JP3897104B2 - Image forming apparatus - Google Patents

Description

【００７１】
表１に示すとおり、バインダー樹脂１００重量部に対して、着色剤は０.５〜１５重量部、好ましくは１〜１０重量部であり、また、離型剤は１〜１０重量部、好ましくは２.５〜８重量部であり、更に、荷電制御剤は０.１〜７重量部、好ましくは０.５〜５重量部である。
このようにして得られる粉砕法トナーとしては、個数基準の５０％径である平均粒径（Ｄ₅₀）が５μｍ〜１０μｍの範囲であり、好ましくは６μｍ〜９μｍの範囲がよく、個数基準で３μｍ以下が２０％以下、好ましくは１０％以下の粒径分布を有する。
【００７２】
この例の粉砕法トナーにあっては、転写効率の向上を目的として、球形化処理により円形度（球状化係数）をアップさせることがよい。粉砕法トナーの円形度をアップさせるためには、
▲１▼ 粉砕工程で、比較的丸い球状で粉砕可能な装置、例えば機械式粉砕機として知られるターボミル（川崎重工（株）製）を使用すれば円形度は０.９３まで可能である。
または、
▲２▼ 粉砕したトナーを市販の熱風球形化装置サーフュージングシステムＳＦＳ−３型（日本ニューマチック工業（株）製）を使用すれば円形度は１.００まで可能である。
なお、本発明におけるトナー粒子等における平均粒径と円形度は、すべて、シスメックス株式会社製のＦＰＩＡ２１００で測定する値である。
【００７３】
次に、重合法によるトナー母粒子を用いたトナー（以下、重合法トナーという）の作製について説明する。
重合法トナーとしては、懸濁重合法、乳化重合法等がある。懸濁重合法においては、重合性単量体、着色顔料、離型剤とを、必要により更に、染料、重合開始剤、架橋剤、荷電制御剤、その他の添加剤を添加した混合物を溶解又は分散させた単量体組成物を、懸濁安定剤（水溶性高分子、難水溶性無機物質）を含む水相中に攪拌しながら添加して造粒し、重合させて所望の粒子サイズを有する着色重合トナー粒子を形成することができる。
【００７４】
また、乳化重合法においては、単量体と離型剤を必要により更に重合開始剤、乳化剤（界面活性剤）などを水中に分散させて重合を行い、次いで凝集過程で着色剤、荷電制御剤と凝集剤（電解質）等を添加することによって所望の粒子サイズを有する着色トナー粒子を形成することができる。
重合法トナー作製に用いられる材料において、着色剤、離型剤、荷電制御剤、流動性改良剤に関しては、前述の粉砕法トナーと同様の材料が使用できる。
【００７５】
重合性単量体（モノマー）としては、公知のビニル系モノマが使用可能であり、例えば、スチレン、ｏ−メチルスチレン、ｍ−メチルスチレン、ｐ−メチルスチレン、α−メチルスチレン、ｐ−メトキシスチレン、ｐ−エチルスチレン、ビニルトルエン、２，４−ジメチルスチレン、ｐ−ｎ−ブチルスチレン、ｐ−フェニルスチレン、ｐ−クロルスチレン、ジビニルベンゼン、アクリル酸メチル、アクリル酸エチル、アクリル酸プロピル、アクリル酸ｎ−ブチル、アクリル酸イソブチル、アクリル酸ｎ−オクチル、アクリル酸ドデシル、アクリル酸ヒドロキシエチル、アクリル酸２−エチルヘキシル、アクリル酸フェニル、アクリル酸ステアリル、アクリル酸２−クロルエチル、メタクリル酸メチル、メタクリル酸エチル、メタクリル酸プロピル、メタクリル酸ｎ−ブチル、メタクリル酸イソブチル、メタクリル酸ｎ−オクチル、メタクリル酸ドデシル、メタクリル酸ヒドロキシエチル、メタクリル酸２−エチルヘキシル、メタクリル酸ステアリル、メタクリル酸フェニル、アクリル酸、メタクリル酸、マレイン酸、フマル酸、ケイ皮酸、エチレングリコール、プロピレングリコール、無水マレイン酸、無水フタル酸、エチレン、プロピレン、ブチレン、イソブチレン、塩化ビニル、塩化ビニリデン、臭化ビニル、フッ化ビニル、酢酸ビニル、プロピレン酸ビニル、アクリロニトリル、メタクリルニトリル、ビニルメチルエーテル、ビニルエチルエーテル、ビニルケトン、ビニルヘキシルケトン、ビニルナフタレン等が挙げられる。なお、フッ素含有モノマーとしては、例えば２，２，２−トリフルオロエチルアクリレート、２，２，３，３−テトラフルオロプロピルアクリレート、フッ化ビニリデン、三フッ化エチレン、四フッ化エチレン、トリフルオロプロピレンなどはフッ素原子が負荷電制御に有効であるので使用が可能である。
【００７６】
乳化剤（界面活性剤）としては公知のものが使用可能である。例えばドデシルベンゼン硫酸ナトリウム、テトラデシル硫酸ナトリウム、ペンタデシル硫酸ナトリウム、オクチル硫酸ナトリウム、オレイン酸ナトリウム、ラウリン酸ナトリウム、ステアリン酸カリウム、オレイン酸カルシウム、ドデシルアンモニウムクロライド、ドデシルアンモニウムブロマイド、ドデシルトリメチルアンモニウムブロマイド、ドデシルピリジニウムクロライド、ヘキサデシルトリメチルアンモニウムブロマイド、ドデシルポリオキシエチレンエーテル、ヘキサデシルポリオキシエチレンエーテル、ラウリルポリオキシエチレンエーテル、ソルビタンモノオレアートポリオキシエチレンエーテル等がある。
【００７７】
重合開始剤としては、公知のものが使用可能である。例えば、過硫酸カリウム、過硫酸ナトリウム、過硫酸アンモニウム、過酸化水素、４，４’−アゾビスシアノ吉草酸、ｔ−ブチルハイドロパーオキサイド、過酸化ベンゾイル、２，２’−アゾビス−イソブチロニトリル等がある。
【００７８】
凝集剤（電解質）としては、公知のものが使用可能である。例えば、塩化ナトリウム、塩化カリウム、塩化リチウム、塩化マグネシウム、塩化カルシウム、硫酸ナトリウム、硫酸カリウム、硫酸リチウム、硫酸マグネシウム、硫酸カルシウム、硫酸亜鉛、硫酸アルミニウム、硫酸鉄等が挙げられる。
【００７９】
乳化重合法トナーにおける成分比（重量）を表２に示す。
【００８０】
【表２】

【００８１】
表２に示すとおり、重合性モノマー１００重量部に対して、重合開始剤は０.０３〜２、好ましくは０.１〜１重量部であり、また、界面活性剤０.０１〜０.１重量部であり、更に、離型剤は１〜４０重量部、好ましくは２〜３５重量部であり、更に、荷電制御剤は０.１〜７重量部、好ましくは０.５〜５重量部であり、着色剤は１〜２０重量部、好ましくは３〜１０重量部であり、更に、凝集剤（電解質）は０.０５〜５重量部、好ましくは０.１〜２重量部である。
【００８２】
この重合法トナーにあっても、転写効率の向上を目的として、球形化処理により円形度をアップさせることがよい。重合法トナーの円形度の調節法としては、
▲１▼ 乳化重合法は２次粒子の凝集過程で温度と時間を制御することで、円形度を自由に変えることができ、その範囲は０.９４〜１.００である。
また、
▲２▼ 懸濁重合法では、真球のトナーが可能であるため、円形度は０.９８〜１.００の範囲となる。また、円形度を調節するためにトナーのＴｇ温度以上で加熱変形させることで、円形度を０.９４〜０.９８まで自由に調節することが可能となる。
【００８３】
重合法トナーは前述の方法以外の分散重合法でも作ることができ、例えば特開平６３−３０４００２号公報に開示されている方法でも作製できる。この場合には、形状が真球に近い形となるため、形状を制御するには、例えばトナーのＴｇ温度以上で加圧し、所望のトナー形状にすることができる。
【００８４】
このようにして得られる重合法トナーは、個数基準の５０％径である平均粒径（Ｄ₅₀）が４〜９μｍの範囲であり、好ましくは４.５〜８μｍの範囲がよく、個数基準で３μｍ以下が５％以下、好ましくは３％以下の粒径分布を有する。
【００８５】
本発明における一成分非磁性トナーの母粒子の円形度として、粉砕法トナーおよび重合法トナーのいずれであっても望ましい円形度（球状化係数）は０.９４以上、好ましくは０.５以上である。このように各色のトナーが、いずれもその円形度（球形度）を０.９４以上に設定することで、トナーと感光体との付着力を低減でき、転写効率をより一層効果的に向上できる。
【００８６】
外添剤である流動性改良剤としては、公知の無機および有機のトナー用流動性改良剤が使用可能である。公知の無機および有機のトナー用流動性改良剤としては、例えば、シリカ、二酸化チタン、アルミナ、フッ化マグネシウム、炭化ケイ素、炭化ホウ素、炭化チタン、炭化ジルコニウム、窒化ホウ素、窒化チタン、窒化ジルコニウム、マグネタイト、二硫化モリブデン、ステアリン酸アルミニウム、ステアリン酸マグネシウム、ステアリン酸亜鉛、ステアリン酸カルシウム、チタン酸金属塩、ケイ素金属塩の各微粒子を使用することができる。これらの微粒子はシランカップリング剤、チタンカップリング剤、高級脂肪酸、シリコーンオイル等で疎水化処理して使用することが好ましい。
【００８７】
疎水化処理剤としては、例えば、ジメチルジクロルシラン、オクチルトリメトキシシラン、ヘキサメチルジシラザン、シリコーンオイル、オクチルートリクロシラン、デシルートリクロルシラン、ノニルートリクロシラン、（４−ｉｓｏ−プロピルフェニル）−トリクロルシラン、ジヘキシルジクロシラン、（４−ｔ−ブチルフェニル）−トリクロシラン、ジペンチルージクロルシラン、ジヘキシル−ジクロルシラン、ジオクチル−ジクロルシラン、ジノニル−ジクロルシラン、ジデシル−ジクロルシラン、ジ−２−エチルヘキシル−ジクロルシラン、ジ−３,３−ジメチルペンチル−ジクロルシラン、トリヘキシル−クロルシラン、トリオクチル−クロルシラン、トリデシル−クロルシラン、ジオクチル−メチル−クロルシラン、オクチル−ジメチル−クロルシラン、（４−ｉｓｏ−プロピルフェニル）−ジエチル−クロルシラン等が例示される。
その他の樹脂微粒子の例としては、アクリル樹脂、スチレン樹脂、フッ素樹脂等が挙げられる。
【００８８】
この流動性改良剤粒子の使用量、一次粒子の平均粒径（Ｄ₅₀）、およびＢＥＴ法による比表面積を表３に示す。
【００８９】
【表３】

【００９０】
この流動性改良剤粒子は単独あるいは混合して使用でき、表３に示すとおり、その使用量は前述のいずれのトナー母粒子においても、トナー母粒子に対して０.１〜５重量％の範囲がよく、より好ましくは０.５〜４.０重量％の範囲がよい。流動性改良剤粒子の一次粒子の平均粒径（Ｄ₅₀）は５〜１５０ｎｍの範囲がよく、より好ましくは７〜１００ｎｍがよく、ＢＥＴ法による比表面積が２〜５００ｍ²／ｇである微粒子を使用するのがよく、より好ましくは５〜４００ｍ²／ｇである微粒子を使用するとよい。
【００９１】
ところで、本発明の画像形成装置では、感光体４１の仕事関数、中間転写ベルト３０の仕事関数、および各色のトナーの仕事関数の大小関係を次のように設定している。
すなわち、
▲１▼ 中間転写媒体（図１に示す例では、中間転写ベルト３０）の回転（移動）方向の最上流側（以下、中間転写媒体の回転方向上流側を単に上流側、また中間転写媒体の回転方向下流側を単に下流側という）のトナー｛図１に示す例では、イエロー（Ｙ）のトナー｝の仕事関数を感光体（図１に示す例では、感光体４１）の仕事関数より大きく設定している。すなわち、
最上流側のトナーの仕事関数 ＞ 感光体の仕事関数
に設定される（図１に示す例では、イエロー（Ｙ）のトナーの仕事関数 ＞ 感光体４１の仕事関数）。
▲２▼ 最上流側のトナーの仕事関数を中間転写媒体の仕事関数より大きく設定している。すなわち、
最上流側のトナーの仕事関数 ＞ 中間転写媒体の仕事関数
に設定される（図１に示す例では、イエロー（Ｙ）のトナーの仕事関数 ＞ 中間転写ベルト３０の仕事関数）。
▲３▼ 複数個の単色トナー像形成手段｛図１に示す例では、４個の単色トナー像形成手段４０（Ｙ）,４０（Ｃ）,４０（Ｍ）,４０（Ｋ）｝にそれぞれ使用されるトナーの各仕事関数を、中間転写媒体の移動方向の上流側から下流側にいくにしたがって順に大きく設定している｛図１に示す例では、イエロー（Ｙ）のトナーの仕事関数 ＜ シアン（Ｃ）のトナーの仕事関数 ＜ マゼンタ（Ｍ）のトナーの仕事関数 ＜ ブラック（Ｋ）のトナーの仕事関数である｝。
【００９２】
次に、これらの仕事関数の測定方法について説明する。
仕事関数（Φ）は、表面分析装置（理研計器（株）製ＡＣ−２）により測定されるものであり、その物質から電子を取り出すために必要なエネルギーてあり、仕事関数が小さいほど電子を出しやすく、大きい程電子を出しにくい。そのため、仕事関数の小さい物質と大きい物質を接触させると、仕事関数の小さい物質は正に、仕事関数の大きい物質は負に帯電するものであるが、仕事関数自体としてはその物質から電子を取り出すためのエネルギー（ｅＶ）として数値化されるものである。
【００９３】
本発明においては、一成分非磁性トナーおよび画像形成装置の各部材のいずれの仕事関数の測定も、すべて次のようにして行われる。すなわち、前述の表面分析装置において、重水素ランプを使用し、金属めっきを施した現像ローラの仕事関数測定では照射光量１０ｎＷに設定し、それ以外の仕事関数測定では照射光量５００ｎＷに設定し、分光器により単色光を選択し、スポットサイズ４ｍｍ角とし、エネルギ走査範囲３.４〜６.２ｅＶ、測定時間１０ｓｅｃ／１ポイントでサンプルに照射する。そして、サンプル表面から放出される光電子を検知し、仕事関数計ソフトを使用して演算処理され得るもので、仕事関数に関しては、繰り返し精度（標準偏差）０.０２ｅＶで測定されるものである。なお、データ再現性を確保するための測定環境としては、使用温度および湿度２５℃、５５％ＲＨの条件下で、２４時間放置品を測定サンプルとする。
【００９４】
サンプルトナーの仕事関数の測定には、図２（ａ）および（ｂ）に示すように直径１３ｍｍ、高さ５ｍｍのステンレス製円盤の中央に直径１０ｍｍで深さ１ｍｍのトナー収容凹部を有する形状のトナー専用測定セルが用いられる。サンプルトナーをセルの凹部内に秤量さじを使用して突き固めないで入れた後、ナイフエッジを使用して表面を均して平らにした状態で測定する。トナーを充填した測定セルをサンプルステージの規定位置上に固定した後、照射光量５００ｎＷに設定し、スポットサイズ４ｍｍ角とし、エネルギ走査範囲４.２〜６.２ｅＶの条件下で後述する図３（ｂ）に示すように方法と同様にして測定される。
【００９５】
また、感光体や現像ローラ等の形状が円筒形状の画像形成装置部材をサンプルとする場合には、円筒形状の画像形成装置部材を１〜１.５ｃｍの幅で切断し、次いで、稜線に沿って横方向に切断して図３（ａ）に示す形状の測定用試料片を得た後、サンプルステージの規定位置上に、図３（ｂ）に示すように、測定光が照射される方向に対して照射面が平行になるように固定する。これにより、放出される光電子が検知器（光電子倍像管）により効率よく検知される。
【００９６】
更に、中間転写ベルト、トナー薄層を規制する規制ブレード、また、感光体がシート形状の場合には、測定光が前述のように，４ｍｍ角スポットで照射されるので、試料片は少なくとも１ｃｍ角の大きさに切り欠いて、図３（ｂ）に示すようにサンプルステージに固定し、同様に測定される。
【００９７】
この表面分析装置においては、単色光の励起エネルギーを低い方から高い方にスキャンしたとき、光量子の放出が始まるが、この光電子の放出が始まるエネルギー値（ｅＶ：仕事関数という）を測定するもので、データとしては、励起エネルギー（ Photon Energy ）（横軸）と規格化光電子収率（ Emmission Yield ）との関係から得られる。例えば、図４に示す外添剤であるＳｉＯ₂の例について説明すると、ＳｉＯ₂粒子の仕事関数（ＷＦ）は、屈曲点（Ａ）における励起エネルギー５.２２ｅＶである。また、傾き（Ｓｌｏｐｅ、規格化光電子収率／ｅＶ）は、その値が大きいと電子を放出しやすい状態であることを示す。
【００９８】
各トナーの仕事関数を上流側から下流側にいくにしたがって大きくする方法としては、各色の外添剤の添加量を上流側から下流側にいくにしたがって各トナーの仕事関数が大きくなるように変化させる方法がある。外添剤はトナー母粒子の表層に添加するものであってトナーの仕事関数に大きく影響するので、このように各色の外添剤の添加量を変化させることで、各トナーの仕事関数を上流側から下流側にいくにしたがって効果的に大きくすることができる。
【００９９】
この方法の一例として、各色のトナーの外添剤として酸化チタンを上流側から下流側にいくにしたがって多く添加する方法がある。酸化チタンの仕事関数は、５.７〜５.８と比較的大きいので、酸化チタンの添加量を増やすとトナーの仕事関数は大きくなる。
また、この方法の他の例として、各色のトナーの外添剤としてシリカ（ＳｉＯ₂）を上流側から下流側にいくにしたがって少なく添加する方法がある。シリカの仕事関数は、５.０〜５.２と比較的小さいので、シリカの添加量を増やすとトナーの仕事関数は小さくなる。
【０１００】
このように構成された中間転写ベルト３０の移動方向の最上流側のトナーの仕事関数 ＞ 感光体の仕事関数に設定するとともに、中間転写ベルト３０の移動方向の最上流側のトナーの仕事関数 ＞ 中間転写ベルト３０の仕事関数に設定し、更に、複数色のトナーの仕事関数が中間転写ベルト３０の移動方向上流側から下流側に向かって順に大きくなるように設定しているので、感光体４１上の転写されようとするトナーと中間転写ベルト３０との間、および感光体４１上の転写されようとするトナーと先に転写された中間転写ベルト３０上のトナーとの間で、転写されようとするトナーが（−）側に帯電し、中間転写ベルト３０およびこの中間転写ベルト３０上のトナーが（＋）側に帯電しようとするので、感光体４１上の転写されようとするトナーが効果的に転写されるようになる。その結果、トナーの転写残りがきわめて少なくなり、転写効率が９８％以上に効果的に向上する。
【０１０１】
一方、最下流のトナーはブラック（Ｋ）のトナーにすることがよい。最下流の転写工程はその前の転写工程の回数が多いので、中間転写媒体上に他の色のトナーが転写されている可能性が高く、しかも他の色のトナーの転写面積が大きい。したがって、最下流の転写工程において最も逆転写する可能性が高い。そして、逆転写したトナーが像担持体上から現像剤担持体へ移ってブラックトナーに他色が混り（コンタミ）、このコンタミの状態で現像されても、このように最下流のトナーをブラック（Ｋ）のトナーにすることで、ブラックトナーはコンタミの影響を一番受けにくい色であるから、出力画像においてこのコンタミを人間の視覚では感知できないようにすることができる。
【０１０２】
更に、感光体の周速度と中間転写媒体の周速度（移動速度）とに所定の速度差を設けるとよい。このように速度差を設けることで、転写ニップ内でトナー粒子が転がってトナー粒子と像担持体および転写媒体との接触の機会が増えるので、転写ニップ内のトナーの帯電極性をより揃えることができる。これにより、逆転写をより一層効果的に抑制でき、転写効率を向上できる。
【０１０３】
図５は、本発明にかかる画像形成装置の実施の形態の他の例を部分的かつ模式的に示す図、図６はこの例の単色トナー像形成手段を模式的に示す図である。なお、前述の例と同じ構成要素には同じ符号を付すことで、その詳細な説明は省略する。
【０１０４】
図５に示すように、この例の画像形成装置は、前述の例と同様にタンデム式のカラー画像形成装置であるが、前述の例の中間転写ベルト３０（中間転写媒体）が設けられていなく、各単色トナー像形成手段４０（Ｙ）,４０（Ｃ）,４０（Ｍ）,４０（Ｋ）のトナー像が紙等の記録媒体Ｐに直接直接転写されるようになっている。したがって、この例のカラー画像形成装置では、紙等の記録媒体Ｐが転写媒体となっている。
【０１０５】
前述の例と同様に各単色トナー像形成手段４０（Ｙ）,４０（Ｃ）,４０（Ｍ）,４０（Ｋ）は互いに同一に構成されており、図６に示すように、各単色トナー像形成手段４０（Ｙ）,４０（Ｃ）,４０（Ｍ）,４０（Ｋ）は、帯電手段としてコロナ帯電器４２′が用いられているとともに、転写手段として転写ローラ５１′,５２′,５３′,５４′が設けられている。この例のカラー画像形成装置の他の構成は、前述の襟と同じである。なお、図６中、符号４６はトナーの薄層を規制する規制ブレードであり、符号４７は現像ローラ４４にトナーを供給する供給ローラである。
【０１０６】
転写ローラ５１′,５２′,５３′,５４′は互いに同一ものであり、直径１０〜２０ｍｍの金属シャフトの周表面に弾性層、導電層、抵抗性表面層の順で積層した構造を有している。抵抗性表面層は、フッ素樹脂、ポリビニルブチラール等の樹脂、ポリウレタン等のゴムに導電性カーボンで等の導電性微粒子を分散させた可撓性に優れた抵抗性シートを使用することができ、表面が平滑であることが好ましく、体積抵抗値は１０⁷〜１０¹¹Ω・ｃｍであり、好ましくは１０⁸〜１０¹⁰〜Ω・ｃｍのものであり、膜厚は０.０２〜２ｍｍである。
【０１０７】
導電層としては、ポリエステル樹脂等に導電性カーボン等の導電性微粒子を分散させた導電性樹脂、金属シート、また、導電性接着剤から選ばれるとよく、体積抵抗値が１０⁵Ω・ｃｍ以下のものである。
弾性層は、転写ローラが有機感光体に圧接して用いられる際にその圧接時に柔軟に変形し、圧接解放時には速やかに原形に復帰することが必要であり、発泡ゴムスポンジ等の弾性体を用いて形成される。発泡構造としては、連続発泡（通泡）構造、独立気泡構造のいずれでもよく、ゴム硬度（アスカーＣ硬度）３０〜８０のものとするとよく、膜厚は１〜５ｍｍである。
【０１０８】
このようにして作製された転写ローラ５１′,５２′,５３′,５４′の弾性変形により、有機感光体と転写媒体とは幅広いニップ幅で密着させることができるが、転写ローラによる有機感光体への押し圧荷重としては２０〜１００ｇｆ／ｃｍ、ニップは幅１〜８ｍｍとするとよい。また、転写ローラ５１′,５２′,５３′,５４′には、＋２００〜＋８００Ｖのトナーの帯電電圧とは逆極性の転写電圧が印加されるとよい。
【０１０９】
次に、本発明の実施例について説明する。
［実施例１および比較例１］
｛有機感光体（ＯＰＣ１）の製造例｝
これらの実施例１および比較例１で使用した有機感光体（ＯＰＣ１）について説明する。
直径３０ｍｍのアルミ引き抜き管を表面研磨した導電性支持体周面に、下引き層として、アルコール可溶性ナイロン｛東レ（株）製「ＣＭ８０００」｝６重量部とアミノシラン処理された酸化チタン微粒子４重量部とをメタノール１００重量部に溶解、分散させてなる塗工液をリングコーティング法で塗工し、温度１００℃で４０分乾燥させ、膜厚１.５〜２μｍの下引き層を形成した。
【０１１０】
次いで、電荷発生顔料としてのｘ型無金属フタロシアニン顔料１重量部と、ブチラール樹脂｛ＢＸ−１、積水化学（株）製｝１重量部と、ジクロルエタン１００重量部とを、φ１ｍｍのガラスビーズを用いたサンドミルで８時間分散させて顔料分散液を得、得られた顔料分散液をこの下引き層上にリングコーティング法で塗工し、８０℃で２０分間乾燥させ、膜厚０.３μｍの電荷発生層を形成した。
【０１１１】
更に、この電荷発生層上に、下記構造式（１）のスチリル化合物の電荷輸送物質４０重量部とポリカーボネート樹脂｛パンライトＴＳ、帝人化成（株）製｝６０重量部をトルエン４００重量部に溶解させ、乾燥膜厚が２２μｍになるように浸漬コーティング法で塗工、乾燥させて電荷輸送層を形成し、積層型の有機感光体（ＯＰＣ１）を作製した。
【０１１２】
得られた有機感光体（ＯＰＣ１）の一部を切り欠いて試料片とし、この試料片の仕事関数を、前述のように市販の表面分析装置（ＡＣ−２型、理研計器（株）製）を用いて照射光量５００ｎＷで測定したところ、５.２７ｅＶを示した。
【０１１３】
【化１】

【０１１４】
（トナーの製造例）
これらの実施例１および比較例１で使用した一成分非磁性トナーについて説明する。
（トナーＡの製造）
スチレンモノマー８０重量部、アクリル酸ブチル２０重量部、およびアクリル酸５重量部からなるモノマー混合物を、
・水 １０５重量部
・ノニオン乳化剤 １重量部
・アニオン乳化剤 １.５重量部
・過硫酸カリウム ０.５５重量部
からなる水溶性混合物に添加し、窒素気流中下で攪拌して７０℃で８時間重合を行った。重合反応後冷却し、乳白色の粒径０.２５μｍの樹脂エマルジョンを得た。
【０１１５】
次に、
・この樹脂エマルジョン ２００重量部
・ポリエチレンワックスエマルジョン｛三洋化成工業（株）製｝ ２０重量部
・フタロシアニンブルー ７重量部
を、界面活性剤のドデシルベンゼンスルホン酸ナトリウム０.２重量部を含んだ水中へ分散し、ジエチルアミンを添加してｐＨを５.５に調整後攪拌しながら電解質の硫酸アルミニウムを０.３重量部を加え、ついでＴＫホモミキサーで高速攪拌し、分散を行った。
【０１１６】
更に、スチレンモノマー４０重量部、アクリル酸ブチル１０重量部、サリチル酸亜鉛５重量部を水４０重量部と共に追加し、窒素気流下で攪拌しながら同様にして９０℃に加熱し、過酸化水素を加えて５時間重合し、粒子を成長させた。重合停止後、この二次粒子の会合と造膜結合強度を上げるため、ｐＨを５以上に調整しながら９５℃に昇温し、５時間保持した。その後、得られた粒子を水洗いし、４５℃で真空乾燥を１０時間行ってシアントナーの母粒子を得た。
【０１１７】
得られたシアントナーの母粒子は、前述のようにして測定した結果、平均粒径が６.８μｍ、円形度が０.９８のトナーであった。このシアントナーの母粒子に対し、ヘキサメチルジシラザン（ＨＭＤＳ）により表面処理した疎水性シリカ（平均粒径が１２ｎｍ、比表面積１４０ｍ²／ｇ）を１重量％、シランカップリング剤により表面処理した酸化チタン（平均粒径が２０ｎｍ、比表面積９０ｍ²／ｇ）を０.８重量％添加し、シアントナーであるトナーＡを製造した。このトナーＡの仕事関数は、前述のようにして測定した結果、５.６５ｅＶであった。
【０１１８】
（トナーＢの製造）
前述のトナーＡにおける顔料（フタロシアニンブルー）をキナクリドンに変更するとともに、トナーＡにおける酸化チタンの０.８重量％を０.６重量％に変更して、マゼンタトナーであるトナーＢをトナーＡの製造と同様にして製造した。このトナーＢは、前述のようにして測定した結果、平均粒径が６.９μｍであり、円形度は０.９６であり、仕事関数は５.５６ｅＶであった。
【０１１９】
（トナーＣの製造）
前述のトナーＡにおける顔料（フタロシアニンブルー）をピグメントイエロー１８０に変更するとともに、トナーＡにおける酸化チタンの０.８重量％を１.０重量％に変更して、イエロートナーであるトナーＣをトナーＡの製造と同様にして製造した。このトナーＣは、前述のようにして測定した結果、平均粒径が６.８μｍであり、円形度は０.９７であり、仕事関数は５.７２ｅＶであった。
【０１２０】
（トナーＤの製造）
前述のトナーＡにおける顔料（フタロシアニンブルー）をカーボンブラックに変更するとともに、トナーＡにおける酸化チタンの０.８重量％を１.２重量％に変更して、ブラックトナーであるトナーＤをトナーＡの製造と同様にして製造した。このトナーＤは、前述のようにして測定した結果、平均粒径が７.０μｍであり、円形度は０.９８であり、仕事関数は５.８ｅＶであった。
【０１２１】
（転写媒体の作製）
これらの実施例１および比較例１に使用する転写媒体として、転写ベルトを作製した。
アルミニウムを蒸着した厚さ１３０μｍのポリエチレンテレフタレート樹脂フィルム上に、
・塩化ビニル−酢酸ビニル共重合体 ３０重量部
・導電性カーボンブラック １０重量部
・メチルアルコール ７０重量部
からなる均一分散液を、厚さが２０μｍになるようにロールコーティング法にて塗工乾燥し、中間導電性層を形成した。
【０１２２】
次いで、この中間導電性層上に

の組成を混合分散してなる塗工液を厚さ１０μｍとなるようにロールコーティング法にて同様に塗工乾燥し、転写層を形成した。
【０１２３】
この塗工シートを長さ５４０ｍｍに裁断し、塗工面を上にして端部を合わせ、超音波溶着を行うことにより転写ベルトを作製した。この転写ベルトの体積抵抗は２.５×１０¹⁰Ω・ｃｍであった。また、仕事関数は５.３７ｅＶ、規格化光電子収率６.９０を示した。
【０１２４】
（転写効率の測定実験）
これらの実施例１および比較例１では、前述のようにしてそれぞれ製造された有機感光体（ＯＰＣ１）、各トナーＡないしＤ、および転写ベルトを用いた図１に示すと同様のカラー画像形成装置を用いて、スコロトロン帯電（ワイヤー電圧：−４.５ｋＶ、グリット電圧：−６００Ｖ）、非接触現像（ギャップ：２００μｍ、Ｖｄｃ＝−２００Ｖ、Ｖｐｐ＝１.３ｋＶ、現像量：０.５５ｍｇ／ｃｍ²）、転写電圧（＋５００Ｖ）にて、全色ベタ印字の多重転写時の転写効率の測定実験を行った。
【０１２５】
（高転写効率時の測定法）
これらの実施例１および比較例１における転写効率の測定方法は、感光体上の転写残りトナーを光学顕微鏡にて画像データとして読み取り、その画像を２値化し、単位面積当たりの転写残りトナーの面積、トナー個数を求め、この値から求めた個数、各トナーの体積と、トナーのメイン樹脂密度から単位面積当たりの転写残りトナー重量を求め、現像量との比によって転写効率を導いている。
【０１２６】
（実施例１の転写順序）
実施例１の各トナーの感光体から転写ベルトへの転写順序（つまり、トナーの上流側からの順序）を、本発明に沿って仕事関数が上流側から下流側に向かって順に大きくなるように、トナーＢ（マゼンタトナー：仕事関数５.５６ｅＶ）、トナーＡ（シアントナー：仕事関数５.６５ｅＶ）、トナーＣ（イエロートナー：仕事関数５.７２ｅＶ）、トナーＤ（ブラックトナー：仕事関数５.８ｅＶ）に設定した。
【０１２７】
（比較例１の転写順序）
比較例１の各トナーの感光体から転写ベルトへの転写順序は、仕事関数が本発明の順序と異なるように、トナーＣ（イエロートナー：仕事関数５.７２ｅＶ）、トナーＢ（マゼンタトナー：仕事関数５.５６ｅＶ）、トナーＤ（ブラックトナー：仕事関数５.８ｅＶ）、トナーＡ（シアントナー：仕事関数５.６５ｅＶ）に設定した。
【０１２８】
（転写効率の測定実験の結果）
実施例１および比較例１の転写効率の測定実験の結果を表４に示す。
【０１２９】
【表４】

【０１３０】
表４に示すように、実施例１では、第１転写（トナーＢの転写）、第２転写（トナーＡの転写）、第３転写（トナーＣの転写）、および第４転写（トナーＤの転写）のいずれもが転写効率が９８％以上を示し、各転写効率に差がほとんど現れなかった。これに対して、比較例１では、第１転写（トナーＣの転写）および第３転写（トナーＤの転写）の転写効率が９８％以上を示したが、第２転写（トナーＢの転写）および第４転写（トナーＡの転写）の転写効率がそれぞれ９４.９２％および９１.２％と低くなり、各転写効率に差が現れた。
【０１３１】
これにより、本発明のように４色のトナーを、中間転写媒体の移動方向上流側から下流側に向かって仕事関数が大きくなるように転写することで、転写残りがきわめて少なくなり、転写効率が効果的に向上できることが確認された。
【０１３２】
そして、実施例１の実験結果により、本発明の画像形成装置は前述のように感光体上に残る転写残りトナーを「色」として感知できないレベルの転写効率が９８％以上であることの必須条件をクリアでき、感光体のクリーナレスを達成することができることを確認できた。
【０１３３】
［実施例２、比較例２および比較例３］
これらの実施例２、比較例２および比較例３で使用した有機感光体（ＯＰＣ１）および転写媒体は前述の実施例１および比較例１と同じである。
【０１３４】
（トナーの製造例）
これらの実施例２、比較例２および比較例４で使用した一成分非磁性トナーについて説明する。
（トナーＥの製造）
スチレンモノマー８０重量部、アクリル酸ブチル２０重量部、およびアクリル酸５重量部からなるモノマー混合物を、
・水 １０５重量部
・ノニオン乳化剤 １重量部
・アニオン乳化剤 １.５重量部
・過硫酸カリウム ０.５５重量部
からなる水溶性混合物に添加し、窒素気流中下で攪拌して７０℃で８時間重合を行った。重合反応後冷却し、乳白色の粒径０.２５μｍの樹脂エマルジョンを得た。
【０１３５】
次に、
・この樹脂エマルジョン ２００重量部
・ポリエチレンワックスエマルジョン｛三洋化成工業（株）製｝ ２０重量部
・フタロシアニンブルー ７重量部
を、界面活性剤のドデシルベンゼンスルホン酸ナトリウム０.２重量部を含んだ水中へ分散し、ジエチルアミンを添加してｐＨを５.５に調整後攪拌しながら電解質の硫酸アルミニウムを０.３重量部を加え、ついでＴＫホモミキサーで高速攪拌し、分散を行った。
【０１３６】
更に、スチレンモノマー４０重量部、アクリル酸ブチル１０重量部、サリチル酸亜鉛５重量部を水４０重量部と共に追加し、窒素気流下で攪拌しながら同様にして９０℃に加熱し、過酸化水素を加えて５時間重合し、粒子を成長させた。重合停止後、この二次粒子の会合と造膜結合強度を上げるため、ｐＨを５以上に調整しながら９５℃に昇温し、５時間保持した。その後、得られた粒子を水洗いし、４５℃で真空乾燥を１０時間行ってシアントナーの母粒子を得た。
【０１３７】
得られたシアントナーの母粒子は、前述のようにして測定した結果、平均粒径が６.８μｍ、円形度が０.９８のトナーであった。このシアントナーの母粒子に対し、ヘキサメチルジシラザン（ＨＭＤＳ）により表面処理した疎水性シリカ（平均粒径が１２ｎｍ、比表面積１４０ｍ²／ｇ）を０.５重量％、シランカップリング剤により表面処理した酸化チタン（平均粒径が２０ｎｍ、比表面積９０ｍ²／ｇ）を１.２重量％添加し、更にアルミナを０.３重量％添加し、シアントナーであるトナーＥを製造した。このトナーＥの仕事関数は、前述のようにして測定した結果、５.７３ｅＶであった。
【０１３８】
（トナーＦの製造）
前述のトナーＥにおける顔料（フタロシアニンブルー）をキナクリドンに変更して、マゼンタトナーであるトナーＦをトナーＥの製造と同様にして製造した。このトナーＦは、前述のようにして測定した結果、平均粒径が６.９μｍであり、円形度は０.９６であり、仕事関数は５.５８ｅＶであった。
【０１３９】
（トナーＧの製造）
前述のトナーＥにおける顔料（フタロシアニンブルー）をカーミン６Ｂに変更して、マゼンタトナーであるトナーＧをトナーＥの製造と同様にして製造した。このトナーＣは、前述のようにして測定した結果、平均粒径が６.８μｍであり、円形度は０.９５であり、仕事関数は５.８８ｅＶであった。
【０１４０】
（トナーＨの製造）
前述のトナーＥにおける顔料（フタロシアニンブルー）をピグメントイエロー１８０に変更して、イエロートナーであるトナーＨをトナーＥの製造と同様にして製造した。このトナーＨは、前述のようにして測定した結果、平均粒径が６.８μｍであり、円形度は０.９７であり、仕事関数は５.６２ｅＶであった。
【０１４１】
（トナーＩの製造）
前述のトナーＥにおける顔料（フタロシアニンブルー）をカーボンブラックに変更して、ブラックトナーであるトナーＩをトナーＥの製造と同様にして製造した。このトナーＤは、前述のようにして測定した結果、平均粒径が７.０μｍであり、円形度は０.９８であり、仕事関数は５.７９ｅＶであった。
【０１４２】
（トナーＪの製造）
前述のトナーＧにおけるサリチル酸亜鉛５重量部を８重量部に変更して、マゼンタトナーであるトナーＪをトナーＧの製造と同様にして製造した。このトナーＪは、前述のようにして測定した結果、平均粒径が６.８μｍであり、円形度は０.９８であり、仕事関数は５.６９ｅＶであった。
【０１４３】
（転写効率の測定実験および高転写効率時の測定法）
これらの実施例２、比較例２および比較例３における転写効率の測定実験および高転写効率時の測定法は、いずれも、前述の実施例１および比較例１と同じである。
【０１４４】
（実施例２の転写順序）
実施例２の各トナーの感光体から転写ベルトへの転写順序（つまり、トナーの上流側からの順序）を、本発明に沿って仕事関数が上流側から下流側に向かって順に大きくなるように、トナーＨ（イエロートナー：仕事関数５.６２ｅＶ）、トナーＪ（マゼンタトナー：仕事関数５.６９ｅＶ）、トナーＥ（シアントナートナー：仕事関数５.７３ｅＶ）、トナーＩ（ブラックトナー：仕事関数５.７９ｅＶ）に設定した。
【０１４５】
（比較例２の転写順序）
比較例２の各トナーの感光体から転写ベルトへの転写順序は、仕事関数が本発明の順序と異なるように、トナーＨ（イエロートナー：仕事関数５.６２ｅＶ）、トナーＦ（マゼンタトナー：仕事関数５.５８ｅＶ）、トナーＥ（シアントナー：仕事関数５.７３ｅＶ）、トナーＩ（ブラックトナー：仕事関数５.７９ｅＶ）に設定した。
【０１４６】
（比較例３の転写順序）
比較例３の各トナーの感光体から転写ベルトへの転写順序は、仕事関数が本発明の順序と異なるように、トナーＨ（イエロートナー：仕事関数５.６２ｅＶ）、トナーＧ（マゼンタトナー：仕事関数５.８８ｅＶ）、トナーＥ（シアントナー：仕事関数５.７３ｅＶ）、トナーＩ（ブラックトナー：仕事関数５.７９ｅＶ）に設定した。
【０１４７】
（転写効率の測定実験の結果）
実施例２、比較例２および比較例３の転写効率の測定実験の結果を表５に示す。
【０１４８】
【表５】

【０１４９】
表５に示すように、実施例２では、第１転写（トナーＨの転写）、第２転写（トナーＪの転写）、第３転写（トナーＥの転写）、および第４転写（トナーＩの転写）のいずれもが転写効率が９８％以上を示し、各転写効率に差がほとんど現れなかった。これに対して、比較例２では、第１転写（トナーＨの転写）、第３転写（トナーＥの転写）および第４転写（トナーＩの転写）の転写効率が９８％以上を示したが、第２転写（トナーＦの転写）の転写効率が９３.９５％と低くなり、各転写効率に差が現れた。また、比較例３では、第１転写（トナーＨの転写）、第２転写（トナーＧの転写）および第４転写（トナーＩの転写）の転写効率が９８％以上を示したが、第３転写（トナーＥの転写）の転写効率が９２.６７％と低くなり、各転写効率に差が現れた。
【０１５０】
これにより、本発明のように４色のトナーを、中間転写媒体の移動方向上流側から下流側に向かって仕事関数が大きくなるように転写することで、転写残りがきわめて少なくなり、転写効率が効果的に向上できることが確認された。
したがって、実施例２の実験結果によっても、本発明の画像形成装置が感光体のクリーナレスを達成することができることを確認できた。
【０１５１】
【発明の効果】
このように構成された本発明の画像形成装置によれば、転写媒体の移動方向の最上流側のトナーの仕事関数 ＞ 感光体の仕事関数に設定するとともに、転写媒体の移動方向の最上流側のトナーの仕事関数 ＞ 転写媒体の仕事関数に設定し、更に、複数色のトナーの仕事関数が転写媒体の移動方向上流側から下流側に向かって順に大きくなるように設定しているので、トナーの転写残りをきわめて少なくでき、転写効率を効果的に向上できる。
したがって、転写材に転写された転写残りのトナー像が画像劣化（地カブリ）としてユーザーに感知できない領域まで転写効率を高めることができ、画像形成装置における感光体のクリーナレスが達成できるようになる。
【０１５２】
特に、請求項２の発明によれば、各色のトナーにそれぞれ添加される外添剤の添加量を転写媒体の移動方向の上流側から下流側にいくにしたがって、各色のトナーの仕事関数を大きくなるように変化させているので、外添剤の添加量を単に変化させるだけで、各色のトナーの仕事関数を転写媒体の移動方向の上流側から下流側にいくにしたがって簡単に大きく設定できる。
【０１５３】
その場合、請求項３の発明によれば、各色のトナーに対して、仕事関数が５.７〜５.８と比較的大きい酸化チタンを外添剤として用い、その添加量を上流側から下流側にいくにしたがって多くなるように設定しているので、各色のトナーの仕事関数を転写媒体の移動方向の上流側から下流側にいくにしたがって簡単に大きく設定できる。
【０１５４】
その場合、請求項４の発明によれば、各色のトナーに対して、仕事関数が５.０〜５.２と比較的小さいシリカを外添剤として用い、その添加量を上流側から下流側にいくにしたがって少なくなるように設定しているので、各色のトナーの仕事関数を転写媒体の移動方向の上流側から下流側にいくにしたがって簡単に大きく設定できる。
【０１５５】
更に、請求項５の発明によれば、複数色毎の像担持体を、すべて同一の層構成にしているので、各色のトナーの仕事関数の設定を容易にできるとともに、各色のトナー毎に像担持体を作製する必要がなく、コストを低減できる。
【０１５６】
更に、請求項６の発明によれば、各色のトナーを、いずれもその円形度（球形度）が０.９４以上に設定しているので、トナーと像担持体との付着力を低減でき、転写効率をより一層効果的に向上できる。
【０１５７】
更に、請求項７の発明によれば、各色毎の像担持体の周速と転写媒体の移動速度とに速度差を設定しているので、転写ニップ内でトナー粒子が転がってトナー粒子と像担持体および転写媒体との接触の機会が増え、転写ニップ内のトナーの帯電極性をより均一に揃えることができる。
【０１５８】
更に、請求項８の発明によれば、ブラックトナーを転写媒体の移動方向の最下流に設定しているので、ブラックトナーが転写される位置には、他色のトナーが転写されている可能性が高い。そして、逆転写したトナーが像担持体上から現像剤担持体へ移ってブラックトナーに他色が混り（コンタミ）、このコンタミの状態で現像されても、このように最下流のトナーをブラック（Ｋ）のトナーにすることで、ブラックトナーはコンタミの影響を一番受けにくい色であるから、出力画像においてこのコンタミを人間の視覚では感知できないようにすることができる。
【図面の簡単な説明】
【図１】 本発明にかかる画像形成装置の実施の形態の一例である４サイクル方式のフルカラープリンターを模式的に示す図である。
【図２】 トナーの仕事関数を測定するために使用される測定セルを示す図で、（ａ）は正面図、（ｂ）は側面図である。
【図３】 円筒形状の画像形成装置部材の仕事関数を測定する方法を説明する図であり、（ａ）は測定試料片の形状を示す斜視図、（ｂ）は測定状態を示す図である。
【図４】 表面分析装置による仕事関数を求める方法を説明する図である。
【図５】 本発明にかかる画像形成装置の実施の形態の他の例を部分的かつ模式的に示す図である。
【図６】 この例の単色トナー像形成手段を模式的に示す図である。
【符号の説明】
１…（カラー）画像形成装置、３０…中間転写ベルト（中間転写媒体）、４０（Ｙ）,４０（Ｃ）,４０（Ｍ）,４０（Ｋ）…単色トナー像形成手段、４１…感光体、４２…帯電ローラ、４３…露光装置、４４…現像ローラ、４５…感光体用クリーニングブレード、５１,５２,５３,５４…一次転写手段、６１…定着ローラ対、６６…二次転写ローラ、６７…中間転写ベルト用クリーニングブレード、Ｐ…記録媒体[0001]
BACKGROUND OF THE INVENTION
The present invention belongs to a technical field of an image forming apparatus that forms an image by electrophotography or the like, and particularly belongs to a technical field of an image forming apparatus that can achieve cleanerless of an image carrier such as a photoconductor.
[0002]
[Prior art]
Conventionally, in an image forming apparatus that forms an image by electrophotography or the like, an electrostatic latent image is formed by exposure on the surface of a photoreceptor, which is a uniformly charged image carrier, and the electrostatic latent image on the photoreceptor is After being developed with toner from the developing device to form a toner image, it is transferred from the photoreceptor to a recording medium such as paper or a transfer medium such as an intermediate transfer medium. The toner image transferred to the intermediate transfer medium is secondarily transferred to a recording medium such as paper. Then, the toner image transferred to a recording medium such as paper is fixed, and an image is formed on the recording medium. Toner that remains untransferred on the photosensitive member without being transferred is removed from the photosensitive member and collected by the cleaning means.
[0003]
Incidentally, in recent years, such an image forming apparatus is required to be small and compact. As one of the measures for downsizing the image forming apparatus, it can be considered to downsize the image forming apparatus by downsizing the periphery of the photosensitive member. Many devices such as a charger, an exposure device, a developing device, a transfer device, and a cleaning unit are disposed around the photoconductor, so that even one of them can be omitted to make the photoconductor compact. It is considered to be.
[0004]
As one of them, it is considered to make the image forming apparatus compact by omitting the cleaning means and eliminating the cleaner. Since this cleaning means removes and collects the toner remaining on the photoconductor after transfer from the photoconductor, the amount of residual toner on the photoconductor after transfer is reduced as much as possible in order to eliminate the cleaner. That is, it is required to improve the transfer efficiency from the photoconductor to the transfer medium as much as possible.
[0005]
As a method of improving transfer efficiency, conventionally, a photoconductor added with a fluorosurfactant is used to reduce the physical force (Van der Waals force) between the photoconductor and the toner, thereby improving the transfer efficiency. An improvement is proposed in JP-A-56-99345. In the method disclosed in this publication, the transfer efficiency is improved because the surface of the photoconductor is very dense and smooth and has a low coefficient of friction.
[0006]
As another method for improving the transfer efficiency, in the transfer unit, by giving a predetermined speed difference between the peripheral speed of the photosensitive member and the moving speed of the transfer medium such as paper, the electrostatic force during transfer is reduced. In addition, the transfer efficiency is improved by applying a frictional force between the photoconductor and the transfer medium to peel off the toner image from the surface of the photoconductor.
[0007]
[Problems to be solved by the invention]
By the way, in recent years, more and more color image forming apparatuses for obtaining a color image by transferring a plurality of toner images in multiple colors have been proposed. Even in this type of color image forming apparatus, it is desired to realize such a cleaner-less photoconductor. To that end, it is possible to employ the transfer efficiency improving method disclosed in the above-mentioned publications. Conceivable.
[0008]
However, in all of the image forming apparatuses disclosed in the above-mentioned publications, it cannot be said that the transfer efficiency is sufficiently improved in order to ensure that the photoreceptor is cleaner-less, and the transfer efficiency is further improved. It is desired to improve.
In addition, the image forming apparatus disclosed in each of the above-mentioned publications is intended for transfer of a toner image between a photoconductor and a transfer medium, and performs multiple transfer, that is, between the photoconductor and the transfer medium. It is not intended for the transfer of the toner image and the transfer of the toner image between the photoreceptor and the toner image transferred to the transfer medium. For this reason, it is difficult to simply adopt the transfer efficiency improvement method disclosed in the above-mentioned publications in an image forming apparatus that performs such multiple transfer, and even if it can be adopted, it is sufficient to improve the transfer efficiency. It is thought that the effect cannot be expected.
[0009]
The present invention has been made in view of such circumstances, and an object of the present invention is to provide an image forming apparatus that can improve transfer efficiency more effectively and more reliably eliminate the cleaner of the image carrier. It is to be.
[0010]
[Means for Solving the Problems]
In order to solve the above-described problems, the invention of claim 1 is directed to an image forming apparatus that sequentially multiplex-transfers toner images of each color of a plurality of colors onto a moving transfer medium. The work function of the toner on the most upstream side of the toner is set to the work function of the image carrier, and the work function of the toner on the most upstream side in the moving direction of the transfer medium is set to the work function of the transfer medium. The work functions of the toners of a plurality of colors are set so as to increase in order from the upstream side to the downstream side in the moving direction of the transfer medium.
[0011]
According to a second aspect of the present invention, external additives are added to the toners of the respective colors, and the amount of these external additives is increased as the transfer medium moves from the upstream side to the downstream side. It is characterized in that the work function of the toner is changed so as to increase.
[0012]
Further, in the invention of claim 3, the external additive added to the toner of each color is titanium oxide, and the addition amount of the titanium oxide goes from the upstream side to the downstream side in the moving direction of the transfer medium. Therefore, it is characterized by being set to increase.
[0013]
Furthermore, in the invention of claim 4, the external additive added to the toner of each color is silica, and the amount of silica added decreases as the transfer medium moves from the upstream side to the downstream side. It is set so that it becomes.
[0014]
Further, the invention according to claim 5 is characterized in that the image carriers for each of the plurality of colors all have the same layer structure.
Further, the invention of claim 6 is characterized in that the toner of each color has a circularity (sphericity) of 0.94 or more.
[0015]
Further, the invention of claim 7 is characterized in that a speed difference is set between the peripheral speed of the image carrier for each color and the moving speed of the transfer medium.
Further, the invention of claim 8 is characterized in that the plurality of color toners include at least a black toner, and the black toner is set at the most downstream side in the moving direction of the transfer medium.
[0016]
[Action]
In the image forming apparatus according to the first to seventh aspects of the present invention, the work function of the toner on the most upstream side in the moving direction of the transfer medium is set to the work function of the image carrier, and the transfer medium is moved. Set the work function of the toner on the most upstream side in the direction> the work function of the transfer medium, and further set the work functions of the toners of multiple colors in order from the upstream side toward the downstream side in the moving direction of the transfer medium. Transfer between the toner to be transferred on the image carrier and the transfer medium, and between the toner to be transferred on the image carrier and the toner on the transfer medium previously transferred. The toner to be transferred is charged on the (−) side, and the transfer medium and the toner on the transfer medium are about to be charged on the (+) side. It will be transcribed. As a result, toner transfer residue is extremely reduced, and transfer efficiency is effectively improved to 98% or more.
[0017]
Therefore, in the image forming apparatus of the present invention, the transfer residual toner on the image carrier is transferred to the transfer material such as paper directly or via the intermediate transfer medium on the next circumference, and the transfer residual transferred to the transfer material. The transfer efficiency is increased up to an area where the toner image cannot be perceived by the user as image degradation (ground fog).
As a result, in the image forming apparatus of the present invention, there is almost no transfer residual toner on the image carrier, and it is possible to achieve cleanerless image carrier.
[0018]
In particular, in the invention of claim 2, the work function of the toner of each color increases as the amount of the external additive added to the toner of each color increases from the upstream side to the downstream side in the moving direction of the transfer medium. To change. As described above, the work function of the toner of each color is simply set larger as it goes from the upstream side to the downstream side in the moving direction of the transfer medium simply by changing the addition amount of the external additive.
[0019]
In that case, in the invention of claim 3, titanium oxide is used as an external additive added to each color toner. Since the work function of this titanium oxide is relatively large as 5.7 to 5.8, the work of each color toner is set by setting the amount of titanium oxide to be increased from the upstream side to the downstream side. The function is easily set larger as it goes from the upstream side to the downstream side in the moving direction of the transfer medium.
[0020]
In that case, in the invention of claim 4, silica is used as an external additive added to the toner of each color. Since the work function of this silica is relatively small at 5.0 to 5.2, the work function of the toner of each color can be reduced by setting the amount of silica added to decrease from the upstream side to the downstream side. The transfer medium is simply set larger as it goes from the upstream side to the downstream side in the moving direction.
[0021]
Further, in the invention of claim 5, since the image carriers for the plurality of colors all have the same layer structure, the work function of the toner of each color can be easily set and the image for each toner of each color can be set. There is no need to produce a carrier and the cost is reduced.
[0022]
Further, in the invention of claim 6, since each color toner has a circularity (sphericity) of 0.94 or more, the adhesion between the toner and the image carrier is reduced, and the transfer efficiency is further improved. Effectively improve.
[0023]
Further, in the invention of claim 7, since a speed difference is set between the peripheral speed of the image carrier for each color and the moving speed of the transfer medium, the toner particles roll in the transfer nip and the toner particles and the image carrier. In addition, since the chance of contact with the transfer medium increases, the charging polarity of the toner in the transfer nip is more evenly aligned.
[0024]
Furthermore, in the invention of claim 8, the black toner is set at the most downstream side in the moving direction of the transfer medium. At the position where the most downstream toner is transferred, there is a high possibility that other color toners are transferred onto the transfer medium because the number of previous transfer steps is large. For this reason, even if the reversely transferred toner moves from the image carrier to the developer carrier and other colors are mixed with the black toner (contamination). Since the downstream toner is a black toner, the black toner is the color that is least susceptible to the influence of the contamination, so this contamination is not perceived by human vision in the output image.
[0025]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 is a front view schematically showing a tandem full-color printer as a color image forming apparatus as an example of an embodiment of an image forming apparatus according to the present invention. In this full-color printer, the photosensitive member cleaning means is provided, but it goes without saying that the cleaning means can be omitted and cleaner of the photosensitive member can be realized.
[0026]
The image forming apparatus of the present invention does not give the unit on the circumference of the photoconductor a recovery function, but transfers the residual toner on the photoconductor onto the intermediate transfer medium in the next circumference, so that the paper finally The transfer residual toner is transferred to a transfer material such as a transfer material, and the transfer efficiency is increased to a region where the transfer residual toner image transferred to the transfer material cannot be perceived by the user as image deterioration (ground fog). For this reason, as a result of various studies, when there is a photoreceptor cleaner, the transfer efficiency is sufficiently high even at 94%. Therefore, a level at which the untransferred toner remaining on the surface cannot be detected as “color” is required. Therefore, in the image forming apparatus of the present invention, it is an essential condition that the transfer efficiency is 98% or more.
[0027]
As shown in FIG. 1, in this example of a color image forming apparatus configured as a full-color printer, a photoconductor as an image carrier and a developing unit can be mounted as the same unit, that is, a process cartridge. . Further, in the example shown in FIG. 1, a color image forming apparatus of a contact development system as described below is used. However, the present invention is a non-contact development system in which the photosensitive member and the development roller are separated from each other with a predetermined gap. The present invention can also be applied to a color image forming apparatus. In the following description, a case where a photoconductor is used as the image carrier will be described, but other image carriers can also be used.
[0028]
The color image forming apparatus 1 in the example shown in FIG. 1 is an image forming apparatus in which the toner image forming method is a tandem method. The color image forming apparatus 1 includes an endless intermediate transfer belt 30 that is an intermediate transfer medium that is temporarily transferred from a photoreceptor. The intermediate transfer belt 30 is stretched between two rollers, a driving roller 10 and a driven roller 20, and is rotated counterclockwise in FIG. 1 by the driving roller 10 driven by a driving motor (not shown). It has become.
[0029]
In addition, the color image forming apparatus 1 is arranged with respect to the intermediate transfer belt 30 and used for each toner of yellow (Y), magenta (M), cyan (C), and black (BK) to be used. Monochrome toner image forming means 40 (Y), 40 (C), 40 (M), and 40 (K).
[0030]
Each of the monochromatic toner image forming means 40 (Y), 40 (C), 40 (M), and 40 (K) has a photosensitive member 41 having a photosensitive layer on the outer peripheral surface and the outer peripheral surface of the photosensitive member 41. A charging roller 42 as a charging means for charging in this manner, an exposure means 43 for selectively exposing the outer peripheral surface uniformly charged by the charging roller 42 to form an electrostatic latent image, and this exposure means A developing roller 44 as a developing unit that applies toner as a developer to the electrostatic latent image formed by the toner 43 to form a visible image (toner image), and cleaning that removes toner remaining on the surface of the photoreceptor 41. And a photoconductor cleaning blade 45.
[0031]
In FIG. 1, reference numerals “41”, “42”, “43”, “44”, “45”, and “L” are omitted depending on the monochromatic toner image forming unit, but the reference numerals are omitted. It goes without saying that the constituent elements correspond to the constituent elements of the single color toner image forming means to which these symbols are attached. In this case, at least the photoreceptors 41 of the single color toner image forming units 40 (Y), 40 (C), 40 (M), and 40 (K) have the same layer configuration.
[0032]
The monochromatic toner image forming units 40 (Y), 40 (C), 40 (M), and 40 (K) are respectively on the slack side of the intermediate transfer belt 30 and in the rotation (movement) direction of the intermediate transfer belt 30. They are arranged in this order from the upstream side.
[0033]
Further, the color image forming apparatus 1 corresponds to each single color toner image forming means 40 (Y), 40 (C), 40 (M), 40 (K) for each color with each photoconductor 41. The four primary transfer portions T1Y, T1C, T1M, and T1K are set, and each primary transfer portion T1Y, T1C, T1M, and T1K includes primary transfer means 51, 52, 53, and 54, respectively. The toner images of the respective colors are sequentially primary transferred onto the intermediate transfer belt 30 by the single-color toner image forming units 40 (Y), 40 (C), 40 (M), and 40 (K), respectively. The toner images of the respective colors are sequentially superimposed on 30 to form a full color toner image by multiple transfer.
[0034]
Further, in the color image forming apparatus 1, one secondary transfer portion T 2 that is common to each color is set with the intermediate transfer belt 30, and the secondary transfer portion T 2 includes a secondary transfer roller 66. Then, the recording medium P such as paper is fed from the paper feed cassette 63 one by one by the pickup roller 64 and fed by the gate roller 65 pair to the secondary transfer portion T2 and fed. A full-color toner image on the intermediate transfer belt 30 is secondarily transferred onto the coming recording medium P by a secondary transfer roller 66.
[0035]
Further, the color image forming apparatus 1 includes a fixing device having a fixing roller pair 61, and the full-color toner image secondarily transferred onto the recording medium P passes through the fixing roller pair 61, thereby allowing the recording medium P Fixed on top.
Then, the recording medium P on which the full-color toner image is fixed is discharged to a predetermined discharge location such as a discharge tray (not shown) by the discharge roller pair 62.
[0036]
Further, an intermediate transfer belt cleaning blade 67 as a cleaning means for the intermediate transfer belt 30 is provided in contact with the intermediate transfer belt 30 at a portion where the intermediate transfer belt 30 is wound around the driving roller 10. The intermediate transfer belt cleaning blade 67 removes toner remaining on the surface of the intermediate transfer belt 30 after the secondary transfer.
[0037]
In the color image forming apparatus 1 of this example configured as described above, first, in each color toner image forming means 40 (Y), 40 (C), 40 (M), 40 (K), each of the photoconductors 41 is provided. After the outer peripheral surfaces are uniformly charged by the respective charging rollers 42, the exposure means 43 exposes the photosensitive members 41 for the respective colors, thereby forming electrostatic latent images of the colors corresponding to the photosensitive members 41, respectively. Is done.
[0038]
Next, the electrostatic latent image on each photoconductor 41 is developed with each color toner conveyed by each developing roller 44 to form each color toner image on each photoconductor 41. Further, the yellow (Y) toner image is primarily transferred to the intermediate transfer belt 30 in the yellow (Y) primary transfer portion T1Y, and thereafter the cyan (C) is transferred to each of the primary transfer portions T1C, T1M, and T1K. The toner image, the magenta (M) toner image, and the black (K) toner image are sequentially primary-transferred and superimposed on the intermediate transfer belt 30 to form a full-color toner image.
[0039]
Then, the primary transfer image on the intermediate transfer belt 30 on which the four color toner images are superposed in this manner is secondarily transferred to the recording medium P fed from the paper feed cassette 63 in the secondary transfer portion T2. Thus, a full-color toner image is formed. Further, the secondary transfer image on the recording medium P is fixed on the recording medium P by passing through the fixing roller pair 61, and then discharged to a predetermined discharge position by the discharge roller pair 62.
[0040]
In the example of the color image forming apparatus 1 shown in FIG. 1, the intermediate transfer belt 30 is used. However, an intermediate transfer drum may be used as the intermediate transfer medium. Such transfer drum type transfer media can also be divided into types using two types of substrates, as with the transfer belt described above. One is a photosensitive drum in which an organic photosensitive layer is provided on a rigid drum, for example, an aluminum drum, and the transfer medium is an elastic surface layer on a rigid drum base such as aluminum. A transfer layer is provided. The other is a so-called “elastic photoreceptor” in which a photosensitive support is provided on a belt-like or rubber or other elastic support, and the transfer medium is made of a rigid material such as aluminum. A transfer layer, which is a surface layer, may be provided directly on a drum base or via a conductive intermediate layer.
[0041]
Further, the color image forming apparatus 1 of the example shown in FIG. 1 is provided with four single-color toner image forming means 40 (Y), 40 (C), 40 (M), and 40 (K). In the image forming apparatus, the number of monochromatic toner image forming units is not limited to four, but a plurality of two or more can be provided. In that case, at least the layer configuration of each photoconductor 41 is set to be the same in the plurality of single color toner image forming units.
[0042]
Next, in the color image forming apparatus 1 of this example, the photoreceptor 41 and the intermediate transfer belt 30 that is an intermediate transfer medium that are particularly related to the present invention will be described. First, the photoconductor 41 will be described. The photoconductors 41 of the single color toner image forming means 40 are all formed identically. The photoreceptor 41 is an organic photoreceptor, and the organic photoreceptor may be an organic single layer type or an organic laminated type.
[0043]
The organic laminated type photoreceptor is obtained by sequentially laminating a charge generation layer and a charge transport layer on a conductive support via an undercoat layer.
As the conductive support, a known conductive support can be used. For example, a volume resistance of 10 ^Ten Forming conductive polyimide resin with conductivity of Ω · cm or less, such as aluminum alloy pipes or polyethylene terephthalate films that have been processed by cutting, etc. Examples thereof include tubular, belt-like, plate-like, and sheet-like supports. As another example, a metal belt in which nickel electroformed pipes, stainless steel pipes and the like are made seamless can also be suitably used.
[0044]
As the undercoat layer provided on the conductive support, a known undercoat layer can be used. For example, the undercoat layer is provided for the purpose of improving adhesion, preventing moire, improving the coatability of the upper charge generation layer, and reducing the residual potential during exposure. The resin used for the undercoat layer is preferably a resin having high resistance to dissolution with respect to the solvent used for the photosensitive layer in view of coating the photosensitive layer thereon. Usable resins include water-soluble resins such as polyvinyl alcohol, casein, and sodium polyacrylate, alcohol-soluble resins such as vinyl acetate, copolymer nylon, and methoxymethylated nylon, polyurethane, melamine resin, and epoxy resin. It can be used alone or in combination of two or more. Moreover, you may make these resins contain metal oxides, such as titanium dioxide and a zinc oxide.
[0045]
As the charge generation pigment in the charge generation layer, known materials can be used. For example, phthalocyanine pigments such as metal phthalocyanine and metal-free phthalocyanine, azulenium salt pigments, squaric acid methine pigments, azo pigments having a carbazole skeleton, azo pigments having a triphenylamine skeleton, azo pigments having a diphenylamine skeleton, dibenzothiophene skeleton Azo pigments having a fluorene skeleton, azo pigments having an oxadiazole skeleton, azo pigments having a bis-stilbene skeleton, azo pigments having a distyryl oxadiazole skeleton, azo pigments having a distyrylcarbazole skeleton, perylene Pigments, anthraquinone or polycyclic quinone pigments, quinoneimine pigments, diphenylmethane and triphenylmethane pigments, benzoquinone and naphthoquinone pigments, cyanine and azomethine pigments Indigoid pigments, and bisbenzimidazole pigments. These charge generation pigments can be used alone or in combination of two or more.
[0046]
Examples of the binder resin in the charge generation layer include polyvinyl butyral resin, partially acetalized polyvinyl butyral resin, polyarylate resin, vinyl chloride-vinyl acetate copolymer, and the like. The component ratio of the binder resin and the charge generating material is used in the range of 10 to 1000 parts by weight with respect to 100 parts by weight of the binder resin.
[0047]
A known material can be used as the charge transport material constituting the charge transport layer, and there are an electron transport material and a hole transport material. Examples of the electron transport material include chloroanil, tetracyanoethylene, tetracyanoquinodimethane, 2,4,7-trinitro-9-fluorenone, paradiphenoquinone derivative, benzoquinone derivative, naphthoquinone derivative, and benzidine derivative having a fluorine atom. An electron accepting substance is mentioned. These electron transport materials can be used alone or in combination of two or more.
[0048]
Examples of hole transport materials include oxazole compounds, oxadiazole compounds, imidazole compounds, triphenylamine compounds, pyrazoline compounds, hydrazone compounds, stilbene compounds, phenazine compounds, benzofuran compounds, butadiene compounds, benzidine compounds, and derivatives of these compounds. These electron donating substances are listed. These hole transport materials can be used alone or in combination of two or more.
[0049]
The charge transport layer may contain an antioxidant, an anti-aging agent, an ultraviolet absorber and the like for preventing the deterioration of these substances.
As the binder resin in the charge transport layer, polyester, polycarbonate, polysulfone, polyarylate, polyvinyl butyral, polymethyl methacrylate, polyvinyl chloride resin, vinyl chloride-vinyl acetate copolymer, silicone resin, etc. can be used. Polycarbonate is preferable in view of compatibility with a transport material, film strength, solubility, and stability as a coating material. The composition ratio of the binder resin and the charge transport material is used in a range of 25 to 300 parts by weight with respect to 100 parts by weight of the binder resin.
[0050]
In order to form the charge generation layer and the charge transport layer, a coating solution may be used, and the solvent varies depending on the type of the binder resin. For example, alcohols such as methanol, ethanol, isopropyl alcohol, acetone, methyl ethyl ketone, cyclohexanone, etc. Ketones, amides such as N, N-dimethylformamide, N, N-dimethylacetamide, ethers such as tetrahydrofuran, dioxane and ethylene glycol monomethyl ether, esters such as methyl acetate and ethyl acetate, chloroform, methylene chloride, Aliphatic halogenated hydrocarbons such as dichloroethylene, carbon tetrachloride, and trichloroethylene, or aromatics such as benzene, toluene, xylene, and monochlorobenzene can be used.
The charge generating pigment may be dispersed and mixed using a mechanical method such as a sand mill, ball mill, attritor, or planetary mill.
[0051]
Coating methods for the undercoat layer, charge generation layer and charge transport layer include dip coating method, ring coating method, spray coating method, wire bar coating method, spin coating, blade coating method, roller coating method, air knife coating method, etc. Use the method. In addition, the drying after coating is preferably performed by drying at room temperature and then heating and drying at a temperature of 30 to 200 ° C. for 30 to 120 minutes. The film thickness after drying in the charge generation layer is in the range of 0.05 to 10 μm, preferably 0.1 to 3 μm. In the charge transport layer, the thickness is in the range of 5 to 50 μm, preferably 10 to 40 μm.
[0052]
In addition, the single-layer organic photoreceptor layer has a binder and a binder, such as a charge generating agent, a charge transport agent, and a sensitizer, on the conductive support described in the above-mentioned organic laminated photoreceptor. It is prepared by coating and forming a single-layer organic photosensitive layer made of a solvent or the like. The organic negatively charged single layer type photoconductor may be produced according to the method disclosed in, for example, Japanese Patent Application Laid-Open No. 2000-19746.
[0053]
Examples of the charge generator in the single-layer organic photosensitive layer include phthalocyanine pigments, azo pigments, quinone pigments, perylene pigments, quinothiaton pigments, indigo pigments, bisbenzimidazole pigments, and quinacridone pigments. These are phthalocyanine pigments and azo pigments. Examples of the charge transport agent include hydrazone-based, stilbene-based, phenylamine-based, arylamine-based, diphenylbutadiene-based, oxazole-based organic hole-transporting compounds, and sensitizers include various electron-withdrawing organic compounds. Examples thereof include paradiphenoquinone derivatives, naphthoquinone derivatives and chloranil which are also known as electron transport agents. Examples of the binder include thermoplastic resins such as polycarbonate resin, polyarylate resin, and polyester resin.
[0054]
The composition ratio of each component is 40 to 75% by weight of binder, 0.5 to 20% by weight of charge generator, 10 to 50% by weight of charge transport agent, and 0.5 to 30% by weight of sensitizer, preferably binder. 45 to 65% by weight, charge generating agent 1 to 20% by weight, charge transporting agent 20 to 40% by weight, and sensitizer 2 to 25% by weight. The solvent is preferably a solvent that is not soluble in the undercoat layer, and examples thereof include toluene, methyl ethyl ketone, and tetrahydrofuran.
[0055]
Each component is pulverized / dispersed and mixed with a stirrer such as a homomixer, a ball mill, a sand mill, an attritor, or a paint conditioner to obtain a coating solution. The coating solution is applied and dried on the undercoat layer by dip coating, ring coating, spray coating or the like so as to have a film thickness of 15 to 40 μm, preferably 20 to 35 μm, to form a single-layer organic photoreceptor layer.
[0056]
The intermediate transfer belt 30 as a transfer medium is classified into a type using two types of substrates. One is to provide a transfer layer as a surface layer on a resin film or a seamless belt, and the other is to provide a transfer layer as a surface layer on an elastic body such as rubber.
[0057]
Materials suitable for films and seamless belts and their production methods include engineering plastics such as modified polyimide, thermosetting polyimide, polycarbonate, ethylene tetrafluoroethylene copolymer, polyvinylidene fluoride, nylon alloy, conductive carbon black, conductive A semiconductive film substrate having a thickness of 50 to 500 μm in which conductive materials such as conductive titanium oxide, conductive tin oxide, and conductive silica are dispersed is formed, and this semiconductive film substrate is formed into a seamless substrate by extrusion molding. Note that a tape such as a PET film with a film thickness of 80 μm and a rib such as urethane rubber are attached to both ends of the transfer belt in order to prevent cracks, elongation and meandering at the end of the transfer belt.
[0058]
In the case of producing an endless belt-like substrate with a film sheet, the endless belt-like substrate can be produced by forming the film sheet into a belt shape and welding the end surfaces thereof by ultrasonic welding. Specifically, a transfer belt having desired physical properties can be produced by performing ultrasonic welding after providing a conductive layer and a surface layer on a sheet film. More specifically, when polyethylene terephthalate having a thickness of 60 to 150 μm is used as the insulating substrate for the substrate, aluminum or the like is vapor-deposited on the surface, and if necessary, further comprises a conductive material such as carbon black and a resin. An intermediate conductive layer is applied, and a semiconductive surface layer made of urethane resin, fluororesin, conductive material, and fluorine-based fine particles having higher surface resistance is provided thereon to form a transfer belt. If it is possible to provide a resistance layer that does not require much heat during drying after coating, a transfer belt can be produced by providing the above-mentioned resistance layer after ultrasonically depositing an aluminum vapor-deposited film first. Is also possible.
[0059]
As a material suitable for an elastic substrate such as rubber and a manufacturing method thereof, for example, a thickness of 0.8 to 2 in which the conductive material is dispersed in silicon rubber, urethane rubber, NBR (nitrile rubber), EPDM (ethylene propylene rubber), or the like. A 0.0 μm semiconductive rubber belt is produced by extrusion molding, and the surface is controlled to a desired surface roughness by an abrasive such as sandpaper or polisher. Although the elastic layer at this time can be used as it is, a surface protective layer can be further provided in the same manner as described above.
[0060]
The intermediate transfer medium can also be constituted by a transfer drum. In the case of this transfer drum, the volume resistance is 10 ^Four -10 ¹² The range of Ω · cm is good, preferably 10 ⁷ -10 ¹¹ A range of Ω · cm is preferable. If necessary, the transfer drum is provided with a conductive intermediate layer of an elastic body on a metal cylinder such as aluminum to form a conductive elastic substrate.
[0061]
Examples of materials suitable for the conductive elastic substrate and methods for producing the same include silicon rubber, urethane rubber, NBR (nitrile rubber), EPDM (ethylene propylene rubber), butadiene rubber, styrene-butadiene rubber, isoprene rubber, chloroprene rubber, butyl rubber, Conductive rubber material containing conductive carbon black, conductive titanium oxide, conductive tin oxide, conductive silica, etc., mixed with rubber material such as epichlorohydrin rubber and fluororubber, kneaded and dispersed in diameter Is closely formed on an aluminum cylinder of 90 to 180 mm, the thickness after polishing is 0.8 to 6 mm, and the volume resistance is 10 ^Four -10 ^Ten It should be Ω · cm. Next, a semiconductive surface layer made of urethane resin, fluororesin, conductive material, and fluorine-based fine particles is provided so that the film thickness is about 15 to 40 μm, and the desired volume resistance is 10 ⁷ -10 ¹¹ A transfer drum having Ω · cm can be obtained. The surface roughness at this time is preferably 1 μmRa or less. As another example, a transfer drum having a desired surface layer and electric resistance is formed by covering a conductive elastic substrate produced as described above with a semiconductive tube such as a fluororesin and shrinking by heating. It is also possible to produce it.
[0062]
As described above, when the transfer medium is a transfer belt or a transfer drum, a voltage of +250 to +800 V is applied as a primary transfer voltage to the conductive layer of the transfer belt or the transfer drum. In the next transfer, a voltage of +400 to +3500 V is preferably applied as the secondary transfer voltage.
[0063]
Next, the toner used in the image forming apparatus of the present invention will be described. The toner used in the image forming apparatus of the present invention is a one-component nonmagnetic toner negatively chargeable toner. The toner base particles used for the one-component non-magnetic toner can be prepared by either a pulverization method or a polymerization method, and the preparation will be described below.
[0064]
First, preparation of a one-component non-magnetic toner (hereinafter referred to as a pulverized toner) using toner mother particles by a pulverization method will be described.
As a pulverized toner, pigment, release agent and charge control agent are uniformly mixed in a resin binder with a Henschel mixer, melted and kneaded with a twin screw extruder, cooled, and then subjected to a coarse pulverization-fine pulverization process, followed by classification. The toner base particles obtained by the treatment are further added with a fluidity improver to obtain a pulverized toner.
[0065]
As the binder resin, a known toner resin can be used, for example, polystyrene, poly-α-methylstyrene, chloropolystyrene, styrene-chlorostyrene copolymer, styrene-propylene copolymer, styrene-butadiene copolymer. Polymer, styrene-vinyl chloride copolymer, styrene-vinyl acetate copolymer, styrene-maleic acid copolymer, styrene-acrylic acid ester copolymer, styrene-methacrylic acid ester copolymer, styrene-acrylic acid ester- Styrene or a styrene-substituted product is obtained with a styrene resin such as a methacrylic acid ester copolymer, a styrene-α-chloroacrylic acid methyl copolymer, a styrene-acrylonitrile-acrylic acid ester copolymer, or a styrene-vinyl methyl ether copolymer. Containing homopolymer or copolymer, poly Ester resin, epoxy resin, urethane modified epoxy resin, silicone modified epoxy resin, vinyl chloride resin, rosin modified maleic acid resin, phenyl resin, polyethylene, polypropylene, ionomer resin, polyurethane resin, silicone resin, ketone resin, ethylene-ethyl acrylate Polymers, xylene resins, polyvinyl butyral resins, terpene resins, phenol resins, aliphatic or alicyclic hydrocarbon resins, and the like can be used alone or in combination. In particular, in the present invention, styrene-acrylic acid ester resins, styrene-methacrylic acid ester resins, polyester resins, and epoxy resins are preferable. In the present invention, the binder resin preferably has a glass transition temperature of 50 to 75 ° C and a flow softening temperature of 100 to 150 ° C.
[0066]
As the colorant, a known toner colorant can be used. For example, carbon black, lamp black, magnetite, titanium black, chrome yellow, ultramarine blue, aniline blue, phthalocyanine blue, phthalocyanine green, Hansa Yellow G, rhodamine 6G, calco oil blue, quinacridone, benzidine yellow, rose bengal, malachite green lake, Quinoline Yellow, C.I. I. Pigment red 48: 1, C.I. I. Pigment red 122, C.I. I. Pigment red 57: 1, C.I. I. Pigment red 122, C.I. I. Pigment red 184, C.I. I. Pigment yellow 12, C.I. I. Pigment yellow 17, C.I. I. Pigment yellow 97, C.I. I. Pigment yellow 180, C.I. I. Solvent Yellow 162, C.I. I. Pigment blue 5: 1, C.I. I. Dye and pigment such as CI Pigment Blue 15: 3 can be used alone or in combination.
[0067]
As the release agent, a known toner release agent can be used. Examples thereof include paraffin wax, micro wax, micro crystallin wax, cadilla wax, carnauba wax, rice wax, montan wax, polyethylene wax, polypropylene wax, oxidized polyethylene wax, oxidized polypropylene wax and the like. Among these, it is preferable to use polyethylene wax, polypropylene wax, carnauba wax, ester wax and the like.
[0068]
As the charge adjusting agent, a known toner charge adjusting agent can be used. For example, oil black, oil black BY, Bontron S-22 (manufactured by Orient Chemical Industries, Ltd.), Bontron S-34 (manufactured by Orient Chemical Industries, Ltd.), salicylic acid metal complex E-81 (Orient Chemical Industries, Ltd.) Manufactured), thioindigo pigment, sulfonylamine derivative of copper phthalocyanine, Spiron Black TRH (manufactured by Hodogaya Chemical Co., Ltd.), calixarene compound, organic boron compound, fluorine-containing quaternary ammonium salt compound, monoazo metal complex, Aromatic hydroxyl carboxylic acid metal complexes, aromatic dicarboxylic acid metal complexes, polysaccharides and the like can be mentioned. Of these, colorless or white toners are preferred for color toners.
[0069]
The component ratio (weight ratio) in the pulverized toner is shown in Table 1.
[0070]
[Table 1]

[0071]
As shown in Table 1, the colorant is 0.5 to 15 parts by weight, preferably 1 to 10 parts by weight, and the release agent is 1 to 10 parts by weight, preferably 100 parts by weight of the binder resin. The charge control agent is 0.1 to 7 parts by weight, preferably 0.5 to 5 parts by weight.
As the pulverized toner thus obtained, an average particle diameter (D ₅₀ ) Is in the range of 5 μm to 10 μm, preferably in the range of 6 μm to 9 μm, and 3 μm or less has a particle size distribution of 20% or less, preferably 10% or less on a number basis.
[0072]
In the pulverized toner of this example, it is preferable to increase the circularity (spheroidizing coefficient) by spheroidizing treatment for the purpose of improving the transfer efficiency. In order to increase the circularity of the pulverized toner,
{Circle around (1)} When using a relatively round spherical and pulverizable apparatus, for example, a turbo mill (manufactured by Kawasaki Heavy Industries, Ltd.) known as a mechanical pulverizer, the circularity can reach 0.93.
Or
{Circle around (2)} If the pulverized toner is used with a commercially available hot-air spheronizer surfing system SFS-3 type (manufactured by Nippon Pneumatic Industry Co., Ltd.), the circularity can be up to 1.00.
The average particle diameter and the circularity of the toner particles and the like in the present invention are all values measured with an FPIA 2100 manufactured by Sysmex Corporation.
[0073]
Next, preparation of a toner using toner mother particles by a polymerization method (hereinafter referred to as polymerization method toner) will be described.
Examples of the polymerization toner include suspension polymerization and emulsion polymerization. In the suspension polymerization method, a polymerizable monomer, a color pigment, and a release agent are dissolved or mixed with a dye, a polymerization initiator, a crosslinking agent, a charge control agent, and other additives as necessary. The dispersed monomer composition is added to an aqueous phase containing a suspension stabilizer (water-soluble polymer, poorly water-soluble inorganic substance) with stirring, granulated, and polymerized to obtain a desired particle size. It is possible to form colored polymer toner particles having the same.
[0074]
In the emulsion polymerization method, if necessary, a polymerization initiator, an emulsifier (surfactant) and the like are further dispersed in water to carry out the polymerization, if necessary, and then a colorant and a charge control agent in the aggregation process. Colored toner particles having a desired particle size can be formed by adding a flocculant (electrolyte) and the like.
In the materials used for the preparation of the polymerization toner, the same materials as those for the above-mentioned pulverization toner can be used for the colorant, release agent, charge control agent, and fluidity improver.
[0075]
As the polymerizable monomer (monomer), known vinyl monomers can be used. For example, styrene, o-methylstyrene, m-methylstyrene, p-methylstyrene, α-methylstyrene, p-methoxystyrene. , P-ethylstyrene, vinyltoluene, 2,4-dimethylstyrene, pn-butylstyrene, p-phenylstyrene, p-chlorostyrene, divinylbenzene, methyl acrylate, ethyl acrylate, propyl acrylate, acrylic acid n-butyl, isobutyl acrylate, n-octyl acrylate, dodecyl acrylate, hydroxyethyl acrylate, 2-ethylhexyl acrylate, phenyl acrylate, stearyl acrylate, 2-chloroethyl acrylate, methyl methacrylate, ethyl methacrylate , Methacrylic acid pro , N-butyl methacrylate, isobutyl methacrylate, n-octyl methacrylate, dodecyl methacrylate, hydroxyethyl methacrylate, 2-ethylhexyl methacrylate, stearyl methacrylate, phenyl methacrylate, acrylic acid, methacrylic acid, maleic acid, Fumaric acid, cinnamic acid, ethylene glycol, propylene glycol, maleic anhydride, phthalic anhydride, ethylene, propylene, butylene, isobutylene, vinyl chloride, vinylidene chloride, vinyl bromide, vinyl fluoride, vinyl acetate, vinyl propyleneate, Examples include acrylonitrile, methacrylonitrile, vinyl methyl ether, vinyl ethyl ether, vinyl ketone, vinyl hexyl ketone, and vinyl naphthalene. Examples of the fluorine-containing monomer include 2,2,2-trifluoroethyl acrylate, 2,2,3,3-tetrafluoropropyl acrylate, vinylidene fluoride, ethylene trifluoride, tetrafluoroethylene, and trifluoropropylene. Can be used because fluorine atoms are effective for negative charge control.
[0076]
Known emulsifiers (surfactants) can be used. For example, sodium dodecylbenzene sulfate, sodium tetradecyl sulfate, sodium pentadecyl sulfate, sodium octyl sulfate, sodium oleate, sodium laurate, potassium stearate, calcium oleate, dodecyl ammonium chloride, dodecyl ammonium bromide, dodecyl trimethyl ammonium bromide, dodecyl pyridinium chloride Hexadecyl trimethyl ammonium bromide, dodecyl polyoxyethylene ether, hexadecyl polyoxyethylene ether, lauryl polyoxyethylene ether, sorbitan monooleate polyoxyethylene ether, and the like.
[0077]
A well-known thing can be used as a polymerization initiator. For example, potassium persulfate, sodium persulfate, ammonium persulfate, hydrogen peroxide, 4,4′-azobiscyanovaleric acid, t-butyl hydroperoxide, benzoyl peroxide, 2,2′-azobis-isobutyronitrile, etc. is there.
[0078]
As the flocculant (electrolyte), known ones can be used. Examples thereof include sodium chloride, potassium chloride, lithium chloride, magnesium chloride, calcium chloride, sodium sulfate, potassium sulfate, lithium sulfate, magnesium sulfate, calcium sulfate, zinc sulfate, aluminum sulfate, and iron sulfate.
[0079]
The component ratio (weight) in the emulsion polymerization toner is shown in Table 2.
[0080]
[Table 2]

[0081]
As shown in Table 2, with respect to 100 parts by weight of the polymerizable monomer, the polymerization initiator is 0.03 to 2, preferably 0.1 to 1 part by weight, and the surfactant is 0.01 to 0.1 part. In addition, the release agent is 1 to 40 parts by weight, preferably 2 to 35 parts by weight, and the charge control agent is 0.1 to 7 parts by weight, preferably 0.5 to 5 parts by weight. The colorant is 1 to 20 parts by weight, preferably 3 to 10 parts by weight, and the flocculant (electrolyte) is 0.05 to 5 parts by weight, preferably 0.1 to 2 parts by weight.
[0082]
Even in this polymerized toner, it is preferable to increase the circularity by a spheroidizing process for the purpose of improving the transfer efficiency. As a method of adjusting the circularity of the polymerization toner,
(1) In the emulsion polymerization method, the degree of circularity can be freely changed by controlling the temperature and time during the aggregation process of the secondary particles, and the range thereof is 0.94 to 1.00.
Also,
{Circle around (2)} In the suspension polymerization method, since a true spherical toner is possible, the circularity is in the range of 0.98 to 1.00. In addition, the degree of circularity can be freely adjusted from 0.94 to 0.98 by heating and deforming at a temperature equal to or higher than the Tg temperature of the toner in order to adjust the degree of circularity.
[0083]
The polymerization toner can be prepared by a dispersion polymerization method other than the above-described method, for example, a method disclosed in JP-A-63-304002. In this case, since the shape is close to a true sphere, in order to control the shape, for example, pressurization can be performed at a temperature equal to or higher than the Tg temperature of the toner to obtain a desired toner shape.
[0084]
The polymerization toner thus obtained has an average particle diameter (D ₅₀ ) Is in the range of 4-9 μm, preferably in the range of 4.5-8 μm, and 3 μm or less has a particle size distribution of 5% or less, preferably 3% or less on the number basis.
[0085]
As the circularity of the base particles of the one-component non-magnetic toner in the present invention, the desirable circularity (spheroidization coefficient) is 0.94 or more, preferably 0.5 or more, for both the pulverized toner and the polymerized toner. is there. As described above, by setting the circularity (sphericity) of each color toner to 0.94 or more, the adhesive force between the toner and the photoreceptor can be reduced, and the transfer efficiency can be further improved more effectively. .
[0086]
As the fluidity improver which is an external additive, known inorganic and organic toner fluidity improvers can be used. Known fluidity improvers for inorganic and organic toners include, for example, silica, titanium dioxide, alumina, magnesium fluoride, silicon carbide, boron carbide, titanium carbide, zirconium carbide, boron nitride, titanium nitride, zirconium nitride, magnetite. In addition, fine particles of molybdenum disulfide, aluminum stearate, magnesium stearate, zinc stearate, calcium stearate, metal titanate and silicon metal salt can be used. These fine particles are preferably used after being hydrophobized with a silane coupling agent, a titanium coupling agent, a higher fatty acid, silicone oil or the like.
[0087]
Examples of the hydrophobizing agent include dimethyldichlorosilane, octyltrimethoxysilane, hexamethyldisilazane, silicone oil, octylutecrochlorosilane, decylutetrichlorosilane, nonirute trichlorosilane, and (4-iso-propylphenyl). -Trichlorosilane, dihexyldichlorosilane, (4-t-butylphenyl) -trichlorosilane, dipentyl-dichlorosilane, dihexyl-dichlorosilane, dioctyl-dichlorosilane, dinonyl-dichlorosilane, didecyl-dichlorosilane, di-2-ethylhexyl-dichlorosilane, Di-3,3-dimethylpentyl-dichlorosilane, trihexyl-chlorosilane, trioctyl-chlorosilane, tridecyl-chlorosilane, dioctyl-methyl-chlorosilane, octyl- Examples thereof include dimethyl-chlorosilane and (4-iso-propylphenyl) -diethyl-chlorosilane.
Examples of other resin fine particles include acrylic resin, styrene resin, and fluororesin.
[0088]
Use amount of the fluidity improver particles, average particle size of primary particles (D ₅₀ ), And the specific surface area by the BET method is shown in Table 3.
[0089]
[Table 3]

[0090]
These fluidity improver particles can be used alone or in combination, and as shown in Table 3, the amount used is in the range of 0.1 to 5% by weight with respect to the toner base particles in any of the toner base particles described above. More preferably, the range is 0.5 to 4.0% by weight. Average particle size of primary particles of flow improver particles (D ₅₀ ) Is preferably in the range of 5 to 150 nm, more preferably 7 to 100 nm, and the specific surface area by the BET method is 2 to 500 m. ² / G fine particles should be used, more preferably 5 to 400 m. ² It is better to use fine particles that are / g.
[0091]
By the way, in the image forming apparatus of the present invention, the magnitude relationship among the work function of the photoconductor 41, the work function of the intermediate transfer belt 30, and the work function of each color toner is set as follows.
That is,
(1) The most upstream side in the rotation (movement) direction of the intermediate transfer medium (in the example shown in FIG. 1, the intermediate transfer belt 30) (hereinafter, the upstream side in the rotation direction of the intermediate transfer medium is simply the upstream side, and the intermediate transfer medium The work function of the toner in the rotation direction downstream side (simply referred to as the downstream side) {yellow (Y) toner in the example shown in FIG. 1] is larger than the work function of the photosensitive member (photosensitive member 41 in the example shown in FIG. 1). It is set. That is,
Topmost toner work function> Photoconductor work function
(In the example shown in FIG. 1, the work function of yellow (Y) toner> the work function of the photoconductor 41).
(2) The work function of the toner on the most upstream side is set larger than the work function of the intermediate transfer medium. That is,
Work function of the toner on the most upstream side> Work function of the intermediate transfer medium
(In the example shown in FIG. 1, the work function of yellow (Y) toner> the work function of the intermediate transfer belt 30).
(3) A plurality of single color toner image forming means {in the example shown in FIG. 1, four single color toner image forming means 40 (Y), 40 (C), 40 (M), 40 (K)} respectively. Each work function of the toner to be applied is set to increase in order from the upstream side to the downstream side in the moving direction of the intermediate transfer medium {in the example shown in FIG. 1, the work function of yellow (Y) toner <cyan (C) toner work function <magenta (M) toner work function <black (K) toner work function}.
[0092]
Next, a method for measuring these work functions will be described.
The work function (Φ) is measured by a surface analyzer (AC-2 manufactured by Riken Keiki Co., Ltd.), and is the energy required to extract electrons from the material. It is easy to emit, and the larger it is, the harder it is to emit electrons. Therefore, when a substance with a small work function is brought into contact with a substance with a large work function, a substance with a small work function is positively charged, while a substance with a large work function is negatively charged, but the work function itself takes out electrons from the substance. Therefore, the energy (eV) is quantified.
[0093]
In the present invention, the measurement of the work function of each component of the one-component nonmagnetic toner and each member of the image forming apparatus is performed as follows. That is, in the above-described surface analysis apparatus, a deuterium lamp is used, the irradiation function is set to 10 nW in the work function measurement of the developing roller subjected to metal plating, and the irradiation function is set to 500 nW in the other work function measurement. The monochromatic light is selected by the instrument, the spot size is 4 mm square, and the sample is irradiated with an energy scanning range of 3.4 to 6.2 eV and a measurement time of 10 sec / 1 point. The photoelectrons emitted from the sample surface can be detected and processed using work function meter software. The work function is measured with a repeatability (standard deviation) of 0.02 eV. In addition, as a measurement environment for ensuring data reproducibility, a 24 hour standing product is used as a measurement sample under the conditions of operating temperature and humidity of 25 ° C. and 55% RH.
[0094]
For the measurement of the work function of the sample toner, as shown in FIGS. 2 (a) and 2 (b), a stainless steel disk having a diameter of 13 mm and a height of 5 mm has a toner containing recess having a diameter of 10 mm and a depth of 1 mm. A toner dedicated measurement cell is used. After the sample toner is put into the concave portion of the cell without using a measuring spoon, it is measured in a state where the surface is leveled and flattened using a knife edge. After the measurement cell filled with toner is fixed on the specified position of the sample stage, the irradiation light quantity is set to 500 nW, the spot size is 4 mm square, and the energy scanning range is 4.2 to 6.2 eV, which will be described later with reference to FIG. It is measured in the same way as shown in b).
[0095]
In addition, when an image forming apparatus member having a cylindrical shape such as a photoconductor or a developing roller is used as a sample, the cylindrical image forming apparatus member is cut to a width of 1 to 1.5 cm, and then along the ridgeline. 3b, the measurement sample piece having the shape shown in FIG. 3 (a) is obtained, and then the measurement light is irradiated on the specified position of the sample stage as shown in FIG. 3 (b). And fixed so that the irradiated surface is parallel to the surface. Thereby, the emitted photoelectrons are efficiently detected by the detector (photoelectron tube).
[0096]
Further, when the intermediate transfer belt, the regulating blade for regulating the toner thin layer, and the photosensitive member are in the form of a sheet, the measurement light is irradiated with a 4 mm square spot as described above, so that the sample piece is at least 1 cm square. And is fixed to the sample stage as shown in FIG. 3B and measured in the same manner.
[0097]
In this surface analyzer, photon emission starts when the excitation energy of monochromatic light is scanned from low to high, and the energy value (eV: work function) at which photon emission starts is measured. The data is obtained from the relationship between excitation energy (Photon Energy) (horizontal axis) and normalized photoelectron yield (Emission Yield). For example, the external additive SiO shown in FIG. ₂ An example of SiO will be described. ₂ The work function (WF) of the particles is an excitation energy of 5.22 eV at the inflection point (A). Further, the slope (Slope, normalized photoelectron yield / eV) indicates that it is easy to emit electrons when the value is large.
[0098]
As a method of increasing the work function of each toner from the upstream side to the downstream side, the amount of the external additive added for each color is changed so that the work function of each toner increases as it goes from the upstream side to the downstream side. There is a way to make it. The external additive is added to the surface layer of the toner base particles and greatly affects the work function of the toner. Thus, by changing the amount of the external additive added for each color, the work function of each toner is increased upstream. The size can be effectively increased from the side to the downstream side.
[0099]
As an example of this method, there is a method in which a large amount of titanium oxide is added from the upstream side to the downstream side as an external additive for each color toner. Since the work function of titanium oxide is relatively large at 5.7 to 5.8, the work function of the toner increases as the amount of titanium oxide added is increased.
As another example of this method, silica (SiO 2) is used as an external additive for each color toner. ₂ There is a method of adding a small amount of) as it goes from the upstream side to the downstream side. Since the work function of silica is relatively small, 5.0 to 5.2, the work function of the toner decreases as the addition amount of silica increases.
[0100]
The work function of the toner on the most upstream side in the moving direction of the intermediate transfer belt 30 configured as described above> The work function of the toner on the most upstream side in the moving direction of the intermediate transfer belt 30> The work function of the intermediate transfer belt 30 is set, and further, the work functions of the toners of a plurality of colors are set so as to increase in order from the upstream side to the downstream side in the moving direction of the intermediate transfer belt 30. Transfer is performed between the toner to be transferred on the intermediate transfer belt 30 and between the toner to be transferred on the photosensitive member 41 and the toner on the intermediate transfer belt 30 transferred previously. The toner to be charged is charged on the (−) side and the toner on the intermediate transfer belt 30 and the toner on the intermediate transfer belt 30 are about to be charged on the (+) side. The toner is effectively transferred. As a result, toner transfer residue is extremely reduced, and transfer efficiency is effectively improved to 98% or more.
[0101]
On the other hand, the most downstream toner is preferably black (K) toner. Since the most downstream transfer process involves a large number of previous transfer processes, there is a high possibility that the other color toner is transferred onto the intermediate transfer medium, and the transfer area of the other color toner is large. Therefore, there is a high possibility of reverse transfer in the most downstream transfer step. Then, even if the reversely transferred toner moves from the image carrier to the developer carrier and other colors are mixed in the black toner (contamination) and developed in this contamination state, the toner on the most downstream side is blackened. By using the toner of (K), the black toner is the color that is hardly affected by the contamination, so that this contamination can be prevented from being perceived by human vision in the output image.
[0102]
Further, a predetermined speed difference may be provided between the peripheral speed of the photosensitive member and the peripheral speed (moving speed) of the intermediate transfer medium. By providing the speed difference in this way, the toner particles roll in the transfer nip and the chance of contact between the toner particles and the image carrier and the transfer medium increases, so that the charging polarity of the toner in the transfer nip can be made more uniform. it can. Thereby, reverse transfer can be more effectively suppressed and transfer efficiency can be improved.
[0103]
FIG. 5 is a diagram schematically and partially showing another example of an embodiment of an image forming apparatus according to the present invention, and FIG. 6 is a diagram schematically showing a monochromatic toner image forming unit of this example. The same components as those in the above-described example are denoted by the same reference numerals, and detailed description thereof is omitted.
[0104]
As shown in FIG. 5, the image forming apparatus of this example is a tandem type color image forming apparatus as in the above example, but the intermediate transfer belt 30 (intermediate transfer medium) of the above example is not provided. The toner images of the single color toner image forming means 40 (Y), 40 (C), 40 (M), and 40 (K) are directly transferred directly to a recording medium P such as paper. Therefore, in the color image forming apparatus of this example, the recording medium P such as paper is the transfer medium.
[0105]
Similarly to the above-described example, the single color toner image forming means 40 (Y), 40 (C), 40 (M), and 40 (K) are configured identically to each other, and as shown in FIG. The image forming means 40 (Y), 40 (C), 40 (M), 40 (K) use a corona charger 42 ′ as a charging means, and transfer rollers 51 ′, 52 ′, as transfer means. 53 'and 54' are provided. Other configurations of the color image forming apparatus of this example are the same as those of the collar described above. In FIG. 6, reference numeral 46 denotes a regulating blade that regulates a thin layer of toner, and reference numeral 47 denotes a supply roller that supplies toner to the developing roller 44.
[0106]
The transfer rollers 51 ', 52', 53 ', and 54' are identical to each other, and have a structure in which an elastic layer, a conductive layer, and a resistive surface layer are laminated in this order on the peripheral surface of a metal shaft having a diameter of 10 to 20 mm. ing. The resistive surface layer can use a highly flexible resistive sheet in which conductive fine particles such as conductive carbon are dispersed in a resin such as a fluororesin or polyvinyl butyral, or a rubber such as polyurethane. Is preferably smooth, and the volume resistance value is 10 ⁷ -10 ¹¹ Ω · cm, preferably 10 ⁸ -10 ^Ten ~ Ω · cm, and the film thickness is 0.02 to 2 mm.
[0107]
The conductive layer may be selected from a conductive resin in which conductive fine particles such as conductive carbon are dispersed in a polyester resin, a metal sheet, or a conductive adhesive, and has a volume resistance of 10 ^Five Ω · cm or less.
The elastic layer needs to be deformed flexibly when the transfer roller is pressed against the organic photoreceptor, and to return to its original shape quickly when the pressure is released. An elastic layer such as foam rubber sponge is used. Formed. The foam structure may be either a continuous foam (foaming) structure or a closed cell structure, and may have a rubber hardness (Asker C hardness) of 30 to 80, and a film thickness of 1 to 5 mm.
[0108]
The organic photoconductor and the transfer medium can be brought into close contact with each other with a wide nip width by the elastic deformation of the transfer rollers 51 ', 52', 53 'and 54' thus produced. It is preferable that the pressing load is 20 to 100 gf / cm, and the nip is 1 to 8 mm in width. Further, a transfer voltage having a polarity opposite to the toner charging voltage of +200 to +800 V may be applied to the transfer rollers 51 ′, 52 ′, 53 ′, and 54 ′.
[0109]
Next, examples of the present invention will be described.
[Example 1 and Comparative Example 1]
{Example of production of organic photoreceptor (OPC1)}
The organic photoreceptor (OPC1) used in Example 1 and Comparative Example 1 will be described.
6 parts by weight of alcohol-soluble nylon {"CM8000" manufactured by Toray Industries, Inc.} as an undercoat layer and 4 parts by weight of titanium oxide fine particles treated with aminosilane are provided as an undercoat layer on the peripheral surface of a conductive support whose surface has been polished on an aluminum extraction tube having a diameter of 30 mm. A coating solution obtained by dissolving and dispersing in 100 parts by weight of methanol was applied by a ring coating method and dried at a temperature of 100 ° C. for 40 minutes to form an undercoat layer having a thickness of 1.5 to 2 μm.
[0110]
Next, 1 part by weight of x-type metal-free phthalocyanine pigment as a charge generating pigment, 1 part by weight of butyral resin {BX-1, manufactured by Sekisui Chemical Co., Ltd.), and 100 parts by weight of dichloroethane are used for glass beads having a diameter of 1 mm. A pigment dispersion is obtained by dispersing in a sand mill for 8 hours, and the resulting pigment dispersion is coated on the undercoat layer by a ring coating method and dried at 80 ° C. for 20 minutes to obtain a charge having a thickness of 0.3 μm. A generation layer was formed.
[0111]
Further, 40 parts by weight of a charge transport material of a styryl compound of the following structural formula (1) and 60 parts by weight of a polycarbonate resin {Panlite TS, manufactured by Teijin Chemicals Ltd.) are dissolved in 400 parts by weight of toluene on the charge generation layer. Then, it was applied and dried by a dip coating method so as to have a dry film thickness of 22 μm, and a charge transport layer was formed to produce a multilayer organic photoreceptor (OPC1).
[0112]
A part of the obtained organic photoreceptor (OPC1) was cut out to obtain a sample piece, and the work function of this sample piece was determined by using a commercially available surface analyzer (AC-2 type, manufactured by Riken Keiki Co., Ltd.) as described above. Was measured at an irradiation light amount of 500 nW to show 5.27 eV.
[0113]
[Chemical 1]

[0114]
(Example of toner production)
The one-component nonmagnetic toner used in Example 1 and Comparative Example 1 will be described.
(Manufacture of toner A)
A monomer mixture comprising 80 parts by weight of styrene monomer, 20 parts by weight of butyl acrylate, and 5 parts by weight of acrylic acid,
・ 105 parts by weight of water
-Nonionic emulsifier 1 part by weight
・ Anionic emulsifier 1.5 parts by weight
・ 0.55 parts by weight of potassium persulfate
The mixture was added to the water-soluble mixture consisting of the following, stirred in a nitrogen stream, and polymerized at 70 ° C. for 8 hours. After the polymerization reaction, the mixture was cooled to obtain a milky white resin emulsion having a particle size of 0.25 μm.
[0115]
next,
・ 200 parts by weight of this resin emulsion
・ Polyethylene wax emulsion {manufactured by Sanyo Chemical Industries Ltd.} 20 parts by weight
・ Phthalocyanine blue 7 parts by weight
Is dispersed in water containing 0.2 part by weight of sodium dodecylbenzenesulfonate as a surfactant, pH is adjusted to 5.5 by adding diethylamine, and 0.3 part by weight of aluminum sulfate as an electrolyte is stirred. Then, the mixture was stirred at high speed with a TK homomixer and dispersed.
[0116]
Further, 40 parts by weight of styrene monomer, 10 parts by weight of butyl acrylate and 5 parts by weight of zinc salicylate were added together with 40 parts by weight of water, and the mixture was heated to 90 ° C. while stirring under a nitrogen stream, and hydrogen peroxide was added. And polymerized for 5 hours to grow particles. After the termination of the polymerization, the temperature was raised to 95 ° C. and maintained for 5 hours while adjusting the pH to 5 or more in order to increase the association of the secondary particles and the film-forming bond strength. Thereafter, the obtained particles were washed with water and vacuum dried at 45 ° C. for 10 hours to obtain mother particles of cyan toner.
[0117]
As a result of measurement as described above, the mother particles of the obtained cyan toner were toner having an average particle diameter of 6.8 μm and a circularity of 0.98. Hydrophobic silica surface-treated with hexamethyldisilazane (HMDS) on the cyan toner base particles (average particle size 12 nm, specific surface area 140 m ² / G) of titanium oxide surface-treated with a silane coupling agent (average particle size 20 nm, specific surface area 90 m) ² / G) was added in an amount of 0.8% by weight to produce toner A as a cyan toner. The work function of the toner A was 5.65 eV as a result of measurement as described above.
[0118]
(Manufacture of toner B)
The pigment (phthalocyanine blue) in the toner A is changed to quinacridone, and 0.8% by weight of titanium oxide in the toner A is changed to 0.6% by weight. And manufactured in the same manner. As a result of measurement as described above, this toner B had an average particle size of 6.9 μm, a circularity of 0.96, and a work function of 5.56 eV.
[0119]
(Manufacture of toner C)
The pigment (phthalocyanine blue) in the toner A is changed to Pigment Yellow 180, and 0.8% by weight of titanium oxide in the toner A is changed to 1.0% by weight. It was manufactured in the same manner as the above. As a result of measurement as described above, this toner C had an average particle size of 6.8 μm, a circularity of 0.97, and a work function of 5.72 eV.
[0120]
(Manufacture of toner D)
The pigment (phthalocyanine blue) in the toner A is changed to carbon black, and 0.8% by weight of titanium oxide in the toner A is changed to 1.2% by weight. Manufactured in the same manner as the manufacture. As a result of measurement as described above, this toner D had an average particle size of 7.0 μm, a circularity of 0.98, and a work function of 5.8 eV.
[0121]
(Production of transfer media)
A transfer belt was produced as a transfer medium used in Example 1 and Comparative Example 1.
On a polyethylene terephthalate resin film having a thickness of 130 μm deposited with aluminum,
・ 30 parts by weight of vinyl chloride-vinyl acetate copolymer
・ Conductive carbon black 10 parts by weight
・ Methyl alcohol 70 parts by weight
The uniform dispersion consisting of was coated and dried by a roll coating method so as to have a thickness of 20 μm to form an intermediate conductive layer.
[0122]
Then on this intermediate conductive layer

The coating solution obtained by mixing and dispersing the composition was similarly applied and dried by a roll coating method so as to have a thickness of 10 μm to form a transfer layer.
[0123]
This coated sheet was cut to a length of 540 mm, the ends were aligned with the coated surface facing up, and ultrasonic transfer was performed to produce a transfer belt. The volume resistance of this transfer belt is 2.5 × 10 ^Ten It was Ω · cm. The work function was 5.37 eV, and the normalized photoelectron yield was 6.90.
[0124]
(Transfer efficiency measurement experiment)
In these Example 1 and Comparative Example 1, the same color image forming apparatus as shown in FIG. 1 using the organic photoreceptor (OPC1), the toners A to D, and the transfer belt manufactured as described above. , Scorotron charging (wire voltage: −4.5 kV, grit voltage: −600 V), non-contact development (gap: 200 μm, Vdc = −200 V, Vpp = 1.3 kV, development amount: 0.55 mg / cm) ² ) And a transfer voltage (+500 V), and an experiment for measuring transfer efficiency at the time of multiple transfer of all-color solid printing was performed.
[0125]
(Measurement method at high transfer efficiency)
In these Example 1 and Comparative Example 1, the transfer efficiency is measured by reading the untransferred toner on the photoconductor as image data with an optical microscope, binarizing the image, and determining the transfer remaining toner area per unit area. Then, the number of toners is obtained, the number of toners obtained from this value, the volume of each toner, and the residual toner weight per unit area are obtained from the main resin density of the toner, and the transfer efficiency is derived from the ratio to the development amount.
[0126]
(Transfer order of Example 1)
The transfer order of each toner from the photoreceptor to the transfer belt in Example 1 (that is, the order from the upstream side of the toner) is set so that the work function increases in order from the upstream side to the downstream side according to the present invention. , Toner B (magenta toner: work function 5.56 eV), toner A (cyan toner: work function 5.65 eV), toner C (yellow toner: work function 5.72 eV), toner D (black toner: work function 5. 8 eV).
[0127]
(Transfer order of Comparative Example 1)
The transfer order of each toner from the photosensitive member to the transfer belt in Comparative Example 1 is such that toner C (yellow toner: work function 5.72 eV) and toner B (magenta toner: work) so that the work functions are different from the order of the present invention. Function 5.56 eV), toner D (black toner: work function 5.8 eV), and toner A (cyan toner: work function 5.65 eV).
[0128]
(Results of transfer efficiency measurement experiment)
Table 4 shows the results of the transfer efficiency measurement experiments of Example 1 and Comparative Example 1.
[0129]
[Table 4]

[0130]
As shown in Table 4, in Example 1, the first transfer (transfer of toner B), the second transfer (transfer of toner A), the third transfer (transfer of toner C), and the fourth transfer (transfer of toner D) All of (transfer) showed a transfer efficiency of 98% or more, and there was almost no difference in each transfer efficiency. In contrast, in Comparative Example 1, the transfer efficiency of the first transfer (transfer of toner C) and the third transfer (transfer of toner D) was 98% or more, but the second transfer (transfer of toner B). The transfer efficiency of the fourth transfer (transfer of toner A) was lowered to 94.92% and 91.2%, respectively, and a difference appeared in each transfer efficiency.
[0131]
As a result, the toner of four colors is transferred so that the work function increases from the upstream side toward the downstream side in the moving direction of the intermediate transfer medium as in the present invention, so that the transfer residue is extremely reduced and the transfer efficiency is improved. It was confirmed that it can be effectively improved.
[0132]
As a result of the experimental results of Example 1, the image forming apparatus according to the present invention is required to have a transfer efficiency of 98% or more at a level where the transfer residual toner remaining on the photosensitive member cannot be detected as “color” as described above. It was confirmed that it was possible to achieve a cleaner-less photoconductor.
[0133]
[Example 2, Comparative Example 2 and Comparative Example 3]
The organic photoreceptor (OPC1) and transfer medium used in Example 2, Comparative Example 2 and Comparative Example 3 are the same as those in Example 1 and Comparative Example 1 described above.
[0134]
(Example of toner production)
The one-component nonmagnetic toner used in Example 2, Comparative Example 2 and Comparative Example 4 will be described.
(Manufacture of toner E)
A monomer mixture comprising 80 parts by weight of styrene monomer, 20 parts by weight of butyl acrylate, and 5 parts by weight of acrylic acid,
・ 105 parts by weight of water
-Nonionic emulsifier 1 part by weight
・ Anionic emulsifier 1.5 parts by weight
・ 0.55 parts by weight of potassium persulfate
The mixture was added to the water-soluble mixture consisting of the following, stirred in a nitrogen stream, and polymerized at 70 ° C. for 8 hours. After the polymerization reaction, the mixture was cooled to obtain a milky white resin emulsion having a particle size of 0.25 μm.
[0135]
next,
・ 200 parts by weight of this resin emulsion
・ Polyethylene wax emulsion {manufactured by Sanyo Chemical Industries Ltd.} 20 parts by weight
・ Phthalocyanine blue 7 parts by weight
Is dispersed in water containing 0.2 part by weight of sodium dodecylbenzenesulfonate as a surfactant, pH is adjusted to 5.5 by adding diethylamine, and 0.3 part by weight of aluminum sulfate as an electrolyte is stirred. Then, the mixture was stirred at high speed with a TK homomixer and dispersed.
[0136]
Further, 40 parts by weight of styrene monomer, 10 parts by weight of butyl acrylate and 5 parts by weight of zinc salicylate were added together with 40 parts by weight of water, and the mixture was heated to 90 ° C. while stirring under a nitrogen stream, and hydrogen peroxide was added. And polymerized for 5 hours to grow particles. After the termination of the polymerization, the temperature was raised to 95 ° C. and maintained for 5 hours while adjusting the pH to 5 or more in order to increase the association of the secondary particles and the film-forming bond strength. Thereafter, the obtained particles were washed with water and vacuum dried at 45 ° C. for 10 hours to obtain mother particles of cyan toner.
[0137]
As a result of measurement as described above, the mother particles of the obtained cyan toner were toner having an average particle diameter of 6.8 μm and a circularity of 0.98. Hydrophobic silica surface-treated with hexamethyldisilazane (HMDS) on the cyan toner base particles (average particle size 12 nm, specific surface area 140 m ² / G) of titanium oxide surface-treated with a silane coupling agent (average particle size 20 nm, specific surface area 90 m) ² / G) was added in an amount of 1.2% by weight, and alumina was further added in an amount of 0.3% by weight to produce toner E as a cyan toner. The work function of the toner E was measured as described above, and was 5.73 eV.
[0138]
(Manufacture of toner F)
The pigment (phthalocyanine blue) in the toner E described above was changed to quinacridone, and the toner F as a magenta toner was produced in the same manner as in the production of the toner E. As a result of measurement as described above, this toner F had an average particle size of 6.9 μm, a circularity of 0.96, and a work function of 5.58 eV.
[0139]
(Manufacture of toner G)
The pigment (phthalocyanine blue) in toner E described above was changed to carmine 6B, and magenta toner Toner G was produced in the same manner as toner E. As a result of measurement as described above, this toner C had an average particle diameter of 6.8 μm, a circularity of 0.95, and a work function of 5.88 eV.
[0140]
(Manufacture of toner H)
The pigment (phthalocyanine blue) in the toner E described above was changed to Pigment Yellow 180, and a toner H as a yellow toner was produced in the same manner as in the production of the toner E. The toner H was measured as described above. As a result, the average particle size was 6.8 μm, the circularity was 0.97, and the work function was 5.62 eV.
[0141]
(Production of Toner I)
The pigment (phthalocyanine blue) in toner E described above was changed to carbon black, and toner I, which is a black toner, was produced in the same manner as toner E. As a result of measurement as described above, this toner D had an average particle size of 7.0 μm, a circularity of 0.98, and a work function of 5.79 eV.
[0142]
(Manufacture of toner J)
Toner J, which is a magenta toner, was manufactured in the same manner as toner G, except that 5 parts by weight of zinc salicylate in toner G was changed to 8 parts by weight. The toner J was measured as described above. As a result, the average particle size was 6.8 μm, the circularity was 0.98, and the work function was 5.69 eV.
[0143]
(Transfer efficiency measurement experiment and measurement method at high transfer efficiency)
The transfer efficiency measurement experiment and the measurement method at the time of high transfer efficiency in Example 2, Comparative Example 2 and Comparative Example 3 are all the same as those in Example 1 and Comparative Example 1 described above.
[0144]
(Transfer order of Example 2)
The transfer order of each toner from the photosensitive member to the transfer belt in Example 2 (that is, the order from the upstream side of the toner) is set so that the work function increases in order from the upstream side to the downstream side according to the present invention. , Toner H (yellow toner: work function 5.62 eV), toner J (magenta toner: work function 5.69 eV), toner E (cyan toner toner: work function 5.73 eV), toner I (black toner: work function 5) .79 eV).
[0145]
(Transfer order of Comparative Example 2)
The transfer order of each toner of the comparative example 2 from the photosensitive member to the transfer belt is such that toner H (yellow toner: work function 5.62 eV) and toner F (magenta toner: work) so that the work functions are different from the order of the present invention. Function 5.58 eV), toner E (cyan toner: work function 5.73 eV), and toner I (black toner: work function 5.79 eV).
[0146]
(Transfer order of Comparative Example 3)
The transfer order of each toner of the comparative example 3 from the photosensitive member to the transfer belt is such that toner H (yellow toner: work function 5.62 eV) and toner G (magenta toner: work) so that the work function is different from the order of the present invention. Function 5.88 eV), toner E (cyan toner: work function 5.73 eV), and toner I (black toner: work function 5.79 eV).
[0147]
(Results of transfer efficiency measurement experiment)
Table 5 shows the results of the transfer efficiency measurement experiments of Example 2, Comparative Example 2, and Comparative Example 3.
[0148]
[Table 5]

[0149]
As shown in Table 5, in Example 2, the first transfer (transfer of toner H), the second transfer (transfer of toner J), the third transfer (transfer of toner E), and the fourth transfer (transfer of toner I) All of (transfer) showed a transfer efficiency of 98% or more, and there was almost no difference in each transfer efficiency. On the other hand, in Comparative Example 2, the transfer efficiency of the first transfer (transfer of toner H), the third transfer (transfer of toner E), and the fourth transfer (transfer of toner I) was 98% or more. The transfer efficiency of the second transfer (transfer of toner F) was as low as 93.95%, and a difference appeared in each transfer efficiency. In Comparative Example 3, the transfer efficiency of the first transfer (transfer of toner H), the second transfer (transfer of toner G), and the fourth transfer (transfer of toner I) was 98% or more. The transfer efficiency of transfer (transfer of toner E) was as low as 92.67%, and a difference appeared in each transfer efficiency.
[0150]
As a result, the toner of four colors is transferred so that the work function increases from the upstream side toward the downstream side in the moving direction of the intermediate transfer medium as in the present invention, so that the transfer residue is extremely reduced and the transfer efficiency is improved. It was confirmed that it can be effectively improved.
Therefore, it was confirmed from the experimental results of Example 2 that the image forming apparatus of the present invention can achieve cleaner-less photoconductor.
[0151]
【The invention's effect】
According to the image forming apparatus of the present invention configured as described above, the work function of the toner on the most upstream side in the moving direction of the transfer medium is set to the work function of the photoconductor, and the most upstream side in the moving direction of the transfer medium. Since the work function of the transfer medium is set to be greater than the work function of the transfer medium, and further, the work functions of the toners of the plurality of colors are set so as to increase in order from the upstream side toward the downstream side in the moving direction of the transfer medium. Transfer residue can be extremely reduced, and transfer efficiency can be effectively improved.
Therefore, the transfer efficiency can be increased to a region where the residual toner image transferred to the transfer material cannot be perceived by the user as image deterioration (ground fog), and the cleaner of the photoconductor in the image forming apparatus can be achieved. .
[0152]
In particular, according to the second aspect of the invention, the work function of each color toner increases as the amount of the external additive added to each color toner increases from the upstream side to the downstream side in the moving direction of the transfer medium. Therefore, the work function of the toner of each color can be easily set larger from the upstream side to the downstream side in the moving direction of the transfer medium simply by changing the addition amount of the external additive.
[0153]
In that case, according to the invention of claim 3, for the toner of each color, titanium oxide having a relatively large work function of 5.7 to 5.8 is used as an external additive, and the amount added is from the upstream to the downstream. Since it is set to increase as it goes to the side, the work function of the toner of each color can be easily set larger as it goes from the upstream side to the downstream side in the moving direction of the transfer medium.
[0154]
In that case, according to the invention of claim 4, for each color toner, silica having a relatively small work function of 5.0 to 5.2 is used as an external additive, and the amount added is determined from the upstream side to the downstream side. Therefore, the work function of each color toner can be easily set larger as it goes from the upstream side to the downstream side in the moving direction of the transfer medium.
[0155]
According to the fifth aspect of the present invention, since the image carriers for each of the plurality of colors have the same layer structure, the work function of each color toner can be easily set, and the image for each color toner can be set. There is no need to produce a carrier and costs can be reduced.
[0156]
Furthermore, according to the invention of claim 6, since the circularity (sphericity) of each color toner is set to 0.94 or more, the adhesion force between the toner and the image carrier can be reduced, The transfer efficiency can be further effectively improved.
[0157]
Further, according to the invention of claim 7, since the speed difference is set between the peripheral speed of the image carrier and the moving speed of the transfer medium for each color, the toner particles roll in the transfer nip and the toner particles and the image are transferred. Opportunities for contact with the carrier and the transfer medium are increased, and the charging polarity of the toner in the transfer nip can be made more uniform.
[0158]
Further, according to the invention of claim 8, since the black toner is set at the most downstream in the moving direction of the transfer medium, there is a possibility that another color toner is transferred to the position where the black toner is transferred. Is expensive. Then, even if the reversely transferred toner moves from the image carrier to the developer carrier and other colors are mixed in the black toner (contamination) and developed in this contamination state, the toner on the most downstream side is blackened. By using the toner of (K), the black toner is the color that is hardly affected by the contamination, so that this contamination can be prevented from being perceived by human vision in the output image.
[Brief description of the drawings]
FIG. 1 is a diagram schematically illustrating a four-cycle full-color printer as an example of an embodiment of an image forming apparatus according to the present invention.
FIGS. 2A and 2B are diagrams showing a measurement cell used for measuring the work function of toner, in which FIG. 2A is a front view and FIG. 2B is a side view;
3A and 3B are diagrams for explaining a method for measuring a work function of a cylindrical image forming apparatus member. FIG. 3A is a perspective view showing a shape of a measurement sample piece, and FIG. 3B is a diagram showing a measurement state. .
FIG. 4 is a diagram illustrating a method for obtaining a work function by a surface analysis apparatus.
FIG. 5 is a diagram schematically and partially showing another example of an embodiment of an image forming apparatus according to the present invention.
FIG. 6 is a diagram schematically illustrating a monochromatic toner image forming unit of this example.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... (Color) image forming apparatus, 30 ... Intermediate transfer belt (intermediate transfer medium), 40 (Y), 40 (C), 40 (M), 40 (K) ... Monochromatic toner image formation means, 41 ... Photoconductor , 42 ... charging roller, 43 ... exposure device, 44 ... developing roller, 45 ... photoconductor cleaning blade, 51, 52, 53, 54 ... primary transfer means, 61 ... fixing roller pair, 66 ... secondary transfer roller, 67 ... Cleaning blade for intermediate transfer belt, P ... Recording medium

Claims (8)

In an image forming apparatus that sequentially multiplex-transfers toner images of each color of an image carrier for each of a plurality of colors onto a moving transfer medium,
The work function of the toner on the most upstream side in the moving direction of the transfer medium is set to the work function of the image carrier,
The work function of the toner on the most upstream side in the moving direction of the transfer medium is set to the work function of the transfer medium.
An image forming apparatus, wherein work functions of toners of a plurality of colors are set to increase in order from an upstream side to a downstream side in the moving direction of the transfer medium. External additives are added to the toners of the respective colors, and the work function of each toner increases as the amount of these external additives increases from the upstream side to the downstream side in the moving direction of the transfer medium. 2. The image forming apparatus according to claim 1, wherein the image forming apparatus is changed. The external additive added to each color toner is titanium oxide, and the amount of titanium oxide added is set to increase from the upstream side to the downstream side in the moving direction of the transfer medium. The image forming apparatus according to claim 2. The external additive added to each color toner is silica, and the amount of silica added is set so as to decrease from the upstream side to the downstream side in the moving direction of the transfer medium. The image forming apparatus according to claim 2. 5. The image forming apparatus according to claim 1, wherein the image carriers for each of the plurality of colors all have the same layer structure. 6. The image forming apparatus according to claim 1, wherein the toner of each color has a circularity (sphericity) of 0.94 or more. 7. The image forming apparatus according to claim 1, wherein a speed difference is set between a peripheral speed of the image carrier for each color and a moving speed of the transfer medium. The image according to any one of claims 1 to 7, wherein the plurality of color toners include at least a black toner, and the black toner is set on the most downstream side in the moving direction of the transfer medium. Forming equipment.

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