JP3656473B2

JP3656473B2 - Image forming apparatus and image forming method

Info

Publication number: JP3656473B2
Application number: JP23151899A
Authority: JP
Inventors: 護臨; 俊一郎栗原; 牧野　　要
Original assignee: Mitsubishi Chemical Corp
Current assignee: Mitsubishi Chemical Corp
Priority date: 1999-08-18
Filing date: 1999-08-18
Publication date: 2005-06-08
Anticipated expiration: 2019-08-18
Also published as: JP2001056595A

Description

【０００１】
【発明の属する技術分野】
本発明は画像形成装置及び方法に関するものである。詳しくは電子写真装置に用いられる画像形成装置及び方法に関するものである。
【０００２】
【従来の技術】
従来、電子写真装置たとえば普通紙複写機、レーザプリンタ、ＬＥＤプリンタなどに用いられる潜像保持部材への帯電装置はコロナ放電装置を使うのが一般的でこれまで広く使われてきている。しかしコロナ放電装置には以下の問題点がある。
（１）放電を生じさせるために高圧電源が必要で、およそ４ＫＶ以上が要求される。従って電源コストが高くなり、配線などにも高圧ケーブルが必要、かつ電気的な高圧絶縁材も使用しなければならないので更にコストを押し上げることになる。
（２）気中放電であるためオゾンやＮＯｘの発生が避けられない。近年環境問題のため人体に好ましくないオゾンやＮＯｘの発生は極力避けなければならない。
（３）帯電が不均一になりがちである。すなわち放電現象を生じさせるために、一般的にはワイアとその回りにシールドケースを配置し、これらの間に高電圧を印加することになるが、長時間使用すると放電による生成物がワイア及びケースに沈着し放電が不安定になる。従って潜像保持部材の帯電が不均一になり、画像上にムラが生じる。特に負コロナ放電時にはこの生成物がワイアの汚れとなり著しく放電を不安定にする。従って定期的なワイア清掃が不可欠になりメンテナンスに手間がかかる。
【０００３】
これらのコロナ放電装置の欠点を改良するために接触帯電装置を使用し、低圧電源でオゾンの発生の少ないコンパクトな帯電装置とすることが提案されている。（例えば特開昭６３―１４９６６９号公報参照。）
一方、電子写真技術の中核をなす感光体については、現在一部にアモルファスシリコン、砒素―セレン系などの無機光導電材料が使われているが、主流は有機系感光体である。有機系感光体としてはいくつかの層構成が考案されているが、電荷発生と電荷輸送の機能を分離し電荷発生層、電荷輸送層を積層したいわゆる積層型感光体が、設計がやりやすい、生産性が高い、より高性能な感光体が得られることなどから、精力的に研究・開発されており、現在では中高速の複写機やプリンタにまで使用範囲が広がっている。
【０００４】
【発明が解決しようとする課題】
しかるに有機系光導電層からなる潜像保持部材に接触させて帯電させる帯電装置及び方法を用いて画像形成を行った場合、これまで以下のような点が非常に大きな問題となっている。
（１）一般に潜像保持部材の光導電層は導電性基体上に設けられるが、光導電層に直接帯電部材が接触するので、光導電層中に何らかの欠陥があると帯電部材からの電流がその部分に集中し、潜像保持部材が不均一に帯電してしまうため点状或いは帯状といった画像欠陥が生じる。またこの様な欠陥部への帯電部材からの電流の集中が激しい場合には、光導電層自身が絶縁破壊されてしまい、以降正常な画像形成が不能になる。更に帯電部材自体もそのようなリーク電流により損傷を受けて使用に耐えなくなる。
（２）基体の表面に異物の付着、汚れ、微細な穴等の欠陥が存在すると、それらに起因する画像欠陥がコピー或いはプリント上に現れる場合がある。
（３）反転現像方式の場合、微小黒点、地カブリ等の画像欠陥がコピー或いはプリント上に現れる場合がある。特に高湿環境条件下で地カブリが著しくなり実用に耐えなくなる場合がある。
【０００５】
（１）の光導電層の絶縁破壊は有機系感光体の本質的弱さに由来するところ大であり、これまで有効な手段はほとんど知られていないのが実状である。（３）の問題に対しては、反転現像方式においては暗部電位が白地となり、明部電位が黒地部（画線部）となるが、このシステムにおいては潜像保持部材上に欠陥などによる局所的帯電不良が存在すると、白地への黒点あるいはそれらが多数存在すると地カブリのような現象となり、著しい画像不良となって現れる。
このような局所的帯電不良は正規現像において使用した場合には何ら問題を引き起こすことのないレベルであっても、反転現像においては画像不良と成りやすく、しかも従来より得られている積層型潜像保持部材では程度の差こそあれ、黒点、カブリに問題を持っていることが判った。
【０００６】
この問題の原因、すなわち局所的帯電不良には種々の原因が考えられるが、電極である導電性基体と光導電層との間で電荷の注入が局所的に起こり帯電電位があがらなくなるものと考えられる。
そこで本発明者らはこれらの問題を解決するために種々検討した結果、帯電部材を潜像保持部材に直接接触させて帯電させる装置及び方法において、特定の潜像保持部材を用いることによって画像欠陥が生じにくい画像形成装置及び方法が得られることを見出し本発明に到達した。
【０００７】
【課題を解決するための手段】
すなわち、本発明の要旨は、潜像保持部材、潜像保持部材に帯電させるための帯電部材、潜像保持部材に静電荷潜像を形成させるための露光手段、及び潜像を可視化するための現像手段とを有する画像形成装置において、帯電部材が潜像保持部材に接触させて帯電させる接触帯電部材であり、潜像保持部材が導電性基体上に少なくともバインダー樹脂、下記構造の電荷輸送剤（Ａ）又は（Ｂ）、及び電荷発生剤を含む有機系光導電層を設けたものであって、かつ、該電荷輸送剤を含む層における電荷輸送剤の量が、該層におけるバインダー樹脂１００重量部に対して１０〜５０重量部であることを特徴とする画像形成装置、およびかかる装置を用いた画像形成方法に関する。
【化２】

【０００８】
【発明の実施の形態】
まずはじめに、本発明で用いる潜像保持部材について説明する。
本発明で用いる潜像保持部材は、導電性基体上に、少なくとも有機系光導電層を設けた構成となっている。
導電性支持体としては、アルミニウム、ステンレス鋼、銅、ニッケルなどの金属材料、もしくは、ポリエステルフィルム、紙等の絶縁性支持体の表面に導電性層を設けたもの、をシート状、ベルト状、ドラム状、またはロール状にして使用される。
【０００９】
絶縁静支持体の表面に設けられる導電性層としては、アルミニウム、銅、パラジウム、酸化スズ、酸化インジウム等が好ましい。
導電性支持体と有機系光導電層との間には、通常使用されるような公知のバリアー層が設けられていてもよい。バリアー層としては、例えばアルミニウム陽極酸化被膜、酸化アルミニウム、水酸化アルミニウム等の無機層、ポリビニルアルコール、カゼイン、ポリビニルピロリドン、ポリアクリル酸、セルロース類、ゼラチン、デンプン、ポリウレタン、ポリイミド、ポリアミドなどの有機層が使用される。有機層をバリアー層として用いる場合には、有機化合物単独あるいはチタニア、アルミナ、シリカ、酸化ジルコニウム等の金属酸化物、あるいは銅、銀、アルミニウム等の金属微粉末を分散させて用いてもよい。これらのバリアー層の膜厚は適宜設定できるが、０．０５μm から２０μm 、好ましくは０．１μm から１０μm の範囲で用いることが好ましい。
【００１０】
光導電層は電荷発生層、電荷輸送層をこの順に積層したもの、電荷輸送媒体中に電荷発生物質を分散した、いわゆる分散型、などのいずれもが用いることができ、特に積層型が好ましい。
積層型光導電層の場合、電荷発生層に用いられる電荷発生物質としてはフタロシアニン顔料、アゾ、キナクリドン、多環キノン、ペリレン、インジゴ、ベンズイミダゾールなどの各種有機顔料が単独或いは併用して用いられる。中でもビスアゾ、トリスアゾ等のアゾ顔料並びに、無金属フタロシアニンまたは銅、インジウム、ガリウム、スズ、チタン、鉛、アルミニウム等の金属もしくはその酸化物、塩化物、水酸化物、アルコキシ化物の配位したフタロシアニン類が好ましい。これらは単独或いは併用して用いても構わない。電荷発生層はこれら物質の均一層としてあるいはバインダー中に微粒子分散された状態で形成される。
【００１１】
電荷発生層で使用されるバインダー樹脂としては、例えばポリエステル樹脂、ポリビニルアセテート、ポリアクリル酸エステル、ポリメタクリル酸エステル、ポリエステル、ポリカーボネート、ポリビニルアセトアセタール、ポリビニルプロピオナール、ポリビニルブチラール、フェノキシ樹脂、エポキシ樹脂、ウレタン樹脂、セルロースエステル、セルロースエーテル等が挙げられる。この場合の使用比率はバインダー樹脂１００重量部に対して電荷発生物質１０から５００重量部の範囲より使用され、その膜厚は通常０．０１μm から５μm 、好ましくは０．０５μm から２μm である。また電荷発生層には必要に応じて塗布性を改善するためのレベリング剤や酸化防止剤、増感剤等の各種添加剤を含んでいてもよい。また電荷発生層は上記電荷発生物質の蒸着膜であってもよい。
【００１２】
電荷輸送層に用いる電荷輸送物質としては、たとえばヒドラゾン誘導体、ピラゾリン誘導体、カルバゾール、インドール、オキサジアゾール等の複素環誘導体、トリフェニルアミン、トリトリルアミン等のアリールアミンの誘導体、スチルベン誘導体、ブタジエン誘導体、或いはこれらの構造を側鎖または主鎖に有する高分子化合物等が挙げられる。中でもヒドラゾン誘導体、アリールアミン類、スチルベン誘導体、ブタジエン誘導体等は電荷輸送能に優れたものが多く、好ましい例である。具体的には例えば特開平２―２３０２５５号公報、特開昭６３―２２５６６０号公報、特開昭５８―１９８０４３号公報、特公昭５８―３２３７２号公報、特開平１―１０２４６９号公報、特公平７―２１６４６号公報、特開平５―１１９４８９号公報、ＵＳＰ−５８０４３４４に記載されている化合物などが挙げられる。本発明では、電荷輸送物質の使用量が通常よりも少ないので、電荷輸送能の特に優れた材料を選択する方がよい。
【００１３】
電荷輸送層に使用されるバインダー樹脂としては、例えばポリメチルメタクリレート、ポリスチレン、ポリ塩化ビニルなどのビニル重合体、及びその共重合体、ポリカーボネート、ポリエステル、ポリエステルカーボネート、ポリスルホン、ポリイミド、フェノキシ、エポキシ、シリコーン樹脂などが挙げられ、またこれらの部分的架橋硬化物も使用できる。中でもポリカーボネート樹脂、ポリアリレート（ポリエステル）樹脂は機械的強度面等で好ましい例である。具体的には例えば、特開平５―８０５４８号公報、特開平２―６６５５５号公報、特開昭６１―１０５５５０号公報、特開昭６１―１３７１５７号公報、特開昭６０―１７２０４４号公報、特開昭６２―２１２６６１号公報、特開平３―２２１９６２号公報に記載されているバインダー樹脂などが挙げられる。
【００１４】
ここでバインダー樹脂と電荷輸送物質との割合は、バインダー樹脂１００重量部に対して１０〜５０重量部の範囲で用いられる。より好ましくは１５〜４５重量部、特に好ましくは２０〜４０重量部の範囲で使用される。電荷輸送物質の量が少なすぎると、電荷輸送の役割を十分に果たすことができず、多すぎると耐リーク特性が悪化する。
また電荷輸送層には、必要に応じて酸化防止剤、増感剤等の各種添加剤を含んでいてもよい。電荷輸送層の膜厚は１０〜６０μm 、好ましくは１０〜４５μm の厚みで使用される。
潜像保持部材の最表面層として従来公知の例えば熱可塑性あるいは熱硬化性ポリマーを主体とするオーバーコート層を設けてもよい。
【００１５】
また、通常は電荷発生層の上に電荷輸送層を形成するがまた逆も可能である。積層型光導電層の各層の形成方法としては層に含有させる物質を溶剤に溶解または分散させて得られた塗布液を順次塗布する等の公知の方法が適用できる。
分散型光導電層の場合には、上記のような配合比のバインダー樹脂と電荷輸送剤を主成分とするマトリックス中に、前記電荷発生物質が分散される。その場合の電荷発生物質の粒子径は十分小さいことが必要であり、好ましくは１μm 以下より好ましくは０．５μm 以下で使用される。感光層内に分散される前記電荷発生物質の量は少なすぎると十分な感度が得られず、多すぎると帯電性の低下、感度の低下などの弊害があり、例えば好ましくは０．５〜５０重量％、より好ましくは１０〜４５重量％で使用される。また、バインダー樹脂と電荷輸送物質の使用比率は、バインダー樹脂１００重量部に対して、電荷輸送物質１０〜５０重量部、好ましくは１５〜４５重量部、より好ましくは２０〜４０重量部である。感光層の膜厚は通常５〜５０μm 、より好ましくは１０〜４５μm で使用される。またこの場合にも成膜性、可とう性、機械的強度等を改良するための公知の可塑剤を、残留電位を抑制するための添加剤を、分散安定性向上のための分散補助剤を、塗布性を改善するためのレベリング剤、界面活性剤、例えばシリコンオイル、フッ素系オイルその他の添加剤を添加してもよい。
【００１６】
上記の潜像保持部材に帯電を行う帯電部材の形状はブラシ状、ブレード状、フィルム状或いはローラ状等潜像保持部材に接触すればその形態は問わない。
例えば帯電装置がローラ状の場合、通常少なくとも芯材とその周囲を覆う帯電部材から構成される。
帯電部材としては潜像保持部材に密着させて接触させる必要から、比較的硬度が低い導電性または半導電性の弾性体が好ましく、例えばゴム材にカーボンなどの導電性粒子或いはその他の半導電性粒子を含有させた導電性ゴムが使用される。また帯電部材を支持部材と表面部材に分けて、支持部材に適当に硬度を持たせ潜像保持部材への密着性を保ちながら、表面部材で適度な電気抵抗を保持させた機能分離型帯電部材を使用することもできる。
ローラ状の帯電部材を用いた態様を例にとって、本発明の画像形成装置の一例を図１に示す。以下図１を参照しながら、本発明の一態様を説明する。
【００１７】
図１中、１は潜像保持部材であり、形状はドラム状、シート状或いはベルト状などいずれでもよい。
２は帯電部材を支える芯材である。この芯材の両端は潜像保持部材に帯電部材を接触させるために適当な圧力印加装置、たとえば金属バネなどで支えられた軸受けに保持される。そしてこの芯材の軸受け或いは他の電気的接触手段を使ってバイアス電位が印加される。芯材の材質としては導電性を持つものならば何でもよく通常は金属が使われる。金属の例として鉄、銅、真鍮、ステンレス材、アルミニウムなどがある。その他の導電性の有機材料例えばカーボンを練り込んだ樹脂成型品等を用いることもできる。
【００１８】
３はローラ状の支持部材であり、潜像保持部材に密着して接触し回転する。回転の駆動力は外部から加えてもよく、又は潜像保持部材との接触摩擦力で自由に回転させても良い。支持部材の材質としては導電性或いは半導電性を持つものなら何でも良い。通常は潜像保持部材と密着させて接触させる必要から、比較的表面硬度が低い弾性体であるゴム材、例えばＮＢＲ，ＥＰＤＭ，シリコン、ネオプレンあるいは天然のゴム材及びこれらのゴムにカーボン等の導電性粒子或いは半導電性粒子を練り込んだ導電性ゴム等が使用される。もちろん良好な密着性が保たれるようによく精密加工された表面を持てば、ゴムのような弾性体以外の材料を用いても良い。しかるにこのような接触帯電装置を用いた場合、帯電の均一性が問題となり、帯電部材の電気伝導度が大きすぎると潜像保持部材の帯電ムラが生じて、正規現像時は黒部分の画像ムラ、反転現像時は白部分のカブリとなる画像欠陥になる。逆に電気伝導度が小さすぎると帯電不良が生じて像担持体が十分に帯電されない。従って、支持体の抵抗率としては１０²〜１０¹⁵Ωcmが好ましく、特に１０⁴〜１０¹²Ωcmが好ましい。
【００１９】
４は表面部材で機能分離型帯電部材を使用する場合に設けられる。材質としてはポリアミド樹脂、フッ素樹脂、塩化ビニル樹脂、アクリル樹脂、その他種々のポリエステル樹脂などが主成分として使用される。表面部材の抵抗率としては１０³〜１０¹⁴Ωcmが好ましく、特に１０⁵〜１０¹²Ωcmが好ましい。表面部材の膜厚は、帯電部材としての摩耗による耐久性を考慮すると厚い方が良いが、厚くしすぎると潜像保持部材への帯電能が悪くなるので通常0.01〜1000μm 、好ましくは0.1 〜500 μm の範囲で使用される。
表面部材の製法としては支持部材の上にデイップ法、スプレー法、真空蒸着法、プラズマコーテイング法等で形成される。
【００２０】
潜像保持部材を帯電させるために、帯電部材、すなわち芯材に印加する電圧としては直流電圧のみ、或いは直流に交流を重畳しても良い。交流としては周期的に変化する電圧であれば何でも良い。電圧の範囲としては直流電圧の場合、正または負の１００〜４０００Ｖ、好ましくは３００〜３０００Ｖである。重畳する交流電圧としてはピーク間電圧が１００〜４０００Ｖ、好ましくは３００〜３０００Ｖである。
【００２１】
ブラシ状接触帯電器としては通常回転しながら使う回転型と、平板上にブラシを固定して使う固定型とに分けられるがいずれの方式も用いることができる。いずれの場合もブラシの特性としては直径約１０μｍ、抵抗率１０³〜１０⁷Ωｃｍのものが一般的である。図２に代表的なブラシ状帯電器の構成例を示す。
露光手段としては、電子写真に通常に用いられるものであればいずれでもよく、特にＬＥＤや半導体レーザーなどが好ましい。
【００２２】
現像手段としては、電子写真で通常に用いられるものであれば特に制限はない。例えば、磁性キャリヤ粒子と非磁性トナーとからなる２成分トナー、磁性１成分トナー、非磁性１成分トナーなどの現像剤を、適宜設計された現像剤供給機構により潜像保持部材上に供給することにより現像できる。
現像された潜像保持部材上の可視化像は、紙、転写シートなどに転写され、潜像保持部材上のトナーはクリーニング機構により除去される。
【００２３】
【実施例】
以下本発明を実施例及び比較例により更に詳細に説明するが、特にこれらに限定されるものではない。
【００２４】
実施例−１
図３に示されるCuK α線による粉末X 線回折パターンを有するオキシチタニウムフタロシアニン１０重量部にジメトキシエタン２００重量部を加え、サンドブラインドミルで１０時間粉砕し微粒化分散処理を行った。次にポリビニルブチラール（電気化学工業（株）製、商品名「デンカブチラール」＃６０００Ｃ）５重量部の１０％ジメトキシエタン溶液を混合し分散液を作成した。
【００２５】
次にこの分散液を表面粗さ（Ｒmax ）が1.0 μｍになるように表面切削された直径３０ｍｍのアルミニウムシリンダー上に、浸漬塗布により乾燥後の膜厚が０．４μm となるように塗布し電荷発生層を設けた。
この電荷発生層の上に、下記構造の電荷輸送物質を２５重量部、２、６−ジ−ｔ−ブチル−４−ヒドロキシトルエンを４重量部及び下記構造のポリカーボネート樹脂（１００重量部をテトラヒドロフラン１０００重量部に溶解させた溶液を浸漬塗布により塗布し、乾燥後の膜厚が１８μm となるように電荷輸送層を設けた。
【００２６】
【化３】

【００２７】
【化４】

【００２８】
この様にして潜像保持部材A を作成した。
【００２９】
実施例−２
実施例−１において電荷輸送層に用いた電荷輸送物質を下記構造の化合物に変えた以外は実施例−１と同様に行い潜像保持部材Ｂを作成した。
【００３０】
【化５】

【００３１】
実施例―３
実施例−１において電荷輸送層に用いた電荷輸送物質の重量部数を３５部に変えた以外は実施例−１と同様に行い潜像保持部材Ｃを作成した。
【００３２】
比較例−１
実施例−１において電荷輸送層に用いた電荷輸送剤を下記構造の化合物に代え、かつ重量部数を７０部に変えた以外実施例−１と同様に行い比較潜像保持部材Ｄを作成した。
【００３３】
【化６】

【００３４】
以上のようにして作成した潜像保持部材をセイコーエプソン社製レーザプリンタ「ＬＰ―１８００」（帯電器は接触式の帯電ブラシ使用）に装着し、連続実写耐刷試験を行った。
その結果を表―１に示す。
【００３５】
【表１】

【００３６】
【発明の効果】
本発明により得られる画像形成装置及び方法によれば、特に絶縁リーク特性に対し極めて優れているため長期にわたり安定した画像を得ることができる。
【図面の簡単な説明】
【図１】本発明で用いる帯電部材の一例を説明する説明図。
【図２】帯電ブラシの説明図。
【図３】実施例で用いたオキシチタニウムフタロシアニン結晶の粉末Ｘ線回折パターン。
【符号の説明】
１潜像保持部材
２芯材
３支持部材
４表面部材[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an image forming apparatus and method. More particularly, the present invention relates to an image forming apparatus and method used in an electrophotographic apparatus.
[0002]
[Prior art]
Conventionally, a corona discharge device is generally used as a charging device for a latent image holding member used in an electrophotographic apparatus such as a plain paper copier, a laser printer, and an LED printer, and has been widely used so far. However, the corona discharge device has the following problems.
(1) A high-voltage power supply is necessary to cause discharge, and approximately 4 KV or more is required. Accordingly, the power supply cost is increased, and a high-voltage cable is required for wiring and an electric high-voltage insulating material must be used, which further increases the cost.
(2) Ozone and NOx are unavoidable due to air discharge. In recent years, ozone and NOx, which are undesirable for the human body due to environmental problems, must be avoided as much as possible.
(3) The charge tends to be non-uniform. That is, in order to cause a discharge phenomenon, generally a wire and a shield case are arranged around it, and a high voltage is applied between them. The discharge becomes unstable. Therefore, the latent image holding member is non-uniformly charged and unevenness occurs on the image. In particular, during negative corona discharge, this product becomes a fouling of the wire, making the discharge extremely unstable. Therefore, regular wire cleaning becomes indispensable and labor is required for maintenance.
[0003]
In order to improve the shortcomings of these corona discharge devices, it has been proposed to use a contact charging device and to make it a compact charging device that generates less ozone with a low-voltage power supply. (For example, refer to Japanese Patent Laid-Open No. 63-149669.)
On the other hand, as for the photoreceptors that form the core of electrophotographic technology, inorganic photoconductive materials such as amorphous silicon and arsenic-selenium are currently used, but the mainstream is organic photoreceptors. Several layer configurations have been devised as organic photoreceptors, but a so-called multilayer photoreceptor in which charge generation and charge transport functions are separated and a charge generation layer and a charge transport layer are laminated is easy to design. It has been researched and developed energetically because of its higher productivity and higher performance photoconductors, and now the range of use extends to medium and high speed copying machines and printers.
[0004]
[Problems to be solved by the invention]
However, when an image is formed by using a charging device and a method for charging by bringing it into contact with a latent image holding member made of an organic photoconductive layer, the following points have become very serious problems.
(1) Generally, the photoconductive layer of the latent image holding member is provided on the conductive substrate. However, since the charging member is in direct contact with the photoconductive layer, if there is any defect in the photoconductive layer, the current from the charging member is The latent image holding member is unevenly charged due to the concentration on the portion, and image defects such as dot-like or belt-like are generated. In addition, when the current from the charging member is intensely concentrated on such a defective portion, the photoconductive layer itself breaks down and normal image formation becomes impossible thereafter. Further, the charging member itself is damaged by such a leakage current and cannot be used.
(2) If there are defects such as adhesion of foreign matter, dirt, and fine holes on the surface of the substrate, image defects resulting from such defects may appear on the copy or print.
(3) In the case of the reversal development method, image defects such as minute black spots and ground fog may appear on a copy or print. In particular, the background fog may become remarkable under high humidity environment conditions and may not be practically used.
[0005]
The dielectric breakdown of the photoconductive layer of (1) is large because of the intrinsic weakness of the organic photoreceptor, and the fact is that few effective means have been known so far. To solve the problem (3), in the reversal development method, the dark portion potential is white and the bright portion potential is black (image portion). However, in this system, the latent image holding member is locally affected by a defect or the like. If there is a static charging failure, a black spot on a white background or a large number of them will cause a phenomenon such as background fogging, resulting in a marked image failure.
Even if such local charging failure does not cause any problems when used in regular development, it tends to cause image failure in reversal development, and a laminated latent image obtained in the past. It was found that the holding member had problems with sunspots and fogging to some extent.
[0006]
There are various causes for this problem, that is, local charging failure, but it is considered that charge injection occurs locally between the conductive substrate, which is an electrode, and the photoconductive layer, and the charged potential does not increase. It is done.
Accordingly, as a result of various studies to solve these problems, the present inventors have determined that image defects can be obtained by using a specific latent image holding member in an apparatus and method for charging a charging member by directly contacting the latent image holding member. The present inventors have found that an image forming apparatus and a method that hardly cause the occurrence of the problem can be obtained.
[0007]
[Means for Solving the Problems]
That is, the gist of the present invention is to provide a latent image holding member, a charging member for charging the latent image holding member, an exposure means for forming an electrostatic latent image on the latent image holding member, and a visualization of the latent image. In the image forming apparatus having the developing unit, the charging member is a contact charging member that is charged by contacting the latent image holding member, and the latent image holding member has at least a binder resin on the conductive substrate, and a charge transfer agent having the following structure ( A) or (B), and an organic photoconductive layer containing a charge generating agent, and the amount of the charge transporting agent in the layer containing the charge transporting agent is 100% by weight of the binder resin in the layer. image forming apparatus, characterized in that 10 to 50 parts by weight with respect to parts, and an image forming method using such a device.
[Chemical formula 2]

[0008]
DETAILED DESCRIPTION OF THE INVENTION
First, the latent image holding member used in the present invention will be described.
The latent image holding member used in the present invention has a configuration in which at least an organic photoconductive layer is provided on a conductive substrate.
As the conductive support, a metal material such as aluminum, stainless steel, copper, or nickel, or a material provided with a conductive layer on the surface of an insulating support such as polyester film or paper, a sheet shape, a belt shape, Used in the form of a drum or a roll.
[0009]
As the conductive layer provided on the surface of the insulating static support, aluminum, copper, palladium, tin oxide, indium oxide and the like are preferable.
Between the conductive support and the organic photoconductive layer, a known barrier layer that is usually used may be provided. Examples of the barrier layer include inorganic layers such as aluminum anodized film, aluminum oxide, and aluminum hydroxide, organic layers such as polyvinyl alcohol, casein, polyvinyl pyrrolidone, polyacrylic acid, celluloses, gelatin, starch, polyurethane, polyimide, and polyamide. Is used. When the organic layer is used as a barrier layer, an organic compound alone or a metal oxide such as titania, alumina, silica, or zirconium oxide, or a metal fine powder such as copper, silver, or aluminum may be dispersed. The film thickness of these barrier layers can be set as appropriate, but it is preferably used in the range of 0.05 μm to 20 μm, preferably 0.1 μm to 10 μm.
[0010]
As the photoconductive layer, any of a charge generation layer, a charge transport layer laminated in this order, a so-called dispersion type in which a charge generation material is dispersed in a charge transport medium, and the like can be used.
In the case of a multilayer photoconductive layer, various organic pigments such as phthalocyanine pigment, azo, quinacridone, polycyclic quinone, perylene, indigo, and benzimidazole are used alone or in combination as charge generating materials used in the charge generating layer. Among them, azo pigments such as bisazo and trisazo, and metal-free phthalocyanines or phthalocyanines coordinated with metals such as copper, indium, gallium, tin, titanium, lead, and aluminum, or oxides, chlorides, hydroxides, and alkoxylates thereof Is preferred. These may be used alone or in combination. The charge generation layer is formed as a uniform layer of these substances or in a state where fine particles are dispersed in a binder.
[0011]
Examples of the binder resin used in the charge generation layer include polyester resin, polyvinyl acetate, polyacrylate ester, polymethacrylate ester, polyester, polycarbonate, polyvinyl acetoacetal, polyvinyl propional, polyvinyl butyral, phenoxy resin, epoxy resin, Examples include urethane resins, cellulose esters, and cellulose ethers. The use ratio in this case is used in the range of 10 to 500 parts by weight of the charge generating material with respect to 100 parts by weight of the binder resin, and the film thickness is usually 0.01 to 5 μm, preferably 0.05 to 2 μm. In addition, the charge generation layer may contain various additives such as a leveling agent, an antioxidant, and a sensitizer for improving the coating property as necessary. The charge generation layer may be a vapor deposition film of the charge generation material.
[0012]
Examples of the charge transport material used for the charge transport layer include hydrazone derivatives, pyrazoline derivatives, heterocyclic derivatives such as carbazole, indole and oxadiazole, arylamine derivatives such as triphenylamine and tolylamine, stilbene derivatives, butadiene derivatives, Or the high molecular compound etc. which have these structures in a side chain or a principal chain are mentioned. Among them, hydrazone derivatives, arylamines, stilbene derivatives, butadiene derivatives, and the like are preferable examples because many of them have excellent charge transporting ability. Specifically, for example, JP-A-2-230255, JP-A-63-225660, JP-A-58-198043, JP-B-58-32372, JP-A-1-102469, JP-B-7. And the compounds described in JP-A No. 21646, JP-A No. 5-119489, and USP-5804344. In the present invention, since the amount of charge transporting substance used is less than usual, it is better to select a material that is particularly excellent in charge transporting ability.
[0013]
Examples of the binder resin used in the charge transport layer include vinyl polymers such as polymethyl methacrylate, polystyrene, and polyvinyl chloride, and copolymers thereof, polycarbonate, polyester, polyester carbonate, polysulfone, polyimide, phenoxy, epoxy, and silicone. Resins etc. are mentioned, and these partially crosslinked cured products can also be used. Among them, polycarbonate resin and polyarylate (polyester) resin are preferable examples in terms of mechanical strength. Specifically, for example, JP-A-5-80548, JP-A-2-66555, JP-A-61-105550, JP-A-61-137157, JP-A-60-172044, Examples thereof include binder resins described in JP-A-62-212661 and JP-A-3-2211962.
[0014]
Here, the ratio of the binder resin to the charge transport material is used in the range of 10 to 50 parts by weight with respect to 100 parts by weight of the binder resin. More preferably 15 to 45 parts by weight, particularly preferably 20 to 40 parts by weight. If the amount of the charge transport material is too small, the role of charge transport cannot be sufficiently achieved, and if it is too large, the leak resistance is deteriorated.
The charge transport layer may contain various additives such as an antioxidant and a sensitizer as necessary. The thickness of the charge transport layer is 10 to 60 μm, preferably 10 to 45 μm.
As the outermost surface layer of the latent image holding member, a conventionally known overcoat layer mainly composed of a thermoplastic or thermosetting polymer may be provided.
[0015]
Usually, a charge transport layer is formed on the charge generation layer, or vice versa. As a method for forming each layer of the laminated photoconductive layer, a known method such as sequentially applying a coating solution obtained by dissolving or dispersing a substance contained in the layer in a solvent can be applied.
In the case of a dispersive photoconductive layer, the charge generating material is dispersed in a matrix mainly composed of the binder resin and the charge transporting agent having the above-described blending ratio. In this case, the particle size of the charge generation material needs to be sufficiently small, and is preferably 1 μm or less, more preferably 0.5 μm or less. If the amount of the charge generating material dispersed in the photosensitive layer is too small, sufficient sensitivity cannot be obtained. If the amount is too large, there are adverse effects such as a decrease in chargeability and a decrease in sensitivity. % By weight, more preferably 10 to 45% by weight. In addition, the usage ratio of the binder resin and the charge transport material is 10 to 50 parts by weight, preferably 15 to 45 parts by weight, and more preferably 20 to 40 parts by weight with respect to 100 parts by weight of the binder resin. The film thickness of the photosensitive layer is usually 5 to 50 μm, more preferably 10 to 45 μm. Also in this case, a known plasticizer for improving film formability, flexibility, mechanical strength, etc., an additive for suppressing residual potential, and a dispersion aid for improving dispersion stability. Further, a leveling agent for improving the coating property, a surfactant, for example, silicon oil, fluorine-based oil or other additives may be added.
[0016]
The shape of the charging member that charges the latent image holding member is not limited as long as it contacts the latent image holding member such as a brush shape, a blade shape, a film shape, or a roller shape.
For example, when the charging device is in the form of a roller, the charging device is usually composed of at least a core member and a charging member covering the periphery thereof.
As the charging member, a conductive or semiconductive elastic body having a relatively low hardness is preferable because it needs to be brought into close contact with the latent image holding member. For example, conductive particles such as carbon or other semiconductive materials are used as a rubber material. Conductive rubber containing particles is used. In addition, the charging member is divided into a supporting member and a surface member, and the function-separating charging member that maintains an appropriate electrical resistance with the surface member while maintaining the adhesion to the latent image holding member by appropriately hardnessing the supporting member. Can also be used.
An example of the image forming apparatus of the present invention is shown in FIG. 1, taking an example using a roller-shaped charging member. Hereinafter, an embodiment of the present invention will be described with reference to FIG.
[0017]
In FIG. 1, reference numeral 1 denotes a latent image holding member, and the shape may be any of a drum shape, a sheet shape, or a belt shape.
Reference numeral 2 denotes a core material that supports the charging member. Both ends of the core member are held by a bearing supported by a suitable pressure application device, for example, a metal spring, for bringing the charging member into contact with the latent image holding member. A bias potential is applied using a bearing of the core member or other electrical contact means. Any material can be used as the core material as long as it has electrical conductivity, and metal is usually used. Examples of metals include iron, copper, brass, stainless steel, and aluminum. Other conductive organic materials such as resin molded products in which carbon is kneaded can also be used.
[0018]
Reference numeral 3 denotes a roller-shaped support member that is in close contact with the latent image holding member and rotates. The rotational driving force may be applied from the outside, or may be freely rotated by the contact frictional force with the latent image holding member. Any material may be used for the support member as long as it has conductivity or semi-conductivity. Usually, since it is necessary to make contact with the latent image holding member in close contact, a rubber material which is an elastic body having a relatively low surface hardness, such as NBR, EPDM, silicon, neoprene or natural rubber material, and conductive rubber such as carbon to these rubbers. Conductive rubber or the like in which conductive particles or semiconductive particles are kneaded is used. Of course, a material other than an elastic body such as rubber may be used as long as it has a surface that has been precisely machined so as to maintain good adhesion. However, when such a contact charging device is used, the uniformity of charging becomes a problem. If the electrical conductivity of the charging member is too large, uneven charging of the latent image holding member occurs. At the time of reversal development, an image defect becomes a fogging of a white portion. On the contrary, if the electric conductivity is too low, charging failure occurs and the image carrier is not sufficiently charged. Accordingly, the resistivity of the support is preferably 10 ² to 10 ¹⁵ Ωcm, and particularly preferably 10 ⁴ to 10 ¹² Ωcm.
[0019]
4 is a surface member provided when a function separation type charging member is used. As the material, polyamide resin, fluororesin, vinyl chloride resin, acrylic resin, and other various polyester resins are used as main components. The resistivity of the surface member is preferably 10 ³ to 10 ¹⁴ Ωcm, particularly preferably 10 ⁵ to 10 ¹² Ωcm. The film thickness of the surface member is preferably thick considering durability due to wear as a charging member, but if it is too thick, the charging ability to the latent image holding member deteriorates, so it is usually 0.01 to 1000 μm, preferably 0.1 to 500. Used in the μm range.
As a manufacturing method of the surface member, it is formed on the support member by a dip method, a spray method, a vacuum deposition method, a plasma coating method or the like.
[0020]
In order to charge the latent image holding member, only a direct current voltage may be applied to the charging member, that is, the core member, or an alternating current may be superimposed on the direct current. Any voltage may be used as the alternating current as long as the voltage changes periodically. The voltage range is 100 to 4000 V, preferably 300 to 3000 V, in the case of a DC voltage. As the alternating voltage to be superimposed, the peak-to-peak voltage is 100 to 4000 V, preferably 300 to 3000 V.
[0021]
There are two types of brush-type contact chargers: a rotating type that is normally used while rotating, and a fixed type that is used by fixing a brush on a flat plate. In either case, the characteristics of the brush are generally those having a diameter of about 10 μm and a resistivity of 10 ³ to 10 ⁷ Ωcm. FIG. 2 shows a configuration example of a typical brush charger.
Any exposure means may be used as long as it is usually used in electrophotography, and an LED or a semiconductor laser is particularly preferable.
[0022]
The developing means is not particularly limited as long as it is usually used in electrophotography. For example, a developer such as a two-component toner composed of magnetic carrier particles and a non-magnetic toner, a magnetic one-component toner, and a non-magnetic one-component toner is supplied onto the latent image holding member by an appropriately designed developer supply mechanism. Can be developed.
The developed visualized image on the latent image holding member is transferred to paper, a transfer sheet or the like, and the toner on the latent image holding member is removed by a cleaning mechanism.
[0023]
【Example】
Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples, but is not particularly limited thereto.
[0024]
Example-1
200 parts by weight of dimethoxyethane was added to 10 parts by weight of oxytitanium phthalocyanine having a powder X-ray diffraction pattern by CuK α rays shown in FIG. 3, and the mixture was pulverized by a sand blind mill for 10 hours for atomization dispersion treatment. Next, 10% dimethoxyethane solution of 5 parts by weight of polyvinyl butyral (trade name “Denkabutyral” # 6000C, manufactured by Denki Kagaku Kogyo Co., Ltd.) was mixed to prepare a dispersion.
[0025]
Next, this dispersion is applied onto an aluminum cylinder having a diameter of 30 mm, which has been surface-cut to have a surface roughness (Rmax) of 1.0 μm, by dip coating so that the film thickness after drying is 0.4 μm. A generation layer was provided.
On this charge generation layer, 25 parts by weight of a charge transport material having the following structure, 4 parts by weight of 2,6-di-t-butyl-4-hydroxytoluene and a polycarbonate resin having the following structure (100 parts by weight of tetrahydrofuran 1000 A solution dissolved in parts by weight was applied by dip coating, and a charge transport layer was provided so that the film thickness after drying was 18 μm.
[0026]
[Chemical 3]

[0027]
[Formula 4]

[0028]
In this way, a latent image holding member A was prepared.
[0029]
Example-2
A latent image holding member B was prepared in the same manner as in Example 1 except that the charge transport material used in the charge transport layer in Example-1 was changed to a compound having the following structure.
[0030]
[Chemical formula 5]

[0031]
Example-3
A latent image holding member C was prepared in the same manner as in Example 1 except that the weight part of the charge transport material used in the charge transport layer in Example 1 was changed to 35 parts.
[0032]
Comparative Example-1
A comparative latent image holding member D was prepared in the same manner as in Example 1 except that the charge transporting agent used in the charge transporting layer in Example-1 was replaced with a compound having the following structure and the number of parts by weight was changed to 70 parts.
[0033]
[Chemical 6]

[0034]
The latent image holding member prepared as described above was attached to a laser printer “LP-1800” manufactured by Seiko Epson Corporation (the charger uses a contact-type charging brush), and a continuous actual printing durability test was performed.
The results are shown in Table-1.
[0035]
[Table 1]

[0036]
【The invention's effect】
According to the image forming apparatus and method obtained by the present invention, since the insulation leak characteristic is particularly excellent, a stable image can be obtained over a long period of time.
[Brief description of the drawings]
FIG. 1 is an explanatory diagram illustrating an example of a charging member used in the present invention.
FIG. 2 is an explanatory diagram of a charging brush.
FIG. 3 is a powder X-ray diffraction pattern of the oxytitanium phthalocyanine crystal used in the examples.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Latent image holding member 2 Core material 3 Support member 4 Surface member

Claims

An image forming apparatus having a latent image holding member, a charging member for charging the latent image holding member, an exposure unit for forming an electrostatic charge latent image on the latent image holding member, and a developing unit for visualizing the latent image The charging member is a contact charging member that is brought into contact with the latent image holding member to be charged, and the latent image holding member has at least a binder resin on the conductive substrate, a charge transfer agent (A) or (B) having the following structure, and be those provided organic photoconductive layer comprising a charge generating agent, and the amount of the charge transport material in the layer containing a charge transport agent, 10 to 50 weight per 100 parts by weight of the binder resin in the layer An image forming apparatus.

2. The image forming apparatus according to claim 1, wherein the latent image holding member is a laminated organic photoconductor in which at least a charge generation layer and a charge transport layer are provided in this order on a conductive substrate.

In an image forming method including a step of charging a latent image holding member, a step of forming an electrostatic latent image on the latent image holding member by exposure, and a developing step of visualizing the electrostatic charge latent image, the charging step includes the charging member and the latent image. Organic light having contact charging with which the holding member comes into contact and the latent image holding member contains at least a binder resin, the charge transporting agent (A) or (B) having the above structure , and a charge generating agent on a conductive substrate. it is those provided conductive layer, and the amount of the charge transport material in the layer containing a charge transport agent, characterized in that 10 to 50 parts by weight per 100 parts by weight of the binder resin in the layer Image forming method.

4. The image forming method according to claim 3, wherein the latent image holding member is a laminated organic photoreceptor in which at least a charge generation layer and a charge transport layer are provided in this order on a conductive substrate.