JP3897292B2 - Image forming apparatus - Google Patents

Description

式（Ｉ）中、Ｒ_１、Ｒ_２、Ｒ_３はそれぞれ独立して置換もしくは無置換のアルキル基又はハロゲン原子、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及びＲ_６は置換もしくは無置換のアリール基、ｏ、ｐ、ｑはそれぞれ独立して０〜４の整数、ｋ、ｊは組成を表し、０．１≦ｋ≦１、０≦ｊ≦０．９、ｎは繰り返し単位数を表し５〜５０００の整数である。Ｘは脂肪族の２価基、環状脂肪族の２価基、又は下記一般式で表される２価基を表す。
【００７３】
【化２】

上記式中、Ｒ_１０１、Ｒ_１０２は各々独立して置換もしくは無置換のアルキル基、アリール基又はハロゲン原子を表す。ｌ、ｍは０〜４の整数、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−（式中Ｚは脂肪族の２価基を表す。）
【００７４】
【化３】
又は、（Ｉ）式中Ｘは、

（式中、ａは１〜２０の整数、ｂは１〜２０００の整数、Ｒ_１０３、Ｒ_１０４は置換又は無置換のアルキル基又はアリール基を表す。）を表す。ここで、Ｒ_１０１とＲ_１０２、Ｒ_１０３とＲ_１０４は、それぞれ同一でも異なってもよい。
【００７５】
【化４】
（ＩＩ）式

式（ＩＩ）中、Ｒ_７及びＲ_８は置換もしくは無置換のアリール基、Ａｒ_１、Ａｒ_２、Ａｒ_３は同一あるいは異なるアリレン基を表す。Ｘ、ｋ、ｊ及びｎは、（Ｉ）式の場合と同じである。
【００７６】
【化５】
（ＩＩＩ）式

式（ＩＩＩ）中、Ｒ_９及びＲ_１０は置換もしくは無置換のアリール基、Ａｒ_４、Ａｒ_５、Ａｒ_６は同一あるいは異なるアリレン基を表す。Ｘ、ｋ、ｊ及びｎは、（Ｉ）式の場合と同じである。
【００７７】
【化６】
（ＩＶ）式

式（ＩＶ）中、Ｒ_１１、Ｒ_１２は置換もしくは無置換のアリール基、Ａｒ_７、Ａｒ_８、Ａｒ_９は同一あるいは異なるアリレン基を表す。Ｘ、ｋ、ｊ及びｎは、（Ｉ）式の場合と同じである。
【００７８】
【化７】
（Ｖ）式

式（Ｖ）中、Ｒ_１３、Ｒ_１４は置換もしくは無置換のアリール基、Ａｒ_１０、Ａｒ_１１、Ａｒ_１２は同一あるいは異なるアリレン基、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す。Ｘ、ｋ、ｊ及びｎは、（Ｉ）式の場合と同じである。
【００７９】
【化８】
（ＶＩ）式

式（ＶＩ）中、Ｒ_１５、Ｒ_１６、Ｒ_１７、Ｒ_１８は置換もしくは無置換のアリール基、Ａｒ_１３、Ａｒ_１４、Ａｒ_１５、Ａｒ_１６は同一あるいは異なるアリレン基、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の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、ビニレン基を表し同一であっても異なってもよい。Ｘ、ｋ、ｊ及びｎは、（Ｉ）式の場合と同じである。
【００８０】
【化９】
（ＶＩＩ）式

式中、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し、Ｒ_１９とＲ_２０は環を形成していてもよい。Ａｒ_１７、Ａｒ_１８、Ａｒ_１９は同一あるいは異なるアリレン基を表す。Ｘ、ｋ、ｊ及びｎは、（Ｉ）式の場合と同じである。
【００８１】
【化１０】
（ＶＩＩＩ）式

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は同一あるいは異なるアリレン基を表す。Ｘ、ｋ、ｊ及びｎは、（Ｉ）式の場合と同じである。
【００８２】
【化１１】
（ＩＸ）式

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、Ａｒ_２４、Ａｒ_２５、Ａｒ_２６、Ａｒ_２７、Ａｒ_２８は同一又は異なるアリレン基を表す。Ｘ、ｋ、ｊ及びｎは、（Ｉ）式の場合と同じである。
【００８３】
【化１２】
（Ｘ）式

式（Ｘ）中、Ｒ_２６、Ｒ_２７は置換もしくは無置換のアリール基、Ａｒ_２９、Ａｒ_３０、Ａｒ_３１は同一あるいは異なるアリレン基を表す。Ｘ、ｋ、ｊ及びｎは、（Ｉ）式の場合と同じである。
【００８４】
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することができる。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、メノウ等すべて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。また、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より添加することが好ましい。一方、結着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、結着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。
【００８５】
以上のようにして得られた分散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。保護層全体の膜厚としては、１〜１０μｍ、好ましくは２〜６μｍが適当である。
【００８６】
本発明の感光体においては、導電性支持体３１と電荷発生層３５との間に中間層（下引き層）３３を設けることができる。中間層３３は一般には樹脂を主成分とするが、これらの樹脂はその上に感光層を溶剤で塗布することを考えると、一般の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。また、下引き層にはモアレ防止、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の微粉末顔料を加えてもよい。これらの下引き層は、前述の感光層の如く適当な溶媒及び塗工法を用いて形成することができる。更に本発明の下引き層として、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、各種分散剤を添加することも可能である。この他、本発明の下引き層には、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製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。下引き層の膜厚は０〜５μｍが適当である。
【００８７】
また、本発明の感光体においては、感光層（電荷発生層及び電荷輸送層）と保護層との間に中間層を設けることも可能である。中間層には、一般に結着樹脂を主成分として用いる。これら樹脂としては、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。中間層の形成法としては、前述のごとく一般に用いられる塗布法が採用される。なお、中間層の厚さは０．０５〜２μｍ程度が適当である。
【００８８】
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及びレベリング剤を添加することができる。
【００８９】
【発明の実施の形態】
以下、本発明を実施例を用いて具体的に説明する。ただし、本発明は以下の実施例に限定されない。
【００９０】
［実施例１］
本発明の実施例１の画像形成装置の概略を、図１を用いて、以下、１〜７の画像形成の手順に沿って説明する。
１ 図１において、感光体ドラム１はアルミニウム等の導体の表面に、感光体を膜厚２０μｍ（ＦＲ層（表面保護層５μｍ、電荷輸送層１５μｍ）、電荷発生層０．２μｍ、下引き層３．５μｍの積層型ＯＰＣである。）で塗布することによって形成され、図４中の矢印方向に回転する。感光体ドラムの直径は６０ｍｍであり、周速は２３０ｍｍ／ｓである。
【００９１】
２ 帯電手段２は、いわゆる接触ローラ帯電装置であり、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構成の帯電ローラに、電源によって−１．２１ｋＶの直流電圧を印加し、感光体を均一に−５５０Ｖに帯電する。
【００９２】
３ 露光手段３は、帯電手段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。いわゆるビーム径は、下記で詳しく説明するように主走査方向３５μｍ、副走査方向３５μｍである。
【００９３】
４ 現像手段は、いわゆる２成分現像装置であり、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％に混合した現像剤が現像容器内には収納されている。現像装置では、この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である。現像スリーブには電源により−４００Ｖの直流電圧が印加されているため、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する。いわゆる反転現像である。また、現像スリーブの周速は４６０ｍｍ／ｓであり、いわゆる周速比は２．０である。
【００９４】
５ 転写手段５は、現像手段で現像されたトナー像を不図示の給紙手段から搬送された記録シート６上に転写する。図４の転写手段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。印加する電圧は定電流制御とし、３０μＡである。
【００９５】
６ 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う。
【００９６】
７ 転写手段によっての記録シート（紙等）上に転写されたトナー像は、定着手段に搬送され、定着手段で加熱加圧することによって、トナー像が記録紙シート上に定着され、画像形成装置機外へと排出され、出力画像となる。
上述の１〜７の工程を繰り返すことによって、所望の画像を記録シート上に形成することが可能になる。
【００９７】
図９は図１に示した画像形成装置の書き込みユニットである。図１に示した装置では、波長７８０ｎｍの４つのＬＤ（レーザーダイオード）をもつ４ｃｈ（４チャンネル）タイプのＬＤアレイを搭載している。ＬＤからのレーザー光は、コリメートレンズ１２、ＮＤフィルタ１３、アパーチャー１４、シリンドリカルレンズ１５を介して、ポリゴンミラー１６へと照射される。実施例１ではポリゴンミラー１６は、６面タイプであり、２７１６５ｒｐｍの回転数で回転している。ポリゴンミラー１６で反射されたレーザー光は、折り返しミラー１８、１９、ｆ−θレンズ１７、２０を介して、感光体面２１上で結像するようになっている。後述する実施例では、レーザービームの感光体上でのいわゆるビーム径は、３５μｍ（主走査方向）×３５μｍ（副走査方向）になるように調整されている。図１の装置ではｆ−θレンズはプラスチックを成形加工したプラスチックレンズであり、いわゆるＡＣ面によってレンズ形状の設計がなされており、この結果、３５μｍ（主走査方向）×３５μｍ（副走査方向）という極めて細いビーム径を実現している。また、レーザー光はポリゴンミラー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１２００ｄｐｉの画像形成装置であり、１ｐｉｘｃｅｌの大きさは、２１．３μｍ×２１．３μｍである。実施例１では、１ｐｉｘｃｅｌあたりを１６．９ｎｓ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。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を光変調することを意味している。
【００９８】
また、実施例１では、上述のようにレーザー光がポリゴンミラーの回転によって、感光体上を走査するが、非画像領域にレーザー光が位置するときには、図９に図示された同期検知板に、レーザー光が入射するようになっている。この同期検知板は、レーザービームの入射によって基準信号が発生するような機構を有し、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うようになっている。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ができるようになっている。
【００９９】
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値書きこみを行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こみを行っている。
【０１００】
以下に実施例１に使用する感光体の具体例を示す。部はすべて重量部である。なお、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。
【０１０１】
（感光体仕様）
直径６０ｍｍ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、電荷発生層塗工液及び電荷輸送層塗工液を、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。
【０１０２】
（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
【０１０３】
（電荷発生層用塗工液）
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（積水化学製、エスレックＢＭ−２） １．０部
テトラヒドロフラン ５０部
【０１０４】
（電荷輸送層塗工液）
ポリカーボネート（帝人化成製、Ｚポリカ） １０部
下記構造式（２）の電荷輸送物質（Ｉｐ：５．４ｅＶ） ６部
【化１３】

テトラヒドロフラン １００部
【０１０５】
上記電荷輸送層上にさらに下記組成の保護層塗工液１を用いて、スプレー塗工によって保護層を塗工し、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。

【０１０６】
（画質評価方法）
画質評価は、画質の重要項目である階調性を測定するという方法で行った。階調性の評価は、線数を変えて中間調処理をほどこしたパッチ（１７段）を出力し、このパッチの明度（Ｌ＊）を測定する。中間調処理としては、いわゆる線数を１５０、２００、２４０ｌｐｉの３水準で画像を出力した。また、明度（Ｌ＊）の測定には、分光濃度測色計（Ｘ−Ｒｉｔｅ製９３８）を使用した。階調性の数値化は、入力（データ上の面積率）に対する、１７段のパッチを測色してもとめた明度値の直線性から、いわゆるＲ＾２（一次式近似での自己相関係数の２乗）を計算するという方法で行った。Ｒ＾２の値は、上述の入力データと明度（Ｌ＊）との関係が直線的ならば図１０に示す１．０に近い値になり、直線からずれるにしたがって図１１に示す小さな値になる。また、発明者らは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うことによって、Ｒ＾２の値が０．９８以上であることを優れた階調性の条件とした。また、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。しかしながら、線数が２００ｌｐｉ以下の場合には、いわゆるディザのテクスチャが認識できるようになってしまい、自然画像などにおいては不自然な印象をあたえる結果、画質劣化の要因となってしまう。このことから、発明者は、中間調処理の線数を２００線以上で階調性Ｒ＾２の値０．９８以上であれば高画質であると判断した。
【０１０７】
発明者らは、上記感光体を用い、実験機は、リコー製ＭＦ４５７０を１２００ｄｐｉ２ｂｉｔ書き込みに改造したものを使用し、上記手段により画像を出力し画質評価を行った。また、ビーム径はＰＨＯＴＯＮ製ビームスキャン、ＯＰＣ膜厚はフィッシャースコープ製膜厚計でそれぞれ測定したものである。
【０１０８】
［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（処方は後述する）、露光時の書き込みドット系、書き込み密度を以下の表１のように変えた他は実施例１と同様にして画像出力・画質評価を行った。
【０１０９】
【表１】

【０１１０】

【０１１１】

【０１１２】
画質の評価結果を以下の表２に示す。表２は、ビーム径、電荷輸送層及び保護層の膜厚、保護層透過率及び中間調処理の線数の組み合わせにおける、階調性を測定した結果である。この結果からから分かるように、階調性の優れた画像を形成にするためには、本発明に規定するビーム径、電荷輸送層及び保護層の膜厚、保護層透過率及び中間調処理の線数を特定の組み合わせで用いる必要があることが分かる。
【０１１３】
【表２】

【０１１４】
［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。
【０１１５】
［実施例９］
実施例１において、保護層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。
不飽和ポリカルボン酸ポリマー
（ＢＹＫケミー製、酸価：１３０ｍｇＫＯＨ／ｇ） ０．０６部
【０１１６】
［実施例１０］
実施例１において、保護層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。
不飽和ポリカルボン酸ポリマー
（ＢＹＫケミー製、酸価：３６５ｍｇＫＯＨ／ｇ） ０．０３部
【０１１７】
［実施例１１］
実施例１において、保護層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。
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
【０１１８】
［実施例１２］
実施例１において、保護層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。
アルミナ（平均粒径：０．１５μｍ ｐＨ：５．３） ３．０部
【０１１９】
［実施例１３］
実施例１において、保護層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。
アルミナ（平均粒径：０．４５μｍ ｐＨ：５．７） ３．０部
【０１２０】
［実施例１４］
実施例１において、保護層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。
チタネートカップリング処理アルミナ（処理量３％） ３．０部
【０１２１】
［実施例１５］
実施例１において、保護層塗工液に含有される電荷輸送物質を、下記構造式（３）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・評価した。
【化１４】

【０１２２】
［実施例１６］
実施例１において、保護層塗工液に含有される電荷輸送物質を、下記構造式（４）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・評価した。
【化１５】

【０１２３】
［実施例１７］
実施例１において、保護層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・評価した。
下記構造式の高分子電荷輸送物質（Ｉｐ：５．４ｅＶ） １５部
【化１６】

【０１２４】
［実施例１８］
実施例１において、保護層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・評価した。
ポリアリレート樹脂（ユニチカ製、Ｕポリマー／ＰＥＴ） ７．０部
【０１２５】
［実施例１９］
実施例１において、保護層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・評価した。
ポリカーボネート（帝人化成製、Ｃポリカ） ７．０部
【０１２６】
以上のように作製した比較例１３、実施例９〜１９の電子写真感光体、及び前述の実施例１、比較例３で用いた電子写真感光体につき、リコー製ＭＦ４５７０によりランニング評価を及び先に示した実験機：リコー製ＭＦ４５７０を１２００ｄｐｉ２ｂｉｔ書き込みに改造したものを使用し画像評価を行った。なおビーム径は３５μｍ、書き込み密度は１２００ｄｐｉ、中間調処理としては、いわゆる線数を２００ｌｐｉの水準で画像を出力した。上記手段により画像を出力し画質評価を行った。
【０１２７】
また、評価の手順としては、最初に実験機により画像を出力し画質評価を行い、次にリコー製ＭＦ３５７０にて明部電位（ＶＤ＝−８００Ｖに設定）の測定及び１ｔｏ２にて計２万枚の印刷を行った後の明部電位の測定、さらに再度実験機により画像を出力し画質評価を行った。また初期及び１０万枚印刷後での膜厚差より摩耗量の評価に付いても行った。また、階調性以外の画質に関しては画像品質の項目に記した。その結果を表３に示す。
【０１２８】
【表３】

【０１２９】
［実施例２０〜３０及び比較例１４］
上記実施例９〜１９とそれぞれ同じ処方で電荷輸送層＋保護層の膜厚差（０．５〜４．０μｍ）を意図的に変化させた感光体を試作して、画像だし実験を行った。このとき感光体の膜厚差は次のようにして定義した。感光体ドラムの円筒方向には１０ｍｍ間隔で１９箇所（先述の膜厚計を使用して測定）、また感光体軸方向には１０ｍｍ間隔で３１箇所、膜厚を測定する。この５８９点の中から最大値と最小値を導出して、膜厚差＝最大値−最小値 として計算してある。
【０１３０】
電荷輸送層及び保護層を合わせた膜厚の、感光体画像領域全面での最大膜厚箇所と最小膜厚箇所とでの膜厚差は、電荷輸送層の塗工条件を変更することで変化させた。具体的には、塗工液の固形分濃度を低くし、引き上げ速度を大きくすることで、比較例に示すような膜厚差４μｍ以上の感光体を得ることができる。また、固形分濃度を高くし引き上げ速度を小さくすることで膜厚差２〜４μｍの感光体を得ることができる。さらに膜厚差１．５μｍ以下の感光体は、特開平２００１−１９４８１４号公報に記載の製造方法により作製した。
【０１３１】
保護層については、スプレーの塗工条件を、気流の乱れがないように気流設計した塗工室内で、スプレーガンと感光体基体間の距離、液吐出量、スプレーガンの送り速度、感光体基体の回転速度が一定かつ、均一であるようにして、ほとんど膜厚差の発生しない条件で塗工した。
【０１３２】
このようにして製作した感光体ドラムを先述の実験機（ｉｍａｇｉｏＭＦ４５７７０改造機）に搭載して画像だし評価を行った。このときの出力画像は、明度５０となるようなパターンを全面に形成して紙出力を行い、感光体ドラム１周分に相当する領域を縦横１０ｍｍ間隔で明度測定して評価した。（この明度測定にもやはりＸ―Ｒｉｔｅ製のＸ−Ｒｉｔｅ９３８を使用した。）明度５０のパターンを選択した理由としては、感光体膜厚の変化などで画像濃度の変化が、もっとも出現しやすいのが中濃度領域であり、その代表として明度５０のパターンを使用した。出力画像の明度測定もはやり、５８９点について行い平均値からのズレ量が明度差５以上となる測定点が得られた場合に、その条件は許容範囲外であると考えた。
【０１３３】
このような、出力画像の明度均一性の評価を初期状態及び１０万枚の通紙後において行った。次にその実験結果を示す。
後掲の表４は、帯電手段として直流電圧を印加した接触帯電方式の場合の結果である。表４に記載のデータは、実施例２０として、先述の実施例９の処方で初期の膜厚差が０．５μｍ〜４．５μｍまでの５水準を振った感光体を作製し、出力画像の明度差を記録する、その後そのすべての感光体について１０万枚の通紙を行い、感光体の膜厚差及び出力画像の明度差を初期状態のときと同じ手順で測定する。このようにして得られた結果が表４に記載されている。このような評価実験を実施例９〜１９及び比較例１３の感光体作製処方について（それぞれ実施例２０〜３０及び比較例１４）行い、表４の結果を得た。表４から初期の状態で感光体の膜厚差が１．５μｍ以下であれば、出力画像の明度差は５以下となり、この範囲が出力画像の安定性を保証する条件であることが分かる。しかしながら、１０万枚の通紙を行った後では、実施例２０〜３０の感光体では、膜厚差の増大は比較的少なく出力画像の明度差もそれほど大きくはならない。これに対して、比較例１４のようなフィラーを含有する保護層のない構成の感光体では、膜削れによる偏磨耗が発生し、出力画像の明度差が許容できない範囲にまで増大してしまう。
【０１３４】
直流電圧を印加した接触帯電方式を使用する画像形成装置では、感光体の膜厚に依存して帯電電位が変化するといった特徴がある。上述のように発明者らの行った実験では、感光体膜厚の変化１μｍにつき帯電電位は１０Ｖ程度変化するが、この大きさの変化は、画像濃度を一定にする観点からは非常に影響が大きく、結果として出力画像に濃度差が発生する。表４の結果から、この帯電方式の装置では、長期の使用にわたって出力画像の明度を一定にするという観点から、さらに１．５μｍ以下の膜厚差が有効であることが分かる。
【０１３５】
【表４】

【０１３６】
［実施例３１〜４１及び比較例１５］
後掲の表５に結果を示した実施例３１〜４１及び比較例１５は、帯電装置としてスコロトロンを使用した以外は、実施例２０〜３０及び比較例１４と同様の試験の結果である。表５も上記表４と同じ構成になっている。帯電装置がスコロトロンの場合、表５の結果から初期の状態で感光体の膜厚差が１．５μｍ以下であれば、出力画像の明度差は５以下となり、この範囲が出力画像の安定性を保証する条件であることが分かる。また１０万枚の通紙を行った後では、実施例３１〜４１の構成の感光体では、膜厚差の増大は比較的少なく出力画像の明度差もそれほど大きくはならない。しかしながらこれに対して、比較例１５のようなフィラーを含有する保護層のない構成の感光体では、膜削れによる偏磨耗が発生している。したがって、さらに出力画像の明度差を許容できる範囲に収めるためには、感光体の膜厚差が初期状態において０．５μｍ以下であることが望ましい。
【０１３７】
しかしながら、感光体の膜厚差を感光体ドラムの画像形成領域の全面にわたって０．５μｍ以下にコントロールすることは、感光体ドラムの製造という点ではあまり現実的ではない。このような、感光体ドラムの製造という観点まで含めた場合には、感光体を保護層のある構成にして膜厚差を１．５μｍ程度に抑えることが、長期の使用においても出力画像の明度安定性を保証する最も望ましい方法であると考えられる。
【０１３８】
【表５】

【０１３９】
［実施例４２〜５２及び比較例１６］
後掲の表６に結果を示した実施例４２〜５２及び比較例１６は、帯電装置として交流重畳電圧を印加した接触帯電装置を使用した以外は、実施例２０〜３０及び比較例１４と同様の試験の結果である。表６も表４と同じ構成になっている。帯電装置が交流重畳電圧を印加した接触帯電装置の場合、表６の結果から初期の状態で感光体の膜厚差が３．５μｍ以下であれば、出力画像の明度差は５以下となり、この範囲が出力画像の安定性を保証する好ましい条件であることが分かる。また、１０万枚の通紙を行った後では、実施例４２〜５２の構成の感光体では、膜厚差の増大は比較的少なく出力画像の明度差もそれほど大きくはならない。しかしながらこれに対して、比較例１６のようなフィラーを含有した保護層のない構成の感光体では、膜削れによる偏磨耗が発生している。したがって、出力画像の明度差を許容できる範囲に収めるためには、感光体の膜厚差が初期状態において１．５μｍ以下であることが望ましい。
【０１４０】
しかしながら、感光体の膜厚差を感光体ドラムの画像出力範囲の全面に亘って１．５μｍ以下にコントロールすることは、感光体ドラムの製造という点では感光体製造上のネックとなり、歩留まりの悪化を引き起こし、コストアップの要因となってしまう。このような、感光体ドラムの製造という観点まで含めた場合には、さらに膜厚差を３．５μｍ〜１．５μｍ程度に抑える方法が、長期の使用においても出力画像の明度安定性を保証する、コストの点からみて優れた方法であると考えられる。
【０１４１】
下記の表６と上記表４や表５を比較すると、帯電手段として交流重畳電圧を印加した接触帯電装置を使用した場合には、直流電圧を印加した帯電装置やスコロトロンを使用した場合に比べて、感光体の膜厚差の許容範囲が広いことが分かる。先に詳述したように、直流電圧を印加した接触帯電装置やスコロトロンでは帯電電位が変化するのに対して、交流重畳電圧を印加した帯電装置では帯電電位は感光体の膜厚に依存せず一定であり、このことにより、感光体の膜厚の変化によって、感光体の静電容量が変化し感光体上に蓄積される電荷量が変化するためである。
【０１４２】
したがって、例えば直流電圧印加方式の接触帯電装置やスコロトロンを使用した場合においても、制御装置などを用いて感光体の帯電電位を一定（感光体膜厚に依存せず）にすることができれば、表６のように比較的感光体の膜厚差に対して許容範囲の広い条件を提示することができる。
【０１４３】
【表６】

【０１４４】
【発明の効果】
【０１４５】
本発明の画像形成装置によれば、中間調処理の線数、レーザービーム径、電荷輸送層及び保護層の膜厚及び保護層透過率の適切な組み合わせによって、階調性Ｒ＾２の値が０．９８以上を確保することができる高画質な画像が得られることが明らかになった。
【０１４６】
さらに保護層がフィラー、分散剤及び電荷輸送物質、結着樹脂を含有したものである感光体を用いた場合、残留電位の上昇を抑制すると同時に、画像ムラの発生や階調性の低下等の画質劣化を抑制し、さらに偏摩耗や異常摩耗をも抑制することが可能となり、高耐久化と高画質化の両立を実現する画像形成装置を提供することが可能となった。
【０１４７】
また、帯電手段として、直流電圧を印加した接触帯電装置やスコロトロンを使用して、感光体の膜厚差を１．５μｍ以下であるようにするすることにより、長期にわたって使用した場合においても、▲１▼ 偏磨耗による感光体の膜厚差、▲２▼ ▲１▼による帯電電位の変化、▲３▼ ▲２▼による出力画像の明度の変化、の影響が抑制できる。すなわち、出力画像の明度を変化させることなく一定に保つことができるので、長期に亘って一定明度の出力画像を実現することができる。
【０１４８】
また、帯電手段として、交流重畳電圧を印加した接触帯電装置を使用して、上記作製の感光体の膜厚差を３．５μｍ以下であるようにすることにより、長期に亘って使用した場合においても、▲１▼ 偏磨耗による感光体の膜厚差、▲２▼ ▲１▼による帯電電位の変化、▲３▼ ▲２▼による出力画像の明度の変化、の影響が抑制できる。すなわち、出力画像の明度を変化させることなく一定に保つことができるので、長期に亘って一定明度の出力画像を実現することができる。特に、この帯電手段の場合は、感光体の膜厚許容差が比較的ゆるく、感光体ドラム製造上の歩留まりがよく、コストアップの要因がないといった特徴を持つ画像形成装置を実現することができる。
【図面の簡単な説明】
【図１】 実施例１に係る画像形成装置の概略断面図である。
【図２】 本発明に用いる感光体の断面図である。
【図３】 本発明に用いる別の感光体の断面図である。
【図４】 従来の画像形成装置の概略断面図である。
【図５】 ワイヤ型のコロナ帯電装置を模式的に示した図である。
【図６】 鋸刃状電極のコロナ帯電装置を模式的に示した図である。
【図７】 鋸刃状電極を模式的に示した拡大図である。
【図８】 接触帯電装置を模式的に示した図である。
【図９】 実施例１に係る画像形成装置の書き込みユニットを模式的に示した図である。
【図１０】 階調性がよい例の明度と入力データのグラフである。
【図１１】 階調性が悪い例の明度と入力データのグラフである。
【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
９ 電源
１１ ４チャンネルレーザーダイオード
１２ コリメートレンズ
１３ ＮＤフィルタ
１４ アパーチャー
１５ シリンドリカルレンズ
１６ ポリゴンミラー
１７ ｆ−θレンズ１
１８ 折り返しミラー１
１９ 折り返しミラー２
２０ ｆ−θレンズ２
２１ 感光体面
２２ 同期検知板
３１ 導電性支持体
３３ 中間層（下引き層）
３５ 電荷発生層
３７ 電荷輸送層
３９ 保護層[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]
An outline of an image forming apparatus using an electrophotographic process, which is conventionally used, will be described below with reference to FIG. In FIG. 4, the photosensitive drum 1 is formed by applying a photosensitive member to the surface of a conductor and rotates in the direction of the arrow. In general, an image forming apparatus forms an image in the following procedure.
1 The charging means 2 charges the surface of the photoreceptor to a desired potential.
2 The exposure unit 3 exposes the photoconductor to form an electrostatic latent image corresponding to a desired image on the photoconductor.
3 In the developing unit 4, the electrostatic latent image formed by the exposing unit is developed with toner to form a toner image on the photoreceptor.
4 The transfer unit 5 transfers the toner image on the photoreceptor onto a recording sheet 6 such as paper conveyed by a conveyance unit (not shown).
5 The cleaning unit 7 cleans the toner that is not transferred onto the recording sheet by the transfer unit but remains on the photosensitive member.
6 The recording sheet to which the toner image has been transferred by the transfer unit is conveyed to the fixing unit 8. In the fixing unit 8, the toner is heated and fixed on the recording sheet.
7. Since the photosensitive drum rotates in the direction of the arrow in FIG. 1, a desired image is formed on the recording sheet by repeating the above steps 1-6.
[0003]
Of the steps 1 to 7, one charging means will be described. As a charging device in an electrophotographic process, a corona charging device that charges a photoreceptor using corona discharge has been conventionally used. FIG. 5 is a schematic diagram of an example of such a corona charging device. The material of the wire is tungsten in the example of FIG. 5, and the wire has a wire diameter of 60 μm. The wire is stretched in the axial direction of the photosensitive drum at a position (center of the case) as shown in FIG. 5, and a high voltage of about −7 kV is applied. This wire is covered with a charging case. The material of the case is stainless steel that is not easily oxidized. Further, a grid is stretched between the wire and the photoconductor, and a voltage of about −0.6 kV is applied. The grid is obtained by cutting a stainless steel plate having a thickness of 0.1 mm into a mesh shape.
[0004]
In the corona charging device shown in FIG. 5, the photosensitive member is charged as follows. In the vicinity of the stretched wire, a strong electric field is formed, air breakdown occurs, and ions are generated. Some of these ions move by the electric field between the wire and the photoconductor, and the surface of the photoconductor is charged. Since the charging of the photoconductor continues until the surface potential becomes substantially equal to the potential applied to the grid, the surface potential of the photoconductor can be controlled by the potential applied to the grid.
[0005]
As corona charging devices other than the corona charging device using a wire as a charging means, there are devices using a sawtooth electrode as a discharge electrode (Japanese Patent Laid-Open Nos. Hei 8-20210 and Hei 6-301286). FIG. 6 is a schematic view of an example of a corona charging device using the sawtooth electrode. The sawtooth electrode has a shape as shown in FIG. 7 and is made of a stainless steel plate having a thickness of 0.1 mm, and the apex pitch is 3 mm. This sawtooth electrode is fixed to a support member as shown in FIG. 6, and a high voltage of −5 kV is applied by a power source. Similarly to the corona charging device using a wire, the corona charging device using a sawtooth electrode is covered with a stainless steel charging case, and a grid is arranged between the sawtooth electrode and the photosensitive member. ing. The charging of the photosensitive member in the corona charging device using the sawtooth electrode is the same as that in the case of using the wire, and corona discharge occurs near the apex of the sawtooth electrode. Other corona charging devices have been devised in which the discharge electrode is a needle-like (pin-like) electrode.
[0006]
A corona charging device using a sawtooth electrode has advantages of small size and low ozone generation compared to the case of using a wire. In the sawtooth electrode, corona discharge occurs with directionality (the flow of ions toward the charging case is smaller than the flow of ions toward the grid (photoreceptor)). The opening width on the photoconductor side) can be reduced. This is important for realizing downsizing of the entire image forming apparatus. In addition, since the corona discharge has directionality, the charging efficiency of the photosensitive member is increased, and the current flowing through the corona charging device can be reduced. As a result, the amount of ozone generated is reduced.
[0007]
In addition to these corona charging devices, there are so-called contact charging devices as charging devices for image forming apparatuses. This contact charging device was a problem with the corona charging device,
1. A lot of ozone is generated
2. Large applied voltage (5-7 kV)
Etc. can be improved. For this reason, it is widely used as a charging device in low- and medium-speed electrophotographic image forming apparatuses.
[0008]
The contact charging device charges a photosensitive member by bringing a charging unit into contact with a photosensitive member (hereinafter simply referred to as a photosensitive member) as a member to be charged, and applying a voltage to the charging unit. FIG. 8 is an example of a conventional contact charging device, and shows a cross-sectional view thereof. The charging means 2 has a roller shape and has a diameter of 5 to 20 mm and a length of about 300 mm, and an elastic layer 2a is formed on the conductor 2b. The photoreceptor drum has a diameter of 30 to 80 mm and a length of about 300 mm, and the photoreceptor 1a is formed on the conductor 1b. The charging means comes into contact with the rotating photosensitive drum and rotates in a driven manner. The elastic layer of the charging means has a resistivity of 10 ⁷ -10 ⁹ Consists of Ω · cm material. Further, a surface protective layer having a thickness of about 10 to 20 μm may be formed on the surface of the charging means (the surface of the elastic layer). A voltage is applied to the charging means by the power source 9 to charge the photoreceptor. The applied voltage is -1.5 to -2.0 kV in direct current. With such a configuration, the contact charging device can uniformly charge the photosensitive member to −500 to −800V.
[0009]
Of the steps 1 to 7, the exposure means 2 will be described next. An exposure unit in an image forming apparatus using an electrophotographic process performs light modulation by causing a so-called LD (laser diode) to correspond to an output image. The laser light emitted from the LD forms an image on the photoconductor via a collimating lens, an aperture, a cylindrical lens, a polygon mirror, and an f-θ lens. The polygon mirror is a rotating polygon mirror, and the laser beam is scanned on the photosensitive member by this rotation. Therefore, the photosensitive member can be exposed to form an electrostatic latent image corresponding to a desired image on the photosensitive member.
[0010]
By the way, a so-called organic photoreceptor (OPC) has become the mainstream as a photoreceptor of an image forming apparatus using an electrophotographic process. In this organic photoreceptor, a laminated type in which a so-called charge generation layer and charge transport layer are laminated on a conductive substrate is mainly used. However, organic photoconductors are prone to film scraping due to repeated use, and as the photoconductive layer progresses, the photoconductor is charged, the photosensitivity is deteriorated, and the surface of the photoconductor is soiled due to scratches. However, there is a strong tendency for image density reduction or image quality degradation to be accelerated, and the wear resistance of photoreceptors has been cited as a major issue. Further, in recent years, with the increase in the speed of an electrophotographic apparatus or the reduction in the diameter of the photoreceptor accompanying the downsizing of the apparatus, it has become a more important issue to improve the durability of the photoreceptor. Therefore, in an organic electrophotographic photosensitive member, it has been cited as the most important issue particularly to achieve both high image quality and high durability.
[0011]
The following are examples of conventional techniques for achieving both high image quality and high durability.
JP-A-8-286407
In the present invention, the surface resistivity of the photoreceptor is 0.05 to 1 μm and the volume resistivity is 1 × 10. ⁸ It is characterized by containing inorganic particles of Ω · cm or more and further exposing such a photoreceptor with an exposure spot diameter of 80 μm or less. With such a combination, even when repeated use is performed, the film thickness of the photoreceptor is not reduced, and a stable image can be obtained without occurrence of defective cleaning. Further, it is assumed that defects such as image blurring that occur peculiarly when the exposure spot diameter is reduced and that occur when the surface of the photoreceptor deteriorates do not occur.
[0012]
Japanese Patent Laid-Open No. 9-319164
In the present invention, when the contrast potential is Vc (V), the initial charging potential is Vo (V), and the laser beam diameter is S μm, these are constant conditions,
Vc / Vo ≦ 0.92 · log (S) −0.018 · L−0.29
It is the feature to satisfy. By doing so, even if the thickness of the charge transport layer has the same thickness as the conventional film, it is possible to suppress the latent image deterioration and increase the resolution, and to reproduce a high-density and high-definition image. It is possible.
[0013]
Japanese Patent Laid-Open No. 11-95462
In this invention, the charge transport layer of the photoreceptor is
R1m-M- (OR2) n (M = Si, Al, Ti, Zr)
It contains at least one kind of reaction product of the compound represented by In this way, film formation due to wear and scratches is reduced during continuous image formation by repeated charging and exposure, and because it has excellent durability, the photosensitive layer can be made thin, and as a result, excellent gradation reproduction It is said that an electrophotographic photosensitive member capable of obtaining a high image quality output having the property can be obtained.
[0014]
Japanese Patent Laid-Open No. 6-138672 (Japanese Patent No. 3227230)
In the present invention, in an electrophotographic apparatus in which only the DC voltage is applied to the charging member to charge the photosensitive member, the difference between the maximum film thickness and the minimum film thickness of the charge transport layer in the image forming region is 1.0 μm or less. The charge generation layer contains a compound represented by a specific structural formula. By configuring the photoconductor as described above, it is possible to solve problems such as (1) non-uniform charging and (2) dielectric breakdown of the photoconductor, which could not be solved conventionally. Yes.
[0015]
Japanese Patent Laid-Open No. 7-175230 (Japanese Patent No. 03001761)
In the present invention, an image for forming an electrostatic latent image using a laser beam on a photosensitive member containing a conductive metal powder having a primary particle size of 0.3 μm or less or a fluororesin on the surface layer of the photosensitive layer. In the forming apparatus, when the area of the basic pixel unit is S and the laser beam area on the photosensitive member surface is S ′, S ′ / S <1/2. By doing so, an image forming apparatus with high reproducibility of the highlight portion can be provided.
[0016]
[Problems to be solved by the invention]
In general, in an image forming apparatus using an electrophotographic method, it is known that the film thickness of a photosensitive member needs to be reduced (thinned) in order to follow a developing electric field up to a high spatial frequency (in electrophotographic technology). Basics and application: Corona p.150-151). However, as pointed out in the prior art (Japanese Patent Laid-Open No. 11-95462, etc.), when the photosensitive member film thickness is reduced, the durability against abrasion and scratches due to cleaning deteriorates, and charging There is a problem in that deterioration is accelerated when the process and the exposure process are repeated. In conventional laminated organic photoreceptors, polycarbonate is generally used as the binder resin for the charge transport layer, but due to these problems, the thickness of the charge transport layer is set to about 20 to 30 μm. It is common.
[0017]
However, in this case, particularly when writing halftone processed image data with a line number of 200 lpi or more, gradation is poor, and for an image that needs gradation expression such as a photographic image, A satisfactory image was not obtained. In the electrophotographic image forming apparatus, as described above, the elastic blade is in contact with the photosensitive member for the purpose of removing the untransferred toner from the photosensitive member. At this time, since the photoconductor is rubbed by the elastic blade, there is a problem that the photoconductor is scraped by long-term use and the film thickness gradually decreases. This is film removal of the photoreceptor. When the film thickness of the photoconductor is reduced from the initial state as described above, for example, when a photoconductor having a film thickness of 20 μm is used in the initial state, the film of the photoconductor is scraped off during use of the image forming apparatus. Since the film thickness gradually becomes smaller, the problem that the photoconductor breaks down has been pointed out.
[0018]
The present invention also proposes the realization of an image forming apparatus in which a density difference does not occur in an output image not only in the initial stage but also in a long-term use. That is, in the past, uneven wear occurred in the photoconductor during long-term use, causing density differences. However, in the present invention, an image forming apparatus that does not cause density differences that are expected to be caused by such uneven wear. The purpose is realization. On the other hand, for example, the technique described in Japanese Patent Laid-Open No. 6-138672 has a technical problem of a difference in film thickness (coating unevenness) of the photosensitive member in the initial state. This is different from the present invention.
[0019]
SUMMARY OF THE INVENTION Accordingly, an object of the present invention is an image forming apparatus capable of achieving both high durability and high image quality, and can stably obtain a high quality image even when it is repeatedly used. An image forming apparatus is provided.
[0020]
[Means for Solving the Problems]
As a result of intensive studies, the present inventors have found that an intended image forming apparatus can be provided by satisfying the following configuration requirements.
That is, according to the first aspect of the present invention, at least a photosensitive member, a charging unit whose charging potential is changed by a change in the film thickness of the photosensitive member, and optical writing to the photosensitive member to form an electrostatic latent image. An image forming apparatus having an optical writing unit that performs image processing, and an image processing unit that performs halftone processing on an input image, wherein optical writing by the writing unit is performed with a halftone level of 200 lpi or more on an input image. Based on the processed image data, a charge generation layer and a charge transport material, which are formed with a laser beam having a beam diameter of 35 μm or less and the photosensitive member contains at least a charge generation material on a conductive support, A charge transport layer, and a protective layer containing a charge transport material and a filler on the charge transport layer and having a transmittance for writing light of 90% or more. Image forming apparatus is provided that the total thickness of the layer and the protective layer is equal to or is 20μm or less.
[0021]
Further, in the second aspect of the present invention, at least a photosensitive member, a charging unit having a constant charging potential independent of a change in the film thickness of the photosensitive member, and an electrostatic latent image by performing optical writing on the photosensitive member. In an image forming apparatus having an optical writing unit that forms a halftone image and an image processing unit that performs a halftone process on an input image, the optical writing is performed by the writing unit with a halftone of 200 lpi or more on the input image. A charge generation layer and a charge transport material, which are processed with a laser beam having a beam diameter of 35 μm or less based on the processed image data, and the photoconductor includes at least a charge generation material on a conductive support A charge transport layer containing a charge transport material and a charge transport layer and a protective layer containing a filler and having a transmittance of 90% or more with respect to writing light. Image forming apparatus is provided that the total thickness of the transmission layer and the protective layer is equal to or is 20μm or less.
[0022]
Until the completion of the present invention, the present inventors conducted the following experiments or considerations. According to experiments conducted by the present inventors, when a photoconductor having a charge transport layer of about 30 μm is used, image data is written by performing halftone processing with a line number of 200 lpi or more. When output, there is a problem that a satisfactory image cannot be obtained with respect to an image which has poor gradation and requires gradation expression such as a photographic image. On the other hand, when the halftone processing is less than 200 lpi, there is a problem that although the gradation property is ensured, the texture of the dither is visually perceived and a fine image cannot be obtained. Furthermore, it has also been clarified that under the condition of poor gradation, that is, when halftone processing of 200 lpi or more is performed in this case, so-called banding is likely to occur and only a noisy image can be obtained. .
[0023]
Furthermore, the experiments by the present inventors have revealed that when a thinned photoconductor having a film thickness of about 20 μm is used, the influence of so-called photoconductor film shaving becomes larger. In addition to this, the film scraping described in the column of the problem to be solved by the invention does not occur uniformly, and the film scraping occurs in a state biased in the circumferential direction or the axial direction of the photosensitive member (uneven wear). ) That is, when used over a long period of time, even if the thickness of the photoreceptor is initially uniform (constant), the thickness of the photoreceptor becomes non-uniform over time. The reason why the photoconductor is subject to uneven wear is that the circumferential wear of the photoconductor is different in the contact pressure of the blade in the circumferential direction of the photoconductor due to the eccentricity of the photoconductor drum, etc. The wear is considered to be caused by the non-uniformity of the blade contact pressure due to the deformation of the blade support member.
[0024]
The inventors' experiments have revealed that the following problems occur in the entire image forming apparatus system when the film thickness difference occurs on the photosensitive member for the above-described reason. When a difference in film thickness of the photoconductor occurs, there arises a problem that the charging potential of the photoconductor at the charging means changes. The charging potential depends on the thickness of the photoconductor, such as a scorotron or a contact charging method that applies a DC voltage. Unless there is a mechanism to control, the charging potential changes depending on the film thickness of the photoreceptor. Such a change in charging potential causes a difference in density in the output image obtained when development is performed by the developing unit after writing by the exposure unit. That is, patches that should originally have the same density have different densities depending on the film thickness of the photoreceptor. The first aspect of the present invention is a means for solving the problem in the case of the charging means of the type in which the charging potential is changed according to the change in the film thickness of the photosensitive member mainly using a DC voltage.
[0025]
On the other hand, when there is a difference in the film thickness of the photoconductor, for example, the charging potential is constant without depending on the film thickness change of the photoconductor such as the contact charging method or the contact AC charging roller method to which an AC superimposed voltage is applied. Even if the charging potential can be set to a constant voltage by the charging means, the electrostatic capacity determined by the film thickness of the photoconductor is different, so that there is still a difference in the charge amount on the photoconductor. As a result, when optical writing is performed by the exposure means, the result is that the sensitivity characteristics of the photoconductor are different, and the potential after exposure is different. For this reason, the patches that should originally have the same density have different densities depending on the film thickness of the photoreceptor. The second aspect of the present invention is a means for solving the problem in the case of the charging means in which the charging potential of the photoreceptor is constant, mainly using an AC voltage.
[0026]
In the present invention, in both the first and second embodiments, the surface of the charge transport layer is further reduced by disposing a surface protective layer on the charge transport layer. By satisfying this and other conditions such as the number of lines in halftone processing, the laser beam diameter, the transmittance of the photoconductor protective layer, the thickness of the charge transport layer and the protective layer, a high value of 200 lpi or more as described above is achieved. Even in an image that has been subjected to halftone processing with the number of lines, it is possible to provide an image forming apparatus that does not suffer from the problem that gradation is deteriorated and sufficient image quality cannot be obtained. This is as specifically shown in the examples described later. Further, the structure of the surface protective layer in the present invention is different from any of the conventional methods (JP-A-8-286470, JP-A-9-319164, JP-A-11-95462, JP-A-7-175230) and is unique. belongs to.
[0027]
Although the material and manufacturing method of the protective layer will be described later, the protective layer together with the charge transport layer is set to 20 μm or less from the viewpoint of resolution in the present invention. If the protective layer thickness is extremely thin, the uniformity of the film may be reduced and sufficient wear resistance may not be obtained.If the film thickness is extremely thick, there is an effect of an increase in residual potential. In some cases, the resolution or dot reproducibility may decrease due to an increase in light transmittance.
[0028]
Furthermore, in the present invention, in addition to the total film thickness of the charge transport layer and the protective layer being 20 μm or less, the film thickness difference between the maximum film thickness location and the minimum film thickness location on the entire surface of the photoreceptor image region is When the charging means according to the first aspect is a charging means whose charging potential changes according to the change in film thickness of the photosensitive member (for example, a contact DC charging roller system, scorotron), the charging means according to the second aspect is 1.5 μm or less. However, in the case of a charging unit (for example, a contact AC charging roller system) in which the charging potential is constant without depending on the change in the film thickness of the photosensitive member, the thickness is preferably 3.5 μm or less. As a result, in addition to the above-described improvement in gradation, the obtained image has improved brightness differences.
[0029]
As specifically shown in the examples to be described later, in the case of the charging method to which a DC voltage is applied, which is the first aspect of the present invention, the maximum film thickness portion on the entire surface of the photoreceptor image area in the initial state If the film thickness difference from the minimum film thickness location (hereinafter simply referred to as film thickness difference) is 1.5 μm or less, the density change of the output image that can be measured by the brightness difference is small, and this range of film thickness difference is output. It was found to guarantee the stability of the image. In the apparatus of the present invention, even after a large amount of paper is passed, uneven wear is suppressed, so that the difference in film thickness is relatively small and the brightness difference in the output image is not so large.
[0030]
An image forming apparatus that uses a contact charging method or a scorotron to which a DC voltage is applied has a feature that the charging potential changes depending on the film thickness of the photoreceptor. Actually, an experiment conducted by the inventors has obtained a result that changes about 10 V per 1 μm change of the photosensitive member film thickness. The change in the charging potential of 10V has a great influence in terms of making the image density constant, and as a result, a density difference occurs in the output image. Therefore, in an image forming apparatus using a contact charging method in which a DC voltage is applied as a charging means, in addition to the above conditions, the difference in film thickness is 1.5 μm or less. It is important from the viewpoint of making it constant.
[0031]
On the other hand, in the case where the charging device is a contact charging device to which an AC superimposed voltage is applied, as specifically shown in the examples described later, if the difference in film thickness of the photosensitive member is 3.5 μm or less in the initial state, It was found that the change in the density of the output image that can be measured by the brightness difference is small, and this film thickness difference range ensures the stability of the output image. Within this film thickness difference range, the increase in film thickness difference is relatively small even after a large amount of paper is passed, and the brightness difference in the output image does not become so large. However, when the conditions such as the transmittance of the protective layer as described above are not satisfied, the difference in film thickness of the photoconductor is 1.5 μm or less over the entire image output range of the photoconductor drum in order to prevent the density change. In terms of manufacturing the photosensitive drum, it becomes a bottleneck in the manufacturing of the photosensitive member, causing a deterioration in yield and increasing the cost. Therefore, in the second aspect of the present invention, in addition to the above conditions, the method of suppressing the film thickness difference to about 3.5 to 1.5 μm is a cost for guaranteeing the lightness stability of the output image even in long-term use. From the point of view, it is excellent.
[0032]
It can be seen that when a contact charging device to which an AC superimposed voltage is applied is used as the charging means, the allowable range of the difference in film thickness of the photoconductor is wider than when a charging device to which a DC voltage is applied or a scorotron is used. . This is because the charging potential changes in a contact charging device or scorotron to which a DC voltage is applied, whereas in a charging device to which an AC superimposed voltage is applied, the charging potential does not depend on the film thickness of the photoconductor. This is the reason for the difference. Even when a charging unit to which an AC superimposed voltage is applied is used, the brightness of the output image changes. The reason for changing the lightness at this time is that the capacitance of the photoconductor changes and the amount of charge accumulated on the photoconductor changes due to the change in the film thickness of the photoconductor. Since the amount of photocarriers generated in the charge generation layer by writing has little relation to the amount of charge accumulated on the photoreceptor, the way in which the potential decreases after exposure varies depending on the film thickness of the photoreceptor. From the viewpoint of exposure energy, it can be seen that the sensitivity of the photoreceptor changes. This is the cause of the difference in the allowable range of the change in the photoreceptor film thickness that guarantees the brightness of the output image to be constant depending on the method of the charging means.
[0033]
The reason why the allowable range of the photosensitive member film thickness varies depending on the charging means used is as described above. Therefore, for example, even when a DC voltage application type contact charging device or scorotron is used, if the charging potential of the photosensitive member can be made constant (independent of the photosensitive member film thickness) using a control device, etc. It is possible to present conditions with a wide allowable range with respect to the film thickness difference of the photosensitive member.
[0034]
The film thickness difference will be described with reference to a generally used dip coating method. As its name suggests, the dip coating method involves moving the container (immersion coating tank) containing the photosensitive material coating solution and the photosensitive substrate relative to each other, immersing the photosensitive substrate in the coating solution, and then pulling it up. In this method, a coating solution is applied on the photoreceptor substrate. Usually, further, the pulled-up photoconductor substrate is allowed to stand still, naturally dried (touch-drying), and then completely dried in an oven or the like to produce a photoconductor. And in order to manufacture an electrophotographic photoreceptor in a short time, a fast-drying solvent is usually used as the solvent for the coating solution. As a result, the drying speed of the coating liquid can be increased to solidify in a short time, but after the immersion, the solvent vapor generated thereby can be removed even in the weak air flow from the pulling up to the touch drying. The flow gives a thickness unevenness to the formed photosensitive layer.
[0035]
Usually, in order to reduce such thickness unevenness, the vapor density of the solvent is controlled, the flow of the surrounding air is made constant, the solid content concentration of the coating liquid is increased, and it is pulled up slowly. Is taking the way. By adopting such a method, the film thickness difference can be made 3.5 μm or less. Further, as in the method described in Japanese Patent Application Laid-Open No. 2001-194814, a film thickness difference is set to 1. by using a method in which a hood is installed around the photoreceptor substrate in order to optimize ambient influences and airflow. It can be 5 μm or less.
[0036]
In the case of spray coating, the airflow during spraying, the amount of liquid discharged, the distance between the spray gun and the photoconductor substrate, the feed rate of the spray gun (feed rate in the longitudinal direction of the photoconductor substrate) and the photoconductor substrate The uniformity of the rotation speed changes the uniformity (thickness difference) of the photosensitive layer, and generally there is no turbulence in the airflow. The distance between the spray gun and the photosensitive substrate, the liquid discharge amount, the spray gun feed speed, If the rotational speed of the photosensitive substrate is constant and uniform, it is possible to provide a photosensitive layer with little difference in film thickness. Conversely, the film thickness difference can be changed by changing these conditions.
[0037]
The maximum electric field strength of the electric field applied to the charge transport layer and the protective layer by the charging means is preferably −30 V / μm. If the value is smaller (in absolute value), the charge transport layer is electrostatically irreversible during repeated use of the photoreceptor, and the possibility of local breakdown is reduced. is there. On the other hand, when the value exceeds this value, the charge transport layer locally causes dielectric breakdown, and the background fog is extremely increased in the output image.
[0038]
Hereinafter, an electrophotographic photosensitive member used in the image forming apparatus of the present invention will be described with reference to the drawings.
FIG. 2 shows a configuration in which a charge generation layer 35 mainly composed of a charge generation material and a charge transport layer 37 containing a charge transport material are laminated on a conductive support 31. Further, the protective layer 39 containing a filler and a charge transport material is formed thereon. FIG. 3 shows a configuration in which an intermediate layer (undercoat layer) 33 is provided between the conductive support 31 and the charge generation layer 35 in FIG.
[0039]
2 and 3, the following is used as the conductive support 31. That is, the volume resistance is 10 ¹⁰ Films having conductivity of Ω · cm or less, for example, metals such as aluminum, nickel, chromium, nichrome, copper, gold, silver, platinum, and metal oxides such as tin oxide and indium oxide are deposited or sputtered. Shaped or cylindrical plastic, paper-coated, or aluminum, aluminum alloy, nickel, stainless steel, etc., and then making them into bare tubes by methods such as extrusion and drawing, cutting, super finishing, polishing, etc. A surface-treated tube or the like can be used. Further, an endless nickel belt or an endless stainless steel belt disclosed in Japanese Patent Application Laid-Open No. 52-36016 can also be used as the conductive support 31.
[0040]
In addition, a material obtained by dispersing conductive powder in an appropriate binder resin and coating it on the support can also be used as the conductive support 31 of the present invention. Examples of the conductive powder include carbon black, acetylene black, metal powder such as aluminum, nickel, iron, nichrome, copper, zinc and silver, or metal oxide powder such as conductive tin oxide and ITO. It is done. The binder resin used at the same time is polystyrene, styrene-acrylonitrile copolymer, styrene-butadiene copolymer, styrene-maleic anhydride copolymer, polyester, polyvinyl chloride, vinyl chloride-vinyl acetate copolymer. , Polyvinyl acetate, polyvinylidene chloride, polyarylate resin, phenoxy resin, polycarbonate, cellulose acetate resin, ethyl cellulose resin, polyvinyl butyral, polyvinyl formal, polyvinyl toluene, poly-N-vinyl carbazole, acrylic resin, silicone resin, epoxy resin, Examples thereof include thermoplastic, thermosetting resins, and photocurable resins such as melamine resin, urethane resin, phenol resin, and alkyd resin. Such a conductive layer can be provided by dispersing and applying these conductive powder and binder resin in a suitable solvent such as tetrahydrofuran, dichloromethane, methyl ethyl ketone, toluene, and the like.
[0041]
Furthermore, it is electrically conductive by a heat-shrinkable tube in which the conductive powder is contained in a material such as polyvinyl chloride, polypropylene, polyester, polystyrene, polyvinylidene chloride, polyethylene, chlorinated rubber, and Teflon (registered trademark) on a suitable cylindrical substrate. Those provided with a conductive layer can also be used favorably as the conductive support 31 of the present invention.
[0042]
Next, the charge generation layer 35 is a layer mainly composed of a charge generation material, in which the charge generation material, the binder resin or the like is dispersed or dissolved in an appropriate solvent, and this is applied to the conductive support or the undercoat layer. It can be formed by coating and drying. For the charge generation layer 35, it is possible to use all known charge generation materials, and representative examples thereof include phthalocyanine pigments such as titanyl phthalocyanine, vanadyl phthalocyanine, copper phthalocyanine, hydroxygallium phthalocyanine, and metal-free phthalocyanine, monoazo pigments, Known azo pigments such as disazo pigments, asymmetric disazo pigments, trisazo pigments, perylene pigments, perinone pigments, indigo pigments, pyrrolopyrrole pigments, anthraquinone pigments, quinacridone pigments, quinone condensed polycyclic compounds, squalium pigments, etc. Materials are mentioned, and these are preferably used. These charge generating materials can be used alone or in combination of two or more.
[0043]
In the charge generation layer 35, a charge generation material is dispersed in a suitable solvent together with a binder resin as necessary using a ball mill, an attritor, a sand mill, an ultrasonic wave, etc., and this is applied onto a conductive support. It is formed by drying.
[0044]
As the binder resin used for the charge generation layer 35 as necessary, polyamide, polyurethane, epoxy resin, polyketone, polycarbonate, silicone resin, acrylic resin, polyvinyl butyral, polyvinyl formal, polyvinyl ketone, polystyrene, polysulfone, poly-N -Vinylcarbazole, polyacrylamide, polyvinyl benzal, polyester, phenoxy resin, vinyl chloride-vinyl acetate copolymer, polyvinyl acetate, polyphenylene oxide, polyamide, polyvinyl pyridine, cellulosic resin, casein, polyvinyl alcohol, polyvinyl pyrrolidone, etc. Can be mentioned. The amount of the binder resin is suitably 0 to 500 parts by weight, preferably 10 to 300 parts by weight with respect to 100 parts by weight of the charge generating material. The binder resin may be added before or after dispersion.
[0045]
Solvents for dispersing the charge generating material include isopropanol, acetone, methyl ethyl ketone, cyclohexanone, tetrahydrofuran, dioxane, ethyl cellosolve, ethyl acetate, methyl acetate, dichloromethane, dichloroethane, monochlorobenzene, cyclohexane, toluene, xylene, ligroin, etc. Among them, ketone solvents, ester solvents, and ether solvents are particularly preferably used. These may be used alone or in combination of two or more.
[0046]
The charge generation layer 35 includes a charge generation material, a solvent, and a binder resin as main components, and includes any additive such as a sensitizer, a dispersant, a surfactant, and silicone oil. Also good.
[0047]
As a coating method for the coating solution, a dip coating method, spray coating, beat coating, nozzle coating, spinner coating, ring coating, or the like can be used. The thickness of the charge generation layer 35 is suitably about 0.01 to 5 μm, preferably 0.1 to 2 μm.
[0048]
The charge transport layer 37 can be formed by dissolving or dispersing a charge transport material and a binder resin in a suitable solvent, and applying and drying the solution on the charge generation layer. If necessary, one or more plasticizers, leveling agents, antioxidants, lubricants and the like can be added.
[0049]
As the solvent used for forming the charge transport layer, tetrahydrofuran, dioxane, toluene, dichloromethane, monochlorobenzene, dichloroethane, cyclohexanone, methyl ethyl ketone, acetone and the like are used. These may be used alone or in combination of two or more. As a coating method for the coating solution, a dip coating method, spray coating, beat coating, nozzle coating, spinner coating, ring coating, or the like can be used.
[0050]
Charge transport materials are classified into hole transport materials and electron transport materials. Examples of the electron transporting material include chloroanil, bromoanil, 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-tri Examples thereof include electron-accepting substances such as nitrodibenzothiophene-5,5-dioxide and benzoquinone derivatives.
[0051]
Among the charge transport materials, the hole transport materials include poly-N-vinylcarbazole and derivatives thereof, poly-γ-carbazolylethyl glutamate and derivatives thereof, pyrene-formaldehyde condensates and derivatives thereof, polyvinylpyrene, and polyvinylphenanthrene. , Polysilane, oxazole derivative, oxadiazole derivative, imidazole derivative, monoarylamine derivative, diarylamine derivative, triarylamine derivative, stilbene derivative, α-phenylstilbene derivative, benzidine derivative, diarylmethane derivative, triarylmethane derivative, 9 -Styryl anthracene derivatives, pyrazoline derivatives, divinylbenzene derivatives, hydrazone derivatives, indene derivatives, butadiene derivatives, pyrene derivatives, etc., bis-stilbene derivatives, ena Other known materials such as a min derivative are included. These charge transport materials may be used alone or in combination of two or more.
[0052]
As the binder resin for the charge transport layer, polystyrene, styrene-acrylonitrile copolymer, styrene-butadiene copolymer, styrene-maleic anhydride copolymer, polyester, polyvinyl chloride, vinyl chloride-vinyl acetate copolymer, Polyvinyl acetate, polyvinylidene chloride, polyarylate, phenoxy resin, polycarbonate, cellulose acetate resin, ethyl cellulose resin, polyvinyl butyral, polyvinyl formal, polyvinyl toluene, poly-N-vinyl carbazole, acrylic resin, silicone resin, epoxy resin, melamine resin And thermoplastic or thermosetting resins such as urethane resin, phenol resin, and alkyd resin.
[0053]
In the device of the present invention, the thickness of the charge transport layer is set to 20 μm or less from the viewpoint of resolution together with the protective layer. The lower limit varies depending on the system to be used (particularly charging potential), but is preferably 5 μm or more.
[0054]
A protective layer 39 is formed on the charge transport layer 37 by dispersing or dissolving a filler, a charge transport material, and a binder resin in an appropriate solvent for the purpose of improving durability, and applying and drying. Is done.
[0055]
A filler material is added to the protective layer for the purpose of improving wear resistance. The transmittance of the protective layer containing the filler with respect to writing light is 90% or more in the device of the present invention. If it is 90% or more, the image quality is not affected. However, if it is less than 90%, the reproducibility of the written dot in the latent image is lowered and the image quality is lowered. Note that the transmittance of the protective layer with respect to the writing light is a coating film obtained by coating the protective layer on a highly transparent film such as PET when the protective layer is peelable, and when the protective layer is not peelable. Can be obtained by measuring the transmittance with a spectrophotometer using an integrating sphere.
[0056]
The refractive index of the filler is preferably 1.0 to 2.0, and the same applies to this, and when the refractive index is less than 1.0 and greater than 2.0, the transmittance of the protective layer decreases, and therefore The reproducibility of the written dot in the latent image is lowered and the image quality is lowered. The refractive index of the filler can be determined, for example, from the refractive index of a liquid in which particles are immersed in a liquid whose refractive index value can be changed little by little and the particle interface becomes unclear. The refractive index of the liquid can be obtained by an Abbe refractometer or the like.
[0057]
Fillers are classified into organic fillers and inorganic fillers, and examples of organic filler materials include fluororesin fine particles such as polytetrafluoroethylene, silicone resin fine particles, and a-carbon powder. Inorganic filler materials include copper, Metal powder such as tin, aluminum and indium, silica, tin oxide, zinc oxide, titanium oxide, alumina, zirconium oxide, indium oxide, antimony oxide, bismuth oxide, calcium oxide, antimony doped tin oxide, tin doped oxide Examples thereof include metal oxides such as indium, metal fluorides such as tin fluoride, calcium fluoride, and aluminum fluoride, and inorganic materials such as potassium titanate and boron nitride. Among these fillers, it is advantageous to use an inorganic material from the viewpoint of the hardness of the filler to improve the wear resistance.
[0058]
As the filler that is less likely to cause image blurring, a filler having high electrical insulation is preferable, and those having a pH of the aqueous dispersion of the filler of 5 or more are particularly effective, such as titanium oxide, alumina, zinc oxide, zirconium oxide, and the like. It can be used particularly effectively. In addition, the fillers can be used alone or in combination of two or more.
[0059]
The pH was measured by dispersing the filler in water and measuring the pH. Specifically, the pH was measured according to JIS K5101 / 24. The pH of the filler aqueous dispersion also varies depending on the filler production method, for example, the pH control during production, and also varies depending on the pH of water during final filler washing, as shown in the present invention. In particular, those having a value of 5 or more are particularly effective.
[0060]
Due to the requirements described above, α-type alumina, which has a high insulation property among these fillers, has high thermal stability, and has high wear resistance, is a hexagonal close-packed structure, which suppresses image blurring and wear resistance. This is particularly useful in terms of improvement.
[0061]
The average primary particle size of the filler is preferably 0.01 to 0.5 μm from the viewpoint of light transmittance and wear resistance of the protective layer. When the average primary particle size of the filler is less than 0.01 μm, it causes a decrease in wear resistance due to agglomeration and dispersibility, and when it exceeds 0.5 μm, the settling of the filler is promoted. There is a possibility that an abnormal image may be generated in an image obtained by a photoconductor produced using the above.
[0062]
Moreover, these fillers can be surface-treated with at least one kind of surface treatment agent, and it is preferable to do so from the viewpoint of dispersibility of the filler. Decreasing the dispersibility of the filler not only increases the residual potential, but also decreases the transparency of the coating film and causes coating film defects, as well as a decrease in wear resistance and an increase in uneven wear. There is a possibility that it will develop into a big problem that prevents high image quality. As the surface treatment agent, all conventionally used surface treatment agents can be used, but a surface treatment agent capable of maintaining the insulating properties of the filler is preferable. For example, titanate coupling agents, aluminum coupling agents, zircoaluminate coupling agents, metal salts such as higher fatty acids or aluminum stearate, or mixed treatments thereof, Al ₂ O ₃ TiO ₂ , ZrO ₂ , Silicone, aluminum stearate, etc., or a mixture thereof is more preferable from the viewpoint of filler dispersibility and image blur. Single treatment with a silane coupling agent has a strong influence on image blur especially at high temperature and high humidity, but the influence may be suppressed by applying a mixture treatment of the above surface treatment agent and silane coupling agent. . The surface treatment amount varies depending on the average primary particle size of the filler used, but is preferably 2 to 30 wt%, more preferably 3 to 20 wt%. 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. Further, even when the filler has low insulation and image blur is likely to occur, these surface treatments can increase the insulation and reduce the influence of image blur.
[0063]
By containing these fillers, it is possible to suppress image blur at the time of high temperature and high humidity simultaneously with realization of high durability, but the influence of the increase in residual potential increases. In order to suppress the increase in the residual potential, an organic compound having a carboxyl group in the structure is added as a dispersant, so that the dispersibility of the filler can be improved and the charge trap sites can be reduced. In order to reduce the residual potential, it is also important that the dispersant has an acid value of 10 to 400 mgKOH / g, and among these, polycarboxylic acid derivatives can be used particularly effectively. The acid value is defined as the number of milligrams of potassium hydroxide required to neutralize free fatty acids contained in 1 g. Further, the dispersant and the material having an acid value can be made to function by different materials. For example, even if the acid value of the dispersant is not in the range of 10 to 400 mgKOH / g, it can function sufficiently by mixing a resin or additive having an acid value of 10 to 400 mgKOH / g. It is also possible to mix generally known organic fatty acids, high acid value resins and the like.
[0064]
Known dispersants can be used as the dispersant, but the acid value of these dispersants is preferably 10 to 400 mgKOH / g, more preferably 30 to 200 mgKOH / g. . In particular, an organic compound having a structure containing at least one carboxyl group in a polymer or copolymer is preferred. If the acid value is higher than necessary, the influence of image blur may appear. If the acid value is too low, it is necessary to increase the amount of addition, and the effect of reducing the residual potential becomes 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 reducing 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. In addition, since the vicinity of the interface between the protective layer and the charge transport layer has a great influence on the residual potential, in the protective layer in the present invention, a material having a higher acid value is formed near the protective layer / photosensitive layer interface than on the surface side. It can also be contained, and is useful in suppressing an increase in residual potential.
[0065]
As the dispersant, a polycarboxylic acid derivative is more preferable from the viewpoint of dispersibility. The carboxylic acid moiety in the dispersant plays an important role of giving an acid value and increasing dispersibility. A hydrophilic inorganic filler has low affinity with an organic solvent or a binder resin, and often does not disperse well as it is. However, the dispersant in the present invention 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. It becomes possible to increase the affinity with an organic solvent, a binder resin and the like. This makes it possible to greatly increase the dispersibility of the filler. Furthermore, although the effect is recognized even if the dispersant has one carboxyl group, the polycarboxylic acid derivative having more carboxyl groups improves the dispersibility of the filler, reduces the residual potential, etc. Is effective. In that case, not only the affinity between the dispersant and the filler is further increased, but also by having the 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 It is possible to obtain the effect of suppressing the above.
[0066]
The amount of the dispersant added preferably satisfies the following relational expression depending on the acid value of the dispersant used.
0.1 ≦ (addition amount of dispersing agent × acid value of dispersing agent)
/ (Addition amount of filler) ≦ 20
Furthermore, it is more preferable to set the required minimum amount as well as satisfying this relational expression. 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 dispersibility and reducing the residual potential will not be sufficiently exerted, resulting in the occurrence of abnormal images. Become.
[0067]
As the binder resin contained in the protective layer, it is possible to use all of the binder resins used in the charge transport layer 37 described above, but the filler dispersibility is also affected by the binder resin. It is important not to adversely affect the dispersibility. In addition, the resin having an acid value is useful for reducing the residual potential, and can be used as a binder resin all or mixed with other binder resins and partially added. . Examples of usable resins include polyester, polycarbonate, acrylic resin, polyethylene terephthalate, polybutylene terephthalate, various copolymers using acrylic acid and methacrylic acid, styrene acrylic copolymer, 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, poly Methylbenten, polypropylene, polyphenylene oxide, polysulfone, AS resin, butadiene-styrene copolymer, polyurethane, polyvinyl chloride, polyvinylidene chloride Mentioned resins or copolymers and the like. These materials can be used in combination of two or more.
[0068]
In addition, the binder resin has a significant effect on image blur. Using a binder resin having high NOx resistance or ozone resistance not only suppresses image blur but also improves wear resistance. And is very effective in maintaining high image quality over time. As these binder resins, polymer alloys can also be used effectively, and at least a polymer alloy with polyethylene terephthalate has a high image blur suppression effect and is useful.
[0069]
In the protective layer of the photoreceptor used in the apparatus of the present invention, at least one kind of charge transport material is contained in order to reduce the residual potential. As the charge transport material contained in the protective layer, it is possible to use all the charge transport materials contained in the charge transport layer 37 formed on the above-described charge generation layer, but the charge contained in the protective layer. The transport material and the charge transport material contained in the charge transport layer may be different from each other. In that case, the charge transport material contained in the protective layer has a lower ionization potential than the charge transport material contained in the charge transport layer, thereby improving the charge injection property at the charge transport layer / protective layer interface. This is very effective in reducing the residual potential. That is, the following relationship exists between the ionization potential Ip of the charge transport material contained in the protective layer and the ionization potential Ip of the charge transport material contained in the charge transport layer.
(Ip of charge transport material contained in protective layer) ≦ (Ip of charge transport material contained in charge transport layer)
Is preferably satisfied. Note that the ionization potential can be measured using various methods such as a spectroscopic method and an electrochemical method.
[0070]
Further, the protective layer is changed by NOx or ozone gas without greatly affecting the residual potential by changing the concentration so that the concentration of the charge transport material contained in the protective layer becomes the lowest in the outermost surface region of the protective layer. It is possible to reduce the influence of image quality deterioration. In particular, it is more preferable to provide a concentration gradient in which the concentration of the charge transport material continuously decreases from the protective layer / photosensitive layer interface toward the outermost surface of the protective layer in order to suppress an increase in residual potential. These deteriorations in image quality are considered to be caused by the decomposition and alteration of the charge transport material, which can be mitigated by reducing the concentration of the charge transport material contained in the protective layer. Is possible.
[0071]
For the protective layer, a polymer charge transport material having a function as a charge transport material and a function as a binder resin is also preferably used. The charge transport layer composed of these polymer charge transport materials is excellent in wear resistance. A known material can be used as the polymer charge transporting material, but any of polycarbonate resins, polyarylate resins and polyester resins, or a mixture of two or more thereof is useful. 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 formulas (I) to (X) are preferably used. These are illustrated below and specific examples are shown.
[0072]
[Chemical 1]
(I) Formula

In formula (I), R ₁ , R ₂ , R ₃ Each independently represents a substituted or unsubstituted alkyl group or a halogen atom, R ₄ Is a hydrogen atom or a substituted or unsubstituted alkyl group, R ₅ And R ₆ Is a substituted or unsubstituted aryl group, o, p, q are each independently an integer of 0-4, k, j are compositions, 0.1 ≦ k ≦ 1, 0 ≦ j ≦ 0.9, n Represents the number of repeating units and is an integer of 5 to 5000. X represents an aliphatic divalent group, a cycloaliphatic divalent group, or a divalent group represented by the following general formula.
[0073]
[Chemical 2]

In the above formula, R ₁₀₁ , R ₁₀₂ Each independently represents a substituted or unsubstituted alkyl group, aryl group or halogen atom. l and m are integers of 0 to 4, Y is 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- (wherein Z represents an aliphatic divalent group).
[0074]
[Chemical 3]
Or, in formula (I), X is

(Wherein, 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. ). Where R ₁₀₁ And R ₁₀₂ , R ₁₀₃ And R ₁₀₄ May be the same or different.
[0075]
[Formula 4]
(II) Formula

In formula (II), R ₇ And R ₈ Is a substituted or unsubstituted aryl group, Ar ₁ , Ar ₂ , Ar ₃ Represent the same or different arylene groups. X, k, j, and n are the same as in the formula (I).
[0076]
[Chemical formula 5]
(III) Formula

In formula (III), R ₉ And R ₁₀ Is a substituted or unsubstituted aryl group, Ar ₄ , Ar ₅ , Ar ₆ Represent the same or different arylene groups. X, k, j, and n are the same as in the formula (I).
[0077]
[Chemical 6]
(IV) Formula

In formula (IV), R ₁₁ , R ₁₂ Is a substituted or unsubstituted aryl group, Ar ₇ , Ar ₈ , Ar ₉ Represent the same or different arylene groups. X, k, j, and n are the same as in the formula (I).
[0078]
[Chemical 7]
(V) Formula

In formula (V), R ₁₃ , R ₁₄ Is a substituted or unsubstituted aryl group, Ar ₁₀ , Ar ₁₁ , Ar ₁₂ Are the same or different arylene groups, X ₁ , X ₂ Represents a substituted or unsubstituted ethylene group or a substituted or unsubstituted vinylene group. X, k, j, and n are the same as in the formula (I).
[0079]
[Chemical 8]
Formula (VI)

In formula (VI), R ₁₅ , R ₁₆ , R ₁₇ , R ₁₈ Is a substituted or unsubstituted aryl group, Ar ₁₃ , Ar ₁₄ , Ar ₁₅ , Ar ₁₆ Are the same or different arylene groups, 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 formula (I).
[0080]
[Chemical 9]
(VII) Formula

Where R ₁₉ , R ₂₀ Represents a hydrogen atom, a substituted or unsubstituted aryl group, and R ₁₉ And R ₂₀ May form a ring. Ar ₁₇ , Ar ₁₈ , Ar ₁₉ Represent the same or different arylene groups. X, k, j, and n are the same as in the formula (I).
[0081]
[Chemical Formula 10]
(VIII) Formula

In formula (VIII), R ₂₁ Is a substituted or unsubstituted aryl group, Ar ₂₀ , Ar ₂₁ , Ar ₂₂ , Ar ₂₃ Represent the same or different arylene groups. X, k, j, and n are the same as in the formula (I).
[0082]
Embedded image
(IX) Formula

In formula (IX), R ₂₂ , R ₂₃ , R ₂₄ , R ₂₅ Is a substituted or unsubstituted aryl group, Ar ₂₄ , Ar ₂₅ , Ar ₂₆ , Ar ₂₇ , Ar ₂₈ Represent the same or different arylene groups. X, k, j, and n are the same as in the formula (I).
[0083]
Embedded image
(X) Formula

In formula (X), R ₂₆ , R ₂₇ Is a substituted or unsubstituted aryl group, Ar ₂₉ , Ar ₃₀ , Ar ₃₁ Represent the same or different arylene groups. X, k, j, and n are the same as in the formula (I).
[0084]
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 for the material of the media used, all media such as zirconia, alumina, and agate that have been used in the past 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 excellent in 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. In addition, 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 filler sedimentation 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 dispersion in a state dissolved in an organic solvent.
[0085]
As a coating method of the dispersion obtained as described above, conventional coating methods such as dip coating, spray coating, beat coating, nozzle coating, spinner coating, ring coating, etc. can be used. Spray coating is most suitable for forming a thin film uniformly and with a good filler dispersibility. The film thickness of the entire protective layer is 1 to 10 μm, preferably 2 to 6 μm.
[0086]
In the photoreceptor of the present invention, an intermediate layer (undercoat 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, considering that the photosensitive layer is coated with a solvent on these resins, the intermediate layer 33 may be a resin having a high solvent resistance with respect to a general organic solvent. desirable. 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. Further, a metal oxide fine powder pigment exemplified by titanium oxide, silica, alumina, zirconium oxide, tin oxide, indium oxide and the like may be added to the undercoat layer in order to prevent moire and reduce residual potential. These undercoat layers can be formed using an appropriate solvent and a coating method like the above-mentioned photosensitive layer. Furthermore, a silane coupling agent, a titanium coupling agent, a chromium coupling agent, or the like can be used as the undercoat layer of the present invention. Furthermore, various dispersing agents can be added. In addition, the undercoat layer of the present invention includes 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. The thickness of the undercoat layer is suitably from 0 to 5 μm.
[0087]
In the photoreceptor of the present invention, an intermediate layer can be provided between the photosensitive layer (charge generation layer and charge transport layer) and the protective layer. In the intermediate layer, a binder resin is generally used as a main component. Examples of these resins include polyamide, alcohol-soluble nylon, water-soluble polyvinyl butyral, polyvinyl butyral, and polyvinyl alcohol. As a method for forming the intermediate layer, a generally used coating method as described above is employed. In addition, about 0.05-2 micrometers is suitable for the thickness of an intermediate | middle layer.
[0088]
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.
[0089]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be specifically described with reference to examples. However, the present invention is not limited to the following examples.
[0090]
[Example 1]
An outline of the image forming apparatus according to the first embodiment of the present invention will be described below with reference to FIG.
1 In FIG. 1, a photosensitive drum 1 has a surface of a conductor, such as aluminum, having a thickness of 20 μm (FR layer (surface protective layer 5 μm, charge transport layer 15 μm), charge generation layer 0.2 μm, undercoat layer 3). .5 μm stacked OPC)) and rotates in the direction of the arrow in FIG. The diameter of the photosensitive drum is 60 mm, and the peripheral speed is 230 mm / s.
[0091]
2 Charging means 2 is a so-called contact roller charging device, and a direct current voltage of −1.21 kV is applied to a charging roller having a structure in which a so-called medium resistance conductive elastic layer having a thickness of 3 mm is formed on a metal core by a power source. To uniformly charge the photoconductor to -550V.
[0092]
3 The exposure unit 3 forms an electrostatic latent image by irradiating the surface of the photoreceptor uniformly charged by the charging unit with light corresponding to the target image. The light source of the exposure means is a laser diode, and the photosensitive member is scanned while being irradiated with a laser beam by a polygon mirror. The so-called beam diameter is 35 μm in the main scanning direction and 35 μm in the sub-scanning direction as will be described in detail below.
[0093]
4. The developing means is a so-called two-component developing device, and a developer in which toner (volume average particle diameter 6.8 μm) and carrier (particle diameter 50 μm) are mixed at a toner concentration of 5.0% is accommodated in the developing container. ing. In the developing device, the developer is conveyed to the photosensitive member-developing sleeve facing portion by the developing sleeve. The distance between the photoreceptor and the developing sleeve, the so-called developing gap is 0.3 mm. Since a DC voltage of −400 V is applied to the developing sleeve from the power source, toner adheres to the photosensitive member corresponding to the electrostatic latent image on the photosensitive member. This is so-called reversal development. The peripheral speed of the developing sleeve is 460 mm / s, and the so-called peripheral speed ratio is 2.0.
[0094]
5 The transfer unit 5 transfers the toner image developed by the developing unit onto the recording sheet 6 conveyed from a paper supply unit (not shown). 4 includes a transfer belt and a power source, and a voltage is applied from the power source to the transfer belt. The applied voltage is constant current control and is 30 μA.
[0095]
6 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.
[0096]
7. The toner image transferred onto the recording sheet (paper or the like) by the transfer unit is conveyed to the fixing unit and heated and pressed by the fixing unit to fix the toner image on the recording paper sheet. It is discharged outside and becomes an output image.
By repeating the above steps 1 to 7, a desired image can be formed on the recording sheet.
[0097]
FIG. 9 shows a writing unit of the image forming apparatus shown in FIG. In the apparatus shown in FIG. 1, a 4ch (4-channel) type LD array having four LDs (laser diodes) having a wavelength of 780 nm is mounted. Laser light from the LD is irradiated onto the polygon mirror 16 via the collimating lens 12, the ND filter 13, the aperture 14, and the cylindrical lens 15. In the first embodiment, the polygon mirror 16 is a six-surface type and rotates at a rotation speed of 27165 rpm. The laser beam reflected by the polygon mirror 16 forms an image on the photoreceptor surface 21 via the folding mirrors 18 and 19 and the f-θ lenses 17 and 20. In the examples described later, the so-called beam diameter of the laser beam on the photosensitive member is adjusted to be 35 μm (main scanning direction) × 35 μm (sub-scanning direction). In the apparatus of FIG. 1, the f-θ lens is a plastic lens obtained by molding plastic, and the lens shape is designed by a so-called AC surface. As a result, it is 35 μm (main scanning direction) × 35 μm (sub-scanning direction). An extremely narrow beam diameter is achieved. Further, the laser beam scans on the photosensitive member as the polygon mirror rotates. The first exemplary embodiment is an image forming apparatus with a resolution of 1200 dpi, and the size of 1 pixel is 21.3 μm × 21.3 μm. In Example 1, the photosensitive member is irradiated with a laser beam while moving around 1pixel in a time of 16.9 ns. At this time, the so-called pixel clock is 59.2 MHz, which means that the LD is optically modulated at a frequency of 59.2 MHz.
[0098]
In the first embodiment, as described above, the laser beam is scanned on the photosensitive member by the rotation of the polygon mirror. When the laser beam is located in the non-image area, the synchronization detection plate illustrated in FIG. Laser light is incident. This synchronization detection plate has a mechanism that generates a reference signal by the incidence of a laser beam, and based on this reference signal, resets the timing of the image writing position, that is, the clock signal that forms a so-called pixel clock. It has become. As a result, the light-modulated laser beam can be incident on a predetermined position on the photosensitive member.
[0099]
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 can be performed, in which four gradations can be expressed per pixel. We are doing garbage.
[0100]
Specific examples of the photoreceptor used in Example 1 are shown below. All parts are 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).
[0101]
(Photoreceptor specifications)
An undercoat layer coating solution, a charge generation layer coating solution and a charge transport layer coating solution having the following composition are sequentially applied by dip coating on an aluminum cylinder having a diameter of 60 mm and dried to a thickness of 3.5 μm. A pulling layer, a 0.2 μm charge generation layer, and a 15 μm charge transport layer were formed.
[0102]
(Undercoat layer coating solution)
400 parts of titanium dioxide powder
65 parts of melamine resin
120 parts alkyd resin
2-butanone 400 parts
[0103]
(Coating solution for charge generation layer)
2 parts of Y-type oxotitanium phthalocyanine pigment
Polyvinyl butyral (Sekisui Chemical, ESREC BM-2) 1.0 part
50 parts of tetrahydrofuran
[0104]
(Charge transport layer coating solution)
10 parts of polycarbonate (manufactured by Teijin Chemicals, Z polycarbonate)
6 parts of charge transport material of the following structural formula (2) (Ip: 5.4 eV)
Embedded image

Tetrahydrofuran 100 parts
[0105]
On the charge transport layer, a protective layer coating solution 1 having the following composition was further applied by spray coating to form a protective layer having a total film thickness of 5 μm to produce an electrophotographic photosensitive member. .

[0106]
(Image quality evaluation method)
The image quality evaluation was performed by a method of measuring gradation which is an important item of image quality. Tone evaluation is performed by outputting a patch (17 steps) subjected to halftone processing by changing the number of lines, and measuring the lightness (L *) of this patch. As halftone processing, an image was output at three levels of 150, 200, and 240 lpi. Further, a spectral density colorimeter (X-Rite 938) was used for the measurement of lightness (L *). The numerical value of gradation is derived from the linearity of the brightness value obtained by measuring the 17-stage patch with respect to the input (area ratio on the data), so-called R ^ 2 (autocorrelation coefficient in linear approximation). (Square of 2) was performed. The value of R ^ 2 is close to 1.0 shown in FIG. 10 if the relationship between the input data and the lightness (L *) is linear, and becomes smaller as shown in FIG. 11 as it deviates from the straight line. Become. In addition, the inventors conducted subjective evaluation of an image that requires high gradation such as a natural image, so that the value of R ^ 2 is 0.98 or more and an excellent gradation condition. did. Further, the value of R ^ 2 tends to be larger in a so-called low line number image. However, when the number of lines is 200 lpi or less, a so-called dither texture can be recognized, resulting in an unnatural impression in a natural image or the like, resulting in image quality deterioration. From this, the inventor determined that the image quality is high when the number of lines of halftone processing is 200 lines or more and the gradation R ^ 2 value is 0.98 or more.
[0107]
The inventors used the above-described photoreceptor, and used an experimental machine modified from Ricoh's MF4570 for 1200 dpi 2-bit writing. The beam diameter was measured with a beam scan manufactured by PHOTON, and the OPC film thickness was measured with a Fischerscope film thickness meter.
[0108]
[Examples 2-8, Comparative Examples 1-12]
Example 1 except that the charge transport layer thickness of the photoconductor, the transmittance of the protective layer (formulation will be described later), the writing dot system at the time of exposure, and the writing density were changed as shown in Table 1 in Example 1. In the same way, image output and image quality evaluation were performed.
[0109]
[Table 1]

[0110]

[0111]

[0112]
The evaluation results of the image quality are shown in Table 2 below. Table 2 shows the results of measuring the gradation in a combination of the beam diameter, the thickness of the charge transport layer and the protective layer, the protective layer transmittance, and the number of lines in the halftone process. As can be seen from these results, in order to form an image with excellent gradation, the beam diameter, the thickness of the charge transport layer and the protective layer, the transmittance of the protective layer, and the halftone processing specified in the present invention are used. It can be seen that the number of lines needs to be used in a specific combination.
[0113]
[Table 2]

[0114]
[Comparative Example 13]
In Example 1, 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 coating solution.
[0115]
[Example 9]
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 coating solution was changed as follows.
Unsaturated polycarboxylic acid polymer
(BYK Chemie, acid value: 130 mgKOH / g) 0.06 parts
[0116]
[Example 10]
In Example 1, an electrophotographic photosensitive member was produced and evaluated in the same manner as in Example 1 except that the unsaturated polycarboxylic acid polymer contained in the protective layer coating solution was changed as follows.
Unsaturated polycarboxylic acid polymer
(BYK Chemie, acid value: 365 mgKOH / g) 0.03 parts
[0117]
[Example 11]
In Example 1, an electrophotographic photosensitive member was produced and evaluated in the same manner as in Example 1 except that the unsaturated polycarboxylic acid polymer contained in the protective layer coating solution was changed as follows.
Acrylic acid / hydroxyethyl methacrylate copolymer
(Acid value: 130 mgKOH / g) 0.10 parts
[0118]
[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 coating solution was changed as follows.
Alumina (average particle size: 0.15 μm, pH: 5.3) 3.0 parts
[0119]
[Example 13]
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 coating solution was changed as follows.
Alumina (average particle size: 0.45 μm, pH: 5.7) 3.0 parts
[0120]
[Example 14]
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 coating solution was changed as follows.
Titanate coupling-treated alumina (treatment amount 3%) 3.0 parts
[0121]
[Example 15]
In Example 1, except that the charge transport material contained in the protective layer coating solution was changed to the charge transport material (Ip: 5.3 eV) of the following structural formula (3), all the same as in Example 1. An electrophotographic photoreceptor was prepared and evaluated.
Embedded image

[0122]
[Example 16]
In Example 1, except that the charge transport material contained in the protective layer coating solution was changed to the charge transport material of the following structural formula (4) (Ip: 5.5 eV), all the same as in Example 1. An electrophotographic photoreceptor was prepared and evaluated.
Embedded image

[0123]
[Example 17]
In Example 1, an electrophotographic photoreceptor was prepared and evaluated in the same manner as in Example 1 except that the charge transport material and the binder resin contained in the protective layer coating solution were changed to the following materials.
15 parts of a polymer charge transport material (Ip: 5.4 eV) having the following structural formula
Embedded image

[0124]
[Example 18]
In Example 1, an electrophotographic photosensitive member was produced and evaluated in the same manner as in Example 1 except that the binder resin contained in the protective layer coating solution was changed as follows.
7.0 parts polyarylate resin (Unitika, U polymer / PET)
[0125]
[Example 19]
In Example 1, an electrophotographic photosensitive member was produced and evaluated in the same manner as in Example 1 except that the binder resin contained in the protective layer coating solution was changed as follows.
7.0 parts polycarbonate (manufactured by Teijin Chemicals, C polycarbonate)
[0126]
For the electrophotographic photoreceptors of Comparative Example 13 and Examples 9 to 19 produced as described above, and the electrophotographic photoreceptors used in Example 1 and Comparative Example 3 described above, the running evaluation was performed first using Ricoh MF4570. The shown experimental machine: Ricoh MF4570 modified to 1200 dpi 2 bit writing was used for image evaluation. The beam diameter was 35 μm, the writing density was 1200 dpi, and as halftone processing, an image was output at a so-called line number of 200 lpi. Images were output by the above means and image quality evaluation was performed.
[0127]
In addition, as an evaluation procedure, first, an image is output by an experimental machine and image quality evaluation is performed. Next, a bright part potential (VD = −800V is set) is measured by RICOH MF3570 and a total of 20,000 sheets is obtained at 1 to 2. After printing, the bright part potential was measured, and an image was output again by an experimental machine to evaluate the image quality. Further, the wear amount was evaluated based on the difference in film thickness at the initial stage and after printing 100,000 sheets. The image quality other than the gradation is described in the item of image quality. The results are shown in Table 3.
[0128]
[Table 3]

[0129]
[Examples 20 to 30 and Comparative Example 14]
An image forming experiment was conducted by making a prototype of a photoreceptor in which the difference in film thickness (0.5 to 4.0 μm) between the charge transport layer and the protective layer was intentionally changed in the same formulation as in Examples 9 to 19 above. . At this time, the film thickness difference of the photoconductor was defined as follows. The film thickness is measured at 19 points (measured using the above-mentioned film thickness meter) in the cylindrical direction of the photoconductive drum and 31 points at 10 mm intervals in the photoconductor axis direction. The maximum value and the minimum value are derived from these 589 points, and the film thickness difference = maximum value−minimum value is calculated.
[0130]
The difference in film thickness between the maximum film thickness and the minimum film thickness over the entire surface of the photoreceptor image area of the combined film thickness of the charge transport layer and the protective layer can be changed by changing the coating conditions of the charge transport layer. I let you. Specifically, a photoconductor with a film thickness difference of 4 μm or more as shown in the comparative example can be obtained by lowering the solid content concentration of the coating liquid and increasing the pulling speed. Further, by increasing the solid content concentration and decreasing the pulling speed, it is possible to obtain a photoreceptor having a film thickness difference of 2 to 4 μm. Further, a photoreceptor having a film thickness difference of 1.5 μm or less was produced by the production method described in JP-A No. 2001-194814.
[0131]
For the protective layer, in the coating chamber where the spray coating conditions are designed so that there is no turbulence in the air flow, the distance between the spray gun and the photoconductor substrate, the liquid discharge amount, the feed rate of the spray gun, the photoconductor substrate The coating was performed under the condition that the difference in film thickness hardly occurred so that the rotational speed of the film was constant and uniform.
[0132]
The photosensitive drum thus produced was mounted on the above-described experimental machine (imagino MF45770 modified machine), and the image was evaluated. The output image at this time was evaluated by measuring the lightness at intervals of 10 mm in length and breadth in a region corresponding to one circumference of the photosensitive drum by performing paper output by forming a pattern having a lightness of 50 on the entire surface. (The X-Rite 938 made by X-Rite was also used for the lightness measurement.) The reason for selecting the lightness 50 pattern is that changes in image density are most likely to occur due to changes in the film thickness of the photoreceptor. Is an intermediate density region, and a pattern having a brightness of 50 was used as a representative example. It was considered that the condition was out of the allowable range when the brightness of the output image was measured and 589 points were obtained and a measurement point where the amount of deviation from the average value had a brightness difference of 5 or more was obtained.
[0133]
Such evaluation of the brightness uniformity of the output image was performed in the initial state and after passing 100,000 sheets. The experimental results are shown below.
Table 4 below shows the results of the contact charging method in which a DC voltage is applied as the charging means. The data shown in Table 4 shows that, as Example 20, a photoconductor having five levels of initial film thickness difference of 0.5 μm to 4.5 μm with the prescription of Example 9 described above was prepared, and the output image The brightness difference is recorded, and then 100,000 sheets are passed through all the photoreceptors, and the film thickness difference of the photoreceptor and the brightness difference of the output image are measured in the same procedure as in the initial state. The results thus obtained are listed in Table 4. Such an evaluation experiment was performed for the photoconductor preparations of Examples 9 to 19 and Comparative Example 13 (Examples 20 to 30 and Comparative Example 14 respectively), and the results in Table 4 were obtained. From Table 4, it can be seen that if the film thickness difference of the photoconductor is 1.5 μm or less in the initial state, the brightness difference of the output image is 5 or less, and this range is a condition for guaranteeing the stability of the output image. However, after passing 100,000 sheets, in the photoconductors of Examples 20 to 30, the increase in the film thickness difference is relatively small and the brightness difference in the output image is not so large. On the other hand, in the photoconductor having no protective layer containing the filler as in Comparative Example 14, uneven wear due to film abrasion occurs, and the brightness difference of the output image increases to an unacceptable range.
[0134]
An image forming apparatus using a contact charging method to which a DC voltage is applied has a feature that the charging potential changes depending on the film thickness of the photoreceptor. In the experiment conducted by the inventors as described above, the charging potential changes by about 10 V per 1 μm change in the thickness of the photosensitive member. This change in size has a great influence from the viewpoint of making the image density constant. As a result, a density difference occurs in the output image. From the results of Table 4, it can be seen that in this charging system apparatus, a film thickness difference of 1.5 μm or less is effective from the viewpoint of making the brightness of the output image constant over a long period of use.
[0135]
[Table 4]

[0136]
[Examples 31 to 41 and Comparative Example 15]
Examples 31 to 41 and Comparative Example 15 whose results are shown in Table 5 below are the results of tests similar to Examples 20 to 30 and Comparative Example 14, except that scorotron was used as the charging device. Table 5 has the same configuration as Table 4 above. When the charging device is a scorotron, if the difference in the film thickness of the photoconductor is 1.5 μm or less in the initial state from the results shown in Table 5, the brightness difference of the output image is 5 or less, and this range improves the stability of the output image. It can be seen that the conditions are guaranteed. In addition, after passing 100,000 sheets, in the photoconductors having the configurations of Examples 31 to 41, the increase in the film thickness difference is relatively small and the brightness difference in the output image is not so large. However, in contrast to the photoconductor having a protective layer containing no filler as in Comparative Example 15, uneven wear due to film abrasion occurs. Therefore, in order to keep the brightness difference of the output image within an allowable range, it is desirable that the difference in film thickness of the photoconductor is 0.5 μm or less in the initial state.
[0137]
However, controlling the difference in the film thickness of the photoreceptor to 0.5 μm or less over the entire surface of the image forming area of the photoreceptor drum is not very practical in terms of manufacturing the photoreceptor drum. When including the viewpoint of manufacturing such a photosensitive drum, it is possible to suppress the difference in film thickness to about 1.5 μm by configuring the photosensitive member with a protective layer so that the brightness of the output image can be maintained even in long-term use. It seems to be the most desirable way to ensure stability.
[0138]
[Table 5]

[0139]
[Examples 42 to 52 and Comparative Example 16]
Examples 42 to 52 and Comparative Example 16 whose results are shown in Table 6 below are the same as Examples 20 to 30 and Comparative Example 14, except that a contact charging device to which an AC superimposed voltage was applied was used as the charging device. This is the result of the test. Table 6 has the same configuration as Table 4. In the case where the charging device is a contact charging device to which an AC superimposed voltage is applied, the brightness difference of the output image is 5 or less if the film thickness difference of the photosensitive member is 3.5 μm or less in the initial state from the results of Table 6. It can be seen that the range is a preferable condition for guaranteeing the stability of the output image. In addition, after passing 100,000 sheets, in the photoconductors having the configurations of Examples 42 to 52, the increase in the film thickness difference is relatively small and the brightness difference in the output image does not become so large. However, in contrast to the photosensitive member having no protective layer containing the filler as in Comparative Example 16, uneven wear due to film abrasion occurs. Therefore, in order to keep the brightness difference of the output image within an allowable range, it is desirable that the difference in the film thickness of the photoconductor is 1.5 μm or less in the initial state.
[0140]
However, controlling the film thickness difference of the photoconductor to 1.5 μm or less over the entire image output range of the photoconductor drum becomes a bottleneck in the production of the photoconductor drum and deteriorates the yield. Cause cost increase. When including the viewpoint of manufacturing the photosensitive drum as described above, the method of further suppressing the film thickness difference to about 3.5 μm to 1.5 μm ensures the lightness stability of the output image even in the long-term use. From the viewpoint of cost, it is considered to be an excellent method.
[0141]
Comparing Table 6 below with Tables 4 and 5 above, when a contact charging device to which an AC superimposed voltage is applied is used as a charging means, compared to a case where a charging device to which a DC voltage is applied or a scorotron is used. It can be seen that the allowable range of the difference in film thickness of the photoconductor is wide. As described in detail above, the charging potential changes in contact charging devices and scorotrons to which a DC voltage is applied, whereas in the charging device to which an AC superimposed voltage is applied, the charging potential does not depend on the film thickness of the photoreceptor. This is because the capacitance of the photoconductor changes and the amount of charge accumulated on the photoconductor changes due to the change in the film thickness of the photoconductor.
[0142]
Therefore, for example, even when a DC voltage application type contact charging device or scorotron is used, if the charging potential of the photosensitive member can be made constant (independent of the photosensitive member film thickness) using a control device, etc. As shown in FIG. 6, it is possible to present conditions with a relatively wide allowable range with respect to the film thickness difference of the photosensitive member.
[0143]
[Table 6]

[0144]
【The invention's effect】
[0145]
According to the image forming apparatus of the present invention, the value of the gradation R ^ 2 is determined by an appropriate combination of the number of halftone processing lines, the laser beam diameter, the thickness of the charge transport layer and the protective layer, and the protective layer transmittance. It was revealed that a high-quality image that can ensure 0.98 or more can be obtained.
[0146]
Furthermore, when using a photoreceptor in which the protective layer contains a filler, a dispersant, a charge transporting material, and a binder resin, the increase in residual potential is suppressed, and at the same time, the occurrence of image unevenness and gradation degradation It has become possible to suppress image quality deterioration, further suppress uneven wear and abnormal wear, and provide an image forming apparatus that achieves both high durability and high image quality.
[0147]
Further, by using a contact charging device or a scorotron to which a DC voltage is applied as a charging means so that the film thickness difference of the photoconductor is 1.5 μm or less, even when used over a long period of time, ▲ 1) The influence of the difference in the film thickness of the photoconductor due to uneven wear, the change in charging potential due to (2) and (1), and the change in brightness of the output image due to (3) and (2) can be suppressed. In other words, since the brightness of the output image can be kept constant without being changed, an output image with a constant brightness can be realized over a long period of time.
[0148]
In addition, when a contact charging device to which an AC superimposed voltage is applied is used as a charging means so that the difference in film thickness of the photoconductor produced above is 3.5 μm or less, it is used over a long period of time. In addition, it is possible to suppress the effects of (1) a difference in film thickness of the photosensitive member due to uneven wear, (2) a change in charging potential due to (1), and (3) a change in brightness of the output image due to (2). In other words, since the brightness of the output image can be kept constant without being changed, an output image with a constant brightness can be realized over a long period of time. In particular, in the case of this charging unit, it is possible to realize an image forming apparatus having characteristics such that the tolerance of the film thickness of the photosensitive member is relatively loose, the yield in manufacturing the photosensitive drum is good, and there is no cost increase factor. .
[Brief description of the drawings]
FIG. 1 is a schematic sectional view of an image forming apparatus according to a first embodiment.
FIG. 2 is a cross-sectional view of a photoreceptor used in the present invention.
FIG. 3 is a cross-sectional view of another photoconductor used in the present invention.
FIG. 4 is a schematic sectional view of a conventional image forming apparatus.
FIG. 5 is a diagram schematically showing a wire-type corona charging device.
FIG. 6 is a diagram schematically showing a corona charging device for a sawtooth electrode.
FIG. 7 is an enlarged view schematically showing a sawtooth electrode.
FIG. 8 is a diagram schematically showing a contact charging device.
FIG. 9 is a diagram schematically illustrating a writing unit of the image forming apparatus according to the first embodiment.
FIG. 10 is a graph of lightness and input data in an example with good gradation.
FIG. 11 is a graph of brightness and input data in an example with poor gradation.
[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
9 Power supply
11 4-channel laser diode
12 Collimating lens
13 ND filter
14 Aperture
15 Cylindrical lens
16 Polygon mirror
17 f-θ lens 1
18 Folding mirror 1
19 Folding mirror 2
20 f-θ lens 2
21 photoconductor surface
22 Synchronization detection plate
31 Conductive support
33 Intermediate layer (undercoat layer)
35 Charge generation layer
37 Charge transport layer
39 Protective layer

Claims (16)

  At least a photosensitive member, a charging unit that changes a charging potential according to a change in film thickness of the photosensitive member, a light writing unit that performs optical writing on the photosensitive member to form an electrostatic latent image, and a halftone for an input image. An image forming apparatus including an image processing unit that performs processing, wherein the optical writing by the writing unit is performed based on image data obtained by performing halftone processing on an input image with a line number of 200 lpi or more. The photosensitive member has 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, and the charge transport is further performed with a laser beam of 35 μm or less. On the layer, there is a protective layer containing a charge transporting substance and a filler and having a transmittance for writing light of 90% or more, and the total thickness of the charge transporting layer and the protective layer is 20 μm. An image forming apparatus comprising:   The image forming apparatus according to claim 1, wherein a difference in film thickness between the maximum film thickness portion and the minimum film thickness portion of the entire surface of the image area of the photoconductor is 1.5 μm or less.   At least a photosensitive member, a charging unit having a constant charging potential independent of a change in film thickness of the photosensitive member, a light writing unit that performs optical writing on the photosensitive member to form an electrostatic latent image, and an input image On the other hand, in an image forming apparatus having an image processing unit that performs halftone processing on the basis of image data in which optical writing is performed by the writing unit and halftone processing is performed on the input image with a line number of 200 lpi or more, The photosensitive member has 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; and The charge transporting layer has a protective layer containing a charge transporting substance and a filler and having a transmittance for writing light of 90% or more, and the combined thickness of the charge transporting layer and the protective layer is Image forming apparatus characterized by 0μm or less.   The image forming apparatus according to claim 3, wherein a difference in film thickness between the maximum film thickness portion and the minimum film thickness portion on the entire image area of the photoconductor is 3.5 μm or less.   The image forming apparatus according to claim 1, wherein the protective layer further contains a binder resin.   The image forming apparatus according to claim 1, wherein the filler has a refractive index of 1.0 to 2.0.   The image forming apparatus according to claim 1, wherein the filler is at least one inorganic material.   The image forming apparatus according to claim 7, wherein the inorganic material is a metal oxide.   The image forming apparatus according to claim 7, wherein the pH of the aqueous dispersion of the inorganic material is 5 or more. The following relationship between the ionization potential Ip of the charge transport material contained in the protective layer and the ionization potential Ip of the charge transport material contained in the charge transport layer (Ip of the charge transport material contained in the protective layer) )
≦ (Ip of charge transport material contained in charge transport layer)
The image forming apparatus according to any one of claims 1 to 9, characterized in that hold. As the charge transporting substance contained in the protective layer, the image forming apparatus according to any one of claims 1 to 10, characterized in that the polymer charge-transporting material is contained at least in part. Any binder resin contained in the protective layer is a polycarbonate-based resin, any of the polyarylate resin and polyester resin, or of claim 5-11, characterized in that a mixture of two or more thereof The image forming apparatus according to claim 1. The image forming apparatus according to any one of claims 5-12 in which the acid value of the binder resin is characterized in that it is a 10~400mgKOH / g. Said containing protective layer further dispersing agent, the dispersant, the acid value image forming apparatus according to any one of claims 1 to 13, characterized in that an organic compound 10~400mgKOH / g . The image forming apparatus according to claim 14 , wherein the dispersant is a polycarboxylic acid derivative. Wherein the charging unit, an image forming apparatus according to any one of claims 1 to 15, the maximum intensity of the electric field applied to the charge transport layer and the protective layer is characterized by a -30 V / [mu] m.

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