JP4016440B2 - Electrophotographic equipment - Google Patents

Description

【００１３】
〔式中、〔式中、Ｌは感光体の幅（ｍ）、υは感光体の周速（mm／ｓ）、Ｃ_S は、現像時に感光体上に静電潜像を形成するために付着された現像剤の、感光体の単位面積当たりの静電容量（Ｆ／m²）であり、そしてＩ_O は、感光体を均一に帯電させた後であって潜像形成のための露光を行う前において感光体と現像ローラ間に流れる電流（Ａ）である〕でありかつυ≧５００mm／ｓであることを特徴とする電子写真用現像剤によって達成することができる。
【００１４】
【発明の実施の形態】
本発明者らは、このたび、特にアモルファスシリコン感光体上に形成した静電潜像を絶縁性トナーの反転現像で可視化する方式の電子写真装置において、適正な現像電界強度で現像するための現像剤、現像方法、そして現像装置を改良することにより、良好な印字特性が得られ、特に、高速の印刷装置に適した現像方法を提供し得るということを見い出した。
【００１５】
本発明は、したがって、その１つの面において、アモルファスシリコン感光体上に形成された静電潜像を現像ローラで搬送される磁性２成分現像剤で擦過して現像する方式において用いられる電子写真用現像剤にある。本発明の電子写真用現像剤は、（１）磁性キャリヤと絶縁性トナーの２成分から構成されていること、そして（２）この現像剤を現像に供したとき、その現像能力Ｉ_O ／（Ｃ_S ・Ｌ・υ）（式中、Ｌ、υ、Ｃ_S 及びＩ_O は、それぞれ、上記定義に同じである）が、１０Ｖよりも大でありかつ１００Ｖよりも小であり、そしてυ≧５００mm／ｓであることを特徴としている。
【００１６】
上記現像能力の規定において、電流Ｉ_O は、非露光時に感光体と現像ローラ間に流れる電流である。ここで、「非露光」とは、感光体を例えばコロナ放電等により均一に帯電させた後、レーザ光等で全く露光しない状態を指している。この状態は、すなわち、いわゆる現像における表面電位に相当する電荷が一様に帯電している状態である。また、「感光体と現像ローラ間に流れる電流」とは、上記の表面電位と現像剤に印加する現像バイアス電位の電位差により、現像剤を介して感光体と現像ローラ間に流れる電流である。なお、電流Ｉ_O は、現像バイアス線に対して直列に接続した電流計で測定することができる。
【００１７】
前式（１）で示される値は、本発明の現像剤あるいはそれを使用した現像装置が奏する現像能力を表すパラメータになっており、その値が大きければ大きいほど現像能力も大である。すなわち、前式（１）の値を大きくすればするほど、高速印刷に適する現像方法、現像装置が提供されることとなる。本発明者らの知見によれば、前式（１）の値を概ね３０Ｖ以上とすることが好ましい。
【００１８】
本発明の実施において、前式（１）中のＬ、υ、Ｃ_S 及びＩ_O は、それぞれ、上記の規定を満たし得る限りにおいて任意であるけれども、本発明者らの鋭意研究の結果、特に電流Ｉ_O を５μＡ≦Ｉ_O ≦２００μＡの範囲とした時に、最も優れた性能を達成し得るということが判明した。
本発明の電子写真用現像剤は、磁性キャリヤと絶縁性トナーの２成分から構成されている。絶縁性トナーは、この技術分野において常用の着色トナー粒子をそのままあるいは必要に応じて組成等を調整した後に使用することができる。すなわち、絶縁性トナーは、その構成成分として、主剤としてのバインダ樹脂、着色剤、帯電制御剤等の各種の添加剤を含有することができる。ここで、バインダ樹脂としては、例えば、スチレン樹脂、スチレンアクリル樹脂、ポリエステル樹脂、エポキシ樹脂、アミド樹脂、イミド樹脂、ウレタン樹脂等の熱可塑性樹脂を有利に用いることができる。これらの樹脂は、単独で使用してもよく、さもなければ、２種類もしくはそれ以上の樹脂を混合して使用してもよい。これらのバインダ樹脂は、一般的に、トナーの全量を基準にして８０〜９９重量部で使用するのが好ましく、さらに好ましい使用量は、８５〜９７重量部である。
【００１９】
絶縁性トナーには、着色剤、例えばカーボンブラックやその他の顔料又は染料を添加すること及び、これに加えて、帯電制御剤、例えばニグロシン染料、第４級アンモニウム塩、有機金属錯体、キレート錯体などを添加することが好ましい。着色剤及び帯電制御剤は、それぞれ、単独で使用してもよく、さもなければ、２種類もしくはそれ以上の物質を混合して使用してもよい。着色剤の使用量は、一般的に、トナーの全量を基準にして好ましくは１〜２０重量部、さらに好ましくは１〜１０重量部であり、また、帯電制御剤の使用量は、好ましくは０．１〜７重量部、さらに好ましくは０．５〜５重量部である。さらに、トナーに求められている電気抵抗の要件（概ね１０¹⁰Ωcm以上）を満たし得る範囲内で、必要に応じて、ワックス、磁性粉、粘性調整剤、その他を添加してもよい。
【００２０】
バインダ樹脂を各種の添加剤と溶融混練することによって絶縁性トナーを調製する。バインダ樹脂等の溶融混練に当たっては、例えば、加圧ニーダ、ロールミル、エクストルーダなどの常用の混練装置を使用することができる。次いで、得られた均一な分散体を例えばジェットミルなどの常用の微粉砕手段によって磨砕し、得られた微粉体を例えば風力分級機などにより分級する。このような一連の処理を経て、所望とする平均粒径を有するトナーを調製することができる。
【００２１】
本発明の実施において用いられる絶縁性トナーは、好ましくは、５〜１５μm の平均粒径（体積平均粒径）を有している。使用するトナーの粒径が小さくなればなるほど、解像性の高い、優れた印字品質を得ることができるけれども、反面、粉砕に要する製造コストが非常に高くなり、実用的ではない。また、反対に平均粒径が大きくなりすぎると、印字品質が低下する。絶縁性トナーの平均粒径は、さらに好ましくは、５〜１３μm の範囲である。
【００２２】
本発明の電子写真用現像剤において、磁性キャリヤとともに用いられる絶縁性トナーに対して導電性磁性微粒子が外添されていることが好ましい。適当な導電性磁性微粒子としては、以下に列挙するものに限定されないけれども、鉄粉や、マグネタイト、ヘマタイト、フェライト、マグヘマタイト等の微粒子を挙げることができる。これらの微粒子は、例えば、ＭＴＳ−００５ＨＤ、ＭＴＳ−０１０、ＷＡＴ−３０５Ｂ、ＥＰＴ−１００２（いずれも戸田工業社製）などとして商業的に入手可能である。これらの磁性微粒子は、単独で使用してもよく、さもなければ、必要に応じて、２種類もしくはそれ以上を混合して使用してもよい。
【００２３】
好ましくは、絶縁性トナーに外添されるべき導電性磁性微粒子は、マグネタイト及びフェライトの少なくとも１種を主成分として含有しているものであって、その電気抵抗は１０⁶ 〜１０¹⁰Ωcmであり、そしてその平均粒径は０．１〜１μm である。
本発明の現像剤において、絶縁性トナーに導電性磁性微粒子を外添するに際して、その磁性微粒子の外添量の変化に応じて前式（１）における電流Ｉ_O が変化する。すなわち、磁性微粒子の外添量に比例して電流Ｉ_O が増加する。磁性微粒子の絶縁性トナーに対する外添量は、好ましくは、０．１〜５重量％である。
【００２４】
本発明の現像剤において、上記したように絶縁性トナーに導電性磁性微粒子を外添することに加えて、この技術分野において必要に応じて行われているように、その他の外添剤、例えばシリカ微粉末、酸化チタン、チタン酸バリウム等の微粒子、フッ素微粒子、アクリル微粒子などを併用してもよい。適当なシリカ微粉末の一例を示すと、Ｒ−９７４（日本アエロジル社製）や、Ｈ−２０００、Ｈ−２０００／４、ＨＶＫ−２１５０及びＨＶＫ−２１５５（いずれもヘキスト社製）がある。
【００２５】
導電性磁性微粒子やその他の外添剤微粒子のトナーへの外添は、いろいろな手法に従って行うことができる。例えば、先に調製したトナーの表面に外添剤の微粒子を被覆することが好ましい。この微粒子被覆工程は、従来常用の手法に従って、例えば、ヘンシェルミキサーにトナーの粉末と外添剤の微粒子を適量で装填した後、所定の時間にわたって攪拌、混合を継続することによって、容易に微粒子の被覆を完了することができる。
【００２６】
本発明の電子写真用現像剤において、前記した絶縁性トナーとともに用いられる磁性キャリヤは、この技術分野において常用の磁性キャリヤをそのままあるいは必要に応じて組成等を調整した後に使用することができる。本発明の実施において有利に使用することのできる磁性キャリヤは、マグネタイト、フェライト及び鉄の少なくとも１種を主成分として含有している磁性粒子と、この磁性粒子の周囲を被覆した、１０〜３０ｄｙｎ／cmの臨界表面張力を有する樹脂材料を主成分とするコート層とから構成されるものである。
【００２７】
磁性キャリヤにおいてそのコアを構成する磁性粒子を被覆するコート層は、いろいろな樹脂材料から形成することができる。適当なコート樹脂としては、以下に列挙するものに限定されないけれども、シリコーン樹脂、フッ素樹脂、ポリエチレン樹脂等を挙げることができる。これらのコート樹脂は、単独で使用してもよく、さもなければ、必要に応じて、２種類もしくはそれ以上を混合して使用してもよい。また、上記した範囲の臨界表面張力を実現できる範囲内で、必要に応じて、これらのコート樹脂を、従来から使用されているコート樹脂、例えばアクリル樹脂、スチレンアクリル樹脂、エポキシ樹脂、ウレタン樹脂、イミド樹脂、アミド樹脂、ポリエチレン樹脂等と組み合わせて使用してもよい。コート樹脂は、熱可塑性であっても、あるいは熱硬化性であってもよい。また、このコート樹脂には、必要に応じて、例えば、カーボンブラック、酸化チタン等の抵抗調整剤、帯電制御剤などを添加してもよい。コート樹脂の臨界表面張力が上記した範囲の上限を上回ると、キャリヤのコート層にトナーが付着し易くなり、また、したがって、キャリヤを繰り返し使用するような場合、キャリヤ物性、例えば帯電量、電気抵抗等が変化することになる。換言すると、コート樹脂の臨界表面張力が大きい場合、現像剤を繰り返し使用すると、前記した式（１）に示す現像能力の条件を安定に維持することができなくなりやすい。本発明者らの調査によると、例えば、臨界表面張力が大きい場合、前式（１）の電流Ｉ_O が小さくなりやすく、現像能力が低下することが確認されている。反対に、コート樹脂の臨界表面張力が上記した範囲の下限を下回った場合、キャリヤ基材、例えばマグネタイト、フェライト、鉄等のコアとの密着性が劣化し、コアからコート層が剥離し易く、また、繰り返しの使用により帯電量等が変化する傾向にあり、好ましくない。
【００２８】
磁性キャリヤは、広い範囲の電気抵抗及び平均粒径を有することができるというものの、好ましくは、１０³ 〜１０¹⁰Ωcmの電気抵抗及び４０〜２００μm の平均粒径を有している。磁性キャリヤの電気抵抗は、それが低すぎると、感光体ドラムの表面にキャリヤが付着してコロナ放電器等まで運ばれ、そして、ドラムに高電圧が印加されると、放電等によりドラムに傷が生じたりするため、好ましくない。また、高抵抗になればなるほど、前式（１）の電流Ｉ_O が小さくなりすぎ、前式（１）の条件を満たしにくくなる。さらに好ましくは、キャリヤ電気抵抗を１０³ 〜１０⁷ Ωcmの範囲とするのがよい。磁性キャリヤの平均粒径は、もしもそれが４０μm を下回ると、感光体ドラム面にキャリヤが付着してしまうというような不都合を生じ、また、反対に２００μm を上回ると、前式（１）に示す範囲の現像能力を有する現像剤を得ることが困難になるであろう。
【００２９】
磁性キャリヤは、先に説明した絶縁性トナーの調製と同様、常用の技法を使用して調製することができる。例えば、樹脂及び必要に応じて帯電制御剤、導電性制御剤等を溶剤に溶解し、得られた溶液あるいは分散液をキャリヤ基材、例えば鉄粉、マグネタイト粉、フェライト粉等と混合し、そして、その後、例えばロータリードライ方式によりコーティングすることができる。このようにして得られる磁性キャリヤを、先に説明したようにして調製した絶縁性トナーとボールミル攪拌等により混合することにより、所期の現像剤を得ることができる。
【００３０】
本発明の電子写真用現像剤において、それに含まれる磁性キャリヤと絶縁性トナーの混合比は、所望とする結果、前式（１）の条件、その他の種々のファクタに応じて広く変更し得るというものの、一般に、磁性キャリヤのトナーに対する混合比が１〜２０重量％であることが好ましい。これは、キャリヤ量がトナー量に較べて少なすぎる場合、現像剤をマグネットロールで、静電潜像を現像する帯域まで搬送できなかったり、また、キャリヤとトナーが十分接触し、攪拌されることによって帯電しないため、現像剤をマグネットロールで搬送する際にトナーがキャリヤから分離し、装置内を汚染したりするというような不都合を生じるからである。また、反対にキャリヤ量が多すぎる場合、十分なトナーが静電潜像に供給されなくなるため、結果的に十分な印字濃度を得るための現像能力を得ることができないというような不都合が発生するからである。
【００３１】
本発明の電子写真用現像剤は、それを流動性に関して規定することもできる。本発明の現像剤は、好ましくは、０．３〜０．４の川北式流動性指数を有している。現像剤の流動性が極端に悪くなると、現像器の内部における現像剤の偏った分布が発生し、均一な現像を行うことができなくなる。また、現像剤の流動性が良くなりすぎると、前式（１）における電流Ｉ_O が小さくなりすぎ、前式（１）の条件を満たしにくくなる。ここで、「川北式流動性指数」とは、多機能型粉体特性測定装置（セイシン企業社製マルチテスタＭＴ−１０００）を用いてタップ密度を求め、川北の式により流動性指数を算出した値であり、川北式についての詳細は、「材料」、第１４巻、１４４、７０２〜７１２頁（１９６５年）、粉体測定技術センター刊、を参照されたい。
【００３２】
本発明による電子写真用現像剤は、電子写真複写機、電子写真プリンタ、静電印刷機などの電子写真装置において静電潜像を現像するための現像剤として有利に使用することができる。したがって、本発明は、そのもう１つの面において、電子写真法に基づく画像形成方法にある。本発明による画像形成方法は、感光体上に電子写真法により形成された静電潜像を、現像ローラから搬送されてきた本発明の電子写真用現像剤で擦過して現像することを特徴としている。
【００３３】
本発明による画像形成方法は、いろいろな手順に従って有利に実施することができるというものの、好ましくは、次のような手順に従って実施することができる。なお、本発明方法の容易な理解のため、図１に概要を示す画像形成装置を併せて参照されたい。
先ず、光導電性感光体（絶縁体）１を用意する。感光体１は、好ましくは図示のようにドラムの形状とすることができ、また、この技術分野において常用のように、金属ドラムの表面にアモルファスシリコン、Ｓｅ−Ａｓ、光導電性有機物などの物質を被覆して使用することができる。本発明の実施に当たっては、特に高速印刷に対応するため、アモルファスシリコン感光体を有利に使用することができる。また、光導電性感光体１は、図示の矢印の方向に回転せしめられ、その際、その回転速度（周速）は、好ましくは、５００〜２０００mm／ｓである。
【００３４】
上記の周速で回転中の感光体１の表面に、帯電器２を使用して静電荷を付与する。この帯電プロセスは、コロナ帯電装置、接触帯電装置などを使用して行うことができる。引き続いて、帯電器２により静電的に帯電せしめられた感光体１に露光装置３から光像を照射して静電潜像を形成する。この潜像形成プロセスは、光源として蛍光灯、ハロゲンランプ等を使用した複写光学系、レーザ走査光学系などを使用して行うことができる。引き続いて、感光体１上の静電潜像を可視化する。この現像プロセスは、常用の乾式現像法のいずれかを使用することによって有利に行うことができる。図示の例では、現像器４の現像ローラ５によって現像剤６の必要量を感光体１の潜像保持面に搬送し、その場で擦過することによって現像を行っている。現像の完了後、感光体１の表面に形成されたトナー像を印刷媒体１０（ここでは紙を使用、搬送方向を矢印で図示）に転写し、付着させる。この転写プロセスは、転写器７上で、例えばコロナ転写法、ローラ転写法などによって行うことができる。最後に、印刷媒体１０上に弱い力で付着しているトナー像を強固に付着させる。この定着プロセスは、常用の熱ローラ定着、フラッシュ定着などによって行うことができ、図示の例では、この目的のためにフラッシュ定着器８が使用されている。フラッシュ定着器は、構造が比較的に簡単であり、装置のコンパクト化に寄与する；非接触の定着であるため、記録用紙の搬送が容易となるばかりか、現像時、画像の解像度が劣化されることもない；システムダウンにより定着器内に記録用紙が詰まっても、発火を生じることがない；記録用紙の材質や厚さに無関係に定着を行うことができ、従って、例えば粘着面を有する紙、プレプリント紙、厚さの異なる紙なども使用することができる；といった利点を得ることができる。定着の完了後、印刷媒体１０において印刷物１１が得られる。なお、図示の印刷媒体１０は長尺物であるけれども、用紙ホッパー等を使用することにより、普通紙なども同様に印刷することができる。
【００３５】
以上において本発明の具体的な態様を説明してきたけれども、引き続いて、従来の技術に較べて本発明が優れる点について、具体的に説明する。
第１に、印刷速度が速い装置、例えば、印刷速度が１０００mm／ｓ以上の電子写真装置においても、高い現像能力を得ることができ、また、これは、現像剤に用いられるキャリヤの電気抵抗をあまり低くしなくても可能である。従来から提案されているキャリヤの低抵抗化では、このような高速現像を行うためには、例えば、キャリヤの電気抵抗を１０² Ωcm程度まで低くしなければならなかった。これに対して、本発明の現像方法を使用すると、キャリヤの電気抵抗を、例えば、１０⁴ Ωcm程度まで低くすればよく、このため、キャリヤが光導電性感光体上の表面電荷に接触した際にも、表面電荷が現像剤に移行して、帯電不正を生じることがない。ちなみに、従来の現像方法では、帯電不正により、印字背景部にカブリ等が発生し、印字品質の劣化が発生した。また、キャリヤが光導電性感光体の表面に付着し、そしてその後、例えばコロナ帯電器等により高電圧が印加された場合においても、放電等によりドラムに傷が発生することもない。
【００３６】
第２に、現像剤のキャリヤを臨界表面張力の低いキャリヤとすることにより、トナーがキャリヤ表面に付着することによる帯電能力、電気抵抗等の物性変化を回避することができ、前式（１）の現像能力の条件を満たす限りにおいて、良好な印字を行うことができる。
【００３７】
【実施例】
以下、本発明をそのいくつかのの実施例を参照して説明する。しかし、本発明はこれらの実施例によって限定されるものではないことを理解されたい。また、下記の実施例において本発明の現像剤を評価するため、キャリヤの電気抵抗及び臨界表面張力、現像剤の流動性、そして現像能力をそれぞれ下記のような手順に従って測定した。
キャリヤの電気抵抗：
体積１cm² のキャリヤを、磁束密度９５０ガウス及び磁界強度３４０Ｏｅの磁界が働いている電極面積１cm² の平行電極間に装填し、タッピングして緊密に詰め込んだ。次いで、１００Ｖの直流電圧を印加した時に流れる電流を電流計で測定し、測定された電流ｉ（Ａ）から式：Ｒ＝１００／ｉにより電気抵抗Ｒ（Ωcm）を求めた。
キャリヤの臨界表面張力：
金属板にキャリヤコート樹脂を塗布し、キャリヤ製造と同一の条件下で処理して試験片を調製した。得られた試験片の表面に、表面張力を異にする８種類の溶媒（水、グリセリン、ジメチルスルホキシド、ニトロメタン、クロロベンゼン、アセトニトリル、シクロヘキサン及びヘプタン）を滴下し、エルマゴニオメータ式接触角測定器で接触角を測定した。接触角の測定値から、ジスマンプロット（Ｚｉｓｍａｎｎ Ｐｌｏｔ）にて臨界表面張力（ｄｙｎ／cm）を求めた。
現像剤の流動性：
多機能型粉体特性測定装置（セイシン企業社製、マルチテスタＭＴ−１０００）によりタップ密度を求め、さらに川北の式により流動性指数を算出した。
現像能力（前式１を参照）：
各現像剤を電子写真プリンタ（富士通社製、Ｆ６７６０Ｄ）に搭載し、感光体と現像ローラ間を流れる電流Ｉ_O を測定した。電流Ｉ_O の測定のため、現像剤に印加する現像バイアス線に直列に電流計を接続した。ちなみに、以下に説明するように、現像剤１（図中、Ｎｏ．１として表示）では、印加された現像バイアスが２００Ｖの時、電流Ｉ_O が１５０μＡであった。Ｃ_S ＝３×１０^-6Ｆ、Ｌ＝４００mm、そしてυ＝１５００mm／ｓであることから、現像能力は８３Ｖであった。
例１：
現像剤１〜９の調製
１．トナーの調製
９０重量部のポリエステル樹脂〔重量平均分子量＝２５０００（ＧＰＣ、ポリスチレン換算値）、バインダ樹脂として〕に、７重量部の着色剤としてのカーボンブラック（ブラックパールズＬ、キャボット社製）及び３重量部の帯電制御剤としてのニグロシン染料（ボントロンＮ−０４、オリエント化学社製）を添加し、エクストルーダにより溶融温度１３０℃で３０分間溶融混練した。その冷却後に得られたトナー塊をロートプレックス粉砕機により磨砕したところ、平均粒径約２mmの粗粉砕トナーが得られた。次いで、得られた粗粉砕トナーをジェットミル（ＰＪＭ粉砕機、日本ニューマチック工業社製）を用いて微粉砕し、さらに微粉砕物を風力分級機（アルビネ社製）により分級した。正帯電性トナーが得られた。得られた正帯電トナーの粒径分布をコールカウンタ（ＴＡ−II、コールタ社製）により測定したところ、体積中心粒径は９μm であった。
【００３８】
さらに、上記のようにして調製したトナー１０重量部に対して、外添剤としてのマグネタイト微粉末（ＥＰＴ−１００２、戸田工業社製；電気抵抗＝１０⁸ Ωcm、平均粒径＝０．１３μm ）及び（又は）シリカ微粉末（ＨＶＫ−２１５０、ヘキスト社製）を下記の第１表に記載の混合比率（重量％）で添加し、ヘンシェルミキサで５分間にわたって混合した。マグネタイト微粉末及び（又は）シリカ微粉末が表面を被覆した非磁性トナー１〜９が得られた。

２．キャリヤの調製
キャリヤ１〜９を下記の第２表に記載するようにコート樹脂及び基材（コア）と組み合わせて調製した。得られた磁性キャリヤ１〜９のそれぞれについて上記した手順に従って電気抵抗（Ωcm）及び臨界表面張力（ｄｙｎ／cm）を測定したところ、次の第２表に記載のような結果が得られた。また、得られたキャリヤの平均粒径（μm ）も併せて記載する。

３．現像剤の調製
上記したトナー１及びキャリヤ１をボールミルを使用して十分に混合し、現像剤１を調製した。また、残りのトナー及びキャリヤについても、同一の番号どうしの組み合わせでボールミルすることによって、現像剤２〜９を調製した。
【００３９】
次いで、得られた現像剤１〜９のそれぞれについて上記した手順に従って流動性及び現像能力（Ｖ）を測定したところ、次の第３表に記載のような結果が得られた。また、現像剤の印刷特性（現像量、カブリの有無）ならびに判定結果も併せて記載する。

次いで、上記した結果のうち現像剤の現像能力（Ｖ）を印刷用紙上のトナー付着量（mg／cm² ）とともにグラフにプロットした。図２に示すようなグラフが得られた。このグラフから明らかなように、前式（１）で求められる値により、トナー付着量、すなわち、現像能力の大きさが変化し、前式（１）で求められる値を１０Ｖより大、１００Ｖ未満とすることにより、トナーの付着量を０．５mg／cm² 以上とすることができる。前式（１）の値が上記の範囲を上回ると、印字背景部においてカブリが発生し、良好な印字が得られず、また、反対に上記の範囲を下回ると、十分な現像能力を得ることができない。
例２：
現像剤１０〜１２の調製
前記例１に記載の手法を繰り返して現像剤を調製した。しかし、本例では、トナー及びキャリヤを下記の第４表及び第５表に記載のような組成及び特性とし、また、特性測定のための電子写真プリンタとして、Ｆ６７１２Ｅ（富士通社製）を使用した。得られた結果を下記の第６表に示す。

【００４０】
【発明の効果】
本発明によれば、アモルファスシリコン感光体上に形成した静電潜像に絶縁性トナーを反転現像する電子写真装置において、印字背景部にカブリがなく、印字濃度が高い、良好な印字特性を得ることができる。特に、１０００mm／ｓ以上の高速印字を行う現像装置において、安定して、良好な印字を行うことが可能になる。また、感光体のドラムにキャリヤが付着した時においても、ドラムに傷が付くのを防止することができる。さらに、フィルミング等によるキャリヤ特性の変化が少なく、連続印刷において、安定した現像を行うことが可能となる。
【図面の簡単な説明】
【図１】本発明の現像剤を使用した画像形成装置の１構成例を示した略示図である。
【図２】現像剤の現像能力とトナー付着量の関係を示すグラフである。
【符号の説明】
１…光導電性感光体
２…帯電器
３…露光装置
４…現像器
５…現像ローラ
６…現像剤
７…転写器
８…フラッシュ定着器
１０…印刷媒体
１１…印刷物[0001]
BACKGROUND OF THE INVENTION
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic developer, and more particularly, an electronic that can be advantageously used to develop an electrostatic latent image in an electrophotographic apparatus such as an electrophotographic copying machine, an electrophotographic printer, and an electrostatic printing machine. The present invention relates to a photographic developer. The electrophotographic developer of the present invention can be advantageously used particularly in a high-speed printing type electrophotographic apparatus in which a photoreceptor is rotated at a high speed, and good printing characteristics can be obtained. The present invention also relates to an image forming method using such an electrophotographic developer.
[0002]
[Prior art]
Conventionally, as an electrophotographic method widely used in copying machines, printers, printing machines, etc., a method described in US Pat. No. 2,297,691 is well known. In general, this electrophotographic system uses a photoconductive photosensitive member such as a photosensitive drum (also called a photocon drum), and gives a uniform electrostatic charge thereon by corona discharge or the like. By irradiating the photoconductive photosensitive member with a light image by means, the electrostatic charge on the insulator is partially erased to form an electrostatic latent image, and then the electrostatic latent image is converted into fine powder called toner. Development and visualization using the body. The toner image thus obtained is transferred to a recording medium such as paper, if necessary, and then fixed to the recording medium by a process such as pressurization, heating, spraying of solvent vapor, irradiation with light, etc. It can be a copy.
[0003]
Conventionally, as a toner for developing an electrostatic latent image in an electrophotographic system, a colorant such as carbon black, a charge control agent, and the like are dispersed in a binder resin made of a natural or synthetic polymer substance. Is used to obtain a fine powder having a particle size of about 1 to 20 μm. These toner fine powders are usually used alone or otherwise mixed with a carrier substance (carrier) such as iron powder, ferrite powder or glass beads. When iron powder or other ferromagnetic particles are used as the carrier, the developer composed of the toner and the carrier is frictionally charged by being mixed and stirred in the developing device, and the magnet roll in the developing device rotates. As a result, a magnetic brush is formed, and is carried to the electrostatic latent image portion on the photoconductive photosensitive member with the rotation of the magnet roll, and only the charged toner is attached to the electrostatic latent image by the electric attractive force. . In this way, the developer used for visualizing the latent image is added with a new toner corresponding to the amount of decrease in the toner density so that it can be used repeatedly, and a constant toner density is maintained. .
[0004]
By the way, as the photoconductive photoreceptor (insulator) for forming the electrostatic latent image as described above, conventionally, substances such as amorphous silicon, Se-As, and photoconductive organic substances have been used. Moreover, these substances are usually used by coating the surface of a substrate such as a metal drum or a conductive sheet. Among these photoconductive photoreceptors, amorphous silicon photoreceptors have a high surface hardness, are not easily damaged or worn even when exposed to external mechanical stress, and should be used stably over a long period of time. Therefore, it is frequently used in a high-speed developing device in which mechanical stress is particularly large.
[0005]
Further, as a method of developing and visualizing the electrostatic latent image portion on the photoconductive photosensitive member with toner, for example, a reversal developing method can be used. This method includes uniformly charging the surface of the photoconductive photosensitive member by corona discharge or the like, and then irradiating a portion to be printed with laser light or the like to erase the charge only at the portion to be printed. . Next, a bias is applied to the developer in order to attach the toner to the portion where the charge has been erased. Then, due to the potential difference between the potential of the developer and the light portion potential of the photoconductive photoconductor, an electrical attractive force is generated in the toner brought into contact with the latent image, and the toner can be attached to the latent image.
[0006]
Further, the toner image formed on the photoconductive photoreceptor as described above is copied onto a recording medium such as paper by a transfer means such as corona transfer or roller transfer. When the toner image is transferred to the recording medium, the toner image adheres to the surface of the medium in the form of fine powder to form an image. Therefore, for example, the image can be crushed simply by rubbing the image with a finger. . In order to fix the toner image on the recording medium to such an extent that it does not rub off, it is necessary to melt the fine powder of the toner image and fix it to the recording medium. Various fixing methods such as spraying of solvent vapor and irradiation with light are used. Among these methods, flash fixing, which is a typical method of light fixing, is a method of fixing a toner image by flashing a discharge tube such as a xenon flash lamp, and has a relatively simple structure. There is an advantage that the waiting time is short.
[0007]
[Problems to be solved by the invention]
However, the electrostatic latent image developing method in the electrophotographic method as described above has several problems to be solved. The first problem is a decrease in printing characteristics in a developing device that performs high-speed printing. As described above, when an amorphous silicon photoconductor that is resistant to mechanical stress is used as a photoconductive photoconductor, the surface of the photoconductor is uniformly charged in a range of about 10 to 500 V by corona discharge. be able to. Next, when the uniformly charged photoconductive surface is selectively irradiated with laser light or the like, the charge is lost at the selectively irradiated portion, and the potential (bright portion potential) is lowered to approximately 20 to 100V. On the other hand, when a development bias potential is applied to the developer used in combination, the electrostatic latent image is electrically attracted from the toner according to the potential difference between the development bias potential and the light portion potential (hereinafter referred to as the development potential). Development is performed until the force is applied and the development potential is neutralized by the toner charge. However, in actual development, the photosensitive member and the developer are not in contact with each other until the development potential is completely neutralized. Therefore, as the printing speed in the developing device increases, the contact area between the photosensitive member and the developer decreases. Therefore, the toner cannot be sufficiently adhered to the photoconductor, that is, only a low developing ability can be obtained, and as a result, there is a problem that it is difficult to obtain good printing.
[0008]
First, a developing method for performing high-speed printing based on the prior art and its problems will be described.
As a method for increasing the electric attractive force of toner, a method for reducing the electric resistance of a carrier has been proposed. However, as a result of the study by the present inventors, the optimum level of carrier electric resistance with respect to the printing speed is a parameter determined mainly from two factors of the photosensitive material and the printing speed. It turned out to be. That is, taking the case of using an amorphous silicon photoconductor as an example, the optimum electrical resistance of the carrier mainly depends on the printing speed, and the developing device having a low printing speed (the peripheral speed of the photoconductor is approximately 500 mm / mm). less than s), which is relatively high resistance, approximately 10 ^Ten -10 ⁸ In a developing device having a good Ωcm carrier and a high printing speed (peripheral speed of photoreceptor is approximately 500 to 1000 mm / s), the resistance is approximately 10 ⁷ -10 ^Five An Ωcm carrier is good. In higher speed devices (over 1000 mm / s), the resistance is very low, specifically around 10 ^Four -10 ² An Ωcm carrier must be used.
[0009]
Here, when the resistance of the carrier to be used is lowered, when the charge on the photoconductive photoreceptor comes into contact with the developer, a part of the charge is transferred to the developer, and for example, the toner charge amount can be changed. Therefore, it is possible to cause fogging in the printed background portion. It is also possible for a low-resistance carrier to adhere to the drum of the photosensitive member. When a high voltage such as a corona discharger is applied to the adhered carrier, a discharge or the like occurs and damages the drum. There is a possibility. When fogging occurs, the printing quality deteriorates, and when the drum is scratched, printing stains occur, and the cost for replacing the drum increases. Further, in an apparatus with a high printing speed, for example, an apparatus having a peripheral speed υ ≧ 500 mm / s, it is necessary to make the electrical resistance of the developer very low, and there is a high need to solve the above problems.
[0010]
In the above description, problems and problems in the case of using amorphous silicon for the photosensitive member have been described with respect to the developing method of the electrostatic latent image. Next, problems and problems in the case of using a Se-As photoreceptor or a photoconductive organic photoreceptor as the photoreceptor will be described. Even when a Se-As photoreceptor or a photoconductive organic photoreceptor is used as the photoreceptor, the electrostatic latent image can be developed. In particular, when using a photoconductive organic photoconductor, the photoconductor is highly insulating in the dark, so even when a very low resistance carrier is used, the photoconductor drum is not easily damaged by discharge due to carrier adhesion or the like. . However, compared to amorphous silicon photoconductors, Se-As photoconductors and photoconductive organic photoconductors are easily damaged and worn by mechanical stress, and these photoconductors are used in high-speed printing devices and are rubbed with a developer. Then, the surface is easily worn, and it is necessary to frequently replace the photoconductor, which is not preferable because troublesome work for exchanging the photoconductor increases. Further, if it is necessary to frequently replace the photoconductor, it is not preferable because the printing cost is increased accordingly.
An object of the present invention is to provide a developer for electrophotography that solves the problems of the prior art as described above and that is particularly suitable for high-speed printing and does not cause deterioration in printing characteristics.
[0011]
[Means for Solving the Problems]
According to the present invention, the above-described object is to develop an electrophotographic developer used in a method in which an electrostatic latent image formed on an amorphous silicon photoreceptor is developed by rubbing with a magnetic two-component developer conveyed by a developing roller. An agent,
Consists of two components, a magnetic carrier and an insulating toner, and
When subjected to the above development, the following formula (1):
[0012]
[Expression 2]

[0013]
[Where, L is the width of the photoreceptor (m), υ is Photoconductor Peripheral speed (mm / s), C _S Is The developer deposited to form an electrostatic latent image on the photoreceptor during development. Capacitance per unit area (F / m ² ) And I _O Is After the photoconductor is uniformly charged and before exposure for latent image formation The current (A) flowing between the photosensitive member and the developing roller] and υ ≧ 500 mm / s.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
The inventors of the present invention have recently developed for developing with an appropriate developing electric field strength in an electrophotographic apparatus that visualizes an electrostatic latent image formed on an amorphous silicon photoreceptor by reversal development of insulating toner. It has been found that by improving the agent, the developing method, and the developing device, good printing characteristics can be obtained, and in particular, a developing method suitable for a high-speed printing device can be provided.
[0015]
Accordingly, the present invention provides, in one aspect thereof, an electrophotographic image used in a system in which an electrostatic latent image formed on an amorphous silicon photoreceptor is developed by rubbing with a magnetic two-component developer conveyed by a developing roller. In the developer. The electrophotographic developer of the present invention is composed of (1) two components of a magnetic carrier and an insulating toner, and (2) when the developer is subjected to development, its developing ability I _O / (C _S ・ L ・ υ) (where L, υ, C _S And I _O Are the same as defined above), but are characterized by being larger than 10V and smaller than 100V and υ ≧ 500 mm / s.
[0016]
In the definition of the developing ability, the current I _O Is a current that flows between the photoreceptor and the developing roller during non-exposure. Here, “non-exposure” refers to a state in which the photosensitive member is uniformly charged by, for example, corona discharge and then not exposed at all by laser light or the like. This state is a state where charges corresponding to the surface potential in so-called development are uniformly charged. The “current flowing between the photosensitive member and the developing roller” is a current flowing between the photosensitive member and the developing roller via the developer due to the potential difference between the surface potential and the developing bias potential applied to the developer. Note that the current I _O Can be measured by an ammeter connected in series with the developing bias line.
[0017]
The value represented by the above formula (1) is a parameter representing the developing ability exhibited by the developer of the present invention or the developing device using the developer. The larger the value, the larger the developing ability. That is, the larger the value of the previous formula (1), the more a development method and a development apparatus suitable for high-speed printing are provided. According to the knowledge of the present inventors, it is preferable that the value of the previous equation (1) is approximately 30 V or more.
[0018]
In the practice of the present invention, L, υ, C in the formula (1) _S And I _O Are arbitrary as long as each of the above requirements can be satisfied. _O 5μA ≦ I _O It has been found that the best performance can be achieved when the range is ≦ 200 μA.
The electrophotographic developer of the present invention comprises two components, a magnetic carrier and an insulating toner. The insulating toner can be used as it is or after adjusting the composition or the like as it is, if necessary, in this technical field. That is, the insulating toner can contain various additives such as a binder resin, a colorant, and a charge control agent as main components. Here, as the binder resin, for example, a thermoplastic resin such as a styrene resin, a styrene acrylic resin, a polyester resin, an epoxy resin, an amide resin, an imide resin, or a urethane resin can be advantageously used. These resins may be used alone, or two or more resins may be mixed and used. These binder resins are generally preferably used in an amount of 80 to 99 parts by weight based on the total amount of toner, and more preferably 85 to 97 parts by weight.
[0019]
A colorant such as carbon black or other pigment or dye is added to the insulating toner, and in addition to this, a charge control agent such as nigrosine dye, quaternary ammonium salt, organometallic complex, chelate complex, etc. Is preferably added. Each of the colorant and the charge control agent may be used alone, or two or more kinds of substances may be mixed and used. In general, the amount of the colorant used is preferably 1 to 20 parts by weight, more preferably 1 to 10 parts by weight based on the total amount of the toner, and the amount of the charge control agent used is preferably 0. 0.1-7 parts by weight, more preferably 0.5-5 parts by weight. Further, the electrical resistance requirement (approximately 10%) required for the toner. ^Ten As long as it can satisfy (Ωcm or more), wax, magnetic powder, viscosity modifier, etc. may be added as necessary.
[0020]
An insulating toner is prepared by melt-kneading a binder resin with various additives. For melt kneading of the binder resin or the like, a conventional kneading apparatus such as a pressure kneader, a roll mill, or an extruder can be used. Next, the obtained uniform dispersion is ground by a conventional fine pulverizing means such as a jet mill, and the obtained fine powder is classified by an air classifier or the like. Through such a series of processing, a toner having a desired average particle diameter can be prepared.
[0021]
The insulating toner used in the practice of the present invention preferably has an average particle size (volume average particle size) of 5 to 15 μm. The smaller the particle size of the toner used, the higher the resolution and the better print quality. However, on the other hand, the manufacturing cost required for pulverization becomes very high, which is not practical. On the other hand, if the average particle size is too large, the print quality is degraded. The average particle diameter of the insulating toner is more preferably in the range of 5 to 13 μm.
[0022]
In the electrophotographic developer of the present invention, it is preferable that conductive magnetic fine particles are externally added to the insulating toner used together with the magnetic carrier. Suitable conductive magnetic fine particles are not limited to those listed below, but may include fine particles such as iron powder, magnetite, hematite, ferrite, and maghematite. These fine particles are commercially available as, for example, MTS-005HD, MTS-010, WAT-305B, EPT-1002 (all manufactured by Toda Kogyo Co., Ltd.). These magnetic fine particles may be used alone, or in combination of two or more, if necessary.
[0023]
Preferably, the conductive magnetic fine particles to be externally added to the insulating toner contain at least one of magnetite and ferrite as a main component and have an electric resistance of 10 ⁶ -10 ^Ten Ωcm, and its average particle size is 0.1-1 μm.
In the developer of the present invention, when the conductive magnetic fine particles are externally added to the insulating toner, the current I in the above formula (1) is changed according to the change in the amount of the magnetic fine particles added. _O Changes. That is, the current I is proportional to the amount of magnetic fine particles added. _O Will increase. The amount of magnetic fine particles added to the insulating toner is preferably 0.1 to 5% by weight.
[0024]
In the developer of the present invention, in addition to externally adding conductive magnetic fine particles to the insulating toner as described above, other external additives such as, for example, as required in this technical field, such as Silica fine powder, fine particles such as titanium oxide and barium titanate, fluorine fine particles, and acrylic fine particles may be used in combination. Examples of suitable silica fine powders include R-974 (manufactured by Nippon Aerosil Co., Ltd.), H-2000, H-2000 / 4, HVK-2150, and HVK-2155 (all manufactured by Hoechst).
[0025]
External addition of the conductive magnetic fine particles and other external additive fine particles to the toner can be performed according to various methods. For example, it is preferable to coat the surface of the previously prepared toner with fine particles of the external additive. In this fine particle coating step, according to a conventional method, for example, a proper amount of toner powder and external additive fine particles are loaded into a Henschel mixer, and then stirring and mixing are continued for a predetermined time. The coating can be completed.
[0026]
In the developer for electrophotography of the present invention, the magnetic carrier used together with the above-mentioned insulating toner can be used as it is or after adjusting the composition or the like as needed in this technical field. Magnetic carriers that can be advantageously used in the practice of the present invention include magnetic particles containing at least one of magnetite, ferrite and iron as main components, and 10 to 30 dyn / coating coated around the magnetic particles. and a coating layer mainly composed of a resin material having a critical surface tension of cm.
[0027]
The coating layer covering the magnetic particles constituting the core of the magnetic carrier can be formed from various resin materials. Suitable coating resins are not limited to those listed below, but include silicone resins, fluororesins, polyethylene resins, and the like. These coating resins may be used alone, or in combination of two or more, if necessary. In addition, within the range in which the critical surface tension in the above-described range can be realized, these coat resins may be used as needed, for example, conventionally used coat resins such as acrylic resins, styrene acrylic resins, epoxy resins, urethane resins, You may use it in combination with an imide resin, an amide resin, a polyethylene resin, or the like. The coating resin may be thermoplastic or thermosetting. In addition, for example, a resistance adjusting agent such as carbon black or titanium oxide, a charge control agent, or the like may be added to the coating resin as necessary. When the critical surface tension of the coating resin exceeds the upper limit of the above range, the toner easily adheres to the coating layer of the carrier. Therefore, when the carrier is repeatedly used, the carrier physical properties such as charge amount, electric resistance, etc. Etc. will change. In other words, when the critical surface tension of the coating resin is large, if the developer is repeatedly used, the condition of the developing ability shown in the above formula (1) cannot be maintained stably. According to the inventors' investigation, for example, when the critical surface tension is large, the current I of the above formula (1) _O Has been confirmed to be small and the developing ability is lowered. On the other hand, when the critical surface tension of the coating resin is below the lower limit of the above range, the adhesion with the core of the carrier substrate, for example, magnetite, ferrite, iron, etc. is deteriorated, and the coating layer is easily peeled from the core, Further, the charge amount and the like tend to change due to repeated use, which is not preferable.
[0028]
Although the magnetic carrier can have a wide range of electrical resistance and average particle size, it is preferably 10 ^Three -10 ^Ten It has an electrical resistance of Ωcm and an average particle size of 40 to 200 μm. If the electric resistance of the magnetic carrier is too low, the carrier adheres to the surface of the photosensitive drum and is carried to the corona discharger, etc., and when a high voltage is applied to the drum, the drum is damaged by discharge or the like. Is not preferable. In addition, the higher the resistance, the current I of the previous formula (1). _O Becomes too small and it becomes difficult to satisfy the condition of the previous formula (1). More preferably, the carrier electrical resistance is 10 ^Three -10 ⁷ It should be in the range of Ωcm. If the average particle diameter of the magnetic carrier is less than 40 μm, there is a disadvantage that the carrier adheres to the surface of the photosensitive drum. It will be difficult to obtain a developer having a range of development capabilities.
[0029]
The magnetic carrier can be prepared using conventional techniques similar to the preparation of the insulating toner described above. For example, a resin and, if necessary, a charge control agent, a conductivity control agent, etc. are dissolved in a solvent, and the resulting solution or dispersion is mixed with a carrier substrate such as iron powder, magnetite powder, ferrite powder, etc., and Thereafter, coating can be performed, for example, by a rotary dry method. The intended developer can be obtained by mixing the magnetic carrier thus obtained with the insulating toner prepared as described above by ball mill stirring or the like.
[0030]
In the electrophotographic developer of the present invention, the mixing ratio of the magnetic carrier and the insulating toner contained therein can be widely changed depending on the desired result and the conditions of the above formula (1) and various other factors. However, in general, the mixing ratio of the magnetic carrier to the toner is preferably 1 to 20% by weight. This is because when the carrier amount is too small compared to the toner amount, the developer cannot be transported to the zone where the electrostatic latent image is developed with the magnet roll, or the carrier and the toner are sufficiently in contact and stirred. This is because the toner is separated from the carrier when the developer is conveyed by the magnet roll, and the inside of the apparatus is contaminated. On the other hand, when the amount of carrier is too large, sufficient toner is not supplied to the electrostatic latent image, and as a result, there arises a disadvantage that the developing ability to obtain a sufficient print density cannot be obtained. Because.
[0031]
The electrophotographic developer of the present invention can also be defined in terms of fluidity. The developer of the present invention preferably has a Kawakita-type fluidity index of 0.3 to 0.4. When the flowability of the developer is extremely deteriorated, an uneven distribution of the developer occurs inside the developing device, and uniform development cannot be performed. Also, if the developer fluidity becomes too good, the current I in the above equation (1) _O Becomes too small and it becomes difficult to satisfy the condition of the previous formula (1). Here, the “Kawakita-type liquidity index” was obtained by calculating the tap density using a multifunctional powder characteristic measuring device (Multitester MT-1000 manufactured by Seishin Enterprise Co., Ltd.), and calculating the liquidity index by the Kawakita formula. For details about the Kawakita formula, see “Materials”, Volume 14, 144 702-712 (1965), published by Powder Measurement Technology Center.
[0032]
The electrophotographic developer according to the present invention can be advantageously used as a developer for developing an electrostatic latent image in an electrophotographic apparatus such as an electrophotographic copying machine, an electrophotographic printer, or an electrostatic printing machine. Accordingly, the present invention, in another aspect thereof, resides in an image forming method based on electrophotography. The image forming method according to the present invention is characterized in that an electrostatic latent image formed by electrophotography on a photoreceptor is developed by rubbing with the electrophotographic developer of the present invention conveyed from a developing roller. Yes.
[0033]
Although the image forming method according to the present invention can be advantageously carried out according to various procedures, it can be preferably carried out according to the following procedure. For easy understanding of the method of the present invention, please refer to the image forming apparatus schematically shown in FIG.
First, a photoconductive photoreceptor (insulator) 1 is prepared. The photoreceptor 1 can preferably be in the form of a drum as shown, and as usual in this technical field, a material such as amorphous silicon, Se-As, or a photoconductive organic substance on the surface of the metal drum. Can be used. In practicing the present invention, an amorphous silicon photoreceptor can be advantageously used to cope with high-speed printing. Further, the photoconductive photoreceptor 1 is rotated in the direction of the arrow shown in the drawing, and the rotation speed (peripheral speed) is preferably 500 to 2000 mm / s.
[0034]
An electrostatic charge is applied to the surface of the photoreceptor 1 rotating at the above peripheral speed by using the charger 2. This charging process can be performed using a corona charging device, a contact charging device or the like. Subsequently, the photosensitive member 1 electrostatically charged by the charger 2 is irradiated with a light image from the exposure device 3 to form an electrostatic latent image. This latent image forming process can be performed using a copying optical system using a fluorescent lamp, a halogen lamp, or the like as a light source, a laser scanning optical system, or the like. Subsequently, the electrostatic latent image on the photoreceptor 1 is visualized. This development process can be advantageously carried out by using any of the conventional dry development methods. In the illustrated example, the developing roller 5 of the developing device 4 conveys a necessary amount of the developer 6 to the latent image holding surface of the photoreceptor 1 and develops it by rubbing on the spot. After the development is completed, the toner image formed on the surface of the photoreceptor 1 is transferred to the printing medium 10 (here, paper is used, and the conveyance direction is indicated by an arrow) and attached. This transfer process can be performed on the transfer unit 7 by, for example, a corona transfer method, a roller transfer method, or the like. Finally, the toner image adhering to the print medium 10 with a weak force is firmly attached. This fixing process can be performed by conventional heat roller fixing, flash fixing, or the like. In the illustrated example, the flash fixing device 8 is used for this purpose. The flash fixing device has a relatively simple structure and contributes to the compactness of the apparatus; non-contact fixing not only facilitates the conveyance of recording paper but also degrades the image resolution during development. Even if the recording paper is jammed in the fixing device due to the system down, there is no ignition; the fixing can be performed regardless of the material and thickness of the recording paper, and for example, it has an adhesive surface Paper, preprinted paper, paper of different thickness, etc. can also be used; After the fixing is completed, a printed material 11 is obtained on the printing medium 10. Although the illustrated print medium 10 is a long object, plain paper or the like can be printed in the same manner by using a paper hopper or the like.
[0035]
Although specific embodiments of the present invention have been described above, the points that the present invention is superior to conventional techniques will be specifically described.
First, even in an apparatus having a high printing speed, for example, an electrophotographic apparatus having a printing speed of 1000 mm / s or more, a high developing ability can be obtained, and this can reduce the electric resistance of the carrier used for the developer. It is possible without making it too low. In the conventionally proposed low resistance of the carrier, in order to perform such high speed development, for example, the electric resistance of the carrier is set to 10%. ² It had to be lowered to about Ωcm. On the other hand, when the developing method of the present invention is used, the electrical resistance of the carrier is, for example, 10 ^Four Therefore, even when the carrier comes into contact with the surface charge on the photoconductive photoreceptor, the surface charge is transferred to the developer and charging improperness does not occur. Incidentally, in the conventional developing method, fogging or the like occurred in the printed background due to improper charging, and the printing quality deteriorated. Further, even when the carrier adheres to the surface of the photoconductive photosensitive member and a high voltage is applied by, for example, a corona charger, the drum is not damaged by discharge or the like.
[0036]
Second, by making the developer carrier a carrier having a low critical surface tension, it is possible to avoid changes in physical properties such as charging ability and electrical resistance due to the toner adhering to the carrier surface. As long as the conditions of the developing ability are satisfied, good printing can be performed.
[0037]
【Example】
The invention will now be described with reference to several examples thereof. However, it should be understood that the invention is not limited to these examples. Further, in order to evaluate the developer of the present invention in the following examples, the electric resistance and critical surface tension of the carrier, the flowability of the developer, and the developing ability were measured according to the following procedures.
Carrier electrical resistance:
Volume 1cm ² The electrode area is 1 cm on which a magnetic field having a magnetic flux density of 950 gauss and a magnetic field strength of 340 Oe works. ² Were loaded between parallel electrodes, and tapped and packed tightly. Next, the current flowing when a DC voltage of 100 V was applied was measured with an ammeter, and the electric resistance R (Ωcm) was obtained from the measured current i (A) by the formula: R = 100 / i.
Carrier critical surface tension:
A test piece was prepared by applying a carrier coat resin to a metal plate and treating it under the same conditions as for carrier production. Eight types of solvents (water, glycerin, dimethyl sulfoxide, nitromethane, chlorobenzene, acetonitrile, cyclohexane and heptane) with different surface tensions are dropped on the surface of the obtained test piece and contacted with an elmagnometer contact angle measuring instrument. The corner was measured. From the measured value of the contact angle, the critical surface tension (dyn / cm) was determined by Zismann Plot.
Developer fluidity:
The tap density was determined by a multi-functional powder property measuring apparatus (manufactured by Seishin Enterprise Co., Ltd., Multi Tester MT-1000), and the fluidity index was calculated by the Kawakita equation.
Developing capacity (see formula 1):
Each developer is mounted on an electrophotographic printer (F6760D, manufactured by Fujitsu Limited), and the current I flowing between the photosensitive member and the developing roller _O Was measured. Current I _O For the measurement, an ammeter was connected in series with the developing bias line applied to the developer. Incidentally, as described below, with developer 1 (shown as No. 1 in the figure), when the applied developing bias is 200 V, the current I _O Was 150 μA. C _S = 3 × 10 ^-6 Since F, L = 400 mm, and υ = 1500 mm / s, the developing ability was 83V.
Example 1 :
Preparation of developers 1-9
1. Toner preparation
90 parts by weight of polyester resin (weight average molecular weight = 25000 (GPC, polystyrene equivalent), as binder resin), 7 parts by weight of carbon black (Black Pearls L, manufactured by Cabot) and 3 parts by weight of colorant Nigrosine dye (Bontron N-04, manufactured by Orient Chemical Co., Ltd.) as a charge control agent was added, and melt kneaded for 30 minutes at a melting temperature of 130 ° C. using an extruder. The toner mass obtained after the cooling was ground with a rotoplex grinder, whereby a coarsely ground toner having an average particle diameter of about 2 mm was obtained. Next, the coarsely pulverized toner obtained was finely pulverized using a jet mill (PJM pulverizer, manufactured by Nippon Pneumatic Kogyo Co., Ltd.), and the finely pulverized product was classified by an air classifier (Albine). A positively chargeable toner was obtained. When the particle size distribution of the obtained positively charged toner was measured with a coal counter (TA-II, manufactured by Coulter), the volume center particle size was 9 μm.
[0038]
Furthermore, with respect to 10 parts by weight of the toner prepared as described above, magnetite fine powder (EPT-1002, manufactured by Toda Kogyo Co., Ltd .; electrical resistance = 10) as an external additive. ⁸ Ωcm, average particle size = 0.13 μm) and / or fine silica powder (HVK-2150, manufactured by Hoechst) at a mixing ratio (% by weight) shown in Table 1 below, and added for 5 minutes with a Henschel mixer Mixed over. Nonmagnetic toners 1 to 9 having surfaces coated with magnetite fine powder and / or silica fine powder were obtained.

2. Carrier preparation
Carriers 1-9 were prepared in combination with a coating resin and substrate (core) as described in Table 2 below. When the electrical resistance (Ωcm) and critical surface tension (dyn / cm) were measured for each of the obtained magnetic carriers 1 to 9 according to the procedure described above, the results shown in the following Table 2 were obtained. The average particle size (μm) of the obtained carrier is also described.

3. Preparation of developer
The toner 1 and the carrier 1 described above were sufficiently mixed using a ball mill to prepare a developer 1. For the remaining toner and carrier, developers 2 to 9 were prepared by ball milling with combinations of the same numbers.
[0039]
Next, the flowability and developing ability (V) of each of the obtained developers 1 to 9 were measured according to the procedure described above, and the results shown in the following Table 3 were obtained. In addition, the printing characteristics (development amount, presence / absence of fog) of the developer and the determination result are also described.

Next, of the above results, the developing ability (V) of the developer is determined based on the toner adhesion amount (mg / cm on the printing paper). ² ) And plotted on a graph. A graph as shown in FIG. 2 was obtained. As is apparent from this graph, the amount of toner adhesion, that is, the developing ability varies depending on the value obtained by the previous equation (1), and the value obtained by the previous equation (1) is greater than 10 V and less than 100 V. As a result, the toner adhesion amount is 0.5 mg / cm. ² This can be done. If the value of the previous formula (1) exceeds the above range, fogging occurs in the printed background, and good printing cannot be obtained. Conversely, if the value falls below the above range, sufficient developing ability is obtained. I can't.
Example 2 :
Preparation of developers 10-12
A developer was prepared by repeating the procedure described in Example 1. However, in this example, the toner and carrier have the composition and characteristics as shown in Tables 4 and 5 below, and F6712E (manufactured by Fujitsu Ltd.) is used as an electrophotographic printer for measuring the characteristics. . The obtained results are shown in Table 6 below.

[0040]
【The invention's effect】
According to the present invention, in an electrophotographic apparatus that inverts and develops an insulating toner on an electrostatic latent image formed on an amorphous silicon photoconductor, the print background portion is free from fogging and high print density is obtained. be able to. In particular, in a developing device that performs high-speed printing at 1000 mm / s or higher, stable and good printing can be performed. Further, even when the carrier adheres to the photosensitive drum, it is possible to prevent the drum from being damaged. Furthermore, there is little change in carrier characteristics due to filming or the like, and stable development can be performed in continuous printing.
[Brief description of the drawings]
FIG. 1 is a schematic diagram showing one configuration example of an image forming apparatus using a developer of the present invention.
FIG. 2 is a graph showing the relationship between the developing ability of a developer and the toner adhesion amount.
[Explanation of symbols]
1 ... Photoconductive photoconductor
2. Charger
3. Exposure device
4 ... Developer
5 ... Developing roller
6 ... Developer
7 ... Transfer
8 ... Flash fixing unit
10 ... Print media
11 ... Printed matter

Claims (10)

An amorphous silicon photosensitive member capable of forming an electrostatic latent image by exposure; a magnetic two-component developer that rubs and develops the electrostatic latent image formed on the photosensitive member; and a developing roller that conveys the developer An electrophotographic apparatus having a developing device provided with the developer,
It is composed of two components, a magnetic carrier and an insulating toner, and when subjected to the above development, the following formula (1):

[In the formula, L is the width (m) of the photosensitive member, υ is the peripheral speed (mm / s) of the photosensitive member, and C _S is the development attached to form an electrostatic latent image on the photosensitive member during development. The electrostatic capacity per unit area of the photoconductor (F / m ² ) of the agent , and I 2 _O after the photoconductor is uniformly charged and before exposure for latent image formation. In which the current flows between the photoconductor and the developing roller (A)] and ν ≧ 500 mm / s.   The electrophotographic apparatus according to claim 1, wherein conductive toner particles are externally added to the toner.   The electrophotographic apparatus according to claim 1, wherein the toner has an average particle diameter of 5 to 15 μm. The magnetic fine particles contain at least one of magnetite and ferrite as a main component, and have an electric resistance of 10 ⁶ to 10 ¹⁰ Ωcm and an average particle diameter of 0.1 to 1 μm. The electrophotographic apparatus according to claim 2, wherein:   The electrophotographic apparatus according to claim 2, wherein an amount of the magnetic fine particles added to the toner is 0.1 to 5% by weight.   The magnetic carrier is mainly composed of magnetic particles containing at least one of magnetite, ferrite and iron as a main component, and a resin material having a critical surface tension of 10 to 30 dyn / cm covering the periphery of the magnetic particles. The electrophotographic apparatus according to claim 1, further comprising a coat layer as a component. The electrophotographic apparatus according to claim 1, wherein the magnetic carrier has an electric resistance of 10 ³ to 10 ¹⁰ Ωcm and an average particle diameter of 40 to 200 μm.   The electrophotographic apparatus according to claim 1, wherein a mixing ratio of the magnetic carrier to the toner is 1 to 20% by weight.   The electrophotographic apparatus according to claim 1, wherein the developer has a Kawakita fluidity index of 0.3 to 0.4.   The electrophotographic apparatus according to claim 1, wherein the photosensitive member rotates at a peripheral speed of 500 to 20000 mm / s.

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