JP3865676B2 - Image forming apparatus - Google Patents

Description

【００７５】
上記式（Ｉ）中、Ｒ_１、Ｒ_２、Ｒ_３は、置換もしくは無置換のアルキル基又はハロゲン原子で、それぞれ同一でも異なっていてもよい：Ｒ_４は、水素原子又は置換もしくは無置換のアルキル基：Ｒ_５、Ｒ_６は置換もしくは無置換のアリール基で、それぞれ同一でも異なっていてもよい：ｏ，ｐ，ｑはそれぞれ異なっていてもよく、０〜４の整数：ｋ、ｊは組成を表わし、０．１≦ｋ≦１、０≦ｊ≦０．９：ｎは繰り返し単位数を表わし５〜５０００の整数：Ｘは脂肪族の２価基、環状脂肪族の２価基、または下記一般式（２）で表わされる２価基を表わす。
【００７６】
【化２】

【００７７】
上記式（２）中、Ｒ_１０１、Ｒ_１０２は、置換もしくは無置換のアルキル基、アリール基またはハロゲン原子を表わし、それぞれ同一でも異なっていてもよい。ｌ、ｍは０〜４の整数を表わす。Ｙは、単結合、炭素原子数１〜１２の直鎖状、分岐状もしくは環状のアルキレン基、−Ｏ−、−Ｓ−、−ＳＯ−、−ＳＯ_２−、−ＣＯ−、−ＣＯ−Ｏ−Ｚ−Ｏ−ＣＯ−（Ｚは脂肪族の２価基を表わす。）、または下記式（３）により表わされる構造を示す。
【００７８】
【化３】

【００７９】
（上記式（３）中、ａは１〜２０の整数、ｂは１〜２０００の整数、Ｒ_１０３、Ｒ_１０４は置換または無置換のアルキル基又はアリール基を表わす。Ｒ_１０１、Ｒ_１０２、Ｒ_１０３、Ｒ_１０４は、それぞれ同一でも異なってもよい。）
【００８０】
【化４】

【００８１】
上記式（II）中、Ｒ_７、Ｒ_８は、置換もしくは無置換のアリール基で、それぞれ同一でも異なっていてもよい：Ａｒ_１、Ａｒ_２、Ａｒ_３は、アリレン基を表わす。それぞれ同一でも異なっていてもよい。Ｘ，ｋ，ｊ及びｎは、上記式（Ｉ）と同じである。
【００８２】
【化５】

【００８３】
上記式（III）中、Ｒ_９、Ｒ_１０は、置換もしくは無置換のアリール基で、それぞれ同一でも異なっていてもよい：Ａｒ_４、Ａｒ_５、Ａｒ_６はアリレン基を表わし、それぞれ同一でも異なっていてもよい。Ｘ，ｋ，ｊおよびｎは、上記式（Ｉ）と同じである。
【００８４】
【化６】

【００８５】
上記式（IV）中、Ｒ_１１、Ｒ_１２は、置換もしくは無置換のアリール基で、それぞれ同一でも異なっていてもよい：Ａｒ_７、Ａｒ_８、Ａｒ_９は、アリレン基で、それぞれ同一でも異なっていてもよい。Ｘ，ｋ，ｊおよびｎは、上記式（Ｉ）と同じである。
【００８６】
【化７】

【００８７】
上記式（Ｖ）中、Ｒ_１３、Ｒ_１４は、置換もしくは無置換のアリール基で、それぞれ同一でも異なっていてもよい：Ａｒ_１０、Ａｒ_１１、Ａｒ_１２は、アリレン基で、それぞれ同一でも異なっていてもよい。：Ｘ_１、Ｘ_２は、置換もしくは無置換のエチレン基、又は置換もしくは無置換のビニレン基を表わし、それぞれ同一でも異なっていてもよい。Ｘ，ｋ，ｊおよびｎは、上記式（Ｉ）と同じである。
【００８８】
【化８】

【００８９】
上記式（VI）中、Ｒ_１５、Ｒ_１６、Ｒ_１７、Ｒ_１８は、置換又は無置換のアリール基で、それぞれ同一でも異なっていてもよい：Ａｒ_１３、Ａｒ_１４、Ａｒ_１５、Ａｒ_１６はアリレン基で、それぞれ同一でも異なっていてもよい。：Ｙ_１、Ｙ_２、Ｙ_３は、単結合、置換もしくは無置換のアルキレン基、置換もしくは無置換シクロアルキレン基、置換もしくは無置換のアルキレンエーテル基、酸素原子、硫黄原子、ビニレン基を表わし、それぞれ同一でも異なっていてもよい。Ｘ、ｋ、ｊおよびｎは、上記式（Ｉ）と同じである。
【００９０】
【化９】

【００９１】
上記式（VII）中、Ｒ_１９、Ｒ_２０は、水素原子、置換もしくは無置換のアリール基を表わし、Ｒ_１９とＲ_２０は環を形成していてもよい。それぞれ同一でも異なっていてもよい。Ａｒ_１７、Ａｒ_１８、Ａｒ_１９はアリレン基を表わす。それぞれ同一でも異なっていてもよい。Ｘ、ｋ、ｊおよびｎは、上記式（Ｉ）と同じである。
【００９２】
【化１０】

【００９３】
上記式（VIII）中、Ｒ_２１は置換もしくは無置換のアリール基、Ａｒ_２０、Ａｒ_２１、Ａｒ_２２、Ａｒ_２３はアリレン基を表わす。それぞれ同一でも異なっていてもよい。Ｘ、ｋ、ｊおよびｎは、上記式（Ｉ）と同じである。
【００９４】
【化１１】

【００９５】
上記式（IX）中、Ｒ_２２、Ｒ_２３、Ｒ_２４、Ｒ_２５は置換もしくは無置換のアリール基で、それぞれ同一でも異なっていてもよい。Ａｒ_２４、Ａｒ_２５、Ａｒ_２６、Ａｒ_２７、Ａｒ_２８はアリレン基を表わす。それぞれ同一でも異なっていてもよい。Ｘ、ｋ、ｊおよびｎは、上記式（Ｉ）と同じである。
【００９６】
【化１２】

【００９７】
上記式（Ｘ）中、Ｒ_２６、Ｒ_２７は置換もしくは無置換のアリール基で、それぞれ同一でも異なっていてもよい。Ａｒ_２９、Ａｒ_３０、Ａｒ_３１はアリレン基を表わす。それぞれ同一でも異なっていてもよい。Ｘ、ｋ、ｊおよびｎは、上記式（Ｉ）と同じである。
【００９８】
保護層（３９）は、保護層形成用材料を溶媒又は分散媒に溶解又は分散させ、これを電荷輸送層（３７）上に塗布し、乾燥させることで形成できる。なお、電荷輸送層（３７）上に他の層が設けられている場合には、この層上に塗布する。
前記フィラー材料は、少なくとも有機溶剤、さらに必要であれば分散剤とともにボールミル、アトライター、サンドミル、超音波などの従来方法を用いて分散できる。使用されるメディアの材質については、従来使用されているジルコニア、アルミナ、メノウ等のメディアを使用することができるが、フィラーの分散性及び残留電位低減効果の点からアルミナを使用することがより好ましく、耐摩耗性に優れたα型アルミナが特に好ましい。ジルコニアは、分散時のメディアの摩耗量が大きく、それらの混入によって残留電位が著しく増加するだけでなく、その摩耗粉の混入によって分散性が低下し、フィラーの沈降性が大幅に低下する。一方、メディアにアルミナを使用した場合には、分散時のメディアの摩耗量は低く抑えられる上に、混入した摩耗粉が残留電位に与える影響が非常に小さい。また、摩耗粉が混入しても分散性に対する影響が他のメディアに比べて少ない。したがって、分散に使用するメディアにはアルミナを使用することがより好ましい。
【００９９】
分散剤は、塗工液中のフィラーの凝集、さらにはフィラーの沈降性を抑制し、フィラーの分散性が著しく向上させることから、フィラーや有機溶剤とともに分散前に添加することが好ましい。
一方、バインダー樹脂や電荷輸送物質は、分散前に添加することも可能であるが、その場合分散性が若干低下する場合が見られる。したがって、バインダー樹脂や電荷輸送物質は、有機溶剤に溶解された状態で分散後に添加することが好ましい。
【０１００】
分散液又は溶液の塗工法としては、浸漬塗工法、スプレーコート、ビートコート、ノズルコート、スピナーコート、リングコート等、従来の塗工方法を用いることができるが、比較的薄い膜を均一に、かつフィラー分散性の良好な膜を形成するためにはスプレー塗工が最も適している。
【０１０１】
保護層（３９）全体の膜厚は、５μｍ〜１０μｍが適当である。いずれにしても、保護層（３９）の膜厚は、前記したように、電荷輸送層（３７）の膜厚とあわせて２０μｍ以下とすることが好ましい。
保護層（３９）の膜厚が極度に薄い場合には、膜の均一性が低下したり、充分な耐摩耗性が得られない場合があり、膜厚が極度に厚い場合には、残留電位上昇の影響が増大したり、光透過率の低下により解像度やドット再現性の低下を引き起こす場合がある。
【０１０２】
（他の層）
上記感光体は、任意の位置に任意の層を適宜設けることができる。この層は、電荷発生層（３５）、電荷輸送層（３７）、保護層（３９）の塗工方法と同様の方法により設けることができる。
【０１０３】
導電性支持体（３１）と電荷発生層（３５）との間に中間層（３３）を設けることができる。
中間層（３３）は、一般に、樹脂を主成分とするが、これらの樹脂はその上に感光層が塗布されるため、有機溶剤に対して耐溶剤性の高い樹脂であることが望ましい。このような樹脂としては、ポリビニルアルコール、カゼイン、ポリアクリル酸ナトリウム等の水溶性樹脂、共重合ナイロン、メトキシメチル化ナイロン等のアルコール可溶性樹脂、ポリウレタン、メラミン樹脂、フェノール樹脂、アルキッド−メラミン樹脂、エポキシ樹脂等、三次元網目構造を形成する硬化型樹脂等が挙げられる。これらは単独で用いても２種以上混合して用いてもよい。
【０１０４】
また、前記したように下引き層を設ける場合には、モアレ防止、残留電位の低減等のために酸化チタン、シリカ、アルミナ、酸化ジルコニウム、酸化スズ、酸化インジウム等で例示できる金属酸化物などの微粉末顔料を下引き層に含有させることが好ましい。また、シランカップリング剤、チタンカップリング剤、クロムカップリング剤等を使用することもできる。さらに、各種分散剤を添加してもよい。この他、Ａｌ_２Ｏ_３を陽極酸化にて設けたものや、ポリパラキシリレン（パリレン）等の有機物やＳｉＯ_２、ＳｎＯ_２、ＴｉＯ_２、ＩＴＯ、ＣｅＯ_２等の無機物を真空薄膜作成法にて設けたものも良好に使用できる。このほかにも公知のものを用いることができる。これらは単独で用いても２種以上混合して用いてもよい。下引き層の膜厚は０〜５μｍが適当である。
【０１０５】
また、感光層（電荷発生層（３５）／電荷輸送層（３７））と保護層（３９）との間に層（中間層）を設けてもよい。この中間層は、一般に、バインダー樹脂を主成分とする。バインダー樹脂は、ポリアミド、アルコール可溶性ナイロン、水溶性ポリビニルブチラール、ポリビニルブチラール、ポリビニルアルコールなどが挙げられる。これらは単独で用いても２種以上混合して用いてもよい。中間層の厚さは０．０５〜２μｍ程度が適当である。
【０１０６】
本発明においては、耐環境性の改善のため、とりわけ、感度低下、残留電位の上昇を防止する目的で、電荷発生層、電荷輸送層、下引き層、保護層、中間層等の各層に従来公知の酸化防止剤、可塑剤、滑剤、紫外線吸収剤、低分子電荷輸送物質およびレベリング剤を適宜添加できる。
【０１０７】
【実施例】
以下、本発明を実施例によりさらに詳説するが、本発明は、これら実施例に限定されて解釈されるものではない。
【０１０８】
［実施例１］
実施例１で作成した画像形成装置の概略を、図４を用いて説明する。
【０１０９】
感光体ドラム（１）は、アルミニウムの導体表面に膜厚２０μｍの感光体が設けられている。感光体は、保護層（３９）、電荷輸送層（３７）、下引き層、電荷発生層（３５）を有する積層型電子写真感光体（ＯＰＣ）であり、図４中の矢印方向に回転される。感光体ドラム（１）の直径は６０ｍｍとし、周速は２３０ｍｍ／ｓｅｃとした。
【０１１０】
帯電手段（２）は、いわゆる接触ローラ帯電装置である。芯金上にいわゆる中抵抗の導電性をもつ厚み３ｍｍの弾性層が形成された帯電ローラに、電源によって直流電圧（−１．２１ｋＶ）が印加され、感光体を均一（−５５０Ｖ）に帯電する。
【０１１１】
露光手段（３）は、帯電手段（２）で均一に帯電された感光体の表面に、目的の画像に対応した光を照射することによって、静電潜像を形成する。露光手段（３）の光源はレーザーダイオードであり、ポリゴンミラーによって、感光体上をレーザービームで照射しながら走査していく。ビーム径は、主走査方向３５μｍ、副走査方向３５μｍとした。
【０１１２】
図５は、露光手段（３）の構成図を示す。図３に示すように、露光手段（３）は、波長７８０ｎｍの４つのＬＤ（レーザーダイオード）（５１）をもつ４ｃｈ（４チャンネル）タイプのＬＤアレイを搭載する。ＬＤからのレーザー光は、コリメートレンズ（５２）、ＮＤフィルタ（５３）、アパーチャー（５４）、シリンドリカルレンズ（シリンダレンズ）（５５）を介して、ポリゴンミラー（５６）へと照射される。ポリゴンミラー（５６）は、６面タイプのものを採用し、２７１６５ｒｐｍの回転数で回転させた。
ポリゴンミラー５６で反射されたレーザー光は、折り返しミラー５８、５９、ｆ−θレンズ５７、６０を介して感光体上で結像するように設定した。
【０１１３】
実施例１では、レーザービームの感光上でのビーム径を３５μｍ（主走査方向）×３５μｍ（副走査方向）になるように調整した。ｆ−θレンズ（５７）、（６０）はプラスチックを成形加工したプラスチックレンズを採用し、いわゆるＡＣ面によってレンズ形状の設計した。これにより、３５μｍ（主走査方向）×３５μｍ（副走査方向）というきわめて細いビーム径を実現した。
【０１１４】
レーザー光は、ポリゴンミラー（５６）が回転することによって、感光体上を走査する。実施例１では、解像度を１２００ｄｐｉとし、１pixcelの大きさを２１．３μｍ×２１．３μｍとした。つまり、１pixcelあたりを１６．９ｎｓｅｃの時間で移動しながら、感光体にレーザービームを照射していく構成とした。このとき、いわゆる画素クロックは５９．２ＭＨｚであり、５９．２ＭＨｚの周波数でＬＤを光変調している。
【０１１５】
なお、非画像領域にレーザー光が照射された場合には、同期検知板（１２）に、レーザー光が入射するように構成した。同期検知板（１２）は、レーザービームの入射によって基準信号が発生し、この基準信号に基づいて画像書き出し位置のタイミング（いわゆる画素クロック）を形成するクロック信号のリセットを行なう。これにより、感光体上の所定の位置に、光変調をなされたレーザー光を入射することを実現した。
また、実施例１では、１pixcelあたり４階調の階調表現が可能な、いわゆる４値書き込みを行なうことができるように、ＬＤのパルス幅を４段階で変化させてこのような多値書き込みを行なっている。
【０１１６】
現像手段（４）は、いわゆる２成分現像装置を採用した。現像容器には、トナー（体積平均粒径６．８μｍ）とキャリア（粒径５０μｍ）をトナー濃度５．０％に混合した現像剤を納めた。
現像装置は、上記現像剤を、現像スリーブによって感光体−現像スリーブ対向部へと搬送する。感光体−現像スリーブ間の距離（いわゆる現像ギャップ）は０．３ｍｍとした。現像スリーブには電源により直流電圧（−４００Ｖ）が印加し、感光体上の静電潜像の対応してトナーが感光体上に付着させた（いわゆる反転現像）。現像スリーブの周速は４６０ｍｍ／ｓｅｃ、いわゆる周速比は２．０とした。
【０１１７】
転写手段（５）は、現像手段（４）で現像されたトナー像を、図示しない給紙手段から搬送された記録シート（６）上に転写する。実施例１の転写手段（５）は、転写ベルトと電源とからなり、電源から転写ベルトに電圧を印加するものを用いた。印加する電圧は定電流制御とし、３０μＡとした。
【０１１８】
クリーニング手段（７）は、弾性体から形成されるブレードによって構成され、感光体上の残留トナー像（いわゆる転写残トナー）のクリーニングを行なう。
【０１１９】
転写手段（５）によって紙などの記録シート上に転写されたトナー像は、定着手段（８）に搬送され、定着手段（８）で加熱加圧されることでトナー像が記録紙シート上に定着される。記録シートは、画像形成装置機外へと排出される。
【０１２０】
実施例１で用いた画像形成装置は、感光体ドラム（１）が回転しながら上記処理を順次行なうことで、記録シート上に画像を形成していく。
【０１２１】
次に、実施例１で用いた感光体の作成法を詳細に記す。なお、以下で用いる「部」はすべて「重量部」を意味する。また、電荷輸送物質のイオン化ポテンシャルＩｐは、表面分析装置（理研計器製、ＡＣ−１）にて測定した。
【０１２２】
（感光体仕様）
φ６０のアルミニウムシリンダー上に下記組成の下引き層塗工液、電荷発生層（３５）塗工液、および電荷輸送層（３７）塗工液を、浸漬塗工によって順次塗布、乾燥し、膜厚３．５μｍの下引き層、０．２μｍの電荷発生層、１５μｍの電荷輸送層を形成した。
【０１２３】
下引き層塗工液
二酸化チタン粉末 ４００部
メラミン樹脂 ６５部
アルキッド樹脂 １２０部
２−ブタノン ４００部
電荷発生層（３５）用塗工液
Ｙ型オキソチタニウムフタロシアニン顔料 ２部
ポリビニルブチラール（エスレックＢＭ−２：積水化学製）１．０部
テトラヒドロフラン ５０部
電荷輸送層（３７）塗工液
ポリカーボネート（Ｚポリカ、帝人化成製） １０部
下記構造式（XI）の電荷輸送物質（Ｉｐ：５．４ｅＶ） ６部
テトラヒドロフラン １００部
【０１２４】
【化１３】

【０１２５】
電荷輸送層（３５）上に、さらに下記組成の保護層（３９）塗工液を用いて、スプレー塗工によって塗工し、全膜厚が５μｍの保護層を形成し、電子写真感光体を作製した。

【０１２６】
（画質評価方法）
画質評価は、画質に与える影響が極めて大きい階調性を測定することで行なった。
階調性の評価は、線数を変えて中間調処理をほどこした１７段のパッチを出力し、このパッチの明度（Ｌ＊）を測定した。中間調処理は、線数１５０、２００、２４０ｌｐｉで行なった。
明度（Ｌ＊）の測定には、分光濃度測色計（Ｘ−Ｒｉｔｅ社製９３８）を使用した。
階調性の数値化は、データ上の面積率（すなわち入力値）に対する１７段のパッチを測色して求めた明度値の直線性から、一次式近似での自己相関係数の２乗（いわゆるＲ＾２）を計算して算出した。Ｒ＾２の値は、図６に示すように、入力データと明度（Ｌ＊）との関係が直線的ならば１．０に近い値になる。また、図７に示すように、直線からずれるにしたがって小さな値になる。
【０１２７】
本願発明者らは、予め自然画像などの高い階調性が要求される画像の主観的評価を行なった結果、Ｒ＾２の値が０．９８以上である場合に優れた階調性（良好な画質）を有すると評価することにした。
Ｒ＾２の値は、いわゆる低線数画像のほうが大きくなる傾向がある。しかし、線数が２００ｌｐｉ以下の場合には、いわゆるディザのテクスチャをユーザに認識させてしまい、得られた画像は不自然な印象を与えることがわかった。そこで、本発明者らは、中間調処理の線数２００線以上において、階調性Ｒ＾２の値０．９８以上であれば高画質であると評価することとした。
評価結果を表２に示す。
【０１２８】
なお、記録密度は、文字・線画の画質に影響し、特にジャギー特性に大きな影響を与える。一般に、ジャギーが目立たなくなる書込密度は、９００ｄｐｉ以上、好ましくは１２００ｄｐｉ以上である。
そこで、本発明者らは、２ｂｉｔ書き込み可能なように改造し、解像度１２００ｄｐｉにセットした画像形成装置（株式会社リコー製、商品名ＭＦ４５７０）に上記感光体を用いて画像を出力した。
ビーム径はＰＨＯＴＯＮ社製ビームスキャンで、感光体膜厚はフィッシャースコープ社製膜厚計でそれぞれ測定した。
評価を表２に示す。
【０１２９】
［実施例２〜８、比較例１〜１２］
実施例１において、感光体の電荷輸送層膜厚、保護層の透過率（処方は後述）、露光時の書込ドット系、書込密度を表１のように変えたほかは実施例１と同様にして画像出力及び画質評価を行なった。
【０１３０】
【表１】

【０１３１】
透過率（保護層透過率）９８％保護層（３９）、及び８５％の保護層（３９）は、下記組成の保護層（３９）塗工液を用い、実施例１と同様に作成した。
作成した画像形成装置を用いて実施例１と同様に画像を形成し、得られた画像を実施例１と同様に評価した。実施例２〜８、比較例１〜１２の画質の評価結果を表２に示す。
【０１３２】

【０１３３】

【０１３４】
【表２】

【０１３５】
［比較例１３］
実施例１において、フィラーであるアルミナを保護層（３９）塗工液に無添加とした以外は、すべて実施例１と同様にして電子写真感光体を作製した。作成した画像形成装置を用いて実施例１と同様に画像を形成した。
【０１３６】
以上のように作製した電子写真感光体を、画像形成装置（株式会社リコー製、商品名ＭＦ４５７０）によりランニング評価を行なった。また、実施例１と同様に画像評価を行なった。なおビーム径は３５μｍ、書き込み密度は１２００ｄｐｉとした。
中間調処理は、２００ｌｐｉの水準で画像を出力した。
評価手法は次の通りである。
【０１３７】
（１）感光体の膜厚測定。
（２）１部画像形成後、画像評価（階調性Ｒ＾２の測定）。
（３）明部電位（ＶＤ＝−８００Ｖに設定）の測定。
（４）１ｔｏ２にてトータル２万枚の印刷を行なった後、（３）と同様に明部電位の測定。
（５）（２）と同様に画像評価。
（６）さらに８万枚（トータル１０万枚）画像形成後、感光体の膜厚測定。（１）における膜厚（膜厚の初期値）との膜厚差より摩耗量の評価を行なう。
また、階調性以外の画質に関しては、本願発明者らが目視にて確認した。
評価結果を表３に示す。
また、実施例１、比較例３についても同様に評価した。結果を表３に示す。
【０１３８】
［実施例９］
実施例１において、保護層（３９）塗工液に含有される不飽和ポリカルボン酸ポリマーを下記のように変更した以外は、すべて実施例１と同様にして、電子写真感光体を作製した。作成した画像形成装置を用いて比較例１３と同様に評価した評価結果を表３に示す。
塗工液：不飽和ポリカルボン酸ポリマー
（酸価１３０ｍｇＫＯＨ／ｇ、ＢＹＫケミー製） ０．０６部
【０１３９】
［実施例１０］
実施例１において、保護層（３９）塗工液に含有される不飽和ポリカルボン酸ポリマーを下記ように変更した以外は、すべて実施例１と同様にして、電子写真感光体を作製した。作成した画像形成装置を用いて比較例１３と同様に評価した評価結果を表３に示す。
塗工液：不飽和ポリカルボン酸ポリマー
（酸価３６５ｍｇＫＯＨ／ｇ、ＢＹＫケミー製） ０．０３部
【０１４０】
［実施例１１］
実施例１において、保護層（３９）塗工液に含有される不飽和ポリカルボン酸ポリマーを下記のようにに変更した以外は、すべて実施例１と同様にして、電子写真感光体を作製した。作成した画像形成装置を用いて比較例１３と同様に評価した結果を表３に示す。
塗工液：アクリル酸／ヒドロキシエチルメタクリレート共重合体
（酸価１３０ｍｇＫＯＨ／ｇ） ０．１０部
【０１４１】
［実施例１２］
実施例１において、保護層（３９）塗工液に含有されるフィラーを下記のとおりに変更した以外は、すべて実施例１と同様にして、電子写真感光体を作製・評価した。作成した画像形成装置を用いて比較例１３と同様に評価した結果を表３に示す。
アルミナ（平均粒径０．１５μｍ ｐＨ：５．３） ３．０部
【０１４２】
［実施例１３］
実施例１において、保護層（３９）塗工液に含有されるフィラーを下記のとおりに変更した以外は、すべて実施例１と同様にして、電子写真感光体を作製した。作成した画像形成装置を用いて比較例１３と同様に評価した結果を表３に示す。
アルミナ（平均粒径０．４５μｍ ｐＨ：５．７） ３．０部
【０１４３】
［実施例１４］
実施例１において、保護層（３９）塗工液に含有されるフィラーを下記のとおりに変更した以外は、すべて実施例１と同様にして、電子写真感光体を作製した。作成した画像形成装置を用いて比較例１３と同様に評価した結果を表３に示す。
チタネートカップリング処理アルミナ（処理量３％） ３．０部
【０１４４】
［実施例１５］
実施例１において、保護層（３９）塗工液に含有される電荷輸送物質を、下記構造式（XII）の電荷輸送物質（Ｉｐ：５．３ｅＶ）に変更した以外は、すべて実施例１と同様にして、電子写真感光体を作製した。作成した画像形成装置を用いて比較例１３と同様に評価した結果を表３に示す。
【０１４５】
【化１４】

【０１４６】
［実施例１６］
実施例１において、保護層（３９）塗工液に含有される電荷輸送物質を、下記構造式（XIII）の電荷輸送物質（Ｉｐ：５．５ｅＶ）に変更した以外は、すべて実施例１と同様にして、電子写真感光体を作製した。作成した画像形成装置を用いて比較例１３と同様に評価した結果を表３に示す。
【０１４７】
【化１５】

【０１４８】
［実施例１７］
実施例１において、保護層（３９）塗工液に含有される電荷輸送物質及び結着樹脂を下記の材料に変更した以外は、すべて実施例１と同様にして、電子写真感光体を作製した。作成した画像形成装置を用いて比較例１３と同様に評価した結果を表３に示す。
下記構造式（XIV）の高分子電荷輸送物質（Ｉｐ：５．４ｅＶ） ５部
【０１４９】
【化１６】

【０１５０】
［実施例１８］
実施例１において、保護層（３９）塗工液に含有される結着樹脂を下記のとおりに変更した以外は、すべて実施例１と同様にして、電子写真感光体を作製した。作成した画像形成装置を用いて比較例１３と同様に評価した結果を表３に示す。
ポリアリレート樹脂（Ｕポリマー／ＰＥＴ、ユニチカ製） ７．０部
【０１５１】
［実施例１９］
実施例１において、保護層（３９）塗工液に含有される結着樹脂を下記のとおりに変更した以外は、すべて実施例１と同様にして、電子写真感光体を作製した。作成した画像形成装置を用いて比較例１３と同様に評価した結果を表３に示す。
ポリカーボネート（Ｃポリカ、帝人化成製） ７．０部
【０１５２】
【表３】

【０１５３】
（評価結果）
表２から、階調性の優れた画像を形成にするためには、ビーム径、電荷輸送層膜厚、保護層透過率を特定の組み合わせとする必要があることがわかる。この組み合わせ（階調性の優れた画像を形成するための条件）を以下に示す。
【０１５４】
（前提条件）
光書き込みの解像度が１２００ｄｐｉ以上の電子写真方式を用いた画像形成装置及び／又は、入力画像に対して２００ｌｐｉ以上の線数によって中間調処理を施された画像データを画像形成する電子写真方式を用いた画像形成装置。
▲１▼光書き込み手段のビーム径は、３５μｍ以下。
▲２▼光書き込み手段からのレーザ光に対する透過率が９０％以上である保護層を有する。
▲３▼保護層と電荷輸送層の膜厚の合計値が２０μｍ以下。
【０１５５】
また、保護層に、フィラー、分散、電荷輸送物質及び／又は結着樹脂を含有された感光体を用いれば、残留電位の上昇を抑制でき、画像ムラの発生や階調性の低下等の画質劣化を抑制でき、かつ、偏摩耗や異常摩耗をも抑制できることが分かった。
【０１５６】
ビーム径３５μｍ以下とし、透過率９０％以上の保護層を設け、電荷輸送層および保護層を合わせた膜厚が２０μｍ以下とすれば、いわゆるバンディングを低減できることが分かった。
バンディングとは、電子写真画像の主走査方向（通紙方向）への濃度変動のことである。特に、中濃度（明度Ｌ＊＝４０〜７０）の均一画像を出力した場合に、比較的長周期（１〜２０ｍｍ周期）でスジ状に濃度が変動する。出力画像中にこのようなスジ状の濃度変動が発生してしまうと、得られた画像は極めて不自然なものとなってしまう。
バンディングを発生させる要因としては、ビームの走査ムラ（いわゆるポリゴンミラーの面倒れ、光学素子の振動）、感光体ドラムの回転速度ムラ、現像スリーブの回転速度ムラ、現像ギャップの変動（感光体ドラム、現像スリーブの振れ）などが挙げられる。
従来から、これらの原因に対してはそれぞれ対策が施されているが、装置の大型化、コストアップを引き起こす結果となり現実的には難しい面がある。上記の原因を完全に解消するには、装置全体を強固に製作し、各部品の精度を向上させることなどが要求されるからである。
【０１５７】
本発明者らは、上記の実施例１〜８、比較例１〜１２の条件において、明度Ｌ＊＝５０となるような均一画像を２００ｌｐｉおよび２４０ｌｐｉで形成し、バンディングを目視評価する実験を行なった。実施例に記載の実験機を使用して上述のバンディング評価用の画像を出力した。この画像の評価を目視を以下の判定基準により評価した。
ランク５：２００ｌｐｉ、２４０ｌｐｉともにバンディングを知覚することができない。
ランク４：２００ｌｐｉでは知覚することができないが、２４０ｌｐｉではわずかに知覚することができる
ランク３：２００ｌｐｉでもわずかに知覚することができる。（２４０ｌｐｉでもわずかに知覚することができる）
ランク２：２００ｌｐｉでもはっきりと知覚することができる。（２４０ｌｐｉでもはっきりと知覚することができる）
ランク１：２００ｌｐｉにおいてもバンディングが非常に悪い。（２４０ｌｐｉにおいてもバンディングが非常に悪い。）
【０１５８】
発明者らは、バンディングは高線数ほど悪いことを見い出した。そこで、上述のような２００ｌｐｉの画像を中心とした判定基準を設定した。
【０１５９】
上記の判定基準を用いて実施例１〜８、比較例１〜１２のバンディングを評価した結果を下記に記す。中間調処理の線数としては、２００ｌｐｉ以上であれば、ほぼディザのテクスチャが知覚されることはなくなる。このため、上記判定基準のランク４以上をバンディングに関しての合格ラインと考える。
【０１６０】
実施例１：ランク４
実施例２：ランク５
実施例３：ランク５
実施例４：ランク４
実施例５：ランク４
実施例６：ランク５
実施例７：ランク５
実施例８：ランク４
比較例１：ランク３
比較例２：ランク２
比較例３：ランク３
比較例４：ランク２
比較例５：ランク３
比較例６：ランク１
比較例７：ランク２
比較例８：ランク２
比較例９：ランク２
比較例１０：ランク３
比較例１１：ランク３
比較例１２：ランク１
【０１６１】
実験結果から、上記条件を満たす画像形成装置は、バンディングが良好となることが分かった。すなわち良好な画像が得られることが分かった。
【０１６２】
γリニアリティは、前述のような階調性が良好であるような画像形成装置を実現するのみではなく、γリニアリティが０．９８以上である場合には、実験結果からわかるようにバンディングが実質的に知覚されることがない画像形成装置を実現できる。
【０１６３】
【発明の効果】
以上の説明から明らかなように、本発明によれば、高耐久性を有し、かつ、光書き込みの解像度が１２００ｄｐｉ以上で、入力画像に対して２００ｌｐｉ以上の線数によって中間調処理を施された画像データを、画質を落とさずに画像形成可能な画像形成装置を提供できる。
【図面の簡単な説明】
【図１】本発明による感光体の層構成例を示す。
【図２】本発明による感光体の別の層構成例を示す。
【図３】従来の画像形成装置の概略構成図である。
【図４】本発明による画像形成装置の概略構成例を示す。
【図５】図４の画像形成装置の光学ユニット構成例を示す。
【図６】入力データと明度（Ｌ＊）との関係を示す。
【図７】入力データと明度（Ｌ＊）との関係を示す。
【図８】ワイヤを使用したコロナ耐電装置の概略図である。
【図９】鋸歯状電極を使用したコロナ耐電装置の概略図である。
【図１０】接触耐電装置の概略図である。
【符号の説明】
１ 感光体ドラム
１ａ 感光体
１ｂ 導体
２ 帯電手段（帯電装置）
２ａ 弾性層
２ｂ 導体
３ 露光手段
４ 現像手段
５ 転写手段
６ 記録シート
７ クリーニング手段
８ 定着手段
３０ 電源
３１ 導電性支持体
３３ 中間層
３５ 電荷発生層
３７ 電荷輸送層
３９ 保護層
５１ ４ｃｈＬＤ（レーザダイオード）
５２ コリメートレンズ
５３ ＮＤフィルタ
５４ アパーチャー
５５ シリンダレンズ
５６ ポリゴンミラー
５７ ｆ−θレンズ１
５８ 折返しミラー１
５９ 折返しミラー２
６０ ｆ−θレンズ２
６１ 感光体面
６２ 同期検知板
８０ 帯電ケース
８１ グリッド
８２ ワイヤ（タングステン）
８３、８４ 電源
９０ 鋸歯状電極
９１ 支持部材
９２ 帯電ケース
９３ グリッド
９４、９５ 電源[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an image forming apparatus using an electrophotographic process such as an electrostatic copying machine or a laser printer, and more particularly to an image forming apparatus having a so-called fixing process for fixing a toner image onto a recording sheet (paper or the like).
[0002]
[Prior art]
In recent years, an image forming apparatus using an electrophotographic process as described above has become widespread. The image forming process of this image forming apparatus will be described below with reference to FIG.
As shown in FIG. 3, the image forming apparatus includes a photosensitive drum (1), a charging unit (charging device) (2), an exposure unit (3), a developing unit (4), a transfer unit (5), and a recording sheet. (6) having a cleaning means (7) and a fixing means (8); The photoreceptor drum (1) is formed by applying a photoreceptor on the surface of a conductor.
[0003]
The image forming apparatus rotates the photosensitive drum (1) in the direction of the arrow in FIG. 3 and repeats the following steps 1 to 6 to form a desired image on the recording sheet.
1. The charging means (2) charges the surface of the photoreceptor to a desired potential.
2. The exposure means (3) exposes the photoconductor to form an electrostatic latent image corresponding to a desired image on the photoconductor.
3. The developing means (4) develops the electrostatic latent image created by the exposure means with toner to form a toner image on the photoreceptor.
4). The transfer means (5) transfers the toner image on the photosensitive member onto a recording sheet (6) such as paper conveyed by a conveyance means (not shown).
5). A cleaning means (7) cleans the toner remaining on the photoreceptor.
6). Fixing means (8) heats the recording sheet to which the toner image has been transferred to fix the image on the recording sheet.
[0004]
As the charging means (2), generally, a corona charging device that charges the photoreceptor using corona discharge is used. FIG. 8 shows a schematic example of a corona charging device.
In the corona charging device as shown in FIG. 8, a wire (82) made of tungsten or the like and having a wire diameter of about 60 μm is usually used. The wire (82) is stretched in the axial direction of the photosensitive drum (1) at the center of the charging case (80), and a voltage (high voltage) of about −7 kV is applied. The charging case (80) is formed of stainless steel which is not easily oxidized. A grid (81) is stretched between the wire (82) and the photosensitive drum (1), and a voltage of about -0.6 kV is applied. The grid (81) is obtained by cutting a stainless steel plate having a thickness of about 0.1 mm into a mesh shape.
This corona charging device charges the photosensitive member as follows.
[0005]
Since the voltage is applied to the wire (82) as described above, a strong electric field is formed in the vicinity of the wire (82), air breakdown occurs, and ions are generated. Some of these ions move to the photoconductor side by the electric field between the wire and the photoconductor, and the surface of the photoconductor is charged. This phenomenon continues until the surface potential of the photoreceptor becomes substantially equal to the potential applied to the grid (81).
Therefore, the surface potential of the photoreceptor can be controlled by the potential applied to the grid.
[0006]
As another corona charging device, one using a sawtooth electrode as a discharge electrode is known (for example, see Patent Documents 1 and 2).
[0007]
FIG. 9 shows a schematic example of a corona charging device using a sawtooth electrode.
The sawtooth electrode (90) has a shape as shown in FIG. 9B, and is usually formed of a stainless steel plate having a thickness of about 0.1 mm. The pitch of the vertices is about 3 mm. The sawtooth electrode is fixed to the support member (91) as shown in FIG. 9A, and a voltage (high voltage) of about −5 kV is applied by the power source.
Similarly to the corona charging device shown in FIG. 8, this corona charging device is also covered with a charging case (92) formed of stainless steel or the like, and between the sawtooth electrode (90) and the photosensitive drum (1). The grid (93) is arranged. Then, similarly to the corona charging device shown in FIG. 8, corona discharge occurs near the apex of the sawtooth electrode (90), and the photosensitive member is charged.
In addition, an electrode having a needle-like (pin-like) discharge electrode has been proposed.
[0008]
The corona charging device using the sawtooth electrode has the advantage that it can be downsized and the generation of ozone is less than the corona charging device using the wire.
When the sawtooth electrode is employed, it is possible to give directionality to the corona discharge, so that the width of the charging device can be reduced. That is, since the ion flow toward the grid side (photoreceptor side) can be made larger than the ion flow toward the charging case side, the opening width of the charging case on the photoconductor side can be reduced. Thus, not only the charging device but also the image forming apparatus can be reduced in size.
Further, since the corona discharge has directionality, the charging efficiency of the photosensitive member is extremely good, and the current flowing through the corona charging device can be reduced. Therefore, the amount of ozone generated can be reduced.
[0009]
As the charging device (2), in addition to the corona charging device, a so-called contact charging device is also known. The contact charging device can improve the problem inherent to the corona charging device, in which a large amount of ozone is generated and the applied voltage is as large as 5 to 7 kV. For this reason, it is widely used in low- and medium-speed electrophotographic image forming apparatuses. (For example, refer to Patent Documents 3 and 4).
[0010]
A configuration example of the contact charging device is shown in FIG. As shown in FIG. 10, in the contact charging device, a charging member (2) is brought into contact with a photosensitive drum (1) as a member to be charged, and a voltage is applied to the charging member (2) to thereby apply a photosensitive member (1a). ) Is charged.
The charging member (2) usually takes the shape of a roller having a diameter of 5 to 20 mm and a length of about 300 mm, in which an elastic layer (2b) is formed on the conductor (2a). The charging member 2 contacts the rotated photosensitive drum (1) and rotates in a driven manner. The elastic layer (2b) usually has a resistivity of 10 ⁷ -10 ⁹ It is made of Ωcm material. A surface protective layer having a thickness of about 10 to 20 μm may be formed on the surface of the charging member (2) (the surface of the elastic layer (2b)).
The photosensitive drum (1) usually takes a roller shape having a diameter of 30 to 80 mm and a length of about 300 mm in which the photosensitive member (1b) is formed on the conductor (1a).
[0011]
The contact charging device applies a voltage to the charging member (2) by the power source (30) to charge the photoreceptor (1a). The applied voltage is usually -1.5 to -2.0 kV for direct current.
With such a configuration, the contact charging device uniformly charges the photoreceptor (1a) to −500 to −800V.
[0012]
An exposure unit in an image forming apparatus using an electrophotographic process performs light modulation with an LD (laser diode) corresponding to an output image. The laser light emitted from the LD is imaged on the photoreceptor via a collimating lens, an aperture, a cylindrical lens, a polygon mirror, an f-θ lens, and the like. The polygon mirror is a rotating polygon mirror, and reflects incident laser light so as to scan on the photosensitive member. (For example, see Patent Documents 5, 6, and 7.)
By adopting such a configuration, the exposure unit exposes the photoconductor to form an electrostatic latent image corresponding to a desired image on the photoconductor.
[0013]
As a photoreceptor of an image forming apparatus using an electrophotographic process, a so-called organic photoreceptor has become mainstream. The organic photoreceptor is mainly a laminated type in which a charge generation layer and a charge transport layer are laminated as a photosensitive layer on a conductive substrate. (For example, refer to Patent Documents 3, 4, 5, 7, and 8.)
[0014]
However, so-called film scraping occurs when the organic photoreceptor is repeatedly used. In particular, when the film of the photosensitive layer progresses, the charged potential of the photosensitive member decreases, the photosensitivity deteriorates, the background stains due to scratches on the surface of the photosensitive member, the image density decreases, and the image quality deteriorates. Therefore, the wear resistance of the photoreceptor is required.
In addition, due to the recent increase in the speed of electrophotographic apparatuses and the reduction in diameter of the photoreceptors accompanying the downsizing of the apparatus, the photoreceptors are required to have higher durability.
[0015]
On the other hand, in an image forming apparatus using an electrophotographic system, it is necessary to make the photoconductor film thickness small (thin) in order to make the developing electric field follow up to a high spatial frequency (for example, see Non-Patent Document 1).
However, when the photosensitive member film thickness is reduced, the durability against abrasion and scratches due to cleaning is deteriorated, and deterioration due to repeated charging and exposure processes is accelerated.
[0016]
Conventionally, in multilayer organic photoreceptors, polycarbonate is generally used as the binder resin for the charge transport layer, and the thickness of the charge transport layer is set to about 20 to 30 μm in order to improve wear resistance.
[0017]
[Patent Document 1]
JP-A-8-20210
[Patent Document 2]
JP-A-6-301286
[Patent Document 3]
JP-A-8-234455 (Page (5), right column, paragraph [0046])
[Patent Document 4]
JP 2000-206710 A (page (6), right column, paragraph [0046])
[Patent Document 5]
JP-A-9-319164 (page (3), right column to page (4), left column, paragraph [0014], page (3), left column, paragraph [0008]))
[Patent Document 6]
JP-A-10-171221
[Patent Document 7]
JP 11-95462 (right column of page (6), paragraph [0058])
[Patent Document 8]
JP-A-7-181705 (page (3), left column, paragraph [0010])
[Non-Patent Document 1]
“Basics and Applications of Electrophotographic Technology” Corona, p. 150-151
[0018]
[Problems to be solved by the invention]
On the other hand, when forming an image having a resolution of 1200 dpi or higher using a photoconductor having a charge transport layer of about 20 to 30 μm, the present inventors have a so-called high space such as one isolated dot or one dot line. I found out that the image of the frequency cannot be reproduced. That is, it has been found that an image forming apparatus having a charge transport layer as described above is virtually impossible to output a bitmap image or the like through (directly without image processing).
[0019]
In order to solve the above problem, the conventional image forming apparatus forms an image by reducing the resolution to 600 dpi, 400 dpi, or the like. However, in order to lower the resolution, the isolated 1 dot or 1 dot line becomes large, resulting in a rough image.
Further, in an image including so-called diagonal lines, jaggies are deteriorated due to a decrease in resolution, and image quality is deteriorated.
In addition, since the resolution of character images is usually 1200 dpi or higher, which enables identification of various fonts, it is extremely difficult to simultaneously reproduce a character image and isolated 1-dot and 1-dot lines. That is, there is a problem that the texture of the character image becomes rough.
[0020]
The present inventors further formed an image using a photoconductor having a charge transport layer of about 20 to 30 μm, and written the image data on which halftone processing was performed with a line number of 200 lpi or more. It has been found that only an image with extremely poor gradation can be formed. On the other hand, when the halftone processing is less than 200 lpi, although the gradation is ensured, there is a problem that the texture of the dither is perceived visually and a fine image cannot be obtained. Further, it has been found that when halftone processing of 200 lpi or more is performed, so-called banding is likely to occur and only a noisy image can be obtained.
[0021]
The present invention has been made in view of the above-described problems, has high durability, and has a halftone process with a resolution of optical writing of 1200 dpi or higher and / or a line number of 200 lpi or higher for an input image. An object of the present invention is to provide an image forming apparatus capable of forming an image of the image data subjected to the processing without degrading the image quality.
[0022]
[Means for Solving the Problems]
In order to achieve the above object, an invention of an image forming apparatus according to claim 1 is an image forming apparatus that includes a charging unit, a photosensitive member, and an optical writing unit, and forms an image having a resolution of at least 1200 dpi. The optical writing means emits a laser beam having a beam diameter of 35 μm or less, and the photosensitive member is provided with a charge generation layer containing at least a charge generation material and a charge transport layer containing a charge transport material on a conductive support. A protective layer is provided on the surface side of the photoreceptor from the charge generation layer and the charge transport layer, and the protective layer has a transmittance of 90% or more for the laser beam light. And a film thickness is 5-10 micrometers, The total thickness of the charge transport layer and the protective layer is 20 μm or less.
[0023]
According to a second aspect of the present invention, there is provided an image forming apparatus comprising: an image processing unit that performs halftone processing on an input image; a charging unit; a photoconductor; and an optical writing unit. An image forming apparatus for performing halftone processing on an image with a line number of 200 lpi or more, wherein the light writing means emits a laser beam having a beam diameter of 35 μm or less, and the photosensitive member is placed on a conductive support. A charge generation layer containing at least a charge generation material and a charge transport layer containing a charge transport material are provided, and a protective layer is provided on the photoreceptor surface side of the charge generation layer and the charge transport layer. When the laser beam transmittance is 90% or more And a film thickness is 5-10 micrometers, The total thickness of the charge transport layer and the protective layer is 20 μm or less.
[0024]
According to a third aspect of the present invention, in the image forming apparatus according to the first or second aspect, the protective layer contains a filler, a charge transport material and / or a binder resin.
[0025]
According to a fourth aspect of the present invention, in the image forming apparatus of the third aspect, the filler has a refractive index of 1.0 to 2.0.
[0026]
According to a fifth aspect of the present invention, in the image forming apparatus according to the third or fourth aspect, at least an inorganic pigment is employed as the filler.
[0027]
According to a sixth aspect of the present invention, in the image forming apparatus according to any one of the third to fifth aspects, at least a metal oxide is employed as the filler.
[0029]
Claim 7 The invention described in claims 1 to 6 In any one of the image forming apparatuses, the protective layer contains an inorganic pigment and / or a metal oxide that has been surface-treated with at least one surface treatment agent.
[0030]
Claim 8 The invention described in claims 1 to 6 In any one of the image forming apparatuses, the protective layer contains at least an inorganic pigment and / or a metal oxide surface-treated with a titanate coupling agent, a higher fatty acid and / or a higher fatty acid metal salt. And
[0031]
Claim 9 The described invention is claimed. 7 Or 8 In the item image forming apparatus, the inorganic pigment and / or the metal oxide is surface-treated with a surface treatment amount of 2 to 30 wt%.
[0032]
Claim 10 The invention described in claims 1 to 9 In the image forming apparatus, the protective layer has an acid value of 10 to 400 (mgKOH / g). resin It contains the binder resin containing this.
[0033]
Claim 11 The invention described in claims 1 to 10 In any of the image forming apparatuses, the protective layer contains a dispersant, and the dispersant is an organic compound containing at least one carboxyl group in the structure.
[0034]
Claim 12 The described invention is claimed. 11 In the image forming apparatus, the dispersant is a polycarboxylic acid derivative.
[0035]
Claim 13 The described invention is claimed. 11 Or 12 In the image forming apparatus, the dispersant is an organic compound having an acid value of 10 to 400 (mgKOH / g).
[0036]
Claim 14 The described invention is claimed. 11 Thru 13 In any of the image forming apparatuses, the amount of the dispersant added is selected from the amounts satisfying the following formula.
0.1 ≦ (addition amount of dispersing agent × acid value of dispersing agent) / (addition amount of filler) ≦ 20
[0037]
Claim 15 The invention described in claims 1 to 14 In any of the image forming apparatuses, the maximum electric field strength applied by the charging means to the charge transport layer and the protective layer is -30 V / μm.
[0038]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an image forming apparatus according to the present invention will be described in detail by embodiments.
[0039]
The first image forming apparatus according to the present invention includes at least a charging unit, a photoreceptor, and an optical writing unit.
The optical writing means performs optical writing with a laser beam having a beam diameter of 35 μm or less on the charging means and the photosensitive member to form an electrostatic latent image on the photosensitive member. The optical writing resolution is 1200 dpi or more.
The beam diameter is 1 / e of the maximum value of the light intensity profile expressed by a Gaussian function. ² It is the diameter at the place. The beam diameter is measured with a beam scanning device manufactured by PHOTON.
In the photoreceptor, at least a charge generation layer and a charge transport layer are formed on a conductive support. Preferably, a charge transport layer is formed on the charge generation layer. A protective layer is provided above the charge generation layer and the charge transport layer.
The charge generation layer contains a charge generation material. The charge transport layer contains a charge transport material. The protective layer has a transmittance of 90% or more for the laser beam light from the optical writing means. The total thickness of the charge transport layer and the protective layer is 20 μm or less.
In addition, layers other than these may be provided in arbitrary places.
Further, the upper side of the photoconductor means a direction outside the photoconductor with respect to the conductive support.
[0040]
The second image forming apparatus according to the present invention is different from the first image forming apparatus in the following points.
An image processing unit that performs halftone processing on the input image is provided.
The image processing means performs halftone processing with a line number of 200 lpi or more.
-There is no limitation on the resolution of the optical writing means.
[0041]
The electric resistance means, the optical writing means, and the image processing means may each employ a known electric resistance means, optical writing means, and image processing means that can realize at least the performance described above.
The first and second image forming apparatuses only need to adopt the above configuration. In addition, it is free to employ other configurations.
Next, the photoconductor will be described in detail.
[0042]
<Photoconductor: Electrophotographic photoconductor>
FIG. 1 shows an example of the layer structure of the photoreceptor of the present invention. As shown in FIG. 1, the photoconductor is formed by sequentially laminating a charge generation layer (35), a charge transport layer (37), and a protective layer (39) on at least a conductive support (31) (photoreceptor surface side). Has a structured.
The charge generation layer (35) is mainly composed of a charge generation material.
The charge transport layer (37) contains a charge transport material as a main component.
The protective layer (39) contains at least a charge transport material, and preferably contains a filler and / or a dispersant.
The photoconductor is not limited to the configuration shown in FIG. 1, and an arbitrary layer can be provided at an arbitrary location. For example, as shown in FIG. 2, an intermediate layer (33) may be provided between the conductive support (31) and the charge generation layer (35).
[0043]
(Conductive support)
A well-known thing can be employ | adopted for an electroconductive support body (31). Preferably, the volume resistance is 10 ¹⁰ A material obtained by processing a material having conductivity of Ω · cm or less into a cylindrical shape is employed. Examples of the materials include metals such as aluminum, nickel, chromium, nichrome, copper, gold, silver, and platinum and / or metal oxides such as tin oxide and indium oxide. Alternatively, a material covered with cylindrical plastic or paper can be used. In addition, a tube made of aluminum, aluminum alloy, nickel, stainless steel, or the like is formed into a raw tube by a method such as extrusion / pulling, and then a surface-treated tube such as cutting, superfinishing, or polishing can be used. Further, an endless nickel belt and an endless stainless steel belt disclosed in JP-A-52-36016 can also be used as the conductive support (31).
[0044]
In addition, the conductive support (31) is formed by dispersing conductive powder in a suitable binder resin on a cylindrical support and coating the conductive support, preferably the above volume. Those satisfying the resistance condition can also be adopted.
Examples of the conductive powder include metal powders such as aluminum, nickel, iron, nichrome, copper, zinc, and silver, metal oxide powders such as conductive tin oxide and ITO, carbon black, and acetylene black. These 1 type (s) or 2 or more types can be employ | adopted suitably.
The binder resin is polystyrene, styrene-acrylonitrile copolymer, styrene-butadiene copolymer, styrene-maleic anhydride copolymer, polyester, polyvinyl chloride, vinyl chloride-vinyl acetate copolymer, polyvinyl acetate, poly Vinylidene chloride, polyarylate resin, phenoxy resin, polycarbonate, cellulose acetate resin, ethyl cellulose resin, polyvinyl butyral, polyvinyl formal, polyvinyl toluene, poly-N-vinylcarbazole, acrylic resin, silicone resin, epoxy resin, melamine resin, urethane resin, Examples thereof include thermoplastic resins such as phenol resins and alkyd resins, thermosetting resins, and photocurable resins. These materials may be used alone or in combination of two or more.
As the solvent or dispersion medium for forming the conductive layer, for example, tetrahydrofuran, dichloromethane, methyl ethyl ketone, toluene and the like can be employed.
[0045]
The conductive support (31) is also formed on a material such as polyvinyl chloride, polypropylene, polyester, polystyrene, polyvinylidene chloride, polyethylene, chlorinated rubber and / or Teflon (registered trademark) on a suitable cylindrical substrate. It is also possible to preferably employ a conductive layer provided by covering a heat-shrinkable tube containing a conductive powder.
[0046]
(Charge generation layer)
The charge generation layer (35) is a layer mainly composed of a charge generation material. It can be formed by dispersing or dissolving the charge generation layer (35) forming material in a suitable solvent, applying the dispersion or solution onto the conductive support (31) and drying. In addition, when the other layer (undercoat layer etc.) is provided on the electroconductive support body (31), the said dispersion liquid or solution is apply | coated on another layer.
[0047]
A known charge generation material may be used as the charge generation material. For example, phthalocyanine pigments such as titanyl phthalocyanine, vanadyl phthalocyanine, copper phthalocyanine, hydroxygallium phthalocyanine, and metal-free phthalocyanine, monoazo pigments, disazo pigments, asymmetric disazo pigments, trisazo pigments and other azo pigments, perylene pigments, perinone pigments, indigo Known materials such as pigments, pyrrolopyrrole pigments, anthraquinone pigments, quinacridone pigments, quinone condensed polycyclic compounds, squalium pigments, and the like are useful. These charge generating materials can be used alone or in combination of two or more.
[0048]
A binder resin is used for the charge generation layer (35) as necessary.
Examples of the binder resin include polyamide, polyurethane, epoxy resin, polyketone, polycarbonate, silicone resin, acrylic resin, polyvinyl butyral, polyvinyl formal, polyvinyl ketone, polystyrene, polysulfone, poly-N-vinylcarbazole, polyacrylamide, and polyvinyl benzine. Examples thereof include saar, polyester, phenoxy resin, vinyl chloride-vinyl acetate copolymer, polyvinyl acetate, polyphenylene oxide, polyamide, polyvinyl pyridine, cellulose resin, casein, polyvinyl alcohol, polyvinyl pyrrolidone and the like. These may be used alone or in combination of two or more.
The amount of the binder resin is suitably more than 0 and 500 parts by weight or less, preferably 10 or more and 300 parts by weight or less with respect to 100 parts by weight of the charge generation material.
The binder resin may be added before or after dispersion.
[0049]
As the solvent or dispersion medium for forming the charge generation layer (35), for example, isopropanol, acetone, methyl ethyl ketone, cyclohexanone, tetrahydrofuran, dioxane, ethyl cellosolve, ethyl acetate, methyl acetate, dichloromethane, dichloroethane, monochlorobenzene, cyclohexane, toluene , Xylene, ligroin and the like, and ketone solvents, ester solvents, and ether solvents are particularly preferably used. These may be used alone or in combination of two or more.
[0050]
The charge generation layer (35) may further contain additives such as a sensitizer, a dispersant, a surfactant, and silicone oil. Additives include all known additives.
[0051]
As a coating method of the charge generation layer (35), a dip coating method, spray coating, beat coating, nozzle coating, spinner coating, ring coating, or the like can be used. For example, the charge generating material is dispersed in a suitable solvent together with a binder resin as necessary using a ball mill, attritor, sand mill, ultrasonic wave, etc., and this is applied onto a conductive support and dried. A charge generation layer (35) may be formed.
The film thickness of the charge generation layer (35) is suitably about 0.01 to 5 μm, preferably 0.1 to 2 μm.
[0052]
(Charge transport layer)
The charge transport layer (37) contains a charge transport material. Further, if necessary, additives such as one or two or more kinds of plasticizers, leveling agents, antioxidants, and lubricants can be contained.
[0053]
Charge transport materials are classified into hole transport materials and electron transport materials.
Examples of the electron transport material include chloroanil, bromanyl, tetracyanoethylene, tetracyanoquinodimethane, 2,4,7-trinitro-9-fluorenone, 2,4,5,7-tetranitro-9-fluorenone, 2, 4,5,7-tetranitroxanthone, 2,4,8-trinitrothioxanthone, 2,6,8-trinitro-4H-indeno [1,2-b] thiophen-4-one, 1,3,7- Examples thereof include trinitrodibenzothiophene-5,5-dioxide, benzoquinone derivatives and the like.
Examples of hole transport materials include poly-N-vinylcarbazole and derivatives thereof, poly-γ-carbazolylethyl glutamate and derivatives thereof, pyrene-formaldehyde condensates and derivatives thereof, polyvinylpyrene, polyvinylphenanthrene, polysilane, oxazole derivatives, Oxadiazole derivatives, imidazole derivatives, monoarylamine derivatives, diarylamine derivatives, triarylamine derivatives, stilbene derivatives, α-phenylstilbene derivatives, benzidine derivatives, diarylmethane derivatives, triarylmethane derivatives, 9-styrylanthracene derivatives, pyrazolines Derivatives, divinylbenzene derivatives, hydrazone derivatives, indene derivatives, butadiene derivatives, pyrene derivatives, bisstilbene derivatives, enamine derivatives, etc. Other known materials may be used. These charge transport materials may be used alone or in combination of two or more.
[0054]
The charge transport layer (37) may contain a binder resin. The binder resin is polystyrene, styrene-acrylonitrile copolymer, styrene-butadiene copolymer, styrene-maleic anhydride copolymer, polyester, polyvinyl chloride, vinyl chloride-vinyl acetate copolymer, polyvinyl acetate, poly Vinylidene chloride, polyarylate, phenoxy resin, polycarbonate, cellulose acetate resin, ethyl cellulose resin, polyvinyl butyral, polyvinyl formal, polyvinyl toluene, poly-N-vinylcarbazole, acrylic resin, silicone resin, epoxy resin, melamine resin, urethane resin, phenol Examples thereof include thermoplastic or thermosetting resins such as resins and alkyd resins. These may be used alone or in combination of two or more.
[0055]
Examples of the solvent or dispersion medium used for forming the charge transport layer (37) include tetrahydrofuran, dioxane, toluene, dichloromethane, monochlorobenzene, dichloroethane, cyclohexanone, methyl ethyl ketone, and acetone. These may be used alone or in combination of two or more.
[0056]
The charge transport layer (37) can be formed by dissolving or dispersing a charge transport layer-forming material containing a charge transport material in a solvent or dispersion medium, and applying and drying this on the charge generation layer (35). In addition, when another layer is provided on the charge generation layer (35), it is coated on this other layer.
[0057]
The film thickness of the charge transport layer (37) is set to 20 μm or less together with the film thickness of the protective layer (39) from the viewpoint of resolution. The lower limit varies depending on the system to be used (particularly the charging potential), but is preferably 5 μm or more. Further, it is preferable that the total thickness of the charge transport layer (37) and all the layers provided above the charge transport layer (37) is 20 μm or less.
[0058]
(Protective layer)
The protective layer (39) is provided above the charge transport layer (37). In addition, a filler, a binder resin, and the like are appropriately contained for the purpose of improving the durability of the photoreceptor. Moreover, it is preferable to contain a charge transport layer.
Further, the transmittance with respect to light (writing light) from the optical writing means is set to 90% or more. The present inventors have found that when the transmittance is less than 90%, the reproducibility of the written dot in the latent image is lowered and the image quality is lowered. In addition, the transmittance | permeability uses the coating film which applied the protective layer on highly transparent films, such as PET, when the peeling is impossible when the protective layer (39) is peelable. The transmittance was determined by measuring the transmittance with a spectrophotometer using an integrating sphere.
[0059]
(Filler)
The protective layer (39) preferably contains a filler material for the purpose of improving the wear resistance of the photoreceptor.
A filler having a refractive index of 1.0 or more and 2.0 or less is preferably employed. When the refractive index is less than 1.0 or greater than 2.0, the light transmittance of the protective layer (39) is lowered, the reproducibility of the writing dot latent image is lowered, and the image quality is lowered. . The refractive index of the filler was determined from the refractive index of the liquid in which the filler particles were immersed in a liquid in which the value of the refractive index could be changed little by little and the particle interface became unclear. The refractive index of the liquid was determined with an Abbe refractometer.
[0060]
Fillers are classified into organic fillers and inorganic fillers.
Examples of the organic filler material include fluorine resin fine particles such as polytetrafluoroethylene, silicone resin fine particles, and a-carbon powder. These may be used alone or in combination of two or more.
Inorganic filler materials are metal powders such as copper, tin, aluminum, indium, silica, tin oxide, zinc oxide, titanium oxide, alumina, zirconium oxide, indium oxide, antimony oxide, bismuth oxide, calcium oxide, antimony-doped oxide Examples thereof include metal oxides such as tin and tin-doped indium oxide, metal fluorides such as tin fluoride, calcium fluoride, and aluminum fluoride, and inorganic materials such as potassium titanate and boron nitride. These may be used alone or in combination of two or more.
An inorganic filler having a hardness advantageous for improving the wear resistance of the photoreceptor is preferably used.
[0061]
A filler having high electrical insulation is preferably used because image blurring hardly occurs. As such fillers, those having a pH of 5 or more of the aqueous dispersion of the filler are particularly effective, and titanium oxide, alumina, zinc oxide, zirconium oxide and the like are preferably used. The pH is measured by dispersing the filler in water and measuring the pH. Specifically, it was carried out according to JIS K 5101/24.
[0062]
The hexagonal close-packed α-type alumina has the highest insulating properties among the fillers described above, has high thermal stability, and high wear resistance, so that the occurrence of image blur can be extremely reduced and the photoconductor can be used. Since extremely high abrasion resistance can be provided, it is particularly preferably employed.
[0063]
The average primary particle size of the filler is preferably 0.01 to 0.5 μm, which is a size that ensures sufficient light transmittance of the protective layer (39) and imparts good wear resistance to the photoreceptor. adopt. When the average primary particle size of the filler is 0.01 μm or less, wear resistance is reduced due to aggregation, dispersibility, and the like. When the thickness is 0.5 μm or more, the sedimentation property of the filler is promoted, or an abnormal image may be generated in an image obtained by a photoconductor produced using the filler.
[0064]
In order to improve the dispersibility, a filler that has been surface-treated with at least one surface treatment agent is preferably used. A filler with low dispersibility increases the residual potential of the photoreceptor, decreases the transparency of the coating film, generates coating film defects, decreases wear resistance, and increases uneven wear. That is, it becomes a factor that hinders the high durability and high image quality of the image forming apparatus.
As the surface treatment agent, any of the conventionally used surface treatment agents may be used, but those capable of maintaining the insulating properties of the filler are preferred. For example, titanate coupling agents, aluminum coupling agents, zircoaluminate coupling agents, metal salts such as higher fatty acids and aluminum stearate, etc., or mixed treatments thereof, Al ₂ O ₃ TiO ₂ , ZrO ₂ , Silicone, aluminum stearate, or the like, or a mixed treatment solution thereof is preferably used from the viewpoint of filler dispersibility and image blur prevention. Treatment with only the silane coupling agent causes image blurring especially at high temperatures and high humidity, but it effectively suppresses the occurrence of image blurring by mixing the surface treatment agent with the silane coupling agent. it can. The amount of the surface treatment agent used varies depending on the average primary particle size of the filler, but generally, an amount of 2 to 30 wt% is suitable for the filler, and an amount of 3 to 20 wt% is more preferable. If the surface treatment amount is less than this, the filler dispersion effect cannot be obtained, and if it is too much, the residual potential is increased. Even when the filler has low insulation and image blur is likely to occur, the filler can be surface-treated to increase insulation and reduce the influence of image blur.
[0065]
Since the protective layer (39) contains a filler, it can realize high durability and suppression of image blur at high temperature and high humidity, but may increase the residual potential.
In order to suppress this, an organic compound having a carboxyl group in the structure may be employed as the dispersion medium. Such a dispersion medium improves the dispersibility of the filler and reduces charge trap sites.
In order to reduce the residual potential, a dispersion medium having an acid value of 10 to 400 (mg KOH / g) is preferably employed. Of these, polycarboxylic acid derivatives are particularly preferably used. The acid value is the number of milligrams of potassium hydroxide required to neutralize free fatty acids contained in 1 g.
Moreover, even if the acid value of the dispersing agent is not in the range of 10 to 400 (mgKOH / g), a mixture of a resin or additive having an acid value of 10 to 400 (mgKOH / g) may be adopted. Good. As such a resin or additive, for example, an organic fatty acid, a high acid value resin, or the like can be employed.
[0066]
As the dispersant (dispersion medium) used for forming the protective layer (39), any known dispersant may be used, but an organic compound having a structure containing at least one carboxyl group in the polymer or copolymer. Is preferably used, and a polycarboxylic acid derivative that improves dispersibility is particularly preferably used.
The carboxylic acid site in the dispersing agent plays an important role of imparting an acid value and enhancing dispersibility. The hydrophilic inorganic filler has a low affinity with an organic solvent or a binder resin, and as such is not dispersed well by any dispersing means. In contrast, the dispersant has a high affinity with the inorganic filler at the carboxylic acid site, and a high affinity with the binder resin or organic solvent at the other polymer sites. Affinity with resin and the like can be increased. This makes it possible to greatly increase the dispersibility of the filler.
The dispersant is effective even if it has one carboxyl group, but the polycarboxylic acid derivative having more carboxyl groups improves the dispersibility of the filler and reduces the residual potential. Etc. are effective. Not only the affinity between the dispersant and the filler is further increased, but also by having an affinity between the dispersants, the dispersibility of the filler is improved, and at the same time, the effect is maintained and the sedimentation property of the filler is suppressed. This is because an effect can be obtained.
[0067]
The acid value of the dispersant is preferably 10 to 400 mgKOH / g, more preferably 30 to 200 mgKOH / g. If the acid value is higher than necessary, the influence of image blur will appear, and if the acid value is too low, the amount added must be increased, and the residual potential reduction effect will be insufficient. It is necessary to determine the acid value of the dispersant by a balance with the amount added. The acid value of the dispersant does not directly affect the residual potential reduction effect, but is influenced by the structure, molecular weight, filler type, and dispersibility of the dispersant used. In some cases, the effect of reducing the residual potential may be increased by mixing these materials with organic fatty acids and the like.
Further, since the vicinity of the interface between the protective layer (39) and the charge transport layer (37) has a large influence on the residual potential, the protective layer (39) is more protective layer (39) / photosensitive layer than the photosensitive member surface side. It is preferable to contain a material having a high acid value near the interface of (charge transport layer (37)) to suppress an increase in residual potential.
[0068]
The addition amount of the dispersant preferably satisfies the following relational expression.
0.1 ≦ (addition amount of dispersing agent × acid value of dispersing agent) / (addition amount of filler) ≦ 20
In particular, in the above relational expression, it is preferable to set the required minimum amount.
If the added amount is increased more than necessary, the effect of image blur may appear, and if the added amount is too small, the effect of improving the dispersibility and reducing the residual potential cannot be sufficiently exerted, resulting in the occurrence of abnormal images. Become.
[0069]
(Binder resin)
The protective layer (39) can contain a binder resin.
As the binder resin, the binder resin used for the charge transport layer (37) can be used, but one that does not adversely affect the filler dispersibility is appropriately selected and preferably employed.
In addition, the binder resin having an acid value is useful for reducing the residual potential, and such a binder resin is used alone or in combination with other binder resins.
Examples of the binder resin preferably used for the protective layer (39) include polyester, polycarbonate, acrylic resin, polyethylene terephthalate, polybutylene terephthalate, various copolymers using acrylic acid and methacrylic acid, and styrene acrylic copolymer. Polymer, Polyarylate, Polyacrylate, Polystyrene, Epoxy resin, ABS resin, ACS resin, Olefin-vinyl monomer copolymer, Chlorinated polyether, Aryl resin, Phenol resin, Polyacetal, Polyamide, Polyamideimide, Polyallylsulfone, Polybutylene , Polyethersulfone, polyethylene, polyimide, polymethylbenten, polypropylene, polyphenylene oxide, polysulfone, AS resin, butadiene-styrene copolymer, polyurethane, polysalt Vinyl resin or a copolymer of polyvinylidene chloride and the like. These materials can be used in combination of two or more.
[0070]
The binder resin has a great influence on image blur. Since the binder resin having high NOx resistance or ozone resistance effectively suppresses image blurring and improves the wear resistance of the photoreceptor, a high-quality image can be provided over a long period of time. As such a binder resin, a polymer alloy is particularly effective, and at least a polymer alloy with polyethylene terephthalate has a high image blur suppression effect and is useful.
[0071]
(Charge transport layer)
It is preferable that the protective layer (39) contains a charge transport material because the residual potential of the photoreceptor can be lowered. As the charge transport material contained in the protective layer (39), a charge transport material usable for the charge transport layer (37) can be used.
In addition, you may employ | adopt the substance different from the charge transport material contained in a charge transport layer (37). In particular, if a material having an ionization potential lower than that of the charge transport material contained in the charge transport layer (37) is adopted, the charge injection property at the interface of the charge transport layer (37) / protective layer (39) can be improved. This is very effective in reducing the residual potential. The ionization potential can be measured using various methods such as a method for obtaining spectroscopically and a method for obtaining electrochemically.
[0072]
Furthermore, if the concentration distribution of the charge transport material is made the lowest in the outermost surface region of the protective layer (39), the influence of image quality deterioration due to NOx or ozone gas can be reduced without greatly affecting the residual potential. It becomes possible. In particular, if the concentration of the charge transport material is set continuously low from the interface of the protective layer (39) / photosensitive layer (charge transport layer (37)) to the outermost surface side of the protective layer (39), the residual potential rises extremely. It can be effectively suppressed. Image quality degradation is considered to be one of the causes of charge transport materials being decomposed and altered, and the effect can be reduced by reducing the concentration of charge transport materials contained in the protective layer. It is.
[0073]
As the charge transport material, a polymer charge transport material having a function of a binder resin is also preferably used. The protective layer (39) containing the polymer charge transport material is extremely excellent in wear resistance.
As the polymer charge transporting material, any one or more of known materials can be used, and in particular, a polycarbonate containing a triarylamine structure in the main chain and / or side chain is preferably used. Among these, polymer charge transport materials represented by the following chemical formulas (I) to (X) are preferably used. A polymer charge transport material may be employed in the charge transport layer (37).
[0074]
[Chemical 1]

[0075]
In the above formula (I), R ₁ , R ₂ , R ₃ Are substituted or unsubstituted alkyl groups or halogen atoms, which may be the same or different from each other: R ₄ Is a hydrogen atom or a substituted or unsubstituted alkyl group: R ₅ , R ₆ Are substituted or unsubstituted aryl groups, which may be the same or different from each other: o, p, and q may be different from each other; integers from 0 to 4: k and j represent compositions; k ≦ 1, 0 ≦ j ≦ 0.9: n represents the number of repeating units, and is an integer of 5 to 5000: X is an aliphatic divalent group, a cycloaliphatic divalent group, or the following general formula (2) The divalent group represented is represented.
[0076]
[Chemical 2]

[0077]
In the above formula (2), R ₁₀₁ , R ₁₀₂ Represents a substituted or unsubstituted alkyl group, an aryl group or a halogen atom, which may be the same or different. l and m represent an integer of 0 to 4; Y represents a single bond, a linear, branched or cyclic alkylene group having 1 to 12 carbon atoms, —O—, —S—, —SO—, —SO. ₂ —, —CO—, —CO—O—Z—O—CO— (Z represents an aliphatic divalent group), or a structure represented by the following formula (3).
[0078]
[Chemical 3]

[0079]
(In the above formula (3), a is an integer of 1 to 20, b is an integer of 1 to 2000, R ₁₀₃ , R ₁₀₄ Represents a substituted or unsubstituted alkyl group or aryl group. R ₁₀₁ , R ₁₀₂ , R ₁₀₃ , R ₁₀₄ May be the same or different. )
[0080]
[Formula 4]

[0081]
In the above formula (II), R ₇ , R ₈ Are substituted or unsubstituted aryl groups, each of which may be the same or different: Ar ₁ , Ar ₂ , Ar ₃ Represents an arylene group. Each may be the same or different. X, k, j and n are the same as in the above formula (I).
[0082]
[Chemical formula 5]

[0083]
In the above formula (III), R ₉ , R ₁₀ Are substituted or unsubstituted aryl groups, each of which may be the same or different: Ar ₄ , Ar ₅ , Ar ₆ Represents an arylene group, which may be the same or different. X, k, j and n are the same as in the above formula (I).
[0084]
[Chemical 6]

[0085]
In the above formula (IV), R ₁₁ , R ₁₂ Are substituted or unsubstituted aryl groups, each of which may be the same or different: Ar ₇ , Ar ₈ , Ar ₉ Are arylene groups, which may be the same or different. X, k, j and n are the same as in the above formula (I).
[0086]
[Chemical 7]

[0087]
In the above formula (V), R ₁₃ , R ₁₄ Are substituted or unsubstituted aryl groups, each of which may be the same or different: Ar ₁₀ , Ar ₁₁ , Ar ₁₂ Are arylene groups, which may be the same or different. : X ₁ , X ₂ Represents a substituted or unsubstituted ethylene group or a substituted or unsubstituted vinylene group, which may be the same or different. X, k, j and n are the same as in the above formula (I).
[0088]
[Chemical 8]

[0089]
In the above formula (VI), R ₁₅ , R ₁₆ , R ₁₇ , R ₁₈ Are substituted or unsubstituted aryl groups, each of which may be the same or different: Ar ₁₃ , Ar ₁₄ , Ar ₁₅ , Ar ₁₆ Are arylene groups, which may be the same or different. : Y ₁ , Y ₂ , Y ₃ Represents a single bond, a substituted or unsubstituted alkylene group, a substituted or unsubstituted cycloalkylene group, a substituted or unsubstituted alkylene ether group, an oxygen atom, a sulfur atom, or a vinylene group, which may be the same or different. X, k, j and n are the same as in the above formula (I).
[0090]
[Chemical 9]

[0091]
In the above formula (VII), R ₁₉ , R ₂₀ Represents a hydrogen atom, a substituted or unsubstituted aryl group, and R ₁₉ And R ₂₀ May form a ring. Each may be the same or different. Ar ₁₇ , Ar ₁₈ , Ar ₁₉ Represents an arylene group. Each may be the same or different. X, k, j and n are the same as in the above formula (I).
[0092]
Embedded image

[0093]
In the above formula (VIII), R ₂₁ Is a substituted or unsubstituted aryl group, Ar ₂₀ , Ar ₂₁ , Ar ₂₂ , Ar ₂₃ Represents an arylene group. Each may be the same or different. X, k, j and n are the same as in the above formula (I).
[0094]
Embedded image

[0095]
In the above formula (IX), R ₂₂ , R ₂₃ , R ₂₄ , R ₂₅ Are substituted or unsubstituted aryl groups which may be the same or different. Ar ₂₄ , Ar ₂₅ , Ar ₂₆ , Ar ₂₇ , Ar ₂₈ Represents an arylene group. Each may be the same or different. X, k, j and n are the same as in the above formula (I).
[0096]
Embedded image

[0097]
In the above formula (X), R ₂₆ , R ₂₇ Are substituted or unsubstituted aryl groups which may be the same or different. Ar ₂₉ , Ar ₃₀ , Ar ₃₁ Represents an arylene group. Each may be the same or different. X, k, j and n are the same as in the above formula (I).
[0098]
The protective layer (39) can be formed by dissolving or dispersing the protective layer-forming material in a solvent or dispersion medium, applying the material on the charge transporting layer (37), and drying. In addition, when another layer is provided on the charge transport layer (37), it is coated on this layer.
The filler material can be dispersed by using a conventional method such as a ball mill, attritor, sand mill, or ultrasonic wave together with at least an organic solvent and, if necessary, a dispersant. As the material of the media used, conventionally used media such as zirconia, alumina, and agate can be used, but it is more preferable to use alumina from the viewpoint of filler dispersibility and residual potential reduction effect. Α-type alumina having excellent wear resistance is particularly preferable. Zirconia has a large amount of media wear at the time of dispersion, and not only does the residual potential increase significantly due to the mixing of these media, but also the dispersibility decreases due to the mixing of the wear powder, and the sedimentation of the filler significantly decreases. On the other hand, when alumina is used as the medium, the wear amount of the medium during dispersion can be kept low, and the influence of the mixed wear powder on the residual potential is very small. Even if wear powder is mixed, the influence on dispersibility is small compared to other media. Therefore, it is more preferable to use alumina as a medium used for dispersion.
[0099]
The dispersant is preferably added before the dispersion together with the filler and the organic solvent, since it suppresses the aggregation of the filler in the coating liquid and further suppresses the sedimentation property of the filler and remarkably improves the dispersibility of the filler.
On the other hand, the binder resin and the charge transport material can be added before the dispersion, but in that case, the dispersibility is slightly lowered. Therefore, the binder resin and the charge transport material are preferably added after being dispersed in a state dissolved in an organic solvent.
[0100]
As a dispersion or solution coating method, conventional coating methods such as dip coating, spray coating, beat coating, nozzle coating, spinner coating, ring coating, etc. can be used. In order to form a film with good filler dispersibility, spray coating is most suitable.
[0101]
The film thickness of the entire protective layer (39) is 5 μm-10μ m Is appropriate. In any case, the thickness of the protective layer (39) is preferably 20 μm or less in combination with the thickness of the charge transport layer (37) as described above.
When the thickness of the protective layer (39) is extremely thin, the uniformity of the film may be reduced or sufficient wear resistance may not be obtained. When the thickness is extremely thick, the residual potential The effect of the increase may increase or the resolution and dot reproducibility may decrease due to a decrease in light transmittance.
[0102]
(Other layers)
The photoconductor can be provided with an arbitrary layer at an arbitrary position. This layer can be provided by a method similar to the coating method of the charge generation layer (35), the charge transport layer (37), and the protective layer (39).
[0103]
An intermediate layer (33) can be provided between the conductive support (31) and the charge generation layer (35).
The intermediate layer (33) generally contains a resin as a main component. However, since these resins are coated with a photosensitive layer thereon, it is desirable that the intermediate layer (33) be a resin having high solvent resistance against an organic solvent. Examples of such resins include water-soluble resins such as polyvinyl alcohol, casein, and sodium polyacrylate, alcohol-soluble resins such as copolymer nylon and methoxymethylated nylon, polyurethane, melamine resin, phenol resin, alkyd-melamine resin, and epoxy. Examples thereof include a curable resin that forms a three-dimensional network structure such as a resin. These may be used alone or in combination of two or more.
[0104]
Further, when the undercoat layer is provided as described above, for example, a metal oxide that can be exemplified by titanium oxide, silica, alumina, zirconium oxide, tin oxide, indium oxide, etc. in order to prevent moire and reduce residual potential. It is preferable to contain a fine powder pigment in the undercoat layer. Moreover, a silane coupling agent, a titanium coupling agent, a chromium coupling agent, etc. can also be used. Further, various dispersants may be added. In addition, Al ₂ O ₃ Anodic oxidation, organic materials such as polyparaxylylene (parylene), and SiO ₂ , SnO ₂ TiO ₂ , ITO, CeO ₂ A material provided with an inorganic material such as a vacuum thin film can also be used favorably. In addition, known ones can be used. These may be used alone or in combination of two or more. The thickness of the undercoat layer is suitably from 0 to 5 μm.
[0105]
A layer (intermediate layer) may be provided between the photosensitive layer (charge generation layer (35) / charge transport layer (37)) and protective layer (39). This intermediate layer generally contains a binder resin as a main component. Examples of the binder resin include polyamide, alcohol-soluble nylon, water-soluble polyvinyl butyral, polyvinyl butyral, and polyvinyl alcohol. These may be used alone or in combination of two or more. The thickness of the intermediate layer is suitably about 0.05 to 2 μm.
[0106]
In the present invention, in order to improve environment resistance, in particular, for the purpose of preventing a decrease in sensitivity and an increase in residual potential, each layer such as a charge generation layer, a charge transport layer, an undercoat layer, a protective layer, and an intermediate layer is conventionally used. Known antioxidants, plasticizers, lubricants, ultraviolet absorbers, low molecular charge transport materials and leveling agents can be added as appropriate.
[0107]
【Example】
EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is limited to these Examples and is not interpreted.
[0108]
[Example 1]
An outline of the image forming apparatus created in the first embodiment will be described with reference to FIG.
[0109]
The photoreceptor drum (1) is provided with a photoreceptor having a film thickness of 20 μm on the surface of an aluminum conductor. The photoreceptor is a laminated electrophotographic photoreceptor (OPC) having a protective layer (39), a charge transport layer (37), an undercoat layer, and a charge generation layer (35), and is rotated in the direction of the arrow in FIG. The The diameter of the photosensitive drum (1) was 60 mm, and the peripheral speed was 230 mm / sec.
[0110]
The charging means (2) is a so-called contact roller charging device. A DC voltage (−1.21 kV) is applied by a power source to a charging roller in which a 3 mm thick elastic layer having a so-called medium resistance conductivity is formed on a mandrel to charge the photoreceptor uniformly (−550 V). .
[0111]
The exposure means (3) forms an electrostatic latent image by irradiating the surface of the photoreceptor uniformly charged by the charging means (2) with light corresponding to the target image. The light source of the exposure means (3) is a laser diode, and the photosensitive member is scanned while being irradiated with a laser beam by a polygon mirror. The beam diameter was set to 35 μm in the main scanning direction and 35 μm in the sub-scanning direction.
[0112]
FIG. 5 shows a block diagram of the exposure means (3). As shown in FIG. 3, the exposure means (3) mounts a 4ch (4-channel) type LD array having four LDs (laser diodes) (51) with a wavelength of 780 nm. Laser light from the LD is irradiated to the polygon mirror (56) via the collimating lens (52), the ND filter (53), the aperture (54), and the cylindrical lens (cylinder lens) (55). The polygon mirror (56) was a 6-sided type and was rotated at a rotational speed of 27165 rpm.
The laser beam reflected by the polygon mirror 56 was set so as to form an image on the photosensitive member via the folding mirrors 58 and 59 and the f-θ lenses 57 and 60.
[0113]
In Example 1, the beam diameter of the laser beam on the photosensitive was adjusted to be 35 μm (main scanning direction) × 35 μm (sub-scanning direction). As the f-θ lenses (57) and (60), plastic lenses obtained by molding plastic are adopted, and the lens shape is designed by a so-called AC surface. As a result, a very thin beam diameter of 35 μm (main scanning direction) × 35 μm (sub-scanning direction) was realized.
[0114]
The laser beam scans the photosensitive member as the polygon mirror (56) rotates. In Example 1, the resolution was 1200 dpi, and the size of 1 pixcel was 21.3 μm × 21.3 μm. That is, the photosensitive member is irradiated with a laser beam while moving per pixcel in a time of 16.9 nsec. At this time, the so-called pixel clock is 59.2 MHz, and the LD is optically modulated at a frequency of 59.2 MHz.
[0115]
In addition, when the laser beam was irradiated to the non-image area, the laser beam was configured to be incident on the synchronization detection plate (12). The synchronization detection plate (12) generates a reference signal by the incidence of the laser beam, and resets a clock signal that forms the timing of the image writing position (so-called pixel clock) based on the reference signal. As a result, it was realized that light modulated laser light was incident on a predetermined position on the photosensitive member.
Further, in the first embodiment, such multi-level writing is performed by changing the pulse width of the LD in four stages so that so-called four-level writing that can express four gradations per pixcel can be performed. Is doing.
[0116]
The developing means (4) employs a so-called two-component developing device. In the developer container, a developer in which toner (volume average particle diameter 6.8 μm) and carrier (particle diameter 50 μm) are mixed to a toner concentration of 5.0% was placed.
The developing device conveys the developer to the photosensitive member-developing sleeve facing portion by the developing sleeve. The distance between the photoreceptor and the developing sleeve (so-called developing gap) was set to 0.3 mm. A DC voltage (−400 V) was applied to the developing sleeve from a power source, and toner was deposited on the photosensitive member corresponding to the electrostatic latent image on the photosensitive member (so-called reverse development). The peripheral speed of the developing sleeve was 460 mm / sec, and the so-called peripheral speed ratio was 2.0.
[0117]
The transfer means (5) transfers the toner image developed by the developing means (4) onto a recording sheet (6) conveyed from a paper supply means (not shown). The transfer means (5) of Example 1 is composed of a transfer belt and a power source, and applies a voltage from the power source to the transfer belt. The voltage to be applied was constant current control and 30 μA.
[0118]
The cleaning means (7) is constituted by a blade formed of an elastic body, and cleans a residual toner image (so-called transfer residual toner) on the photoconductor.
[0119]
The toner image transferred onto the recording sheet such as paper by the transfer means (5) is conveyed to the fixing means (8) and heated and pressed by the fixing means (8), so that the toner image is transferred onto the recording paper sheet. It is fixed. The recording sheet is discharged out of the image forming apparatus.
[0120]
The image forming apparatus used in Example 1 forms an image on a recording sheet by sequentially performing the above processing while the photosensitive drum (1) rotates.
[0121]
Next, a method for producing the photoreceptor used in Example 1 will be described in detail. Note that “parts” used below mean “parts by weight”. The ionization potential Ip of the charge transport material was measured with a surface analyzer (manufactured by Riken Keiki Co., Ltd., AC-1).
[0122]
(Photoreceptor specifications)
The undercoat layer coating solution, charge generation layer (35) coating solution, and charge transport layer (37) coating solution of the following composition are sequentially applied onto a φ60 aluminum cylinder by dip coating, dried, and dried. An undercoat layer of 3.5 μm, a charge generation layer of 0.2 μm, and a charge transport layer of 15 μm were formed.
[0123]
Undercoat layer coating solution
400 parts of titanium dioxide powder
65 parts of melamine resin
120 parts alkyd resin
2-butanone 400 parts
Coating solution for charge generation layer (35)
2 parts of Y-type oxotitanium phthalocyanine pigment
Polyvinyl butyral (ESREC BM-2: Sekisui Chemical Co., Ltd.) 1.0 part
50 parts of tetrahydrofuran
Charge transport layer (37) coating solution
10 parts of polycarbonate (Z Polyca, manufactured by Teijin Chemicals)
6 parts of charge transport material (Ip: 5.4 eV) of the following structural formula (XI)
Tetrahydrofuran 100 parts
[0124]
Embedded image

[0125]
On the charge transport layer (35), a protective layer (39) coating solution having the following composition was further applied by spray coating to form a protective layer having a total film thickness of 5 μm. Produced.

[0126]
(Image quality evaluation method)
The image quality evaluation was performed by measuring the gradation that has a great influence on the image quality.
For evaluation of gradation, a 17-step patch subjected to halftone processing by changing the number of lines was output, and the lightness (L *) of this patch was measured. Halftone processing was performed with 150, 200, and 240 lpi lines.
A spectral density colorimeter (938 manufactured by X-Rite) was used for the measurement of lightness (L *).
The numerical value of the gradation is obtained by calculating the square of the autocorrelation coefficient in the linear approximation from the linearity of the brightness value obtained by measuring the 17-step patch with respect to the area ratio (that is, the input value) on the data. The so-called R ^ 2) was calculated. As shown in FIG. 6, the value of R ^ 2 is close to 1.0 if the relationship between the input data and the lightness (L *) is linear. Further, as shown in FIG. 7, the value becomes smaller as it deviates from the straight line.
[0127]
As a result of subjective evaluation of an image such as a natural image that requires high gradation, the inventors of the present application have obtained excellent gradation (good) when the value of R ^ 2 is 0.98 or more. It was decided that it would have a good image quality.
The value of R ^ 2 tends to be larger in a so-called low line number image. However, it was found that when the number of lines is 200 lpi or less, the user recognizes a so-called dither texture, and the obtained image gives an unnatural impression. Therefore, the present inventors have determined that the image quality is high when the gradation R ^ 2 value is 0.98 or more when the number of lines of halftone processing is 200 lines or more.
The evaluation results are shown in Table 2.
[0128]
Note that the recording density affects the image quality of characters and line drawings, and particularly has a great influence on jaggy characteristics. In general, the writing density at which jaggies are inconspicuous is 900 dpi or more, preferably 1200 dpi or more.
Therefore, the present inventors modified the image to be writable by 2 bits and output an image using the photosensitive member to an image forming apparatus (trade name: MF4570, manufactured by Ricoh Co., Ltd.) set at a resolution of 1200 dpi.
The beam diameter was measured with a beam scan manufactured by PHOTON, and the photoconductor film thickness was measured with a film thickness meter manufactured by Fischerscope.
The evaluation is shown in Table 2.
[0129]
[Examples 2-8, Comparative Examples 1-12]
Example 1 is the same as Example 1 except that the charge transport layer thickness of the photoreceptor, the transmittance of the protective layer (formulation will be described later), the writing dot system at the time of exposure, and the writing density are changed as shown in Table 1. Similarly, image output and image quality evaluation were performed.
[0130]
[Table 1]

[0131]
The transmittance (protective layer transmittance) 98% protective layer (39) and 85% protective layer (39) were prepared in the same manner as in Example 1 using a protective layer (39) coating solution having the following composition.
An image was formed in the same manner as in Example 1 using the created image forming apparatus, and the obtained image was evaluated in the same manner as in Example 1. Table 2 shows the image quality evaluation results of Examples 2 to 8 and Comparative Examples 1 to 12.
[0132]

[0133]

[0134]
[Table 2]

[0135]
[Comparative Example 13]
An electrophotographic photosensitive member was produced in the same manner as in Example 1 except that alumina as a filler was not added to the protective layer (39) coating solution in Example 1. An image was formed in the same manner as in Example 1 using the created image forming apparatus.
[0136]
The electrophotographic photosensitive member produced as described above was subjected to running evaluation using an image forming apparatus (trade name: MF4570, manufactured by Ricoh Co., Ltd.). In addition, image evaluation was performed in the same manner as in Example 1. The beam diameter was 35 μm and the writing density was 1200 dpi.
In the halftone process, an image was output at a level of 200 lpi.
The evaluation method is as follows.
[0137]
(1) Measurement of the film thickness of the photoreceptor.
(2) Image evaluation after 1-part image formation (measurement of gradation R ^ 2).
(3) Measurement of bright part potential (set to VD = −800V).
(4) After printing a total of 20,000 sheets at 1 to 2, the bright portion potential is measured as in (3).
(5) Image evaluation as in (2).
(6) Further, after the image formation of 80,000 sheets (total 100,000 sheets), the film thickness of the photoreceptor is measured. The amount of wear is evaluated from the film thickness difference from the film thickness (initial value of the film thickness) in (1).
Further, the inventors of the present application visually confirmed the image quality other than the gradation.
The evaluation results are shown in Table 3.
Moreover, Example 1 and Comparative Example 3 were similarly evaluated. The results are shown in Table 3.
[0138]
[Example 9]
An electrophotographic photosensitive member was produced in the same manner as in Example 1 except that the unsaturated polycarboxylic acid polymer contained in the protective layer (39) coating solution was changed as described below. Table 3 shows the evaluation results evaluated in the same manner as in Comparative Example 13 using the created image forming apparatus.
Coating liquid: unsaturated polycarboxylic acid polymer
(Acid value 130 mgKOH / g, manufactured by BYK Chemie) 0.06 parts
[0139]
[Example 10]
In Example 1, an electrophotographic photosensitive member was produced in the same manner as in Example 1 except that the unsaturated polycarboxylic acid polymer contained in the protective layer (39) coating solution was changed as follows. Table 3 shows the evaluation results evaluated in the same manner as in Comparative Example 13 using the created image forming apparatus.
Coating liquid: unsaturated polycarboxylic acid polymer
(Acid value 365 mgKOH / g, manufactured by BYK Chemie) 0.03 parts
[0140]
[Example 11]
In Example 1, an electrophotographic photosensitive member was produced in the same manner as in Example 1 except that the unsaturated polycarboxylic acid polymer contained in the protective layer (39) coating solution was changed as follows. . Table 3 shows the results of evaluation in the same manner as in Comparative Example 13 using the created image forming apparatus.
Coating liquid: acrylic acid / hydroxyethyl methacrylate copolymer
(Acid value 130 mgKOH / g) 0.10 parts
[0141]
[Example 12]
In Example 1, an electrophotographic photosensitive member was produced and evaluated in the same manner as in Example 1 except that the filler contained in the protective layer (39) coating solution was changed as follows. Table 3 shows the results of evaluation in the same manner as in Comparative Example 13 using the created image forming apparatus.
Alumina (average particle size 0.15 μm pH: 5.3) 3.0 parts
[0142]
[Example 13]
In Example 1, an electrophotographic photosensitive member was produced in the same manner as in Example 1 except that the filler contained in the protective layer (39) coating solution was changed as follows. Table 3 shows the results of evaluation in the same manner as in Comparative Example 13 using the created image forming apparatus.
Alumina (average particle size 0.45 μm pH: 5.7) 3.0 parts
[0143]
[Example 14]
In Example 1, an electrophotographic photosensitive member was produced in the same manner as in Example 1 except that the filler contained in the protective layer (39) coating solution was changed as follows. Table 3 shows the results of evaluation in the same manner as in Comparative Example 13 using the created image forming apparatus.
Titanate coupling-treated alumina (treatment amount 3%) 3.0 parts
[0144]
[Example 15]
Example 1 is the same as Example 1 except that the charge transport material contained in the coating liquid for the protective layer (39) is changed to the charge transport material (Ip: 5.3 eV) of the following structural formula (XII). Similarly, an electrophotographic photosensitive member was produced. Table 3 shows the results of evaluation in the same manner as in Comparative Example 13 using the created image forming apparatus.
[0145]
Embedded image

[0146]
[Example 16]
In Example 1, all except that the charge transport material contained in the coating liquid for the protective layer (39) was changed to the charge transport material (Ip: 5.5 eV) of the following structural formula (XIII) Similarly, an electrophotographic photosensitive member was produced. Table 3 shows the results of evaluation in the same manner as in Comparative Example 13 using the created image forming apparatus.
[0147]
Embedded image

[0148]
[Example 17]
In Example 1, an electrophotographic photosensitive member was produced in the same manner as in Example 1 except that the charge transport material and the binder resin contained in the protective layer (39) coating solution were changed to the following materials. . Table 3 shows the results of evaluation in the same manner as in Comparative Example 13 using the created image forming apparatus.
Polymer charge transport material (Ip: 5.4 eV) of the following structural formula (XIV) 5 parts
[0149]
Embedded image

[0150]
[Example 18]
An electrophotographic photosensitive member was produced in the same manner as in Example 1 except that the binder resin contained in the protective layer (39) coating solution in Example 1 was changed as follows. Table 3 shows the results of evaluation in the same manner as in Comparative Example 13 using the created image forming apparatus.
7.0 parts of polyarylate resin (U polymer / PET, manufactured by Unitika)
[0151]
[Example 19]
An electrophotographic photosensitive member was produced in the same manner as in Example 1 except that the binder resin contained in the protective layer (39) coating solution in Example 1 was changed as follows. Table 3 shows the results of evaluation in the same manner as in Comparative Example 13 using the created image forming apparatus.
Polycarbonate (C Polyca, Teijin Chemicals) 7.0 parts
[0152]
[Table 3]

[0153]
(Evaluation results)
From Table 2, it can be seen that in order to form an image with excellent gradation, the beam diameter, the charge transport layer thickness, and the protective layer transmittance must be in a specific combination. This combination (conditions for forming an image with excellent gradation) is shown below.
[0154]
(Prerequisite)
An image forming apparatus using an electrophotographic method with an optical writing resolution of 1200 dpi or higher and / or an electrophotographic method for forming image data obtained by performing halftone processing on an input image with a line number of 200 lpi or higher is used. The image forming apparatus.
(1) The beam diameter of the optical writing means is 35 μm or less.
(2) A protective layer having a transmittance of 90% or more with respect to the laser beam from the optical writing means is provided.
(3) The total thickness of the protective layer and the charge transport layer is 20 μm or less.
[0155]
In addition, if a photoreceptor containing a filler, dispersion, charge transporting material and / or binder resin is used for the protective layer, an increase in residual potential can be suppressed, and image quality such as occurrence of image unevenness and deterioration in gradation can be suppressed. It was found that deterioration can be suppressed and uneven wear and abnormal wear can also be suppressed.
[0156]
It was found that so-called banding can be reduced if a protective layer having a beam diameter of 35 μm or less, a transmittance of 90% or more is provided, and the combined thickness of the charge transport layer and the protective layer is 20 μm or less.
Banding is a density variation in the main scanning direction (paper feeding direction) of an electrophotographic image. In particular, when a uniform image of medium density (lightness L * = 40 to 70) is output, the density fluctuates in a streak pattern with a relatively long period (1 to 20 mm period). If such streak-like density fluctuations occur in the output image, the obtained image becomes extremely unnatural.
Factors that cause banding include beam scanning unevenness (so-called polygon mirror tilting, optical element vibration), photosensitive drum rotational speed unevenness, developing sleeve rotational speed unevenness, development gap fluctuation (photosensitive drum, (Development of the developing sleeve).
Conventionally, countermeasures have been taken for each of these causes, but there are practically difficult aspects resulting in an increase in size and cost of the apparatus. This is because, in order to completely eliminate the above causes, it is required to manufacture the entire apparatus firmly and improve the accuracy of each component.
[0157]
The present inventors conducted an experiment in which uniform images with lightness L * = 50 were formed at 200 lpi and 240 lpi under the conditions of Examples 1 to 8 and Comparative Examples 1 to 12, and the banding was visually evaluated. It was. The image for banding evaluation described above was output using the experimental machine described in the examples. Visual evaluation of this image was evaluated according to the following criteria.
Rank 5: Banding cannot be perceived for both 200 lpi and 240 lpi.
Rank 4: Not perceptible at 200 lpi, but slightly perceptible at 240 lpi
Rank 3: Even 200 lpi can be perceived slightly. (Slight perception even at 240 lpi)
Rank 2: It can be clearly perceived even at 200 lpi. (Can be clearly perceived even at 240 lpi)
Rank 1: Banding is very bad even at 200 lpi. (Banding is very bad even at 240 lpi.)
[0158]
The inventors have found that banding is as bad as the number of high lines. Therefore, a determination criterion centered on the 200 lpi image as described above was set.
[0159]
The results of evaluating banding in Examples 1 to 8 and Comparative Examples 1 to 12 using the above criteria will be described below. If the number of halftone lines is 200 lpi or more, almost no dither texture is perceived. For this reason, rank 4 or higher of the above criterion is considered as a passing line for banding.
[0160]
Example 1: Rank 4
Example 2: Rank 5
Example 3: Rank 5
Example 4: Rank 4
Example 5: Rank 4
Example 6: Rank 5
Example 7: Rank 5
Example 8: Rank 4
Comparative Example 1: Rank 3
Comparative Example 2: Rank 2
Comparative Example 3: Rank 3
Comparative Example 4: Rank 2
Comparative Example 5: Rank 3
Comparative Example 6: Rank 1
Comparative Example 7: Rank 2
Comparative Example 8: Rank 2
Comparative Example 9: Rank 2
Comparative Example 10: Rank 3
Comparative Example 11: Rank 3
Comparative Example 12: Rank 1
[0161]
From the experimental results, it was found that an image forming apparatus that satisfies the above conditions has good banding. That is, it was found that a good image can be obtained.
[0162]
The γ linearity not only realizes the image forming apparatus having the above-mentioned good gradation, but if the γ linearity is 0.98 or more, the banding is substantially as can be seen from the experimental results. An image forming apparatus that is not perceived by the user can be realized.
[0163]
【The invention's effect】
As is apparent from the above description, according to the present invention, halftone processing is applied to the input image with a high durability, a resolution of optical writing of 1200 dpi or more, and a line number of 200 lpi or more. Therefore, it is possible to provide an image forming apparatus capable of forming an image of the image data without degrading the image quality.
[Brief description of the drawings]
FIG. 1 shows an example of a layer structure of a photoreceptor according to the present invention.
FIG. 2 shows another example of the layer structure of the photoreceptor according to the present invention.
FIG. 3 is a schematic configuration diagram of a conventional image forming apparatus.
FIG. 4 shows a schematic configuration example of an image forming apparatus according to the present invention.
5 shows an example of the configuration of an optical unit of the image forming apparatus of FIG.
FIG. 6 shows the relationship between input data and lightness (L *).
FIG. 7 shows a relationship between input data and lightness (L *).
FIG. 8 is a schematic view of a corona electric withstand device using a wire.
FIG. 9 is a schematic view of a corona electric withstand device using a sawtooth electrode.
FIG. 10 is a schematic view of a contact electric resistance device.
[Explanation of symbols]
1 Photosensitive drum
1a photoconductor
1b conductor
2 Charging means (charging device)
2a Elastic layer
2b conductor
3 Exposure means
4 Development means
5 Transfer means
6 Recording sheet
7 Cleaning means
8 Fixing means
30 power supply
31 Conductive support
33 Middle layer
35 Charge generation layer
37 Charge transport layer
39 Protective layer
51 4chLD (Laser Diode)
52 Collimating lens
53 ND filter
54 Aperture
55 Cylinder lens
56 polygon mirror
57 f-θ lens 1
58 Folding mirror 1
59 Folding mirror 2
60 f-θ lens 2
61 photoconductor surface
62 Sync detection board
80 Charging case
81 grid
82 Wire (Tungsten)
83, 84 Power supply
90 Sawtooth electrode
91 Support member
92 Charging case
93 grid
94, 95 power supply

Claims (15)

The image forming apparatus includes a charging unit, a photosensitive member, and an optical writing unit, and forms an image having a resolution of at least 1200 dpi. The optical writing unit emits a laser beam having a beam diameter of 35 μm or less. A charge generation layer containing at least a charge generation material and a charge transport layer containing a charge transport material are provided on the conductive support, and a protective layer is provided on the surface of the photoreceptor more than the charge generation layer and the charge transport layer. The protective layer has a transmittance of the laser beam of 90% or more and a thickness of 5 to 10 μm, and the total thickness of the charge transport layer and the protective layer is 20 μm or less. Image forming apparatus. An image processing unit that performs halftone processing on an input image, a charging unit, a photoconductor, and an optical writing unit. An image forming apparatus that performs processing, wherein the optical writing unit emits a laser beam having a beam diameter of 35 μm or less, and the photoconductor includes a charge generation layer containing at least a charge generation material and a charge on a conductive support. A charge transport layer containing a transport material is provided, and a protective layer is provided on the surface side of the photoreceptor from the charge generation layer and the charge transport layer, and the protective layer has a transmittance of 90% or more for the laser beam light and thickness is 5 to 10 [mu] m, the image forming apparatus, wherein the total thickness of the charge transport layer and the protective layer is 20μm or less.   The image forming apparatus according to claim 1, wherein the protective layer contains a filler, a charge transport material, and / or a binder resin.   The image forming apparatus according to claim 3, wherein the filler has a refractive index of 1.0 to 2.0.   The image forming apparatus according to claim 3, wherein at least an inorganic pigment is used as the filler.   The image forming apparatus according to claim 3, wherein at least a metal oxide is used as the filler. The image forming apparatus according to claim 1, wherein the protective layer contains an inorganic pigment and / or a metal oxide that has been surface-treated with at least one surface treatment agent. . The said protective layer contains the inorganic pigment and / or metal oxide which were surface-treated by the titanate coupling agent, the higher fatty acid, and / or the higher fatty acid metal salt at least. The image forming apparatus according to claim 1. 9. The image forming apparatus according to claim 7, wherein the inorganic pigment and / or the metal oxide is surface-treated with a surface treatment amount of 2 to 30 wt%. The image forming apparatus according to claim 1, wherein the protective layer includes a binder resin containing a resin having an acid value of 10 to 400 (mgKOH / g). The image according to any one of claims 1 to 10, wherein the protective layer contains a dispersant, and the dispersant is an organic compound containing at least one carboxyl group in the structure. Forming equipment. The image forming apparatus according to claim 11, wherein the dispersant is a polycarboxylic acid derivative. The image forming apparatus according to claim 11, wherein the dispersant is an organic compound having an acid value of 10 to 400 (mgKOH / g). The image forming apparatus according to claim 11, wherein the amount of the dispersant added is selected from an amount satisfying the following formula.
0.1 ≦ (addition amount of dispersing agent × acid value of dispersing agent) / (addition amount of filler) ≦ 20 15. The image forming apparatus according to claim 1, wherein a maximum electric field strength applied to the charge transport layer and the protective layer by the charging unit is −30 V / μm.

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