JP4292698B2 - Image forming method - Google Patents

Description

【００４５】

【００４６】
図５より明らかなように、剥離時の記録媒体の表面温度が、記録媒体表面に設けられた透明樹脂の軟化点（Ｔｍｐ）に対して１０℃を下回る温度差である場合、剥離後の画像形成された記録媒体の表面状態が良好であるが、これは、記録媒体表面に設けられた透明樹脂層が十分な凝集力を保持していない、軟化した状態のまま剥離されると、剥離時に画像保持体に記録媒体表面の透明樹脂が転移したり記録媒体表面が粗れた状態になるオフセット現象が発生し、得られた画像の光沢を低下させる場合があるためと考えられる。
【００４７】
ここで、記録媒体の表面温度は、記録媒体表面に予め熱電対を設置しておき、画像保持体とトナーが転写・定着された後、記録媒体が画像保持体から剥離されるまでの温度をモニターすることで測定することができる。
【００４８】
記録媒体の表面温度を下げる冷却手段は必ずしも必要ではなく、例えば、転写・定着位置から剥離位置までの距離を長くする、雰囲気温度を低くするなどの方法により、好適な剥離状態とすることができるが、転写・定着位置の下流であって、且つ、剥離位置の上流部分に冷却手段を設けることにより、効率的に好適な表面状態の画像を形成しうる。
【００４９】
図６は中間転写体１０とトナー像１２及び記録媒体１４が密着したまま搬送される転写・定着位置の下流部分に、冷却ファン２４を配置して、冷風をあてて冷却している状態を示す概略図である。
【００５０】
冷却手段としては、前記冷却ファン２４を配置する方法、中間転写体又は記録媒体に室温程度の低温部材を冷却手段として接触させて、熱を高温部から低温部へ移動させる方法等により上述の効率的な冷却効果を得ることができる。後者の場合、接触させる冷却手段をベルト状にして循環移動させ、ベルト周上の一部を加熱・加圧ニップ出口の中間転写体又は記録媒体に接触させ、冷却位置とは別の場所でベルトを冷却した後、再利用することで、連続して冷却効果を得ることができる。このように、加熱・加圧ニップ出口下流における中間転写体又は記録媒体の冷却位置とは別の場所で、冷却手段であるベルトなどの冷却媒体を他の低温体との熱交換を行うことにより、画像形成装置内の温度等に影響を与えることなく、効率的な冷却を行うことができる。この低温体との熱交換としては、例えば、加熱・加圧領域に到達する前の低温の中間転写体に接触させるなどして、行うこともできる。
【００５１】
また、加熱・加圧ニップ出口の冷却手段として、ヒートパイプの様な熱交換機を用いて熱移動させることもできる。
【００５２】
上記加熱・加圧ニップ出口の冷却手段は、加熱体側と加圧体側のどちらか一方又は、両側に設けても効果があるが、比較的低温の加圧体側に設けることで、冷却手段の昇温が抑えられ、また加熱体の熱を奪う量も少なくでき、熱的に効率良く転写・定着ができる。
【００５３】
本発明の画像形成方法に用いるトナーの結着樹脂としては、公知のものが使用可能である。例えば、スチレン、ビニルトルエン、α−メチルトルエン、クロルスチレン、アミノスチレン等のスチレン及びその誘導体、あるいは置換体の単独重合体、共重合体、メタクリル酸及びメチルメタクリレート、エチルメタクリレート等のメタクリル酸エステル類の単独又は共重合体、アクリル酸及びメチルアクリレート、ブチルアクリレート、２−エチルヘキシルアクリレート等のアクリル酸エステル類の単独又は、共重合体、ブタジエン、イソプレン等のジエン類、アクリロニトリル、ビニルエーテル類、無水マレイン酸、塩化ビニル、酢酸ビニル等のビニル系単量体等のビニル系単量体の単独又は、他の単量体との共重合体、ポリアミド、ポリエステル、ポリウレタン等を単独もしくは、混合した形で用いることができるが、特にポリエステル系の構成単位を含むものが好適である。
【００５４】
上記ポリエステルは、多価アルコールと多塩基性カルボン酸との反応によって製造することができる。ポリエステルを構成する多価アルコールとして、例えばエチレングリコール、ジエチレングリコール、トリエチレングリコール、１、２−プロピレングリコール、１，３−プロピレングリコール、１，４−ブタンジオール、ネオペンチルグリコール、１，４−ブタンジオール、シクロヘキサンジメタノール等のジオール類、水素添加ビスフェノールＡ、ポリオキシプロピレン化ビスフェノールＡ等のビスフェノールＡアルキレンオキサイド付加物、その他の２価のアルコールを挙げることができる。
【００５５】
多塩基性カルボン酸としては、マレイン酸、フマル酸、メタコン酸、シトラコン酸、イタコン酸、テレフタル酸、イソフタル酸、シクロヘキサンジカルンボン酸、コハク酸、これらの酸無水物、アルキルエステル、その他の２塩基性カルボン酸を挙げることができるがこれに限定されるものではない。
【００５６】
これらトナー結着樹脂に混合する着色剤としては、公知の顔料、染料が使用できる。また、帯電制御の目的などで、従来知られているトナー用外添剤を使用することができる。
【００５７】
本発明の画像形成方法に好適に使用しうる記録媒体は、基材上に特定の軟化点を有する熱可塑性の透明樹脂層が形成されてなるものである。ここで、基材に用いられる材料は、特に限定するものではなく、従来知られている記録媒体の基材材料を任意に選択して用いることができる。具体的には、例えば、酸性又は中性の上質紙や中質紙、更紙、再生紙、合成紙等が使用できる。これらに使用される填料は特に限定されるものではなく、重質炭酸カルシウム、軽質炭酸カルシウム、チョーク等の炭酸カルシウムや、カオリン、焼成クレー、パイロフィライト、セリサイト、タルク等のケイ酸類や、二酸化チタン等の無機填料及び、尿素樹脂、スチレン等の有機顔料が利用できる。サイズ剤も特に限定されるものではない。ロジン系サイズ剤、合成サイズ剤、石油樹脂系サイズ剤、中性サイズ剤等のサイズ剤が使用でき硫酸バンド、カチオン化澱粉等、適当なサイズ剤と繊維との定着剤を組み合せて使用する。このほかに、紙力増強剤、染料、ｐＨ調整剤等を添加してもかまわない。
【００５８】
さらにこれら基材には白色顔料塗工層を設けてもよい。
白色顔料塗工層に使用する白色顔料としては、重質炭酸カルシウム、軽質炭酸カルシウム、二酸化チタン、水酸化アルミニウム、サチンホワイト、タルク、硫酸カルシウム、硫酸バリウム、酸化亜鉛、酸化マグネシウム、炭酸マグネシウム、非晶質シリカ、コロイダルシリカ、ホワイトカーボン、カオリン、焼成カオリン、デラミネートカオリン、アルミノ珪酸塩、セリサイト、ベントナイト、スメクサイト等の鉱物質顔料やポリスチレン樹脂微粒子、尿素ホリマリン樹脂微粒子、微小中空粒子やその他の有機系顔料等を単独もしくは複数組み合せて使用できるがこれに限るものではない。白色顔料を結着するための樹脂は、水溶性接着剤あるいはエマルジョン、ラテックス等を単独、又は混合して使用できる。例えば、ポリビニルアルコール、変性ポリビニルアルコール、澱粉類、ゼラチン、カゼイン、メチルセルロース、ヒドロキシエチルセルロース、アクリル酸アミドーアクリル酸エステル共重合体、アクリル酸アミドーアクリル酸ーメタクリル酸３元共重合体、スチレンーアクリル樹脂、イソブチレンー無水マレイン酸樹脂、カルボキシメチルセルロース等の水溶性樹脂やアクリル系エマルジョン、酢ビ系エマルジョン、塩化ビニリデンエマルジョン、ポリエステル系エマルジョン、スチレンーブタジエンラテックス、アクリルニトリルーブタジエンラテックス等が使用されるが、特に限定されるものではない。また、上述した白色顔料とカゼインなどをもちいて、キャストーティング法で塗工面を仕上げたものはより高平滑となり望ましい。このほか白色顔料塗工層には、色調を調整するため染料や有色顔料を微量添加したり、視感的白さを向上させるため蛍光染料を添加することもできる。さらに、分散剤、消泡剤、可塑剤、ｐＨ調整剤、滑剤、流動変性剤、固化促進剤、耐水化剤、サイズ剤等の各種助剤を必要に応じて適宜添加することもできる。
【００５９】
上述する紙系基材以外では、耐熱温度が１００℃以上のポリエチレンテレフタレートフィルム、ポリスルフォンフィルム、ポリフェニレンオキサイドフィルム、ポリイミドフィルム、ポリカーボネートフィルム、セルロースエステルフィルム等の耐熱性のフィルム状物も利用できる。
本発明の記録媒体は、これら基材又は基材に白色顔料層を設けたシートの少なくともトナー像を転写する面に、溶融トナーを転写・定着し、記録媒体表面層内に浸透させるための熱可塑性の透明樹脂層を設けてなるものである。樹脂層を形成する熱可塑性の透明樹脂は、スチレン、ビニルトルエン、α−メチルトルエン、クロルスチレン、アミノスチレン等のスチレン及びその誘導体、あるいは置換体の単独重合体、共重合体、メタクリル酸及びメチルメタクリレート、エチルメタクリレート等のメタクリル酸エステル類の単独又は共重合体、アクリル酸及びメチルアクリレート、ブチルアクリレート、２−エチルヘキシルアクリレート等のアクリル酸エステル類の単独又は、共重合体、ブタジエン、イソプレン等のジエン類、アクリロニトリル、ビニルエーテル類、無水マレイン酸、塩化ビニル、酢酸ビニル等のビニル系単量体等のビニル系単量体の単独又は、他の単量体との共重合体、ポリアミド、ポリエステル、ポリウレタン等を単独もしくは、混合した形で用いることができるが、特にポリエステル系の構成単位を含む樹脂（以下、適宜、ポリエステル系樹脂と称する）が好適である。ポリエステル系樹脂は、多価アルコールと多塩基性カルボン酸との反応によって製造することができる。ポリエステルを構成する多価アルコールとして、例えばエチレングリコール、ジエチレングリコール、トリエチレングリコール、１、２−プロピレングリコール、１，３−プロピレングリコール、１，４−ブタンジオール、ネオペンチルグリコール、１，４−ブタンジオール、シクロヘキサンジメタノール等のジオール類、水素添加ビスフェノールＡ、ポリオキシプロピレン化ビスフェノールＡ等のビスフェノールＡアルキレンオキサイド付加物、その他の２価のアルコールをあげることができるがこれらに限られるものではない。好ましくは、ポリオキシプロピレン化ビスフェノールＡ等のビスフェノールＡアルキレンオキサイド付加物が望ましい。
【００６０】
多塩基性カルボン酸としては、マレイン酸、フマル酸、メタコン酸、シトラコン酸、イタコン酸、テレフタル酸、イソフタル酸、シクロヘキサンジカルンボン酸、コハク酸、これらの酸無水物、アルキルエステル、その他の２塩基性カルボン酸を挙げることができるがこれに限定されるものではない。
【００６１】
またこれらの透明樹脂層に、その表面電気抵抗を調整する目的で、画質を損なわない程度の配合量につき、塩化ナトリウム、塩化カリウム、塩化カリシウム、硫酸ナトリウム、酸化亜鉛、二酸化チタン、酸化錫、酸化アルミニウム、酸化マグネシウム等の無機物を単独又は２種以上混合して配合しても構わない。また、記録媒体の摩擦係数制御等の目的で、画質を損なわない程度の微量に限り、スチレン系等の硬質プラスチック微粒子を混合することができる。
【００６２】
前記基材上に設けられる熱可塑性透明樹脂層の厚さは、２μｍから２０μｍが好ましく、さらに好ましくは、４μｍから１５μｍの範囲である。この範囲を下回ると溶融したトナーを樹脂層中に十分に埋め込むことができず、表面にトナーに起因する凸部を有する平滑ではない画像が形成され、光沢も不十分となる。また、厚みがこの範囲を超えると透明樹脂層の屈折率に起因する画像鮮鋭度や発色性の低下を生じる虞があり、さらに、厚みのある樹脂層を軟化させるための加熱に要するエネルギーが増加するため、いずれも好ましくない。
【００６３】
これらのポリエステル系樹脂の軟化点（Ｔｍｐ）は、前述したように、トナーの軟化点（Ｔｍｔ）に対して＋１０℃から−３０℃好ましくは、±０℃から−２０℃の範囲を選択する。
【００６４】
重量平均分子量（Ｍｗ）は５０００〜６００００の範囲にあり、数平均分子量（Ｍｎ）が２０００〜５０００であり、Ｍｗ／Ｍｎは２〜１５の範囲にあることが望ましい。分子量及び分子量分布がこの範囲の上限を超えると熱可塑性の透明樹脂層の軟化点が上昇し、トナーの埋まり込みがわるくなる。また、この範囲の下限を下回ると熱可塑性の透明樹脂層が柔らかくなりすぎるために、場合によっては、オフセット現象を引き起こすことがあるため好ましくない。
【００６５】
熱可塑性透明樹脂の分子量の測定方法は、ゲルパーミエーションクロマトグラフィーによって行った。すなわち、測定装置として、全自動高温高速クロマトグラフ（Ｗａｔｅｒｓ ＡＬＳ／ＧＰＣ １５０Ｃ，Ｗａｔｅｒｓ社製）を使用し、溶媒として、テトラヒドロフランを用いて、流速＝１．０ｍｌ／ｍｉｎ、温度＝４０℃、検出器＝示差屈折計（ＲＩ）の条件で測定した。
【００６６】
記録媒体表面に形成された透明樹脂層と溶融トナーとの界面で生じる光の散乱や、溶融トナーが記録媒体の透明樹脂層表面から盛り上がる状態は、溶融トナーと透明樹脂層との相溶性にも関連しており、相溶性が良好な樹脂同士を用いることにより、より平滑で優れた均一の光沢を有する画像を形成しうる。これらの樹脂の相溶性の基準として、本発明においては溶融状態となったトナーと透明樹脂層の接触角を採用し、この接触角が４０度以下であるものを相溶性が良好であると判定する。この接触角の測定は、つぎの方法による。
【００６７】
（１）島津製作所（株）製の錠剤成形器ハンドプレスＳＳＰ−１０型の直径１３ｍｍ高さ３３ｍｍの凹状形状をした錠剤枠に粉体トナーを充填し、ハンドプレスで１トンの荷重を１分間加え、トナーディスクを成形する。この時の標準的なディスクの大きさは、直径１３ｍ、厚さ１．２ｍｍ、重さ０．１８ｇである。
【００６８】
（２）ホットプレート上に記録媒体を基材がホットプレート面に接するように配置し、トナーディスクを該記録媒体の透明樹脂層と接するように置き、９０秒間設定温度で放置する。その後、記録媒体とトナーディスクを２３℃の大気中に放置してあるアルミプレート上に記録媒体を接するように置いて急冷させる。この時、設定温度は、トナーの軟化点（Ｔｍｔ）＋１０℃とする。
【００６９】
（３）共和界面化学（株）製の接触角測定装置を使用し、トナーが固化した後の透明樹脂層と接する裾野の角度を４点（９０°ずつ回転させて）測定し、その平均値をトナー接触角とした。
【００７０】
透明樹脂層の溶融トナーとの接触角は、４０度以下が好ましくは、さらには、３０度以下であることが望ましい。この上限を超える場合には、転写・定着後に中間転写体から記録媒体を剥離した後に記録媒体表面層にトナー像の隆起が生じる場合があり、特に中間調画像領域やハイライト画像領域において光沢の低下を招いたり、発色が悪化することがある。
【００７１】
以上詳述したように本発明の画像形成方法によれば、画像の乱れや、色むらの発生なくトナー像を記録媒体の透明樹脂層に埋めこむことができるため、全画像面積率領域で均一な光沢を得ることができ、粒状性が良好で、色むらの発生の無いカラー画像を形成することができる。
【００７２】
また、この画像形成方法に好適に使用し得る記録媒体の構成は前記のとおりであり、この記録媒体を用いることにより、本発明の画像形成方法の効果が達成できる。
【００７３】
【実施例】
以下に実施例を用いてさらに詳細に本発明を説明するが、本発明は、以下の実施例に限定されるものではない。
【００７４】
〔記録媒体の作製１〕
記録媒体は、市販のキャストコート紙である坪量１２７．９ｇ／ｍ² のエナメルコート紙（米子加工紙株式会社）を基材として用い、その表面に、下記表１にしめす特性を有するポリエステル系樹脂６種類からなる透明樹脂層を形成することにより作製した。
【００７５】
下記表１に示す如きポリエステル系樹脂６種類（ＰＥ１、ＰＥ２、ＰＥ３、ＰＥ４、ＰＥ５、ＰＥ６）を用意し、それぞれ２０重量部を酢酸エチル８０重量部に混合し、溶解するまで撹拌したのち、得られた６種類のポリエステル溶液を前記エナメルコート紙（基材）上にメイヤーバーを用いて塗工した。十分乾燥させた後の樹脂層の厚みが７μｍとなるようにした。このようにして得られた記録媒体をそれぞれ、Ｐ１、Ｐ２、Ｐ３、Ｐ４、Ｐ５及びＰ６とした。
【００７６】
さらに、基材として１００μｍ厚の透明ポリエチレンテレフタレートフィルムを用い、該基材上にポリエステル系樹脂ＰＥ１、ＰＥ３、ＰＥ６を紙基材の場合と同様の方法で３μｍ厚になるように塗工し、表１にしめすような３種類のＯＨＰフィルムを得て、それぞれＯＨＰ１、ＯＨＰ２及びＯＨＰ３とした。これらの記録媒体を用いて、次に示すトナーと画像形成装置で画像を形成した。
【００７７】
これら透明樹脂層を構成するポリエステル系樹脂６種類（ＰＥ１、ＰＥ２、ＰＥ３、ＰＥ４、ＰＥ５、ＰＥ６）の軟化点（Ｔｍｐ）、重量平均分子量（Ｍｗ）、数平均分子量（Ｍｎ）を前記した方法で測定した結果及びＭｗ／Ｍｎを算出した結果を表１に合わせて示した。
【００７８】
【表１】

【００７９】
〔トナーの作製〕
下記表２に示した原料組成の多価アルコールと、多価カルボン酸をステンレススチール製撹拌機、ガラス製窒素ガス導入管及び硫化式コンデンサーを持つ１リットル容量の４つ口丸底フラスコ中に入れ、このフラスコをマントルヒータにセットした。次いで、ガス導入管から窒素ガスを導入し、フラスコ内を不活性ガス雰囲気に保ちながら昇温した。その後、０．０５のジブチルスズオキシドを加えて、反応物の温度を２００℃に保ち、所定の時間反応させてポリエステル系樹脂ＰＥ７及びＰＥ８を得た。
【００８０】
得られたポリエステル系樹脂（ＰＥ７）１００重量部に対して、イエロー顔料６重量部を混合し、エクストリューダーにより溶融し、混練した後、冷却して、ジェットミルにより粉砕し、粉砕物を分級して体積平均直径７μｍのイエロートナーを得た。同様に、ポリエステル系樹脂（ＰＥ７）１００重量部に対して、マゼンタ顔料４．５重量部、シアン顔料４．５重量部及びカーボンブラック４重量部をそれぞれ混合し、体積平均直径７μｍのマゼンタトナー、シアントナー、黒トナーを得た。前記イエロートナーを加えて４色のトナーセットＡを得た。（トナーＡと称する。）
また、ポリエステル系樹脂（ＰＥ８）を用いて、同様の方法によりトナーセットＢ（トナーＢと称する。）を得た。
【００８１】
なお、トナーの平均粒径は７μｍのものを用いた。図７にこれらのトナーの温度／粘度特性を示す。
【００８２】
【表２】

【００８３】
〔画像の記録１〕
図８は、本実施例の画像形成方法に用いる画像形成装置２６を示す構成図である。
【００８４】
この画像形成装置２６において、ベルト状の中間転写体１０は、ローラ２８、２９、及び加熱ロール２２により支持されて図中に示す矢印方向に回転を行う。転写・定着位置には、加熱ロール２２に対向して加圧ロール２０が配置されている。加熱ロール２２と加圧ロール２０は図８とは逆の配置とすることもでき、また、加圧ロール２０を内部に熱源を持つ加熱ロールとしてもよい。中間転写体１０の周辺にはイエロー、マゼンタ、シアン、黒に対応する４つの感光体３０Ｙ、３０Ｍ、３０Ｃ、３０Ｂが配置され、それぞれ帯電器３２Ｙ、３２Ｍ、３２Ｃ、３２Ｂにより一様に帯電された後、濃度信号に応じ光ビームパルス幅変調装置によってオンオフされる光ビーム走査装置３４により露光され、静電潜像が形成される。各感光体上の静電潜像は、それぞれ、黒、イエロー、マゼンタ、シアン色のトナーが入った現像器３６Ｙ、３６Ｍ、３６Ｃ、３６Ｂにより現像され、面積変調により濃度を表すいわゆるディジタル画像の各色トナー像が各感光体３０Ｙ、３０Ｍ、３０Ｃ、３０Ｂ上に形成される。この各色トナー像は、順次、転写器３８Ｙ、３８Ｍ、３８Ｃ、３８Ｂにより、中間転写体１０に転写され、中間転写体１０上に複数色のトナー像が形成される。
【００８５】
加圧ロール２０は、トレイ４０からの記録媒体Ｐの送紙に伴い、加熱ロール２２に圧接する。その後、前記複数色のトナー像を保持した中間転写体１０と記録媒体Ｐが、タイミングを合わせて加熱、加圧ロール２２及び２０の間を移動し、加圧・加熱される。軟化点以上に加熱されたトナーは軟化、溶融し、記録媒体Ｐに浸透し、その後固化することで転写・定着が行われる。
【００８６】
この転写・定着位置より加硫に配置された冷却装置２４は、加熱領域から一体となって搬送される中間転写体１０及び記録媒体Ｐを冷却するもので、これによりトナーは凝集固化し、記録媒体Ｐとの強い接着力が生じ、記録媒体の透明樹脂も固化して、オフセットを防止できる。冷却装置２４により冷却された中間転写体１０及び記録媒体Ｐは搬送され、曲率半径の小さなロール２９において記録媒体Ｐが記録媒体Ｐ自体の腰の強さによって中間転写体１０からトナーとともに分離され、カラー画像が形成される。
【００８７】
記録媒体Ｐに転写・定着されたトナー像の表面及び記録媒体表面は、密着状態で搬送される中間転写体１０の表面により平滑化されるため、表面が均一で、且つ、高い光沢を有する画像が形成される。
【００８８】
本発明の方法に用いられる画像形成装置の感光体３０Ｙ、３０Ｍ、３０Ｃ、３０Ｂは公知のものが使用でき、例えば、各種無機感光体（Ｓｅ、ａ−Ｓｉ、ａ−ＳｉＣ、ＣｄＳ等）の他に、各種有機感光体等も用いることができる。
【００８９】
この感光体３０Ｙ、３０Ｍ、３０Ｃ、３０Ｂによって、前記表１に示す記録媒体及び表２に示すトナーを用いて画像を形成した。各色の記録媒体上のトナー量は、０．６５ｍｇ／ｃｍ² に設定した。
【００９０】
光ビーム走査装置３４に用いる光ビームの径は、２０μｍとし、コントラストの高い画像が得られるようにした。
【００９１】
中間転写体１０は、ベース層と表面層の２層構造のものを用いた。ベース層は、カーボンブラックを添加した厚さ７０μｍのポリイミドフィルムを用いた。本実施例では、トナー像を感光体から中間転写体に静電的に、画像乱れなく転写するために、ベース層の体積抵抗率はカーボンブラックの添加量を変化させ、１０¹⁰Ωｃｍに調整した。
【００９２】
なお、ベース層としては、本実施例では厚さ７０μｍのポリイミドフィルムを用いたが、例えば厚さ１０〜３００μｍの耐熱性の高いシートを使用することが可能であり、ポリエステル、ポリエチレンテレフタレート、ポリエーテルサルフォン、ポリエーテルケトン、ポリサルフォン、ポリイミド、ポリイミドアミド、ポリアミドなどのポリマーシート等を用いることが可能である。
【００９３】
また、表面層は、トナー像を感光体から中間転写体に静電的に画像乱れなく転写するために、その体積抵抗率を１０¹⁴Ωｃｍに調整し、中間転写体から記録媒体への同時転写・定着を行うときに、トナー像を挟み中間転写体と記録媒体の密着をよくするために、ゴム硬度４０度、厚さ５０μｍのシリコーン共重合体による弾性体層を設けた。シリコーン共重合体は弾性を有し、その表面が常温でトナーに対して粘着性を示し、さらに、記録媒体へトナーを効率的に移行させるために、溶融して流動化したトナーを離し易くする特性を有しているため、中間転写体の表面層には最適である。
【００９４】
なお、この表面層は、例えば厚さ１〜１００μｍの離型性の高い樹脂層を使用することが可能であり、例えば、テトラフルオロエチレン−パーフルオロアルキルビニルエーテル共重合体、ポリテトラフルオロエチレン等を用いることが可能である。
【００９５】
加熱及び加圧ロールとしては金属ロール、又は、金属ロール上にシリコーンゴム等の耐熱弾性層を有したものを用いることができる。加熱ロールの内部には熱源が配置され、その加熱温度は、中間転写体が記録媒体にトナーを転写・定着する上流で、トナー軟化点（Ｔｍｔ）以上となるように設定、制御した。また、加熱領域は、加熱領域での感光体１とトナー像及び記録紙Ｐが十分に密着し部分的な浮きが発生せず、かつ記録媒体Ｐにしわやずれが発生しないように設定した。そのニップ圧力は１×１０³ Ｐａ〜１×１０⁶ Ｐａの範囲が適当である。本実施例では加熱、加圧ロールとして、アルミニウムの中空ロール上に硬度５５度のシリコーンゴムを厚さ３ｍｍで積層したものを用い、加熱ロール内部の熱源としては、ハロゲンランプを使用した。なお、ニップ圧力は５．０×１０⁵ Ｐａに設定した。
【００９６】
また、本実施例では、冷却装置２４の風量を調整することにより、記録媒体の中間転写体からの剥離時の、中間転写体と接する記録媒体表面の温度が７０℃となるように調整した。
【００９７】
また、中間転写体、トナー像の搬送速度は１６０ｍｍ／ｓであり、スクリーンは垂直万線を用い、線数は２００線で行った。
〔画像の評価〕
上記方法にて形成されたトナー画像の画像光沢、発色性、粒状性及び、色むらの評価を行った。
【００９８】
画像光沢、発色性、粒状性、色むらの評価は、入力画像面積率０〜１００％について、１０％きざみで２×２ｃｍのＹ（イエロー）、Ｍ（マゼンタ）、Ｃ（シアン）、Ｋ（黒）、Ｒ（レッド）、Ｇ（グリーン）、Ｂ（ブルー）、ＰＢ（三色黒）のパッチを出力し、目視により画像光沢の均一性、発色性、粒状性、色むらをを下記基準により判定することで行った。
【００９９】
（画像評価基準）
◎：特に良好。
○：良好。
△：やや良好（許容できるレベル）。
×：悪い（許容できない）。
【０１００】
（実施例１〜８、比較例１〜４）
記録媒体Ｐ１〜６と、トナーＡ、Ｂの組合せを用いて、前述した〔画像の記録１〕記載の手順で画像を形成し、得られた画像を前記基準で評価した結果を表３に示す。
【０１０１】
また、記録媒体ＯＨＰ１〜３とトナーＡの組合せを用いて、前記と同様に画像を形成し、得られた画像を下記の基準で評価した結果を表４に示す。
【０１０２】
【表３】

【０１０３】
【表４】

【０１０４】
この結果より、本発明の画像形成方法である〔画像の記録１〕を適用して、記録媒体の表面に設けられた熱可塑性のポリエステル系樹脂の軟化点（Ｔｍｐ）がトナーの軟化点（Ｔｍｔ）に対し、＋１０〜−３０℃の範囲にあり、記録媒体の表面に設けられた熱可塑性のポリエステル系樹脂の重量平均分子量（Ｍｗ）が５０００〜６００００であり、数平均分子量（Ｍｎ）が２０００〜５０００であり、Ｍｗ／Ｍｎが２〜１５である実施例１〜５については、すべての画像面積率領域において同一光沢を示し、色むらがなく、粒状性に優れ、微小な光沢むらも無い発色が良好な画像が得られた。また、同様の範囲にある実施例７〜８については、ＯＨＰで投影した場合の発色性がよく、濁りの無いシャープな画像が得られた。また、実施例においても、Ｍｗ、Ｍｎ、Ｍｗ／Ｍｎの範囲が上述した好ましい範囲を外れている実施例６は、粒状性に優れ、微小な光沢むらが無い発色が良好な画像が得られたが、光沢均一性及び発色性については許容レベルではあるものの、分子量が好適な範囲にある前記各実施例に比較するとやや低下しいることがわかった。
【０１０５】
また、Ｔｍｐ−Ｔｍｔが本発明の範囲を外れている比較例１〜４は、画像面積率に対する光沢の均一性が劣ったり、発色性、粒状性などに劣る画像となった。
【０１０６】
図９に結果の一例として、実施例２、実施例４と比較例１の用紙部及び各入力画像面積率に対する７５度鏡面光沢度の測定結果をしめす。比較例とくらべて前記各実施例の光沢が画像面積率に依存せず、均一で且つ、優れた光沢を有する画像であることが分かる。
【０１０７】
〔画像の記録２〕
図１０に示すように、加圧ロール２０と加熱ロール２２の位置を逆に配置した他は前記〔画像の記録１〕に用いのと同様の装置４２を用いて、加熱ロール２２の加熱温度をトナー軟化点（Ｔｍｔ）＋３０℃となるように設定、制御した以外は、前記〔画像の記録１〕と同様の方法を用いて画像を形成した。図１０は、本実施例の〔画像の記録２〕記載の画像形成方法に用いる画像形成装置４２を示す構成図である。
【０１０８】
（実施例９〜１２、比較例５、６）
記録媒体Ｐ１〜６と、トナーＡの組合せを用いて、前述した〔画像の記録２〕記載の手順で画像を形成し、得られた画像を前記基準で評価した結果を表５に示す。
【０１０９】
【表５】

【０１１０】
実施例９〜１２で形成された画像は、粒状性に優れ、微小な光沢むらが無く、また、光沢の均一性、発色性についてもほぼ良好であった。ただし、加熱ロールと加圧ロールのニップに入る時の上流で、中間転写体及びトナー像が加熱ロールと密着して、トナーの軟化点以上に加熱されている実施例１〜５と比較すると、光沢の均一性、発色性ともに若干の低下がみられた。即ち、転写位置の上流においてトナー像がその軟化点以上に加熱されることにより、本発明の製造方法のなかでも、特に優れた画像を形成しうることがわかる。
【０１１１】
〔記録媒体の作製２〕
記録媒体Ｐ２に用いるポリエステルＰＥ２を基材である紙に塗工する際に、記録媒体の電気抵抗を調整する目的で、ポリエステルＰＥ２に予めリン酸エステル系界面活性剤を、酢酸エチル８０重量部、ポリエステルＰＥ２、２０重量部に対して、０．１重量部、０．２重量部、０．４重量部、１重量部混合した他は、前記実施例２に用いた記録媒体Ｐ２と同様にして記録媒体を作成し、それぞれの記録媒体をＰ７、Ｐ８、Ｐ９、Ｐ１０とした。また、これらの樹脂の軟化点（Ｔｍｐ）はそれぞれ９０℃、９０℃、８９℃、８８℃であった。
【０１１２】
（実施例１３〜１６）
記録媒体Ｐ２及び、前記〔記録媒体の作製２〕により得られた記録媒体Ｐ７、Ｐ８、Ｐ９、Ｐ１０のトナーＡとの接触角を、前記発明の詳細な説明の欄に記載したのと同様の方法により測定した結果を表６に示す。
【０１１３】
さらに、これらの記録媒体とトナーＡとの組合せで前記〔画像の記録２〕記載の手順で画像を形成し、得られた画像を前記基準で評価した結果を表６に示す。
【０１１４】
【表６】

【０１１５】
表６に示すように、記録媒体の表面に設けられた熱可塑性のポリエステル系樹脂の軟化点（Ｔｍｐ）がトナーの軟化点（Ｔｍｔ）に対し、＋１０〜−３０℃の範囲にあり、記録媒体の表面に設けられた熱可塑性のポリエステル系樹脂の重量平均分子量（Ｍｗ）が５０００〜６００００であり、数平均分子量（Ｍｎ）が２０００〜５０００であり、Ｍｗ／Ｍｎが２〜１５であり、トナーとの接触角が４０度以下である実施例２、１３、１４については、すべての画像面積率領域において同一光沢を示し、色むらがなく、粒状性に優れ、微小な光沢むらが無い発色が良好な画像が得られた。一方、トナーとの接触角が大きく、相溶性の低い透明樹脂表面を有する記録媒体を用いた実施例１５及び１６については、粒状性に優れ、微小な光沢むらが無い発色が良好な画像が得られたが、光沢均一性及び発色性は許容レベルではあるものの、前記の相溶性の良好な各実施例に比較するとやや低下していた。これらの実施例のなかでも、表面に形成された透明樹脂層中に界面活性剤を含有せず、接触角が最も小さい実施例２が特に優れていた。
【０１１６】
これらの実施例及び比較例からも明らかなように、本発明の画像形成方法よれば、転写電界の乱れや、トナー同士のクーロン反発力に起因すると見られる中間調画像品質の劣化を生じることなく、転写率が良好で、記録媒体そのものや、ハイライト領域から中濃度部、高濃度部の全領域において画像光沢が均一で、粒状性がよく、さらに色バランスが良好でトナーの透明性に優れた高発色高画質の画像を得ることができた。
【０１１７】
本発明の画像形成方法は、プリンタ及び複写機等の画像形成に好適に使用しうる。
【０１１８】
【発明の効果】
この発明は、以上の画像形成方法よりなるもので、画像濃度や画像面積率に拘らず、画像光沢が記録媒体と同一であり、色再現性に優れ、色むらの発生がなく、粒状性に優れ、さらに、微少な光沢の不均一性もない、画像光沢の均一性に優れた効果を奏する。
【図面の簡単な説明】
【図１】 各種基材上に入力画像面積率を変えて作成した画像の７５度鏡面光沢度を測定した結果を示すグラフである。
【図２】 キャストコート紙上に形成されたトナー画像の三次元表面粗さ計による４０％画像面積率部分の画像プロファイルである。
【図３】 本発明の画像形成方法におけるトナー像の転写・定着位置における挙動を示す模式図である。
【図４】 本発明の画像形成方法において、好ましいトナー像の予熱を行った場合の転写・定着位置における挙動を示す模式図である。
【図５】 透明樹脂の軟化点（Ｔｍｐ）と剥離位置における記録媒体の温度差と、剥離された記録媒体表面のオフセットグレードとの関係を示すグラフである。
【図６】 転写・定着位置の下流部分に配置された冷却ファンにより、密着したまま搬送される中間転写体、トナー像及び記録媒体が冷却される状態を示す概略図である。
【図７】 実施例に用いたトナーの温度／粘度特性を示す図である。
【図８】 実施例の〔画像の形成１〕に用いられる画像形成装置の構成図である。
【図９】 発明の実施例及び比較例の画像面積率と光沢の関係を示す図である。
【図１０】 実施例の〔画像の形成２〕に用いられる画像形成装置の構成図である。
【符号の説明】
１０ トナー像保持体（中間転写体、画像保持体）
１２ トナー像
１２Ａ 溶融状態のトナー像
１４ 記録媒体
１６ 基材
１８ 透明樹脂層
２０ 加圧ロール
２２ 加熱ロール
２４ 冷却装置
２６ 画像形成装置
２８、２９ 中間転写体搬送ロール
３０Ｙ、３０Ｍ、３０Ｃ、３０Ｂ 感光体
３２Ｙ、３２Ｍ、３２Ｃ、３２Ｂ 帯電器
３４ 露光装置（ビーム走査装置）
３６Ｙ、３６Ｍ、３６Ｃ、３６Ｂ 現像器
４０ 用紙トレイ
Ｐ 記録媒体
４２ 画像形成装置[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a printer, a copying machine, or the like that employs a transfer / fixing simultaneous system in which a toner image created by indirect electrophotography is transferred onto a recording medium and the toner image is fixed on the recording medium during the transfer. The present invention relates to an image forming method, an image forming apparatus, and a recording medium used therefor, which can provide good gloss characteristics and image quality.
[0002]
[Prior art]
In recent years, color images have been actively created using digital indirect electrophotography. In digital indirect dry electrophotography, yellow, magenta, cyan, and black color toners, in which pigments and dyes are mixed with a thermoplastic resin, are converted into light information by converting image information into light information. A toner image is formed by electrostatically carrying it on a photoconductor that is a digitally addressed image carrier, and after the toner image is electrostatically transferred to a recording medium, it is melted and fixed by heating and pressing. Image.
[0003]
The toner used in the indirect dry electrophotography has a particle diameter of 5 μm to 12 μm, and 0.3 to 1.2 mg / cm per color on the recording medium.²Is generally transferred. In addition, the thermoplastic toner is transferred from one layer to a four-layer recording medium, and when heated and melted, it softens and becomes a molten state. However, it is formed so as to rise from about 5 μm to about 20 μm on the recording medium.
[0004]
The relationship between the input image area ratio of the image on the recording medium formed in this way and the image gloss is shown in FIG. FIG. 1 shows, as recording media, cast coated paper (Enamel Coat / Yonago Processing Paper Co., Ltd.) that is high gloss coated paper, J coated paper (Fuji Xerox) that is medium gloss coated paper, and non-coated paper that is low gloss paper. It is the result of measuring the 75-degree specular glossiness based on JIS P 8142 of an image created by changing the input image area ratio using a line screen to magenta images on plain J paper (Fuji Xerox). FIG. 2 is an image profile of a 40% image area ratio portion obtained by the three-dimensional surface roughness meter of the image on the cast-coated paper thus obtained. As can be seen from FIGS. 1 and 2, the solid image portion has a relatively high glossiness, but in the halftone area and the highlight area, the structure of lines and dots bulges from the recording medium in a convex shape. Therefore, scattering of incident light becomes large, and when an image having a relatively large density gradation such as a human image is formed, an image in which a high gloss region and a low gloss region are mixed becomes uncomfortable. Furthermore, it is known that such a concavo-convex image is an image with low vividness due to a decrease in color reproducibility due to the influence of irregular reflection on the image surface. Furthermore, it is known that the surface unevenness image on the transparent recording medium has a reduced color due to scattering of transmitted light even when projected by OHP.
[0005]
In order to improve the quality of such a color image, Japanese Patent Application Laid-Open No. 63-92965 discloses that a transparent resin layer is provided on a recording medium, the toner is transferred onto the recording medium, and then the toner is transferred by a roll heat fixing machine. There has been proposed a method of embedding in the transparent resin layer. According to this method, although the unevenness of the image is alleviated to some extent, a low surface tension is applied between the toner and the transparent resin due to the effect of applying silicone oil as a release agent to the heating roll for fixing as in the past. The silicone oil film is formed, and the toner is not sufficiently embedded in the transparent resin layer, and the toner image portion protrudes on the surface in a convex shape.
[0006]
Further, for example, in JP-A-5-216322, for the same purpose, toner is electrostatically transferred to a recording medium provided with a transparent resin layer made of a thermoplastic resin having a thickness of 20 to 200 μm on the surface, and then belt-shaped. A method of embedding toner in a transparent resin layer with a fixing machine has been proposed. Since the belt-like fixing machine can be peeled off from the belt after the toner is fixed on the recording medium and cooled, the self-cohesion force of the toner can be used as an adhesion preventing force to the belt, no release agent is required, and Since sufficient heating time can be obtained, surface irregularities are alleviated. However, in the types of the toner resin and the thermoplastic surface layer resin described in the publication, the melted toner resin and the thermoplastic resin are not sufficiently compatible in the recording medium surface layer, and at the interface inside the surface coating layer. It was clarified that a difference in refractive index was caused, resulting in a decrease in color reproducibility and a slight unevenness remained.
[0007]
Further, in the image forming methods described in the above publications, the transfer of the toner image onto the recording medium is all performed electrostatically, and the thermoplastic resin provided on the surface of the recording medium has a low dielectric constant. In addition, for example, when multi-color toner is multiplex-transferred, there is a problem that the transfer rate is lowered particularly in the final transfer color, color unevenness occurs, and the color reproduction region is lowered.
[0008]
In order to eliminate the drawbacks of image transfer due to this decrease in dielectric constant, Japanese Patent Laid-Open No. 5-273811 proposes a recording method in which inorganic oxide fine particles are dispersed and contained in a thermoplastic transparent resin to increase the dielectric constant. Yes. However, in general, the structure of the paper used for the substrate of the recording medium is non-uniform when viewed microscopically, and it is difficult to avoid the disturbance of the electric field during transfer due to the electric non-uniformity of the recording medium. There is a problem that color unevenness and graininess are deteriorated.
[0009]
[Problems to be solved by the invention]
  The present invention has been made in view of the above-described problems, and the object thereof is to provide the same image gloss as that of a recording medium regardless of image density and image area ratio, excellent color reproducibility, and occurrence of color unevenness. No graininess, excellent graininess, and no non-uniform glossiness of 1 to 3 mm diameter, excellent image gloss uniformityImage forming methodIt is to provide.
[0010]
[Means for Solving the Problems]
The present inventors paid attention to the correlation between the properties of the transparent resin layer on the surface of the recording medium and the toner resin used for the toner, and a method for transferring the toner to the recording medium, and the transparent resin material and toner used for the recording medium. The present invention was completed by finding that the above-mentioned object can be achieved by adjusting the softening point.
[0011]
  That is, in the image forming method of the present invention, the toner image transported to the transfer position is transferred to a predetermined recording medium by the toner image holder that holds the toner image and transports the toner image from the toner image forming position to the toner image transfer position. The image forming method includes a transfer / fixing process in which the conveyed toner image is brought into close contact with a recording medium, transferred and fixed while being heated, and the recording medium is heated on at least a surface of the substrate on which the toner image is transferred. It has a plastic transparent resin layer, and the apparent viscosity η ′ (Pa · s) of the transparent resin measured by a flow tester is 1 × 10^FourThe softening point (Tmp) defined as the temperature at which Pa · s is obtained has an apparent viscosity η ′ (Pa · s) of 1 × 10 5 measured by weighing the toner itself with a flow tester.^FourThe resin material that is in the range of + 10 ° C. to −30 ° C. with respect to the softening point (Tmt) of the toner defined as the temperature at which Pa · s is formed, and that is in the molten state A recording medium having a contact angle with the toner of 40 ° or less or a resin material constituting the transparent resin layer containing a structural unit of polyester resin is used.When the temperature of the transparent resin on the surface of the recording medium is 10 ° C. or more lower than the softening point (Tmp) of the transparent resin downstream from the toner image transfer position, the recording medium is peeled from the toner image holding member.It is characterized by that.
[0012]
By setting the softening point (Tmp) of the thermoplastic transparent resin and the softening point (Tmt) of the toner within the above ranges, the compatibility of the two resins at a predetermined temperature is improved, and the toner image becomes a transparent resin layer on the surface of the recording medium. It is possible to form a flat image that is smoothly embedded and has no irregularities due to toner adhesion on the surface.
[0013]
Further, the above-mentioned method includes a step of preheating so that the surface temperature of the toner image reaches a temperature equal to or higher than the softening point (Tmt) of the toner before reaching the toner image transfer position. The method is more preferred.
[0014]
Further, in the above method, when the temperature of the transparent resin on the surface of the recording medium becomes 10 ° C. or more lower than the softening point (Tmp) of the transparent resin downstream from the toner image transfer position, the recording medium is removed from the toner image. An image forming method characterized by peeling from the holding body is preferable.
[0015]
A more preferable aspect as a recording medium used in the above method is a recording medium provided with a transparent resin layer in which the contact angle between the molten toner and the transparent resin constituting the transparent resin layer provided on the surface of the recording medium is 40 degrees or less. It is an image forming method characterized by being used.
[0016]
Further, the thermoplastic transparent resin constituting the layer provided on the surface of the recording medium has a weight average molecular weight (Mw) in the range of 5000 to 60000, a number average molecular weight (Mn) in the range of 2000 to 5000, and Mw / It is a more preferable image forming method that Mn is in the range of 2 to 15.
[0017]
Further, as the thermoplastic transparent resin provided on the surface of the recording medium, it is desirable to use a resin containing a polyester resin-based structural unit.
[0023]
DETAILED DESCRIPTION OF THE INVENTION
The image forming method of the present invention and the image forming apparatus that can be suitably used in this method will be described in detail according to the flow of the electrophotographic system.
[0024]
In printers and copiers, the digital electrophotographic method is widely adopted as a method that can provide high-speed and high image quality. In this method, a light beam adjusted to a spot size of a predetermined size by an imaging optical system is used for optical scanning of the photosensitive medium, and the light beam is turned on / off according to the image density signal determined by the pulse width modulation means. Depending on the time, an area-modulated latent image corresponding to the image density signal is formed on the photosensitive medium. This latent image is visualized with toner and image formation is performed.
[0025]
Note that the image forming process for forming a toner image is not limited to the above-described electrophotographic method. For example, by directly flying toner on a predetermined toner image holding body based on digitally processed image data. A step of forming a toner image on the toner image holding member may be used. The image forming step forms a magnetic latent image on a predetermined toner image holding body based on digitally processed image data, and the toner image is formed on the toner image holding body based on the magnetic latent image. The image forming step may directly write a charge image on a predetermined toner image holding body based on digitally processed image data to form an electrostatic latent image. Thereafter, a step of forming a toner image on the toner image holding member based on the electrostatic latent image may be used.
[0026]
The amount of toner on the recording medium of each color when forming a color image is generally 0.4 mg / cm 2 depending on the content of the dye.²~ 0.7mg / cm²The exposure conditions or development conditions are set so that
[0027]
The toner image thus formed on the toner image holding member may be conveyed along with the movable toner image holding member, and once transferred onto the intermediate transfer medium, then transferred to the transfer position to the recording medium. In addition, transfer and fixing may be performed simultaneously. In the latter case, the intermediate transfer member corresponds to the toner image holding member referred to in the present invention.
[0028]
In the following, the toner image is electrostatically transferred onto a toner image holding member (hereinafter referred to as an intermediate transfer member in accordance with the image holding member or mode as appropriate) and then transferred to a recording medium based on the electrophotographic method. A method of performing fixing simultaneously will be described.
[0029]
The intermediate transfer member is not easily affected by the environment (temperature and humidity) and is stable in terms of physical properties such as surface properties and resistance, like paper, which is a general recording medium. If an appropriate physical property value is given, the toner image is hardly disturbed or uneven due to the transfer electric field or the like as described above. The important factors required for the intermediate transfer member at the time of electrostatic transfer are its surface resistivity Rs (Ω / □) and its volume resistivity Rv (Ω · cm), and Rs is 10⁸<Rs <10¹⁶And the Rv is 10⁷<Rv <10¹⁵It is desirable to be in the range. This is because if Rs and Rv are smaller than these ranges, the charges are spread, and if Rs and Rv are larger than these ranges, the charges are accumulated too much.
[0030]
The toner image electrostatically transferred onto the intermediate transfer member is formed by a halftone dot or line structure that is a pixel in which toner is gathered, and an image density is obtained by the area ratio. This toner image is transferred / fixed to the recording medium at the transfer / fixing position. Therefore, since the toner image is not electrostatically multiple-transferred directly to the recording medium, the image is not disturbed as described above, and a clear and non-uniform transfer image can be obtained on the image carrier.
[0031]
In the transfer / fixing unit, the intermediate transfer member, which is an image carrier, the toner image, and the recording medium are brought into close contact with each other and heated, so that the powder toner is melted and individual toners are fused. It becomes a smooth film. At this time, the intermediate transfer member and the recording medium need to be closely contacted with each other for the purpose of efficient heat transfer to the toner image and forming an image without unevenness by sinking the molten toner into the recording medium. However, if air enters in some places, the heat capacity changes where there is air, and the toner image does not melt uniformly, and transfer / fixing unevenness becomes minute gloss irregularities with a diameter of several millimeters.
[0032]
As described above, in order to smooth the surface by sinking the molten toner into the recording medium and to prevent fine gloss unevenness, in the image forming method of the present invention, the surface of the recording medium to be used is heated. It is necessary to provide a plastic transparent resin layer. As a result of intensive studies by the present inventors, the thermoplastic resin provided on the surface of the recording medium has a softening point (Tmp) that is substantially equal to or lower than the softening point (Tmt) of the toner. Even when the toner is heated to the same temperature, the effect of sinking the toner is high, and the recording medium has a higher adhesive force to the image holding member and is more closely attached. That is, the thermoplastic resin provided on the surface of the recording medium has a softening point (Tmp) in the range of + 10 ° C. to −30 ° C. with respect to the softening point (Tmt) of the toner [Tmt−30 (° C.) ≦ Tmp (° C.). ≦ Tmt + 10 (° C.)] is preferable. More desirably, the thermoplastic resin provided on the surface of the recording medium has a softening point (Tmp) in a range of ± 0 ° C. or −20 ° C. with respect to the softening point (Tmt) of the toner [Tmt−20 (° C.) ≦ Tmp (° C.) ≦ Tmt (° C.)]. When the softening point (Tmp) of the thermoplastic resin provided on the surface of the recording medium exceeds the softening point (Tmt) of the toner by more than 10 ° C., the sinking of the melted toner into the transparent resin layer on the surface of the recording medium is deteriorated. Further, when a resin having a thermoplastic resin softening point (Tmp) lower than 30 ° C. with respect to the toner softening point (Tmt) is used, the melted toner is excessively diffused in the surface layer of the recording medium. When the recording medium surface layer resin is deteriorated, the melt viscosity of the recording medium surface layer resin is excessively lowered, and therefore, a peeling failure from the toner image holding member is likely to occur.
[0033]
Here, the softening point (Tmt) of the toner and the softening point (Tmp) of the resin material constituting the transparent resin layer provided on the surface of the recording medium are defined as follows.
[0034]
Using a flow tester CFT500C manufactured by Shimadzu Corporation, start temperature 80 ° C. to max temperature 170 ° C., temperature rising rate 3 ° C./min, preheating time 300 sec, cylinder pressure 10 kgf / cm²Then, the softened state is measured when the die L × D = 1.0 mm × 1.0 mm is heated at a constant speed. As the sample, since it is difficult to separate only the toner resin for the toner, the toner itself is weighed and used, and the transparent resin provided on the surface of the recording medium is a fine powder precisely weighed 1 to 3 g. Plunger cross section is 10cm²And In the measuring method, as the temperature is increased at a constant speed, the sample is gradually heated and the outflow begins. When the temperature is further raised, the molten sample largely flows out, the plunger descending stops, and one measurement is completed. The outflow amount at each temperature is measured in increments of 3 ° C. from 60 to 150 ° C., and the apparent viscosity η ′ (Pa · s) is obtained. At this time, the apparent viscosity η ′ (Pa · s) is 1 × 10.^FourThe temperature at which Pa · s is obtained is defined as the softening point (Tmt) of the toner and the softening point (Tmp) of the transparent resin provided on the surface of the recording medium.
[0035]
At the transfer position of the toner image, it is preferable to provide an elastic layer on the surface of the intermediate transfer body in order to improve the close contact between the toner intermediate transfer body and the recording medium facing each other with the toner image interposed therebetween. The elastic layer preferably has a rubber hardness of 10 to 80 degrees and a thickness of 10 to 300 μm. When the rubber hardness of the elastic layer on the surface of the intermediate transfer member is less than 10 degrees, the surface of the intermediate transfer member is quickly worn and image gloss cannot be obtained. Further, when the angle exceeds 80 degrees, it becomes difficult to enclose the toner, so that minute gloss unevenness is likely to occur. In addition, when the thickness of the elastic layer is less than 10 μm, it becomes difficult to enclose the toner, so that minute gloss unevenness is likely to occur. When the thickness exceeds 300 μm, power for effective heating in the transfer / fixing unit is generated. Both are unfavorable.
[0036]
Usually, this transfer / fixing section is composed of a heating roll having a heat source such as a halogen lamp inside, and a pressure roll that presses the intermediate transfer body, toner image and recording medium with the intermediate roll, a nip pressure of 1 × 10^ThreePa ~ 1 × 10⁶A range of Pa is desirable, and if the pressure is lower than this range, the intermediate transfer member, the toner image and the recording medium are not sufficiently adhered, and the penetration of the molten toner into the recording medium is insufficient, or minute gloss unevenness is likely to occur. If the pressure is high, the stress on the intermediate transfer member and the recording medium is increased, causing wrinkles, and the mechanism and apparatus for supporting the high pressure are complicated. Instead of the heating roll described above, a fixed heating member in which an energizing heating element is provided on a heat-resistant support and the surface is covered with a heat-resistant / abrasion-resistant layer may be used.
[0037]
FIG. 3 is a schematic view showing the behavior of the toner image at the transfer / fixing position in the image forming method of the present invention. The toner image 12 formed and conveyed on the surface of the toner image holding member (intermediate transfer member) 10 is in close contact with the recording medium 14 at the transfer / fixing position. The recording medium 14 has a structure in which a transparent resin layer 18 is formed on a substrate 16, and the toner image 12 is heated and adhered to the transparent resin layer 18 on the surface of the recording medium 14 by a pressure roll 20 and a heating roll 22. And transferred. At this time, the softening point (Tmp) of the resin layer 18 on the surface of the recording medium 14 is in the range of + 10 ° C. to −30 ° C. with respect to the softening point (Tmt) of the toner. In the region where the three members of the body 10 are in close contact with each other, the toner image 12 melts and sinks into the transparent resin layer 18 on the surface of the recording medium 14, so that the transferred image has good color development, and Smooth and glossy. Depending on the heating and pressing conditions at this time, the viscosity of the resin material constituting the transparent resin layer 18 on the surface of the recording medium 14 is lowered before the melt viscosity of the toner image 12 is lowered, and the toner retains its elastic force. It will sink into the transparent resin layer 18 and may rise slightly after the adhesion is released or may not be sufficiently melted in the transparent resin layer 18. In that case, since the color development and gloss may be slightly inferior, the time required for the region where the recording medium 14, the toner image 12, and the image carrier 10 are in close contact with each other is sufficient, or the heating temperature is increased. It is preferable to control the transfer / fixing conditions.
[0038]
Further, the present inventors preheat the toner image 12 by heating the surface in contact with the toner image 12 of the image carrier 10 in the upstream portion of the transfer / fixing position that is the image carrier, thereby transferring the image. It has been found that an excellent transfer image can be formed without complicated adjustment of the fixing conditions, and that this preheating is preferably set to be equal to or higher than the softening point (Tmt) of the toner.
[0039]
FIG. 4 is a schematic diagram showing the behavior at the transfer / fixing position when the above-mentioned preferable toner image is preheated in the image forming method of the present invention. The toner image on the surface of the toner image holding member (intermediate transfer member) 10 is heated to the vicinity of the softening point (Tmt) of the toner in advance upstream of the transfer / fixing position to become a molten toner image 12A. That is, the toner enters the nip region where the three members of the recording medium 14, the toner image 12A, and the image carrier 10 are in close contact with each other in a state of low viscosity in advance.
[0040]
Here, the toner image 12A is heated, adhered, and transferred to the transparent resin layer 18 on the surface of the recording medium 14 by the pressure roll 20 and the heating roll 22, and at this time, the softening point of the resin layer 18 on the surface of the recording medium 14 is transferred. (Tmp) is in the range of + 10 ° C. to −30 ° C. with respect to the softening point (Tmt) of the toner. Further, the transparent resin layer on the surface of the recording medium 14 is melted, and the already melted toner image 12A is Since the storage elastic modulus of the toner itself is reduced, the image portion may protrude from the recording medium surface resin layer after releasing the adhesive force. An image excellent in both gloss characteristics and color development can be formed without insufficient melting.
[0041]
As the means for preheating the intermediate transfer member, which is an image holding member, and the toner image, as shown in FIG. 4, the heating means for transfer such as a heating roll fixed at the transfer / fixing position is provided upstream of the transfer position. If heating is performed by transporting the intermediate transfer member and the toner image so that they are in close contact with each other over a predetermined transport time, the heating means for transfer / fixing is used without adding any special heating means. Although a preheating step can be performed, a heating (preheating) means such as a heat generating lamp and a heating roll having a heat source inside is transferred and fixed separately from a heat generating member for transfer fixed at a transfer / fixing position. It may be provided upstream of the position. The heating means is not limited to these, and any known heating means may be applied as long as the toner image can be heated to a suitable temperature.
[0042]
  The recording medium onto which the toner has been transferred and the intermediate transfer body, which is an image holding body, are conveyed in close contact with each other, and are peeled off at the peeling position. At the time of peeling, the recording medium is in contact with the image holding body of the recording medium. Peel from the image carrier at a surface temperature of 10 ° C. or more lower than the softening point (Tmp) of the transparent resin provided on the surface of the recording medium..
[0043]
FIG. 5 is a graph showing the relationship between the softening point (Tmp) of the transparent resin and the temperature difference of the recording medium at the peeling position and the offset grade of the surface of the recording medium peeled at that time. Here, the offset grade was evaluated according to the following criteria.
[0044]

[0045]

[0046]
As is clear from FIG. 5, when the surface temperature of the recording medium at the time of peeling is a temperature difference lower than 10 ° C. with respect to the softening point (Tmp) of the transparent resin provided on the surface of the recording medium, the image after peeling. The surface state of the formed recording medium is good, but this is because the transparent resin layer provided on the surface of the recording medium does not retain a sufficient cohesive force and is peeled in a softened state. This is probably because an offset phenomenon occurs in which the transparent resin on the surface of the recording medium is transferred to the image holding member or the surface of the recording medium becomes rough, and the gloss of the obtained image may be lowered.
[0047]
Here, the surface temperature of the recording medium is the temperature until the recording medium is peeled off from the image holding body after a thermocouple is previously installed on the surface of the recording medium and the image holding body and the toner are transferred and fixed. It can be measured by monitoring.
[0048]
A cooling means for lowering the surface temperature of the recording medium is not necessarily required. For example, a suitable peeling state can be obtained by increasing the distance from the transfer / fixing position to the peeling position or lowering the ambient temperature. However, by providing a cooling means downstream of the transfer / fixing position and upstream of the peeling position, an image having a suitable surface state can be efficiently formed.
[0049]
FIG. 6 shows a state in which a cooling fan 24 is disposed in the downstream portion of the transfer / fixing position where the intermediate transfer body 10, the toner image 12 and the recording medium 14 are transported in close contact with each other, and is cooled by applying cool air. FIG.
[0050]
As the cooling means, the above-described efficiency is achieved by a method of disposing the cooling fan 24, a method of bringing a low temperature member of about room temperature into contact with the intermediate transfer member or the recording medium as a cooling means, and transferring heat from the high temperature portion to the low temperature portion. Cooling effect can be obtained. In the latter case, the cooling means to be contacted is circulated and moved in a belt shape, and a part of the belt circumference is brought into contact with the intermediate transfer member or recording medium at the outlet of the heating / pressurizing nip, and the belt is separated from the cooling position. After cooling, the cooling effect can be continuously obtained by reuse. In this way, by performing heat exchange of a cooling medium such as a belt as a cooling means with another low-temperature body at a location different from the cooling position of the intermediate transfer body or the recording medium downstream of the heating / pressure nip outlet. Thus, efficient cooling can be performed without affecting the temperature in the image forming apparatus. The heat exchange with the low-temperature body can be performed, for example, by bringing it into contact with a low-temperature intermediate transfer body before reaching the heating / pressurizing region.
[0051]
In addition, heat can be transferred using a heat exchanger such as a heat pipe as a cooling means at the heating / pressurizing nip outlet.
[0052]
The cooling means at the heating / pressurizing nip outlet can be provided on either the heating body side or the pressing body side, or on both sides. The temperature can be suppressed, and the amount of heat taken away from the heating body can be reduced, so that transfer and fixing can be performed efficiently and thermally.
[0053]
As the toner binder resin used in the image forming method of the present invention, known resins can be used. For example, styrene such as styrene, vinyltoluene, α-methyltoluene, chlorostyrene, aminostyrene, and derivatives thereof, or homopolymers, copolymers, methacrylic acid, methyl methacrylate, and methacrylates such as ethyl methacrylate. Homopolymers or copolymers, acrylic acid and acrylic acid esters such as methyl acrylate, butyl acrylate, 2-ethylhexyl acrylate alone or copolymers, dienes such as butadiene and isoprene, acrylonitrile, vinyl ethers, maleic anhydride , Vinyl monomers such as vinyl chloride and vinyl acetate, alone or in combination with other monomers, copolymers, polyamides, polyesters, polyurethanes, etc. Can be especially poly Those containing structural units of the ether system is preferred.
[0054]
The polyester can be produced by a reaction between a polyhydric alcohol and a polybasic carboxylic acid. Examples of the polyhydric alcohol constituting the polyester include ethylene glycol, diethylene glycol, triethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, 1,4-butanediol, neopentyl glycol, and 1,4-butanediol. Diols such as cyclohexanedimethanol, hydrogenated bisphenol A, bisphenol A alkylene oxide adducts such as polyoxypropylenated bisphenol A, and other divalent alcohols.
[0055]
Examples of polybasic carboxylic acids include maleic acid, fumaric acid, metaconic acid, citraconic acid, itaconic acid, terephthalic acid, isophthalic acid, cyclohexanedicarbomonic acid, succinic acid, their acid anhydrides, alkyl esters, and other 2 Although basic carboxylic acid can be mentioned, it is not limited to this.
[0056]
As the colorant to be mixed with the toner binder resin, known pigments and dyes can be used. For the purpose of charge control, conventionally known external additives for toner can be used.
[0057]
The recording medium that can be suitably used in the image forming method of the present invention is obtained by forming a thermoplastic transparent resin layer having a specific softening point on a substrate. Here, the material used for the substrate is not particularly limited, and any conventionally known substrate material for recording media can be selected and used. Specifically, for example, acidic or neutral high-quality paper, medium-quality paper, renewed paper, recycled paper, synthetic paper, and the like can be used. The filler used in these is not particularly limited, calcium carbonate such as heavy calcium carbonate, light calcium carbonate, chalk, silicic acids such as kaolin, calcined clay, pyrophyllite, sericite, talc, Inorganic fillers such as titanium dioxide and organic pigments such as urea resin and styrene can be used. The sizing agent is not particularly limited. A sizing agent such as a rosin-based sizing agent, a synthetic sizing agent, a petroleum resin-based sizing agent, or a neutral sizing agent can be used, and a fixing agent of an appropriate sizing agent and fiber, such as a sulfuric acid band and cationized starch, is used in combination. In addition, a paper strength enhancer, a dye, a pH adjuster, etc. may be added.
[0058]
Furthermore, you may provide a white pigment coating layer in these base materials.
White pigments used in the white pigment coating layer include heavy calcium carbonate, light calcium carbonate, titanium dioxide, aluminum hydroxide, satin white, talc, calcium sulfate, barium sulfate, zinc oxide, magnesium oxide, magnesium carbonate, non- Mineral pigments such as crystalline silica, colloidal silica, white carbon, kaolin, calcined kaolin, delaminated kaolin, aluminosilicate, sericite, bentonite, smectite, polystyrene resin fine particles, urea polymorpholine resin fine particles, fine hollow particles and other An organic pigment or the like can be used alone or in combination, but is not limited thereto. As the resin for binding the white pigment, a water-soluble adhesive, an emulsion, a latex, or the like can be used alone or in combination. For example, polyvinyl alcohol, modified polyvinyl alcohol, starches, gelatin, casein, methyl cellulose, hydroxyethyl cellulose, acrylic acid amide-acrylic acid ester copolymer, acrylic acid amide-acrylic acid-methacrylic acid terpolymer, styrene-acrylic resin Water-soluble resins such as isobutylene-maleic anhydride resin, carboxymethyl cellulose, acrylic emulsion, vinyl acetate emulsion, vinylidene chloride emulsion, polyester emulsion, styrene-butadiene latex, acrylonitrile-butadiene latex, etc. It is not limited. In addition, it is desirable to use the above-described white pigment, casein, and the like and finish the coated surface by a cast coating method because it becomes more smooth. In addition, a small amount of a dye or a colored pigment may be added to the white pigment coating layer to adjust the color tone, or a fluorescent dye may be added to improve the visual whiteness. Furthermore, various auxiliary agents such as a dispersant, an antifoaming agent, a plasticizer, a pH adjuster, a lubricant, a flow modifier, a solidification accelerator, a water-proofing agent, and a sizing agent can be appropriately added as necessary.
[0059]
Other than the paper-based substrate described above, heat-resistant film-like materials such as a polyethylene terephthalate film, a polysulfone film, a polyphenylene oxide film, a polyimide film, a polycarbonate film, and a cellulose ester film having a heat-resistant temperature of 100 ° C. or higher can also be used.
The recording medium of the present invention has a heat for transferring and fixing the molten toner to at least the surface to which the toner image is transferred on the base material or a sheet provided with a white pigment layer on the base material, and to penetrate the surface of the recording medium. A plastic transparent resin layer is provided. The thermoplastic transparent resin forming the resin layer is made of styrene such as styrene, vinyltoluene, α-methyltoluene, chlorostyrene, aminostyrene, or a derivative thereof, or a substituted homopolymer, copolymer, methacrylic acid and methyl. Methacrylic acid esters such as methacrylate and ethyl methacrylate or copolymers, acrylic acid and acrylic acid esters such as methyl acrylate, butyl acrylate and 2-ethylhexyl acrylate alone or copolymers, dienes such as butadiene and isoprene , Acrylonitrile, vinyl ethers, vinyl monomers such as maleic anhydride, vinyl chloride, vinyl acetate, etc., or copolymers with other monomers, polyamides, polyesters, polyurethanes Etc. alone or in a mixed form Although it is Rukoto, especially resins containing structural units of the polyester (hereinafter, appropriately referred to as a polyester resin) is advantageous. The polyester resin can be produced by a reaction between a polyhydric alcohol and a polybasic carboxylic acid. Examples of the polyhydric alcohol constituting the polyester include ethylene glycol, diethylene glycol, triethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, 1,4-butanediol, neopentyl glycol, and 1,4-butanediol. And diols such as cyclohexanedimethanol, hydrogenated bisphenol A, bisphenol A alkylene oxide adducts such as polyoxypropylenated bisphenol A, and other dihydric alcohols, but are not limited thereto. Preferably, bisphenol A alkylene oxide adducts such as polyoxypropylenated bisphenol A are desirable.
[0060]
Examples of polybasic carboxylic acids include maleic acid, fumaric acid, metaconic acid, citraconic acid, itaconic acid, terephthalic acid, isophthalic acid, cyclohexanedicarbomonic acid, succinic acid, their acid anhydrides, alkyl esters, and other 2 Although basic carboxylic acid can be mentioned, it is not limited to this.
[0061]
In addition, for the purpose of adjusting the surface electrical resistance of these transparent resin layers, sodium chloride, potassium chloride, calcium chloride, sodium sulfate, zinc oxide, titanium dioxide, tin oxide, oxidation are used in amounts that do not impair image quality. You may mix | blend inorganic substances, such as aluminum and magnesium oxide, individually or in mixture of 2 or more types. Further, for the purpose of controlling the friction coefficient of the recording medium, hard plastic fine particles such as styrene can be mixed as long as the amount is not impaired.
[0062]
The thickness of the thermoplastic transparent resin layer provided on the substrate is preferably 2 μm to 20 μm, and more preferably 4 μm to 15 μm. Below this range, the melted toner cannot be sufficiently embedded in the resin layer, a non-smooth image having convex portions due to the toner on the surface is formed, and gloss is insufficient. In addition, if the thickness exceeds this range, image sharpness and color developability may be reduced due to the refractive index of the transparent resin layer, and more energy is required for heating to soften the thick resin layer. Therefore, neither is preferable.
[0063]
As described above, the softening point (Tmp) of these polyester resins is selected from the range of + 10 ° C. to −30 ° C., preferably ± 0 ° C. to −20 ° C., with respect to the softening point (Tmt) of the toner.
[0064]
It is desirable that the weight average molecular weight (Mw) is in the range of 5000 to 60000, the number average molecular weight (Mn) is 2000 to 5000, and Mw / Mn is in the range of 2-15. When the molecular weight and the molecular weight distribution exceed the upper limit of this range, the softening point of the thermoplastic transparent resin layer rises and the embedding of the toner becomes difficult. On the other hand, if the lower limit of this range is not reached, the thermoplastic transparent resin layer becomes too soft, which may cause an offset phenomenon in some cases, which is not preferable.
[0065]
The method for measuring the molecular weight of the thermoplastic transparent resin was performed by gel permeation chromatography. That is, a fully automatic high-temperature high-speed chromatograph (Waters ALS / GPC 150C, manufactured by Waters) is used as a measuring device, tetrahydrofuran is used as a solvent, flow rate = 1.0 ml / min, temperature = 40 ° C., detector. = Measured under differential refractometer (RI) conditions.
[0066]
Light scattering occurring at the interface between the transparent resin layer formed on the surface of the recording medium and the molten toner, and the state where the molten toner swells from the surface of the transparent resin layer of the recording medium also affect the compatibility between the molten toner and the transparent resin layer. By using resins having good compatibility with each other, an image having smoother and more excellent uniform gloss can be formed. In the present invention, the contact angle between the toner in a molten state and the transparent resin layer is adopted as the compatibility standard of these resins, and those having a contact angle of 40 degrees or less are determined to have good compatibility. To do. The contact angle is measured by the following method.
[0067]
(1) A tablet press made by Shimadzu Corp. Hand press SSP-10, a tablet frame having a concave shape with a diameter of 13 mm and a height of 33 mm is filled with powdered toner, and a load of 1 ton is applied for 1 minute with a hand press. In addition, a toner disk is formed. The standard disk size at this time is 13 m in diameter, 1.2 mm in thickness, and 0.18 g in weight.
[0068]
(2) The recording medium is placed on the hot plate so that the substrate is in contact with the hot plate surface, and the toner disk is placed in contact with the transparent resin layer of the recording medium, and left at the set temperature for 90 seconds. Thereafter, the recording medium and the toner disk are placed on an aluminum plate that is left in the air at 23 ° C. so as to be in contact with the recording medium, and then rapidly cooled. At this time, the set temperature is set to a toner softening point (Tmt) + 10 ° C.
[0069]
(3) Using a contact angle measuring device manufactured by Kyowa Interface Chemical Co., Ltd., measure the angle of the skirt contacting the transparent resin layer after the toner is solidified (rotated by 90 °), and average the values. Was defined as a toner contact angle.
[0070]
The contact angle of the transparent resin layer with the molten toner is preferably 40 degrees or less, and more preferably 30 degrees or less. When this upper limit is exceeded, the toner image may be raised on the surface layer of the recording medium after the recording medium is peeled off from the intermediate transfer member after transfer / fixing, particularly in the halftone image area and the highlight image area. It may cause a decrease or color development may be worsened.
[0071]
As described above in detail, according to the image forming method of the present invention, the toner image can be embedded in the transparent resin layer of the recording medium without causing image distortion or color unevenness, so that the entire image area ratio region is uniform. High glossiness, good graininess, and no color unevenness can be formed.
[0072]
The configuration of the recording medium that can be suitably used for this image forming method is as described above, and the effect of the image forming method of the present invention can be achieved by using this recording medium.
[0073]
【Example】
Hereinafter, the present invention will be described in more detail with reference to examples. However, the present invention is not limited to the following examples.
[0074]
[Preparation of recording medium 1]
The recording medium is a commercially available cast coated paper with a basis weight of 127.9 g / m.²The enamel-coated paper (Yonago Processed Paper Co., Ltd.) was used as a base material, and a transparent resin layer composed of six types of polyester resins having the characteristics shown in Table 1 below was formed on the surface.
[0075]
Prepare 6 types of polyester resins (PE1, PE2, PE3, PE4, PE5, PE6) as shown in Table 1 below, mix 20 parts by weight with 80 parts by weight of ethyl acetate, and stir until dissolved. The obtained 6 types of polyester solutions were coated on the enamel-coated paper (base material) using a Mayer bar. The thickness of the resin layer after sufficiently drying was set to 7 μm. The recording media thus obtained were designated as P1, P2, P3, P4, P5 and P6, respectively.
[0076]
Furthermore, a transparent polyethylene terephthalate film having a thickness of 100 μm is used as a base material, and polyester resins PE1, PE3, and PE6 are coated on the base material so as to have a thickness of 3 μm in the same manner as in the case of a paper base material. Three types of OHP films as shown in Fig. 1 were obtained, which were designated as OHP1, OHP2, and OHP3, respectively. Using these recording media, an image was formed with the following toner and image forming apparatus.
[0077]
The softening point (Tmp), weight average molecular weight (Mw), and number average molecular weight (Mn) of 6 types of polyester resins (PE1, PE2, PE3, PE4, PE5, PE6) constituting these transparent resin layers are as described above. The measurement results and the results of calculating Mw / Mn are shown in Table 1.
[0078]
[Table 1]

[0079]
[Production of toner]
The polyhydric alcohol having the raw material composition shown in Table 2 below and polyvalent carboxylic acid are placed in a 1 liter four-necked round bottom flask having a stainless steel stirrer, a glass nitrogen gas inlet tube and a sulfide condenser. The flask was set on a mantle heater. Next, nitrogen gas was introduced from the gas introduction tube, and the temperature was raised while keeping the inside of the flask in an inert gas atmosphere. Thereafter, 0.05 dibutyltin oxide was added, the temperature of the reaction product was kept at 200 ° C., and reaction was carried out for a predetermined time to obtain polyester resins PE7 and PE8.
[0080]
6 parts by weight of yellow pigment is mixed with 100 parts by weight of the obtained polyester resin (PE7), melted with an extruder, kneaded, cooled, pulverized with a jet mill, and the pulverized product was classified. As a result, a yellow toner having a volume average diameter of 7 μm was obtained. Similarly, with respect to 100 parts by weight of the polyester resin (PE7), 4.5 parts by weight of a magenta pigment, 4.5 parts by weight of a cyan pigment, and 4 parts by weight of carbon black are mixed, and a magenta toner having a volume average diameter of 7 μm, Cyan toner and black toner were obtained. The yellow toner was added to obtain a four-color toner set A. (Referred to as toner A)
Further, a toner set B (referred to as toner B) was obtained in the same manner using a polyester resin (PE8).
[0081]
The average particle diameter of the toner is 7 μm. FIG. 7 shows the temperature / viscosity characteristics of these toners.
[0082]
[Table 2]

[0083]
[Image recording 1]
FIG. 8 is a configuration diagram showing the image forming apparatus 26 used in the image forming method of this embodiment.
[0084]
In this image forming apparatus 26, the belt-shaped intermediate transfer member 10 is supported by rollers 28 and 29 and a heating roll 22, and rotates in the direction of the arrow shown in the drawing. A pressure roll 20 is disposed at the transfer / fixing position so as to face the heating roll 22. The heating roll 22 and the pressure roll 20 can be arranged opposite to those in FIG. 8, and the pressure roll 20 may be a heating roll having a heat source inside. Four photoconductors 30Y, 30M, 30C, and 30B corresponding to yellow, magenta, cyan, and black are arranged around the intermediate transfer member 10, and are uniformly charged by the chargers 32Y, 32M, 32C, and 32B, respectively. Thereafter, exposure is performed by a light beam scanning device 34 which is turned on / off by a light beam pulse width modulation device in accordance with the density signal, and an electrostatic latent image is formed. The electrostatic latent image on each photoconductor is developed by developing units 36Y, 36M, 36C, and 36B containing black, yellow, magenta, and cyan toners, and each color of a so-called digital image that expresses density by area modulation. Toner images are formed on the photoreceptors 30Y, 30M, 30C, and 30B. Each color toner image is sequentially transferred to the intermediate transfer member 10 by the transfer devices 38Y, 38M, 38C, and 38B, and a toner image of a plurality of colors is formed on the intermediate transfer member 10.
[0085]
The pressure roll 20 comes into pressure contact with the heating roll 22 as the recording medium P is fed from the tray 40. Thereafter, the intermediate transfer body 10 holding the toner images of the plurality of colors and the recording medium P are heated and moved between the pressure rolls 22 and 20 in time, and are pressed and heated. The toner heated above the softening point is softened and melted, penetrates into the recording medium P, and then solidifies, thereby transferring and fixing.
[0086]
The cooling device 24 arranged for vulcanization from the transfer / fixing position cools the intermediate transfer body 10 and the recording medium P which are conveyed integrally from the heating region, and the toner is agglomerated and solidified, thereby recording. A strong adhesive force with the medium P is generated, and the transparent resin of the recording medium is solidified to prevent offset. The intermediate transfer body 10 and the recording medium P cooled by the cooling device 24 are conveyed, and the recording medium P is separated from the intermediate transfer body 10 together with the toner by the stiffness of the recording medium P itself in a roll 29 having a small curvature radius. A color image is formed.
[0087]
Since the surface of the toner image transferred and fixed on the recording medium P and the surface of the recording medium are smoothed by the surface of the intermediate transfer member 10 conveyed in close contact, the surface is uniform and the image has high gloss. Is formed.
[0088]
As the photoreceptors 30Y, 30M, 30C, and 30B of the image forming apparatus used in the method of the present invention, known ones can be used. For example, various inorganic photoreceptors (Se, a-Si, a-SiC, CdS, etc.) In addition, various organic photoreceptors can also be used.
[0089]
Images were formed on the photoreceptors 30Y, 30M, 30C, and 30B using the recording medium shown in Table 1 and the toner shown in Table 2. The amount of toner on the recording medium of each color is 0.65 mg / cm²Set to.
[0090]
The diameter of the light beam used for the light beam scanning device 34 is 20 μm so that an image with high contrast can be obtained.
[0091]
The intermediate transfer member 10 has a two-layer structure of a base layer and a surface layer. As the base layer, a 70 μm thick polyimide film added with carbon black was used. In this embodiment, in order to electrostatically transfer a toner image from a photosensitive member to an intermediate transfer member without image distortion, the volume resistivity of the base layer varies with the amount of carbon black added.^TenAdjusted to Ωcm.
[0092]
As the base layer, a polyimide film having a thickness of 70 μm was used in this example. However, for example, a sheet having a high heat resistance having a thickness of 10 to 300 μm can be used, and polyester, polyethylene terephthalate, polyether can be used. Polymer sheets such as sulfone, polyether ketone, polysulfone, polyimide, polyimide amide, and polyamide can be used.
[0093]
Further, the surface layer has a volume resistivity of 10 to transfer the toner image from the photosensitive member to the intermediate transfer member without electrostatic image distortion.¹⁴Silicone with a rubber hardness of 40 degrees and a thickness of 50 μm is used to improve the adhesion between the intermediate transfer member and the recording medium while sandwiching the toner image when performing simultaneous transfer and fixing from the intermediate transfer member to the recording medium. An elastic layer made of a copolymer was provided. The silicone copolymer has elasticity, its surface is sticky to the toner at room temperature, and further facilitates the release of the melted and fluidized toner in order to efficiently transfer the toner to the recording medium. Since it has characteristics, it is optimal for the surface layer of the intermediate transfer member.
[0094]
As this surface layer, for example, a resin layer having a high releasability having a thickness of 1 to 100 μm can be used. For example, a tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer, polytetrafluoroethylene or the like can be used. It is possible to use.
[0095]
As the heating and pressure roll, a metal roll or a roll having a heat-resistant elastic layer such as silicone rubber on the metal roll can be used. A heat source is disposed inside the heating roll, and the heating temperature is set and controlled so that it is equal to or higher than the toner softening point (Tmt) upstream of the intermediate transfer member transferring and fixing the toner onto the recording medium. Further, the heating area was set so that the photosensitive member 1 and the toner image and the recording paper P in the heating area were sufficiently in close contact with each other and no partial float occurred and the recording medium P did not wrinkle or shift. The nip pressure is 1 × 10^ThreePa ~ 1 × 10⁶A range of Pa is appropriate. In this example, a heating and pressing roll using a laminate of silicone rubber having a hardness of 55 degrees and a thickness of 3 mm on a hollow aluminum roll was used, and a halogen lamp was used as a heat source inside the heating roll. The nip pressure is 5.0 × 10^FivePa was set.
[0096]
Further, in this embodiment, by adjusting the air volume of the cooling device 24, the temperature of the surface of the recording medium in contact with the intermediate transfer member when the recording medium is peeled from the intermediate transfer member is adjusted to 70 ° C.
[0097]
Further, the conveyance speed of the intermediate transfer member and the toner image was 160 mm / s, the screen was a vertical line, and the number of lines was 200 lines.
[Evaluation of image]
The toner image formed by the above method was evaluated for image gloss, color development, graininess, and color unevenness.
[0098]
The evaluation of image gloss, color developability, graininess, and color unevenness is as follows: Y (yellow), M (magenta), C (cyan), K (2 × 2 cm in 10% increments for an input image area ratio of 0 to 100%. Black), R (red), G (green), B (blue), and PB (three-color black) patches are output, and the visual gloss uniformity, color developability, graininess, and color unevenness are determined by the following criteria. It was done by judging by.
[0099]
(Image evaluation criteria)
A: Particularly good.
○: Good.
Δ: Slightly good (acceptable level)
X: Bad (unacceptable).
[0100]
(Examples 1-8, Comparative Examples 1-4)
Table 3 shows the results of forming an image according to the procedure described in [Image Recording 1] using the combination of the recording media P1 to 6 and the toners A and B, and evaluating the obtained image based on the above criteria. .
[0101]
Table 4 shows the results of forming images in the same manner as described above using the combinations of the recording media OHP1 to 3 and the toner A, and evaluating the obtained images according to the following criteria.
[0102]
[Table 3]

[0103]
[Table 4]

[0104]
From this result, applying [Image recording 1] which is the image forming method of the present invention, the softening point (Tmp) of the thermoplastic polyester resin provided on the surface of the recording medium is changed to the softening point (Tmt) of the toner. ) In the range of +10 to −30 ° C., the weight average molecular weight (Mw) of the thermoplastic polyester resin provided on the surface of the recording medium is 5000 to 60000, and the number average molecular weight (Mn) is 2000. In Examples 1 to 5 in which Mw / Mn is 2 to 15, the same gloss is exhibited in all image area ratio regions, there is no color unevenness, excellent graininess, and no minute gloss unevenness. An image with good color development was obtained. Moreover, about Examples 7-8 in the same range, the color developability was good when projected by OHP, and sharp images without turbidity were obtained. Also in Example, Example 6 in which the ranges of Mw, Mn, and Mw / Mn are out of the above-described preferable ranges was excellent in granularity, and an image with good color development without minute gloss unevenness was obtained. However, it was found that although the gloss uniformity and color developability were at acceptable levels, they were slightly lower than those of the above examples in which the molecular weight was in a suitable range.
[0105]
In Comparative Examples 1 to 4 where Tmp-Tmt is outside the range of the present invention, the gloss uniformity with respect to the image area ratio is inferior, and the image is inferior in color developability and graininess.
[0106]
As an example of the results, FIG. 9 shows the measurement results of the 75-degree specular gloss for the paper portions and the input image area ratios of Example 2, Example 4, and Comparative Example 1. Compared with the comparative example, it can be seen that the gloss of each of the above examples does not depend on the image area ratio, and is an image having a uniform and excellent gloss.
[0107]
[Image recording 2]
As shown in FIG. 10, the heating temperature of the heating roll 22 is set using the same apparatus 42 as used in [Image recording 1] except that the positions of the pressure roll 20 and the heating roll 22 are reversed. An image was formed using the same method as in [Image recording 1] except that the toner softening point (Tmt) was set and controlled to be 30 ° C. FIG. 10 is a configuration diagram showing an image forming apparatus 42 used in the image forming method described in [Image Recording 2] of this embodiment.
[0108]
(Examples 9 to 12, Comparative Examples 5 and 6)
Table 5 shows the results of forming an image by the procedure described in [Image Recording 2] described above using the combination of the recording media P1 to 6 and the toner A, and evaluating the obtained image based on the above criteria.
[0109]
[Table 5]

[0110]
The images formed in Examples 9 to 12 were excellent in graininess, no slight gloss unevenness, and almost uniform gloss and color developability. However, compared with Examples 1 to 5 in which the intermediate transfer member and the toner image are in close contact with the heating roll and heated above the softening point of the toner, upstream when entering the nip between the heating roll and the pressure roll. There was a slight decrease in both gloss uniformity and color development. That is, it can be seen that a particularly excellent image can be formed in the production method of the present invention by heating the toner image to the softening point or more upstream of the transfer position.
[0111]
[Preparation of recording medium 2]
When the polyester PE2 used for the recording medium P2 is applied to paper as a base material, a phosphoric acid ester surfactant is added to the polyester PE2 in advance for the purpose of adjusting the electric resistance of the recording medium, The same as the recording medium P2 used in Example 2, except that 0.1 parts by weight, 0.2 parts by weight, 0.4 parts by weight, and 1 part by weight were mixed with 20 parts by weight of polyester PE2. Recording media were created, and the recording media were designated as P7, P8, P9, and P10. The softening points (Tmp) of these resins were 90 ° C., 90 ° C., 89 ° C., and 88 ° C., respectively.
[0112]
(Examples 13 to 16)
The contact angles of the recording medium P2 and the recording media P7, P8, P9, and P10 obtained in [Preparation of recording medium 2] with the toner A are the same as those described in the detailed description of the invention. The results measured by the method are shown in Table 6.
[0113]
Further, Table 6 shows the results of forming an image by the procedure described in [Image Recording 2] using a combination of these recording media and toner A, and evaluating the obtained image based on the above criteria.
[0114]
[Table 6]

[0115]
As shown in Table 6, the softening point (Tmp) of the thermoplastic polyester resin provided on the surface of the recording medium is in the range of +10 to −30 ° C. with respect to the softening point (Tmt) of the toner. The weight average molecular weight (Mw) of the thermoplastic polyester resin provided on the surface of the toner is 5000 to 60000, the number average molecular weight (Mn) is 2000 to 5000, Mw / Mn is 2 to 15, and the toner In Examples 2, 13, and 14 in which the contact angle is 40 degrees or less, all the image area ratio regions exhibit the same gloss, no color unevenness, excellent graininess, and no color uneven gloss. A good image was obtained. On the other hand, in Examples 15 and 16 using a recording medium having a transparent resin surface with a large contact angle with toner and low compatibility, an image with excellent granularity and good color development without uneven gloss is obtained. However, although the gloss uniformity and color developability were at acceptable levels, they were slightly lower than those of the examples having good compatibility. Among these examples, Example 2 which does not contain a surfactant in the transparent resin layer formed on the surface and has the smallest contact angle was particularly excellent.
[0116]
As is clear from these examples and comparative examples, according to the image forming method of the present invention, there is no deterioration in the halftone image quality which is considered to be caused by the disturbance of the transfer electric field or the Coulomb repulsion between the toners. The transfer rate is good, the image gloss is uniform, the graininess is good, the color balance is good, and the transparency of the toner is excellent in the recording medium itself and in all areas from the highlight area to the medium density area and high density area High color and high quality images could be obtained.
[0117]
The image forming method of the present invention can be suitably used for image formation of printers and copiers.
[0118]
【The invention's effect】
  The present invention comprises the above image forming method. Regardless of the image density and the image area ratio, the image gloss is the same as that of the recording medium, excellent in color reproducibility, no color unevenness, and graininess. Excellent, and there is no slight non-uniformity of gloss, and it has an excellent effect on image gloss uniformity..
[Brief description of the drawings]
FIG. 1 is a graph showing the results of measuring the 75-degree specular gloss of images created by changing the input image area ratio on various substrates.
FIG. 2 is an image profile of a 40% image area ratio portion measured by a three-dimensional surface roughness meter of a toner image formed on cast-coated paper.
FIG. 3 is a schematic diagram illustrating the behavior of a toner image at a transfer / fixing position in the image forming method of the present invention.
FIG. 4 is a schematic diagram showing a behavior at a transfer / fixing position when a preferable toner image is preheated in the image forming method of the present invention.
FIG. 5 is a graph showing the relationship between the softening point (Tmp) of a transparent resin, the temperature difference of the recording medium at the peeling position, and the offset grade of the peeled recording medium surface.
FIG. 6 is a schematic diagram illustrating a state in which an intermediate transfer member, a toner image, and a recording medium that are conveyed in close contact with each other are cooled by a cooling fan disposed in a downstream portion of a transfer / fixing position.
FIG. 7 is a graph showing temperature / viscosity characteristics of toner used in Examples.
FIG. 8 is a configuration diagram of an image forming apparatus used for [image formation 1] in the embodiment.
FIG. 9 is a diagram showing the relationship between the image area ratio and gloss in Examples and Comparative Examples of the invention.
FIG. 10 is a configuration diagram of an image forming apparatus used for [image formation 2] in the embodiment.
[Explanation of symbols]
10 Toner image carrier (intermediate transfer member, image carrier)
12 Toner image
12A Molten toner image
14 Recording media
16 Base material
18 Transparent resin layer
20 Pressure roll
22 Heating roll
24 Cooling device
26 Image forming apparatus
28, 29 Intermediate transfer member conveyance roll
30Y, 30M, 30C, 30B photoconductor
32Y, 32M, 32C, 32B charger
34 Exposure equipment (beam scanning equipment)
36Y, 36M, 36C, 36B Developer
40 Paper tray
P Recording medium
42 Image forming apparatus

Claims (4)

In an image forming method for transferring a toner image conveyed to a transfer position onto a predetermined recording medium by a toner image holding member that holds the toner image and conveys the toner image from a toner image formation position to a toner image transfer position.
A transfer / fixing step in which the conveyed toner image is brought into close contact with a recording medium, transferred and fixed while being heated,
As the recording medium, a thermoplastic transparent resin layer is provided on at least the surface of the substrate to which the toner image is transferred, and the apparent viscosity η ′ (Pa · s) measured by a flow tester of the transparent resin is 1 × 10 ⁴ Pa. The softening point (Tmp) defined as the temperature at which s becomes the softening point of the toner defined as the temperature at which the apparent viscosity η ′ (Pa · s) measured by the flow tester is 1 × 10 ⁴ Pa · s. (Tmt) is in the range of + 10 ° C to -30 ° C
And, using a recording medium having a contact angle of 40 ° or less between the resin material constituting the transparent resin layer and the toner in a molten state ,
The recording medium after the surface temperature of the transparent resin layer of the recording medium is lower than the softening point (Tmp) of the transparent resin defined as described above by 10 ° C. or more downstream from the toner image transfer position. And a step of peeling the toner image holding member from the toner image holding member . In an image forming method for transferring a toner image conveyed to a transfer position onto a predetermined recording medium by a toner image holding member that holds the toner image and conveys the toner image from a toner image formation position to a toner image transfer position.
A transfer / fixing step in which the conveyed toner image is brought into close contact with a recording medium, transferred and fixed while being heated,
As the recording medium, a thermoplastic transparent resin layer is provided on at least a surface of the substrate to which a toner image is transferred, and the resin material constituting the transparent resin layer includes a polyester resin-based structural unit, and the flow of the transparent resin The softening point (Tmp) defined as the temperature at which the apparent viscosity η ′ (Pa · s) measured with a tester is 1 × 10 ⁴ Pa · s is the apparent viscosity η ′ (Pa · s) measured with a flow tester. Using a recording medium in the range of + 10 ° C. to −30 ° C. with respect to the softening point (Tmt) of the toner defined as a temperature of 1 × 10 ⁴ Pa · s ,
The recording medium after the surface temperature of the transparent resin layer of the recording medium is lower than the softening point (Tmp) of the transparent resin defined as described above by 10 ° C. or more downstream from the toner image transfer position. And a step of peeling the toner image holding member from the toner image holding member .   The toner image held on the toner image holding body is preheated so that the surface temperature of the toner image is equal to or higher than the softening point (Tmt) of the toner defined as described above until the toner image is conveyed to the toner image transfer position. The image forming method according to claim 1, further comprising a step of: The resin material constituting the transparent resin layer has a weight average molecular weight (Mw) in the range of 5000 to 60000, a number average molecular weight (Mn) in the range of 2000 to 5000, and Mw / Mn of 2 to 15. The image forming method according to any one of claims 1 to 3, wherein the image forming method is in a range.

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