JP3984901B2

JP3984901B2 - Image forming apparatus

Info

Publication number: JP3984901B2
Application number: JP2002303764A
Authority: JP
Inventors: 昭人金森
Original assignee: Canon Inc
Current assignee: Canon Inc
Priority date: 2002-10-18
Filing date: 2002-10-18
Publication date: 2007-10-03
Anticipated expiration: 2022-10-18
Also published as: JP2004138841A

Description

【０００１】
【発明の属する技術分野】
本発明は、電子写真式プリンター、複写機、及び静電記録装置等の画像形成装置、及びその画像形成装置に用いられる、記録材上にトナー等を定着させる定着装置に関するものである。
【０００２】
【従来の技術】
従来、電子写真方式の複写機、プリンタ等の多くは、加熱定着手段として熱効率、安全性の良好な接触加熱型の熱ローラ定着方式や、省エネルギータイプのフィルム加熱方式を採用している。
【０００３】
熱ローラ定着方式の加熱定着装置は、内部にハロゲンヒータを内包する加熱用回転体としての加熱ローラ（以下、定着ローラ）と、これに圧接させた加圧用回転体としての弾性加圧ローラ（以下、加圧ローラ）を基本構成とする。この一対のローラを回転させ、この一対のローラの圧接ニップ部である定着ニップ部に、未定着画像（以下、トナー画像）を形成担持した被加熱材としての記録材（転写材シート・静電記録材・エレクトロファックス紙・印字用紙等）を導入し、挟持搬送することで、定着ローラからの熱と定着ニップ部の加圧力により、トナー画像を記録材面に永久固着画像として熱圧定着させるものである。
【０００４】
一方、フィルム加熱方式の加熱定着装置は、例えば特開昭６３−３１３１８２号公報、特開平２−１５７８７８号公報、４−４４０７５〜４４０８３号公報、４−２０４９８０〜２０４９８４号公報等に提案されているように、固定配置したセラミックヒータ等の加熱体に、加熱用回転体である耐熱性フィルム（以下、定着フィルム）を加圧用回転体（以下、加圧ローラ）で密着、そして摺動回動させて、定着フィルムを挟んで加熱体と加圧ローラとで形成される圧接ニップ部である定着ニップ部に、トナー画像を担持形成した記録材を導入し、定着フィルムと一緒に搬送させて、定着フィルムを介して付与される加熱体からの熱と定着ニップ部の加圧力によってトナー画像を記録材面に永久固着画像として熱圧定着させるものである。
【０００５】
フィルム加熱方式の加熱定着装置は、加熱体としてセラミックヒータ等の低熱容量線状加熱体を、定着フィルムとして薄膜の低熱容量のものを用いることができるため、省電力化、ウェイトタイム短縮化（クイックスタート）が可能である。また、フィルム加熱方式の加熱定着装置は、定着フィルム駆動方法として定着フィルム内面に駆動ローラを設ける方法、また加圧ローラを駆動ローラとして用い加圧ローラとの摩擦力で定着フィルムを駆動する方法が知られているが、近年では部品点数が少なく低コストな構成である加圧ローラ駆動方式が多く用いられている。
【０００６】
以上のような定着装置を用いた電子写真式プリンタ等の画像形成装置は、近年画質の向上とともに、プリント速度の高速化が強く求められている。高速化の実現のため、メインモータの出力を大きくして加圧ローラや定着フィルム等の回転速度の高速化するとともに、高速化により定着ニップ部での滞留時間が短縮された記録材に充分な熱エネルギーを供給するため、定着温度アップ、定着ニップの拡大、ヒータ基板や定着フィルムの材質の熱伝導性アップ等の改良が必要である。
【０００７】
しかしながらこれら改良の実施により、定着部における弊害が生じやすくなる。一例として、図７のフィルム加熱方式の定着器の定着ニップ導入部の断面図に示すように、定着ニップ導入部の直前において、記録材Ｐ上のトナーＴが部分的に記録材搬送方向の上流側に吹き飛ばされるような現象（以下、後方トナー飛び散り現象）が発生し、プリント速度を高速にすればするほど、この現象は悪化する傾向にある。
【０００８】
この後方トナー飛び散り現象の発生メカニズムとしては、記録材Ｐに含まれる水分は定着ニップ部における加熱により水蒸気となるが、高速化に伴って定着温度をアップすると水蒸気の発生量も多くなり、逃げ場を求めた水蒸気が定着ニップの前後方向に強く吹き出るようになる。同時に記録材Ｐの搬送速度も速くなっているため、定着ニップ導入部において、記録材Ｐ上の未定着トナーＴには定着ニップから吹き出す水蒸気の速度に記録材Ｐの搬送速度を合成した風速で水蒸気が吹き付けられるため、記録材Ｐに対する付着力が弱く、水蒸気流の影響を受けやすいトナー像の一部が、水蒸気の風圧によって吹き飛ばされたと考えられる。この現象は記録材Ｐの電気抵抗や表面性等で大きく左右されるが、特に横線のように記録材の搬送方向に垂直なパターンのトナー像で最も発生しやすい。
【０００９】
この現象の抑制対策として、従来トナーＴの記録材Ｐに対する静電的な付着力をアップさせる方法が試みられている。一例として、フィルム加熱方式において、図５に示すように、表面から離型層−導電層−基材層から成る定着フィルム３１の導電層部に、バイアス電源４３につながる導電ブラシ等の給電手段４１からトナーＴと同極性のバイアスを所定量印加し、加圧ローラ３２表面の絶縁性離型層を挟んで、電界の作用により記録材Ｐ上のトナーＴを印字面側から反発電界によって押え込む方式が行なわれている。
【００１０】
さらに効果を高めるため、図６に示すように、定着ニップの記録材搬送方向の下流側に接地された導電ローラ等の除電手段４２を設けて、定着ニップ通過後の記録材Ｐの印字面の裏面に除電手段４２が接触するような構成をとり、前記方式と同様に定着フィルム３１にトナーＴと同極性のバイアスを所定量印加することで、記録材Ｐの抵抗を介して除電手段４２の接地部から印加したバイアスと逆極性の電荷を記録材Ｐの印字面の裏面に誘起させ、誘起した電荷で逆極性であるトナーＴを記録材Ｐに引き付け固定する方式が行われている。
【００１１】
【発明が解決しようとする課題】
プリント速度の高速化により、後方トナー飛び散り現象の抑制に必要な記録材に印加するバイアス量は増大する。また後方トナー飛び散り現象は、プリント速度の他に、未定着画像におけるトナーの摩擦電荷量（以下、トリボ量）や記録材の状態により大きな影響を受ける。具体的には、トナーカートリッジの新品状態では、現像装置内での撹拌や現像ブレードとの摺擦が不充分のためトナーのトリボ量は低く、記録材への保持力が弱くなるとともに、バイアス印加による記録材への静電的な押え込みの効果も弱くなってしまうため、後方トナー飛び散り現象を悪化させてしまう。
【００１２】
また、記録材の状態に大きな影響を与える、例えばプリントする周辺環境が高湿環境の場合、記録材は吸湿しやすく抵抗も低下するため、記録材へのトナーの保持力が弱くなるとともに、定着ニップで発生する水蒸気量が増加して、後方トナー飛び散り現象を悪化させてしまう。これら要因による後方トナー飛び散り現象を抑制するためには、記録材へのバイアス印加量をさらに増大して、電界作用を強くすることが必要である。
【００１３】
しかしながら、記録材の種類によりプラス極性の強い炭酸カルシウムを填量として含む記録材がある。従来方式でマイナス極性のトナーを用いる系の場合、マイナス極性の定着バイアスを印加して定着フィルム表面をマイナス電位に保持させているため、定着フィルム表面に炭酸カルシウムが付着する可能性がある。特に、定着バイアスとして強いマイナスバイアスを印加し、定着フィルムの表面電位を強いマイナス電位に保持すると付着は起こりやすい。その付着は、定着フィルムの離型性の低下や、静電的な吸着によるトナー付着を引き起こした後、そのトナーは加圧ローラ表面に転移、蓄積され、最終的に記録材の印字面裏面にトナー汚れとして排出され画像問題となってしまう可能性がある。
【００１４】
そこで本発明は、上記課題を解決するものであり、その目的とするところは、後方トナー飛び散り現象の抑制と、記録材の印字面裏面へのトナー汚れ防止を両立させ、プリント速度を高速化しても良好な画像を得られる定着装置を提供することにある。
【００１５】
【課題を解決するための手段】
上記課題を解決するため、
静電潜像が形成される像担持体と、帯電極性が負極性のトナーを収納しており前記像担持体にトナーを供給し前記静電潜像を現像する現像手段と、前記像担持体に形成されたトナー像を記録材上に転写する手段と、記録材上に担持された未定着トナー像と接触する回転体と、前記回転体の表面と圧接する加圧部材と、を備え、前記回転体と前記加圧部材の圧接ニップ部で未定着トナー像を担持する記録材を挟持搬送して未定着トナー像を記録材に加熱定着する加熱定着手段と、前記回転体に負極性の電圧を印加する印加手段と、前記電圧を制御する制御手段と、を有する画像形成装置において、
前記現像手段は前記画像形成装置の本体に対して着脱可能なトナーカートリッジとなっており、現在装着されている前記トナーカートリッジの新品状態からの使用量を記憶する記憶手段と、周辺環境の湿度を検知する湿度検知手段と、を有し、前記制御手段は、前記印加手段が印加する前記電圧の絶対値を、前記記憶手段が記憶する前記使用量が多いほど小さく、且つ前記湿度検知手段が検知した湿度が低いほど小さく設定することを特徴とするものである。
【００１６】
また本発明は、静電潜像が形成される像担持体と、帯電極性が負極性のトナーを収納しており前記像担持体にトナーを供給し前記静電潜像を現像する現像手段と、前記像担持体に形成されたトナー像を記録材上に転写する手段と、記録材上に担持された未定着トナー像と接触する回転体と、前記回転体の表面と圧接する加圧部材と、を備え、前記回転体と前記加圧部材の圧接ニップ部で未定着トナー像を担持する記録材を挟持搬送して未定着トナー像を記録材に加熱定着する加熱定着手段と、前記回転体に負極性の電圧を印加する印加手段と、前記電圧を制御する制御手段と、を有する画像形成装置において、
前記現像手段は前記画像形成装置の本体に対して着脱可能なトナーカートリッジとなっており、現在装着されている前記トナーカートリッジの新品状態からの使用量を記憶する記憶手段と、周辺環境の温度を検知する温度検知手段と、を有し、前記制御手段は、前記印加手段が印加する前記電圧の絶対値を、前記記憶手段が記憶する前記使用量が多いほど小さく、且つ前記温度検知手段が検知した温度が低いほど小さく設定することを特徴とするものである。
【００１７】
また本発明は、静電潜像が形成される像担持体と、帯電極性が負極性のトナーを収納しており前記像担持体にトナーを供給し前記静電潜像を現像する現像手段と、前記像担持体に形成されたトナー像を記録材上に転写する手段と、記録材上に担持された未定着トナー像と接触する回転体と、前記回転体の表面と圧接する加圧部材と、を備え、前記回転体と前記加圧部材の圧接ニップ部で未定着トナー像を担持する記録材を挟持搬送して未定着トナー像を記録材に加熱定着する加熱定着手段と、前記回転体に負極性の電圧を印加する印加手段と、前記電圧を制御する制御手段と、前記圧接ニップ部よりも記録材搬送方向の下流側で記録材の未定着トナー像担持面とは反対側の面に接触する導電部材と、を有し、記録材が前記回転体と前記導電部材の両方に接触している時に前記回転体に印加される負極性の電圧により記録材に電流が流れ記録材の未定着トナー像担持面とは反対側の面に正極性の電荷が誘起され未定着トナー像が記録材に引き付けられており、記録材の第１面にトナー像を形成し前記加熱定着手段により加熱定着した後に記録材の表裏を反転させて記録材の第２面にトナー像を形成し前記加熱定着手段により加熱定着することにより記録材の両面に画像を形成する機能を有する画像形成装置において、
前記現像手段は前記画像形成装置の本体に対して着脱可能なトナーカートリッジとなっており、現在装着されている前記トナーカートリッジの新品状態からの使用量を記憶する記憶手段を有し、前記制御手段は、前記印加手段が印加する前記電圧の絶対値を、前記記憶手段が記憶した前記使用量が多いほど小さく設定し、且つ前記第２面上に担持された未定着トナー像を加熱定着する場合は前記第１面上に担持された未定着トナー像を加熱定着する場合より大きく設定することを特徴とするものである。
【００１９】
【発明の実施の形態】
次に本発明の好適な実施例の説明として、まず実施例１について説明し、次に実施例２、３について説明する。
【００２０】
（実施例１）
（電子写真画像形成装置）
図１は、本発明の加熱定着装置３を有する電子写真画像形成装置１の断面図である。
【００２１】
図１において、像担持体たる感光ドラム２１は、ＯＰＣ、アモルファスシリコン等の感光材料をアルミニウムやニッケル等のシリンダ状の基板上に形成して構成されている。
【００２２】
まず初めに、感光ドラム２１の表面は帯電装置としての帯電ローラ２２によって一様に帯電される。次に、露光手段であるレーザービーム１１を画像情報に応じてＯＮ／ＯＦＦ制御し走査露光がなされ、感光ドラム２１上に静電潜像が形成される。この静電潜像は現像装置２３で現像され可視化される。現像方法としては、ジャンピング現像法、２成分現像法等が用いられ、イメージ露光と反転現像との組み合わせで用いられることが多い。
【００２３】
記録材Ｐはカセット１２から給紙ローラ１３によって取り出され、レジストローラ１４に送られる。記録材サイズは不図示のレジストセンサで行なっても良い。記録材Ｐはレジストローラ１４によって、感光ドラム２１表面に形成されたトナー像と同期を取り、感光ドラム２１と転写ローラ１５とで形成される転写ニップ部に供給される。転写ニップ部において、感光ドラム２１上のトナー像は不図示の電源による転写バイアスの作用で記録材Ｐに転写される。トナー像を保持した記録材Ｐは定着装置３へ搬送され、定着装置３のニップ部で加熱・加圧されてトナー像が記録材Ｐ上に定着され永久画像となり機外へ排出される。一方、転写後に感光ドラム２１上に残留する転写残留トナーは、クリーニング装置２４により感光ドラム２１表面より除去される。
【００２４】
（トナーカートリッジ）
現像装置２３を画像形成装置１本体から脱着可能に構成し、現像装置２３内にトナーＴを充填したトナーカートリッジ２方式を採用することで、消耗品であるトナーＴの補給を簡便化している。もちろん、現像装置２３に加えて、感光ドラム２１、帯電ローラ２２、クリーニング装置２４を一体化したプロセスカートリッジとしても構わない。
【００２５】
（加熱定着装置）
図２は、本発明の加熱定着装置の一例であるフィルム加熱方式の定着装置３の断面図である。
【００２６】
(1)定着フィルム
図２において、エンドレスベルト状の耐熱性フィルム（定着フィルム）３１は、可撓性を有し、半円弧状のフィルムガイド部材３５に対して周長に余裕を持たせた形（テンションが加わらない状態）で外嵌している。定着フィルム３１は、ポリイミド、ポリアミドイミド、ＰＥＥＫ、ＰＥＳ等の低熱容量の耐熱性樹脂フィルム表面に、導電性プライマー層を介して、ＰＴＦＥ、ＰＦＡ、ＦＥＰ等にカーボンブラック等の導電性部材を混入させた離型層をコーティングした複合層フィルムである。離型層は様々な画像不良を引き起こさないよう最適な抵抗値に設計されている。また、後述する定着バイアスを印加するため、前記導電性プライマー層は定着フィルム３１表面に一部露出している
定着フィルム３１は、ステンレス等の薄い金属製素管の表面に、プライマー層を介して、前記離型層をコーティングした金属スリーブでも良い。この場合、定着バイアスの印加のため、金属製素管が金属スリーブ表面に一部露出している。
【００２７】
(2)ヒータ
ヒータ３３は、セラミック基板上に発熱ペーストを印刷した発熱体、発熱体の保護と絶縁性を確保するためのガラスコーティング層を順次形成したものであり、ヒータ３３上の発熱体へ電力制御されたＡＣ電流を流すことにより発熱される。セラミック基板の材質としてはチッ化アルミニウムや酸化アルミニウム等を使用している。セラミック基板の裏にはサーミスタ３４を当接させてある。
【００２８】
(3)加圧ローラ
加圧部材としての加圧ローラ３２は、金属製の芯金上に、シリコンゴム等の耐熱性ゴムの弾性層、あるいは発泡スポンジ弾性層を挟んで、ＰＦＡ、ＰＴＦＥ、ＦＥＰ等のフッ素樹脂から成る絶縁性の離型層から構成される回転体である。弾性層は絶縁性の離型層表面のチャージアップを抑制するため、カーボンブラック等の導電性部材を混入させて導電化し、芯金を接地させた方が好ましい。
【００２９】
加圧ローラ３２は不図示のバネにより加熱部材（フィルム３１及びヒータ３３）に圧接され、不図示の駆動系により回転駆動し、記録材Ｐと定着フィルム３１は上記加圧ローラ３２によって従動回転して搬送される構成となっている。未定着のトナー像Ｔを担持した記録材Ｐは、定着装置３の加熱部材（フィルム３１及びヒータ３３）と加圧ローラ３２により形成された圧接ニップ（定着ニップ）部内で加熱・加圧され、記録材Ｐ上にトナー像Ｔは定着し、定着後の記録材Ｐは機外へ排出される。
【００３０】
加圧部材の形態としては、本実施例における加圧ローラ３２以外に、回動ベルト等の形態でも構わない。
【００３１】
(4)潤滑剤
定着ニップ部のヒータ３３の下表面、すなわちヒータ３３のガラスコーティング層と、定着フィルム３１の裏面（内周面）、すなわち記録材Ｐのトナー像Ｔと接する側とは反対側の面との間に潤滑剤を介在させて、定着ニップ部内における定着フィルム３１とヒータ３３間の摺動トルクを低く安定化し、定着フィルム３１と記録材Ｐ間のスリップを防止している。なお潤滑剤としては、フッ素系グリス（例えば、ＨＰ−３００ＧＲＥＡＳＥ（ダウコーニング社）や、ＤＥＭＮＵＭＧＲＥＡＳＥＬ−６５（ダイキン工業社））等の耐熱品を使用している。
【００３２】
(5)定着バイアス印加手段
バイアス電源４３から、導電ブラシ等の給電手段４１を介して、定着フィルム３１表面に一部露出している導電性プライマー層に、トナーＴ（ここではマイナス極性トナーを使用する）と同極性のマイナス極性の定着バイアスを印加する。定着バイアスの印加は、少なくとも記録材Ｐが定着ニップ部内を通過している間は行われる。またバイアスの印加量は、後述の制御手段４４により可変とする。
【００３３】
(6)トナーカートリッジの情報記憶手段
トナーカートリッジ２に関わる情報の記憶手段５１は、情報の読み出し及び書き込みは画像形成装置１との接点もしくは無線により行なう。情報としては、トナーＴのトリボ量と相関のあるトナーカートリッジ２の使用量を記憶させている。なお前記記憶手段５１は画像形成装置１のＣＰＵ内に設けても構わないが、トナーカートリッジ２交換等による記憶内容の整合性を保つため、トナーカートリッジ２に設けた方が好ましい。
【００３４】
(7)トナーカートリッジの使用量情報の記憶方法
トナーカートリッジ２の使用量情報として、ここでは記録材Ｐの通紙枚数について説明する。記録材Ｐの通紙枚数は、画像形成装置１につながるコンピュータからのジョブ信号をカウントして算出し、前記記憶手段５１に書き込みを行なう。なお通紙枚数は、排紙センサーのＯＮ／ＯＦＦ回数や、感光ドラム２１の回転数、現像装置２３へのバイアス通電時間等から算出しても良い。
【００３５】
(8)湿度検知手段
湿度検知手段５２は、画像形成装置１内の昇温を防ぐため熱源の定着装置３から遠い位置、そして周辺環境と雰囲気が近い、例えば吸気ファン付近に設けることが好ましい。
【００３６】
(9)定着バイアスの制御方法
制御手段４４は、記憶手段５１からトナーカートリッジ２の通紙枚数情報と、湿度検知手段５２から周辺湿度情報の読み出しを行ない、通紙枚数と周辺湿度に対応した最適定着バイアス量を算出し、定着フィルム３１へ印加する。
【００３７】
具体的には、トナーカートリッジは、初期状態では現像装置内でのトナーの撹拌や現像ブレードとの摺擦が不充分のためトナーのトリボ量は低いが、通紙枚数が増えるにしたがって、トリボは上昇していく。そして、記録材への保持力や、バイアス印加による記録材への静電的な押え込みの効果も、通紙枚数が増えるにしたがって増加していく。そのため、後方トナー飛び散り現象を抑制するのに必要な定着バイアスは、トナーカートリッジの通紙枚数が増えるにしたがって減少する。
【００３８】
周辺が高湿度環境の場合、記録材は吸湿しやすく抵抗も下がり、記録材へのトナーの保持力も弱くなるとともに、定着ニップで発生する水蒸気量が増加するため、後方トナー飛び散り現象を抑制するのに必要な定着バイアスは、低湿度環境の場合に比べて増加する。
【００３９】
印字面裏面へのトナー汚れの原因である定着フィルム表面への記録材の填量である炭酸カルシウムの付着は、記録材の吸湿状態によって差があり、記録材が吸湿している場合は、炭酸カルシウムの帯電量も小さいため定着フィルムへの付着も起こりにくいが、記録材が乾燥している場合は、炭酸カルシウムの帯電量も大きいため定着フィルムへの付着も起こりやすい。そのため低湿度環境の場合は、炭酸カルシウムの付着の抑制のため、高湿度環境に比べて定着バイアスを低減させた方が良い。
【００４０】
これらを踏まえ、本発明では寿命が１２，０００枚のトナーカートリッジでマイナス極性に帯電するトナーを使用した場合、表１に示す通紙枚数と周辺湿度に対応した定着バイアス量を印加する。
【００４１】
【表１】

【００４２】
もちろん表１に示す数値は一例にすぎず、トナーやトナーカートリッジ、そして定着装置の構成により通紙枚数及び周辺湿度のしきい値としきい値の数、そして定着バイアス量の数値は、適時変更される。
【００４３】
（従来例との比較実験）
本実施例における上記装置を用いた場合と、従来例のように定着バイアスとして定着フィルムに所定量（−４００Ｖ、−７００Ｖ、−１０００Ｖ）を印加し続ける場合とについて、各環境下（２３℃／１５％ＲＨ、２３℃／６０％ＲＨ、２３℃／８５％ＲＨ）において評価試験を行ない、後方トナー飛び散り現象レベルと、定着フィルムへの炭酸カルシウム付着を原因とする記録材Ｐの印字面裏面へのトナー汚れレベルを比較した。その結果を表２に示す。表中の○はＯＫレベル、△は実用上問題の無いレベル、×はＮＧレベルを示す。
【００４４】
なお後方トナー飛び散り現象は、各環境下で２４時間以上放置された普通紙に、紙の搬送方向と直交する向きに線を並べたパターンを印字して評価を行なった。また記録材Ｐの印字面裏面へのトナー汚れは、各環境下で炭酸カルシウムを含有する紙に、文字パターンを２枚／１０分の間欠でカートリッジの使用状態に合わせた所定枚数（１，０００枚、４，０００枚、７，０００枚）を通紙して評価を行なった。
【００４５】
【表２】

【００４６】
表２に示すように、本実施例と従来例１、２、３の間に、後方トナー飛び散り現象レベルと、印字面裏面へのトナー汚れレベルに差がみられた。すなわち、トナーカートリッジの通紙枚数と周辺湿度に対応した最適定着バイアス量を印加するよう制御させることにより、トナーのトリボ変化と周辺湿度による記録材の抵抗変化があっても、常に適度な電界作用を維持できるため、後方トナー飛び散り現象の抑制と、記録材Ｐの印字面裏面へのトナー汚れ防止を両立させることが可能となったのである。
【００４７】
本実施例ではフィルム加熱方式を定着装置の一例として説明を行なっているが、熱ローラ定着方式を用いても同等の効果が得られることは言うまでもない。
【００４８】
（定着バイアス印加方法の他例）
本実施例では、一例として定着フィルムにトナーと同極性の定着バイアスを印加する方式について説明してきたが、他例として、加圧ローラにトナーと逆極性の定着バイアスを印加方式、定着ニップ近傍に設けられた電極にトナーと逆極性の定着バイアスを印加方式、またはこれらを混合させた方式等がある。そして上述した図６のように、定着バイアスの印加とともに、定着ニップの記録材搬送方向の下流側に接地された導電ローラ等の除電手段を設け、記録材の印字面の裏面にトナーと逆極性の電荷を誘起させる方式もある。少なくとも記録材が定着ニップ部内を通過している間、定着バイアスを記録材に印加できる方式ならば定着バイアス印加方式の限定は無い。
【００４９】
（実施例２）
次に実施例２として、定着バイアス量制御の他例を図３に示す。本実施例では、トナーカートリッジの通紙枚数と、プリントする画像形成装置１の周辺温度の情報とから、最適定着バイアス量を算出している。なお、上述した実施例１と同一箇所の説明は省略する。
【００５０】
(10)温度検知手段
温度検知手段５３は、画像形成装置１内の昇温を防ぐため熱源の定着装置３から遠い位置、そして周辺環境と雰囲気が近い、例えば吸気ファン付近に設けることが好ましい。
【００５１】
(11)定着バイアスの制御方法
制御手段は、記憶手段からトナーカートリッジの通紙枚数情報と、温度検知手段５３から周辺温度情報の読み出しを行ない、通紙枚数と周辺温度に対応した最適定着バイアス量を算出し、定着フィルムへ印加する。
【００５２】
具体的には、トナーカートリッジは、実施例１で述べたように、通紙枚数によりトナーのトリボが変化するため、後方トナー飛び散り現象を抑制するのに必要な定着バイアスは、トナーカートリッジの通紙枚数が増えるにしたがって減少する。
【００５３】
周辺が高温環境の場合、記録材の温度も高く、定着ニップ内における記録材の温度上昇も高くなるため、定着ニップで発生する水蒸気量が増加し、後方トナー飛び散り現象を抑制するのに必要な定着バイアスは、低温環境の場合に比べて増加する。
【００５４】
印字面裏面へのトナー汚れは、炭酸カルシウムの付着により離型性の低下した定着フィルム表面にトナーが付着し、そのトナーが加圧ローラに転移、蓄積されて発生しているのだが、周辺が高温環境の場合、加圧ローラの温度も高く、定着ニップ内における加圧ローラ表面の温度上昇も高くなるため、定着フィルムから転移したトナーを加圧ローラ表面に蓄積させずに、定着ニップ内で記録材の印字面裏面に問題の無いレベルでトナーを少しずつ排出することができる。そのため高温環境の場合は、加圧ローラ表面でトナーを蓄積させやすい低温環境よりも印字面裏面へのトナー汚れにマージンがあるため、定着バイアスを増加することができる。
【００５５】
これらを踏まえ、実施例１と同様に、表３に示すような通紙枚数と周辺温度に対応した定着バイアス量を印加する。
【００５６】
【表３】

【００５７】
もちろん表３に示す数値は一例にすぎず、トナーやトナーカートリッジ、そして定着装置の構成により通紙枚数及び周辺温度のしきい値としきい値の数、そして定着バイアス量の数値は、適時変更される。
【００５８】
（従来例との比較実験）
本実施例における上記装置を用いた場合と、従来例のように定着バイアスとして定着フィルムに所定量（−４００Ｖ、−６００Ｖ、−９００Ｖ）を印加し続ける場合とについて、各環境下（１５℃／６０％ＲＨ、２３℃／６０％ＲＨ、３０℃／６０％ＲＨ）において評価試験を行ない、後方トナー飛び散り現象レベルと、定着フィルムへの炭酸カルシウム付着を原因とする記録材Ｐの印字面裏面へのトナー汚れレベルを比較した。その結果を表４に示す。表中の○はＯＫレベル、△は実用上問題の無いレベル、×はＮＧレベルを示す。
【００５９】
なお後方トナー飛び散り現象は、各環境下で２４時間以上放置された普通紙に、紙の搬送方向と直交する向きに線を並べたパターンを印字して評価を行なった。また記録材Ｐの印字面裏面へのトナー汚れは、各環境下で炭酸カルシウムを含有する紙に、文字パターンを２枚／１０分の間欠でカートリッジの使用状態に合わせた所定枚数（１，０００枚、４，０００枚、７，０００枚）を通紙して評価を行なった。
【００６０】
【表４】

【００６１】
表４に示すように、本実施例と従来例４、５、６の間に、後方トナー飛び散り現象レベルと、印字面裏面へのトナー汚れレベルに差がみられた。すなわち、トナーカートリッジの通紙枚数と周辺温度に対応した最適定着バイアス量を印加するよう制御させることにより、トナーのトリボ変化と周辺温度による加圧ローラ表面へのトナーの蓄積しやすさの違いがあっても、常に適度な電界作用を維持できるため、後方トナー飛び散り現象の抑制と、記録材Ｐの印字面裏面へのトナー汚れ防止を両立させることが可能となったのである。
【００６２】
（定着バイアス制御の他例）
本実施例と実施例１では、トナーカートリッジの通紙枚数と、記録材の状態に大きな影響を与える情報として周辺湿度あるいは周辺温度と、による定着バイアス量制御を説明してきたが、もちろん記録材の状態に大きな影響を与える情報として周辺湿度と周辺温度のマトリックスを採用しても構わない。
【００６３】
（実施例３）
次に実施例３として、定着バイアス量制御の他例を図４に示す。本実施例では、トナーカートリッジの通紙枚数と、記録材の印字面情報とから、最適定着バイアス量を算出している。なお、上述した実施例１、２と同一箇所の説明は省略する。
【００６４】
(12)除電手段
本実施例では、後方トナー飛び散り現象の抑制効果を高めるため、定着ニップの記録材搬送方向の下流側に接地された導電ローラ等の除電手段４２を設けて、定着ニップ通過後の記録材Ｐの印字面の裏面に除電手段４２が接触するような構成をとり、定着フィルム３１にトナーＴ（ここではマイナス極性トナーを使用する）と同極性のマイナスバイアスを所定量印加することで、記録材Ｐの抵抗を介して除電手段４２の接地部から印加したマイナスバイアスと逆極性のプラス電荷を記録材Ｐの印字面の裏面に誘起させ、誘起したプラス電荷で逆極性であるトナーＴを記録材Ｐに引き付け固定させている。
【００６５】
除電手段４２の形態としては、導電性を有していればブラシやガイド等の形態でも構わない。
【００６６】
(13)記録材の印字面検知手段
記録材の印字面検知手段５４は、画像形成装置１のＣＰＵ内に設ける。
【００６７】
(14)定着バイアスの制御方法
制御手段４４は、トナーカートリッジ２の記憶手段５１からトナーカートリッジの通紙枚数情報と、印字面検知手段５４から印字面情報の読み出しを行ない、通紙枚数と印字面に対応した最適定着バイアス量を算出し、定着フィルム３１へ印加する。
【００６８】
具体的には、トナーカートリッジは、実施例１で述べたように、通紙枚数によりトナーのトリボが変化するため、後方トナー飛び散り現象を抑制するのに必要な定着バイアスは、トナーカートリッジの通紙枚数が増えるにしたがって減少する。
【００６９】
記録材がプリンター本体に両面機を使用した自動両面における２面めの場合、１面めに比べて一度定着器を通過しているため、含水率が低下し、記録材としての抵抗は上昇している。そのため、定着バイアスの印加により、除電手段の接地部から記録材の印字面の裏面に誘起されトナーを記録材に保持する電荷の量が減少し、後方トナー飛び散り現象を抑制するのに必要な定着バイアスは増加する。
【００７０】
印字面裏面へのトナー汚れの原因である定着フィルム表面への記録材の填量である炭酸カルシウムの付着は、記録材の２面めの方が１面めに比べて乾燥しているため、炭酸カルシウムの帯電量も大きく定着フィルムへの付着も起こりやすいが、１面めに比べて２面めの方が加圧ローラ及び記録材の温度が高いため、定着ニップ内で記録材の印字面裏面に問題の無いレベルでトナーを少しずつ排出することができる。そのため、印字面裏面へのトナー汚れは、１面めよりも２面めの方がマージンがあり、定着バイアスを増加することができる。これらを踏まえ、実施例１と同様に、一例として表５に示すような通紙枚数と印字面に対応した定着バイアス量を印加する。
【００７１】
【表５】

【００７２】
（従来例との比較実験）
本実施例における上記装置を用いた場合と、従来例のように定着バイアスとして定着フィルムに所定量（−５００Ｖ、−７００Ｖ、−１０００Ｖ）を印加し続ける場合とについて、各印字モード（片面印字、両面機を用いた自動両面印字）において評価試験（２３℃／６０％ＲＨ環境下）を行ない、後方トナー飛び散り現象レベルと、定着フィルムへの炭酸カルシウム付着を原因とする記録材Ｐの印字面裏面へのトナー汚れレベルを比較した。その結果を表６に示す。表中の○はＯＫレベル、△は実用上問題の無いレベル、×はＮＧレベルを示す。
【００７３】
なお後方トナー飛び散り現象は、２３℃／６０％ＲＨの環境下で２４時間以上放置された普通紙に、紙の搬送方向と直交する向きに線を並べたパターンを印字して評価を行なった。また記録材Ｐの印字面裏面へのトナー汚れは、１５℃／１０％ＲＨの環境下で炭酸カルシウムを含有する紙に、文字パターンを２枚／１０分の間欠でカートリッジの使用状態に合わせた所定枚数（１，０００枚、４，０００枚、７，０００枚）を通紙して評価を行なった。
【００７４】
【表６】

【００７５】
表６に示すように、本実施例と従来例７、８、９の間に、後方トナー飛び散り現象レベルと、印字面裏面へのトナー汚れレベルに差がみられた。すなわち、トナーカートリッジの通紙枚数と印字面に対応した最適定着バイアス量を印加するよう制御させることにより、トナーのトリボ変化と印字面による記録材の抵抗変化があっても、常に適度な電界作用を維持できるため、後方トナー飛び散り現象の抑制と、記録材Ｐの印字面裏面へのトナー汚れ防止を両立させることが可能となったのである。
【００７６】
（定着バイアス制御の他例）
本実施例と実施例１及び２では、トナーカートリッジの通紙枚数と、記録材の状態に大きな影響を与える情報（周辺湿度、周辺温度、印字面）の内の一つの情報と、による定着バイアス量制御を説明してきたが、もちろん記録材の状態に大きな影響を与える情報として、これら複数の情報のマトリックスを採用しても構わない。次にその一例として、周辺湿度と印字面情報のマトリックスを採用した場合を説明する。
【００７７】
記録材の印字面が１面めの場合は、周辺湿度によって記録材の吸湿具合が異なるため、実施例１の表１に示すトナーカートリッジの通紙枚数と周辺湿度に対応した定着バイアス量の印加が適正な制御となる。一方プリンター本体に両面機を使用した自動両面における２面め場合は、１面定着時の定着器の通過により記録材の状態は均一化されるとともに、１面定着から２面印字までの時間も短く、周辺環境による記録材への影響もほとんど無視できるため、周辺湿度に関わらず本実施例の表５に示すトナーカートリッジの通紙枚数と印字面２面めに対応した定着バイアス量の印加が適正な制御となる。
【００７８】
これらのことから、一例として表７に示すような通紙枚数と周辺湿度、そして印字面に対応した定着バイアス量を印加するよう制御させることにより、トナーのトリボ変化と周辺湿度による記録材の抵抗変化、そして印字面による記録材の抵抗変化があっても、常に適度な電界作用を維持できるため、後方トナー飛び散り現象の抑制と、記録材Ｐの印字面裏面へのトナー汚れ防止を両立させることが可能となる。
【００７９】
【表７】

【００８０】
【発明の効果】
本発明は前述したように、トナーカートリッジの新品状態からの使用量と、記録材の状態に影響を与える情報から記録材へ印加するバイアス量を制御し、常に適度な電界作用を維持できるため、後方トナー飛び散り現象の抑制と、記録材の印字面裏面へのトナー汚れ防止を両立が可能となり、プリント速度を高速化しても良好な画像を得ることができる。
【図面の簡単な説明】
【図１】本発明の第１実施例に示す電子写真画像形成装置の断面図である。
【図２】本発明の第１実施例に示す加熱定着装置の断面図である。
【図３】本発明の第２実施例に示す加熱定着装置の断面図である。
【図４】本発明の第３実施例に示す加熱定着装置の断面図である。
【図５】従来例の断面図である。
【図６】従来例の断面図である。
【図７】従来例の断面図である。
【符号の説明】
１・・・電子写真画像形成装置
１１・・・レーザービーム
１２・・・カセット
１３・・・給紙ローラ
１４・・・レジストローラ
１５・・・転写ローラ
２・・・トナーカートリッジ
２１・・・感光ドラム
２２・・・帯電ローラ
２３・・・現像装置
２４・・・クリーニング装置
３・・・定着装置
３１・・・定着フィルム
３２・・・加圧ローラ
３３・・・ヒータ
３４・・・サーミスタ
３５・・・フィルムガイド
４１・・・給電手段
４２・・・除電手段
４３・・・バイアス電源
４４・・・バイアス制御手段
５１・・・トナーカートリッジの情報記憶手段
５２・・・湿度検知手段
５３・・・温度検知手段
５４・・・印字面検知手段[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an image forming apparatus such as an electrophotographic printer, a copying machine, and an electrostatic recording apparatus, and a fixing device used in the image forming apparatus for fixing toner or the like on a recording material.
[0002]
[Prior art]
Conventionally, many electrophotographic copying machines, printers, and the like employ a contact heating type heat roller fixing method and an energy saving type film heating method, which have good thermal efficiency and safety, as a heat fixing means.
[0003]
A heat roller fixing type heat fixing apparatus includes a heating roller (hereinafter referred to as a fixing roller) as a heating rotating body including a halogen heater therein, and an elastic pressure roller (hereinafter referred to as a pressing rotating body) pressed against the heating roller. , A pressure roller). The pair of rollers is rotated, and a recording material (transfer material sheet / electrostatic sheet) as a heated material that forms and supports an unfixed image (hereinafter, toner image) in a fixing nip portion that is a pressure nip portion of the pair of rollers. Introducing recording material, electrofax paper, printing paper, etc.), and nipping and conveying the toner image as a permanently fixed image on the recording material surface by heat from the fixing roller and pressure applied to the fixing nip. Is.
[0004]
On the other hand, film heating type heat fixing devices have been proposed in, for example, Japanese Patent Application Laid-Open No. 63-313182, Japanese Patent Application Laid-Open No. 2-157878, Japanese Patent Application Laid-Open No. 4-44075 to 44083, Japanese Patent Application Laid-Open No. As described above, a heat-resistant film (hereinafter referred to as a fixing film), which is a rotating body for heating, is closely attached to a heating body such as a ceramic heater or the like by a pressure rotating body (hereinafter referred to as a pressure roller), and is slid and rotated. Then, a recording material carrying a toner image is introduced into a fixing nip portion, which is a pressure nip portion formed by a heating body and a pressure roller with a fixing film interposed therebetween, and is conveyed together with the fixing film to be fixed. The toner image is fixed on the recording material surface as a permanently fixed image by heat and pressure by heat from a heating member applied through a film and pressure applied to the fixing nip portion.
[0005]
A film heating type heat fixing device can use a low heat capacity linear heating element such as a ceramic heater as a heating element, and a thin film having a low heat capacity as a fixing film, thereby reducing power consumption and shortening the wait time. Start) is possible. In addition, the film heating type heat fixing device includes a method of providing a driving roller on the inner surface of the fixing film as a fixing film driving method, and a method of driving the fixing film by a frictional force with the pressure roller using the pressure roller as a driving roller. As is known, in recent years, a pressure roller driving system having a low number of parts and a low cost has been widely used.
[0006]
In recent years, an image forming apparatus such as an electrophotographic printer using the fixing device as described above has been strongly demanded to improve the image quality and increase the printing speed. In order to achieve high speed, the output of the main motor is increased to increase the rotation speed of the pressure roller, fixing film, etc., and the high speed is sufficient for recording materials whose residence time at the fixing nip is shortened. In order to supply thermal energy, it is necessary to improve the fixing temperature, enlarge the fixing nip, and increase the thermal conductivity of the heater substrate and the fixing film.
[0007]
However, the implementation of these improvements tends to cause adverse effects in the fixing unit. As an example, as shown in the sectional view of the fixing nip introducing portion of the film heating type fixing device in FIG. 7, the toner T on the recording material P is partially upstream in the recording material conveying direction immediately before the fixing nip introducing portion. This phenomenon tends to get worse as the printing speed is increased.
[0008]
As a mechanism of the occurrence of the rear toner scattering phenomenon, the water contained in the recording material P becomes water vapor by heating in the fixing nip portion. However, when the fixing temperature is increased as the speed increases, the amount of water vapor generated increases, and the escape place is avoided. The obtained water vapor is strongly blown out in the front-rear direction of the fixing nip. At the same time, since the conveyance speed of the recording material P is increased, the unfixed toner T on the recording material P in the fixing nip introducing portion is a wind speed obtained by combining the conveyance speed of the recording material P with the speed of water vapor blown from the fixing nip. Since water vapor is blown, it is considered that a part of the toner image that is weak in adhesion to the recording material P and easily affected by the water vapor flow was blown off by the wind pressure of the water vapor. This phenomenon is greatly affected by the electrical resistance, surface properties, etc. of the recording material P, but is most likely to occur particularly in a toner image having a pattern perpendicular to the conveying direction of the recording material, such as a horizontal line.
[0009]
As a countermeasure for suppressing this phenomenon, a method of increasing the electrostatic adhesion force of the toner T to the recording material P has been attempted. As an example, in the film heating method, as shown in FIG. 5, the power supply means 41 such as a conductive brush connected to the bias power source 43 is provided on the conductive layer portion of the fixing film 31 composed of the release layer-conductive layer-base material layer from the surface. A predetermined amount of bias having the same polarity as that of the toner T is applied, and the insulating release layer on the surface of the pressure roller 32 is sandwiched, and the toner T on the recording material P is pressed from the printing surface side by a repulsive electric field by the action of an electric field. The scheme has been carried out.
[0010]
In order to further enhance the effect, as shown in FIG. 6, a discharging means 42 such as a conductive roller, which is grounded, is provided on the downstream side of the fixing nip in the recording material conveyance direction so that the printing surface of the recording material P after passing through the fixing nip The structure is such that the charge eliminating means 42 contacts the back surface, and a predetermined amount of bias having the same polarity as that of the toner T is applied to the fixing film 31 in the same manner as in the above-described method. There is a method in which a charge having a reverse polarity to the bias applied from the grounding portion is induced on the back surface of the printing surface of the recording material P, and the toner T having a reverse polarity is attracted and fixed to the recording material P by the induced charge.
[0011]
[Problems to be solved by the invention]
As the printing speed increases, the amount of bias applied to the recording material necessary to suppress the rear toner scattering phenomenon increases. The rear toner scattering phenomenon is greatly influenced by the amount of triboelectric charge (hereinafter referred to as tribo amount) of the toner in the unfixed image and the state of the recording material in addition to the printing speed. Specifically, when the toner cartridge is new, the amount of toner tribo is low due to insufficient stirring and rubbing with the developing blade in the developing device, the holding force to the recording material becomes weak, and bias is applied. As a result, the effect of electrostatic pressing on the recording material due to the toner becomes weak, and the rear toner scattering phenomenon is worsened.
[0012]
In addition, when the surrounding environment for printing has a high humidity environment, for example, the recording material has a great influence on the state of the recording material. The amount of water vapor generated at the nip increases, and the rear toner scattering phenomenon is exacerbated. In order to suppress the back toner scattering phenomenon due to these factors, it is necessary to further increase the amount of bias applied to the recording material to strengthen the electric field effect.
[0013]
However, there is a recording material containing calcium carbonate having a strong positive polarity as a filling amount depending on the type of the recording material. In the case of a system using negative polarity toner in the conventional method, since the fixing film surface is held at a negative potential by applying a negative polarity fixing bias, calcium carbonate may adhere to the fixing film surface. In particular, adhesion is likely to occur when a strong negative bias is applied as the fixing bias and the surface potential of the fixing film is maintained at a strong negative potential. The adhesion causes deterioration of the releasability of the fixing film and adhesion of toner due to electrostatic adsorption, and then the toner is transferred and accumulated on the surface of the pressure roller, and finally on the back side of the printing surface of the recording material. There is a possibility of being discharged as toner stains and causing an image problem.
[0014]
Therefore, the present invention solves the above-described problems, and the object of the present invention is to achieve both the suppression of the back toner scattering phenomenon and the prevention of toner smearing on the back side of the printing surface of the recording material, and increase the printing speed. Another object of the present invention is to provide a fixing device capable of obtaining a good image.
[0015]
[Means for Solving the Problems]
  To solve the above problem,
  An image carrier on which an electrostatic latent image is formed; a developing unit that stores toner having a negative charge polarity and supplies the toner to the image carrier to develop the electrostatic latent image; and the image carrier Means for transferring the toner image formed on the recording material, a rotating body that contacts an unfixed toner image carried on the recording material, and a pressure member that presses the surface of the rotating body, A heating and fixing unit that sandwiches and conveys a recording material carrying an unfixed toner image at a pressure nip portion between the rotating body and the pressure member and heat-fixes the unfixed toner image on the recording material, and a negative polarity on the rotating body. In an image forming apparatus comprising: an application unit that applies a voltage; and a control unit that controls the voltage.
  The developing unit is a toner cartridge that can be attached to and detached from the main body of the image forming apparatus, and a storage unit that stores a used amount of the toner cartridge that is currently installed from a new state, and a humidity of the surrounding environment. A humidity detecting means for detecting, wherein the control means detects the absolute value of the voltage applied by the applying means as the amount of use stored in the storage means decreases, and the humidity detecting means detects the absolute value of the voltage. Set smaller as the humidity is lowerIt is characterized by this.
[0016]
  The present invention also providesAn image carrier on which an electrostatic latent image is formed; a developing unit that stores toner having a negative charge polarity and supplies the toner to the image carrier to develop the electrostatic latent image; and the image carrier Means for transferring the toner image formed on the recording material, a rotating body that contacts an unfixed toner image carried on the recording material, and a pressure member that presses the surface of the rotating body, A heating and fixing unit that sandwiches and conveys a recording material carrying an unfixed toner image at a pressure nip portion between the rotating body and the pressure member and heat-fixes the unfixed toner image on the recording material, and a negative polarity on the rotating body. In an image forming apparatus comprising: an application unit that applies a voltage; and a control unit that controls the voltage.
  The developing unit is a toner cartridge that can be attached to and detached from the main body of the image forming apparatus, and a storage unit that stores a used amount of the toner cartridge that is currently installed from a new state, and a temperature of the surrounding environment Temperature detecting means for detecting, and the control means detects the absolute value of the voltage applied by the applying means as the amount of use stored in the storage means decreases and the temperature detecting means detects Set smaller as the temperature is lowerIt is characterized by this.
[0017]
  The present invention also providesAn image carrier on which an electrostatic latent image is formed; a developing unit that stores toner having a negative charge polarity and supplies the toner to the image carrier to develop the electrostatic latent image; and the image carrier Means for transferring the toner image formed on the recording material, a rotating body that contacts an unfixed toner image carried on the recording material, and a pressure member that presses the surface of the rotating body, A heating and fixing unit that sandwiches and conveys a recording material carrying an unfixed toner image at a pressure nip portion between the rotating body and the pressure member and heat-fixes the unfixed toner image on the recording material, and a negative polarity on the rotating body. An application unit that applies a voltage, a control unit that controls the voltage, and a conductive material that is in contact with a surface opposite to the unfixed toner image carrying surface of the recording material on the downstream side of the pressing nip portion in the recording material conveyance direction. And the recording material is in contact with both the rotating body and the conductive member. When a negative voltage is applied to the rotator, a current flows through the recording material, and a positive charge is induced on the surface of the recording material opposite to the unfixed toner image carrying surface, thereby recording an unfixed toner image. The toner image is formed on the first surface of the recording material, and is heated and fixed by the heating and fixing means. Then, the recording material is turned upside down to form a toner image on the second surface of the recording material, and the heating is performed. In an image forming apparatus having a function of forming images on both sides of a recording material by heat fixing with a fixing unit,
  The developing means is a toner cartridge that can be attached to and detached from the main body of the image forming apparatus, and has a storage means for storing a used amount of the currently installed toner cartridge from a new state, and the control means In the case where the absolute value of the voltage applied by the applying unit is set to be smaller as the usage amount stored by the storage unit is larger, and the unfixed toner image carried on the second surface is heated and fixed. Is set larger than the case where the unfixed toner image carried on the first surface is fixed by heating.It is characterized by this.
[0019]
DETAILED DESCRIPTION OF THE INVENTION
Next, as a description of a preferred embodiment of the present invention, Example 1 will be described first, and then Examples 2 and 3 will be described.
[0020]
Example 1
(Electrophotographic image forming apparatus)
FIG. 1 is a cross-sectional view of an electrophotographic image forming apparatus 1 having a heat fixing device 3 of the present invention.
[0021]
In FIG. 1, a photosensitive drum 21 as an image carrier is configured by forming a photosensitive material such as OPC or amorphous silicon on a cylindrical substrate such as aluminum or nickel.
[0022]
First, the surface of the photosensitive drum 21 is uniformly charged by a charging roller 22 as a charging device. Next, the laser beam 11 serving as an exposure unit is controlled to be turned on / off in accordance with image information to perform scanning exposure, and an electrostatic latent image is formed on the photosensitive drum 21. This electrostatic latent image is developed and visualized by the developing device 23. As a development method, a jumping development method, a two-component development method, or the like is used, and is often used in combination with image exposure and reversal development.
[0023]
The recording material P is taken out from the cassette 12 by the paper feed roller 13 and sent to the registration roller 14. The recording material size may be measured by a resist sensor (not shown). The recording material P is synchronized with the toner image formed on the surface of the photosensitive drum 21 by the registration roller 14 and is supplied to a transfer nip portion formed by the photosensitive drum 21 and the transfer roller 15. In the transfer nip portion, the toner image on the photosensitive drum 21 is transferred to the recording material P by the action of a transfer bias by a power source (not shown). The recording material P holding the toner image is conveyed to the fixing device 3, heated and pressurized at the nip portion of the fixing device 3, and the toner image is fixed on the recording material P to become a permanent image and discharged outside the apparatus. On the other hand, the transfer residual toner remaining on the photosensitive drum 21 after the transfer is removed from the surface of the photosensitive drum 21 by the cleaning device 24.
[0024]
(Toner cartridge)
The developing device 23 is configured to be detachable from the main body of the image forming apparatus 1 and adopts a toner cartridge 2 system in which the developing device 23 is filled with the toner T, thereby simplifying the supply of toner T, which is a consumable item. Of course, in addition to the developing device 23, the photosensitive drum 21, the charging roller 22, and the cleaning device 24 may be integrated into a process cartridge.
[0025]
(Heat fixing device)
FIG. 2 is a cross-sectional view of a film heating type fixing device 3 which is an example of the heat fixing device of the present invention.
[0026]
(1) Fixing film
In FIG. 2, an endless belt-like heat-resistant film (fixing film) 31 is flexible and has a shape with a margin in the circumferential length with respect to the semicircular arc-shaped film guide member 35 (no tension is applied). State). The fixing film 31 is made by mixing a conductive member such as carbon black into PTFE, PFA, FEP or the like via a conductive primer layer on the surface of a low heat capacity heat resistant resin film such as polyimide, polyamideimide, PEEK, PES or the like. A composite layer film coated with a release layer. The release layer is designed to have an optimum resistance value so as not to cause various image defects. Further, in order to apply a fixing bias described later, the conductive primer layer is partially exposed on the surface of the fixing film 31.
The fixing film 31 may be a metal sleeve in which the release layer is coated on the surface of a thin metal base tube such as stainless steel via a primer layer. In this case, the metal base tube is partially exposed on the surface of the metal sleeve for applying the fixing bias.
[0027]
(2) Heater
The heater 33 is formed by sequentially forming a heating element on which a heating paste is printed on a ceramic substrate and a glass coating layer for ensuring the protection and insulation of the heating element, and power is controlled to the heating element on the heater 33. Heat is generated by passing an AC current. As a material of the ceramic substrate, aluminum nitride, aluminum oxide or the like is used. A thermistor 34 is in contact with the back of the ceramic substrate.
[0028]
(3) Pressure roller
The pressure roller 32 as a pressure member is made of a fluororesin such as PFA, PTFE, FEP, etc., sandwiching an elastic layer of heat-resistant rubber such as silicon rubber or a foamed sponge elastic layer on a metal core. It is a rotating body composed of an insulating release layer. In order to suppress the charge-up on the surface of the insulating release layer, the elastic layer is preferably made conductive by mixing a conductive member such as carbon black and the cored bar is grounded.
[0029]
The pressure roller 32 is pressed against a heating member (film 31 and heater 33) by a spring (not shown) and is rotationally driven by a drive system (not shown). The recording material P and the fixing film 31 are driven to rotate by the pressure roller 32. It is configured to be conveyed. The recording material P carrying the unfixed toner image T is heated and pressurized in a pressure nip (fixing nip) portion formed by the heating member (film 31 and heater 33) and the pressure roller 32 of the fixing device 3, The toner image T is fixed on the recording material P, and the recording material P after fixing is discharged out of the apparatus.
[0030]
As a form of the pressure member, in addition to the pressure roller 32 in the present embodiment, a form such as a rotating belt may be used.
[0031]
(4) Lubricant
Between the lower surface of the heater 33 in the fixing nip, that is, the glass coating layer of the heater 33, and the back surface (inner peripheral surface) of the fixing film 31, that is, the surface opposite to the side in contact with the toner image T of the recording material P. In the fixing nip, the sliding torque between the fixing film 31 and the heater 33 is stabilized to be low, and slip between the fixing film 31 and the recording material P is prevented. As the lubricant, heat-resistant products such as fluorine-based grease (for example, HP-300 GREASE (Dow Corning) or DENNUM GREASE L-65 (Daikin Industries)) are used.
[0032]
(5) Fixing bias application means
A negative polarity having the same polarity as that of the toner T (here, negative polarity toner is used) is applied from the bias power source 43 to the conductive primer layer partially exposed on the surface of the fixing film 31 through the power supply means 41 such as a conductive brush. A polar fixing bias is applied. The fixing bias is applied at least while the recording material P passes through the fixing nip portion. The amount of bias applied is variable by the control means 44 described later.
[0033]
(6) Toner cartridge information storage means
The information storage unit 51 related to the toner cartridge 2 reads and writes information by contact with the image forming apparatus 1 or wirelessly. As information, the usage amount of the toner cartridge 2 correlated with the tribo amount of the toner T is stored. The storage unit 51 may be provided in the CPU of the image forming apparatus 1, but it is preferable that the storage unit 51 is provided in the toner cartridge 2 in order to maintain consistency of stored contents when the toner cartridge 2 is replaced.
[0034]
(7) Toner cartridge usage information storage method
Here, as the usage amount information of the toner cartridge 2, the number of sheets of the recording material P will be described. The number of sheets of recording material P is calculated by counting job signals from a computer connected to the image forming apparatus 1 and writing to the storage means 51. Note that the number of sheets to be passed may be calculated from the number of times the sheet discharge sensor is turned ON / OFF, the number of rotations of the photosensitive drum 21, the bias energization time to the developing device 23, and the like.
[0035]
(8) Humidity detection means
The humidity detecting means 52 is preferably provided at a position far from the fixing device 3 of the heat source and near the ambient environment, for example, in the vicinity of the intake fan, in order to prevent temperature rise in the image forming apparatus 1.
[0036]
(9) Fixing bias control method
The control unit 44 reads out the number of passing sheets of the toner cartridge 2 from the storage unit 51 and the surrounding humidity information from the humidity detecting unit 52, calculates the optimum fixing bias amount corresponding to the number of passing sheets and the surrounding humidity, and fixes it. Apply to film 31.
[0037]
Specifically, in the initial state, the toner cartridge is low in the initial state due to insufficient stirring of the toner in the developing device and sliding friction with the developing blade. However, as the number of sheets passed increases, It rises. The holding force on the recording material and the effect of electrostatic pressing on the recording material by applying a bias also increase as the number of sheets passed increases. For this reason, the fixing bias necessary for suppressing the rear toner scattering phenomenon decreases as the number of sheets passing through the toner cartridge increases.
[0038]
When the surroundings are in a high humidity environment, the recording material is easy to absorb moisture, the resistance is lowered, the toner holding force to the recording material is weakened, and the amount of water vapor generated in the fixing nip is increased, which suppresses the phenomenon of toner scattering from the rear. The fixing bias necessary for the increase is higher than that in a low humidity environment.
[0039]
The adhesion of calcium carbonate, which is the filling amount of the recording material, to the fixing film surface, which causes toner stains on the back side of the print surface, varies depending on the moisture absorption state of the recording material. Although the calcium charge amount is small, adhesion to the fixing film is unlikely to occur. However, when the recording material is dry, the calcium carbonate charge amount is large, and adhesion to the fixing film is likely to occur. Therefore, in a low humidity environment, it is better to reduce the fixing bias than in a high humidity environment in order to suppress the adhesion of calcium carbonate.
[0040]
Based on these considerations, in the present invention, when a toner cartridge having a lifetime of 12,000 sheets and a negatively charged toner is used, a fixing bias amount corresponding to the number of passing sheets and the ambient humidity shown in Table 1 is applied.
[0041]
[Table 1]

[0042]
Of course, the numerical values shown in Table 1 are merely examples, and the number of sheets to be passed, the threshold value of the ambient humidity and the number of threshold values, and the numerical value of the fixing bias amount are appropriately changed depending on the configuration of the toner, the toner cartridge, and the fixing device. The
[0043]
(Comparison experiment with conventional example)
In each environment (23 ° C./23° C.), the case where the above apparatus in the present embodiment is used and the case where a predetermined amount (−400 V, −700 V, −1000 V) is continuously applied to the fixing film as a fixing bias as in the conventional example. 15% RH, 23 ° C./60% RH, 23 ° C./85% RH) to the back side of the printing surface of the recording material P due to the level of rear toner scatter phenomenon and calcium carbonate adhesion to the fixing film. The toner stain levels were compared. The results are shown in Table 2. In the table, ◯ indicates an OK level, Δ indicates a level having no practical problem, and × indicates an NG level.
[0044]
The rear toner scattering phenomenon was evaluated by printing a pattern in which lines were arranged in a direction perpendicular to the paper transport direction on plain paper that had been left for 24 hours or more in each environment. In addition, toner smears on the back side of the printing surface of the recording material P are caused by a predetermined number (1,000 thousand) of paper patterns containing calcium carbonate in each environment in accordance with the cartridge usage state intermittently at 2 sheets / 10 minutes. Sheet, 4,000 sheets, and 7,000 sheets) were evaluated.
[0045]
[Table 2]

[0046]
As shown in Table 2, there was a difference between the rear toner scattering phenomenon level and the toner smearing level on the back surface of the print surface between this example and conventional examples 1, 2, and 3. In other words, by controlling the application of the optimum fixing bias amount corresponding to the number of sheets to be passed through the toner cartridge and the ambient humidity, even if there is a change in toner tribo and a change in the resistance of the recording material due to the ambient humidity, an appropriate electric field effect is always obtained. Therefore, it is possible to achieve both the suppression of the back toner scattering phenomenon and the prevention of toner smearing on the back side of the printing surface of the recording material P.
[0047]
In this embodiment, the film heating method is described as an example of the fixing device, but it goes without saying that the same effect can be obtained even if the heat roller fixing method is used.
[0048]
(Other examples of fixing bias application method)
In this embodiment, a method of applying a fixing bias having the same polarity as the toner to the fixing film has been described as an example. However, as another example, a fixing bias having a polarity opposite to that of the toner is applied to the pressure roller, in the vicinity of the fixing nip. There are a system in which a fixing bias having a polarity opposite to that of the toner is applied to the provided electrode, or a system in which these are mixed. Then, as shown in FIG. 6 above, along with the application of the fixing bias, a discharging means such as a conductive roller grounded is provided on the downstream side of the fixing nip in the recording material conveyance direction, and the reverse polarity of the toner is provided on the back side of the printing surface of the recording material. There is also a method for inducing the electric charge. There is no limitation on the fixing bias application method as long as the fixing bias can be applied to the recording material at least while the recording material passes through the fixing nip portion.
[0049]
(Example 2)
Next, as Example 2, another example of fixing bias amount control is shown in FIG. In this embodiment, the optimum fixing bias amount is calculated from the number of sheets of toner cartridges to be passed and information on the ambient temperature of the image forming apparatus 1 to be printed. In addition, description of the same location as Example 1 mentioned above is abbreviate | omitted.
[0050]
(10) Temperature detection means
The temperature detection means 53 is preferably provided at a position far from the fixing device 3 of the heat source and near the surrounding environment, for example, in the vicinity of the intake fan, in order to prevent temperature rise in the image forming apparatus 1.
[0051]
(11) Fixing bias control method
The control means reads out the number of passing sheets of toner cartridge from the storage means and the ambient temperature information from the temperature detecting means 53, calculates the optimum fixing bias amount corresponding to the number of passing sheets and the ambient temperature, and applies it to the fixing film. To do.
[0052]
Specifically, as described in Embodiment 1, in the toner cartridge, the toner tribo changes depending on the number of sheets to be passed. Therefore, the fixing bias necessary for suppressing the rear toner scattering phenomenon is the toner cartridge passing sheet. Decreases as the number increases.
[0053]
When the surroundings are in a high temperature environment, the temperature of the recording material is high, and the temperature rise of the recording material in the fixing nip is also high, so that the amount of water vapor generated in the fixing nip increases, which is necessary to suppress the back toner scattering phenomenon. The fixing bias increases as compared with the low temperature environment.
[0054]
Toner stains on the back side of the print surface are caused by the toner adhering to the surface of the fixing film, which has deteriorated releasability due to the adhesion of calcium carbonate, and the toner is transferred and accumulated on the pressure roller. In a high-temperature environment, the temperature of the pressure roller is high, and the temperature rise of the pressure roller surface in the fixing nip also increases, so that the toner transferred from the fixing film does not accumulate on the surface of the pressure roller and accumulates in the fixing nip. The toner can be discharged little by little at a level where there is no problem on the back side of the printing surface of the recording material. Therefore, in the high temperature environment, the toner contamination on the back surface of the printing surface has a margin compared to the low temperature environment where the toner is easily accumulated on the pressure roller surface, so that the fixing bias can be increased.
[0055]
Based on these, as in the first embodiment, a fixing bias amount corresponding to the number of passing sheets and the ambient temperature as shown in Table 3 is applied.
[0056]
[Table 3]

[0057]
Of course, the numerical values shown in Table 3 are merely examples, and the number of sheets to be passed, the threshold of the ambient temperature, the number of thresholds, and the numerical value of the fixing bias amount are appropriately changed depending on the configuration of the toner, the toner cartridge, and the fixing device. The
[0058]
(Comparison experiment with conventional example)
In each environment (15 ° C./15° C.), the case where the above-described apparatus is used in this embodiment and the case where a predetermined amount (−400 V, −600 V, −900 V) is continuously applied to the fixing film as a fixing bias as in the conventional example. 60% RH, 23 ° C./60% RH, 30 ° C./60% RH) to the back side of the printing surface of the recording material P due to the back toner scattering phenomenon level and calcium carbonate adhesion to the fixing film. The toner stain levels were compared. The results are shown in Table 4. In the table, ◯ indicates an OK level, Δ indicates a level having no practical problem, and × indicates an NG level.
[0059]
The rear toner scattering phenomenon was evaluated by printing a pattern in which lines were arranged in a direction perpendicular to the paper transport direction on plain paper that had been left for 24 hours or more in each environment. In addition, toner smears on the back side of the printing surface of the recording material P are caused by a predetermined number (1,000 thousand) of paper patterns containing calcium carbonate in each environment in accordance with the cartridge usage state intermittently at 2 sheets / 10 minutes. Sheet, 4,000 sheets, and 7,000 sheets) were evaluated.
[0060]
[Table 4]

[0061]
As shown in Table 4, there was a difference between the rear toner scattering phenomenon level and the toner smearing level on the back surface of the print surface between this example and the conventional examples 4, 5, and 6. In other words, by controlling the application of the optimum fixing bias amount corresponding to the number of sheets to be passed through the toner cartridge and the ambient temperature, there is a difference between the toner tribo change and the ease of toner accumulation on the pressure roller surface due to the ambient temperature. Even in such a case, an appropriate electric field action can always be maintained, so that it is possible to achieve both the suppression of the backside toner scattering phenomenon and the prevention of toner smearing on the back side of the printing surface of the recording material P.
[0062]
(Other examples of fixing bias control)
In the present exemplary embodiment and the first exemplary embodiment, the fixing bias amount control based on the ambient humidity or the ambient temperature as information having a large influence on the number of sheets of the toner cartridge and the recording material state has been described. A matrix of ambient humidity and ambient temperature may be adopted as information that greatly affects the state.
[0063]
(Example 3)
Next, as Example 3, another example of fixing bias amount control is shown in FIG. In this embodiment, the optimum fixing bias amount is calculated from the number of sheets of toner cartridges to be passed and the printing surface information of the recording material. In addition, description of the same location as Example 1 and 2 mentioned above is abbreviate | omitted.
[0064]
(12) Static elimination means
In this embodiment, in order to enhance the effect of suppressing the rear toner scattering phenomenon, a neutralizing means 42 such as a conductive roller grounded is provided on the downstream side of the fixing nip in the recording material conveyance direction, and the recording material P after passing through the fixing nip is provided. The structure is such that the charge removing means 42 is in contact with the back surface of the printing surface, and a predetermined amount of minus bias having the same polarity as the toner T (here, minus polarity toner is used) is applied to the fixing film 31, whereby the recording material P A positive charge having a polarity opposite to that of the negative bias applied from the grounding portion of the charge removing means 42 is induced on the back surface of the printing surface of the recording material P, and the toner T having the opposite polarity due to the induced positive charge is induced on the recording material P. It is attracted to and fixed.
[0065]
As a form of the charge removal means 42, a form such as a brush or a guide may be used as long as it has conductivity.
[0066]
(13) Printing surface detection means of recording material
The recording material print surface detection means 54 is provided in the CPU of the image forming apparatus 1.
[0067]
(14) Fixing bias control method
The control unit 44 reads out the number of passing sheets of the toner cartridge from the storage unit 51 of the toner cartridge 2 and the printing surface information from the printing surface detection unit 54, and sets the optimum fixing bias amount corresponding to the number of passing sheets and the printing surface. Calculate and apply to the fixing film 31.
[0068]
Specifically, as described in Embodiment 1, in the toner cartridge, the toner tribo changes depending on the number of sheets to be passed. Therefore, the fixing bias necessary for suppressing the rear toner scattering phenomenon is the toner cartridge passing sheet. Decreases as the number increases.
[0069]
When the recording material is on the second side of the automatic two-sided machine that uses a double-sided machine in the printer body, the moisture content decreases and the resistance as the recording material increases because it passes through the fixing device once compared to the first side. ing. For this reason, the application of the fixing bias reduces the amount of charge that is induced from the grounding portion of the static elimination means to the back side of the printing surface of the recording material and retains the toner on the recording material, and fixing necessary to suppress the back toner scattering phenomenon. The bias increases.
[0070]
The adhesion of calcium carbonate, which is the filling amount of the recording material, to the fixing film surface, which is the cause of toner stains on the back side of the printing surface, is dry on the second side of the recording material compared to the first side. Calcium carbonate has a large charge amount and is likely to adhere to the fixing film, but the printing surface of the recording material in the fixing nip is higher on the second surface than the first surface because the temperature of the pressure roller and recording material is higher. The toner can be discharged little by little at a level where there is no problem on the back side. Therefore, the toner stain on the back side of the print surface has a margin on the second side rather than the first side, and the fixing bias can be increased. Based on these considerations, similarly to the first embodiment, as an example, the number of passing sheets and the fixing bias amount corresponding to the printing surface as shown in Table 5 are applied.
[0071]
[Table 5]

[0072]
(Comparison experiment with conventional example)
Each printing mode (single-sided printing, single-sided printing, and the case where the above-described apparatus in this embodiment is used and the case where a predetermined amount (−500 V, −700 V, −1000 V) is continuously applied to the fixing film as a fixing bias as in the conventional example. An evaluation test (under an environment of 23 ° C./60% RH) is performed in an automatic double-sided printing using a double-sided machine, and the back side of the printing surface of the recording material P due to the level of back toner scatter phenomenon and calcium carbonate adhesion to the fixing film. The toner stain level was compared. The results are shown in Table 6. In the table, ◯ indicates an OK level, Δ indicates a level having no practical problem, and × indicates an NG level.
[0073]
The rear toner scattering phenomenon was evaluated by printing a pattern in which lines were arranged in a direction perpendicular to the paper transport direction on plain paper that was left for 24 hours or more in an environment of 23 ° C./60% RH. In addition, the toner stain on the back side of the printing surface of the recording material P was adjusted to the use state of the cartridge intermittently on a sheet containing calcium carbonate in an environment of 15 ° C./10% RH for 2/10 minutes. Evaluation was performed by passing a predetermined number of sheets (1,000 sheets, 4,000 sheets, 7,000 sheets).
[0074]
[Table 6]

[0075]
As shown in Table 6, there was a difference between the rear toner scattering phenomenon level and the toner smearing level on the back surface of the print surface between this example and conventional examples 7, 8, and 9. In other words, by controlling the application of the optimum fixing bias amount corresponding to the number of sheets to be passed through the toner cartridge and the print surface, even if there is a change in toner tribo and a change in resistance of the recording material due to the print surface, an appropriate electric field effect is always obtained. Therefore, it is possible to achieve both the suppression of the rear toner scattering phenomenon and the prevention of toner smearing on the back side of the printing surface of the recording material P.
[0076]
(Other examples of fixing bias control)
In this embodiment and Embodiments 1 and 2, the fixing bias is based on the number of passing toner cartridges and information on one of the information (ambient humidity, ambient temperature, and printing surface) that greatly affects the state of the recording material. Although the amount control has been described, of course, a matrix of a plurality of information may be adopted as information that greatly affects the state of the recording material. Next, as an example, a case where a matrix of ambient humidity and printing surface information is employed will be described.
[0077]
When the printing surface of the recording material is the first, the moisture absorption of the recording material varies depending on the ambient humidity. Therefore, the number of sheets of the toner cartridge shown in Table 1 of Example 1 and the application of the fixing bias amount corresponding to the ambient humidity are applied. Is appropriate control. On the other hand, in the case of the second page in automatic duplex using a double-sided machine for the printer body, the state of the recording material is made uniform by passing through the fixing device at the time of one-side fixing, and the time from one-side fixing to two-side printing is Since the influence on the recording material due to the surrounding environment is negligible, it is possible to apply a fixing bias amount corresponding to the number of sheets of the toner cartridge shown in Table 5 of this embodiment and the second printing surface regardless of the surrounding humidity. Appropriate control.
[0078]
For these reasons, by controlling the number of sheets to be passed and the surrounding humidity as shown in Table 7 as an example and applying a fixing bias amount corresponding to the print surface, the resistance of the recording material due to the toner tribo change and the surrounding humidity is controlled. Even if there is a change and a change in the resistance of the recording material due to the printing surface, an appropriate electric field action can be maintained at all times, so that both the suppression of the back toner scattering phenomenon and the prevention of toner smearing on the back surface of the recording material P can be achieved. Is possible.
[0079]
[Table 7]

[0080]
【The invention's effect】
As described above, the present inventionToner cartridge usage from new conditionAnd the state of the recording materialInformation that affectsThe amount of bias applied to the recording material can be controlled from time to time, and an appropriate electric field effect can be maintained at all times, so it is possible to achieve both suppression of the backside toner scattering phenomenon and prevention of toner smearing on the back surface of the recording material, and increase the printing speed. Even if the speed is increased, a good image can be obtained.
[Brief description of the drawings]
FIG. 1 is a sectional view of an electrophotographic image forming apparatus according to a first embodiment of the present invention.
FIG. 2 is a cross-sectional view of the heat fixing apparatus shown in the first embodiment of the present invention.
FIG. 3 is a cross-sectional view of a heat fixing apparatus shown in a second embodiment of the present invention.
FIG. 4 is a cross-sectional view of a heat fixing apparatus shown in a third embodiment of the present invention.
FIG. 5 is a cross-sectional view of a conventional example.
FIG. 6 is a cross-sectional view of a conventional example.
FIG. 7 is a cross-sectional view of a conventional example.
[Explanation of symbols]
1. Electrophotographic image forming apparatus
11 ... Laser beam
12 ... cassette
13: Paper feed roller
14 ... Registration roller
15 ... Transfer roller
2. Toner cartridge
21 ... Photosensitive drum
22 ... Charging roller
23. Developing device
24 ... Cleaning device
3. Fixing device
31 ... Fixing film
32 ... Pressure roller
33 ... Heater
34 ... Thermistor
35 ... Film guide
41 ... Power supply means
42 ... Static elimination means
43 ... Bias power supply
44... Bias control means
51. Information storage means of toner cartridge
52 ... Humidity detection means
53 ... Temperature detection means
54. Printing surface detection means

Claims

An image carrier on which an electrostatic latent image is formed; a developing unit that stores toner having a negative charge polarity and supplies the toner to the image carrier to develop the electrostatic latent image; and the image carrier Means for transferring the toner image formed on the recording material, a rotating body that contacts an unfixed toner image carried on the recording material, and a pressure member that presses the surface of the rotating body, A heating and fixing unit that sandwiches and conveys a recording material carrying an unfixed toner image at a pressure nip portion between the rotating body and the pressure member and heat-fixes the unfixed toner image on the recording material, and a negative polarity on the rotating body. In an image forming apparatus comprising: an application unit that applies a voltage; and a control unit that controls the voltage.
The developing unit is a toner cartridge that can be attached to and detached from the main body of the image forming apparatus, and a storage unit that stores a used amount of the toner cartridge that is currently installed from a new state, and a humidity of the surrounding environment. A humidity detecting means for detecting, wherein the control means detects the absolute value of the voltage applied by the applying means as the amount of use stored in the storage means decreases, and the humidity detecting means detects the absolute value of the voltage. The image forming apparatus is characterized in that the lower the humidity, the smaller is set.

An image carrier on which an electrostatic latent image is formed; a developing unit that stores toner having a negative charge polarity and supplies the toner to the image carrier to develop the electrostatic latent image; and the image carrier Means for transferring the toner image formed on the recording material, a rotating body that contacts an unfixed toner image carried on the recording material, and a pressure member that presses the surface of the rotating body, A heating and fixing unit that sandwiches and conveys a recording material carrying an unfixed toner image at a pressure nip portion between the rotating body and the pressure member and heat-fixes the unfixed toner image on the recording material, and a negative polarity on the rotating body. In an image forming apparatus comprising: an application unit that applies a voltage; and a control unit that controls the voltage.
The developing unit is a toner cartridge that can be attached to and detached from the main body of the image forming apparatus, and a storage unit that stores a used amount of the toner cartridge that is currently installed from a new state, and a temperature of the surrounding environment. Temperature detecting means for detecting, and the control means detects the absolute value of the voltage applied by the applying means as the amount of use stored in the storage means decreases and the temperature detecting means detects The image forming apparatus is characterized in that the lower the temperature, the smaller the setting.

An image carrier on which an electrostatic latent image is formed; a developing unit that stores toner having a negative charge polarity and supplies the toner to the image carrier to develop the electrostatic latent image; and the image carrier Means for transferring the toner image formed on the recording material, a rotating body that contacts an unfixed toner image carried on the recording material, and a pressure member that presses the surface of the rotating body, A heating and fixing unit that sandwiches and conveys a recording material carrying an unfixed toner image at a pressure nip portion between the rotating body and the pressure member and heat-fixes the unfixed toner image on the recording material, and a negative polarity on the rotating body. An application unit that applies a voltage, a control unit that controls the voltage, and a conductive material that is in contact with a surface opposite to the unfixed toner image carrying surface of the recording material on the downstream side of the pressing nip portion in the recording material conveyance direction. And the recording material is in contact with both the rotating body and the conductive member. When a negative voltage is applied to the rotator, a current flows through the recording material, and a positive charge is induced on the surface of the recording material opposite to the unfixed toner image carrying surface, thereby recording an unfixed toner image. The toner image is formed on the first surface of the recording material, and is heated and fixed by the heating and fixing means. Then, the recording material is turned upside down to form a toner image on the second surface of the recording material, and the heating is performed. In an image forming apparatus having a function of forming images on both sides of a recording material by heat fixing with a fixing unit,
The developing means is a toner cartridge that can be attached to and detached from the main body of the image forming apparatus, and has a storage means for storing a used amount of the currently installed toner cartridge from a new state, and the control means In the case where the absolute value of the voltage applied by the applying unit is set to be smaller as the usage amount stored by the storage unit is larger, and the unfixed toner image carried on the second surface is heated and fixed. Is set larger than the case where the unfixed toner image carried on the first surface is heated and fixed.