２にのみトナー像Ｔ２が形成されている場合は、加圧部材２側に沿った挙動となる。
すなわち、記録媒体Ｐは、圧接部Ｎを通過することにより、そのトナー像Ｔ２が加熱溶融され、その粘着作用により加圧部材２の表面２ａに沿って移動しようとするが、通常、加熱部材２にも、これに対向して剥離部材４が設けられているので、記録媒体Ｐはこの剥離部材４で加圧部材２の表面２ａから剥離され、仮想線で示すように移動し、矢印ｂで示すように所定の場所（例えば上記排紙トレイ）に向けて搬送される。なお、加圧部材は熱源を有している場合もあるし、有していない場合もある。
【０００７】
３．図４に示すように、圧接部Ｎを通過する記録媒体Ｐの両側Ｐ１，Ｐ２にトナー像Ｔ１，Ｔ２が形成されている場合は、各側へのトナーの付着量によって記録媒体Ｐの挙動は異なる。
（ａ）例えば図４（ａ）に示すようにトナー付着状態が両側Ｐ１，Ｐ２で同じであれば、仮想線Ｐおよび矢印ａで示すように定着部材１側へ沿った挙動となる。通常、加圧部材２に比べて定着部材１の方が高温であるため、加圧部材２側のトナーＴ２に比べて定着部材１側のトナーＴ１の方が十分に溶けて、加圧部材２の表面２ａに対してよりも定着部材表面１ａに対しての密着性が高くなるためである。
（ｂ）一方、例えば図４（ｂ）に示すように、記録媒体Ｐの定着部材１側Ｐ１のトナー像Ｔ１のそのトナー量（トナー密度）が少なく、加圧部材２側Ｐ２のトナー像Ｔ２のそのトナー量が多い場合（トナー密度の差に起因してトナー像Ｔ２による加圧部材２への接着力がトナー像Ｔ１による定着部材１への接着力よりも大きくなった場合）には、仮想線Ｐおよび矢印ｂで示すように加圧部材２側へ沿った挙動となる。
【０００８】
（ｃ）さらに、例えば図５に示すように、記録媒体Ｐが圧接部Ｎに進入する際の先端側となる端部において、定着部材１側Ｐ１と加圧部材２側Ｐ２の両方に密度の高いトナー像Ｔ１，Ｔ２が形成されており、かつ加圧部材２側のトナー像Ｔ２が定着部材１側のトナー像Ｔ１よりも先に（先行量を符号ｇで示す）、圧接部Ｎに進入し排出される場合がある。このような事態は、例えば、記録媒体Ｐの片面にトナー像（例えばＴ２）を形成して記録媒体Ｐを途中まで排出した後、その記録媒体Ｐをスイッチバックさせて再び画像形成部へ返送して他方の面にもトナー像（例えばＴ１）を形成して圧接部Ｎに供給する場合における、記録媒体Ｐの搬送精度上の誤差（ｇ）によって生じ得る。
このような場合、記録媒体Ｐの挙動は、仮想線矢印ｂで示すように一旦加圧部材２側に沿った後、仮想線矢印ａで示すように定着部材１側に沿う挙動となる。
すなわち、圧接部Ｎにはトナー像Ｔ２の先端部分が先行して進入することから、記録媒体Ｐはトナー像Ｔ２の粘着力によって、先ず仮想線矢印ｂで示すように加圧部材２側に沿って移動することとなるが、その後、定着部材１側のトナー像Ｔ１が圧接部Ｎに進入すると、前述したようにトナー像Ｔ１の定着部材１に対する粘着力の方がトナー像Ｔ２による加圧部材２に対する粘着力よりも大きいことから、基本的には、トナー像Ｔ２による加圧部材２に対する総体的な粘着力（図示Ｌ２部分における総体的な粘着力）に比べてトナー像Ｔ１による定着部材１に対する総体的な粘着力の方が大きくなった時点で、記録媒体Ｐは矢印ｃで示すに大きく進路変更し、仮想線矢印ａで示すように定着部材１側に沿って移動することとなる。
【０００９】
そして、このような事態が生じると、次のような問題が生じることが分かった。
すなわち、定着部材１側のトナー像Ｔ１に関してみれば、記録媒体Ｐが矢印ａ側（定着部材１側）へ進路変更するまでは、トナー像Ｔ１の先端部分Ｔ１ａの受熱時間は圧接部Ｎを通過する時間（距離Ｌ１（＝圧接部Ｎの記録媒体Ｐの移動方向に関する長さ）を通過する時間）であるのに対し、記録媒体Ｐが矢印ａ側（定着部材１側）へ進路変更した後の、トナー像Ｔ１の上記先端部分Ｔ１ａ以外の部位（当該先端部分Ｔ１ａに後続する部位）Ｔ１ｂの受熱時間は、前記圧接部Ｎを通過する時間に加えてさらに剥離部材３によって剥離されるまでの時間（距離Ｌ１＋Ｌ２を通過する時間）となる。
このため、トナー像Ｔ１における先端部分Ｔ１ａとそれ例外の部分Ｔ１ｂとではグロス差が生じることとなる。
また、図６に示すように、記録媒体Ｐが加圧部材２側から定着部材１側へと矢印ｃで示すように進路変更する際、記録媒体Ｐに作用する反作用によって、記録媒体Ｐの一部（トナー像Ｔ１の一部）Ｔ１ｃが定着部材１の表面１ａから剥離されてしまい、この剥離部分Ｔ１ｃも他の部位とは受熱時間が異なってしまうために、グロス差が生じる。
以上のようなグロス差は、トナー像Ｔ１の先端部分Ｔ１ａおよびその下流側近くにおいてグロスムラとなって現れ、記録媒体Ｐの幅方向に伸びるスジ状のグロスムラとなって、画質を低下させる。
【００１０】
一方、加圧部材２側のトナー像Ｔ２に関してみれば、記録媒体Ｐが矢印ａ側（定着部材１側）へ進路変更するまでのトナー像Ｔ２の先端部分Ｔ２ａの受熱時間は圧接部Ｎを通過する時間に加えてさらに剥離部材４によって剥離されるまでの時間（距離Ｌ１＋Ｌ２を通過する時間）あるいは、記録媒体Ｐの定着部材１側への進路変更によって加圧部材２の表面２ａから剥離されるまでの時間であるのに対し、記録媒体Ｐが矢印ａ側（定着部材１側）へ進路変更した後の、上記先端部分Ｔ２ａ以外の部位（当該先端部分Ｔ２ａに後続する部位）Ｔ２ｂの受熱時間は、圧接部Ｎを通過する時間（距離Ｌ１を通過する時間）となる。
このため、トナー像Ｔ２における先端部分Ｔ２ａとそれ例外の部分Ｔ２ｂとではグロス差が生じることとなる。なお、加圧部材２の温度は定着部材１の温度に比べて一般に低いことから、トナー像Ｔ２のグラスムラはトナー像Ｔ１のグラスムラに比べればそれほど目立たないが、グロスムラが生じることに変わりはない。
【００１１】
この発明の目的は、以上のような問題を解決し、記録媒体の両面に画像を形成する場合でもグロスムラが生じにくい画像形成方法および画像形成装置を提供することにある。
【００１２】
【課題を解決するための手段】
上記目的を達成するために本願発明の画像形成方法は、シート状の記録媒体の片面または両面にトナー像を形成し、回転駆動される定着部材とこの定着部材に圧接されて回転する加圧部材との圧接部に前記記録媒体を通過させて前記トナー像を記録媒体に対して定着させる画像形成方法であって、
前記記録媒体の両面にトナー像を形成する場合には、ユーザーによる余白設定にかかわらず、当該両面にトナー像が形成された記録媒体が前記圧接部に進入する際の先端側となる記録媒体端部における記録媒体移動方向に関する余白を、前記定着部材に接する側の余白に比べて、前記加圧部材に接する側の余白の方を長くすることを特徴とする。
また、本願発明の画像形成装置は、シート状の記録媒体の両面にトナー像を形成可能な画像形成部と、
回転駆動される定着部材とこの定着部材に圧接されて回転する加圧部材とを有し、これら定着部材と加圧部材との圧接部に前記記録媒体を通過させて前記トナー像を記録媒体に対して定着させる定着部とを備えた装置であって、
前記画像形成部は、前記記録媒体の両面にトナー像を形成する場合には、ユーザーによる余白設定にかかわらず、当該両面にトナー像が形成された記録媒体が前記圧接部に進入する際の先端側となる記録媒体端部における記録媒体移動方向に関する余白が、前記定着部材に接する側の余白に比べて、前記加圧部材に接する側の余白の方が長くなるように前記記録媒体の両面に前記トナー像を形成する画像形成部であることを特徴とする。
【００１３】
【作用効果】
本願発明の画像形成方法ないし装置によれば、記録媒体の両面にトナー像を形成する場合には、当該両面にトナー像が形成された記録媒体が前記圧接部に進入する際の先端側となる記録媒体端部における記録媒体移動方向に関する余白が、前記定着部材に接する側の余白に比べて、前記加圧部材に接する側の余白の方が長くなっているので、基本的に、定着部材側のトナー像の方が加圧部材側のトナー像に比べてより早く上記圧接部に進入し通過することとなる。
このため、記録媒体の挙動は定着部材に沿った挙動となり、記録媒体が一旦加圧部材側に沿った後に進路変更して定着部材側に沿うという事態（上記３（ｃ）で説明した事態）は著しく生じにくくなる。
したがって、この画像形成方法ないし装置によれば、記録媒体の両面に画像を形成する場合でもグロスムラが生じにくくなり、両面の画質向上を図ることができるようになる。
【００１４】
【発明の実施の形態】
以下、本発明の実施の形態について図面を参照して説明する。
図１は本発明に係る画像形成方法を用いた画像形成装置の一実施の形態の内部構造を示す概略側面図である。
この画像形成装置は、Ａ３サイズの用紙（記録媒体の一例）の両面にフルカラー画像を形成することのできるカラー画像形成装置であり、ケース１０と、このケース１０内に収容された、像担持体ユニット２０、露光手段としての露光ユニット３０、現像手段としての現像器４０、中間転写体ユニット５０、および記録媒体の搬送路１６，１７を有する画像形成部と、定着部をなす定着装置である定着ユニット６０と、画像形成部を含む装置全体の制御を行う制御部７０とを備えている。
ケース１０には装置本体の図示しないフレームが設けられており、このフレームに各ユニット等が取り付けられている。
【００１５】
像担持体ユニット２０は、外周面に感光層を有する感光体（像担持体）２１と、この感光体２１の外周面を一様に帯電させる帯電手段（スコロトロン帯電器）２２とを有しており、この帯電手段２２により一様に帯電させられた感光体２１の外周面を露光ユニット３０からのレーザー光Ｌで選択的に露光して静電潜像を形成し、この静電潜像に現像器４０で現像剤であるトナーを付与して可視像（トナー像）とし、このトナー像を中間転写体ユニット５０の中間転写ベルト５１に一次転写部ｔ１で一次転写し、さらに、二次転写部ｔ２で、転写対象である用紙に二次転写させるようになっている。
像担持体ユニット２０には、一次転写後に感光体２１の表面に残留しているトナーを除去するクリーニング手段（クリーニングブレード）２３と、このクリーニング手段２３で除去された廃トナーを収容する廃トナー収容部２４が設けられている。
【００１６】
ケース１０内には、後述する給紙トレイ１８からの用紙を上記二次転写部ｔ２に搬送し、二次転写部ｔ２で片面に画像が形成された用紙をケース１０上面の用紙排出部（排紙トレイ部）１５に向けて搬送する搬送路１６と、この搬送路１６により用紙排出部１５に向けて途中まで搬送された用紙をスイッチバックさせて他面にも画像を形成すべく前記二次転写部ｔ２に向けて返送する返送路１７とが設けられている。
ケース１０の下部には、複数枚の用紙を積層保持する給紙トレイ１８と、その用紙を一枚ずつ上記二次転写部ｔ２に向けて給送する給紙ローラ１９とが設けられている。
また、搬送路１６および返送路１７から二次転写部ｔ２に至る経路内には、二次転写部ｔ２への記録媒体の供給タイミングを制御するためのゲートローラ７１が設けられている。
【００１７】
現像器４０はロータリ現像器であり、回転体本体４１に対して、それぞれトナーが収容された複数の現像器カートリッジが着脱可能に装着されている。この実施の形態では、イエロー用の現像器カートリッジ４２Ｙと、マゼンタ用の現像器カートリッジ４２Ｍと、シアン用の現像器カートリッジ４２Ｃと、ブラック用の現像器カートリッジ４２Ｋとが設けられていて（図ではイエロー用の現像器カートリッジ４２Ｙのみを直接描いてある）、回転体本体４１が矢印方向に９０度ピッチで回転することによって、感光体２１に現像ローラ４３を選択的に当接させ、感光体２１の表面を選択的に現像することが可能となっている。
【００１８】
露光ユニット３０は、板ガラス等で構成された露光窓３１から上記レーザー光Ｌを感光体２１に向けて照射するようになっている。
【００１９】
中間転写体ユニット５０は、図示しないユニットフレームと、このフレームで回転可能に支持された駆動ローラ５４，従動ローラ５５，一次転写ローラ５６、一次転写部ｔ１でのベルト５１の状態を安定させるためのガイドローラ５７，およびテンションローラ５８と、これらローラに掛け回されて張架された前記中間転写ベルト５１とを備えており、ベルト５１が図示矢印方向に循環駆動される。感光体２１と一次転写ローラ５６との間において前記一次転写部ｔ１が形成されており、駆動ローラ５４と本体側に設けられた二次転写ローラ１０ｂとの圧接部において前記二次転写部ｔ２が形成される。
二次転写ローラ１０ｂは、前記駆動ローラ５４に対して（したがって中間転写ベルト５１に対して）接離可能であり、接触した際に二次転写部ｔ２が形成される。
したがって、カラー画像を形成する際には、二次転写ローラ１０ｂが中間転写ベルト５１から離間している状態で中間転写ベルト５１上において複数色のトナー像が重ね合わされてカラー画像が形成され、その後、二次転写ローラ１０ｂが中間転写ベルト５１に当接し、その当接部（二次転写部ｔ２）に用紙が供給されることによって用紙上にカラー画像（トナー像）が転写されることとなる。
トナー像が転写された用紙は、定着ユニット（定着部）６０を通ることでトナー像が溶融定着され、排紙ローラ対１４で搬送されて上記排紙トレイ部１５に向けて排出される。
【００２０】
記録媒体（用紙）の両面に画像を形成する場合、先ず記録媒体の片面にトナー像Ｔ２（図２参照）を形成して記録媒体Ｐを排紙トレイ１５の途中まで排出した後、その記録媒体Ｐをスイッチバックさせて返送路１７へ供給し、さらにゲートローラ７１を経て二次転写部ｔ２へ供給して他方の面にもトナー像Ｔ１（図２参照）を形成し、定着部６０へ供給する。
【００２１】
図２は定着部６０およびこれに供給される記録媒体Ｐの部分拡大概略側面図である。
図１および図２に示すように、定着部６０は、図示しない駆動機構により回転駆動される定着部材としての定着ローラ６１と、この定着ローラ６１に圧接されて回転する加圧部材としての加圧ローラ６２と、これら定着ローラ６１、加圧ローラ６２に対して設けられ、定着ローラ６１と加圧ローラ６２との圧接部Ｎを通過してきたシート状の記録媒体Ｐを定着ローラ６１または加圧ローラ６２の表面から剥離しかつ案内する剥離部材６３，６４とを有している。
【００２２】
前述した画像形成部は、図２に示すように記録媒体Ｐの両面Ｐ１，Ｐ２にトナー像Ｔ１、Ｔ２を形成する場合には、当該両面にトナー像Ｔ１，Ｔ２が形成された記録媒体Ｐが定着部６０の上記圧接部Ｎに進入する際の先端側となる記録媒体端部における記録媒体移動方向に関する余白（Ｓ１，Ｓ２）が、定着部材６１に接する側の余白Ｓ１に比べて、加圧部材６２に接する側の余白Ｓ２の方が長くなるように記録媒体Ｐの両面に前記トナー像Ｔ１，Ｔ２を形成するようになっている。余白Ｓ１とＳ２の長さの差をΔＳで示す。
【００２３】
具体的には、制御部７０が、記録媒体Ｐに対する画像形成位置を決定する決定手段を有しており、定着部材６１に接する側の余白Ｓ１に比べて、加圧部材６２に接する側の余白Ｓ２の方が長くなるように画像形成部を制御して記録媒体Ｐの両面に前記トナー像Ｔ１，Ｔ２を形成させる。
より具体的には、例えば、制御部７０は、ゲートローラ７１による記録媒体Ｐの二次転写部ｔ２への供給タイミングを制御し、トナー像Ｔ２形成時の供給タイミングに対し、トナー像Ｔ１形成時の供給タイミングをΔＳ分だけ早めることによって、余白Ｓ１に比べて、余白Ｓ２の方がΔＳだけ長くなるように前記トナー像Ｔ１，Ｔ２を形成させる。
あるいはまた、例えば、制御部７０は、露光ユニット３０による感光体２１への潜像書き込みタイミングを制御し、トナー像Ｔ２形成時の書き込みタイミングに対し、トナー像Ｔ１形成時の書き込みタイミングをΔＳ分だけ早めることによって、余白Ｓ１に比べて、余白Ｓ２の方がΔＳだけ長くなるように前記トナー像Ｔ１，Ｔ２を形成させる。
このような制御は、この画像形成装置のユーザーによる余白設定にかかわらず、行う。
【００２４】
また以上のような画像形成方法は、画像形成装置が接続されているコンピュータに導入されているプリンタドライバで行うこともできる。
例えば、ユーザーによる余白設定にかかわらず、余白Ｓ１に比べて、余白Ｓ２の方がΔＳだけ長くなるようにプリンタドライバをプログラムする。具体的には、例えばユーザによる余白設定（この設定は現状のプリンタドライバでは表裏両面とも同一値となる）が１０ｍｍであった場合、余白Ｓ１に比べて、余白Ｓ２の方がΔＳ（例えば２ｍｍ）だけ長くなるように（Ｓ１＝８ｍｍ、あるいはＳ２＝１２ｍｍとなるように）プリンタドライバをプログラムする。結果的に、ユーザーが余白を１０ｍｍに設定したにもかかわらず、実際に記録媒体Ｐに形成される画像は、表裏において２ｍｍ程度ずれることとなる。
【００２５】
なお、ΔＳは記録媒体Ｐをスイッチバックさせて再び画像形成部へ返送して他方の面にもトナー像を形成する際における記録媒体Ｐの搬送精度上の誤差を吸収し得る（前記誤差があっても定着部材側のトナー像Ｔ１が先に圧接部Ｎに進入する）範囲内でできるだけ小さく設定することが望ましく、通常、２ｍｍ程度に設定する。
【００２６】
以上のような画像形成方法ないし画像形成装置によれば、記録媒体Ｐの両面Ｐ１，Ｐ２にトナー像Ｔ１，Ｔ２を形成する場合には、当該両面にトナー像Ｔ１，Ｔ２が形成された記録媒体Ｐが前記圧接部Ｎに進入する際の先端側となる記録媒体端部における記録媒体移動方向に関する余白が、定着部材６１に接する側の余白Ｓ１に比べて、加圧部材６２に接する側の余白Ｓ２の方が長くなっているので、基本的に（例えば記録媒体Ｐの搬送精度が著しく悪くない限り）、定着部材６１側のトナー像Ｔ１の方が加圧部材６２側のトナー像Ｔ２に比べてより早く上記圧接部Ｎに進入し通過することとなる。
このため、記録媒体Ｐの挙動は、図２に仮想線Ｐおよび矢印ａで示すように定着部材６１に沿った挙動となり、記録媒体Ｐが一旦加圧部材６２側に沿った後に進路変更して定着部材６１側に沿うという事態（上記３（ｃ）で説明した事態）は著しく生じにくくなる。
したがって、この画像形成方法ないし画像形成装置によれば、記録媒体Ｐの両面に画像を形成する場合でもグロスムラが生じにくくなり、両面の画質向上を図ることができるようになる。
【００２７】
以上、本発明の実施の形態について説明したが、本発明は上記の実施の形態または実施例に限定されるものではなく、本発明の要旨の範囲内において適宜変形実施可能である。
【００２８】
【図面の簡単な説明】
【図１】本発明に係る画像形成方法を用いた画像形成装置の一実施の形態の内部構造を示す概略側面図。
【図２】定着部およびこれに供給される記録媒体の部分拡大概略側面図。
【図３】（ａ）（ｂ）は課題の説明図。
【図４】（ａ）（ｂ）は課題の説明図。
【図５】課題の説明図。
【図６】課題の説明図。
【符号の説明】
Ｐ：記録媒体、６０：定着部、６１：定着部材、６２：加圧部材、Ｎ：圧接部、Ｔ１，Ｔ２：トナー像、Ｓ１：定着部材に接する側の余白、Ｓ２：加圧部材に接する側の余白。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an image forming method applied to an image forming apparatus such as a printer, a facsimile machine, and a copying machine that forms an image using electrophotographic technology, and an image forming apparatus using this method.
[0002]
[Prior art]
In general, an image forming apparatus using an electrophotographic technique has a photosensitive member having a photosensitive layer on an outer peripheral surface, a charging unit that uniformly charges the outer peripheral surface of the photosensitive member, and a charging unit that is uniformly charged by the charging unit. An exposure unit that selectively exposes the outer peripheral surface to form an electrostatic latent image, and a toner that is a developer is applied to the electrostatic latent image formed by the exposure unit to form a visible image (toner image). Developing means, transfer means for transferring the toner image developed by the developing means to a sheet-like recording medium such as paper to be transferred, and the toner image on the recording medium to which the toner image is transferred by the transferring means And a fixing device for fixing the toner.
The fixing device includes a fixing member (for example, a fixing roller having a heat source or a fixing belt) that is driven to rotate, and a pressure member (for example, a pressure roller) that rotates while being pressed against the fixing member. The toner image is melted and fixed on the recording medium by heating while passing the recording medium through the pressure contact portion between the member and the pressure member.
As a conventional image forming apparatus, an image forming apparatus capable of forming a toner image on one side or both sides of a sheet-like recording medium is known (for example, see Patent Document 1).
[0003]
[Patent Document 1]
Japanese Patent Laid-Open No. 1-145975 (first page, lower right column, FIG. 6)
[0004]
[Problems to be solved by the invention]
The difference in heat receiving time from the fixing surface of the toner adhesion surface and the toner image on the recording medium causes temperature unevenness on the toner adhesion surface and the toner image, and gloss unevenness (gloss unevenness of the image) on the toner image.
On the other hand, the behavior of the recording medium when the recording medium having a toner image formed on one side or both sides passes through the pressure contact portion between the fixing member and the pressure member is as follows. It becomes like this.
[0005]
1. As shown in FIG. 3A, when the toner image T1 is formed only on the fixing member 1 side P1 of the recording medium P passing through the pressure contact portion N between the fixing member 1 and the pressure member 2, the fixing member It becomes the behavior along the 1 side.
That is, as the recording medium P passes through the press contact portion N, the toner image T1 is heated and melted and tends to move along the surface 1a of the fixing member 1 by the adhesive action. Since the peeling member 3 is provided opposite to the recording medium P, the recording medium P is peeled off from the surface 1a of the fixing member 1 by the peeling member 3, and moves as indicated by an imaginary line, as indicated by an arrow a. Are conveyed toward a predetermined place (for example, a paper discharge tray).
In the figure, S is a margin (a front end portion on which the toner image T is not formed on the recording medium P).
[0006]
2. As shown in FIG. 3B, when the toner image T2 is formed only on the pressure member 2 side P2 of the recording medium P passing through the press contact portion N, the behavior along the pressure member 2 side is obtained. .
That is, as the recording medium P passes through the press contact portion N, the toner image T2 is heated and melted and tends to move along the surface 2a of the pressure member 2 by the adhesive action. In addition, since the peeling member 4 is provided opposite to this, the recording medium P is peeled from the surface 2a of the pressure member 2 by the peeling member 4, and moves as indicated by an imaginary line. As shown, the sheet is conveyed toward a predetermined place (for example, the paper discharge tray). Note that the pressure member may or may not have a heat source.
[0007]
3. As shown in FIG. 4, when the toner images T1 and T2 are formed on both sides P1 and P2 of the recording medium P passing through the press contact portion N, the behavior of the recording medium P depends on the amount of toner adhering to each side. Different.
(A) For example, as shown in FIG. 4A, if the toner adhesion state is the same on both sides P1 and P2, the behavior follows the fixing member 1 side as indicated by the phantom line P and the arrow a. Usually, the fixing member 1 has a higher temperature than the pressure member 2, and therefore, the toner T 1 on the fixing member 1 side is sufficiently melted compared to the toner T 2 on the pressure member 2 side. This is because the adhesion to the fixing member surface 1a is higher than that of the surface 2a.
(B) On the other hand, for example, as shown in FIG. 4B, the toner amount (toner density) of the toner image T1 on the fixing member 1 side P1 of the recording medium P is small and the toner image T2 on the pressure member 2 side P2 is small. When the toner amount is large (when the adhesive force of the toner image T2 to the pressure member 2 is larger than the adhesive force of the toner image T1 to the fixing member 1 due to the difference in toner density) As indicated by the phantom line P and the arrow b, the behavior is along the pressure member 2 side.
[0008]
(C) Further, as shown in FIG. 5, for example, at the end portion that is the leading end side when the recording medium P enters the press contact portion N, both the fixing member 1 side P1 and the pressure member 2 side P2 have a density. High toner images T1 and T2 are formed, and the toner image T2 on the pressure member 2 side enters the pressure contact portion N before the toner image T1 on the fixing member 1 side (the preceding amount is indicated by a symbol g). May be discharged. For example, after a toner image (for example, T2) is formed on one side of the recording medium P and the recording medium P is discharged halfway, the recording medium P is switched back and returned to the image forming unit again. This may occur due to an error (g) in the conveyance accuracy of the recording medium P when a toner image (for example, T1) is formed on the other surface and supplied to the press contact portion N.
In such a case, the behavior of the recording medium P is once along the pressure member 2 side as indicated by the phantom arrow b and then along the fixing member 1 side as indicated by the phantom arrow a.
That is, since the leading end portion of the toner image T2 enters the press contact portion N first, the recording medium P is first moved along the pressure member 2 side as indicated by the phantom arrow b by the adhesive force of the toner image T2. After that, when the toner image T1 on the fixing member 1 side enters the press contact portion N, the adhesive force of the toner image T1 to the fixing member 1 as described above is the pressure member by the toner image T2. Therefore, basically, the fixing member 1 based on the toner image T1 is compared with the total adhesive strength (total adhesive strength in the portion L2 in the drawing) of the toner image T2 with respect to the pressure member 2. When the overall adhesive force on the recording medium P becomes larger, the recording medium P changes its course as indicated by an arrow c and moves along the fixing member 1 side as indicated by an imaginary line arrow a.
[0009]
And when such a situation occurred, it turned out that the following problems arise.
That is, regarding the toner image T1 on the fixing member 1 side, the heat receiving time of the leading end portion T1a of the toner image T1 passes through the pressure contact portion N until the recording medium P changes its path to the arrow a side (fixing member 1 side). After the recording medium P has changed its course to the arrow a side (fixing member 1 side). The heat receiving time of a portion other than the tip portion T1a of the toner image T1 (the portion following the tip portion T1a) T1b is the time until it is further peeled off by the peeling member 3 in addition to the time passing through the pressure contact portion N. Time (time to pass through the distance L1 + L2).
Therefore, a gloss difference is generated between the tip portion T1a and the exceptional portion T1b in the toner image T1.
In addition, as shown in FIG. 6, when the recording medium P changes its course from the pressure member 2 side to the fixing member 1 side as indicated by an arrow c, the reaction medium acts on the recording medium P due to a reaction acting on the recording medium P. The portion (a part of the toner image T1) T1c is peeled off from the surface 1a of the fixing member 1, and the peeled portion T1c also has a different heat receiving time from other parts, so that a gloss difference is generated.
The gloss difference as described above appears as gloss unevenness near the front end portion T1a of the toner image T1 and the downstream side thereof, and becomes a stripe-like gloss unevenness extending in the width direction of the recording medium P, thereby degrading the image quality.
[0010]
On the other hand, regarding the toner image T2 on the pressure member 2 side, the heat receiving time of the front end portion T2a of the toner image T2 until the recording medium P changes its path to the arrow a side (fixing member 1 side) passes through the pressure contact portion N. In addition to the time to be peeled off, it is peeled off from the surface 2a of the pressure member 2 by the time until it is further peeled off by the peeling member 4 (time passing through the distance L1 + L2) or by changing the path of the recording medium P to the fixing member 1 side. Heat receiving time of a part (part following the leading end part T2a) T2b other than the leading end part T2a after the path of the recording medium P is changed to the arrow a side (fixing member 1 side). Is the time for passing the pressure contact portion N (time for passing the distance L1).
Therefore, a gloss difference is generated between the tip portion T2a and the exceptional portion T2b in the toner image T2. Since the temperature of the pressure member 2 is generally lower than the temperature of the fixing member 1, the glass unevenness of the toner image T2 is less noticeable than the glass unevenness of the toner image T1, but the gloss unevenness is still generated.
[0011]
SUMMARY OF THE INVENTION An object of the present invention is to provide an image forming method and an image forming apparatus which solve the above-described problems and hardly cause gloss unevenness even when images are formed on both sides of a recording medium.
[0012]
[Means for Solving the Problems]
In order to achieve the above object, the image forming method of the present invention includes a fixing member that forms a toner image on one side or both sides of a sheet-like recording medium, and is rotated by being pressed against the fixing member. An image forming method in which the recording medium is passed through a pressure contact portion and the toner image is fixed to the recording medium.
When a toner image is formed on both sides of the recording medium, regardless of the margin setting by the user, the recording medium end serving as the leading end when the recording medium having the toner image formed on both sides enters the press contact portion. The margin in the moving direction of the recording medium in the printing unit is longer than the margin on the side in contact with the fixing member, compared to the margin on the side in contact with the fixing member.
The image forming apparatus of the present invention includes an image forming unit capable of forming a toner image on both sides of a sheet-like recording medium,
A fixing member which is driven to rotate; and a pressure member which is pressed against and rotates with the fixing member. The recording medium is passed through a pressure contact portion between the fixing member and the pressure member so that the toner image is transferred to the recording medium. And a fixing unit for fixing to the device,
When the toner image is formed on both sides of the recording medium, the image forming unit has a leading edge when the recording medium having the toner image formed on both sides enters the pressure contact portion regardless of a margin setting by the user. The margin on the recording medium moving direction at the end of the recording medium on the side is longer on both sides of the recording medium so that the margin on the side in contact with the pressure member is longer than the margin on the side in contact with the fixing member. It is an image forming unit for forming the toner image.
[0013]
[Function and effect]
According to the image forming method or apparatus of the present invention, when a toner image is formed on both sides of a recording medium, the recording medium on which the toner image is formed on both sides is the leading end side when entering the pressure contact portion. The margin on the recording medium moving direction at the end of the recording medium is basically longer on the side in contact with the pressure member than on the side in contact with the fixing member. The toner image enters and passes through the pressure contact portion earlier than the toner image on the pressure member side.
For this reason, the behavior of the recording medium becomes behavior along the fixing member, and the situation where the recording medium is once changed along the pressing member side and then changed in the course (the situation described in the above 3 (c)). Is significantly less likely to occur.
Therefore, according to this image forming method or apparatus, even when images are formed on both sides of the recording medium, gloss unevenness is less likely to occur, and image quality on both sides can be improved.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a schematic side view showing an internal structure of an embodiment of an image forming apparatus using an image forming method according to the present invention.
This image forming apparatus is a color image forming apparatus capable of forming a full color image on both sides of an A3 size paper (an example of a recording medium). A case 10 and an image carrier housed in the case 10 Image forming unit having unit 20, exposure unit 30 as exposure unit, developing unit 40 as development unit, intermediate transfer body unit 50, and recording medium conveyance paths 16 and 17, and a fixing device as a fixing unit forming a fixing unit A unit 60 and a control unit 70 that controls the entire apparatus including the image forming unit are provided.
The case 10 is provided with a frame (not shown) of the apparatus main body, and each unit is attached to the frame.
[0015]
The image carrier unit 20 includes a photoconductor (image carrier) 21 having a photosensitive layer on the outer peripheral surface, and a charging unit (scorotron charger) 22 for uniformly charging the outer peripheral surface of the photoconductor 21. Then, the outer peripheral surface of the photoconductor 21 uniformly charged by the charging means 22 is selectively exposed with the laser light L from the exposure unit 30 to form an electrostatic latent image. The developing device 40 applies toner as a developer to form a visible image (toner image). The toner image is primarily transferred to the intermediate transfer belt 51 of the intermediate transfer body unit 50 by the primary transfer portion t1, and further, the secondary image is transferred. Secondary transfer is performed on the paper to be transferred at the transfer portion t2.
The image carrier unit 20 includes a cleaning unit (cleaning blade) 23 that removes toner remaining on the surface of the photoconductor 21 after the primary transfer, and a waste toner storage that stores the waste toner removed by the cleaning unit 23. A portion 24 is provided.
[0016]
In the case 10, a sheet from a sheet feeding tray 18 to be described later is conveyed to the secondary transfer unit t 2, and the sheet on which an image is formed on one side by the secondary transfer unit t 2 is discharged on the upper side of the case 10. A paper path 16 transported toward the paper tray section 15 and the secondary to switch back the paper transported halfway toward the paper discharge section 15 by the transport path 16 and form an image on the other side. A return path 17 for returning toward the transfer portion t2 is provided.
Under the case 10, there are provided a paper feed tray 18 for laminating and holding a plurality of sheets, and a paper feed roller 19 for feeding the sheets one by one toward the secondary transfer portion t2.
Further, a gate roller 71 for controlling the supply timing of the recording medium to the secondary transfer unit t2 is provided in the path from the conveyance path 16 and the return path 17 to the secondary transfer unit t2.
[0017]
The developing device 40 is a rotary developing device, and a plurality of developing device cartridges each containing toner are detachably attached to the rotating body main body 41. In this embodiment, a yellow developer cartridge 42Y, a magenta developer cartridge 42M, a cyan developer cartridge 42C, and a black developer cartridge 42K are provided (in the drawing, yellow Only the developing device cartridge 42Y is directly drawn), and the rotating body main body 41 is rotated at a pitch of 90 degrees in the direction of the arrow so that the developing roller 43 is selectively brought into contact with the photosensitive body 21 and the photosensitive body 21 The surface can be selectively developed.
[0018]
The exposure unit 30 is configured to irradiate the photosensitive member 21 with the laser light L from an exposure window 31 made of plate glass or the like.
[0019]
The intermediate transfer body unit 50 stabilizes the state of the belt 51 at a unit frame (not shown), a driving roller 54, a driven roller 55, a primary transfer roller 56, and a primary transfer portion t1 that are rotatably supported by the frame. A guide roller 57, a tension roller 58, and the intermediate transfer belt 51 stretched around these rollers are provided, and the belt 51 is circulated and driven in the direction of the arrow in the figure. The primary transfer portion t1 is formed between the photosensitive member 21 and the primary transfer roller 56, and the secondary transfer portion t2 is in a pressure contact portion between the driving roller 54 and the secondary transfer roller 10b provided on the main body side. It is formed.
The secondary transfer roller 10b can be brought into contact with and separated from the drive roller 54 (and therefore with respect to the intermediate transfer belt 51), and a secondary transfer portion t2 is formed when contacted.
Therefore, when forming a color image, a toner image of a plurality of colors is superimposed on the intermediate transfer belt 51 with the secondary transfer roller 10b being separated from the intermediate transfer belt 51, and then a color image is formed. The secondary transfer roller 10b comes into contact with the intermediate transfer belt 51, and the paper is supplied to the contact portion (secondary transfer portion t2), whereby a color image (toner image) is transferred onto the paper. .
The sheet on which the toner image has been transferred passes through a fixing unit (fixing unit) 60 to melt and fix the toner image, and is conveyed by a pair of discharge rollers 14 and discharged toward the discharge tray unit 15.
[0020]
When images are formed on both sides of a recording medium (paper), a toner image T2 (see FIG. 2) is first formed on one side of the recording medium, and the recording medium P is discharged to the middle of the paper discharge tray 15 and then the recording medium. P is switched back and supplied to the return path 17 and further supplied to the secondary transfer portion t2 via the gate roller 71 to form a toner image T1 (see FIG. 2) on the other surface and supplied to the fixing portion 60. To do.
[0021]
FIG. 2 is a partially enlarged schematic side view of the fixing unit 60 and the recording medium P supplied thereto.
As shown in FIGS. 1 and 2, the fixing unit 60 includes a fixing roller 61 as a fixing member that is rotationally driven by a driving mechanism (not shown), and a pressurizing member as a pressing member that rotates by being pressed against the fixing roller 61. A sheet-like recording medium P that is provided for the roller 62 and the fixing roller 61 and the pressure roller 62 and passes through the pressure contact portion N between the fixing roller 61 and the pressure roller 62 is used as the fixing roller 61 or the pressure roller. And peeling members 63 and 64 for peeling and guiding from the surface of 62.
[0022]
When the above-described image forming unit forms toner images T1 and T2 on both sides P1 and P2 of the recording medium P as shown in FIG. 2, the recording medium P on which the toner images T1 and T2 are formed on both sides is provided. The margins (S1, S2) regarding the recording medium moving direction at the end of the recording medium at the leading end side when entering the pressure contact portion N of the fixing unit 60 are more pressed than the margin S1 on the side in contact with the fixing member 61. The toner images T1 and T2 are formed on both sides of the recording medium P so that the margin S2 on the side in contact with the member 62 is longer. The difference between the lengths of the margins S1 and S2 is indicated by ΔS.
[0023]
Specifically, the control unit 70 includes a determination unit that determines an image forming position with respect to the recording medium P, and the margin on the side in contact with the pressing member 62 is larger than the margin S1 on the side in contact with the fixing member 61. The image forming unit is controlled so that the length of S2 is longer, and the toner images T1 and T2 are formed on both sides of the recording medium P.
More specifically, for example, the control unit 70 controls the supply timing of the recording medium P to the secondary transfer unit t2 by the gate roller 71, and when the toner image T1 is formed with respect to the supply timing when the toner image T2 is formed. The toner images T1 and T2 are formed such that the margin S2 is longer by ΔS than the margin S1 by advancing the supply timing of.
Alternatively, for example, the control unit 70 controls the timing of writing the latent image on the photoconductor 21 by the exposure unit 30, and the writing timing at the time of forming the toner image T1 by ΔS relative to the timing of writing at the time of forming the toner image T2. By speeding up, the toner images T1 and T2 are formed such that the margin S2 is longer by ΔS than the margin S1.
Such control is performed regardless of the margin setting by the user of the image forming apparatus.
[0024]
The image forming method as described above can also be performed by a printer driver installed in a computer to which the image forming apparatus is connected.
For example, the printer driver is programmed so that the margin S2 is longer than the margin S1 by ΔS, regardless of the margin setting by the user. Specifically, for example, when the margin setting by the user (this setting is the same value for both the front and back sides in the current printer driver) is 10 mm, the margin S2 is ΔS (for example, 2 mm) compared to the margin S1. The printer driver is programmed so as to be longer (S1 = 8 mm or S2 = 12 mm). As a result, even though the user sets the margin to 10 mm, the image actually formed on the recording medium P is shifted by about 2 mm on the front and back.
[0025]
Note that ΔS can absorb an error in the conveyance accuracy of the recording medium P when the recording medium P is switched back and returned to the image forming unit to form a toner image on the other surface (the above error is present). However, it is desirable to set it as small as possible within a range in which the toner image T1 on the fixing member side first enters the press contact portion N), and is usually set to about 2 mm.
[0026]
According to the image forming method or the image forming apparatus as described above, when the toner images T1 and T2 are formed on both sides P1 and P2 of the recording medium P, the recording medium on which the toner images T1 and T2 are formed on both sides. The margin on the recording medium moving direction at the end of the recording medium at the leading end side when P enters the pressure contact portion N is larger than the margin S1 on the side in contact with the fixing member 61 on the side in contact with the pressure member 62. Since S2 is longer, basically, the toner image T1 on the fixing member 61 side is compared with the toner image T2 on the pressure member 62 side (for example, unless the conveyance accuracy of the recording medium P is extremely poor). As a result, the pressure contact portion N is entered and passed through earlier.
For this reason, the behavior of the recording medium P becomes the behavior along the fixing member 61 as indicated by the phantom line P and the arrow a in FIG. 2, and the course is changed after the recording medium P once along the pressing member 62 side. The situation along the fixing member 61 side (the situation described in 3 (c) above) is extremely difficult to occur.
Therefore, according to this image forming method or image forming apparatus, even when images are formed on both sides of the recording medium P, gloss unevenness is less likely to occur, and image quality on both sides can be improved.
[0027]
Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments or examples, and can be appropriately modified within the scope of the gist of the present invention.
[0028]
[Brief description of the drawings]
FIG. 1 is a schematic side view showing the internal structure of an embodiment of an image forming apparatus using an image forming method according to the present invention.
FIG. 2 is a partially enlarged schematic side view of a fixing unit and a recording medium supplied thereto.
FIGS. 3A and 3B are explanatory diagrams of problems. FIGS.
4A and 4B are explanatory diagrams of problems. FIG.
FIG. 5 is an explanatory diagram of a problem.
FIG. 6 is an explanatory diagram of a problem.
[Explanation of symbols]
P: recording medium, 60: fixing portion, 61: fixing member, 62: pressure member, N: pressure contact portion, T1, T2: toner image, S1: margin on the side in contact with the fixing member, S2: contact with the pressure member Side margins.

Claims

A toner image is formed on one side or both sides of a sheet-like recording medium, and the toner image is passed through the recording medium through a pressure contact portion between a rotation driving fixing member and a pressure member rotating in pressure contact with the fixing member. Forming an image on a recording medium,
When a toner image is formed on both sides of the recording medium, regardless of the margin setting by the user, the recording medium end serving as the leading end when the recording medium having the toner image formed on both sides enters the press contact portion. An image forming method characterized in that a margin on a recording medium moving direction in a portion is made longer on a side in contact with the pressure member than on a side in contact with the fixing member.

An image forming unit capable of forming a toner image on both sides of a sheet-like recording medium;
A fixing member which is driven to rotate; and a pressure member which is pressed against and rotates with the fixing member. The recording medium is passed through a pressure contact portion between the fixing member and the pressure member so that the toner image is transferred to the recording medium. And a fixing unit for fixing to the device,
When the toner image is formed on both sides of the recording medium, the image forming unit has a leading edge when the recording medium having the toner image formed on both sides enters the pressure contact portion regardless of a margin setting by the user. The margin on the recording medium moving direction at the end of the recording medium on the side is longer on both sides of the recording medium so that the margin on the side in contact with the pressure member is longer than the margin on the side in contact with the fixing member. An image forming apparatus that is an image forming unit that forms the toner image.