JP4343499B2 - Multicolor image forming apparatus and multicolor image forming method - Google Patents

Description

【００６４】
１−１）転写用紙搬送ベルト（中間転写体、記録材搬送ベルト）
転写用紙搬送ベルト２ａは、電気抵抗が1×１０¹⁰Ω・ｃｍ程度の半導電性の材料としてカーボンが分散されたポリカーボネイトで形成されており、感光体ドラム６４（Ｙ〜Ｋ）の下方で複写機本体内の左右両側に配設された駆動ローラおよび従動ローラに巻回されて張設されている。その他、ポリエチレンテレフタレート樹脂シート（ＰＥＴシート）や、ポリフッ化ビニリデン樹脂シート、ポリウレタン樹脂シートなどの誘電体樹脂のシートが使用されることもある。
【００６５】
これらの素材からなるシート両端部を互に重ね合わせて接合し、エンドレス形状にしたものか、或いは継ぎ目を有しない（シームレス）ベルト状としたものが、転写用紙搬送ベルト２ａとして用いられ、このような転写用紙搬送ベルト２ａは、例えば、図３、図４に示すように、その上流側を装置本体に対して回動自在に枢支させる、その下流側を、下方に傾動自在となるように構成することができる。
【００６６】
このような構成により、転写用紙搬送ベルト２ａに逐次一次転写をおこなった後、その転写用紙搬送ベルト２ａの下流側を下方に傾動させることにより、転写用紙搬送ベルト２ａの上流側に設けたバイアス転写ローラ３１（図３の場合）または転写用紙搬送ベルト２ａの下流側に設けたバイアス転写ローラ３１（図４の場合）で、給紙トレイ４から送られた転写用紙５の裏面に一括二次転写をおこなった後、用紙排出部１３への排紙が可能となる。なお、図６の場合についても同様に転写用紙搬送ベルト２ａを下方に傾動させるように構成することができるが、その図示と説明は省略する。
【００６７】
また、転写用紙搬送ベルト２ａの周長は、本実施の形態の複写機にて使用可能な最大紙サイズであるＡ３より長く設定してある。また、転写用紙搬送ベルト２ａには、その位置を検知するための図示しないホワイトマークが施されていて、図示しない光学式の位置検知センサによって転写用紙搬送ベルト２ａの位置が常に検知できるようになっている。
【００６８】
１−２）転写ローラ
各色の画像形成ステーション１では、感光体ドラム６４（Ｙ〜Ｋ）と転写用紙搬送ベルト２ａとが接触する転写位置において、転写用紙搬送ベルト２ａのベルトループ内側にはトナーの正規帯電極性と逆のプラスの転写バイアス電圧が印加された転写ローラ７（Ｙ〜Ｋ）が設けられている。
【００６９】
転写ローラ７（Ｙ〜Ｋ）は、電気抵抗が1×１０⁶Ω・ｃｍ以下のカーボンが分散された発泡ウレタンゴムで形成され、転写用紙搬送ベルト２ａの裏面側から感光体ドラム６４（Ｙ〜Ｋ）に向けて所定の圧力で押圧され、転写用紙搬送ベルト２ａの図中矢印方向への走行に従動して回転されるようになっている。
【００７０】
１−３）定着装置
転写用紙５上に転写されたトナー像を定着させるための定着装置３は、転写用紙搬送ベルト２ａの下流側に設けられており、この定着装置３は、互いに転接された一対のローラを有し、転写用紙５を所定温度に加熱して転写用紙５に保持されたトナー像を溶融定着する。
【００７１】
この定着装置３の下流側には、両面印字または裏面印字を実行する際に、転写用紙５を下方へＵターンさせることによって転写用紙搬送ベルト２ａへ誘導する切替えゲート２１と、転写用紙５を機外に排出するための用紙排出部１３と、が設けられている。
【００７２】
切替えゲート２１は、印字モードに応じて、定着装置３から用紙排出部１３への経路と、定着装置３から下部搬送路１２または転写用紙搬送ベルト２ａの下部走行辺への反転路１５とを切り替えるために設けられ、図１，図６の状態では、用紙排出部１３への経路が開かれ、図２，図７の状態では、反転路１５への経路が開かれている。なお、用紙排出部１３は、一対の排紙ローラを具備し、複写機本体の外側に突出して設けられた排紙トレイ（図示省略）に転写用紙５を排出する。
【００７３】
（２）画像データの入出力順序
次いで、各印字モードに対応した画像データの入出力順序について説明する。
【００７４】
２−１）片面・上向排紙の場合（１）
原稿処理部へセットされた原稿束の１ページ目から順次原稿画像を読取り、画像を出力する際には、入力時とは逆順で原稿束の最終ページのデータから全てのデータについて転写用紙のＡ面へ逐次転写で順次出力する。
【００７５】
（片面原稿の場合）
画像入力時（昇順）：1→2→3→4→5
画像出力時（降順）：5→4→3→2→1（逐次転写）
（両面原稿の場合）
画像入力時（昇順）：1Ａ→1Ｂ→2Ａ→2Ｂ→3Ａ→3Ｂ→4Ａ→4Ｂ→5Ａ→5Ｂ
画像出力時（降順）：5Ｂ→5Ａ→4Ｂ→4Ａ→3Ｂ→3Ａ→2Ｂ→2Ａ→1Ｂ→1Ａ
２−２）片面・上向排紙の場合（２）
原稿処理部へセットされた原稿束の最終ページから順次原稿画像を読取り、画像を出力する際には、入力時と同順で原稿束の最終ページのデータから全てのデータについて転写用紙のＡ面への逐次転写で順次出力してゆく。
【００７６】
（片面原稿の場合）
画像入力時（降順）：5→4→3→2→1
画像出力時（降順）：5→4→3→2→1（逐次転写）
（両面原稿の場合）
画像入力時（降順）：5Ｂ→5Ａ→4Ｂ→4Ａ→3Ｂ→3Ａ→2Ｂ→2Ａ→1Ｂ→1Ａ
画像出力時（降順）：5Ｂ→5Ａ→4Ｂ→4Ａ→3Ｂ→3Ａ→2Ｂ→2Ａ→1Ｂ→1Ａ
２−３）片面・下向排紙の場合（１）
原稿処理部へセットされた原稿束の１ページ目から順次原稿画像を読取り、画像を出力する際には、入力時と同順で原稿束の１ページ目のデータから全てのデータについて転写用紙のＢ面への一括転写で順次出力する。
【００７７】
（片面原稿の場合）
画像入力時（昇順）：1→2→3→4→5
画像出力時（昇順）：1→2→3→4→5（全てＢ面へ一括転写）
（両面原稿の場合）
画像入力時（昇順）：1Ａ→1Ｂ→2Ａ→2Ｂ→3Ａ→3Ｂ→4Ａ→4Ｂ→5Ａ→5Ｂ
画像出力時（昇順）：1Ａ→1Ｂ→2Ａ→2Ｂ→3Ａ→3Ｂ→4Ａ→4Ｂ→5Ａ→5Ｂ
２−４）片面・下向排紙の場合（２）
原稿処理部へセットされた原稿束の最終ページから順次原稿画像を読取り、画像を出力する際には、入力時とは逆順で原稿束の１ページ目のデータから全てのデータについて転写用紙のＢ面への一括転写で順次出力してゆく。
【００７８】
（片面原稿の場合）
画像入力時（降順）：5→4→3→2→1
画像出力時（昇順）：1→2→3→4→5（全てＢ面へ一括転写）
（両面原稿の場合）
画像入力時（降順）：5Ｂ→5Ａ→4Ｂ→4Ａ→3Ｂ→3Ａ→2Ｂ→2Ａ→1Ｂ→1Ａ
画像出力時（昇順）：1Ａ→1Ｂ→2Ａ→2Ｂ→3Ａ→3Ｂ→4Ａ→4Ｂ→5Ａ→5Ｂ
２−５）両面・上向排紙の場合（１）
原稿処理部へセットされた原稿束の１ページ目から順次原稿画像を読取り、画像を出力する際には、原稿束の最終ページのデータから一括転写と逐次転写を繰り返し、降順で順次出力してゆく。原稿束の構成ページ数によって、最初に画像出力される転写用紙の面が異なってくる。
【００７９】
（原稿が奇数ページの場合）
画像入力時（昇順）：1→2→3→4→5
画像出力時（降順）：5（Ａ面へ逐次）→4（Ｂ面へ一括）→3→2→1
（原稿が偶数ページの場合）
画像入力時（昇順）：1→2→3→4
画像出力時（降順）：4（Ｂ面へ一括）→3（Ａ面へ逐次）→2→1
２−６）両面・上向排紙の場合（２）
原稿処理部へセットされた原稿束の最終ページから順次原稿画像を読取り、画像を出力する際には、原稿束の最終ページのデータから一括転写と逐次転写とを繰り返し、降順で順次出力してゆく。原稿束の構成ページ数によって、最初に画像出力される転写用紙の面が異なってくる。
【００８０】
（原稿が奇数ページの場合）
画像入力時（降順）：5→4→3→2→1
画像出力時（降順）：5（Ａ面へ逐次）→4（Ｂ面へ一括）→3→2→1
（原稿が偶数ページの場合）
画像入力時（降順）：4→3→2→1
画像出力時（降順）：4（Ｂ面へ一括）→3（Ａ面へ逐次）→2→1
２−７）両面・下向排紙の場合（１）
原稿処理部へセットされた原稿束の１ページ目から順次原稿画像を読取り、画像を出力する際には、原稿束の１ページ目のデータから一括転写の後に逐次転写を行うことを繰り返し、昇順で順次出力してゆく。画像出力は必ず転写用紙のＢ面への一括転写から開始される。
【００８１】
（原稿入力順及び画像出力順）
画像入力時（昇順）：1→2→3→4→5
画像出力時（昇順）：1（Ｂ面へ一括）→2（Ａ面へ逐次）→3→4→5
２−８）両面・下向排紙の場合（２）
原稿処理部へセットされた原稿束の最終ページから順次原稿画像を読取り、画像を出力する際には、原稿束の１ページ目のデータから一括転写の後に逐次転写を行なうことを繰り返し、昇順で順次出力してゆく。画像出力は必ず転写用紙のＢ面への一括転写から開始される。
【００８２】
（原稿入力順及び画像出力順）
画像入力時（降順）：5→4→3→2→1
画像出力時（昇順）：1（Ｂ面へ一括）→2（Ａ面へ逐次）→3→4→5
以上の画像データの入出力順序を一覧表にまとめると、表２のようになる。
【００８３】
【表２】

【００８４】
（３）転写方法
３−１）片面印字で転写用紙Ａ面を上向き排紙する場合（図１，図６参照）
画像形成ステーション１の各感光体ドラム６４（Ｙ〜Ｋ）上に、原稿画像に対して鏡像のトナー像を形成すると共に、タイミングをとってレジストローラ２４から送られてきた転写用紙５が、各感光体ドラム６４（Ｙ〜Ｋ）と転写用紙搬送ベルト２１ａとの間の転写位置へ順に給紙されると、転写用紙５上へ所定の転写電圧が印加された転写ローラ７（Ｙ〜Ｋ）によってトナー像が順次多重転写（逐次転写）されて、原稿画像に対して正像の４色フルカラートナー像を形成する。
【００８５】
転写用紙５が定着装置３を通過すると、この正像のトナー像が最終的な画像として定着およびフルカラーの発色がなされる。この画像形成（転写用紙Ａ面への印字）モードにおいては、転写用紙搬送ベルト２ａは転写用紙５を定着装置３まで搬送する転写搬送手段として用いられる。
【００８６】
３−２）片面印字で転写用紙Ｂ面を下向き排紙する場合（図１，図６参照）
画像形成ステーション１の各感光体ドラム６４（Ｙ〜Ｋ）上に、原稿画像に対して正像のトナー像を形成し、所定の転写電圧が印加された転写ローラ７（Ｙ〜Ｋ）によって転写用紙搬送ベルト２ａ上へ順次一次転写（逐次転写）する。転写用紙搬送ベルト２ａ上のトナー像は原稿画像に対して鏡像のフルカラートナー像となっている。
【００８７】
そして、この転写用紙搬送ベルト２ａ上の原稿画像に対して鏡像の４色フルカラートナー像を、転写用紙搬送ベルト２ａの回動動作とタイミングをとって給送されてきた転写用紙５のＢ面へ、吸着帯電ローラ３１をバイアス転写ローラとして用い、所定の電圧を印加することによって一括二次転写する。したがって、転写用紙のＢ面上には原稿画像に対して正像の４色フルカラートナー像が形成される。
【００８８】
吸着帯電ローラ３１をバイアス転写ローラとして使用しない場合には、何れかの画像形成ステーション１の転写ローラ７（Ｙ〜Ｋ）によって一括二次転写を行なってもよい。転写用紙５が定着装置３を通過すると、この正像のトナー像が最終的な画像として定着およびフルカラーの発色がなされる。この画像形成（転写用紙Ｂ面への印字）モードにおいては、転写用紙搬送ベルト２ａは中間転写体として用いられる。
【００８９】
３−３）両面印字の場合（図１，図２および図６，図７参照）
転写用紙５の両面に画像形成する場合の転写動作については、上記３−１）および３−２）の動作を組合せて制御することによって、表裏両面に画像を形成することができる。すなわち、まず、転写用紙Ａ面に逐次転写により画像形成をおこない定着装置３を通過させた後、転写用紙５を反転させて下部搬送路１２または下部走行辺を経由させた後、バイアス転写ローラ３１により、転写用紙Ｂ面に一括二次転写をおこなえばよい。
【００９０】
（４）バイアス転写ローラ（図５（ａ）（ｂ）参照）
バイアス転写ローラ３１は、両面印字における裏面（第２面）への印字またはフェイスダウン排出の片面印字において、中間転写体としての転写用紙搬送ベルト２ａに形成されたトナー像を転写用紙５に一括二次転写するためのローラ部材であるが、本来は、吸着帯電ローラとして設けられ、転写用紙５の転写搬送ベルトへ２ａへの給紙時に、転写用紙５の上から転写搬送ベルト２ａに作用して、その転写搬送ベルト２ａをトナー像の転写と逆極性に帯電させ、転写用紙を転写搬送ベルト２ａ上に静電吸着させる機能を有する。
【００９１】
ちなみに、吸着帯電ローラ３１からプラス極性の電流が転写用紙５へ印加される結果、転写用紙５はプラス電荷に帯電するので、これに対して転写搬送ベルト２ａにはマイナス極性の誘電電荷が発生し、転写用紙５が転写搬送ベルト２ａへ静電的に吸着され、安定的に保持される。従って、転写搬送ベルト２ａは、トナー像を転写する場合のプラス極性とは逆極性に帯電したことになる。なお、バイアス転写ローラ３１は、特に、ローラ部材に限定することなく、ブラシ部材、シート部材、またはチャージャーなどを用いてもよい。
【００９２】
４−１）画像形成ステーションの上流側に配置（図３参照）
バイアス転写ローラ３１が、転写用紙搬送ベルト２ａに沿ってＫ（ブラック）の画像形成ステーション１よりも上流側に配置されている場合、バイアス転写ローラ３１と対向する領域に画像の先端部が移動してくるタイミングに合致するように、給紙トレイ４から転写用紙５が供給され、転写用紙５への二次転写が一括転写で行われる。なお、バイアス転写ローラ３１を、転写搬送ベルト２ａがなすベルトループの外側に配置すると、ベルトループ内のレイアウトの自由度が向上し、また、転写搬送ベルト２ａのユニット化等に対処しやすくなる。
【００９３】
４−２）画像形成ステーションの下流側に配置（図４参照）
また、裏面画像の一括二次転写を行うためのバイアス転写ローラ３１は、転写用紙搬送ベルト２ａに沿って最も下流側の作像ユニット６Ｙの下流側に配置してもよい。この場合にも、そのバイアス転写ローラ３１を転写搬送ベルト２ａがなすベルトループの外側に配置すると、ベルトループ内のレイアウトの自由度を向上させることができ、また、転写搬送ベルト２ａのユニット化等に対処しやすくなる。
【００９４】
４−３）一括二次転写における転写効率の向上
転写用紙５の裏面へ、転写搬送ベルト２ａ上で保持するトナー像の一括二次転写を行なう場合に、転写効率を高めるためには、一括転写に先立って、転写時とは逆の電界（マイナス極性）を印加し、転写用紙搬送ベルト２ａを帯電させることが有効である。
【００９５】
この帯電器としては、図８に示すように、転写搬送ベルト２ａの搬送方向下流部で転写用紙５を転写搬送ベルト２ａから分離するために、画像形成ステーション１の最も下流側の作像ユニット６Ｙの下流側に配置される分離帯電器３２、或いは、図９に示すように、転写用紙５の分離後に転写搬送ベルト２ａの除電を行うために、上述の分離帯電器３２の転写搬送ベルト２ａを挟んだ反対側に設けられる除電帯電器（ベルト除電器）３３等を用いることができる。
【００９６】
そして、二次転写が終わった転写用紙５は定着装置３で画像を定着され、フェイスダウン排紙の片面印字が指定されている場合には、装置外の用紙排出部１３へと排出され、両面印字が指定されている場合には、転写用紙５の他面への画像形成（逐次転写）を行なうために下方へ向ってＵターンし、転写用紙搬送ベルト２ａへ誘導される。
【００９７】
すなわち、転写用紙５の反転操作を伴わないため、先に一括二次転写によって多色画像を定着された転写用紙５の一方の面が転写用紙搬送ベルト２ａがなすベルトループに沿って内側を向く状態で面し、次いで逐次転写を受ける転写用紙５の他方の面がベルトループに沿って外側を向く状態となる。
【００９８】
以上のような、片面印字および両面印字における、書き込む潜像の向き、転写方法（手段・方式）、転写搬送ベルト２ａと画像形成ステーション１との間の相対的な離間の有無について、以下の表３に示す。
【００９９】
【表３】

【０１００】
なお、本発明は、多色画像形成装置を、図１等の実施形態に示した構成に限定するものではなく、少なくとも、感光体と現像装置を備えた画像形成ステーションが記録材搬送方向に沿って複数組配列され、記録材の片面または両面に単色または多色の画像形成を行なえるようにした多色画像形成装置であれば、その構成や形式の如何を問わず、本発明を適用することができる。
【０１０１】
【発明の効果】
以上の説明から明らかなように、本発明は、以下の効果を奏する。
【０１０２】
（１）片面印字、あるいは両面印字における記録材表面への印字の場合はトナー色毎に逐次転写（多重転写）を適用し、両面印字における記録材裏面への印字の場合は一括転写（一括転写が複数回行なわれてもよい）を適用して多色画像を形成するので、従来のような嵩高い記録材反転手段（中間トレイを有する反転搬送路）の配置を不要とした上で、多色画像を記録材の表面、裏面または両面に対して自在に形成することができる。従って、反転に要する時間を短縮化することができるため、印字速度の高速化が可能となり、かつ安定した画像形成が可能となる。また、ジャムの発生も少なくなり、かつ、部品点数の削減により、装置の小型化・単純化・コストの低減化を図ることもできる。
【０１０３】
（２）片面印字、あるいは両面印字における記録材表面への印字の場合は逐次的に一次転写（多重転写）をおこない、両面印字における記録材裏面への印字の場合は、一括二次転写により多色画像を形成するので、従来のような嵩高い記録材の反転ユニットを用いずに、記録材の表面、裏面または両面に高画質の多色画像を自在に形成することができるため、反転に要する時間を短縮でき、印字速度の高速化が可能となり、また、ジャムの発生も少なくなり、かつ、部品点数の削減により、装置の小型化・単純化・コストの低減化を図ることができる。
【０１０４】
さらに、一括二次転写された記録材の裏面（一方の面）のトナー像を定着させた後に、逐次的な一次転写によって表面印字を行うため、記録材搬送時におけるトナー色像の保持・安定性を両面未定着のままで定着部まで搬送する場合よりも向上させることができ、画質の安定的な向上を図ることができる。
【０１０５】
（３）一括転写を行うための二次転写手段を全ての画像形成ステーションに対して記録材搬送方向の上流側に配置しているので、記録材搬送ベルトと画像形成ステーションとを相対的に離間させることによって、一旦転写された記録材裏面のトナー像が、記録材搬送ベルトと各画像形成ステーションの感光体との間に挟まれて撹乱されるのを防止することができる。
【０１０６】
（４）一括転写を行うための二次転写手段を全ての画像形成ステーションに対して記録材搬送方向の下流側、すなわち定着装置の直前に配置して記録材の裏面にトナー像を転写するので、一旦転写された記録材裏面のトナー像が、記録材搬送ベルトによる搬送中に撹乱されるのを防止することができる。
【０１０７】
（５）記録材片面または記録材表面への画像形成時と、記録材裏面への画像形成時とで、原稿画像に対して感光体への静電潜像書き込み方向を異ならせるので、従来のような嵩高い記録材の反転ユニットを用いずに、転写紙の表面、裏面または両面に高画質の多色画像を自在に形成することができるため、反転に要する時間を短縮化できるため、印字速度の高速化が可能となり、かつ安定した画像形成が可能となる。また、ジャムの発生も少なくなる。そして、記録材搬送ベルト上のトナー像の極性を転換させる極性転換手段を設けることなく、記録材の両面に対して安定した転写性を得ることができる。
【０１０８】
（６）記録材の一方の面への画像形成を行う場合には、逐次転写により多色画像を形成し、記録材の他方の面への画像形成を行う場合には、一括二次転写により多色画像を形成するので、記録材の反転ユニットを用いずに、転写紙の表面、裏面または両面に高画質の多色画像を自在に形成することができる。
【図面の簡単な説明】
【図１】本発明の実施形態に係る多色画像形成装置の表面画像形成および逐次転写時の構成説明図である。
【図２】同裏面画像形成時の構成説明図である。
【図３】同裏面一括転写および排出時の構成説明図である。
【図４】同二次転写手段を最下流側に配設した場合の構成説明図である。
【図５】同二次転写手段の構成説明図である。
【図６】同表面画像形成および逐次転写の場合の別の構成説明図である。
【図７】同両面画像形成時の裏面画像形成時の構成説明図である。
【図８】同分離帯電器の配置位置示す構成説明図である。
【図９】同除電帯電器の配置位置を示す構成説明図である。
【図１０】従来の多色画像形成装置の一例を示す構成図である。
【図１１】同別の多色画像形成装置の構成説明図である。
【図１２】同片面印字の説明図である。
【図１３】同両面印字の説明図である。
【図１４】同異なる多色画像形成装置の構成説明図である。
【符号の説明】
１−画像形成ステーション
２ａ−記録材搬送ベルト
５−記録材
３１−二次転写手段
６１（Ｙ〜Ｋ）−現像装置
６４（Ｙ〜Ｋ）−感光体[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a multicolor image forming apparatus and a multicolor image forming method such as a color copying machine and a laser beam printer, and more particularly to a multicolor image forming apparatus capable of forming a single color image or a multicolor image on both sides of a recording material. And a multicolor image forming method.
[0002]
[Prior art]
Conventionally, various apparatuses such as a copying machine, a printer, and a facsimile have been put to practical use as an image forming apparatus using an electrophotographic system. In this type of image forming apparatus, the surface of a drum-shaped or belt-shaped photoconductor is uniformly charged with a corona charger or the like so as to have a predetermined charging polarity, and the surface of the photosensitive body charged to a predetermined polarity is obtained. An electrostatic latent image is formed by exposure in accordance with an image signal, and the electrostatic latent image is developed and visualized by supplying a developer charged to a predetermined polarity, and recorded on the surface of the photoreceptor. The recording paper as the material is supplied, the visualized developer image is transferred onto the recording paper by a corona charger or the like, and the developer image transferred onto the recording paper is heated and fixed via the fixing device. Thus, an image is formed on the recording paper.
[0003]
In recent years, the amount of recording paper used has continued to increase as devices such as copiers, printers, and facsimiles are actively used in offices. Therefore, from the viewpoint of resource saving, a double-sided image forming apparatus capable of forming images on both sides of a recording sheet has been put into practical use. In particular, double-sided copying is an essential function in a copying machine.
[0004]
When images are formed on both sides of a recording sheet by a copying machine, first, a toner image based on the image of the first page is formed on the photosensitive member, and the recording sheet is supplied to the photosensitive member in synchronization with the toner image. After the image is transferred to the recording paper, it is fixed by passing through a fixing device. Then, the recording paper on which the image of the first page is formed is reversed in the apparatus, and is supplied again to the photosensitive member in synchronization with the toner image of the second page formed on the photosensitive member. The image is formed on both sides of the recording paper by transferring and fixing the image on the recording paper.
[0005]
In recent years, with the progress of colorization in the OA field, there has been an increasing demand for forming color images on both sides of a recording material. Therefore, for example, a color electrophotographic recording apparatus as shown in FIG. 10 has been proposed, and it is widely spread today. In this color electrophotographic recording apparatus, first, second, third and fourth image forming portions Pa, Pb, Pc and Pd are arranged in parallel in the apparatus main body, and toner images of different colors are respectively latent images. It is formed through development and transfer processes.
[0006]
Each of the image forming portions Pa, Pb, Pc and Pd includes a dedicated image carrier, in this example, electrophotographic photosensitive drums 3a, 3b, 3c and 3d, and each color is provided on each photosensitive drum 3a, 3b, 3c and 3d. The toner image is formed. A recording material carrying member (conveying belt) 130 is disposed adjacent to each of the photosensitive drums 3a, 3b, 3c, and 3d, and the toner images of the respective colors formed on the photosensitive drums 3a, 3b, 3c, and 3d are The image is transferred onto the recording material P that is carried and conveyed on the conveying belt 130. Further, the recording material P onto which the toner image of each color is transferred is heated and pressed by the fixing device 9 to fix the toner image, and is then discharged out of the apparatus as a recorded image.
[0007]
On the outer periphery of the photosensitive drums 3a, 3b, 3c and 3d, exposure lamps 111a, 111b, 111c and 111d, drum chargers 2a, 2b, 2c and 2d, potential sensors 113a, 113b, 113c and 113d, a developing device 1a, 1b, 1c and 1d, brush transfer chargers 24a, 24b, 24c and 24d, and cleaners 4a, 4b, 4c and 4d are disposed, and a light source device and polygon mirror 117 (not shown) are further installed above the apparatus. ing.
[0008]
With such a configuration, the laser light emitted from the light source device is irradiated onto the polygon mirror 117 that is rotationally driven and scanned, the light beam of the scanning light is polarized by the reflection mirror, and the photosensitive drums 3a and 3b are obtained by the fθ lens. By condensing and exposing on the 3c and 3d buses, latent images corresponding to the image signals are formed on the photosensitive drums 3a, 3b, 3c and 3d. The developing devices 1a, 1b, 1c, and 1d are filled with a predetermined amount of cyan, magenta, yellow, and black toners as developers, respectively, by a supply device (not shown). The developing devices 1a, 1b, 1c and 1d develop the latent images on the photosensitive drums 3a, 3b, 3c and 3d, respectively, and visualize them as cyan toner images, magenta toner images, yellow toner images and black toner images.
[0009]
The recording material P is accommodated in the recording material cassette 10, supplied from the recording material cassette 10 to the conveying belt 130 through a plurality of conveying rollers and registration rollers 12, and opposed to the photosensitive drums 3 a, 3 b, 3 c and 3 d by the conveying belt 130. Sequentially sent to the transfer section. The conveyor belt 130 is formed of a sheet of dielectric resin such as a polyethylene terephthalate resin sheet (PET sheet), a polyvinylidene fluoride resin sheet, or a polyurethane resin sheet, and both end portions thereof are overlapped and joined to each other. A shape or a belt (seamless) formed with no seam is used.
[0010]
When it is confirmed that the conveying belt 130 rotates and is in a predetermined position, the recording material P is sent from the registration roller 12 to the conveying belt 130, and the recording material P is directed to the transfer portion of the first image forming portion Pa. Are transported. At the same time, the image writing signal is turned on, and image formation is performed on the photosensitive drum 3a of the first image forming portion Pa at a certain timing based on the signal. Then, the toner image of the first color formed on the photosensitive drum 3a is transferred onto the recording material P by the brush transfer charger 24a applying an electric field or electric charge at the lower transfer portion of the photosensitive drum 3a. . By this transfer, the recording material P is firmly held on the conveying belt 130 by the electrostatic attraction force, and is conveyed after the second image forming portion Pb.
[0011]
In the same manner, image formation and transfer are performed in the second image forming unit Pb to the fourth image forming unit Pd. Next, the recording material P to which the four color toner images have been transferred is discharged at the end of the conveying belt 130 by removing electricity by the separation charger 32 at the downstream portion in the conveying direction of the conveying belt 130 and attenuating the electrostatic adsorption force. To do. The separated recording material P is conveyed to the fixing device 9.
[0012]
The fixing device 9 includes a fixing roller 51, a pressure roller 52, heat resistant cleaning members 54 and 55 for cleaning each of them, roller heaters 56 and 57 installed in the rollers 51 and 52, and a fixing roller 51. An application roller 50 for applying a release agent oil such as dimethyl silicone oil, a reservoir 53 for the oil, and a thermistor 58 for detecting the temperature of the surface of the pressure roller 52 and controlling the fixing temperature are provided. The recording material P to which the four color toner images have been transferred is mixed to the toner image and fixed (fixed) to the recording material P by fixing to form a full-color copy image.
[0013]
After the transfer, the photosensitive drums 3a, 3b, 3c, and 3d are cleaned and removed by the respective cleaners 4a, 4b, 4c, and 4d, and are subsequently prepared for the next latent image forming step. On the other hand, the toner adhering to the surface of the conveyor belt 130 is removed from the surface of the conveyor belt 130 by the static elimination charger 33 and the counter electrode 34 on the back side of the belt, and then is contacted with the surface of the conveyor belt 130 (nonwoven fabric). 35 and the backup member 36 on the back side of the belt are wiped off. As another cleaning means, a blade or a fur brush is used alone or in combination.
[0014]
When double-sided image formation is performed on the recording material P, the transfer of the first surface (A surface) is completed, and after passing through the fixing device 9, the recording material P is not conveyed to the paper discharge tray 63, but the reversing path 61 or the like. The recording material P is turned upside down (front and back), and the recording material P is temporarily stored in the intermediate tray 65 in the inverted state. Thereafter, the recording material P is fed out and retransmitted by the conveying belt 130, and image formation is performed again on the second surface (B surface) opposite to the first surface A on which image formation has been completed. Then, after fixing the B surface of the recording material P by the fixing device 9, the recording material P is discharged to the discharge tray 63.
[0015]
A general method for forming a double-sided image is performed as described above. For the sake of unification in the following description, the upper surface of the recording material without transfer of the toner image newly supplied to the conveyance belt 130 is defined as A surface, and the opposite back surface is defined as B. The first A surface and the second B surface correspond to this rule.
[0016]
[Problems to be solved by the invention]
As described above, conventionally, when double-sided image formation is performed, images are formed on each side, such as A side and then B side of the recording material P. Therefore, as a matter of course, the output time at the time of double-sided image formation takes more than double that at the time of single-sided image formation. In other words, when forming the second page image on the back side of the recording material, it is necessary to reverse the recording material on which the first page image is fixed while circulating in the apparatus. Time is required, and 3 to 4 times as long as the time for forming an image on only one side is required.
[0017]
For example, in the case of a monochrome copying machine, the copy speed for single-sided copying on an A4 size recording material has reached 60 sheets / minute, whereas the copying speed for double-sided copying ranges from 15 sheets / minute to 20 sheets / minute. It was a significant drop in minutes. Also, when copying on both sides, the recording material needs to be reversed while being circulated in the apparatus and fed again, so a mechanism (reversing unit) for reversing the recording material is required, and the apparatus becomes complicated and large. There is a problem, and there is also a problem that paper jam easily occurs in the reverse path.
[0018]
With the recent progress in OA and the rapid spread of personal computers, color image forming apparatuses typified by color copying machines and color printers have become widespread and are used on a daily basis. The demand for higher speeds is also imposed on color copiers and printers, as is the case with printing speeds on monochrome copiers.
[0019]
By the way, there are two types of color image recording apparatuses, a single drum type and a multi-stage drum type (tandem type). In the single drum type, for example, as shown in FIG. 11, Y (yellow: yellow) toner, M (magenta: red dye) toner, and C (cyan) which are three primary colors of subtractive color mixing for one page of a recording material. : A greenish blue) toner for each color toner, and Bk (black: black) toner applied for printing characters and the like, a total of four types of toner, charger 2, exposure device 3, and developing devices 4a to 4d. Are used for multiple transcription.
[0020]
First, the semiconductive drum 5 is attached to the recording material conveyed in the arrow A direction and rotated in the arrow B direction. On the other hand, while the photosensitive drum 1 rotates in the direction of the arrow C, for example, first, an M toner image is formed using the developing device 4a. When the recording material and the M toner image reach the transfer portion, the M toner image is transferred to the recording material by the discharge current of the corona discharger 6.
[0021]
Next, the semiconductive drum 5 again rotates once with the recording material attached, and in response to this, the photosensitive drum 1 forms a C toner image using the developing device 4b. The image is transferred by the corona discharger 6 and superimposed on the M toner image. Similarly, the Y toner image and the Bk toner image are also overlapped to form one toner image.
[0022]
In this way, when the transfer (coating) of the four color toner images is completed, the winding of the recording material is released, and the recording material is conveyed to the fixing device 8 by the conveying belt 7 and is overlaid 4 The color toner image is heat-fixed on the paper surface. Therefore, since the printing (image forming) process is performed for each toner, the printing process is repeated four times for one page of the recording material. Therefore, the printing process requires a long time. It is difficult to deal with the speeding up.
[0023]
On the other hand, the tandem color image forming apparatus includes, for example, as shown in FIGS. 12 and 13, one that sequentially transfers four types of toner onto a recording material in one step (sequential transfer method), As shown in FIG. 14, there is a method (multiple transfer method) in which multiple transfer is sequentially performed on the intermediate transfer member 10 and then retransferred to a recording material at once.
[0024]
When performing double-sided printing with a tandem color image forming apparatus, as shown in FIG. 13, the recording material 5 on which the single-sided image has been formed is reversed on the discharge unit 13 side in order to form a double-sided image on the recording material 5. A reversing unit having a reversing conveyance unit 14 for conveying the sheet is provided.
[0025]
12 to 14, 1 is an image forming station, 2 is a recording material conveying belt, 3 is a fixing device, 4 is a paper feed tray, 5 is a recording material, and 6 is an image forming unit (Y, M, C). , K) is a photosensitive drum, 7 (Y, M, C, K) is a transfer roller, 10 is an intermediate transfer member, 11 is a reversing (intermediate) tray, 12 is a transport path, 13 is a paper discharge unit, and 14 is reverse. A transport unit, 15 is a batch transfer unit, and 16 is a cleaning device.
[0026]
Each of the transfer systems shown in FIGS. 12 to 14 has a processing speed almost four times that of the single drum type shown in FIG. In recent years, combined with the fact that the internal devices have been reduced in size and assembled into a unit (unitized) and have become relatively inexpensive, various color image recording apparatuses having a tandem configuration have been put into practical use. ing.
[0027]
However, in such a tandem type color image forming apparatus, as shown in FIG. 13, in the case of double-sided printing, after passing through the fixing device 3, the recording material 5 is switched back and reversely conveyed. It passes through the section 14 and is accommodated in the reverse (intermediate) tray 11. Then, the paper is fed again to the reverse conveyance path 12. As described above, a large reversing unit for reversing the recording material 5 is necessary. For this reason, an increase in the size and complexity of the apparatus accompanying an increase in the number of parts is inevitable.
[0028]
Therefore, image forming apparatuses that can perform double-sided image formation without using such a reversing unit are disclosed in, for example, Japanese Patent Laid-Open Nos. 8-160703, 1-444457, and 10-97144. It is proposed in the gazette.
[0029]
In the image forming apparatus described in JP-A-8-160703, a first intermediate transfer member (intermediate transfer belt) that transfers a toner image on a photosensitive member is configured so as not to require a reversing unit for reversing the recording material. And a second intermediate transfer member (which also serves as an intermediate transfer belt and a recording material conveyance belt) for transferring the toner image on the first intermediate transfer member, and the toner images on the respective intermediate transfer members, to the recording material And a secondary transfer unit that performs the transfer.
[0030]
However, when the intermediate transfer member (intermediate transfer belt) is provided in two stages as described above, the image transferred to the back surface of the recording material is finally recorded after passing the intermediate transfer member twice. Since it will be transferred to the material, there is a concern that the image quality will deteriorate due to a decrease in transferability when compared with the image transferred to the surface, and the difference between the images formed on both the front and back sides will be noticeable. There is.
[0031]
In JP-A-1-44457 and JP-A-10-97144, a toner image of an image to be printed on one side of a recording material is used as a transfer belt in a configuration that does not require a reversing unit for reversing the recording material. Once transferred onto the photosensitive drum, a toner image of an image to be printed on the other side of the recording material is formed on the photosensitive drum, and the recording material is conveyed between the transfer belt and the photosensitive drum. A configuration for simultaneously transferring images is disclosed.
[0032]
In this case, the unfixed toner images on both sides of the recording material are conveyed to the fixing device while being unfixed, and the toner images on the front and back surfaces of the recording material are fixed simultaneously. Therefore, the toner adhering to both the front and back sides of the recording material remains unfixed in the conveyance process from the transfer to the fixing device, so that the toner is extremely unstable, and a slight disturbance element intervenes. There is a risk that unfixed toner may be modulated. Therefore, it is not easy to stably form a high-quality image, particularly in the case of multicolor image formation in which the subtle reproducibility of each color greatly affects the image quality.
[0033]
The present invention has been made in view of such circumstances, and can provide high-quality multicolor images at high speed and stably on the front, back, or both sides of the recording material without providing a bulky intermediate tray or the like for inverting the recording material. It is an object of the present invention to provide a multicolor image forming apparatus and a multicolor image forming method that can be formed.
[0034]
[Means for Solving the Problems]
In the present invention, means for solving the above-described problems are configured as follows.
[0035]
  (1) A multicolor image in which a plurality of image forming stations including a photosensitive member and a developing device are arranged along the recording material conveyance direction so that a single color or a multicolor image can be formed on one or both sides of the recording material. In the forming device,
  When forming an image on both sides of a recording material, an image that becomes a normal or mirror image of the original image when forming an image on one side of the recording material and when forming an image on the other side of the recording material An image processing unit for selecting and outputting signals;
  An image forming unit that receives the image signal output from the image processing unit and forms images by applying different transfer methods to both sides of the recording material, and
  A recording material conveying belt capable of conveying the recording material over each image forming station and capable of intermediate transfer of the toner color image formed at each image forming station;
  Secondary transfer means for performing secondary transfer of the toner color image intermediately transferred onto the recording material conveying belt to the recording material;
  A return conveyance path configured to return the recording material from the downstream side of the fixing device in the recording material conveyance path to the upstream side of the image forming station, and a registration roller provided in the path;
With
  The return conveyance path includes a lower traveling side of the recording material conveyance belt and a reversing path extending from the downstream side of the fixing device in the recording material conveyance path to be connected to the lower traveling side of the recording material conveyance belt. And
  A switching gate for controlling the conveyance timing of the recording material is provided at the downstream end of the reversing path.It is characterized by that.
[0036]
In this configuration, sequential transfer (multiple transfer) is applied for each toner color in the case of printing on the recording material surface in single-sided printing or double-sided printing, and batch transfer in the case of printing on the back side of the recording material in double-sided printing ( By applying multi-color images by applying batch transfer a plurality of times, the arrangement of the conventional recording material reversing means (reversing conveyance path provided with an intermediate tray) is made unnecessary. A multicolor image can be freely formed on the front surface, back surface, or both surfaces of the recording material. Thereby, since the time required for inversion can be shortened, the printing speed can be increased and stable image formation can be achieved. Further, the occurrence of jams is reduced, and the number of parts can be reduced, whereby the apparatus can be reduced in size, simplified, and reduced in cost.
[0037]
  (2)RecordWhen an image is formed on one side of a recording material, the toner color image formed at each image forming station is primarily transferred to the recording material conveyance belt, and the toner color image on the recording material conveyance belt is transferred to the recording material conveyance belt. The secondary transfer means forms a multicolor image by batch secondary transfer to a recording material,
  When performing image formation on the other surface of the recording material, the toner color image formed on one surface of the recording material is fixed, and then the toner color image formed at each image forming station is recorded on the recording material. A multi-color image is formed by sequentially performing primary transfer sequentially to the other surface of the recording material conveyed by the material conveying belt.
[0038]
In this configuration, when printing on the surface of the recording material in single-sided printing or double-sided printing, primary transfer is performed sequentially (multiple transfer). By forming an image, a high-quality multicolor image can be freely formed on the front surface, back surface, or both surfaces of the recording material without using a conventional bulky recording material reversing unit. As a result, the time required for inversion can be shortened, the printing speed can be increased, the occurrence of jamming can be reduced, and the apparatus can be miniaturized, simplified, and cost reduced.
[0039]
In addition, after fixing the toner image on the back surface (one surface) of the recording material that has been batch-transferred, the surface printing is performed by sequential primary transfer, so the toner color image is held and stabilized during transport of the recording material. The image quality can be improved as compared with the case where the sheet is conveyed to the fixing unit with both sides unfixed, and the image quality can be improved stably.
[0040]
(3) Secondary transfer means for performing batch secondary transfer to one surface of the recording material is upstream of all image forming stations arranged in parallel along the recording material conveyance belt. In addition, the recording material conveyance belt is disposed outside the belt loop formed by the recording material conveyance belt, and the recording material conveyance belt and all the image forming stations are disposed so as to be relatively close to each other. And
[0041]
In this configuration, since the secondary transfer means for performing batch transfer is arranged upstream of all the image forming stations in the recording material conveyance direction, the recording material conveyance belt and the image formation station are relatively arranged. By separating them, the toner image on the back surface of the recording material once transferred can be prevented from being disturbed by being sandwiched between the recording material conveyance belt and the photosensitive member of each image forming station.
[0042]
(4) Secondary transfer means for performing batch secondary transfer to one surface of the recording material is downstream of all image forming stations arranged in parallel along the recording material conveyance belt. In addition, the recording material conveyance belt is disposed at a position outside a belt loop formed by the recording material conveyance belt.
[0043]
In this configuration, secondary transfer means for performing batch transfer is arranged downstream of all image forming stations in the recording material conveyance direction, that is, immediately before the fixing device, and the toner image is transferred to the back surface of the recording material. By doing so, the toner image on the back surface of the recording material once transferred can be prevented from being disturbed during conveyance by the recording material conveyance belt.
[0044]
  (5)A multicolor image forming method applied to the multicolor image forming apparatus according to (1),
  When forming an image on one side of the recording material and when forming an image on the other side of the recording materialDepending on whether the image is a normal image or mirror image of the original imageIt is characterized by that.
[0045]
In this method, the electrostatic latent image writing direction on the photoconductor is made different between the original image when the image is formed on one surface of the recording material or the surface of the recording material and when the image is formed on the back surface of the recording material. Image or mirror image), it is possible to freely form a high-quality multicolor image on the front, back or both sides of the transfer paper without using a bulky recording material reversing unit as in the past. The time required for reversal can be shortened, the printing speed can be increased, and stable image formation is possible. Also, the occurrence of jam is reduced. In addition, stable transferability can be obtained on both sides of the recording material without providing a polarity changing means for changing the polarity of the toner image on the recording material conveying belt.
[0046]
(6) When an image is formed on one surface of the recording material, a toner color image obtained by forming an electrostatic latent image that is a mirror image of the original image on the photosensitive member of each image forming station is recorded. When a multi-color image is formed by sequential primary transfer onto a recording material conveyed by a material conveying belt, and an image is formed on the other surface of the recording material, the original image is transferred to the photoreceptor of each image forming station. On the other hand, a toner color image obtained by forming an electrostatic latent image to be a positive image is primarily transferred onto a recording material conveyance belt, and then a secondary transfer is collectively performed on the recording material to form a multicolor image. Features.
[0047]
In this method, when an image is formed on one surface of a recording material, a multicolor image is sequentially formed by primary transfer, and when an image is formed on the other surface of the recording material, two images are collectively collected. Since a multicolor image is formed by the next transfer, a high-quality multicolor image can be freely formed on the front surface, back surface, or both surfaces of the transfer paper without using a recording material reversing unit.
[0048]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, a multicolor image forming apparatus and a multicolor image forming method according to an embodiment of the present invention will be described in detail.
[0049]
(1) Configuration of multicolor image forming apparatus
A tandem multicolor image forming apparatus capable of single-sided printing and double-sided printing is configured, for example, as shown in FIGS. This multicolor image forming apparatus includes a color image forming station (image forming station) 1, an image transfer unit 2, a fixing device 3, a paper cassette 4, a paper discharge unit 13, a paper delivery unit 14, and the like for forming an image. The transfer paper (recording material, sheet-like medium) 5 is housed in a paper cassette 4 and is fed out by the paper feed section 14 and carried into the color image forming station 1 to form a color image during image formation. Thereafter, the paper is discharged from the paper discharge unit 13 to the outside of the apparatus.
[0050]
The color image forming station 1 and the image transfer unit 2 constitute an image forming unit referred to in the present invention. Further, when image formation is performed on both sides of the transfer paper 5, the original image or the mirror image of the original image is formed when the image is formed on one side of the transfer paper 5 and when the image is formed on the other side. An image processing unit (not shown) that selects and outputs an image signal is provided.
[0051]
Each color image forming station 1 is provided with image forming units (toner image forming means) 6Y, 6M, 6C, 6K, and below each image forming unit 6Y, 6M, 6C, 6K, an image transfer unit 2 is provided. The recording material conveying belt (transfer belt conveying belt such as an electrostatic adsorption belt) 2a constituting the recording material is provided. The recording material conveying belt 2a is made of a flexible endless resin material and functions as an intermediate transfer member. In addition, it has a function of conveying the transfer paper 5. A fixing device 3 for fixing an image on the transfer paper 5 is disposed on the downstream side of the recording material conveyance belt 2a.
[0052]
The image forming units 6Y, 6M, 6C, and 6K respectively develop developing devices 61 (Y to K) to develop toner images of yellow (Y), magenta (M), cyan (C), and black (K). ), A charger 62 (Y to K), an exposure device 63 (Y to K), and a photosensitive drum 64 (Y to K). Note that an image signal from the image processing unit is input to the exposure device 63 (Y to K).
[0053]
Further, transfer rollers 7Y, 7M, 7C, and 7K as transfer means (primary transfer means) are disposed along the transfer paper conveyance belt 2a so as to be paired with the image forming units 6Y, 6M, 6C, and 6K. Has been. The transfer rollers 7Y, 7M, 7C, and 7K attract and transfer the toner images formed by the image forming units 6Y, 6M, 6C, and 6K to the transfer paper 5. The image forming units 6Y, 6M, 6C, and 6K have substantially the same configuration except that different color developers are used, and are operated.
[0054]
Below the image forming units 6Y, 6M, 6C, and 6K, a transfer paper transport belt 2a is disposed. The transfer paper transport belt 2a is wound around a driving roller and a driven roller and stretched. The image forming units 6Y, 6M, 6C, and 6K travel endlessly while being in rolling contact with the photosensitive drums 64 (Y to K). The transfer rollers 7Y, 7M, 7C, and the transfer rollers 7Y, 7C, 7C, 7C, 7C, 7C, 7C, 7C, 7C, and 7C are disposed inside the belt loop of the transfer paper transport belt 2a. 7K is provided.
[0055]
A bias transfer roller 31 that functions as a secondary transfer unit is disposed on the upstream side of the transfer paper conveyance belt 2a, and a registration roller 24 is disposed on the immediately upstream side thereof. The transfer paper transport belt 2a is capable of intermediate transfer of toner color images formed at the color image forming station 1 (functions as an intermediate transfer member), and adsorbs the transfer paper 5 onto the belt to fix the fixing device 3. Also plays the role of transporting to. The fixing device 3 fixes the toner image on the transfer paper 5 to the transfer paper 5 by heat, pressure, or the like.
[0056]
As described above, in the tandem multicolor image forming apparatus, images are formed on the transfer sheet 5 by sequentially superimposing different colors on the transfer sheet 5 in each of the image forming units 6Y, 6M, 6C, and 6K. A color image is formed. In addition, the image forming process is speeded up by forming an image with a plurality of image forming units 6Y, 6M, 6C, and 6K.
[0057]
Further, a switching gate 21 is provided between the fixing device 3 and the paper discharge unit 13, and an inversion path 15 (U-turn conveyance path) that reaches the lower conveyance path 12 from the position of the switching gate 21 is formed. ing. The reversing path 15 is not provided with a bulky reversing unit such as a conventional intermediate tray, and the apparatus can be made compact by arranging it so as to loop below the fixing device 3. It becomes. A reverse path registration roller 22 is provided at the end of the reverse path 15, and a pre-registration sensor (not shown) is provided in the vicinity of the reverse path registration roller 22.
[0058]
When such a switching gate 21 is provided, as shown in FIGS. 6 and 7, the reversing path 15 is connected to the lower running side (lower belt loop) of the transfer paper transport belt 2a. For example, the lower conveyance path 12 in the case of FIGS. 1 and 2 can be omitted. As a result, the number of parts can be further reduced, further downsizing can be realized, the time required for the conventional reversal can be shortened, and the printing speed can be increased. Because it is simplified, the occurrence of jam is reduced. In the example shown in FIGS. 6 and 7, a switching gate 25 is also provided just before the lower running side of the transfer paper transport belt 2a, so that the opening / closing operation is controlled in combination with the reverse path registration roller 22. It has become.
[0059]
In the configuration as described above, the switching gate 21 closes the sheet conveyance path to the sheet discharge unit 13 so that the toner image is transferred to one side and the image is also formed on the other side of the fixed transfer sheet 5. In the case where the transfer sheet 5 has been transferred (see FIGS. 2 and 7), the transfer sheet 5 is guided to the reverse path 15 and is conveyed to the reverse path registration roller 22 by the conveying roller 23 provided in the reverse path 15. At this time, the pre-registration sensor detects the leading edge of the transfer paper 5, and after a predetermined time, the reverse path registration roller 22 stops rotating and waits in a state where the leading edge of the transfer paper 5 is regulated by the reverse path registration roller 22. In this standby state, when the image formation on the other side of the transfer paper 5 can be started immediately, the reverse path registration roller 22 is rotated without substantially waiting.
[0060]
As described above, when the conveyance of the transfer sheet 5 is restricted by the reverse path registration roller 22 (standby state), the fixing apparatus 3 to the reverse path registration roller 22 so that the rear end of the transfer sheet 5 does not reach the fixing apparatus 3. Needs to be set to a length equal to or larger than the maximum size of the recording sheet that can be combined on both sides. If the maximum size capable of double-sided printing on the transfer sheet 5 is A4 size, the length from the fixing device 3 to the reverse path registration roller 22 is required to be longer than that.
[0061]
When performing double-sided printing (printing on the other side of the transfer paper 5), the transfer paper 5 that has been reversed by the reversing path 15 through the fixing device 3 travels below the transfer paper transport belt 2a. In order to promote electrostatic attraction to the side, a negative polarity bias is applied to a pulley located downstream of the belt loop. When the transfer sheet 5 is conveyed along the lower running side of the transfer sheet conveying belt 2 and reaches the pulley located upstream of the belt loop, the other side while the transfer sheet 5 is still conveyed along the upper running side. Since it is necessary to stably hold the transfer sheet 5 on the transfer sheet transport belt 2a for the sequential transfer to the surface, a negative polarity bias is applied to the pulley located on the upstream side of the belt loop. The bias is applied by a bias transfer roller 31 as will be described later.
[0062]
Table 1 shows the relationship between the charge removal / charging of the transfer paper transport belt 2a and the transfer paper transport direction.
[0063]
[Table 1]

[0064]
1-1) Transfer paper conveyance belt (intermediate transfer member, recording material conveyance belt)
The transfer paper transport belt 2a has an electric resistance of 1 × 10.^TenA driving roller formed of polycarbonate in which carbon is dispersed as a semiconductive material of about Ω · cm, and disposed on both the left and right sides in the copier body below the photosensitive drum 64 (Y to K); It is wound around a driven roller and stretched. In addition, a sheet of dielectric resin such as a polyethylene terephthalate resin sheet (PET sheet), a polyvinylidene fluoride resin sheet, or a polyurethane resin sheet may be used.
[0065]
Sheets made of these materials are overlapped with each other and joined to form an endless shape, or a (seamless) belt shape having no seam is used as the transfer paper conveyance belt 2a. For example, as shown in FIGS. 3 and 4, the transfer paper transport belt 2a is pivotally supported on the upstream side with respect to the apparatus main body, and the downstream side thereof is tiltable downward. Can be configured.
[0066]
With such a configuration, the bias transfer provided on the upstream side of the transfer paper transport belt 2a is performed by sequentially performing primary transfer on the transfer paper transport belt 2a and then tilting the downstream side of the transfer paper transport belt 2a downward. The secondary transfer is performed on the back surface of the transfer paper 5 fed from the paper feed tray 4 by the roller 31 (in the case of FIG. 3) or the bias transfer roller 31 (in the case of FIG. 4) provided on the downstream side of the transfer paper transport belt 2a. After performing this operation, the paper can be discharged to the paper discharge unit 13. In the case of FIG. 6 as well, the transfer paper transport belt 2a can be similarly tilted downward, but its illustration and description are omitted.
[0067]
The peripheral length of the transfer paper transport belt 2a is set longer than A3 which is the maximum paper size that can be used in the copying machine of the present embodiment. The transfer paper transport belt 2a is provided with a white mark (not shown) for detecting its position, and the position of the transfer paper transport belt 2a can always be detected by an optical position detection sensor (not shown). ing.
[0068]
1-2) Transfer roller
In the image forming station 1 of each color, at the transfer position where the photosensitive drum 64 (Y to K) and the transfer paper transport belt 2a are in contact, the reverse side of the normal charging polarity of the toner is placed inside the belt loop of the transfer paper transport belt 2a. A transfer roller 7 (Y to K) to which a positive transfer bias voltage is applied is provided.
[0069]
The transfer roller 7 (Y to K) has an electric resistance of 1 × 10⁶The transfer paper transport belt 2a is formed of urethane foam rubber in which carbon of Ω · cm or less is dispersed, and is pressed with a predetermined pressure from the back surface side of the transfer paper transport belt 2a toward the photosensitive drum 64 (Y to K). In the figure, it is driven to rotate in the direction of the arrow.
[0070]
1-3) Fixing device
A fixing device 3 for fixing the toner image transferred onto the transfer paper 5 is provided on the downstream side of the transfer paper transport belt 2a. The fixing device 3 has a pair of rollers in contact with each other. Then, the transfer paper 5 is heated to a predetermined temperature to melt and fix the toner image held on the transfer paper 5.
[0071]
On the downstream side of the fixing device 3, a switching gate 21 that guides the transfer paper 5 to the transfer paper transport belt 2a by making a U-turn downward when performing double-sided printing or backside printing, and the transfer paper 5 are provided. A paper discharge unit 13 for discharging to the outside is provided.
[0072]
The switching gate 21 switches between a path from the fixing device 3 to the paper discharge unit 13 and a reverse path 15 from the fixing device 3 to the lower conveyance path 12 or the lower traveling side of the transfer paper conveyance belt 2a according to the print mode. 1 and 6, the path to the paper discharge unit 13 is opened, and in the states of FIGS. 2 and 7, the path to the reversing path 15 is opened. The paper discharge unit 13 includes a pair of paper discharge rollers, and discharges the transfer paper 5 to a paper discharge tray (not shown) provided outside the copying machine main body.
[0073]
(2) Image data input / output sequence
Next, the input / output order of image data corresponding to each print mode will be described.
[0074]
2-1) Single-sided / upward delivery (1)
When reading the original image sequentially from the first page of the original bundle set in the original processing section and outputting the image, all the data from the data of the last page of the original bundle in the reverse order to the input are transferred. Output sequentially to the surface by sequential transfer.
[0075]
(For single-sided originals)
During image input (ascending order): 1 → 2 → 3 → 4 → 5
During image output (descending order): 5 → 4 → 3 → 2 → 1 (sequential transfer)
(For double-sided originals)
During image input (ascending order): 1A → 1B → 2A → 2B → 3A → 3B → 4A → 4B → 5A → 5B
During image output (descending order): 5B → 5A → 4B → 4A → 3B → 3A → 2B → 2A → 1B → 1A
2-2) Single-sided / upward delivery (2)
When reading the original image sequentially from the last page of the original bundle set in the original processing section and outputting the image, the A side of the transfer sheet for all data from the last page data of the original bundle in the same order as the input Output sequentially with sequential transfer to.
[0076]
(For single-sided originals)
During image input (descending order): 5 → 4 → 3 → 2 → 1
During image output (descending order): 5 → 4 → 3 → 2 → 1 (sequential transfer)
(For double-sided originals)
When inputting images (descending order): 5B → 5A → 4B → 4A → 3B → 3A → 2B → 2A → 1B → 1A
During image output (descending order): 5B → 5A → 4B → 4A → 3B → 3A → 2B → 2A → 1B → 1A
2-3) Single-sided / downward delivery (1)
When reading the original image sequentially from the first page of the original bundle set in the original processing section and outputting the image, all the data from the first page of the original bundle is transferred in the same order as the input. Output sequentially by batch transfer to B side.
[0077]
(For single-sided originals)
During image input (ascending order): 1 → 2 → 3 → 4 → 5
During image output (ascending order): 1 → 2 → 3 → 4 → 5 (all transferred to B side at once)
(For double-sided originals)
During image input (ascending order): 1A → 1B → 2A → 2B → 3A → 3B → 4A → 4B → 5A → 5B
During image output (ascending order): 1A → 1B → 2A → 2B → 3A → 3B → 4A → 4B → 5A → 5B
2-4) Single-sided / downward delivery (2)
When reading the original image sequentially from the last page of the original bundle set in the original processing section and outputting the image, all the data from the first page data of the original bundle in the reverse order to the input are transferred B Output sequentially by batch transfer to the surface.
[0078]
(For single-sided originals)
During image input (descending order): 5 → 4 → 3 → 2 → 1
During image output (ascending order): 1 → 2 → 3 → 4 → 5 (all transferred to B side at once)
(For double-sided originals)
When inputting images (descending order): 5B → 5A → 4B → 4A → 3B → 3A → 2B → 2A → 1B → 1A
During image output (ascending order): 1A → 1B → 2A → 2B → 3A → 3B → 4A → 4B → 5A → 5B
2-5) For double-sided / upward delivery (1)
When reading the original image sequentially from the first page of the original bundle set in the original processing unit and outputting the image, batch transfer and sequential transfer are repeated from the data of the last page of the original bundle, and output sequentially in descending order. go. The surface of the transfer paper on which an image is first output varies depending on the number of pages constituting the original bundle.
[0079]
(When the manuscript is an odd page)
During image input (ascending order): 1 → 2 → 3 → 4 → 5
During image output (descending order): 5 (sequentially to side A) → 4 (batch to side B) → 3 → 2 → 1
(When the original is an even page)
During image input (ascending order): 1 → 2 → 3 → 4
At the time of image output (descending order): 4 (collectively to side B) → 3 (sequentially to side A) → 2 → 1
2-6) Duplex / Upward delivery (2)
When reading the original image sequentially from the last page of the original bundle set in the original processing unit and outputting the image, batch transfer and sequential transfer are repeated from the last page data of the original bundle, and output sequentially in descending order. go. The surface of the transfer paper on which an image is first output varies depending on the number of pages constituting the original bundle.
[0080]
(When the manuscript is an odd page)
During image input (descending order): 5 → 4 → 3 → 2 → 1
During image output (descending order): 5 (sequentially to side A) → 4 (batch to side B) → 3 → 2 → 1
(When the original is an even page)
During image input (descending order): 4 → 3 → 2 → 1
At the time of image output (descending order): 4 (collectively to side B) → 3 (sequentially to side A) → 2 → 1
2-7) Duplex / Downward delivery (1)
When reading the original image sequentially from the first page of the original bundle set in the original processing section and outputting the image, the sequential transfer is repeated after the batch transfer from the first page data of the original bundle, in ascending order. Output sequentially. The image output always starts from batch transfer onto the B side of the transfer paper.
[0081]
(Original input order and image output order)
During image input (ascending order): 1 → 2 → 3 → 4 → 5
During image output (ascending order): 1 (Batch to B side) → 2 (Sequential to A side) → 3 → 4 → 5
2-8) For double-sided / downward delivery (2)
When reading the original image sequentially from the last page of the original bundle set in the original processing unit and outputting the image, sequential transfer is performed after batch transfer from the first page data of the original bundle in ascending order. Output sequentially. The image output always starts from batch transfer onto the B side of the transfer paper.
[0082]
(Original input order and image output order)
During image input (descending order): 5 → 4 → 3 → 2 → 1
During image output (ascending order): 1 (Batch to B side) → 2 (Sequential to A side) → 3 → 4 → 5
The input / output order of the above image data is summarized in a list as shown in Table 2.
[0083]
[Table 2]

[0084]
(3) Transfer method
3-1) When the transfer paper A side is discharged upward in single-sided printing (see FIGS. 1 and 6)
On each photosensitive drum 64 (Y to K) of the image forming station 1, a toner image of a mirror image is formed with respect to the original image, and the transfer paper 5 sent from the registration roller 24 at a timing is When the sheet is sequentially fed to the transfer position between the photosensitive drum 64 (Y to K) and the transfer sheet conveying belt 21a, the transfer roller 7 (Y to K) to which a predetermined transfer voltage is applied onto the transfer sheet 5 is transferred. As a result, the toner image is sequentially multiple-transferred (sequentially transferred) to form a normal four-color full-color toner image on the original image.
[0085]
When the transfer paper 5 passes through the fixing device 3, the toner image of the normal image is fixed as a final image and full color is developed. In this image forming (printing on the transfer paper A surface) mode, the transfer paper transport belt 2 a is used as a transfer transport means for transporting the transfer paper 5 to the fixing device 3.
[0086]
3-2) When the transfer paper B side is discharged downward in single-sided printing (see FIGS. 1 and 6)
A normal toner image is formed on each photosensitive drum 64 (Y to K) of the image forming station 1 and transferred by a transfer roller 7 (Y to K) to which a predetermined transfer voltage is applied. Primary transfer (sequential transfer) is sequentially performed on the sheet conveying belt 2a. The toner image on the transfer paper transport belt 2a is a full-color toner image that is a mirror image of the original image.
[0087]
Then, a four-color full-color toner image, which is a mirror image of the original image on the transfer paper transport belt 2a, is fed to the B surface of the transfer paper 5 fed in accordance with the rotational operation and timing of the transfer paper transport belt 2a. The adsorption charging roller 31 is used as a bias transfer roller, and a predetermined secondary voltage is applied to perform batch secondary transfer. Therefore, a normal four-color full-color toner image is formed with respect to the original image on the B side of the transfer paper.
[0088]
When the suction charging roller 31 is not used as a bias transfer roller, batch secondary transfer may be performed by the transfer roller 7 (Y to K) of any of the image forming stations 1. When the transfer paper 5 passes through the fixing device 3, the toner image of the normal image is fixed as a final image and full color is developed. In this image formation (printing on the transfer paper B surface) mode, the transfer paper transport belt 2a is used as an intermediate transfer member.
[0089]
3-3) In the case of double-sided printing (see FIGS. 1, 2, 6 and 7)
With respect to the transfer operation when images are formed on both surfaces of the transfer paper 5, images can be formed on both the front and back surfaces by controlling the operations of 3-1) and 3-2) in combination. That is, first, images are sequentially formed on the surface of the transfer paper A, passed through the fixing device 3, then the transfer paper 5 is reversed and passed through the lower conveyance path 12 or the lower running side, and then the bias transfer roller 31. Thus, batch secondary transfer may be performed on the transfer paper B side.
[0090]
(4) Bias transfer roller (see FIGS. 5A and 5B)
The bias transfer roller 31 collects the toner image formed on the transfer paper conveyance belt 2a as an intermediate transfer member on the transfer paper 5 in a batch operation when printing on the back surface (second surface) in double-sided printing or single-sided printing with face-down discharge. Although it is a roller member for the next transfer, it is originally provided as an adsorption charging roller, and acts on the transfer conveying belt 2a from above the transfer sheet 5 when feeding the transfer sheet 5 to the transfer conveying belt 2a. The transfer / conveying belt 2a is charged to a polarity opposite to that of the transfer of the toner image, and the transfer paper is electrostatically adsorbed onto the transfer / conveying belt 2a.
[0091]
Incidentally, as a result of applying a positive polarity current from the adsorption charging roller 31 to the transfer paper 5, the transfer paper 5 is charged with a positive charge. On the other hand, a negative polarity dielectric charge is generated on the transfer conveyance belt 2a. The transfer paper 5 is electrostatically attracted to the transfer conveyance belt 2a and is stably held. Therefore, the transfer / conveying belt 2a is charged with a polarity opposite to the positive polarity when the toner image is transferred. The bias transfer roller 31 is not particularly limited to a roller member, and a brush member, a sheet member, or a charger may be used.
[0092]
4-1) Arranged upstream of the image forming station (see FIG. 3)
When the bias transfer roller 31 is disposed on the upstream side of the K (black) image forming station 1 along the transfer sheet conveyance belt 2a, the leading end of the image moves to a region facing the bias transfer roller 31. The transfer paper 5 is supplied from the paper feed tray 4 so as to coincide with the incoming timing, and the secondary transfer to the transfer paper 5 is performed by batch transfer. If the bias transfer roller 31 is disposed outside the belt loop formed by the transfer / conveyance belt 2a, the degree of freedom in layout within the belt loop is improved, and it becomes easy to deal with unitization of the transfer / conveyance belt 2a.
[0093]
4-2) Arranged downstream of the image forming station (see FIG. 4)
Further, the bias transfer roller 31 for performing batch secondary transfer of the back surface image may be arranged on the downstream side of the image forming unit 6Y on the most downstream side along the transfer paper transport belt 2a. Also in this case, if the bias transfer roller 31 is disposed outside the belt loop formed by the transfer / conveyance belt 2a, the degree of freedom of layout in the belt loop can be improved, and the transfer / conveyance belt 2a can be unitized. It becomes easy to deal with.
[0094]
4-3) Improving transfer efficiency in batch secondary transfer
In order to increase the transfer efficiency when performing batch secondary transfer of the toner image held on the transfer conveyance belt 2a to the back surface of the transfer paper 5, prior to batch transfer, an electric field (minus minus) at the time of transfer is applied. It is effective to charge the transfer paper conveyance belt 2a by applying a polarity).
[0095]
As the charger, as shown in FIG. 8, in order to separate the transfer paper 5 from the transfer conveyance belt 2a at the downstream portion in the conveyance direction of the transfer conveyance belt 2a, the image forming unit 6Y on the most downstream side of the image forming station 1 is used. The separation charger 32 disposed on the downstream side of the transfer charger, or as shown in FIG. 9, the transfer conveyance belt 2a of the separation charger 32 described above is used to remove the charge of the transfer conveyance belt 2a after the transfer paper 5 is separated. A neutralizing charger (belt neutralizer) 33 provided on the opposite side of the sheet can be used.
[0096]
Then, the transfer sheet 5 after the secondary transfer is fixed with an image by the fixing device 3, and when the single-sided printing of the face-down discharge is designated, the transfer sheet 5 is discharged to the sheet discharge unit 13 outside the apparatus. When printing is designated, the U-turn is turned downward to perform image formation (sequential transfer) on the other surface of the transfer paper 5 and guided to the transfer paper transport belt 2a.
[0097]
That is, since there is no reversing operation of the transfer sheet 5, one surface of the transfer sheet 5 on which the multicolor image has been fixed by batch secondary transfer is directed inward along the belt loop formed by the transfer sheet transport belt 2a. Then, the other surface of the transfer paper 5 that is successively transferred is directed to the outside along the belt loop.
[0098]
The following table shows the orientation of the latent image to be written, the transfer method (means / method), and the presence / absence of relative separation between the transfer conveyance belt 2a and the image forming station 1 in single-sided printing and double-sided printing as described above. 3 shows.
[0099]
[Table 3]

[0100]
In the present invention, the multicolor image forming apparatus is not limited to the configuration shown in the embodiment of FIG. 1 or the like, and at least an image forming station including a photoconductor and a developing device is provided along the recording material conveyance direction. The present invention can be applied to any multi-color image forming apparatus that can form a single color or a multi-color image on one side or both sides of a recording material. be able to.
[0101]
【The invention's effect】
As is clear from the above description, the present invention has the following effects.
[0102]
(1) For single-sided or double-sided printing on the recording material surface, sequential transfer (multiple transfer) is applied for each toner color, and for double-sided printing on the backside of the recording material, batch transfer (batch transfer) Can be performed a plurality of times) to form a multi-color image, so that the arrangement of the bulky recording material reversing means (reversing conveyance path having an intermediate tray) as in the prior art is not required, A color image can be freely formed on the front surface, back surface, or both surfaces of the recording material. Accordingly, since the time required for reversal can be shortened, the printing speed can be increased and stable image formation can be achieved. Further, the occurrence of jams is reduced, and the number of parts can be reduced, whereby the apparatus can be reduced in size, simplified, and reduced in cost.
[0103]
(2) For single-sided printing or double-sided printing on the surface of the recording material, primary transfer (multiple transfer) is performed sequentially. Since color images are formed, high-quality multicolor images can be freely formed on the front, back, or both sides of recording materials without using a bulky recording material reversing unit as in the past. The time required can be shortened, the printing speed can be increased, the occurrence of jams can be reduced, and the number of parts can be reduced to reduce the size, simplification, and cost of the apparatus.
[0104]
In addition, after fixing the toner image on the back surface (one surface) of the recording material that has been batch-transferred, the surface printing is performed by sequential primary transfer, so the toner color image is held and stabilized during transport of the recording material. The image quality can be improved as compared with the case where the sheet is conveyed to the fixing unit with both sides unfixed, and the image quality can be improved stably.
[0105]
(3) Since the secondary transfer means for performing batch transfer is arranged upstream of all image forming stations in the recording material conveyance direction, the recording material conveyance belt and the image forming station are relatively separated from each other. By doing so, it is possible to prevent the toner image on the back surface of the recording material once transferred from being disturbed by being sandwiched between the recording material conveyance belt and the photosensitive member of each image forming station.
[0106]
(4) Since the secondary transfer means for performing batch transfer is arranged downstream of all image forming stations in the recording material conveyance direction, that is, immediately before the fixing device, the toner image is transferred to the back surface of the recording material. The toner image on the back surface of the recording material once transferred can be prevented from being disturbed during conveyance by the recording material conveyance belt.
[0107]
(5) Since the electrostatic latent image writing direction on the photoconductor is made different between the original image and the image formation on the recording material one side or the recording material surface and the image formation on the recording material back surface, Without using such a bulky recording material reversing unit, high-quality multicolor images can be freely formed on the front, back or both sides of transfer paper, so the time required for reversal can be shortened, so printing The speed can be increased, and a stable image can be formed. Also, the occurrence of jam is reduced. Further, stable transferability can be obtained on both sides of the recording material without providing a polarity changing means for changing the polarity of the toner image on the recording material conveying belt.
[0108]
(6) When image formation is performed on one side of the recording material, a multicolor image is formed by sequential transfer, and when image formation is performed on the other side of the recording material, batch secondary transfer is performed. Since a multi-color image is formed, a high-quality multi-color image can be freely formed on the front surface, back surface, or both surfaces of the transfer paper without using a recording material reversing unit.
[Brief description of the drawings]
FIG. 1 is an explanatory diagram of a configuration during surface image formation and sequential transfer of a multicolor image forming apparatus according to an embodiment of the present invention.
FIG. 2 is an explanatory diagram of a configuration when the back side image is formed.
FIG. 3 is an explanatory diagram of a configuration at the time of back surface batch transfer and discharge.
FIG. 4 is an explanatory diagram of the configuration when the secondary transfer unit is disposed on the most downstream side.
FIG. 5 is a diagram illustrating the configuration of the secondary transfer unit.
FIG. 6 is another configuration explanatory diagram in the case of the same surface image formation and sequential transfer.
FIG. 7 is an explanatory diagram of a configuration when a back surface image is formed when the double-sided image is formed.
FIG. 8 is a configuration explanatory view showing an arrangement position of the separation charger.
FIG. 9 is an explanatory diagram of a configuration showing an arrangement position of the static elimination charger.
FIG. 10 is a configuration diagram illustrating an example of a conventional multicolor image forming apparatus.
FIG. 11 is a diagram illustrating a configuration of another multicolor image forming apparatus.
FIG. 12 is an explanatory diagram of the single-sided printing.
FIG. 13 is an explanatory diagram of the double-sided printing.
FIG. 14 is a configuration explanatory diagram of the same multicolor image forming apparatus.
[Explanation of symbols]
1-Image forming station
2a-Recording material conveyance belt
5-Recording material
31-secondary transfer means
61 (YK) -Developing device
64 (Y to K) -photosensitive member

Claims (6)

In a multicolor image forming apparatus in which a plurality of image forming stations each including a photoconductor and a developing device are arranged along the recording material conveyance direction so that a single color or a multicolor image can be formed on one side or both sides of the recording material. ,
When forming an image on both sides of a recording material, an image that becomes a normal or mirror image of the original image when forming an image on one side of the recording material and when forming an image on the other side of the recording material An image processing unit for selecting and outputting signals;
An image forming unit that receives the image signal output from the image processing unit and forms images by applying different transfer methods to both sides of the recording material, and
A recording material conveying belt capable of conveying the recording material over each image forming station and capable of intermediate transfer of the toner color image formed at each image forming station;
Secondary transfer means for performing secondary transfer of the toner color image intermediately transferred onto the recording material conveying belt to the recording material;
A return conveyance path configured to return the recording material from the downstream side of the fixing device in the recording material conveyance path to the upstream side of the image forming station, and a registration roller provided in the path;
With
The return conveyance path includes a lower traveling side of the recording material conveyance belt and a reversing path extending from the downstream side of the fixing device in the recording material conveyance path to be connected to the lower traveling side of the recording material conveyance belt. And
A multicolor image forming apparatus, wherein a switching gate for controlling a recording material conveyance timing is provided at a downstream end of the reversing path . When forming an image on one side of the recording material, the toner color image formed at each image forming station is primarily transferred to the recording material conveyance belt, and the toner color image on the recording material conveyance belt is transferred to the recording material conveyance belt. The secondary transfer means forms a multicolor image by batch secondary transfer to a recording material,
When performing image formation on the other surface of the recording material, the toner color image formed on one surface of the recording material is fixed, and then the toner color image formed at each image forming station is recorded on the recording material. The multicolor image forming apparatus according to claim 1, wherein a multicolor image is formed by sequentially performing primary transfer sequentially to the other surface of the recording material conveyed by the material conveying belt. Secondary transfer means for performing batch secondary transfer to one surface of the recording material is upstream of all image forming stations arranged in parallel along the recording material conveyance belt, and Arranged at a position outside the belt loop formed by the recording material conveyance belt,
The multi-color image forming apparatus according to claim 1, wherein the recording material conveyance belt and all the image forming stations are disposed so as to be relatively close to each other.   Secondary transfer means for performing batch secondary transfer to one surface of the recording material, downstream of all image forming stations arranged in parallel along the recording material transport belt, and the above The multicolor image forming apparatus according to claim 1, wherein the multicolor image forming apparatus is disposed at a position outside a belt loop formed by the recording material conveyance belt. A multicolor image forming method applied to the multicolor image forming apparatus according to claim 1,
An image that is a normal image or a mirror image of a document image is formed depending on whether an image is formed on one side of the recording material or an image is formed on the other side of the recording material. A multicolor image forming method. When forming an image on one surface of a recording material, a toner color image obtained by forming an electrostatic latent image that is a mirror image of the original image on the photosensitive member of each image forming station is transferred to the recording material transport belt. While forming a multicolor image by primary transfer sequentially to the recording material conveyed by
When forming an image on the other surface of the recording material, the toner color image obtained by forming an electrostatic latent image that is a normal image with respect to the original image on the photosensitive member of each image forming station is conveyed to the recording material. 6. The multicolor image forming method according to claim 5, wherein after the primary transfer onto the belt, a multicolor image is formed by batch secondary transfer onto the recording material.

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